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Ecological Crop Geography
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ECOLOGICAL
CROP
GEOGRAPHY
BY Karl H. W. KlageS PROFESSOR
O F A < i K C) N O MY, I N I V K K S I I Y < ) I IDAHO, A N 1)
AGRONOMIST, IDAHO AGRICULTURAL KXPKR1-
MKNT STATION
NEW YORK
The Macmillan Company
TO MY
FATHER AND MOTHER
PREFACE
This book is a direct outgrowth of a course in Crop Ecology
offered by Dr. W. L. Burlison of the University of Illinois, and
taken by the author as a graduate student in 1921-22. It was under
the guidance of Dr. Burlison that the author received his original
inspiration to pursue the many interesting possibilities of the
ecological phases of crop production and distribution. No small
amount of credit for the development of this book is therefore
due to my former teacher. Dr. Burlison accomplished one of the
great realizations of a teacher in that he created in his student a
definite interest in a subject, implanted a new trend of thought,
and imbued him with a desire to pursue a line of study started in
the classroom.
It has been the good fortune of the author to have had the
opportunity to carry on this line of study in a number of institutions
in widely separated agricultural areas in the United States, as at
the Colorado Agricultural College, at the Oklahoma Agricultural
and Mechanical College, at the South Dakota State College, and
of late in the University of Idaho. The reactions of the author's
students to the subject matter presented in this book have played
an important part in its development and in its appearance in
final form. The materials covered in this book have with modifica-
tions been presented to Agronomy students over a period of eighteen
years.
In 1928 the author published a paper in the Journal of the American
Society of Agronomy setting forth the place that may be occupied by
a course in Crop Ecology and Ecological Crop Geography. The
favorable response of many Agronomists to this paper offered a
further stimulation to the compilation of a more comprehensive
outline and to the eventual working over of the materials of the
outline into book form.
The title of the book was originally designated as Crop Ecology.
Since, however, the subject materials cover a very broad field
viii PREFACE
dealing not only with the ecological aspects but also with the more
general factors determining, or involved in, the distribution of
crops, the present title, Ecological Crop Geography, was deemed more
appropriate. Credit for suggesting this particular title is due to
Dr. C. R. Ball of the United States Department of Agriculture,
who proposed it in connection with the review of the paper in the
Journal of the American Society of Agronomy referred to above.
The book is divided into four parts. Part I treats the social
environment. Part II gives a generalized discussion of the physi-
ological environment. Part III deals with 'the separate ecological
factors. These three parts provide the background for the discussion
pertaining to the distribution of agronomically important crops
in Part IV.
Part I develops the concept of the social environment of
crop plants. In order to keep this volume within the desired size
limitations, the factors of the social environment are intention-
ally discussed in a summary fashion. It is fully recognized that
this phase of the subject may be enlarged upon considerably.
But, it is also recognized that further elaboration on this important
and often neglected phase of the study of crop distribution is best
left as a task for Economists rather than to a writer with an Agro-
nomic background. Since, however, the field of crop production,
and especially as it relates to the distribution of crop plants, is
so intimately related to economic, political, social, technological
and historical forces, it is essential that the student of Agronomy
be given an opportunity to consider these factors and their numer-
ous interrelationships in their effects on world crop distribution.
Part II deals with the general aspects of the physiological environ-
ment. It has been the author's experience that a better perspective
of the many and complex interactions of the plant with the factors
of its environment can be given to students by first considering
these interactions in their general aspects before taking up the
more precise analysis of the environmental factors.
The detailed discussion of the factors of the physiological environ-
ment and the responses of plants to these various stimuli is presented
in Part III. These ecological factors produce not only local but
also regional responses. In view of this, and again in order to
give the student a more complete outlook of world crop distribu-
tion, one chapter was devoted to the classification of climates. This
PREFACE «
particular chapter was written with considerable hesitancy, even
though no original classification was added to the many now in
existence. While all the present available classifications of climate
have been severely criticized, it can nevertheless not be denied
that such classifications serve to identify and show relationships.
They can be used to advantage by students of crop distribution
when applied with a recognition of their definite limitations.
Part IV treats the actual distribution of crop plants. In this
emphasis is given to the physiological growth requirements of the
crop plants discussed, rather than to the statistical phases of the
subject. In other words, while crop statistics are important in that
they provide basic information, it is assumed that the reader is
interested more in crop adaptations, the epharmony of crop plants,
than in crop statistics as such. It is exactly in this feature, and
in that the distribution of crop plants is discussed primarily on a
physiological basis, that this book differs from the now available
works dealing with the distribution of the World's agricultural
resources.
The statistical data used were obtained from the United States De-
partment of Agriculture, Agricultural Statistics, 1940. Some difficulty
was encountered in the tabulation of the crops produced in the
European countries for the obvious reason that the national bounda-
ries of that continent are at the present writing undergoing rapid
change. Yet, while the boundaries of the countries now engaged
in the conflict will be altered, the land areas involved with their
potentialities for production will remain, even though the social
environments will undergo change.
The author has drawn freely on the available literature relating
to the various phases of the topics presented. No claim is made
for the complete exhaustion of the available literature, and no
doubt many contributions of distinct value and with a direct
bearing on the subject in hand have not been included in the
discussions presented. The great breadth of the field of Ecological
Crop Geography makes it impossible or impracticable to review
in one limited volume all the numerous contributions having a
direct bearing on the subject. Free use has also been made of crop
distribution maps from the various publications of the United
States Department of Agriculture.
The author is indebted to Professor G. O. Baker, Soil Tech-
x PREFACE
nologist of the Idaho Agricultural Experiment Station, for checking
the chapter on Edaphic and Physiographic Factors.
The author wishes to express his appreciation for the helpful
suggestions of the Editorial Staff of The Macmillan Company in
the preparation of the materials for publication.
This book represents a first attempt to place the many problems
incident to the distribution of crop plants on a physiological basis.
It is written to fill a long-felt need by Agronomists, Economists,
Geographers, and other workers. While this volume covers a wide
field it is fully realized that the study presented is by no means
complete. Many of the subject matter problems touched upon
are awaiting elaboration and solution. It is the sincere hope of
the author that this book may serve to encourage other investigators
to initiate and complete projects leading to a more comprehensive
understanding of the problems of crop distribution, to a wiser and
more beneficial use of the products of the soil, and to the conserva-
tion of the agricultural resources of the United States and of the
World.
K. H. W. K.
UNIVERSITY OF IDAHO
Moscow
March, 1942
CONTENTS
PART I. THE SOCIAL ENVIRONMENT OF CROP PLANTS
I. THE SCOPE OF ECOLOGICAL CROP GEOGRAPHY . 3
Crop Ecology and Ecological Crop Geography and Studies in
Agronomy .......... 3
Ecology — Plant Ecology — Crop Ecology — Ecological Crop
Geography 4
Ecological Plant Geography and Ecological Crop Geography . 7
Floristic and Ecological Plant Geography ..... 8
Ecological Crop Geography and Crop Statistics .... 8
Ecological Basis for Agricultural Policies 9
II. THE HISTORICAL BACKGROUND TO AGRICULTURAL
PRODUCTION 12
Primitive Society 12
Probable Stages in Early Agricultural Development . . .13
Hunting and fishing stage — Pastoral stage — Plant culture
stage 13-15
Hoe-Culture and Plow-Culture -15
Communal Farming 17
The Manorial System 18
Transition from the Medieval to the Modern Period ... 20
The Mercantile System 21
The Physiocratic System 22
Recent Stages in Agricultural Production ..... 23
Scientific agriculture — Commercial agriculture — Mecha-
nized and highly specialized agriculture — Intense nationalism 23-26
III. POPULATION IN RELATION TO AGRICULTURAL DE-
VELOPMENT 28
Population and Agriculture ....... 28
The Population Problem 28
Growth of Population in Primitive Societies .... 30
Centers of Civilization 31
Greek and Roman Population Theories 31
Influences of Christianity 32
Population of Medieval Europe : 32
Effects of Mercantilism 33
The Industrial Revolution 34
Vegetable and Machine Civilizations 35
MI CONTENTS
CHAPTER PAGE
World Population Increases from the Beginning of the Nineteenth
Century 36
Population Trends during the Early Part of the Twentieth Cen-
tury 37
The Man-Land Ratio 39
Optimum Population Density 41
IV. FACTORS DETERMINING WORLD CENTERS OF POPU-
LATION AND AGRICULTURAL PRODUCTION . 44
The Human Environment 44
Potential Centers of World Population 46
Factors Determining World Centers of Population ... 47
Temperature — Rainfall and humidity — Variability — Re-
sources — Soil fertility 48-52
The Econograph 53
Population Centers and Food Producing Areas .... 54
V. THE SOCIAL ENVIRONMENT 57
Environment Defined 57
The Physiological and Social Environments .... 57
[Natural and Artificial Social Environments .... 58
Agricultural Areas in Relation to Population and Transportation 60
Transportation and Interregional Competition .... 62
Technological Advances thitmgh Improvement of Crops . . 63
Improvements in soil management — Development of power
machinery 65-66
Intensity of Production 68
PART II. THE PHYSIOLOGICAL ENVIRONMENT OF
CROP PLANTS
VI. THE PHYSIOLOGICAL ENVIRONMENT .... 73
Primary Importance of the Physiological Environment . . 73
Habitat 73
Actual and Potential Habitats 73
Factors of the Habitat 75
The climatic factor — The physiographic factor — The
edaphic factor — The biotic factor — The anthropeic factor
— The pyric factor 75-81
The Time Element and the Habitat 82
VII. EXTERNAL FACTORS IN RELATION TO DEVELOPMENT 84
External and Internal Factors 84
Ontogeny and Phylogeny 85
Units of Heredity and Development 86
The Course of Growth in Plants 88
Mathematical Formulation of Growth Curves .... 90
Rhythm in Development 92
External Factors in Relation to Periodicity .... 94
CONTENTS xiii
CHAPTER PAGE
VIII. PHYSIOLOGICAL LIMITS 100
Cardinal Points of Vital Activity 100
The Time Factor in Relation to Cardinal Points . . .101
The Stage of Development in Relation to Cardinal Points . 102
Schimper's Optima 102
The Ecological Optimum and Crop Distribution . . .103
Limiting Factors 105
Practical Applications of the Theory of Optima and Limiting
Factors 106
IX. CROP YIELDS AND VARIABILITY IN RELATION TO
THE ECOLOGICAL OPTIMUM Ill
Broad Conception of the Ecological Optimum . . .111
Yields and Variabilities of Yields of Corn — - Oats — Wheat —
Barley — Rye .112-117
The Ecological Optimum and Factors of the Physiological and
Social Environment 118
Variability in Yields in the Eastern and Central Great Plains
Area 119
Yield and Variability of Crops in Eastern and Central South
Dakota 121
X. ADAPTATION 124
Adaptation Defined 124
Direct and Indirect Adaptation . . . . . .124
Selection for Fitness 125
Stahl's Classification of Adaptations . . . . .'126
Adaptation in Relation to the Vegetation and Climatic rhythms 127
Critical Periods 127
Hazards in Production 129
Range of Adaptation 130
PART III. THE ECOLOGICAL FACTORS
XI. GENERAL ASPECTS OF MOISTURE RELATIONSHIPS 135
Importance of Water in the Physiological Environment . .135
Moisture and Temperature Relationships . . . .136
ftie^ynbloji^ . . . .137
Moisture as a Climatic and Edaphic Factor . . . .138
Ecological Classification of Prahte~ according to Their Water
Rdatibrohtpar . . . . . . . . . 140
Hydrophytes — Mesophytes — Xerophytes . , 140-141
Factors Interfering with the Absorption of Water by Plants . 143
The Wilting of Plants 144
Drought ... 145
Excessive Moisture and Humidity ; 147
xiv CONTENTS
CHAPTER PAGE
XII. QUANTITATIVE ASPECTS OF MOISTURE RELATION-
SHIPS 151
Vapor in the Atmosphere 151
Vapor pressure and dew point — Absolute humidity —
Relative humidity — Relative and absolute saturation
deficit 151-153
Forms of Precipitation 153
Measurement of Precipitation 156
Annual Precipitation 156
Seasonal Precipitation 158
Losses of Moisture — Sources of Loss — Runoff — Rainfall
Intensity — Evaporation — Measurement of Evaporation —
Transpiration 158-161
XIII. HUMIDITY PROVINCES 163
Efficiency of Precipitation . . . . . . .163
Precipitation evaporation ratio — Meyer's P-SD quo-
tient — Lang's rain factor — Index of aridity — Thorn-
thwaite's precipitation effectiveness index . . . 163-167
Koppen's Boundaries between Dry and Humid Areas . .169
Vegetation as an Index of Moisture Conditions . . .171
XIV. THE USE OF WATER BY PLANTS 174
*
The Efficiency of Transpiratton 174
The Transpiration Coefficients of Various Crop and Weed
Plants 175
Factors Influencing the Efficiency of Transpiration — Climatic
Factors — Edaphic Factors — Plant Characteristics — Crop
Varieties 178-184
Efficiency of Transpiration and Drought Resistance — Applica-
tion to Field Conditions — Efficiency Based on a Ratio — As
an Index of Ecological Status 184-185
XV. SPECIAL RESPONSES OF CROP PLANTS TO THE
MOISTURE FACTOR 188
Response to an Isolated Factor . . . . . .188
Moisture and the Ecological Optimum 1 88
Importance of Moisture in Minimal Regions . . . . 1 89
Calculations of Wheat Yields on the Basis of the Amount of
Water Used 191
Crop Yields and Precipitation Amounts for Specified Periods 193
An Illustration of Precipitation-Yield Relationships in an
Optimal Area . .196
The Water Factor in Relation to the Degree of Correlation
between the Yields of Separate Crops . . . . .198
Cardinal Points for Water . . . . . . .199
Influence of Differing Amounts of Water on the Development of
Cereals . .200
CONTENTS zv
CHAPTER PAGE
Critical Periods 201
Drought Reactions of Wheat 203
Comparative Drought Resistance of Corn and the Sorghums . 204
Types of Cropping in Relation to the Moisture Factor . . 207
XVI. TEMPERATURE .211
General Aspects of the Temperature Factor — Temperature
Provides a Working Condition — Recording of Tempera-
tures — Average and Normal Temperatures — Length of
Growing Season — Thermal and Physiological Growing
Season — Thermal Belts — Limits of Crop Production 21 1-216
Effects of Low Temperatures — Chilling and Freezing of Plants 218
Effects of Low Temperatures above the Freezing Point — Chill-
ing of Plants — Effects of Cold Irrigation Water — Effects
of Low Night Temperatures 219-220
Effects of Temperatures Below the Freezing Point — Early
Conceptions of Freezing Injuries — Ice Crystals Usually
Formed in Intercellular Spaces — The Desiccation Theory —
Chemical Injury to Protoplasm — Evaluation of Degrees of
Hardiness 221-223
Plant Characteristics Associated with Cold Resistance —
Morphological Plant Structures — Habit of Growth —
Anatomical Features — Rate of Growth — Chemical Fac-
tors — Variations in Frost Resistance of Plant Parts and
Effect of Age of Plants 224-228
External Factors Modifying Frost Injury — Rate of Freezing
and Hardening — Rate of Thawing — Alternate Freezing
and Thawing — Heaving — Soil Moisture and Soil Type — •
Protection of Winter AnnuaPCrops . . . . 228-231
Effects of High Temperatures — External Temperatures and
Plant Temperatures — Death Due to High Temperatures 232-233
XVII. TEMPERATURE EFFICIENCIES AND BIOCLIMATICS
IN RELATION TO CROP DISTRIBUTION . . 238
Introduction 238
Temperature Efficiency Indices — Length of Growing Season —
Temperature Summation or the Remainder Index — Thorn-
thwaite's Temperature Efficiency Index — The Exponential
Index — Physiological Index — Limitations of Physiological
Summation Indices — The Moisture-Temperature Index 238-250
Correlation of Methods of Temperature Efficiency Evalu-
ation — Interrelationships — Indices in Specific Crop Pro-
ducing Centers — Correlation of Magnitude of Indices to
Crop Distribution 252-254
Bioclimatics — Temperature Zones — Astronomical and
Isothermal Temperature Zones — Bioclimatic Zones —
Merriam's Life Zones and Areas 258-263
xvi CONTENTS
CHAPTER PAGE
XVIII. LIGHT 266
General Aspects — In Relation to Growth Requirements and
as a Factor in Geographical Distribution — Heating and
Chemical Effects — Interrelationships of Environmental
Factors — Action of Light on Plants .... 266-268
Quality of Light — Differential Effects of the Rays of the
Spectrum — Effects of Atmospheric Conditions — Altitude
and Composition — Seasonal Variation in Composition 268-270
Quantity of Light — Dependence of Plants on Quantity of
Light — In Relation to Plant Structure — Competitive
Plant Cover — Measurement of Light Intensity and Du-
ration 271-275
Length of Day — Latitude and Length of Day — Photoperiod-
ism and Photocritical Periods — Photoperiodism and Plant
Distribution — Utilization of Artificial Light . . 276-279
XIX. AIR MOVEMENT 283
Introduction 283
Air Movements and Their Relation to Climate . . . 284
Migratory Cyclones and Anticyclones 287
Measurement of Wind Velocity 289
The Beaufort Wind Scale 289
Effects of Wind on Plant Distribution 290
Physiological Effects of Wind 291
Wind Erosion. . . „ 291
XX. CLASSIFICATION OF CLIMATE 294
•
Introduction — Objectives of Classification — Basis for Classi-
fication— Limitations 294-295
Classification Based on Relative Distribution of Land and
Water — Marine Climates — Continental Climates —
Mountain Climates 296-300
Classification Based on Natural Vegetation — Plant Physiog-
nomy and Climatic Conditions — Woodland Climates —
Savanna and Forest-Steppe Climates — Grassland Cli-
mates 296-305
Koppen's Classification of Climates — Basis — Zonal Subdi-
visions — Complete Formulation of Climatic Characteristics
— Maps of Climatic Regions . . . . . 307-313
Thornthwaite's Classification of Climates — Basis — Formu-
lation of Climatic Characteristics — Maps of Climatic
Regions 314-321
XXI. EDAPHIC AND PHYSIOGRAPHIC FACTORS . . .323
The Edaphic Factors — Introduction — Nature of Soil —
Major Soil Groups — Zonal Group of Soils — Physical
Aspects — Chemical Aspects — Soil Nitrogen-Climate
Relations and Corn Yields — Soil Reaction — Water
Relations 323-333
CONTENTS
xrti
CHAPTER PAGE
The Physiographic Factors — Edaphic and Physiographic
Factors — Topography — Altitude — Importance in studies
of Local Conditions 334-336
PART IV. THE GEOGRAPHICAL DISTRIBUTION
OF CROP PLANTS
XXII. THE SMALL GRAIN CROPS
Wheat
Rye .
Barley
Oats
Rice
XXIII. THE COARSE CEREALS
Corn
Sorghums
XXIV.
Millets .
EDIBLE LEGUMES
v Beans .
"Peas .
Lentils .
Peanuts
341
341
355
362
372
381
389
389
405
412
416
416
422
425
42§
XXV.
POTATOES, SWEET POTATOES, YAMS, AND OTHER
ROOT CROPS 430
"White Potatoes 430
v Sweet Potatoes 443
Yams 447
v/ Various Root Crops 448
XXVI. SUGAR 451
Introduction — Sugar as a Food — By-products — Com-
petition between the Tropical and Temperate Zones 451-452
Sugar Cane and Cane Sugar 453
The Sugar Beet and Beet Sugar 463
XXVII. OIL PRODUCING CROPS
Introduction ....
Animal and Vegetable Fats and Oils
Cotton and Cottonseed Oil .
Flax and Linseed Oil .
Soybeans
Safflower
472
472
476
478
479
486
489
CONTENTS
CHAPTER
i
PAGE
XXVIII.
FIBER CROPS
492
Introduction .........
492
Cotton ...........
493
Fiber Flax
510
Other Fiber Plants
512
XXIX.
ANNUAL LEGUMINOUS FORAGE CROPS .
517
Soybeans ..........
517
Cowpeas ..........
517
Lespedeza ..........
520
Crimson Clover .........
522
Bur Clover ..........
523
Vetches
526
Other Annual Leguminous Plants .....
528
XXX.
BIENNIAL AND PERENNIAL LEGUMINOUS FORAGE
CROPS
532
Alfalfa . .
532
The Clovers
541
Red Clover
541
Alsike Clover ........
546
White Clover
547
Ladino Clover . * .
548
Strawberry Clover % .
549
Other Biennial and Perennial Legumes ....
549
XXXI.
PERENNIAL FORAGE GRASSES
553
Appreciation of Grasses and Grassland Agriculture
553
Grasses of Cool, Humid Regions ......
557
Grasses of Cool, Dry Regions ......
563
Wild or Prairie Hay
566
Grasses of Warm, Humid Regions
568
XXXII.
MISCELLANEOUS CROPS
572
Tobacco ..........
572
Hops ...........
587
Buckwheat ..........
591
AUTHOR
INDEX
595
SUBJECT
INDEX ;
601
PART I
THE SOCIAL ENVIRONMENT OF
CR@P PLANTS
Chapter I
THE SCOPE OF ECOLOGICAL CROP GEOGRAPHY
Crop Ecology and Ecological Crop Geography and Studies
in Agronomy and Agronomic Investigations. Ball (2) very ably
defines agronomy as the "art and science of field crop culture."
He enlarges on this definition by continuing that agronomy "more
specifically is the art and underlying science of so handling the
crop plant and the soil substrate as to produce the highest possible
quantity and quality of the desired crop product from each unit of
land and soil and water and light, with a minimum of immediate
or future expense in labor and soil fertility." In standard diction-
aries agronomy is generally defined as "the management of land"
and as "rural economy." The general public has learned that the
term applies to the study of problems connected with the production
of farm crops.
• Two facts are in evidence from the attempts of defining agron-
omy; (a) the physiological and (b) the economic relationships.
The present divisions of agronomic studies are in themselves
indicative of the far-reaching activities in this general field of
agricultural research. The main lines are generally drawn along
crops and soils studies. These divisions are subdivided into special
phases even though the lines between crops and soils studies may
not always be definite. Plants grow in the soil, and results of soil
treatment are generally "measured by plant responses.
Developments, especially in recent years, have brought out force-
fully the necessity for what may be termed a world outlook on
agricultural production. Agricultural production, or any other
form of production, is influenced not only by local but to a great
extent by world conditions. The development of such a conception
of agricultural production demands a broad outlook; it cannot
confine itself to the physiological and mechanical phases of produc-
tion in any one locality but must consider also the world economic
and social forces influencing production of specified crop plants.
3
ECOLOGICAL CROP GEOGRAPHY
It is essential for the agronomist, in order to obtain a well-rounded
concept of his field, not only to consider local factors of production
but also to become acquainted with the main factors determining
the location of centers of crop production within the confines of his
own country and with those forces determining world centers of
production. Jevons, the English economist, summed up the condi-
tion in an admirable fashion when as early as 1865 he wrote the
following :
"The plains of North America and Russia are our corn fields;
Chicago and Odessa our granaries; Canada and the Baltic are our
timber-forests; Australia contains our sheep farms; and in Argentina
and on the western prairies of North America are our herds of oxen;
Peru sends her silver, and the gold of South Africa and Australia flows
to London; the Hindus and the Chinese grow tea for us, and our sugar
and spice plantations are in all the Indies. Spain and France are our
vineyards, and the Mediterranean our fruit garden; and our cotton
grounds, which for long have occupied the southern United States, are
now being extended everywhere in the warm regions of the earth."
Klages (11) discussed in detail the place that may be given to
crop ecology and ecological crqp geography in the agronomic
curriculum.
Ecology. The word "ecology" is derived from the Greek "oikos"
meaning house, abode, or dwelling. The term, according to Han-
sen (8), was first introduced by E. Haeckel. Tansley (15) used the
term in its "widest meaning" as the study of organisms as they exist
in their natural homes; or as the economy, household affairs, of
organisms. Adaptations to external conditions may be designated
as ecological; or, as Warming (16) terms it, adaptation involves
detailed studies in ecological relationships.
Investigations during the past half century have set ecology and
ecological relationships more and more on a scientific and, it may
be said, an experimental basis. To explain how organisms adapt
themselves to a precise environment calls for a mustering of all
available knowledge of plant morphology, anatomy, and physiology.
It is not too inclusive to say that most agronomic investigations
touch very directly on the ecological relationships of crop plants.
Soil investigations, work in crop breeding, variety testing, choice
of special crops to meet certain conditions, and numerous other
agronomic projects are definitely based on ecology and ecological
relationships.
SCOPE OF ECOLOGICAL CROP GEOGRAPHY 5
Plant Ecology. Plant ecology deals with plants in relation to
their environments. Since the herbivorous animals obtain their
sustenance from plant life, it is not always possible or desirable to
divorce plant and animal ecology (Hesse, 9). The plant ecologist is
concerned mainly with the habitats of plants and associations of
plants or with the physiology of the plant or group of plants in a
particular environment.
Crop Ecology. On first consideration it may seem hardly neces-
sary to set up a separate definition for crop ecology as differentiated
from plant ecology except to limit and to outline more definitely
the scope of each. Crop ecology may be defined as the ecology of
crop plants. In order to avoid confusion between the tasks of crop
ecology and ecological crop geography, the study of the former
should be confined to investigations of the relationships of crop
plants to their physiological environments to the exclusion of the
economic factors encountered in the production and distribution
of a crop or group of crops. The effects of both the physiological
and economic factors on production and distribution of crops will
be treated under the more comprehensive and general field of
ecological crop geography.
Ecological Crop Geography. Ecological crop geography1 deals
with the broad distribution of crop plants and with the underlying
reasons for such distributions. The ecological crop geographer is
concerned with more than the direct relationships of crop plants
to their physiological environment. He must consider the points
taken into account by the crop ecologist and in addition must
recognize the operation of economic, political, historical, tech-
nological, and social forces. These additional forces are grouped
under the general term "social environment." Thus, ecological crop
geography may be defined as the study of crop plants in relation to
their physiological and social environments. It is sufficient to state
that the main ecological factors such as water relationships, tem-
perature relationships, light relationships, and the form and availa-
bility of plant nutrients determine the physiological limits of crop
production. All these factors not only are necessary for the normal
development of plants but must again be taken into consideration
1 The author is indebted to Dr. G. R. Ball of the United States Department of
Agriculture for the suggestion to differentiate between crop ecology and ecological
crop geography. Originally he defined crop ecology by the definition now given to
ecological crop geography.
ECOLOGICAL CROP GEOGRAPHY
in the studies of abnormal manifestations of plant life. Plant
pathologists are aware of the fact that disorders in plants, be they
physiogenic or parasitic in nature, are either . augmented or de-
creased in their severity by the influence of the environmental
factors. Entomologists find a similar connection between the
development and relative abundance of plant pests and these same
factors.
Centers of crop production are determined in part by economic
forces such as demand, facilities for handling the crop, costs of
transportation, various labor problems, and competition. For
instance, there is a close correlation between the centers of potato
production and world centers of population, more especially centers
of the white population. Comparatively nonperishable crops are
often grown at considerable distances from such centers of popula-
tion. In many instances an improvement in the prevailing systems
of transportation may throw two rather remote sections into active
competition.
The westward movement of agricultural production in the
United States during the last century was influenced by a great
variety of ecological, social, and%economic factors. The fertility
and ease with which the soils of the Mississippi Valley could be
brought into production was the great magnet attracting settlors
and prospective producers. Social and political circumstances
immediately before and following the Civil War — notably the
ease with which land could be acquired by means of the liberal
federal homestead laws; the influx of the land-hungry immigrants
from the overpopulated European countries together with the
amazingly high rates of increase of the foreign-born and native
stocks; the simplicity of life in the new country; and the placement
of men following release from military duties after the close of the
Civil War — were potent factors in the settlement of the West.
Improvements in transportation greatly facilitated settlement and
the development of the great resources of the newly opened areas.
However, the rapid development of the agricultural potentialities
of the West did not have an entirely favorable effect on the older
agricultural regions of the eastern states. In many of these areas
the competition from the newer, more favored sections soon was
keenly felt and necessitated adjustments in eastern production
enterprises.
SCOPE OF ECOLOGICAL CROP GEOGRAPHY 7
Economic conditions, both as such and as they influence social
conditions and the purchasing powers of a people, have an impor-
tant bearing on crop distribution and the methods of handling
crops. These factors determine in the main the standards of living
found. In some instances, as with rice production in parts of the
Orient and the potato crop in parts of northwestern Europe, a crop
is produced and assumes a place of primary importance largely
because it yields a greater amount of total food material per unit
of area than can be produced by any other crop in that region.
The relation of historical and political influences to present world
distribution of crops opens an unlimited field, and a field of study
almost untouched by either historians or agriculturists.
Bensin (3) proposes the term "agroecology" to apply to detailed
studies of commercially important crop plants by the use of ecologi-
cal methods. He proposes a systematic collection of data so that
the main agricultural regions (agrochoras) of the world and the
characteristics of local cultivated varieties of important crops
(chorotypes) may be described and recorded by the employment of
standardized methods and by a prescribed and uniform terminol-
ogy. It will be observed that Bensin deals only with the physio-
logical environment of crop plants to the entire exclusion of the
socfal environment.
The excellent works of Finch and Baker (7) on Geography of the
World's Agriculture and more recent publications, by Buechel (4)
on Commerce of Agriculture, by Zimmermann (18) on World Resources
and Industries, and by Jasny (10) on Competition among Grains, as well
as publications on economic and social geography, will be of great
help to the student of ecological crop geography.
Ecological Plant Geography and Ecological Crop Geography.
The earlier floristic plant geography gave way with the develop-
ment and the application of the experimental method to ecological
plant geography. Ecological plant geography, put on a firm basis
by the works of such men as von Humboldt, Schouw, Meyen,
Griesebach, Schimper, and Warming, has a very direct bearing
on the subject of ecological crop geography. Distribution and
growth characteristics of native plants together with evident soil
characteristics offer the most reliable index to the cropping possi-
bilities of a region. As stated by Weaver and Clements (17), "every
plant is a product of the conditions under which it grows. It indi-
ECOLOGICAL CROP GEOGRAPHY
cates in general and often in a specific manner what other species
would do if grown in the same place."
Alexander von Humboldt may, with right, be called the father of
plant geography. He gave a preliminary outline of the problems
involved in his book Ideen zu einer Physiognomik der Gewdchse in 1806.
His work was followed by Schouw's Grundzuge einer allgemeinen
Pflanzengeographie in 1836. These were followed by the well-known
works: De Candolle's Geographic botanique raison'ee in 1856; Griese-
bach's Die Vegetation der Erde in 1872; and by the better known and
more recent publications of Drude (6), Schimper (13), Warming
(16), Clements (5), and Livingston and Shreve (12).
The ecological plant geographer considers only the physiological
factors of the environment; since he is dealing with native and
primary vegetations he need not take into consideration the effects
of the social environment so important to the student of ecological
crop geography.
Floristic and Ecological Plant Geography. Floristic plant
geography treats the compilation of "floras" and the division of
areas into natural "floristic" trfects, together with a discussion of
the limits of the species, genera, and families encountered. Eco-
logical plant geography, on the other hand, deals with the under-
lying causes of the adjustments made by plant communities in tfieir
forms and modes of behavior to the ecological factors of their
environment. The physiognomy of a vegetation, that is, its general
appearance or aspect, is determined not only by the mode of re-
action of individual species to environmental factors, but also to a
greater extent by the joint response of all species found in a habitat
and the consequent grouping and existence or competition, as the
case may be, of various species in communities, associations, or
formations.
Ecological Crop Geography and Crop Statistics. Ecological
crop geography differs from the study of crop statistics as ecologi-
cal plant geography differs from floristic plant geography. Crop
statistics are indeed valuable and essential to the ecological crop
geographer as are flora to the botanist or plant ecologist. His task,
however, involves more than compilation of figures showing dis-
tribution. The ecological crop geographer is concerned especially
with the underlying reasons for such distributions, with the group-
ing of separate crops and the resulting systems of cropping prac-
SCOPE OF ECOLOGICAL CROP GEOGRAPHY 9
ticed, as well as the competition found to exist between crops.
Above all, crop ecology is concerned with the study of adaptation,
or, as Warming speaks of it, the "epharmony" of crop plants.
Only through comprehensive investigations of the requirements
exacted by various crop plants of their environment can progress
in the improvement of these crops be made with the minimum of
effort and expense.
Ecological Basis for Agricultural Policies. Under unrestricted
conditions centers of crop production tend to develop in those areas
to which a specific crop is best adapted. Various national or inter-
national circumstances, regulations, and interventions, however
brought about, can and have greatly altered the normal or the to-
be-expected development of such centers. Production can and has
frequently been set up on an artificial basis. The extent to which
international trade, including that in agricultural products, is
under the influence of widespread governmental intervention is
well brought out by a recent study of world trade barriers in rela-
tion to American agriculture (1).
Any permanent policy for adjusting production to meet demands
brought about largely by curtailment of foreign demand and in-
terference with the movement of agricultural commodities should,
to have maximum beneficial effects, be based on ecological relation-
ships. It is necessary to differentiate between emergency and per-
manent programs. A policy of land utilization, in which ecological
and economic relationships would play a prominent part, may well
be taken as a basis for the ultimate solution of this perplexing
problem. Stewart (14) has outlined such a policy for the public
domain with special reference to the management of the grazing
lands of the West. A minimum of interference with production in
those sections recognized to be adapted to the growing of a certain
crop seems logical. If and when curtailment of production is
deemed necessary, it is from an ecological standpoint best accom-
plished by reduction of acreages, or perhaps total elimination, of
the crop in those sections where production records have shown that
the crop in question is least adapted, or where production is most
hazardous, or where the crop has been grown in an artificial
environment.
The vital importance of proper land utilization is well recognized
by such recently organized agencies as the Soil Conservation Serv-
10 ECOLOGICAL CROP GEOGRAPHY
ice, the Agricultural Adjustment Administration, and the Farm
Security Administration. The efforts of these agencies have resulted
in marked shifts in agricultural production and in the conservation
of both human and agricultural resources. In addition they have
decided educational values, stimulate cooperation among pro-
ducers, and are instrumental in calling national attention to the
urgency of the agricultural problem.
REFERENCES
1. "World trade barriers in relation to American agriculture," Senate
Document No. 70, 1933.
2. Ball, C. R., "Why agronomy needs research in plant physiology,"
Jour. Amer. Soc. Agron., 17:661-675 (1925).
3. Bensin, B. M., "Possibilities for international cooperation in agroeco-
logical investigations," Internatl. Rev. Agr. Mo. Bull. Agr. Sci. and Pract.
(Rome), 21:277-284 (1930).
4. Buechel, F. A., The Commerce of Agriculture. Wiley, New York,
1926.
5. Clements, F. E., Plant Physiology and Ecology. Holt, New York, 1907.
6. Drude, O., Oecologie der Pflan&n. %F. Vieweg & Sohn, Braunschweig,
1913.
7. Finch, V. C., and O. E. Baker, Geography of the World's Agriculture.
Govt. Printing Press, Washington, 1917.
8. Hansen, A., Die Pflan&ndecke der Erde. Bibliographisches Inst., Leipsic,
1920.
9. Hesse, R., Tier geographic auf Okologischer Grundlage. Gustav Fischer,
Jena, 1924.
10. Jasny, N., Competition among Grains. Food Research Institute, Stanford
University, California, 1940.
11. Klages, K. H. W., "Crop ecology and ecological crop geography in
the agronomic curriculum," Jour. Amer. Soc. Agron., 20:336-353
(1928).
12. Livingston, B. E., and F. Shreve, The Distribution of Vegetation in the
United States as Related to Climatic Conditions. Carnegie Inst. Publ. No.
284, Washington, 1921.
13. Schimper, A. 'F. W., Plant Geography upon a Physiological Basis, trans.
German by W. R. Fisher. Clarendon Press, Oxford, 1903.
14. Stewart, Geo. R., "A land policy for the public domain," Econ. Geog.,
1:89-106 (1925).
15. Tansley, A. G., Practical Plant Ecology. Allen & Unwin, London,
1926.
SCOPE OF ECOLOGICAL CROP GEOGRAPHY 11
16. Warming, E., Oecological Plant Geography, trans. German by Percy
Groom and I. B. Balfour. Clarendon Press, Oxford, 1909.
17. Weaver, J. E., and F. E. Clements, Plant Ecology. McGraw-Hill,
New York, 1929.
18. Zimmermann, E. W., Wo*ld Resources and Industries. Harper, New
York, 1933.
Chapter il
THE HISTORICAL BACKGROUND OF AGRI-
CULTURAL PRODUCTION
Primitive Society. Agricultural pursuits antedate recorded his-
tory. The earliest means employed by man to obtain a livelihood
cannot be designated as agriculture; rather, life was sustained by
those gifts that nature had to offer. Yet the problem of
securing food and shelter always has been and always will be
of greatest concern to man. Social development had no
doubt progressed considerably before endeavors to obtain food
could be graced with the term "agriculture" or "agricultural
practice."
A knowledge of the functions o^ seeds was of primary importance
to agricultural development. The growing of food plants developed
to a rather high degree in some areas, notably in portions of both
North and South America, without the aid of domesticated animals.
The Indian had no beast of burden, unless it was his squaw, of
whom Champlain said, "woman is the Indian's mule." Forms of
hoe-culture still persist in certain areas, especially in the Orient.
Carrier (3) gives a brief summary of speculations relative to primi-
tive agriculture and at the same time points out perhaps the main
motivating force for progress.
"Agricultural pursuits antedate by thousands of years recorded
history. Many writers have speculated on the origin of agricultural
practices. Some have held that primitive man was first of all a hunter
of wild game. Others with perhaps more reasons to justify their con-
clusions argue that the first human beings on the earth were vegetarians,
that they collected plants and seeds for food before they became ac-
quainted with the taste of flesh in their diet. Necessity for sustenance
has been the primary force in agricultural progress. The greater the
need the greater and more rapid has been the advancement, provided
means were available for satisfying that need. Primitive people with
a scanty food supply take up new productions with less conservatism
than do well-established races with adequate rations."
12
BACKGROUND OF AGRICULTURAL PRODUCTION 15
The Indians of the Great Plains area, having an abundance of
food from the hunting of the bison and other animals, were slow
to take up plant culture.
The energies of primitive people are directed primarily toward
satisfying their few immediate wants, not infrequently with a total
disregard of their future existence or well-being. In some instances,
as in portions of the tropics, nature may be so abundant with her
gifts as not to offer incentives for development or progress. The
statement is frequently made that primitive man is completely a
creature of his environment, whereas civilized man transforms his
environment to suit his needs; yet primitive modes of living and
means of sustaining life embody some remarkable adjustments.
Thus Tozzer (18) brings out that among the Eskimos the relation
of population to land, clothing, food, shelter, tools, and weapons
all combine to make life possible in an Arctic environment. Stefans-
son has shown that the native methods of living are more suitable
in every way to the prevailing climatic conditions than anything
that the white man can devise. "Man is a most versatile animal
when it comes to an adjustment to his geographical environment."
Probable Stages in Early Agricultural Development. Man's
methods of securing food for himself and others passed, from all
indications, through a series of evolutionary stages. Three more or
less well-defined stages in the development of early means of obtain-
ing food and shelter are generally recognized: (1) the hunting and
fishing stage, (2) the pastoral stage, and (3) the plant culture stage.
These three generally recognized stages were not identical in all
regions; local conditions greatly modified developmental trends,
even to the extent of total elimination of one stage, as the pastoral
stage in the case of the American Indian. Likewise, it is not always
possible to draw clear distinctions between these stages. Neither
does the stage in which a particular tribe or group is found always
denote the plane of civilization. It is entirely possible that some
hunting and fishing people had developed a higher scale of culture
than their agricultural neighbors, although that was generally not
the case.
The hunting and fishing stage. The hunting and fishing stage
has often been glorified by poetic sentiments. Passarge (15) deals
at length with the personal and racial attributes that allow only
the strongest to survive among tribes gaining their livelihood by the
14 ECOLOGICAL CROP GEOGRAPHY
spoils of the chase. At the same time he points out that an exclusive
or nearly exclusive meat diet predisposes these people to various
nervous disorders. Some recent investigations by Hahn (9) seem
to show that this stage was very indefinite. It is considered doubtful
if there ever was a time when man subsisted entirely on the flesh
of animals slain in the chase. It is highly probable that early man
was on the search for both the animal and plant food products
that his environment had to offer.
It can be assumed that primitive man early recognized the im-
portance of obtaining and utilizing a variety of food products for
his well-being. Utilizing vegetable foods and realizing their values,
man soon observed how his prized plants were propagated. The
knowledge of plant reproduction gave rise to plant cultivation.
The pastoral stage. In most cases the second advance was
brought about through the domestication of animals. Extensive
agricultural development demands the possession of an efficient
beast of burden. The transition from hoe- to plow-culture necessi-
tated the presence and use of such animals. The pastoral stage
was found especially in the grass regions of Europe and Asia.
Certain tribes, such as the Khirghiz of Central Asia, still live the
nomadic life of herdsmen. Man now, instead of gorging himself in
times of plenty and starving in times of want, had means by which
he could tide himself over those periods when natural food supplies
were low. The concept of capital was born at this time ; wealth was
estimated by the ownership of cattle and sheep. Likewise, ownership
of land made its first appearance; certain families felt entitled to the
utilization of certain areas to the exclusion of others. The system
gave rise to the patriarchal family. Land was held not as private
but as tribal property. All members of a tribe claimed descent from
a common male ancestor. With the increase in the number of tribes
and the consequent restriction in the area allotted to each, it be-
came necessary to resort to the production of crops. This led to a
more settled population and eventually to the building of villages.
The plant culture stage. The origin of plant culture has already
been alluded to. Various planes of plant culture such as hoe- and
plow-culture can be pointed out. It is quite remarkable that many
of our present crop plants were improved and grown by primitive
people. Thus, according to Braungart cited by Dettweiler (4), the
Lake-Dwellers of Switzerland living in the Neolithic or late Stone
BACKGROUND OF AGRICULTURAL PRODUCTION 15
Age, extending perhaps up into the Bronze Age, that is from about
4000 to 2000 B.C., produced a great variety of crops such as: (1) the
dense-cored, six-rowed barley, Hordeum hexastichon, var. densum;
(2) the short-eared, six-rowed barley, H. sanctum of the ancients;
(3) two-rowed barley, H. distichon; (4) small lake-dwelling wheat,
Triticum vulgare antiquorum; (5) the so-called Binkel or club wheat,
T. vulgare compactum; (6) Egyptian or English wheat, T. turgidum;
(7) a dense-eared awnless emmer, T. dicoccum; (8) Einkorn, T.
monococcum; (9) two kinds of millets designated as Panicum miliaceum.,
and P. italicum; and (10) a type of wild flax still growing wild in
Greece, Linum angustifolium. Munro (14) also lists these same plants
as having been grown by the Lake-Dwellers.
The people around the Mediterranean had long grown the
cereals and were acquainted with numerous leguminous plants.
Oats and dwarf field beans were introduced into northern Europe
during the Bronze Age. Millet and oats were the most important
crops grown by the Nordic races of Europe.
Carrier gives a detailed description of the crop plants grown by
the Indians of North America. The far-reaching effect of Indian
contributions to American agriculture is shown in that our agri-
culture is at least one- third "native American." From the Indian
we have such important crop plants as maize, potatoes (both sweet
and white), tobacco, peanuts, some varieties of cotton, all the edible
beans except horsebeans and soybeans, all varieties of squashes,
field pumpkins, sunflowers, Jerusalem artichokes, tomatoes, garden
peppers, pineapples, and watermelons. Hedrick (11) gives a long
list of plants used by the Indians for food, medicinal, and industrial
purposes.
Hoe-Culture and Plow-Culture. Notable civilizations of an-
tiquity, such as those of Egypt and Babylon and, in America,
those of the Incas of Peru and of the Aztecs of Mexico, were built
on a system of hoe-culture. In the fertile valleys of the Nile and the
Tigris and Euphrates, hoe-culture soon gave way to a system of
plow-culture. At the time of the Spanish conquest of Peru hoe-
culture was still the prevailing system among the Incas; no beast
of burden had been domesticated. It is remarkable that these
early civilizations — as also the civilizations of Syria and those of
the most highly developed tribes of the North American Indians,
the Aztecs and Montezumas — developed in arid and semiarid
16 ECOLOGICAL CROP GEOGRAPHY
regions. The practice of irrigation among the peoples of these
sections merits attention. The conditions under which crops were
grown were worthy of the admiration of the present-day investi-
gator. The methods employed for bringing water from streams
or from the mountains to the thirsty fields have astounded even
modern engineers.
A number of explanations have been advanced in an endeavor
to account for the development of civilizations of antiquity in semi-
arid regions where irrigation was necessary for crop production.
The native vegetation in arid sections can be more readily subdued
by human efforts than the heavy forest type of vegetations found in
humid areas. Land grown up to trees and even to heavy sods was
difficult to clear, especially with the crude tools at the disposal of
early civilizations. The open formations common to the semiarid
regions were easily cleared and could be made to produce abundant
crops with the aid of water. Huntington and Gushing (12) bring
out the fact that the development of irrigation farming not only
demanded a settled population but also instilled into that popula-
tion the desire to improve on their physical and social environments.
Such improvements could be accomplished only by forethought,
industry, peace, and close cooperation of all the people of a given
area. Such conditions were conducive to the formation of systems
of government, to the development of relatively dense populations,
and to the advancement of civilization in general.
The agricultural development of China and India can be traced
back beyond the Christian era. In many sections of these countries
the agriculture even of today may be classed as a form of hoe-
culture. Since the English occupation of India, the agricultural
system in some sections of that country has been modified along
European lines. In the extremely densely populated sections of
southern China and throughout most of Japan the ox (the water
buffalo) cannot compete against the cheap human labor.
In the northern European region hoe-culture persisted much
longer than farther south, as in the Mediterranean region. It was
the system in use by the Germanic tribes at the time of the Roman
invasion. After that it soon gave way to a system of plow-culture.
Various forms of hoe-culture can be pointed out. The system
followed was dependent mainly on the food requirements of the
tribes concerned. In its lowest form seeds were merely put into the
BACKGROUND OF AGRICULTURAL PRODUCTION 17
soil and whatever crop resulted was harvested. In more advanced
stages certain definite cultural methods were followed. The Indians
of North America had prescribed methods of cultivating corn,
tobacco, and other crops. It was not long before man observed
that certain materials added to the soil tended to increase produc-
tion. First among such materials were the ashes resulting from the
burning of the native vegetations in the process of clearing the land.
Numerous references can be found to the early application of marl
in European countries. The Indians of Massachusetts adopted the
practice of fertilizing their fields with fish. The ancient Peruvians
early discovered the value of guano when applied to their fields.
The crude beginnings of crop rotation can also be traced back to
this early period. Worn-out fields were left fallow, and the grasses
and shrubs that were allowed to grow up were burned before the
field was again utilized. This system was followed even in early
American agriculture. Since land was abundant, little attention
was paid to enriching it. Thomas Jefferson said, "We can buy an
acre of new land cheaper than we can manure an old one." This
is the condition commonly encountered in new agricultural regions.
In older civilizations lacking suitable land the question of soil fer-
tility came more and more to the front. It is reported by Middlen-
dgrf (13) that the Incas of Peru laboriously removed the surface
soils of some of their fields upon exhaustion in order to provide
fresh soils for the plants, a practice hardly applicable to humid
sections.
Communal Farming. Space does not permit the historical
treatment of ownership of land. Early agricultural pursuits may be
classified under the heading of communal farming. The total
area of crop land surrounding a village was held in common by the
inhabitants. Every child in the village became a joint owner of
the land. Later the available land for cropping was allotted to the
different families. To ensure justice in dividing lands of varying
grades of fertility the land allotted to each family was broken up
into numerous small strips, scattered over the open fields. Meadow,
pasture, and waste lands were held in common for a longer period
than the arable lands. After this method of allotting land to families
was instituted, private ownership in land began to be recognized.
With it came the stratification of society. Various changes took
place in land tenure; however, the actual field operations remained
18 ECOLOGICAL CROP GEOGRAPHY
unchanged for many centuries. Venn (19), speaking of conditions
existing in England, states, "it is scarcely an exaggeration to say
that until the tardy introduction of root-crops, followed by the
enclosures of the eighteenth century, the methods of arable farmers
had remained substantially unchanged from Anglo-Saxon times.5'
Changes in economic conditions had a greater effect on contraction
or expansion of lands under plow than on the methods used in
crop production. Yields during medieval times were extremely
low; wheat yielded six to eight and barley around ten bushels per
acre.
Various forms of land tenure existed in early times. Gras (7),
for instance, discusses the small hereditary estates, the slave estates,
estates with free tenants, and estates with servile tenants in early
Roman agrarian history in the period from 200 B.C. to about 400
A.D. After that period a form of manorial system, later common
to central Europe and England, was developed in the Roman
Empire.
The Manorial System. A survey of the historical background to
agricultural production would not be complete without a brief
account of the medieval manor. The manorial system sprang up
in all the European countries ; its influences are still apparent in the
agricultures of these countries. The chief cause for the development
of this system, which greatly infringed on the personal liberties
of the mass of the population, can be found in the general trend of
thought prevailing during medieval times. Eucken (5) states that
"authority" more than any other word characterized the spirit of
submission fostered by the church and its allied agencies during
the Middle Ages. This spirit more than any other factor provided
a fertile soil for the development of the manorial system and the
general mental stagnation of the masses.
The transformation from the village community to the manor
was complex. In England, according to Fordham (6), it was
brought about by three major causes: (1) the distribution of the
ruler's rights to some favorite ; (2) the growth of the military class ;
and (3) the increase of the burden of taxation on the peasant class.
The movement toward the manorial system in England started
some time before the Norman Conquest. The Normans found the
manor well suited to their needs and did much to strengthen the
system. In Germany the manorial system was well established by
BACKGROUND OF AGRICULTURAL PRODUCTION 19
the eleventh century. It is held by some investigators that the
development of a more extensive system of agriculture through the
introduction of the plow was a contributing factor to the establish-
ment of the manorial system. "Whithersoever this implement
[the plow] hath gone, bondage and shame have followed in its
wake." The rise of the manorial system can also be explained,
probably with more weight than should be attributed to some of
the other reasons advanced, by the need for security and protection
from foes at home and from abroad.
The manor was a complex institution; it was self-sufficient, as was
all early and medieval agriculture, except for the necessity of
purchasing a limited number of manufactured articles. Along with
the system came great specialization of labor; all trades and duties
came to be hereditary. Rigid customs, allowing little play for
individual initiative, prevailed. Agricultural production made
little progress. The manor was instrumental in perpetuating the
open-field system with all its disadvantages.
The manor in England may be said to have had four ages:
its growth period extended from 800 to 1200 ; its height was reached
in the thirteenth century; it was on the decline from 1300 to 1500;
after 1500 it survived only in nonessentials. The conditions directly
leading to the fall of the system in western Europe were (t) the
numerous wars; (2) the Black Death; (3) religious and social agita-
tions ; and (4) the peasant revolts. The incessant warfare indulged
in by the nobility led to heavy taxation, with the peasants carrying
the major burden. Of these wars the Hundred Years' War, 1338-
1453, between England and France was of greatest consequence.
The Black Death, striking England in 1348-1350, after having
swept Europe from east to west, cut down on the supply of available
labor. It is estimated that one-third of the population of England
succumbed to the disease. Religious and social agitations, often
lacking in leadership and close cooperation, kept the masses stirred
up and clamoring for reform.
The manorial system survived longer in central and eastern
Europe than in the west. In Prussia and Austria the system survived
more or less unaltered up to the reigns of Frederick the Great and
Maria Theresa. The backwardness of these countries can be
attributed in a large degree to the devastating influences of the
Thirty Years' War.
20 ECOLOGICAL CROP GEOGRAPHY
The Seven Years5 War convinced Frederick the Great that the
military value of the peasant classes could be enhanced by some
degree of liberation. This, more than any other consideration,
caused him to take steps in that direction in the Act of 1749. Yet
really effective reforms did not come to Prussia until after the
Napoleonic invasion. The disaster of the battle of Jena, 1806,
brought out the need of definite reform (Abbott, 1). The revolu-
tionary principles of "liberty, equality, and fraternity" were of
tremendous help to Napoleon in his successive victories over Austria
and Prussia.
In Russia the manorial system survived even longer. It was
shaken somewhat by the after-effects of Russia's defeat in the
Crimean War, 1853-1856. The decree of 1861 abolished all legal
rights of noblemen over peasants, but even then complete liberation
was not accomplished. As stated by Hayes (10), "it has been re-
marked wisely, though possibly a little strongly, that the decree of
Alexander II freed the peasants from the nobles only to make them
serfs of the state." The disaster of the Russo-Japanese War of
1904-1905 was followed by agitations and some degree of libera-
tion. The final rupture came in 1917 following the herding of the
peasants to slaughter in the first World War.
Transition from the Medieval to the Modern Period. All
progress from the Middle Ages to the modern period was intimately
associated with the transition in trends of thought from the former
to the latter period. This phase of the discussion may well be sum-
marized by the main characteristics of modern philosophy enu-
merated below.
1 . Belief in the possibility of progress. Medieval thought was con-
cerned with maintaining the status quo. More thought by far was given
to spiritual than to the material existence of man.
2. Discovery of nature as interesting in itself and promising much for
improvement when properly understood and controlled. Here is given
a place for the development of modern science. Credit belongs pri-
marily to Francis Bacon for investigating and arousing interest in this
phase of human speculation after long neglect and periods of inactivity
since the days of the active Greek philosophers.
3. The repudiation of tradition.
4. The growing appreciation of the value of human life on its own
account.
5. Emphasis on the natural possibilities of man.
BACKGROUND OF AGRICULTURAL PRODUCTION 21
6. The development of individualism. The liberation from traditions
together with the realization of man's own possibilities resulted in a
freedom not before possible and an expression of individual ideas.
7. The attempt to free man from the domain of the supernatural.
This effort directed his attentions more to his physical and less to his
spiritual existence.
8. Thought tends to be revolutionary in that modern man is not
only willing but anxious to put to a test new ideas in the solution of his
problems.1
Eucken (5) sums up the transitions of thought from the early to
the modern period in an admirable manner.
The march of progress in agricultural pursuits as well as in other
lines of endeavor was markedly influenced by this change in
philosophy. The further progress of agriculture was also closely
associated with progress in the sciences and in experimental re-
search.
The Mercantile System. Mercantilism, according to Spann
(17), may be termed a new kind of economic practice involving a
number of novel and interdependent theories making their ap-
pearance at the opening of the modern era. The advocates of the
system were concerned with the exchange of merchandise and
the promotion of industrial development. The dominating feature
of these series of economic policies was a great esteem for money
and for foreign trade. Industry was looked upon as the precursor
of commerce. The primary object of the mercantilists was to
achieve for their respective countries a favorable "balance of trade"
with the objective of increasing the amount of money in the country.
To do this it was necessary to stimulate export trade of manufac-
tured articles and to reduce to a minimum the purchase of such
goods. While such a system led to a certain amount of freedom of
trade and laid the foundations of our present industrial state, it
was not always favorable to agricultural development. In the
effort to gain the object considered of prime importance to the
advocates of the system the export of raw materials was prohibited
in many countries. France prohibited the export of grain ; Frederick
the Great, of Prussia, decreed corporal punishment to any one who
should export wool. This was a decided disadvantage to agricul-
ture. It impoverished the agricultural classes and prevented the
1 These points are taken from a series of lectures on the "History of Philosophy"
given by Dr. M. T. McClure at the University of Illinois in 1925.
22 ECOLOGICAL CROP GEOGRAPHY
formation of centers of production of commodities to which certain
countries were best adapted. It tended to preserve self-sufficient
types of agriculture since it hindered application of the theory of
comparative advantage. In passing it should be mentioned that
the mercantile system provided fertile groundwork for the develop-
ment of intense nationalism with its drastic effects on the world
distribution of crop plants.
The Physiocratic System. The mercantilists' confusion of
economic wealth with the possession of precious metal led eventu-
ally to the belief that the system was responsible for certain fiscal
difficulties. This together with the restrictions against the export
of grain and the consequent low prices for that commodity resulted
in the swing of the pendulum to the opposite extreme. The physio-
crats under the leadership of Quesnay enthroned agriculture as the
only creative occupation; other workers, he held, performed only
a work of addition, of transformation, or of transport. "L'agricul-
ture est la source de toutes les richesses de 1'etat." To the physio-
crat the essentials of an equitable economic system should guaran-
tee to the individual personal libertfvthe free choice of occupation,
freedom of industry and consumption, freedom of movement from
place to place, and freedom of private property. These essentials
are summarized in the famous motto "Laissez faire et laissez passer,
le monde va de lui-m&ne" (Let do and let be, the world goes of
itself).
The physiocrats expounded their theories in France; the poor
state of agriculture during the eighteenth century had, no doubt,
much to do with the formation of their ideas. That the tiller of the
soil be considered as the only creative worker is, of course, a gross
overstatement. True, the agriculturist produces food products and
feeds other toilers of industry, commerce, and the professions. Yet,
from the standpoint of utility, the services rendered by these latter
classes are by no means sterile.
Even though the main theories promulgated by the physiocrats
rested on an infirm foundation, they had a very decided effect on
agricultural production. They promoted a degree of individualism
without which commercial agriculture could not have developed.
Their influence was great, especially in the new agricultural regions
of the world opened up for settlement during the course of the
nineteenth century.
BACKGROUND OF AGRICULTURAL PRODUCTION 23
Recent Stages in Agricultural Production. The main changes
in philosophy from the medieval to the modern period have been
discussed. These decided changes in trends of thought had a
profound effect on agricultural development. Four more or less
well-defined stages in the development of agriculture during the
modern period may be pointed out: (1) the development of scien-
tific agriculture; (2) the development of commercial agriculture;
(3) the development of mechanized and highly specialized agri-
culture; and (4) the very recent period of intense national feeling
and attempts to achieve national self-sufficiency in agricultural
production.
Scientific agriculture. The development of scientific agriculture
is intimately associated with discoveries in science and with the
applications of these findings to agricultural problems. Scientific
rotation of crops with the view of establishing a permanent system
of agriculture became established with the greater and more ex-
tensive use of legumes. As a result crop yields were increased and
periods of scarcity and actual famine became less frequent. Speciali-
zation in production, the growing of crops in sections especially
adapted to their production, had its beginnings during this period.
This was decidedly at variance with the old medieval self-sufficient
type of agriculture. The marked improvements in methods of
transportation during the seventeenth century and the transition
from village to town economy greatly furthered specialization in
production.
Russell (16) outlines three periods in the historical development
of conceptions of the requirements of plant growth: (1) the search
for the "principle" of vegetation, 1630-1750; (2) the search for
plant nutrients, 1750-1800; and (3) the modern period.
During the early period investigators were imbued with the idea
of discovering some one "principle" to account for the phenomenon
of soil fertility and plant growth. Space does not permit the enu-
meration of the accomplishments of the modern period. There
were the great accomplishments of Boussingault, who laid out a
series of field plot experiments on his farm at Bechelbronn in
Alsace in 1834; SprengePs work on the ash constituents of plants;
Schiibler's investigations in soil physics; the great works of Liebig
in Germany and of Lawes and Gilbert in England. It remained the
cask of Hellriegel and Wilfarth to demonstrate that the fixation of
24 ECOLOGICAL CROP GEOGRAPHY
nitrogen by legumes was a biological process. This was accom-
plished in 1886 ; two years later the organism concerned was isolated
by Beijerinck. During this period very marked improvements
were made in all crops and animals as also in general agricultural
practices.
Commercial agriculture. Agriculture was greatly influenced
by the establishment of metropolitan economy during the last
century. Vast new regions in North and South America, Africa,
and Australia were thrown open to agricultural production, and
agriculture in the older sections greatly improved. The tremendous
increase in world population and the impetus given by the indus-
trial revolution were influential in the ever-greater specialization
in the production of agricultural commodities. The self-sufficient
agriculture of older regions gave way to specialization ; production
here was modified through the availability of cheap products
from the newly exploited areas. Food and other commodities
became more abundant than in any previous period of history.
The warning of the possible dangers in increasing populations
sounded by Malthus at the end of the eighteenth century was not
considered serious in the face of the new abundance. Scientific
discoveries were effectively applied to agricultural production,
industry, and transportation. The "tempo" of exploitation, as it is
called by Zimmermann (22), was speeded up to tremendous rates.
A spirit of optimism promising an entirely new basis of civilization
was engendered by the new tools put at the disposal of mankind.
Wright (21) presents a vivid picture of the new age with special
reference to the population problem.
"The progress of civilization has enabled man to exercise a constantly
i increasing control over nature and to wring a larger and larger supply
i \ of food from the earth, but never, probably, until the middle of the
; ' nineteenth century has human subsistence been brought within meas-
/ urable distance of the reproductive power of the race. At that period,
i the rapid development of natural resources in North America, ren-
dered possible by the no-less-rapid development in Europe, especially
in Great Britain, of coal and iron and the manufactures depending
upon them, gave to the white races of Western Europe the extraordinary
experience of a supply of things for human consumption increasing
even more rapidly than the population could do with an almost unre-
stricted birth-rate. Increasing returns to every dose of capital and labor
applied either to agriculture in the New World or to manufacturing in
BACKGROUND OF AGRICULTURAL PRODUCTION 25
the Old were obtained for a time. The standard of living rose, the cost
of living continued to fall, and man's conquest over nature seemed well-
nigh complete. Then it was that in spite of the warning voices of Mill
and Jevons the progress of the human race towards material and
spiritual perfection was generally in Western Europe believed to be
continuous and inevitable. Malthus with his Principle of Population
and Ricardo with his Law of Diminishing Returns were discredited."
Mechanized and highly-specialized agriculture. Call (2)
in speaking of the efficiency of American agriculture calls attention
to four factors: (1) the discovery and introduction of new crop
plants, especially of such plants as early varieties of spring wheat,
hardy varieties of winter wheat, the sorghums, and legumes such
as alfalfa and sweet clover, all of which were effective in advancing
the agricultural frontier into the drier areas of the west and the
shorter season areas of the north; (2) the use of mechanical inven-
tions and power which shifted the burden of production from
human to horse- and motor-driven equipment, making the tasks
of the producer less arduous and greatly increasing his efficiency;
(3) the application of science to production, improvement, and
protection of plants and animals; and (4) the education of the
American farmer and his family.
The application of power equipment opened vast areas to pro-
duction. To what an extent harvesting operations alone have been
simplified and brought to a high state of efficiency since the days
of the invention of the reaper by McCormick in 1831 is shown by a
citation from Walker (20).
"A century ago an able-bodied man could cradle two acres of wheat
in a day, and it took two other men to bind and shock what he had cut.
Or in other words it required three men to cut, bind and shock two
acres of wheat in a day. With the present day harvesting machines,
such as a 20-foot combine pulled by a modern tractor and with a farm
motor truck for hauling grain, an equal number of men in a western
Kansas wheat field can cut, thresh and deliver to market a distance of
two miles forty-five acres of wheat in a day. This is fifteen times the
acreage cut, bound and shocked by the three men of a century ago.
Moreover, the work of the present-day harvest hand is less arduous and
much more interesting."
The application of motive power increased agricultural produc-
tion in two ways: (1) by causing new lands not previously used for
the production of crops to be brought into production; and (2) by
26 ECOLOGICAL CROP GEOGRAPHY
releasing large acreages of crop and pasture land formerly re-
quired to feed work animals replaced by tractors and trucks for the
direct production of cash crops. According to Gray and Baker (8),
around 20 to 25 million acres of crop land were released for other
uses as a result of the rapid adoption of tractors, trucks, and auto-
mobiles in the United States from 1918 to 1929, truly a substitu-
tion of inanimate for animate sources of energy. Stored-up solar
radiation is used as a source of energy.
It has been stated that a greater expansion in agricultural pro-
duction resulted from the above factors than subsequent world
economic conditions at the time demanded. For the time being a
halt has been called. Retrenchment of production appears immi-
nent. It should be carried out along lines of logical land utiliza-
tion. Production should recede on an ecological basis.
Intense nationalism. The first World War and the world de-
pression ushered in a period of intense striving toward a national
agricultural self-sufficiency. This caused developments running
counter to the trends toward specialization in the world production
of agricultural commodities and called for decided changes in
agricultural policies in the import and adjustments in the export
countries.
REFERENCES
1. Abbott, J. S. C., The Life of Napoleon Bonaparte^ Vol. 1. Harper, New
York, 1854.
2. Call, L. E., "The increased efficiency of American agriculture,"
Science, N. S. 69:54-60 (1929).
3. Carrier, L., The Beginnings of Agriculture in America. McGraw-Hill,
New York, 1923.
4. Dettweiler, "Aryan agriculture," Jour. Heredity, 5:473-481 (1914).
5. Eucken, R., The Problem of Human Life, trans. German by Williston
S. Hough. Scribner, New York, 1910.
6. Fordham, M. A., Short History of English Rural Life. G. Allen & Unwin,
Ltd., London, 1911.
7. Gras, N. S. B., A History of Agriculture in Europe and America. Croft,
New York, 1925.
8. Gray, L. C., and O. E. Baker, "Land utilization and the farm prob-
lem," U. S. Dept. Agr. Misc. Pub. 97, 1930.
9. Hahn, E., Das Alter der Wirtschaftlichen Kultur. Heidelberg, 1905.
10. Hayes, C. J. H., Political and Cultural History of Modern Europe. Mao
millan, New York, 1932.
BACKGROUND OF AGRICULTURAL PRODUCTION 27
11. Hedrick, U. P., A History of Agriculture in the State of New York. New
York, Agr. Exp. Sta., Geneva, 1933.
12. Huntington, E., and S. W. Gushing, Principles of Human Geography.
Wiley, New York, 1924.
13. Middlendorf, Peru. Berlin, 1894.
14. Munro, R., The Lake-Dwellers of Europe. London, 1890.
15. Passarge, S., Landschaft und Kulturentwicklung in unseren Klimabreiten.
Friederichsen & Co., Hamburg, 1922.
16. Russell, E. J., Soil Conditions and Plant Growth. Longmans, London,
1927.
17. Spann, O., The History of Economics, trans. German (19th ed.) by
Eden and Cedar Paul. Norton, New York, 1930.
18. Tozzer, A. M., Social Origins and Social Constituents. Macmillan, New
York, 1925.
19. Venn, J. A., Foundations of Agricultural Economics. University Press,
Cambridge, England, 1923.
20. Walker, H. B., "The combine, a factor in wheat production," Report
of Kansas State Board of Agriculture of the quarter ending March,
1927.
21. Wright, H., Population. Harcourt, Brace, New York, 1923.
22. Zimmermann, E. W., World Resources and Industries. Harper, New
York, 1933.
Chapter HI
POPULATION IN RELATION TO AGRICULr-
TURAL DEVELOPMENT
Population and Agriculture. "Hunger and new ideas are two
advocates of change which plead best in each other's company;
hunger makes men willing to act, and new ideas give them matter
for enactment." These words of Bonar (1) may well be applied
to the problem created by increasing population and less rapidly
increasing supplies of available food. Population growth and food
supplies are closely related. Yet, because of the complexity of the
problem, a great variety of factors must be considered in the rela-
tion of agricultural development to increases, and rates of increases,
in the numbers of the human spefcies. While the pressure for the
means of subsistence often may have stirred man to activity, it
was by no means the only factor making for advance. As a matter
of fact, the time and energy of a people may be drawn upon to the
extent of greatly interfering with advance and the furthering of
culture traits. Again, nature may be so abundant with her gifts
as to offer no incentive for exertion and progress. If under such
conditions population increases beyond the means of subsistence,
drastic means may be resorted to in order to keep the numbers of a
tribe within certain limits. Not infrequently, however, necessity
becomes the mother of invention. An increasing population and
the subsequent pressure for food have in times past and will, no
doubt, in the future lead to more and more intensive studies of
problems involved in the production and the distribution of food
and other agricultural products. A brief consideration of the growth
and demands of population merits the attention of the agricultural
scientist.
The Population Problem. No attempt will be made here to
summarize the voluminous literature on population and population
growth. Exhaustive studies of the problem may be found in the
published works of Bowen (2), Carr-Saunders (3), East (4), Pearl
28
POPULATION AND AGRICULTURE 29
(10), Thompson (16), Reuter (12), Wright (20), and other investi-
gators.
The population problem divides itself into two phases, (a) the
quantitative and (b) the qualitative features. Obviously both are
of great importance. The qualitative aspects of the problem fall
mainly in the fields of eugenics and genetics. The quantitative
feature, dealing more directly with the numbers of a population
rather than with its composition, has a more direct bearing upon
the questions under discussion here.
The main features of the population problem, some of them quitt
evident, having a direct bearing on agricultural production may
be briefly stated in the following twelve points. These twelve
points by no means circumscribe the entire problem; there are
many social and economic aspects.
1. Man in order to survive must have food, clothing, and shelter.
2. It is the task of agriculture to provide the major portion of thfc
means by which life can be sustained.
3. There is a definite man-land ratio which cannot be greatly altered
without effecting modifications in the arts, the standard of living, or
the cultural development of a people. Changing conditions demand
adjustments either on the man side or on the land side of the ratio.
4. Agricultural production can be increased greatly, through
development and application of the arts, beyond its present limits
should the demand arise and society feel inclined to pay for such
expansion.
5. The law of diminishing returns applies to agricultural produc-
tion; it cannot be set aside. Beyond a certain limit an increasing number
of either hands or heads cannot produce a corresponding increase in
food supplies.
6. Economy in production and the judicial use of land demands
recognition of the population problem. Agricultural production until
recently was geared to rapidly increasing populations. The recent
slowing down of such rates of increase calls for adjustments in the
tempo of agricultural production and exploitation.
7. Man has a great propagating capacity or fecundity.
8. Without the intervention of definite checks, either imposed by
nature or self-imposed by man, population would soon increase to a
point beyond the most optimistic estimate of the possible means of
subsistence.
9. World population has been increasing over a long period of
time; it has increased at an especially rapid pace throughout the last
century and during the beginning of the present century and is still
increasing. .
30 ECOLOGICAL CROP GEOGRAPHY
10. Psycho-economic forces and the spread of knowledge of birth*
control methods have been instrumental in lowering birth rates in
Western civilizations and may be expected in the future to hold rates of
increase down to certain more or less desired limits. In the over-
populated sections of the Orient natural forces are most effective in
preventing rapid increases in population. The more enlightened na-
tions of the Orient, like Japan, may from all indications soon be expected
to apply Western methods to their population problem.
11. While birth rates in countries of Western civilization have de-
creased markedly, mortality rates have also decreased. The salvage of
human life resulting from this may be explained by the great advances
made in medical science, in sanitation, in engineering devices affecting
water supplies and disposal of sewage, and above all by the greater
abundance, quality, and variety of food products available. Improved
nutriment is the greatest foe of death and disease.
12. It is exceedingly difficult to make reliable predictions relative to
future behavior of populations, rates of increase, or even possible
declines. With an increasing desire for a higher standard of living and
means at hand to regulate birth rates, intelligent population control
may be expected to keep population within the limits of the means of
subsistence.
The Growth of Population im Primitive Societies. The rate
of increase in population of primitive societies is dependent mainly
on their state of culture. Wissler (19) points out that the number
of Indians inhabiting the plains of North America was extremely
low in relation to the present and the potential population of that
region. The culture of the Red Man of necessity had to succumb to
that of the advancing white settlers before the region could support
a larger population than was possible under the hunting and crude
plant culture complex. As stated by Wissler, "one fact stands out
in human ecology, viz., that under a given culture the tribal group
expands until it reaches the limit of its food supply; then if it does
not succumb, or remain static, it evolves a new mechanism for
feeding itself, only to repeat the phenomenon over once more."
Sumner and Keller (14) make a similar observation.
Aside from the stage of culture, which in itself is determined to a
large degree by environmental factors, the population of a primitive
tribe is determined mainly by factors leading to a scarcity or abun-
dance of food. The elements of the climate are in this respect of
greatest consequence insofar as they determine the availability of
food as well as the food requirements of man. Since population
tended to increase up to and often beyond the limits of its food
POPULATION AND AGRICULTURE 31
supply, there resulted a constant struggle to provide the means of
subsistence. According to Keller (8), savages have no real "pop-
ulation policy" even though such practices as abortion and in-
fanticide are frequently resorted to in order to keep down numbers.
Keller terms such practices traditional rather than rational.
Centers of Civilization. Favorable environments favor increase
in numbers. Culture traits developed in those areas where en-
vironmental conditions were favorable to a relative concentration
of members of the human species. The man-land ratio was then
influenced by means of improvement in the arts. Using Sumner
and Keller's terminology, "it is the arts that must carry any in-
creasing burden of numbers." Areas favorable to the necessary
initial concentration of population and the beginning and develop-
ment of the arts of cultivation were found in the river bottoms of the
warmer temperate regions of the Old World — in China, Northern
India, Assyria, and Egypt. Here were found, according to Greg-
ory et al. (7), the first foci of civilization. Attention is called to the
fact that these early centers of civilization developed in relatively
dry regions where irrigation became necessary to ensure stable
crop production. The early centers of civilization in America,
those of the Incas, Aztecs, and Montezumas, also developed in dry
areas. The possible influence of irrigation on the promotion t>f
civilization has already been discussed.
Greek and Roman Population Theories. The ancient Greeks
approached the population problem from the standpoint of the
ideal City State. Both Plato and Aristotle were conscious of the
dangers involved in overpopulation. One of Aristotle's criticisms
of Plato's Republic was that Plato did not sufficiently meet this
difficulty.
More drastic means were resorted to in Sparta than in Athens
to secure the proper man power for military purposes. Here,
greater emphasis was placed on the quality of the population;
weak infants were exposed so that they would not fall burden to the
state. There seems to have been little fear of overpopulation in
Sparta; the number of slaves was kept in check by infanticide,
while frequent wars served to keep down the number of freemen.
Population policies aimed primarily toward an increase in the
numbers of the states' military forces.
In Rome, an increase in population was actively stimulated.
32 ECOLOGICAL CROP GEOGRAPHY
The rearing of legitimate offspring was conceived to be a public
duty. Marriage existed for the purpose of rearing citizens for the
state and soldiers for the army. Various laws against celibacy and
childlessness were passed. As in Sparta, awards were given for
large families. Yet the experience was identical with that ol
nations of modern times who have attempted to increase birth
rates; the rates of increase among the upper classes remained low.
The numerous military expeditions were a heavy drain on the man
power of the empire.
Influences of Christianity. Early Christianity rather dis-
couraged marriage, which was looked upon as an inferior state,
to be tolerated but not to be encouraged. This was a decided
reaction to trends in Rome. The fathers of the church paid scanl
attention to political and economic considerations. As stated by
Reuter, "in its medieval form the Christian doctrine was not
favorable to fecundity.35
The Middle Ages finally gave rise to a period of strong national
feeling. With this rise of national consciousness came profound
changes. The church with its authority no longer discouraged in-
creases in population but, seeing strength in numbers and being
closely associated with the military parties, began to foster fruit-
fulness and proceeded to bestow its blessing upon it. Thus,» ac-
cording to Bowen, "in the Middle Ages a great deal was heard oi
Christian soldiers and the armies of Christ ; the cross and the sword
became so mixed up that swords were made in the form of the
cross, and the impress of the cross and the blessings of the churct
were given to all implements of destruction." Attention should be
called to the numerous religious wars of medieval Europe, of which
the Crusades and the Thirty Years' War stand out as bloody ex-
amples.
Even after the Reformation, authorities of the church had little
conception of the population problem. Thus, Luther states,
"Gott macht Kinder der wird sie auch wohl ernahren." Because
of theological bias the problem was seen as a moral one; an im-
plicit faith in nature was cultivated.
Population of Medieval Europe. No accurate figures of the
population of medieval Europe are available. Some estimates
have been made, however. At the time of Christ, the populatior
of Europe was probably less than* 5 million. At the time of the
POPULATION AND AGRICULTURE $3
Norman Conquest, A.D. 1066, it was estimated at around 10 million.
Mulhall estimated the population of Europe in the fifteenth
century as around 50 million. Willcox (18) approximates that the
constituents of the six language groups, English, French, German,
Italian, Russian, and Spanish, amounted to probably 50 million
in 1492, or about one-ninth of their present number.
From all indications, population increased rather slowly during
medieval times. Plagues, epidemics, famines, wars, and other
catastrophes were interpreted as the instruments of God, used to
chastise and to teach his people, and were, therefore, regarded as
natural happenings. It was considered irreligious and a form of
heresy to inquire into the causes of these disasters which swept
down on unsuspecting humanity from time to time and kept their
numbers in check.
Effects of Mercantilism. A definite trend toward denser popu-
lation became evident around the middle of the sixteenth century.
The efforts of the mercantilists to foster foreign trade and industry
created a demand for laborers. As a result, all possible agencies
were applied to foster increase in population. Improvements in
commerce and the means of transportation had much to do with
the realization of this desire. An exchange economy took more
definite shape than before; agriculture started to drift from the* old
self-sufficient pattern to one of specialization. Conditions in general
favored the growth of population.
Population growth was fostered through economic and mili-
taristic motives. A few quotations from writers and theorists of
the time will serve to bring out the emphasis put on the importance
of numbers. Thus, Thomas Mun in advocating denser popula-
tions wrote: "For when a people are many and the arts are good,
there the traffic must be great and the country rich." Thomas
Temple wrote: "The true and natural wealth of nations is the
number of people in proportion of the compass of the ground they
inhabit." Zincke states: "All legitimate means must be used to
maintain a constant increase in the population of a country."
And the words of Justi read: "A land can never have too many
inhabitants." Vauban makes a very typical statement: "By the
number of their subjects is measured the grandeur of kings."
Even Adam Smith comes out with a statement taken from Bowen
very much in line with the philosophy of the mercantilist, the
34 ECOLOGICAL CROP GEOGRAPHY
militarist, and the churchman of the time: "The most decisive
mark of the prosperity of any country is the increase in the number
of its inhabitants." Later Smith makes a statement with a slightly
Malthusian color: "Countries are populous, not in proportion to
the number of people whom its produce can clothe and lodge, but
in proportion to that of those whom it can feed."
The mercantilists placed emphasis on numbers; they were
concerned only slightly with the living conditions of the masses.
Scant attention was given to the relationship between increasing
populations, possible food supplies, and the comforts of life. It
is undeniably true that the most favorably endowed areas of the
world are the most populous. However, the reason for the richness
of these areas is not to be found in the density of the population ;
rather, populations are dense because of the favorable environment.
The mercantilists had not realized the fact brought out so well by
Bowen, who states: "This theory of progress through over-propa-
gation results in two opposed doctrines of population; the political
and the economic. The political exhorts man to propagate and
prevail; the economic to be cautidx^s and comfortable."
The Industrial Revolution. By the end of the eighteenth
century practically all sections of Europe were populated to the
greatest possible extent that could be supported under the agri-
cultural, economic, and social regime then prevailing; there was a
definite approach to ideas of Malthus. Certain sections had reached
the saturation point, and emigration on a large scale had not yet
begun. Population had increased rapidly, while the art of food
production had made but little progress. Exchange economy was
still backward, and while agriculture had made some progress
toward specialization, it was still of rather local proportions.
World trade in agricultural commodities was only beginning.
The masses were destitute. Yet, many political economists still
clung to the old idea that national strength was determined by
numbers alone. It is no small wonder that many of them were
distrustful of the doctrines advanced by Malthus.
Then came a rapid succession of mechanical inventions, and
with them was ushered into existence a new industrial system.
Home industries gave way to machine and the factory type of
industry, accompanied by a wage system. The development of
manufacturing was more rapid in England than on the Continent,
POPULATION AND AGRICULTURE 35
which remained largely agricultural, except for small areas, until
the latter part of the nineteenth century.
After the initial period of adjustment, the development of manu-
facturing gave work to the masses. With the increasing develop-
ment of an exchange economy, the fruits of their labors were used
to bring food supplies to the new industrial centers. The new
agricultural regions, especially in North America and later in
South America, Africa, and Australia, served as ready markets for
manufactured articles offered in exchange for the raw products and
especially the agricultural products that they produced. With
relatively unrestricted, or free, trade relationships, with marked
improvements in means of communication and transportation,
and with vast natural resources at man's disposal for exploitation,
world trade developed at a very rapid rate. Agriculture grew
from a task of merely local proportions to a world industry. The
industrial revolution resulted in the specialization of labor in the
field of industry ; in agriculture, it resulted in the specialization of
production. Sections with climatic and soil conditions especially
adapted to certain crops, such as wheat, rye, or tobacco, specialized
in the production of these crops. The advantage of such a system
from the standpoint of conserving human energy is quite evident.
Hdwever, it does call for a complicated system of distribution.
As a result, when the established economic systems are thrown out
of adjustment for any reason, one may expect, for the time being,
a reversal in the process, or a tendency to revert to the older self-
sufficient type of production.
Vegetable and Machine Civilizations. All sources of energy
in the final analysis may be traced to stellar, chiefly solar, radiation.
There are two main sources of energy available to man: (a) the
current and very recent receipts, and (b} the stored-up supplies.
The first would be the energy derived either from the direct utiliza-
tion of plants or plant products or from the utilization of animals
or animal products. This energy is directly traceable to recent
plant and vegetable growths. The second class of energy is also
traceable to plant life, but was fixed at some distant period. Under
this class are found the fuels, such as coal, oil, natural gas, and
peat, and the various products that can be derived from them.
All these forms of energy are fixed by means of the photosynthetic
process of plants. The first form of energy supply is called animate,
36 ECOLOGICAL CROP GEOGRAPHY
the second inanimate, energy. Civilizations dependent solely
upon muscle power, that is, the energies produced by man and
domesticated animals, are designated by Zimmermann (21) as
"vegetable civilizations." Civilizations making extensive use of
motive power are referred to as "machine civilizations."
One of the greatest handicaps in the vegetable civilization is the
lack of mobility. The energy available is not sufficient for the
development of rapid and efficient means of communication and
transportation. As a result of this deficiency, a closed or locally
self-sufficient economy prevails. The development of a machine or
technological civilization with its greater employment of inanimate
energy in production, communication, and transportation was a
vital factor in the establishment of world trade and in the resulting
specialization in agricultural production.
World Population Increases from the Beginning of the
Nineteenth Century. The nineteenth century witnessed a most
remarkable increase in population, not only in Europe but also
in all the other continents. This was to be expected in view of the
abundance of natural resources to t>£ exploited with the new tools
so recently placed at the disposal of humanity. It was decidedly a
period of expansion. Another contributing factor is to be found in
the fact that birth rates remained at rather high levels throughout
the nineteenth century while death rates in all the Western countries
were markedly lowered by improved living conditions, improve-
ments in sanitation, and advances made in medical knowledge.
The population of Europe increased from 200 million to 456
million, of Asia from 400 to 870 million, of Africa from 100 to 140
million, and of the Americas from 20 to 205 million.
The remarkable increase in the population of both North and
South America is readily explained by immigration and the high
birth rates of the new settlers. The high birth rates are directly
traceable to the abundance of natural resources and the general
philosophy of the times favoring large families. These two conti-
nents offered room for expansion for the multitudes of overcrowded
Europe.
The most amazing fact is the great increase in the population of
Asia. The reason for this may best be found by an analysis of
population increases in the three great centers of population of that
vast continent, namely, China, Japan, and India.
POPULATION AND AGRICULTURE 57
The best estimates available place the population of China at
around 400 million. Indications are that it remained practically
constant during the nineteenth century. The birth rate is high —
according to some authorities, 50 per 1,000 as against 18 per 1,000
in nations of the Western civilizations. But the death rate is also
high. Sanitary conditions are poor, and proper food for infants is
not available. "China," says Ross (13), "offers a living example of
conditions as they existed in Medieval Europe. The lack of sanita-
tion and proper food is counteracted by the great fecundity of man,
a wasteful method indeed, but the Chinese survive."
Japan experienced a great increase in population after opening
its doors to European and American commerce. Before that time
the population of the islands seems to have been practically sta-
tionary. The Japanese, unlike the Chinese, sifted from the Euro-
American culture those traits that could be of help and use to them
and could be readily assimilated. The population of Japan has
increased almost threefold during the past century.
India, like Japan, through European intervention, was able to
increase its numbers greatly. As stated by Wright: "British rule
has done much to improve conditions of life in India but it has also
cut away many of the checks to population which formerly pre-
vailed there." In 1851, the population of India was estimated at
178.5 million; in 1930, India had a population of 352.4 million
souls. As pointed out by Wattal (17), British intervention not only
served to remove in part the existing checks but also provided
means for improving and increasing agricultural production. Vast
sums have been expended for irrigation developments and on
research of pressing agricultural problems.
Population Trends during the Early Part of the Twentieth
Century up to the First World War. The industrial or mechanical
revolution gave rise to centers of manufacturing and the consequent
ability of the masses to purchase food supplies from distant centers
of production. Technological advances and advances in medical
science ensured better health and greatly lowered the death rate,
while birth rates continued at fairly high levels. These were in
brief the main factors responsible for the phenomenal increases
in world population during the last century. That rates of increase
remained high during the very early part of the present century is
evident from Table 1, showing the rapidity with which certain
38
ECOLOGICAL CROP GEOGRAPHY
countries were increasing their populations in the period 1905-
1911.1
TABLE 1. RATE OF POPULATION GROWTH IN CERTAIN COUNTRIES FOR
THE PERIOD 1905-1911
Country
Rate of Increase
per 1,000
Number of Tears Required
to Double
France
1 6
436
Norway
6.6
105
Sweden
8.4
83
Austria-Hungary
8.5
82
Spain
8.7
80
England
10.4
67
Taoan
10.8
64
Holland
12.2
57
Germany
13.6
51
Rumania
14.8
47
United States
18 2
38
Australia
20 3
34
Canada
29.3
24
The rate of increase of the whift%race was especially high. The
reasons for this are not far to seek. At the present time the white
race has political control of 90 per cent of the habitable areas of the
globe. This alone removes the check under which the colored rac'es,
especially the yellow, are laboring. There are yet many regions
under control of the white race which have reached neither the
saturation point for population nor their point of maximum produc-
tion.
1 To the white race can be attributed the distinction of having a
wider range of climatic adaptation than any other race. This,
together with their knowledge and skill in making a region origi-
nally unfit for white colonization fit for the white race, has been of
great help in gaining the present supremacy in numbers.
Another factor contributing to the supremacy of the white race is
brought out in the studies reported by Sweeney (15). The vital
index or, as Pearl designates it, the birth-death ratio, computed by
the formula
100 X births
was used to evaluate the health of dif-
deaths
ferent populations. If the ratio for a given population yields values
1 This table, taken from East, was cited from Knibb's work, The Shadow of the World? t
Future.
POPULATION AND AGRICULTURE 39
of over 100, then it is growing and in a healthy condition. If the
ratio is less than 100, the population may be considered biologically
unhealthy. It became evident from the studies conducted by
Sweeney that the populations of the northern European races, of
the Australian races, and of Canada and the United States had
higher vital indices and may, therefore, be regarded biologically
healthier than other peoples.
The Man-Land Ratio. At the rate of increase prevailing in 1 923,
the population of the world will reach, according to East, 5,200 mil-
lion in a little over a century. Since this statement was written there
has been a decided decrease in the birth rates in all Western coun-
tries, and it may be said that there is no immediate prospect of the
rates regaining their former levels. Another factor to be considered
is that with declining birth rates the mean and mode of the age
classes tend to shift to a higher age level, which will result, unless
counteracted by other factors, in a somewhat higher death rate in
the future. It is safe to say that the experiments reported by Pearl
(10) on the rates of growth of populations of fruit flies (Drosophila)
influenced East in arriving at his estimate of future human popula-
tion. That the rates of increase of man are to a considerable extent
determined by his own volition is becoming increasingly evident
by 'the falling birth rates of the countries influenced by machine
civilization. Psycho-economic factors have affected rates of increase
and no doubt will affect them in the future. The desire for a higher
individual standard of living, especially on the part of people
who have experienced a fuller life, has a very decided depressing
effect on birth rates. Or, as one notably moral reviewer of Senior's
Oxford Lectures of 1828 quaintly phrased it: "More persons will
rather dine alone on champagne and chicken than share their
roast beef and pudding with a wife and family." The "wife and
family" add, no doubt, to the joy of life of a great number of people,
but the tendency is to keep the family small. To quote Bowen:
"Having children for the greater glory of God or Country, which is
to say the manufacture of pew renters and cannon fodder, is not the
modern mode."
Gray and Baker (5) give graphically the trends of birth rates in
five countries of northwestern Europe. All countries show a decided
downward trend. According to these authors: "The rate of de-
crease in birth rates is greater than in death rates. If the trend con-
40 ECOLOGICAL CROP GEOGRAPHY
tinues, stationary population in the highly industrialized countries
appears inevitable.55
Birth rates are following the same general trend in the United
States as in the industrial countries of Europe. The birth rates are
higher in the rural states than in the urban states; however, both
have been decreasing at about the same rate since 1 921 . The higher
birth rates in the rural states are to be expected in view of the fact
that children on the farm are less of a liability and interfere less
with the freedom of their parents than under urban conditions.
To use the words of Gray and Baker:
"The birth rate is declining so rapidly that if the rate of decline con-
tinues for another seven years the number of births will not be sufficient
to maintain the population of the country when the children of today
reach maturity. Assuming no important change in the volume of
immigration, our population appears to be gradually approaching a
stationary stage, which will be attained in from 30 to 40 years, when,
it seems probable, the Nation's population will be between 150,000,000
and 170,000,000."
Pearl et al. (11) estimate the population of the United States to
reach about 175,000,000 in the year 2000. The implications of a
possible stationary population in the United States and in other
countries to agricultural production trends are evident. Agri-
cultural production during the past century was geared to supply
the demands of rapidly increasing populations. Now agricultural
producers must recognize the far-reaching effect of reduction in the
rate of increase of populations and with it the slowing down of
demand for food products.
The spirit of the new civilization is well expressed by Thompson :
"Industrialism, which for almost a century bade fair to flood the
world with people, so that not even its continued advance in efficiency
could ensure them a good living, has provided its own cure in making
living conditions such that a steadily increasing proportion of people
refuse to raise large families. Indeed, many of them refuse to raise
children at all."
The fact must not be disregarded, however, that there are in the
world, according to the figures compiled by the International
Institute of Agriculture, only 13,000 million acres of land available
for food production. The likelihood of synthetic foods is very
remote. At any rate, synthetic foods would make a poor substitute
POPULATION AND AGRICULTURE 41
for beefsteak. It is also well to keep in mind that the supply of
natural resources is not unlimited. The rate at which natural re-
sources have been exploited and wasted is alarming and by no
means a credit to humanity. This applies to mineral and plant
resources, and especially to the greatest of all natural resources,
the soil. Much of agriculture can rightly be classed as soil mining.
Vast areas have been ruined for agricultural production by faulty
soil management. Want and scarcity have played a great part in
the events of human history. Many people, even at this date, are
continually on the verge of starvation. Reuter cites a long list of
comparatively recent famines and gives estimates of the millions
of human lives lost through starvation. While the farmers of the
plains of North America were burning corn in 1921, starvation
stalked the plains of Russia. The supposed "curse" of surpluses
and carry-overs is a recent innovation.
Should the population of the world ever reach 5,200 million,
which is not likely for a considerable period of time at present rates
of increase, then, keeping in mind that there are but 13,000 million
acres of arable land, there would be but 2.5 acres per capita, which
is close to the minimum amount of land required for the support
of one human being. Agricultural production can be supple-
me'nted, of course, by the utilization of sea foods, but the importance
of sea foods can be readily overemphasized. Gray et al. (6) point
out that the amount of land in Germany prior to 1914, after allow-
ances were made for importations of food products, was 2.0 acres
per capita.
Optimum Population Density. The problem of determining
an "ideal man-land ratio" is fraught with difficulties. Obviously
some countries and sections are ovcrpopulated, while others have
resources to support larger populations than they now have. Opin-
ions relative to optimum densities differ. Nevertheless, populations
show certain rather definite tendencies in reaction to particular
resource patterns. The population history in a new country such
as the United States is largely a response of population to a most
favorable supply of natural resources. Reuter summarizes popula-
tion tendencies leading to the theoretical optimum in the following
manner:
"1. So long as there exists uncultivated fertile areas within a coun-
try, a sparse population is unfavorable to the best economic returns.
42 ECOLOGICAL CROP GEOGRAPHY
^ 2. A reasonably dense and increasing population is favorable to
occupational specialization, and the consequent rise of intellectual and
leisure classes is conducive to progress especially in intellectual, artistic,
and other lines not immediately nor primarily productive of utilitarian
values.
3. A sparse population, in the presence of undeveloped resources,
gives rise to the phenomenon of migration and the consequent mon-
grelization or displacement of peoples and the cross-fertilization or
substitution of cultures.
4. A sparsity of numbers hinders and density favors communica-
tion, and communication is the fundamental prerequisite to cultural
advance.
5. The welfare of the individual units of a society is closely de-
pendent upon the relation of numbers and the means of subsistence."
The factors determining world centers of population will be
discussed in the next chapter.
REFERENCES
1. Bonar, J., Malthus and His Work. *411en & Unwin, London, 1885.
2. Bowen, E., An Hypothesis of Population Growth. Columbia University
Press, New York, 1931.
3. Carr-Saunders, A. M., The Population Problem. Clarendon Press,
Oxford, 1922.
4. East, E. M., Mankind at the Crossroads. Scribner, New York, 1923.
5. Gray, L. C., and O. E. Baker, "Land utilization and the agricultural
problem," U. S. Dept. Agr. Misc. Pub. 97, 1930.
6. Gray, L. C., O. E. Baker, F. J. Marschner, B. O. Weitz, W. R. Chap-
line, W. Shepard, and R. Zon, "The utilization of our lands for crops,
pasture, and forests," U. S. Dept. Agr. Yearbook 1923:415-506.
7. Gregory, H. E., A. G. Keller, and A. L. Bishop, Physical and Com-
mercial Geography. Ginn, Boston, 1910.
8. Keller, A. G., Societal Evolution. Macmillan, New York, 1931.
9. Malthus, T. R., An Essay on the Principle of Population. Ward Lock &
Company, London, 1872.
10. Pearl, R., The Biology of Population Growth. Knopf, New York, 1925.
U. 9 L. j. Reed, and J. F. Kish. "The logistic curve and the
census of 1940," Science, N. S. 92:486-488 (1940).
12. Reuter, E. B., Population Problems. Lippincott, Philadelphia, 1923.
13. Ross, E. A., The Changing Chinese. Century, New York, 1919.
14. Sumner, W. G., and A. G. Keller, The Science of Society, Vol. 1. Yale
University Press, New Haven, 1927.
POPULATION AND AGRICULTURE 43
15. Sweeney, J. S., The Natural Increase of Mankind. Williams & Wilkins,
Baltimore, 1926.
16. Thompson, W. S., Population Problems. McGraw-Hill, New York,
1930.
17. Wattal, P. K., The Population Problem in India. Bennett, Coleman
& Company, Bombay, 1916.
18. Willcox, W. F., "The expansion of European population," Amer.
Econ. Rev., 5:737-752 (1915).
19. Wissler, C., Man and Culture, Crowell, New York, 1923.
20. Wright, H., Population. Harcourt, Brace, New York, 1923.
21. Zimmermann, E. W., World Resources and Industries. Harper, New
York, 1933.
Chapter IV
FACTORS DETERMINING WORLD CENTERS
OF POPULATION AND AGRICULTURAL PRO-
DUCTION
The Human Environment. At the beginning of his work on
Political Geography, Ratzel makes the far-reaching statement:
"Jeder Staat ist ein Stuck Boden und Menschheit" (every nation
is a bit of soil and humanity). The extent to which the development
of society, social institutions, and the welfare of the individual
human being is influenced by environmental factors has been
discussed by numerous authors. Man, of course, can adapt his
modes of living and means of gaining a livelihood to quite a variety
of climatic and other environmental factors. Yet it cannot be
denied that the physical environment sets quite definite limits to
practically all lines of endeavor and that particular elements of the
environment not infrequently determine the extent to which it may
be modified to make a given area more or less habitable and suitable
for human occupation. Any given area must either directly or
indirectly be able to produce the means by which man may modify
the direct effects of his physical environment.
The general relationship of world population to agricultural
pursuit and development has been pointed out in the previous
chapter; it is the object of this chapter to discuss more directly
the factors determining the fitness of a given region for a more or
less dense population.
The present population of the world is estimated as somewhat
above 2 billion. There are at the present time four very distinct
world centers of population, namely (1) western Europe, (2) the
eastern temperate part of North America, (3) China and Japan, and
(4) India and the East Indies. The first two of these are white
centers while the last two represent population centers of colored
races. The Caucasian and Mongolian races are the two ruling
races. Figure 1, taken from Zimmermann (9), shows the distribu-
tion of population over the surface of the earth.
44
I
a
46 ECOLOGICAL CROP GEOGRAPHY
Potential Centers of World Population. Certain definite fac-
tors have been operative in the establishment of the present large
centers of population. Other centers, no doubt, will develop in the
future in such generally favorable regions as along the western coast
of North America, at the southern and especially southeastern tip of
Africa, the southeastern part of Australia and New Zealand, and in
the more temperate regions of South America. It will be noted that
all the probable future centers of population are in regions now
occupied by the white race and, therefore, logically may be counted
on to be white centers. Since the white race occupies by far the
greater expanse of the earth's surface, conditions favorable to its
requirements will determine mainly the future of the existing centers
of white population as well as the development of potential centers.
The areas available to the colored races are already densely popu-
lated; great increases in their numbers cannot be expected unless
they can muster sufficient force to occupy new areas with environ-
mental conditions favorable for the support of dense populations.
Probably as important as possession to the future of the existing
centers of population and to the development of potential centers
is that lands now in the possession of the white race are high in
climatic energy, well endowed with natural resources, and acces-
sible to world trade. In other words, these areas are quite habitable.
Taylor (7) presents maps based on physiographic data which "in-
dicate that white settlement will tend to congregate around five
world centers, or cluster of cities of a type which Geddes named
conurbations. These are London, Chicago, Sydney, Durban, and
Buenos Aires. Of these, the center in the United States will prob-
ably be the largest." This prediction is somewhat at variance with
the theory of the establishment of stable populations in the near
future, as discussed in the previous chapter.
The potential possibilities for the future development of a region,
as stated by Olbricht (6), were formerly evaluated mainly on the
basis of the fertility of its soil, the amount and distribution of pre-
cipitation, its wealth of mineral resources, and above all its accessi-
bility, so essential to economic means of communication. To these
factors, states Olbricht, must be added the new bioclimatic factor
or the influence of the climatic energy of the region in question.
The lack of climatic energy in the Mediterranean type of climate
is looked upon by Olbricht as a contributing, if not the most im-
CENTERS OF POPULATION AND PRODUCTION 47
portant, factor in the decay of early centers of civilization of antiq-
uity in the Orient and in the disintegration of the cultures of
ancient Greece and Rome. The strength and vigor of populations
living in areas of low climatic energy, if they are to be maintained,
must be revived continually by an influx of emigrants from areas
of high climatic energy. Unless that is possible, a deterioration in
energy and a desire for accomplishments, according to Olbricht,
is bound to take place
Advancements in medical knowledge particularly along the lines
of disease prevention have been effective in recent years in contrib-
uting to the habitability of otherwise uninhabitable areas.
Factors Determining World Centers of Population. Climatic
conditions are no doubt of primary importance in determining the
distribution of human energy, since the climate of a region deter-
mines more than any other single factor, not only the health of a
people but also the type and fertility of the soil and its most eco-
nomic utilization. All the great present and potential centers of
population are located in the world's great agricultural regions.
Some of them, notably those which Huntington (4) so aptly desig-
nated as the rice civilizations, developed in strictly agricultural
regions under the impetus of an available and abundant supply of
food- Climatic conditions producing good health and an energetic
race are essential to the establishment of great and progressive
centers of population. The vegetable civilizations of the Far East,
notably in China and India, produced and still support great
populations. They have developed and continue to survive in
regions lacking in climatic energy. These people did not have the
energy to progress like the people of northwestern Europe even
though their civilization is much older. They clung instead to the
old ways and were complacent under existing conditions. The
Japanese developed, on the other hand, in a more energetic type
of climate and, as evidenced by their activities, are embued with
the spirit of progress.
"But," states Taylor, "however energetic a race may be it has
not much chance in the struggle for existence if natural resources
are wanting." Abundant natural, especially mineral, resources
make possible a great concentration of population within limited
areas, provided that these areas are readily accessible. The brief
survey of the effects of the industrial revolution served to emphasize
48 ECOLOGICAL CROP GEOGRAPHY
the relationship between industrial activities and population in-
creases.
The factors determining density of population are interrelated so
that it is difficult to discuss them separately. But man's health and
energy depend upon climate and weather more than on any other
single factor. It is for this reason that the effects of climatic factors
will be considered first. All elements of climate enter into play,
viz., temperature, rainfall and humidity, amount of sunlight, air
movements, and variability. Each of these factors will be taken up
in order insofar as possible.
Temperature. Temperature, as a single factor, is of greatest
importance in determining the fitness of a region for human occupa-
tion and endeavor. The direct effect of temperature on man is to a
great degree modified by other climatic factors. This must be kept
in mind when optimum temperatures are discussed. Temperature
sensibility (Temperaturgefuhl), as Hann (2) designates it, is in-
fluenced especially by the humidity of the air, more particularly
by the relative humidity. It is affected in a smaller degree by wind
velocity and the intensity of the«unlight; these factors, of course,
are associated more or less with variations in humidity.
The northern boundary of white settlement corresponds with the
northern limits of cereal production, running from the southern
part of Alaska across Canada, striking the southern end of Hudson
Bay, across Eurasia from the northern portions of Norway and
Sweden, across Finland, European Russia, and Siberia to the south-
ern extremity of Kamchatka. This same line also cuts off the south-
ern tip of South America. The polar boundary of agriculture is
not far from the annual isotherm of 30°F.
For physical health the optimum temperature for the white
race is given by Huntington (4) as around 64°F as an average for
day and night together. The optimum for mental labor is given
a good deal lower, probably at around 40°F. These figures given
by Huntington do not take seasonal variations into consideration.
Olbricht also distinguishes between optima for mental and physical
energy, giving the points of 4°C (40°F) and 16°G (52°F) for each.
Taylor gives the annual optimum temperature best suited for the
white race as around 55°F. He classes annual temperatures into
groups, in order of their favorable effects, as (1) 50 to 60°F, (2) 40
to 50°F, (3) 60 to 70°F, (4) 30 to 40°F, (5) 70 to 80°F, (6) 20 to
CENTERS OF POPULATION AND PRODUCTION 49
30°F, (7) above 80°F, and lastly (8) below 20°F. Taylor considers
the annual isotherm of 70°F as marking the maximum for the
growth of the white race. Likewise, dense populations cannot be
expected to develop in regions with an annual temperature of less
than 40°F. It must be considered that these figures have general
application only. They do not take into account the factors in-
fluencing temperature sensibility.
Olbricht observes a slower shading off of civilization from the
optima in the temperate zones toward the equator than toward the
poles. In other words, the tundra of the polar regions are greater
enemies to civilization than the rainy tropical forests which, not-
withstanding their unfavorable influences, are able to produce
plant products.
The classification of regions with regard to prevailing annual
temperatures has general application only. The variability of the
climate is of considerable importance. The temperature sensibility
is also of great consequence and cannot be left out of consideration
in the evaluation of temperature belts. Since, however, it is affected
by a variety of climatic phenomena, it would be difficult to set up
reliable indices. Temperature sensibility is influenced to the great-
est degree by the amount of moisture in the air and also by. air
movements (Visher, 9).
The conditions pointed out by Visher explain why the south-
western portion of the United States and regions with similar cli-
mates, with rather high annual and especially high summer tem-
peratures but with relatively low humidities and prevailing winds,
are nevertheless quite healthful and well suited for human occupa-
tion. Except for these conditions man could not endure without
danger or great discomfort the high summer temperatures in regions
with extreme continental types of climates.
Likewise, the interior northern regions of the larger continents
would be quite unsuitable for human habitation were it not for
the low humidity and the comparative calm during the extremely
cold winter months. Owing to these conditions of the atmosphere,
the prevailing low winter temperatures can be endured without too
much discomfort. This refers especially to the continental regions
of the northern Great Plains area in the United States, to the prairie
provinces of Canada, and to the central areas of Russia, both in
Europe and in Asia. While these areas do not at present and cannot
50 ECOLOGICAL CROP GEOGRAPHY
in the future be expected to have dense populations, they are,
nevertheless, of great importance from the standpoint ot supplying
food products, especially cereals, to the world's great population
centers. The low humidity of the air makes these regions habitable,
but since this low humidity is rather closely correlated, not only
with the amounts of precipitation, but also with seasonal variability
in the to-be-expected amounts of rainfall, it offers a great obstacle
to stable crop production and to the establishment of even mod-
erately dense populations. "Not only are the grasslands on the
western border of the plains country in a climatically dry region,"
states Bowman (1) in speaking of climatic conditions prevailing in
eastern Montana, "they are in a climatically variable region. They
are in the grip of a general law, that the drier the climate the less
dependable the rainfall. It is not true that deserts are always dry.
What makes them undesirable for most humans is that one cannot
depend upon their being wet." This statement applies to all regions
with markedly continental, more specifically grassland, types of
climates as does his statement that "the marginal belts of light
rainfall, where farming is barely possible, are the regions of greatest
agricultural insecurity.55
Rainfall and humidity. Rainfall and the humidity of the air in
general are, next to temperature, the greatest factors in determin-
ing the fitness of a region for human endeavor. The interrela-
tionships of humidity and temperature sensations have already
been discussed. Rainfall is unlike temperature in that it is not
possible, at least not without stating a considerable number of
modifying factors, to determine any optimum amount. Taylor
states that the lower limit of important settlement can be placed at
about 1 5 to 20 inches of precipitation per annum. A rainfall of more
than 60 inches is generally considered a disadvantage. Taylor sets
up a provisional optimum of 50 inches per annum in the construc-
tion of his "econograph.55 This appears fairly high. The effective-
ness of precipitation as it relates to plant life is modified by a variety
of climatic factors such as temperature, seasonal distribution, and,
above all, evaporation. More will be said about this in discussions
relating to plant habitats, classification of climates, and studies of
particular ecological factors.1 Since centers of population cor-
respond well with centers of intensive crop production, it is prudent
1 See Chapter XIII, "Humidity Provinces." '••
CENTERS OF POPULATION AND PRODUCTION 51
at least to mention these various interrelationships at this point.
A high temperature during the rainy season in regions with well-
defined seasonal precipitation, as in Japan, is objectionable. A
combination of high humidity and high temperatures is decidedly
unhealthful. On the other hand, heavy precipitation during the
cooler seasons of the year, as in the Pacific Northwest, is not nearly
so objectionable.
Variability. The other climatic factor of importance in deter-
mining the suitability of a region for the development of dense
populations is variability or variation in weather. This refers to
seasonal as well as to intraseasonal variations. As pointed out by
Huntington (3) and Olbricht (6) the greatest climatic energy is
found in regions with frequent cyclonic disturbances, such as in
northwestern Europe around the North Sea and the Baltic, north-
eastern and central United States, the southeastern portion of
Canada, and at the southeastern tip of Australia. Huntington
(3 and 4) and Huntington and Gushing (5) present numerous maps
showing interrelationships of climatic energy and various measures
of degrees of civilization. The region of greatest climatic energy in
the United States and Canada is interrupted to the west by an
area with long summer heat and drought, and to the south* by
higher than optimum temperatures and lack of variation during the
summer months. The climate along the Pacific coast is not con-
sidered variable enough to be classed by Huntington among the
most energetic. The same objection is made to the climate of the
Mediterranean region. The belt of greatest climatic energy in
Europe extends over the region adjacent to the northern Atlantic,
the North Sea, and the Baltic, where cyclonic storms are com-
mon. Climatic energy decreases as the unbroken plains of
Poland and Russia with their long monotonous winters are en-
countered.
It is in these regions of greatest climatic energy that the greatest
advances in civilization have been made. It is also in the regions of
greatest climatic energy that the excess of human energy has fre-
quently been spent in destructive wars.
Resources. Centers of population are not determined by climatic
factors alone. If that were the case, they would have to be self-
supporting, which they are not. Present centers of population are
based on an exchange economy. Because of their extreme concen-
52 ECOLOGICAL CROP GEOGRAPHY
tration of population in limited areas, such centers must draw on
distant areas for their food and other supplies.
It is fortunate for the development of centers of population that
the regions of highest climatic energy and the regions with the
greatest wealth of natural resources are coincident, or nearly so.
The natural resources which come into play here are fertile soils;
minerals ; a source of power and heat, such as coal, oil, and water
power; timber products; returns from fisheries; etc. The develop-
ment of a manufacturing center demands the presence of raw
products to be converted into finished goods, the power necessary
to accomplish this economically, accessibility to trade channels, the
necessary capital to finance the undertakings, and last, but not
least, the necessary labor to man the factories. Where a source of
power and the required raw materials are available, the other re-
quirements will be forthcoming, providing, of course, that the loca-
tion is favored by accessibility and that there is a demand for the
product or products to be manufactured.
Taylor, after considering the close relationship between the
abundance of coal and the density* of populations, made the far-
reaching statement that "the more one studies the resources of the
world the more astounding is the position of the United States.
That country is most highly favored in respect to temperature,
rainfall, coal — so that the center of the world's industry and of the
white population will inevitably move across the Atlantic from
Europe to North America." The significance of this statement is
evident, though to one agriculturally minded and recognizing that
populations must above all be fed, it is difficult to see why the Aus-
tralian geographer does not include the wide expanses of fertile
soils on the North American continent in his enumeration of great
natural resources.
Space does not permit the discussion of other natural resources
influencing population densities. Hydroelectric power and power
from petroleum products may be expected to replace coal at least
in part and in certain locations. A good illustration of the substi-
tution of hydroelectric power for coal is found in the highly cen-
tralized industrial development in parts of Norway and Sweden.
Soil fertility. That the fertility and the producing capacity of
the soil has a great influence on the density of population that a
region can support is shown by the fact that the most densely
CENTERS OF POPULATION AND PRODUCTION 53
populated areas of the world are located in regions where soil and
climatic conditions are generally favorable to the growth of crop
plants. A fertile soil, together with climatic conditions favorable
to an abundant growth of plant life, is essential to the development
of a dense population in regions where vegetable civilizations
predominate. The phenomenally dense populations of such regions
as southeastern China, eastern India, and Java owe their existence
almost entirely to the fertility and producing capacity of the soils
in those areas. Industrial civilizations are not so directly dependent
on native soil fertility as are the vegetable civilizations. They
produce manufactured goods that can be exchanged for food and
other necessities of life. But since their food and clothing come from
the soil, expanses of fertile soil are, nevertheless, a great asset to
industrial centers. Large expanses of fertile soil are essential to
agricultural development. Progressive agricultural regions con-
tribute very directly to the growth of industry. Not only does
agriculture supply many of the raw products to be processed; it
also provides an outlet for a wide variety of manufactured articles.
No industrial region can develop and prosper without a source of
raw materials or a market able and willing to utilize the articles
manufactured. The western movement of the center of population
in the United States can be attributed largely to the extensive and
progressive agricultural development of the lands of the Mississippi
Valley and the eastern Great Plains area.
Some of the world centers of population, notably those of the
industrial sections of northwestern Europe, are not located in areas
with high native soil fertility. The soils contiguous to these popula-
tion centers have, however, been brought up to a high producing
capacity through the expenditure of human energy and the applica-
tion of scientific methods of soil management. Agriculture in the
sandy lowlands of Germany and in similar sections was given a great
impetus through the intelligent application of potassium salts and
other commercial fertilizers. In other places vast sums have been
expended for drainage and other forms of improvement. Though
one thinks of white centers of population as highly industrialized,
which they are, a rather high percentage of the inhabitants of those
areas gain their livelihood directly from the soil.
The Econograph. Taylor points out four factors determining
the establishment of centers of white population, namely (1) tern-
54
ECOLOGICAL CROP GEOGRAPHY
perature, (2) rainfall, (3) coal reserves, and (4) the average eleva-
tion of the region, which reflects on accessibility and ease of com-
munication within the area in question. Of these factors the least
weight is given to the last, the elevation factor. On the basis of these
four factors Taylor constructs a quadrangular graph which he
calls the "econograph." The four determining factors are graphed
on the axes of the figure.
An optimum econograph
is presented in Fig. 2.
Taylor considers 55°F the
optimum annual tempera-
ture and 50 inches of rain-
fall per annum as most
favorable. The most favor-
able location is taken at
near sea level. The coal
supply is graphed in units
of 10,000 tons per square
mile. The maximum area
of the econograph is 1 ,000
units. Lines connecting
regions of equal econo-
graph area, to indicate
equal habitability, are
designated as "isoiketes."
Taylor gives the theoreti-
FIG. 2.
An optimum econograph.
Taylor.)
(After
cal isoiketes for Europe. The values of these isoiketes correspond
well with the location of the great centers of population in that the
isoikete 600 embraces the great industrial areas of the continent.
The econograph is of value also from the standpoint of variations
in its shape in that it reflects directly on the utilization of the area
in question, that is, whether the area is primarily suited to some
form of agriculture or to the development of industry. Where the
area is suited to both, a symmetrical graph results.
Population Centers and Food Producing Areas. After discuss-
ing centers of population it will be interesting to consider briefly
the relationship of these centers to the world's important food pro-
ducing areas. As has been pointed out before, the distribution of
any specific crop is determined by physiological and social factors
CENTERS OF POPULATION AND PRODUCTION 55
that need not be discussed here. It is well, however, to call atten-
tion to the fact that, in order to make possible the intensive produc-
tion of food and other agricultural products, climatic conditions
must be healthful to the people engaged in agriculture. Further-
more, most of the great staple crops used by the white race are
grown to best advantage in those regions now largely occupied by
this race and under climatic conditions favorable to white civiliza-
tion. There are, of course, notable exceptions to this, as for instance,
the production of sugar from sugar cane, the production of rice, and
some of the world's cotton producing areas. In order to include the
world's great food producing areas it is necessary to add to the four
great centers of population but a few other areas, some of which
were spoken of as potential centers of population. Ten rather well-
defined important world agricultural areas can be pointed out as:
(1) the central portion of the United States and the prairie provinces
of Canada; (2) Argentina and southern Brazil; (3) northwestern
Europe; (4) central and southern Russia; (5) the Balkan area;
(6) the Mediterranean region; (7) China and Japan; (8) India;
(9) southern Africa ; and (10) southeastern Australia. The limiting
factors to crop production in each of these areas will be discussed
in Chapter VIII, which deals with the physiological limits of pro-
duction.
The factors of location and accessibility apply to centers of
production as well as to centers of population. This is true especially
for the production of products for export. New agricultural regions,
as in South America and in the interior of Asia, can be brought into
production by making them accessible to world commerce. For
more than a century Russia has attempted to secure a seaport on the
Mediterranean so that her excess products could move out while
her northern harbors are frozen. Russia has become involved in
two major European wars in an effort to realize this objective.
REFERENCES
1. Bowman, I., "Jordan country," Geog. Rev., 21:22-55 (1931).
2. Hann, J., Handbuch der Klimatologie, Vol. 1. Verlag von J. Engelhorn,
Stuttgart, 1908.
5. Huntington, E., Civilization and Climate. Yale University Press, New
Haven, 1915.
4. , The Human Habitat. Van Nostrand, New York, 1927.
56 ECOLOGICAL CROP GEOGRAPHY
5. Huntington, E., and S. W. Gushing, Principles of Human Geography.
Wiley, New York, 1924.
6. Olbricht, K., Klima und Entwicklung. Versuch einer Bioklimatik des Men-
schen und der Sdugetiere. Gustav Fischer, Jena, 1923.
7. Taylor, G., "The distribution of future white settlement. A world
survey based on physiographic data," Geog. Rev., 12:375-402 (1922).
8. Visher, S. S., Climatic Laws. Wiley, New York, 1924.
9. Zimmermann, E. W., World Resources and Industries. Harper, New York.
1933.
Chapter V
THE SOCIAL ENVIRONMENT
Environment Defined. The terms "environment" and "habi-
tat" may be used interchangeably; they refer to one and the same
thing. Both terms were used originally in the sense of describing
the particular locus inhabited by an organism or group of organ-
isms. With the advance of scientific methods, the ecologist is not
entirely satisfied with a mere description of the places inhabited by
organisms but aims rather to evaluate definitely the conditions
under which living beings exist and survive. The application of the
word "habitat," in relation to plant life, for that reason has been
extended to mean, as Tansley (16) speaks of it, "the sum total of
effective conditions under which a plant or community lives."
Fitting (4) has the same conception of the environment, speaking
of it (Standort) as "die Gesamtheit der Umweltsfaktoren eines
Org&nismus." Nichols (11) defines the term in the same manner
as Tansley and Fitting but stresses the response of the individual
organism to environmental factors by stating that "the environ-
ment of any organism may be described as the sum total, or per-
haps better, the resultant of all the external conditions which act
upon it."
This chapter will be devoted to an evaluation of some of the
factors of the social environment of crop plants ; the physiological
environment and its components will be discussed in the following
chapter. Since, however, the two have such a direct bearing on
crop distribution, it will not be possible always to keep them entirely
apart ; they are so closely related that certain phases of one cannot
be considered without bringing in the other.
The Physiological and Social Environments. The distribution
of crop plants, as has been pointed out in Chapter I, is determined
not only by physiological, but also by economic and social factors.
The physiological growth requirements of any crop plant set defi-
nite limits to the production of that particular crop.
57
58 ECOLOGICAL CROP GEOGRAPHY
The social environment, as is evident from its definition, includes
a great variety of factors. The distribution of crop plants is in-
fluenced by many economic and social forces; consequently, the
field to be considered under the social environment cannot well
be circumscribed. Obviously the various factors of this social en-
vironment cannot all be treated in detail in a general publication;
volumes could be and have been devoted to discussions of each
phase of this great problem. The entire field of economics has a more
or less direct bearing on the problem of crop distribution. Cardon
(3) assigns to the field of agricultural economics a coordinating
position in relation to other lines of agricultural research. The
economics of production may not set quite so definite a limit to the
production of a certain crop as the physiological requirements of
that crop, but, nevertheless, it determines the eventual limits of
production. A crop cannot survive for any great length of time in a
given area unless its production represents a profitable enterprise.
As stated by Hughes and Henson (6), "the major crop of most
sections is a high profit crop for that section."
The need of differentiating between the physiological and the
social environments, in relation to the general study of crop distri-
bution, is brought out by the comprehensive definition of land as
given by Black and Black (1). These authors not only include in
their definition the nature-given surface of the earth and the ma-
terials comprising this surface but recognize also the importance of
the prevailing climatic conditions, its location with respect to
markets, and any alteration of the surface instituted by man during
his use or improvement of the land.
Natural and Artificial Social Environments. World trade is
based on the exchange of commodities and services. Since the
production of goods can be stimulated or retarded by various
economic and political devices, it becomes necessary to differentiate
between natural and artificial environments. Where a production
enterprise is developed and survives on its own merit without the
aid or interference of definitely superimposed economic or political
stimulation or inhibition, it may be considered as existing and
surviving in a natural environment. An artificial environment is
created by the establishment of various forms of subsidies or in some
cases possible inhibitions to production. Import duties, tariffs, and
import quotas offer the most notable examples of the creation of
THE SOCIAL ENVIRONMENT 59
artificial social environments. Such subsidies may be considered as
economic or man-made barriers to the free movement and in-
directly to the production of goods.
The world-wide operation of the principle of comparative ad-
vantage to the production of any commodity is definitely interfered
with by the creation of such economic or political barriers. It
enables producers to grow certain crops in areas where soil and
climatic or other conditions are not altogether favorable to their
production. Since prices are elevated to an artificial level, it en-
courages also the employment of a higher intensity of production
than would otherwise be possible. It goes without saying that
artificial environments are created at the expense of the consumer
of the products so produced. Likewise, the height of the barriers
created depends upon such factors as the docility of the consumer,
the degree of economic stress prevailing, and not infrequently the
creation and fostering of a spirit of intense nationalism by various
agencies. That the erection of man-made barriers influences the
normal or the to-be-expected world-wide distribution of field crops
on the basis of their physiological growth requirements is self-evi-
dent. The producers of commodities protected by subsidies are
placed in an artificial environment and at an advantage over those
producers operating in unprotected regions. Unless climatic and
soil conditions in competing areas are comparatively so much su-
perior as to overcome the effects of these man-created barriers
erected by normally importing countries, or countries where the
physiological environment may not be especially favorable to the
production of the crop in question, the production of the crop will
increase in response to the creation of the artificial social environ-
ment at the expense of areas in countries with favorable climatic
and soil conditions for the production of the crop, but where the
production of that crop is not subsidized.
How import duties and the establishment of import quotas
affect the world market of agricultural commodities has already
been pointed out in Chapter I. Natural barriers set definite and
constant limits to production, while artificially created barriers are
subject to rapid revisions depending on changes in political and
economic moods.
A word of caution is necessary in discussing the operation of the
principle of comparative advantage, in that factors other than those
60 ECOLOGICAL CROP GEOGRAPHY
of the physiological environments of competing regions have a
direct bearing on the subject. Differences in the social environ-
ments and, above all, differences in the standards of living of vari-
ous regions may have profound effects. The production of spices,
drugs, and perfume plants may be cited as an example. Climatic
and soil conditions in many sections of the United States are favor-
able to the production of these specialized plants but, until the
crises brought about by the second World War, not at a price to
compete with foreign products. The greatest item of cost in the
production of such crops consists of labor. In enterprises demanding
great amounts of hand labor, a country with high labor costs cannot
compete with those of low labor costs and low standards of living.
Agricultural Areas in Relation to Population and Transporta-
tion. Von Thuenen represented agricultural production zones
surrounding a center of population located on a fertile unbroken
plain, without navigable rivers or any means of communication
except by wagon, by concentric circles drawn around the city.
Zone 1 produces products that are both bulky and highly perish-
able. Zone 2 produces less perishable and less bulky products such
as potatoes or milk. In the third zone the milk is made into butter,
a product still less bulky. Farther out, grain crops are fed to live-
stock and transported on the hoof. Finally comes the range.
Figure 3 gives a graphical view of the transformation of the pro-
duction zones occasioned by introducing a ready means of trans-
portation such as a navigable river. Modern city markets represent
a more or less exaggerated form of von Thuenen's graphic presenta-
tion. Every means of transportation, by water, by rail, or by paved
highways, entering a city or group of cities creates .bulges in the
surrounding production zones.
With the introduction of refrigeration, even more or less per-
ishable agricultural commodities can be moved over great distances.
Nevertheless, the distance over which a commodity can be moved
economically is in proportion to its value and bulk. Prairie hay
can be moved but short distances before the equivalent of its value
is expended for transportation costs, while alfalfa hay, because of
its greater value per unit, can be moved economically over greater
distances. Likewise, the coarse grains like oats and barley, unless
they are intended for some special use, cannot be moved economi-
cally over as great distances as wheat or flax, which are of greater
THE SOCIAL ENVIRONMENT 61
unit value. Wheat, because of its value and special use, moves over
great distances from its numerous points of production to milling
and consuming centers.
The production zones of any crop are shaped also by the physio-
logical limitations encountered. Furthermore, the methods of
FIG. 3. Zones of production surrounding a city on a plain, with a river flowing
through it. (Adapted from Von Thuenen.)
production employed may be modified materially by variations
in existing economic, climatic, and soil conditions in various areas.
Differences will be found in the degree of specialization in produc-
tion, in the amount of power machinery employed, and in the
intensity of production.
A good illustration of the effects of definite agronomic, economic,
social, distribution, and transportation factors on the development
and continuance of the main large milling centers of the United
States is given by Pickett and Vaile (13). Space does not permit
the discussion of these various phases as they influence the milling
industry. They are mentioned to bring out the fact that the produc-
tion zones and the industries they supply with raw products to be
processed are influenced by a great variety of factors.
62 ECOLOGICAL CROP GEOGRAPHY
Transportation as a Factor in Interregional Competition.
The cost of moving a commodity to market has a very direct bearing
on the possibilities of deriving profit from any production enterprise.
The greater the cost of transportation the more remunerative must
be the enterprise in order to survive. Not infrequently the greater
transportation costs from distant producing areas are in part coun-
terbalanced by other factors of the social environment or by more
favorable conditions of the physiological environment. If that is
not the case, or if environmental factors are even less favorable at
the points distant from the market than near it, the enterprise is at
a considerable disadvantage. Under such conditions expansions in
production can and do take place only during periods of compara-
tively high prices, to be followed by painful retractions upon the
return of prices to more normal levels.
Lower transportation costs have the same effect as the moving of
an area of production, if that were possible, nearer to the market.
Such a condition would serve to put the more distant producing
centers in a more advantageous competitive position with those
areas near the terminal markets. It might even call for major
adjustments in the sections near the market. Change in any other
factor, such as the more extensive employment of power machinery,
which might lead to a lower cost of production in one or another
section would have similar effects.
It must be borne in mind that transportation costs do not always
vary directly with the distance over which commodities must be
moved. Land transportation, especially where mountain ranges
or other physical barriers are encountered, is notoriously more
expensive than water transportation. The development of crop
producing areas of such great importance in the world commerce
of agricultural commodities as those in South America, notably
Argentina, in Australia, and in southern Africa, was greatly fur-
thered by their fortunate location with respect to cheap water
transportation. The fortunate location of these distant areas
(distant, that is, from the world's main centers of population) with
respect to trade routes by water enables them to compete actively
with those areas located near the great markets of the world.
As stated by Gregory et al. (5),
"the wealth of a country cannot be utilized to the greatest advantage
unless there are good transportation facilities; our great iron and steel
THE SOCIAL ENVIRONMENT 63
industries would still be in their infancy, were it not for the excellently
organized service afforded by the transportation companies on the
Great Lakes. The great wealth in our farm lands in the central West
would still be unavailable, were it not for the railways which connect
those regions with the seaboard."
Before the advent of truck transportation and the subsequent
improvement of highways, production of even the less bulky prod-
ucts was out of the question in areas without railroad facilities.
The perfection of automobiles, trucks, and tractors has had material
influences on local production. These various devices for travel,
transportation, and motive power have established what Bowman
(2) quite aptly terms a "gasoline culture."
Technological Advances through the Improvement of Crops.
Very marked improvements in nearly all commercially important
crop plants have been made through the efforts of plant breeders.
Improvements have been made not only along the line of increasing
yielding capacity but also in developing crops of required market
characteristics.
Table 2, taken from Klages (7), shows the secular trends in the
yields of the major grain crops in the states of the Mississippi Valley
over a 37-year period 1891-1927, inclusive. Since the slope of the
trend lines of the annual average yields, fitted by the method of
least squares, is positive in most instances, the trends shown point
to increased yields over the 37-year period of the study. The highest
annual increment shown by any crop was for corn in Iowa, namely,
0.285 bushel per acre annually. Wallace (17) reports an annual
increase of 0.25 bushel in Iowa corn yields from 1891 to 1919.
Reed (14) found an annual increase of 0.283 bushel per acre in the
years 1890-1926, while Mattice (10) reports an annual increment
of 0.486 bushel of corn per acre for the state of Iowa for the period
1901-1925. The introduction of hybrid corn in recent years has
resulted in still greater increases in yields.
These increases in unit crop yields cannot be ascribed altogether
to activities in the improvement of crops ; improvements have also
been made in methods of tilling and managing the soil on which
the crops are grown. A permanent system of agricultural produc-
tion concerned above all with the preservation of the fertility of the
soil or with the actual improvement of the soil, however, is not so
readily or generally adopted by producers as are new and improved
64
ECOLOGICAL CROP GEOGRAPHY
varieties of crop plants. Much of American agriculture, as pointed
out before, can be classified rightfully and unfortunately as a system
of mining soil fertility. How long that may go on is not the question
here. The point is that crop yields have increased in spite of this
condition. And it may be stated that the improvement in crop
plants has counterbalanced in part the effects of trends toward
lower yields induced by soil depletion and depreciation. This
statement is not made to infer that all producers allow their soils
to depreciate. Prevailing economic conditions not infrequently
may determine the effectiveness or the feasibility of establishing a
permanent system of agricultural production. The direct effect
of crop-improvement work is well illustrated by the comparative
performance of two varieties of hard red spring wheat at three
South Dakota stations, Brookings, Highmore, and Eureka. Klages
(8) showed that Ceres, the new variety, over a five-year period of
comparison at these three South Dakota stations yielded respec-
tively 23.8, 36.1, and 10.3 per cent more than Marquis, the older
established variety which was beyig replaced.
«
TABLE 2. ANNUAL INCREMENTS IN THE YIELDS OF CORN, OATS, WHEAT,
BARLEY, AND RYE IN THE STATES OF THE MISSISSIPPI VALLEY, AS INDICATED
BY THE SLOPE OF THE TREND LINES OF YIELDS AS FITTED BY THE METHOD OF
LEAST SQUARES FOR THE 37-YEAR PERIOD 1891-1927, INCLUSIVE
States, Arranged
Jrom East to
West
Yields
Corn
Oats
Wheat
Barley
Rye
Michigan . .
+ 0.128
+ 0.138
+ 0.133
+ 0.126
+ 0.006
Wisconsin
+ 0.267
+ 0.243
+ 0.169
+ 0.153
+ 0.021
Minnesota
-f 0.259
+ 0.100
- 0.017
- 0.003
- 0.050
North Dakota
-f 0.100
+ 0.138
- 0.092
- 0.100
-0.151
South Dakota
+ 0.203
+ 0.155
+ 0.018
+ 0.029
+ 0.038
Ohio . . .
+ 0.254
+ 0.157
+ 0.099
+ 0.073
+ 0.004
Indiana . .
+ 0.158
+ 0.103
+ 0.091
+ 0.081
- 0.022
Illinois . . .
+ 0.094
+ 0.105
+ 0.087
+ 0.248
- 0.007
Iowa . . .
-f 0.285*
+ 0.222
+ 0.178
+ 0.200
+ 0.023
Nebraska . .
+ 0.015
+ 0.138
+ 0.080
+ 0.122
+ 0.027
Kentucky
+ 0.069
+ 0.044
+ 0.019
+ 0.184
- 0.005
Missouri .
+ 0.001
+ 0.079
+ 0.034
+ 0.187
- 0.037
Kansas . .
- 0.118
+ 0.062
+ 0.002
- 0.022
+ 0.032
* The figure 0.048 as published in Ecology was wrong and is hereby corrected to
read 0.285.
THE SOCIAL ENVIRONMENT 65
The greatest advances in the breeding of crop plants have been
made in providing producers with varieties or strains able to over-
come, in part if not in entirety, certain limiting factors in crop
production, such as varieties resistant to certain diseases, varieties
resistant to lodging, and the early-maturing varieties. The develop-
ment of early-maturing varieties of crop plants has had the direct
effect of increasing the acreage to be devoted to these crops in
northern areas or in increasing the yields in areas especially adapted
to them.
Technological advances through improvements in soil man-
agement. Great advances have been made in the management of
crop production enterprises. Reference is made here to improve-
ments in handling the details of production with special reference
to soil management.
It is a recognized fact that a type of cropping tending toward a
permanent system of agriculture and an improvement in the soil
is more easily inaugurated in regions with an abundant supply of
moisture, where conditions are favorable to the establishment and
growth of legumes, than in moisture-deficient areas where either
the production of legumes is altogether out of the question or they
can be established only in seasons with more than the norhial
ambunt of rainfall. Humid regions are more suited to the develop-
ment of diversified systems of cropping and a general diversification
of all agricultural enterprises, while the more hazardous and ex-
tensive one-crop systems tend to prevail in the drier areas. The
yields of crops in sections with an abundance of moisture, if natural
fertility is lacking, can be increased greatly by the application of
either barnyard manure or commercial fertilizers, or both. In dry
areas the addition of fertilizers will not increase yields materially
except in those occasional seasons when the moisture supply is great
enough to allow plants to utilize the extra elements of nutrition
supplied them.
A comparison of humid and subhumid regions will show that the
fertility of the soil in humid areas can be maintained more readily
and that producers there have at their command a greater variety
of devices for increasing and stabilizing production than do pro-
ducers in the latter areas, where the trend is toward extensive
rather than intensive systems of production. From a competitive
standpoint, the extensive systems of production of the subhumid
66 ECOLOGICAL CROP GEOGRAPHY
areas, while returning lower and more uncertain yields, enable
producers to utilize power machinery to a greater extent, thereby
reducing costs of production, than is possible in the areas with the
more diversified and intensive systems of agriculture. The per-
manency of agricultural production in some of the dry areas of the
frontier fringe, however, remains to be demonstrated.
Technological advances through the development of power
machinery. The direct effects of the development and employment
of power machinery in agricultural production have been men-
tioned in Chapter II. At this point the effect of this development
on inter-regional competition is to be considered. The one great
influence of the rapid adaptation of power equipment to agri-
cultural production has been the movement of crop areas into the
drier and, strictly from a climatological standpoint, less favorable
areas. Large unbroken areas ideally adapted to extensive systems
of farming with power machinery have been brought into produc-
tion. The production of wheat and cotton has been especially in-
fluenced by these developments. From a competitive standpoint
it is necessary to consider first the relative costs of production in the
new and in the older producing areas.
Recent expansions, at least expansions following the first World
War, of crop acreages, notably those of wheat and of cotton, Have
been into the more arid sections. This happened not only in the
United States but also in other wheat producing countries. The
expansion of crop acreages due to the creation of artificial social
environments is not considered at this point. That the feasibility
of continued extensive production by the employment of power
equipment is yet to be demonstrated in many of the drier areas with
erratic types of climates is a well-recognized fact. No attempt is
made here to evaluate the hazards of production in those areas;
that will be left to another chapter. It is enough to say that the
employment of such power equipment as the tractor, the combine,
and the truck has brought a lot of land into production, and in
many instances the costs of production have been lowered.
One very pertinent fact must not be overlooked. While it is true
that cereal crops in many localities may be sown more cheaply and
harvested more cheaply by the employment of the most modern
types of power machinery than by means of horse-drawn equip-
ment, it is also true that in order to harvest a crop it is first neces-
THE SOCIAL ENVIRONMENT 67
sary to produce one. Even the most modern mechanical methods
of tillage cannot produce the moisture so essential to the growing of
a crop. The fact cannot be denied that the main limiting factor to
crop production in subhumid or semiarid sections, whichever name
is selected, is a lack of a sufficient and reliable supply of moisture in
a high percentage of the growing seasons. Low-cost production is
not possible unless fair to good yields are obtained. The employ-
ment of no amount of power equipment can eliminate the powerful
check imposed by this limiting factor.
It is hardly fair to draw an analogy between agricultural produc-
tion and a mining enterprise, as was done by Nourse (12) in the
following paragraph.
"If the changes in technique which are now upon us prove to be as
revolutionary a character as has been suggested in the present chapter,
the result would apparently be to alter permanently the schemes of
valuation in different agricultural sections, which were built up under
the older traditions of American farming. From the immemorial past,
the predominance of hand-labor methods in farming has given great
differential superiority to those well-watered and fertile lands which
showed the greatest capacity to absorb large amounts of human toil.
But much as in the field of mining the progress of scientific metallurgy
and heavy power machinery have made profitable the utilization of
low-grade ores, so the development of scientific and machine agriculture
have brought into cultivation considerable areas of formerly sub-
marginal land, and have indeed put a premium upon extensive methods
of utilizing lighter soils in the remoter agricultural areas, and regions
of scanty rainfall. Profits are being found by going rapidly over large
areas of comparatively low-yield land, and the scarcity value of lands
in the older sections has quite possibly lessened as a result. Their dif-
ferential superiority has shrunk under the new technique, and market
values must ultimately establish themselves in the light of this fact."
While it is true that agricultural production will and must be
modified in the older areas as a result of competitive influences
from the lands newly brought into production, it is also true that
an expansion into the "areas of formerly submarginal lands" is not
infrequently a hazardous undertaking. If agriculture can be main-
tained in these areas only by means of successive governmental
grants and aids, then agricultural production proceeds in an arti-
ficial social environment, an environment created at public expense
and to the detriment of the older, more stable agricultural sections
Of ECOLOGICAL CROP GEOGRAPHY
of the country. Furthermore, coming back to the analogy between
agricultural production and mining, there is one great difference
between these two enterprises which makes an analogy between
the two imperfect. The yield of the refined product that will be
obtained from working over any given ore can be determined by
chemical means before the initiation of mining operations, while
this is by no means the case in agricultural production, where the
yields to be obtained are determined to such a high degree by the
vicissitudes of the climate. This applies especially to attempts at
agricultural production in areas with highly variable and erratic
climates or where lack of moisture is a limiting factor. The timely
employment of heavy power equipment aids in the conservation of
moisture. Moisture, however, can be conserved only when and
where it is present. Agriculture, as will be pointed out presently,
can and does modify its methods of production in response to varia-
tions in climatic and economic conditions; yet it cannot be denied
that favorable soil and climatic conditions remain the basis of a
prosperous and well-balanced agriculture.
The Intensity of Production. Agricultural production obeys
the law of diminishing returns. That is, for every successive unit of
labor or capital applied per unit of area there will not result an
equal and proportionate return. Only a given amount of labor,
seed, fertilizer, etc. can be applied to any given area of land with
an expectation of increasing the net return. The relationship be-
tween expenditures and net, rather than gross, return is the all-
important consideration in deciding whether or not a given produc-
tion enterprise can survive under a given set of economic and
physiographic conditions.
Space does not permit the discussion of all phases of the applica-
tion of the law of diminishing returns to agricultural production.
Only the main factors affecting the optimum intensity for returns
in different regions and under varied soil conditions can be con-
sidered.
Intensive systems, that is, systems using liberal amounts of capital
and labor per unit of area, prevail in densely populated areas
whose soil and climatic conditions are generally favorable to
agricultural production, while extensive systems are the rule in
sparsely populated regions, especially if the climatic conditions are
not favorable to the attainment of high average yields.
THE SOCIAL ENVIRONMENT 69
Krzymowski (9) gives an interesting discussion of the various
problems relating to the intensity of agricultural production. His
paper has an especial appeal to students who may be mathemati-
cally inclined, since it goes in detail into the mathematics forming
the foundation of von Thuenen's theory of intensity. Attention is
given to both gross and net returns and to the factors influencing
the point of most favorable degree of intensity for greatest net
return under a variety of conditions.
Agricultural production has been and still is going through a
process of adapting the size of individual holdings to prevailing
climatic, soil, and economic conditions. Spafford (15) showed the
relationship of moisture and soil conditions to size of farms from
the eastern to the western Great Plains area. As the lower rainfall
portions in the central and western parts of this great area are
approached, the size of the individual holdings definitely increases.
Likewise, regions with poor soils in this area have larger farms than
those blessed with better soils.
Changes and trends in economic conditions have a great and
very direct effect on the optimum degree of intensity to be applied
to the individual farm for the production of a maximum net
return. Likewise, major economic changes demand regional
adjustments in production programs. These adjustments can be
made as far as existing climatic and soil conditions allow. Narture
is dynamic; crop producing areas, as the past has shown, may shift
in response to a great variety of factors of the physiological and
social environments.
REFERENCES
1. Black, J. D., and A. G. Black, Production Organization. Holt, New York,
1929.
2. Bowman, I., "Jordan country," Geog. Rev., 21:22-55 (1931).
3. Garden, P. V., "Relating research in agricultural economics to other
fields of agricultural science," Jour. Farm Econ., 16:189-199 (1934).
4. Fitting, H., Aufgaben und Qele finer vergleichenden Physiologie auf geog-
raphischer Grundlage. Verlag von Gustav Fischer, Jena, 1922.
5. Gregory, H. E., A. G. Keller, and A. L. Bishop, Physical and Com-
mercial Geography. Ginn, Boston, 1910.
6. Hughes, H. D., and E. R. Henson, Crop Production. Macmillan, New
York, 1930.
70 ECOLOGICAL CROP GEOGRAPHY
7. Klages, K. H. W., "Geographical distribution of variability in the
yields of field crops in the states of the Mississippi Valley," Ecology, \ 1 :
293-306 (1930).
8. 9 "Small grain and flax varieties in South Dakota,*' S. Dak.
Agr. Exp. Sta. Bull. 291, 1934.
9. Krzymowski, R., "Graphische Darstellung der Thuenenschen Intensi-
tatstheorie," Fuhlings Landw. %eit, 69:201-219 (1920). (A translation
of this paper is presented by P. G. Minneman in Jour. Farm EC on.,
10:461-482 (1928).)
10. Mattice, W. A., "Weather and corn yields," Mo. Wea. Rev., 59:105-
112 (1931).
11. Nichols, G. E., "The terrestrial environment in its relation to plant
life," in Organic Adaptation to Environment, M. R. Thorpe, ed., Chap. 1,
pp. 1-43. Yale University Press, New Haven, 1924.
12. Nourse, E. G., Agriculture, Recent Economic Changes in the United States,
vol. 2, pp. 547-602. McGraw-Hill, New York, 1929.
13. Pickett, V. G., and R. S. Vaile, "The decline of Northwestern flour
milling," Univ. of Minn. Studies in Economics and Business, No. 5. Uni-
versity of Minnesota Press, Minneapolis, 1933.
14. Reed, G. D., "Weather and corn maturity in Iowa," Mo. Wea. Rev.,
55:485-488 (1927).
15. Spafford, R. R., "Farm types in Nebraska as determined by climatic,
soil, and economic factors," Nebr. Agr. Exp. Sta. Res. Bull. 15, 1919.
16. Tansley, A. G., Practical Plant Ecology. Allen and Unwin, London,
1926.
17. Wallace, H. A., "Mathematical inquiry into the effects of weather on
corn yields in eight corn-belt states," Mo. Wea. Rev., 48:439-446
(1920).
PART II
THE PHYSIOLOGICAL ENVIRONMENT
OF CROP PLANTS
Chapter VI
THE PHYSIOLOGICAL ENVIRONMENT
Primary Importance of the Physiological Environment.
"Life is able to proceed, then, in any particular plant, only so long
as the external conditions do not surpass the physiological limits
of the life processes of the form considered" (Livingston and
Shreve, 10). That the distribution of crop plants is determined
by the combined influence of physiological, economic, social, tech-
nological, and historic forces has been stated on several occasions.
It is well to keep that in mind at all times. Obviously, however, no
crop plant can attain a place of importance in the cropping system
of any given locality unless it exhibits a certain degree of adaptation
to the external conditions prevailing in that locality. Some of the
factors involved in the study of adaptation will be taken up in
detail in a later chapter. In this chapter the general and broad
relationships of plants to their physiological environments will- be
discussed without consideration of causal relationships.
Habitat. The terms "environment" and "habitat" may be used
interchangeably. They both refer to one and the same thing,
namely, to the sum total of all external conditions affecting the
development, special responses, and the growth of plants. Since
the term "habitat" was first used by botanists, and especially by
ecologists, it is best to apply it to the description of the physiological
conditions influencing the distribution and growth of plants as con-
trasted with the social environment which deals with the influence
of a variety of factors other than those concerned with the direct
growth requirements determining the distribution of crop plants.
Actual and Potential Habitats. It has been stated that "no
two spots on the face of this earth have exactly the same climate."
While such a statement may be true when the various components
of the climate are examined in their minutest detail, it also is a
I recognized fact that regions with similar climates tend to exhibit
similar life forms. This does not mean that the identical species
73
74 ECOLOGICAL CROP GEOGRAPHY
necessarily will be represented or predominate in remote regions
with similar climates but only that certain sets of climatic conditions
will lead to the development of certain types of climax vegetations
or a corresponding physiognomy. Certain species may be excluded
from distant regions, not because conditions there are not suited
to their growth, but simply because the spread of such species may
have been prevented by various kinds of barriers. If once intro-
duced, by artificial or normal means, they may spread rapidly in
the new area. The introduction of European weeds and grasses in
America and other areas of the world offers a good example of this
phenomenon. It is well, therefore, to recognize an actual and a
potential habitat of plants.
Plants may have either a wide or a narrow range of adaptation.
That is, they may be very exacting in their requirements of the
environment and therefore be limited in their distribution; or they
may have a great tolerance to factors either working in excess or
lacking in intensity. The distribution of some crop plants may be
limited, not because of this condition, but because conditions were
adverse to migration. The distribution of the sorghums was greatly
furthered by man's taking a part? in aiding their migration. This
was true also with such important cultivated plants as corn, wheat,
potatoes, tobacco, and to some degree all plants since they became
objects of world trade. It would be difficult to visualize the present
agriculture of the Great Plains area of the United States without
such important introduced crop plants as hard red winter wheat,
hard red spring wheat, durum wheat, the sorghums, and alfalfa.
The production program is centered largely around these impor-
tant crops which exhibit a remarkable degree of adaptation to the
prevailing environmental conditions. Much of agronomic experi-
mental work in the last analysis is a test designed to find the limits
of the potential habitat of crop plants.
Attempts to grow crop plants beyond the limits of their potential
habitats have resulted in great losses to private enterprise as well
as in great damage to the public domain. Many of the marginal
lands of humid regions for their best utilization should have been
allowed to retain their natural vegetation rather than to have been
put under cultivation. High, often abnormal, prices of agricultural
products prevailing for but short periods played a prominent part
in divesting such marginal lands of their natural protective cover-
THE PHYSIOLOGICAL ENVIRONMENT 75
ings. In semiarid regions lands either too shallow, too light, or
lacking in permeability sufficient for the storage of moisture in the
past years have been broken up with no regard for the future.
Such lands were often cultivated but for a short time, until it be-
came evident that crops could not be grown on them with profit;
they were then allowed to lie idle and to waste away. Lands
approaching the limits of the potential habitat should not be
devoted to the production of crop plants. The natural vegetation
such as timber or grass will yield better and more certain returns,
at least until the time when they may be forced into the production
of specialized crops by economic demand.
Factors of the Habitat. Livingston and Shreve criticize the
usual classification of habitat factors from the standpoint that they
are largely based on "origin or source, rather than according to
their mode of physically affecting the plant." While classifications
of habitat factors may not, and are not expected to, explain the
very complex relationships of a plant during its various phases of
development to its also changing environment as a growing season
progresses, nevertheless, they may be of great help to the student
in arriving at some conception regarding the processes involved.
Most of the investigations dealing with the many reactions of the
plant with environmental factors of necessity have been descriptive
rather than quantitative. With increasing refinements in methods
available to investigators, more and more exacting quantitative
work may be expected. But, for the time being, many investiga-
tions will continue to be descriptive in nature.
Livingston and Shreve point out that progress is being made
by means of refined laboratory methods toward obtaining more
definite knowledge of the relationships of a plant to environmental
factors, but that "a large amount of laboratory experimentation of
the most refined physical sort will be required before we shall ever
approach an adequate knowledge of the influence of single condi-
tions upon plants, the far more difficult study of the complex
environmental systems of which these single conditions are always
components has already begun to attract attention."
Fitting (5) calls attention to the fact that the behavior of plants
can be explained only when investigations regarding such behavior
are actually conducted in their natural environments. Unless this
is done the reactions studied may be pathological rather than
76 ECOLOGICAL CROP GEOGRAPHY _
physiological in nature. Geographical and ecological physiology
can be expected to provide the basis of information for the study of
plant and crop geography upon a physiological basis as fostered by
the monumental work of Schimper (12).
Livingston and Shreve classify the environmental conditions
that are most influential in the determination of plant development
and distribution as: (a) moisture conditions; (b) temperature con-
ditions; (c) light conditions; (d) chemical conditions; and (e) me-
chanical conditions. Tansley (17) throws the factors of the habitat
Fio. 4. Diagrammatic scheme to suggest the nature of the terrestrial environ-
ment in its relation to the organic world, together with the ecological sources
(left column) and the various physiological conditions (right column) that in-
fluence the form and structure, the development and behavior, and the geo-
graphical distribution of living organisms. (After Nichols.)
into the following classes of factors: (a) climatic, (b) physiographic,
(c) edaphic, and (d) biotic. Nichols (11) uses the factors given by
Livingston and Shreve and by Tansley and adds the anthropcic,
the activities of man, and the pyric conditions, the effects and
results of the action of fire. Nichols considers the edaphic factors
as given by Tansley under the class of physiographic conditions.
Figure 4? taken from Nichols, gives an interesting diagrammatic
presentation of the nature and the interrelationships of the various
factors of the habitat on the organic world. Figure 4 not only lists
the various outstanding factors but also shows how they react upon
one another. The various ecological factors of the environment will
be discussed separately and in detail as they relate to the distribution
of crop plants.
THE PHYSIOLOGICAL ENVIRONMENT 77
The climatic factor of the environment. The climatic factors
are many. Since their effects are interrelated, the influences of any
specific factor must be considered in the light of the others. The
main climatic factors are temperature, moisture, and light; of less
importance are atmospheric pressure and air currents. Superim-
posed on these but not of less importance is periodicity.
The interpretation of climatic data necessitates a knowledge of
seasonal variations. Information on the periodicity of climatic
phenomena at times or in certain regions may be of far greater
value than mere averages. A section may have a high annual rain-
fall, yet be quite dry at a time of year when plants may be in special
need of moisture. Or the average temperature of a region may be
neither too high nor too low but at times may exceed a maximum
or drop below a certain minimum and thus limit plant production
or at least modify the cropping system to be adopted.
Chilcott (1), in his investigations on "The relations between
crop yields and precipitation in the Great Plains area," came to
the conclusion that "notwithstanding the fact that annual precipi-
tation is a vital factor in determining crop yield, it is seldom if
ever the dominant factor; but the limitation of crop yield is most
frequently due to the operation of one or of several inhibiting factors
other than shortage of rainfall." This conclusion brings out the
fact that the specific influences of the various climatic forced are
interrelated. The investigations on which this far-reaching state-
ment is based may be criticized from the standpoint that no atten-
tion was given to the economy of water utilization by the crop
plants discussed. This is a vital factor and should be taken into
consideration; moisture, for instance, that falls on the ground only
to run off rapidly in the extremely heavy rains quite common in
the southern Great Plains area cannot be expected to be of benefit
to plant life. Not all moisture falling into a rain gauge produces
favorable plant responses.
Periodic climatic manifestations leave a lasting impression on
natural vegetation and in like degree have a great influence on the
selection of crop plants. As brought out by Hildebrandt (6), uni-
form climates are conducive to the production of perennial plants,
while climates with periodic changes give rise to annual plants.
In the tropics uniformly high temperatures make continuous growth
possible except under conditions where a period of drought may
78 ECOLOGICAL CROP GEOGRAPHY
throw the plants into a period of dormancy. Perennial forage
plants predominate in regions where there is sufficient moisture for
the vegetative parts to live over from year to year. In the arid and
semiarid sections many plants are able to take advantage of the
fact that seeds are less susceptible to unfavorable climatic condi-
tions than vegetative organs; consequently, the plants found either
are annuals or are protected from damage during periods of ex-
treme drought by special morphological, structural, or physiological
characteristics.
The influence of periodicity of climatic factors especially with
regard to moisture has a decided effect on crop distribution. As
pointed out by Klages (9), perennial crop plants such as meadow
grasses and legumes predominate in regions with a comparatively
uniform distribution of rainfall. Most of the forage plants grown
in the eastern humid part of the United States, such as timothy,
redtop, and the clovers, are perennials requiring relatively abun-
dant supplies of moisture. In the northern Great Plains area a
larger number of annual forage plants, such as millets, sudan grass,
and early varieties of sorghums, are encountered. In the southern
Great Plains area annual plants aisume even a greater importance
than in the north. The reasons Tor this distribution are quite
apparent in the light of what has been said. Alfalfa, though the
dominant forage crop of the western states, is limited primarily to
irrigated regions. Alfalfa and sweet clover are also grown exten-
sively in the annual forage area of the Great Plains region. Because
of its unusually extensive root system, alfalfa is able to capitalize
on the subsoil moisture out of reach of ordinary field crops. As
brought out by the works of Duley (3) in eastern Kansas and
Kiesselbach et al. (7) in eastern Nebraska, the yields of alfalfa de-
clined rapidly after four or five years of growth on land that had
not previously been cropped to it. These decreases in yields corre-
sponded to definite decreases and eventual depletion of the available
subsoil moisture. A considerable number of years may elapse before
the subsoil moisture in subhumid areas may again come up to its
original point after once being exhausted. High yields of alfalfa
cannot be expected until moisture again becomes available in the
lower levels of the soil.
The physiographic factor of the environment. The physio-
graphic factors may be classified as (a) the nature of the geologic
THE PHYSIOLOGICAL ENVIRONMENT 79
strata, (b) the topography, and (c) the altitude. The soil, or the
so-called edaphic factor, will be discussed separately.
In relation to soil formation, the nature of the geologic strata may
be considered as an edaphic factor. It is a physiographic factor
insofar as it is active in accounting for a given topography. Geolo-
gists in the past have attributed too much importance to the nature
of the underlying parent rock material with regard to soil forma-
tion. While the original material from which soil is formed is of
importance, it must be recognized that identical parent rock under
varying climatic conditions will give rise to soils of greatly differing
physical and chemical properties (Shantz and Marbut, 13).
Topography is a great factor in determining climate. General
topography, direction of main mountain ranges to prevailing
winds, is important from the standpoint of determining precipita-
tion. Together with the nature of the geological strata, it is a
factor in determining the natural drainage of a region.
The slope and exposure of given areas is highly important in the
production of certain crops. A southern exposure is warm in the
northern hemisphere and desirable for the production of early
crops. Yet in areas of limited rainfall such slopes are undesirable.
Because of the higher surface temperature and the resulting greater
lo'SS of moisture by means of increased transpiration, they often. are
too droughty for profitable crop production. Good air drainage is
essential to the production of tender crops in all regions, especially
in high altitudes where there may be danger of frost damage, even
in the cereal crops. Precautions against soil erosion must be taken
on lands with excessive slopes. The effect of slope on the rate of
erosion, as shown by the works of Dickson (2) and Duley and Miller
(4), is greatly modified by a variety of factors such as the nature of
the soil, the type of cropping, and the intensity of the rainfall.
Topography has a great influence on local climate. It may serve
to protect an area from excessive evaporation and may modify the
temperature. Klages (8) gives the rates of evaporation as recorded
by Livingston's cup atmometers at five different locations in
central Oklahoma, showing how such rates of evaporation correlate
with plant responses.
More attention will be given in another chapter to the general
relationship of topography and altitude to climatic variations.
It is sufficient to summarize here the interactions of climatic and
80 ECOLOGICAL CROP GEOGRAPHY
physiographic factors by using the words of Nichols, "The nature
of the environment of any locality is determined primarily by the
combined influence of climatic and physiographic factors."
The edaphic factor of the environment. It is unnecessary at
this point to go into detail on the relationship of various soil condi-
tions such as texture, structure, aeration, reaction, and chemical
makeup to various phases of crop production. The edaphic factors
(taken from the Greek "edaphos," meaning "the ground") are not
static but subject to continual change. The modifications produced
may be slow, proceeding in an orderly fashion as in the slow disin-
tegration of the parent rock or the slow removal of soluble elements
either by plants or by leaching; again, they may be precipitous, as
in certain phases of erosion. But, as aptly stated by Tarr and
Martin (18), the soil is the basis of agriculture.
While the bulk of the material making up the soil is inert matter,
a soil must always be considered in its three general phases, namely,
the physical, the chemical, and the biological. The interactions of
these various phases make it very complex.
The soil is one of the most important factors of the habitat. This
is true especially in studies limbed to a given locus as are most of
the investigations of the agronomist. Climatic factors are spoken
of as being regional, while the soil factors are local in effect/ As
Spafford (16) speaks of it, "Soil effects are often submerged by
climate." Schimper speaks of climatic and edaphic formations;
Tansley [taken from Waterman (19)] criticizes the term "climatic
formations" from the standpoint that "Nothing like a sharp line
can be drawn between one climatic region and another so that it
becomes impossible to delimit climatic formations." While it is
true that one type of vegetation gradually shades into another
without a distinct boundary between them, it is also true that the
climates of the world may be grouped into a relatively small number
of classes each of which affects large regions. Within such larger
regions soil variations play a prominent part in determining the
agricultural utilization of particular areas.
The habitats of two plants in the same field may differ markedly
because of soil and physiographic factors. Within a given climatic
region the local climate may be modified to a small degree, as
brought out by Smith (14 and 15), by the joint effects of edaphic
and physiographic factors.
THE PHYSIOLOGICAL ENVIRONMENT 81
The biotic factor of the environment. It has been said that
nature abhors a pure population of organisms almost as much as a
vacuum. Pure cultures of plants, as well as of other organisms, are
very much the exception rather than the rule. Under the biotic
factors are considered the effects of other plants or animals on the
particular plant or animal studied. The associates of a habitat may
be helpful, neutral, or harmful; there are symbiotic as well as
parasitic relationships. In limiting this phase of the discussion to
crop plants, the effects of the wanted plants and of the unwanted
associates — weeds — and the effects of parasites and of animals
must be considered.
The agronomist deals with natural and with man-created associ-
ations. The various growth requirements, qualities, and charac-
teristics of the separate plants used in compounding a pasture or
meadow mixture must be taken into account if maximum returns
are to be expected. Young clover or alfalfa plants growing with a
companion crop, not infrequently called a nurse crop, are living
in quite a different environment than plants of the same species
grown in pure cultures or in competition with various weeds.
Crop rotations and systems of annual cropping involve numerous
biotic relationships. In certain areas, as in the drier sections of the
Cheat Plains area, corn in itself may not be a very profitable grop,
but it is of considerable value to and results in material increases
in the yields of subsequent cereal crops. The survival of disease
producing organisms from year to year involves a definite biotic
relationship demanding that the same crop or group of crops
affected by the same causal organism not be grown too frequently
or at too frequent intervals in the rotation. Likewise the reaction
of plants to insect injuries involves biotic relationships.
The anthropeic factor of the environment. Man has produced
profound changes in plant environments. The various factors
discussed in the previous chapter on the social environment have a
direct bearing and may again be mentioned at this point. That is
hardly necessary. The introduction of grazing animals and of
various exotic plants leaves lasting impressions.
The pyric factor of the environment. The action of fire pro-
duces great changes, especially in the environment of natural
vegetations, and in addition leaves lasting impressions on the
soil.
82 ECOLOGICAL CROP GEOGRAPHY
The Time Element and the Habitat. A plant may be charac-
terized, as by Livingston and Shreve, by its "powers or capabilities
to respond to stimuli." It must also be recognized that plants pass
through rather well-defined and definite phases in the course of
their development. The responses to environmental complexes
differ materially during these different phases. A wheat seedling
demands for maximum development quite a different environment
than a flowering or ripening plant. Not only is it necessary to con-
sider the various separate factors but it is equally important to
investigate and consider the effects of the duration of the com-
ponent factors or the time interval in which plants may be exposed
to certain stimuli. An exposure to a high temperature for a short
interval may result in no lasting detrimental effects, while a longer
exposure to a lower temperature under some conditions may lead
to death. More will be said about the time factor in the discussion
of adaptation and during the course of the consideration of plant
responses to various ecological factors. But, since no summary
review of plant habitats can be considered at all complete without
giving attention to the time factor, it has been very briefly referred
to at this point. *
»
REFERENCES
1. Ghilcott, E. C., "The relations between crop yields and precipitation
in the Great Plains Area," U. S. D. A. Misc. Circ. 81, 1927.
2. Dickson, R. E., "The results and significance of the Spur (Texas)
runoff and erosion experiments," Jour. Amer. Soc. Agron., 21:415-422
(1929).
3. Duley, F. L., "The effect of alfalfa on soil moisture," Jour. Amer. Soc.
Agron., 21:224-231 (1929).
4. , and M. F. Miller, "Erosion and surface runoff under dif-
ferent soil conditions," Mo. Agr. Exp. Sta. Res. Bull. 63, 1923.
5. Fitting, H., Aujgabe und Qele einer vergleichender Physiologic auj geo-
graphischer Grundlagc. Verlag von Gustav Fischer, Jena, 1922.
6. Hildebrandt, F., "Die Lebensdauer und Vegetationsweise der Pflan-
zen, ihre Uhrsachen und Entwicklung," Englers Bot. Jahrb., 2:51-134
(1882).
7. Kiesselbach, T. A., J. C. Russel, and A. Anderson, "The significance
of subsoil moisture in alfalfa production," Jour. Amer. Soc. Agron.,
21:241-268 (1929).
THE PHYSIOLOGICAL ENVIRONMENT 83
8. Klages, K. H. W., "Crop ecology and ecological crop geography, in
the agronomic curriculum," Jour. Amer. Soc. Agron., 20:336-353(1928).
9. , "Comparative ranges of adaptation of species of cultivated
grasses and legumes in Oklahoma," Jour. Amer. Soc. Agron., 21:201-
223 (1929).
10. Livingston, B. E., and F. Shreve, The Distribution of Vegetation in the
United States, as Related to Climatic Conditions. Carnegie Institution Pub.
284, Washington, 1921.
11. Nichols, G. E., "The Terrestrial Environment in Its Relation to Plant
Life," in Organic Adaptation to Environment, M. R. Thorpe, ed., Chap.
1, pp. 1-43. Yale University Press, New Haven, 1924.
12. Schimper, A. F. W., Plant Geography upon a Physiological Basis. Claren-
don Press, Oxford, 1903.
13. Shantz, A. L., and C. F. Marbut, The Vegetation and Soils of Africa.
National Research Council and the American Geographical Society,
New York, 1923.
14. Smith, A., "A contribution to the study of interrelations between the
temperature of the soil and of the atmosphere and a new type of
thermometer for such study," Soil Science, 22:447-458 (1926).
15. , "Effect of local influences in modifying the general atmos-
pheric conditions," Soil Science, 23:363-376 (1927).
16. Spafford, R. R., "Farm types in Nebraska, as determined by climatic,
_ soil and economic factors," Nebr. Res. Bull. 15, 1919.
17. Tansley, A. G., Practical Plant Ecology. Dodd, Mead, New York, 1-923.
18. Tarr, R. S., and L. Martin, College Physiography. Macmillan, New
York, 1915.
19. Waterman, W. G., "Development of plant communities of the sand
ridge region of Michigan," Bot. Gaz., 74:1-31 (1922).
Chapter VII
EXTERNAL FACTORS IN RELATION TO
DEVELOPMENT
External and Internal Factors in Their Relation to Develop-
ment. The many interesting and not infrequently perplexing
problems encountered in studies pertaining to development and
adaptation are fittingly introduced by a portion of the first para-
graph found in Morgan's (34) volume Evolution and Adaptation.
"Between an organism and its environment there takes place a con-
stant interchange of energy and material. This, in general, is also true
of all bodies whether living or lifeless; but in the living organism this is
a peculiar one; first because the plant or animal is so constructed that
it is suited to a particular set of physical conditions, and, second, be-
cause it may so respond to a charge in the outer world that it further
adjusts itself to changing conditions, i.e.9 the response may be such a
kind that it better insures the existence of the individual, or of the race.
The two ideas contained in the foregoing statement cover, in a general
way, what we mean by adaptation of living things."
The external factors under which an organism develops provide
no doubt the direct stimuli for the various responses. Yet the extent
of the responses that an organism is capable of exhibiting are
limited by definite internal factors. Under «uch a broad term as
"the internal factors" may be considered the hereditary factors,
or the genetic constitution of the individual, the various physico-
chemical occurrences within the plant, and the general physio-
logical limitations imposed on all organisms. The first of these will
be treated, as it reflects on the problem in hand, in this chapter.
The physiological factors will be taken up in a subsequent chapter.
The various interactions between the internal, more specifically
the hereditary, factors and the constellation of external factors
under which the plant develops are complex.
The influence of external factors on the development of plants
and animals has long been recognized. The rediscovery of MendePs
84
EXTERNAL FACTORS AND DEVELOPMENT 85
law toward the end of the last century did much to lead discussion
and research toward the internal factors concerning and deter-
mining the course of development and the characteristics of the
individual organism. Nearly all investigators were soon convinced
that neither the internal nor the external factors alone were active
in ontogeny. It is quite obvious then that arguments as to whether
the one set of factors or the other is of greater importance are of no
avail; both are necessary. The genetic constitution of the organism
is vital to the ultimate form and characteristics produced. They
could not be produced except by interaction with the factors of the
environment.
Ontogeny and Phylogcny. Ontogeny, the development of the
individual, cannot be considered in detail without attention to
phylogeny, the history of the race. The two work together; one
must be considered in the light of the other. As Conklin (5) states it,
"ontogeny and phylogeny are not wholly distinct phenomena, but
are only two aspects of the one general process of organic development.
The evolution of races and of species is sufficiently rare and unfamiliar
to attract much attention and serious thought; while the development
of an individual is a phenomenon of such universal occurrence that it
is taken as a matter of course by most people, something so evident
that it seems to require no explanation; but familiarity with the fact
of development does not remove the mystery which lies back of it,
though it may make plain many of the processes concerned."
The agronomist, the plant breeder in particular, is concerned
far more with races and varieties or even with physiological strains
of crop plants than with species. As brought out by Werneck (43),
"agricultural phenology takes as its lowest unit the race or variety
of cultivated plants in their area of agricultural distribution."
The interest of the agronomist also extends to uncultivated species
of crop plants as sources of needed genetic characters for crop
improvement purposes. Thus Triticum timopheevi is being used as
a source of resistance to major wheat diseases, wild species of
Solanum are of value in potato breeding.
Investigators during the truly descriptive period of biology,
especially of zoology and more particularly of embryology, dealt
with both the internal and external factors concerned in develop-
ment. It is beyond the scope of this chapter to discuss in detail the
preformation view as contrasted with the theory of epigenesis.
86 ECOLOGICAL CROP GEOGRAPHY
The adherents of the first view attached special importance to and
overemphasized the internal factors of development. The pro-
pounders of the preformation theory assumed development to
consist simply of the unfolding and enlarging of what was present
already in the germ. Such a theory of "emboitement" or "infinite
encasement" would give the external factors of the environment
little or no opportunity to take part or to become instrumental in
the molding of the characteristics of the organism. While Harvey's
epigram "omne vivurri ex ovo" has found abundant confirmation,
it has been found also that external factors have a profound influ-
ence and that they cannot be disregarded. Under strict adherence
to the preformation theory it would be difficult to account for
progressive evolution. Furthermore, adaptation, direct or indirect,
would be difficult to explain.
The Units of Heredity and Development. A detailed discus-
sion of the units of inheritance, genes, is rather out of place here;
nevertheless, these units are definitely involved in development and
for that reason merit some attention. It is difficult to give a clear-
cut definition of the term "gene" without becoming involved in a
detailed discussion of the behavior of somatic characters in inherit-
ance.
The terms "factor" and "gene" are used interchangeably in the
literature. Some writers make no differentiation between the
terms "factor" and "determiner." Coulter (7), however, advocates
the restriction of the use of the term "determiner" to cases where
but one hereditary unit is involved in the production of a character.
He uses the term "factor" in cases where two or more units interact
in the production of a character. Johannsen (19) considers the
genes as hereditary germinal units that may sometimes need to
combine to produce a visible somatic character. Babcock and
Clausen (1) speak of the gene as "an internal condition or element
of the hereditary material upon which some morphological or
physiological condition of the organism is dependent." Frost (13)
gives two distinct meanings as to the term gene: (a) a definite
physical unit of segregation, and (b) a developmental potentiality.
East (11) states, "the regularity with which characters occur in
breeding experiments justifies the use of a notation in which theo-
retical factors or genes, located in the germ cells, replace the actual
somatic characters."
EXTERNAL FACTORS AND DEVELOPMENT 87
McGee (31) makes the point that "the career of the organism, as
individual species or as a larger group, may be considered as the
resultant of two forces, (a) the initial or directing force operating
through heredity, and (b) the secondary or modifying force operat-
ing through interaction with the environment. Neither one nor
the other of these forces is of greater importance to development."
As stated by Lefevre (28), "every organic individual is the product
of two sets of conditions both of which contribute to the sum-total
of its qualities." He continues, "the organism, then, as we see it,
is the product of constant interaction between internal and external
conditions, and if either of these factors is varied, a difference in
the result is observed." Likewise, Haecker (17) brings out that
investigators of Mendelian inheritance are confronted constantly
by a great obstacle in that it is necessary to deal always with two
sets of variables, the visible external factors and the invisible
hypothetical units of heredity of the germ plasm. There is a con-
stant interaction between these two factors, and, while progress is
being made, a complete analysis of the nature of this highly complex
interaction has not yet been made. Numerous hypotheses as to its
nature have been put forth from time to time.
Most of the early workers, in their attempts to describe or to
explain the nature of the units or, perhaps better stated, the
"something" connected with the phenomena observed in heredity,
undervalued the influence of external conditions on the course of
development. This was the case with Darwin's "provisional
hypothesis of pangenesis" and with Weismann's elaborate theory
with its biophores, determinants, ids, and idants. As stated by
Sharp (42), "for Weismann . . . development (ontogenesis) was
definitely bound up with the evolution or unfolding of a complex
contained in the fertilized egg. Although he did not hold that the
units of the egg have the same spatial relations as their corre-
sponding characters or structures in the adult, it has been said
with some degree of truth that he transferred preformation to the
nucleus."
Herbert Spencer made provisions for his "physiological units,"
formulated as a material conception of heredity, to be influenced
by external circumstances in that variation in the environment
could induce slight changes during the process of their multiplica-
tion. De Vries (9), in his theory of "intracellular pangenesis," also
88
ECOLOGICAL CROP GEOGRAPHY
paid considerable attention to the effects of external conditions.
These early theories of development and differentiation can no
longer be adhered to; yet it is interesting to note that these early
investigators were aware of the effects of the external factors of the
environment.
One more factor must be mentioned relative to the inheritance
of quantitative characters. Here the environment plays a very
important part. The plant breeder in selecting from the progeny
of hybrids attempts to isolate genotypes with the largest possible
number of favorable characters. The environment plays a prom-
inent part in enabling full expression of the various genotypes of
the segregating population. It is highly desirable in such cases to
have favorable climatic and soil conditions so that the genetic
constitution of the population under observation is found within
the limit of physiological expression.
The Course of Growth in Plants.
The various responses of plants to the
external factors of the environment
may well be studied and observed by
th£ various modifications called forth
by these factors in the course of
growth and in the growth habits of
plants. The course of growth and
development in plants may be pre-
sented graphically by means of growth
curves based on either the successive
successive weights or heights or on periodic in-
crements. These increments may be
given as actual increases over a previ-
Time (weeks from emergence)
FIG. 5. The growth curve con-
structed by plotting
height on the ordinate against
time on the abscissa.
ous measurement, as proportionate increases, or may be placed on a
percentage basis. The growth curve based on successive measure-
ments of mass, given on the ordinate, plotted against time, on the
abscissa, can be used to good advantage and gives perhaps a better
and more workable interpretation than any other method to the
various activities summarized under the general term "growth."
When the growth curve is presented in this fashion, a logarith-
metic curve, shown in Fig. 5, results. Whether or not the curve
is smooth and symmetrical depends entirely on the environmental
conditions under which the plant may happen to grow.
EXTERNAL FACTORS AND DEVELOPMENT 89
The various conceptions of growth — whether it consists of
increase in size, volume, bulk, or a change in form — may be
summarized by the statement that growth is evidenced by an in-
crease in size or bulk accompanied by changes in form resulting
from an excess of assimilation over disassimilation.
Growth curves of plants may be presented either on the basis of
successive weights, or, since there is a close correlation between
weight and height, they may be constructed on the basis of suc-
cessive height measurements taken at stated intervals. The author
has on numerous occasions found the value of r for correlations of
height of green plants with the dry weights of such plants to be 0.90
or higher. It is a decided advantage to base the successive measure-
ments required on the same plants. When successive plant weights
are relied upon as a measure of rate of growth, it is necessary, of
course, to make use of different individuals for each weighing and
dry-weight determination. Such procedure, unless based on large
numbers, adds materially to the magnitude of the experimental
error. Since the dry-matter content of plants varies greatly
from youth to age and with changes in growing conditions,
the use of green weights as an index of activity is out of the
question.
Friestley and Pearsall (36), in their study of the rate of increase
in the number of yeast cells, point out three phases in the course of
the growth curve. These three phases are also in evidence in the
growth curves of plants. They are marked 0, i, and c in Fig. 5.
These phases may be readily detected in symmetrical curves pro-
duced under normal growing conditions. They are not so out-
standing under highly abnormal climatic conditions with their
erratic plant responses.
In relating the above to plant activities it is but necessary to point
out that the plant is relatively most active during the initial stages
of growth, that is, during phase a. The increase in mass during
this phase is an exponential function of time. The percentage
activity is high; a high percentage of the cells are actively engaged
in the process of division. The amount of material actually assim-
ilated is not large. This is due, not to the lack of activity, but to
the small size of the plant. The activities of the plant during this
stage may be compared to those of a small factory working at a
high rate of speed in a most efficient manner. The output is small
90 ECOLOGICAL CROP GEOGRAPHY
not because of lack of activity but because of the size of the estab-
lishment or factory.
During phase b of the curve, the rate of growth is more or less
proportional to time. The relative activity is not so high as in the
initial phase, but the number of cells engaged in active assimilation
is large, and materials are rapidly accumulated. This phase has
been designated as the grand period of growth. During this phase
an ever-increasing number of cells is required for supportive struc-
tures, reserve materials, etc.; the number of plant cells actively
engaged in the processes of active growth is constantly being re-
duced. Growth during this phase may be compared to the activities
of a large factory with a large output, with the magnitude of the
output accounted for rather by the size than by the rate of activity
of the plant.
The final, c phase of the growth curve is characterized by a rapid
falling off of the rate of activity and the eventual suspension of
growth. The main processes during this phase are concerned with
the translocation and the fixing of materials previously assimilated
rather than with the assimilation of new materials.
The growth cycles of plants $i.th determinate and indeterminate
habits of growth differ. They are both affected and definitely
respond to environmental factors. In the former, the end-point is
more pronounced and definite than in the latter. In other words,
the inherent characteristics of these two types of plants respond
differently to environmental factors; in plants with indeterminate
habits the final point may not be reached until either climatic or
soil conditions become unfavorable to further activity while the
formation and maturity of the seeds mark the end of the growth
cycle of plants with the determinate habit.
Mathematical Formulation of Growth Curves. It is beyond
the scope of this chapter to attempt even a brief summary of the
numerous equations that have been advanced by various workers
on growth and rates of growth in plants and animals. Gaines and
Nevens (14) suggest the possibilities of making use of the constant
K of Robertson's growth equation. Robertson (38) made use of
the equation expressing the course of an autocatalytic monomolec-
ular reaction in formulating his growth curves. His equation in its
simplest form, that is, upon integration, is expressed in the following
formula:
EXTERNAL FACTORS AND DEVELOPMENT 91
= K (t — *i), in which X = the growth (height or
weight) which has been attained in time t; A = the total amount of
growth attained during the cycle ; K = a constant, the magnitude
of which determines the general slope of the curve ; and t\ = the
time at which growth is half completed, the number of days re-
quired for the plant to attain half of its final growth. Rippel (37)
shows graphically how the slopes of growth curves of plants are
affected by variations in the magnitude of K. The slopes of the
curves increase with increases in the values of the constant.
Klages (21) reports that an analysis of the growth curves of
cereals grown in field plats may yield information of value to sup-
plement performance data from such plat experiments, especially
since such curves may provide an index on the basis of which the
different seasons encountered during the course of the experiment
may be evaluated and compared. Annual growth curves of cereals
were analyzed from the standpoints of symmetry shown, maximum
height attained, and interval of time from emergence to the attain-
ment of maximum height on the basis of the generalized or average
slopes of the curves produced. Attempts were made to evaluate the
slopes of the growth curves by the employment of Robertson's
equations. It was found, however, that the differences in the cal-
culated values of K (the constant) in any variety fluctuated* so
widely for the different values of t (the time factor) that but little
significance could be attached to the average of the separate values
of K for the different values of t. This was the case especially when
the curves deviated greatly from the symmetrical. The fitting of the
growth data to straight-line trends by the method of least squares
gave the most reliable and workable means of expressing the general
slope of growth curves of crop plants grown under field conditions.
Brody (3) gives a very complete summary of the various mathe-
matical attempts at the formulation of growth curves. There is a
certain fascination in the appearance and employment of smooth
and regular curves even though such curves are the exception rather
than the rule in natural phenomena. Beautiful symmetrical curves
more often result when plants are grown under controlled labora-
tory conditions than when the plants are grown under the more
variable conditions found in the field. It is exceedingly difficult
to clothe with the dignity of a mathematical formula the rather
92 ECOLOGICAL CROP GEOGRAPHY
unsymmetrical growth curves produced when plants are exposed
to the various favorable and unfavorable factors of the environment.
That the slopes and shapes of growth curves are directly in-
fluenced by environmental factors is to be expected. A growth
curve may be regarded as a graphic summary of the many and
complex plant activities culminating in the building up of plant
reserves and associated with continual change in form. Variations
from the normal growth requirements find expression in the form of
the growth curves produced. During abnormal or erratic seasons
very irregular and unsymmetrical curves defying mathematical
formulation result. The reaction of plants to a variety of environ-
mental conditions can frequently be studied by means of the modi-
fications produced by these environmental factors on their respec-
tive growth curves. The cause of these deviations from the regular
and to-be-expected course of development not infrequently make
up interesting and important problems for the agronomist and
ccologist. There is no doubt that numerous growth equations de-
veloped and used by different investigators have been of value to
particular lines of research. It is well to keep in mind, however,
that the numerous processes concerned in organic growth are too
complex to yield in all cases to a single master equation.
Rhythm in Development. Plants in their course of development
pass through a series of orderly and consecutive stages. As Schar-
fetter (39) states it, "plants pass through an annual stage of diffusion
during which they undergo development in foliage, blossom and
fruitage followed by a period of repose." As already pointed out,
this course of orderly development is determined by both the in-
ternal, inherent characteristics of the plant and by the external,
environmental factors under which development and growth pro-
ceed. The constant recurrence of environmental factors from season
to season plays an important part in regulating the course of devel-
opment of plants adapted to certain environments so that they fit
into such environments. Obviously, the development of an annual
plant from emergence to maturity is one of continuity; the first
phase in the process is essential to the ones to follow.
The course of development of cereals may be illustrated by an
outline of the phases of the growth cycle. Since fall-sown cereals
pass through a period adverse to growth, their courses of develop-
ment will differ from those of the spring-sown grains which are not
EXTERNAL FACTORS AND DEVELOPMENT 93
forced by environmental factors to pass through a resting period.
The classification, given below, of the various phases of the course
of development for fall- and spring-sown cereals has been adopted
with slight modifications from Schmidt's (41) outline.
Fall-Sown Cereals Spring-Sown Cereals
1. Germination and emergence 1. Germination and emergence
2. Fall tillering 2. Tillering
3. Vegetative rest 3. Jointing
4. Vegetative awakening and 4. Flowering
spring tillering 5. Maturity
5. Jointing
6. Flowering
7. Maturity
Each of the above phases may be subdivided as the nature of the
investigation to be conducted may demand. Thus, under germina-
tion may be considered various phases such as the initial period,
concerned largely with the imbibition of water; the period of rapid
chemical changes within the embryo and endosperm; the rupture
of the seed coat ; the appearance of the plumule, coleorhiza, and
primary roots; and finally emergence. The early vegetative phases
may be designated at first by the number of leaves formed and later
by the number of stools, or tillers, produced. The jointing stage is
characterized by a rapid increase in the height and weight of the
plant and by the emergence of the inflorescence out of the boot.
The flowering phase is of interest from the standpoint of the time
when fertilization actually takes place, whether before the emer-
gence of the head out of the boot, as usually is the case in barley,
or after complete emergence, as in rye or wheat. The final phase
may be subdivided into the milk, the soft-dough, the hard-dough,
the ripe, and the dead-ripe stages. The first stages up to the flower-
ing and heading period are conveniently referred to as the vegeta-
tive phases, while the posthcading phases are not infrequently
designated as the sexual phases of development. The time intervals
of the different stages are subject to wide variations; they are in-
fluenced not only by the inherent characteristics of the plant but
also by a great variety of climatic, nutritional, and special relation-
ships.
Since development is orderly, continuous, and definitely asso-
ciated with seasonal advance and progressive changes in the
climatic factors, il has been appropriately designated as rhythmic.
94 ECOLOGICAL CROP GEOGRAPHY
The general course of development in plants may well be designated
as by Scharfetter as the "vegetation rhythm." Often it is convenient
to present the vegetation rhythm graphically. Since growth may be
regarded as the summation or the end product of all plant activity,
the vegetation rhythm may be expressed by the growth curve.
The course of development and the particular vegetation rhythm
manifested by any plant is so intimately associated with climatic
phenomena that it becomes necessary to bring Scharfetter's second
term, the "climatic rhythm," defined as the annual course of
meteorological phenomena, into the discussion at this point. The
vegetation rhythm embodies the phenomena of the development
of a plant during the course of the season and may be expressed
readily in a graphic form by the growth curve; obviously, since
climate is made up of the combined activities of numerous meteor-
ological factors, the climatic rhythm cannot be so easily expressed
by any single graphic expression.
External Factors in Relation to Periodicity. That all organisms
pass through a definite cycle in their course of development has
been pointed out. The exact course of this cycle is determined by
both internal and external factofs. In some instances, or in rela-
tion to certain phases, the external factors seem to have a greater
influence in shaping the course of development than in others.
Thus, Hildebrandt (18) and also Costantin (6) show that the length
of life of a plant, that is, its behavior as an annual, winter annual,
biennial, or perennial, is determined to a high degree by the ex-
ternal factors under which development proceeds. Muenscher (35)
also points out that the behavior of weeds relative to their duration
of life is not constant but "may be determined to a large extent by
climatic factors. Many weeds that are annuals or biennials in very
severe climates may act as biennials or perennials in milder climates
or in seasons with mild winters." Red clover is generally regarded
as biennial; however, in sections with mild climates, as in the Pacific
Northwest, in the absence of plant diseases or insect pests, stands
will survive for three to four years. The cotton plant behaves, or in
reality is forced to behave under field conditions, as an annual;
however, plants protected from low temperatures will survive for
many years.
De Vries (10) reports an interesting case where deviations from the
normal course of development were induced by nutritional changes.
EXTERNAL FACTORS AND DEVELOPMENT 95
Ordinarily, the normal course of development observed in nature
or in cultivated plants, as stated by Klebs (22), is not determined
from start to finish by the inherent constitution of the species.
Klebs considers the constellation of external factors with which the
plant comes in contact as constituting the primary force determin-
ing the course of development. Consequently, under altered exter-
nal conditions an enforced deviation from the previously followed
course may become evident. Exposure to low temperatures is not
essential to the normal development of winter wheat. The rhythm
in development ordinarily observed in its growth is an enforced
rhythm. Low temperatures and low intensities of light constitute
the limiting factors in autumn and during the winter months.
No doubt there is a distinct difference in the genetic constitution
of true winter and spring wheats. This can be proved readily by
hybridization and a study of the segregates resulting from such
hybrids. When the differences in these two types of wheat are
considered from the vegetative standpoint, it is evident that spring
wheat varieties will not tiller as much or remain in the tillering
stage as long as winter wheats. According to Kornicke (26), both
spring and winter wheats undergo pauses in their respective courses
of development. This pause is short in the case of the former and
long in the case of the latter. In either instance the length of time
that the plant will remain in the true vegetative phase can be in-
fluenced by environmental factors, especially by temperature,
moisture, and light relationships. Klages (20) has shown that the
differences in the vegetative behaviors of winter and spring wheats
may be accentuated by variations in the amount of light provided
to these plants.1
The time interval that winter wheats will remain in the vegeta-
tive stage can be reduced materially by vernalization. This process
is also referred to under the terms of "iarovization" or "yaroviza-
tion." As indicated by McKee (32), "vernalization is practically
a seed treatment that influences the plant in its later stages of devel-
opment." In the process of vernalization the seed is brought to
visible germination and is then transferred and held at relatively
low temperatures (3 to 5°C), with the moisture content maintained
for from 35 to 45 days.
In view of the fact that the cycles of development in plants can
1 See page 280, Chapter XVIII.
96 ECOLOGICAL CROP GEOGRAPHY
be modified by external conditions, their periodic behavior cannot
be considered as resulting from internal factors only. In the case
of winter wheat, dormancy is determined by external factors; it
cannot be regarded, as Kiister regards it [cited by Klebs (25)], as
autogenous. One would hesitate to agree with Clements (4) that
"changes or conditions connected with the resting period become
fixed habits owing to their constant recurrence." Schimper (40)
in his account of periodic phenomena of tropical vegetations states
that "internal factors are mainly or solely responsible for the altera-
tion of rest and activity in a nearly uniform climate." Klebs (24),
however, not only doubts the accuracy of Schimper's statement as
to the necessity of a period of dormancy in tropical plants, but also
presents evidence to show that such periods of quiescence, when
they do occur, are not produced by internal or hereditary factors
but result from external conditions, either climatic or edaphic in
nature. Under conditions of proper nutrition, tropical plants were
grown in the greenhouse for a number of years without the inter-
vention of a period of dormancy.
Klebs (23) comes to the conclusion that in the last analysis all
variations from the commonly observed course of development are
produced through changes in the environment which allow the
inner potentialities of the organism to come to expression. Darwin
(8) even earlier stated that "if it were possible to expose all the
individuals of a species during many generations to absolutely
uniform conditions of life there would be no variations." In order
to determine the limits of variability, it is necessary to expose a
plant to a great diversity of external conditions.
It must not be overlooked that in reality the external factors with
which the plant comes in contact modify certain internal conditions
within the plant so that the resulting behavior is due not directly
but only indirectly to the reaction with the factors of the environ-
ment. It is not to be understood that external factors, as such, in-
duce changes in the hereditary makeup or the genetic constitution
of the plant. Reference is made here to certain definite chemical
changes within the plant induced by variations in the factors of
environment. Thus, the time of flowering, as pointed out by
Mobius (33), is influenced markedly by external conditions, es-
pecially by light and moisture relationships. Fischer (12) and
Loew (30) point out the importance of an abundant production of
EXTERNAL FACTORS AND DEVELOPMENT 97
carbohydrate materials to flowering. Kraus and Kraybill (27) are
more specific in showing that the behavior of a plant with regard to
vegetative growth and reproduction depends on the relative pro-
portion of carbohydrates to nitrogenous materials within the plant.
Such proportions, of course, are influenced greatly by external
growing conditions. The more recent works of Garner and Allard
(15) and (16) on photoperiodism in its relation to plant responses
show definitely that plant reactions may be influenced greatly by
exposure to varying lengths of days. More will be said about these
interesting responses in the discussion of light relationships. It is
not far afield to state then that in relation to factors determining
their courses of development there is much the same condition in
plants as Loeb (29) has indicated in his tropism theory of animal
conduct. Thus, Loeb states and presents evidence to the effect
that "motions caused by light or other agencies appear to the lay-
man as expressions of will and purpose on the part of the animal,
whereas in reality, the animal is forced to go where carried by its
legs, for the conduct of animals consists of forced movements,"
REFERENCES
1. Babcock, E. B., and R. E. Clausen, Genetics in Relation to Agriculture.
McGraw-Hill, New York, 1918.
2. Baur, E., Einfuhrung in die experimented Vererbungslehre. Gebriider
Borntraeger, Berlin, 1911.
3. Brody, S., "Growth and development with special reference to
domestic animals: III. Growth rates, their evaluation and signifi-
cance," Mo. Res. Bull. 97 (1927).
4. Clements, F. E., Plant Physiology and Ecology. Holt, New York, 1907.
5. Conklin, E. G., Heredity and Environment. Princeton Univ. Press,
Princeton, 1916.
6. Costantin, J., Les Vegetaux et les Milieux Cosmiques. Paris, 1898.
7. Coulter, M. C., Outlines of Genetics. University of Chicago Press,
Chicago, 1923.
8. Darwin, C., The Origin of Species. Appleton, New York, 1881.
9. De Vries, H., Intracellular Pangenesis. Open Court Pub. Co., Chicago,
1910 (first published in 1889).
10. , The Mutation Theory, Vol. 1. Open Court Pub. Co., Chicago,
1909 (first published in 1903).
11. East, E. M., "The Mendelian notation as a description of physiologi-
cal facts," Am. Nat., 46:633-655 (1912).
98 ECOLOGICAL CROP GEOGRAPHY
12. Fischer, H., "Uber die Bliitenbildung in ihrer Abhangigkeit vom
Licht und iiber bliitenbildenden Substanzen," Flora, 94:478-490
(1905).
13. Frost, H. B., "The different meanings of the term 'factor' as affecting
clearness in genetic discussion," Am. Nat., 51:244-250 (1917).
14. Gaines, W. L., and W. B. Nevens, "Growth-equation constants in
crop studies," Jour. Agr. Res., 31:973-985 (1925).
15. Garner, W. W., and H. A. Allard, "Flowering and fruiting of plants
as controlled by length of day," U. S. Dept. Agr. Yearbook 1920:377-
400.
16. , "Further studies in photoperiodism, the response of the
plant to relative length of day and night," Jour. Agr. Res., 23:871-921
(1923).
17. Haecker, V., Entwicklungsgesctichtliche Eigenschaftsanalyse. Jena, 1918.
18. Hildebrandt, F., "Die Lebensdauer und Vegetationsweise der
Pflanzen, ihre Uhrsachen und ihre Entwicklung," Englers. Bot. Jahrb.
2:51-134 (1882).
19. Johannsen, W., Elemente der Exakten Erblichkeitslehre. Jena, 1913.
20. Klages, K. H. W., "Metrical attributes and the physiology of hardy
varieties of winter wheat," Jour. Amer. Soc. Agron., 18:529-566 (1926).
21. , "The value and application of growth curves to field plat
experiments," Jour. Amer. Soc. Agron., 25:453-464 (1933).
22. Klebs, G., "Problem der Entwicklung," Biol. Centrlbl. 24:257-267,
289-305 (1904).
23. , "Uber Variationen der Bluten," Jahrb. f. wiss. Bot. 42:155-
320 (1905).
24. , "Uber die periodischen Erscheinungen tropischer Pflan-
zen," Biol. Centrlbl. 32:257-285 (1912).
25. , Uber das Verhdltnis der Aussenwelt zur Entwicklung der Pflan&n.
Sitzungsbr. der Heidelberger Akad. D. Wissenschaften. Jahrgang
1913. SAbhandlung. 1913.
26. Kornicke, F., Arten und Varietdten des Getreides. Berlin, 1885.
27. Kraus, E. J., and H. R. Kraybill, "Vegetation and reproduction with
special reference to the tomato," Ore. Agr. Exp. Sta. Bull. 149, 1918.
28. Lefevre, G., "Heredity and environment," Amer. Orthodontist 1:1-23
(1906).
29. Loeb, J., Forced Movements, Tropism, and Animal Conduct. Lippincott,
Philadelphia, 1918.
30. Loew, O., "Zur Theorie der blutenbildenden Stoffe," Flora 94:124-
128 (1905).
31. McGee, W. J., "The relation of institutions to environment," Ann.
Rpt. Smithsonian Inst., 1895. V. 50, Pt. 1:701.
EXTERNAL FACTORS AND DEVELOPMENT 99
32. McKee, R., "Vernalization experiments with forage crops," U. S.
Dept. Agr. Cir. 377, 1935.
33. Mobius, M., "Welche Umstande fordern und welche hemmen das
Bluhen der Pflanzen," Biol. Centrlbl. 12:609-624, 673-687 (1892).
34. Morgan, T. H., Evolution and Adaptation. Macmillan, New York, 1908.
35. Muenscher, W. C., Weeds. Macmillan, New York, 1935.
36. Priestley, J. H., and W. H. Pearsall, "An interpretation of some
growth curves," Ann. Bot.y 36:238-249 (1922).
37. Rippel, A., "Uber die Wachstumskurve der Pflanzen," Landn. Vers.
Stat., 97:357-380 (1920).
38. Robertson, B. R., "On the normal rate of growth of an individual and
its biochemical significance," Arch. Entw. Mech., 25:581-614 (1908).
39. Scharfetter, R., "Phenology and agriculture," Int. Rev. Sci. & Pract.
of Agr., 1:561-572 (1923).
40. Schimper, A. F. W., Plant Geography upon a Physiological Basis. Claren-
don Press, Oxford, 1903.
41. Schmidt, O., "Uber den Entwicklungsverlauf beim Getreide," Landw.
Jahrb. 45:267-324 (1913).
42. Sharp, L. W., Introduction to Cytology. McGraw-Hill, New York, 1921.
43. Werneck, H. L., "Phenology in its application to agriculture," Int.
Rev. Sci. & Pract. of Agr., 2:13-21 (1924).
Chapter VIII
PHYSIOLOGICAL LIMITS
The Cardinal Points of Vital Activity. The general reactions
of an organism to the factors of the environment were discussed in
some detail in the previous chapter. Special reactions will now be
dealt with. All plant activities operate within certain more or less
well-defined limits. A seed cannot germinate and a young seedling
is incapable of development unless the environment supplies certain
definite requirements as to temperature, moisture, oxygen, carbon
dioxide, mineral nutrients, etc. The requirements of life must be
present at least in the minimum quantity, concentration, or form
before the manifestations of life and growth can be either initiated
TABLE 3. THE CARDINAL POINTS F^R GERMINATION OF SOME IMPORTANT
CROPS, TAKEN FROM HABERLANDT
Crop
Cardinal Points, in Degrees
Centigrade
Number of Days Required for Ger-
mination (the breaking through of
the roots) at the Indicated Tempera-
tures^ in Degrees Centigrade.
Minimum
Maximum
Optimum
4.38
10.25
15.75
19.00
Wheat . . .
3-4.5
30-32
25
6
3.0
2.0
1.75
Rye ....
Barley . . .
Oats ....
1-2
3-4.5
4-5
30
28-30
30
25
20
25
4
6
7
2.5
3.0
3.75
1.0
2.0
2.75
1.0
1.75
2.0
Corn ....
8-10
40-44
32-35
—
11.25
3.25
3.0
Sorghums
Rice ....
8-10
10-12
40
36-38
32-35
30-32
—
11.5
4.75
4.0
Timothy . . .
Flax ....
3-4
2-3
30
30
26
25
8
6.5
4.5
3.25
2.0
3.0
2.0
Tobacco . . .
13-14
35
28
—
—
9.0
6.25
Hemp . . .
Sugar Beet . .
Red Clover . .
1-2
4-5
1
45
28-30
37
35
25
30
3
22
7.5
2.0
9.0
3.0
1.0
3.75
1.75
1.0
3.75
1.0
Alfalfa . . .
1
37
30
6
3.75
2.75
2.0
Peas ....
1-2
35
30
5
3.0
1.75
1.75
Lentils . . .
4-5
36
30
6
4.0
2.0
1.75
Vetch. . . .
1-2
35
30
6
5.0
2.0
2.0
100
PHYSIOLOGICAL LIMITS 101
or sustained; these manifestations proceed at the highest rate of
activity at the optimum and again come sooner or later to a close
at the maximum point. These three points of relative rate of
activity are referred to as the cardinal points.
The cardinal points are not so definite as was formerly supposed;
they are subject to a considerable range, depending on the environ-
mental factors under which the plant develops and the condition
and age of the plant. Pfeffer (11) early recognized that "the
cardinal points can never be determined with more than the
approximate accuracy, since their position is involved by the
external conditions, by the duration of exposure, by the age of the
plant, and by its previous treatment."
Haberlandt, cited by Grafe (4), gives the cardinal temperature
points for the germination of seeds of a large number of plants.
Table 3 gives these cardinal points as represented by him for some
of the more important crop plants.
The Time Factor in Relation to the Location of Cardinal
Points. The activity of separate environmental factors such as
temperature above the maximum will sooner or later result in a
cessation of all manifestations of life. For short periods supra-
maximal temperatures may not have lasting detrimental effects; if
the plant, however, remains for any length of time exposed to juch
supramaximal factors, death is certain to result. The effect of
length of exposure to given temperatures on the location of the
optimum is shown in Fig. 6, taken from the work of Talma cited
by Benecke and Jost (1). The rate of activity of Lepidium sativum
exposed to the temperatures indicated for intervals of 3|, 7, and 14
hours was measured by the increases in the length of the roots. A
short exposure, 3| hours, showed an optimum temperature at 30°C.
With the doubling of the time interval the optimum was found at
29°C, and when the period of exposure was lengthened to 14 hours,
the highest rate of activity was in evidence at 27.2°C. The increase
in temperature, especially with the longer periods of exposure,
exerts influences depressing to growth. These growth-depressing
factors become more and more active with the approach of the
optimum point and beyond it account for the rapid downward
trend of the growth curves. This is only one example of the influ-
ence of the time factor on the exact position of the optimum.
Numerous other illustrations could be given.
102
ECOLOGICAL CROP GEOGRAPHY
The Stage of Development in Relation to Cardinal Points.
The determination of cardinal points is of practical value only
when correlated with a particular developmental stage in the life
rhythm of the plant. It is obvious from Table 3 that most of the
heat-loving plants such as corn, the sorghums, rice, and tobacco
exhibit rather high minima. It does not follow, however, that a
22
20
10
7 hrsv ...'•
.X -r
^<-<. — - * 3J4hrs/
«^^-r , , • ,
10 15 20 25 27.2 2930
Temperatures in degrees centigrade
35
40
Fio. 6. Relationship of the time of exposure in hours to the rate of growth,
elongation in the length of the roots of Lepidium sativum, and the location of the
optima for the various time intervals. (After Talma.)
high temperature requirement during an early stage of develop-
ment such as germination is necessarily correlated with a high
temperature requirement during subsequent periods of develop-
ment. It will be noted that while the minimum temperature for
the germination of hemp is low, this plant can nevertheless be
classified as a heat-loving crop during its later stages of growth.
Some indications of this fact are given by the high values of the
maximum and optimum temperatures for its germination.
Schimper's Optima. Schimper (12) coined three terms which
can be used to good advantage for purposes of illustrating the
reactions of plants to increasing intensities of a particular factor of
the environment. These terms are the "absolute/* "harmonic,"
and "ecological optima." These optima may be taken in a broader
sense than the previously considered cardinal points, and their
meanings can be extended as was done by Werneck-Willingrain
PHYSIOLOGICAL LIMITS 103
(16 and 17) and Klages (8 and 9) to apply to problems encountered
in the general distribution of crop plants.
The absolute optimum corresponds to the highest degree of activity
of any one function of a plant such as transpiration or respiration.
With increasing temperatures the plant, up to a certain point,
transpires at given intervals ever-increasing amounts of water.
Beyond this particular point, because of interference or the break-
down of certain of the intricate portions of the organism, the rate
of activity decreases sharply. The optimum point of activity may,
therefore, be defined as that point where limiting factors or checks
come into activity.
The harmonic optimum corresponds to the most favorable intensity
of any one function in relation to the other functions of the plant.
Transpiration increases up to a certain point with increasing tem-
peratures. While transpiration is a necessary function of the plant,
an excessive activity of this particular, or of any other, function
would soon lead to the destruction of the plant. The plant reaches
its highest activity at that particular point where the rates of ac-
tivities of the various functions are in harmony with each other or,
in other words, at that point where they are properly coordinated.
The theoretical ecological optimum consists of the summation of the
various harmonic optima. It is difficult to give the exact locatiop.
of the summation of the various harmonic optima or the exact
location of the ecological optimum. In speaking of the summation
of the various harmonic optima, it is necessary not only to locate
an average point but also to consider the relative importance of
each of the various functions of the plant in their relation to the
growth and behavior of the entire organism.
The Ecological Optimum and Crop Distribution. Schimper's
theoretical ecological optimum can, according to Lundeg&rdh (10),
hardly be realized under a constant set of external conditions but
corresponds rather to a definite type of climate in which the various
phases of development proceed under changing climatic conditions
with the advance of the season. Klages (8 and 9), working with
the yields of cereal and corn crops in the states of the Mississippi
Valley and in South Dakota, made use of Schimper's terminology.
The fact that a crop or a group of crops is well adapted to a given
region is shown by uniformly high average yields for such crops
with a minimum of variability in seasonal yields. The theoretical
104 ECOLOGICAL CROP GEOGRAPHY
ecological optimum for a crop is approached in those particular
geographical locations where it exhibits high average yields with a
relatively low seasonal variability in such yields, or, in other words,
in those sections where the yields are high and the hazards of pro-
duction are low, ensuring a high degree of stability to production
enterprises.
Werneck-Willingrain, in his attempts to place the tasks of the
crop breeder upon a physiological basis, also makes good use of
Schimper's theoretical ecological optimum. A plant breeder in
his efforts to breed crops adapted to a particular environmental
complex must, if he expects to produce improved varieties with a
minimum of effort and expense, first of all have a good understand-
ing of the external factors with which his new creations will react.
It must be recognized that cropping areas, and in them varietal
areas, extend from minimal to optimal sections. In the former,
environmental conditions barely satisfy the life requirements in an
average season, or as Werneck-Willingrain (16) puts it, only the
minimal life requirements (Minimum der Lebensbedingungen) are
present. Under such conditions marked seasonal fluctuations in
yields can be expected. In the optimal sections average conditions
approach the optimum. These are the locations where uniformly
high yields and stability of production are to be found. Figure 7
taken from Werneck-Willingrain's (17) paper, shows graphically
a natural distribution of a plant species over regions with variable
environmental conditions. The species, and this may apply in
equal degree to a crop or more specifically to a variety of a given
crop, is distributed from a minimal to an optimal area which may
or may not be contiguous. Climatic and edaphic factors come
definitely into play in these areas and in the transitional zones
separating them.
Huntington et al. (7) in their studies of interrelations of climatic
factors to yields make use of isopleths (lines connecting regions with
equal crop yields) and climographs. Such a method brings out
some interesting relationships between yields and climatic factors.
It has general application, however, only to sections where the
crop under consideration is general or is being grown on an exten-
sive scale and not to those regions where the crop is grown only on
highly selective or highly favored dreas, as corn in the New Eng-
land states. High yields of corn in the New England and North
PHYSIOLOGICAL LIMITS
105
Atlantic states are due to the special attention given the corn crop
there rather than to favorable climatic conditions. When Hunt-
ington's analysis of yields in relation to climatic conditions is em-
ployed in such regions, misleading deductions can easily be made.
FIG. 7. Model of the natural distribution of a species. (After Werneck-Willin-
grain.) A, transition lines: 1, minimal threshold; 2, threshold of the moderate
area; 3, threshold of the most favored area, ay minimal region; b, moderate region;
c, optimal region. B and C, separated distribution areas of the same species.
B9 c, most favored belt on account of high humus content of soil or abundance of
moisture. C, bt remains in moderate region due to unfavorable soil relationships;
c9 most favored belt due to optimal moisture relationships.
Limiting Factors. On the question of limiting factors, a very
considerable literature has developed, and numerous theories have
been advanced, since the appearance of Blackman's (2) initial
paper. Blackman set forth the axiom that "when a process is con-
ditioned as to its rapidity by a number of separate factors, the rate
of the process is limited by the pace of the slowest factor." Black-
man's axiom of limiting factors is in reality an elaboration of
106 ECOLOGICAL CROP GEOGRAPHY
MjHHMBMBBMMHMHBHMMMMMHBMMaiBBMMMMnMBMHBMMBaHMBaMM^ ^••••••••••••••••MM
Liebig's law of the minimum which in its essence, as may be
noted from its wording, is very similar. "The yield of any crop
always depends on that nutrient constituent which is present in
the minimum amount." Both statements are firm and exact-
ing, giving little play for the effects of other factors influencing
activity.
Hooker (6), in a study of the law of the minimum, comes to the
conclusion that "a biological phenomenon is dependent not on a
single variable, but on a complex or constellation of factors." From
this he continues that "individual processes obey the law of the
minimum; but the grand total is governed by what may be termed
a principle of integration."
Harder (5), in a critical study concerning Blackman's limiting
factors in carbon dioxide assimilation, found no evidence of the
sharp angle at the point where the limiting factor is supposedly to
enter. Instead his curves approached the horizontal position
gradually.
The above contentions are borne out by numerous other investi-
gations. Crocker (3) concludes that the law of limiting factors does
not apply to plant activities so g^erally or with anything like the
degree of rigidity assumed by some investigators. He suggests that
the question should be not so much what external factor is the
limiting one, but rather what internal condition or inhibitor must
this factor act upon in order to indicate the reaction that is under
consideration.
More will be said regarding optima and limiting factors in rela-
tion to crop adaptation in Chapter X in connection with a discus-
sion on critical periods in crop production. At this time a considera-
tion of the general aspects of the topic is sufficient.
Practical Applications of the Theory of Optima and Limiting
Factors. In a consideration of the great crop producing provinces
of the world, it is possible to take each particular area and classify
for each one the factors favorable to the production of a particular
crop or group of crops. Finally, as the outer fringe of cultivation is
approached, it is also possible to classify various factors that are
adverse to crop production. This task is best accomplished in con-
nection with the discussion of ranges of adaptation of each indi-
vidual crop. It is well at this time, however, to give a broad outline
of limits to crop production. As stated by Spafford (13),
PHYSIOLOGICAL LIMITS 107
"the boundaries of the four great agricultural regions in the Northern
Hemisphere are determined by low temperature, low rainfall and coast
line. In southern Canada, Norway, Sweden and Finland and in
northern Russia, Manchuria and Japan agriculture is limited by low
temperature. The principal boundaries determined by low rainfall in
North America are found (a) in the states of the Great Plains and
(b) in the states of the Pacific Coast region. In Eurasia^ the principal
agricultural boundaries determined by low rainfajl are found (a) in
southeastern Russia and (b) in western China proper and Manchuria."
FIG. 8. The principal boundaries of the agricultural regions of North America.
The small circles mark temperature limits and the dashes rainfall limits. (After
Spafford.)
These agricultural boundaries for the continents of North Amer-
ica, Europe, and Asia are presented in Figs. 8, 9, and 10. Similar
limitations for crop production can be pointed out for Africa, where
production in the north and also in the south is definitely limited by
areas of low rainfall. A very good discussion of factors limiting
agricultural production in southern Africa is given by C. G. Taylor
(14). In South America agricultural production is limited by low
rainfall in the interior and in the western areas, by low temperatures
in the extreme south, and by poor soil and climatic conditions in
the equatorial regions. These same limiting factors are also very
108
ECOLOGICAL CROP GEOGRAPHY
much in evidence in Australia. Griffith Taylor (15) points out
that 94 per cent of the total rural population of Australia is found
on the margins of that continent and only 6 per cent on the "sparse-
lands." The strictly agricultural lands of the continent, excluding
the pastoral regions, are even more limited than the above figures
on distribution of population indicate.
Fio. 9. The principal boundaries of the agricultural regions of Europe. The
small circles mark temperature limits and the dashes rainfall limits. (After
Spafford.)
Producers in any given area can, insofar as environmental factors
permit, arrange their cropping practices so that conditions in gen-
eral may approach the optimum. It is necessary, as has previously
been pointed out, to recognize the physiological limitations of any
given locus in order to arrive at an economic utilization of the land
resources of any region. Crop yields may be increased by various
methods such as proper cultural practices, sequences of cropping,
addition of elements present in minimal quantities, addition of
water, utilization of adapted varieties, and control of diseases, in-
sect pests, etc. All of these various means of increasing yields can,
however, be expected to produce economic gains only insofar as
environmental complexes permit. Willcox (18) attempts to cal-
PHYSIOLOGICAL LIMITS
109
culate the "limits of crop yields" with the aid of the much-discussed
and debated Mitscherlich formula. That the yield curve of any
plant under the action of any specific growth factor is definitely
asymptotic has long been known. The exact shape of the curve
produced depends, however, not only on the factor added at given
increasing rates, but rather on the sum total of all environmental
FIG. 10. The principal boundaries of the agricultural regions of Asia. The
small circles mark temperature limits and the dashes rainfall limits. (After
Spafford.)
factors with which the plant reacts. In the light of this, the theo-
retical determinations of Willcox's upper "limits of crop yields"
become of very questionable value. The all-important problem of
agricultural production is not one of obtaining simply the highest
possible yields but rather of so shaping the production program
that economic production may result and a permanent agricultural
system be established and maintained.
REFERENCES
1. Benecke, W., and L. Jost, Pflan&nphysiologic, Vol. 2. Gustav Fischer,
Jena, 1923.
2. Blackman, F. F., "Optima and limiting factors," Ann. Bot., 19:281-
295 (1905).
110 ECOLOGICAL CROP GEOGRAPHY
3. Crocker, W., "Law of the minimum — a review of Hooker's work,"
Bot. Gaz., 65:287-288 (1918).
4. Grafe, V., Erndhrungsphysiologisches Praktikum der hoheren Pflanzen.
Paul Parey, Berlin, 1914.
5. Harder, R., "Kritische Versuche zu Blackman's Theorie der 'be-
grenzenden Faktoren5 bei der Kohlensaure Assimilation," Jahrb. f.
wiss. Bot., 60:531-571 (1921).
6. Hooker, H. D., "Liebig's law of the minimum in relation to general
biological problems," Science, 46:197-204 (1917).
7. Huntington, E., F. E. Williams, and S. Van Valkenburg, Economic
and Social Geography. Wiley, New York, 1933.
8. Klages, K. H. W., "Geographical distribution of variability in the
yields of field crops in the states of the Mississippi Valley," Ecology, 1 1 :
293-306 (1930).
9. , "Geographical distribution of variability in the yields of
cereal crops in South Dakota," Ecology, 12:334-345 (1931).
10. Lundegardh, Henrik, Klima und Boden in ihrer Wirkung auj das Pflan&n-
leben. Gustav Fischer, Jena, 1925.
11. PfefFer, W., The Physiology of Plants, trans, and rev. by A. J. Ewart,
Vol. 2. Clarendon Press, Oxford, 1903.
12. Schimper, A. F. W., Plant Geography upon a Physiological Basis.
Clarendon Press, Oxford, 1903. *
13. Spafford, R. R., "Farm types in Nebraska, as determined by climatic,
soil and economic factors," Nebr. Res. Bull. 15, 1919.
14. Taylor, C. C., "Agriculture in southern Africa," U. S. Dept. Agr. Tech.
Bull. 466, 1935.
15. Taylor, Griffith, "The frontiers of settlement in Australia," Geog. Rev.,
16:1-25 (1926).
16. Werneck-Willingrain, G. L., "Die Pflanzenziichtung auf pflanzen-
geographischer Grundlage," Pflan&nbau. Jahrg., 1924:145-150.
17. ^ "Der Getreidebau auf pflanzengeographischer Grundlage,"
Pflan&nbau., Jahrg., 1924-25:393-404, 419-425.
18. Willcox, O. W., "What is agrobiology?" Econ. Forum, Winter 1936
issue: 302-310.
Chapter IX
CROP YIELDS AND VARIABILITY IN RELATION
TO THE ECOLOGICAL OPTIMUM
Broad Conception of the Ecological Optimum. The ecological
optimum, as defined by Schimper, is generally regarded as a purely
hypothetical entity. It will now be shown that a broad conception
of this term can be of considerable value in the study of ecological
crop geography. The materials used in this chapter are taken
largely from two papers by the author, Klages (4 and 5).
The potential crop producing ability of a given area is dependent
primarily upon the existing climatic and soil conditions under which
the crops in question must be grown. Since climatic factors exert
mainly a regional influence on plant life, the differences in the be-
havior of a crop or a group of crops over extensive areas, as in a
given state or a group of states, may be considered due, primarily,
to differences in climatic rather than soil conditions.
«
In regions of the ecological optimum of a crop, it is to be expected
that the yields should be uniformly high, while the variations in
such yields from season to season should be fairly low. A low varia-
tion in the yields of a crop over a period of years serves as a measure
of stability of production insofar as the returns from a given acreage
can be ascertained in advance with a reasonable degree of certainty.
An excessively high degree of variability in the yields of one or more
crops in a given area indicates that certain hazards are encountered
in the production of that particular crop or series of crops. As
stated by Clements (1), "every plant is a measure of the conditions
under which it grows. To this extent it is an index of soil and
climate, and consequently an indicator of the behavior of other
plants and animals in the same spot."
With the above factors in mind, Klages (4) tabulated the yields
of grain crops in the states of the Mississippi Valley, and calculated
the degree of variability in the seasonal yields of these respective
crops. The average yields of these states offered very suitable data
ill
U2 ECOLOGICAL CROP GEOGRAPHY
as the eastern states of this extensive crop area have typical wood-
land climates, while the climates of the states of the Great Plains
area, especially in the central and western portions of these states,
are decidedly of a grassland type.
All yields and tabulations, with the exception of those of the state
of Oklahoma, are based on results reported for a period of 37 years,
1891-1927, inclusive. The data for Oklahoma were available only
for a 27-year period, 1901-1927, inclusive. Since the data pertain-
ing to the discussion of the facts presented in this chapter can be
given readily in graphical form, tabulations of these data are not
included here. Students interested in greater detail than space
permits here are referred to the original papers (Klages, 4 and 5).
In the graphic presentation, the same linear scale was used for
both the yield and variability data. This method may be criticized
from a strictly mathematical standpoint in that the variability ex-
pressed on a percentage basis is in certain instances greater than
the yield expressed in bushels. It is justifiable in this case as it pre-
sents the clearest possible graphical presentation of the facts. It also
is to be recognized that the coefficient of variability is not beyond
reproach in all instances as an expression of degree of variation;
however, the type of data here analyzed may well be treated on the
basis of percentage variability. Klages (5) made use of both the
coefficient of variability and Weinberg's formula and arrived at
the same conclusion.
Yields and Variability of Yields of Corn. Corn is an important
crop in all the states of the Mississippi Valley. Figure 11 shows
graphically the average yields and variability of the yields of corn
in the separate states.
It will be seen that the yields decrease in all instances in going
from east to west, except in the most southern tier of states. The
average yields of the Great Plains states are significantly lower than
those of the states to the east of this area. These differences are
brought out not only by the respective means but also by the lower
values of the modal classes. This condition is to be expected in
view of the lower amounts of precipitation in the Great Plains area.
As stated by Waller (9), "to say that there is more abundant mois-
ture in the prairies than in the plains is only another way of saying
that there is more abundant vegetation." Another factor to be
considered in the Great Plains area is the higher rate of evaporation.
YIELDS AND THE ECOLOGICAL OPTIMUM
115
The tendency for yields to decrease either to the north or to the
south of the heart of the Corn Belt is apparent. This holds true
along the line from Ohio through to Nebraska.
The coefficients of variability of corn yields increase decidedly
from the eastern to the western states, as do also the ranges in yield
FIG. 1 1 . Average yields (cross-hatched columns) and coefficients of variability for
the yields (solid columns) of corn in the states of the Mississippi Valley.
from year to year, but to a lesser degree. The lowest yields reported
for each tier of states from north to south are invariably to be found
in the states of the Great Plains area.
It is apparent that the region of the ecological optimum for corn
production is to a great extent determined by the specific inter-
action of climatic factors. Weaver (12) points out the specific effects
of climatic factors on the development of the corn plant in the drier
sections of the Great Plains area, while Miller (6) shows from a
physiological standpoint why the production of grain sorghums is
114
ECOLOGICAL CROP GEOGRAPHY
less hazardous in this region than corn production. Since soil
factors vary within the units selected, no attempt is made to evaluate
them in this chapter.
Yields and Variability in the Yields of Oats. The average
yields and degrees of variability for oats are shown graphically in
Fig. 12.
FIG. 12. Average yields (cross-hatched columns) and coefficients of variability
for the yields (solid columns) of oats in the states of the upper and central Missis-
sippi Valley.
As in the case of corn, a material reduction of the yields in the
western states is in evidence. The lowest yields for the respective
groups of states are also to be found here.
The variability of yields increases from east to west as in the
case of corn; the differences are not so pronounced, however. The
detrimental effects of high summer temperatures occasionally en-
countered in the Corn Beit states are brought out by the relatively
YIELDS AND THE ECOLOGICAL OPTIMUM 115
high coefficients for such states as Indiana, Illinois, and Missouri.
The low coefficients of variability of the yields of such states as
Kentucky, Tennessee, and Arkansas may be accounted for by the
fact that these states produce but few oats.
The highest yields, especially as shown by the modal classes, are
encountered in Ohio, Michigan, Wisconsin, and Minnesota. The
Corn Belt states show fairly high average yields but lower modal
classes. Of the southern states, Oklahoma and Texas show high
yields. These states show, however, like other states of the Great
Plains area, high degrees of variability in yields.
The data presented show that the region with the most favorable
climatic conditions, the ecological optimum, for oat production is
to be found somewhat to the north of the heart of the Corn Belt,
where moderate summer temperatures prevail.
Yields and Variability in the Yields of Wheat. The yield
data available on wheat allowed for no distinctions between spring
and winter wheat except insofar as states producing predominately
one or the other of these wheats are represented. The yield and
variability data for the crop are presented in Fig. 13.
The data presented indicate that different types of hazards are
encountered in the various wheat producing areas of the Mississippi
Valley. The spring wheat producing states, from Wisconsin to. the
Dakotas, show the same yield and variability relationships as
shown by corn and oats, namely, lower yields and higher variability
in the drier western states. The high degree of variability in the
yields of the spring wheat producing states of the Great Plains area
is accounted for by the rather high frequencies of droughts and
occasional severe epidemics of stem rust. It should be noted also
that spring wheat production is generally more hazardous than
the production of winter wheat. Since winter wheat matures earlier
than the spring-sown crop, it is in a 'better position to escape
damage from drought and rust. The lower degree of variability in
Nebraska as compared to South Dakota is due in part to the fact
that the former state produces largely winter wheat and the latter
produces mainly spring wheat. It is interesting to note the rather
high degrees of variability for the eastern soft red winter wheat pro-
ducing states. The coefficients for the western hard red winter
wheat producing states are comparatively low, especially when
compared with the uniformly high degrees of variability shown by
116
ECOLOGICAL CROP GEOGRAPHY
other crops in these states. Winterkilling constituted a hazard in
all the winter wheat producing areas of this region. Both stem and
leaf rusts are of greater consequence in the more humid eastern
states than in the drier western areas. On the other hand, lack of
moisture in autumn at the time of seeding, or later, as well as during
j M mvt£as£
T.O&HOM* 1 m^L ._ j~rm~~ w"**?--
"««— i || r«K«r^- iy »K /'
I ^Hl91 ' .__ ^ / •••^a.^-.-^T*"/
FIG. 13. Average yields (cross-hatched columns) and coefficients of variability for
the yields (solid columns) of wheat in the states of the Mississippi Valley.
the growing season of the crop, constitutes a greater hazard in the
western areas than in the eastern areas of this region.
Yields and Variability in the Yields of Barley. The yields
of barley in the several states do not differ so greatly as those of
other crops reported. Differences in the variability of yields, how-
ever, are very pronounced, as shown graphically in Fig. 14. The
states of the Great Plains, especially Kansas and North Dakota,
exhibit exceedingly high coefficients of variability.
It is rather significant that the degrees of variability for the yields
YIELDS AND THE ECOLOGICAL OPTIMUM
117
of barley are much lower than those of oats, except in the Great
Plains; this is apparent from a comparison of Figs. 12 and 14.
There may be several reasons for this. It may be that more atten-
tion is devoted to barley production, both from the standpoint of
cultural practices and the selection of more favored locations, as
FIG. 14. Average yields (cross-hatched columns) and coefficients of variability
for the yields (solid columns) of barley in the states of the upper Mississippi
Valley.
«
on more fertile and better watered soils. Barley generally matures
somewhat earlier than oats, especially in sections where medium-
to late-maturing varieties of oats are commonly grown. This
enables the barley crop to escape some of the high summer tem-
peratures occasionally encountered in the states of the Mississippi
Valley. On the other hand, as brought out by Hutcheson and
Quantz (3) and by Walster (10), barley is more sensitive to high
temperatures than oats. This may account for the slightly higher
degrees of variability of the yields of barley as compared to those
shown by oats in the states of the Great Plains, where summer
temperatures are fairly high and where the production of early-
maturing varieties of oats is the rule.
Yields and Variability in the Yields of Rye. The yields and
degrees of variability for rye (Fig. 1 5) show much the same trend
as those given for barley. The coefficients of variability are sig-
nificantly higher for the western than for the eastern states.
118
ECOLOGICAL CROP GEOGRAPHY
It will be observed that the degrees of variability for the yields of
rye are less than those of any other crop. The ability of rye to grow
under more unfavorable conditions than other cereal may account
for this fact.
TARKANSAS
Xrf "KENTUCKY c'~~~/
(J rl-J— TENNESSEE ^'
FIG. 15. Average yields (cross-hatched columns) and coefficients of variability
for the yields (solid columns) of rye in the states of the upper Mississippi
Valley.
The Ecological Optimum Region of a Crop Is Determined by
the Factors of the Physiological and Social Environment. The
foregoing discussion based on the analysis of yield data of the states
of the Mississippi Valley serves to substantiate the theory previously
stated, namely, that the region to which a crop is best adapted may
often be located on the basis of uniformly high yields of the crop in
question. Exceptions to this general statement were found in the
case of states where the production of the crop under question was
of relatively little importance. Another exception was the behavior
of yields of wheat in the states producing hard red spring wheat.
Yields in these states were fairly low while the degrees of variability
were high. Still, the type of crop grown in this section can hardly
be compared with that grown in the states to the east; its very
nature is determined by the climatic conditions under which it is
produced. Hard red spring wheats cannot be produced in the
humid eastern area of the United States or Canada. The hard
vitreous character of the kernels and the high nitrogen content of
YIELDS AND THE ECOLOGICAL OPTIMUM 119
this class of wheat are determined not only by the genetic factors of
the varieties employed, but to a large degree by the type of climate
and the soil conditions under which the crop is grown. The typi-
cally grassland climates prevailing in the northern Great Plains
area are characterized by a relatively abundant supply of moisture
during the early vegetative period but a rapidly decreasing avail-
ability of moisture during the early part of the summer. The de-
crease in moisture available to the plants corresponds well with the
postheading period of spring wheat. This more or less progressive
decrease in the availability of moisture tends to cut down the time
interval from flowering to maturity. The climatic conditions and
the types of soil produced under such climatic complexes account
for the relatively low yields, yet at the same time they play an
important part in determining the chemical and physical prop-
erties of the crop produced.
Variability in the Yields of Crops in the Eastern and Central
Great Plains Area. The foregoing discussions on crop yields and
variabilities of such yields in the states of the Mississippi Valley in
their relation to the ecological optimum is subject to criticism from
the standpoint of the size of the units used. Climatic conditions
of as large an area as the confines of a state are far from uniform.
This is true especially for the states of the Great Plains region, the
eastern portions of which show a type of climate entirely different
from that of the central and western parts. As may be observed
from the maps of natural vegetations given by Shantz and Zon (8),
and from the numerous root studies of native plants by Weaver (11),
and by Weaver and Crist (13), entirely different types of vegeta-
tions, which reflect directly the prevailing climatic conditions, are
encountered in the eastern and western portions of these states.
Consequently, the yield data of such large units have all the short-
comings of average values.
The distribution of the main station and the various substations
of the South Dakota Agricultural Experiment Station was found
favorable for a more definite investigation on variability of crop
yields (Klages, 5). The main station at Brookings is located in the
east-central part of the state, only 18 miles from the Minnesota line.
The Highmore substation is located in the central part, 150 miles
west of Brookings, while the Eureka substation is found 100 miles
north of Highmore, near the North Dakota state line.
120
ECOLOGICAL CROP GEOGRAPHY
Figures 16 and 17 give a graphic presentation for a 21 -year
period, 1909-1929, inclusive, of the yields and seasonal variabilities
• BROOKINGS
^ HIGHMOR
^EUREKA
Winter
Wheat
Durum
Wheat
Common
Spring
Wheat
Early Oats
Sixty Day
Late Oats
Swedish
Select
Six Rowed
Barley
Two Rowed
Barley
FIG. 16. Yields of cereal crops grown on variety test plats at Brookings, High-
more, and Eureka, South Dakota for the 21 -year period, 1909-1929. (After
Klages, 5.)
in the yields for the three South t)akota stations. It is evident that
the yields of all crops considered were higher at Brookings than at
Winter
Wheat
Durum
Wheat
Common
Spring
Wheat
Early Oats
Sixty Day
Late Oats
Swedish
Select
Six Rowed
Barley
Two Rowed
Barley
Fio. 17. Variability in the yields of cereal crops grown on variety test plats at
Brookings, Highmore, and Eureka, South Dakota, for the 21-year period 1909-
1929. (After Klages, 5.)
YIELDS AND THE ECOLOGICAL OPTIMUM 121
the two stations to the west. This is to be expected in view of the
more favorable moisture relationships in the eastern than in the
central parts of the state. Figures 16 and 17 show very definitely
that the seasonal variability in the yields of the various crops con-
sidered is decidedly less at Brookings than at the two stations in the
central portion of the state. This substantiates the theory that
climatic conditions approach the ecological optimum to a higher
degree in the eastern portion of South Dakota than in the central
portion of the state. This condition holds true for all of the Great
Plains states.
Yield and Variability Responses of Individual Crops in
Eastern and Central South Dakota. The comparative yield and
variability figures for crops grown in eastern and central South
Dakota serve well to illustrate the performance of such crops in a
transitional region grading from a section near the ecological
optimum to a section farther distant from it.
The smallest differences in the yields of any of the crops at the
three respective stations are those for durum wheat. The same is
true for the differences in the degrees of variability of seasonal yields
at the several stations.
Winter wheat was grown at only two stations, Brookings and
Highmore. The differences in the yields and variability of such
yields are very pronounced, primarily because of a greater amount
of winterkilling in the central than in the eastern part of the state.
Over a 23-year period, eight complete failures due to winterkilling
are on record for Highmore as compared to only one for Brookings
during the same period.
Attention is called to the relative performance of early and later
maturing varieties of oats. It is evident from the higher average
yields and the lower variability of such yields that early varieties
of the Sixty Day type are better adapted to prevailing climatic
conditions than later maturing varieties of the Swedish Select type.
This is true for the eastern as well as for the central part of the
state. In the northern part of the state, at Eureka, the difference
in the yields of these two types is not of significance; at Brookings
and Highmore the differences, however, are very pronounced.
Even at Eureka, while the differences in the yields of Sixty Day
and Swedish Select oats are not great, the yields of the latter variety
show a considerably higher degree of variability.
122 ECOLOGICAL CROP GEOGRAPHY
Since, according to Harlan et al. (2), the six-rowed barleys of the
Manchuria type yield best in the eastern portion of the northern
Great Plains area, while the two-rowed barleys of the White
Smyrna type are reported to do better in the western drier portion
of this region, it was deemed advisable to include in this investi-
gation performance records of representative two- and six-rowed
varieties. With the exception of the returns at Brookings, the dif-
ferences in the yields of the six- and two-rowed barleys are not very
significant. It is interesting to note, however, that the coefficients
of variability of the yields of these two types are lower in the central
portion of the state for the barleys of the White Smyrna (two-rowed)
than of the Manchuria (six-rowed) type. This suggests, even
though the differences in the two values are not great enough to be
statistically significant, that barleys of the White Smyrna type may,
on account of their earlier maturity, be more drought-resistant, or
in reality more drought-escaping, than barleys of the Manchuria
type such as Odessa. It is common knowledge that White Smyrna
will frequently produce at least a partial crop under seasonal con-
ditions too severe for the survival of Odessa. On the other hand,
White Smyrna lacks yielding ability under favorable conditions.
Unpublished data by the authoV indicate a lower percentage of
sterility in two-rowed barleys grown under high temperature con-
ditions than in six-rowed barleys of the Manchuria type. This may
help to explain the higher relative average yields of the two-rowed
over the six-rowed varieties of barley in central South Dakota.
Only at Highmore were yields of flax available for a long enough
period of time to be compared with those shown by the cereals.
It was observed that the degree of variability shown by flax is
considerably higher than that shown by any of the cereals. Flax,
as brought out by Rotmistroff (7), has a relatively shallow root
system; consequently, it is dependent on surface moisture or on
precipitation during the growing season to a greater extent than
the deeper rooted cereal crops. Furthermore, since young flax
plants are rather tender and slower to establish themselves than
the cereals, they are more susceptible to unfavorable environmental
factors.
YIELDS AND THE ECOLOGICAL OPTIMUM 123
REFERENCES
1 . Clements, F. E., Plant Indicators. Carnegie Inst. of Washington Pub.
290, 1920.
2. Harlan, H. V., M. L. Martini, and M. N. Pope, "Test of barley
varieties in America," U. S. Dept. Agr. Bull. 1334, 1925.
3. Hutcheson, T. B., and K. E. Quantz, "The effects of greenhouse
temperatures on the growth of small grains," Jour. Amer. Soc. Agron.y
9:17-21 (1917).
4. Klages, K. H. W., "Geographical distribution of variability in the
yields of field crops in the states of the Mississippi Valley," Ecology,
11:293-306 (1930).
5. , "Geographical distribution of variability in the yields of
cereal crops in South Dakota," Ecology, 12:334-345 (1934).
6. Miller, E. C., "Comparative studies of the root systems and leaf areas
of corn and sorghums," Jour. Agr. Res., 6:311-332 (1916).
7. Rotmistroff, W. G., Das Wesen der Durre, ihre Ursache und Verhutung.
Theodor Steinkoff, Dresden, 1926.
8. Shantz, H. L., and R. Zon, Atlas of American Agriculture, Part 1, Sec. E,
"Natural vegetation." Washington, Govt. Printing Press, 1924.
9. Waller, A. E., "Crop centers of the United States," Jour. Amer. Soc.
Agron., 10:49-83 (1918).
10. Walster, H. L., "Formative effect of high and low temperatures upon
growth of barley: a chemical correlation," Bot. Ga%., 69:97-126 (1920).
11. Weaver, J. E., Root Development in the Grassland Formation, Carnegie
Inst. of Washington Pub. 292, 1920.
12. , "Some ecological aspects of agriculture in the prairie,"
Ecology, 8:1-17 (1927).
13. , and J. W. Crist, "Relation of hardpan to root penetration
in the Great Plains," Ecology, 3:237-249 (1922).
Chapter X
ADAPTATION
Adaptation Defined. Perhaps one of the best examples of the
interaction of internal factors with external conditions may be
found in a consideration of adaptation. Adaptation has been
defined by numerous biologists; thus Lamarck [cited from Neger
(9)] states that organisms are endowed with the ability to alter their
organs quantitatively and qualitatively to meet the requirements
of life. Herbert Spencer says life is that ability to bring the inner
forces into adjustment with the exterior. Neger defines adaptation
as that phenomenon by which plants react with the environment
through alteration of their inner organization, this reaction leading
to the production of more or less expedient characters.
Direct or Indirect Adaptation.* In the older literature on adap-
tation the question of direct versus indirect causes for the production
of characteristics enabling a plant to survive in a given environ-
ment was discussed at some length and at times with considerable
feeling. The proponents of the theory of direct adaptation assumed
that organisms were endowed with the ability to build up structures
or alter their respective cycles of development to their own advan-
tage as existing external conditions demanded. With the indirect
conception of adaptation the development of such characteristics
as may prove to be beneficial to the plant in its struggle for existence
is considered strictly the result of chance.
According to Hayek (5) it may be considered immaterial whether
adaptation characteristics (Anpassungsmerkmale) are produced by
means of selection, through direct interaction with the environment,
or by any other means. But, he continues, it will always be observed
that members of greatly divergent systematic groups show identical
or analogous adaptation characteristics when growing under similar
external conditions. This is the same condition recognized by
Schimper (12) in coining the term "climatic formation" as con-
trasted to the "edaphic formations."
124
ADAPTATION 125
The view of direct adaptation tends to lean too much to the
teleological conception of nature. The close connection between ,
the theory of direct adaptation and the Lamarckian theory of de-
velopment of suitable characteristics in organisms is quite evident.
The impossibility of direct adaptation is also brought out by
DeVries (4).
"If in order to secure one good novelty, nature must produce ten or
twenty or perhaps more bad ones at a time, the possibility of improve-
ment coming by pure chance must be granted at once. All hypotheses
concerning the direct causes of adaptation at once become superfluous,
and the great principle enunciated by Darwin once more reigns su-
preme. . . . Darwin's idea was that mutability took place in all direc-
tions and that the most favorable mutations were preserved."
De Vries (3) gave strong support to the theory of indirect adap-
tation according to which sudden discontinuous variates better
adapted to a particular environment arc produced. These sudden
variates originate, according to De Vries, through mutations or, as
taken by other authors, through fluctuating variability. From the
viewpoint of indirect adaptation, selection during the struggle for
existence decides the question of fitness. Thus, the environment in
this view has not the "power of directly evoking in the organism an
adaptive response" as was held by Warming (14). Rather, chance
variates better able to cope with the factors of a given environment
are able to multiply more rapidly and will in time replace those
variates not so well adapted.
Selection for Fitness. The fact remains that variates, whatever
their origin, be it through mutations, chromosome aberrations,
hybridization, or other causes, are always present. The phenome-
non of adaptation would, as stated by Lundegardh (7), be indeed
peculiar if organic life were fixed and unchangeable.
It is almost an axiom that plants growing naturally in a given
environment exhibit a certain degree of fitness to the essential fac-
tors of their habitat. Those particular plants best suited by their
structure or their functions gain the upper hand in the struggle for
existence. Selection decides the question of fitness. As stated by
DeVries (3), "natural selection is a sieve. It creates nothing, as is
so often assumed; it only sifts. It retains only what variability puts
into the sieve. Whence the material comes that is put into it, should
be kept separate from the theory of its selection.'* According to
126 ECOLOGICAL CROP GEOGRAPHY
Crampton (2), "Selection is not regarded in any way originative
but only as judicial, so to speak. As the members of any species
present themselves at the bar, selection decides the question of
survival or destruction on the basis of the conditions of correlation
that is exhibited."
Crampton lays great stress on functional correlation of characters.
"Separate characters do not serve directly as adaptive or inadaptive
elements of the organism, but they do so only insofar as they exist
in close or loose correlation with other structural or functional
characteristics."
Stahl's Classification of Adaptations. Stahl (cited from Neger)
grouped adaptations with respect to the selective factor or factors
into three classes: (a) the converse, (b) the adverse, and (c) the
biversale. In the converse type, the organism utilizes some par-
ticular factor of its habitat to its own advantage and to such an
extent that it gains the upper hand over competing species. In the
adverse type of adaptation the organism is through its functional or
structural characteristics better protected against some dangerous
element of its environment. In the biversale type the organism is
considered as utilizing the favorable factors of the environment to
its fullest extent, but at the same* time it must be able to protect
itself against some factor or factors working in excess.
Of the above three categories the last, or biversale, type no doubt
offers the best explanation of how plants are able to adapt them-
selves to natural environments. It is difficult to find an environment
where all conditions are at all times, for the entire vegetative rhythm
of the plant, favorable or at the optimum. Again while a plant must
have the ability to protect itself against some unfavorable factor in
its environment it must of necessity utilize those factors favorable
to growth; otherwise it could not survive. This is well summarized
by Lundeg&rdh. In the uninterrupted struggle against external
conditions and against competitors plants able to establish and
maintain themselves are those best adapted to the environment
by virtue of their particular structures and functions. The word
"adapted" is taken as being descriptive. A particular plant or
group of plants is better adapted than another if it is able to econ-
omize to a greater extent than its competitors the available energy
and nutrients provided by the environment and at the same time
is protected against unfavorable influences. Degrees of utilization
ADAPTATION 127
of favorable factors and protection against unfavorable or detri-
mental factors must be considered on a relative basis.
Adaptation in Relation to Scharfetter's Vegetation and Cli-
matic Rhythms. Scharfetter's (11) terms, the "vegetation" and
the "climatic rhythm," discussed in Chapter VII in relation to
development, may be used to advantage in discussing the factors
involved in adaptation. A plant cannot adapt itself to a given
region unless it can so shape its vegetation rhythm as to fit into the
particular climatic rhythm of that region. This does not mean that
plants utilize all of the available climatic rhythm; often they do not,
as for instance with the cereals in central Europe and in the eastern
part of the United States. Spring wheat and oats in these sections
mature during early summer, they do not take full advantage of the
growing season. This does not mean that late-maturing varieties
should be recommended for those regions, for other factors come
into play on that point, such as ability to avert critical periods and
ability to escape disease damage, as rust in wheat. A perfect har-
mony between the vegetation rhythm of a plant and the climatic
rhythm of a particular region is hardly to be found; the climatic
rhythm is made up of too many component parts for such a condi-
tion to be attained. Yet a high degree of harmony between these
two rhythms is found in certain sections. The predominating im-
portance of the corn crop in the Corn Belt of the United States and
of the potato in northern Europe can be readily explained on the
basis of the high degrees of harmony between the vegetation
rhythms of these two crops and the prevailing climatic rhythms in
the two areas. Both of these crops are outstanding from the stand-
point of carbohydrate production. They make use of nearly the
entire vegetation rhythm as against competing crops having their
vegetative periods extending over only a portion of the climatic
rhythm.
Critical Periods in Crop Production. Under conditions of the
ecological optimum the harmony between the vegetation and
climatic rhythms of plants may be considered complete. This con-
dition, if realized at all, develops at rare intervals only. Under
natural conditions it is to be expected that at certain stages in the
growth cycle of a plant some factor of the environment either will be
at the minimum or may be operating in excess of the growth re-
quirements. It must also be recognized that during certain phases
128 ECOLOGICAL CROP GEOGRAPHY
of development the plant either makes more definite and exacting
demands of the factors of the environment, or is more easily dam-
aged by factors operating at either the minimum or the maximum
rate. These periods of stress may be designated as critical. Van de
Sande-Bakhuyzen (10) states "by the term critical period is meant
the period in the life cycle of the plant during which the correlation
between external conditions, i.e., rainfall or temperature, and the
final yield is highest."
The question of critical periods in crop production is closely
related to the general topic of crop risks or hazards. The plant
passes during its course of development through easily vulnerable
phases, the critical periods. Also the climates of certain areas have
their favorable and unfavorable phases or as it may be stated their
optimum and erratic periods. If climatic data for any given region
are available for any considerable length of time, it is possible to
establish a common or average sequence of climatic phenomena or
the so-called phenological mean. The phcnological mean would
tend to put on a statistical basis the probabilities of the availability
of the ecological factors such as moisture, temperature, and light
at given intervals throughout the year and especially during the
growing season. Where the degree df Jiarmony between the vegeta-
tion and climatic rhythms is not complete, there is a possibility
that the phase of development at which reductions in yields may
most likely be expected may sometimes be shifted so that the critical
period may fall at a time when better climatic conditions may pre-
vail. Also a choice of variety may be made to shift the critical
period or periods to a time when favorable climatic conditions may
reasonably be expected. In a typical grassland climate a drought
may be expected toward the middle of summer. The employment
of early-maturing varieties, as has already been pointed out, may
avert loss from such to-be-expected phases of the climatic rhythms.
This would be a case of drought evasion. Martin and Sieglinger
(8) give a good illustration of the above in their experiments with
dates of seeding for different varieties of grain sorghums in the
southern Great Plains area. At many stations a delay in the plant-
ing dates served to avoid critical periods. It was found especially
desirable to shift the dates of flowering and seed development to
late summer or early autumn when more moderate temperatures
could be expected.
ADAPTATION 129
Critical periods may in limited instances be avoided by supplying
artificially the factor of the environment which may happen to be
at the minimum. Thus, water may be supplied by means of irriga-
tion, or a mineral element may be supplied by a commercial ferti-
lizer. Furthermore, special systems of cropping may be initiated
to supply or to conserve the factor most likely to cut down yields.
Critical periods due to the effects of disease may be avoided by
the breeding of varieties or strains resistant to the particular
disease encountered. The same may be said relative to insect
damage.
Hazards in Crop Production. The question of hazards in crop
production was discussed in relation to the geographical location
of producing areas in the previous chapter. Diversification in the
cropping program, where this is possible, may frequently be resorted
to in order to stabilize production. Thus if the general cropping in
a section, as in the northern Great Plains area, is of the spring-sum-
mer type, according to Spafford's (13) classification, the inclusion
of a winter crop such as winter wheat, where its production is
feasible, or winter rye, where winter conditions are too severe for
wheat, will lead to a greater diversification of the cropping program.
Such a change in the cropping system will not only serve to spread
risks but will also enable producers to make better use of their
labor and equipment.
Producers show a decided tendency to adjust their cropping
enterprises with reference to the probable risks that may be ex-
pected. This may apply to physiological as well as to economic
risks. Klages (6) pointed out one of the many illustrations that
may be presented by showing the relationship between the rate of
abandonment of winter wheat acreage in the state of South Dakota
in any one year and the acreage planted for the following crop year.
A close relationship between the acreage abandoned on May 1 of
any one year and the acreage sown in September of that year is in
evidence. This is brought out by the graphic presentation of these
two factors in Fig. 18. Periods of high abandonment of acreage
sown in fall, which are more or less synonymous to periods with
winter conditions unfavorable to the survival of the crop, have in
all years with the exception of the season of 1931 led to significant
curtailments of acreage sown to winter wheat. Likewise a succes-
sion of years, or even separate seasons, with a low abandonment
150
ECOLOGICAL CROP GEOGRAPHY
resulted invariably in marked increases in winter wheat acreage.
The high abandonment of acreage in 1931, of the crop sown in the
fall of 1930, was due primarily to drought and factors incident to
it rather than to heavy winterkilling. The above illustration is
ACRCAGf PLANTEQ IN S£PT£M8SR
ACP£A6C A&ANDOrtCD
MAY I"
/9ZO 19& I9W tm 1923 1990 J9X2
FIG. 18. Acreage of winter wheat in South Dakota abandoned on May 1 of any
year and acreage sown in September of that year, 1914-1932. (After Klages.)
especially interesting insofar as it deals with a crop approaching its
physiological limit of production.
Range of Adaptation. Some plants, crops, and varieties of
crops are limited to rather restricted areas by their particular
growth requirements or by economic conditions, while others are
found or are grown over very extensive areas. These crops may
be considered as having narrow or wide ranges of adaptation.
Cotton is limited to those areas where the growing season is at
ADAPTATION 131
least 190 days. Alfalfa, on the other hand, is found from Canada
to the Gulf and from the Atlantic to the Pacific. The areas pro-
ducing rice or buckwheat are limited both by physiological and
economic barriers, while wheat and corn are grown under a great
variety of conditions. The reasons for this are definite; it is not
necessary to go into them at this time.
It is well to note that some crop varieties have a narrow or
limited, others a wide, range of adaptation. Thus, according to
Clark and Bayles (1), the acreage of Turkey wheat, including that
grown under the name of Kharkof and other synonyms, in 1929
comprised 15,925,677 acres, or 25.69 per cent of the total wheat
acreage of the country. It was reported from 28 states. Red Wave
was grown in 17 states over an area of 255,737 acres.
REFERENCES
1. Clark, J. A., and B. B. Bayles, "Classification of wheat varieties grown
in the United States," U. S. Dept. Agr. Tech. Bull. 459, 1935.
2. Crampton, H. E., "On a general theory of adaptation and selection,'*
Jour. Exp. ZooL, 2:425-430 (1905).
3. De Vries, H., The Mutation Theory, Vol. 1. Open Court Pub. Co.,
Chicago, 1909 (first published in 1903).
4 ^ Species and Varieties and Their Origin by Mutation. Open
Court Pub. Co., Chicago, 1904.
5. Hayek, A., Allgemeine Pflan&ngeographie. Gebriider Borntraeger,
Berlin, 1926.
6. Klages, K. H. W., "Winter wheat production in South Dakota,'*
S. D. Agr. Exp. Sta. Bull. 276, 1933.
7. LundegSrdh, H., Klima und Boden in ihrer Wirkung auf das Pflan&nleben.
Gustav Fischer, Jena, 1925.
8. Martin, J. H., and J. B. Sieglinger, "Spacing and date of seeding experi-
ments with grain sorghums," U. S. Dept. Agr. Tech. Bull. 131, 1929.
9. Neger, F., Biologie der Pflan&n. Stuttgart, 1923.
10. Sande-Bakhuyzen, van de H. L., "Studies upon wheat grown under
constant conditions," Plant Physiology, 3:1-30 (1928).
11. Scharfetter, R., "Phenology and agriculture," Int. Rev. Sci. and Pract.
Agr., 1:561-572 (1923).
12. Schimper, A. F. W., Plant Geography upon a Physiological Basis. Claren-
don Press, Oxford, 1903.
13. Spafford, R. R., "Farm types in Nebraska as determined by climate,
soil and economic factors," Nebr. Agr. Exp. Sta. Res. Bull. 15, 1919.
14. Warming, E.,0ecological Plant Geography. Clarendon Press, Oxford, 1 909.
PART III
THE ECOLOGICAL FACTORS
Chapter XI
GENERAL ASPECTS OF MOISTURE
RELATIONSHIPS
The Relative Importance of Water in the Physiological
Environment. The three most outstanding factors of the physi-
ological environment are moisture, temperature, and light. The
numerous factors of the environment are of necessity closely inter-
related. Nevertheless, over large areas with similar temperature
conditions the relative abundance of moisture available to plants
has a more pronounced effect on the type of vegetation and on
the adaptability of the area, or any portion of it, to crop production
than does any other single factor of the environment. Robbins (26)
states this emphatically in the following paragraph:
"Water is the chief limiting factor in the growth of most crops. For
the majority of crops, there is ample sunshine, and an abundance of
oxygen and carbon dioxide in the air; the temperature of the air and
soil is seldom seriously unfavorable; as a rule, there are sufficient
nutrients in the soil; but the farmer, except in the most rainy sections of
the country, is usually confronted at some time during the season with
a shortage of water. This is particularly true in arid and semi-arid
regions."
Warming (34) is not quite as emphatic as Robbins in stating that
"The ecological importance of water to the plant is fundamental
an^atmost surpasses^that of light or heat." However, after deal-
ing with the significance of water to the vital activities of plants,
he comes out with a stronger statement: u It is ... not surprising
that no other influence impresses its mark to such a degree upon
the internal and external structures of the plant as does the amount
of water present in the air and soil (or medium), and that no
other influence calls forth such great and striking differences in the
vegetation as do differences in the supply of water."
Schimper (28) also emphasizes strongly the manifold influences
of water on the expressions and appearances of plant life by stating
135
156 ECOLOGICAL CROP GEOGRAPHY
that "no factor affecting plant life is so thoroughly clear as the
influence of water."
Thompson (32) states that "moisture is unquestionably the
dominant factor in the production of crops and animals in South
Africa. ... It overrules all other aspects of farming enterprise in
the Union and is closely related to the national welfare." Hann (11)
supports the above statement with the following sentence: "The
rainfall determines the productiveness of a country. Temperature
and rainfall together are one of the most important natural re-
sources of a country."
These various statements relative to the importance of the
moisture factor are well summarized by McDougall (23). "It has
long been recognized that the vegetative organs of different species
were adapted to various conditions of water supply; and also that
the occurrence of the larger plant formations was mainly deter-
mined by the moisture factor in the climate."
Moisture and Temperature Relationships. The close relation-
ship existing between the moisture and temperature factors of the
environment has been referred to on several occasions and will be
further developed in the course of the discussion of these two im-
portant factors. From an ecological standpoint the intimate
association of these two factors and also the light factor as related
to the actual availability and economic utilization of water by
plants is of prime importance.
The characteristics of adaptation to moisture relationships are
usually very evident and apparent even to the layman. The
internal as well as the external organizations of many plants are
readily modified by variations in the amount of available moisture
at their disposal. Some plants exhibit very wide ranges of adapta-
tion with regard to the water factor; others again are quite specific
in their requirements. The tall, leafy type of corn common in the
heart of the Corn Belt, as compared with the progressively shorter
and less leafy type of plant found in approaching the drier Great
Plains area, offers a good illustration of both the range of adapta-
tion and adaptation characteristics in the corn plant as related
to the moisture factor. In the southern Great Plains Grain Sorghum
Belt, the same factor finds expression in the types of sorghums
produced, with the tall broad-leafed kafir in the eastern and the
dwarf feterita and milo in the drier western sections of this area.
MOISTURE — GENERAL ASPECTS 137
Adaptations to the water factor of the environment are usually
more spectacular than adaptations to the temperature factor.
Adaptations of crop plants to the water factor of the environment
are in most instances concerned with a lack or scarcity of moisture
during certain phases of development rather than with the presence
of excessive amounts. This manifestation has, no doubt, much to
do with the frequent and perhaps just designation of the moisture
factor as being of primary importance.
The moisture factor is largely responsible for the designation of
the type of climate based on natural vegetation such as the wood-
land, grassland, and desert types. As has been pointed out previ-
ously, the relative abundance of available moisture is intimately
associated with the diversification of crop production in any given
area. Abundance of moisture leads not only to a rich natural flora
but also to a wide choice of crops that may be grown by the pro-
ducer. Scarcity of moisture favors the development of the more or
less hazardous one-crop system of production.
The Physiological Significance of Water to Plant Life. The
fundamental significance of water to life is well brought out by the
fact that all of the vital processes of both the plant and the animal
cell take place in a water medium. The actual amount of water
assimilated is very small. According to Maximov (22), even in
moist climates not in excess of 2 to 3 grams of water for every
1,000 grams extracted from the soil are assimilated. In dry
continental climates not more than 1 gram of 1,000 grams of water
absorbed from the soil may be assimilated; the remaining 999 grams
merely pass through the plant unchanged, to be dispersed into
the atmosphere, but not without performing vital functions.
The importance of water in relation to the development of
land plants is brought out in an interesting fashion in the following
paragraph taken from the introduction of Maximov's book The
Plant in Relation to Water:
"Organic life in all probability originated in water, and all living
cells and tissues of animal as well as plant organisms must be saturated
with water in order to carry on their normal life activities. The migra-
tion from water to dry land represented a great step forward in the
development of the organic world. But the change of conditions
threatened the organism with the danger of desiccation and the con-
sequent loss of its vital properties. The migration, therefore, was
138 ECOLOGICAL CROP GEOGRAPHY
necessarily accompanied by the development of numerous adaptations,
which allowed the cell to be saturated with water under the new con-
ditions, as it was during its life in an aquatic medium."
Moisture as a Climatic and Edaphic Factor. The amount of
water present in a soil at any given time has a direct influence on
the concentration of the soil solution and constitutes one of the
main factors determining the ease with which water and the
soluble nutrients can be absorbed by the root& of plants. In this
respect, soil moisture becomes an edaphic factor. Soil moisture
in relation to its numerous direct and indirect influences can,
without doubt, be designated as one of the most significant factors
determining the subterranean habitats of plants.
Soil moisture is important not only from the standpoint of the
immediate responses it may evoke but also from the standpoint
of its accumulative effects. The amount and more specifically
the efficiency of the precipitation received in any given locality
determine more than any other single factor the characteristics
of the soil itself. The continued percolation of water through
the soil in humid areas or the absence of the leaching process in
arid sections is associated to a high Degree with the development
of specific soil characteristics.
Kellogg (15) in stating the factors of soil genesis brings out
that any soil in relation to its development is to be considered
as a function of climate, vegetation, relief, age, and parent material.
Moisture and temperature make up the important climatic factors.
These two factors are interrelated as will be brought out in Chapter
XIII in connection with the presentation of indices of moisture
efficiencies. The relative abundance, intensity, and form of the
precipitation not only influence the type and luxuriance of the
vegetation of a region but also are definitely associated with the
relief, that is, with the development of the topographical and
drainage features.
Marbut (20) classified soils into two major groups on the basis
of the presence or absence of calcium carbonate accumulations in
some horizon of the soil, usually in the subsoil. The pedocals or the
lime-accumulating soils are found in arid or semiarid while the
pedalfers or nonlime-accumulating soils occur in humid areas.
In the United States the dividing line between these two major
groups of soils extends from western Minnesota, through north-
MOISTURE —GENERAL ASPECTS
139
western Iowa, southeastern Nebraska, east-central Kansas, central
Oklahoma, and east-central Texas to the Gulf, with the pedalfers
to the east and the pedocals to the west of the line.1 The effects of
climatic conditions in general and the moisture factor in particular
on the location of this boundary line are self-evident. While the
accumulation of lime in pedalferic soils is effectively prevented by
the more or less continuous percolation of water through these
soils and the resulting leaching, they show, nevertheless, that iron,
COLD
DRY
COLD
WET
TUNDRA
NORTHERN
DESERT
NORTHERN
SIER02EM
NORTHERN
BROWN
NORTHERN
CHESTNUT
NORTHERN
CHERNOZEM
NORTHERN
PRAIRIE
PODZOL
GRAY BROWN PODZOLIC
MIDDLE
DESERT
MIDDLE
SIEROZEM
MIDDLE
BROWN
MIDDLE
CHESTNUT
MIDDLE
CHERNOZEM
MIDDLE
PRAIRIE
RED AND YELLOW
RED
DESERT
SOUTHERN
SIEROZEM
SOUTHERN
BROWN
SOUTHERN
CHESTNUT
SOUTHERN
CHERNOZEM
SOUTHERN
• PRAIRIE
LATERITE
JOT HO
)RY WE
IG. 19. Relative positions of the important zonal groups of soils in relation to th
moisture and temperature factors. (After Kellogg.)
aluminum, and the soil colloids have been shifted to a lower
horizon and accumulated during the process of soil-profile develop-
ment in temperate regions. The place of accumulation is marked
by the formation of hardpans, the so-called "ortstein," of podzolized
soils in northern areas. Under tropical high-temperature condi-
tions lateritic soil types are formed in which iron and aluminum
remain in the surface horizons while the silica is moved to lower
horizons of the profile. This accounts for the typical red color
of those soils.
Figure 19 gives an idealized distribution of the zonal groups of
soils with respect to variations in climate, moisture, and temper-
1 See Fig. 63, Chapter XXI.
140 ECOLOGICAL CROP GEOGRAPHY
ature and the resulting natural vegetation. Thornthwaite (33)
produced a similar figure with the employment of his precipitation
and the temperature efficiency indices. Lang (16) used average
annual temperatures and his rain factor in constructing his graphic
presentation of the interrelations of climatic factors to the develop-
ment of soil characteristics.
Ecological Classification of Plants According to Their Water
Relationships. Early in the history of ecology, because of the
striking differences in vegetation produced by the water factor in
the environment, plants were divided into more or less well-defined
groups according to their water relations. Warming's classification
of vegetation types into three groups, the hydrophytes, mesophytes,
and xerophytes, is generally accepted. Plants growing in "fresh"
water or in very humid habitats are hydrophytes. The mesophytes,
or typical land plants, grow under medium climatic and soil
conditions. Plants "capable of enduring without injury a prolonged
period of drought," using Maximov's definition, are xerophytes.
Schimper used the terms "hygrophytes," "tropophytes," and
"xerophytes" for the designation of vegetation types of habitats
of increasing degrees of dryness. Th^are practically synonymous
with the groups established by Warming.
Maximov points out and presents data to show that "the limits of
these groups are naturally ill defined, and in practice it is sometimes
difficult to decide to which group a given plant shall be assigned."
Hydrophytes. The hydrophytes grow either in a water environ-
ment or in places where the air is so moist that a too rapid loss of
water from the aerial organs is hindered.
Mesophytes. The mesophytes or common land plants take an
intermediate position between the hydrophytes and the true
xerophytes. Practically all crop plants can be assigned to this
group. Rice is the only cereal that may be classified as a hydro-
phyte. The sorghums, more particularly the grain sorghums,
are the only crop plants with characteristics approaching the true
xerophytes. But even this group of plants falls short of satisfying
the requirements of the genuine xerophytes in that they are not
able to endure prolonged periods of drought without injury.
According to the terminology advanced by Kearney and Shantz
(14), crop plants grown in dry areas, as well as the desert ephem-
erals, are either drought-escaping or drought-evading.
MOISTURE —GENERAL ASPECTS 141
Xerophytes. An interesting and controversial literature is avail-
able on the question of which particular plants should be designated
as true xerophytes. The older viewpoints on this topic are well
represented by the following paragraph from Pfeffer (25).
"Many plants are compelled to use the little water they can obtain
in the most economical manner possible, and in such cases adaptations
to protect them from excessive transpiration are most markedly devel-
oped. Indeed the special shape and structure of typical xerophilous
plants have mainly this importance, for in order that they may cope
with the conditions under which they exist, the surface-area is reduced
as far as possible, although this places the plant at a disadvantage in
other ways. Thus the regulatory diminution of transpiration which
becomes necessary when the supply of water is limited involves a
hindrance to gaseous exchange, and thus prevents the full functional
activity of the chlorophyll-apparatus from being exercised."
Kamerling (13) proposes that plants designated as true xero-
phytes should be limited to those plants expending not more than
from 2 to 10 per cent of their water content daily. This statement
obviously can be applied only to the behavior of those plants under
conditions not found infrequently, "when the supply of water is
limited," otherwise the term "xerophytes" could be applied to
but few plants.
The newer views regarding the structures and organization
of xerophytes are championed by Maximov. He points out that,
even though xerophitic plants are found in dry habitats, they
are as a class not compelled to reduce transpiration. Maximov
goes into considerable detail to make the point that a low intensity
of transpiration is not characteristic of xerophytes.
It is interesting to note, however, that in making this statement
and in advancing evidence to support it, he does not differentiate
between the behavior of the plants relative to their intensities of
transpiration for times when moisture is, and is not, available for
their use. Xerophytes are defined as "plants capable of enduring
without injury a prolonged period of drought." The reader will
find no objections to this definition or to the one advanced by
Delf (8), who defines "xerophilous plants as those which with the
help of certain structural modifications can continue to perform
their normal functions when exposed to climatic conditions involv-
ing atmospheric or edaphic drought, or both." The fact remains
142 ECOLOGICAL CROP GEOGRAPHY
that moisture during periods of "drought" is either only slowly or
not at all available for the use of plants. Consequently plants able
to survive such periods of stress must be able to preserve life either
by certain "structural modifications" or special characteristics
of their protoplasm. Maximov himself comes out with a statement
to the effect that "the chief importance ... of the high osmotic
pressures found in desert plants is during wilting, when there is
real danger of excessive loss of moisture." In this connection it
is well to point out the behavior of hardy varieties of winter wheat.
Newton (24) and also Martin (21) show that the winter-hardiness
of certain varieties of wheat is associated with the relative quantities
of hydrophilic colloids, measured by "bound water," contained
in their tissues. The presence of these hydrophilic colloids may
account, in part, for differences in resistance to desiccation found
in certain varieties when exposed to physiological drought.
The adaptation characteristics of all xerophytes are by no means
alike. "An examination of the physiological, anatomical, and
morphological peculiarities of xerophytes leads us to the con-
clusion," states Maximov, "that the same results, i.e., adaptation
to life in a dry habitat, may be attaitied in diverse ways. Within
the group of xerophytes, therefore, distinct and even contrasting
types must be recognized."
Considerable confusion can be avoided in a discussion of the
characteristics of xerophytes by excluding from this group of
plants the cacti and similar succulents, as well as the desert
ephemerals.
The physiological peculiarities of the cacti and similar succulents
relative to respiration, assimilation, and transpiration are not
characteristic of other desert plants. The respiratory processes of
these succulents differ from those of other plants in that organic
acids are formed in the dark which later decompose to form carbon
dioxide. In ordinary plants, the carbon dioxide is dispersed into
the air; in the cacti it is utilized in the process of carbon assimilation,
without leaving the chlorenchyma. This results in a material saving
of moisture. Livingston (17) and Shreve (30) called attention
to the fact that the relative transpiration of the cacti is lower
in the daytime than at night. These peculiarities of the cacti and
certain other succulents separate them into a special ecological
type. Their low osmotic pressures and not infrequent superficial
MOISTURE — GENERAL ASPECTS 143
root systems make them more like the epiphytes (air plants) than
the true xerophytes in that they are primarily dependent on water
absorbed during or soon after rains.
The desert ephemerals are annual plants which spring up after
the occurrence of rains but soon succumb as moisture in the surface
soil becomes less available. These plants do not differ from ordinary
mesophytes; they are simply drought-escaping.
Factors Interfering with the Absorption of Water by Plants.
Schimper lists four factors impeding the absorption of water by
plants: (a) low water content of the soil, (b) abundant supplies
of soluble salts in the soil, (c) the presence of humic acids in the
soil, and (d) low soil temperature. To these may be added the
lack of oxygen in soils with excessive amounts of water.
As the thickness of the water film around individual soil particles
is reduced it becomes increasingly difficult for the root hairs to
remove water from the soil. Eventually, as the wilting coefficient
of the soil is approached, the force with which the water is held
around the soil particles becomes so great that the root hairs, the
absorbing cells of the plant, are unable to overcome it. Since the
plant continues to transpire water, it wilts. The wilting coefficients
of different soils differ materially; they are directly associated with
the water-holding capacity of the soil. The wilting coefficients
of soils may be determined physiologically. Generally, however,*
they are calculated from either the moisture equivalents or the
hygroscopic coefficients of soils (Briggs and McLane, 2).
Aside from the fact that certain soluble salts may be directly
toxic to the roots of plants, a high concentration of soluble salts in
the soil definitely impedes the absorption of water by plants in
relation to the extent to which they serve to increase the con-
centration of the soil solution. Certain plants can overcome this
obstacle by means of high concentration of their cell saps. Many
desert plants, as Fitting (9) and also Maximov and his associates
have shown, are characterized by the ability to produce high
osmotic pressures and as a result can develop a suction force
sufficient to overcome the resistance to absorption of even relatively
concentrated soil solutions.
Schimper first advanced the hypothesis of "physiological dryness"
of bog soils by suggesting that the presence of humic acids interferes
with the absorption of water. Dachnowski (6 and 7) substituted
144 ECOLOGICAL CROP GEOGRAPHY
soil toxins for humic acids, while Shroter (29) regarded the high
water-retaining capacities of bog and peat soils as the chief factor
bringing about physiological dry ness. Lundeg&rdh (19) points out
that trees have difficulty in establishing themselves on bog and
peat soils, not because of the excess of water, but rather because
of the lack of oxygen and the surplus of carbon dioxide.
The temperature of the soil has a direct bearing on the rate of
water absorption. Frozen soils, and for nonhardy plants even cold
soil, are physiologically dry.
The Wilting of Plants. Not infrequently plants lose greater
quantities of moisture to the surrounding atmosphere than they
are able, for the time being, to absorb from the soil. Such a condi-
tion leads to a more or less marked water deficit in the plant.
Under conditions of a high saturation deficit of the atmosphere
in immediate contact with the plant the loss of water may be so
great that an optimum water balance cannot be maintained by
plants even though the soil may contain an abundance of moisture.
Such atmospheric droughts are encountered during periods of hot,
dry winds. Pronounced water deficits in plants result most com-
monly from a scarcity of available *vyater in the soil; they become
critical when a slow rate of absorption is combined with a high
loss of water by increased transpiration. It must be kept in mind
that increased transpiration, while rapidly diminishing the water
content of plants, also leads to significant increases in leaf suction
and absorption of water when it is available. Also, the aerial
portions of plants are not entirely without certain protective
devices against excessive losses of moisture. Instituted economies
in water utilization are effective, however, only within rather well-
defined and limited ranges.
The water content of plants is reduced whenever the loss of water
through transpiration is in excess of that absorbed. Increasing
water deficits are usually accompanied by a perceptible loss in
turgor, though not enough in the initial stages to produce definite
wilting. Livingston and Brown (18) refer to such conditions of
decreased water content and partial loss of turgor, up to but not
including definite wilting, as "incipient drying." Such incipient
drying serves to increase the osmotic pressure of the cells of leaves.
Furthermore, as the vapor pressure in the intercellular spaces of
the leaves is reduced by continued high rates of transpiration,
MOISTURE —GENERAL ASPECTS 145
the loss of water from leaves is in part slowed down by this reduction
in vapor pressure even before the stomata are closed.
With the continued giving off of water by plants, especially when
the reserve in the soil is exhausted to the extent that the losses
cannot be compensated, the plant soon reaches the stage of transient
wilting. This stage is marked by a partial folding up or collapse
of the leaves and tender tissues. Unless conditions either favoring
absorption of water or serving to reduce transpiration are provided
at this point to restore the water balance to a normal level, the
final stage, permanent wilting, is soon reached. The leaves transpiring
most rapidly show the greatest water deficits, and since they also
possess the greatest power of suction they draw water from other
portions of the plant. By successive stages the upper and younger
leaves withdraw water from the older ones, from the growing points
of the stems, and eventually from the absorbing regions of the roots.
As a result all parts of the plants are to a considerable extent
deprived of water.
Transient wilting occurs in plants at rather frequent intervals.
While it is instrumental in slowing down rates of assimilation of
carbon dioxide, it has mostly temporary effects; with the restoration
of moisture in the soil or with a return of conditions less favorable
to rapid transpiration a proper water balance is reestablished,
turgor regained, and growth proceeds at fairly normal rates. Thfe
difference between transient and permanent wilting is, according
to Maximov, one of degree rather than of kind. Plants having
their water content reduced to the point of permanent wilting
recover but slowly and then only under the most favorable soil
moisture and environmental conditions. Even though recovery
takes place under exceptional conditions, the wilting has lasting
detrimental effects. Successive repetitions of wilting are especially
detrimental to plants. CaldwelPs (5) experiments have shown
that more water remained in soils with repeated wilting than
after an initial wilting of plants. This is no doubt due to a partial
destruction of the root hairs.
Drought. The term "drought" is used freely by both agrono-
mists and laymen. While the term may be readily defined in the
descriptive sense, the exact designation of droughts in the quanti-
tative sense is fraught with difficulties in that water deficits in
plants and the causes for such reductions in water content mav be
146 ECOLOGICAL CROP GEOGRAPHY
numerous and varied depending on environmental conditions and
differences in the reactions of plants during the various stages of
development.
Smith (31) defines drought as "a condition under which plants
fail to develop and mature properly because of an insufficient
supply of moisture." Rotmistroff (27) defines the term as a
temporary lack of moisture in the soil, which is felt by the plant
and interferes with the normal course of the life processes. Blair
(1) checks closely with the above authors by designating drought
as "a continuous lack of moisture, so serious that crops fail to
develop and mature properly."
Maximov speaks of atmospheric and soil drought. Since reduc-
tions in the water content of plants severe enough to cause material
damage may be produced by hot dry winds, even when an abun-
dant moisture supply is found in the soil, this point is well taken.
Wilting due to atmospheric drought is usually temporary. It
may result from either an inadequate root system or sheer physical
inability to conduct water fast enough to compensate the losses
from the leaves and tender portions of plants during periods of
stress. Atmospheric drought occuite especially in areas near the
physiological moisture limits of production. Extensive dry areas
with sparse vegetative covers favor the occurrence of dry winds
and the development of atmospheric drought. The hot dry winds
of the Great Plains area and the Italian sirocco winds are notable
examples.
Soil drought is most disastrous to crop plants when occurring
at times of greatest need of water such as during the grand period
of growth and well-defined critical periods. It is at such times that
the plant makes its greatest demands for the expansion of its
tissues and the building up of structures correlated with yield
performance. Plants do not differ materially in the amounts of
moisture that they are able to withdraw from a given soil.
Droughts occur more frequently in minimal than in optimal
areas. But slight deviations from the normal receipts, or in instances
increases in the utilization of moisture by plants as a result of the
intensification of environmental factors, may lead to severe reduc-
tions in yields in the minimal areas, while significantly greater
deviations from the to-be-expected rainfall may have no material
influence on the growth of plants in optimal areas. Droughts, on
MOISTURE — GENERAL ASPECTS 147
the other hand, are likely to occur at intervals even in humid
climates. "Periods of excessive and deficient rainfall," states
Holzman (12), "are normal to all climates."
It is necessary to take into consideration the normal rainfall
cycle of a region in connection with the designation of droughts.
In areas with a Mediterranean type of climate the occurrence of
dry periods toward the middle of summer, severe enough to
inhibit the growth of crop plants, is a normal phenomenon. This
condition is met with in the Pacific Coast states. Crop production
is more or less arranged to correspond with the prevailing type of
rainfall distribution. While influencing the cropping systems,
such reoccurring summer droughts do no particular damage. The
other extreme is found when the expected rainfall fails to make its
appearance. If such periods coincide with the critical periods of
the crops grown in the area reduced yields and even complete
failures may result. The term "drought" should therefore be
applied to moisture deficiencies deviating sufficiently from the
phenological mean to interfere with the normal life processes of
plants to the extent that the balance of nutrition is shifted far
enough in an unfavorable direction to result in material reductions
in crop yields.
Excessive Moisture and Humidity. Cardinal points of vital
activity apply to the moisture factor as well as to the temperature
factor in connection with which they are most commonly employed.
Even though the points may not be as specific when applied to
water as to temperature relationships, it is nevertheless permissible
to speak of minimal, optimal, and maximal moisture conditions.
Excessive amounts of water in the soil interfere with the biological
processes and limit the amount of oxygen. The lack of oxygen,
in turn, initiates numerous detrimental chemical processes such
as reductions and the formation of substances toxic to the roots
of plants. An optimum soil moisture content must allow for proper
aeration. The continued percolation of water through a soil may
also lead to leaching and the removal of nutrients, especially
nitrogen, in sufficient quantities to interfere with the normal
growth of plants.
Excessive rainfall during critical periods may have decided
detrimental effects as during the germination and emergence of
leguminous plants and during flowering. Heavy rains interfere
148 ECOLOGICAL CROP GEOGRAPHY
not only with the oxygen relationships of soils but may compact
the surface of the soil so as to make emergence of dicotyledonous
and other tender plants difficult. Excessive precipitation also
interferes with the pollination of fruits, oats, and sorghums.
High temperatures in connection with intense sunlight, air
currents, and a low atmospheric humidity lead to high rates of
transpiration and losses of water from the tissues of plants. The
transpiration ratios of plants of humid areas are significantly lower
than those of the same plants grown in arid regions. Thus a given
amount of water will, other factors being equal, produce a greater
amount of dry matter in humid than in arid areas. Some physi-
ologists, notably Haberlandt (10), have expressed the opinion that
a very high atmospheric humidity may reduce transpiration to a
point detrimental to the plant. Lundeg&rdh points out that
"a continued saturation of the air, and a continued turgescence
of leaf cells, exert an unfavorable influence upon the uptake of salts
and upon translocation."
Biirgerstein (4) indicates that the ratio of transpiration in the
tropical rain forests may be sufficiently high for the requirements
of the plants. It may be assumed that the transpiration ratios of
crop plants even when grown in humid climates are high enough
so as not to interfere with other plant functions.
A combination of high atmospheric humidity and temperature
is very effective in excluding certain plants from areas where such
conditions prevail. The reason for this is pathological rather than
physiological in that such environments are exceptionally favorable
to the development of definite plant diseases such as rusts, mildews,
scabs, and leaf spots. The conditions for the development of such
pathogens are so ideal under humid high-temperature environ-
ments as very effectively to exclude wheat, barley, alfalfa, and
clover from such humid megathermal areas. The above plants
and others become important crops in humid areas with more
moderate temperatures or in regions with high temperatures but
relatively low atmospheric humidities.
Another factor to be considered is the curing and storing of crops
after they have been produced. The curing of hay represents a
serious problem in wet areas. One contributing reason for the
overwhelming importance of rice as a cereal crop in humid,
tropical areas is that it lends itself better to storage under existing
MOISTURE — GENERAL ASPECTS 149
conditions than wheat or other cereals, the nature of the endosperm
being such that it does not absorb moisture as readily as that of
the wheat kernel.
REFERENCES
1. Blair, T. A., Weather Elements. Prentice-Hall, New York, 1937.
2. Briggs, L. J., and J. W. McLane, "Moisture equivalent determinations
and their application," Proc. Amer. Soc. of Agron., 2:138-147 (1910).
3. , and H. L. Shantz, "The relative wilting coefficients for
different plants," Bot. Ga*., 53:229-235 (1912).
4. Biirgerstein, A., Die Transpiration der Pflan&n. Verlag von Gustav
Fischer, Jena, 1904.
5. Caldwell, J. S., "The relation of environmental conditions to the
phenomenon of permanent wilting in plants," Physiol. Res., 1:1-56
(1913).
6. Dachnowski, A., "The toxic property of bog water and soil," Bot. Gaz.y
46:130-143 (1908).
7. , "Physiologically arid habitats and drought resistance in
plants," Bot. Gat., 49:325-339 (1910).
8. Delf, M., "The meaning of xerophily," Jour. Ecol., 3:110-121 (1915).
9. Fitting, H., "Die Wasserversorgung und die osmotischen Druckver-
haltnisse der Wustenpflanzen," Qitschr. f. Bot., 3:209-275 (1911).
10. Haberlandt, F., "Anatomisch physiologische Untersuchungen fiber
das tropische Laubblatt," Sitzb d. K. Akad. der Wissensch. in Wien,
101:785 (1892).
11. Hann, J., Handbook of Climatology, trans. German by R. DeCov*»x,7
Ward, Part I. "General climatology." Macmillan, New York, 1903.
12. Holzman, B., "Sources of moisture for precipitation in the United
States," U. S. Dept. Agr. Tech. Bull. 589, 1937.
13. Kamerling, Z., "Welche Pflanzen sollen wir 'Xerophyten* nennens."
Flora, 106:433-454 (1914).
14. Kearney, T. H., and H. L. Shantz, "The water economy of dry land
crops," U. S. Dept. Agr. Yearbook 1911, 351-361.
15. Kellogg, C. E., "Development and significance of the great soil groups
of the United States," U. S. Dept. Agr. Misc. Pub. 229, 1936.
16. Lang, R., Verwitterung und Bodenbildung als Einjuhrung in die Bodenkunde.
Stuttgart, 1920.
17. Livingston, B. E., "Relative transpiration in Cacti," Plant World,
10:110-114(1907).
18. , and W. H. Brown, "Relation of the daily march of trans-
piration to variations in the water content of foliage leaves," Bot.
53:309-330 (1912).
150 ECOLOGICAL CROP GEOGRAPHY
19. Lundegardh, H., Environment and Plant Development, trans, and ed.
from 2d German ed. by E. Ashby. Edward Arnold & Co., London,
1931.
20. Marbut, G. F., Atlas of American Agriculture, Part III, Soils of the
United States. U. S. Govt. Printing Office, Washington, 1935.
21. Martin, J. H., "Comparative studies of winter hardiness in wheat,"
Jour. Agr. Res., 35:493-535 (1927).
22. Maximov, N. A., The Plant in Relation to Water, authorized trans, by
R. H. Yapp. Allen and Unwin, London, 1929.
23. McDougall, E., "The moisture belts of North America," EcoL, 6:325-
332 (1925).
24. Newton, R., "A comparative study of winter wheat varieties, with
especial reference to winter-killing," Jour. Agri. Sci., 12:1-19 (1922).
25. Pfeffer, W., The Physiology of Plants, trans. German by A. J. Ewart,
Vol. I. Clarendon Press, Oxford, 1900.
26. Robbins, W. W., Principles of Plant Growth. Wiley, New York, 1927.
27. Rotmistroff, W. G., Das Wesen der Diirre, ihre Ursache und Verhutung,
trans. Russian by E. von Riesen. Theodor Steinkopff, Dresden, 1926.
28. Schimper, A. F. W., Plant Geography upon a Physiological Basis,
trans. German by W. R. Fisher. Clarendon Press, Oxford, 1903.
29. Schroter, C., Das Pflan&nleben der Alpen. Zurich, 1908.
30. Shreve, E., "An analysis of the causes of variations in the transpiring
power of Cacti," Physiol. Res., 2:73-127 (1916).
31. Smith, J. W., Agricultural Meteorology. Macmillan, New York, 1920.
32. Thompson, W. R., Moisture and Farming in South Africa. Central News
Agency, South Africa, 1936.
33. Thornthwaite, C. W., "The climates of North America according to a
new classification," Geog. Rev., 21:633-655 (1931).
34. Warming, E., Oecology of Plants, trans. German by P. Groom and
I. B. Balfour. Clarendon Press, Oxford, 1909.
Chapter XII
QUANTITATIVE ASPECTS OF MOISTURE
RELATIONSHIPS
Vapor in the Atmosphere. The atmosphere contains many
gaseous constituents; the proportions of nitrogen, oxygen, carbon
dioxide, and other gases remain fairly constant; but the water
vapor present is extremely variable. The other gases are indi-
vidually of no special meteorological significance, but the water
vapor is very important in that not only the direct receipts of rain-
fall but also the losses of moisture from either the soil or plants are
greatly influenced by it. The amount of moisture present in the
atmosphere at any given time may be expressed as vapor pressure,
absolute humidity, relative humidity, or on the basis of the sat-
uration deficit.
Vapor pressure and dew point. When water vapor escapes
into space and mixes with the other gases of the air, it exerts a
pressure in all directions, as do the other gases. This is known as
the vapor pressure of the air. The force exerted depends upon the
concentration of the vapor or upon the number of molecules per
unit of volume. At the saturation point the number of molecules
returning to the liquid becomes equal to the number escaping.
Consequently the net evaporation is zero. At any given tempera-
ture the saturation vapor pressure has a definite, fixed value, but
the values change rapidly with changing temperatures. Vapor
pressure is commonly expressed in the same units as total air pres-
sure, that is, either in millibars or in inches or millimeters of mer-
cury, referring to the length of the barometer column that the
partial pressure of the water vapor would sustain. The saturated
vapor pressure at 0, 25, 50, 75, and 100°F is 0.038, 0.130, 0.360,
0.866, and 1.916 inches, respectively.
The temperature at which saturation occurs is called the dew
point. Air having a vapor pressure of 0.130 inches has a dew point
at 25°F at a barometric pressure of 30.00 inches. When the vapor
151
152 ECOLOGICAL CROP GEOGRAPHY
is cooled below its dew point, some of it is changed from a gas to
the liquid form, that is, it condenses.
Absolute humidity. The amount, or the actual mass, of water
vapor present in the air at any given time can be measured by
aspirating a measured quantity of air through a hygroscopic sub-
stance, weighing the substance before and after. The increase in
weight corresponds to the absolute humidity; it can be expressed
in grains per cubic foot of air. Air is saturated when it contains 1.9
grains of water vapor when the temperature is 30, 4.1 with a tem-
perature of 50, 8.0 with a temperature of 70, and 14.7 grains per
cubic foot when the temperature is 90°F.
The absolute humidity and vapor pressure refer to one and the
same phenomenon, namely, the actual amount of water vapor
present in the air. The difference is only in the manner of expres-
sion. Since the determination of vapor pressure and the absolute
humidity require elaborate instruments, they are not ordinarily
given by most weather stations.
Relative humidity. The relative humidity of the air refers to
the ratio, expressed as a percentage, between the amount of mois-
ture in the atmosphere and the amount that could be present,
without condensation, at the same temperature and under the
same pressure. Thus heating a given volume of air, as in a room,
does not increase its absolute but greatly reduces its relative humid-
ity. The increased temperature increases the vapor-holding capac-
ity of the air.
The relative humidity of the atmosphere is readily determined.
The most common instrument is the sling psychrometer. This
consists of two thermometers fastened to a metal strip which whirls
upon a pivoted handle or by means of a geared mechanism, the
whirling table. The two thermometers are alike, but one has a thin
piece of clean muslin tied around the bulb. This bulb is dipped
into clean water before the instrument is whirled. The difference
in the temperatures of the dry- and wet-bulb thermometers is
directly proportional to the dryness (vapor pressure) of the air.
The relative humidity of the air may then be read directly from
the prepared psychrometric tables of the United States Weather
Bureau. Records of relative humidity can be obtained from hair
hygrometers and hygrographs, that is, hygrometers with recording
mechanisms.
MOISTURE — QUANTITATIVE ASPECTS 153
Hann (7) summarizes the application and relative significance
of the relative humidity as follows. "For purely climatological
purposes the relative humidity is unquestionably the most con-
venient expression for the amount of water vapor in the air. When
we describe the air as being damp or dry, we are usually speaking
quite unconsciously of the relative humidity."
Relative and absolute saturation deficit. When the atmosphere
has a relative humidity of 65 it is carrying 65 per cent of its possible
capacity of water vapor at the given temperature and pressure; an
additional 35 per cent of water vapor would saturate the air. This
additional amount of vapor required to bring the air up to the
saturation point is referred to as the saturation deficit. The abso-
lute saturation deficit in terms of millimeters of mercury is expressed
by the difference between the observed vapor pressure and the
maximum vapor pressure possible at the temperature then pre-
vailing.
Forms of Precipitation. The form of precipitation is dependent
on the temperature at which condensation takes place and the
conditions encountered as the particles pass through the air. The
term "precipitation" refers to measurable moisture received,
whether in the form of rain, snow, dew, hail, graupel, sleet, or
glaze, and is expressed either in inches or in millimeters.
Rain is by far the most important form of precipitation not only
in amount but also in relation to its effects on vegetation. In areas
of winter precipitation receipts of snow are of considerable impor-
tance, as a matter of fact so much so in northern areas as to be
definitely associated with crop yields. Snow provides in such areas
not only moisture but significant protection to perennial and winter
annual plants.
Dew and even light rains, insofar as they moisten only the leaves
of plants or the surface of the soil, are of little value to plant life
except that they decrease for the time being the rate of either
transpiration or evaporation.
While hail does provide moisture, it has an injurious effect on
plants and especially crop plants if occurring during the vegetative
season. Hail damage is dependent on the intensity of the hail storm
and on the stage of development of the plants subjected to it. It
is most detrimental if occurring during the grand period of growth,
but in the cereals great damage can also be inflicted during the
154
ECOLOGICAL CROP GEOGRAPHY
mature stage or immediately prior to maturity. Figure 20, taken
from Ward (20), shows the average number of days with hail during
the frostless season in various sections of the United States. The
Great Plains and the Rocky Mountain regions show the greatest hail
hazards. Hail is generally a warm-season phenomenon and falls
in connection with thunderstorms. Condensation frequently
1 day
I to I days
I to 3 dtf s
Over 4 days
FIG. 20. Average annual number of days with hail during the frostless season.
(Reproduced from Ward, The Climates of the United States, by permission of Ginn
and Company.)
begins as rain, but the drops instead of falling may be carried up-
ward by rapidly ascending currents of air into cloud areas where
temperatures are below freezing. Blair (2) points out that the
distinct layers of snow or ice frequently observed in hailstones are
acquired by successive upward and downward movements of
developing stones. Various attempts have been made by investi-
gators to evaluate the extent of hail damage either by direct obser-
vation or by means of simulated injuries. Schander (16) and also
Eldredge (5) worked with the cereal crops; Dungan (4), Hume
and Franzke (9), and Garber and Hoover (6) with corn; and
Klages (12) with flax.
Soft, moist snowflakes, falling through gusty air, are sometimes
blown together and reach the ground as relatively soft pellets.
155
156 ECOLOGICAL CROP GEOGRAPHY
They are designated by their German name, graupel, and corre-
spond to soft hail.
Sleet means precipitation in the form of small particles of clear
ice. It is formed by raindrops falling through layers of cold air.
In popular terminology a mixture of rain and snow or partly
melted snow is also referred to as sleet.
Glaze, popularly called an ice storm, is caused by ice forming
on the surface of the soil or over vegetation from the freezing of rain
as it strikes. Considerable damage is at times caused to upright
vegetation by the accumulated weight of the ice so formed. If the
ice layer remains long enough, winter wheat or other winter annual
plants may be damaged by suffocation.
Measurement of precipitation. The ordinary rain gauge as
used by the United States Weather Bureau consists of a galvanized
iron cylindrical can, 8 inches in diameter, the mouth of which is
circular, beveled on the outside to form a sharp edge. The receiver
is funnel-shaped; the orifice leading from the funnel discharges
into a brass cylinder, 20 inches in depth, the inside area of which is
exactly one-tenth of the area of the receiver rim. The water caught
is measured by a wooden scale arid recorded in hundrcdths of
' »
an inch. Precipitation in the form of snow and ice is melted
and recorded as water. Various types of recording gauges are
also available. Such equipment is valuable for rainfall intensity
studies.
Annual precipitation. The normal annual rainfall over the
surface of the globe is subject to wide variations, ranging from less
than 8 inches in certain desert areas to more than 400 inches
as at Gherra Punji, India, where a rainfall of 428 inches per an-
num has been recorded. Figure '21, taken from Henry et al.
(8), shows in a generalized way the world distribution of annual
precipitation.
The older classifications of climates were based strictly on
amounts of annual precipitation received in different regions. The
humidity provinces thus established are presented in Table 4,
together with the approximate percentage of the land area of the
world covered by each (Smith, 17).
Figure 22, taken from Baker (1), shows the average annual pre-
cipitation over the United States, together with the land area and
the percentage distribution of each frequency class.
157
158
ECOLOGICAL CROP GEOGRAPHY
TABLE 4. DISTRIBUTION OF PRECIPITATION OVER THE LAND AREA OF THE
WORLD TOGETHER WITH THE CLIMATIC CLASSIFICATION AND THE PER-
CENTAGE IN EACH AREA.
Annual Precipitation, in
Inches
Climatic Classification
Percentage of Land Area
Less than 10
Arid
25.0
10-20
Semiarid
30.0
20-40
Subhumid
20.0
40-60
Humid
11.0
60-80
Wet
9.0
80-120
Wet
4.0
120-160
Wet
0.5
Above 160
Wet
0.5
Seasonal Distribution of Precipitation. The seasonal distri-
bution of precipitation is directly associated with the effective use
of moisture by plants, adaptation of crop plants, and the agricul-
tural utilization of any given area. This factor is discussed in detail
in Chapter XIII dealing with moisture efficiency and again in
Chapter XX on the classification of climates.
t
LOSSES OF MOISTURE
Sources of Loss. Moisture falling on the surface of the earth
may either enter the soil, run off the surface, or be lost by direct
evaporation. The amount that runs off is of no benefit to plants,
but may cause severe damage through erosion. Of the moisture
entering the soil, some may percolate to a depth beyond reach of
the roots of plants and be thus lost in the drainage water, or it may
be dissipated into the air by direct evaporation or by means of
transpiration through plants.
Runoff. The amount of moisture lost by runoff is determined
by a great variety of factors such as intensity of rainfall, topographi-
cal features, vegetative cover, and condition of the soil. Soil con-
ditions influencing runoff are: texture; type; mechanical condition,
especially of the surface, as to structure, amount of water present,
and the form in which the water is held (that is, whether in the
liquid or solid phase) ; and temperature. The amount and form of
organic matter in the soil greatly influence its structure and ability
to take on and hold moisture.
MOISTURE — QUANTITATIVE ASPECTS 159
The influence of topographical features on runoff is self-evident.
The effects of rainfall intensities will be briefly dealt with.
Rainfall Intensity. The term "rainfall intensity" refers to the
receipts of precipitation at given time intervals. Yarnell (21) pre-
sents rainfall intensity-frequency data for the various areas of the
United States. Charts prepared by Yarnell show the maximum
precipitations in periods of five minutes to two hours that may be
expected to occur with average frequencies in from 2 to 100 years.
The numerous charts presented by Yarnell and maps given by
Kincer (11) show material differences in rainfall intensities in the
various portions of the United States. The highest intensities occur
along the Gulf and along the South Atlantic coast. Relatively high
intensities are also found in the Great Plains and especially in the
southern Great Plains area. The intensities in the Corn Belt states
are significantly lower than in the Cotton Belt. The lowest inten-
sities are found in the Pacific Northwest. The direct relationship
of precipitation-intensity data to crop production and erosion con-
trol problems is evident. Unfortunately the intensity is highest in
those areas of the United States where a high percentage of the
crop land is planted to intertilled crops such as cotton, sorghums,
and corn. This adds materially to the problem of controlling soil
erosion losses.
Evaporation. The loss of moisture through evaporation in
relation to the receipt of precipitation is of great agricultural impor-
tance and will be dealt with in detail under the heading of moisture
efficiency. It becomes a problem of special significance in those
agricultural areas bordering upon the minimal thresholds of crop
production.
According to Kincer, "the rate of evaporation of moisture from
the soil depends principally upon the amount of moisture present,
the soil texture, the temperature, wind movement, and relative
humidity of the atmosphere.'*
Briggs and Belz (3) show the intimate relationship between rain-
fall and evaporation in its application to crop production by con-
structing lines of equal and equivalent rainfall for the states of the
Great Plains area. Their outline map is reproduced as Fig. 23.
Near the Canadian border the lines of equal and equivalent rain-
falls for 20 and 1 5 inches per annum coincide. It will be observed,
however, that they become separated by increasing distances in
160
ECOLOGICAL CROP GEOGRAPHY
passing to the south, owing to increases in rates of evaporation. It
is necessary to move more and more to the eastward from the lines
representing the actual 20- and 15-inch isohythes, lines of equal
rainfall, in order to find conditions that are equally favorable for
crop production so far as rain-
fall is concerned, that is, to
enter the so-called equivalent
rainfall region.
Exacting data of rates of
evaporation from free water
surfaces are limited. The rates
are variable but depend prima-
rily on the temperature, relative
humidity, and wind velocity.
Thompson (19) reports an
annual evaporation of 87.64
inches, that is, five times the
annual rainfall, from Kimber-
ley, South Africa. Livingston
FIG. 23. Outline map of the states of* i14) Sives the rainfall evapora-
the Great Plains area, showing lines of tion ratios for 112 stations in
equal and equivalent rainfall. The solid
lines marked 15 and 20 pass through
points of equal annual rainfall; the cor-
responding dotted lines pass through
points having rainfalls equivalent to 15
and 20 inches, respectively, on the Ca-
nadian boundary. (After Briggs and
Belz.)
the United States. This ratio
refers to the quotient of the
division of the total rainfall for
the average frostless season by
the total evaporation from a
water surface during that
period. The values vary from
0.04 for Winnemucca, Nevada, to 1.76 for Hatteras, North Caro-
lina, and to the extremely high ratio of 3.84 for Tatoosh Island,
Washington.
Mead (15) brings out that while evaporation from a free water
surface is subject to variations from year to year it is less variable
than precipitation.
Measurement of Evaporation. Any measurement of evapora-
tion is an approximation of the actual loss of water that takes place
through this source. Various types of evaporimeters have been
used. The most common type of evaporation pan used in the
United States is described by Kadel (10). In Europe the Piche
MOISTURE — QUANTITATIVE ASPECTS 161
atmometer is extensively used for purposes of evaluating the capac-
ity of the air to take up moisture. In this instrument a disk of filter
paper withdraws water from a graduated glass reservoir.
Livingston's porous porcelain cup atmometers are widely used,
especially in connection with transpiration experiments. Water
evaporates from the unglazed portions of these atmometer cups
which are connected by means of a glass tube to a water reservoir.
Transpiration. Transpiration, the taking up of water from the
soil by plants and dispersing it into the atmosphere, is one of the
most important sources of losses of soil moisture. Transpiration
has been referred to as a necessary evil. This may be so, but it is
also necessary to keep in mind that transpiration is a vital function;
without it, since it is so closely related to photosynthesis, growth is
impossible.
REFERENCES
1. Baker, O. E., "A graphic summary of American agriculture," U. S.
Dept. Agr. Yearbook 1921, 407-506.
2. Blair, T. A., Weather Elements. Prentice-Hall, New York, 1937.
3. Briggs, L. J., and J. O. Belz, "Dry farming in relation to rainfall and
evaporation," U. S. Dept. Agr., Bur. of Plant Industry, Bull. 188, 1910.
4. Dungan, G. H., "Effect of hail injury on the development of the corn
plant," Jour. Amer. Soc. Agron., 20:51-54 (1928).
5. Eldredge, J. C., "The effect of injury in imitation of hail damage on
the development of small grain," Iowa Agr. Exp. Sta. Res. Bull. 219,
1937.
6. Garber, R. S., and M. M. Hoover, "Influence of corn smut and hail
damage on the yield of certain first generation hybrids between
synthetic varieties," Jour. Amer. Soc. Agron., 27:38-45 (1935).
7. Hann, J., Handbook of Climatology, trans. German by R. DeCourcy
Ward, Part I, "General Climatology," Macmillan, New York, 1903.
8. Henry, A. J., J. B. Kincer, H. C. Frankenfield, W. B. Gregg, B. B.
Smith, and E. N. Munns, "Weather and Agriculture," U. S. Dept.
Agr. Yearbook 1024:457-558.
9. Hume, A. N., and C. Franzke, "The effect of certain injuries to leaves
of corn plants upon weights of grain produced," Jour. Amer. Soc.
Agron., 21:1156-1164 (1929).
10. Kadel, B. C., "Instructions for the installation and operation of class
'A' evaporation stations," U. S. Dept. Agr., Weather Bur. Cir. L. In-
strument Division, 1919.
162 ECOLOGICAL CROP GEOGRAPHY
11. Kincer, J. B., Atlas of American Agriculture, Part II, Sec. A., "Precipita-
tion and humidity." Govt. Print. Office, Washington, 1922.
12. Klages, K. H. W., "The effects of simulated hail injuries on flax,"
Jour. Amer. Soc. Agron., 25:534-540 (1933).
13. Koppen, W., "Klassification der Klimate nach Temperatur, Nieder-
schlag und Jahreslauf," Petermanris Mitteilungen, 64:193-203, and
243-248 (1918).
14. Livingston, B. E., "A single index to represent both moisture and
temperature conditions as related to plants," Physiol. Res., 1:421-440
(1916).
15. Mead, D. W., Hydrology. McGraw-Hill, New York, 1919.
16. Schander, R., "Uber Hagelbeschadigungen an Roggen, Weizen und
Hafer," Fuhlings Landw. %eit., 63:657-703 (1914).
17. Smith, J. W., Agricultural Meteorology. Macmillan, New York, 1920.
18. Taylor, G., "The frontiers of settlement in Australia," Geog. Rev., 16:
1-25 (1926).
19. Thompson, W. R., Moisture and Farming in South Africa. Central News
Agency, South Africa, 1936.
20. Ward, R. D., The Climates of the United States. Ginn, Boston, 1925.
21. Yarnell, D. L., "Rainfall intensity — frequency data," U. S. Dept. Agr.
Misc. Pub. 204, 1935.
Chapter XIII
HUMIDITY PROVINCES
Efficiency of Precipitation. The effectiveness of a given amount
of annual precipitation is not the same in different regions with
varying climatic conditions. The influence of rates of evaporation
on efficiency of precipitation was alluded to in the previous chapter.
It, together with the seasonal distribution of the precipitation in
relation to the requirements of crops grown, constitutes the main
factor determining the effectiveness of a given amount of precipi-
tation.
Numerous efforts have been made to improve upon the establish-
ment of humidity provinces based strictly on receipts of annual
precipitation. The main objections to this older system of desig-
nating such humidity provinces, with a total disregard of possible
losses of the moisture received, are obvious. The most refined and
useful method of establishing humidity provinces would be to
determine available moisture in the soil during the course of tKe
growing season in relation to the special requirements of the pre-
dominating crops grown. This would require a tremendous
amount of detailed work. Since such data are not available, more
expedient criteria of the utilization of moisture receipts must of
necessity be resorted to even though they may not take into con-
sideration all possible losses of moisture. None of the methods for
determining the efficiency of precipitation takes into consideration
the losses due to runoff and percolation. The fact remains that
the establishment of humidity provinces must be based on the
particular climatological data that are available over large ter-
ritories so that the classification setup may be extensively applied
in comparat ve studies of the humidity factor in the various crop
producing areas of the world.
Precipitation-evaporation ratio. Transeau (15) as early as
1905 suggested the use of both precipitation and evaporation data
in an attempt to combine in a single number the influences of the
163
164 ECOLOGICAL CROP GEOGRAPHY
temperature and moisture factors of the environment in their
effects on the distribution of forest trees in the eastern portion of
the United States. Reasoning that evaporation depends upon the
temperature of the evaporating surface, the relative humidity of the
air, and the velocity of the wind, and that these same factors affect
transpiration, he suggested an index of precipitation effectiveness
by using the quotient of total annual precipitation and annual
evaporation.
Penck (9) used precipitation and evaporation data in his classi-
fication of climates. He placed the boundary between the arid and
humid provinces at the point where precipitation and evaporation
were equal, or where the precipitation-evaporation ratio is unity.
Meyer's P-SD quotient. Since reliable evaporation data are
not available from many stations, Meyer (8) recommended an
evaporation substitute in setting up his "Niederschlag-Sattigungs-
defizit" or precipitation-saturation deficit quotient, also referred
to as the N-S ratio. The P-SD quotient is calculated by dividing
the annual precipitation in millimeters by the absolute saturation
deficit of the air expressed in millimeters of mercury. Jenny (5)
gives the values of the P-SD quotient! #s well as the values of Lang's
rain factor for 144 stations in the United States. Figure 24, taken
from Jenny and based upon his calculations, gives the humidity
provinces of the United States as indicated by P-SD ratios. Pres-
cott (11) made use of the same ratio in his studies of moisture con-
ditions in Australia.
Meyer recognizes that his P-SD ratio does not take account of
wind velocity and atmospheric pressure in their effects on evapora-
tion, or of such features as the distribution of rainfall, sunlight, fog,
or temperature except insofar as these factors are reflected by the
saturation deficit. His ratio has the advantage of relative sim-
plicity. Szymkiewicz (12) recommends a very complex measure
of evaluating the effectiveness of precipitation by dividing the
amount of precipitation received by his index of evaporation.
Since this index of evaporation is determined from an equation
involving vapor pressure deficit, water vapor pressure, and atmos-
pheric pressure as well as temperature, it can be calculated only
for stations where complete meteorological records are available.
The P-SD ratio can be determined for any station recording pre-
cipitation, temperature, and relative humidity. Furthermore,
HUMIDITY PROVINCES
165
evaporation may for practical purposes be regarded as a function
of the saturation deficit.
Trumble (16) made use of "saturation deficiency and its relation
to rainfall as expressed by the Meyer ratio" in studies of effective
soil moisture in Australia.
1601-800
(501-600
401-500
ES3301-400
S|§3 201-300
EE]Les$ than 100
FIG. 24. Humidity provinces of the United States as determined by Meyer's
P-SD quotient, and annual isotherms of 4, 12, and 20°C, or 39.2, 53.6, and 68°E.
(After Jenny.)
Jenny states that the P-SD quotient "is a satisfactory substitute
for Transeau's precipitation-evaporation ratio and has the advan-
tage of international application."
The limits of the major humidity provinces based on the P-SD
quotients are given in Table 5.
Lang's rain factor. Lang (7) used the rain factor in connection
with his investigations of possible temperature and rainfall limits
of soil zones. It is calculated by dividing the annual precipitation
expressed in millimeters by the mean annual temperature in
degrees centigrade. This index of precipitation efficiency is com-
monly referred to as the P-T ratio.
The climates of regions with rain factor values of from 10 to 40
are classified as arid, those with values of from 40 to 160 as
humid} while those with values of more than 160 are designated
as wet.
166
ECOLOGICAL CROP GEOGRAPHY
Jenny gives a map of the United States based on Lang's rain
factor. This map is reproduced as Fig. 25. The rain factors were
calculated for over 2,000 meteorological stations by using the data
collected by the United States Weather Bureau (17). Hirth (4)
published a map of the world showing the humidity provinces
based on Lang's rain factor. Hirth points out that the isonotides,
lines of eaual rain factors, should not be regarded as lines but as
FIG. 25. Humidity provinces of the United States as determined by Lang's rain
factor or the P-T ratio. (After Jenny.)
zones of varying breadths; that is, every designated humidity
province is separated from the adjoining province by a transition
zone.
A comparison of Figs. 24 and 25, that is, the humidity maps of
the United States based on Meyer's P-SD and Lang's P-T quo-
tients, respectively, brings out certain discrepancies between these
two indices. On the basis of distribution of native vegetations and
utilization of areas for crop production purposes the P-T quotients
are entirely too high for the northern Great Plains area. It is
evident that Meyer's P-SD ratios give a truer picture of existing
humidity conditions than Lang's P-T quotients.
While temperature is one of the climatic factors influencing rates
of evaporation, it must be recognized that other factors are definitely
involved. Generally the saturation deficit provides a more reliable
HUMIDITY PROVINCES 167
index of the combined effect of all the factors involved in deter-
mining rates of evaporation than temperature.
Index of aridity. De Martonne's (2) index of aridity represents
a slight modification of Lang's rain factor in that he suggests a
division of the annual precipitation in millimeters by the mean
annual temperature in degrees centigrade plus ten. The values
of the index would consequently be lower than for the P-T quo-
tients. Andrews and Maze (1) defined the monthly conditions of
aridity in Australia by using De Martonne's index, by assuming a
monthly index of 1 as a significant indication of a condition of
aridity. Perrin (10) observes that the factor does not apply well
to cool zones owing to the high values obtained during the cold
months. De Martonne (3) presents a world map of the index of
aridity.
The same objections made to the broad application of Lang's
rain factor, P-T quotients, apply also to De Martonne's index of
aridity, in that they are both based on temperature and assume
evaporation to be a function of temperature.
Thornthwaite's precipitation effectiveness index. Thorn-
thwaite (13 and 14) in his classification of the climates of North
America and of the world expressed Transeau's precipitation-
evaporation ratio in an empirical form so that the values obtained
would correspond to the values of his temperature index. The
formula for the precipitation effectiveness, P-E, index is given as:
P-E index = ^ II
n = 1
In calculating this index it is necessary to obtain the P/E ratios
of each of the 12 months of the year. These are multiplied by ten
to avoid the inconvenience of dealing with fractions. The P-E
index is then ten times the sum of the 12 monthly P/E ratios.
In this respect it differs from Transeau's precipitation-evaporation
ratio, which was based directly on the total annual precipitation
and evaporation. Evaporation refers to the evaporation from a
free water surface in inches.
Thornthwaite also presents a formula for calculating the pre-
cipitation-effectiveness index for stations for which evaporation
data are not available by making use of the mean monthly tern-
168
ECOLOGICAL CROP GEOGRAPHY
perature and precipitation values. According to Thornthwaitc,
the values obtained by this formula correspond sufficiently close
for practical purposes to the one based on evaporation data. The
formula for the P-E index based on mean monthly precipitation in
inches and temperatures in degrees Fahrenheit is presented below:
P-E index
12
1
115
P W
Thornthwaite (13) states that the data used in the development
of the above formula were most abundant in the temperature range
between 40 and 80°F and did not extend below 30 or above 90°F.
He recommends that temperatures below 28.4°F be calculated on
the basis of the effectiveness at that temperature.
Table 5 gives the values of the limits of the P-E indices of the
five major humidity provinces established by Thornthwaite and
the characteristic vegetation of each province. For purposes of
comparison the limits of the values of the P-SD quotients for each
province as calculated by Prescott are also presented. Thorn-
thwaite indicates that the P-E index of 48 approximately separates
the humid east from the semiarid ancl arid west in the United States.
TABLE 5. THE LIMITS OF FIVE MAJOR HUMIDITY PROVINCES AND CHARAC-
TERISTIC VEGETATIONS OF EACH PROVINCE BASED ON THORNTHWAITE'S
PRECIPITATION EFFECTIVENESS (P-E) INDEX. FOR PURPOSES OF COMPARISON
THE LIMITS OF MEYER'S P~SD QUOTIENTS AS CALCULATED BY PRESCOTT ARE
ALSO GIVEN
Humidity Province
Characteristic
Vegetation
P-E Index
Calculated
P-SD Quotient *
A Wet
Rain forest
128 and above
277 and above
B Humid
Forest
64-127
177-277
C Subhumid
Grassland
32-63
89-177
D Semiarid
Steppe
16-31
44-89
£ Arid
Desert
Less than 16
0-44
* Assuming E = 260 S.D.
Figure 26, reproduced from Thornthwaite5 s (13) map, gives the
humidity provinces of the United States based on the P-E index.
Thornthwaite also takes into consideration the seasonal distribu-
tion of precipitation effectiveness in his classification of climates.
HUMIDITY PROVINCES
169
Four subtypes are recognized: "r," designating abundance of
moisture at all seasons; "s," moisture deficient in summer; "w," .
moisture deficient in winter; and "d," moisture deficient at all
seasons.
The P-E index can be used to good advantage in crop distribu-
tion studies, especially when used in connection with Thorn-
thwaite's classification of climates. When possible the index should
it Humid)
|
0 {
E
FIG. 26. Humidity provinces of the United States based on the precipitation
effectiveness (P-E) index. (After Thornthwaite.)
be based on evaporation rather than on monthly temperatures.
When the P-E index is based on temperatures it becomes subject
to the criticisms pointed out in connection with the application of
Lang's P-T quotients.
Koppen's Designation of Boundaries between Dry and More
Humid Areas. Koppen (6) in his classification of climates assumes
evaporation to be a function of temperature. The critical division
between his dry, the B, and more humid, C and D, climates is
arbitrarily placed at the point where the annual precipitation and
evaporation are in equilibrium. In this he does not, however,
make use of direct evaporation data, but evaluates them on the
basis of mean annual temperature plus a variable factor. Koppen
introduced the novel idea of greater efficiency of precipitation in
170 ECOLOGICAL CROP GEOGRAPHY
areas of winter than in areas of summer precipitation by assuming
that a higher percentage of the moisture is lost by direct evapora-
tion in summer than in winter. The efficiency is placed at the
neutral point in areas of moderate temperatures with rainfall
rather evenly distributed throughout the year. In areas of summer
rainfall the variable factor is increased by 30 per cent to give a
corresponding efficiency. Likewise 30 per cent is taken from the
variable factor in regions of winter precipitation. In other words,
the annual amount of precipitation required to place an area in
the more humid province need not be so great in areas of winter
precipitation as in areas with rather uniform or with summer pre-
cipitation. The equilibrium at the outer boundary of the steppe
regions is then stated by:
/> = t+y
P, expressed in centimeters, refers to the amount of the critical
annual precipitation; / is the annual mean temperature in degrees
centigrade; and y^ the variable factor, can have three different
values, 22, 33, or 44, in accordance with the seasonal distribution
of precipitation for the area in question. The value of y at the
neutral point, that is, for areas wfth fairly uniform precipitation, is
placed at 33; with summer rainfall at 44; and with precipitation
concentrated in the winter months at 22.
Koppen illustrates the application of the above by using the
annual mean moisture and temperature data for Seville, Spain,
P = 47, t = 20. Assuming that the annual precipitation was
uniformly distributed throughout the year, then the boundary of
the steppe climate would be at 20 + 33 = 53, which would place
Seville in the dry, B, climate. It would fall within the boundary
of the steppe since the annual precipitation P is less than / + y.
Since, however, Seville is located in an area of winter precipitation,
the boundary of the steppe climate is placed at 20 + 22 = 42,
that is, the climate classifies as C though close to the boundary of
the dryer B climates. With the introduced value of y for areas of
winter rains the amplitude of the / + y becomes less than that of P.
Areas having less than the critical amounts of precipitation are
designated as steppes while those with less than half the critical
amounts are deserts.
Table 6, taken from Koppen, shows the outer boundaries of the
desert and steppe areas in relation to prevailing mean annual
HUMIDITY PROVINCES
171
temperatures. The values given by him are for the neutral point
only. The corresponding values for regions with a summer and
winter concentration of moisture were calculated by the formula
P = t + y. The boundaries of the desert and steppe are determined
by a combination of precipitation, temperature, and seasonal dis-
tribution of precipitation. It will be observed that the desert
boundary is in every case half that of the steppe, also that Koppen
did not consider the formula of the equilibrium of precipitation
to temperature plus^ as an exact mathematical value.
TABLE 6. THE OUTER BOUNDARIES OF DESERT AND STEPPE AREAS IN RELA-
TION TO PREVAILING MEAN ANNUAL TEMPERATURES ACCORDING TO KOPPEN
Mean Annual Temperatures
in Degrees Centigrade
25
25-20
20-15
75-70
70-5
5
Neutral zone — uniform distribution of
precipi
tation -
--X-:
.3
Outer boundary of steppe (cm)
Outer boundary of desert (cm) . . .
64
32
58
29
52
26
46
23
40
20
32
16
Precipitation concentrated in summer months — y — 44
Outer boundary of steppe (cm) . . .
Outer boundary of desert (cm) . . .
75
37.5
69
34.5
63
31.5
57
28.5
51
25.5
43
21.5
Precipitation concentrated in winter months — y — 22
Outer boundary of steppe (cm) . . .
Outer boundary of desert (cm) . . .
53
26.5
47
23.5
41
20.5
35
17.5
29
14.5
21
10.5
Van Roycn (18) points out some of the limitations of applying
Koppen's formula to conditions met with in North America. He
not only expresses the main criticism to the employment of a for-
mula based on temperature, even with the modifications introduced
by Koppen, but also gives the present limitations to be recognized
in basing an index of precipitation effectiveness strictly upon
evaporation data.
Vegetation as an Index of Moisture Conditions. Any vegeta-
tion must, in order to survive, establish an equilibrium with the
environmental factors under which it develops. Since the avail-
ability of water is one of the most important factors of the environ-
ment, it is evident that the relative development of native as well as
introduced species provides a direct index of existing moisture con-
ditions. Plants provide an index of existing moisture conditions
both by means of the species represented and by the relative amount
172 ECOLOGICAL CROP GEOGRAPHY
of growth or luxuriance of individual species or groups of species.
Furthermore, the response of plants is directly related not only to
the existing climatic but also to the edaphic factors of the environ-
ment. In this respect the existing plant cover provides a more
renable and comprehensive index of moisture conditions than any
possible mathematical formulation of precipitation and evapora-
tion data. This does not mean that it is of no value to establish
humidity provinces based on the climatic factors involved in the
efficient use of water by plants. It simply means that the responses
of plants provide the best possible index of existing moisture con-
ditions. However, it must be recognized in this connection that
the evaluation of plant responses demands a great deal of experi-
mental work. Such data are now available for only limited areas,
and even where available they are not comparable. Consequently,
for the time being, the ecologist must be satisfied with the delinea-
tion of humidity provinces based on meteorological elements. It
is quite evident from the discussion presented in this chapter that
humidity provinces based on both precipitation and evaporation
data provide a far better index of existing moisture conditions than
the establishment of such provinces based on moisture receipts
alone.
REFERENCES
1. Andrews J., and W. H. Maze, Proc. Linn. Soc., N. S. W., 58:105 (1933).
2. De Martonne, E., Ardisme et indice d'aridit6, Comptes Rendus de FAcad.
desSci. (de Paris), 182:1395-1398 (1926).
3. 9 "Regions of interior drainage," Geog. Rev., 17:397-414
(1927).
4. Hirth, P., "Die Isonotiden," Petermann's Mitt. 72:145-149 (1926).
Reviewed in Geog. Rev., 17:335-338 (1927).
5. Jenny, H., "A study on the influence of climate upon the nitrogen and
organic matter content of the soil," Mo. Agr. Exp. Sta. Res. Bull. 152,
1930.
6. Koppen, W., Die Klimate der Erde. Walter De Gruyter & Co., Berlin,
1923.
7. Lang, R., Verwitterung und Bodenbildung als Einfuhrung in die Bodenkunde.
Schweizerbart 'sche Verlagsbuchhdlg, Stuttgart, 1920.
S. Meyer, A., "Uber einige Zuzammenhange Zwischen Klima und
Boden in Europa," Chemie der Erde, 2:209-347 (1926).
HUMIDITY PROVINCES ITS
9. Pcnck, A., "Versuch einer Klimaklassifikation auf physiographischer
Grundlage," Sit*. Ber. phys. math. Kl. Preuss. Akad. Wiss., Berlin, 1910,
p. 236.
10. Perrin, H., Complex Rendus de VAcad. des Set. (de Paris), 192:1271
(1931).
11. Prescott, J. A., "Single value climatic factors," Trans. Roy. Soc. So.
Australia, 58:48-61 (1934).
12. Szymkiewicz, D., "Etudes climatologiques," Ada Societatis Botanicorum
Poloniae, 2:130 and 239 (1925).
13. Thornthwaite, C. W., "The climates of North America according to a
new classification," Geog. Rev., 21:633-655 (1931).
14. , "The climates of the earth," Geog. Rev., 23:433-440 (1933).
15. Transeau, E. N., "Forest centers of eastern America," Amer. Nat., 39:
875-889 (1905).
16. Trumble, H. C., "The climatic control of agriculture in South Aus-
tralia," Trans. Roy. Soc. So. Australia, 61:41-62 (1937).
17. U. S. Dept. Agr. Weather Bureau, Bull. W. Ed. 2, 1926.
18. Van Royen, W., "The climatic regions of North America," Mo. Wta.
R*v.% 55:315-319 (1927).
Chapter XIV
THE USE OF WATER BY PLANTS
The Efficiency of Transpiration. The relationship between
the units of water transpired by a plant and the equivalent units
of dry matter produced is expressed in a variety of fashions. The
terms commonly used are the transpiration ratio, the transpiration
coefficient, and water requirement. Since a ratio is definitely
involved, the term "transpiration ratio" is quite appropriate. The
transpiration ratio refers to the ratio between the amount of dry
matter accumulated by a plant, exclusive of the roots, to the amount
of water transpired for a given interval of time; in the case of
annual plants this period is, unless otherwise stated, from emergence
to maturity. Only in the case of root crops is the weight of under-
ground portions of plants included in the calculations of the ratios.
Thus if a plant producing 4 grams of dry matter transpired 2,000
grams of water during its course of development, the transpiration
ratio would be 1:500. This figure is, according to the definition
presented by Briggs and Shantz (3), subject to a minor correction
for the amount of water remaining in the plant at maturity.
It is to be noted that the transpiration ratio depends on both the
amount of dry matter produced and the amount of water tran-
spired. It is important to keep this in mind. Any factor of the
environment affecting the growth processes of the plant becomes
directly effective in determining the transpiration ratio to the
extent to which it influences the amount of dry matter assimilated.
The term "transpiration coefficient" has the advantage over the
term "transpiration ratio" that it obviates the necessity of stating
the figure obtained in the form of a ratio.
The term "water requirement" should not be confused with the
water utilization of plants growing under field conditions. In
controlled water-requirement or transpiration-ratio experiments
losses of soil moisture other than through the leaves and stems
of plants are prevented by the experimental methods used. This
174
THE USE OF WATER BY PLANTS 175
is decidedly not the case when plants are grown under field con-
ditions. Thus when Hughes and Henson (7) define the term
"water requirement" as "the pounds or units of water required to
produce a pound or unit of dry matter" it must be kept in mind that
such a definition applies only to the results obtained in controlled
experiments and not to actual field conditions.
Maximov (12) uses the term "efficiency of transpiration," re-
ferring to the amount of dry matter accumulated by plants for each
1,000 parts of water transpired, using equivalent units. Thus if
the transpiration coefficient is 400 the efficiency of transpiration
becomes 1,000/400 or 2.5.
The Transpiration Coefficients of Various Crop and Weed
Plants. The most extensive investigations dealing with the com-
parative transpiration ratios of plants in this country are reported
by Briggs and Shantz (1, 2, 3), Shantz and Piemeisel (16), and by
Dillman (5). Table 7 gives the transpiration coefficients and
efficiencies of transpiration of important crop plants and weeds
compiled from the data presented by Shantz and Piemeisel from
experiments conducted at Akron, Colorado, and by Dillman from
tests at Newell, South Dakota, and Mandan, North Dakota.
Figure 27 gives a graphical presentation of the transpiration
coefficients of important crop plants at Akron for the years 1911-
1917, inclusive, in relation to the evaporation from a free water
surface for each year at that station.
The experimental methods employed by Shantz and Piemeisel
and by Dillman were essentially the same; it is therefore possible
to make direct comparisons between the results reported. The
plants were grown inside a screened enclosure, which reduced the
solar radiation to about 80 per cent of its normal value. Control
experiments with freely exposed plants showed that the enclosure
reduced the transpiration coefficients about 22 per cent.
The figures reported by Shantz and Piemeisel from Akron and
by Dillman for the northern Great Plains area stand in close agree-
ment as far as the relative values for the different crops tested are
concerned. It will be observed, however, that the transpiration
coefficients reported by Dillman are in all instances lower than
those given by Shantz and Piemeisel. This is to be expected in view
of the lower temperatures and lower rates of evaporation at Newell
and Mandan as compared with those prevailing at Akron. The
.KfX/P
/OO
FIG. 27. The transpiration coefficients of different crops and evaporation in
tenths of an inch at Akron, Colorado, for the years 191 1-1917. (After Shantz and
Piemefoel.)
176
THE USE OF WATER BY PLANTS
177
April to September, inclusive, evaporation at Akron was 42.11
inches as compared to 32.56 inches at Newell.
TABLE 7. THE TRANSPIRATION COEFFICIENTS AND EFFICIENCIES OF TRAN-
SPIRATION OF IMPORTANT CROP AND WEED PLANTS, COMPILED FROM THE
RESULTS REPORTED BY SHANTZ AND PIEMEISEL FROM AKRON, COLORADO, AND
FROM DILLMAN FOR THE NORTHERN GREAT PLAINS AREA
Plants
Shantz and
Pienuisel
Dillman
Trans.
Cocff.
Effi-
ciency
Trans.
Coeff.
Effi-
ciency
Millet (Chactochloa italica)
Kursk
274
285
287
380
361
377
499
455
550
491
523
604
634
752
977
835
731
759
646
656
745
540
314
305
«; * *
3.65
3.51
3.48
2.63
2.77
2.65
2.00
2.20
1.82
2.04
1.91
1.66
1.58
1.33
1.02
1.20
1.37
1.32
1.55
1.52
1.34
1.85
3.18
3.28
1.52
251
268
253
335
304
403
430
536
618
784
795
224
261
435
3.98
3.73
3.95
2.99
3.29
2.48
2.33
1.87
1.62
1.28
1.26
4.46
3.83
2.30
Sorghum (Andropogon sorghum)
Dakota Amber Sorgo
Red Amber Sorgo
Sudan Grass
Corn (Zea mays)
Northwestern Dent
Sugar Beet (Beta vulgaris)
Irish Cobbler Potato (Solanum tuberosum) . .
Turkey Wheat (Triticum vulgare) ....
Marquis Wheat (Triticum vulgare)
Kubanka Wheat (Triticum durum)
Hannchen Barley (Hordeum distichon) ....
Swedish Select Oats (Avena sativa)
Vern Rye (Secale cerealc)
Flax (Linum usitatissimum)
North Dakota Resistant No. 114
Brome Grass (Bromus inermis) .......
Grimm Alfalfa (Medicago sativa)
Sweet Clover (Melilotus alba)
Red Clover (Trifolium pratense)
Soybeans (Soja max)
Navy Beans (Phascolus vulgaris)
Field Peas (Pisum sativum) ........
Buckwheat (Fagopyrum vulgare)
Russian Thistle (Salsola pcstifer)
Pigweed (Amaranthus retroflexus)
Lambs Quarter (Chenopodium album) ....
The millets, sorghums, and corn are the most efficient of the
crop plants in the utilization of water. The small grains require
almost twice as much water, while the legumes use almost three
times as much.
178 ECOLOGICAL CROP GEOGRAPHY
FACTORS INFLUENCING THE EFFICIENCY OF
TRANSPIRATION
Introductory Statement. Generally those particular environ-
mental conditions or factors favoring a healthy growth of plants
also make for efficiency in the use of water. Efficiency in the use of
water is in part determined by inherent plant characters but more
directly by climatic and edaphic factors. The effective climatic
factors were discussed in connection with the topic of humidity
provinces and their establishment, Chapter XIII. The soil factors
influence the transpiration ratio in relation to the extent to which
they favor plant development. The plant characteristics corre-
lated with the utilization of water and specific requirements for
moisture were discussed in Chapter XI.
Kiesselbach (8) presents an outline of factors influencing tran-
spiration, after which is patterned the outline given below.
A. Climatic
1. Temperature 5. Radiant heat
2. Saturation deficit 6. Air pressure
3. Wind velocity 7. Evaporation from a free water surface
4. Light
B. Ediphic
1. Nonnutrient salts 5. Soil type
2. Soil fertility 6. Soil texture
3. Cropping system 7. Soil temperature
4. Available moisture
C. Plant Characters
1. Root development 6. Course of development
2. Leaf area 7. Structure of plant and especially of the
3. Ratio of absorbing to transpir ing sur- leaves
face 8. Surface modifications of leaves
4. Chlorophyll content of leaves 9. Osmotic pressure
5. Diseases and presence of insects 10. Ability to withstand drought
In relation to the influence of the above factors on transpiration
it may be stated, as was done by Kiesselbach, that some of them
"are very profound in their effect, while others are comparatively
insignificant."
Climatic Factors. The transpiration coefficient of plants is
especially associated with factors influencing rates of evaporation.
This is well brought out in Fig. 27. The close relationship between
evaporation and the transpiration coefficients is very evident. As
the evaporation index increases the efficiency of transpiration
definitely decreases. This is of special importance to the water
THE USE OF WATER BY PLANTS 179
economy of plants. The need for water is greatest during seasons
with high temperatures, low humidity, and generally for those
conditions favoring great losses of water not only from the crop
plants but also from the soil through evaporation.
The transpiration coefficients of crop plants show material
variations from season to season. Dillman gives an interesting
illustration in the variations of the actual values of the transpiration
coefficients of several crops grown during an 11 -year period.
The ranges were as follows:
Alfalfa from 602 + 5 in 1915 to 1,036 + 14 in 1914
Kubanka wheat from 333 ± 2 in 1915 to 531 + 8 in 1921
Sudan grass from 272 ± 2 in 1915 to 347 ± 4 in 1919
Millet from 177 ± 1 in 1915 to 316 ± 2 in 1913
Sorgo from 210 ± 4 in 1915 to 284 + 3 in 1918
In connection with the above figures it is well to point out that
the season of 1915 had the lowest evaporation index for the 11 years
of the experiment, namely, 77 as compared to the average of 100.
Special attention must be given to the effects of humidity of the
air in relationship to transpiration efficiency. Thus Kiesselbach
reports a transpiration ratio of 1 :340 for corn plants grown in a dry
as compared to a ratio of 1 :191 for plants grown in a humid green-
house. Generally, it is to be expected that the transpiration coef-
ficients for dry areas and climates run materially higher than for
humid areas and climates. This point is substantiated by the co-
efficients of transpiration reported upon by investigators in different
climatic areas. Thus Lawes and Gilbert report a coefficient of 225
for wheat in England as compared to coefficients of 359 by Hill-
riegel in Germany, 513 by Briggs and Shantz at Akron, Colorado,
and 1,006 by Widtsoe in Utah. While these values may not be
directly comparable owing to differences in the experimental
methods used, they give valid indications of the greater require-
ment for moisture in semiarid and arid regions. This is a vital
point to be taken into consideration in the agricultural utilization
of dry areas.
Edaphic Factors. As with the climatic factors of the environment
so also with the edaphic factors. Those particular soil conditions
favoring a healthy and well-balanced growth of plants also favor
an economic utilization of water. Generally variations in soil
180 ECOLOGICAL CROP GEOGRAPHY
factors do not produce the outstanding differences called forth by
variations in climatic factors.
The amount of moisture in a soil available to plants at any given
time may be a function of several conditions such as the amount
of precipitation received, the time interval since the last effective
rain, the method of handling the soil, conditions favoring penetra-
tion and percolation of moisture, and the sequence of cropping.
In controlled experiments, that is, when the moisture content of
the soil is held at definite levels, the highest efficiency in the use of
moisture may be expected near or slightly lower than the level
required for optimum growth. Kiesselbach and Montgomery (9)
report transpiration coefficients of 290, 262, 239, 229, and 252 for
corn grown in containers with moisture contents of 38, 31, 23, 17,
and 13.5 per cent, respectively. Extremely high soil moisture con-
tents interfere with normal growth; this accounts for the high
coefficients at the higher moisture levels. The lower efficiency of
transpiration of plants grown on soils with a high moisture con-
tent has been referred to by some investigators as being more or less
caused by an induced extravagance in the use of water by plants
grown under such conditions (Pfefffer et al., 13). Lack of available
nutrients, especially lack of nitrogen resulting from the surplus of
water in the soil, has been pointed out by Kiesselbach as a factor
of importance. Should the water level of the soil become so high
as to interfere with root development of plants, the transpiration
ratio would be automatically increased on account of the lower
efficiency of the plant in assimilation. On the other hand, should
the moisture content of the soil be reduced to the point of inducing
wilting, the efficiency of transpiration will be markedly reduced.
This was the cause of the higher transpiration coefficient in the
corn plants grown in the containers with only 13.5 per cent of
moisture.
The direct effects of varying degrees of fertility of soils on the
transpiration coefficient of corn is shown in Table 8, taken from
Kiesselbach, giving the average results obtained in his experiments
of 1911 and 1914. Variations in the transpiration coefficients of
plants grown on different soil types are due more to variations in
the plant nutrients of such soils than to differences in type or texture.
It will be observed from Table 8 that the transpiration coefficients
varied directly with the six degrees of soil fertility and the dry matter
THE USE OF WATER BY PLANTS
181
produced. The efficiency of transpiration increased with increasing
fertility, especially for grain production. It will also be observed
that applications of manure resulted in a proportionately greater
increase in the efficiency of transpiration in the relatively infertile
soils.
TABLE 8. RELATIVE DRY MATTER, EAR WEIGHT, AND TRANSPIRATION
COEFFICIENTS OF CORN GROWN ON DIFFERENT SOIL TYPES WITH AND WITHOUT
APPLICATIONS OF MANURE (compiled from results given by Kiesselbach)
Character
of
Soil
Dry Matter
per Plant, in Grams
Total Water Tran-
spired per Plant ,
in Kilograms
Grams of Water
Used per Gram
of Dry Matter
Without
Manure
With
Manure
Without
Manure
With
Manure
Without
Manure
With
Manure
Based on entire plant
Infertile
128
257
344
370
426
460
57.76
91.87
107.51
119.63
130.44
137.83
463
384
327
323
308
298
Intermediate . . .
Fertile .
Based on dry weight ears
Infertile
Intermediate . . .
Fertile
54
121
181
192
219
246
—
—
1223
861
634
623
599.
563
The results presented in Table 8 show definitely that the plants
grown on the soils of higher fertility used considerably greater
quantities of water than did those grown on the series of lower
fertility. This is to be expected. However, in the application of
the results to existing conditions in the field it is important to keep
in mind that these results were produced under conditions of
optimum soil moisture content for the entire period of growth.
This is not always the case in the field. It must therefore be pointed
out again that the maintenance of a proper balance, established
in part by plant nutrient additions to the soil, is of vital impor-
tance to adaptation and economy in the use of available moisture.
A high fertility, especially if unbalanced and conducive to excessive
production of vegetative development, need therefore not always
be correlated with a high efficiency of transpiration. Nitrogen
182 ECOLOGICAL CROP GEOGRAPHY
fertilizers must for this reason be used with caution, in dry areas.
The overstimulation of plants during the early portion of the
season, when moisture is available, may lead to disaster later when
the amount of moisture becomes insufficient to support the luxuri-
ant growth produced. Thus Leather (10) found in India that while
the application of commercial fertilizers and manures decreased
the transpiration coefficients of plants grown in controlled experi-
ments they had no marked effect in increasing the efficiency of
transpiration of plants grown in the field.
The effects of systems of cropping on the efficiency of transpira-
tion are sometimes pronounced. Thus Thorn and Holtz (18) report
that wheat following wheat in the Palouse area had a transpiration
coefficient of 518, as compared to 341 for wheat after fallow. In
another instance the transpiration coefficient for wheat following
wheat was 487, as compared to 400, 391, 360, and 310 for wheat
following oats, alfalfa, corn, and clover, respectively. Widtsoe (20)
found a transpiration ratio of 512 for corn following three years of
fallow, while continuous corn gave a coefficient of 593.
Plant Characteristics. It has been shown that certain plants
have a higher or lower transpiraHon coefficient than others when
grown under the same soil and climatic conditions. It is hard to
account for these differences. One statement can be made, how-
ever, that the causes are more or less correlated with adaptation
characteristics. These characteristics may be of a morphological,
chemical, or development nature. The time element as related
to the course of development of the plants in question is no doubt
a factor that should not be left out of consideration. This has been
referred to under the discussion of factors associated with drought
resistance. The questions of efficiency of transpiration and drought
resistance should not be confused. The one deals with the use of
water made by plants, the other with the reaction of plants faced
with a scarcity of available water.
Certain steps can be taken by producers in influencing the course
of development of plants so that the water available may be uti-
lized to the best advantage. In this, factors associated with relative
foot development merit attention. In humid areas and under
irrigation rates of seeding of all crops are higher than in dry loca-
tions. Dense stands result in interplant competition and serve to
limit the extent of root development and penetration. Kiesselbach
THE USE OF WATER BY PLANTS 183
suggests that thinner plantings may lead to a more efficient use of
water because they may serve to overcome the possible detrimental
effects of higher levels of soil fertility and the associated greater
development of plants beyond the point justified by the amount of
water present in the soil during later phases of growth. Reduced
rates of seeding not only favor a greater individual development
per plant but also result in most instances in a lower amount of
vegetative growth to be supported per unit of area during the early
portion of the season. As a result less water is removed from the soil
during early phases of development. Furthermore, relative root
development of plants is more or less correlated with individual top
growth of plants.
Von Seelhorst (14) and von Seelhorst and Tucker (15) pointed
out that an abundant supply of moisture in the soil tends to limit
root penetration of cereals. This agrees with the later work reported
by Weaver (19). Harris (6) showed in tests with corn and wheat
that "the ratio of tops to roots was affected by soil moisture even
during the germination stage."
Crop plants produced in dry areas have generally a smaller top
growth than those produced under humid conditions. This is due
mainly to the greater amounts of moisture available to them in the
humid than in dry areas, but also in part to the varieties grown.
Dwarf types of plants show in most instances a more favorable ratio
of absorbing to transpiring surfaces. Sorauer (17), as early as 1880,
pointed out that plants held back in their growth by limited
amounts of moisture, while having a smaller absolute root system
than plants grown under optimum soil moisture conditions, had,
nevertheless, a greater relative root system. Von Seelhorst and
Tucker report a ratio of roots to total harvest of 1 :5.41, 1 :8.95, and
1 :9.41 for oat plants grown with small, medium, and large amounts
of water. When a complete fertilizer was added to the soil the
ratios became even wider, being 1:6.80, 1:13.13, and 1:15.68 for
the plants grown with small, medium, and large amounts of water,
respectively.
The efficiency of transpiration may to some extent be modified
by structural modifications of the leaves, by surface modifications,
and especially by the chlorophyll content of the leaves. The
amount of water transpired by plants is largely a function of the
area of leaf surface exposed to the elements. Since the efficiency
184 ECOLOGICAL CROP GEOGRAPHY
of assimilation is closely dependent on the chlorophyll content
per unit area of the leaves, the relationship between chlorophyll
content and efficiency of transpiration is apparent. Lundeg&rdh
(11) found that leaves with a high chlorophyll content assimilate
more per unit of area than leaves low in chlorophyll.
Effects of Crop Varieties. Variations in the efficiency of tran-
spiration of different plants are correlated more or less with the
characteristics of larger groups such as genera, less with those of
species, and even less with varietal differences of plants of the same
species. Varieties with similar courses of development show as a
rule no consistent statistically significant differences.
The Seasonal March of Transpiration. The transpiring
surfaces of plants increase with the advance of the season, and also
the intensity of the climatic factors favoring transpiration. In most
plants the maximum vegetative growth is attained during the
middle of summer when the intensities of the climatic factors
favoring transpiration are at their highest level. The transpiration
rate then decreases with the reduction of active leaf surface as the
plant approaches maturity.
The above gives the general course of the seasonal march of
transpiration. The rate of water loss from the plant for any given
interval of time is dependent on the leaf area exposed and the
intensity of the climatic factors. There is also a daily march of
transpiration. The general topic of seasonal march of transpira-
tion is mentioned here to bring out the fact that plants generally
pass through a period of stress as they develop their maximum leaf
areas. Depending upon the phenological mean, this phase of
development is often associated with the critical period of crop
plants. Thus Briggs and Shantz (4) show that during a ten-day
period of maximum transpiration at Akron, Colorado, annual
crops lost about one-fourth of the total water lost during the season.
EFFICIENCY OF TRANSPIRATION AND DROUGHT
RESISTANCE
The Application of Efficiency of Transpiration Studies to
Field Conditions. The early assumptions of Briggs and Shantz (2)
that determinations of transpiration ratios and information relating
to the efficiency of transpiration of plants would be of interest
THE USE OF WATER BY PLANTS 185
and value to agriculture and particularly to crop producers in
areas with limited rainfall is fully justified. But the extensive experi-
mental work on this subject has given no complete evidence that
plants expending water most productively are necessarily best
adapted to regions with a limited water supply. As stated earlier
in this chapter, the problems of efficiency of transpiration and
drought resistance, while related, should not be confused; the one
deals with utilization of water by plants grown in a favorable en-
vironment as far as moisture relationships are concerned, the other
with the reactions of plants faced either with a scarcity of water
in the soil or with excessive losses of water to the atmosphere.
Efficiency of Transpiration Based on a Ratio. As has been
pointed out previously in this chapter, it is necessary to keep in
mind that studies relating to the efficiency of transpiration of
plants arc definitely based on a ratio of dry matter produced to
amounts of water transpired in the assimilation of such dry matter.
Factors influencing the amount of dry matter produced by a plant
in its cycle of development enter into the determination of the
transpiration ratio as much as the amount of water transpired.
Transpiration is influenced in its intensities by a variety of factors.
It is not a simple function. Rates of assimilation, also, arc not
determined by single climatic or edaphic factors but rather by a
great variety of environmental conditions. To complicate matters
still more, drought manifests itself in a variety of fashions. Consider-
ing all these factors, it is not altogether surprising that no direct
correlation exists between the transpiration coefficients and the
degrees of drought resistance of given crop plants.
The Transpiration Ratio as an Index of Ecological Status.
Even though the relationship between the efficiency of transpiration
and drought resistance is not so close as was formerly supposed,
the transpiration ratio is of definite ecological value. This is well
brought out in the following paragraph taken from Maximov's
book, The Plant in Relation to Water.
"Having thus established the lack of direct proportionality between
the efficiency of transpiration and the degree of drought resistance, we
cannot go to the opposite extreme and assert that the degree of effi-
ciency affords no indication of the ecological character of a plant.
On the contrary, owing to its relative constancy, the magnitude of the
efficiency of transpiration affords one of the most satisfactory tests of
186 ECOLOGICAL CROP GEOGRAPHY
the ecological status of a plant. It is, indeed, the expression of the
correlation between two most important physiological processes — the
accumulation of dry substance and the expenditure of water."
The topic of drought resistance has always had a great popular
appeal. Much has been written about the breeding of drought-
resistant plants without due recognition of the physiological limi-
tations of the plants considered. Many fond hopes have been
blasted. Transpiration-ratio studies show that plants must tran-
spire large quantities of water to produce limited amounts of dry
matter. It takes water to make the desert bloom.
REFERENCES
1. Briggs, I. J., and H. L. Shantz, "The water requirement of plants:
I, Investigations in the Great Plains in 1910 and 1911," U. S. Dept.
Agr., Bur. Plant Indus., Bull. 284, 1913.
2. , "The water requirements of plants: II, A review of the
literature," U. S. Dept. Agr., Bur. Plant Ind., Bull. 285, 1913.
3. , "Relative water requirement of plants," Jour. Agr. Res.,
3:1-64 (1914).
4. ^ "Daily transpiration during the normal growth period and
its correlation with the weather," Jour. Agr. Res., 7:155-212 (1916).
5. Dillman, A. C., "The water requirements of certain crop plants and
weeds in the Northern Great Plains," Jour. Agr. Res., 42:187-238
(1931).
6. Harris, F. S., "The effect of soil moisture, plant food, and age on the
ratio of tops to roots in plants," Jour. Amer. Soc. Agron., 6:65-75
(1914).
7. Hughes, H. D., and E. R. Henson, Crop Production. Macmillan, New
York, 1930.
8. Kiesselbach, T. A., "Transpiration as a factor in crop production,"
Nebr. Agr. Exp. Sta. Res. Bull. 6, 1915.
9. , and E. G. Montgomery, "The relation of climatic factors to
the water used by the corn plant," Nebr. Agr. Exp. Sta. Ann. Rpt. 24,
1910, p. 94.
10. Leather, J. W., "Water requirements of crops in India," Mem. Dept.
Agr. India, Chem. Ser., 1:133-184 (1910).
11. LundegSrdh, H., Klima und Boden in ihrer Wirkung auf das Pflan&nleben.
Gustav Fischer, Jena, 1925.
12. Maximov, N. A., The Plant in Relation to Water, authorized trans, by
R. H. Yapp. Allen & Unwin, London, 1935.
THE USE OF WATER BY PLANTS 187
13. Pfeiffer, T., A. Rippel, and C. Photenhauer, "Uber den Einfluss von
Durstperioden auf das Wachtum der Pflanzen," Landw. Ver. Stat.,
96:353-363 (1920).
14. Seelhorst, C. von., "Die Bedeutung des Wassers im Leben der Kul-
turpflanzen," jfour.f. Landw., 59:259-291 (1911).
15. , and M. Tucker, "Der Einfluss welchen der Wassergehalt
und der Reichtum des Bodens auf die Ausbildung der Wurzeln und
der oberirdischen Organe der Haferpflanze ausiiben," Jour.f. Landw.,
46:52-63 (1898).
16. Shantz, H. L., and L. N. Piemeisel, "The water requirements of plants
at Akron, Colo.," Jour. Agr. Res., 34:1093-1190 (1927).
17. Sorauer, D., Die Krankheiten der Pflanzen. Breslau, 1880.
18. Thorn, G. C., and H. F. Holtz, "Factors influencing the water require-
ments of plants," Wash. Agr. Exp. Sta. Bull. 146, 1917.
19. Weaver, J. E., Root Development of Field Crops. McGraw-Hill, New
York, 1926.
20. Widtsoe, J. A., "Irrigation investigations," Utah Agr. Exp. Sta. Bull.
105, 1909.
Chapter XV
SPECIAL RESPONSES OF CROP PLANTS TO
THE MOISTURE FACTOR
The Response of Plants to Any Single Isolated Climatic
Factor. Growth may be considered as a summation of the responses
to an environmental complex. It is necessary to keep in mind,
however, that responses to the climatic factor must be regarded
as composite reactions to the climatic variables. Under given
environmental conditions a specific climatic factor may exert a
more immediate and a more readily measurable response than
other factors. This is especially noticeable during phases of develop-
ment that are recognized as critical. If it could be assumed that
the transpiration of a given amount of water by plants growing
in different environments would result always in the building up
of identical amounts of dry matter, there would be little necessity
of evaluating precipitation effectiveness except that various methods
may succeed in reflecting water losses through sources other than
transpiration.
A good illustration of this is presented by Rose (28) in the
results of correlation studies of climatic factors in relation to corn
yields. In the heart of the Corn Belt, correlations with yield of
single climatic factors, such as rainfall and temperature, failed to
give significant values; that is, variations in any one factor in this
area had but slight effects on corn yields. Multiple correlations,
that is, the consideration of several factors in their effects on
yields, gave more significant coefficients.
Moisture and the Ecological Optimum. It was brought out in
Chapter IX that the region of the ecological optimum for the
production of a particular crop is indicated by the performance of
that crop relative to the amplitude and stability of its yield. The
availability of moisture throughout the period of growth, especially
during critical periods, is directly related to yield performance.
Furthermore, when the moisture-yield relationships are consid-
188
SPECIAL RESPONSES TO MOISTURE 189
ered over a period of years it becomes evident that the stability
of moisture availability is reflected on the stability of the seasonal
yields obtained. This broad conception of the ecological optimum
is supported by the results of correlating yields of corn with climatic
factors in the Corn Belt as reported by Rose. In the center of the
Corn Belt the coefficients of correlation between July rainfall and
corn yields are insignificant, fluctuating mostly between 0.00 to
0.20. This should not be interpreted to mean that an abundance
of moisture is unnecessary for successful corn production in this
area; rather, such low coefficients indicate that the existing moisture
conditions approach the optimum for the crop.
In the moderate and minimal regions of corn production the
degrees of correlation between climatic factors in general, the
availability of moisture in particular, and yield performance are
significant and in places even critical. That is, as the threshold
of the moderate area is crossed and the minimal region entered,
the crop becomes more dependent on existing moisture conditions
than in the optimal region. This same condition applies also to
temperature conditions and, to a somewhat less marked degree,
to combinations of climatic factors.
The Importance of Moisture in Minimal Regions. Moisture
is an important factor in all crop producing areas. It is the all-
important factor in the minimal regions, where the average or
normal rainfall is generally necessary for successful crop production.
In such areas the systems of crop production must be correlated
more or less with existing moisture conditions; as a matter of fact,
the entire program of crop production is more or less dominated
by the moisture factor. The hopes of producers for bonanza crops
are realized in those particular seasons when moisture receipts
arc considerably above normal, with factors influencing the loss
of moisture from the soil and also from the plants at relatively
low levels. Seasons with an abundance of rain are usually some-
what cooler than drought years so that the moisture received not
only provides the plants with more water but also makes for better
utilization of the moisture received. This statement of a general
fact will hold true especially if considered in connection with the
critical periods of the plants involved.
While hope for the occurrence of bonanza years constitutes one
of the imoortant social features of crop production in dry areas,
190 ECOLOGICAL CROP GEOGRAPHY
such optimism is often negated by the fact that dry climates are
notoriously variable. A variation of but a few inches from the
normal may spell the difference between success and failure in dry
climates while significantly higher deviations from the average
may have but minor effects or no effect at all on the crop yields
obtained in the optimum regions of humid climates. This is force-
fully brought out by Mathews and Brown (20). These investigators
give the annual estimated yields of winter wheat at each of 43 pre-
cipitation stations located in the southern Great Plains area;
the stations were grouped according to the amounts of their
annual average precipitation.
The lowest rainfall station, less than 13 inches of annual pre-
cipitation, is represented by Las Animas, Colorado. The estimated
percentage of failures was 81; the expectancy of failure is 4 years
out of 5. "The utter impossibility of profitably producing wheat
under those rainfall conditions is fully recognized." Even the
next rainfall group, 13 to 14.9 inches, constitutes extremely hazard-
ous conditions in that the crop may be expected to fail 3 years out
of 5. More than one-half of the crops may be expected to result
in failures in the 15- to 15.9-inoh group with an expectancy of
only 1 good crop in 5 years. The* group with 16 to 16.9 inches
of precipitation still shows more than 2 failures in 5 years; the
number of good crops to be expected has, however, increased to
1 in 4 years. The number of good crops to be expected does not
increase materially until the 17- to 17.9-inch group is reached;
however, the number of failures in 5 years still remains at 2. The
percentage of good crops is further increased at that group of
stations with average precipitations of from 18 to 18.9 inches, yet
3 failures due to drought may be expected in 10 years. At the
highest rainfall stations, 19 inches or more per annum, the number
of good crops is increased rapidly; still 1 year out of 4 can be
expected to result in failures.
The facts pointed out in Chapter XIII relative to factors deter-
mining the efficiency of precipitation must be kept definitely in
mind in any attempted application of the findings of Mathews
and Brown to any region other than the southern Great Plains
area. The performance of wheat at similar rainfall stations in the
Pacific Northwest would be quite different for each rainfall group
than in Oklahoma or Kansas primarily because of the pronounced
SPECIAL RESPONSES TO MOISTURE 191
differences in temperature, evaporation, and seasonal distribution
of rainfall.
In the light of the data presented by Mathews and Brown the
point emphasized by Shantz (34), in dealing with moisture rela-
tionships in the short-grass plains, to the effect that "average
rainfall alone gives almost no idea of conditions favorable or
unfavorable for crop production," is entirely too comprehensive.
Even though crop failures sometimes do occur during years with
high rainfall, such seasons are exceptional. Before moisture can
be used efficiently it must be available first of all. Thus, Cole (9),
in investigating correlations between annual precipitation and
the yield of spring wheat in the Great Plains, comes to the con-
clusion that "the years when distribution of the precipitation
exercises a major control of yield as compared with the control
exercised by the quantity of precipitations are relatively few."
Calculations of Yields of Wheat on the Basis of the Amount
of Water Used by the Crop. The interesting relationships of
seasonal precipitation to yields of wheat given by Mathews and
Brown were based on estimated yields. These investigators found
correlations of 0.70 ± 0.049 and 0.827 ± 0.037 between the
quantity of water used by the crops and yields at Colby and
Garden City, Kansas, respectively. The term "water used" refers
to the amount of water, expressed in inches, removed from the soil
from seeding time to harvest, plus precipitation received during
that period. Yield and precipitation data for 16 years during the
period, 1915-1934, were available for analysis at Colby. The
derivation of the equation for calculating yields of winter wheat
on the basis of the amount of water used by the crop is given by
the authors in the following paragraph.
"There appears to be a definite minimum quantity of water required
to produce specified yields under climatic conditions like those at
Colby. No paying yield was obtained during the experiments from
the use of less than 10 inches of water, no yield of as much as 20 bushels
per acre was obtained from less than 14 inches of water, and no yield
of as much as 30 bushels per acre was obtained from less than 17 inches
of water. The following equation was used for determining yield from
the quantity of water:
. ,. , , Water used — 7.13
Yldd 053
192 ECOLOGICAL CROP GEOGRAPHY
In other words, 7.13 inches of water were required before any grair
was produced. Each additional 0.53 inch of water resulted in a bushel
of increased yield."
The equation set up on the basis of the data from Garden City
was very similar to that for Colby:
v. . , Water used — 7.69
Yield = p-^T-
The equation
v. , , Water used — 7.37
Yield = oTi
was established on the basis of the combined data from the tw<
stations.
Mathews and Brown present evidence to show that it was possible
with the employment of the above formulas to estimate yield
with a fair degree of accuracy. The degree of exactness wit!
which failures were estimated was striking. Nevertheless, th<
formulas have certain limitations in that the relationship betweei
water used and yield is not a straight-line regression throughout
Estimates of yields are too higk for quantities of water less thai
10 inches. In general, yields increased at the rate of 3.5 bushel
per acre for each additional inch of water used above 10 to ;
maximum of 20 inches. Since the formulas are based on bad a
well as good years, the yields in years of high production an
generally estimated too low.
In. working with the correlations between annual precipitatioi
and the yield of spring wheat in the northern Great Plains area
Cole found a regression equation based on 272 station years o
yield on precipitation:
Yield = (precipitation - 8.02) 2.19.
"In round numbers, 8 inches of precipitation results in a 0 yield
and the increment of yield is 2.19 bushels for each inch above tha
quantity." The precipitation data were taken for the crop yea
ending July 31.
When the number of paired variables was reduced from 272 ti
30 by combining the average yield and precipitation data of al
14 stations considered for each of the 30 years of the study, rathe
than taking the data for each individual station and year separately
SPECIAL RESPONSES TO MOISTURE 193
the regression equations for all plats, plats of continuous cropping,
and plats grown after fallow were as follows:
All plats: Yield = (precipitation - 10.07) 3.19
Continuous cropping: Yield = (precipitation — 1 1 .02) 3.07
Plats after fallow: Yield = (precipitation - 8.70) 2.99
It is interesting to note that both methods of analysis of the
precipitation-yield data, that is, the employment of 272 and
30 paired variables, show that spring wheat is less dependent on
the occurrence of precipitation during the crop year when grown
in a fallow than in a continuous system of cropping.
The yield-precipitation regression equations given by Cole
arc not directly comparable to the yield-water-used equations
given by Mathews and Brown. The yield-precipitation equations
take into account only indirectly the carry-over effects of water
in the soil from the previous year, but this factor enters directly
into the formulation of the yicld-water-used equations. Cole
eliminated from his calculations all those seasons when the crop
was either destroyed or heavily damaged by hail or rust. Mathews
and Brown utilized all the yield data over the test period regardless
of disturbances introduced by other climatic or pathological factors.
Correlation of Crop Yields and Precipitation Amounts for
Specified Periods. In general, the values of coefficients of correla-
tion between crop yields and receipts of precipitation for specified
periods of time are relatively low and frequently not great enough
to be of significance in humid regions. In dry regions the values
are generally high but even there hardly high enough to be used
for prediction purposes.
The results obtained by Rose, previously discussed, fall in line
with the above statement. Smith (36) presents a wealth of data
on precipitation-yield correlations.
Table 9, taken from Smith, shows the relationships of precip-
itation and the final yield of corn in relation to the stages of
development of the crop. The highest value found of the coeffi-
cient of correlation r was for the ten-day period after blossoming
or tassel production. From this Smith concludes that "rainfall
immediately after blossoming has a very dominating effect on the
yield of corn." The average date of blossoming of corn in Ohio
is July 25. The close relationship of July rainfall to corn yields
is brought out by Smith in his statement that "if all the years
194 ECOLOGICAL CROP GEOGRAPHY
when the rainfall for July in Ohio has been less than three inches
be grouped together, it will be found that the yield of corn averaged
30.3 bushels to the acre, and when the rainfall has been five inches
or more the yield has averaged 38.1 bushels to the acre. This
difference of 7.8 bushels an acre means a variation of 27,300,000
bushels of corn to the state."
TABLE 9. RESULTS OF CORRELATIONS BETWEEN RAINFALL AT GIVEN PERIODS
IN RELATION TO THE DEVELOPMENT OF THE CORN PLANT AND YIELD,
WAUSEON, OHIO, 1893-1912 (after Smith)
Period
Value
Off
Ten days before plowing
4- 0.01
From date of plowing to date above ground
— 0.06
From date above ground to date of blossoming
— 0.03
From date of blossoming to date ripe
4- 0.29
± 0.11
From 5 days before blossoming to 5 days after blossoming . .
For 10 days before blossoming
4-0.45
4- 0.20
±0.10
For 10 days after blossoming
-f 0.74
±005
For 20 days after blossoming
4- 0.57
±008
For 30 days after blossoming
4- 0.46
+ 0.09
Blair (5) indicates that temperature relationships may be cor-
related more directly with spring wheat yields in eastern North
and South Dakota than moisture conditions. Correlations between
rainfall and wheat yields show only moderate values, while lower
than normal temperatures show greater relationships to the yields
obtained. High June temperatures have especially depressing
effects on yields. Such high temperatures, of course, call for less
efficient expenditures of water.
Cole gives the mean precipitation, average yields of spring wheat,
correlation of these two variables, and the regression of yield on
precipitation at 14 stations in the northern and 5 stations in the
central and southern Great Plains area for the number of years
specified at each during the 30-year period 1906-1935. According
to Fisher's £test (10), the precipitation-yield correlations are high
enough to be significant at all stations except Hettinger, North
Dakota.
Before leaving this topic it is necessary to point out again that
higher correlations between precipitation and yields are more
in evidence for the minimal than for the optimal areas of produc-
SPECIAL RESPONSES TO MOISTURE 195
tion. This is well illustrated by the results reported by Henney (11)
dealing with precipitation and wheat yields in the nine crop.-
reporting districts of Kansas. In taking the northern third of
Kansas crop-reporting districts 1, 2, and 3 — insignificant indices
of correlations were in evidence in the eastern portion of the state,
that is, in district 3; in the central third, district 2, the September-
November index was + 0.825; while in the western third of the
state, district 1, the index of correlation between precipitation
for September, October, and November and wheat yields was
+ 0.872.
Koeppe (16), in correlating annual precipitation with wheat
yields of Ford County, Kansas, found no general outstanding con-
nections between these two factors in southwestern Kansas. How-
ever, when limiting his observations to specified periods, he agrees
quite well with the findings of Henney, as will be recognized from
the following statement from his paper: "Probably the most
significant relationship was the fact that fairly moist Augusts,
Septembers, Octobers, Januarys, and Februarys, and distinctly
dry Aprils, were followed by good yields of wheat the following
Junes or Julys." It is worth while to quote another significant
remark from Koeppe's paper, especially since it sums up in a concise
fashion the probable reasons for differences in the results so fre-
quently obtained from correlation studies in two remote regions.
Two probable causes for these differences in results are presumed:
"(0) The difference in geographic location and consequently in
physical conditions, for example, rainfall seems to be less critical in
Ohio than in Kansas, because in Kansas available moisture frequently
is insufficient, while in Ohio wheat rarely suffers from lack of moisture;
(6) the interrelations of meteorological elements are so complex that
it is difficult to establish, for example, whether a poor yield of wheat is
due to too little rain in September, too high temperatures in October,
lack of snowfall in January, too much rain in April, too strong winds in
May, or whatnot else."
The above statement bears out the remark made by Chilcott (7)
to the effect that "notwithstanding the fact that annual precipita-
tion is a vital factor in determining crop yields, it is seldom, if ever,
the dominant factor; but the limitation of crop yield is most fre-
quently due to the operation of one or several inhibiting factors
other than shortage of rainfall."
196 ECOLOGICAL CROP GEOGRAPHY
That drought and the factors associated with drought often
:ause crop failures cannot be denied. Drought, as pointed out in
Chapter XII, does not consist of lack of rainfall alone. Lack of
rainfall is generally associated with factors calling forth high
expenditure of water by plants. Whether or not lack of rainfall
is, under those conditions, referred to as "the dominant factor"
is of no consequence to the end result, crop failure. In a later
publication dealing more specifically with crop rotation and tillage
methods in the Great Plains area, Chilcott (8) comes to the point
with a very strong statement regarding the importance of soil
moisture in this area by writing that "the conservation and utiliza-
tion of the scanty rainfall is of such predominant importance as
completely to eliminate some factors and to relegate all others
to minor positions." The droughts in the Great Plains area since
1931, when the above statement was made, serve well to emphasize
it in every way.
An Illustration of Precipitation — Yield Relationships in an
Optimal Area. The performance record of winter wheat in the
Palouse area of northern Idaho and eastern Washington as exempli-
fied by the yields of this crop in teg different crop rotations on the
University Farm at Moscow, Idaho, gives evidence that this
particular area may be classified as optimal. The average yields
of wheat and the coefficients of correlation between amounts of
precipitation at stated intervals as well as for the entire season
and annual yields are presented in Table 10 for the 22-year period
1915-1936, inclusive. All the coefficients of correlation between
rainfall and yield are relatively low. The average annual rainfall
during the period of the test was 21.13 inches. The fact that in
excess of 50 bushels of wheat per acre can be produced on an annual
average precipitation of only 21.13 inches indicates a high efficiency
of moisture utilization by the wheat crop in this area. Furthermore,
the seasonal variability of the yields is relatively low. The coeffi-
cient of variability is as low as 22.15 per cent in rotation number 6
and fluctuates between that value and 30.00 per cent for the better
rotations. In other words, the performance record of wheat in
the Palouse area shows not only high yields but also a high yield
expectancy.
One of the weak points of the numerous studies of precipitation-
yield relationships is that no recognition is made of the moisture
SPECIAL RESPONSES TO MOISTURE
197
present in the soil prior to the period covered by the investigation.
Such stored moisture may be very effective in the production of
plants and may be a factor of considerable importance in the
determination of the final yield.
TABLE 10. COEFFICIENTS OF CORRELATION BETWEEN THE WINTER WHEAT
YIELDS IN TEN SYSTEMS OF CROPPING AND PRECIPITATION DURING FOUR
MONTH PERIODS AND FOR THE ENTIRE CROP YEAR ON THE UNIVERSITY FARM,
MOSCOW, IDAHO, FOR THE 22-YEAR PERIOD 1915-1936, INCLUSIVE
Rotation Number and
Sequence of Cropping
Average
TieldoJ
Wheat
in Bush-
els per
Acre
Coefficients of Correlation
Late Sum-
mer and
Fall —
Aug. 1-
Nov. 30
Winter,
Dec. 1-
Mar. 31
Spring and
Early Sum-
mer, April 1
-July 31
Entire
Season,
Sept. 1-
Aug. 31
1. Wheat, oats, peas plus
manure
52.5
42.9
56.0
52.2
49.4
47.4
34.2
49.4
33.8
23.0
0.42 ±0.12
0.47 ±0.11
0.42 ±0.12
0.33±0.13
0.42 ±0.12
0.52±0.11
0.43+0.12
0.28 ±0.13
0.33 ±0.13
0.29 ±0.13
0.39 ±0.13
0.17 ±0.14
0.10±0.14
0.20 ±0.14
0.08 ±0.14
0.26 ±0.13
0.15±0.14
0.29 ±0.13
0.05 ±0.14
0.22 ±0.14
0.09 ±0.14
0.15 ±0.06
0.06 ±0.14
0.09 ±0.15
0.02 ±0.14
0.07 ±0.14
0.17 ±0.14
0.28 ±0.13
0.32 ±0.13
0.02 ±0.14
0.40 ±0.12
0.58 ±0.10
0.20 ±0.08
0.41 ±0.12
0.41 ±0.12
0.39 ±0.12
0.02 ±0.14
0.50 ±0.11
0.40 ±0.; 2
0.58 ±0.08
0.23 ±0.14
0.53 ±0.10
0.48 ±0,11
0.40 ±0.13
2. Wheat, oats, peas . .
3. Wheat, oats, fallow plus
manure
4. Wheat, oats, fallow . .
5. Wheat, oats, corn plus
manure
6. Wheat plus 200 Ibs.
NaNOi, oats, corn .
7. Wheat, oats, corn
8. Wheat, oats, potatoes .
11. Continuous wheat plus
manure
12. Continuous wheat . .
Average value of r . .
Sievers and Holtz (35) point out that precipitation when in
excess of 18 inches per annum does not become a limiting factor
to crop production in the Palouse area. The above correlation
studies bear out this contention. Seely (33) found no correlation
of yield with total seasonal rainfall at the Washington Agricultural
Experiment Station at Pullman. Contrasted to this, at Lind,
70 miles west of Pullman, annual precipitation constituted the
largest single factor determining the yield of wheat. The average
annual precipitation at Pullman of 19.80 compared to 8.02 inches
at Lind illustrates well the differences in rainfall-yield correlations
in optimal and minimal areas.
198 ECOLOGICAL CROP GEOGRAPHY
The Water Factor in Relation to the Degree of Correlation
between the Yields of Separate Crops. Klages (14), in dealing
with the variability in the yields of field crops in the states of the
Mississippi Valley, pointed out material differences in the degrees
of correlation shown between the average yields of separate crops
in the various states of that great agricultural region. The correla-
tions between the yields of the separate crops vary in most instances
with the geographical position of the several states. The states of
the Great Plains show higher values as a rule for the coefficients
of correlation between the yields of individual crops than states
to the east of this moisture tension area. High coefficients for the
western states are in evidence, especially for those crops growing
throughout the same part of the season, as between the yields of
oats and barley, or spring wheat and barley or oats. The yields
of corn and wheat in no case show very significant correlations.
This is to be expected in view of the fact that the critical periods
in the development of these two respective crops fall at entirely
different times.
The same point was illustrated by Klages (15) for the degrees of
correlation between the annual yiftlds of six different cereal crops
grown at the South Dakota Agricultural Experiment Station at
Brookings, in the extreme eastern, and at the Highmore Sub-
station, in the central part of the state. Moisture conditions in
eastern South Dakota may be designated as moderate, while
the central portion of the state can well be classified as a minimal
area. The values of r were in all instances higher in the minimal
than in the moderate area.
Seely correlated the yields of two varieties of wheat, Baart and
Bluestem, at Pullman and Lind, Washington. For a 10-year
period the value of r at Pullman was 0.741, as compared to a value
of 0.961 for a 17-year period at Lind. The growth habits of these
two varieties differ materially, but even with that, the differences
in the degrees of correlation at Pullman, a relatively humid area,
and at Lind, a very dry area, are pronounced.
Climatic, and especially moisture, conditions favoring one crop
in relatively dry areas prove favorable to other crops to a greater
extent in such areas than in more humid environments. Likewise,
conditions leading to a reduced yield of one crop are more likely
to result in reduced yields of other crops in dry areas, with their
SPECIAL RESPONSES TO MOISTURE
199
more rigorous and often erratic climates, than in the humid areas
with generally more uniform climatic conditions. This condition
holds true especially in cases where the critical periods of the crops
concerned nearly coincide.
Cardinal Points for Water. Sufficient evidence has been pre-
sented to show that at least a minimum amount of water must be
present in the soil for the preservation of plant life. There is also
an optimum or a moisture level at which plants over a period of
time may be expected to give a maximum response. Furthermore,
there is a maximum. When the water content of a soil increases
above the optimum, it begins by degrees to interfere with the
normal process in the soil and growth suffers accordingly.
The exact location of the cardinal points is determined by a
variety of factors such as the specific requirements of the plants
grown, the age of the plants, type of soil, and the constellation of the
environmental factors especially as they affect the need for moisture
during any given time interval. Since so many factors are involved,
the cardinal points for water are generally not so distinct as arc
temperature relationships.
Table 11, taken from Mitscherlich (26), serves well to illustrate
the above. The maximum yields of spring rye were obtained when
the soil contained 60 per cent of its water-holding capacity. In
the other crops given, the highest yields were obtained at 80 per
cent of the water-holding capacity of the soil. Yields declined
rapidly beyond the optimum.
TABLE 11. RELATIVE YIELDS OF DESIGNATED PLANTS GROWN ON SOILS OF
VARYING MOISTURE CONTENTS (after Mitscherlich)
Crop
Water Content in Percentage of Water-Holding
Capacity
20
40
60
80
100
Spring ry
Peas . .
c
30.7
14.1
16.0
15.8
71.4
50.3
48.4
48.3
92.8
87.4
63.9
89.0
77.6
100.0
100.0
100.0
19.7
9.3
33.8
62.5
Horsebea
Potatoes
ns . . . .
According to Kolkunov's experiments, reported by Maximov
(21), different pure-line selections of a given crop, in this case
200 ECOLOGICAL CROP GEOGRAPHY
Beloturka wheat, may show quite different reactions to the moisture
factor.
The yield data reported by Miischerlich and Kolkunov do not
support the statement made by Willcox (37) in his A B C of Agro-
biology. Willcox makes free use of Mitscherlich's data and comes
on the basis of it to the conclusion that "when the moisture con-
tent of the soil is 100 per cent plants are growing at the fastest
possible rate." Mitscherlich (25) grew plants with increasing
amounts of water but at the same time increased the volume of soil
available to the plants. What Willcox took for a moisture content
of 100 per cent was the full water-holding capacity of the soil less
the amount of the hygroscopic capacity; consequently the soil
used was not saturated.
The effects of excessive amounts of moisture in the soil lead
directly and indirectly to difficulties. The most immediate is a
lack of soil aeration limiting the supply of oxygen to plant roots.
The second factor is that carbon dioxide accumulates in nonaerated
soils and produces toxic effects. As indicated by Russell (29),
plants vary considerably in their sensitiveness to these factors.
They do not all stand in equal nftqd of oxygen for their roots.
According to Livingston and Free (18), "the exclusion of oxygen
from the roots of most plants interferes with the respiration of the
protoplasm of the root cells, resulting in its death and the conse-
quent failure of the roots to function as absorbers for the plant.
The cessation of water intake is soon followed by the progressively
decreasing turgor of the shoot and leaves and finally by wilting
and death."
In contrast with the "agrobiologist" the agronomist is not
dealing with a "pure" science. The facts he gathers must have
practical application and economic justification and must be
interpreted on the basis of both immediate and future effects.
Agrobiology is defined by Willcox as a "pure" science, "concerned
only with the eternal verities of nature. It acknowledges no
'taint' of economics and never looks at a bill of cost or a market
quotation." The agronomist cannot afford to have his field of
action so closely delineated.
The Influence of Differing Quantities of Water on the Devel-
opment of Cereals. The relative availability of water during
different periods of growth has a pronounced effect on the develop-
SPECIAL RESPONSES TO MOISTURE 201
ment of plants. This is well illustrated by von Seelhorst (30). His
conclusions, based on a series of pot experiments with oats and
spring wheat, were as stated below:
1. The height of plants is determined by an abundance of moisture
prior to the jointing stage.
2. The thickness of the culms depends mainly on the availability of
moisture at jointing and thereafter.
3. The length of the panicles and spikes is dependent upon a good supply
of moisture at jointing.
4. The number of branches of the panicle are determined primarily by a
good supply of moisture during the early phases of growth.
5. The development of a large number of spike lets per panicle or spike is
favored by the same factors favoring length of the panicles and spikes.
6. The number of florets per spikelet is dependent upon an abundant
supply of moisture following jointing.
7. The weight of grain per panicle or spike is influenced by the same
factors determining yield.
8. The weight of 100 kernels was about equal for the continuously low
and high moisture lots; it was the lowest where an abundance of
moisture was available during the early phases of vegetation followed
by reduced moisture after jointing.
9. The specific gravity of kernels was lower where an abundance of
moisture was available at flowering and thereafter than for those lots
grown with less moisture during the later phases of development.
Under extreme moisture conditions during the later phases of growth
the specific weight of the grain may be expected to be low.
10. The percentage of hull was less in the continuously dry lots than in
those receiving more moisture. A strong development of the panicles
is apparently associated with the production of heavy hulls.
1 1 . The percentage of nitrogen was highest in the lot grown with limited
moisture.
12. The weight of grain harvested is determined primarily by an abun-
dance of moisture at the time of jointing and flowering.
13. The relationship of yield of grain to straw is influenced by the avail-
ability of moisture, especially during the later phases of growth. An
abundant supply of moisture at the time of jointing increases the yield
of both grain and straw.
Critical Periods. The findings of von Seelhorst serve well to
illustrate the need of moisture by cereal crops during the jointing,
flowering, and early filling stages. Since an available supply of
moisture at the shooting or the jointing stage is essential to the
production of high yields, this period in the development of cereals
can be designated as critical.
202 ECOLOGICAL CROP GEOGRAPHY
Von Seelhorst's pot experiments and also the experiments of
von Seelhorst and Tucker (32) are well supported by the data
reported by Kezer and Robertson (13) based on small field plat
tests. The outstanding results of Kezer and Robertson's studies
on critical periods with spring wheat under controlled irrigation
conditions are presented in the following paragraph.
"The time of applying irrigation water is an important factor in
spring wheat production. Water applied at 'jointing' increases the
yield of straw and grain but not the quality of the grain as indicated by
bushel weight and weight per 1,000 kernels. When water is applied at
'heading,' slightly lower yields of grain and straw arc obtained than
when water is applied at 'jointing.' But the quality of grain is materially
improved as indicated by bushel weight and weight per 1 ,000 kernels.
Irrigation as late as 'blossoming' and 'filling' has very little effect on
yields of grain or straw, but has a marked effect on grain quality as
indicated by weight per measured bushel. Late irrigations at 'heading,'
'blossoming,' and Tilling' have a residual effect on the following crop.
Early irrigations at 'germination' and 'tillering' increase the straw yield
to a greater extent than the grain yield but produce a grain of poor
quality. Irrigations of small amounts (1 inch) distributed through the
growing season give the best results but are impractical."
£'
Miller and Duky (24) showed 4n the case of corn that "the
production of grain depended more than any other part of the
plant upon a plentiful supply of moisture during the last 30-day
period of growth." This last 30-day period here referred to cor-
responded to the phase in the growth of the crop when the more
advanced plants began to tassel.
The reader should not come to the conclusion that critical periods
in the production of crop plants are limited to the later phases of
development. Their occurrence is definitely associated with the
phenological means of climatic phenomena for given areas. Thus,
in the southern Great Plains area wheat encounters a critical
period immediately after seeding, or even before seeding, in that
moisture may be lacking to bring about germination or emergence.
Critical periods may also develop on account of an excess of
moisture, especially during the postheading periods of cereals.
Such conditions lead to reduced quality and lodging and, if com-
bined with proper temperatures, to crop damage from various
fungus pests. "In humid areas," states Cajrleton (6), "it is not so
much an excess of rainfall that causes an inferior quality of kernel
as the great humidity and lack of sunshine." Von Seelhorst and
SPECIAL RESPONSES TO MOISTURE
203
Krzymowski (31) studied the relationship of soil moisture to the
delay of maturity in cereals.
Drought Reactions of Wheat. As pointed out in Chapter XII,
drought is a complex phenomenon. The topic is again brought
up to show that plants and even plants of the same species, wheat
for instance, exhibit quite different reactions with regard to the
water deficits produced in their structures by droughty conditions.
It is known that given varieties will produce greater yields under
conditions of stress with regard to the moisture factor than others,
even though their respective stages of development are so com-
parable that these differences in reactions cannot be explained
on the basis of drought escape. In this connection Bayles et al.
(4) call attention to the fact "that the ability of wheat plants to
produce grain under drought conditions might be due to two
somewhat distinct phenomena, viz., (a) the ability to limit tran-
spiration and to carry on the processes of photosynthesis and assim-
ilation under conditions conducive to high evaporation, and (b) the
ability of the root systems to take in moisture as fast or faster than
it is transpired. ... It would seem logical, that varieties and
species might differ in one or both of these respects and also in
resistance to high temperatures."
Aamodt (1) described a drought chamber to be used in the
evaluation of drought resistance in plants.
TABLE 12. RATE OF WATER LOSS FROM PLANTS OF EIGHT VARIETIES OF
SPRING WHEAT UPON REMOVAL FROM THE SOIL (after Bayles, et al.)
Variety
Percentage of Water Remaining in Plants after the
Number of Hours of Drying Indicated
0
4hrs.
22 hrs.
28 hrs.
48 hrs.
Kubanka . . .
Baart
88.8
88.6
88.6
88.1
88.4
87.8
88.4
88.2
85.9
85.2
83.7
83.5
83.8
82.6
82.5
81.9
75.7
70.0
65.9
64.5
61.9
61.0
58.6
56.7
72.3
65.4
61.5
59.5
56.2
56.2
53.7
50.6
60.7
51.9
49.7
43.3
43.9
43.4
42.8
38.9
Onas
Ceres
Marquis ....
Huston ....
Hope
Hope-Ceres . . .
Table 12, reported by Bayles et al.y gives the rates of water lost
from the plants of eight varieties of spring wheat grown in a green-
204 ECOLOGICAL CROP GEOGRAPHY
house at 75°F and with optimum soil moisture conditions. The
plants were pulled from the soil and dried at a temperature of 77°F.
The table shows the percentage of water remaining in the plants
after the number of hours of drying indicated.
The field performance of these varieties under drought conditions
is well correlated with their respective losses of moisture as reported
in Table 12. Hope and Hope-Ceres are known to lack in drought
resistance, while Kubanka and Baart are well adapted to areas
with low atmospheric humidity and relatively high temperatures.
This would indicate that the specific structural modifications,
differences in chemical composition of the cell saps, or functional
causes, i.e., differences in behavior of the stomata of these more
drought-resistant varieties are instrumental in slowing down rates
of water losses from the tissues of the plants, within significant
limits.
Kolkunov (17) investigated the relationship of size and number
of stomata of wheat varieties possessing varying degrees of drought
resistance, and found the more resistant varieties to be characterized
by small stomata. Maximov reports a later study by Kolkunov
in which four pure lines of Belofeirka wheat differing in cell size
were grown under high and low soil moisture conditions. Under
high soil moisture conditions, the larger celled varieties produced
the highest grain yields, while the reverse was true under low soil
moisture conditions. Pavlov (27) reports that, in general, the more
drought-resistant and early-maturing varieties of winter wheat
had small stomata; no such relationships were apparent, however,
in spring wheat and oats.
Aamodt and Johnston (2) found, upon comparing certain
physiological and morphological features of two fairly drought-
resisting Russian varieties of wheat, Milturum and Caesium, with
the characteristics of commonly grown varieties of spring wheat,
that the relatively greater drought-resistant qualities of these two
outstanding Russian varieties could be accounted for by specific
differences in their growth characteristics.
Comparative Drought Resistance of Corn and the Sorghums.
The sorghums as a group occupy a unique position in that they
may be designated as the most drought-resistant of field crops.
The special characteristics of this group of plants merit the attention
of students of ecological relationships of crop plants. Corn and the
SPECIAL RESPONSES TO MOISTURE 205
sorghums have similar growth habits, are similar in size and
appearance, and are grown under comparable cultural conditions.
Because of recognized greater drought resistance the sorghums
are grown extensively in drier territories than corn. Nevertheless
there is considerable overlapping in the producing areas of these
two important crops.
The main outstanding difference between the two crops is that
corn has a very definite critical period with regard to both moisture
and temperature relationships at the time of tasseling. While the
yields of sorghums are also influenced to a marked degree by
unfavorable climatic conditions at flowering, the sorghums have
one decided advantage over corn in that they are not forced ahead
during periods unfavorable to growth. The ability of the sorghums
to remain in an almost quiescent stage, or enter into a period of
anabiosis, as Maximov chooses to call it, when confronted with
conditions unfavorable to growth is outstanding and of great value
to the plant. When revived by rain, a vigorous growth rate is
resumed, unless, of course, conditions are too severe. Thus, the
sorghums may make at least a partial grain crop under conditions
of interrupted growth, under which corn would either perish or,
if such drought periods occurred at the time of tasseling, produce
but a low grade of fodder on account of interference with fertiliza-
tion. Hot dry weather at the time corn develops tassels hastens
the shedding of the pollen before the silks emerge from the husks.
Martin (19) expresses the opinion that sorghum stalks revive
from a dormancy produced by drought chiefly because they have
not wilted beyond recovery. In that connection special xerophytic
structures, such as small cells, a waxy cuticle, and a high osmotic
pressure come definitely into play. Another factor of great impor-
tance in the sorghums is the dormancy of the basal buds during
periods of drought and their ability to develop into tillers rapidly
enough to produce a crop of grain after moisture becomes available.
Thus, Martin states that
"frequently the suckers have produced a good crop of grain after the
main stalks have died from extreme drought. Corn plants, even of
suckering types, apparently lack the ability to develop fruitful tillers
after the main stalks have perished from drought. The viability of the
tiller buds of sorghum plants may be maintained partly because of the
slow drying of sorghum stalks. The relatively higher osmotic concen-
206 ECOLOGICAL CROP GEOGRAPHY
tration of the juices of sorghum crowns and roots as compared with
corn may be of some importance. A short drought followed by rains
usually causes a temporary dormancy in the sorghum stalks which
already have developed, while a prolonged drought followed by rains
kills the old stalks yet permits a crop of 'suckers' to develop."
Another difference between these crops is the variations in the
development of their root systems. Miller (22) found that for a
given stage of growth Pride of Saline corn possessed the same
number of primary roots as Dwarf milo and Blackhull kafir, also
that the depth of penetration and spread of the roots of these three
crop plants were the same. The sorghums, however, had more
efficient root systems in that they "possessed approximately twice
as many secondary roots per unit of primary root as did the corn
plant."
Kearney and Shantz (12) suggest that the slow rate of growth
of sorghum plants early in the season may help in the conservation
of the soil moisture which is needed later.
In considering the rates of transpiration of corn and sorghums,
Miller and Coffman (23) found that corn always transpired more
water per plant during any given period than any of the sorghums
tested. The amount of water transpired per plant, however, was
not proportional to the extent of leaf surface. The rates of trans-
piration per unit of leaf surface for the sorghums were considerably
higher than those of corn. They state:
"The results of these experiments seem to indicate that in most
cases a small leaf surface is the most important factor in reducing the
loss of water from these plants. The corn plant is not capable of sup-
plying its large extent of leaf surface with a sufficient amount of water
to satisfy the evaporating power of the air, and as a result its rate
of transpiration per unit of leaf surface falls below what it would be
if the needed amount of water were supplied. The sorghums, on the
other hand, with their small leaf surface are able to supply water in
amounts sufficient to satisfy the evaporating power of the air, and, as a
result, their rate of transpiration per unit of leaf surface is higher than
that of the corn."
The smaller leaf area of the sorghums, together with the fact
that they possess more efficient root systems than corn, as indicated
by the greater development of secondary roots, places them in an
advantageous position in that a highly efficient absorbing surface
has to supply water for a smaller transpiring area. This condition
SPECIAL RESPONSES TO MOISTURE 207
more than makes up for their higher rate of transpiration per
unit of leaf area.
Types of Cropping in Relation to the Moisture Factor. In
humid areas continuous cropping is the rule; fallows are instituted
for reasons other than conservation of moisture. In dry areas
crops are grown with the intervention of fallows, the purpose being
to store in the soil as much as possible of the moisture received
during the fallow year so that it may be used by the next crop
grown. The frequency of fallows necessary to attain profitable
yields depends on the amount of the annual precipitation, the
efficiency of precipitation, and also on the seasonal distribution
of the moisture received. Under extreme conditions crops are
grown in alternate crop, fallow systems. In other instances a
fallow every third year may suffice.
Fallows are most effective in areas with winter and early spring
precipitation. It is difficult to conserve moisture supplied by
summer rains, especially when such rains come in light showers.
A good fallow not only must be fairly effective in the conservation
of moisture already in the soil when cultural operations are started,
it also must leave the surface of the soil so that moisture falling
during the fallow period may enter readily and thus not be lost
by immediate evaporation. In the past the importance of soil
mulches has been overemphasized. While they were fairly effective
in retaining moisture in the soil at the time the fallow was instituted,
they left the surface layer in a deflocculated condition so that
considerable resistance was offered to the penetration of moisture.
Aside from the question of penetration of moisture, a deflocculated
soil condition brought about by frequent workings of the soil to
leave the surface finely pulverized is too conducive to soil erosion
either by wind or water to be justified.
Fertility and structure are factors to be considered in all soils.
In dry areas moisture is the main and not infrequently the only
factor limiting crop production. Consequently, cropping systems
in such areas must be arranged with due regard to the ever-impor-
tant factor of moisture conservation. Crops usually exhausting
all available soil moisture during any one season should be selected
with care and incorporated into a cropping system with due con-
sideration of the likely effects on other crops to follow. Thus,
Baker and Klages (3) report a yield of winter wheat in a wheat,
208 ECOLOGICAL CROP GEOGRAPHY
oats, sunflower rotation of 25.9 bushels as compared to a yield
of 35.5 bushels per acre when the wheat was grown in a wheat,
oats, corn rotation. The inclusion of a high soil-moisture-removing
crop such as sunflowers in a rotation system in the Palouse area
served to reduce the wheat yield by 9.6 bushels per acre.
REFERENCES
1. Aamodt, O. S., "A machine for testing the resistance of plants to
injury by atmospheric drought," Can. Jour. Res., 12:788-795 (1935).
2. , and W. H. Johnston, "Studies on drought resistance in
spring wheat," Can. Jour. Res., 14:122-152 (1936).
3. Baker, G. O., and K. H. W. Klages, "Crop rotation studies," Idaho
Agr. Exp. Sta. Bull. 227, 1938.
4. Bayles, B. B., J. W. Taylor, and A. T. Bartel, "Rate of water loss in
wheat varieties and resistance to artificial drouth," Jour. Amer. Soc.
Agron., 29:40-52 (1937).
5. Blair, T. A., "Temperature and spring wheat," Mo. Wea. Rev., Jan.,
1915.
6. Carleton, M. A., The Small Grains. Macmillan, New York, 1916.
7. Chilcott, E. C., "The relations Between crop yields and precipitation
in the Great Plains area," U. S. Dept. Agr. Misc. Circ. 81, 1927.
3 } "The relations between crop yields and precipitation in the
Great Plains area," U. S. Dept. Agr. Misc. Circ. 81, Supplement 1,
Crop rotations and tillage methods, 1931.
9. Cole, J. S., "Correlations between annual precipitation and the
yield of spring wheat in the Great Plains," U. S. Dept. Agr. Tech. Bull.
636, 1938.
10. Fisher, R. A., Statistical Methods for Research Workers. Oliver and Boyd,
London, 1936.
11. Henney, H. J., "Estimation of future wheat production from rain-
fall," Mo. Wea. Rev., 63:185-187 (1935).
12. Kearney, T. H., and H. L. Shantz, "The water economy of dry-land
crops," U. S. Dept. Agr. Yearbook 1911:351-362 (1912).
13. Kezer, A., and D. W. Robertson, "The critical period of applying
irrigation water to wheat," Jour. Amer. Soc. Agron., 19:80-116 (1927).
14. Klages, K. H. W., "Geographical distribution of variability in the
yields of field crops in the states of the Mississippi Valley," Ecology,
11:293-306(1930).
15. , "Geographical distribution of variability in the yields of
cereal crops in South Dakota," Ecology, 12:334-345 (1931).
SPECIAL RESPONSES TO MOISTURE 209
16. Koeppe, C. E., "Meteorological conditions and wheat yields in Ford
county, Kansas," Mo. Wca. Rev., 62:132-133 (1934).
17. Kolkunov, V. R., "The role of selection in the study of drought,"
Int. Rev. Sci. & Pract. Agr., 12:386-390 (1926).
18. Livingston, B. E., and E. E. Free, "The effect of deficient soil oxygen
on the roots of higher plants," The Johns Hopkins Univ. Circ. 1917:380
(1917).
19. Martin, J. H., "The comparative drought resistance of sorghums and
corn," Jour. Amer. Soc. Agron., 22:993-1003 (1930).
20. Mathews, O. R., and L. A. Brown, "Winter wheat and sorghum pro-
duction in the Southern Great Plains under limited rainfall," U. S.
Dept. Agr. Circ. 477, 1938.
21. Maximov, N. A., The Plant in Relation to Water, authorized trans, ed.
with notes by R. H. Yapp. Allen and Unwin, London, 1928.
22. Miller, E. C., "Comparative study of the root systems and leaf areas
of corn and the sorghums," Jour. Agr. Res., 6:311-332 (1916).
23. y and W. B. Coffman, "Comparative transpiration of corn
and the sorghums," Jour. Agr. Res., 13:579-604 (1918).
24. Miller, M. F., and F. L. Duley, "The effect of a varying moisture
supply upon the development and composition of the maize plant
at different periods of growth," Mo. Agr. Exp. Sta. Res. Bull. 76,
1925.
25. Mitscherlich, E. A., Bodenhunde fur Land — und Forstwirte. 2d ed.,
- Paul Parey, Berlin, 1913.
26. , Bodenkunde fur Land — und Forstwirte. 3d ed., Paul Parey,
Berlin, 1920.
27. Pavlov, K., "Results of investigations on the number, size of stomata
and osmotic pressure as an aid in the determination of the physiologi-
cal properties of wheat and oats varieties produced by the breeder,
with particular reference to their resistance to drought," Sbornik
(annals) Ceskoslov. Acad. £emed., 6:565-616 [Abstract in Plant Breed.
Abstr. 2 (3)]:120, entry 396 (1932).
28. Rose, y. K., "Corn yield and climate in the Corn Belt," Geog. Rev.,
26:88-102 (1936).
29. Russell, E. J., Soil Conditions and Plant Growth. 6th ed., Longmans,
London, 1935.
30. Seelhorst, C. von., "Neuer Beitrag zur Frage des Einflusses des Was-
sergehalts des Bodens auf die Entwicklung der Pflanzen," Jour. f.
Landw., 48:165-177 (1900).
31. , and Krzymowski, "Das Reifen verschiedener Sommer-
weizen-varietaten bei verschiedener Bodenfeuchtigkeit," Jour. f.
Landw., 57:113-115 (1909).
210 ECOLOGICAL CROP GEOGRAPHY
32. Seelhorst, G. von, and M. Tucker, "Der Einfluss welchen der Wasser-
gehalt und der Reichtum des Bodens auf die Ausbildung der Wurzeln
und der oberirdischen Organe der Haferpflanze ausiiben, "Jour.f.
Landw., 46:52-63 (1898).
33. Seely, G. I., "The effect of moisture and temperature on the growth
and yield of Baart and Bluestem wheat." Thesis, Washington State
College, 1935.
34. Shantz, H. L., "Natural vegetation as an indicator of the capabilities
of land for crop production in the Great Plains Area," U. S. Dept. Agr.y
Bur. Plant 2nd., Bull. 201, 1911.
35. Sievers, F. J., and H. F. Holtz, "The influence of precipitation on soil
composition and on soil organic matter maintenance," Wash. Agr.
Exp. Sta. Bull. 176, 1923.
36. Smith, J. W., Agricultural Meteorology. Macmillan, New York, 1920.
37. Willcox, O. W., ABC of Agrobiology. Norton, New York, 1937.
Chapter XVI
TEMPERATURE
GENERAL ASPECTS OF THE TEMPERATURE
FACTOR
Temperature Provides a Working Condition. No description
of a physiological environment is complete without a notation of
the existing temperature conditions. Temperature provides a
working condition for nearly all plant functions. More than that,
it provides the necessary energy for some processes; radiant energy,
for example, is absorbed in photosynthesis and released in respira-
tion. Certain winter-hardy plants by virtue of their structural and
chemical modifications are able to survive periods of low temper-
atures but are unable to renew growth until proper temperatures
are again established to provide the necessary working condition.
Recording of Temperatures. Temperatures for any given
interval of time are evaluated readily by the expansion or contrac-
tion of a column of mercury or in some instances alcohol in the
bore of a thermometer. A continuous record of temperatures is
made available by the use of thermographs. Thermograph records
are of considerable value. However, they do not register temper-
atures with the degree of accuracy or the precision of standard
thermometers.
From the standpoint of plant responses, temperatures may be
evaluated in the light of the mean, or average, or in relation to the
extremes for any given interval of time. Extremes are recorded
as minima or maxima. Temperature extremes call forth more
outstanding and obvious responses than mere averages. The mean
temperature for any given day is calculated from the average of the
recorded minimum and maximum temperature for that day. For
this special maximum and minimum, thermometers are used.
The mean or average temperature for any given day calculated
from the average readings of the minimum and maximum temper-
atures corresponds sufficiently closely to the averages taken at more
211
ECOLOGICAL CROP GEOGRAPHY
frequent intervals, or from thermograph records, to be of practical
value. It is evident that the calculation of the mean temperature
for the day from the average of the minimum and maximum
amounts to an approximation. For the study of detailed physi-
ological responses readings at shorter intervals or from a calibrated
thermograph record are highly desirable and often essential.
Average and Normal Temperatures. The daily normal
temperatures for a station are the averages of each day of the year
for a period of not less than ten years. The monthly normal con-
sists of the average for the particular month for not less than the
same length of time; the yearly normal is computed from an
average of the monthly normals. Calculations of normal temper-
atures become more reliable and representative with increasing
number of years. Normals once established seldom change materi-
ally.
Obviously the greatest fluctuations will be found in the daily
normals. Certain days showing wide departures from normal
seasonal trends may influence the values calculated on the basis of
daily averages. The curve of the normal trend may be conven-
iently smoothed by means of five-^r seven-day moving averages.
The comparison of temperature and also moisture conditions
of any given season with the normal for the area often can be used
to advantage for explaining observed crop responses. Figure 28
gives the normal monthly temperatures and monthly accumulated
precipitation at Moscow, Idaho, also the average monthly temper-
atures and accumulations of precipitation for the crop year 1 937-38,
September 1 to August 31 . Since winter wheat is the predominating
crop of the Palouse area, the employment of the crop season gives
a more concise picture of crop responses in relation to climatic
conditions than could be obtained by the use of the calendar
year. This particular season was exceptionally favorable for the
production of winter wheat; yields on the University Farm and the
region in general were high. On the other hand, the deficiency of
moisture in May, June, July, and August together with the higher
than normal temperatures for these months was decidedly detri-
mental to spring wheat. The winter wheat escaped the period of
drought, brought about by low precipitation and higher than
normal temperatures, serving definitely to decrease the efficiency
of transpiration, while the yields of the spring wheat were low
TEMPERATURE 213
because the critical period for this crop coincided with the period
of stress induced by the indicated moisture and temperature
relationships.
22
21
PRECIPITATION
20 j" _ -— Normal monthly accumulation
19
» Monthly accumulation
1Q L Season of 1937-38
17
16
15
14
13
12
I10
I 9
§ 8
t '
^ 6
5
4
TEMPERATURE
— • — Monthly mean • normal
• Monthly mean
3 1 // Season of 3
2
I
Sept Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug.
FIG. 28. Precipitation and temperature data, University Farm, Moscow, Idaho,
for the crop year 1937-38 as compared with the normal. Precipitation data are
presented on the basis of monthly accumulations, temperature data as monthly
averages.
Length of the Growing Season. The length of the growing
season is generally defined as the interval in days between the last
killing frost in spring and the first killing frost in fall. A temper-
ature depression of sufficient severity to be generally destructive
to the staple crop plants of the locality is regarded as a killing
frost. Frequently vegetation has not developed sufficiently in spring
to be injured by frost, or the main crops of a region may be fully
matured before the occurrence of the first frost in fall. It is difficult
under such conditions to determine the dates of the killing frosts by
214 ECOLOGICAL CROP GEOGRAPHY
direct observations of effects on vegetation. In such cases the
length of the growing season is determined by the interval between
the last date in spring on which a temperature of 32°F was recorded,
and the first date at which the temperature again dropped to that
point in fall.
The length of the growing season for any given location may
vary materially from year to year. For a 45-year period, 1 893-1 938,
at Moscow, Idaho, the average was 149.71 days; the range extended
from 83 to 192 days; the standard deviation was 24.36.
Figure 29, after Day and taken from Redway's Handbook of
Meteorology (43), gives the length of the growing season for the
different parts of the United States. More detailed maps of the
length of the growing season and also of the dates of occurrence of
the last killing frosts in spring and the first in fall are given by
Reed (44). In the Mississippi Valley the lines show a trend from
east to west, the effects of river bottoms and topographical features;
proximity of large bodies of water is apparent, however. The
length of the growing season is extremely variable in the various
areas of the mountainous western portion of the country. These
differences are accounted for by* variations in elevation and in
part by the influences of the Pacific Ocean and the particular
topographical features enabling the influence of this large body
of water to be felt inland.
Thermal and Physiological Growing Season. It will be well
at this point to refer back to Chapter X, particularly to the topic
of vegetation and climatic rhythms in their relation to adaptation.
The term "length of growing season" is generally used, as in the
previous discussion, to designate the frostfree period of any region;
that is, it is determined strictly by the prevailing temperature
conditions with a total disregard of the other factors of the environ-
ment. It is useful as such and has its place, but it must be recog-
nized that it expresses only what may be designated as the thermal
growing season. The growth of plants or the ability of an environ-
ment to support active growth is dependent on a constellation of
factors of which temperature is but one. As a matter of fact the
intensity of the temperature factor may, and in many instances
does, in the course of the season, bring about the very condition
throwing some other essential factor of the environment below the
minimal requirements for growth. In many habitats the lack of
215
216 ECOLOGICAL CROP GEOGRAPHY
moisture during the frostfree season may force vegetation into a
period of dormancy so that two periods of plant activity, rather
than one, may be in evidence. This is the case in the Mediterranean
type of climate. Those periods when not only temperature but
also the other essential factors of the environment are favorable
to growth may be designated as the physiological growing season.
The agronomic significance of this distinction is evident.
Thermal Belts. The effects of local topography on the occur-
rence of killing frosts is well illustrated by the location of warmer or
"frostfree" zones on slopes or up on the sides of valleys. The down
drainage of cool heavy air results, in the absence of equalizing
winds, in higher temperatures at adjacent heights of moderate
elevations than in the bottoms of the valleys where the cool air
settles. The air on the slopes may be replaced for some time by
somewhat warmer air from the higher slopes. Not infrequently a
difference of as much as 10°F may be recorded between the tem-
perature at valley bottoms and that some distance up the sides.
This may result on concentric belts on the slopes where vegetation
will escape frost damage. These thermal belts and the question of
air drainage in general are of considerable importance in selecting
areas for the production of crops subject to frost damage.
The phenomenon of the rather common occurrence of higher
night and early-morning temperatures at higher rather than at
lower altitudes in areas of rough topography is known in meteor-
ology as temperature inversion.
Limits to Crop Production. Figure 30, taken from Baker (4),
gives the great agricultural regions of the United States. They are
designated primarily on the basis of the important crops grown in
the various agricultural provinces. The six regions of the West
have been given topographic and geographic names because of the
dominating influence of topography and the Pacific Ocean. A
comparison of Figs. 29 and 30 shows the effect of the length of the
growing season and temperature in general on the location of the
great agricultural regions.
Figure 31 gives the northern limits of general production of the
four winter cereals in order of their respective degrees of winter-
hardiness. The northern limit of winter rye production is found in
the prairie provinces of Canada. Salmon (47) points out that the
isotherm of 10°F for the daily minimum temperatures of January
217
218
ECOLOGICAL CROP GEOGRAPHY
and February corresponds in general to the line separating the
areas of extensive winter and spring wheat production.
The extreme northern limit of all crop production is determined
almost entirely by temperature conditions. The longer length of
the days at higher latitudes compensates in part for the lower
average temperatures of these regions.
Fio. 31. The northern limits of production of winter oats, barley, wheat, and rye.
EFFECTS OF LOW TEMPERATURES
Chilling and Freezing of Plants. A summary of the extensive
literature available on the effects of low temperatures on plant
growth and survival would be entirely beyond the scope of this
chapter. An extensive, annotated bibliography of the literature is
presented by Harvey (12).
In discussing the effects of low temperatures on plant life, it is
well to differentiate between the results of freezing and chilling.
The discussion dealing with freezing temperatures will be presented
here primarily as it relates to the winterkilling or survival of cereals
and such other crop plants which ordinarily survive one or more
winters. The chilling of plants, that is, exposure to temperatures
that are low but above the freezing point, has decided detrimental
effects, especially on certain plants of southern origin, and thus
TEMPERATURE 219
serves to limit their distribution. The effect of relatively low night
temperatures also has interesting agronomic ramifications.
EFFECTS OF LOW TEMPERATURES ABOVE THE
FREEZING POINT
The Chilling of Plants. The chilling of plants not only has
retarding effects but may leave some species definitely injured.
Molisch (29) critically reviewed the early literature on this subject.
Molisch (31) referred to the early work of Sachs with tobacco,
squash, and kidney beans. The leaves of these plants wilted when
exposed to temperatures of from 2 to 4°C. When the plants were
covered with bell jars, so that transpiration was reduced, they were
undamaged by the low temperatures. Evidently the injury could
be attributed in many instances to the inability of the roots to absorb
and convey sufficient water from the cold soil to the leaves to correct
the transpiration deficit; hence, the plants were exposed to physi-
ological drought. This, however, Molisch showed was not the case
in all plants.
Sellschop and Salmon (56) report on recent experiments on the
responses of crop plants to chilling. On the basis of their results
they divided the plants investigated into five classes in accordance
with their respective reactions to low temperatures above the
freezing point.
1. Plants killed by an exposure of 60 hours to temperatures from
0.5 to 5°C — rice, velvet beans, cowpeas, and cotton.
2. Plants decidedly injured by the above indicated exposure but
able to recover with favorable conditions — sudan grass, Teff grass,
Spanish and Valencia peanuts.
3. Plants which in general are not likely to suffer serious injury by
the conditions specified above — Virginia Bunch peanuts, maize, sor-
ghum, watermelons, and pumpkins.
4. Plants noticeably injured by prolonged chilling, but in which
injury by the conditions specified above is likely to be nominal — buck-
wheat, Tepary beans, and soybeans.
5. Plants which when exposed at 0.5 to 5°C were not injured so far
as could be observed — potatoes, sunflowers, tomatoes, and flax.
Temperatures of around 40°F, especially if followed by a period
of rainfall, may result in injuries to tender plants growing under
field conditions. Paris (8) observed white bands two to four inches
in width across the leaves of sugar cane plants. Cold weather not
220 ECOLOGICAL CROP GEOGRAPHY
preceded by rainfall resulted in only slight chlorotic bands. Sells-
chop and Salmon also report the occurrence of irregular chlorotic
areas on the leaves of sorghum and corn plants that had been
chilled for 60 hours at 2 to 4°C. These commonly observed white
bands are referred to as Paris or chill bands.
Sellschop and Salmon suggest the deficiency of oxygen in wet
soils as a contributing factor to the accentuation of chilling in-
juries on such soils. Possibly low temperatures interfere with the
respiratory ratios of plants; in the event of incomplete oxidation
harmful products will accumulate in the plant cells. Nelson (35)
suggests the possibility that there may be at low temperatures a
liberation or accumulation of certain toxic fragments resulting
from the mixing of hydrolytic enzymes and glucosides. Interference
with the proper functioning of the protoplasm prevents the removal
of these toxic compounds in the normal manner at low temperatures.
Effect of Cold Irrigation Water. Instances have been observed
where the applications of irrigation water of low temperature tem-
porarily checked the growth of plants. The lowering of soil tem-
peratures by applications of cold water tends to slow down all
biological processes in the soil anfi jndirectly influences nutritional
relationships, especially the supply of available nitrogen.
Effects of Relatively Low Night Temperatures. The rate of
accumulation of carbohydrates for any given interval of time in
plants is determined by the balance of assimilation over respiration.
While the absence of sunlight does not interfere with metabolism
and the translocation of assimilates at night, green plants are able,
owing to their dependence in photosynthesis on light, to produce
organic food only in the daytime. Growth in the absence of light
is due of course to the reworking of the carbohydrates accumulated
during the previous day.
Night temperatures low enough to interfere with metabolism
are detrimental. The cardinal points may be expected to show
material differences in this respect not only for different plants, but
also during the various phases of development of the same plant.
It is fairly safe to venture the statement, though detailed experi-
mental data are needed on this point, that plants of southern origin
such as cotton, tobacco, sorghums, and corn demand higher night
temperatures for maximum growth than such northern plants as
potatoes, sugar beets, and the cereals.
TEMPERATURE 221
So much for growth in general. Respiration, it must be kept in
mind, plays an ever-important part in plant life, not only during
the hours of sunlight, but also during the hours of darkness. Ratios
of respiratory activity and with them losses of carbohydrates are
determined largely by the temperatures to which plants are ex-
posed. The lower the night temperature the lower will be the loss of
organic materials through respiration. In those plants not damaged
by low night temperatures, or in cases where the temperature is not
sufficiently low to interfere with metabolic processes and trans-
location, it is entirely possible to ascribe beneficial effects to rela-
tively low night temperatures on the basis of the reduced losses of
carbohydrates.
Lundegardh (23) gives an example of the above. If the assimila-
tion of an oat field is taken at 300 kilograms per day with the losses
through respiration set at 175 kilograms (at 20°C), then the net
gain will be 300 — 175 = 125 kilograms. If now the night tem-
perature drops to 10°C, then the losses through respiration are,
according to Lundegardh5 s estimate, reduced to 44 + 88 = 132
kilograms (12 hours at 20°C, 12 hours at 10°C). The net gain under
those conditions would then amount to 300 — 132 = 168 kilograms,
or an increase of 30 per cent.
The very rapid building up of carbohydrates in late potatoes and
sugar beets and to a lesser degree in the cereals is associated rto
doubt not only with favorable light, moisture, and temperature
conditions during the day, but also with the favorable effects of
relatively low night temperatures.
EFFECTS OF TEMPERATURES BELOW THE
FREEZING POINT
Early Conceptions of Freezing Injuries. The early Greek
philosophers attributed plant injury in freezing to the rendering
and mashing of the various plant organs by the formation of ice
which they found often enough to make such injury appear plausi-
ble. It was not until some knowledge had been gained of the
cellular structure of plants that a more definite theory was advanced
by Buffon and Duhamel in 1737. They ascribed the cause of death
to the formation of ice within the plant cells. It was assumed that
cell sap would, upon freezing, expand enough to rupture the cell
walls.
222 ECOLOGICAL CROP GEOGRAPHY
Ice Crystals Usually Formed in Intercellular Spaces. Goep-
pert in 1830 showed for the first time that the cell walls remained
intact during the freezing process and even after thawing. He also
pointed out that the formation of ice crystals occurred in some
instances in the intercellular spaces rather than within the cells.
Sachs (46) in 1860 showed that the ice formed in nearly all cases
in the intercellular spaces. Both Sachs and Nageli demonstrated
that the expansion of all the cell sap in freezing would not exert
sufficient pressure to rupture the cell walls. Relatively large aggre-
gations of ice may be formed in the intercellular spaces without
necessarily resulting in irreparable damage to the protoplasm or to
protoplasmic arrangement.
The Desiccation Theory. Muller-Thurgau (32) and Molisch
(30) advanced the theory that death was primarily due, not to the
direct effects of low temperatures, but rather to the physical and
chemical changes induced by the removal of water from the cell.
It is a well-known physical phenomenon that water freezing out of
solutions is almost chemically pure. Since almost pure water is
removed from the cells and crystallized in the intercellular spaces,
the concentration of the cell sap if increased with the continuance
of the freezing process and successive removals of water from the
cells. Muller-Thurgau and Molisch concluded that some of the cell
water of plants surviving exposures to low temperatures remained
in the liquid form as thin films surrounding the protoplasm or
between the ice crystals and the cell walls. In cases where such
plants failed to survive, death was attributed to alterations of the
proteid bodies such that the cells were unable to reabsorb the
extracted water upon thawing.
Chemical Injury to Protoplasm. Gorke (9) found upon ex-
amining the cell sap of barley plants that less nitrogen could be
precipitated from the extracted sap of frozen than of unfrozen
plants. The data so obtained were used as evidence to show that a
portion of the cell proteids had been precipitated during the freez-
ing process. The reaction of the cell sap is acid; with successive
removals of water from the cell the concentration of the cell solution
is increased under conditions to the point where a portion of the
proteins may be precipitated or "salted out." The precipitation of
cell contents is not limited to the protein constituents; soluble
carbohydrates may also be affected.
TEMPERATURE
225
Schaffnit (51) brings out that death traceable to the precipitation
of cell proteids is likely to occur especially in spring or even in
summer, or at any time when an active plant is suddenly checked
by low temperatures. The complex proteins produced during
periods of rapid growth are readily precipitated. On the other
hand, plants grown at relatively low temperatures produce less
complex and more resistant proteins. During the hardening
process, complexes in the plasma are transformed into simpler
combinations more resistant to possible precipitation.
Phase Sequence of events in the tissues of plants
I
2
Attractive action to
centers of crystallization
Increasing concentration
of salts in cell solution
Continued
growth of
ice crystals
Formation of
cryohydrates
with continued
depression of
temperatures
Extracellular ice formation
Frost plasmolysis -
Accumulation of water
from adjoining cells
— Removal of cell sap
Injury to
the inner
plasma
layer
Coagulation
plasma wall
Interference with
• the osmotk functions
of the plasma layer
Coagulation of the
proteins of the -
protoplasm
Entrance of concentrated
solutions of electrolytes
and acids in the cell sap
Death of the cell
FIG. 32. The course of events incident to the freezing of plants. (After
Schander and Schaffnit.)
Schander and Schaffnit (52) give an outline of the sequence of
events in the tissue of plants during the freezing process. The vari-
ous phases and occurrences are presented in Fig. 32.
Evaluation of Degree of Hardiness of Crop Plants Living over
Winter. Various methods for evaluating relative degrees of winter-
hardiness of varieties and strains of crop plants ordinarily surviving
one or more winters have been advocated from time to time. The
physical and chemical properties of the winter wheat especially
have been investigated in detail in this connection. Standards of
hardiness, while showing fair degrees of correlation with actual
field survival for a given locality, are often found to lack universal
application. Also a given criterion for hardiness may be of value
224 ECOLOGICAL CROP GEOGRAPHY
for a definite period or for a certain set of conditions only. Since
death may result from a number of causes and since winter annuals
and perennials are grown under a wide range of environmental
conditions, it is not surprising that no one standard of hardiness
so far advanced has universal application. Even in the same lo-
cality, damage to the crop may result from a different set of condi-
tions in different seasons. In this same connection it must be
recognized that plants differ not only with respect to one specified
characteristic but with regard to many factors. This fact has often
been overlooked in the evaluation of hardiness in different species.
Because of differences in cell structure and other peculiarities, only
closely related plants and in crop plants only varieties of the same
species should be compared in the evaluation of any one specific
factor associated with hardiness. This would avoid much confusion
and conflict of data.
As a result of his studies on winter wheat, Martin (25) comes to
the conclusion "that no laboratory method yet devised, except per-
haps controlled freezing, is any more accurate for determining
hardiness than is careful field study." Salmon (50) points out that
artificial freezing under control^d conditions may be used to ad-
vantage for the evaluation of winter survival of thoroughly hard-
ened varieties of wheat. Peltier (39), Peltier and Tysdal (41), and
Suneson and Peltier (62) have also demonstrated the value of arti-
ficial freezing in the evaluation of the comparative hardiness in
crop plants. Weibel and Quisenberry (66) report close correlations
between the results of controlled freezing and field tests in the
evaluation of cold resistance of varieties of winter wheat. Holbert
and Burlison (14) subjected corn plants growing under natural
conditions in the field to a range of low temperatures artificially
produced by means of a portable refrigeration unit. Some strains
of corn were found to show marked differences in their reactions
to above-freezing and subfreezing temperatures.
PLANT CHARACTERISTICS ASSOCIATED WITH
COLD RESISTANCE
Morphological Plant Structures. An extensive literature is
available on the topic of plant form and general morphological
structures in relation to cold resistance. It can be but briefly
touched upon here.
TEMPERATURE 225
Schaffnit found no relationship between the development of
external plant characteristics and cold resistance. Schimper (53)
comes out with the definite statement that the "capacity to withstand
intense cold is a specific property of protoplasm and is quite un-
assisted by protective measures that are external.5" Nilsson-Ehle
(37), as a result of his breeding experiments, concluded that the
degree of winter-hardiness of wheat stands in no definite relation
to the ordinary morphological varietal characteristics.
In contrast to the above, a considerable number of other inves-
tigators report varying degrees of correlation between certain
obvious external plant characteristics and hardiness. Sinz (57)
designated hardy varieties of wheat as having narrow, firm, and
well-cutinizcd leaves. Buhlert (7) in comparing the winter-hardi-
ness of a limited number of varieties of winter wheat and rye found
that the hardy varieties, especially of the winter rye, had thicker
and narrower leaves than nonhardy types. Arnin-Schlangenthin
(3) points out a correlation between dwarfness and hardiness in
winter wheat.
Schlicphackc (54) characterizes hardy varieties of winter wheat
by narrow, cuneiform leaves. He also calls attention to physio-
logical drought as a possible factor in the winter survival of cereals.
"Physiological drought," states Salmon (48), "has never been
proved to be a cause of winterkilling of cereals, but has long been
regarded as a cause of injury to shrubs and trees." In the same
paper, however, he points out that "most of our hardy cereals
such as winter rye, Turkey and Kharkof wheat, and the Winter
Turf variety of oats, do have certain xerophytic structures charac-
terized by a narrow leaf and a prostrate habit of growth. The soft
winter wheats, winter barley, and common varieties of oats, on the
other hand, have broad leaves which usually assume a more or less
upright position and hence are more exposed to the wind." Con-
sidering the role of desiccation as a cause of injury in freezing and
keeping in mind the outstanding characteristics of hardy varieties
of cereals, most of which would serve to promote water economy in
the plant, the part played by physiological drought as a contribut-
ing cause for winter injury merits attention.
Klages (18) in investigating the relationship of leaf area of winter
wheat plants came to the conclusion that most hardy varieties have
comparatively small leaf areas. Though not an infallible index to
226 ECOLOGICAL CROP GEOGRAPHY
hardiness because of the great variety of factors that may lead to
winter injury, leaf area, nevertheless, is a characteristic worthy of
consideration in the selection of hardy types of winter wheat. It
is entirely possible that the degree of association between exposed
leaf surface and hardiness may be closer in semiarid than in humid
areas. A dry atmosphere during the winter months when the
ground is frozen puts winter annuals to a severe test.
Habit of Growth. Hardy varieties of winter wheat are com-
monly believed to have a more or less procumbent habit of growth
(Salmon, 48, Summerby, 61, and Schmidt, 55). While this is
generally true and readily explained on the basis of less exposure to
desiccating winds, some notable unconformities prevent the utiliza-
tion of this particular varietal characteristic as an absolute criterion
of hardiness.
Klages (18) pointed out that while differences in habits of growth
do not stand in absolute relationship to hardiness, an erect growth
habit of seedlings during the fall and winter months is a better
indicator of lack of resistance than a recumbent habit of growth an
indicator of hardiness.
Profuse tillering has frequently been associated with hardi-
ness. No such relationship was found, however, by Barulina (5) or
Klages (18).
Anatomical Features. Molisch (30) and Muller-Thurgau (32)
expressed the opinion that the microscopic minuteness of the plant
cell had to be considered, at least to a certain degree, as a protective
means against the effects of low temperatures.
Nonhardy varieties of wheat generally have larger cells than the
hardy wheats of the Turkey type; however, this is but one of the
numerous differences between these types. On the other hand,
firmness of leaves and in part highly cutinized leaves are not in-
frequently associated with a small compact cellular structure.
Rate of Growth. "Any treatment materially checking the
growth of plants," states Rosa (45), "increases cold resistance."
Horticulturists have long recognized the importance of dormancy,
and reduced activity, as a protective measure against frost injury*
It would appear, then, that hardy varieties of winter wheat should
show a slowey rate of growth than nonhardy types. This was found
to be generally true by Buhlert (7) and Hedlund (13). Wall&i (65)
pointed out the undesirability of high autumn temperatures in
TEMPERATURE 227
relation to the winter survival of wheat in southern Sweden. Such
supranormal temperatures would of course lead to increased activity
on the part of fall-sown wheat. Klages (18) found that hardy varie-
ties of winter wheat generally showed a less rapid rate of growth in
the field in autumn than did nonhardy types.
Chemical Factors. Since the lowering of the freezing point of a
solution is directly proportional to its molecular concentration, it
has been assumed by numerous investigators that the freezing point
of cell sap would be lowered as its density increases. Thus Ohlweiler
(38) states that extreme differences in cell sap density, in general,
are accompanied by corresponding differences in their resistance
to cold. Macfarlane (24) notes that "all thermo-resistant plants
have a relatively dense protoplasm, or a stored mass of reserve
material in their cells that contribute to their thermo-resistant
qualities." Graber and his associates (10) point out the relation-
ship of organic reserves to winter-hardiness in alfalfa. Late cutting
of alfalfa lowered organic reserves to the extent that the plants
were subject to severe winterkilling.
Lidforss (22) reports that the starch in plants remaining green
during the winter months is converted into sugar upon the approach
of low temperatures. Miiller-Thurgau (33) notes the increase in the
sugar content of potato tubers upon exposure to low temperatures.
Ackerman and Johannson (2) report the various degrees of frost
resistance of the principal Swedish wheats to be correlated with
their sugar and dry-matter contents. Maximov (26) increased
resistance to freezing by introducing such substances as sugar,
glycerine, and alcohol into the tissues of plants.
The protective action of sugar has been accounted for, not only
by its effect on lowering the freezing point of the cell sap, but also
by the fact that the increased concentration of the cell sap is instru-
mental in decreasing water losses through transpiration.
Hooker (15) found a correlation between hardiness and the
pentosan content of plants. He called attention to the great water-
holding abilities of the pentosans. The water is held in an adsorbed
or colloidal condition. The capacity of hardy plants to resist the
desiccating effects of extreme cold was by him accounted for by the
lower free but proportionately greater colloidal water content
of such plants. Newton (36) found that hardened tissue of winter
wheat was able to retain its water content against great force;
228 ECOLOGICAL CROP GEOGRAPHY
such tissue contained a high amount of bound water. Steinmetz
(60) found that the roots of a hardy variety of alfalfa contained more
sugar than those of a less hardy variety. Sugar content was ex-
pressed in terms of total carbohydrates. Steinmetz was unable to
demonstrate quantitative relationships between pentosan content
and hardiness in alfalfa.
Variations in Frost Resistance of Plant Parts and Effect of
Age of Plants. Schaffnit found that the tips of young growing
sprouts of wheat showed considerable resistance to cold. This he
attributed to the presence of bud scales and to the colloidal state of
certain cell contents. Martin reports the crown as the most hardy
portion of wheat plants above the soil surface. Young leaves were
found to be more hardy than older ones, and the bases of leaves
more hardy than the tips.
Klages (17) showed that unhardened winter wheat seedlings
become more susceptible to low temperatures with advance in age.
This was confirmed by Suneson and Peltier (63), who showed that
the "youngest plants appear to be most hardy, regardless of the
type of hardening." Peltier and Kiesselbach (40) report that spring
cereals "just emerging from the soiLor in the one-leaf stage were
found materially more resistant to cold than seedlings in the two-
and three-leaf stages."
EXTERNAL FACTORS MODIFYING THE DEGREE
OF FROST INJURY IN PLANTS
Rate of Freezing and Hardening. Ohlwcilcr brings out that
the effect of cold upon vegetation in general depends largely upon
the rapidity with which destructive changes in temperature are
brought about, being far greater when the change takes place
within narrow limits of time.
The main effect of hardening is that time and opportunity are
given the plant to adjust itself to its changing environment. Thus,
Salmon (48) states, "slow freezing may decrease the injury by
preventing the formation of ice within the cells, by giving the tissue
an opportunity to dry out and by permitting the protoplasm to
adjust itself to the new condition."
That the formation of protective substances is dependent upon
the rate of cooling was well illustrated by Miiller-Thurgau (33).
Potato tubers held at a temperature of — 1 to — 2°C contained
TEMPERATURE 229
from 1.62 to 2.43 per cent of sugar as compared to a sugar content
of 0.4 to 0.7 per cent before the hardening.
"The principal effect of the hardening process for cabbages,"
states Harvey (11), "is a change in the constitution of the proto-
plasm which prevents their precipitation as a result of the physical
and chemical changes incident upon freezing."
Rate of Thawing. Death of nonhardy plants is most likely to
occur during the freezing process and in cases even before freezing
temperatures are reached; that is, the protoplasm is injured beyond
possible repair. Pfeffer (42) observed that "a non-resistant plant
is killed by the actual freezing and cannot be saved by the most
careful thawing, whereas resistant plants remain living however
rapidly they may be thawed."
Abbe (1) gives a good summary on the question of rate of thawing
in its relation to survival in the following paragraph.
"When the frozen plant is thawed out and evaporation is rapid, the
loss of water cither from the surface of the tender plant or through the
stomata of the mature plant is much more rapid than under normal
conditions and the plant wilts, but when there is no evaporation, the
sap has time to return into the cells, and the wilting is not so severe.
Therefore, it is proper to say that the injury is not done by more or less
rapid thawing, but by more or less rapid evaporation that accompanies
the thawing. If similar plants are thawed out under warm and cold
water, respectively, the rate of thawing has no influence on its health.
It is now seen that this is because in both these cases there is no special
chance for evaporation, and the cell sap was able to go back into the
cells; the contrary occurs when the plant thaws in the open air."
Alternate Freezing and Thawing. Lamb (21) aptly points
out that winter-hardiness is often loosely considered synonymous
with cold resistance when, as a matter of fact, it must be recognized
that winter injury may be due to secondary effects of low tempera-
tures, such as smothering under ice or tightly packed snow, or up-
heaval of the plants due to alternate freezing and thawing. It is a
well-established fact that successive exposures to low temperatures
are more detrimental than single exposures.
Heaving. "In the soft wheat belt of the Northeastern United
States, it is only in exceptional seasons," states Lamb, "that winter
wheat is killed by the direct effects of low temperature. In the
opinion of workers long associated with this area, the most common
230 ECOLOGICAL CROP GEOGRAPHY
cause of injury is probably heaving; that is, the pulling of the plants
from the soil when the surface is raised up by frost action."
An excellent review of the mechanics of heaving and the condi-
tions necessary for its occurrence is given by Miinichsdorfer (34).
Heaving of soil is not a simple physical process occasioned by the
transformation of soil water from the liquid to the solid state. Maxi-
mum raising of the surface soil takes place under conditions favoring
the separation of ice layers in the surface soil mass. The raising of
the soil surface is almost entirely due to the formation of the ice
layers and is practically equal to the sum of the thickness of these
layers.
The control or possible reduction of heaving injury may be ap-
proached from the soil and plant angles. The water table of the
soil may be lowered by proper drainage. Winter annual crops
may be planted early to allow strong crown and basal foliage
growth to blanket the soil so that surface temperature fluctuations
may be reduced. Lamb was able to measure slight differences in
the extensibility and breaking tension of roots of varieties of winter
wheat. Kokkonen (20) reports dq£nite association between tensile
strength and extensibility of the rbots of winter rye and winter
survival in Finland. Heaving damage in alfalfa and clovers may be
reduced by allowing the plants to enter the winter months with a
sufficient top growth to modify surface soil temperatures.
Soil Moisture and Soil Type. Because of the higher specific
heat of water, 1.000, as compared to that of soil particles, 0.193
for sand, 0.206 for clay, and 0.215 for loam, a soil containing a large
amount of water will cool down less rapidly than a drier soil but,
for the same reason, will warm up more slowly. Bouyoucos (6)
found that the temperatures of different soil types were remarkably
alike throughout the summer, fall, and winter months. The greatest
differences appear in spring, that is, during thawing. Thus, sand
and gravel thaw first, followed by clay and loam one or two days
later and by peat 10 or 15 days later.
Under field conditions the temperature of moist soils is less subject
than dry soils to wide fluctuations at moderately low temperatures.
After soils are once frozen, temperature fluctuations will not differ
greatly. Salmon (49) sums up his investigations of the relationship
of soil moisture and soil type to winterkilling with the statement
that
TEMPERATURE 231
"a sandy soil is colder and the survival of plants growing upon it
less than a dry clay or loam soil, and also colder than a wet clay or a
wet loam during those seasons when the ground remains unfrozen
much of the time. It appears probable that a dry sand is colder during
the winter than a wet sand regardless of the character of the season,
but a dry clay or silt loam is colder than a wet soil of the same kind
only when the ground remains unfrozen."
Hunt (16) states that the loamy soils of the Corn Belt, which are
asually friable and well supplied with organic matter but often
Doorly drained, are not so well adapted to winter wheat as are the
:lay uplands; wheat on the former soils is more likely to winterkill
.n unfavorable seasons. Hunt here refers to damage from heaving
*vhich is definitely favored by wet soils and conditions conducive
:o good capillary movement of water.
Soraucr (59) observed dry parts of fields to suffer more from frost
than moist areas.
Protection of Winter Annual Crops. Various means have been
used from time to time to create a more favorable environment for
winter annual plants during periods of stress. One of the most
effective methods is to provide a favorable place in the rotation
for the winter annual so that the plants may be protected to some
extent by the remains of the previously grown crop. A good ex-
ample of this is the planting of winter wheat in standing corn stalks
Dr on stubble land with a minimum of disturbance to the stubble so
that they may serve to protect the wheat plants during the winter.
Klages (19) reports a yield of 21.5 bushels and only 1 crop failure
in 18 years due to winterkilling of wheat having the protection of
ten-inch-high stubble of checked corn as compared to a yield of
only 13.1 bushels per acre and 5 crop failures due to winterkilling
in the case of the crop grown in a similar rotation but following
oats, after the harvesting of which the land was plowed. The corn
stubble provided little protection, but enough to reduce the velocity
of the wind to some extent and thus reduce water losses from the
leaves of the wheat plants either by the direct protection or, in years
with snowfall, by catching and holding a snow cover.
Furrow drills are used in certain areas for the double purpose of
placing the seed in contact with soil moisture and for providing
protection for the seedlings against drying winds.
232 ECOLOGICAL CROP GEOGRAPHY
EFFECTS OF HIGH TEMPERATURES
External Temperatures in Relation to Plant Temperatures.
In most plants the temperatures of the various plant parts do not
differ materially from those of the surrounding air or medium.
Fleshy leaves may at times have a temperature materially higher
than those of the surrounding atmosphere. Ursprung (64) found
the surface of the leaves of Sempervivum to attain a temperature of
18 to 25°G higher than that of the surrounding air in sunlight.
Owing to the thickness and nature of such leaves, the heat they
absorbed cannot be dissipated as readily by air currents or radiation
as in the case of ordinary leaves.
Miller and Saunders (28) found that the temperatures of the
upper surfaces of leaves of corn, sorghum, cowpeas, soybeans, water-
melon, and pumpkin growing under field conditions in Kansas were
essentially the same as those of the surrounding air. The leaves of
alfalfa, on the other hand, showed under the same condition a tem-
perature of less than 1°C below that of the air. In the case of the
plants enumerated above the he^t absorbed is quickly utilized in
transpiration or rapidly disseminated into the surrounding air, so
that the temperature of the leaves approximated that of the air. "In
the case of alfalfa the rate of transpiration is evidently rapid enough
to reduce the temperature of the leaf slightly below that of the air.
In diffuse light, turgid leaves show a temperature somewhat
below that of the atmosphere. Air currents have a tendency to
lower the temperature of leaves in direct sunlight. Smith (58)
observed that breezes reduce the temperature of leaves in sunlight
by from 2 to 10°C. Obviously thin leaves are more noticeably
affected than thick ones. The leaves of crop plants, states Miller
(27), respond quickly to changes in air temperature; even slight
changes are almost immediately followed by corresponding changes
in the temperature of the leaves.
The temperatures of turgid and rapidly transpiring leaves under
corresponding conditions of exposure are lower than those of wilted
leaves or leaves in which the rate of transpiration was reduced.
Miller and Saunders report a maximum difference between the
wilted and turgid leaves of cowpeas of 6.7°C when the temperature
of the air was 37.6°C. The transpiration of the wilted leaves was
approximately only one-sixteenth that of the turgid ones.
TEMPERATURE 233
Death Due to High Temperatures. Temperature, as pointed
out earlier, provides a working condition for plant functions. The
plant, however, will respond effectively, that is, it will continue to
grow, only at temperatures within certain more or less specific
ranges. These general limits have been taken up in the discussion
of cardinal points, Chapter VIII. The response of plants within
the limits set by the cardinal points will be discussed in detail in the
next chapter relating to temperature efficiencies.
The growth of plants is slowed down materially upon the sur-
passing of the optimal temperature; it ceases beyond the maximum,
but life may not be in immediate danger unless exposure to supra-
maximal temperatures continues for too long a period. Under
field conditions it may be assumed that crop plants or portions of
them arc not killed by the direct effects of the temperature as such,
but rather by the secondary effects induced by high temperatures
such as inability of the plant to reestablish the necessary water
balance, the dehydration of the protoplasm, or sometimes by a
partial precipitation of the cell proteins. Generally, though not
always, heat damage to crops is associated with and is most intense
under a combination of drought and high temperatures. Low
availability of moisture and heat occurring in combination are
disastrous in that high temperatures increase the requirements for
moisture by the exposed portions of the plant. If rapidly moving
air currents are added to this dreaded combination, destruction is
soon complete. Even hot winds alone, with an abundance of water
available for the use of the plants, may be very destructive in that
the ability of the plant to provide water for the rapidly transpiring
more exposed portions may be taxed beyond the limit.
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234 ECOLOGICAL CROP GEOGRAPHY
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wheat seedlings to low temperatures," Jour. Amer. Soc. Agron., 18:184-
193 (1926).
18. , "Metrical attributes and the physiology of hardy varieties
of winter wheat," Jour. Amer. Soc. Agron., 18:529-566 (1926).
19. , "Winter wheat production in South Dakota," S. D. Agr.
Exp. Sta. Bull. 276, 1933.
20. Kokkonen, P., "Uber das Verhaltnis der Winterfestigkeit des Roggens
zur Dehnbarkeit und Dehnungsfestigkeit seiner Wurzeln," Ada
Forestalia Fennica, 33:1-46 (1927).
21. Lamb, C. A., "Tensile strength, extensibility, and other character-
istics of wheat roots in relation to winter injury," Ohio Agr. Exp. Sta.
Bull. 568, 1936.
22. Lidforss, B., "Zur Physiologic und Biologic der Wintergriinen Flora,"
Bot. Ccntbl., 68:33-44 (1896).
TEMPERATURE 235
23. Lundeg&rdh, H., Klima und Boden in ihrcr Wirkung auf das Pflan&nleben.
Gustav Fischer, Jena, 1925.
24. Macfarlane, J. M., The relation of plant protoplasm to its environ-
ment. Jour. Acad. Nat. Sci. Phila. 2, Ser. 15:135-143 (1912) (Abstr. in
Exp. Sta. Rec., 28:326-327 (1913).
25. Martin, J. H., "Comparative studies of winter hardiness in wheat,'*
Jour. Agr. Res., 35:493-535 (1927).
26. Maximov, N. A., "Chemische Schutzmittel der Pflanzen gegen
Erfrieren," Ver. Deut. Bot. Gesell., 30:52-65 (1912).
27. Miller, E. C., Plant Physiology with Reference to Green Plants. McGraw-
Hill, New York, 1938.
28. , and A. R. Saunders, "Some observations on the temperature
of the leaves of crop plants," Jour. Agr. Res., 26:15-43 (1923).
29. Molisch, H., "Das Erfrieren von Pflanzen bei Tempera turen iiber den
Eispunkt," Sitter Akad. wiss. Wien, Math. Naturw. A7., 105 (l):82-95
(1896).
30. f Untersuchungen uber das Erfrieren der Pflanzen. Jena, 1897.
31. , Populdre biologische Vortrdge. Gustav Fischer, Jena, 1922.
32. Miiller-Thurgau, H., "Uber das Gefrieren und Erfrieren der
Pflanzen," Landw. Jahrb., 9:133-189 (1880).
33. , "Uber Zuckeranhaufung in Pflanzenteile in Folge niederer
Temperatur," Landw. Jahrb., 11:751-828 (1882).
34. Miinichsdorfer, F., "Die Mechanik des Bodenfrostes," Die Erndhrung
derPflanze, 31:61-66 (1935).
35. Nelson, R., "Storage and transportational diseases of vegetables due
to suboxidation," Mich. Agr. Exp. Sta. Tech. Bull. 81 (1926).
36. Newton, R., "A comparative study of winter wheat varieties with
especial reference to winterkilling," Jour. Agr. Sci., 12:1-19 (1922).
37. Nilsson-Ehle, H., "Zur Kenntnis der Erblichkeitsverhaltnisse der
Eigenschaft Winterfestigkeit beim Weizen," ^eit. f. Pflanzenzuchtung,
1:3-12(1912).
38. Ohlweiler, W. W., "The relation between density of cell sap and
freezing point of leaves," Twenty-third Ann. Report. Mo. Bot. Gardens,
101-131 (1912).
39. Peltier, G. L., "Control equipment for the study of hardiness in crop
plants," Jour. Agr. Res., 43:177-182 (1931).
40. , and T. A. Kiesselbach, "The comparative cold resist-
ance of spring small grains," Jour. Amer. Soc. Agron., 26:681-687
(1934).
41. , and H. M. Tysdal, "A method for the determination of
comparative hardiness in seedling alfalfas by controlled hardening*
and artificial freezing," Jour. Agr. Res., 44:429-444 (1932).
236 ECOLOGICAL CROP GEOGRAPHY
42. Pfeffer, W., The Physiology of Plants, trans. A. J. Ewart, Vol. 2. Clar-
endon Press, Oxford, 1903.
43. Redway, J. W., Handbook of Meteorology. Wiley, New York, 1921.
44. Reed, W. G., Atlas of American Agriculture, Pt. II, Sec. 1. "Frost and
Growing Season," Gov't Printing Office, Washington, 1918.
45. Rosa, T. J., "Investigations on the hardening process in vegetable
plants," Mo. Agr. Exp. Sta. Res. Bull. 48, 1921.
46. Sachs, J., "Untersuchungen fiber das Erfrieren der Pflanzen," Landw.
Versuchs-Sta., 2:167-201 (1860).
47. Salmon, S. C., "The relation of winter temperature to the distribution
of winter and spring wheat," Jour. Amer. Soc. Agron., 9:21-24 (1917).
48. , "Why cereals winterkill," Jour. Amer. Soc. Agron., 9:353-380
(1917).
49. , "Relation of soil type and moisture content to temperature
and winterkilling," Science, 47:173 (1918).
50. , "Resistance of varieties of winter wheat and rye to low tem-
peratures in relation to winter hardiness and adaptation," Kansas
Agr. Exp. Sta. Tech. Bull. 35, 1933.
51. Schaffnit, E., "Uber den Einfluss niederer Temperaturen auf die
pflanzliche Zelle," %rit. Alg. Phys., 12:323-336 (1912).
52. Schander, R., and E. Schaffnit, "Untersuchungen iiber das Aus-
wintern des Getreides," Landw. Jahrb., 52:1-66 (1918).
53. Schimper, A. F. W., Plant Geography upon a Physiological Basis, trans.
German by W. R. Fisher. Clarendon Press, Oxford, 1903.
54. Schliephacke, K., "Ziele und Erfolge Deutscher Getreidcziichtung,"
Deut. Landw. Presse, 33:11-13 (1906).
55. Schmidt, O., "Uber den Entwicklungsverlauf beim Getreide," Landw.
Jahrb., 45:267-324 (1913).
56. Sellschop, J. P. F., and S. C. Salmon, "The influence of chilling, above
the freezing point, on certain crop plants," Jour. Agr. Res., 37:315-338
(1928).
57. Sinz, E., "Beziehungen zwischen Trockensubstanz und Winterfestig-
keit bei verschiedenen Winterweizen Varietaten," Jour. J. Landw.,
62:301-335 (1914).
58. Smith, A. M., "On the internal temperature of leaves in tropical
isolation with special reference to the effect of color on the tempera-
ture," Ann. Roy. Bot. Card. Peradinya., 4:229-298 (1909).
59. Sorauer, P., "Uber Frostbeschadigungen am Getreide und damit in
Verbindung stehende Pilzkrankheiten," Landw. Jahrb., 32:1-66
(1903).
60. Steinmetz, F. H., "Winter hardiness in alfalfa varieties," Minn. Agr.
Exp. Sta. Tech. Bull. 38, 1926.
TEMPERATURE 237
61. Summerby, R., "A new hardy variety of winter wheat," Sci. Agr.y
2:168-169 (1922).
62. Suneson, C. A., and G. L. Peltier, "Cold resistance adjustments of
field-hardened winter wheat as determined by artificial freezing,"
Jour. Amer. Soc. Agron., 26:50-58 (1934).
53. 9 "Effect of stage of seedling development upon the cold
resistance of winter wheats," Jour. Amer. Soc. Agron., 26:687-692
(1934).
64. Ursprung, A., "Die physikalischen Eigenschaften der Laubblatter,"
Bibt. Bot., 60:1-120 (1903).
65. Wallen, A., "The influence of temperature and rainfall on the yields
of certain kinds of wheat at Svalof and Ultuna, Sweden," Int. Rev.
Sci. & Pract. Agr., 12:804-808 (1921).
66. Weibel, R. O., and K. S. Quisenberry, "Field versus controlled freez-
ing as a measure of cold resistance of winter wheat varieties," Jour.
Amer. Soc. Agron., 33:336-343 (1941).
Chapter XVII
TEMPERATURE EFFICIENCIES AND BIOCLIMATICS
IN RELATION TO CROP DISTRIBUTION
INTRODUCTION
Numerous methods of evaluating effective temperatures have
been recommended from time to time. They may be listed, going
from the simpler to the more complex, as length of growing season,
temperature summations or the direct index, the mean maximum,
Thornthwaite's temperature efficiency index, the temperature
efficiency or exponential index, the physiological index, and the
moisture-temperature or hydrothermal index. Merriam's life zones
may be added to the foregoing array from the historical point of
view.
These various indices will be discussed in this chapter in relation
to the distribution of field crops in the United States. Their physi-
ological ramifications are interesting, but apply rather to detailed
local investigations rather than to the field of general crop distribu-
tion.
TEMPERATURE EFFICIENCY INDICES
Length of Growing Season. Since data regarding the length
of the physiological growing season could be calculated from the
climatological data of but a limited number of stations, it is neces-
sary to make use of the thermal growing season in the present dis-
cussion. The calculation of the comparable lengths of the physio-
logical growing seasons of a number of widely separated stations
representing not only different types of climates, but also a great
variety of predominating crops, would be extremely difficult.
The data for determining the length of the thermal growing season,
on the other hand, are available from all weather stations keeping a
record of minimum temperatures.
The evaluation of effective temperatures strictly on the basis of
the length of the growing season falls short of offering a true status
238
TEMPERATURE EFFICIENCIES AND BIOCLIMATICS 239
of plant behaviors and responses in that it deals only with the inter-
val in days between the last killing frost in spring and the first
killing frost in fall, with a total disregard of temperature intensities
in the interim. All plant activity near the freezing point is ex-
tremely low. Kincer (6) suggests the "zero of vital temperature
point" at 6°C or 42.8°F. This point varies with different plants in
accordance with their temperature requirements. Kincer proposes
that the zero of vital temperature be taken at the temperature
usually encountered at the date of the beginning of planting for the
respective crops considered. These temperatures would be 37 to
40°F for spring wheat, 43°F for oats, 45°F for potatoes, 54 to 57°F
for corn, and 62 to 64°F for cotton. Not infrequently, and espe-
cially in the calculation of the temperature indices to be discussed
presently, a general "zero of vital temperature point" is arbitrarily
placed at 40°F or 4.4°C.
Since the length of the growing season gives no direct indication
of the temperature conditions in the interval of time between
killing frosts the placing of this particular time unit under the head-
ing of "temperature efficiency indices55 requires a stretching of the
imagination. It will be shown later, however, that while the length
of the growing season, as such, may not merit classification as a
temperature efficiency index, it is nevertheless of definite value \n
that it shows high degrees of correlation with the more complex
and theoretically better fortified method of temperature evalua-
tions. It serves very well for the general comparison of temperature
conditions of widely separated regions.
Temperature Summation or the Remainder Index. The
direct, also termed the "remainder," index is derived by a summa-
tion of all daily positive temperatures. Positive temperatures are
those above the established zero of vital temperature point. Thus,
for instance, for a day with a mean temperature of 72, the accumu-
lation of positive temperatures would be 72 — 40 or 32.
The obvious objection to the direct index is that no recognition
whatsoever is made of the increasing rates of vital processes with
increases in temperature. This increase is, as has been pointed out
by numerous investigators, not linear or directly proportional to the
increase in the temperature, but rather (at least within certain
temperature ranges) corresponds to a logarithmic curve, concave
upward. Matthaei (11) showed that the rate of evolution of carbon
240 ECOLOGICAL CROP GEOGRAPHY
dioxide from leaves in darkness and also the fixation of this gas in
the presence of light follows quite closely the chemical principle of
van't Hoff and Arrhenius which states that the velocity of chemical
reactions doubles with each increase of approximately 10°C or 18°F.
Cohen (1) calculated from measurements recorded by Hertwig
(4) that the rate of development of frog eggs is doubled with each
increase of 10°C. The fact that the remainder index does not
evaluate accurately the separate temperatures entering into its
calculation in accordance with their true physiological .effects is well
illustrated by the wide variations found in the number of heat
units required to grow a crop to maturity in different seasons in the
same locality. Thus Seeley (15) reports that the heat units used by
corn in Ohio varied from 1,232 to 1,919 from sprouting to flowering,
and from 897 to 1,607 from flowering to maturity during a period
of 27 years.
The method of direct temperature summation does not take into
consideration the possible detrimental effects of supraoptimal tem-
peratures, although it is less at fault in this respect than the ex-
ponential index in which the effects of such high temperatures are
actually magnified.
Figure 33, taken from Livingston and Livingston (10), gives the
temperature summations for the various areas of the United States.
It will be observed that with the assumption of a "zero" point of
39°F the index for the very southern tip of Florida is given at 14,000,
for southwestern Arizona at 10,000, as compared to an index of
4,000 for the northern portion of the Corn Belt.
Thornthwaite's Temperature Efficiency Index. Thorn thwaite
(17), in developing his temperature efficiency, or T-E, index, used
in his recent classifications of climates, evaluates the effectiveness of
temperatures on a linear basis. He used an empirical formula cal-
culated to give values of the T-E index corresponding to his pre-
cipitation, or P-E, index. That is, the ranges of both of these indices
extend from zero for the least favorable to 128 for the most effective
temperature or rainfall. The empirical formula used by Thorn-
thwaite is as follows:
. 12(T -32)
'~ S 4 "
n - 1
241
242
ECOLOGICAL CROP GEOGRAPHY
In this formula / is the T-E or temperature efficiency index made
up of the summation of the 12 monthly indices for the year. T
represents the monthly mean temperature values in degrees Fahren-
heit. (The value of 32 is used for temperatures below 32°F.)
Six temperature provinces are defined on the basis of temperature
efficiency summations. These are as follows:
Temperature Provinces T-E Index
A' Tropical 128 and above
B' Mesothermal 64 to 127
C' Microthermal 32 to 63
D' Taiga 16 to 31
E' Tundra 1 to 15
F' Frost 0
Figure 34, taken from Thornthwaite, gives the temperature
provinces of the United States according to the above classification.
UNITED STATES
TEMPERATURE EFFICIENCY
Temperature province T/E Index
B'(Mesothermat)
C'( Microthermal)
ff(Taiga)
FIG. 34. Temperature efficiency provinces of the United States according to
Thornthwaite's T-E index. (After Thornthwaite.)
Thornthwaite recognizes the importance of summer concentra-
tion of thermal efficiency. Five temperature subprovinces are de-
fined. Their derivation is stated in the following two paragraphs
cited from his paper.
"The T-E index incompletely expresses the temperature relations
of the climate because of local differences in the annual march of tern-
TEMPERATURE EFFICIENCIES AND BIOCLIMATICS 243
perature. It is possible that in two stations having the same efficiency
index one may have a gradual thermal summation throughout the
whole year and the other a very rapid accumulation during a few
summer months. In order to express this difference the ratio of the
thermal efficiency accumulation of the three summer months to the
total thermal efficiency has been calculated. Expressed in percentages
these ratios range between 25 and 100, for obviously not less than
25 per cent of the total would be accumulated during the most favorable
quarter of the year.
The index of summer concentration varies with latitude and with
distance from the ocean. It is equivalent to annual range of tempera-
ture, but is a more significant climatic factor than annual range.
Although the annual range would be the same where the temperature
varies between 0°F and 40°F as where it varies between 40°F and 80°F,
it is clear that the summer concentration in the latter case would be
very much less than in the former."
The temperature subprovinces recommended are as follows:
Sub province Percentage Summer Concentration
a 25 to 34
b 35 to 49
c 50 to 69
d 70 to 99
e 100
The summer concentration of thermal efficiency for the United
States is given in Fig. 35.
Since Thorthwaite used a linear basis of evaluating the effective-
ness of temperatures, his T-E index does not differ in its application
from the direct summation or remainder index and is, therefore,
subject to the same criticism. It will be observed that the zero of
vital activity point used is 32°F.
The Efficiency or Exponential Index. The efficiency or ex-
ponential index is based on the principle of van't Hoff and Ar
rhenius. The index is derived from the summation of the calculated
efficiency of the mean daily temperatures for the period of the
average frostfree season. The efficiency index, M, for each day of
the growing season is calculated by Livingston and Livingston (10)
from the formula:
t-40
u = 2""^
The growth rate of plants is taken at unity at 40°F and is, in
accordance with the principle of van' t Hoff and Arrhenius, assumed
244
ECOLOGICAL CROP GEOGRAPHY
or
Sub
a e*****~i
I
Off ,i«t
(After Thornthwaite.)
to double with each rise of 18°F. Fdr fractional exponents the above
equation becomes more workable when written in the form:
Log u =
(/ - 40)
In the two above equations, u is the daily temperatuic c
to be calculated, / represents the normal daily mean temperature
on the Fahrenheit scale. The zero point of vital activity is taken at
40°F.
The temperature efficiency of a day with the mean temperature
of 40°F is taken at unity; with an average temperature of 58 it
doubles, and at 76 it becomes 22 or 4.
The exponential index overcomes the objection made to the
remainder index since it recognizes that plant responses to increas-
ing temperatures are not linear but rather, at least within moderate
temperature ranges, exhibit a logarithmic curve, concave upward.
The obvious fault of the exponential index is that an increasingly
high efficiency is ascribed to supraoptimal temperatures during
days or portions of days when the recorded temperatures may be
high enough above the optimum to have decided detrimental
effects.
•
S.U,
&"<=,
ll
•o ~
V
ll
•S'S
c -g
ll
ii
245
246 ECOLOGICAL CROP GEOGRAPHY
Figure 36, taken from Livingston and Livingston, gives the cli-
matic zonation of the United States according to the exponential
summation indices of temperature efficiency for plant growth, for
the period of the average frostfree season. It will be observed that
the accumulated values of the daily efficiency or exponential sum-
mation indices stand at around 1,000 units in the southern portions
of the Gulf States as compared to 400 units for the northern Corn
Belt and 350 units for the hard red spring wheat area.
The Physiological Index. Any discussion of the vital activities
of organisms must recognize the existence of physiological limits for
the various functions met with in existence and growth. It is well
established that the growth rates of organisms sooner or later cease
to increase and begin then to decrease with exposures to increasing
temperatures. The various efficiency indices so far discussed make
no allowances for the existence of the physiological limits.
The physiological temperature index is based on the researches
reported by Lehenbauer (7) on the rates of elongation of maize
shoots. Lehenbauer showed that the hourly rate of elongation of
maize shoots exposed to maintained temperatures for a period of
12 hours was 0.09 millimeters for t2°C, 1.11 millimeters for 32°C,
and 0.06 millimeters for 43°C under the conditions of his experi-
ments. The smoothed graph of the 12-hour exposure period is used
as a basis for determining the physiological indices. The graph is
extended at its ends, by extrapolation, so that the horizontal axis
is intercepted at 2°C (35.6°F) and 48°C (118.4°F). To determine
the physiological indices the ordinates of the smoothed graph are
measured for each degree of temperature considered; the numbers
thus obtained represent the average hourly rate of elongation, in
hundredths of a millimeter. Since it is often desirable to represent
the growth rate as unity at 4.4°C (40°F), all hourly rates of elonga-
tion are divided by the value obtained at 4.4°C, or by 0.907, thus
giving the physiological indices sought.
Livingston (8) presents a chart of the United States showing the
climatic zones according to the physiological summation indices
of temperature efficiency for the period of the average frostless
season. This chart is presented in Fig. 37. The average growing
season for Key West, Florida, is 365 days and shows a physiological
summation index of 31,063 as compared to a growing season of 171
days and an index of 8,417 units at Des Moines, Iowa.
$•3
ll
•is
i
11
Ill
co
248
ECOLOGICAL CROP GEOGRAPHY
Figure 38 shows the magnitude of the remainder, the exponential,
and physiological temperature efficiency indices for increasing
temperatures from 0 to 48°C, also Lehenbauer's graph of the rela-
tion of temperature to the rate of elongation of the shoots of maize
30
15
2 4T 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48
Degrees Centigrade
FIG. 38. Graphs showing increase in value of index of temperature efficiency
for plant growth (ordinates) with rise in temperature itself (abscissas), for the
three systems of indices. Graph I represents the remainder system, graph II, the
exponential one. The broken line is Lehenbauer's graph of the relation of tem-
perature to the rate of elongation of the shoots of maize seedlings. The smoothed
graph corresponding to the latter represents the physiological system of indices.
All graphs pass through unity at 4.5°C. (After Livingston.)
seedlings. The figure brings out the essential differences between
the three above-indicated temperature efficiency indices.
The relative merits of the remainder, exponential, and physio-
logical indices are discussed by Livingston (8) in the following
paragraph.
"Whenever some of the temperatures dealt with in ecological or
physiological studies are above 32°C (89.6°F) this system of physio-
logical indices for growth must give markedly different results from
TEMPERATURE EFFICIENCIES AND BIOCLIMATICS 249
those obtained with the remainder or exponential system. That natural
shade temperatures above this critical point are infrequent in regions
where ecology has been most studied, is apparently the reason why
these two indefinitely increasing series have appeared so satisfactory in
practical application, as in the cases presented by Livingston and
Livingston. But for a general system of temperature interpretation
with respect to plant growth the physiological indices are sure to be
preferred to either of the other kinds."
Pearson (13 and 14), though calling attention to the limitations
of the system of physiological indices, found a good correlation
between the distribution of different forest types and physiological
temperature efficiency summations for the months from May to
September, inclusive, in the San Francisco Mountains of Arizona.
Limitations to the Employment of Physiological Summation
Indices. The physiological indices present a clear concept of the
behavior of the experimental plant, maize, to the particular en-
vironmental conditions maintained by Lehenbauer in his experi-
ments on which the growth values are based. That they give
theoretical values is not denied. Livingston (8) summarizes their
limitations for practical ecological purposes in the following para-
graph.
"While it is quite apparent that the system of physiological indict
here described is far superior, in several respects, to the other systems
heretofore suggested, it is equally clear that these indices are to be
regarded as only a first approximation and that much more physio-
logical study will be required before they may be taken as generally
applicable. In the first place, they are based upon tests of only a single
plant species, maize, and there are probably other plants (perhaps
even other varieties of the same species) for which they are not even
approximately true. Second, these indicies are derived from the growth
of seedlings, and no doubt other phases of growth in the same plant
may exhibit other relations between temperature and the rate of shoot
elongation. Third, these indices refer to rates of shoot elongation, and
there are many other processes involved in plant growth, which may
require other indices for their proper interpretation in terms of tem-
perature efficiency. Fourth, they apply strictly only under the moisture,
light, and chemical conditions that prevailed in Lehenbauer's experi-
ments; with more light or with a different light mixture, with different
humidity conditions, or with different moisture or chemical surroundings
about the roots, these same plants, in the same seedling phase, may
exhibit very different values of the temperature efficiency indices.
Fifth, and finally, plants in nature are never subject to any temperature
250 ECOLOGICAL CROP GEOGRAPHY
maintained for any considerable period of time, and these indices are
derived from 12-hour exposures to maintained temperatures. As Mac-
Dougal has well emphasized, the indices really needed for the ecological
and physiological interpretation of temperature must take account of
the varying temperatures that are almost always encountered in
nature."
The Moisture-Temperature or Hydrothermal Index. The
fact that the activity of plants is not determined entirely by one
factor of the environment to the exclusion of all others has been
pointed out on several occasions. The three most evident factors
of environment are temperature, moisture, and light conditions.
Livingston (9) presents an index of moisture-temperature efficiency
using the formula:
7 — 7 ^P
Imt = It 7
ie
In the above formula, 7m« represents the moisture-temperature
or hydrothermal index. It is the index of temperature efficiency
evaluated on the basis of the physiological index. Ip and L repre-
sent the indices of precipitation intensity and atmospheric evaporat-
ing power, respectively corresponding to the summations of the
rainfall and evaporation for the period considered. The formula-
tion of the hydrothermal index is based on the assumption that
plant growth increases proportionately to the value of the rainfall
index, that it is retarded proportionally to the index of evaporation,
and that the temperature index is correlated with the rates of
activity manifested by the plants. All three of these indices are
interrelated in their relations to plant activity. It is, however,
hardly to be expected that they may call forth a response always
directly proportional to their magnitude.
Livingston (9) gives a chart showing the magnitude of the hydro-
thermal indices for the various sections of the United States. This
chart is presented as Fig. 39. The values for southern Florida
amount to 23,000 units as compared to 6,000 for the northern Corn
Belt area. The rapid decrease of the indices from the heart of the
Corn Belt to the Great Plains area, especially in the southern
portion of this area, is very noticeable.
Moisture-temperature indices bring out very interesting relation-
ships. The hydrothermal index is subject, since it is based in part
on the physiological index, to the same criticism as the latter. The
31
M (U
I I
H
S 8
3*
bo
•8?.
Hi
251
252 ECOLOGICAL CROP GEOGRAPHY
hydrothermal index makes no recognition of accumulation of
supplies of moisture in the soil during the winter months which
may play a very important part in the growth of plants after the
beginning of the frostfree season.
CORRELATION OF DIFFERENT METHODS OF TEM-
PERATURE EFFICIENCY EVALUATIONS TO THE
GENERAL DISTRIBUTION OF CROPS IN THE UNITED
• STATES
Interrelationship of Efficiency Indices. All of the temperature
efficiency indices presented are more or less interrelated. Each
has some particular advantage to recommend it, even if nothing
more than simplicity; each also has some specific limitations either
in actual determination or in broad application. Thornthwaite's
temperature efficiency index amounts to nothing more than a
modification of the remainder index. The length of the growing
season enters into the summations of all of the various methods. It
is not only a matter of interest, it is also of practical value, in studies
relating to crop distributions, to ascertain the extent to which the
various indices are actually interrelated. It is evident that the
simpler indices may have a greater usefulness than the more com-
plex ones if it can be demonstrated that a high degree of correlation
exists between them. This may be true especially when the funda-
mental data required for calculating the more complex indices,
such as the highly theoretical physiological and hydrothermal in-
dices, are not available, or in locations where the application of
these indices is not justifiable because of the indicated limitations to
their utilization.
Magnitude of Indices in the Centers of Production of Specific
Crops. Table 13 gives a comparison of the different methods of
temperature evaluation in relation to the distribution of 16 cool-
and 16 warm-weather crops in the United States. The various
indices for the respective areas of production of each of the crops
listed were taken from the data presented by Livingston. In most
instances the values given for some station located in the center of
most intensive production for each respective crop could be uti-
lized. In a few instances where the particular center of production
of some crop was not represented by a station in Livingston's data,
it was necessary to make use of general values for the region of
TEMPERATURE EFFICIENCIES AND BIOCLIMATICS 253
TABLE 13. THE MAGNITUDE OF VARIOUS TEMPERATURE EFFICIENCY INDICES
IN THE AREAS OF MOST INTENSIVE PRODUCTION OF 16 COOL- AND 16 WARM-
WEATHER CROPS IN THE UNITED STATES
^rost-
Temp.
Temp.
Effi-
Crop
Center of Production
Selected
Free
Sea-
motion
or Re-
ciency
or Ex-
Physio-
logical
Hydro-
thermal
son, in
ponen-
Index
Index
Days
Index
tial
Index
Cool-weather crops
Flax
Moorhead, Minn.
132
3,351
334
4,283
4,043
153
3,696
382
4,942
4,270
Ryo
Devils Lake, N. D.
121
2*939
301
3/754
2*,823
Barley (spring) . . .
Moorhead, Minn.
132
3,351
334
4,283
4,043
Saginaw, Mich.
140
3,700
360
4,500
4,300
Hard red spring wheat
Devils Lake, N. D.
121
2,939
301
3,754
2^823
Soft rod winter wheat .
Indianapolis, Ind.
186
5,341
467
9,441
5,967
Durum wheat .
Devils Lake, N. D.
121
2,939
301
3,754
2,823
Oats (spring) . . .
Charles City, Iowa
133
4,000
403
6,630
7,000
Hard red winter wheat
Central Kansas
170
5,500
475
10,500
7,000
Field beans ....
Lansing, Mich.
145
4,000
400
5,000
4,000
Field peas ....
Green Bay, Wise.
153
3,695
382
4,942
4,270
Buckwheat ....
Ithaca, N. Y.
160
4,017
440
5,659
5,000
Timothy hay . . .
Buffalo, N. Y.
173
3,666
491
5,761
4,511
Soybeans
Springfield, 111.
182
5,344
563
9,464
7,032
Corn (northern) . .
Yankton, S. D.
154
4,464
464
7,616
6,491
Means ....
148.5
3,996.4
406.1
5,892.7
4,774.8
•
Warm-weather crops
Cotton (eastern)
Vicksburg, Miss.
252
8,204
893
16,194
15,125
Cotton (western) .
Fort Worth, Tex.
261
8,637
961
17,652
15,200
Corn (southern) . .
Springfield, 111.
182
5,344
563
9,464
7,032
"Tobacco
Raleigh, N. C.
213
7,584
700
12,329
14,980
Oats (winter)
Fort Worth, Tex.
261
8,637
961
17,652
15',200
Barley (winter)
Charlotte, N. C.
220
6,736
718
12,552
11,022
drain sorghums . .
Amarillo, Tex.
199
5,781
599
10,668
4,673
Broom corn ....
Panhandle of Okla.
187
5,800
600
11,000
5,000
Peanuts
Macon, Ga.
238
7,549
810
14,564
14,000
Velvet beans . . .
Macon, Ga.
238
7,549
810
14,564
14.000
Bermuda grass .
Montgomery, Ala.
243
8,141
886
16,511
12,400
Sugar cane ....
New Orleans, La.
310
9,881
1,077
19,323
23,381
Early potatoes .
Jacksonville, Fla.
293
9,339
1,033
18,791
21,760
Sweet potatoes . . .
Montgomery Ala.
243
8,141
886
16,511
12,400
Cowpeas
Raleigh, N. C.
213
7,584
700
12,329
14,980
Rice
Lake Charles, La.
260
9,800
1,000
17,750
20,000
Means ....
238.3
7,794.2
824.8
14,865.9
13,822.1
intensive production of that crop. It will be observed that the
length of the growing season, as well as the values of the various
254 ECOLOGICAL CROP GEOGRAPHY
temperature indices, such as the remainder, exponential, physio-
logical, and hydrothermal, are in most instances significantly lower
for the cool- than for the warm-weather crops. The difference in
the temperature requirements for each of the groups of crops is
especially well brought out by a comparison of the means for the
cool- and the warm-weather crops. The line of demarcation be-
tween these two groups of crops is of necessity somewhat arbitrary.
It is necessary to call attention to one factor in particular that
should be kept in mind in interpreting the data presented in Table
13 and in the correlation studies which follow, namely, that some
of the crops grown in both the northern and southern portions of
the United States do not make full use of the entire growing season
while the temperature indices are based on the accumulations of
values for the entire length of the frostfree period of the year. The
most outstanding examples of this are in evidence in the production
of early white potatoes in the southern states, and to a lesser degree
in the production of the cereals both in the North and in the South.
The classification of cool- and warm-weather crops as used here
refers more especially to the temperature provinces of the areas of
production of the given crops rathfer than to the temperature con-
ditions prevailing during their respective vegetation rhythms.
Correlation of Magnitude of Temperature Efficiency Indices
to Crop Distribution. Table 14 gives the values of the coefficient
r obtained from multiple correlations of the values of temperature
efficiency indices prevailing in the different areas of most intensive
production of important crops in the United States. Two sets of
supporting correlation data are presented. One, the original study,
is based on the distribution of eight cool- and eight warm-weather
crops in which the magnitudes of the different temperature indices
were taken for the general regions of intensive production of each
crop. The second is based on the data presented in Table 13. The
values of r obtained from these two sets of data are remarkably alike.
The length of the average frostfree season shows a high and very
significant degree of correlation with the other four indices. The
correlations between the various temperature indices are also high.
The values of r are in all instances sufficiently high to be used for
purposes of prediction. The high values for the remainder and
exponential indices are to be expected. It is interesting to note the
high values off obtained between the length of the average frostfree
TEMPERATURE EFFICIENCIES AND BIOCLIMATICS 255
season and the more complex physiological and hydrothermal
indices as well as the high values between the remainder and expo-
nential, and the physiological and hydrothermal indices. It must
be kept in mind that the physiological index enters definitely into
the actual calculation of the hydrothermal index.
TABLE 14. VALUES OF r IN TWO SETS OF MULTIPLE CORRELATIONS OF FIVE
DIFFERENT METHODS OF EVALUATING EFFECTIVE TEMPERATURES BASED
ON THE INDICES PREVAILING IN THE AREAS OF MOST INTENSIVE PRODUCTION
OF EIGHT COOL- AND EIGHT WARM- WEATHER, AND 16 COOL- AND 16 WARM-
WEATHER CROPS IN THE UNITED STATES OF EACH OF THE RESPECTIVE CROPS
Methods of Evaluating
Effective Temperatures
Remainder
Index
Exponential
Index
Physiological
Index
Hydrothermal
Index
Eight cool- and eight warm-weather crops — based on regional values
Length of frostfree
season ....
0 984 4- 0.006
0.981 ± 0.007
0.977 ± 0.008
0.958 ± 0.014
Remainder index
Exponential index .
Physiological index .
0.990 ± 0.003
0.974 ± 0.009
0.979 ± 0.007
0.944 ± 0.019
0.948 ± 0.018
0.933 ± 0.023
16 cool- and 16 warm-weather crops — based on data of specified stations
Length of frostfree
season ....
Remainder index
Exponential index .
Physiological index .
0.980 ± 0.005
0.991 ± 0.002
0.995 ± 0.001
0.976 ± 0.006
0.987 ± 0.003
0.988 ± 0.003
0.933 ± 0.015
0.949 ± 0.012
0.936 ± 0.015
0.919 ± 0.018
Livingston (8) gives data relative to the length of the average
frostfree season and the corresponding calculations of the physiologi-
cal summation indices for 170 stations in the United States. The
correlations of these data are indicated in Fig. 40. The coefficient of
correlation between the length of the growing season and the
physiological index for each of the 170 stations representing all
48 states shows a value of 0.739 ± 0.025. When 15 of the stations
to which the system of physiological summation indices obviously
do not apply are eliminated from the calculation, the value of r for
the data of the remaining 155 stations becomes 0.950 ± 0.005.
The stations eliminated in the second calculation of the relation-
ship between the two factors are indicated in Fig. 40. It will be
observed that all of these stations have climates influenced by
marine locations. Corn is not adapted to marine types of climates
256
ECOLOGICAL CROP GEOGRAPHY
with relatively long but cool growing seasons. Since the calculation
of the physiological index is based on the temperature response of
corn, there is ample justification for the elimination from the cor-
relation studies of these marine stations, or stations located in
sections with relatively long but cool growing seasons such as repre-
sented by Spokane, Washington.
360
340
320
300
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JC
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I220
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160
140
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Value of "r" for all 170 stations .7386 ±.0247
lue of "r" after elimination of 15 stations .9502 i.OO
•
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100
V
~tr
•
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1000 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
Livingstons' physiological temperature indices -in thousands
FIG. 40. Correlation of Livingston's physiological temperature efficiency
indices and length of average frostfree season for 170 stations of the United States.
Correlations are presented for all stations for which data are available and for
155 stations after the elimination of 15 indicated stations to which the physiological
indices obviously do not apply.
The close relationship between the length of the growing season
and the hydrothermal index is brought out in Fig. 41, showing the
correlation of the average length of the frostfree season and the
calculated hydrothermal index for each of the 1 1 2 stations of the
United States, given by Livingston (9). The value of r for all 112
stations is 0.629 + 0.041. When 12 of these stations arc eliminated
from the calculation, for the same reason as given for the elimina-
tion of stations in the correlation of length of growing season and
the physiological index summations, the value of r for the remaining
100 stations is increased to 0.873 + 0.015. The stations eliminated
are indicated in Fig. 41. The hydrothermal index fails to give a
true value for such sections where a high percentage of the annual
TEMPERATURE EFFICIENCIES AND BIOCLIMATICS 257
precipitation falls during the winter months and where conditions
are favorable to the penetration and later utilization of such mois-
ture. Additional stations, notably those in irrigated areas, could
be eliminated from the second correlation and result in a material
increase in the value of r. Thus the lengths of the average frostfree
seasons as given by Livingston are identical for Boise, Idaho, and
360
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340
"^
>*
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r,gel
'1
es
•
•
320
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ancisco
h Head,
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Wash.
•
300
•3280
c 260
% 240
£220
^200
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3
160
140
120
\
•
•
sJ
crar
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nenl
uff,
n
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•
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Cal
r~
•Tatoosh •
ylsl., Wash
•
•
•He
•
•Fresno, Calif.
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•
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•
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reg
•
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•El Paso
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•
•
•
•
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Cal
f.
•
•
•
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•
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Val
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f "r" after elimi
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0-1234567
8 9 10 11 12 13 14 IS 16 17 18
Hytirothermal index -in thousands
19 20 21 22 23 24
Fin. 41. Correlation of Livingston's hydrothermal efficiency indices and the
length of the average frostfree season for 112 stations in the United States. Cor-
relations are presented for all stations for which data are available and for 100
stations after the elimination of 12 indicated stations to which the hydrothcrmal
indices obviously do not apply.
for Albany, New York, namely, 177 days. The hydrothermal index
for the former is given as 598 and for the latter as 5,598 units. Since
natural precipitation in the Boise Valley is supplemented by irriga-
tion, not infrequently to the extent of several times the amount of
the rainfall during the growing season, the differences in the hydro-
thermal indices for the irrigated section in Idaho and the humid
New York station give no index of the relative crop producing
capacities of the two areas.
The employment of the length of the growing season as an index
of effective temperatures for a given locality has definite limitations
258 ECOLOGICAL CROP GEOGRAPHY
even though high degrees of correlations were demonstrated
between it and the more theoretically firmly grounded and complex
indices discussed. On the other hand the evaluation of effective
temperatures for any locality must always be undertaken in con-
nection with the temperature requirements and responses of the
particular crop to be grown regardless of what method of evaluation
may be selected.
The establishment of Thornthwaite's temperature provinces on
a linear basis of evaluating temperature efficiencies has been
criticized from the standpoint of the utilization of the remainder
index in an empirical form. The close correlations here reported
between the length of the growing season and the various other
theoretically better fortified methods of evaluating effective tem-
peratures indicates that either the length of the frostfree season or
the also readily calculated remainder index can be used to ad-
vantage in the establishment of temperature provinces and for pur-
poses of general climatic classification.
BIOCLljdATICS
Temperature Zones. Bioclimatics as defined by Hopkins (5) is
the "science of relations between life, climate, seasons, and geo-
graphical distribution." The sun is the primordial cause of all
bioclimatic phenomena. The rotation of the earth around the sun
accounts for the alteration of light and darkness with its regular
climatic, and especially temperature changes. The inclination of
the earth on its axis causes the variations in seasons and the major
climates, and again the most outstanding phenomenon is tempera-
ture and with it differences in length of days.
Astronomically, three broad temperature zones — the torrid,
temperate, and frigid — are recognized in latitudinal belts around
the world. The torrid zone is bounded to the north by the Tropic
of Cancer and to the south by the Tropic of Capricorn, situated on
each side of the equator at a distance of 23°28' and parallel to it.
These two lines represent the points reached by the sun at its
greatest declination north or south, from which it turns again to
the equator. There are, of course, two temperate zones lying
between either tropic and the corresponding polar circle,, and two
frigid zones.
TEMPERATURE EFFICIENCIES AND BIOCLIMATICS 259
Henry et al. (3) give five temperature belts in relation to plant
life. The main characteristics of each belt are listed as follows:
1. The tropical belt, regions of the megatherms, with all months
warm; that is, the temperature averaging over 68°F.
2. The subtropical belts, with 4 to 1 1 months warm, averaging over
69°F. The plants are largely megatherms.
3. The temperate belts, regions of the mesotherms, with 4 to
12 months of moderate temperature of 50 to 68°F.
4. The cold belts, regions of the microtherms, with 1 to 4 months
temperate, and the rest cold, below 50°F.
5. The polar belts, regions of the hekistotherms, with all months
averaging below 50°F.
Astronomical and Isothermal Temperate Zones. A glance at
Fig. 42 shows that the isotherms, lines connecting points of equal
temperature, follow the astronomical zones in a general manner
only. The astronomical zones are defined strictly by parallels of
latitude; they do not take into consideration the temperature
deviations caused by oceanic and continental influences. Supan
Fio. 42. Mean annual isotherms for 70 and 30°F north and south, and the heat
equator of the world. (After Hopkins.)
260 ECOLOGICAL CROP GEOGRAPHY
(16) based his temperature zones on sea^level isotherms. He recog-
nized three general zones; the hot belt, bounded on the north and
south by the isotherms representing the mean annual temperature
of 20°C (68°F) ; the temperate belts lying between these lines and
the isotherm of 10°C (50°F) for the warmest months; and the cold
caps, extending from the regions around the poles to the isotherm
10°C for the warmest months. The polar boundaries of agriculture
are not far from the annual isotherms of 30°F.
Bioclimatic Zones. Hopkins established bioclimatic zones on
the basis of his bioclimatic law promulgated to take into considera-
tion the effects of oceanic, continental, and physiographical features
on temperature and life zones in general. The bioclimatic law as
stated by Hopkins requires
"that across the continents under equal physiographic conditions the
phenomena of the seasons, climate, and life should be equal at the
same level along lines designated as isophanes, which depart from the
parallels of latitude at the rate of 1° of latitude to 5° of longitude; and
that, with distance in degrees of latitude poleward and equatorward
from such a line, or in feet of altitude above or below a given level, the
required effects should vary at a Uniform constant rate as measured in
units of time or temperature."
The time coordinate for the occurrence of a given periodic event
in plant activity, such as first date of flowering, or maturity of a
given plant, is stated by Hopkins to be at the general average rate
of four days to each degree of latitude and 400 feet of altitude from
a given point later northward in spring and early summer. The
effects of degrees of longitude are explained in the position of the
isophanal lines in relation to the parallels of latitude. The thermal
coordinates are 1°F for each degree of latitude, each 5° of longitude,
and for each difference of 400 feet in elevation.
The above will become clear upon an examination of the iso-
phanal map of the world, Fig. 43. Hopkins presents more detailed
maps of each of the continents, and sea-level isophanal zones of the
continents and oceans. His isophanal map of the world will suffice
for the discussion here. The isophanes are shown in straight lines
at intervals of 20° of latitude to 100° of longitude as unbroken lines
across the continents and broken lines across the oceans.
"It will be noted," states Hopkins, "that, while the numerical
designations are the same on the one hundredth meridian east or west,
261
262 ECOLOGICAL CROP GEOGRAPHY
there is a difference of 40° on pheno-meridian 20 W between those for
the Eastern and Western Hemispheres. This is due to the southeast
trend of the western and northwest trend of the eastern isophanes of
the same numerical designation from the one hundredth meridians
(west and east) to the Atlantic coast. Thus if the isophanes of the
same number were connected across the Atlantic Ocean, isophane 40,
e.g., would appear as a line whose southwestward trend across the
Atlantic corresponds in general with that of the mean annual 40°F
isotherm. There is also a general agreement in the trend of the 40°
isotherm and the fortieth isophane across North America- and Eurasia."
The isophanes as indicated in Fig. 43 apply only to land areas.
The respective isophanal lines are numbered to correspond with
the parallels of latitude intersected by them on the one hundredth
meridian of longitude west and east of Greenwich. Thus isophane
40 W intersects the one hundredth meridian west of Greenwich on
the latitude 40° North, that is, on the western portion of the border
line between Kansas and Nebraska. Likewise, isophane 40 E inter-
sects the one hundredth meridian east of Greenwich on the latitude
40° North, in central China.
The isophanal and bioclimatfc^ maps and data presented by
Hopkins are of value for the rapid general comparisons of life
phenomena of distant areas. In that respect they may become of
definite value to the study of crop distribution. As stated by Hopkins,
"while this system of continental isophanes represents the require-
ments of the bioclimatic law, as related to any sea level or any common
level across the terrestrial areas alone, and while the parallels of lati-
tude represent equal phenomena and apply to both land and water,
it is found that lines of equal effect in phenomena of life and climate
correspond in their trend with the isophanes rather than with the
parallels of latitude."
Evans (2) presents data from his studies of the relation of latitude
to the time of blooming of timothy to the effect that Hopkins5 bio-
climatic law does not give proper emphasis to the gradually increas-
ing length of day, from southern to northern latitudes. The season
of blooming of timothy at a series of stations extending from Savan-
nah, Georgia, to Fairbanks, Alaska, progressed at constantly accel-
erated rates rather than at a uniform constant rate according
to the bioclimatic law. This indicates that "other varying factors
in addition to those of latitude, longitude, and altitude, must be
considered" in bioclimatic relationships.
TEMPERATURE EFFICIENCIES AND BIOCLIMATICS 263
Merriam's Life Zones and Areas. While the life zones recom-
mended by Merriam (12) are at present mainly of historical inter-
est, it must be recognized that his classification of the life zones of
the United States and North America gave a real impetus to the
study of the effects of temperature and rainfall and to the establish-
ment of biothermal lines and of the factors determining the distri-
bution of plants and animals.
Merriam recognized two great lines of stress, heat and rainfall, as
influencing the limits of migration of species in the higher latitudes
and at higher elevations. Likewise, excessive heat constitutes one of
the main contributing factors limiting the growth of many plants
in the lower latitudes. He evaluated heat by the summation of
mean daily temperatures above 6°C (43°F) from the time growth
begins in spring to the time growth ceases in fall, that is, by the
remainder index. Differences in rainfall constitute the second line
of stress. It should be noted that Merriam used total rainfall rather
than a system of precipitation efficiency.
Three transcontinental life regions are recognized in the northern
hemisphere: the Boreal, or northern; the Austral, or southern; and
the Tropical. These regions were first established by Alexander
von Humboldt when he divided the globe into the great life belts.
Humboldt, however, used isothermal lines rather than temperature
summations as did Merriam.
The Boreal region covers the whole of the northern part of North
America, from the Polar Sea southward to near the northern
boundary of the United States, and farther south occupies a narrow
strip along the Pacific coast and the higher parts of the three great
mountain systems, the Sierra Cascade Range, the Rocky Moun-
tains, and the Alleghanies. The Boreal region is subdivided, along
the lines of stress due to heat, into three zones, the Arctic or Arctic-
Alpine, the Hudsonian, and the Canadian. The Arctic or Arctic-
Alpine zone is the northernmost and highest belt; it lies beyond the
limit of tree growth, and the larger part of it is perpetually covered
with snow and ice. The Hudsonian, or subarctic zone, embraces
the most northern part of the great transcontinental coniferous
forests. Because of low temperatures it is of no agricultural impor-
tance. The Canadian zone comprises the southern part of the
great transcontinental coniferous forest of Canada and the very
northern portion of the United States. Favored locations along
264 _ ECOLOGICAL CROP GEOGRAPHY _
the southern border of this belt are suited to the production of
potatoes, hardy vegetables, and cereals.
The Austral region covers the whole of the United States and
Mexico, except the Boreal mountain heights and the tropical low-
lands. It is divided, along lines of stress due to heat, into the
Transition, Upper Austral, and Lower Austral zones. Each of
these zones is subdivided into areas along lines of stress due to rain-
fall and drought. Thus the Transition zone, the meeting place of
the boreal and austral types, located in the northern portion of the
United States, is broken up into the Humid Alleghanian, Arid
Transition, and Pacific Coast Transition areas. The Upper Austral
zone is divided into an eastern humid, or Carolinian area, and a
western arid or Upper Sonoran area. The Lower Austral zone
occupies the southern part of the United States. It, likewise, is
broken up into an eastern, or Austroriparian, and a western, or
Lower Sonoran, area.
The Tropical region has no stress lines due to heat, but is divided
into humid and arid areas.
REFERENCES
1. Cohen, E., Lectures on Physiological Chemistry for Physicians and Biologists,
trans. German by Martin H. Fisher. New York, 1902.
2. Evans, M. W., "Relation of latitude to time of blooming of timothy,"
Ecology, 12:182-187 (1931).
3. Henry, A. J., J. B. Kincer, H. C. Frankenfield, B. B. Smith, and E. N.
Munns, "Weather and agriculture," U. S. Dept. Agr. Tear book 1924:
457-558.
4. Hertwig, O., "Uber den Einfluss der Temperatur auf die Entwicklung
Ranafusca und Rana esculenta," Arch. f. Microscop. Anat. und Entwicklung s-
gesch., 51:318-381 (1898).
5. Hopkins, A. D., "Bioclimatics, a science of life and climate relations,"
U. S. Dept. Agr. Misc. Pub. 280, 1938.
6. Kincer, J. B., "The relation of climate to the geographical distribution
of crops in the United States," Ecology, 3:127-133 (1922).
7. Lehenbauer, P. A., "Growth of maize seedlings in relation to tem-
perature," Phys. Res., 1:247-288 (1914).
8. Livingston, B. E., "Physiological temperature indices for the study of
plant growth in relation to climatic conditions," Phys. Res., 1 :399-420
(1916).
TEMPERATURE EFFICIENCIES AND BIOCLIMATICS 265
9. Livingston, B. E., <CA single index to represent both moisture and
temperature conditions as related to plants," Phys. Res., 1:421-440
(1916).
10. , and Grace J. Livingston, Temperature coefficients in plant
geography and climatology," Bot. Ga%., 56:349-375 (1913).
11. Matthaei, G. L. C., "Experimental researches on vegetable assimila-
tion and respiration, III, On the effect of temperature on carbon
dioxide assimilation," Phil. Trans. Roy. Soc. London, 197:47-105 (1904).
12. Merriam, C. H., "Laws of temperature control of the geographic
distribution of terrestrial animals and plants," Nad Geog. Mag.,
6:229-238 (1894).
13. Pearson, G. A., "Temperature summations with reference to plant
life," Mo. Wea. Rev., 52:218-220 (1924).
14. , "Forest types in the southwest as determined by climate
and soil," U. S. Dept. Agr. Tech. Bull. 247, 1931.
15. Seeley, D. A., "Relation between temperature and crops," Mo. Wea.
Rev., 45:354-359 (1917).
16. Supan, A., Grundzuge der physischen Erdkunde. Aufl. 3, Leipzig, 1903.
17. Thornthwaite, C. W., "The climates of North America according to a
new classification," Geog. Rev., 26:633-655 (1931).
Chapter XVIII
LIGHT
GENERAL ASPECTS
Light in Relation to Growth Requirements and as a Factor
in Geographical Distribution. Schimper (21) designates light
as, next to moisture, the most important environmental factor
determining the structure of plants. Both water and light provide
actual materials essential to the building up of the structures of
higher plants, while temperature, as has been pointed out, provides
the necessary working condition.
Schimper proceeds then to point out that the light factor is of less
importance than the water and temperature factors as it relates to
the geographical distribution of pfcants, notwithstanding its prime
importance to nutritional and structural effects. This is because
the differences in both the quantity and quality of light in relation
to the needs of plants are not so pronounced in different climatic
regions as are differences in the moisture and temperature factors.
This is well brought out by Raunkiaer (20) in the following para-
graph.
"The requirements for the life of plants are all of equal importance
inasmuch as none of them can be dispensed with; but when these
requirements are used as a foundation for dividing up the earth into
equiconditional regions they are very far from being of equal impor-
tance. Some, for example the amount of oxygen and carbon dioxide
in the air, differ so little in different places that they have no signifi-
cance for the life forms, and therefore cannot be used as characters
for equiconditional regions. Others, for example the chemical and
physical nature of the soil, the relationship between plants and animals,
and between plants themselves, vary so widely even within the smallest
districts that they cannot be used for limiting large equiconditional
regions; but on the other hand they are useful in the detailed analysis
of vegetation within these regions. The same is approximately true
of light. If the demand for light always expressed itself sufficiently
obviously in the structure of plants, and if the plants were all of equal
266
LIGHT 267
height and shaded each other equally, then the different intensity of
sunlight in the different degrees of latitude would be an important
factor for limiting large equiconditional areas. But there is a vast
difference in the size of plants, and some grow in the shade of others,
so the relationship of light even in very small areas differs so greatly
that it is impossible to use it for determining what is common to the
environment over extensive tracts."
The Heating and Chemical Effects of Light. The sun is the
source of both heat and light. Furthermore, heat and light are
definitely associated. Two units are therefore employed in measur-
ing the intensity of sunlight, one a heat and the other a light unit.
The gram-calorie, the quantity of heat required to raise the tem-
perature of a gram of water through 1°C, is the unit usually em-
ployed for measuring total radiant energy, that is, the energy of all
wave lengths received from the sun. The foot-candle is the unit
used for measuring brightness, or the wave lengths capable of pro-
ducing the sensation in the human eye commonly referred to as
light. According to Henry et aL (12), the intensity of solar or day-
light illumination on a horizontal surface around noon in midsum-
mer is with a clear sky about 10,000 foot-candles. The intensity
may still be between 2,500 to 3,000 foot-candles when the sky is
completely covered with clouds. An intensity of from 10 to 15 fopt-
candles is considered good indoor illumination.
The shorter waves of the spectrum have primarily chemical
effects, either detrimental or conducive to photosynthesis, while
the longer waves produce mainly temperature effects. Wave
lengths in excess of 0.76 micron have primarily temperature effects;
those shorter than 0.40 micron have decided detrimental effects
on the chlorophyll of higher plants. A micron is a thousandth part
of one millimeter.
Interrelationship of Environmental Factors. That the effects
of light on plants and crop plants in particular must be considered
in relationship with other factors of the environment is obvious.
Under most conditions the quantity of light present is sufficient
for the normal requirements of crop plants. Since light intensity
and duration are associated with temperature, the responses called
forth by a high intensity of light not infrequently amount to tem-
perature responses. Furthermore, the actual amount of radiant
energy which may be utilized by plants is highly dependent on
268 ECOLOGICAL CROP GEOGRAPHY
other factors of the environment either favorable or unfavorable to
the establishment or maintenance of a proper physiological balance.
Thus a plant well supplied with moisture and the necessary nutri-
ents is able to utilize more radiant energy than one growing in an
unfavorable environment. Under some conditions a high intensity
of light may be detrimental not only because of its direct destruc-
tive effects on the chlorophyll but more frequently because of its
indirect and associated temperature effects; the intensifying of
destructive processes may in such cases be attributed to a greater
extent to the temperature than to the light factor. Drought damage
usually occurs under conditions of high intensity and duration of
light, high temperatures, and the associated low atmospheric
humidity. All three of these conditions usually conspire to form
the formidable trio demanding increased expenditures of the little
remaining water available to drought-stricken plants.
The Action of Light on Plants. The action of light on plants
has many important and interesting physiological ramifications
entirely beyond the scope of this chapter. All that can be given
here is a brief summary taken directly from Warming (27). The
part played by light is presented in the following eight points:
"1. By its chemical action on chlorophyll. Without light there would be
no production of chlorophyll, no assimilation of carbon dioxide, and
no life upon the globe.
2. By its heating action.
3. By promoting transpiration through rise of temperature.
4. By promoting growth movements, the position of foliage-leaves, and
nearly all vital phenomena.
5. By influencing the distribution of plants.
6. The development of plants depends not only upon the intensity but
also upon the duration of the light to which they are exposed.
7. Direct light promotes the production of leaves and flowers.
8. The vegetative shapes of plants are greatly influenced by the in-
tensity and direction of the light."
QUALITY OF LIGHT
Differential Effects of the Rays of the Spectrum. Sunlight
is variable in quantity, duration, and quality. The term "quality"
of light is used here in reference to the composition of light in
relation to its effects on plants. When a beam of light is dispersed
by refraction through a prism the rays arrange themselves in a
LIGHT
269
series according to their wave lengths. Thus the composition of
light may be analyzed as to the rays it contains. The relationship
of these rays to plant behavior and to the question of optimum
intensities of light is pointed out by MacDougal (16) in the follow-
ing paragraph.
"Not all of the rays of the spectrum are concerned in the various
influences exerted by light upon living matter, but only waves of certain
wave-lengths are active in each. It is not possible therefore to fix upon
a minimum, optimum, and maximum intensity of light which is com-
mon to all of the relations between the plant and light."
LundegSrdh (15) presents a tabulation showing the effects of
different wave lengths of light on plant life. This is presented as
Table 15.
TABLE 15. THE ACTION OF DIFFERENT RAYS OF RADIANT ENERGY ON PLANT
LIFE (after Lundegardh)
Rays
Wave Lengths
Effects on Plants
Rontgcn . . .
0.00001-0.000018 micron
Decidedly very detrimental
Ultraviolet . . .
0.042-0.40 micron
Very detrimental
Violet \
Blue J ' ' ' '
0.40-0.49 micron
Phototropism. Photomorphosis
Green-red .
0.49-0.76 micron
Carbon-dioxide assimilation
Ultrared . . .
0.76 to around 600 microns
Temperature factor in general
Electric waves .
2 mm. to indefinite length
Unknown
Lundegirdh points out that a distinct differentiation between
the actions of the various rays is usually not possible. All rays that
are physically absorbed exert a certain temperature effect. Yellow
and red rays are also active in phototropism but to a much smaller
degree than blue-violet rays. It is recommended that for ordinary
ecological purposes it is sufficient to evaluate the blue-violet and
the yellow-red rays in addition to the total intensity.
Shirley (24) considers the measurement of separate rays of
secondary importance to the evaluation of the total light intensity.
"The entire visible and ultra-violet solar spectrum is more efficient
for the growth of the plants studied than any portion of it used; the
blue region is more efficient than the red region."
Effects of Atmospheric Conditions on Quality of Light. The
exact composition of light coming in contact with plants is highly
270 ECOLOGICAL CROP GEOGRAPHY
dependent on atmospheric conditions but especially on the amounts
Of moisture and dust in the air. Pulling (19) points out seven ways
by which losses from incoming solar energy occur.
1. General scattering by the permanent gases of the atmosphere.
2. General scattering by water vapor.
3. Selective (banded) absorption by permanent gases.
4. Selective (banded) absorption by water vapor.
5. Absorption and reflection by clouds.
6. Absorption and reflection by dust particles.
7. Absorption in chemical reactions.
According to Dorno, cited by Lundeg&rdh, the short-wave rays
are influenced to a greater extent than the long-wave rays by the
presence of clouds.
Altitude and Composition of Sunlight. Since the atmospheric
strata become less dense with increasing elevation above sea level,
it is evident that there is less absorption of radiant energy at high
than at low altitudes. Hann (10) points out that the rapid increase
in the intensity of solar radiation with increase in altitude is largely
attributable to the decrease andralmost total absence of atmospheric
dust (including under this term aqueous condensation products)
which affects chiefly the shorter waves. Consequently these are
especially strong at high elevations. The diminution of water vapor
also plays a part in this, though not so pronounced a part as the
decrease in atmospheric dust.
The most outstanding difference in the composition of light at low
and high elevations is the marked increase in the intensity of the
ultraviolet rays. Anyone not accustomed to exposure to the direct
rays of the sun will develop a good tan or even a severe sunburn at
great altitudes.
That the great intensity of solar radiation, and especially the
intensity of the ultraviolet rays, has a great influence on the charac-
teristics of Alpine plants has been pointed out by numerous investi-
gators. Thus Alpine plants are characterized by short internodes,
firm leaves, more or less wrinkled surfaces, and a dark color.
Seasonal Variations in the Composition of Sunlight. It has
been pointed out that the composition of sunlight is affected by a
variety of atmospheric factors. There is also a significant change
in composition as the season advances. This is brought out graphi-
LIGHT
271
cally by Dorno in Fig. 44, taken from Lundegardh's book. Accord-
ing to Lundegardh, while the heat rays at noon increase but by
10 per cent from winter to sum-
mer, the red rays increase by 45,
the light rays by 60, the green
rays by 90, the blue-violet rays by
around 1 ,000 per cent.
A study of Fig. 44 reveals that
sunlight in summer and also dur-
ing the autumn months contains
a higher proportion of the chemi-
cally active rays, that is, a rela-
tively greater predominance of the V fet "* * "" June * * «* " Nw
, . , 111 • i FIG. 44. Variations in the com-
ultraviolet and blue-violet rays, position of sunlight at the fifteemh
than in winter or during the spring day of the indicated months through-
months, out the year. (After Dorno, taken from
From the standpoint of plant Lunde^rdh-)
activity the greater length of the days in spring and summer is of
great importance. This factor will be treated in detail later.
QUANTITY OF LIGHT
General Dependence of Plants on Quantity of Light. Under
ordinary conditions of field crop production a sufficient total
amount of light for the normal growth of plants is available. Gen-
erally crop plants do best when grown under full sunlight, provided
that such exposure does not, by the heating action of light, cause
other factors of the environment to drop below the minimum re-
quirements for growth. Blackman and Matthaei (3) and others
have shown that the rate of photosynthesis with low light intensities
is almost directly proportional to the light intensity if other factors
are not limiting. At higher intensities, the slope of the curve show-
ing production of dry weight falls off and approaches according to
Boysen-Jensen (4), and Harder (11), a line parallel to the axis.
Shirley reports that the dry weights of plants studied by him in-
creased almost in direct proportion to the light intensity received
up to about 20 per cent of full summer sunlight. At higher intensi-
ties the slope of the curve fell off, with shade plants showing a
decrease at lower intensities than sun plants.
272 ECOLOGICAL CROP GEOGRAPHY
Tippett (25), working at Rothamsted on the effects of sunshine
on wheat yields, presents data showing that sunshine seems to have
a large positive effect in autumn and winter. It has less effect on
yields in the spring and again a more decided effect in the summer
months "primarily because of its aid to development and ripening
of the grain." The effects during the summer months were not,
however, as great as during the autumn and winter months when
sunshine with the associated slight changes in soil temperature had
favorable effects on the root development of plants.
In humid areas cloudiness may at times be enough, if continuing
over a sufficiently long period, to slow down the growth rate of
plants. Usually, however, this is not the case. Plants are able under
most conditions to develop quite normally with less than full sun-
light. In continental climates and especially during times when
moisture is lacking, exposure to full sunlight is decidedly detri-
mental as it materially increases the demand for and the actual loss
of water from plants and from the soil. Periods with overcast skies
and lower temperatures are very effective in conserving moisture.
Quantity of Light and Plant Structure. All portions of the
plant are modified by the amount pf light to which they are exposed.
The leaves of plants grown in shatle or partial shade are thinner
and show a thinner cdticle than those of plants grown in full sun-
light. The increase in thickness of leaves of sun plants is largely
accounted for by the palisade arrangement of the mesophyll.
Shade plants are able to carry on their functions by structural modi-
fications favoring increased transpiration while plants exposed to
intense light are favored by modifications serving to reduce water
losses.
Wiessmann (29) presents interesting data showing the effects of
light intensity on the yield performances and structural differences
of "light" and "shade" plants in oats. The "shade" plants were
grown in a courtyard where they were exposed to direct sunlight
for only six hours per day while the "light" plants were grown on
the top of a building 1 1 meters high where they were exposed to the
maximum amount of light for the period of vegetation. The differ-
ences in the characteristics of these two groups of plants are stated
below.
1. Abundance of light favors the production of tillers.
2. Light increases the stability and strength of culms.
LIGHT 273
3. The length of the culms was favored by the smaller amount of
light. The shade plants grew taller.
4. The total yield as well as the weight of all plant structures was
greater in the light than in the shade plants.
5. The leaves of the "light" plants produced about 2.5 times as
much grain per unit of area as those of the shade plants.
6. The higher yield of grain in the "light" plants is accounted for
by the larger number and greater individual weight of kernels produced.
7. Light increases the percentage of roots to total crop.
8. Light decreases the percentage of straw to total crop.
9. The percentage portion of grain and chaff increased with abun-
dant light.
The lodging of plants, especially cereals, is occasioned by a
variety of factors as the density of the stand, the rankness of growth
induced either by soil conditions, particularly the availability of
nitrogen or of climatic conditions or both, the firmness of the soil,
as well as by the severity of the climatic factors responsible for the
bending over or the falling down of plants. Except where caused
by the presence of disease or insect damage, lodging is usually
directly induced by wind and rain and frequently by a combination
of both. Favorable light relationships are definitely associated with
the development of structures and characteristics of stems impart-
ing strength to resist lodging. In addition an excessive growth is
very effective in excluding light from the lower portions of plants
grown in dense masses.
Effects of Competitive Plant Cover. Plants growing in partial
shade of other plants live in an environment quite different from
those exposed to full sunlight. They develop in accordance with
the modified environmental conditions. Thus the structures of
clovers and grasses grown in competition with so-called nurse crops
differ materially from those growing in full sunlight. The extent
to which light conditions may be modified by a nurse crop is
illustrated in Table 16, showing the relative light intensities reaching
the upper group of leaves of alfalfa and clover plants grown with
and without the indicated nurse crops. The relative vigor of the
young leguminous plants at the time of harvest of the respective
nurse crops agreed with one exception with the amount of light
available to them. The exception was in evidence in the case of the
flax nurse crop. It is interesting to note that under the moisture
conditions prevailing in northern Idaho, that is, where the vegeta-
274
ECOLOGICAL CROP GEOGRAPHY
tion rhythm is interrupted by a period of summer drought, both
the red clover and alfalfa plants established in competition with
flax were decidedly less vigorous than those grown with the other
nurse crops even though the flax plants allowed more light to reach
the legumes. The shallow-rooted flax plants were in more direct
competition for soil moisture during the summer drought period
than the deeper rooted cereal nurse crops. In this particular in-
stance special moisture conditions constituted the main factor deter-
mining the relative development, vitality, of the clover and alfalfa
plants. This condition offers another example of a fact pointed out
on several occasions, namely, that a crop response may be due not
to the action of one factor but to the effects of a variety of factors.
TABLE 16. RELATIVE LIGHT INTENSITIES MEASURED AT THE LEVEL OF THE
TOP LEAVES OF RED CLOVER AND ALFALFA PLANTS AND THE RELATIVE VIGOR
OF THESE PLANTS AT THE END OF THE FIRST SEASON ESTABLISHED WITHOUT
AND WITH THE NURSE CROPS INDICATED. THE MEASUREMENTS WERE TAKEN
ON THE UNIVERSITY FARM AT MOSCOW, IDAHO, AT 2:00 P.M. ON JULY 2, 1937.
Nurse Crop
Stage of
Develop-
ment of
Nurse Crop
Red Clover
Alfalfa
Light In-
tensity, in
Foot-
Candles
Vigor of
Plants, in
Per Cent
Light In-
tensity, in
Foot-
Candles
Vigor of
Plants, in
Per Cent
Without nurse crop . .
Alaska peas ....
Perfection peas . . .
Trebi barley ....
Federation wheat . . .
Markton oats ....
Pacific Bluestem wheat .
Flax
Pod
Flower
Head
Head
Head
Jointing
Flower
Head
Head
10,800
5,000
4,800
3,300
3,000
1,800
900
3,600
3,600
2,100
100
90
85
70
65
40
30
25
55
50
10,800
7,000
7,000
2,700
3,000
1,500
1,800
6,000
5,100
1,500
100
90
90
60
60
50
40
25
65
45
Federation wheat in al-
ternate drill rows . .
Markton oats in alter-
nate drill rows . . .
In areas of summer precipitation, flax makes a good nurse crop.
Under those conditions, that is, when the intense competition for
moisture is reduced, the grasses and legumes established with it
respond in accordance with the light conditions of their habitats.
The effects of relative abundance of light on the resulting struc-
tures of plants have been indicated. Plants growing in partial
LIGHT 275
shade develop structures common to shade plants. The leaves
especially are readily modified, becoming larger and thinner in the
shady habitat. The environment of grass and leguminous plants
growing in the partial shade of competitive crops changes abruptly
with the removal of these crops. Not infrequently the transition thus
induced is too great for the tender plants to withstand. If the re-
moval of the nurse crop occurs during periods of less intense sunlight,
that is, during an interval of cloudy weather, the sudden change in
environment has no detrimental effects. The plants are then able
to adjust themselves to their new environment. The reflection of
sunlight from the stubble of cereal nurse or competitive crops
definitely increases the intensity of the light and also the tempera-
ture, thus increasing the stress and need for moisture which is often
limited during this critical period in the life of young grass and
leguminous plants.
The ability of plants to grow and survive in partial shade is often
accounted for by differences in their vegetative rhythms as com-
pared with the rhythms of the taller plants producing the shade.
Grasses able to develop early in spring may build up a sufficient
carbohydrate reserve in their systems before the leaves of trees above
them develop enough to exclude much light. Thus Moreillon (17)
presents data showing the loss of dry fodder from grasses growing
under spruce trees to amount to 88 per cent as compared to a loss
of only 30 to 40 per cent for grasses growing under larch trees. ' The
grasses under the larch trees complete a part of their vegetative
rhythm prior to the time that the trees develop their needles.
Furthermore the relative abundance of light influences not only
the quantity but also the quality, chemical composition, of the
forage produced.
Measurement of Light Intensity and Duration. The intensity
of light is difficult to evaluate. Both the quantity and quality of the
light reaching plants comes into play. Furthermore, it is desirable
to have available for habitat studies not only light readings at the
moment of the determination but continuous records extending over
a period of hours or days. Photoelectric cells and appertaining
recording equipment are recommended for the continuous evalua-
tion of the light factor. Such equipment is described by Segelken
(22) and by Shelford and Kunz (23). The reader is referred to
Weaver and Clements (28) for details relating to the construction
276 ECOLOGICAL CROP GEOGRAPHY
and use of a simple photometer for the momentary measurement
of light intensity.
Various investigators have evaluated light intensities on the basis
of the difference in the loss of water from standard, white, and
blackened spherical atmometer cups. The blackened atmometer
cup is covered with lampblack. While this method provides a
rough index of intensity over a period of time it does not lend itself
to momentary evaluations. Furthermore, the intensity of light is
evaluated strictly on the basis of the heat rays striking the atmometer
cups and can for that reason be expected to yield reliable data only
insofar as the heat rays correlate with the chemically active rays.
That this correlation is by no means complete is brought out in
Fig. 44.
The duration of sunshine is measured by means of a sunshine
duration transmitter. This instrument was devised by C. F. Marvin
of the United States Weather Bureau. It consists essentially of a
differential air thermometer enclosed within an evacuated glass
sheath, with platinum wire electrodes fused into the column at the
center. When connected electrically to a sunshine recorder, a con-
tinuous record of the duration of sunshine may be obtained.
«•
LENGTH OF- DAY
Latitude and Length of Day. Owing to the spheroidal shape
of the earth and the inclination of its axis, the duration of the light
period, that is, the length of day, varies from 12 hours at the
equator to increasing lengths at the higher latitudes to finally
continuous sunlight throughout the 24-hour period at the poles
during the middle of summer. Thus in the tropics plants are
exposed to sunlight half of each day, while Arctic plants grow in
nearly continuous light throughout the short summers. This results
in actually greater amounts of insolation at the higher latitudes
than in the tropics at the summer solstices, June 21 and December
21 for the northern and southern hemispheres, respectively.
In the tropics the length of day remains constant or nearly so
for all seasons of the year. At the higher latitudes the length of day
increases up to the summer solstice and then decreases. Thus
plants growing more or less from the time of the beginning to the
end of the growing season develop at first under increasing and
after the middle of summer under decreasing lengths of days.
LIGHT 277
The rapid midsummer growth of plants at high latitudes is no
doubt correlated with the long day and associated temperature
conditions. Albright, in two papers (1 and 2), describes the unusu-
ally rapid growth of various field and garden crops in northern
Canada, near the Arctic Circle.
Photoperiodism and Photocritical Periods. Light may in-
fluence plant behavior by its intensity, its composition, and by its
continuity or duration for any 24-hour period. These variables
in the light factor together with the temperature and other environ-
mental conditions determine not only the quantity of photosynthetic
material formed but also the utilization of these materials.
The response of plants to the relative length of day and night is
referred to as photopcriodism. The term was originally used by
Garner and Allard (7) in the first of their series of papers on the
topic. The length-of-day factor is of special interest in relation
to its formative effects; the action of the duration of light is also
interesting and of importance to plant distribution in initiating
or suppressing sexual reproduction. Certain plants require rela-
tively long days for successful flowering and fruiting, others are
more or less indifferent to light duration, and still others begin
to flower only as the length of the summer days decreases. The
first group are referred to as long-day and the last as short-day
plants, while the so-called ever-bloomers occupy a position inter-
mediate between the two or show some features of both/ The
long-day plants include those normally coming into the flowering
stage in late spring or early summer. Typical examples are the
radish, the smaller cereals, red clover, and the common grasses of
northern origin. The late-summer-blooming annuals such as
tobacco, ragweed, and certain varieties of soybeans continue to
develop only vegetatively during the long summer days at higher
latitudes; the flowering stage is not initiated until the length of
the days decreases in late summer or early autumn. They are
typical short-day plants. The particular length of day required
under normal conditions to initiate flowering is referred to as the
photocritical period.
The term "photocritical period" must be employed with a
degree of caution. Garner (6) states that, while
". . . it is true that there is a fairly definite optimum length of day
for flowering, . . . generally speaking there is also a. wide range in
278 ECOLOGICAL CROP GEOGRAPHY
day length on either side of the optimum in which flowering takes
place with more or less facility. ... In many species representing
both the long-day and the short-day types, it has been found
that under suitable conditions a variation in day length of not
more than one hour (or even less) constitutes the critical range,
on the two sides of which definite contrast in response is obtained.
On the one side the plant flowers readily while on the other side
it tends to remain in the vegetative stage. The important point
in this connection is that the group of plants which we have been
in the habit of classing as the long-day type flower only when exposed
to day lengths in excess of the critical, while the short-day plants are
able to flower only under shorter day lengths than the critical. In the
present stage of our knowledge of the subject this would seem to furnish
a simple and logical basis for differentiating between the two groups of
plants."
It is necessary to point out again that the light factor operates
in connection with the temperature factor. That this is the case
in the regulation and balance between vegetative and reproductive
types of activity in plants is evident. The relationship of the
temperature and the length-of-day factors to spring and fall
flowering is brought out by Garner and Allard (8) in the following
paragraph. 9
%
"Broadly speaking, in cool temperate regions short-day plants will
flower chiefly in the fall rather than in the spring because of the lag
in temperature rise in spring as compared with the lengthening of the
day. In other words in spring the day length is likely to become too long
for flowering of short-day plants before the temperature has risen
sufficiently to permit plants to become active. This is true more par-
ticularly of the annuals and those herbaceous perennials which require
considerable vegetative development as an antecedent to flowering.
That plants of these types which regularly flower in the fall will actu-
ally flower in the spring when the obstacle of low temperature is re-
moved has been demonstrated in a number of cases."
Length of day or the light period has decided effects on the
content of soluble carbohydrates, the form of the carbohydrate
present, and on the acidity relations in plants (Nightingale, 18,
Garner et a/., 9).
Photoperiodism and Plant Distribution. Adaptation has been
defined by the degree of correlation existing between the vegetation
rhythms of plants involved and the climatic rhythm of a region.
Length of day makes up one of the components of the climatic
LIGHT 279
rhythm and exerts selective influences. Certain plants may fail
to fit into given environments on account of their inability to estab-
lish the required balance between vegetative and reproductive
activities in relation to the prevailing length of day and will for
that reason be excluded. Trumble (26) reports from Australia
that "at the Waite Institute it has been observed that herbage
plants from European and North American sources may fail to
flower and set seed normally, although supplied with abundant
water. Examples are Phalaris arundinacea, Avena elatior, Agropyrum
tenerum, and Bromus inermis. This is also true of ecotypes or varieties
of Lolium perenne, Dactylis glomerata, Phleum pratense and cereals
from northern European sources." On the other hand, Forster
et al. (5) and Jenkin (13) point out that types from southern Aus-
tralia, when grown in England and Wales, usually run to stem
and seed rapidly, with comparatively little vegetative growth.
The Utilization of Artificial Light. Natural daylight may be
advantageously supplemented by means of electrical illumination
for purposes of hastening plant development. It has special value
in the growing of plants in the greenhouse during the winter
months where it may be employed to supplement the generally
low intensity of the light during the hours of the day as well as for
the purpose of lengthening the days. The installation of electric
lighting in many instances results in a more efficient utilization of
greenhouse space. Plant breeders have made good use of artificial
illumination. With its help several generations of plants may be
grown in the time interval usually required for the production of
a single generation.
The extent to which artificial illumination may hasten the
development of wheat plants is brought out in Table 17, taken
from Klages (14). Table 17 also serves to bring out an interesting
difference in the light response of spring and winter wheat varieties.
The plants in question were exposed to the light given off by
500-watt, nitrogen-filled tungsten lamps fitted with large enameled
shades. The lights were on from 5 : 00 P.M. to 8 : 00 A.M. To guard
against temperature differences, the lamps were held at a height
of four feet above the highest portions of the illuminated plants.
The employment of electric light reduced the time interval between
the date of planting, November 22, to heading to the extent of
75 per cent for the spring as compared to a reduction of only
280
ECOLOGICAL CROP GEOGRAPHY
29 per cent in the case of the winter wheat varieties. It is interesting
to note that varietal differences within the spring and winter types
did not significantly influence the percentage reduction in the
time interval required for the plants to reach the heading stage.
TABLE 17. EFFECT OF ELECTRICAL ILLUMINATION ON THE REDUCTION OF
THE TIME INTERVAL REQUIRED FROM PLANTING TO HEADING OF SPRING AND
WINTER WHEAT VARIETIES GROWN IN THE GREENHOUSE IN WINTER (Klages)
Varieties
Number of Days from Planting
to Heading
Percentage Reduction in Time
because of Artificial Illumination
Without
Artificial
Illumination
With
Artificial
Illumination
Spring wheat var
Wisconsin Wonder . .
Preston
ieties
144
181
179
184
rieties
185
187
192
190
35
44
48
46
131
t 135
- 137
133
75.69
75.69
73.18
75.00
29.19
27.81
28.65
30.00
Marquis
Kota
Winter wheat vai
Minturki
Red Wave
Turkey Red ....
Hardy Northern . . .
REFERENCES
1. Albright, W. D., "Gardens of the Mackenzie," Geog. Rev., 23:1-22
(1933).
2. , "Crop growth in high latitudes," Geog. Rev., 23:608-620
(1933). .
3. Blackman, F. F., and G. L. C. Matthaei, "On vegetative assimilation
and respiration," Proc. Roy. Soc. London, B 76:402-460 (1905).
4. Boysen-Jensen, P., "Studies on the production of matter in light and
shade plants," Bot. Tidskr., 36:219 (1918).
5. Forster, H. C., M. A. H. Tincker, A. J. Vasey, and S. M. Wadham,
"Experiments in England, Wales and Australia on the effect of length
of day on various cultivated varieties of wheat," Ann. Appl. Biol.,
19:378-412 (1932).
6. Garner, W. W., "Comparative response of long-day and short-day
plants to relative length of day and night," Plant Physiol., 8:347-356
(1933).
• • LIGHT 281
7. Garner, W. W., and H. A. Allard, "Effect of the relative length of
day and night and other factors of the environment on growth and
reproduction in plants," Jour. Agr. Res., 18:553-606 (1920).
8. , "Further studies in photoperiodism, the response of the
plant to relative length of day and night," Jour. Agr. Res., 23:871-920
(1923).
9. , C. W Bacon, and H. A. Allard, "Photoperiodism in relation
to hydrogen-ion concentration of the cell sap and the carbohydrate
content of the plant," Jour. Agr. Res., 27:119-156 (1924).
10. Hann, J., Handbook of Climatology, Part 1, "General Climatology,"
trans. 2d rev. German ed. by Robert DeCourey Ward. Macmillan,
New York, 1903.
11. Harder, R., "Kritische Versuche zu Blackmans Theorie der "begren-
zenden Factoren" bei der Kohlensaureassimilation," Jahrb. wiss. Bot.,
60:531-571 (1921).
12. Henry, A. J., J. B. Kincer, H. C. Frankenfield, W. R. Gregg, B. B.
Smith, and E. N. Munns, "Weather and climate," U. S. Dept. Agr.
Yearbook, 1924:457-558.
13. Jenkin, T. J., "Perennial rye-grass at Aberystwyth," Welsh. Jour. Agr.,
6:140-165 (1930).
14. Klages, K. H. W., "Metrical attributes and the physiology of
hardy varieties of winter wheat," Jour. Amer. Soc. Agron., 18:529-566
(1926).
15. Lundegardh, H., Klima und Boden in ihrer Wirkung auf das Pflan&nleben.
Gustav Fischer, Jena, 1925.
16. MacDougal, D. T., Practical Text-Book of Plant Physiology. Longmans,
New York, 1901.
17. Moreillon, M., "Influence de Tombrage sur la valeur des gazons dans
les pasturages boises," Jour. Forest. Suisse, 70:131-142 (1919).
18. Nightingale, G. T., "Light in relation to the growth and chemical
composition of some horticultural plants," Proc. Amer. Soc. Hort. Sci.,
1922:18-29.
19. Pulling, H. E., "Sunlight and its measurement," Plant World, 22:151-
171 and 187-209 (1919).
20. Raunkiacr, C., The Life Forms of Plants and Statistical Plant Geography.
Clarendon Press, Oxford, 1934.
21. Schimper, A. F. W., Plant Geography upon a Physiological Basis, trans.
German by W. R. Fisher. Clarendon Press, Oxford, 1903.
22. Segelken, J. G., "The determination of light intensity," Ecology,
10:294-297 (1929).
23. Shelford, V. E., and J. Kunz, "Use of photoelectric cells for light
measurement in ecological work," Ecology, 10:298-311 (1929).
282 ECOLOGICAL CROP GEOGRAPHY
24. Shirley, H. L., "The influence of light intensity and light quality upon
the growth of plants," Amcr. Jour. Bot.y 16:354-390 (1929).
25. Tippett, L. H. G., "On the effect of sunshine on wheat yield at Roth-
amsted," Jour. Agr. Sci., 16:159-165 (1926).
26. Trumble, H. G., "The climatic control of agriculture in South Aus-
tralia," Trans. Roy. Soc. So. Australia, 61:41-62 (1937).
27. Warming, E., Q ecology oj Plants. Clarendon Press, Oxford, 1909.
28. Weaver, J. E., and F. C. Clements, Plant Ecology. McGraw-Hill,
New York, 1929.
29. Wiessmann, H., "Einfluss des Lichtes auf Wachstum und Nahrstoff-
aufnahme beim Hafer," Landw. Jahrb., 53:183-190 (1919).
Chapter XIX
AIR MOVEMENT
Introduction. Wind and air movement in general constitutes
an ecological factor of both local and regional significance. The
main climatic types over large regions are determined by the move-
ments of large masses of air. Such movements are called forth
mainly by differences in temperature. Temperature variations
result in differences in the density of the air exerting a pressure
phenomenon conveniently evaluated by means of a barometer.
A line drawn through points having the same value of atmospheric
pressure is known as an isobar. The isobars always encircle areas
of low and of high pressure.
Air flow? from regions of high to regions of low pressure. Since
the variations in pressure or weight of the atmosphere are evaluated
by means of barometric pressures, the difference in air pressure
which causes air movements, or winds, is called the barometric
gradient. The movement of air may be compared to the move-
ment of flowing water, that is, down a gradient.
The movements of air caused by heating, cooling, expansion,
and contraction, as well as the massing of the air in one locality
and the counterbalancing depressions formed in another, include
the general or planetary movements. Obviously, the general
movements of air as well as the composition of these air masses
especially with regard to their moisture content and their temper-
ature are of great geographical importance. The choice of crops
and production of crops in any given area may also be greatly
influenced by the prevailing wind conditions. The wind velocity
especially at critical periods and insofar as it may influence loss of
moisture from the plant or soil is of great practical importance.
Certain special types of wind such as the chinook, foehn, monsoon,
or hot winds, as the sirocco, have decided effects on local crop
production. In addition to this, catastrophic air movements
283
284 ECOLOGICAL CROP GEOGRAPHY
such as tornadoes or hurricanes are of significance to crop produc-
tion in limited areas.
Wind erosion is occasioned by the character of the soil, by the
type of cover, and by the velocity of the wind. The possibilities
and actual devastating effects of wind erosion have a very direct
bearing on the agricultural utilization of given areas. The choice
\uftEEffijX^
FIG. 45. Diagrammatic arrangement of wind systems or pressure belts of the
generalized globe. (Reproduced from Kcndrcw, Climate, by permission of the
Oxford University Press.)
of crops, whether grass cover, cereals, or cultivated crops, as well
as the methods of handling these crops are directly influenced by
danger of wind erosion.
General Air Movements and Their Relations to Climate.
The winds of the earth blow in directions determined by differences
in pressure. The pressure distribution is, as has been indicated,
closely linked with temperature phenomena. And to these great
forces must be added the influence of the rotation of the earth.
It should be kept in mind that the magnitude of the rotational
force increases rapidly with the latitude; as a result of this, the
rotation of the earth has a greater effect in deflecting the great
wind systems as the higher latitudes are approached. The general
AIR MOVEMENT
285
circulation of the atmosphere is largely determined by the set of
forces indicated above. General more or less well-defined broad
belts are recognized encircling the globe. These belts of general
circulation or wind systems are shown diagrammatieally in Figs. 45
and 46, taken from Kendrew (4). Figure 45 outlines the general
belts, while Fig. 46 presents
a plausible explanation of the
movement of the air masses
on a generalized or imagi-
nary globe, that is, if the sur- ' fff ft
(M
^-*
/.'
v>
^
face were homogeneous. "It
must be admitted that the
general circulation of the at-
mosphere," states Kendrew,
"is by no means fully under-
stood, and other presenta-
tions of some of its features
than the scheme of Fig. 46 _, ., TJ .7"*, .. ~~ . , .
° Fio. 46. Idealized diagram ot the general
have been given by meteor- circulation of the atmosphere over the
ologists." homogeneous globe. (Reproduced from
The explanation offered Kcndrew> Climate, by permission of the
. T. . P . Oxford University Press.)
by Kendrew for the more
or less definite development of the wind systems of the globe is
given in the following two paragraphs.
"The air that is warmed and expanded over the Equator rises, and
flows away in the higher strata of the atmosphere towards higher
latitudes, where the cold causes contraction, descent and an inflow
aloft (Fig. 46). Thus there is set up a general movement from the
Equator towards the Poles in the higher atmosphere, and it is probable
that the air pressure at heights above 12,500 feet decreases steadily
from Equator to Poles. But all moving bodies come under the influence
of the rotation of the earth, the magnitude of the rotational force
increasing rapidly with the latitude. Hence in their poleward journey
these air currents become deflected more and more towards the east,
until in high latitudes a gigantic circmnpolar whirl is set up. Another
influence now makes itself felt, for centrifugal force is developed in a
rotating mass of this kind, and the air, instead of reaching its Polar
goal, tends to be thrown back towards the Equator, since its speed is
much greater than that of the earth below. The upper winds are
therefore moving eastward and poleward in low latitudes, eastward
with a slight equatorward component in high latitudes. The result is
286
ECOLOGICAL CROP GEOGRAPHY
a piling up of air between the thermal outflow over the Equator and
the dynamical, centrifugal, movement in high latitudes, giving high
atmospheric pressure in the sub-tropics.
"Poleward of these high-pressure belts pressure becomes less towards
the poles, the centers of the circumpolar whirl, and produce an increase
of pressure, slight but quite sufficient to effect a change in the wind
direction from westerly to easterly."
FIG. 47. Prevailing winds over the United States in January. (Reproduced
from Ward, The Climates of the United States, by permission of Ginn and Com-
pany.)
Because of temperature changes, the pressure belts swing some
5 to 10° toward the north during the summer months in the north-
ern and to the south during the summer months in the southern
hemisphere.
It is possible here to give only a broad outline of the wind systems
of the globe; the reader is referred to standard texts on meteorology
for a more detailed treatment of this topic. A general knowledge
of wind systems is of importance to the understanding of climatic
types. The movements and compositions of great masses of air in
relation to bodies of water and land areas are of prime importance
in determining the main characteristics of the climate of any given
locus. Such movements of air masses are greatly influenced not
only by the general wind systems of the globe but also by the
topographical features of the land areas in that mountain ranges
AIR MOVEMENT
287
and other barriers may deflect the movement of air masses from
their general course.
The movement of great masses of air over the large continents
is quite variable and greatly influenced by the seasons and by
topographical features. This is well illustrated in Figs. 47 and 48
taken from Ward (9), giving the prevailing winds over the area
of the United States in January and July.
FIG. 48. Prevailing winds over the United States in July. (Reproduced from
Ward, The Climates of the United States, by permission of Ginn and Company.)
Migratory Cyclones and Anticyclones. The pressure phe-
nomena and wind belts discussed in the preceding paragraphs
represent the normal, or undisturbed, state of affairs. In many
parts of the world, this normal condition is frequently disturbed
by migrating great masses of air, or atmospheric whirls, known
as cyclones and anticyclones. The centers of these disturbances are
in constant motion.
Piston (7) gives a clear-cut definition of these two terms. "The
cyclone consists of a mass of air several hundred miles in diameter
whirling about a center where the pressure is low, and the anti-
cvclone is a mass of somewhat greater diameter whirling about a
center where the pressure is high. The cyclone is usually associated
with wet or cloudy weather and the anticyclone with dry clear
weather." In cyclonic areas the air moves toward a region of low
288 ECOLOGICAL CROP GEOGRAPHY
pressure, with the winds blowing in all directions toward the
center; in anticyclonic areas the reverse is the case — the air
moves outward from a region of high pressure, with the winds
blowing in all directions from the center. The rate of air move-
ment is determined by the barometric gradient. These two types
of disturbances migrate over long distances over more or less
well-defined routes. The paths of the cyclonic storms in the
middle latitudes, that is, in the areas of the prevailing westerly
winds, extend from the west to east. In the north temperate
zone, the cyclonic storms encircle the earth in a belt which dips
toward the south over the continents and turns north over the
oceans. Their paths become somewhat diffused over great bodies
of land as in Eurasia. As the areas covered by the anticyclonic
movements are greater than those covered by the cyclones, the
northern portion of the United States is under the influence of
anticyclones about 60 per cent of the time, and of cyclones about
40 per cent.
The cyclonic movements and cyclones here discussed should
not be confused with the violent storms sometimes referred to by
that name. These violent ^qrms usually covering but limited
areas are properly called tornadoes.
The tropical cyclones arc quite different from the cyclonic
movements of temperate latitudes. Wind velocities of the temper-
ate-zone cyclones rarely rise to 30 miles per hour; the pressure at
the center of the cyclone is usually less than an inch below normal.
In other words, the winds of extra tropical cyclones are mild.
Tropical cyclones, while of infrequent occurrence, usually have
violent winds. The pressure at the center may be two inches or
more below normal. In tropical cyclones, the wind is of destructive
force, and sometimes attains a speed of 200 miles per hour. As
much as ten or more inches of rain may fall in 24 hours. These are
the hurricanes of the tropics, referred to as typhoons in Asiatic
waters.
Areas in the direct path of cyclonic movements such as the
northeastern section of the United States and the countries of
northwestern Europe have variable weather, that is, the weather
changes at frequent intervals. Areas out of the main paths of these
movements have weather that is more uniform, even to the extent
of being monotonous in nature. The cyclonic movements are
AIR MOVEMENT 289
of great importance in determining not only the kind but also the
degree of variability of the weather.
Since the terms "weather" and "climate" were used in the above
discussion, it is necessary to distinguish between them; they are
not interchangeable. The term "weather" refers to the condition
of the atmosphere with respect to its temperature, moisture content,
pressure, light conditions, its movement, etc., at any given moment.
The term "climate," on the other hand, connotes the average of
the weather conditions as experienced in a definite geographical
location and with the passing of the seasons. The characteristics
of a climate are designated by the means of the factors determining
the weather. After these have once been established by means of
records extending over a period of ten or more years they remain
fairly constant; or, as it is stated by Koppen (5), the weather
changes, while the climate remains.
Measurement of Wind Velocity. The three-cup-type Robinson
anemometer is almost universally used for the measurement of
wind velocity. The speed of rotation of the cups of this instrument
is nearly directly proportional to the velocity of the wind. The
central shaft supporting the cups is connected by a train of gears
to a revolving dial on which the total wind movement is shown.
It is used, together with the time between observations, for calcu-
lating average velocity. The instrument may be fitted with a Cam
on the dial so arranged as to close an electric circuit once for every
mile of wind movement. With the aid of an electromagnet, a
recording pen will inscribe a notch for every mile of wind move-
ment on a record sheet of a revolving time drum. The anemometer
may also be provided with an appliance to operate a buzzer at
intervals of one-sixtieth mile. This device is of special help in the
evaluation of high wind velocities.
The deflection anemometer is useful for giving a quick but rather
rough measure of wind velocity; it has the advantage of being
portable.
A continuous record of the direction of the wind can be obtained
by the use of the recording wind vane used by the United States
Weather Bureau.
The Beaufort Wind Scale. The Beaufort scale was originally
devised by Admiral Beaufort in 1805 to advise sailing masters of
the kind and spread of sail that ships of the line might carry and
290 ECOLOGICAL CROP GEOGRAPHY
their probable speed under such sail. It was recently revised for
the benefit of weather observers and is no doubt of some value in
that it provides a guide to probable wind velocities in the absence
of anemometers. The scale ranges from 0, for calm, to 12, to
designate a hurricane. It is graduated in accordance with such
physical effects of the wind as the movement of smoke, leaves,
branches and trunks of trees, and in the case of high velocities
the extent of damage to structures. Thus a moderate breeze,
Beaufort scale number 4, with a wind velocity of 18 to 23 miles
per hour, raises dust and moves small branches of trees. A moder-
ate gale, scale number 8, wind velocity 40 to 48 miles, breaks
twigs from trees, etc.
Effects of Wind on Plant Distribution. "Wind," states Warm-
ing (10), "exerts an influence upon both the configuration and the
distribution of plants." Since the velocity and force of the wind
increases with height above the ground level, tall growing plants
and especially trees are exposed to both the direct mechanical
and the indirect physiological effects of wind to a greater extent
than low growing plants. In severe cases the exposure to wind
may constitute one of the most important factors determining
height of plants and the distribution of vegetation.
The absence of trees in many locations is due to the effects of
wind. Since air movements tend to increase the rate of water loss
from plants, even of plants in a dormant condition, wind during
the winter months when the soil is frozen is especially responsible
for the delineation of the boundaries of woodlands in the higher
latitudes and in determining the upper limits of tree growth on
mountain ranges. Middendorff (6) was the first investigator to
recognize the significance of wind in assigning the limits to the
extension of forests. Schimper (8) also recognized the importance
of wind and especially wind during the winter months to the
establishment of limits to tree growth.
That air movements and wind play an important part in physi-
ological drought is * evident. In the minimal areas, protection
against wind, by topographical features, by living plants such as
shelter belts, and even by the remains of portions of plants as crop
residues, is of considerable importance to crop growth and survival.
Such protection may serve to reduce the velocity of the wind and
one of the hazards encountered in crop production in such areas*
AIR MOVEMENT 291
The action of wind is not necessarily always detrimental. Wind
is effective in the distribution of seeds and of pollen and thus
influences the rate of invasion of newly introduced plants.
Wind also constitutes a factor in the dispersing .of disease-
producing organisms. As a matter of fact, it may carry spores,
such as the causal organism of cereal stem rust, over great distances.
Prevailing winds from an early to a later crop producing area,
especially when uninterrupted by natural barriers as is the case
in the Great Plains, provide a most efficient vehicle for carrying
the spores of black stem rust of wheat from the lower to the upper
portions of this important wheat producing region. In seasons
favorable to the development of rust epidemics the disease becomes
critical in areas extending from south to north at a rate more or
less corresponding with the progressive development of the host
plants from the early to the later areas of production.
Physiological Effects of Wind. Wind has both mechanical and
physiological effects on plants. The outstanding mechanical ef-
fects as related to crop plants are the partial or complete covering
of plants by soil particles; the breaking over of plants; the breaking
off of portions of plants, as the snapping off of heads in mature
cereals; the shattering of seed from mature heads of cereals; the
laceration of leaves; the damage to seedling plants by soil particles
striking tender portions; and in severe instances the entire removal
of young plants from the soil. The most far-reaching physiological
effects of wind are correlated with the intensification of vital
functions of the plant, especially of transpiration and water loss in
general.
Finnell (3) presents data to the effect that high winds may exert
greater damaging effects upon plant growth "than would be
expected by reason of increased transpiration alone."
In considering the physiological effects of wind on plant growth it
is also necessary to consider the loss of water directly from the soil.
Soil moisture losses even without a plant cover increase materially
with increasing wind velocities.
Wind Erosion. When a dry, partially deflocculated soil un-
protected by vegetative cover is exposed to strong or even moder-
ately strong winds, soil particles will be moved. In the last few
years, the problem of soil blowing has been brought before the
public, especially from the Great Plains area. The problem is,
292 ECOLOGICAL CROP GEOGRAPHY
however, by no means limited to subhumid regions. Even in
humid areas sandy soils have long been regarded as actual or
potential blow soils.
Plant cover offers the most efficient and permanent protection
against soil blowing. If such soils are to be used for the production
of cultivated crops, it becomes essential that their organic matter
contents be built up so that they will be flocculated and not readily
broken up into unit particles. Cultural methods leaving the soil
rough and the leaving of crop residues at the surface aid in holding
particles in place.
The texture of the soils severely eroded by wind may be changed
to a point impairing their usefulness for crop production purposes.
Thus Daniel (2), in working with the physical changes in the soils
of the southern High Plains, reports that "the drifts from nine
different soils that have been shifted at least four times contained
73.0% less silt and clay and 31.28% more sand than the respective
virgin surface."
While wind erosion is influenced by the wind factor, it is to be
borne in mind that it constitutes also a cropping problem. It is
definitely associated with problems of proper land utilization
from the standpoints of use for permanent grass cover, cereal
production, or use for intertilled crops. As a matter of fact the
periodic urgency of the wind erosion question is linked with
improper land use in the past; it will continue to present itself as a
problem unless either shifts in land use in some cases, or pre-
cautionary measures in other instances are taken to prevent its
destructive effects. Certain areas in the United States as well as
in other countries of the world have been inadvisably used for
crop production purposes and thus deprived of their protective
native covers. On the other hand, caution should be exercised
before large areas are condemned as totally unsuited for crop
production. With proper methods many of the areas in which
wind erosion may be expected to become a problem periodically
can be utilized. Thus Call (1), in speaking of conditions prevailing
in the central Great Plains, states that
"there is no reason to expect that wind erosion will not be controlled
in this region unless climatic conditions occur that are much less favor-
able for the growth of vegetation than those that have prevailed during
the past 50 years. The best information available would lead to the
AIR MOVEMENT 293
conclusion that while periods of serious wind erosion will occur in the
future during times of drought, such periods will not lead to the destruc-
tion of the soil or become a major factor that will preclude the utiliza-
tion of this area for successful crop production."
REFERENCES
1. Call, L. E., "Cultural methods of controlling wind erosion," Jour.
Amer. Soc. Agron., 28:193-201 (1936).
2. Daniel, H. A., "The physical changes in soils of the southern High
Plains due to cropping and wind erosion and the relation between the
^^-i-^1™ ratios in these soils," Jour. Amer. Soc. Agron., 28:570-
Clay
580 (1936).
3. Finnell, H. H., "Effect of wind on plant growth," Jour. Amer. Soc.
Agron., 20:1206-1210 (1928).
4. Kendrcw, \V. G., Climate. Clarendon Press, Oxford, 1930.
5. Koppen, W., Die Klimate der Erde. Walter DeGruyter & Co., Berlin,
1923.
6. Middendorff, A. T. von, Reise in dem aussersten Nor den und Osten Si-
biriens. St. Petersburg, 1867.
7. Piston, D. S., Meteorology. Blakiston, Philadelphia, 1931.
8. Schimper, A. F. W., Plant Geography upon a Physiological Basts, trans.
German by W. R. Fisher. Clarendon Press, Oxford, 1903.
9. Ward, R. D., The Climates of the United States. Ginn, Boston, 1925.
10. Warming, E., Oecology of Plants, trans. German by P. Groom and I. B.
Balfour. Clarendon Press, Oxford, 1909.
Chapter XX
CLASSIFICATION OF CLIMATE
INTRODUCTION
Objectives in Classification. Being made up of a variety of
elements active both as to intensity and time, climate is difficult
to classify. The crop ecologist is interested in the factors making
up the climatic rhythm from the standpoint of their separate and
combined effects on plant growth, especially on the vegetation
rhythm of crop plants.
Classification serves to identify and to show relationships. A
concise statement of the main characteristics of the climates of
adjacent or of widely separated areas showing at a glance their
similarities or differences is of g»eat value in the study of ecological
crop geography. Such a statement not only provides the student
with the most probable reason for the production of a particular
crop in a certain area but also reflects on the climatic requirements
and the range of adaptation of the crop in question.
Basis for Classification. The outstanding features of the climate
of any given region are determined by a number of factors, such
as its latitude, its altitude, its proximity to and direction from large
bodies of water, and its local topography. The direction of the
prevailing winds in relation to land areas is of importance in all
instances but affects the climates especially of locations near large
bodies of water and in areas where the position and direction of
mountain ranges deflect the movement and the temperature of
large masses of air.
While the factors indicated above actually determine the main
climatic features of a region, they do not provide the best criteria
to serve as a basis of any but very general and descriptive classifica-
tions. They serve to provide the basis for differentiating, for in-
stance, between marine and continental or woodland and grassland
climates, but do not give detailed and definite enough criteria for
294
CLASSIFICATION OF CLIMATE 295
the numerical evaluation of climatic features upon which a more
comprehensive classification may be based. Comprehensive clas-
sifications of climates such as Koppen's (10) and Thorn thwaite's
(17 and 18) require the actual evaluation of the intensities of the
two most important factors determining the weather from day to
day and with the passing of the seasons, namely temperature and
precipitation. These two factors are of course of prime importance
in determining the distribution of plants. A classification based on
factors that can be evaluated with precision and treated mathe-
matically has the advantage of lending itself to symbolism. The
employment of symbols for the designation of climatic types has
the obvious advantage of simplicity in that a system of codification
may be employed to designate the main features of the climates
classified. While it is recognized that climatic factors other than
moisture and temperature conditions come into play in the evalu-
ation of climate and have their specific effects on the weather at
any given time and on plant responses, it is also evident that all
climatic factors are more or less interrelated and to a high degree
correlated and conditioned as to their respective intensities with
moisture and temperature conditions.
Limitations of Climatic Classifications. To be of greatest
value, designated classes of climates must be definite, yet not too
complex. The number of classes should be held to a minimum. A
classification based on too many factors and on too many fine
distinctions negates the very objectives of classification. Classifica-
tions are in no way expected to take the place of descriptive treatises
on the climates; they have application primarily in broad systematic
groupings showing relationships between the various regions with
respect to climatic similarities and differences. Thus no classifica-
tion of climate will take the place of such extensive works dealing
with the climates of the continents as presented by Hann (3) and
Kendrew (9).
In a designation of groups of climates it must be recognized that
the lines of demarcation of necessity are based on the average
values or intensities of the climatic features considered. This
should not lead to the conclusion that variability of the climatic
features is not considered important. Variability both within and
between seasons is of great significance to the agricultural utiliza-
tion of any given area. The inclusion of a measure of variability
296 ECOLOGICAL CROP GEOGRAPHY
into a system of classification, however, would make such a system
too complex for general application. Whenever climatic types
are cartographically delineated it should be understood that the
boundary lines between the types are not sharp; but rather, that
they represent transition zones and appear in their true role as
indicators of direction of change.
CLASSIFICATION BASED ON THE RELATIVE
DISTRIBUTION OF LAND AND WATER
Marine Climates. "The influence of latitude," states Ward
(22), "may be wholly overcome by the effects of land and water.
Land and water are fundamentally different in their behavior
regarding absorption and radiation." This is accounted for by the
difference in the specific heat and the greater heat-holding capacity
of water as compared to land and soil.
The equalizing effect of bodies of water on temperature is further
enhanced by the fact that water is able to store for future release
a greater quantity of heat than soil. Temperature changes pene-
trate the soil only a few feet, while they reach great depths in
water. This is due to ascending and descending currents in water.
In soil the heat from the surface layers can reach the lower strata
only by conduction.
Ward (22) points out that the climates of large continental areas
of the middle and higher latitudes are characterized by great
seasonal fluctuations in temperature. "They are distinctly radical
in their tendencies. The land areas absorb much heat, but part
with it readily. The oceans, on the other hand, cool but little
during the night and in winter. They take in but little heat, and
part with it reluctantly. Conservatism in temperature is a dis-
tinctive feature of marine climates."
The outstanding characteristic of marine climates is the uni-
formity or smaller range of both the diurnal and seasonal temper-
atures. Continental climates show wide ranges. The other sig-
nificant difference between these two climates, also traceable to
the fundamental differences in the behavior of land and water
regarding absorption and radiation of heat, is found in the varia-
tion in the shape of their annual temperature curves. Temperatures
of continental climates attain their maxima about one month after
the date of the sun's maximum altitude; they attain their minima
CLASSIFICATION OF CLIMATE 297
in a little less than a month after the sun's lowest altitude. In
marine climates the delay in the time of maxima and minima is
much greater. The high temperatures of the year do not occur
until August as contrasted to July for the continental climates.
The lowest temperatures in marine climates do not occur until
two, or even three, months after the greatest declination of the
sun, that is, in February or March.
Not all land areas in close proximity to large bodies of water
have marine climates. The climates of such areas, that is, whether
marine or continental, are determined primarily by their direction
from the water in relation to the prevailing wind. Likewise, the
presence of mountains in the way of onshore winds has decided
effects. The onshore winds can exert their equalizing effects
inland only if their paths are not obstructed by mountain ranges.
The narrow north Pacific coastal slope of this continent, even as
far north as the lower portion of Alaska, has a marine climate.
On the lee side of the Cascade range the climate is decidedly
continental. The effect of a break in a mountain range, on the
other hand, is well illustrated by the effects of the Columbia River
gorge. The relative mildness and transitional character of the
climates of the Columbia River basin and the Palouse region can
be accounted for by the fact that the onshore winds can penetrate
inland through the gap cut by the Columbia through the Cascade
range.
The effect of onshore and offshore winds is well illustrated by
the difference in the climates of the Pacific coastal slope as con-
trasted with those of the Atlantic coastal belt; in the first case the
climates are marine, in the latter case, continental. As stated by
Ward (22), "The influence of the Atlantic Ocean is much dimin-
ished by the fact that the prevailing winds are offshore. Hence, it
follows that there is not very much of the tempering effect usually
associated with the conservative ocean waters. The Atlantic coastal
belt, except when the winds temporarily blow onshore, does not
differ very much from the interior." The effects of onshore winds
are also influenced by the temperature of large bodies of water as
modified by latitudes and ocean currents.
The effect of onshore winds on winter temperatures is evident
from a glance at Fig. 49, showing the mean temperatures in degrees
Fahrenheit for the month of January in different parts of the world.
298 ECOLOGICAL CROP GEOGRAPHY
The isotherms of the northern hemisphere turn sharply to the
south along the Pacific coast of North America and in northwestern
Europe. On the lee side of the continents, that is, along the Atlantic
coast in North America and the northern coast of western Asia,
they turn to the north. The isotherms also show that the marine
climates extend farther inland in northwestern Europe than along
the mountain-braced Pacific coast of North America. Owing to
the absence of mountain barriers, the marine climates of the low-
lands along the Atlantic Ocean and the North Sea merge gradually
into the transitional or littoral, and as the plains of Russia are
approached into the true continental type. In North America,
the lines of demarcation between these two types of climates are
sharp.
Figure 49 also shows that the temperatures over land areas in
summer are higher than over the adjacent oceans. Note the trend
of the isotherms in the southern hemisphere.
Continental Climates. These climates take their name from the
interior of the continents. Their effects may, however, extend, as
has been indicated, right up to the coast line on the lee side of
large areas of land.
Since land areas warm up and also cool down more rapidly
than water, continental climates are characterized by great ranges
of temperature between the winter and summer seasons. Thus
according to Visher (20), "western Oregon has a normal seasonal
range of only about 18°F (10°C), while South Dakota has a range
of 60°F (33°C). The extreme ranges in these places are about
85°F (46°C) and 165°F (91 °C) respectively."
The diurnal range of temperatures is also greater in continental
than in littoral and marine climates. The effect of the proximity
and direction of large bodies of water has been pointed out. Other
factors entering to make for greater ranges in daily temperatures
are the humidity of the atmosphere and the presence of vegetation.
As a general rule the diurnal range in temperature increases with
lower humidities and with aridity. Areas with sparse vegetation
show a greater range of temperature than those heavily covered.
No general statement can be made relative to the differences in
precipitation in marine and continental climates. As indicated
by Hann (4) "the amount and frequency of precipitation as a rule
decreases inland, but this decrease is so irregular, and depends so
299
300 ECOLOGICAL CROP GEOGRAPHY
much upon the topography; upon the position of mountain ranges
with respect to rain-bearing winds, etc., that no general illustra-
tions of this rule can be given."
Mountain Climates. Mountain climates may be regarded as
extreme types of continental climates. The prime factor influ-
encing their characteristics is elevation. The seasons are distinct;
they are initiated and also end abruptly. Variations in slope are
of great importance to the agricultural utilization of areas in
mountain regions in that they affect both soil and local climate.
CLASSIFICATION BASED ON NATURAL VEGETATION
Plant Physiognomy and Climatic Conditions. While it is
not necessary to become involved here in the controversy relative
to the classification of plants into physiognomic forms, it must be
recognized, as has been pointed out on other occasions, that life
forms are greatly influenced by environmental conditions. The
physiognomy, or outward appearance, of the plant cover of any
given habitat is determined not only by the visible structure or
external morphology of individual species but also by the diversity
of the species represented. In $ detailed study of environmental
conditions it becomes necessary, as pointed out by Clements (1),
to consider both the diversity of the species represented and also
the altered individuals, the ecads, of the same species. Both indicate
differences in conditions and trends.
The index value of natural vegetation for proper land use is well
stated by Shantz and Zon (15) in the following paragraph.
"The natural vegetation of a country, when properly analyzed and
classified, may serve a very concrete and practical purpose. As a new
country becomes settled the natural vegetation must be replaced gradu-
ally by agricultural crops, orchards, pastures, and man-made forests.
The suitability of the virgin land for various crops is usually indicated
very clearly by the natural vegetation. After a correlation is established
between different forms of natural vegetation and various agricultural
and forest crops, it provides a means of dividing the country into natural
regions of plant growth, which can be used as indicators of the potential
capabilities of the virgin land for agriculture and forest production."
Numerous other statements based on detailed experimental data
showing the indicator significance of natural vegetation could be
given. This is not necessary. It is essential, however, to point out,
CLASSIFICATION OF CLIMATE 301
in adhering to the general topic of classification of climates, that
the natural vegetation of any given locus is not determined by the
climate alone. The soil factors also enter into play. Furthermore,
the soil conditions both past and present must be considered in
the development and maintenance of a native vegetation. These
statements are of special significance here. They indicate clearly
that any broad classification of climates must be based on regional,
rather than local, flora. This definitely limits the number of classes
based on natural vegetation, and rightly so. Natural vegetations
offer a usable criterion of local climatic and soil conditions rather
than a basis for detailed classifications of climates. Nevertheless,
when quite distinct, larger types of natural vegetation such as
woodlands, grasslands, and deserts are selected, valuable deduc-
tions of the outstanding features of the climates of the areas where
they constitute the climax can be drawn. Also, the utilization of
their habitats for agricultural purposes is definitely associated
with their distribution and relative development. Since these
groups of vegetation extend over large areas any classification of
climates based on them is decidedly regional in nature. The
climatic types thus established are of course separated by transition
zones, and subtypes may be recognized in places where the native
vegetation has been sufficiently analyzed. Thus in the United
States climatic conditions in the climax tall-grass prairie, in the
mixed prairie, and in the short-grass plains differ materially.
Figure 50, taken from Henry ei al. (6), gives "a very generalized
map of the natural vegetation of the world showing its broader
relations to climate." More detailed world vegetation maps are
available. An especially clear map is given by Hayek (5) showing
the distribution of 16 distinct types of vegetation. The types
presented arc: cold desert, mats or meadow lands, tundra, dry
deserts, steppes, savanna, thorny chaparral half deserts, coniferous
forests, summer-green deciduous forests, hard-leaved forests, heather,
temperate rain forests, savanna forests, monsoon forests, subtropical
rain forests, and the tropical rain forests.
Woodland Climates. A glance at Fig. 50 shows that woodland
or forest formations are found in relatively well-watered areas.
This is not surprising. Trees expose a large transpiring surface
to the atmosphere; great quantities of water are a prime necessity.
This is true especially for deciduous trees. Certain of the conifers
302
CLASSIFICATION OF CLIMATE 303
and especially pines have more or less xerophilous leaves and
consequently transpire less water. On the other hand, trees have
well-developed root systems enabling them to draw on water
supplies in the lower strata of the soil.
The seasonal distribution of precipitation is of no great conse-
quence for the development of woodland. The important point
is to have moisture in the soil and subsoil. Trees growing in areas
lacking summer precipitation draw on the moisture stored in the
soil in winter or in early spring. Trees are found, even in close
formations, in areas with both uniform and highly periodic distribu-
tions of precipitation.
The water-vapor content of the atmosphere is important for the
growth of trees. Their transpiring surfaces extend into the higher
and also drier atmosphere. Large hydrophilous trees in full leaf
demand, according to Schimper (16), an average relative humidity
of around 80 per cent, which may drop down to 60 per cent only
for a few hours during the day. Xerophilous trees are satisfied
with less atmospheric humidity. Several species can withstand,
even when in full foliage, a relative humidity of 30 per cent for a
time without damage.
In the higher latitudes drying winds during the winter season
are highly detrimental to tree growth even to the extent of excluding
them under those conditions. Consequently the winters of the
woodland climates have relatively moist atmospheres, and drying
winds are infrequent. Drying winds during winter set the polar
limits for tree growth probably as much as extremely low temper-
atures.
The outstanding characteristics of a woodland climate are
summarized by Schimper as: A warm period of vegetation, con-
stantly moist subsoil, and moist, still air especially during the
winter.
From the above it is evident that the so-called woodland climates
cover a wide range, and that they delineate only a very general
condition. The main shortcoming, as fair as designating definite
climatic conditions to be used for comparative purposes, is that no
indication is given of the seasonal distribution of precipitation.
Areas with a natural cover of the hydrophilous deciduous trees
have, however, under most conditions relatively humid types of
climates with a fairly uniform distribution of rainfall during the
304 ECOLOGICAL CROP GEOGRAPHY
growing season. Furthermore, since these trees demand a high
relative humidity of the atmosphere, the evaporation rates in their
areas of growth are low while the effectiveness of precipitation is
high. For this reason areas with woodland climates are adapted
to crops requiring relatively moist conditions. This is true espe-
cially for areas in the middle and higher latitudes with a climax
of broad-leaved deciduous trees. The main crops of the woodland
areas are: the cereals, corn, potatoes, sugar beets, peas, beans,
tobacco, cotton, and sugar cane. These areas grow soft wheats
as contrasted to the hard, high-protein wheats produced in the
drier grassland areas.
Savanna and Forest-Steppe Climates. Savannas and forest
steppes represent the transitional zone between the woodlands
and the true grasslands. Hayek differentiates between the true
savanna and the savanna forests, the latter being found in India
as a transition between the monsoon forests and the true savanna.
Savannas represent the transition between the tropical rain
forests and the grasslands, and chaparral deserts in the lower
latitudes. The climates are intermediate between those of the true
grasslands and woodlands, *ln areas where the temperature
is not too high they represent some of the most usable areas for
agricultural purposes in the tropics. Because of the generally high
prevailing temperature and a high saturation deficit of the air,
however, the efficiency of precipitation is low and the climate
is highly hazardous. The savannas and grasslands of Africa com-
prise around one-fifth of the area of that continent. Owing to
the critical fluctuations in rainfall, Renner (14) refers to the savanna
and grassland areas of the Sudan and adjoining Nigeria as the
famine zone of Africa.
In the higher latitudes the true woodlands merge into the
grasslands through a transition of parklike areas referred to by
Funk (2) as forest steppes (Waldsteppen). As in the savanna the
trees grow in open or scattered formations with grass in between
them. These areas are of great agricultural importance. The
climates are more humid and less variable than those of the true
grasslands. Owing to the limited or complete absence of leaching,
the soils of the forest steppe are generally more fertile than those
of the humid woodlands. This in part compensates for the greater
fluctuations in rainfall.
CLASSIFICATION OF CLIMATE 305
Grassland Climates. The outstanding characteristics of a grass-
land climate are essentially those features unfavorable to the
establishment of forests, namely, limited precipitation and cold
drying winds during the winter season.
In discussing the characteristics of the climates of grassland
areas it is necessary to distinguish between areas with a dense or
closed and those with an open or bunch-grass formation. The
former are the more widely distributed and are the ones generally
referred to in discussions of conditions on the grasslands. They
may be called the true grasslands.
The main elements of the true grassland climates are: precipita-
tion limited, but abundant enough to keep the surface layers of the
soil moist during late spring and early summer; moderate temper-
atures during the period of vegetative growth, followed by high
temperatures during the middle and later portions of summer;
dry conditions and even severe droughts after early summer and
during the autumn months; and cold drying winds during the
winter. Grassland climates have a decided continental aspect.
These conditions are very effective in preventing the establishment
and the growth of trees. Trees are able to gain a foothold only
in areas where a sufficient moisture supply is available, as along
streams and in places protected from the main force of drying
winds during the cold season. The same conditions also stt the
northern boundaries of autumn-sown cereals in accordance with
their respective degrees of winter-hardiness. As stated by Weaver
and Himmel (25), "water-content of soil and humidity are the
master factors in the environment of the prairie."
Climatic conditions of the bunch-grass areas of the Pacific North-
west are quite different than in grass areas with close formations.
The precipitation in these areas is also highly periodical, but most
of it comes during the winter months. In the true grasslands from
70 to 80 per cent of the annual precipitation falls during the early
portion of the growing season. Bunch-grass formations may,
however, occur also within areas of the true grasslands. Here they
are found in places with open soils or in sandy areas, that is, under
conditions favoring the rapid penetration of practically all the
water that falls.
Climatic conditions in the true grasslands are far from uniform,
nor are they characterized by a uniform vegetation throughout.
306 ECOLOGICAL CROP GEOGRAPHY
The great expanses of grassland in central North America extending
across the Mississippi Valley from the forests of the East to the
foothills of the Rockies show great differences in luxuriance of
growth, indicating great variations in climatic conditions and crop
producing potentialities. As stated by Weaver and Clements (24),
"the tall-grass prairies of the eastern portion are distinctly different
from the short-grass plains of the west and southwest, and between
these two regions is a broad belt of mixed grassland where tall and
short grasses intermingle. The chief causes of these differences in
grassland vegetation are the differences in the quantities' of soil moisture
supplied by the rainfall and the length of time during which soil mois-
ture is available. Decreased relative humidity westward is also an
important factor. Differences in soil structure, resulting from differ-
ences in climate and vegetation during its development, are also pro-
nounced."
Not only do the climates become more arid in going from the
tall-grass prairies to the short-grass plains, the true steppes, but
they also become more variable.
The tall-grass prairie covers approximately one-third of the
Dakotas, Nebraska, Kansas, and large areas in central Oklahoma.
The mixed prairie occupies central Nebraska and Kansas and
practically the entire remaining northern and western portion of
the Great Plains area. The short-grass plains extend from western
Nebraska, Kansas, and Oklahoma to the Rockies in Colorado and
northern New Mexico down to northwestern Texas.
Not all areas originally covered by grasses have grassland
climates. Thus in the more humid eastern portions of the grass-
lands of the United States, that is, in Illinois, Iowa, and Missouri,
grasses occupied potential forest lands. Present as well as past
soil conditions, especially in relation to drainage features, fires,
and perhaps other causes, have delayed the development of the
forest climax. Funk points out these same conditions for the
more humid grassland areas in Europe and particularly in Russia.
Weaver (23) discusses some of the ecological aspects of agriculture
in the prairie. The following paragraph from his paper merits
direct citation.
"Cereal (grass) crops and certain legumes are best adapted to the
grassland. Ecologically these have much in common with the native
grasses. Aside from maize, practically all important crops grown in
CLASSIFICATION OF CLIMATE 307
the grassland have been introduced from regions with a similar grass-
land climate. Successful agriculture has been made possible and
profitable only by such introductions as Durum and Turkey Red wheat,
sorghums, etc. By selection and breeding, crops even better adapted
to a grassland climate have been produced, and agriculture in the
prairie made more certain and more profitable. The larger cereal
maize, like the taller grasses, is best developed in the eastern part of
the grassland, the Corn Belt extending but little beyond the tall-grass
prairie. Sorghum is an excellent crop for the drier, southwest, short-
grass plains. Alfalfa replaces clover as a leguminous crop in all but the
best watered portions of the grassland. It exhausts the water of the
subsoil so thoroughly as to introduce puzzling agronomic problems."
KOPPEN'S CLASSIFICATION OF CLIMATES
Basis of Classification. Koppen published two classifications of
the climates of the world. The first (10) appeared in 1900, the
second (1 1) in 1918. The more recent classification is also discussed
in detail in Koppcn's book Die Klimate der Erde (12). The early
classification was based largely on vegetation zones, while the more
recent one is based upon temperature, rainfall, and seasonal
characteristics. These factors are of course fundamental in the
distribution of vegetation. The earlier and more recent classifica-
tions show many resemblances, both in their larger climatic belts
and in their smaller subdivisions. There is also a broad resemblance
in the general decisive climatic features selected as the basis of the
subdivisions. The discussion here and later applications to the
problems of crop distribution will be limited to Koppen's more
complete classification of 1918. This classification was made
available to the English reader through the reviews presented by
Ward (21) and James (7). Both of these reviewers reproduced
Koppen's map in black and white.
Zonal Subdivisions. The fundamental zonal divisions between
the equator and the poles are designated by six capital letters as
follows:
A. One winterless tropical rain belt.
B. Two incomplete dry belts.
C. Two warm temperate belts without usual winter snow cover.
D. One boreal or subarctic belt with sharp distinction between
summer and winter conditions (this belt does not occur in
the southern hemisphere).
308
ECOLOGICAL CROP GEOGRAPHY
E. Two polar caps beyond the limits of tree growth — the
tundra climate.
F. Regions of perpetual frost.
FIG. 51. Climatic regions of North America according to Koppen's classification,
with modifications by Van Royen.
The first four of these zones are again subdivided on the basis of
rainfall conditions. These subdivisions are given below together
with the symbols employed to designate each of the types. The
first letter in the formula gives the zone, it is always written in
Fio. 52. Climatic regions of South America according to Koppen's
classification.
309
310
ECOLOGICAL CROP GEOGRAPHY
capitals, also the designation of the steppe and desert climates,
BS and BW.
Af — Tropical rain forest climate.
Aw — Periodically dry savanna climate.
BS — Steppe climate.
BW — Desert climate (German Wiiste).
FIG. 53. Climatic regions of Europe according to Koppen's classification.
Gw — Warm climate with dry winters.
Cs — Warm climate with dry summers.
Cf — Moist temperate climate with mild winters (German
feucht).
Dw — Climate with cold dry winters.
Df — Climate with cold moist winters.
Koppen's distinction between the dry, B, and the more humid,
C and D, as well as that between the desert and steppe regions
was discussed in Chapter XIII in connection with the determina-
tion of humidity provinces. The boundary line between the dry
CLASSIFICATION OF CLIMATE
311
and more humid climates is placed arbitrarily at the point where
the annual precipitation and evaporation are in equilibrium
Koppen also designates the temperature limits for each of the
zonal types of climates. Thus in the A type the normal temper-
ature of the coldest month of the year must be more than 18°C.
In the C type the temperature of the coldest month is between
^U Off I.-.-V1 im Sfififil r All ^asESJ***^ ^ JSgir Ji
FIG. 54. Climatic regions of Asia according to Koppcn's classification
dl**/1 — \ I: I^V»<* r»/^l/^<»oi' w^/^r%*V» ir> *-V»*» Ti ^»li»>^ot-*» 10 l/^oo
18 and — 3°C. The coldest month in the D climate is less than
— 3, and the warmest month more than 10°C. In the E climates
the average temperature of the warmest month is less than 10,
and in the F less than 0°C.
Complete Formulation of Climatic Characteristics. In addi-
tion to the zonal subdivisions given above, Koppen enriches his
map with a series of climatic symbols, indicating the variations and
special developments which are found within the more general
regions. This provides a complete formulation of climatic condi-
tions. The climatic symbols are attached to the designated set of
312
ECOLOGICAL CROP GEOGRAPHY
letters for the zonal subdivisions. Thus the climatic formula
Cfb indicates a moist temperate climate with mild winters with
the mean temperature of the warmest month under 22°C and with
FIG. 55. Climatic regions of Africa according to Koppen's classification.
at least four months over 10°C; BSk indicates a steppe climate
with cold winters, with annual temperatures below 18, and the
warmest month above 18°G, etc. The symbols used are as follows,
all temperature designations are on the centigrade scale.
CLASSIFICATION OF CLIMATE 313
a — Mean temperature of the warmest month above 22°.
b — Mean temperature of the warmest month under 22, at least
four months above 10°.
c — Only one to four months above 10, coldest month above
- 38°.
d — Temperature of the coldest month less than — 38°.
f — Constantly moist (sufficient rain or snow in all months),
g — Ganges type of annual temperature trend, with maximum
before the turn of the sun and the summer rainy season,
h — Hot, annual temperature above 18°.
i — Isothermal, difference between extreme months less than 5°.
k — Cold winter, annual temperature less than 18, warmest
month above 18°.
k7 — The same, but warmest month less than 18°.
1 — Mild, all months 10 to 22°.
m — Monsoon rains, primeval forest in spite of one dry period,
n — Frequent fogs,
n' — Infrequent fogs, but high humidity accompanied by lack
of rainfall, and relatively cool (summer below 24°).
p — The same, with summer temperature 24 to 28°.
p' — The same with very high temperatures (summers above 28°).
s — Driest period in summer,
w — Driest period in winter.
s'w' — The same, but rainy season shifted into autumn.
s"w" — The same, but rainy season in two parts, with a short
dry season intervening,
u — (Reversed) Sudan type of temperature variation, with
coolest month after summer solstice,
v — Cape Verde type of temperature variation with warmest
season shifted into autumn.
x — Transition type with early summer rains.
x' — The same with infrequent but intense rain at all seasons
of the year.
S — Steppe climate.
W — Desert climate.
Maps of Koppen's Climatic Regions. Figures 51 to 56 give
the climatic regions of the continents according to Koppen's
classification. Figure 51 includes the modifications of Koppen's
314
ECOLOGICAL CROP GEOGRAPHY
original map as recommended by Van Royen (19) for the eastern
portion of North America. The legends used in this set of maps
correspond with modifications to those given by Passarge (13).
These maps of the climatic regions of the continents together with
the maps based on Thornthwaite's classification, to be discussed
presently, will be referred to at intervals in Part IV; both Koppen's
FIG. 56. Climatic regions of Australia according to Koppen's classification.
and Thornthwaite's maps are given. This will enable the checking
of one against the other. These two classifications of climates have
been used extensively by different investigators of climatic relation-
ships. They will be employed in Part IV for purposes of providing
a readily stated summary of the outstanding climatic features of
the regions of distribution of important field crops.
THORNTHWAITE'S CLASSIFICATION OF CLIMATES
Basis of Classification. The main outstanding features of
Thornthwaite's classification of climates as well as the main points
of variance between this classification and Koppen's are well
stated by Thornthwaite (18) in the following paragraph.
CLASSIFICATION OF CLIMATE
315
"The present classification is like Koppen's in that it is quantitative
and attempts to determine the critical climatic limits significant to the
distribution of vegetation and also in that it employs a symbolic
EB'd
1. BCr
2. CC'd
3. CCrs
4. ACV
5. DB'd
6. BBs
7. DB's
CA'w
B. DB'w
AA'r
FIG. 57. Climatic regions of North America according to Thornthwaite's classi-
fication.
nomenclature in designating the climatic types. It differs from
Koppen's classification in that it makes use of two new climatic con-
cepts, precipitation effectiveness and temperature efficiency. It is in-
ferred that in the tropical rain forest, the most rapidly growing and
the densest vegetation type on the earth, the climate must be the most
FIG. 58. Climatic regions of South America according to Thorn thwaite's
classification.
316
CLASSIFICATION OF CLIMATE
317
favorable of all for plant growth. Temperatures are constantly high
and rainfall is constantly abundant. Here, therefore, the precipitation
effectiveness and the temperature efficiency must be at a maximum.
Diminution of either element will produce conditions less favorable
for the rapid development of vegetation. It is evident that precipita-
tion effectiveness grades from a maximum in the tropical rain forest
to a minimum approaching zero in the tropical desert and that tem-
perature efficiency grades from a maximum in the tropical climate to
FIG. 59. Climatic regions of Europe according to Thornthwaite's classification.
a minimum at zero in the climate of perpetual frost. The vegetation
transitions due to diminished effective rainfall are: (A) rain forest,
(B) forest, (C) grassland, (D) steppe, (E) desert, and those due to
diminished temperature efficiency are: (A') tropical rain forest, (B')
temperate rain forest, (C') microthermal rain forest, (D') taiga, (E')
tundra, (F') perpetual frost (no vegetation). The dry or cold bound-
aries of any of these regions are critical climatic limits beyond which
the vegetation type cannot go. Of course it is understood that because
of edaphic, cultural, or historical factors vegetation types do not
always extend out to their climatic limits."
318
ECOLOGICAL CROP GEOGRAPHY
The boundaries of Thornthwaite's five humidity and six temper-
ature provinces have already been discussed in their respective
places in Chapters XIII and XVII.
When five humidity and six thermal zones or provinces are
combined, 30 theoretical possible climatic regions result. In
addition, seasonal distribution of effective precipitation was con-
sidered on the basis of abundance of: precipitation at all seasons,
FIG. 60. Climatic regions of Asia according to Thornthwaite's classification.
the "r" type; scanty rainfall in summer (abundant in winter), the
"s" type; scanty rainfall in winter (abundant in summer), the "w"
type; and scanty precipitation at all seasons, the "d" type. A
modification of the winter dry or "w" type is recognized in certain
tropical areas. "Here the drought occurs in spring instead of
winter, and the rainy season is in fall instead of summer." The
type is designated as "w'."
Thus, the classification is based on three climatic factors: (a) pre-
cipitation effectiveness, (b) temperature efficiency, and (c) seasonal
distribution of effective precipitation.
CLASSIFICATION OF CLIMATE
319
Formulation of Climatic Characteristics. The factors em-
ployed in Thornthwaite's classification have five, six, and four
aspects respectively. Each is designated by a symbol. The formula
FIG. 61. Climatic regions of Africa according to Thornthwaite's classification.
for a particular climate is then designated by three combined
letters, except for the D', E', and F' types designating strictly
temperature conditions, namely taiga, tundra, and perpetual
frost, respectively. "There are 120 different possible combinations
of these 15 symbols, making 120 theoretically possible climates.
520
ECOLOGICAL CROP GEOGRAPHY
However, certain combinations of symbols are eliminated by
definition; and others, being meteorologically impossible, do not
occur anywhere on the earth, so that of the 120 possible combina-
tions only 32 represent actual climatic types."
In the formulation of any climatic type the humidity conditions
are stated first in the form of capital letters for the respective five
FIG. 62. Climatic regions of Australia according to Thornthwaiie's classification.
types (from A to E). The second letter of the formula, also capital-
ized and graced with a prime mark, represents one of the six possible
temperature efficiency types (from A' to F'). The third letter
of the formula represents the seasonal distribution of effective
precipitation (r, s, w, d); it is designated by a small letter. Thus,
a climate BB'r is humid, mesothermal (has a relatively high annual
temperature), and has abundant precipitation at all seasons;
a DC'd climate is semiarid, microthermal (relatively low temper-
atures), and has scanty rainfall at all seasons.
A fourth letter designating the summer concentration of temper-
atures may be used in the study of local climatic relations. Thorn-
CLASSIFICATION OF CLIMATE 321
thwaite omitted the fourth letter on his maps of the climates of
North America and of the earth. Jones and Bellaire (8) found the
fourth letter of value in the study of the climates of Hawaii.
Maps of Thornthwaite's Climatic Regions. Thornthwaite
published maps of the climates of North America (17) and of the
world (18). Figures 57 to 62, reproduced from Thorn thwaite's
colored maps, give the climatic regions of the continents in black
and white.
REFERENCES
1. Clements, F. E., Plant Indicators. Carnegie Inst. Publ. No. 290, Wash-
ington, 1920.
2. Funk, S., "Die Waldstcppenland-schaften, ihr Wesen und ihre Ver-
breitung," Verdffentlichungen des Geographishen Instituts der Albertus-
Universitat zu Konigsberg. Heft 8:1-65 (1927).
3. Hann, J., Handhuch der Klimatologie. 3 Aufl., Engelhorn, Stuttgart, 1908.
4 ? Handbook of Climatology, Part 1, "General Climatology,"
trans. German by R. D. Ward. Macmillan, New York, 1903.
5. Hayek, A., Allgemeine Pflan&ngeographie. Gebriider Borntraeger,
Berlin, 1926.
6. Henry, A. J., J. B. Kincer, H. C. Frankenfield, W. R. Gregg, B. B.
Smith, and E. N. Munns, "Weather and agriculture," U. S. Dept. Agr.
Yearbook, 1924:457-558.
7. James, P. E., "Koppen's classification of climates: A review," Mo.
Wea. Rev., 50:69-72 (1922).
8. Jones, S. B., and R. Bellaire, "The classification of Hawaiian climates:
A comparison of the Koppen and Thornthwaite systems," Geog. Rev.,
27:112-119 (1937).
9. Kendrcw, W. G., The Climates of the Continents. Clarendon Press,
Oxford, 1937.
10. Koppen, W., "Versuch eincr {Classification der Klimate, vorziigs-
weise nach ihren Bezichungcn zur Pflanzenwelt," Geogr. ^eitschr.,
6:593-611, and 657-679 (1900).
\\ ? "Klassification der Klimate nach Tempcratur, Niederschlag
und Jahrcsverlauf," Petermanrfs Mitteilungen., 64:193-203, and 243-
248 (1918).
12. , Die Klimate der Erde. Walter De Gruyter & Co., Berlin, 1923.
13. Passarge, S., Die Grundlagen der Landschaftskunde. L. Friedrichsen &
Co., Hamburg, 1919.
14. Rcnner, G. T., "A famine zone in Africa: the Sudan," Geog. Rev.,
16:583-596 (1926).
322 ECOLOGICAL CROP GEOGRAPHY
15. Shantz, H. L., and R. Zon, Atlas of American Agriculture, Sec. E,
Natural Vegetation. Govt. Printing Office, Washington, 1924.
16. Schimper, A. F. W., Plant Geography upon a Physiological Basis, trans.
German by W. R. Fisher. Clarendon Press, Oxford, 1903.
17. Thornthwaite, C. W., "The climates of North America according to
a new classification," Geog. Rev., 21:633-655 (1931).
18. , "The climates of the earth," Geog. Rev., 28:433-440 (1933).
19. Van Royen, W., "The climatic regions of North America," Mo. Wea.
Rev., 55:315-319 (1927).
20. Visher, S. S., Climatic Laws. Wiley, New York, 1924.
21. Ward, R. DeC., "A new classification of climates," Geog. Rev., 8:188-
191 (1919).
22. , The Climates of the United States. Ginn, Boston, 1925.
23. Weaver, J. E., "Some ecological aspects of agriculture in the prairie,"
Ecology, 8:1-17 (1927).
24. 9 and F. E. Clements, Plant Ecology. McGraw-Hill, New York,
1929.
25. , and W. J. Himmel, "The environment of the prairie."
Conserv. Dept. ofConserv. and Surv. Div. of the Univ. of Nebr., Bull. 5, 1931.
Chapter XXI
EDAPHIC AND PHYSIOGRAPHIC FACTORS
THE EDAPHIC FACTORS
Introduction. The treatment of as broad a topic as the edaphic
and physiographic factors of the environment demands a statement.
The scope of such a title is so comprehensive that it cannot be
treated in detail within the confines of one chapter. Only some of
its more important aspects can be pointed out. Various phases
of the soil factor have been discussed in previous chapters in con-
nection with their respective interrelationships with the other
factors of the environment. The student interested in specific
phases of the soil and physiographic factors as they relate to crop
and soil studies of necessity must consult the extensive and highly
specialized literature available on these important topics.
The Nature of Soil. The soil is not a static body but should be
regarded as a living and highly dynamic entity with natural
provisions for continued development and renewal. Soil differs
from parent material entering into its formation in color, structure,
texture, physical constitution, chemical composition, biological
characteristics, probably in chemical process, in reaction, and in
morphology.
In relation to its genesis and the development of its character-
istics, soil is regarded by Kellogg (7) as a function of climate,
vegetation, relief, age, and parent material.
Major Soil Groups. The development of the two major groups
of soils, the pedocals or lime-accumulating, and the pedalfers or
nonlime-accumulating, was discussed in connection with the
moisture factor of the environment, Chapter XI. It was logical
to discuss the major soil groups at that point, since existing moisture
and temperature conditions together with the closely associated
vegetative features account for the development of the character-
istics differentiating them. They are mentioned here for the sake
323
324
ECOLOGICAL CROP GEOGRAPHY
of completeness. Figure 63, taken from Kellogg (7), shows the
dividing line between these two major soil groups in the United
States. It will be observed that the pedalfers are found in the
humid, and the pedocals in the semihumid and arid sections
of the country.
Zonal Groups of Soils. Zonal soils are found over large areas
or zones, limited by geographical features. Their well-developed
1 Podzol
2 Gray-Brown Podzolic (Forest)^
3 Prairie
Red & Yellow I^^l7 Brown
5 Chernozem L'v*::l8 Sierozem and Desert
6 Chestnut | 1 9 Mountains and Mountain Valleys (^differentiated)
FIG. 63, General distribution of the important zonal groups of soils in the United
States. (After Kellogg [7].)
soil characteristics indicate that their parent materials have been
in place and exposed to the factors of soil genesis and especially
to the climatic and biological factors long enough to have expressed
their full influence.
The zonal groups of soils constitute rather large units. They
are classified on the basis of their outstanding and fundamental
characteristics which differentiate them. Figure 63, taken from
Kellogg (7), gives the general distribution of the important zonal
groups of soils in the United States. Figure 64, also taken from
Kellogg (8), gives a schematic map of the primary groups of soils
in the world. This map is compiled from materials presented
by Glinka, Marbut, and others. The close agreement between
bfl
I
b
vti
1
"8
.2
'§
"8
8.
<U
-s
"8
(X
I
i
&
325
326 ECOLOGICAL CROP GEOGRAPHY
these maps and maps showing vegetation types is quite evident.
The outstanding characteristics of the profiles, the native vegetation,
climate, soil-development processes, the natural fertility, and the
dominant agricultural utilizations of the zonal and intrazonal
groups of soils are given by Kellogg (7) and by Baldwin et al. (1).
Physical Aspects of the Soil. The physical properties of a
soil may be approached from the standpoint of its texture and
structure. The depth of the soil also is of great importance to its
economic utilization. The close relationship of these factors to
the water economy of plants is evident in that they determine
both the ease with which water may penetrate and the amount
of water the soil is capable of holding. Their effects, however,
are more extensive than that. They also are associated definitely
with the chemical status of the soil, influence microbiological
activities, and, aside from the water factor, determine largely the
extent of root penetration. In connection with the depth of the
water table they determine the sanitary conditions of the soil.
The soil horizons constitute an important and conspicuous part
of the physical aspects of the^oil. Localized ecological studies
demand a close examination of tfte soil profile. Differences in crop
responses often can be accounted for by differences in the soil
environment of the various horizons.
Chemical Aspects of the Soil. The main points of importance
under this heading are the fertility relationships in the soil. Soil
reactions will be discussed under a separate heading.
It is not necessary to discuss here the various elements, both
major and minor, required for normal plant growth. Deficiencies
of plant nutrients and lack of proper balance between the essential
elements have decided depressing effects on crop yield. An abun-
dant supply of nutrients is especially important during the grand
period of growth. Deficiencies may be and often are supplied to
meet specific requirements, either by the inclusion of such crops
as legumes or green manure crops in the course of the rotation or
by means of commercial fertilizers. The need for and the economy
of such applications are determined by the state of fertility of the
soil, by the existence of certain deficiencies, by climatic conditions,
and by the degree of intensity of production demanded by the
social factors of the environment.
The nitrogen content of a soil is more or less associated with its
EDAPHIC AND PHYSIOGRAPHIC FACTORS
327
0.3
• Prairie
o Timber
fertility. The various factors entering into soil genesis, especially
the climatic and temperature factors, come definitely into play in
determining the nitrogen level of soils in various areas. The
relative availability of nitrogen determines not only the type and
luxuriance of the vegetation produced but also its rate of decom-
position upon its return to the soil. Thus, Jenny (5) points out
that the nitrogen content of soils decreases exponentially within
regions of equal moisture and corresponding vegetations with
increasing temperatures. The carbon contents of oils is influenced
by the factors affecting nitro-
gen. The carbon-nitrogen
ratio is of great importance
in soil fertility investigations.
Not only do the carbon and
nitrogen contents of soils de-
crease with increasing tem-
peratures, but the carbon-
nitrogen ratio becomes wider
in going from a southern to a
northern area. The rate of
decomposition of organic ma-
terials increases rapidly, within
limits, with increasing tem-
peratures. Jenny points out a
possible limit to this relation-
ship by calling attention to the
• 0.2
£
z
0.1
Wisconsin Illinois Ky. Tcrai. Mississippi
40°
50° 60°
Annual temperature, F
FIG. 65. Nitrogen-temperature relation
fact that "very high temper- in humid prairie (upper curve) and humid
* j *u j timber soils (lower curve) for silt loams,
atures retard the decompo- (After Jenny.)
sition velocity of organic mat-
ter content, the possibility exists that in tropical regions the nitro-
gen and organic matter content (including the C : N ratio) increase
again, in other words, the nitrogen temperature relation may also
have a minimum."
The nitrogen-temperature relation for silt loams in the humid
prairie and humid timber soils of the United States is shown
in Fig. 65, taken from Jenny.
On account of the limited plant growth, the nitrogen contents
of desert soils are low even under low temperature conditions.
Within the same temperature province the nitrogen contents of
328 ECOLOGICAL CROP GEOGRAPHY
soils increase logarithmically with increases in the humidity factor.
Jenny comes to the conclusion that the nitrogen content of loamy
grassland soils in the United States and no doubt in other sections
of the world is a function of the annual temperature and annual
humidity factors.
When a virgin soil is used for crop production the nitrogen
content decreases. The rate of decrease is dependent on the
system of cropping instituted. Under high temperature conditions
it will be found difficult and even impossible to restore the nitrogen
and organic matter to its virgin level. With the use of a good system
of cropping, that is, a system allowing for the liberal additions
of crop residues, green manures, farm manures, and the use of
legumes in the rotation, it is possible to build up or at least maintain
the nitrogen and organic matter contents in northern areas. In
southern latitudes, and even in the middle latitudes, the high rate
of decomposition of organic materials under high temperatures
makes it difficult, or even impossible, to increase the nitrogen
contents of cultivated soils permanently or profitably. This condi-
tion, together with the fact tj^at these soils were originally low
in nitrogen, no doubt provides one of the reasons for the extensive
use of commercial nitrate fertilizer in the southeastern portion of
the United States. A sufficient supply of nitrogen to satisfy the
requirements of the current crop grown is supplied without attempt-
ing to build up the total amount in the soil. Nitrogen is readily
lost from the soil by leaching. Under conditions of high rainfall
and high temperatures, it is difficult to build up the supply of this
element in the soil.
Soil Nitrogen-Climate Relation and Corn Yields. Yields of
corn as well as yields of any other crop are dependent on both the
climatic and the edaphic factors of the environment. The fore-
going discussion of the nitrogen-climate relation indicates that this
may be of considerable importance in determining the effectiveness
of the edaphic factor. Jenny has shown this to be the case.
Figure 66, taken from Jenny's paper, shows the average corn
yield and soil nitrogen curves from eastern North Dakota, and the
states of Minnesota, Iowa, Missouri, Arkansas, and Louisiana. A
decided parallelism between the nitrogen content of the soil and
corn yields is clearly evident. The downward trend of the corn
yields from central Iowa to Louisiana follows closely the trend of
EDAPHIC AND PHYSIOGRAPHIC FACTORS
329
0.3
40
the soil nitrogen curves. North of central Iowa low prevailing
temperatures apparently overwhelm the beneficial effects of higher
soil fertility as evaluated by soil nitrogen, and the yields decrease.
Climatic conditions in the South arc generally favorable to corn
production. Soil factors and especially low soil nitrogen content
constitute the main limiting
factors to the attainment of
high yields. In this connec-
tion Wallace and Bressman
(10) state, "The cotton states
would undoubtedly be an-
other Corn Belt if the soil
were only richer. As it is,
nearly all the records of corn
yielding over 200 bushels
per acre have come from
30
I
I-
the South, such results being
obtained by planting corn
thickly on land heavily ferti-
lized."
Soil Reaction. The ma-
jority of plants of agricultural
N.Drtoti MionesoU JOM fttooori MMSM LooWwt
!
I
•0.1
i
32°
40°
70*
50° 60°
Annual temperature, F.
FIG. 66. Average corn yield per acre and
average soil nitrogen as a function of an-
nual temperature. In the soil nitrogen
curves the solid line represents the total
nitrogen content of upland prairie soils, the
importance grow best in soils dotted line, that of terrace (timber) soils,
with approximately neutral
reactions. While certain
plants show a high degree of tolerance,
and the line presented in dashes, that of
bottom (timber) soils. (After Jenny.)
any great deviation
from the neutral point will result in either direct or indirect detri-
mental effects. If the deviations are very great, either on the acid
or the alkaline side, direct toxic or destructive effects to plant tissues
will be evident. Another direct effect on plants results from the
unfavorable balance between the acidic and basic constituents of
the soil solutions. This balance is directly influenced by soil
reaction.
The indirect effects are many. The most outstanding are the
changes induced in the physical, more particularly the structural,
relationships. In acid clay soils a supply of calcium bicarbonate
in the soil solution insufficient to keep the base exchange material
well saturated with calcium leads to the establishment of the
undesirable deflocculated condition of the soil with its complica-
330 ECOLOGICAL CROP GEOGRAPHY
tions of poor tilth, poor aeration, and low chemical and micro-
biological activity. Highly acid or highly alkaline conditions, by
inducing dispersion of colloidal particles, may lead to the develop-
ment of detrimental hardpans by creating conditions favoring the
downward movement of these fine particles of the soil into the
subsoil where they may be precipitated. Such conditions materially
interfere not only with the percolation of moisture, but also with
the penetration of the roots. "The availability of all of the essential
elements obtained by plants from the soil," states Truog (9), "is
affected in one way or another by the reaction of the soil. Phos-
phorus in particular becomes less available as the pH value drops
below 6.5 to points of greater acidity." The high calcium content
found in certain alkaline soils also may interfere with the availability
of this element.
There are various designations for soil acidity. Generally it is
expressed in terms of pH values. Thus, in a glossary of special
terms in the United States Department of Agriculture Yearbook of 1938
an acid soil is defined as: "A soil giving an acid reaction (precisely,
below pH 7.0; practically, be^w pH 6.6) throughout most or all
of the portion occupied by root?. More technically, a soil having
a preponderance of hydrogen ions over hydroxyl ions in the solu-
tion." Likewise, an alkaline soil is defined as: "Any soil that is
alkaline in reaction. (Precisely, above pH 7.0; practically, above
pH 7.3.)"
The direct effect of climatic factors and especially of the moisture
factor in the development of either acid or alkaline soil conditions
is evident from the above definitions. In the development of acid
soils the soluble bases are removed by conditions of high rainfall
and the resulting leaching processes, while alkaline conditions
are accounted for by precisely the lack of leaching during the
weathering of the parent material. Contributing factors in the
development of acid soils are the organic acids produced by plants,
the low base content of residual materials added to the soil, and
the character of their decomposition. The development of alkaline
conditions is aggravated by impeded drainage, seepage, and high
rates of evaporation. In the case of soils with alkaline reactions
the specific effects of the salts involved play an important part in
the utilization of these soils. Generally alkaline soils are classified
as solonchak and solonetz soils. In the solonchak soils, also desig-
EDAPHIC AND PHYSIOGRAPHIC FACTORS
331
nated as white alkali soils, the salts most frequently encountered
are the chlorides and sulphates of sodium and calcium and less
frequently those of magnesium and potash salts. The nitrates
usually produce a brown color and are referred to for that reason
as brown alkalies. Alkali-claypan soils are known as solonetz.
They are formed under conditions of low calcium and high sodium
content of the soil. With the removal of the soluble salts the sodium
clays hydrolyze and deflocculate the colloidal particles; as a result
the soil becomes sticky, jellylike, and impermeable to water. The
salts concerned in this are chiefly the carbonates of sodium and
potassium. In the course of the deflocculation of the clays the soil
organic matter may be dispersed, giving the soil mass a dark-brown
or black color. This accounts for the commonly used terminology
of black alkali.
TABLE 18. CROPS GROUPED ACCORDING TO THEIR TOLERANCE TO ACIDITY
(after Jones)
Will tolerate some acidity, but are usually helped by liming.
1 hese crops are not injured by liming unless excessive applica-
Very Sensitive
tions are made
Strong Acidity
to Acidity
Favorable
Will tolerate slight acidity
Will tolerate moderate
acidity
Alfalfa
Red clover
Soybean
Blueberry
Sweet clover
Mammoth clover
Vetch
Cranberry
Barley
Alsike clover
Oats
Holly
Sugar beet
White clover
Rye
Rhododendron
Cabbage
Timothy
Buckwheat
Azalea
Cauliflower
Kentucky bluegrass
Millet
Lettuce
Corn
Sudan grass
Onion
Wheat
Redtop
Spinach
Peas
Bent grasses
Asparagus
Lima, pole, and snap beans
Tobacco
Beets
Carrot
Potato
Parsnip
Cucumber
Field bean
Celery
Brussels sprouts
Parsley
Muskmelon
Kale
Sweet potato
Rutabaga
Kohlrabi
Pumpkin
Radish
Squash
Sweet corn
Tomato
Turnip
i
i
332 ECOLOGICAL CROP GEOGRAPHY
Various crops differ in their tolerance of degrees of acidity and
alkalinity. Thus, alfalfa and sweet clover have a suitable range
of pH values of 6.5 to 7.5, as compared to red clover, 6.0 to 6.5,
and lespedeza, 5.5 to 7.0. Table 18, taken from Jones (4), groups
crops in accordance with their relative tolerance to acidity. It
will be observed that the perennial and biennial legumes are either
very sensitive to acidity or will tolerate only slight acidity. This
fact emphasizes the importance of soil reaction in that these legumi-
nous plants occupy such an important place in crop rotation systems
designed to maintain the soil in a fertile condition.
TABLE 19. CROP PLANTS MOST LIKELY TO SUCCEED IN THE PRESENCE OF
DIFFERENT DEGREES OF SALINITY (after Kearney and Scofield)
1. Strong salinity, 3. Medium salinity,
0.8 to 1.0 per cent 0.4 to 0.6 per cent
Sugar beets Sweet clover
Mangels Cotton
Strawberry clover Asparagus
Rhodes grass Foxtail millet
Bermuda grass Wheat (hay crop)
Bluestem (western wheat grass) Oats (hay crop)
Smooth brome grass * Barley (grain crop)
Tall oat grass * Rye (grain crop)
Rice
Sunflowers
2. Medium-strong salinity, 4. Weak salinity,
0.6 to 0.8 per cent 0.1 to 0.4 per cent
Slender wheat grass Wheat (grain crop)
Crested wheat grass Emmer (grain crop)
Italian rye grass Oats (grain crop)
Meadow fescue Grain sorghums
Rape Proso
Kale Alfalfa
Sorgo Vetch
Barley (hay crop) Horsebean
Field peas
Red clover
Kearney and Scofield (6) present a classification of crops on the
basis of their salt tolerance. This classification is presented in
Table 19. So many different salts and combinations of salts occur
in saline soils that any classification of this type can be of a general
nature only. As stated by these investigators, "the classification
applies most closely where the predominant salts are sulphates.
In localities where common salt (sodium chloride) forms the bulk
EDAPHIC AND PHYSIOGRAPHIC FACTORS 333
of the soluble material it will be found that most of the crop plants
mentioned succeeded best at the lower limits of the respective
grades. If an appreciable quantity of sodium carbonate, con-
stituting the so-called black alkali is present, the classification will
not hold good at all." The various degrees of salinity are expressed
on the basis of the percentage of soluble salts by weight in a depth
of soil ordinarily occupied by the roots of the plants in question.
It is to be assumed that the crops are grown with good farming
practices and under moisture conditions favorable to growth.
The concentration of the soil solution at any given time is obvi-
ously greatly affected by the moisture content of the soil mass.
Water Relations of Soils. One of the important functions of the
soil is to serve as a reservoir for the water required by plants. This
involves two important considerations. First, the conditions of the
surface layer as well as those of the deeper strata must allow the
entrance of water. Second, the soil must have capacity to hold
water for future use.
The ideal soil-water relationship is encountered when textural
and structural factors, and the nature of the organic constituents
of the soil, favor rapid infiltration of water and at the same time
allow for a maximum storage capacity. Such a combination of
conditions would tend to reduce to a minimum water losses through
runoff and also through direct evaporation. A rapid ratd of in-
filtration of water into the soil enables surface moisture to pene-
trate into the deeper layers where it will benefit plants and evapo-
rate less rapidly than when held near the surface. A rapid rate of in-
filtration also allows the surface inches of the soil to become dry
shortly after rains. This breaks the capillary connections so that
the water can then leave the soil only by the slow process of evapo-
ration from the upper capillary fringe and diffusion through the
dry layer above. For this reason soils with rather sandy surfaces
frequently show the effects of drought less rapidly than heavy soils
that are not self-mulching.
Not all water entering the soil is available for plant use. Some
of it percolates downward through the subsoil and drains away.
Since it moves primarily in response to the force of gravity, this is
called the gravitational water. The amount of water left in the soil
after the gravitational water is removed is designated as the field
capacity; this point is slightly below the maximum capillary
334 ECOLOGICAL CROP GEOGRAPHY
capacity. But again, not all of this water can be utilized by plants.
Plants are able to reduce the water content of soils only to their
respective wilting coefficients. The amount of water available for
plant use then represents the difference between the field capacity
and the wilting coefficient. The wilting coefficient of most soils
corresponds fairly close to the lower limit of the capillary water.
The limits to which plants can remove water from a soil depend
to some extent on the crop grown but primarily on the soil and
climatic factors. Briggs and Shantz (2), after considerable work
with a great variety of plants, came to the conclusion that the
wilting coefficient equals the hygroscopic coefficient divided by
0.68 ± 0.012. Capalungan and Murphy (3) formulate the wilting
coefficient as the hygroscopic coefficient divided by 0.61 + 0.014.
The hygroscopic coefficient is referred to usually as the point when
the water content of the soil is so low that the water no longer moves
under the influence of capillary forces. At that point the water
is held very strongly as thin films on soil grains and as minute
wedges and rings at their points of contact. The amount of water
thus held is closely associated with the quantity of both the inor-
ganic and organic colloids in tna soil. In fact, this relationship is
so close that the amount of hygroscopic water can be taken as an
index of the quantity of colloid present in the soil.
THE PHYSIOGRAPHIC FACTORS
Relationship between the Edaphic and Physiographic
Factors. As brought out in Chapter VI, the physiographic factors
of the environment include the nature of the geologic strata, the
topography, and the altitude.
The nature of the geologic strata accounts not only for the kind
of parent material utilized in soil formation but also, to a high
degree, for the topography and the drainage features. All of these
conditions have a direct bearing on the characteristics of the soils
formed and on the proper utilization of such soils.
Topography. The advent of mechanized agricultural produc-
tion has emphasized the importance of topography. Mechanized
equipment can be used to best advantage on relatively level areas,
unbroken by topographical barriers. It is precisely on the great
relatively level expanses of the plains and floodplains that most of
the world's agricultural commodities are produced. Among them
EDAPHIC AND PHYSIOGRAPHIC FACTORS 335
are included the plains of the Mississippi Valley, the Argentine
pampas, the plains extending from the Atlantic Ocean and along
the North and Baltic Seas from France into northern Russia, the
Hungarian plains, the plains of southern Russia, the delta plain of
the lower Nile, and the delta floodplains of India and China. Agri-
cultural production in territories with rough topography is gen-
erally limited to livestock production and not infrequently to
subsistence types of farming. A rough topography increases not
only the cost of production but also the cost of marketing of the
commodities produced.
Not all plains are suited to crop production. Some of them are
too swampy for occupation; some have poor soils, like the sandy
soils of parts of the Atlantic coastal plain; and there are some with
too dry a climate, or so far north that the climate is too cold, as
in northern Canada and Siberia. In the interiors of the continents
many of the plains extend into minimal areas best utilized for
livestock rather than for crop production. In many of these regions
local areas with broken topography have been protected from
unwise exploitation by the fact that their topographical features
prevented the destruction of their native vegetations by an overly
optimistic plowman.
Soil erosion is often a great destructive agent in areas, with
rolling or rough topography. This is especially the case in areas
with high rainfall intensities.
Topographical features are closely related to drainage facilities,
either because the slope gradient may not be sufficient to remove
the excess water fast enough, or because of obstructions in the
drainage channels.
Altitude. In mountainous regions altitude is the most important
factor determining local climate. It influences both temperature
and moisture conditions, and, as pointed out in Chapter XVIII,
the characteristics of alpine plants are accounted for to a high
degree by the altered light conditions. The rarefication of the
atmosphere with increasing elevations also serves to increase
transpiration rates of plants.
In the tropics altitude is of especial significance to the utilization
of areas for agricultural purposes. The moderation of temperature
and not infrequently of humidity conditions associated with in-
creasing elevation make these areas habitable for members of
336 ECOLOGICAL CROP GEOGRAPHY
the white race. The moist tropical lowlands are unsuited for white
occupation on account of the enervating effects of the climate and
the danger of tropical diseases.
Physiographic and Edaphic Factors of Special Importance
in Studies of Local Conditions. This topic was discussed in
Chapter VI. It is mentioned here for the sake of emphasis. Cli-
matic conditions over wide regions, except where significant
differences in altitude are encountered, are more or less similar.
Soil conditions, however, may and do vary considerably and at
times abruptly within limited areas. This is not surprising in view
of the many factors that may alter soil characteristics. It emphasizes
the importance of soil and physiographic features in relation to
localized ecological investigation. The thesis that climatic factors
have regional effects, or are regional in their scope, while the soil
factors are local in effect, is fully supported. This does not mean
that the effects of the soil and climatic factors themselves are distinct
and separate. They are closely related in their direct and indirect
effects on plant life. As a matter of fact, plant responses in a given
place are conditioned as much by one as by the other in that the
climatic factors often find expression through the soil factors. The
climatic factor, for instance, determines the amount of rainfall
received in any given place, but the plant obtains its water and
mineral elements from the soil.
REFERENCES
1. Baldwin, M., C. E. Kellogg, and J. Thorp, "Soil classification," U. S.
Dept. Agr. Yearbook 1938:979-1001.
2. Briggs, L. F., and H. L. Shantz, "The wilting coefficient for different
plants and its indirect determination," U. S. Dept. of Agr., Bur. of
Plant Ind., Bull 230, 1912.
3. Capalungan, A. V., and H. F. Murphy, "Wilting coefficient studies,"
Jour. Amer. Soc. Agron., 22:842-847 (1930).
4. Jones, E., "Liming Ohio soils," Ohio Ext. Bull. Ill, 1936.
5. Jenny, H., "A study of the influence of climate upon the nitrogen and
organic matter content of the soil," Mo. Agr. Exp. Sta. Res. Bull. 152,
1930.
6. Kearney, T. H., and C. S. Scofield, "The choice of crops for saline
land," U. S. Dept. Agr. Circ. 404, 1936.
EDAPHIC AND PHYSIOGRAPHIC FACTORS 337
7. Kellogg, C. E., "Development and significance of the great soil groups
of the United States," U. S. Dept. Agr. Misc. Pub. 229, 1936.
8. , "Soil and society," U. S. Dept. Agr. Yearbook 1938:863-886.
9. Truog, E., "Soil acidity and liming," U. S. Dept. Agr. Yearbook 1938:
563-580.
10. Wallace, H. A., and E. N. Bressman, Corn and Corn-Growing. Wallace
Pub. Co., Des Moines, 1923.
PART IV
THE GEOGRAPHICAL DISTRIBUTION
OF CROP PLANTS
Chapter XXII
THE SMALL GRAIN CROPS
WHEAT
INTRODUCTORY AND HISTORICAL
Commercial Importance. Wheat and rye are the bread crops
of the world. The flours of these two cereals form a dough when
mixed with water which upon leavening and baking produces a
porous bread. This is due to their gluten content which imprisons
the carbon dioxide produced in the fermentative action of yeast.
Wheat produces a lighter, more porous, and generally more palat-
able bread of higher net energy value than rye. It is for this reason
more acceptable and widely used for the making of bread than rye.
So great is the demand for wheat that rye can be considered as a
substitute for wheat. Rye is made use of and assumes a place of
importance in the diet only in countries or areas where soil and
climatic conditions are unfavorable for wheat production. Wher-
ever conditions favor wheat production or the economic status of a
people permits the utilization of wheat the consumption of rye falls
sharply behind the use of wheat bread.
While wheat has no rival as a bread crop, there is some doubt in
the minds of certain investigators as to whether it is more important
as a food crop than rice. In this connection Zimmermann (30)
states that "the statistical data on the production and consumption
of wheat and rice are so incomplete that the question as to the
respective numbers of wheat and rice eaters or the relative size of
wheat and rice crops must remain unanswered." Thus China
produces not only large amounts of rice but also wheat. The
statistical data for China especially are fragmentary and unre-
liable. Rice is prepared for human consumption mostly by boiling
rather than by milling and baking. Percival (18), however, comes
out with a stronger statement than Zimmermann to the effect that
"although rice is the principal food of a large proportion of the
341
342 ECOLOGICAL CROP GEOGRAPHY
human race, a greater amount of wheat is grown and this in the
form of bread, constitutes the chief food of the most highly civilized
races."
Wheat is grown primarily for direct human consumption. How-
ever, in areas removed from the central markets and also during
periods of low prices, a considerable quantity of the crop may be
used for feed. Thus the Pacific Northwest has always used a rather
high percentage of its wheat crop for feed. As a matter of fact in
portions of this area wheat produces more feed per acre than can
be obtained from any other crop. Under ordinary conditions
wheat is generally too valuable to be used for feed, except for
special enterprises, and even then mostly wheat of low quality is
used.
Historical. The cultivation and utilization of wheat is older
than the written history of man. Its cultivation was general in
western Asia at the dawn of history. Wheat was known to the
Chinese in the twenty-eighth century B.C. The Chinese consider
the crop native to their country, but evidence seems to indicate
that wheat is native to the dry Mediterranean climates of Asia
Minor and Mesopotamia.
Wheat is often spoken of as a frontier crop, and rightly so. In all
countries suited to wheat production the wheat crop occupied, and
in regions still occupies, an important place in financing the agri-
cultural, transportational, and other improvements of frontier
communities. This was the case in the United States. As agricul-
tural production moved westward toward the drier plains area,
wheat production advanced with it. In the course of time, as
communities became more firmly established, the relative impor-
tance of the crop decreased in the eastern more humid areas in the
shift from monoculture to more diversified farming.
Not without very important effects on wheat production and
expansions of the world's wheat areas were the advances made in
milling technology. Of special significance was the shift from the
old-fashioned buhr stones to the steel roller milling process. This
change in milling technique encouraged the production of the hard
red spring and winter wheats now the outstanding crops of the
grassland wheat producing areas of the world. Prior to the time
of the introduction of the steel roller, or "gradual reduction,"
process the soft and semisoft wheats commonly produced in humid
THE SMALL GRAIN CROPS 343
areas were regarded as being more desirable for milling than the
hard wheats.
CLIMATIC RELATIONSHIPS
General Climatic Areas. The general climatic relationships in
the important wheat producing areas of the world are summarized
in Table 20. It will be observed that wheat is grown under a great
variety of climatic conditions. Percival points out that the cultiva-
tion of wheat is simple, and "its adaptability to varying soils and
climatic conditions superior to that of any other plant." The most
extensive wheat growing areas have continental, grassland climates,
although wheat production is by no means limited to these climates.
Koppen's and Thornthwaite's classifications bring out that the
crop is grown primarily in areas with moderate temperatures and
under subhumid and even semiarid conditions. Wheat is also
grown under humid conditions as in northwestern Europe (Cfb and
BC'r) and in the eastern portion of the United States (Dfa, Cfa, and
BC'r). In India the crop is produced under high temperature con-
ditions (Cwg and CA'w). Wheat in India is sown in October,
after the cessation of the monsoon rains; that is, the crop is grown
during the cooler and also drier portion of the year. The highest
temperatures in the Indian wheat producing areas come pridr to
the occurrence of the monsoon rains. The wheat crop of China is
also produced in territories with rather high temperatures, but
under conditions of relatively low winter rainfall (Cw and BB'w).
The wheat crop is out of the way before the hot humid weather of
the summer months so favorable to rice growing arrives.
Koppen's and Thornthwaite's climatic formulas will be referred
to from time to time in the discussions of climatic factors in this
and succeeding chapters. It is often desirable to give the formulas
of both classifications. In order to avoid confusion, Koppen's
formula will always be given first, followed by Thornthwaite's.
The two may of course be identified at any time by the fact that the
temperature province of the Thornthwaite formula, the second
capitalized letter, is always graced with a prime mark.
Bennett and Farnsworth (3) utilized Thornthwaite's classifica-
tion of climates in discussing the climatic relationships in the wheat
producing areas of the world. It is interesting to list here their
estimates of the acreages in millions of acres for 14 of Thornthwaite's
344
ECOLOGICAL CROP GEOGRAPHY
TABLE 20. CLIMATIC RELATIONSHIPS IN THE IMPORTANT WHEAT PRODUCING
AREAS OF THE WORLD
Producing Region
Climatic Classification
Relative
Location
Vegetation
Koppen
Thornthwaitc
U. S. southern Great Plains
Cont.
Grassland
Cfa
CB'r
CB'd
.
DB'd
U. S. northern Great Plains
Cont.
Grassland
Dfb
CC'd
BSkw
DC'd
Prairie provinces of Canada
Cont.
Grassland
BSkw
CC'd
Dfb
DC'd
Hungarian plains ....
Cont.
Grassland
Cfx
CC'r
Dfa
BC'r
Southern Russia ....
Cont.
Grassland
Dfc
CC'r
BSk
CB'd
Italy and Mediterranean .
Trans.*
Woodland
Csa
CB's
Dfc
BB'r
France
Marine
Woodland
Cfb
BC'r
Trant.
Argentina
Cont. *
Grassland
Cfx'
CB'r
India
Cont.
Grassland
Cwg
CA'w
China
Cont.
Woodland
Cw
BB'w
Grassland
Dwa
CB'w
Australia
Trans.
Grassland
BSks
CB's
Cont.
Woodland
Csb
CB'd
* Transitional between marine and continental.
climatic types: CC'd, 58; DC'd, 46; CB'w, 40; CB'd, 34; DB'd, 28;
BC'r, 25; CC'r, 25; BB'r, 21; CB'r, 21; CB's, 20; CA'w, 16; BB'w,
13; DB's, 11 ; and DB'w, 9. A tabulation such as this is misleading
in bringing out the climatic relationships of wheat production
unless it is considered in relation to the yields obtained in the various
areas. The highest yields are obtained in the BC'r and CC'r cli-
mates. In these relatively moderate and moist climates wheat
comes of course into more direct competition with other crops than
in cooler and drier climates. Bennett and Farnsworth present an
interesting and instructive map of world wheat yields. This map
is of special value in discussing the limiting factors encountered in
the various wheat producing areas of the world. It is evident from a
tabulation of climatic types prevailing in the wheat producing
THE SMALL GRAIN CROPS 345
areas that production in many of these regions crowds the minimal
areas.
Temperature Relationships. As already indicated, wheat is
grown under a variety of temperature conditions. The prevalence
of extremely low temperatures during the winter months, especially
when there is no protective snow cover, necessitates a shift from
winter to spring wheat. Wheat may be grown under rather high
temperature conditions provided that the period of high tem-
peratures does not coincide with periods of high atmospheric hu-
midity. A combination of high temperature and high humidity
is fatal to wheat. Thus as indicated by Baker (1) very little wheat is
grown in the southeastern portion of the United States where the
average temperature for the two months preceding harvest exceeds
68°F and where the rainfall amounts to 50 inches or more annually.
These same factors are responsible for setting the northern limits
of wheat production in Argentina, the eastern boundary of the
wheat belt in India, and the expansion of wheat into southern
China. In all of these territories the limits of production are set by
the fact that a combination of high temperature and high humidity
is encountered during the growing season of the wheat crop.
Winter wheat in order to survive demands specific temperature
and moisture conditions during the autumn and winter months.
These conditions were discussed in detail in Chapter XVI. Be-
tween 75 and 80 per cent of the world's wheat crop consists of winter
wheat. In regions favoring survival higher and more stable yields
can be generally expected from fall-sown than from spring-sown
wheat.
Spring wheat requires a growing season of at least 100 days.
Some wheat is being grown in areas with shorter growing seasons
than that; production, however, is not extensive. The production
of wheat in regions with short growing seasons is subject to a con-
siderable frost hazard prior to maturity. In these same areas late
spring frosts corresponding with the flowering and early stages of
kernel development constitute a hazard in the production of winter
wheat and also winter rye. In spite of these limitations, Baker states
that only barley, potatoes, and certain hay crops are grown under
colder conditions than wheat. According to Schindler (21) the
northern limit of economical wheat production corresponds with the
May isotherm of 10°C (50°F).
346 ECOLOGICAL CROP GEOGRAPHY
Moisture Relationships. The most important wheat producing
areas of the world have an annual precipitation of less than 30
inches. Moisture conditions are analyzed to best advantage on the
basis of efficiency of precipitation and humidity provinces, rather
than from the standpoint of annual receipts of precipitation alone.
In areas with a high efficiency of precipitation and with the crop
grown under conditions of alternate fallow and cropping, wheat
has been grown under as little as 10 inches of annual precipitation.
It should be kept in mind, however, that the production of the crop
becomes increasingly hazardous as the minimal moisture areas are
approached. The seasonal distribution of precipitation as found in
the grassland areas is ideal for wheat production, and especially
for the growing of high-protein wheats. Since, however, these
regions are characterized by a high variability in rainfall, the yields
realized may be expected to fluctuate materially from season to
season. As already indicated, high rainfall alone does not exclude
wheat except where combined with high temperature. Such a com-
bination favors the development of a host of fungus diseases.
Winter wheat demands for its best development favorable mois-
ture conditions during the autumn months. This is essential to the
proper establishment of the plants prior to the advent of the period
of dormancy enforced by low temperatures during the winter
months. Here is another weakness of the grassland climates. In
occasional seasons a definite critical period is brought about by
the absence of the expected autumn rains. In certain areas adapted
to both spring and winter wheat the relative importance of these
two types is greatly influenced by prevailing moisture conditions
during the autumn months. Dry autumns unfavorable to the
germination and establishment of winter wheat result in increased
acreages of spring wheat and also of spring-sown barley.
Too many economists and geographers in discussions relating to
the wheat producing potentialities of the world are prone to under-
estimate the physiological dependence of the wheat plant upon
climatological factors, and upon moisture relationships in par-
ticular. While wheat is able to grow in relatively dry climates,
the yields obtained in dry regions are not only low but also ex-
tremely variable. Many of the wheat producing areas of the world
border on distinctly minimal moisture areas, and in places extend
into them. Again, the possibilities of increasing yields are often
THE SMALL GRAIN CROPS 347
overstressed. In many areas, and especially in those favored with
proper climatic conditions, increases in yields are possible. Never-
theless, in sections approaching the minimal areas it is necessary
to recognize definite physiological limits. In many of these areas
wheat yields have shown negative trends, even with the employment
of improved varieties and methods of culture, after the level of
fertility of the virgin soils pressed into wheat production has been
reduced. The successive reductions of the organic matter content
of such soils with continued cropping to wheat have a decided
effect on water relationships.
SOIL RELATIONSHIPS
Fertility and Water Relationships. Wheat is grown under a
wide range of soil conditions, yet the crop is quite specific in its
soil requirements. The best wheat soils are fertile, have good water-
holding capacities and fair to good drainage. Extremely sandy
soils are not adapted to wheat production. Since wheat is being
grown primarily in subhumid and even in semiarid sections, the
soils are either neutral to slightly alkaline in reaction. The crop,
while able to withstand a moderate concentration of soluble salts
and even carbonates, is not adapted to strongly saline or alkaline
conditions. Production in humid areas takes place largely on^soils
that are slightly acid.
The Chernozem and Chestnut soils are especially important in
wheat production. Production is less hazardous on the Chernozem
than on the Chestnut soils because the former are found in areas
with higher P-E indices than the latter. Wheat production on the
Grayerths is possible in most areas only with the aid of irrigation.
Good wheat soils contain fairly large amounts of available phos-
phorus. This promotes the formation of grain. A favorable organic
matter content of the soil is desirable to promote good tilth. A
moderate liberation of nitrogen is desirable, not only for the stimu-
lation of growth, but also for the production of high quality, high-
protein wheats.
THE DISTRIBUTION OF WHEAT
World Centers of Production. Figure 67 shows the wheat
producing areas of the world. Twelve more or less distinct wheat
producing areas stand out prominently:
348 ECOLOGICAL CROP GEOGRAPHY
1 . The northern Great Plains area of North America.
2. The southern Great Plains area of the United States.
3. The Columbia River basin and Palouse area of the United
States.
4. Northwestern Europe.
5. The Mediterranean area of Europe and northern Africa.
6. The Hungarian plains.
7. The Danube basin.
8. Southern Russia.
9. Northwestern India.
10. East-central China.
1 1 . Argentina.
12. Southeastern Australia.
Table 21 gives the statistical data of important wheat producing
countries.
The three outstanding wheat producing areas of the North
American continent are in grassland regions. The southern Great
Plains area produces winter yrheat. The northern Great Plains
of the United States extending into the prairie provinces of Canada
represents the largest contiguous highly specialized spring wheat
producing area of the world. The Pacific Northwest produces both
winter and spring wheat.
The United States is still an important exporting country;
exports have, however, been decreasing. This is partly due to in-
creasing population and greater home consumption, but also to a
high degree to complications in international trade since the de-
pression. The fact that the United States changed its status from a
debtor to a creditor country with and after the first World War
materially influenced its position as an exporter of wheat. Canada's
position as an export country remains supreme. The average ex-
ports from Canada for the period 1930-1934 amounted to around
224 millions of bushels as compared to only slightly over 59 millions
of bushels for the United States. Canada is a great producer and on
account of its relatively small population and economic status a
great exporter of wheat. Canada is recognized as the outstanding
producer of exceptionally high quality spring wheat.
Northwestern Europe is not only highly industrialized, but has
also a highly specialized and productive agriculture. This is evident
349
350
ECOLOGICAL CROP GEOGRAPHY
TABLE 21. WHEAT: ACREAGE, YIELD PER ACRE, PRODUCTION, AND PER
CENT OF WORLD TOTAL PRODUCTION IN SPECIFIED COUNTRIES — AVERAGES
FOR THE FIVE-YEAR PERIOD 1930-31 TO 1934-35
Rank
Countries
Acreage,
in Millions
of Acres
Yield, in
Bu.per
Acre
Production
[n Millions
of Bu.
In Per-
centage of
World
Total
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
U.S.S.R., European and Asiatic
China
85.80
54.19
33.34
25.68
13.28
12.17
17.71
7.97
15.49
11.24
10.33
7.70
5.10
3.94
i 4.26
» 1.56
3.08
10.8
13.5
10.7
13.6
23.0
20.8
13.8
29.7
12.5
14.1
11.4
13.4
15.6
19.4
17.4
33.9
17.2
924.54
778
732.63
355.59
348.56
305.32
252.60
243.93
236.54
193.81
158.08
118.16
103.45
79.49
76.51
74.27
52.87
52.86
412.79
16.81
14.14
13.32
6.47
6.34
5.55
4.59
4.44
4.30
3.52
2.87
2.15
1.88
1.45
1.39
1.35
0.96
0.96
7.51
United States
India
Canada
France
Italy
Argentina .......
Germany
Australia and New Zealand
Spain
Northern Africa
Rumania
Yugoslavia
Hungary
Poland
Great Britain
Bulgaria
All others
World total production . . .
—
—
5,500.00
100.00
from the acreage and especially from the yield data presented in
Table 21. Climatic conditions in this area are generally favorable
to wheat production. In many areas soil conditions, however, do
not favor the crop. In such areas, either soil conditions are amel-
iorated through the application of scientific principles, crop rota-
tions, and fertilizations, or, if the soils are sandy, the wheat crop
yields its place to rye. The substitution of rye for wheat holds true
especially on the expanses of sandy and peat soils along the North
and Baltic Seas. Wheat production is highly developed in northern
and central France, western England, and on the heavier soils of
central Germany. The recent trend toward national self-sufficiency
has given a great impetus to the expansion of wheat acreage and
production in central Europe and in Italy.
As stated by Whitbeck and Finch (27), "the agricultural lands of
Europe are the continent's greatest resource, and the quantity of
THE SMALL GRAIN CROPS 351
foodstuffs produced is greater than in North and South America
combined." One of the richest and most dependable of the wheat
producing areas of the continent are the Hungarian plains. Here
is found a happy combination of favorable climatic and soil condi-
tions for wheat production, making it a virtual granary for central
Europe. An even more extensive though not so reliable wheat
producing area is found across the Transylvanian Alps, that is, in
the Danube basin extending through Walachia, Dobruja, Molda-
via, and Bessarabia. In this area, soil conditions favor wheat;
climatic conditions are, however, more hazardous than on the
Hungarian plains. Droughts during the growing season occasion-
ally reduce yields on the Hungarian plains; they are, however, not
so common there as in the Danube basin.
Southern Russia is a wheat producing empire. The heaviest
distribution of wheat in Russia corresponds with the extension of
the Chernozem. The Ukrainian and Crimean areas are of special
importance. The Russian wheat producing areas are with respect
to prevailing soil and climatic conditions quite similar to those of
the Great Plains area of North America. The southern portion of
the Russian wheat belt produces winter, the northern interior,
spring, and the driest interior areas a rather high percentage of
durum wheat. Climatic conditions are extreme. The size of- the
crop in any given season is highly dependent on moisture and tem-
perature conditions, that is, the crop is produced under grassland
and steppe climates and shows the high degree of variability com-
mon to such areas. It should be mentioned that many of the hardy
varieties of wheat and oats produced in the United States originated
in the cereal producing area of Russia with its extremes of dryness,
winter cold, and summer heat. Prior to the first World War, Russia
was the world's most important exporter of wheat. Since that time,
Russian wheat exports have been held within moderate limits.
Russia, while the greatest wheat producing country of the world,
has a large and growing population. Furthermore, indications
are that the standards of living of the masses of the people have
improved since prewar days and will probably continue to improve.
Consequently the prospects of Russia's ability to regain her former
preeminence as an exporter of wheat seems rather remote (Timo-
shenko, 25, 26, and Strong, 24).
The climates of Asiatic Russia are generally too dry and cold
352 ECOLOGICAL CROP GEOGRAPHY
for intensive wheat production. This is evident from the climatic
maps presented in Chapter XX. Marbut (16) overestimated the
wheat producing potentialities of Russia and especially of Siberia.
This statement is borne out by Zimmermann. "The expansion of
agriculture in European Russia is almost impossible, and the
potentialities in Siberia and central Asia are far less than is generally
believed." Also Timoshenko (26) states that
"further expansion of the agricultural area in Asiatic Russia on new
unoccupied lands must go rather slowly, for it will generally require
reclamation and improvement of land (drainage of marshy land in
taiga regions and irrigation on the dry steppes). Comparatively rapid
expansion of the crop area here may proceed for some time only in
the area having from 10 to 14 inches of rainfall annually, where hazard-
ous dry farming must be practiced. Even expansion of the area devoted
to this hazardous dry farming will require considerable development
of the railroad system in Asiatic Russia."
Wheat is an important crop on all the arable lands bordering
the Mediterranean. The Mediterranean climates (Csa, CB's)
with their mild winters and warm bright summers arc favorable
to winter wheat production.* Durum wheat is also a common
crop, especially in northern Africa, Morocco, and Algeria.
Wheat production is an important enterprise in central and
especially in northwestern India, that is, in the upper Ganges
region and the Punjab. Much of the crop is grown under irrigation.
As stated by Bergsmark (4),
"Irrigation works in the Punjab have resulted in the opening to
cultivation of large areas of relatively unleached, fertile soils which had
hitherto been unsuitable for agricultural development because of lack
of water. Such irrigation projects have resulted in the development
of what is known as canal colonies. The results may be gauged from
the fact that Lyallpur, the capital of the upper Chenab colony, now has
a large export trade, and the population of which it is the center
increased from 8,000 to 979,000 in the course of 15 years (1915-1930)."
The size of the wheat crop of India in spite of extensive irrigation
developments is highly dependent on the timely arrival of the mon-
soon rains. If these rains come too late the crop will not mature
before the arrival of high temperatures. Earlincss is a common
characteristic of Indian cereals. Durum and also club varieties
are grown in the drier districts. India is now of only minor impor-
THE SMALL GRAIN CROPS 333
tance as an export country. Its teeming population could, economic
conditions permitting, consume more wheat than is produced even
in favorable seasons. In former years the country exported great
quantities of wheat in favorable seasons. Production, however,
was not dependable. In some years no exportable surplus was
produced, whereas in others it exceeded 80 millions of bushels.
Such fluctuations attest the variations in precipitation.
Statistical data on wheat production in China are fragmentary.
The figure of total production given in Table 21 is at best a rough
estimate. The crop is of special importance in the east-central
portion of the country. There is, however, a considerable over-
lapping with the main rice producing areas farther south. Wheat
occupies the land during the portion of the year too cool for the
growing of rice.
The reason for the limits of wheat expansion in northern Argen-
tina has already been indicated. In the remainder of Argentina
possible expansion is limited by lack of rainfall. The country be-
comes increasingly dry as the interior is approached. The climate
especially in the interior regions is typically grassland, and the crop
is subject to the uncertainties of such climates. Owing to the small
population and low aggregate consumption, Argentina occupies a
prominent place as an export country, being second only to Cataada
as an exporter of wheat. The average annual export for the period
1930-1934 amounted to 134 million bushels. It is followed closely
by Australia, with more than 124 million bushels per annum for
the same period. The fact that the Argentine wheat crop is grown
in close proximity to navigable waters favors export trade. South-
eastern Australia is favored by the same condition but has the
obstacle of greater distance to European markets. Wheat is the
most important crop of Argentina from the standpoint of acreage,
followed by corn, alfalfa, and flax.
Limited rainfall causes the acreage suited to wheat production
in Australia to be relatively small. However, southeastern Aus-
tralia leads all other territories of the world in the proportion of
cultivated land in wheat. Earlincss is a general characteristic of the
varieties used. As southwestern Australia is very dry, production
there is small. Some durum wheats and early-maturing varieties
of common wheat are being grown. Because of a small population,
a high percentage of the crop is available for export.
354 ^ECOLOGICAL CROP GEOGRAPHY
Distribution of Wheat in the United States. The distribution
of wheat in the United States emphasizes the importance of the
grasslands in wheat production. Thus, according to Baker and
Genung (2), 70 per cent of the wheat acreage of the country was
in the Great Plains states in 1929. This is evident from Fig. 68.
Wheat production is, however, not limited to the grassland areas.
It is an important cash crop entering into the rotations common to
the eastern Corn Belt, and in the limestone valleys and Piedmont
from Pennsylvania to North Carolina.
FIG. 68. Distribution of wheat and the classes of wheat produced in the different
areas of the United States, average acreage harvested 1928-1937. Each dot
represents 50,000 acres.
Table 22 gives the statistics of wheat production by important
producing states. The states of the Great Plains area are much in
evidence; other states with acreages in grassland climates with a
winter concentration of rainfall are Washington, Idaho, and
Oregon.
Figure 68 shows not only the distribution of wheat in the United
States but also the classes of wheat produced in the different areas.
The soft red winter wheats in the eastern portion of the country
are accounted for by the high humidity generally encountered
there. In low-moisture years a considerable percentage of the
wheat produced in Illinois and Indiana will grade hard. The line
THE SMALL GRAIN CROPS
355
of demarcation between the spring and winter wheat producing
areas is fairly distinct. There is, however, some overlapping in
South Dakota, Nebraska, and Minnesota. Durum wheat produc-
tion is concentrated in northeastern South Dakota and the eastern
half of North Dakota. The western region grows several types of
wheat, hard red winter, white, and club. Both winter and spring
wheats are grown in the western region. Most of the irrigated
sections specialize on spring wheat, while winter wheats predomi-
nate in the dry land areas.
TABLE 22. WHEAT: ACREAGE HARVESTED, PRODUCTION, AND PERCENTAGE
OF UNITED STATES TOTAL PRODUCTION IN SPECIFIED STATES RANKED ACCORD-
ING TO PRODUCTION — AVERAGES FOR THE TEN-YEAR PERIOD 1928-1937 —
AND 1938 PRODUCTION. ACREAGES AND PRODUCTION EXPRESSED IN MILLIONS
OF ACRES AND BUSHELS.
Production
Rank
States
Acreage
Harvested
Average
1928-1937,
in Bu.
Percentage
of U.S.
Total,
1928-1937
1938, Bu.
1
Kansas
10.68
138.07
18.34
152.18
2
North Dakota
8.02
73.74
9.79
76.38
3
Oklahoma
3.95
47.05
6.25
£l.68
4
Nebraska
3.18
46.25
6.14
55.71
5
Washington
2.21
43.73
5.81
54.59
6
Ohio
1.85
36.57
4.86
46.42
7
Montana
3.35
35.22
4.68
69.52
8
Illinois
2.01
34.53
4.59
41.79
9
Texas
3.00
32.04
4.26
35.05
10
Indiana
1.66
28.45
3.78
28.85
AH others
15.89
237.30
31.50
309.53
Total U. S
55.80
752.95
100.00
931.70
RYE
Commercial Importance. Rye is the world's second most im-
portant bread crop. While rye still holds an important place as a
bread crop in Russia, Germany, and the Scandinavian countries,
the long-time tendency has been to make more and more use of it
as a feed crop. Shollenberger (22) for instance makes the observa-
tion that "in some European countries which formerly were pre-
dominantly rye-bread-consuming rye has already come to be con-
356 ECOLOGICAL CROP GEOGRAPHY
sidered a feed grain. The British Isles offer a notable example of
this; a few centuries ago rye was the principal bread grain but today
annual consumption amounts to less than two pounds per person.
For more recent indications of this tendency Norway and Sweden
offer the best examples." Improvement in means of transportation
and the expansion of world trade no doubt played an important
part in this trend away from rye to greater wheat consumption.
Depressions, stagnations of trade, and national emergencies will
tend to retard this movement toward the greater utilization of
wheat. Rye consumption remains high in Germany and the
Scandinavian countries, as well as in all the other countries border-
ing the Baltic. In some of these countries economic conditions must
improve materially before a great decline in rye consumption may
be expected.
In the United States the consumption of rye bread has never been
of importance; rye bread is considered as a novelty rather than as a
staple food product. Even when rye is used for bread it is in most
instances mixed with wheat. Rye is used extensively in the produc-
tion of distilled spirits and alcohol. The quantity used for this
purpose for the fiscal year endiftg June 30, 1937, amounted to over
11^ million bushels.
Rye has other notable uses than as a bread and grain feed,
namely as a pasture, soiling, cover, and green manure crop. The
long straw of rye is also highly prized.
Historical. Hughes and Hensbn (11) note that "compared to
wheat, rye is a relatively new crop. It is not mentioned in old
Chinese and Japanese literature and DeCandolle states that it has
not been found in Egyptian monuments. The earliest cultivation
of rye appears to have been in western Asia and southern Russia."
According to Engelbrecht's conception, cited by Schindler, culti-
vated rye, Secale cereale, originated from S. anatolicum reported as a
weed admixture in wheat fields of Asia Minor. The wheat with its
admixture of rye is reported to have been carried by the ancient
Greeks to southwestern Russia, where the "weed" was elevated to
the position of a cultivated crop. From there it was carried to the
north and northwest where it was destined to become the most
important bread crop of the Germanic and Slavic peoples.
Climatic Relationships. Rye has the distinction of being the
most winter-hardy of the cereals. Only spring-sown barley is
THE SMALL GRAIN CROPS
357
grown farther north and at higher elevations than winter rye
(Carleton, 6). Both winter and spring varieties of rye are available;
most of the crop is, however, fall-sown.
Table 23, listing the essential features of the climates of the
world's important rye producing areas, brings out that rye is a cool-
weather crop. Its distribution extends from the mild Cf to the
boreal Df climates. It is not found in warm climates except in
instances as a winter cover crop. According to Schindler, the north-
ern limit of rye production in Europe corresponds fairly well with
the July isotherm of 18°C (65°F). Its expansion to the south ex-
tends to the May isotherm of 15°C (59°F) or the July isotherm of
20°C (68°F). South of this line wheat takes its place.
Rye is grown over a wide range of moisture conditions. The
Cfb, Dfb to BSk, and CC'r to CC'd climates are represented in the
producing areas. The fact that the crop matures early enables it
to escape drought.
TABLE 23. CLIMATIC RELATIONSHIPS IN THE IMPORTANT RYE PRODUCING
AREAS OF THE WORLD
Producing Region
Climatic Classification
Relative
Location
Vegetation
Koppen
Thorn-
thtvaite
Russia
Cont.
Trans.
Cont.
Cont.
Grassland
Woodland
Woodland
Grassland
Dfb
BSk
Cfb
Dfb
CC'r
CC'd
CC'r
CC'r
CC'd
Germany and Poland
U. S. northern Great Plains . . .
Soil Conditions. Rye is found and extensively grown as a bread
crop not only in cold and bleak climates but also on poor, sandy
soil. No other cereal can be grown and be depended upon to supply
the "daily bread" under such severe conditions. It is no small
wonder that Thaer designated the crop as the "most benevolent
gift of God."
The soil relationships of rye are well stated by Morgan et al.
(17) in the following paragraph.
"Rye is less exacting in its soil requirements than any of the other
important cereals. It grows well over a wide range of conditions with
.SP
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3
i
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1
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359
360
ECOLOGICAL CROP GEOGRAPHY
respect to soil moisture, although it is adversely affected by deficient
drainage. It is able to withstand considerable degrees of acidity and
alkalinity. The crop makes a reasonable growth at low levels of
fertility, both with respect to available nitrogen and mineral nutrients.
On the other hand, it is able to make a relatively luxuriant growth
under especially favorable conditions without damage to grain quality.
Losses due to lodging from excessive nitrates are much less than with
wheat and oats."
World Distribution of Rye. Rye is essentially a European crop.
That continent accounts for around 96 per cent of the world's total
production.
Table 24 gives the statistical data on world rye production, while
Figures 69a and 69b, compiled from Kirsche (14), compare the world
distribution of wheat and rye. The rye producing area of Europe
extends across the continent as a continuous belt from northern
France into Siberia. The wheat and rye producing areas are some-
what complementary; in general, however, rye occupies a more
TABLE 24. RYE: ACREAGE, YIELD PER ACRE, PRODUCTION, AND PERCENTAGE
OF WORLD TOTAL PRODUCTION IN SPECIFIED COUNTRIES — AVERAGES FOR
THE FIVE-YEAR PERIOD 1930-31 TO 1934-35
Rank
Country
Acreage, in
Millions
of Acres
Tield, in
Bu. per
Acre
Production
In
Millions
of Bu.
In Per-
centage of
World
Total
\
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
U.S.S.R
65.29
14.61
14.20
1.75
2.92
1.58
1.23
1.49
.52
.56
.44
.55
.94
.63
.94
.86
3.78
13.5
27.4
17.9
18.3
10.7
18.0
18.4
14.8
38.6
, 30.2
35.6
24.9
14.6
19.8
10.5
10.4
17.7
881.29
400.76
254.38
32.02
31.27
28.48
22.62
22.16
20.07
16.79
15.66
13.77
13.73
12.40
9.87
8.94
67.08
47.60
21.65
13.74
1.73
1.69
1.54
1.22
1.20
1.08
0.91
0.85
0.74
0.74
0.67
0.53
0.48
3.63
Germany
Poland
France
United States
Hungary
Lithuania
Soain
Belgium
Sweden
Netherlands . t
Finland
Rumania
Latvia
Argentina
Canada
All others
World total
112.29
16.5
1,851.29
100.00
THE SMALL GRAIN CROPS
361
northerly position than wheat. This is accounted for by soil and
climatic factors.
The reader should not draw the conclusion that rye is grown only
in poor soils. This is not the case. In general, the extensive acreages
occupied by the crop in central Russia and also in the northern
Great Plains area of the United States are found on good soils.
On the other hand, rye is the main cereal crop on the great expanses
of sandy and heath soils of northern Germany and the Baltic
countries. In some of these areas crop production would be vir-
tually impossible except for the remarkable characteristics of the
rye plant. It is interesting to note that the yields in the western
European countries are high in spite of the fact that the crop is
widely grown on poor soils.
FIG. 70. Distribution of rye in the United States, average acreage harvested
1928-1937. Each dot represents 10,000 acres.
Distribution of Rye in the United States. Prior to the first
World War rye was grown principally in the sandy sections of
Michigan, Wisconsin, and Minnesota, with a smaller acreage on
poor and depleted soils in Pennsylvania, New Jersey, and eastern
New York. Since that time the states of the northern Great Plains
area have assumed the lead. This is shown in Table 25 and Fig.
70. Since wheat production is excluded by severe winter conditions
of the northern Great Plains, rye fills the distinct need for a fall-
362
ECOLOGICAL CROP GEOGRAPHY
sown crop. Its inclusion in the cropping systems of this area lends
stability and diversification. Winter rye can often be relied upon to
provide feed in seasons disastrous to spring wheat and other spring-
sown crops. In recent years the importance of rye has also increased
in the central and southern Great Plains area. This increase may be
accounted for by the response of rye to droughts experienced in this
area. Owing to dangers of admixtures, winter rye should under
most conditions be excluded from intense winter wheat producing
areas.
TABLE 25. RYE: ACREAGE HARVESTED, PRODUCTION, AND PERCENTAGE OF
UNITED STATES TOTAL PRODUCTION IN SPECIFIED STATES RANKED ACCORDING
TO PRODUCTION — AVERAGES FOR THE TEN-YEAR PERIOD 1928-1937 — AND
1938 PRODUCTION. ACREAGES AND PRODUCTION EXPRESSED IN THOUSANDS.
Production
Rank
States
Acreage
Harvested
Average
1928-1937,
in Bu.
Percentage
of U. S.
Total,
1928-1937
1938, in
Bu.
1
North Dakota
* 812
8,076
22.23
12,974
2
Minnesota
406
6,138
16.90
9,846
3
South Dakota
310
3,714
10.22
10,176
4
Nebraska .......
289
2,770
7.62
4,796
5
Wisconsin
228
2,515
6.92
4,290
6
Michigan
159
1,886
5.19
1,552
7
Pennsylvania
113
1,544
4.25
884
8
Indiana
118
1,370
3.77
1,265
9
Iowa
71
1,124
3.09
1,860
10
Illinois
80
971
2.67
1,350
All others
593
6,222
17.14
6,571
Total U. S
3,179
36,330
100.00
55,564
BARLEY
Commercial Importance. Barley is primarily a feed crop. Its
second most important use is in the production of malt. The
amount used for that purpose is small in relation to the total crop
produced. In the United States, the greatest beer producing coun-
try of the world, the amount of barley used in the making of fer-
mented malt liquors for the fiscal year ending June 30, 1937, was
54.63 million bushels. In addition to this amount, 8.99 million
bushels were used in the production of distilled spirits. Barley
THE SMALL GRAIN CROPS 363
occupies a rather minor place as a cereal for direct human consump-
tion except in some northern areas of Europe and in Asia, and at
high elevations; that is, under conditions too severe for the produc-
tion of either winter wheat or winter rye. It is a staple food in the
highlands of Tibet. In most areas it is used for human food only in
special forms as in breakfast foods and as pearled barley in soups.
Only around 1.5 million bushels of barley are used for pearling
in the United States annually.
Barley is generally used in place of corn for feeding purposes in
areas not adapted to corn production. Likewise barley takes the
place of oats for feed in areas unsuited for oat production; as in
northern Africa where the physiological growing season is cut short
by hot dry weather in early summer.
Historical. Barley is one of the most ancient of cultivated plants.
Kornicke agrees with Plinius in designating it as the oldest of culti-
vated plants. In ancient Egypt it was used as food for man and
beast, and also made into bread. It continued to be one of the chief
bread plants of continental Europe down to the sixteenth century,
when it was gradually replaced by rye and wheat.
According to Carleton, Hordeum spontaneum is generally conceded
to be the oldest ancestor of two-rowed barley now known to be
growing wild. It occurs in all of the region between the Red Sea
and Caucasus Mountains. Six-rowed barley originated, according
to Kornicke, from a wild barley H. ithaburense found by Bornmiiller
in the Kurdistan Mountains of western Asia.
Climatic Relationships. Wheat has the distinction of being the
prime bread crop of the world, rye the distinction of being the most
winter-hardy of the cereals, while barley is outstanding from the
standpoint of being able to mature in a shorter season than any
other cereal crop. The season here referred to is the physiological
growing season; that is, the growing season may be cut short either
by the lack of a sufficient amount of moisture to sustain growth, or
in northern areas and at high altitudes by low temperatures. The
fact that barley is able to mature in a short season has won for it the
reputation of being drought-resistant. This is not exactly the case;
the crop is drought-escaping rather than drought-resistant. During
its short period of growth it demands rather moderate temperatures
and a fairly abundant supply of moisture. The intermountain
states offer a good example of the ability of barley to grow at high
364 ECOLOGICAL CROP GEOGRAPHY
elevations. Robertson et al. (19) report high yields of barley at the
Fort Lewis substation in Colorado at 7,000 feet elevation, with a
growing season of only from 90 to 100 days. Woodward and
Tingey (28) also report good returns from barley at 7,000 feet in
Utah. In eastern Idaho the crop is grown at 6,500 feet. In the
Alps barley is found up to 5,500, in the Caucasus up to 8,500, and
in Tibet even at 10,000 feet above sea level. The northern limit of
barley in Russia is reported at latitude 65°.
Barley is able to grow under conditions of low temperature during
its period of vegetative growth. It is also able to endure high tem-
peratures during and after heading, provided the humidity of the
air is low. A combination of high temperature and high humidity
is as fatal to barley as to wheat. Such a combination is especially
detrimental if occurring during the postheading period.
It is necessary to differentiate between the climatic requirements
of feed and malting barley. One of the main prerequisites of a
malting barley is mellowness, occasioned by a high starch content,
capability of yielding a high percentage of extract, and a relatively
low nitrogen content. The production of this type of barley re-
quires above all temperature and moisture conditions favorable to
the elongation of the postheading period. Hot dry weather after
heading leads to the production of a harsh, flinty type of kernel
unsuited for malting. A flinty type of grain relatively high in nitro-
gen can be used to good advantage in the feeding of livestock.
Consequently areas bordering on sections where the growing season
is tut short by hot dry weather usually produce a feed type of barley.
Table 26 gives the climatic relationships in the important barley
producing areas of the world. The general climatic requirements
of barley, it will be seen, are quite similar to those of wheat. As a
matter of fact, the wheat and barley producing areas in North
America and Europe show a considerable overlapping in most
sections. There are exceptions to this, however; for instance the
central portion of the Corn Belt and the southern Great Plains area
grow but little barley; likewise, Italy has little barley. Both of these
regions are important wheat producing areas. Several factors may
be responsible for these exceptions such as the need for a bread crop,
the competitive position of barley as a feed crop compared with
other available grain feeds such as corn and the sorghums in the
central and southern Great Plains area, and above all the fact that
THE SMALL GRAIN CROPS
365
the production of winter barley is more hazardous than that of
winter wheat. Winter barley is grown only in areas with compara-
tively mild winters. It was pointed out in connection with the
climatic requirements of wheat that the highest yields were obtained
in the BC'r and CC'r climates. This holds true also with barley.
There is a noticeable difference between the climatic responses of
wheat and barley. The highest quality wheats, the high-protein
or strong wheats, are produced in the relatively dry BSk and CC'd
climates while the low-protein wheats are produced in the moister
Cf and CC'r climates. The usually more valuable malting type of
barley is produced in the moister, and the feeding and generally
less valuable types in the drier, climates. The protein relationships
in response to climatic factors are the same in wheat and barley;
the difference comes into play in the designation of the standards
of quality.
TABLE 26. CLIMATIC RELATIONSHIPS IN THE IMPORTANT BARLEY PRODUCING
SECTIONS OF THE WORLD
Producing Region
Climatic Classification
Relative
Location
Vegetation
Koppen
Thorn-
thwaite
U.S. northern Great Plains . . .
Wisconsin and northern Illinois . .
California
Cont.
Trans.*
Trans.
Trans.
Cont.
Trans.
Cont.
Grassland
Woodland
Grassland
Woodland
Woodland
Grassland
Woodland
Grassland
Grassland
Dfb
BSkw
Dfb
Dba
Cfb
Csb
Cfb
Dfb
Dfc
BSk
Csa
BShs
Cwg
•
CC'd
CC'r
DC'd
BC'r
CC'r
CB's
DB'd
BC'r
CC'r
CB'd
CC'r
CB's
DB's
CB'w
CA'w
Southern Russia
Northern Africa
Northern India
* Transitional between marine and continental.
Soil Conditions for Barley. Barley is very specific in its soil
requirements. It demands better drainage than either wheat or
oats. For this reason it is not well adapted to heavy clay soils in
humid areas. It is also more sensitive to mineral deficiencies than
366 ECOLOGICAL CROP GEOGRAPHY
wheat and less tolerant of soil acidity than most other cereals.
On the other hand, barley withstands moderate concentrations of
alkali and soluble salts. Sandy soils are unsuited to barley produc-
tion.
World Distribution of Barley. Six more or less distinct world
centers of barley production may be recognized from Fig. 71 ,
giving the distribution of world barley acreage, and Table 27,
showing the statistical data of barley distribution. These areas are:
1. The north central portion of the United States and the eastern
parts of the prairie provinces of Canada.
2. Northwestern and central Europe.
3. Northern Africa and Spain.
4. Rumania and southern Russia.
5. North-central India.
6. Northeastern China and Japan.
The distribution of barley on the North American continent will
be discussed under a separate heading.
Barley is an important crop on nearly all the better soils of north-
western and central Europe. Climatic conditions favor the pro-
duction of malting barley. Trig crop is of special importance in
Denmark, particularly on the island of Zealand. The great im-
portance of the livestock industry in Denmark and northwestern
Europe in general accounts for the great importance of barley;
furthermore, the cool climate favors high yields. Barley is used
extensively for feed in all of this area but is of less importance for
that purpose than oats. There is a close agreement with the barley
and sugar beet producing areas, barley being one of the crops most
frequently following sugar beets in the rotation. Both of these
crops require good soils.
The barley producing area of Europe extends across the entire
continent from the North and Baltic Seas to the Black Sea. The
crop becomes of special importance on the Chernozem soils of
Rumania and in southern Russia. The climate in this area is rather
dry, but barley is usually able to mature prior to the appearance of
the expected summer drought.
Barley fits well into the Mediterranean climates of northern
Africa and southern Spain. It constitutes the great feed crop of this
area. The climate is sufficiently mild for winter barley which
matures before the summer drought. The low humidity during
1 *
5.
Q
§
03
cx
B-
I
1
I
367
368
ECOLOGICAL CROP GEOGRAPHY
the season when the crop approaches maturity enables it to with-
stand fairly high temperatures.
China and Japan are important barley producing countries.
A considerable portion of the crop produced is used for human
consumption. The producing areas correspond with the wheat
growing sections, the crop filling the same place in the rotation as
wheat in that it is grown during the portion of the year too cool for
the production of rice. The hot, humid summers in this area are
unfavorable to barley production. The barley crop, like fall-sown
wheat, is able to escape this unfavorable season by virtue of its
ability to grow at relatively low temperatures during late winter
and early spring so that it matures before the hot, humid weather
sets in.
In India barley is also grown during the winter half-year. The
Middle Ganges is the most important producing region. Barley is
TABLE 27. BARLEY: ACREAGE, YIELD PER ACRE, PRODUCTION, AND PER-
CENTAGE OF WORLD TOTAL PRODUCTION IN SPECIFIED COUNTRIES — AVER-
AGES FOR THE FIVE-YEAR PERIOD 1930-31 TO 1934-35
Rank
Countries
— f
%
Acreage, in
Millions
of Acres
Yield, in
Bu. per Acre
Production
In Millions
ofBu.
In Per-
centage of
World Total
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
China
16.30
18.22
6.04
10.64
4.44
4.68
7.57
3.94
4.57
3.59
3.00
3.46
1.81
.88
1.13
3.35
1.17
1.21
.42
12.78
22.2
16.0
35.9
20.1
26.8
23.8
14.6
19.1
16.1
19.4
22.1
15.2
26.6
51.8
39.2
10.6
25.0
22.5
18.7
361.15
290.85
214.33
213.67
119.24
111.34
110.46
75.20
73.56
69.85
66.40
52.78
48.06
45.30
43.05
35.38
29.23
27.10
7.84
216.21
16.33
13.15
9.69
9.66
5.39
5.04
5.00
3.40
3.33
3.16
3.00
2.39
2.17
2.05
1.95
1.60
1.32
1.23
0.35
9.79
U.S.S.R
Germany
United States
Japan and Chosen . . .
Spain
India
Canada
Rumania
Turkey
Poland
Morocco
France
Denmark
Great Britain
Algeria
Hungary
Argentina
Australia
All others
World total
109.20
20.2
2,211.00
100.00
THE SMALL GRAIN CROPS 369
used both as food for man and a feed for animals. Barley production
in India is more or less confined to the more humid regions; its
distribution does not extend as far south as that of wheat, but very
little of the crop is grown in the Deccan.
It is evident from Table 27 and also Fig. 71 that little barley is
produced in the southern hemisphere. In Argentina and Australia
wheat provides a more profitable export crop than barley; also in
Argentina climatic conditions are more favorable to corn than to
barley production.
Distribution of Barley in the United States. The production
of barley is of less importance in the United States than that of
either wheat or oats. Since production is evaluated in variable
units of weight, bushels, it is necessary to state the production of
the four important cereals in equivalent units such as millions of
pounds. When this is done for the five-year period, 1930-31 to
1934-35, it is found that the United States produced annually
43,958 millions of pounds of wheat, 31,520 of oats, 10,256 of barley,
and only 1,876 millions of rye. The percentage production of these
cereals on the basis of world total shows the same relationship,
namely 13.32 per cent for wheat, 12.71 for oats, 9.66 for barley, and
1.69 for rye. Barley is grown primarily for feed. For that purpose
it comes into competition especially with corn, also with oat£, and
to some extent even with wheat. In many portions of the United
States, corn is a more efficient producer of feed than barley. Barley
is an important crop in the northern portion of the Corn Belt. The
bulk of the crop is, however, produced north of the intensive corn
growing sections; that is, where temperature conditions are less
favorable to corn. The ecological optimum for corn is found in
regions with moist, warm summers, the very set of conditions un-
favorable to barley production. Barley, on the other hand, with
its low temperature requirement and its ability to mature in a short
physiological growing season, is found in the north and extends
even into the steppe climates. Table 28 gives the statistical data of
barley production by important producing states. Figure 72 gives
the distribution of barley acreage.
The largest contiguous and most important barley producing
area of the country extends from the western shore of Lake Michi-
gan into the Dakotas. The eastern portion of this belt, that is, where
the BC'r and GC'r climates prevail, is admirably suited to the
370
ECOLOGICAL CROP GEOGRAPHY
production of high-quality malting barley; in the drier CC'd cli-
mates, feed barley is grown. Because of variability in climate from
season to season the line separating the malting from the feed barley
producing sections is not distinct; however, as the plains area is
approached an increasing acreage of Trebi is encountered. Malt-
sters generally object to this variety. Prime malting barley in this
area is mostly of the Manchuria-Oderbrucker type which is grown
FIG. 72. Distribution of barley in the United States, average acreage harvested
1928-1937. Each dot represents 10,000 acres.
primarily in the eastern more humid portion of this area. Certain
smooth awned varieties also produce barley suitable for malting
purposes.
The extensive barley producing area of northwestern Kansas,
southwestern Nebraska, and northeastern Colorado is interesting.
The climate classifies as DC'd. In this area barley is largely second
choice to wheat. As stated by Harlan (10), "if the wheat seeding is
successful, wheat is grown. If for some reason the ground cannot
be prepared for wheat, or if it is winterkilled, spring barley is sown
as a catch crop." Barley matures slightly earlier than other spring
cereals; as a matter of fact, in many seasons early varieties mature
fully as early as winter wheat. Barley escapes drought more effec-
tively than other crops.
THE SMALL GRAIN CROPS
371
Barley is an important feed crop in all of the irrigated valleys .of
the Rocky Mountain states. In parts of the area, as in the Columbia
River basin and in the Palouse region, it is grown without irrigation.
Another outstanding barley producing area is found in the
Sacramento and San Joaquin Valleys of California. Here also
barley is grown in competition with wheat. The crop is sown in
winter, December and January. The Sacramento Valley produces
a prime grade of malting barley. The barley produced in the San
Joaquin Valley is not so mellow as that produced in the Sacramento
Valley and is therefore used mostly for feed. In the first area the
climate is EC's; in the second it approaches the warmer and drier
CB's climate.
TABLE 28. BARLEY: ACREAGE HARVESTED, PRODUCTION, AND PERCENTAGE
OF UNITED STATES TOTAL PRODUCTION IN SPECIFIED STATES RANKED ACCORD-
ING TO PRODUCTION — AVERAGES FOR THE TEN-YEAR PERIOD 1928-1937 —
AND 1938 PRODUCTION. ACREAGES AND PRODUCTION EXPRESSED IN MILLIONS.
f
Production
Rank
States
Acreage
Harvested
Average
Percentage of
1928-1937,
U. S. Total,
1938, in Bu.
in Bu.
1928-1937
\
Minnesota ....
1.98
44.09
18.92
48.02
2
California ....
1.09
29.55
12.68
27.55
3
North Dakota . . .
1.85
28.95
12.42
21.32
4
South Dakota . . .
1.45
25.25
10.84
29.24
5
Wisconsin
0.78
21.26
9.12
24.29
6
Iowa
0.54
13.73
5.89
13.63
7
Nebraska
0.65
11.88
5.10
21.53
8
Colorado
0.43
8.08
3.47
11.99
9
Illinois
0.28
7.29
3.13
4.05
10
K^m^.q .
0.41
6.35
2.73
6.68
All others
1.56
36.59
15.70
44.71
Total U. S
11.02
233.02
100.00
253.01
The production of winter barley is of local importance in the
southeastern states and along the Pacific coast. The total acreage of
the crop is small. Winter barley in that area is giving good results in
providing fall and early spring pasturage. Etheridge et al. (8)
regard it as the best pasture crop among the grains in central and
southern Missouri. Barley is not so winter-hardy as wheat; its
distribution to the north is therefore limited.
372 ECOLOGICAL CROP GEOGRAPHY
OATS
Commercial Importance. Oats are produced almost exclusively
as a feed for livestock. They are mostly fed in the form of grain, but
are also more extensively employed for the production of grain hay
than any other cereal. Oats contain more crude fiber than the
other cereals. This makes them bulky and of relatively low volume
value. Most of the crop is fed on the farms where it is produced;
its bulkiness, comparatively low value, and the limited industrial
uses made of it discriminate against its entering into trade
channels. Oats are relatively high in fat, protein, and mineral
matter. This together with their bulkiness makes them a desirable
feed for breeding stock and young animals.
Only around 3 per cent of the oat crop of the United States is
milled or processed for human consumption. Oatmeal and other
oat preparations are used as breakfast foods. Oatmeal crackers and
oat bread are other food products.
Historical. The cultivation of oats is not so old as that of wheat
or barley. The crop was unknown to the Ancient Egyptians,
Hebrews, Chinese, and Hindus. % The first mention of oats in litera-
ture is found in the writings of a Greek physician, Dieuches, living
in the fourth century B.C. Common oats were evidently first culti-
vated by the ancient Slavonic peoples of eastern Europe during the
iron and bronze ages. Plinius was familiar with the crop, desig-
nating it as Avena graeca, thereby inferring its introduction from
Greece. Zade (29) indicates, however, that the oats mentioned by
Plinius, Columella, and other Roman writers were not our common
oats, A. saliva^ but rather the cultivated red oats, A. byzantina.
The cultivated red oats are still grown in the Mediterranean region
and in other sections with warm climates. The Greeks apparently
introduced them from Asia Minor, their probable place of origin.
They used oats for the production of feed, for making porridge, and
also for medicinal purposes. The Greeks apparently made greater
use of oats as a food crop than the Romans who used them largely
as feed for animals.
The place of origin of common oats is not known. Oats appear to
have been the main cereal food crop of the German tribes at the
time of Christ. Later their importance as a food crop decreased,
except in times of need. The Celts also used oats extensively; even
THE SMALL GRAIN CROPS 373
at the present time they play a comparatively important part in
human nutrition in Ireland, the Orkney and Shetland Islands, and
Scotland.
Climatic Relationships. Oats are essentially a crop of moist
temperate regions. The important oat producing areas of the world
are found in the woodland, the Dfa, Dfb, Cfa, Cfb, and BC'r,
BB'r, and CC'r climates, Table 29. Oats thrive in the marine and
littoral climates. While not excluded from the interior of the
continents, they yield decidedly less there and take a secondary
place to wheat and barley. This is true especially in the warmer
regions. They are not adapted to the steppe climates. Since oats
demand a longer growing season than barley their distribution
extends neither as far to the north nor to as high elevations as barley.
The shortness of the season at higher latitudes and the advent of
hot dry summers set the limits of oat production. Continental
areas bordering on the steppe or located where high summer tem-
peratures prevail produce early-maturing varieties; in addition to
this the crop is sown as early as seasonal conditions permit so that
the plants may develop during the cooler and also more humid
portion of the season. Oats of the sterilis type, the red oats, are more
tolerant to high temperatures than the common oats. This, together
with the facts that the crop is sown early and matures in early sum-
mer, accounts for the production of oats of the sterilis type in the
warmer regions such as the central and southern Great Plains area
and the Mediterranean region. The northern expansion of oats
in the Scandinavian countries and in Russia corresponds according
to Engelbrecht, cited by Zade, with the September isotherm of
9°C (48°F). The southern limit of the crop coincides in Russia with
the May isotherm of 15°G (59°F) and with the July isotherm of
21°C (70°F).
Fall-sown oats mature earlier than the spring-sown crop, thus
enabling them to mature before the arrival of high temperatures.
Oats are, however, less winter-hardy than either wheat or barley.
This confines winter oats to areas with mild winters. Occasional
depressions of temperature approaching 0°F are under most soil
conditions fatal to fall-sown oats. Consequently the production
of the crop is hazardous in areas where the temperature is likely
to drop down to that point during the winter months.
374
ECOLOGICAL CROP GEOGRAPHY
TABLE 29. CLIMATIC RELATIONSHIPS IN THE IMPORTANT OAT PRODUCING
AREAS OF THE WORLD
Producing Region
Climatic Classification
Relative
Location
Vegetation
Koppen
Thorn thwaite
Northeastern United States .
Northwestern Europe . .
Russia
Trans.
Trans.
Gont.
Woodland
Woodland
Woodland
Dfa
Dfb
Cfa
Gfb
Dfc
BC'r
CC'r
BB'r
BC'r
CC'r
CC'r
Soil Conditions for Oats. Oats are less specific in their soil re-
quirements than either wheat or barley. A favorable amount of
nitrogen is essential to good yields. Excess nitrates, on the other
hand, may cause serious lodging. Except on sandy soils oats
respond less to phosphorus and potassium than other cereals. All
soils with fair drainage well supplied with moisture are adapted to
oat production; even rather light sandy soils will produce oats under
favorable moisture conditions? %Since oats are so easily satisfied as
to their soil requirements they are often grown in the least favored
place in the rotation, as after a heavy feeder like corn. The highest
yields of oats are obtained on loamy and heavy soils that are reten-
tive of moisture. Oats also do better on cold wet soils than other
cereals. According to Mackie (15), "alkali and saline soils may, if
the climatic conditions are favorable, produce crops of oats where
wheat and barley would fail."
World Distribution of Oats. Table 30 gives the statistics of
world oat distribution by countries, while Figures 73a and 73b give
a comparison of the world's barley and oat acreages. It will be ob-
served from both the tabulated data and the distribution map that
oats are primarily a European and North American crop. But few
oats are grown in the other continents. In this respect the distri-
bution of oats is quite similar to that of rye with the exception that
the oat crop is of much greater importance than rye in the United
States and in Canada. In other words, oats are not so distinctly a
European crop as is rye. The United States and Canada together
produce 30.82 per cent of the world's oat crop as compared to
only 2.17 per cent of the world's rye.
THE SMALL GRAIN CROPS 375
The production of oats in the United States will be discussed
under a separate heading.
Oats rank second in total value among the grain crops of Canada
as a whole, but in Ontario and the other eastern provinces they
take first place by a large margin. The greatest volume of oats is
produced in the prairie provinces; according to Derick (7) 62 per
cent of the total Canadian oat crop in 1935 was produced in the
provinces of Manitoba, Saskatchewan, and Alberta. This large
volume of production in the prairie provinces should not be taken
to mean that the oat crop is of relatively greater importance here
than in the eastern and Maritime provinces. The large volume is
accounted for by the great expanse of agricultural land in the prairie
provinces with climatic conditions fairly favorable to the production
of the crop. Only a small percentage of the Canadian oat crop is
exported. During the ten-year period 1925-1934, the total export
fluctuated between 2 and 34 million bushels. Most of the crop is
grown for feed. The prairie provinces of Canada are far more im-
portant as producers and exporters of wheat than of oats.
Northwestern Europe represents the most intense oat producing
area of the world. The reasons for this are found in the adaptation
of the crop to the moderate and moist climate of this area, its
leniency with regard to soil demands, and its wide employment as a
feed crop. The high average yields of oats in all of this area and
especially in Denmark, 71.9 bushels per acre, and in Great Britain,
60.3 bushels, attest the adaptation of the crop to the marine and
littoral climates of the area. Since more feed can be produced on
the better soils of this area from barley than from oats, there has
been a significant shift from oats to barley in recent years. This is
true especially on the heavier soils of central Germany. On the
other hand, barley is unable to successfully compete with oats on
the sandy soils of this humid area.
Some oats are grown in the Mediterranean and Balkan areas;
the crop is, however, far less important in these areas than either
wheat or barley, which are better adapted to the continental cli-
mates. In this area red oats take the place of the common oats of
northwestern Europe.
Russia is an important oat producing country because of the vast
areas available for the growing of the crop rather than because of
intensive production. The average yields obtained are not high.
I
IF
T3 O
•6 a
& O
oJ bo
5
I
H3
T3
I
376
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£
a
I
'
S'fi
*"O 50
J3 ^
^ fe-
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377
378
ECOLOGICAL CROP GEOGRAPHY
The comparison of the distribution maps presented indicates that the
oat crop of Russia is produced mostly in areas to the north of the
important wheat and barley growing sections. The crop is grown
primarily along the margin of the forested belt rather than on the
grasslands; oats avoid the extremes of the steppe climates. In
locations where the crop is grown near the grasslands early-
maturing varieties capable of completing their cycles of develop-
ment before the arrival of the heat and drought of summer are
employed. This same condition is encountered in the plains areas
of the United States; as a matter of fact many of the important
varieties of oats produced in this and similar areas are of Russian
origin or selected from varieties introduced from Russia. Varieties
of Russian origin are also used in the oat producing areas of the
Corn Belt where high summer temperatures dictate early maturity.
TABLE 30. OATS: ACREAGE, YIELD PER ACRE, PRODUCTION, AND PER CENT
OF WORLD TOTAL PRODUCTION IN SPECIFIED COUNTRIES — AVERAGES FOR
THE FIVE-YEAR PERIOD 1930-31 TO 1934-35
Rank
Countries
Acreage, in
Millions
of Acres
Yield, in
Bu. per Acre
Production
In Millions
of Bu.
In Per-
centage of
World Total
1
2
3
4
5
6
7
8
9
10
11
12
U.S.S.R
42.25
37.56
10.89
12.99
8.38
3.34
5.43
1.62
.95
2.05
2.18
1.20
15.46
23.9
26.2
45.9
27.0
38.8
60.3
31.1
48.3
71.9
31.5
24.3
33.1
29.8
1,007.74
985.00
550.62
350.07
325.42
193.51
169.23
78.37
68.51
64.60
52.90
24.47
460.36
23.27
22.74
12.71
8.08
7.51
4.47
3.91
1.81
1.58
1.49
1.22
0.56
10.65
United States
Germany
Canada
France
Great Britain
Poland
Sweden
Denmark
Argentina
Rumania
Australia and New Zealand
All others
World total
144.30
30.0
4,331.00
100.00
Distribution of Oats in the United States. The distribution of
the oat crop of the United States is determined by the climatic re-
quirements of the crop, the ease with which it fits into established
and recognized rotations, and the demand for it as a feed.
According to Finch and Baker (9) "the oat belt of the United
THE SMALL GRAIN CROPS
579
States consists of a crescent-shaped area extending from New
England to North Dakota bounded on the north by the Great
Lakes, and on the south and west by a curved line across central
Ohio, central Illinois, eastern Nebraska, and thence northward
along the Missouri River." This statement was written more than
•20 years ago. Figure 74 gives the distribution of the oat acreage of
the country for the years 1928-1937. The general distribution of
the crop remains much the same.
FIG. 74. Distribution of oats in the United States, average acreage harvested
1928-1937. Each dot represents 25,000 acres.
Table 31 gives the statistical data of oat distribution by im-
portant producing states. The great corn producing states are
much in evidence in this tabulation. The northern Corn Belt is not
only favored with climatic conditions suited to oats, but also pro-
vides a place for oats in the rotation; in addition to this it represents
the most intensive livestock producing area of the country. Con-
sequently the stage is more or less set for oat production.
Oats commonly follow corn in the rotation. In the northern
portion of the Corn Belt the corn crop is frequently removed too
late in the season for the seeding of winter wheat. The corn stalks
remaining in the field also provide feed for livestock in the late fall
months; it is therefore inadvisable to remove them to prepare the
land for winter wheat. Since plowing is not necessary to prepare
380
ECOLOGICAL CROP GEOGRAPHY
the seedbed for oats the following spring, the crop can be seeded
with but little expense. Oats are also frequently used as a nurse
crop for clovers and grasses. In the southern portion of the Corn
Belt, that is, in the corn and winter wheat region, winter wheat
takes the place of oats in the rotation. Here the corn crop is re-
moved from the field in time to seed winter wheat; furthermore,
summer temperatures in this area are generally too high for best
results with oats.
The importance of oats decreases sharply as the grassland areas
of the Great Plains states are approached, and the crop is practi-
cally eliminated in the short-grass or steppe regions.
TABLE 31. OATS: ACREAGE HARVESTED, PRODUCTION, AND PERCENTAGE OF
UNITED STATES TOTAL PRODUCTION IN SPECIFIED STATES RANKED ACCORDING
TO PRODUCTION AVERAGES FOR THE TEN-YEAR PERIOD 1928-1937
AND 1938 PRODUCTION. ACREAGES AND PRODUCTION EXPRESSED IN MILLIONS.
j§
Production
Rank
States
Acreage
Harvested
9
»
Average
1928-1937,
in Bu.
Percentage of
U. S. Total
1928-1937
1938, in Bu.
1
5.95
193.95
18.48
20902
2
3
Minnesota ....
Illinois
4.29
3.95
134.43
125.12
12.81
11.92
128.70
111 67
4
Wisconsin
2.48
78.02
7.44
76 11
5
Nebraska
2.11
49.92
4.76
5508
6
Indiana
1.75
49.18
4.69
34.06
7
Ohio
1.58
48.83
4.65
36.99
8
9
South Dakota . . .
1.68
1.35
41.22
39.16
3.93
3 73
46.92
42 84
10
Missouri
1.62
34.74
3.31
46.51
All others
10.69
254.73
24.28
280.53
Total U. S
37.45
1,049.30
100.00
1 068 43
An arm extends southward from the main oat producing area
through eastern Kansas, Oklahoma, and into Texas. Oat produc-
tion in this area is made possible by the employment of either very
early-maturing varieties of common oats and to a greater extent
by the use of early-maturing varieties of red oats. The red oats are
often referred to as "warm climate" oats. That there is justification
for this terminology is verified by Stanton and Coffman (23).
The red oats are able to withstand hot dry weather, especially at
heading and filling time, more effectively than the common oats.
THE SMALL GRAIN CROPS 381
In addition, the extreme earliness of some varieties of red oats
often enables them to escape injury by hot weather and drought.
Oat production is of some importance in the Carolinas, Georgia,
and Mississippi. A high percentage of the crop here is fall-sown.
Some spring-sown red oats are also used. The other fall-sown oat
producing areas of the United States are found in California, west-
ern Oregon, and western Washington. According to Salmon (20)
the isotherm of 30°F for the months of January and February cor-
responds with the northern limit of winter oat production.
Oats are an important feed crop in all of the irrigated sections
of the northern portion of the United States.
RICE
Commercial Importance. The relative importance of rice as a
food crop has already been alluded to. The crop is of primary im-
portance to the support of the teeming populations of the Orient.
In the humid lands of the tropics rice has no competitor in its
ability to support dense populations. This is well stated by Hunt-
ington (12) in the following paragraph.
"Few plants except potatoes exceed rice in their capacity to support
a large population on a small area. In Java, for example, the average
yield per acre is something like 2,000 pounds of rough rice. If we rhake
allowance for two or three crops per year, as well as for the parts of
each grain not generally eaten by man, and if we remember that rice
can be grown every year without exhausting the soil, it appears that
Javanese rice land supplies four to six times as much food per acre as
does wheat land in the United States. Similar, although less extreme,
conditions prevail in China, Japan, India, and Egypt."
While rice is used for human consumption in nearly all parts of
the world, its use for that purpose outside of the monsoon region of
Asia and other moist tropical areas is of little importance in com-
parison with that of the bread cereals. Thus, according to Jones
et al. (13), "the per capita consumption of rice in the continental
United States is about six pounds a year, whereas in India, Chosen,
French Indo-China, Java, Madoera, and the Philippines it is over
200 pounds, and in Japan proper, Taiwan, and Siam, from 300 to
400 pounds."
The different standards of living of the yellow and brown races
as compared to the white race influence the relative importance of
382
ECOLOGICAL CROP GEOGRAPHY
rice in the diet of the former and wheat in the diet of the latter.
A majority of the yellow and brown races live more exclusively on
rice than any other people on any other single food crop. In France
wheat plays a greater importance in the national diet than in prob-
ably any other country, yet, according to Zimmermann, this
cereal furnishes probably less than 40 per cent of the total calories
of the French diet, while in vast areas of Asia rice contributes as
much as 80 to 90 per cent of the total food supply measured in
calories.
Historical. Rice probably originated somewhere in the area
extending from southern India to Cochin-China. A number of
species of Oryza are found growing wild in the tropics of both
hemispheres. The cultivated rice in all probability originated from
one or more of these wild forms. The history of the plant goes back
to the unknown past. Rice is reported to have been the most
important cereal of China in 2800 B.C. Its cultivation spread from
China and India to Egypt and North Africa centuries ago. It was
grown in Italy in 1468, and introduced into the colony of South
Carolina, probably from Madagascar, about 1685.
Climatic Relationships. Tfeble 32 gives the climatic classifica-
tions of the world's important rice producing areas. The rice
climates are characterized by high temperatures during the growing
season, an abundance of moisture, and in most instances a high
atmospheric humidity. These very conditions exclude other cereals,
at least during the growing season of the rice crop. In some areas
as in China and India wheat and barley may be grown during the
TABLE 32. CLIMATIC RELATIONSHIPS IN THE IMPORTANT RICE PRODUCING
AREAS OF THE WORLD
Producing Region
Climatic Classification
Relative
Location
Vegetation
Koppen
Thornthwaite
China
Trans.
Trans.
Marine
Marine
Marine
Woodland
Woodland
Woodland
Woodland
Woodland
Cw
Aw
Cwg
Cfa
Af
Aw
Cfa
BB'w
AA'r
CA'w
BB'r
BA'w
BB'r
India
Japan and Chosen . . .
Java and Madoera . . .
Louisiana
THE SMALL GRAIN CROPS 383
cooler and drier portions of the year. To the climatic requirement
must also be added an abundant supply of fresh water for irrigation.
Rice fields are covered with water, usually when the plants are
from six to eight inches high, and the ground is submerged under
three to six inches of water until the crop is nearly mature. The
production of the so-called upland rice is of limited importance.
It is grown without flooding. A high rainfall during the growing
season is essential for its development.
Soil Requirements. Rice is produced on a variety of soils. The
outstanding requirement of the soil is the ability to hold water over
the surface for a considerable period. Furthermore, the drainage
features must be such that the fl6od water may be promptly re-
moved prior to harvest. Where the crop is grown with the aid of
power equipment the soil must provide a solid footing for such
machinery. Rich alluvial soils with impervious subsoils are ideal
for the crop.
World Distribution of Rice. The statistical data of world rice
production are presented in Table 33. Figure 75, taken from Blank-
enburg (5), gives the geographical distribution of the crop. Both
the tabulated data and the cartographical presentation bring out
the importance of the monsoon areas of Asia in world rice produc-
tion. Around 97 per cent of the world's rice crop is produced in the
Far East.
Zimmermann calls attention to the fact that wheat is a "cheap"
while rice is an "expensive" crop. That it costs more to produce
rice than wheat cannot be denied. But, as Zimmermann points out,
"a large portion of the world's rice crop is produced and consumed
outside of the borders of price economy so that ordinarily, for a
large number of rice eaters, the market prices of rice and wheat
have little significance." The subsistence economy of the rice
growing countries come definitely into play at this point.
"Subsistence economy is governed by natural, principally climatic,
considerations. Rice is the most prolific food crop which can be pro-
duced in the monsoon regions. In the second place, wide areas of
continental Asia, especially of China, lie outside of the reach of trans-
portation facilities by means of which wheat can be brought to them
from the outside. Third, there is little or no alternative occupation
for labor. Finally, throughout the world, dietary habits are among the
most tenacious of all human habits."
rd
3
O
I
384
THE SMALL GRAIN CROPS
385
The fact that China is the foremost rice producing country of the
world does not mean that all the inhabitants of that vast country
subsist on rice. That is not the case. To many Chinese, rice is a
luxury; they subsist on the cheaper grains, such as wheat, millets,
corn, and sorghums. Rice is an important crop only of the warmer
and humid southeastern and eastern portion of the country. The
important exporting countries are British India, French Indo-
China, and Siam. Some rice is also exported from Italy, the
United States, Egypt, and Brazil. Rice production in the extra-
tropical countries is of local importance in the United States, Italy,
Spain, Portugal, Bulgaria, and Yugoslovia.
TABLE 33. RICE: ACREAGE, PRODUCTION, AND PERCENTAGE OF WORLD
TOTAL PRODUCTION IN SPECIFIED COUNTRIES AVERAGES FOR THE FIVE-
YEAR PERIOD 1930-31 TO 1934-35
Rank
Country
Acreage, in
Millions
of Acres
Production
In Millions
of Lbs. of
Milled Rice
In Percent-
age of World
Total
\
2
3
4
5
6
7
8
9
10
11
12
13
14
China* ........
India
83.21
12.00
9.16
12.01
5.96
4.23
1.26
1.03
0.88
1.30
0.32
0.35
0.12
84,110
70,541
24,597
8,164
7,755
6,479
2,991
2,607
1,638
1,155
949
907
622
404
4,191
38.74
32.49
11. 33
3.76
3.57
2.98
1.38
1.20
0.75
0.53
0.44
0.42
0.28
0.19
1.94
Japan and Chosen
Java and Madocra ....
French Indo-China ....
Siam
Philippine Islands
Taiwan
Brazil . . .
United States
Madagascar .
Italy .
EfiTVDt ........
Spain ...
All others
World total
—
217,110
100.00
* Official statistics for China arc not available. The figure given is the estimate
of the average production for the six-year period 1930-1935 expressed in terms of
cleaned rice as presented by the Shanghai office of the Bureau of Agricultural Eco-
Distribution of Rice in the United States. It is evident from
Fig. 76 that the production of rice is of only local importance in a
limited number of areas in the United States. This is not surprising
586
ECOLOGICAL CROP GEOGRAPHY
in view of the climatic requirements of the crop. Table 34 gives the
statistical data of rice distribution.
The rice-producing areas of the country have been subject to
considerable shifting in the past 100 years because of the after-
effects of the Civil War and the utilization of power equipment on
the extensive level areas in the central and western areas of produc-
tion. Before the Civil War most of the rice crop of the United States
was produced on the tidal lands of the Carolinas and Georgia. In
1839 South Carolina produced 70 per cent of the crop and Lou-
isiana less than 4 per cent. By 1849 production had increased in
ROUGH RICE: PRODUCTION
Each dot rapmtnt*
700. 000 6usA«/«
FIG. 76. Rice production in the United States in 1935. Each dot represents
100,000 bushels. (After Jones et al.)
Mississippi, Alabama, and Florida, but the Atlantic coastal areas
still led in production. Even in 1859 South Carolina still produced
more than 60 per cent of the crop, and 90 per cent of it was grown
on the tidal lands of the South Atlantic states. The Civil War
practically destroyed the rice industry of these states. In the period
of 1929-1934 only around 8,000 acres of rice were produced in
South Carolina and Georgia. Louisiana became the greatest rice
producing state in 1889; it still holds this lead. From there the
culture of the crop spread to southeastern Texas and to the prairie
section of east-central Arkansas. Rice production is relatively new
in California. The first commercial crop was grown in 1912. Most
THE SMALL GRAIN CROPS
387
of the crop is grown in the Sacramento Valley, with some production
in the San Joaquin Valley.
TABLE 34. RICE: ACREAGE HARVESTED, PRODUCTION, AND PERCENTAGE OF
UNITED STATES TOTAL PRODUCTION IN SPECIFIED STATES RANKED ACCORDING
TO PRODUCTION AVERAGES FOR THE TEN YEAR PERIOD 1928-1937 AND
THE 1938 PRODUCTION. ACREAGES AND PRODUCTION EXPRESSED IN THOU-
SANDS
Production
Rank
States
Acreage
Harvested
Average
1928-1937,
in Bu.
Percentage of
U. S. Total
1928-1937
1938, in Bu.
1
Louisiana
454
18,128
41.78
20,748
2
Texas ... . .
181
9215
21.24
13 668
3
Arkansas
162
8,178
18.85
9,715
4
California
116
7,827
18.04
8,375
All others
39
0.09
Total US..
913
43 387
100 00
52 506
From 1926 to 1932 the United States exported from 20 to 25 per
cent of its total production of milled rice. By 1935 only 10 to 12
per cent of the crop was marketed abroad.
REFERENCES
1. Baker, O. E., "The potential supply of wheat," Econ. Geog., 1:24-27
(1925).
2. -~ ~ } and A. B. Genung, "A graphic summary of farm crops,"
U. S. Dept. Agr. Misc. Pub. 267, 1938.
3. Bennett, M. K., and H. C. Farnsworth, "World wheat acreage, yields
and climates," Wheat Studies of the Food Res. Inst., 8:265-308. Stanford
University, 1937.
4. Bergsmark, D. R., Economic Geography of Asia. Prentice-Hall, New
York, 1936.
5. Blankenburg, P., Der Reis. P. Funk, Berlin. Abstract and map in Die
Ernahrung der Pflanze, 30:116-117 (1934).
6. Carleton, M. A., The Small Grains. Macmillan, New York, 1916.
7. Derick, R. A., "Oats in Canada," Dominion of Canada, Dept. Agr. Pub.
554 (1937).
8. Etheridge, W. C., C. A. Helm, and E. M. Brown, "Winter barley, a
new factor in Missouri agriculture," Mo. Agr. Exp. Sta. Bull. 353, 1935.
9. Finch, V. C., and O. E. Baker, Geography of the world's agriculture.
Gov't Printing Press, Washington, 1917.
388 ECOLOGICAL CROP GEOGRAPHY
10. Harlan, H. V., "Barley: Culture, uses, and varieties," U. S. Dept. Agr.
Farmers Bull. 1464, 1925.
11. Hughes, H. D., and E. R. Henson, Crop Production. Macmillan, New
York, 1930.
12. Huntington, E., The Human Habitat. Van Nostrand, New York, 1927.
13. Jones, J. W., J. M. Jenkins, R. H. Wyche, and M. Nelson, "Rice
culture in the southern states," U. S. Dept. Agr. Farmers Bull. 1 808, 1 938.
14. Kirsche, P., Mensch und Scholle, Kartenwerk zur Geschichte und Geographie
des Kulturbodens. Deutsche Verlagsgesellschaft, Berlin, 1932. Ab-
stracted in Die Ernahrung der Pflanze, 32:350-352 (1936).
15. Mackie, W. W., "Oat varieties in California," Calif. Agr. Exp. Sta. Bull.
467, 1929.
16. Marbut, C. F., "Russia and the United States in the world's wheat
market," Geog. Rev., 21:1-21 (1931).
17. Morgan, M. F., J. H. Gourley, and J. K. Ableiter, "The soil require-
ments of economic plants," U. S. Dept. Agr. Yearbook 1938:753-776.
18. Percival, J., The Wheat Plant. Duckworth & Co., London, 1921.
19. Robertson, D. W., A. Kezer, F. A. Coffman, J. F. Brandon, D.
Koonce, and G. W. Deming, "Barley in Colorado," Colo. Agr. Exp.
Sta. Bull. 371, 1930.
20. Salmon, S. C., "The relation^f winter temperature to the distribution
of winter and spring grains ift the United States," Jour. Amer. Soc.
Agron., 9:21-24 (1917).
21. Schindler, F., Handbuch des Getreidebaus. Paul Parey, Berlin, 1923.
22. Shollenberger, J. H., "Wheat requirements of Europe," U. S. Dept.
Agr. Tech. Bull. 535, 1936.
23. Stanton, T. R., and F. A. Coffman, "Spring-sown red oats," U. S.
Dept. Agr. Farmers Bull. 1583, 1929.
24. Strong, A. L., The Soviets Conquer Wheat. Holt, New York, 1931.
25. Timoshenko, V. P., "Russia as a producer and exporter of wheat,"
condensation by M. K. Bennett, Wheat Studies of the Food Res. Inst.,
8:277-369. Stanford University, 1932.
26. , Agricultural Russia and the Wheat Problem. Food Res. Inst.
and Com. on Russian Res. of the Hoover War Library. Stanford
University, 1932.
27. Whitbeck, R. H., and V. C. Finch, Economic Geography. McGraw-Hill,
New York, 1924.
28. Woodward, R..W., and D. C. Tingey, "Barley variety tests in Utah,"
Utah Agr. Exp. Sta. Bull. 261, 1935.
29. Zade, A., Der Hafer. Gustav Fischer, Jena, 1918.
30. Zimmermann, E. W., World Resources and Industries. Harper, New
York, 1933.
Chapter XXIII
THE COARSE CEREALS
CORN
COMMERCIAL IMPORTANCE
The Great American Feed Crop. Since the United States pro-
duces about 50 per cent of the world's corn crop, it is fitting to
consider the commercial importance of corn in this country before
discussing it as a crop of world importance. Corn is referred to by
Jenkins (11) as the backbone of American agriculture. It repre-
sents the leading crop of the United States in acreage as well as
in value of product. In 1929 corn occupied 27.0 per cent of all
crop land in the United States as compared to 18.7 per cent for
hay, 17.1 per cent for wheat, 11.9 for cotton, 10.1 for oats, 3.6 for
barley, and 2.2 per cent for sorghums (Baker and Genung, 4).
According to Taylor (24), half of the corn crop of the United
States is fed to hogs, and probably more than 90 per cent of it is
fed to animals. Most of the crop is fed on the farms where it is
produced. "Nearly 60 per cent of the hogs and pigs in the United
States are in the Corn Belt, 14 per cent are in the Cotton Belt, and
11 per cent in the Corn and Winter- Wheat Belt." Around 25 per
cent of the beef cattle of the country are found in the Corn Belt.
The Corn Belt also has a dense population of dairy cattle, sheep,
and poultry. It is not necessary to present statistics on these points.
It is sufficient to say that the livestock industry of the United States
is closely associated with corn production. Figure 77 gives the
distribution of the corn acreage of the United States.
Corn is not only the outstanding grain feed crop of the United
States; it is also the foremost silage crop. The acreage of corn cut
for silage, however, constitutes but a little more than 4 per cent of
the total corn acreage. Only 6 per cent of the total crop is cut
solely for fodder.
389
390
ECOLOGICAL CROP GEOGRAPHY
Corn as a Food Crop. According to Leighty et al. (12), about
10 per cent of the corn crop of the United States was used for
human food in the period 1912-1921. Since that time, there
has been a decline in the domestic use of corn meal, corn flour,
hominy, corn breakfast cereals, and corn starch for food purposes.
On the other hand, Taylor (24) is inclined to the view that the use
of corn oil and glucose is on the increase. The supplanting of home
baking by commercial baking served to reduce the use of corn bread.
FIG. 77. Distribution of corn in the United States, average acreage harvested
1928-1937. Each dot represents 50,000 acres.
In the United States, Europe, and Argentina corn is grown
primarily as a feed crop. In many producing areas of the world,
notably in China, India, and Mexico, a high percentage of the crop
is used for direct human consumption. The Balkan States also
utilize a fairly high amount of corn for direct human consumption.
Sweet corn and pop corn are grown almost entirely for human
use.
Industrial Uses. In the neighborhood of 75 million bushels of
corn are used annually by the corn refining industry in the United
States. The main products are starch, dextrins, corn syrup, corn
sugar, and corn oil. Close to 2£ billion pounds of corn and corn
products are used annually in the manufacture of fermented malt
liquors, distilled spirits, and ethyl alcohol.
THE COARSE CEREALS 391
The possibilities of finding a greater use for "industrial alcohols"
are being investigated with increasing interest at the present time
with the double objective of creating a profitable and stable
outlet for surplus agricultural commodities, and from the stand-
point of conservation of natural resources. Jacobs and Newton
(10) discuss the economic possibilities of using alcohol as a motor
fuel. Corn, being the foremost carbohydrate producing crop in
American agriculture, comes definitely into consideration in this
respect.
HISTORICAL
Origin of Corn. Corn represents a distinct contribution of the
Americas to the agriculture and food resources of the world.
According to Mangelsdorf and Reeves (15), corn (£ea mays)
originated from a remote Andropogonaceous ancestor in the low-
lands of South America. The genus Tripsacum is supposed to
have originated from the same ancestor. Thus, according to
Mangelsdorf and Reeves, "had Tripsacum been more promising
as a food plant we may be reasonably certain that there would
have been two Maydeaceous cereals in America instead of only
one. . . . Both %ea and Tripsacum proceeded along parallel
evolutionary paths, so far as monoecism is concerned. Both
exhibited a tendency to separate the sexes and to concentrate
the staminate flowers in the terminal inflorescences and the pistil-
late flowers in the lateral ones. But here the similarity ends, for
while %ea confined itself to, or became reduced to, a single species
and remained a plant with low chromosome numbers and an
annual habit of growth, devoting most of its energies to reproduction
for seed, Tripsacum became a freely speciating genus, increased its
chromosome number, assumed a perennial habit, and began to
devote much of its energy to survival by the storage of food materials
in the roots. Maize became more and more restricted in its range
and was confined to extremely favorable sites scattered through
the tropical forests, and was indeed probably on the road to com-
plete extinction when man appeared on the scene. Tripsacum, in
contrast, continued to spread until it had invaded regions formerly
occupied by continental ice-sheets."
The original maize was probably podded. Even with its small
seed completely enclosed in glumes, it was by far the best cereal
392 ECOLOGICAL CROP GEOGRAPHY
plant available. When the mutation from pod corn to naked corn
occurred, it made a cereal even better suited to the needs of man.
There is no way of determining whether this mutation occurred
first in the lowlands or after maize had been carried by mail into
the Andean region. The next improvement of the plant brought
about either by natural or by human selection in a man-made
environment was in the shortening of the lateral axis or an increase
in the length of the leaf sheaths, or both, to the point where the
lateral inflorescence, the ear, was completely enclosed by the husk.
The Andean maize was in the course of time carried to Central
America where it came in contact with Tripsacum. These two
genera had become so divergent that hybridization was difficult.
But a hybrid between these two plants apparently occurred. This
hybrid, by repeatedly backcrossing with maize, resulted in the
production of a new maizelike plant, later to be known as a sepa-
rate genus, Euchlaena, or Teosinte. Being closely related to maize,
Euchlaena hybridized freely with maize. Thus, in the words of
Mangelsdorf and Reeves,
"the original hybridization of %ea and Tripsacum and later repeated
hybridization of the new genus,+Euchlaena, with its maize parent re-
sulted also in the transfer of some Tripsacum genes to the genetic complex
of cultivated maize. This gave rise to some new types of corn previ-
ously not in existence, including the North American pointed pop
corns, the dent corns, and the long, slender, straight-rowed flint and
flour corns, types which are not represented in the Peruvian pottery
and which even today are still unknown in the Andean region."
The Spreading of Corn Culture. Corn was first cultivated in
the Andean region, from where its culture spread to Central and
finally to North America. The ancient civilizations of Peru,
Central America, and Mexico were based upon the culture of
corn. Corn was unknown to Europe and Asia before the discovery
of the Americas. Its culture even in northern and eastern North
America is comparatively recent. Corn culture is reported to have
reached the Rio Grande around 700 and Maine around 1000 A.D.
Corn was carried to Spain soon after the discovery of America,
where it was grown for a time as an oddity in gardens. The possi-
bilities of the plant as a field crop were, however, soon recognized,
and it spread from Spain to France and Italy. Burtt-Davy (7)
credits the Portuguese voyagers for the early and rapid introduc-
THE COARSE CEREALS 393
tion of maize into India, China, Cochin, and other parts of the
East Indies. Another route of introduction into Asia appears to
have been by way of Turkey, Arabia, or Persia. The exact date
of introduction of maize into Africa is not known, but apparently
the Portuguese also carried it into that continent. This, brings out
Burtt-Davy, is suggested by the African's word for corn "mielie"
which is undoubtedly a corruption of the Portuguese word milho,
meaning grain. Among the native tribes of Africa the newly
introduced maize was used to replace the ancient cultivation of
millet. Corn reached the East Indies soon after the establishment
of the Portuguese settlements there by Vasco da Gama at the
beginning of the sixteenth century. Mendoza, cited by Burtt-
Davy, mentioned maize as one of the plants observed by him
in China as early as 1585. Corn apparently reached the Balkan
States by way of Turkey. It is often referred to there as well as
in other parts of Europe as "Turkish wheat."
CLIMATIC AND SOIL RELATIONSHIPS
Temperature Conditions. The southern origin of corn is re-
flected by its relatively high temperature requirements. For best
results with the crop the growing season should be 140 or more
days in length with a mean summer temperature of around 75,
and with night temperatures exceeding 58°F. According to Finch
and Baker (8), "practically no corn is grown where the mean
summer temperature is less than 66°, or where the average night
temperature during the three summer months falls below 55°."
These temperature requirements set definite limits to corn pro-
duction. There is, on the other hand, a significant difference in the
temperature demands of different varieties; some may be grown
in a season of less than 1 00 days, while other late-maturing types
require a growing season of 180 days and a mean summer temper-
ature of 80°F. The small grains replace corn in sections with
short and relatively cool growing seasons. Under such conditions
they are more productive than corn. This accounts for the rather
sharp decrease in corn production north of the Corn Belt in the
United States and also for the virtual exclusion of corn in the
agriculture of northwestern Europe. The growing of corn for the
production of fodder or silage extends into cooler regions than for
strictly grain production.
394 ECOLOGICAL CROP GEOGRAPHY
Most of the important corn producing areas of the world are
characterized by relatively high summer temperatures with fairly
warm nights. That corn avoids cool climates is evident; neverthe-
less, the importance of warm nights to corn production can be
overemphasized. Apparently the mean temperature during the
growing seasons is of greater importance than the low point at-
tained at night. Obviously, the night temperature enters into the
calculation of the mean. In this connection Wallace and Bressman
(29) make the observation that
"it is a common belief that corn will not grow satisfactorily in
regions where the nights are cool, although the days are warm. Usually
the true explanation why corn is not grown in such sections is some-
thing else. In South Africa, where corn growing has expanded at a
phenomenal rate since 1 900, the minimum temperature at night during
the tasseling season averages only about 60 degrees, and in some
sections it is as low as 50 degrees. Cool nights reduce the rapidity of
growth previous to tasseling, but if the season is long, there is no definite
proof that cool nights (55 to 60 degrees at the low point of the night)
reduce the yield."
It is necessary to point out thatfye slowing up of the rate of growth
occasioned by cool nights would be highly detrimental to corn
in many areas and especially in places where the physiological
growing season is cut short by either low temperatures or the
occurrence of droughts.
While the small grains take the place of corn in the cooler regions
or where the growing season is short, the corn crop is ideally
adapted to take fuller advantage of long and relatively warm
growing seasons than the small grains, provided that moisture
conditions are favorable. In other words, the corn crop is pre-
eminent in the agriculture of the Corn Belt by virtue of its ability
to utilize the physiological growing season to its fullest extent,
whereas the small grains make use of only a part of the season
suitable for growth.
Moisture Conditions. The moisture relationships of corn pro-
duction were discussed in detail in Chapter XV. Special attention
was given to the critical period in corn incident to tasseling and
fertilization and to the comparative drought resistance of corn
and the sorghums. While the corn plant has a high efficiency
of transpiration, it is nevertheless very specific in its moisture
THE COARSE CEREALS 395
requirements, especially at the above indicated critical period.
In considering the water requirements of corn it is well to keep
in mind that the amount of dry matter produced per acre brings
about a heavy demand for water, and, as is pointed out by Morgan
et al. (19), corn "must obtain water from the soil during the period
of its most rapid growth at a faster rate than any other field crop
of the region." A marked summer concentration of rainfall or
availability of moisture is therefore essential to high production.
fWhile corn makes specific moisture demands during its grand
period of growth, the crop is very conservative in the use of water
during its early phases of development. This is due in part to the
small leaf surface exposed by the crop per unit of land area occupied
and also to the fact that the crop is cultivated, that is, the plants
are spaced, and in addition competing plants, weeds, are removed
so that the moisture in the soil may be stored for future use.
General Climatic Regions. The bulk of the corn crop of the
world is grown in climates transitional between marine and con-
tinental and in sections either with distinct woodland climates,
or with climates transitional between woodland and grassland.
The crop does not entirely avoid either strictly continental or
grassland climates. Production in the extremes of these climates is,
however, limited. Thus corn is grown to a limited extent in the
steppe climates of the Great Plains area of the United States, in
the steppe regions of Argentina, South Africa, Rumania, and
southern Russia. In such areas wheat and barley are of greater
relative importance than corn on account of the specific moisture
demands made by corn during midsummer, that is, at a time
when the small grains have completed their cycles of development.
To some extent the detrimental effects of the dry summers of these
climates are avoided by the growing of early-maturing varieties.
On the other hand, corn is an important crop in areas where the
native vegetation consisted largely of tall grasses, which after all
is an index of rather favorable moisture conditions.
Table 35 gives the climatic types of the world's important
corn producing areas. It will be observed that the range of climatic
types encountered is great, from Af to BSk and AA'r to Cb'd. The
ecological optimum for corn is found in the Dfa, Cfa or BC'r, CC'r,
BB'r, CB'r climates. This emphasizes the fact that corn demands
fairly high summer temperatures and above all favorable moisture
396
ECOLOGICAL CROP GEOGRAPHY
conditions during the later part of the summer. While the pro-
duction of the crop extends into regions with the dry BSk or CC'd
and GB'd climates, the yields obtained in such areas are low and
variable. One of the main reasons for growing corn in such dry
areas is that the crop fits well into the system of crop rotation
employed. Corn fills the need for a cultivated crop; it leaves the
soil in good condition for the winter or spring cereals to follow
it in the course of rotations. Since corn is a cultivated crop, the
necessity for plowing preparatory to the seeding, of the cereals is
eliminated.
TABLE 35. CLIMATIC TYPES IN THE IMPORTANT CORN PRODUCING AREAS
OF THE WORLD
Region
Climatic Classification
Koppen
Thornthwaite
United States ....
Balkan States
Dfa, Cfa, Dfb, BSkw
Cfx, Dfc, BSk
Dfb, BSk *
Cfx, Gfa
Cfa, Cw, Dwa
Afwi
Cw, Awi
CB'r, CC'r, BB'r, CB'r
CC'd, CB'd
CB'r, BB'd, CC'r, BC'r
CB'd
CC'r, CB'd
CB'r, BB'r, CB'w
BB'w, CB'w
AA'r
CB'd, CB'w
Southern Russia ....
Argentina
China
East Indies
South Africa
Soil Conditions for Corn. Corn is grown on a great variety of
soils. Fair drainage is essential; poorly drained soils are too cold
in spring. Furthermore, corn demands good soil aeration^ Corn
grows successfully over a wide range of soil reaction, pH 5 to 8,
although yields are usually adversely affected by degrees of acidity
represented by pH values of less than 5.5. Corn requires not only
an abundance of moisture but also an abundance of readily avail-
able plant nutrients during its period of rapid growth in late
summer. Nitrates are especially in demand at that time. The
close relationship between an available supply of nitrogen and
corn yields has already been discussed in Chapter XXI. Corn
also requires a fair supply of phosphorus. A deficiency in this
element is especially reflected in a slow initial growth.
The Corn Belt of the United States is favored with not only
suitable climatic but also with soil conditions well adapted to the
THE COARSE CEREALS 397
production of corn. This is well stated by Morgan et d. in the
following paragraph.
"Of the zonal, or great soil groups, the Prairie soils are inherently
the best suited for corn, since they fulfill its requirements most com-
pletely and are developed in the region in which the climate is especially
favorable. It is no mere accident that the Corn Belt, although more
extensive geographically, centers about the Prairie soils, extending
from western Indiana to eastern Nebraska. Here the climate and grass
vegetation have been largely responsible for the exchangeable bases.
The benefits of the relatively high content of organic matter, such as
tilth, water-holding capacity, and available nutrients, are well known
and scarcely need further comment. The dark color of the surface
of these soils of the grasslands also promotes to some degree a desirable
soil temperature."
DISTRIBUTION OF CORN
World Distribution. The statistical data of world corn distri-
bution are presented in Table 36. Figures 78 and 79 give a carto-
graphical view of the locations of the corn producing areas of the
world. Though the producing areas are widely scattered, the
specific climatic requirements of the crop confine it to a limited
number of heavy producing areas. Corn production, for instance,
is not distributed over the globe as generally as the production
of wheat. The other significant fact that is evident from the
tabulated data and also from the figures showing world distribution
is the concentration of the world's corn acreage and production
in the United States. For the five-year period 1930-31 to 1934-35,
this country produced roughly 50 per cent of the world's corn crop.
Corn production in the United States reached its peak in 1920.
The corn crop of this country for the period 1900-1920 averaged
68 per cent of the world crop, fluctuating from 59.9 to 73.4 per
cent. Since the first World War, the United States has been losing
some of its leadership as a corn producer. Shepherd et al. (22)
show "that the world production of corn has remained roughly
constant during the past 20 years; the decline in the relative
position of the United States has been the result of a decline
in the production of corn in the United States and a compensating
increase in other countries." A number of factors have entered
into the decline of corn production in the United States in recent
years, among which may be mentioned: a series of years of drought
398
ECOLOGICAL CROP GEOGRAPHY
in the western portion of the Corn Belt; a growing realization of
the necessity for proper land use to reduce soil erosion losses —
corn, being an intertilled crop, must be handled with care on
sloping lands or grown in rotation systems planned to reduce soil
FIG. 78. Distribution of corn in the western hemisphere. Average production of
the five-year period 1930-31 to 1934-35. Each dot represents 5 million bushels.
losses to a minimum; the greatly reduced demand by foreign
countries for American-produced pork products, or more cor-
rectly stated the inability of foreign countries to purchase or
exchange goods for pork products produced in the United States;
and lastly the AAA production control program instituted in 1934.
399
400 ECOLOGICAL CROP GEOGRAPHY
While the relative importance of the United States as a world
producer of corn has decreased somewhat during the past decade
there is no reason to believe that this country will lose its eminent
position as a producer of corn. Even with the reduction in the
size of the corn crop and increases in production in other countries
the United States is still far ahead of any competing country.
Furthermore, the United States contains far greater expanses of
land with favorable conditions of both climate and soil than any
other country or any other section of the world. As a matter of
fact, while the production of corn in other countries can be intensi-
fied, the acreage available for corn production in all countries
having territories suitable for the purpose is at the present time
quite well occupied either by corn or by crops grown in direct
competition with corn. Possible exceptions to this may be found
in undeveloped areas of Brazil and in limited sections in the humid
portions of Africa. The tabulation of climatic types prevailing in
certain areas now producing corn, indicated in Table 35, brings
out the fact that some of the crop is being grown in decidedly
moderate and even minimal areas. Further expansion in such
areas will not be possible. f This indicates that possible future
increases in corn production will take place largely through the
adoption of improved methods of handling the crop, especially
in the optimal and moderate areas, rather than through significant
expansion of acreages.
The corn producing regions of the western hemisphere, Fig. 78,
may be classified into three areas, namely, the eastern portion of
the United States, Mexico, and the Argentine-Brazilian areas.
The distribution of corn in the United States will be presented
under a separate heading.
Argentina ranks next to the United States as a producer of corn.
The country has the distinction of being the world's most prominent
exporter of corn. Around 80 per cent of the crop is grown for
export. During the five-year period 1929-30 to 1933-34 the
United States produced over eight times as much corn as Argen-
tina; the latter, however, outranked the United States 40 to 1 as
a corn exporting country. The great importance of Argentina as
a corn exporting country is brought out by the fact that over 70 per
cent of the world trade in corn originated in that country for the
period indicated above. In 1936 Argentina exported 330 million
THE COARSE CEREALS
401
bushels of corn. Its nearest rival was Rumania with 30 million
bushels.
TABLE 36. CORN: ACREAGE, YIELD PER ACRE, PRODUCTION, AND PER-
CENTAGE OF WORLD TOTAL PRODUCTION IN SPECIFIED COUNTRIES — AVER-
AGES FOR THE FIVE-YEAR PERIOD 1930-31 TO 1934-35
Rank
Country
Acreage, in
Millions of
Acres
Average
Yield, in
Bu. per Acre
Production
In Millions
of Bu.
In Per-
centage of
World
Total
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
United States
103.45
10.94
11.07
9.54
11.76
6.18
9.42
3.60
9.17
4.96
2.77
7.84
1.88
2.60
5.87
0.28
20.57
22.1
31.0
21.9
22.6
17.4
25.7
16.3
30.1
9.7
15.3
26.4
9.2
36.6
26.1
25.7
2,289.61
339.12
242.81
215.37
204.53
158.99
153.39
108.18
89.28
76.08
72.94
71.94
68.82
67.77
61.47
7.15
365.55
49.85
7.38
5.29
4.69
4.45
3.46
3.34
2.36
1.94
1.66
1.59
1.57
1.50
1.48
1.34
0.16
7.94
Argentina
China *
Brazil
Rumania
Yugoslavia
U.S.S.R
Italy
India
Java and Madoera . . .
Hungary
Mexico
Eevot
Manchuria . .
Union of South Africa . .
Australia **
All others
World total
221.90
—
4,593.00
100.00
* Four-year average only.
* * Not in rank but given for sake of comparison.
The area suitable for corn production in Argentina, especially
the area with optimal conditions, is limited. Much of the country
is either too dry or too cold. Two provinces, Buenos Aires and
Santa Fe, contain 76 per cent of the corn acreage of the country.
Yields fluctuate materially from year to year, chiefly because of
extreme variations in rainfall. In certain sections rather frequent
attacks of locusts also constitute a menace to the crop. On the other
hand, in the rather limited optimal area conditions are very favor-
able to the production of corn. Of these areas Spafford (23) writes,
"It is difficult to imagine better maize-growing conditions than exist
over an area approaching a couple of hundred of millions of acres in
Argentina, for here are to be found very fertile, free-working, chocolate
402 ECOLOGICAL CROP GEOGRAPHY
coloured soils, from 1 foot to 2 feet in depth, resting upon sufficiently
well-drained subsoils to prevent waterlogging, and receiving from 25 in.
to 45 in. of average annual rainfall, of which 85 per cent to 95 per cent
is distributed fairly evenly throughout the spring, summer, and autumn
months."
This statement appears to be somewhat optimistic with regard to
the acreage available and in view of the extreme annual fluctua-
tions in Argentine corn production. Hughes and Henson (9), for
instance, point out that "the bulk of the cropped land in Argen-
tina corresponds more closely to the area of the Great Plains than
to that of the Corn Belt." Apparently much of the Argentine
corn producing area must be classified as moderate or even minimal.
The high average yield for the country for the period covered in
Table 36 is accounted for by the great concentration of the crop
in the rather limited optimal area. The Argentine corn crop is
grown in competition with wheat, alfalfa, and flax.
Corn production in Brazil has been increasing. Any great ex-
pansion of the crop in this country is precluded by lack of level
expanses of land suitable for corn production. None of the crop is
available for export; a high percentage is utilized for human con-
sumption. f %
The production of corn is of great local importance in Mexico.
Here also the crop is grown largely for human use. The fields are
generally small, and rather primitive methods of culture are
employed. The yields, as indicated in Table 36, are very low.
The distribution of corn in Europe serves to emphasize the
high temperature requirements of the crop. Production is almost
entirely confined to the southern portions of the continent, extend-
ing from Italy and Hungary across the Balkan States and into
southern Russia. Much of this area has a summer deficiency of
rainfall, which accounts for the relatively low yields in Rumania
and southern Russia. The most intensive area of production is
found in Hungary and portions in Rumania, Bulgaria, and Russia.
Michael (16, 17, and 18) points out that increased acreage and
production of corn especially in Hungary and also in Yugoslavia
and Rumania is probably an after-effect of the land reforms insti-
tuted in these countries after the first World War. The breaking
up of large estates and corresponding increases in peasant agri-
culture resulted in decreased emphasis on the production of wheat
THE COARSE CEREALS 403
and barley for export and on oat production in connection with
horse breeding. More emphasis is now placed on the growing
of corn and swine production. In certain sections of the Balkan
States a relatively high percentage of the corn crop is used for
human consumption. Rumania is the only country producing any
appreciable quantity for export.
It is interesting to note an increase in corn production in parts
of central Europe. Becker (5) points out an increase in the corn
acreage of Germany from 5,495 to 125,000 acres between 1932 and
1937. This author brings out that more feed can be produced
per unit of area with the employment of corn than with oats when
proper attention is given to the selection of varieties and when
the crop is produced under conditions of intensive culture.
Corn is a crop of considerable importance in China and Man-
churia, also in the East Indies and in India. In the East Indies
corn is especially important in Java and Madoera. A high per-
centage of the crop is used for human consumption. French Indo-
China exported 18.5 million bushels of corn in 1936.
In Manchuria (Manchukuo) corn is grown under rather severe
conditions as to temperature and moisture relationships. It is
grown only in the most favored areas, yielding its place to kaoliang
and millet in the less favored regions.
China is a great producer of corn. Moisture and temperature
conditions are generally favorable. The corn is often interplantec
with soybeans. The crop is grown in the eastern humid areas oi
the country.
Corn is a relatively unimportant crop in India. According to
Bergsmark (6), corn occupies less than 3 per cent of the cropped
land of the country. The crop is grown both under irrigation and
under natural rainfall conditions. In the humid areas of the
country, the Middle Ganges region, the crop is grown only on the
well-drained lands. Waterlogged soils cause root rot.
The production of corn in Africa is of economic importance
in Egypt and in the Union of South Africa. The Egyptian crop
is grown under irrigation. The entire crop is consumed locally.
The acreage suitable for corn production in South Africa is limited
by a deficiency of rainfall, but it is an important crop. According
to Taylor (25) "corn production is centered chiefly on the high
plateau in those areas in which rainfall is 25 to 40 inches per year,
404
ECOLOGICAL CROP GEOGRAPHY
most of it falling during the summer months, October to April.
In the drier areas Kafir is more important." The principal com-
mercial area of production lies north of Basutoland. The crop is
grown by natives for home consumption over wide areas of the
continent. The Union of South Africa exports around 20 million
bushels of corn annually. The amount available for export from
year to year is subject to a considerable fluctuation. This reflects
on the unreliability of the crop in many of the areas of production.
Distribution in the United States. The distribution of corn in
the United States is shown graphically in Fig. 77. Table 37 gives
the statistical data for the most important states. While only ten
of the highest corn producing states for the ten-year period 1928-
1937 are listed in Table 37, it is evident from Fig. 77 that corn is
an important crop in all of the vast areas from the Atlantic coast to
the high plains. Nevertheless, there is a definite concentration of
acreage in the Corn Belt. This is so outstanding that a defining of
the limits of the Corn Belt is not necessary. It has already been
indicated that the intensive production of corn in the heavily
shaded portion of the map is occasioned by a combination of
favorable climatic and soil conditions; in addition to this the
t
TABLE 37. CORN: ACREAGE HARVESTED, PRODUCTION, AND PERCENTAGE
OF UNITED STATES TOTAL PRODUCTION IN SPECIFIED STATES RANKED ACCORD-
ING TO PRODUCTION AVERAGES FOR THE TEN-YEAR PERIOD 1928-1937
AND 1938 PRODUCTION. ACREAGES AND PRODUCTION EXPRESSED IN MILLIONS.
Production
Rank
States
Acreage
Harvested
Average
1928-1937,
in Bu.
Percentage of
U. S. Total,
1928-1937
1938, in Bu.
1
Iowa
10.98
393.14
17.02
479.18
2
Illinois
9.02
307.59
13.32
385.43
3
Nebraska
8.98
159.18
6.89
107.74
4
Indiana
4.49
151.20
6.55
173.39
5
6
Minnesota ....
Ohio
4.65
3.61
136.35
132.30
5.90
5.73
157.54
156.99
7
Missouri
5.54
113.66
4.92
109.00
8
Kansas
5.47
80.74
3.50
45.20
9
Texas
4.87
75.96
3.29
75.65
10
Wisconsin ...
2.24
71.04
3.07
90.51
All others
39.95
688.51
29.81
781.57
Total U. S
99.80
2,309.67
100.00
2,562.20
THE COARSE CEREALS 405
topography of the land is adapted to the use of modern machinery.
According to Baker and Genung, production in the Corn Belt
exceeds 3,000 bushels per square mile and in some counties rises
to 5,000 bushels. The factors accounting for the diminishing of
the importance of the corn enterprise in all directions from the
Corn Belt have been pointed out in previous discussions and need
therefore not be restated here.
Sweet corn is grown in many sections of the United States;
430,000 acres were grown in 1937. The high producing states are
Illinois, Minnesota, Iowa, Indiana, and Maryland.
Pop corn is also grown in many sections of the United States.
Most of the commercial crop is produced in western Iowa, in Sac
and Ida counties, and in east-central Nebraska, in Valley county.
Iowa produces around 26,000 and Nebraska around 9,000 acres.
These producing areas are shown in Fig. 82.
THE SORGHUMS
Commercial Importance. The sorghums are generally grouped
into four classes in accordance with the characteristics of the plants
and seeds and with regard to the uses made of them.
a. The grain sorghums are grown primarily for grain which may
be used either for feed or food.
b. The sweet sorghums, or sorgos, are grown for forage and for the
manufacture of sirup.
c. Tfie grass sorghums, of which sudan grass is the most important,
are grown for the production of hay and pasturage.
d. Broomcorn is grown primarily for the "brush" used in the
manufacture of brooms.
The grain sorghums constitute the most important of the groups.
In the United States they are used almost exclusively for the pro-
duction of feed for livestock, though they have a limited use in the
making of flour for pancakes and in the preparation of breakfast
foods. In certain sections of the Old World, on the other hand,
they have for centuries occupied the place of a staple food crop.
As stated by Reed (20) "the inhabitants of Bombay and Madras
Presidencies of India, of northern China, Manchuria and Chosen,
of western Asia (including Syria, Turkestan and Mesopotamia),
and of parts of Africa have depended largely upon this cereal
for human, as well as animal, sustenance."
406 ECOLOGICAL CROP GEOGRAPHY
The sorgos are grown for forage and the production of sorgo
sirup. In recent years around 15,000,000 gallons of sorgo sirup has
been made annually in the United States.
Historical. According to Ball (1) "there can be no doubt of the
great antiquity of the sorghum plant in cultivation. The story
of its domestication is lost in the shadows of the past.55 The earliest
known records of its culture come from Egypt. The crop is sup-
posed to have been carried to Egypt by caravans from India where
the crop has been cultivated since a remote period. The sorghums
are also native to Africa; many of the types now being grown in
the United States have been introduced from there.
The introduction of the sorghums into the United States is
comparatively recent. The first recorded introduction was from
China in 1853, by way of France. The Early Amber variety is
reported to have come from this "Chinese sorgo." Seeds of 16 vari-
eties of sorghum from Natal reached the United States in 1857;
among them were Orange, Sumac, and Gooseneck. The first
interest in the crop was from the standpoint of possible sugar
production. In this the sugar beet, which offered a better source
of crystallized sugar than the sorgos, won out. However, sorgo
was found to be of value in making sfrup. The introduction of the
grain sorghums is more recent than that of the sorgos. Brown and
White durra were introduced in 1876, White and Red Kafir in
1876, Milo in 1885. The kafirs and milos did not get into general
cultivation until 1890 (Ball, 2). The sorghums became of real
importance in the agriculture of the southern Great Plains area
during the dry years in the early eighties, and again during the
general drought of 1892-1894. Likewise the recent drought in the
Great Plains area created greater interest in the sorghums not only
in the southern, but also in the central and northern areas of this
agricultural belt. The introduction of the sorghums has had a pro-
found effect in stabilizing the agriculture of the Great Plains area.
Sudan grass was not introduced into the United States until 1909.
Vinall in speaking of sudan grass (27) states that "no other plant
introduction ever gained such immediate and widespread popu-
larity in the United States."
Climatic Relationships. The main outstanding feature of the
sorghums is their ability to grow under dry conditions. In addition
they are able to withstand high temperatures. As a matter of fact,
THE COARSE CEREALS
407
they are the only field crop approaching the true xerophytes. The
comparative drought resistance of corn and the sorghums was
discussed in detail in Chapter XV.
Not all varieties of sorghum are equally drought-resistant. In
general the dwarf types will produce profitable crops under drier
FIG. 80. Comparative distribution of Dwarf Yellow milo and Blackhull kafir
(Standard and Dwarf) in the United States. Each dot represents 500 acres.
Estimated acreages 1,526,000 for the milo and 1,801,400 acres for the kafir.
(After Vinall, Stephens, and Martin.)
conditions than the tall-growing and leafier types. The physi-
ological reasons for this have been discussed in previous chapters.
Figure 80, compiled from Vinall et al. (28), shows the distribution
408 ECOLOGICAL CROP GEOGRAPHY
of Blackhull kafir (Standard and Dwarf) and Dwarf Yellow milo
in the grain sorghum producing area of the United States. It is
evident that the heavy concentration of Dwarf Yellow milo occurs
under drier conditions than that of the kafir. In addition it should
be noted that the tall kafir (the standard type) is grown in the
eastern more humid and the dwarf type more largely in the
western and drier area of distribution of the Blackhull kafir. Like-
wise standard broomcorn is produced under more humid conditions
than the dwarf broomcorn.
Dry, sunny weather at harvest time favors the curing of the brush
of broomcorn so that it will retain its natural green color. Excessive
rain at harvest is detrimental to color and quality, the brush
becoming weather-stained or red.
The sorgos generally require more humid conditions than the
dwarf types of grain sorghums. This is the case especially when
they are being grown for the manufacture of sirup. It is difficult
to produce a high quality sirup under conditions of drought.
Unless the climatic conditions are such as to ensure an uninter-
rupted development of the plants the impurities of the juice ex-
tracted from the stems will be too high to produce a good quality
of sirup. This accounts for the growing of sorgos intended for sirup
making in the humid areas of the Sorghum Belt.
Sudan grass can be grown under lower temperature conditions
than the other sorghums; nevertheless, for best development the
summer temperature must be fairly high.
Soil Conditions. The sorghums are grown over a great range
of soil conditions. They respond to an abundance of organic
matter and a liberal supply of plant nutrients. Since the sorghums
can be grown on fairly light soils not well adapted to the growing
of wheat, their cultivation is locally of importance on light-textured
soils while the heavy-textured soils of the Sorghum Belt are used
more extensively for wheat production. The sorghums do well on
heavy soils, even on soils with a claypan; good aeration is, however,
essential to proper growth.
The highest yields of both the grain and the sweet sorghums are
produced on fertile soils well supplied with moisture. Likewise
the highest yield and quality of brush are produced from broom-
corn grown on fertile, well-watered soils. On fertile soils and
especially in areas where moisture is fairly abundant the grain
THE COARSE CEREALS 409
sorghums as well as the sorgos come into direct competition with
corn. Producers generally prefer to handle corn if conditions favor
its production. On the other hand, the sorghums are the more
reliable crop; on account of their greater drought resistance their
yields fluctuate less from season to season under the erratic climatic
conditions so common in the Sorghum Belt.
World Distribution. Reliable statistics on world sorghum pro-
duction are not available. The crop is extensively grown in northern
China and Manchuria, in India, and is widely distributed in Africa.
Northern China and Manchuria specialize in the production
of a hardy group of sorghums known as "kaoliang." This group of
sorghums can be grown under lower temperatures than other
grain producing types; it is also very drought-resistant. The light-
colored varieties arc principally used for grinding into flour and
making cakes, while the dark-colored types are used mainly for
feed. The grain of kaoliang is also used for distilling the potent
spirit called "Shamshu" so common in North China. The coarse
stalks are used for fuel, for the making of baskets and mats, and
even in the construction of shelter. The sorghums assume a place
of importance mostly in areas too dry for the production of corn.
The sorghums are very important in India. Reed reports that
approximately 25 million acres are produced annually. The
sorghums together with the millets are of special importance in
the drier areas of the country. According to Reed, two distinct
types of sorghum crops are grown: "the summer crop, or Kharif
jowar, sown in the spring and harvested in the fall, and the Rabi
crop, or winter jowar, sown in September or October and harvested
in the following February or March." Throughout India, the grain
of the sorghums is used largely for human consumption. The
sorghums are generally grown on the more fertile, the millets on
less fertile and drier soils.
The sorghums make up the staple cereal for a large proportion
of the native population of Africa. The crop is widely distributed
over Africa. Some of the important varieties used in the United
States originated in this continent; others were introduced from
India.
Europe does not produce any appreciable amount of grain
sorghum. Broomcorn is, however, of local importance in parts of
Italy and Hungary.
410
ECOLOGICAL CROP GEOGRAPHY
Distribution in the United States. Figure 81, taken from
Martin and Stephens (14), gives an outline map showing the
distribution of the grain sorghums and sorgos in the United States.
These authors also give the varietal regions of the country. Table 38
gives the statistical data of the high-producing states of grain
sorghums. It will be observed that the grain sorghum acreage is
centered in the southern Great Plains area. This is accounted
for by the drought resistance of the crop. It is evident that the
eastern extension of the Grain Sorghum Belt and the western
limits of intense corn production are somewhat complementary.
38* 95*
FIG. 81. The sweet and grain sorghum producing areas of the United States
(After Martin and Stephens.)
This offers another good example of the introduction of a new
crop to lend stability to agricultural production. The introduction
and rapid utilization of the grain sorghums with their greater
tolerance to drought and less specific demands of the environment
during pollination as compared with corn have been of great help
in the establishment of a sound agriculture in the southern Great
Plains. During recent years the production of the grain sorghums
has become of increasing importance in the irrigated sections of
southern Arizona and also in California. The recent drought in
the Great Plains area has created a great interest in the sorghums
THE COARSE CEREALS
411
in the central and even northern portions of this region. Note the
high acreages of grain sorghums in Nebraska, South Dakota, and
Colorado in 1938.
TABLE 38. GRAIN SORGHUMS: ACREAGE HARVESTED, PRODUCTION, AND
PERCENTAGE OF UNITED STATES TOTAL PRODUCTION IN SPECIFIED STATES
RANKED ACCORDING TO PRODUCTION AVERAGES FOR THE TEN-YEAR
PERIOD 1928-1937 — AND 1938 PRODUCTION. ACREAGES AND PRODUCTION
EXPRESSED IN THOUSANDS
Production
Rank
States
Acreage
Harvested
Average
1928-1937,
in Bu.
Percentage of
U. S. Total
1928-1937
1938, in Bu.
1
Texas
3 561
47,741
55 32
46 951
2
3
Oklahoma ....
Kansas
1,441
1 268
12,932
12 886
14.98
14 93
12,716
14773
4
5
New Mexico ....
California
305
104
3,484
2,999
4.04
3.47
2,975
4,495
6
Missouri
188
2,085
2.42
3,625
7
Colorado
227
1,816
2.10
4,631
8
Arizona ....
35
947
1 10
1 102
9
Nebraska
92
752
0 87
4 890
10
Arkansas
70*
662*
0.77
570
11
South Dakota . . .
2,408
Total U. S
7,291
86,304
100.00
99,136
*Short-time average.
The sorgos are of greatest importance in the same area devoted
to the intensive production of the grain sorghums; the area of
distribution is, however, not so concentrated. In other words, the
sorgos are grown to a greater extent in the humid area of the
country than the grain sorghums. This is brought out in Fig. 81.
In humid areas corn is in a better competitive position than the
grain sorghums in the production of concentrates. In the western
area the sorgos are produced almost exclusively for forage, while
their production for purposes of making sirup is of considerable
importance in the eastern more humid area. The reason for this
was discussed under the heading of climatic relationships. The
sorgos are used extensively as a silage crop in the central area
of their distribution.
The intense broomcorn producing areas of the United States are
indicated in Fig. 82. Martin and Washburn (13) recognize three
412
ECOLOGICAL CROP GEOGRAPHY
important production districts or centers. The oldest of these is
located in east-central Illinois, with Mattoon as the chief marketing
point. The second is in south-central Oklahoma, with Lindsay
as the marketing point. These two districts produce a high quality
of standard broomcorn. The third or dwarf broomcorn produc-
ing district comprises western Oklahoma, southwestern Kansas,
southeastern Colorado, and eastern New Mexico. Broomcorn is
also grown locally in other central and southern portions of the
United States. The important commercial areas of production are,
however, well concentrated in the above three districts.
J3ROOMCORN, POPCORN, HEMP, AND HOPS
Acreage, 1929
UNITED STATES TOTAL
BROOMCORN 312,000 ACRES
POPCORN 38.000 ACRES
HEMP 2,000 ACRES
HOPS 23,000 ACRES
FIG. 82. Distribution of broomcorn, popcorn, hemp, and hops in the United
States in 1929. Each dot represents 1,000 acres (After Baker and Genung.)
MILLETS
Commercial Importance. Like the sorghums, millets are grown
for feed in the United States but constitute an important cereal
for human consumption in parts of Asia and Africa and practically
in the same areas where the sorghums are produced for that
purpose. Millet is used to some extent in the Balkan States and
Russia in the manufacture of alcohol and fermented alcoholic
drinks.
Four major types of millet are grown: foxtail (Setaria italicd)^
proso (Panicum miliaceum)^ barnyard or Japan millet (Echinochloa
THE COARSE CEREALS 413
frumentacea), and pearl millet (Pennisetum glaucum). The first two
are of greatest importance in the United States. Foxtail millet
is grown for forage, while proso is produced as a grain crop. The
popularity of millets for the production of forage has decreased
materially since the introduction of sudan grass which under most
conditions produces not only a greater quantity but also a better
quality of hay. The proso, also called broomcorn and hog millet,
is used as a short-season crop and in instances can be used to
advantage as a catch crop.
Historical. The cultivation of the millets dates back to ancient
times. They were grown by the lake-dwellers of Switzerland dur-
ing the Stone Age. According to Bretschneider, the millets were
mentioned in connection with religious ceremonies in Chinese
records about 2700 B.C. The millets are native to southern Asia.
Extreme susceptibility to frosts bespeaks their southern origin.
According to Vinall (26), a distribution of millet was made by the
United States Patent Office in 1849; by 1889 the crop was of
considerable importance. The now commercially important va-
rieties of proso millet were not introduced until toward the end
of the past and the beginning of the present century.
Climatic Relationships. All the millets are high temperature
loving plants, but on account of the ability of early varieties to
mature in a short period of time, from 60 to 90 days from sowing
to maturity, they can be grown in northern areas where summer
temperatures are high. The millets are very efficient in the use
of water. The young plants demand a fair amount of moisture,
but after they are once established they are fairly drought-resistant.
The rather limited root system of proso millet accounts for its
lack of resistance to severe drought.
World Distribution. The millets arc of importance in China,
India, Africa, in the Balkan States, and in southern Russia. In
China and India they are grown in the same general areas as the
sorghums. The millets often occupy the poorer and the sorghums
the better lands. The production of millet in Africa is largely
limited to the northern portion of that continent (Schindlcr, 21).
The most important producing section in Europe is found in
southern Russia; the crop is of less importance in the Balkan States,
of somewhat greater importance on the level lands of the Hungarian
plains, and then decreases to a place of but limited importance in
414 ECOLOGICAL CROP GEOGRAPHY
southern Germany. Proso millet is grown to some extent in Asiatic
Russia.
Distribution in the United States. The forage producing mil-
lets are of but limited importance in the United States, where they
have been largely replaced by sudan grass. Some millet hay is,
however, still produced from Kentucky and Tennessee to the
Great Plains area. Proso millet is used as a catch crop in the
central and northern Great Plains region. It is also grown in
the prairie provinces of Canada. Under favorable conditions a
grain crop can be produced from this millet in cases where the
main crop has failed. Generally the millets and especially the
proso millet are not sufficiently productive to replace any main
crop grown in an area.
REFERENCES
1. Ball, C. R., "The history and distribution of sorghum," U. S. Dept.
Agr. Bur. of Plant Ind. Bull. 175, 1910.
2. , "The importance and improvement of the grain sorghums,"
U. S. Dept. Agr. Bur. of Plant Ind. Bull. 203, 1911.
3. Baker, O. E., "A graphic summary of American agriculture based
largely on the census," U. S. Dept. Agr. Misc. Pub. 105, 1931.
4. , and A. B. Genung, "A graphic summary of farm crops,"
U. S. Dept. Agr. Misc. Pub. 267, 1938.
5. Becker, A., "Herkunft, Anbau und Nahrstoffanspriiche des Maises
unter besonderer Beriicksichtigung des deutschen Kornermaises,"
Die Erndhrung der Pflan&, 34:59-65 (1938).
6. Bergsmark, D. R., Economic Geography of Asia. Prentice-Hall, New
York, 1936.
7. Burtt-Davy, J., Maize: Its History, Cultivation, Handling, and Uses.
Longmans, London, 1914.
8. Finch, V. C., and O. E. Baker, Geography of the world's agriculture.
Govt. Printing Office, Washington, 1917.
9. Hughes, H. D., and E. R. Henson, Crop Production. Macmillan, New
York, 1930.
10. Jacobs, P. B., and H. P. Newton, "Motor fuel from farm products,"
U. S. Dept. Agr. Misc. Pub. 327, 1938.
11. Jenkins, M. T., "Corn improvement," U. S. Dept. Agr. Yearbook 1936:
455-522.
12. Leighty, C. E., C. W. Warburton, O. C. Stine, and O. E. Baker,
"The corn crop," U. S. Dept. Agr. Yearbook 1921:161-226.
THE COARSE CEREALS 415
13. Martin, J. H., and R. S. Washburn, "Broomcorn growing and han-
dling," U. S. Dept. Agr. Farmers Bull. 1631, 1930.
14. 9 anci j. c. Stephens, "The culture and use of sorghums for
forage," U. S. Dept. Agr. Farmers Bull. 1844, 1940.
15. Mangelsdorf, P. G., and R. G. Reeves, "The origin of Indian corn
and its relatives," Tex. Agr. Exp. Sta. Bull. 574 (Monograph), 1939.
16. Michael, L. G., "Agricultural survey of Europe," Pt. 1, The Danube
Basin, U. S. Dept. Agr. Bull. 1234, 1924.
17. , "Agricultural survey of Europe," Pt. 2, The Danube Basin,
Rumania, Bulgaria, and Yugoslavia, U. S. Dept. Agr. Tech. Bull. 126,
1929.
18. , "Agricultural survey of Europe," Hungary, U. S. Dept. Agr.
Tech. Bull. 160, 1930.
19. Morgan, M. F., J. H. Gourley, and J. K. Ableiter, "The soil require-
ments of economic plants," U. S. Dept. Agr. Yearbook 1938:753-776.
20. Reed, G. M., "Sorghums," Brooklyn Bot. Garden Leaflets, Series XIII:
1-12, 1925.
21. Schindler, F., Handbuch des Getreidebaus. Paul Parey, Berlin, 1923.
22. Shepherd, G., J. J. Dalton, and J. H. Buchanan, "The agricultural
and industrial demand for corn," Iowa Agr. Exp. Sta. Bull. 335, 1935.
23. Spafford, W. J., "Agriculture in the temperate and sub- tropical
climates of the South," Dept. Agr. of So. Australia, Bull. 310, 1936.
24. Taylor, A. E., Corn and Hog Surplus of the Corn Belt. Food Res. Inst.,
Stanford University, 1932.
25. Taylor, C. C., "Agriculture in Southern Africa," U. S. Dept. Agr.
Tech. Bull. 466, 1935.
26. Vinall, H. N., "Foxtail millet; its culture and utilization in the United
States," U. S. Dept. Agr. Farmers Bull. 793, 1917.
27. , "Sudan grass," U. S. Dept. Agr. Farmers Bull. 1126, 1935.
28. , J. G. Stephens, and J. H. Martin, "Identification, history
and distribution of common sorghum varieties," U. S. Dept. Agr.
Tech. Bull. 506, 1936.
29. Wallace, H. A., and E. N. Bressman, Corn and Corn Growing. Wallace
Pub. Go., Des Moines, 1923.
Chapter XXIV
EDIBLE LEGUMES
INTRODUCTION
Certain of the larger seeded legumes occupy an important
place in human nutrition. They are prized not only for their high
energy values but especially for the highly important protein that
they supply to the diet. The edible legumes are particularly impor-
tant in regions where population pressure, economic stress, or
environmental conditions limit the production of livestock and
the utilization of animal products to provide the necessary protein.
The cereals do not supply a sufficient amount of protein for the
diet; consequently, the seeds of legumes are utilized to provide
the required protein. Under such conditions the seeds of the edible
legumes may be designated as the j^oor man's meat. Thus the
pulses are of great importance in the diets of the masses of Brazil,
the Mediterranean countries, in the Balkans, and especially in
the Far East. All of these areas make but limited use of the more
expensive animal products.
In addition, it is well to keep in mind that a relatively high
percentage of the protein supplied by legumes is traceable to the
fixation of atmospheric nitrogen with the aid of symbiotic bacteria.
The relationship of this to soil fertility is evident.
BEANS
Types of Beans. When the term "bean" is used most readers
will think of the common field or garden bean, Phaseolus vulgaris.
This is the most important species covered under the broad term.
Nevertheless, it represents but one of the 17 species of beans listed
by Thompson (8). The 17 species represent six genera: (1) broad
bean or Windsor bean (Viciajaba\ (2) kidney or common field or
garden bean (Phaseolus vulgaris), (3) Metcalfe bean (P. metcalfei),
(4) tepary bean (P. acutifolius), (5) scarlet runner or multiflora
416
EDIBLE LEGUMES 417
bean (P. coccineus, also called P. multiflorus), (6) small lima or sieva
bean (P. lunatus)^ (7) large lima bean (P. limensis), (8) urd bean
(P. mungo), (9) mung bean (P. aureus), (10) adzuki bean (P. angu-
laris), (11) rice bean (JP. calcaralus), (12) moth bean (P. aconitifolius),
(13) asparagus bean or yard-long bean (Vigna sesquipedalis),
(14) cowpea (Vigna sinensis), (15) hyacinth bean (Dolichoes lablab),
(16) velvet bean (Stizolobium Deeringianum\ and (17) soybean
(Glycine max or Soja max).
Not all of these species are of importance in human nutrition;
many of them arc used only under special conditions. Thus the
broad or Windsor bean is grown in the United States only in
California. It is, however, of some importance in Europe and
especially in the Mediterranean area. The other beans besides the
kidney or common field bean used to any great extent for human
food in the form of the dry seed are the large seeded lima, the sieva
or small seeded lima, the tcpary, and the soybean. The soybean
is used for human consumption to but a limited extent in the
United States; it constitutes a very important article of food in
China, India, and Japan. The cowpea (blackeye bean) consti-
tutes a staple food product especially in the southern states.
Historical. According to Hardcnburg (2), "historical records
contain numerous references to the early cultivation and uses of
beans of various types. These are in many cases not sufficiently
detailed to indicate either the genus or species referred to. Liter-
ature records the cultivation of beans, lupines, and lentils in the
Nile Valley as early as 2000 B.C."
Climatic Requirements. Beans are warm-season annuals, sensi-
tive to extremes of temperature and requiring a relatively high
humidity. The optimal seasonal temperature for beans is about
the same as that for corn. The plants are extremely susceptible
to frost injury. For this reason proper air drainage is essential
where the crop is grown in northern areas. The length of the
growing season is generally not a factor in distribution. Most
varieties of pea beans mature in from 100 to 110 days, while the
latest varieties of the kidney type seldom require more than 125
days from planting to maturity.
Beans demand a fairly uniform supply of moisture during their
vegetative period. Abnormally high rainfall is detrimental to
the crop; likewise overirrigation must be avoided. Since the crop
418 ECOLOGICAL CROP GEOGRAPHY
is readily damaged by weathering, dry conditions at harvest
time are essential to the production of bright, high-quality seed.
Certain varieties of common field beans (P. vulgaris) such as the
Pinto, Pink, and Red Mexican are, according to Hardenburg,
probably more heat- and drought-resistant than ordinary varieties.
This accounts for their production in dry land areas in Colorado
and New Mexico. But even these varieties of common beans are
not so well adapted to semiarid conditions as the tepary bean
(P. acutifolius). Hendry (4) also comments on the ability of the
tepary bean to survive "in the hot, dry climate of the interior valley
uplands35 of California, that is, under conditions too severe for
varieties of common, and lima, beans.
Soil Relationships. Beans are grown on a relatively wide variety
of soils. While the crop responds to an available supply of plant
nutrients and organic matter, soil fertility is usually less likely
to constitute a limiting factor in bean production than in most
other field crops. Soil aeration and temperature are important
factors especially in relation to obtaining good stands. Neither
heavy mineral soils nor soils of organic origin are well suited for
bean production. Clay soils are tgo much subject to puddling,
while peat or muck soils are likely to produce not only a late-
maturing crop but also one with an undue proportion of vine to
seed. The best yields are obtained on medium loams of moderate
fertility. Even relatively light soils can be used for bean production
under favorable moisture conditions.
World Distribution. Table 39 gives the statistics of world pro-
duction of dry edible beans. The United States does not under
normal conditions produce enough beans to supply the domestic
demand. The largest part of the Brazilian crop is consumed locally.
The most important surplus producing region in the world is the
Danube Valley, including Rumania, Bulgaria, and other Balkan
countries. Japan also exports a high percentage of its crop of
white beans.
Table 39 brings out the fact that beans are an important food
crop among southern European and southern Asiatic peoples.
No statistical data are available on bean production in India;
it is known, however, that the crop is of considerable importance
in that country. The Garbanzo bean or the so-called chick pea
(Cicer arietum) is an important article of food of the peoples of India
EDIBLE LEGUMES
419
as well as those of northern Africa, Spain, and of all South and
Central American countries.
TABLE 39. WORLD PRODUCTION OF DRY EDIBLE BEANS IN SPECIFIED COUN-
TRIES FOR THE PERIOD 1930-31 TO 1934-35
Rank
Country
Average Produc-
tion^ in Bags of
100 Lbs.
Production, in Per-
centage of World
Total*
1
Brazil
15,855,000
2261
2
United States
12,443,000
17.74
3
EfifVDt
7,066,000
10.07
4
Rumania
6,280,000
8.95
5
Italy
3,548,000
5.06
6
Spain
3,468,000
4.94
7
Yugoslavia
2,980,000
4.25
g
Mexico
2,910,000
4.15
9
2 806,000
400
10
Great Britain . .
2,804,000
4.00
11
Tapan**
1,933,000
2.76
12
Chile
1,746,000
2.49
13
Bulgaria
1,532,000
2.18
14
Hungary
1,448,000
2.06
All others
3,319,000
4.73
Estimated world total excluding U.S.S.R.
and India
70 138,000
100.00
* Production in Russia and India is not considered in calculation.
** Production in Hakkaido Province, where most of the dry edible bean varieties
are grown.
In the United States the soybean is not classified as a "ury
edible bean," and the crop does not appear in statistical data as
such. It is grown primarily as a forage and oil-producing crop.
However, in recent years a considerable interest has been shown in
the use of soybeans for human consumption in this country. It is
a food crop of great importance in China and Japan. The most
important soybean producing countries of the world in order
of their importance are China, Manchuria, the United States,
Chosen, Japan, and Netherland India. A great variety of food
products ranging from vegetable milk to cheese are produced
from soybean seeds.
Distribution in the United States. Field beans are produced
over a wide range of conditions in the United States. Intensive
humid producing areas are found in Michigan and western New
York. The crop in northern Idaho is grown under subhumid
420
ECOLOGICAL CROP GEOGRAPHY
conditions. The extensive areas devoted to beans in Colorado
and New Mexico are in dry-farming regions, while the crops of
southern Idaho, Montana, and Wyoming are grown under irriga-
tion and the California crop is grown under a variety of conditions.
Table 40 gives the statistics of bean production by states.
Figure 83 shows the distribution of the crop cartographically.
FIG. 83. Distribution of dry edible beans and peanuts in the United States,
average for the years 1934-1938 for beans and for the years 1928-1937 for peanuts.
Each dot represents 50,000 tjags of beans and 10,000 acres of peanuts.
Young (10) presents data dealing with the intensity of bean
production in each of the important bean growing states of the
Union.
Michigan continues to be the most important bean producing
state from the standpoint of acreage devoted to the crop. The
total production is slightly higher in California than in Michigan.
The crop is well distributed throughout the south-central and
eastern parts of Michigan, the greatest intensity of production
being found near Saginaw Bay. Some counties devote as high as
20 per cent of their total harvested crop area to beans. Michigan
produces approximately 90 per cent of the pea beans of the United
States. Conditions in this humid area are quite similar to those
prevailing in the western New York area. Production is not,
however, so intensive in New York as in Michigan.
EDIBLE LEGUMES
421
TABLE 40. BEANS: ACREAGE HARVESTED AND PRODUCTION OF DRY EDIBLE
BEANS IN THE MAIN PRODUCING STATES — AVERAGES FOR THE FIVE-YEAR
PERIOD 1934-1938
Rank
States
Acreage Harvested
Production
In 1,000
Acres
Percentage of
U. S. Total
In 1,000
Bags of 100
Lbs. Each,
Cleaned
Basis
Percentage of
U. S. Total
\
2
3
4
5
6
7
8
9
10
California
344
517
110
152
287
243
20.81
31.28
6.65
9.20
17.36
14.70
4,052
3,940
1,327
1,104
893
434
404
197
123
67
105
32.0
31.2
10.5
8.7
7.1
3.4
3.2
1.6
1.0
0.5
0.8
Michigan
Idaho
New York
Colorado
Wyoming ....
New Mexico ....
Montana
Nebraska
Maine
All others ....
Total U S
1,653
100.00
12,646
100.0
Because of distinct climatic variations, the state of California
produces a large number of types of beans. The interior valleys
grow the Pink, Blackeye, Red Mexican, and White Tepary vari-
eties. Small Whites are grown in the more favored districts.
California is especially important from the standpoint of lima bean
production. This crop is very specific in its environmental de-
mands; as a result the area of production is quite restricted. Virtu-
ally the entire crop of lima beans is limited to portions of five
counties on the coast of southern California. The warm, humid
climate of the southern coastal region is especially adapted to the
growth of this important type of bean.
Idaho has two bean producing areas. The most important one,
the Twin Falls area in the southern part of the state, is irrigated.
A high percentage of the acreage is of the Great Northern and
Red Mexican types. Idaho produces around 58 per cent of the
Great Northern beans of the United States. The crop in the
northern districts, Lewiston-Troy area, is grown without irrigation.
The Small White Flat type is the most important variety.
The rather limited areas of Montana and Wyoming are given
over largely to the production of the Great Northern variety.
422 ECOLOGICAL CROP GEOGRAPHY
Dry conditions cause low and variable yields of the bean crops
of Colorado and New Mexico. Some of the east-central Colorado
counties have in excess of 25 per cent of their harvested crop area
in beans. The production of the crop in central New Mexico is
also very intensive from the standpoint of relative acreage devoted
to beans. Some counties have as high as 30 per cent of their
harvested crop land in beans. In 1924 Torrance county devoted
75.3 per cent of its harvested crop area to this plant. Owing to
dry conditions, Pinto is the most commonly grown variety in
Colorado and New Mexico.
The production trend of dry beans in the United States has been
definitely upward since the early 1920's. Pond (6) brings out that
the "production of dry edible beans in the United States declined
from over 10,000,000 bags of 100 pounds each in 1918 to 6,042,000
bags in 1920, but has since increased on the average, until in the
1937 season the record crop of 15,839,000 bags was produced.
Production averaged 11,927,000 bags during the 5-year period,
1927-31, and 12,179,000 bags in the 5 years, 1932-36." Table 40
gives the average production for the period 1934-1938.
PEAS \
Utilization. Peas are used for canning, as green market or home
garden peas, as dry peas, and recently for freezing. The crop is
also used to a limited extent for forage. The vines of peas used in
canning and for the preparation of frozen peas have value as feed
for livestock.
The production of seed peas for planting the acreages of the
crop for the various purposes indicated above constitutes an
important enterprise. Each of these enterprises demands varieties
with special characteristics as to growth habit and quality.
Peas are used not only as a vegetable but also in the form of dry
peas. The dry peas are used either as whole or split peas and
largely in the preparation of soup. In years when the crop of
canning peas is short, dry peas may upon soaking be utilized for
canning.
Damaged dry peas, or peas of low quality, can be utilized to
advantage in livestock feeding, providing a feed high in protein.
Historical. Peas probably originated in Ethiopia, in Mediter-
ranean Europe, and in southwestern Asia. Their origin is known
EDIBLE LEGUMES 423
to be remote. Peas were first used almost exclusively in the form
of the dry, cooked seeds. The extensive utilization of the crop in
the canned and green state is comparatively recent. The increase
in the use of peas in these forms corresponded with the development
of methods of processing the green seeds and in improvements of
transportation facilities. The development of the "viner," a
machine capable of removing the peas from the vines and pods,
greatly facilitated the handling of the crop for canning purposes.
The early writer distinguished between garden (Pisum sativum)
and field peas (P. arvense). Since, however, these two types are
completely cross-fertile, the distinction is entirely artificial, and
both are now considered under P. sativum. Varieties with colored
flowers were formerly considered as field while those with white
flowers were regarded as garden peas. At the present time the
colored -flowered varieties of edible peas have practically dis-
appeared. About the only extensively grown variety of peas with
colored flowers at the present time is the Austrian Winter pea, and
it is used exclusively for green manure and forage purposes in the
southern states.
Climatic Relationships. Peas thrive best in cool, relatively
humid climates. When grown in the south they must be planted
early so that they may take advantage of the cooler months. Even
in northern areas the highest yield and best quality of crop is
obtained from early seedings. In contrast to beans peas are able
to withstand relatively low temperatures, especially during the
seedling stage. Hot, dry weather interferes with the setting of
seed and lowers the quality of the seed produced. Bright, dry
weather is desirable as the crop approaches maturity and during
harvest.
Soil Relationships. Peas do best on soils of a moderately high
level of fertility. Very high soil fertility leads to excessive vine
production and lodging of the crop. The main essential of soils
suitable for the production of peas is that they be well drained.
For best returns the texture and structure of the soil should be such
as to allow for relatively large amounts of readily available moisture
for the use of the plants. The soil reaction should fall between
slightly acid and slightly alkaline. When peas are used for the
production of hay they are usually sown in combination with a
cereal such as oats. The cereal serves to support the pea vines
424
ECOLOGICAL CROP GEOGRAPHY
and thus reduces the amount of lodging. Furthermore, a mixed
pea and cereal hay cures more readily than straight pea hay.
World Distribution. Statistical data on the distribution of peas
are fragmentary. Peas are an important crop in northern Europe
and especially in England, the Scandinavian countries, Germany,
the Netherlands, and France. The temperature in southern
Europe and in the Mediterranean area is too high for the produc-
tion of the field pea. In these areas lentils and the chick pea take
the place of the field pea. According to Wade (9), Russia at the
present time probably surpasses all other countries in the produc-
tion of dry edible peas. The crop is reported to be of especial
importance in the north-central part of the Soviet Union, east of
Leningrad, west of Moscow, and in southwestern Siberia. The
summer temperature of southern European Russia is too high
for the successful production of peas.
Distribution in the United States. In discussing the distribu-
tion of peas in the United States it is necessary to point out the
specific purposes for which the crop is grown, such as for manu-
General area in which canning peas are produced.
* Section of the state in which the production of canning peas is most
densely concentrated. The areas of the circles roughly indicate the
relative size of the industry in the various states during the five-year
period 1934-38.
FIG. 84. Distribution of canning peas in the United States. (After Rufener.)
EDIBLE LEGUMES 425
facture, that is, either for canning or freezing, for direct marketing,
production of peas for seed purposes, and production for dry peas.
Figure 84, taken from Rufener (7), shows the distribution of
the canning pea producing areas. The important states, together
with the 1939 pack in thousands of cases, are Wisconsin, 4,595;
Oregon, 1,627; Washington, 1,576; New York, 1,385; Minnesota,
1,363; Utah, 1,046; and Illinois, 1,033.
Important producers of market garden peas are California, New
York, Colorado, North Carolina, South Carolina, New Jersey,
and Virginia. The total acreage devoted to this type of pea is small.
The important seed pea producing areas are found in Wisconsin,
California, the Bitterroot and Gallatin Valleys of Montana, the
Upper Snake River Valley of Idaho, and the Palouse region of
northern Idaho and eastern Washington.
Dry peas are produced in the Palouse region, in Colorado,
Wisconsin, Michigan, and Montana. The Palouse region of
northern Idaho and eastern Washington produces around 50 per
cent of the dry edible .pea crop of the United States. Alaska and
First and Best are the two most important green- and yellow-
seeded varieties employed in the production of dry edible peas.
LENTILS
The lentil (Lens esculenta) is a small vetch-like plant highly prized
for its lens-shaped, nutritious seeds, used chiefly for soups and stews.
The lentil is used extensively by the peoples of the Mediterranean
area, and to a lesser degree in western and central Europe. The
seeds are either gray or red; different varieties also differ materially
in the size of the seed. The large-seeded types are especially in
demand in the United States. The main outlet for lentils in this
country is found among the foreign-born populations of our eastern
industrial centers. The Jewish population and peoples of Latin
extraction in these eastern centers are heavy consumers.
According to Hedrick et al. (3), "the lentil has been in cultivation
from very remote times. Lentil seeds were found in the prehistoric
dwellings on the Swiss lakes, in Germany at Schussenried, in
Switzerland, in Italy and Hungary, and also in the ruins of Troy.
It was cultivated to a large extent in Egypt and exported from
there to Greece and Rome. According to Schweinfurth, the lentil
426 ECOLOGICAL CROP GEOGRAPHY
was originally introduced to Egypt from Mesopotamia." The
lentil is probably a native of eastern Asia from Baluchistan and
Afghanistan to southern and eastern Persia.
The lentil demands fairly high temperatures. It thrives in the
climates of the Mediterranean area, where most of the crop is
produced. Production in the United States is very limited. A
small acreage is grown in eastern Washington. Chile produces
lentils in quantities for export. In northern areas the crop is
produced on warm, well-drained soils. Southern slopes are desir-
able.
PEANUTS
The peanut, or groundnut (Arachis hypogaea), is, properly speak-
ing, a pea rather than a nut. The seeds of this plant have the
flavor and many of the other characteristics of true nuts; they are
therefore widely utilized for the same purposes as true nuts. Peanut
oil is one of the world's important food oils. A ton of shelled
peanuts produces from around 500 to 700 pounds of oil depending
on the variety and quality of the crop. Peanut butter is another
valuable and nutritious product. Ttjp peanut is also used exten-
sively in the feeding of livestock. The tops of the plants may be
used for hay. The seed is commonly fed to hogs with the hogs
doing the harvesting.
The peanut is strictly a warm-season crop and is found for that
reason only in tropical or subtropical climates. The crop demands
a moderate amount of moisture throughout the growing season.
Most of the crop is produced in areas with more than 40 inches of
annual precipitation.
Soil conditions influence both the yield and quality of the crop
produced. The highest yields are obtained on the heavier textured
soils provided that these soils do not become too compact. The
best quality of peanuts is produced on light soils. Even light sandy
soils can be used under favorable moisture conditions. Heavy,
dark-colored soils stain the hulls and lower the market value,
especially of the large varieties commonly sold in the hull. Good
soil drainage is essential.
The peanut originated in America; it is probably a native of
Brazil. It has long been used by native tribes in South America.
According to Hutcheson et al. (5),
EDIBLE LEGUMES
427
"the peanut was brought to the United States during the early days
of colonization, but it did not become commercially important until
about 1870. The growth was gradual from that time to about 1900
when the cultivation received a rapid impetus due to the spread of the
boll weevil in the South. In 1909 there were 870,000 acres of peanuts
grown — an increase of 68 per cent over the production of 1900."
Table 41 gives the statistical data of peanut production in the
United States. It will be observed that around 58 per cent of the
crop is harvested for nuts. Figure 83 shows the distribution of
the crop cartographically. Baker and Genung (1) point out that
"peanuts for human consumption are grown mostly in the Virginia-
North Carolina district between Richmond and Raleigh. Those
grown in Georgia, Alabama, and Florida, in Texas and Oklahoma,
are the smaller Spanish variety and are mostly fed to hogs or made
into peanut butter or oil.55
TABLE 41 . PEANUTS: TOTAL ACREAGE, ACREAGE HARVESTED FOR NUTS,
AND PRODUCTION OF NUTS AVERAGES FOR THE TEN-YEAR PERIOD
1928-1937. ACREAGE AND PRODUCTION EXPRESSED IN THOUSANDS.
Acreage
Productio
7 of Nut*
Rank
States
Total
Harvested
for Nuts
Percentage
of U. S.
Total
Average
1928-1937,
in Lbs.
Percentage
of U. S.
Total
1
2
Georgia ....
Alabama ....
798
440
455
224
33.63
18.54
290,346
142,400
29.36
14.40
3
4
Florida ....
Texas
271
262
58
156
11.42
11.04
32,488
73,876
3.28
7.47
5
North Carolina . .
245
226
10.32
238,750
24.14
6
7
Virginia ....
Oklahoma . . .
144
61
143
36
6.07
2.57
148,630
17,104
15.03
1.73
8
Arkansas ....
53
18
2.23
8,965
0.91
9
10
Mississippi . . .
Louisiana ....
37
31
25
11
1.56
1.31
13,484
5,421
1.36
0.55
11
South Carolina . .
18
12
0.76
8,517
0.86
12
Tennessee ....
13
13
0.55
9,032
0.91
Total U. S. . . .
2,373
1,377
100.00
989,013
100.00
World statistics on the distribution of the peanut acreage are not
available. Figures, however, are available on the international
export trade in peanuts. These are presented in Table 42. While
the data in Table 42 show the origin of peanuts entering into
international trade, they do not give all the producing countries.
428
ECOLOGICAL CROP GEOGRAPHY
They do show that the crop is of special importance in the Orient
and in Africa. The crop is also grown in Mediterranean Europe.
The United States generally imports more peanuts than are
exported. The peanut may be expected to become of greater
importance in the southern and particularly in southeastern states
with further developments of the livestock industries and especially
of swine production in these states.
TABLE 42. INTERNATIONAL EXPORT TRADE IN PEANUTS, AVERAGES 1930-
1934
Rank
Principal Exporting Countries
Exports, in 1,000
Pounds
Percentage of
World's Export
Trade
1
British India
1,290773
32.79
2
Senegal
915,385
23.26
3
Nigeria ..........
634,259
16.11
4
China
534,578
13.58
5
Manchuria*
179 149
4.55
6
Gambia
142,543
3.62
7
Mozambique
81,267
2.06
8
Portuguese Guinea
53,036
1.35
9
Netherland India
45,803
1.16
10
Tanganyika
42,665
1.08
All others
16,502
0.44
World total export trade
3,935,960
100.00
* Three-year average.
REFERENCES
1. Baker, O. E., and A. B. Genung, "A graphical summary of farm
crops," U. S. Dept. Agr. Misc. Pub. 267, 1938.
2. Hardenburg, E. V., Bean Culture. Macmillan, New York, 1927.
3. Hedrick, U. P., F. H. Hall, L. R. Hawthorn, and A. Berger, The
Vegetables of New York, Vol. t — Part 1, "Peas of New York." J. B.
Lyon Company, Albany, 1928.
4. Hendry, G. W., "Bean culture in California," Cat. Agr. Exp. Sta. Bull.
294, 1921.
5. Hutcheson, T. B., T. K. Wolfe, and M. S. Kipps, The Production of
Field Crops. McGraw-Hill, New York, 1936.
6. Pond, R. K., "Major economic trends in the dry edible bean indus-
try," U. S. Dept. Agr.y Agr. Adj. Adm.9 Marketing Information Series,
GCM — 6, 1938.
EDIBLE LEGUMES 429
7. Rufener, W. W., "Production and marketing of dry peas in the
Palouse Area," Wash. Agr. Exp. Sta. Bull. 391, 1940.
8. Thompson, H. G., Vegetable Crops. McGraw-Hill, New York, 1931.
9. Wade, B. L., "Breeding and improvement of peas and beans," U. S.
Dept. Agr. Yearbook 1937:251-282.
10. Young, H. N., "Production and marketing of field beans in New
York," New York Agr. Exp. Sta. Bull., 532, 1930.
Chapter XXV
POTATOES, SWEET POTATOES, YAMS, AND
OTHER ROOT CROPS
THE WHITE POTATO
Importance as a Food Crop. The white potato (Solanum tubero-
sum) is one of the most efficient of starch producing plants. In cool
regions and especially in relatively moist, cool areas with soils
too light for the economical production of wheat, the potato has
no rival as a producer of food. Rye is the only crop plant approach-
ing its efficiency under the adverse conditions indicated. Both
rye and potatoes are essentially European crops. Since both are
efficient producers of carbohydrates under conditions of light
soils and moderate to low temperatures, it is not surprising that
their regions of distribution in Europe are practically coincident.
While the potato occupies a prominent ^>lace in the American diet,
the per capita annual consumption is considerably lower in the
United States than in western Europe, amounting to only two
to three bushels as compared with two to three times that much
in the countries of northwestern Europe.
The potato occupies an important place in human nutrition.
Stuart (18) points out that "the average world production of
potatoes far exceeds that of the cereals." This statement is sup-
ported by a listing of the production of the world's important food
crops for the five-year period of 1930-31 to 1934-35. In that
period the aggregate production of the important food crops
expressed in millions of tons amounted to 226.86 for potatoes,
165.00 for wheat, 128.60 for corn, 108.56 for rice, 69.30 for oats,
53.06 for barley, 51.84 for rye, and about 6.00 for beans. Since
statistics on some of these crops are quite fragmentary, the figures
given are subject to a considerable error. It must be pointed
out in interpreting them that the high figure given for potatoes
is not directly comparable to those presented for the cereals and
for beans in that the tubers of potatoes contain much more water
430
POTATOES AND ROOT CROPS 431
than the seeds of the other crops enumerated. According to Fitch
and Bennett (8), the potato contains 78.3 per cent of water. The
percentage of water in the tubers varies to quite an extent with
environmental conditions, but remains high under all conditions
of culture. The cereals contain about 13 per cent of water. In
comparing the potato and wheat crops of the world on the basis
of amounts of dry matter produced by each, using 78 per cent
of water in potatoes and 1 3 per cent of water in wheat, the relative
production of potatoes is cut down from 226.86 to 49.91 millions
of tons, while the world wheat crop is adjusted down from 165.00
to only 143.55 millions of tons of dry matter. Thus, on the basis
of relative amounts of dry matter produced, wheat, corn, and rice
are of greater importance as world food crops than is the potato.
Even the oat plant produces a greater amount of dry matter than
the potato. However, oats contain around 30 per cent of hull
which is of no value as food and little value as feed.
The above should not be interpreted to mean that the potato
is less efficient in the production of human food than the cereals.
That is decidedly not the case. The world wheat acreage may be
estimated at 314 millions of acres as contrasted to only 48 millions
of acres used in potato production. In its optimum environment
the potato is able to supply more human food per unit of area than
can be produced from any of the cereals. The relative importance
of the potato and also of rye in the agriculture of the United
States and in northwestern Europe merits mention. The United
States with its greater population produces only 4.89 and 1.69 per
cent of the world's potato and rye crops as compared to the German
production of 27.96 per cent of the world's potato and 21.65 per
cent of the world's rye crop. On the other hand, the United States
is far ahead of Germany in the production of corn and wheat. The
reasons for this are found in differences in climate, soil, and eco-
nomic conditions. Climatic and soil conditions over vast areas
of the United States are more favorable to cereal than to potato
production. In addition, the masses of northwestern Europe not
infrequently find it necessary to survive on the cheapest food thai
can possibly be obtained. There is no doubt that the introduction
of the potato contributed materially to the very rapid increases
in the population of western Europe during the past 150 years
The very fact that the potato is able to produce an abundant crop
432 ECOLOGICAL CROP GEOGRAPHY
under conditions where wheat will yield but scant returns has
made it possible for the bleak, sandy plains of northwestern Europe
to support dense populations. As stated by Smith (13), "The
potato has revolutionized Europe."
It is necessary to point out one more feature regarding the
relative production of potatoes in the United States and in Ger-
many. Germany produces almost six times as many potatoes as
the United States. This does not mean that the German popula-
tion consumes six or more times as many potatoes as do the people
of this country. In the United States practically the entire potato
crop is grown for human consumption; in years when overproduc-
tion does not occur only culls are used for feed. So far the potato
crop has found but a limited industrial outlet in this country. In
Germany, on the other hand, a high percentage of the potato
crop is produced for feed for livestock. The crop is especially
important in the production of pork. Furthermore, the crop is
extensively employed in the production of industrial alcohol,
potato starch, dextrine, and other commercial products.
Industrial Uses. According to Stuart (18), around 70 per cent
of the potato crop of the United States is used for table purposes.
The remaining 30 per cent is accounted for in about equal pro-
portions by culls or unsalable stock, diseased and frozen tubers
and storage shrinkage, and seed for the ensuing crop. "In Ger-
many,55 states Stuart, "it is claimed that only 28 per cent of a
normal crop is used for table food. The balance of the crop is
disposed of as follows: 40 per cent is fed to livestock; 12 per cent
used for seed; 10 per cent for industrial purposes; and the remaining
10 per cent is regarded as waste, due to decay, shrinkage and other
causes." While a utilization of 10 per cent of the German potato
crop for industrial purposes does not sound like a very high figure,
it nevertheless amounts with their high production to a quantity
equal to around 57 per cent of the total crop normally grown in
the United States.
The main reasons for the limited industrial utilization of the
potato in the United States are that corn generally provides a
cheaper source of starch than does the potato; production of
corn is also more stable and for that reason provides a more
dependable source of raw materials at a lower price than do
potatoes; and the fact that our motor fuels have originated almost
POTATOES AND ROOT CROPS 433
entirely from the petroleum industry. In areas well adapted to
potato production, starch can probably be produced from potatoes
as economically as from corn. On the other hand, it is difficult in
the industrial utilization of a product such as potatoes for manu-
facturers to compete on the basis of a price level determined
largely by a demand for table use. Obviously, the capitalization
of an industry capable of operating economically only in years of
surplus production of the crop on which it depends is fraught with
difficulties.
A great variety of products can be produced from the potato,
such as starch, dextrine, glucose, alcohol, potato flour, and a
number of dehydrated products such as dried, sliced, cubed,
shredded, and riced potatoes. The conversion of the potato into
industrial products has the advantage of carrying these products
over from one season to another. This can, of course, not be done
with the tubers which are subject to rapid deterioration after
a period of storage of several months.
Historical. The potato is an American contribution to the
world's agriculture. It is generally agreed that the potato origi-
nated in the central Andean region of South America. There is
lack of agreement as to whether the original home of the plant
was in Chile, or in Peru and Bolivia. In speaking of the wild
relatives of the potato, Stevenson and Clark (15) state that "all
species seem to require a cool climate, since they are found growing
at high altitudes in regions near the Equator and none is known
to occur under tropical conditions." The Spaniards upon their
invasion of South America found the potato under cultivation
and the tubers used as a common article of food by the natives
in the higher and cooler regions.
According to Fuess (9), potatoes were first introduced into
Europe by the Spaniards. Historical evidence shows that Philip II
of Spain ordered a box of potatoes (Papas) to be sent to Spain
in 1565. This shipment originated from Cuzco, Peru. A portion
of this shipment was sent to the Pope in Rome, who in turn sub-
mitted some of the tubers to a sick Cardinal in the Netherlands.
Like many other exotic plants, the potato was credited with
medicinal qualities. Two of the tubers of this lot also came to the
French botanist Charles de L'Ecluse (Carolus Clusius), who grew
the progenies of these tubers in the imperial gardens at Vienna
434 ECOLOGICAL CROP GEOGRAPHY
and Frankfort. However, the potato was not described until
Clusius published his Rariorum Plantarum Historia in 1601.
The Italians were probably the first to recognize the value of the
potato. There is some indication that the crop was grown in a
garden in Padua as early as 1591. Fuess (10) points out that
potatoes were grown in the garden of the University of Leiden in
1594, and at Montpellier, France, in 1598. The plant was grown
in other gardens as a curiosity at these early dates. Its extensive
production and utilization as a food crop, however, appeared
much later. Thus the Royal Society recommended its extensive
cultivation in England in 1663. The crop did not become of much
importance in France until after the famine years of 1793 and 1817.
Also the years of scarcity of 1745, 1758, 1763, 1770-1772, and
1774 contributed much to the extensive cultivation of potatoes
in central and northern Europe when the plant was found to be
of value as a food crop and became the poor man's bread. Fuess
(9) also points out that the gradual abandonment of the three-
field system in Germany toward the end of the eighteenth century
contributed materially to the extensive cultivation of potatoes in
that the crop was found of value to replace the fallow in the revised
sequences of cropping.
Sir Walter Raleigh is credited with the introduction of the
potato into Ireland around 1580. From there the crop found its
way to England and via Bermuda to the United States. It arrived
in Bermuda in 1613 and in the present territory of the United
States in 1622. The crop was introduced into New England from
Ireland during the early part of the eighteenth century. This
later introduction gave rise to the common terminology of "Irish"
potato.
Climatic Relationships. The main climatic requirement of a
good potato producing area is a cool growing season. Thus,
according to Smith (14),
"In the United States the potato has made its greatest development
in the cooler sections of the country where the mean annual temperature
is between 40 and 50 degrees Fahrenheit and where the mean tem-
perature in July is not over 70 degrees. Furthermore, the greatest
yields of potatoes per acre are in those states where the mean annual
temperature is below 45 and where the mean of the warmest month is
not far from 65."
POTATOES AND ROOT CROPS 435
Bushnell (5) shows that the average yields of potatoes in the
various sections of the United States are inversely proportional
to the isotherms of the highest normal temperature during the
growing season of the crop. Regions with the highest normal
temperature below 65°F show, according to his data, average
yields of 200 bushels, as contrasted to yields of only 120 to 180
and 60 to 80 bushels per acre in areas where the highest normal
temperatures during the growing seasons are 69 to 73 and above
73°F, respectively. Bushnell found in growing potatoes under
controlled temperatures that high temperatures at any time after
the plants emerged reduced the size of the leaflets formed and
called attention to the fact that this reduction in the photosynthetic
areas of the plants undoubtedly had an effect on the yields of
tubers. However, yields were reduced to a greater extent than
could be accounted for by this reduction in photosynthetic area.
On the basis of this and respiration experiments, Bushnell sug-
gested that "deficiency of carbohydrate arising from excessive
respiration may be very generally the limiting factor in plant
growth at temperatures above the optimum." The rate of respira-
tion of potatoes, as well as of other plants, increases materially
with increasing temperatures. High night temperatures are
especially unfavorable to the potato. The downward trends in
yields from northern to southern producing areas both in North
America and in Europe can be largely attributed to the increasing
summer temperatures encountered in going from northern to
southern areas in these continents. An abundance of sunshine
during the growing season is highly desirable insofar as this influ-
ences the efficiency of assimilation of carbohydrates and reduces
the rate of spread of fungus diseases attacking the foliage of the
plants.
Potato yields are affected adversely by high temperatures,
especially during the time the crop is developing its tubers. In
regions where the season is sufficiently long and where lack of
moisture docs not become a limiting factor as the season advances,
the critical period during tuber formation may be avoided or at
least minimized by delaying the date of planting of the crop. How-
ever, when the planting date is delayed too long the temperature
factor is again encountered in germination and in the attainment
of a desirable stand. Thus Werner (20), working in northwestern
436 ECOLOGICAL CROP GEOGRAPHY
Nebraska, reports a mean final stand of plants of 93.0 per cent
from mid-May as compared to stands of only 79.5 per cent from
late-June plantings. Fitch (7) called attention to the detrimental
effects of high soil temperatures to sprouting and growth. Fitch
also brought out that high soil temperatures during sprouting
produced especially detrimental effects if combined with high
soil moisture contents.
Temperature conditions have a decided influence not only on
the yield but also on the quality of the crop harvested. Quality
in potatoes is especially associated with the shape and size of the
tubers produced.
The production of well-shaped tubers acceptable to the market
demands a set of environmental factors favoring the uninterrupted
development of the tubers. Interruptions in development may be
due to unfavorable temperature or moisture relationships, and
not infrequently to both. Any condition causing cessation of
development followed by conditions favoring growth may produce
second growths resulting in knobby and poorly shaped tubers.
Potatoes are quite efficient in the utilization of moisture. Never-
theless, it is essential that a sufficient amount of moisture be avail-
able for the use of the plants during the growing season and espe-
cially after the tubers have started to form. This demands under
most conditions a rainfall of not less than ten inches during the
growing season. The highest yields are obtained under cool and
humid conditions. The high yields obtained in Maine and in
northern Europe are directly traceable to the cool, humid climates
of these areas which provide the ecological optimum for potato
production. In the United States as well as in Europe higher
temperatures and less reliable moisture conditions arc encountered
from north to south. These progressive changes in temperature and
moisture conditions account for the location of the optimal, moder-
ate, and minimal areas of potato production in these two important
potato growing continents. In the production of early potatoes
in southern areas the crop is grown during the cooler and generally
moister portion of the year. Furthermore, in southern producing
areas early-maturing varieties are used. The crop is usually
harvested before attaining full maturity.
Excessive moisture as maturity approaches not only leads to
difficulties in harvesting the potato crop but also increases damage
POTATOES AND ROOT CROPS 437
from diseases and lowers the quality of the tubers. High humidity
results in severe losses in the potato crop due especially to the
ravages of the late blight fungus (Phytophthora infestans).
The high yields of potatoes obtained on the higher plateaus of
the intermountain region of the United States are accounted for
by the relatively low temperatures prevailing at the high elevations,
and the controlled water supply by means of irrigation.
Soil Relationships. The potato crop of the world is grown over
a wide range of soil conditions. Edaphic relationships are generally
speaking of less importance in limiting yields of the crop than the
climatic factors of the environment. Nevertheless, the soil factors
influence yield, length of time required for the crop to attain
maturity, eating quality, keeping quality, and the extent of loss
from diseases. The general soil requirements of the potato are set
forth by Morgan el al. (12) and cited in the following paragraph.
"Loam, fine sandy loam, or silt loam soils having deep, mellow sub-
soils with especially good undcrdrainage are most desirable. The crop
requires moist soil conditions at all times, without any tendency toward
poor aeration. A high state of chemical fertility must be either naturally
present or artificially provided. The potassium requirements are rela-
tively high. The crop does well over a considerable range of soil
reaction. In the Northeast, where scab-sensitive varieties are grown,
reactions between />H 4.8 and 5.4 are considered best. Much of the
western production, however, is on less acid or slightly alkaline soils."
Soil conditions over vast areas of the important producing regions
of northwestern Europe arc not naturally ideal for potato produc-
tion. They have, however, been modified by cropping and cultural
practices, as well as by heavy applications of fertilizers, so that
relatively high yields arc obtained. It is the generally favorable
climatic conditions prevailing in these areas that make possible
the extensive utilization of these rather light, sandy soils. Likewise,
sandy soils can and are being used for potato production in areas
where moisture conditions can be controlled by irrigation. But
again, agronomic practices leading to the building up of the
organic matter contents of these light soils materially increase
yields and lend stability to production. Potatoes also respond
well to organic matter applications to heavy soils. Soil structure
as well as texture has a marked relationship to the quality of the
tubers produced.
438
ECOLOGICAL CROP GEOGRAPHY
Muck and peat soils when properly managed can be used to
advantage in potato production. As stated by Thompson (19),
"There is some prejudice against the quality of muck-grown
potatoes, but this is probably not justified as potatoes of excellent
quality are being grown on well-drained and properly fertilized
soils of this type."
World Distribution. The world's important potato producing
areas are practically confined to two continents, Europe and
North America, with the former producing 91.80 and the latter
5.91 per cent of the total world crop during the five-yeaj: period
1930-31 to 1934-35. The northern hemisphere accounted for
98.72 per cent of the total world production. Climatic, soil, and
economic conditions are responsible for the great preponderance
of the potato in Europe.
Table 43 gives the world statistics on potato production. Only two
non-European countries, the United States and Canada, arc found
among the first 15 producing countries of the world. The southern
hemisphere is not represented. Argentina produces only 34.18 and
Australia only 13.14 millions of bushels of potatoes annually.
TABLE 43. WORLD STATISTICS ON POTATO PRODUCTION: ACREAGE, YIELD
PER ACRE, AND PRODUCTION IN SPECIFIED COUNTRIES, AVERAGES FOR 1930-
31 TO 1934-35
Rank
Countries
Acreage, in
1,000 Acres
Yield per
Acre, in Bu.
Production,
in 1,000 Bu.
Percentage of
Total World
Production
1
Germany
9,335
226.5
2 114 235
27.96
2
U.S.S.R
14,695
119.6
1 758 036
23.25
3
Poland
6,742
167.5
1 129,238
14.93
4
France
3,495
164 4
574 531
7 60
5
United States
3 426
108 0
369 907
4 89
6
Great Britain
1 098
252.3
277 062
3 66
7
Spain
1,031
167.6
172 759
2.28
8
Belgium
412
319.8
131 758
1.74
9
10
Netherlands ....
Italy
395
981
276.6
88 7
109,253
87 017
1.44
1 15
11
Canada
556
138 4
76 934
1 02
12
Lithuania
423
173 6
73 428
0 97
13
Sweden
331
208 1
68 888
0 91
14
Rumania
521
1307
68 085
0 90
15
Hungary
711
91.2
64 821
0 86
All others
3,848
486,148
6.44
World total
48,000
157.6
7 562 100
10000
POTATOES AND ROOT CROPS
439
Figure 85 gives the distribution of potato production in Europe.
Production is centered around Germany and the former Poland.
Russia is also a very important producer, but production there
is not so concentrated as in Germany, Belgium, and the Nether-
lands.
•"•••*••• •"• "• •"• »«*»"»/*»* J** * * •*
"v
FIG. 85. Distribution of potato production in Europe. Average production for
the five-year period of 1930-31 to 1934-35. Each dot represents 5,000,000 bushels.
Attention is called to the high average yields obtained in the
countries of northern Europe. Belgium leads with 319.8 bushels
per acre. The Netherlands, Great Britain, Germany, and Sweden
follow in the order named; all have average yields of more than
200 bushels. These high yields are accounted for by favorable
climatic conditions and intensive methods of cultivation.
Distribution in the United States. It is customary to classify
the potato producing states according to the earliness or lateness
of the bulk of production in each state and the period during which
the crop is harvested. The late or main crop of the country is pro-
duced north of the Corn Belt, at higher elevations in the inter-
440
ECOLOGICAL CROP GEOGRAPHY
mountain area, and in the Pacific Northwest. The early crop is
produced in the states along the Atlantic from Virginia south,
and in those bordering the Gulf of Mexico. Intermediate sections
of commercial importance are found in eastern Oklahoma, eastern
Kansas, and northwestern Missouri, in Arkansas, Tennessee, and
California.
TABLE 44. POTATOES: ACREAGE HARVESTED, YIELD PER ACRE, AVERAGE
PRODUCTION FOR THE TEN-YEAR PERIOD 1928-1937, AND 1938 PRODUCTION.
ACREAGES AND PRODUCTION EXPRESSED IN THOUSANDS
V" / J
Production
Rank
States
Acreage
Yield
per Acre,
in Bu.
Average
1928-1937,
Percentage
of U. S.
Total
1938,
in Bu.
in Bu.
1928-1937
Late
\
Maine
169
267
44,968
12.08
40,414
2
New York
236
123
29,005
7.79
26,840
3
Michigan ....
280
92
25,922
6.96
30,000
4
Minnesota . . .
331
77
25,691
6.90
20,700
5
Pennsylvania . .
213
120
25,584
6.87
22,002
6
Wisconsin ....
265
8#¥
23,380
6.28
19,080
7
Idaho
109
214
23,308
6.26
28,750
8
Colorado ....
102
146
14,762
3.97
11,830
9
Ohio .
128
96
12,308
3.31
12,626
10
North Dakota . .
128
72
9,137
2.45
12,070
Other states .
634
104.9
66,494
17.87
64,707
Total late potatoes .
2,595
115.8
300,559
80.74
289,017
Early and Intermediate
1
Virginia ....
101
121
12,352
3.32
10,428
2
North Carolina . .
80
100
8,028
2.16
8,690
3
New Jersey . . .
46
163
7,615
2.05
10,530
4
Missouri ....
57
77
4,411
1.18
5,832
5
Kentucky ....
50
76
3,818
1.03
4,635
6
California ....
17
220
3,739
1.00
9,690
7
Kansas ....
38
83
3,365
0.90
3,219
8
Texas
51
66
3,361
0.90
2,950
9
Maryland ....
31
103
3,257
0.87
2,990
10
Florida ....
27
110
2,995
0.80
4,488
Other states . . .
250
75.0
18,758
5.05
21,694
Total early and in-
termediate potatoes
748
95.9
71,699
19.26
85,146
Total U. S. . . .
3,343
111.4
372,258
100.00
374,163
Table 44 gives the potato statistics for the leading late, early,
and intermediate producing states. It is striking to find * that
POTATOES AND ROOT CROPS 441
only one of the early-crop states ranks among the ten high produc-
ing states of the country. Over 80 per cent of the potato crop is
produced in the late or northern states.
Figure 86, taken from Strowbridge (16), gives the origin of
carlot shipments of potatoes in 1935. While this map shows the
location of the important areas of commercial production, it does
not give an entirely satisfactory picture of the general distribution
of the crop. A fairly high percentage of the crop is moved by means
of trucks. This holds true especially in the areas in close proximity
to central markets. Also a high percentage of the crop outside of
the main shipping areas is used for direct home consumption.
Pennsylvania, for instance, is a high producing state; however, it
docs not show up prominently in Fig. 86. The potato is grown
for home use in practically all sections of the United States. Ac-
cording to Baker and Genung (1), "No other crop, except hay,
is reported from so many counties in the United States as potatoes."
General production of the crop is common throughout all of the
northeastern quarter of the country and especially in the areas
north of the Corn Belt. Nevertheless, the commercial production
of the crop is centered in fairly definite districts.
The4 primary reason for the great importance of the northern
or late-crop section can be attributed to the favorable response of
the potato to cool climates. The fact that the potato encounters
less competition from other intertilled crops in cool than in the
warmer areas to the south is also of importance. Thus, potatoes
and com require intensive cultivation at the same time. The
most important commercial producing centers of the northern
portion of the United States arc Aroostook County, Maine; the
Long Island and northern New Jersey districts; the western New
York and Pennsylvania districts; the northern Michigan and
Wisconsin districts; the Red River Valley of Minnesota and North
Dakota; the western Nebraska district; the Greeley, San Luis
Valley, and Gunnison and Montrose districts of Colorado; the
Idaho Falls, Barley-Twin Falls, and Caldwell districts of the
Snake River Valley of Idaho; and the Yakima and Wenatchee
Valley districts of Washington. It will be observed from Fig. 86
that not all of these districts are located in close proximity to
centers of population. The handicap of long hauls to markets
from such districts must be overcome by exceptionally favorable
442
ECOLOGICAL CROP GEOGRAPHY
environmental conditions leading to high yields, and corresponding
low unit costs of production, as well as by the production of a high
quality potato. Both of these factors are of importance, but empha-
sis must be given to the production of a potato of quality to merit
price premiums.
While the early and intermediate crop states produce but a
relatively small proportion of the total potato crop of the United
States, they are nevertheless of considerable importance in that
POTATO-SHIPPING AREAS: CARLOT SHIPMENTS. 1935
FIG. 86. Points of origin of carlot shipment of potatoes in 1935. Each dot repre-
sents 50 carloads. (After Strowbridgc.)
they compete with the late crop producing areas. Early potatoes
produced in Florida appear on the northern market in February
and early March. At first these potatoes are more or less a luxury
product, but as the season advances and the volume of southern-
grown potatoes increases they come into more direct competition
with the stocks of old potatoes produced in the northern states.
The more important early or truck crop producing districts are
enumerated by Stuart (17) as the Hastings district in Florida;
the Savannah district in Georgia; the Beaufort and Charleston
districts in South Carolina; Beaufort county, North Carolina;
the Norfolk district and the eastern shore of Virginia; the eastern
shore of Maryland; the districts centering around Louisville,
POTATOES AND ROOT CROPS 443
Kentucky; Columbia, Tennessee; Fort Gibson, Oklahoma; and
Fort Smith, Arkansas; the Eagle Lake, Wharton, and Brownsville
districts in Texas; the Alexandria and Bayou Lafourche districts
in Louisiana; and the Mobile, Alabama, district.
The production of potatoes in the southern states may be
expected to become of greater importance in the future. The
industry has expanded during the past ten years and in view of the
present cotton situation may be expected to make additional
progress.
The southern early-market potato producing sections look to
northern growers for a major portion of their seed stock. This has
created an important and specialized industry in northern areas
and at higher elevations, or in sections adapted to the production
of good quality seed potatoes to supply the southern demand for
relatively disease-free seed. The virus, or so-called degenerative,
diseases of the potato make rapid progress under southern condi-
tions so that it is difficult and in places impossible to produce seed
stock having the same vigor as that grown in the North. Further-
more, under the temperatures prevailing in the South it is difficult
to carry over seed stock from one season to the next. This is
especially the case in areas where no fall crop is grown, where
the seed stock would have to be carried throughout the summer
months.
Long-time trend studies of the potato acreage of the United
States by Strowbridge indicate a downward trend from 1911-
1915, when a yearly average acreage of 3,473,000 acres was re-
ported, until the low point of 3,123,000 acres was reached for the
yearly average for the five-year period of 1926-1930. In recent
years the acreage has increased somewhat. The yearly average
for 1931-1935 was reported as 3,515,000 acres. The total produc-
tion of the potato crop showed an upward trend because of in-
creased yields per acre. The United States per capita production
shows a definite downward trend since 1911, indicating that the
increase in population has been greater in proportion than the
increase in the total production of potatoes.
THE SWEET POTATO
Importance as a Food Crop. Since but a relatively small pro-
portion of the world's sweet potato crop enters commercial chan-
444 ECOLOGICAL CROP GEOGRAPHY
nels, statistical data regarding the extent of its production are
fragmentary. The crop is of importance in practically all tropical
and subtropical regions where it is a standard article of food, being
served baked, fried, candied, and used as a filling in pies. With
improvements in handling and storage, the crop is becoming of
increasing importance in northern markets. However, in most
northern sections the crop must still be classified as a luxury food.
The higher prices paid by consumers of sweet potatoes in northern
markets are accounted for not only by the transportation charges
involved in moving the crop to these markets, but by 'the more
exacting storage conditions demanded by sweet than by white
potatoes. The safe storage of sweet potatoes entails a greater outlay
for facilities and a more careful handling of the crop than is the
case in white potatoes. Even under the best of conditions the
delivery of sweet potatoes to the ultimate consumer involves
greater risks and expenditures than are encountered in marketing
white potatoes.
Historical. Authorities have not been able to agree as to whether
the sweet potato (Ipomoea batatas) originated in tropical America or
in the East Indies. Many investigators consider the crop native
to tropical America, and believe that it was widely distributed
by early Spanish and Portuguese navigators. Chung (6), however,
states that although it has not been definitely determined when
the sweet potato was first introduced into Hawaii, it is thought
that the crop has been under cultivation on the island since about
500 A.D.
Sir Francis Drake is credited by some authorities with the intro-
duction of the white potato into England in 1580. This gave rise
to the terminology for the white potato by Gerard in 1596 as the
"potatoes of Virginia, Rattata Virginiana sive Virginianwum vet
Pappus" It is well established now that the potatoes brought by
Drake from Virginia were sweet rather than white potatoes.
The white potato was not grown in Virginia during the sixteenth
century.
Climatic and Soil Relationships. The high temperature re-
quirement of the sweet potato bespeaks its tropical origin. The
plant requires a growing season of at least four months, but even
if the season is that long the sweet potato does not produce satis-
factory yields unless the nights, as well as the days, arc warm for
POTATOES AND ROOT CROPS 445
a considerable portion of the time. For this reason around 90 per
cent of the crop is produced in the 1 5 states south of the Mason
and Dixon line. The southern half of New Jersey is the most
northern area of large commercial production; the crop is of local
commercial importance in southeastern Pennsylvania, and in
parts of Ohio, Indiana, Illinois, and Iowa.
In northern sweet potato sections a large part of the commercial
crop is grown from slips produced by sprouting the tuberous roots
in warm beds of soil. The temperature of the plant bed is held
more or less constant at 70 to 75° F during the greater part of the
period that the plants are growing in the bed or until planting-
out time. South of Virginia the crop is often propagated from
vine cuttings taken from the vines of plants, originally produced
from slips, after these plants have started to run.
Although the sweet potato is fairly tolerant of dry weather, it
thrives best under conditions of moderate rainfall. A fair amount
of moisture is desirable from the time the plants are set out in the
field until the vines cover the ground. After that heavy rainfall
or irrigations may cause excessive vine growth at the expense of
root development. High amounts of precipitation in autumn
interfere with the proper ripening of the tuberous roots. Unless
the roots arc allowed to mature properly storage losses are likely
to be high. The sweet potato demands an abundance of sunshine.
The distribution of the sweet potato like that of the white potato
is determined to a far greater extent by clinuuic rather than by
soil conditions. The plant is rather lenient in its soil requirements.
A moderate proportion of sand in the top soil, with a fairly retentive
subsoil, provides ideal conditions. Whatever the soil type, it should
be warm, friable, and well drained. A high level of fertility is not
required. As a matter of fact, on very fertile or on heavy soils
the crop tends to run to vines at the expense of the roots; moreover,
the sweet potatoes formed are likely to be rough and irregular
in appearance. The crop is especially well adapted to newly
cleared lands, such as the cutover pine lands of the South. It can
also be grown on land too poor for the successful production of
cotton or tobacco.
Distribution. With the exception of the production in southern
New Jersey, Delaware, and eastern Maryland practically the
entire commercial crop of sweet potatoes of the United States is
446
ECOLOGICAL CROP GEOGRAPHY
FIG. 87. Distribution of sweet potato production in the United States. Each dot
represents 20,000 bushels. (After Miller.)
produced in the southeastern states. Table 45 gives the statistical
data for the ten most important producing states. Figure 87, taken
from Miller (11), shows the areas where sweet potatoes are grown.
TABLE 45. SWEET POTATOES: ACREAGE HARVESTED, YIELD PER ACRE,
PRODUCTION AVERAGE FOR THE TEN-YEAR PERIOD 1928-1937 — AND
1938 PRODUCTION. ACREAGE AND PRODUCTION EXPRESSED IN THOUSANDS
/V" tJ
Production
Rank
States
Acreage
Harvested
Yield
per Acre
in Bu.
Average
1928-1937,
in Bu.
Percentage
ofU. S.
Total
1928-1937
1938,
in Bu.
1
2
3
4
5
6
7
8
Georgia ....
North Carolina . .
Alabama ....
Mississippi
Louisiana ....
Tennessee ....
South Carolina . .
Texas .....
111
84
88
76
92
57
59
63
73
95
83
92
70
90
85
73
8,102
7,896
7,312
6,939
6,471
5,122
4,965
4,630
11.46
11.17
10.34
9.82
9.15
7.25
7.02
6.55
9,225
8,748
8,560
7,743
6,930
5,459
6,468
4,350
9
10
Virginia ....
Arkansas ....
Other states . . .
37
38
130
115
76
93.4
4,285
2,820
12,148
6.06
3.99
17.19
3,570
3,225
12,369
Total U. S. . . .
835
85.2
70,690
100.00
76,647
POTATOES AND ROOT CROPS 447
New Jersey produces around 2,000,000, Maryland around 1,300,-
000, and Delaware around 900,000 bushels of sweet potatoes
annually. In general, New Jersey sweet potatoes are drier than
those produced in the South; they are highly esteemed for their
quality.
Baker and Genung list the four areas of greatest importance in
commercial sweet potato production as follows: the Weakley and
Henry county district in western Tennessee, the Lafayette-
Opelousas district in Southern Louisiana, the Eastern Shore area
of Virginia, Maryland, and Delaware, and southern New Jersey.
YAMS
Distinction between Sweet Potatoes and True Yams. Sweet
potatoes differ in their texture upon cooking or baking. Certain
varieties cook or bake dry and remain more or less firm while
others are moist and have a soft texture. Unfortunately the term
"yam" has been used quite freely in designating those varieties of
sweet potatoes that cook or bake moist. The sweet potato (Ipomoea
batatas) belongs to the morning glory family (Convolvulaceae)\ the
true yams belong to the genus Dioscorea. As stated by Young (21),
"true yams and sweet potatoes are unrelated botanically and,
although the plants of both are vines and produce underground
tubers or tuberous roots, neither the vines nor the tubers of the
two groups bear a real resemblance to each other." The name
"yam" should therefore not be applied to moist varieties of sweet
potatoes.
Utilization and Distribution. The edible species of yams, ac-
cording to Young, produce starchy tubers similar to the white
potato in food value and taste. Young lists six species of yams;
of these the greater yam (Dioscorea alata) is the most important as
well as the most widely distributed. In general the flesh of the
tubers of this species is white; certain varieties, however, have
yellowish and even light or deep purple flesh. Under favorable
conditions the tubers become quite large; they often weigh ten
pounds or more.
The fact that the true yam requires from 8 to 10 months for the
development of a good crop limits it to the very southern portion
of the United States. Yams furnish a considerable part of the
food supply of the peoples of many humid tropical areas. They
448 ECOLOGICAL CROP GEOGRAPHY
are used to but a limited extent outside of the tropics. The yam
takes its place with taro, dasheen, and cassava in providing tropical
populations with starchy foods.
VARIOUS ROOT CROPS
Importance and Uses. A great variety of root crops are grown
for human food and for feed for livestock. The most important
food root crops are carrots, turnips, rutabagas, and table beets.
With the exception of the table beet these same crops as well as
mangels and sugar beets are also produced for feed.
In 1937 over 14 million bushels of commercial carrots were
harvested from 38,540 acres in the United States. According to
Beattie (2), "the carrot succeeds under a wide range of climatic
and soil conditions." The crop has high food value and good
shipping and storage qualities. Recent investigations regarding
the value of vitamins in the diet have contributed much to popular-
ize carrots as a food crop. Carrot production is of two general
classes — the northern, summer, or main crop, considerable
quantities of which go into storage, and the southern or winter
crop, which appears on the markett during the winter in the form
of bunched carrots. The state of New York leads in the produc-
tion of the main crop while California leads in the production of
bunched carrots.
"Turnips and rutabagas are essentially cool-climate crops and
make their most vigorous root growth at relatively low growing
temperatures regardless of date of seeding" (Beattie, 4). Turnips
can be grown as a spring or fall crop. In the South they are grown
mainly as a late fall, winter, or early spring vegetable. In the North
they are grown mainly as a fall crop for winter storage and stock
feeding. Since rutabagas require a longer growing season than
turnips, only one crop is usually possible in the North, this being
spring-planted and harvested late in fall.
Table or garden beets are also grown under a great variety of
climatic and soil conditions. They are grown for direct table use
and for commercial canning. According to Beattie (3), "beets arc
grown in the South as a fall, winter, and spring crop and as an
early summer and fall crop in the northern part of the country."
Root crops are used to but a limited extent for forage in the
United States. The main reason for this is that root and succulent
POTATOES AND ROOT CROPS 449
crops in general have not been able to compete with the two
extensively grown American silage crops, corn and the sorghums.
Their production is confined more or less to cases where such
succulents are in demand by specialized enterprises, as in con-
nection with highly specialized poultry and dairy production
projects. Because of the great amount of hand labor required
in producing and even in preparing root crops for feeding, silage
crops provide a more economical source of succulent feed than
can be produced under American conditions from root crops.
Root crops for forage are extensively grown in the countries oi
northern Europe, especially in Great Britain, Ireland, the Nether-
lands, Germany, and the Scandinavian countries. The cool,
humid climates of these regions are conducive to the production oi
high yields of mangels, turnips, rutabagas, and sugar beets. Fur-
thermore, these root crops are able to absorb a large amount oi
labor. The differences in the agricultural labor situation in Europe
and America have much to do with the relative importance oi
root crops for forage purposes in these two continents.
REFERENCES
1. Baker, O. E., and A. B. Genung, "A graphic summary of farm crops,'
U. S. Dept. Agr. Misc. Pub. 267, 1938.
2. Beattie, J. IL, "Production of carrots," U. S. Dept. Agr. Leaflet 125, 1937
3. , "The culture of table beets," U. S. Dept. Agr. Leaflet 127
1937.
4. Beattie, W. R., "Production of turnips and rutabagas," U. S. Dept
Agr. Leaflet 142, 1937.
5. Bushncll, J., "The relation of temperature to growth and rcspiratior
in the potato plant," Minn. Agr. Exp. Sta. Tech. Bull. 34, 1925.
6. Chung, H. L., "The sweet potato in Hawaii," Hawaii Agr. Exp. Sta
Bull. 50, 1923.
7. Fitch, C. L., "Studies of health in potatoes," Colo. Agr. Exp. Sta. Bull
216, 1915.
8. } anci p.. R. Bennett, "The potato industry of Colorado,'
Colo. Agr. Exp. Sta. Bull. 175, 1910.
9. Fuess, W., "Die Urheimat der Kartoflel, ihrc Finfiihrung und Aus
breitung in Europa," Die Erndhrung der PJlan&, 31:288-293 (1935).
10. , "Die Kartoffel als Gartenpflanze und der Nachweis ihrer
ertmaligen Vorkommens in den Garten in Europa," Die Ernahrun,
der Pflanze, 34:277-281 (1938).
450 ECOLOGICAL CROP GEOGRAPHY
11. Miller, F. E., "Sweetpotato growing," U. S. Dept. Agr. Farmer's Bull.
999, rev. by J. H. Beattie, and H. H. Zimmerley, 1932.
12. Morgan, M. F., J. H. Gourley, and J. K. Ableiter, "The soil require-
ments of economic plants," U. S. Dept. Agr. Yearbook 1938:753-776.
13. Smith, J. R., The World's Food Resources. Holt, New York, 1919.
14. Smith, J. W., "The effect of weather upon the yield of potatoes,"
Mo. Wea. Rev. 43:222-228 (1915).
15. Stevenson, E. J., and C. F. Clark, "Breeding and genetics in potato
improvement," U. S. Dept. Agr. Yearbook 1937:405-444.
16. Strowbridge, J. W., "The origin and distribution of the commercial
potato crop," U. S. Dept. Agr. Tech. Bull. 7, 1939.
17. Stuart, W., "Potato production in the South," U. S. Dept. Agr. Farmer's
Bull. 1205, 1931.
18. , The Potato, Its Culture, Uses, History and Classification. Lip-
pincott, Philadelphia, 1937.
19. Thompson, H. C., Vegetable Crops. McGraw-Hill, New York, 1931.
20. Werner, H. O., "Tuber development in Triumph potatoes as influ-
enced by time of planting on dry land in northwestern Nebraska,"
Nebr. Agr. Exp. Sta. Res. Bull. 61, 1932.
21. Young, R. A., "Cultivation of the true yams in the Gulf Region,"
U. S. Dept. Agr. Bull. 1167, 1923. e
Chapter XXVI
SUGAR
INTRODUCTION
Sugar as a Food. The general use of sugar among the peoples
of the temperate zones is comparatively recent. Nevertheless, the
product rapidly passed from the status of a luxury to a virtual
necessity. Most of this shift in the position of sugar in the diets
of inhabitants of the temperate zone took place within the past
century. In 1821, the people of the United States consumed only
8 pounds of sugar per capita. By 1850, the amount had increased
to 30 pounds, and at present the amount consumed per capita per
annum is above 100 pounds.
According to Brandes et al. (4), "sugar provides about 13 per
cent of all the energy obtained from food consumed by the people
of the United States." It is necessary in this connection to point
out, however, that the per capita consumption of sugar in the
United States is higher than in most other parts of the world. The
extensive use of candies and sweet drinks no doubt contributes to
the importance of sugar in the diet of the American people.
Sugar, while providing none of the nitrogenous or mineral
substances required for the building up of muscle or other body
tissues, is extremely economical as a source of fuel. A pound of
sugar yields 1 ,820 calories of energy. However, sugar is not used
in the diet only as a source of energy. It also imparts an agreeable
flavor to food. The introduction and extensive use of coffee served
greatly to stimulate the world demand for sugar.
By-products of Sugar. Not all sugar products are put on the
market in the purified and crystallized form. Sirup offers one of
these products. The so-called inverted sugar yields a high grade
of molasses. Some of the molasses is used as a food product, some
of it as feed for livestock, and some for the making of alcohol. The
early rum trade played an important part in the colonial history
of the United States. In addition, the sugar industry yields such
451
452 ECOLOGICAL CROP GEOGRAPHY
important by-products as beet tops, beet pulp, and bagasse. The
first two are by-products in the production and manufacture of
beet sugar. They make a valuable feed and have contributed to
the development of livestock industries near beet processing plants.
Bagasse, the ground and crushed stems of sugar cane, with the addi-
tion of small quantities of crude oil, is used to supply fuel to cane
mills. The excess, not required for fuel, is utilized in the manu-
facture of cheap paper, insulating material, wall board, packing
material, etc.
Competition between the Tropical and Temperate Zones.
The agricultural products so far discussed are grown in either one
climatic zone or another. Any competition is only indirect or to
the extent that one product can be substituted for another. How-
ever, as stated by Robertson (12), "the world trade in sugar
presents the interesting feature of bringing into direct competition
agricultural production of tropical and temperate zones, an identi-
cal product being obtained from two widely different plants under
two very diverse sets of geographical conditions." The world trade
in sugar is not unique in this respect. Other noteworthy instances
of such interzonal competition ar£ found in the production of
vegetable oils, starches, and fibers. Nevertheless, the position
of sugar is outstanding in this respect, in that an identical product
is produced, and that political factors have long played an impor-
tant part in fostering its production and distribution. This is well
stated by Robertson: "The production of sugar has been a pecu-
liarly widespread national ambition from the origins of the modern
cane-sugar industry under the old mercantilist colonial systems and
those of the beet sugar industry in the earlier part of the nineteenth
century to the present day, when it is calculated that three-quarters
of the world's output receives some protection or preference." In
other words, the competitive position of sugar is in many areas
fortified by the creation of an artificial social environment.
Table 46 shows the race between the two rival sugars, cane and
beet, during the past 85 years. It is necessary to point out that any
statistical data on sugar production are subject to certain errors.
Not all countries refine their sugar to the same degree of purity.
Thus India produces a low grade of sugar polarizing between 50
and 60 degrees, designated as "gur." Table 46 is compiled from
data presented by Palmer (11), Zimmermann (15), and from the
SUGAR
453
United States Department of Agriculture, Agricultural Statistics,
1940.
Since cane and beet sugar are grown under widely different
conditions, they will be discussed separately.
TABLE 46. WORLD PRODUCTION OF CANE AND BEET SUGAR !
Tear
Cane Sugar ',
in Tons
Beet Sugar,
in Tons
Total , in
Tons
Percentage of Total
Cane
Beet
1841-42 . . .
1,288,000
51,522
1,339,522
96.2
3.8
1850-51 . . .
1,365,905
141,478
1,507,383
90.6
9.4
1855-56 . . .
1,346,240
269,920
1,616,160
83.3
16.7
1860-61 . . .
1,447,040
393,120
1,840,160
78.6
21.4
1865-66 . . .
1,587,040
702,240
2,289,280
69.3
30.7
1870-71 . . .
1,862,560
1,008,000
2,870,560
64.9
35.1
1875 76 . . .
1,780,800
1,504,160
3,284,960
54.2
45.8
1880-81 . . .
2,140,320
1,957,760
4,098,080
52.2
47.8
1885-86 . . .
2,546,016
2,497,570
5,061,586
50.7
49.3
1890-91 . . .
2,989,168
4,139,035
7,128,203
41.9
58.1
1895-96 . . .
3,146,614
4,832,407
7,979,021
39.4
60.6
1900-01 . . .
6,633,544
6,794,972
13,428,516
49.4
50.6
1905-06 . . .
7,538,905
8,081,987
15,620,892
48.3
51.7
1910-11 . . .
9,433,141
9,587,587
19,020,728
49.6
50.4
1915-16 . . .
11,954,387
6,580,176
18,534,563
64.5
35.5
1920-21 . . .
9,367,000
4,685,000
14,052,000
66.7
33.3
1925-26 . . .
13,347,000
8,290,000
21,637,000
61.8
38.2
1930-31 . . .
13,739,000
11,539,000
25,278,000
54.4
45.6
1935-36 . . .
20,919,000
10,687,000
31,606,000
66.2
33.8 «
1939* . . . .
22,067,960
12,668,165
34,736,125
63.5
36.5
* Preliminary.
SUGAR CANE AND CANE SUGAR
Historical. Man, even in the cool regions, has long been aware
of the fact that some plant products, such as fruits and certain
fleshy roots, contain sugar. Another natural sweet product long
known to man was wild honey. As a matter of fact, throughout
many centuries honey provided the chief sweetening to populations
of the temperate zones. In the tropics the value of cane has long
been recognized. Sirups, and possibly a crude form of sugar, have
been produced in India for several thousand years. Sugar cane
spread from India to adjoining countries. According to Taggart
lData from 1841-42 to 1915-16 from T. G. Palmer, Concerning Sugar, Loose Leaf
Service; 1920-21 to 1930-31 from Zimmermann, World Resources and Industries; 1935-
1939 from U. S. Dept. Agr., Agricultural Statistics, 1940.
454 ECOLOGICAL CROP GEOGRAPHY
and Simons (13), it reached China around 766 B.C. The Nestorian
monks at Gondishapur, at the mouth of the Euphrates River, are
the first reported to have produced a white sugar, as early as
600 A.D. According to Zimmermann, "the soldiers of Alexander
the Great became familiar with sugar cane when that great con-
queror pushed eastward as far as India. But it was not until around
one thousand years after Christ that Europe became familiar with
cane sugar through the Arabs, who in turn owed their knowledge
to the Persians and Hindus."
The word "sugar" (su-gur) is of Hindu origin; carie juice in
India today is called "gur."
The Arabs were instrumental in fostering the growing of sugar
cane in the Mediterranean area, especially in Spain and Egypt.
The Crusades during the twelfth and thirteenth centuries served
to spread the fame of cane sugar to western Europe. Venice built
up a considerable trade with sugar and spices. During the four-
teenth and fifteenth centuries, this city state had virtually a monop-
oly of supplying Europe with sugar. This profitable trade came to
an end with the capture of Constantinople by the Turks in 1453,
and the opening of an all-water roate to India around the Cape
by Vasco da Gama, in 1498.
The Portuguese and Spanish navigators carried sugar cane along
their colonizing routes. It was introduced from Sicily and Cyprus
to Madeira in 1420, and soon afterwards to the Canaries, the
Azores, the Cape Verde Islands, and to the Portuguese West
African settlements. Columbus carried both sugar cane and
Canary Island cane growers with him on his second voyage to
Hispaniola, but the growers died and this first shipment of cane
seems to have been lost. A second introduction in 1 506 established
the crop. The first sugar in the western hemisphere was made
in 1510. In 1515 Gonzales de Velosa, generally given credit as the
founder of the sugar industry in the Caribbean area, erected a
horse-driven mill at Rio Nigue, Santo Domingo.
The efforts of the Spanish and Portuguese colonizers contributed
materially toward early sugar production. This resulted in lowering
the price of the commodity and in changing the status of sugar from
a luxury to a general food product. Prior to the increased produc-
tion initiated by them, sugar was used chiefly in the prescriptions
of physicians and in the homes of the wealthy.
•' SUGAR 455
Sugar cane was introduced into Louisiana from Santo Domingo
in 1741. The actual production of sugar did not, however, materi-
alize until 1791, and the first commercial production not until
1794. From then on, the sugar industry grew rapidly. Much of
the acreage formerly devoted to the growing of indigo was taken
over by sugar cane.
This brief discussion of the history of sugar cane would not be
complete without at least some reference to the great technological
advances made during the past century in the cultivation and
processing of the crop. Extensive breeding work on the sugar cane
plant has resulted in the development of varieties resistant to
various fungous, bacterial, and virus diseases. The successful
breeding for resistance against sugar cane mosaic merits special
mention. The significance of this achievement is apparent when
it is recognized that only such resistance makes possible the profit-
able production of sugar cane in many of its present areas of distri-
bution. This is illustrated by the recent trends of cane sugar
production in Louisiana. In 1926 and 1927, Louisiana produced
less than 75,000 tons of raw sugar; with the development and
utilization of disease-resistant varieties, production increased
rapidly, exceeding 400,000 tons of raw sugar in 1937.
Climatic Relationships. Sugar cane is a strictly tropical plant.
In places such as in Louisiana and Argentina the crop is groWn
outside of the tropics, that is, on the climatic margin of the cane
sugar zone. The cane plant usually requires from 12 to 24 months
to reach maturity. Even though the temperature in the Louisiana
cane districts averages 81°F and the frostfree season is over 250
days, the crop is cut in an immature stage. It is, however, left
standing in the field as long as temperature conditions permit so
that as high a sugar content as possible may be built up. In the
tropics the sugar cane plant is a perennial, producing more than
one crop from one planting of seed cane. But, even in the tropics,
the second crop from a planting, known as the stubble or ratoon
crop, yields less than the first. For this reason, and because the
restricted area available results in a pressure for food crops, the
government of Java not only restricts the area devoted to cane but
also prevents the practice of ratooning. In subtropical areas
usually only one sugar crop is harvested from a planting.
Sugar cane requires not only a uniformly high temperature,
456 ECOLOGICAL CROP GEOGRAPHY
but ample sunshine and an abundance of moisture. Cool, cloudy
weather, especially toward the end of the season, greatly interferes
with the deposition of sugar in the plants. A sugar cane producing
area should have from 50 to 65 inches of rain annually. The
importance of an abundant supply of moisture for the crop is
emphasized by Brandes et al. in the statement that around 85 per
cent of the subnormal crops in Louisiana are attributed to drought.
In Hawaii, Java, Taiwan, Egypt, British India, Peru, Mauritius,
and southern Puerto Rico maximum crops are produced by sup-
plementary irrigation. According to Brandes et al., "the more
nearly the weather approaches humid tropical conditions, such as
heavy precipitation followed almost immediately by bright sun-
shine rather than a succession of overcast, cool days with drizzling
rain, the better will be its effect on the rapidly growing crop."
Sugar cane production extends from the Af, Cf to the Cw or from
the BA'w, CA'r to the BB'r and BB'w climates.
In certain sugar cane producing areas, such as Taiwan, the
West Indies, Louisiana, Mauritius, and Reunion, hurricanes or
typhoons constitute a hazard to the crop, the plantations, and the
sugar factories. •
Soil Relationships. Sugar cane will grow on a variety of soils.
Either natural high fertility or rapidly available nitrogen and an
abundant supply of available nutrients supplied by commercial
fertilizers are essential for maximum yields. Good cane soils have
the ability to retain moisture, are deep and friable, and must have
good drainage. "Sugar cane is tolerant of moderately acid to
moderately alkaline conditions" (Morgan et al., 7).
World Distribution. Table 47 gives the production of raw cane
sugar by important producing countries and the percentage of the
world total cane and all sugar produced in each country. The
distribution of cane sugar production for the eastern and the
western hemispheres is shown cartographically in Figs. 88 and 89.
The statistical and cartographical data presented show that the
production of cane sugar is widely distributed in the tropical and
subtropical regions; as a matter of fact, so much so that attempts
to group the various producing areas are of little value.
A word is in order with reference to the high production of cane
sugar recorded for India. Almost the entire production is in the
form of gur, solidified cane juice, without much purification.
SUGAR
457
Religious scruples of a large part of the native population dictate
against the use of purified sugar. The fact that the sugar is not
purified creates a bias in the tabulated data presented in Table 47,
which serves to overemphasize the importance of India as a sugar
producing country. Even with its high production, India does not
supply enough sugar to satisfy the needs of its vast population. The
unprogressive methods employed in production result in low yields.
Java is the main source of white sugar for India.
TABLE 47. PRODUCTION OF RAW CANE SUGAR IN SPECIFIED COUNTRIES TO-
GETHER WITH PERCENTAGE OF TOTAL WORLD CANE AND ALL SUGAR PRO-
DUCTION — CANE AND BEET SUGAR. AVERAGES FOR THE FIVE-YEAR PERIOD
1930-31 TO 1934-35
Rank
Country
Cane Sugar
All Sugar
Production,
in 1,000 Tons
Percentage of
World Total
Production
Percentage of
World Total
Production
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
India * . . ...
4,909
2,803
1,731
1,170
1,134
991
893
886
667
441
439
384
331
241
240
236
236
1,491
25.54
14.58
9.00
6.09
5.90
5.16
4.65
4.61
3.47
2.29
2.28
2.00
1.72
1.25
1.25
1.23
1.23
7.75
16.81
9.60
5.93
4.01
3.88
3.39
3.06
3.03
2.30
1.51
1.50
1.31
1.13
0.83
0.82
5.59
0.81
5.51
Cuba
[ava
Philippine Islands
Brazil
Hawaii
Puerto Rico
Taiwan
Australia **
Peru
Dominican Republic ....
Argentina
British West Indies ....
China
Mexico
United States ** ....
Union of South Africa . . .
All others
World total cane sugar . . .
World total beet sugar . . .
World total sugar production .
19,223
9,979
100.00
—
29,202
* The figures for India are for the production of gur, a low grade sugar polarizing
between 50 and 60 degrees.
** Produce both cane and beet sugar.
Cuba is the world's leading producer and exporter of refined
sugar. According to Robertson, this important island accounted
for 18 per cent of the world's production of sugar in the period of
•a
.&
I
< £
Is
O
-o
2 w
a
!a >n
F
•°
458
SUGAR
459
1925-26 to 1929-30, and in 1925-1929 for 34 per cent of the
world export of the commodity. The figure of 2.8 million tons
for the period covered by the data presented in Table 47, 1930-31
FIG. 89. Distribution of cane and beet sugar production in the western hemi-
sphere. Averages for the five-year period of 1930-31 to 1934-35. Each dot
represents 50,000 tons of raw sugar.
to 1934-35, does not do full justice to the sugar producing poten-
tialities of Cuba. Prior to the break in world sugar prices, Cuba
produced 4.1 million tons of sugar in 1918-19, 5.2 million in the
season of 1924-25, and again the same high amount in 1928-29.
The average annual production for the five-year period, 1925-
460 ECOLOGICAL CROP GEOGRAPHY
26 to 1929-30, amounted to 4.7 million tons. The great increase
in Cuban sugar production since the turn of the century was due
not only to favorable climatic and soil conditions but to no small
degree to its proximity to the large and expanding markets of the
United States and preferences extended to Cuban sugar producers
by this country. As stated by Robertson,
"in the period 1909-1910 to 1913-1914, the United States took
92 per cent of the island's total export of raw sugar. Under the reci-
procity treaty of 1902 Cuba received a 20 per cent preference in the
United States, most of which in the earlier years was actually obtained
by the Cuban producers, with a consequence that North American
capital flowed into the island, modernizing the mills and transport
system and permitting economies of large-scale production to an
unprecedented degree."
As an exporter of sugar, Java has attained a position second only
to that of Cuba. Java produced an average of 2.5 million tons of
sugar for the period of 1925-26 to 1929-30. Dutch colonial policies
and the scientific cane-breeding work fostered by the Dutch are
responsible for much of the relative importance of Java as a sugar
producing territory. Production of%cane in Java is an intensive
enterprise; 90 per cent of the area devoted to the crop is irrigated,
and large amounts of commercial fertilizers are used. Such methods
and the managerial abilities of the Dutch account for the signifi-
cantly higher yields than those secured in Cuba. Most of the
Javanese sugar is marketed in British India and in the Far East.
"Unlike Cuba, Java," states Robertson, "receives no preferential
treatment but relies on a skillful sales policy." The country is
favored by low labor costs. This, together with favorable climatic
conditions and high unit yields, brings the costs of production to
the lowest in existence.
Louisiana and Florida and the insular possessions of the United
States, Philippine Islands, Hawaii, and Puerto Rico, owe their
rise and continued great importance as sugar producing areas to
tariff policies and free access to the United States markets.
Expansion of the industry in the Philippines has been due more to
modernization of the milling side and improvements of agricultural
methods of small farmers rather than to increases in acreage. Ac-
cording to Robertson, "soil and climatic advantages are offset
by scarcity of labor and capital."
SUGAR 461
Hawaii has favorable soil and temperature conditions and the
advantages of highly developed research. On the other side of
the ledger, it is confronted with heavy expenditures for irrigation
and fertilizer, and it lacks abundant cheap labor. Much the
same conditions prevail in Puerto Rico.
Sugar production in Brazil was, quoting Robertson, "stimulated
by the high prices of the years during and immediately after the
war but is now faced with the problem of disposing of a surplus
produced at relatively high cost. Backward methods, labor diffi-
culties, capital shortage, and inadequate transport facilities together
militate against the sound utilization of much otherwise potentially
suitable sugar-cane land."
Some of the important phases of cane sugar production in the
British Empire, excluding India, are summarized by Robertson
in the following paragraph.
"Australia, despite its extremely high cost of production on account
of the compulsory employment of white labor, shows the most rapid
increase, thanks to the embargo on sugar imports that gives a monopoly
of the Australian market to the home producer. The rise in production
in Natal, too, where also conditions are marginal, is due to heavy pro-
tection in the domestic market. Both countries market their surplus
in Great Britain, where the preference on Empire raw sugars reduces
the loss on their exports. In the British West Indies, which had already
some preference in Canada, the Imperial preference has to some extent
maintained and even stimulated output in recent years. In Mauritius
and Fiji, conditions of production are more favorable; but both areas
are approaching the limits of their potential output, and production
in recent years has, with the assistance of the Imperial preference,
remained fairly steady."
A feature of considerable importance to the world sugar situation
and of particular import to the Far East has been the rapid and
forced growth in sugar production in Taiwan (Formosa). The
production of the crop was definitely stimulated by Japan to supply
its needs for sugar from within its own territories, thus offering
another example of the effects of intense nationalism on world crop
distribution.
Sugar Cane Production in the United States. Sugar cane in
the United States is grown for the production of sugar and table
sirup.
Temperature limitations confine the use of the crop for the
462
ECOLOGICAL CROP GEOGRAPHY
making of sugar to the very southern parts. The most extensive
sugar producing area is found in southern Louisiana. Southern
Florida is of secondary importance. Southeastern Texas produces
but a limited amount of cane sugar. In 1936, Louisiana harvested
227,000 acres of cane, from which 444,000 tons of raw sugar were
produced. The corresponding data for Florida were 17,000 acres
and 51,000 tons of raw sugar. In recent years the production of
sugar cane and cane sugar has shown rapid increases in the Ever-
glades of southern Florida. According to data presented by the
SUGAR AND SIRUP CROPS
UNITED STATES TOTAL
SU6AR SECTS M4.000 ACRES
SUCAICANC ZSt.000 ACRES
SOR60 FOR SIRUP IU.OOO ACRES
FIG. 90. The distribution of sugar and sirup crops, sugar cane, sorgo, and sugar
beets in the United States. Each dot represents 1,000 acres. (After Baker and
Genung.)
United States Sugar Corporation (2), production in this area
increased from 745 tons of raw sugar in 1928-29 to 85,663 tons for
the season of 1938-39.
Since the noncrystallizable sugars present in immature cane
are desirable in sirup, the growing of sugar cane for the production
of sirup is less restricted by temperature conditions. Cane is grown
for the production of sirup in eastern Texas, most of Louisiana, and
across to the eastern half of South Carolina. This is shown in
Fig. 90, giving the distribution of sugar and sirup crops in the
United States (Baker and Genung, 3).
SUGAR 463
The production of sugar cane (Saccharum officinarum) should not
be confused with the growing of the so-called Japanese or Zwinga
sugar cane (S. sinense), which is strictly a forage crop.
THE SUGAR BEET AND BEET SUGAR
Historical. The history of the development of the sugar beet to
its present high efficiency as a producer of sugar represents one
of the glowing achievements of the plant breeder. Most of the real
improvement of the crop has taken place during the past century.
The German chemist, Margraff, succeeded as early as 1747 in
separating sugar crystals from a number of plants. The white
beet yielded the largest quantity of extracted sugar. Margraff,
however, failed in his attempts to devise a method whereby extrac-
tions could be made on a large scale. This task remained for one
of his students, Carl Franz Archard, who established the com-
mercial importance of his master's discovery. With the aid of the
Prussian government, the first beet sugar factory was built at
Cunern, in Lower Silesia, in 1802. Archard was able to produce
only a few hundred pounds of sugar daily. In view of the fact that
the beets he had to work with contained only from 3 to 4 per cent
of sugar, his accomplishments were quite outstanding. Archard's
factory attracted the attention of Napoleon, who sent a body of
scientists to inspect it. Two factories were erected in France on
the strength of their report. The costs of production were high
on account of the low quality of the beets available for processing
and the low efficiency of the factories.
An index of the improvement of the sugar beet is provided by a
record of the sugar extractions in Germany since the middle of
the last century, cited from Bowling (5). By ten-year periods from
1850-1859 to 1900-1909 the extraction percentages were 7.8,
8.1, 8.6, 11.3, 13.3, 15.6. The sugar production per acre during
this same period increased from 1,636 to 4,048 pounds. Much of
the credit for the early improvement of the sugar beet must be
given to the Frenchman, P. Louis Leveque de Vilmorin.
Beet sugar production owes much of its development and main-
tenance to tariffs and subsidies. Archard's original factory was
built with aid from the Prussian government. Likewise, early
production in France was subsidized. The Berlin decree issued
by Napoleon in 1806 was aimed to keep British goods, among which
464 ECOLOGICAL CROP GEOGRAPHY
cane sugar was an important item, out of continental Europe.
This gave a great impetus to sugar beet production. Then in 1811
Napoleon gave his now famous command to stimulate the produc-
tion of sugar beets and proceeded to subsidize the industry, thus
initiating a policy that has been followed since in most of the beet
producing countries of the world to protect beet sugar from the
cheaper cane sugar.
The political events of France in 1814 led to the withdrawal
of the legislation designed to encourage beet sugar production;
as a result, all but one of the several hundred small beet sugar
factories of the country failed. The continuous support given
to the beet sugar industry in Germany accounts to a large degree
for the importance of this country as a world producer of sugar.
The first sugar beet factory in the United States was erected at
Alvarado, California, in 1870. In 1888, only two factories were
in existence; in 1892, 16; in 1908, 62; in 1915, 67; and in 1924-25,
90 factories were operating.
The relative dependence of the American and European beet
sugar industry on governmental protection is briefly discussed by
Robertson. f %
"United States beet sugar production is much more dependent on
this protection than is European production since it does not have the
peculiar complex of labor conditions and the strong position in the
crop rotation or, in several districts, the association with the livestock
industry that give to the crop in Europe a certain independent power
of resistance to adverse conditions. Given protection, further expansion
is not, however, hindered by any lack of suitable soil areas."
The production of sugar beets and the beet sugar industry in
general have the capacity to absorb a large amount of labor.
Climatic Relationships. A discussion of the climatic require-
ments of the sugar beet amounts to practically a restatement of
the temperature, moisture, and light demands of the potato. The
two crops are grown in the same general areas.
The sugar beet demands a temperate climate, with the mean
temperature during the summer months not far from 70°F. Lill (6)
points out that all the beet factories of the north-central states are
located between the isotherms of 67 and 72°F mean summer
temperature (May to September, inclusive). A uniform availability
of moisture, supplied by either natural precipitation or irrigation,
SUGAR 465
is essential to maximum yields and high quality. Unless temper-
ature and moisture conditions are favorable, it is difficult to produce
beets of a quality for economic processing. Under adverse climatic
conditions the percentage of impurities in the roots increases
materially. The presence of such impurities, and especially salts,
increases the costs of processing as they interfere with the recovery
of sucrose. Beets suitable for processing should have a sugar
content in excess of 12 per cent and a coefficient of purity of 80 per
cent or more.
Long days and an abundance of sunlight are necessary for the
production of a high sugar content. Chemical tests by Tottingham
et al. (14) substantiate the practical observation that bright, autumn
days followed by relatively cool nights are favorable to the storage
of high percentages of sugar in the root of the sugar beet. This is
the condition met with in continental areas and no doubt contrib-
utes to the quality of the beets grown in such areas, especially
if the moisture conditions can be controlled by means of irrigation.
A fairly long growing season is desirable. The best beet produc-
ing areas have a growing season of around 150 days or longer.
Conditions during the growing season favoring a rapid and con-
tinuous growth are highly desirable and indeed essential to the
production of beets of the highest quality. The fall months should
be sufficiently dry to check the vegetative growth to some extent,
but not so dry as to stop it altogether. The producer in irrigated
areas has the advantage over those in areas dependent on natural
precipitation in that he can control the moisture supply in his
fields and thus to a greater extent influence the yield and quality
of the crop.
Soil Relationships. The sugar beet is grown on a variety of
soils, yet the plant is quite specific in its soil requirements. Soil
conditions influence both the yield and the quality of the crop.
Thus, while the heavier soils usually produce the higher yields
of beets, the quality of the crop produced on lighter soils is gen-
erally superior. Good yields can be obtained on certain organic
soils, but again the sugar content of the roots produced on such
soils is likely to be fairly low.
For best results with the crop the soil should be deep, friable,
free working, and well drained. In addition the water-holding
capacity should be high. It is difficult to establish full stands on
466 ECOLOGICAL CROP GEOGRAPHY
soils that are inclined to puddle. A high organic matter content,
since it influences the tilth of the seedbed, is desirable. The fertility
level of good beet soils should be comparatively high; furthermore,
the best sugar beet soils have relatively high lime contents. While
the crop is fairly tolerant with respect to soil reaction, field observa-
tions indicate that it is easier to establish and maintain full stands
of beets on soils that are either neutral or slightly alkaline in reac-
tion. According to Adams (1), sugar beets will tolerate more alkali
than most field crops; however, lands heavily charged with sodium
salts will not produce the best crops. Sodium sulphate is less
injurious than sodium chloride or sodium carbonate.
The tonnage obtained is not determined by soil type alone.
Generally, the crop does best on the heavier types of soils, such
as loams, silt loams, clay loams, and with a proper organic matter
content on clays; however, satisfactory yields can be obtained upon
sandy loams and with favorable moisture conditions even on fairly
light-textured sandy soils.
Sugar beets provide an excellent cultivated crop in the rotation,
leaving the soil in good condition for the crops to follow in the
sequence.
World Distribution. Like the potato, the sugar beet is essen-
tially a European crop; around 85 per cent of the world's produc-
tion is found on that continent. The reasons for this are not only
climatic; economic, social, and political factors play an important
part in determining the location and continuance of sugar beet
producing areas. Soil conditions exert but a minor influence in
limiting production.
Table 48 gives the statistical data on world beet sugar produc-
tion, while Figs. 88 and 89 give the geographical locations of the
producing areas in the eastern and western hemispheres.
The European beet sugar producing belt extends across the
great plains of northwestern Europe from northeastern France
through Belgium, the Netherlands, Germany, and Poland to the
Ukraine. Significant points of concentration are found in north-
eastern France and the Low Countries; in the basin of the upper
Elbe, the Magdeburg and Quedlinburg area; lower Silesia;
Moravia and Czechoslovakia; and in the Russian Ukraine. A
minor concentration area is found in the valley of the Po River in
northern Italy.
SUGAR
467
TABLE 48. PRODUCTION OF SUGAR BEETS, AND RAW BEET SUGAR IN SPECIFIED
COUNTRIES, TOGETHER WITH PERCENTAGE OF TOTAL WORLD BEET AND ALL
AVERAGES FOR THE FIVE-YEAR PERIOD 1930-31 TO
1934-35
SUGAR PRODUCTION.
Rank
Country
Sugar Beets
Beet Sugar
All
Sugar.
Cane and
Beet
Acre-
age, in
1,000
Acres
Yield
per
Acre, in
Tons
Pro-
duction,
in 1,000
Tons
Raw
Sugar,
in 1,000
Tons
Percent-
age of
Total
World
Produc-
tion
Percent-
age of
Total
World
Produc-
tion
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Germany
1,418
801
3,144
666
327
341
238
133
111
106
223
95
128
81
96
42
118
12.7
11.2
3.7
12.9
9.6
10.4
11.9
13.7
17.0
15.3
7.9
14.1
9.8
7.6
7.3
10.5
8.2
18,014
8,944
11,680
8,607
3,147
3,545
2,825
1,824
1,886
1,620
1,772
1,336
1,134
614
700
439
962
2,856
1,396
1,371
1,112
546
535
397
274
262
252
216
174
158
112
90
66
162
28.62
13.99
13.74
11.14
5.47
5.36
3.98
2.75
2.63
2.53
2.16
1.74
1.58
1.12
0.90
0.66
1.63
9.78
5.59
4.69
3.81
1.87
1.83
1.36
0.94
0.90
0.86
0.80
0.60
0.54
0.38
0.31
0.23
0.55
United States * ....
U.S.S.R
France
Poland
Great Britain and Ireland
Italy
Belgium
Netherlands
Sweden
Spain *
Denmark
Hungary
Rumania ....
Yugoslavia ....
Ganada ....
All others
World total
8,068
on — bc<
8.5
[?t and ca
68,939
nc suear
9,979
100.00
World total sucrar uroducti
29.202
* Produce both cane and beet sugar.
The beet producing area extends from the humid marine climates
of the northeastern coast of France to the continental climates oi
the Russian plains, that is, from the Cfb to the Dfb and the CC'i
to the CB'd climates. In the west the amount of moisture is mon
than sufficient for the needs of the crop; as a matter of fact, cool
cloudy weather during the autumn months reduces sugar yields
In the central area conditions become drier, and light relationship
more favorable. In this area are also found certain islands o
Chernozem soils which are well adapted to beet culture. Th<
Russian areas suffer from lack of precipitation during the summe]
468 ECOLOGICAL CROP GEOGRAPHY
months. Favorable soil conditions counteract in part the dearth
of moisture, but, as is evident from Table 48, the yields obtained
are low. The low average yield of 3.7 tons of beets per acre for
the five-year period covered in Table 48, 1930-31 to 1934-35, is
no doubt below normal; nevertheless, while the preceding five-
year period showed a somewhat higher average yield, it was still
at the comparatively low level of 5.6 tons per acre. The combina-
tion of lack of sufficient moisture and higher than optimum summer
temperatures in the Russian beet producing areas is also in evidence
in the lower yield of raw sugar obtained per ton of beets worked
as compared with areas with more favorable moisture and temper-
ature conditions. Thus, per ton of beets worked, Poland obtains
350 pounds of raw sugar, Germany 335, and the United States
323 pounds. The yield in Russia is only 268 pounds per ton. The
yield of raw sugar per ton of beets worked is also somewhat lower
in areas with a marine type of climate than in those favored with
a continental type. The reason for this has already been indicated.
Distribution in the United States. Table 49 gives the statistical
data relating to the distribution of sugar beets and beet sugar
production in the United States. Fi^iyre 90 gives the geographical
distribution of the acreage.
In 1938, 23.19 per cent of the nation's sugar requirements
originated from United States grown beets, as contrasted to 6.29
per cent from Louisiana and Florida cane. The balance was
contributed by Cuba and the insular possessions of the United
States to the extent of 28.60 per cent from Cuba, 15.41 per cent
from the Philippine Islands, 14.04 per cent from Hawaii, 11.94 per
cent from Puerto Rico, and to complete the circle 0.53 per cent
from other sources.
The beet producing areas of the United States may be divided
into three fairly distinct groups; the humid area of the North
Central states, the Mountain States area, and the Pacific Coast area.
Only around 1 5 per cent of the country's beet sugar production
is found in the humid areas of the North Central states. The two
most important centers of production are the Saginaw district
in eastern Michigan and the Toledo district in northwestern Ohio.
Other centers of lesser importance are found around Green Bay,
Wisconsin; Mason City, Iowa; Chaska, Minnesota; East Grand
Forks in the Red River Valley; and Grand Island, Nebraska.
SUGAR
469
TABLE 49. SUGAR BEETS AND BEET SUGAR: ACREAGE HARVESTED, YIELD
PER ACRE, AND PRODUCTION AVERAGES FOR THE TEN-YEAR PERIOD 1928-
1937. ACREAGE AND PRODUCTION ARE EXPRESSED IN THOUSANDS
Rank
State
Sugar Beets
Beet Sugar
Acreage
Yield per
Acre, in
Short Tons
Produc-
tion, in
Short Tons
Produc-
tion, in
Short Tons
Percentage
of U. S.
Total
1
2
3
4
5
6
7
8
9
Colorado ....
California ....
Nebraska ....
Michigan ....
Montana ....
Utah
186
96
72
94
53
47
45
47
31
92
12.3
13.0
12.4
7.7
11.6
12.2
11.8
10.9
8.4
8.7
2,287
1,268
888
736
627
584
530
517
248
798
339
208
118
107
89
86
85
79
29
98
27.38
16.80
9.53
8.64
7.19
6.95
6.87
6.38
2.34
7.92
Wyoming ....
Idaho
Ohio
Other states . . .
Total U. S. . . .
763
11.1
8,483
1,238
100.00
The continuity of the beet belt is broken by the dry, unirrigated
section of the Great Plains. But the crop assumes a place of real
importance in the irrigated lands of the mountain states and the
adjoining irrigated sections in the western Great Plains area.
Colorado continues to be the leading state. The Utah-Idaho area
is of considerable importance. Figure 90 shows the scattered areas
in Wyoming and Montana.
Most of the production in the Pacific Coast area is localized in
California, only one factory being located at Bellingham in north-
western Washington. Practically the entire area in California is
under irrigation.
The Production of Sugar Beet Seed. Prior to the first World
War practically all the sugar beet seed used in the United States
was imported from Europe. Even for the five-year period ending
with 1929 the annual imports of sugar beet seed from Europe
averaged 12,500,000 pounds. European breeders were responsible
for bringing the sugar beet up to a high standard of quality. Fur-
thermore, under the conventional European practice of producing
seed a great amount of hand labor was required. Under the labor
conditions existing in the United States it was difficult to compete
with European seed producers.
470 ECOLOGICAL CROP GEOGRAPHY
In 1928, Overpeck (8), working in New Mexico, showed that by
taking advantage of the mild winters of the Southwest, late-
summer- or early-fall-planted beets could be overwintered in the
field, and satisfactory seed crops could be produced from such
field plantings during the following season. This method eliminated
the labor of lifting the stecklings in autumn, storing them over
winter, and replanting them in spring.
Another important feature of growing seed in this country
rather than importing it is that it facilitates the production of
disease-resistant strains. Curly-top, a serious virus disease of the
sugar beet in the United States, according to Overpeck and Elcock
(9) does not occur in Europe. Consequently, no progress has yet
been made by European seed breeders to breed resistant types.
Several resistant strains are now being extensively grown in this
country; as a matter of fact, in many of our western beet producing
areas profitable beet production would be impossible were it not
for the availability of these curly-top-resistant strains.
According to Overpeck et al. (10), it is estimated that the 1936
beet seed crop of the United States was adequate to plant from
30 to 40 per cent of the 1937 commefcjial beet acreage. The leading
seed producing states in 1937 were Arizona, 53,478; California,
29,654; New Mexico, 19,219; and Utah, 11,602 bags of 100 pounds
each. Favorable moisture conditions or irrigation are essential
to getting the seedlings established in late summer.
REFERENCES
1. Adams, R. L., "The sugar beet in California," Calif. Agr. Exp. Sta.
Circ. 302, 1926.
2. Anonymous, Sugar in the Everglades. United States Sugar Corporation,
Clewiston, Florida, 1939.
3. Baker, O. E., and A. B. Genung, "A graphical summary of farm
crops," U. S. Dept. Agr. Misc. Pub. 267, 1938.
4. Brandes, E. W., C. O. Townsend, P. A. Yoder, S. F. Sherwood,
G. B. Washburn, L. Arner, O. E. Baker, F. C. Stevens, F. H. Chitten-
den, and C. F. Langworthy, "Sugar," U. S. Dept. Agr. Yearbook 1923:
151-228.
5. Bowling, R. N., Sugar Beet and Beet Sugar. Ernest Benn, Ltd., London,
1928.
SUGAR 471
6. Lill, J. G., "Sugar-beet culture in the humid areas of the United
States," U. S. Dept. Agr. Farmers Bull. 1637, 1930.
7. Morgan, M. F., J. H. Gourley, and J. K. Ableiter, "The soil require-
ments of economic plants," U. S. Dept. Agr. Yearbook 1938:753-776.
8. Overpeck, J. C., "Seed production from sugar beets overwintered in
the field," U. S. Dept. Agr. Circ. 20, 1928.
9. , and H. A. Elcock, "Methods of seed production from sugar
beets overwintered in the field," U. S. Dept. Agr. Circ. 153, 1931.
10. , , W. H. Morrow, and R. Stroud, "Sugar beet seed
production studies in southern New Mexico," JV. M. Agr. Exp. Sta.
Bull. 252, 1937.
1 1 . Palmer, T. G., Concerning Sugar; Loose Leaf Service. Bureau of Statistics,
U. S. Sugar Manufacturers Association, C 1-c, Washington, 1920.
12. Robertson, C. J., "Geographical trends in sugar production," Geog.
Rev. 22:120-130 (1932).
13. Taggart, W. G., and E. C. Simons, "A brief discussion of the history of
sugar cane," La. State Dept. Agr. and Immig., 1939.
14. Tottingham, W. E., S. Lepkovsky, E. R. Schulz, and K. P. Link,
"Climatic effects in the metabolism of the sugar beet," Jour. Agr. Res.,
31:59-76 (1926).
15. Zimmermann, E. W., World Resources and Industries. Harper, New
York, 1933.
Chapter XXVII
OIL PRODUCING CROPS
INTRODUCTION
Oils and Fats. The distinction between oils and fats is a physical
one, the oils being liquid and the fats solid. The concept is also
relative. The materials appear either as liquids or solids, depending
on whether the temperature to which they are exposed is above or
below their melting points. Thus, coconut oil is liquid in the tropics
but solidifies into a fat at average temperate zone temperatures.
Kinds of Oils. The term "oil" covers very different kinds of
substances. They may, however, be roughly classified into three
groups: mineral oils, essential or volatile oils, and fatty oils. The
first, while of tremendous commercial importance, will not be dis-
cussed. The essential oils are of co&siderable interest to the agron-
omist, but owing to the special uses for which they are employed
they are of less importance than the fatty oils with their great variety
of uses for food and industrial purposes.
The Essential Oils. Two types of oils are derived from plants,
namely, the essential and the fatty oils. The essential oils are dis-
tinguished from the fatty oils by the fact that they evaporate or
volatilize in contact with the air and give off an aromatic odor, or
possess a pleasant taste. All distinctly aromatic plants owe their
odor to the presence of these oils. Important essential oils are tur-
pentine, camphor, peppermint, menthol, thymol, and such per-
fume oils as attar of roses, ylang-ylang, neroli, bergamot, and orris.
In addition, there are certain grass oils like oil of citronella, lemon-
grass oil, palmarosa, and oil of vetiver.
The perfume oils are of special importance in the group of es-
sential oils. These oils arc extracted from the flowers, leaves, or
woods of many different species of plants in various ways depending
on the quality and stability of the compounds. The usual method
is by steam distillation. The origin of the important perfume oils
is discussed by Hill (5) in the following paragraph.
472
OIL PRODUCING CROPS 473
"Most of the natural perfumes are made in southern France, the
industry centering around Grasse and Cannes in the French Riviera.
In this area garden flowers are cultivated on a large scale, and from
10,000,000 to 12,000,000 pounds of flowers are gathered annually.
These include 5,500,000 pounds of orange blossoms, 4,400,000 pounds
of roses, 440,000 pounds of jasmine, and 330,000 pounds of violets.
Large quantities of cassia, tuberoses, jonquils, thyme, lavender, and
geraniums are grown, and many other fragrant species, to a lesser
degree. Flowers are also grown for the perfume industry to some
extent in England, Reunion, North Africa, and various European and
Asiatic countries."
The use of the essential oils is by no means limited to the perfume
industry; they have varied applications. Turpentine is used ex-
tensively in the paint and varnish industries. Many are used as
flavoring materials or essences in candy, ice cream, soft drinks,
liquors, tobacco, etc. Others have certain therapeutic, antiseptic, or
bactericidal properties which make them valuable in medicine
and dentistry. Still others are used as deodorants in a variety of
products, as in soaps, glues, shoe polish, and printer's ink.
With the exception of three products, the United States is not an
important producer of essential oils. One of these products, tur-
pentine, is a forest product. The turpentine industry, yielding
both the essential oil, or spirit of turpentine, and rosin, is closely
identified with the economic development of the South. The othei
essential oils of considerable importance in the United States an
peppermint and spearmint oils. These mints are classified as fielc
crops. As stated by Sievers (13), this country is the principal pro-
ducer of these oils.
"England, Germany, France, and Italy produce relatively small
quantities. Japan has under cultivation a vast acreage of a different
species of mint which yields an oil of different quality, used largely as
a source of natural menthol, of which it contains a high percentage.
Accurate statistics on the world's production of mint oils are not avail-
able. In this country the production averages about half a million
pounds. In 1926 and 1927 the production of peppermint oil reached
approximately 700,000 pounds, but in the two years immediately pre-
ceding the crop was considerably below the average. The production
of spearmint oil averages about 50,000 pounds."
Peppermint oils are produced from the species Mentha piperita,
spearmint from M. viridis, while M . arvensis var. piperascens is exten-
sively cultivated in Japan as a source of menthol.
474 ECOLOGICAL CROP GEOGRAPHY
Mint production in the United States is centered largely on the
fertile muck lands in southern Michigan and northern Indiana.
Around 40,000 acres are devoted to the crop in this area. Other
producing centers of less importance are found on the reclaimed
muck lands in the Willamette Valley of Oregon and along the
Columbia River in Oregon and Washington to the extent of about
2,000 acres. The crop is also produced to a limited extent in south-
western Oregon, in the Yakima Valley of southern Washington,
on the San Joaquin River lands in Tulare and King counties in
California, and on the reclaimed muck lands in the Dismal Swamps
section of eastern North Carolina.
The Fatty Oils. A great variety of plants produce fatty oils.
These oils, while of less value from the aesthetic standpoint than
the essential oils, are more stable and are of far greater value as
food products and for industrial uses than the essential oils. For
that reason, the term "oil" as it will be used in the remainder
of this chapter will refer to the fatty oils.
So great is the variety of species of plants producing vegetable
oils that even their enumeration is beyond the scope of this chapter.
The reader interested in the greatfnumber of oil producing plants
and in the more or less specific properties of each oil is referred to
Jamieson's comprehensive book, Vegetable Fats and Oils (6). Table
50 gives in tabular form a list of the more important oils and their
origin and outstanding properties. It will be observed that the oils
are presented in two groups, those coming from trees and those from
annual plants. They may also be classified as originating in the
tropics, subtropics, or the temperate zone. Furthermore, certain
plants, such as flax and castor beans, are grown primarily for the
oil they produce. In others, such as cotton, the oil is a by-product.
Again, other crops, for instance, soybeans and peanuts, may be
grown for forage, for human consumption or as oil producing crops.
A tabulation of the consumption of fats and oils in the United
States in 1938, including both vegetable and animal fats and oils,
gives an idea of the great variety of products utilized. These prod-
ucts as listed by the Bureau of Agricultural Economics together
with the percentage consumption of each are: butter, 24; cotton-
seed, 18; lard, 16; tallow, grease, and other inedible animal fats, 12;
coconut, 6; palm kernel and babussa, 1; linseed, 5; tung, perilla,
and viticica, 1; corn, peanut, and soybean, 6; palm, olive, rape,
TABLE 50. ORIGIN AND PROPERTIES OF SOME IMPORTANT VEGETABLE OILS
Oil
Source
Properties and Uses
I. TREES — PERENNIALS
Coconut
Palm
Palm kernel
Olive
Chinawood and
Tung
Oiticica
II. ANNUALS
Cottonseed
Corn
Soybean
Unseed
Peanut
Perilla
Safflower
Castor
Dried meat of coconut palm
(Cocus nucifera)
Fibrous pulp of the oil palm
(Elaesis guineensis)
Kernels of the oil palm
(E. guineensis)
Fruit of the olive
(OUa ewopaea)
Nuts of two species of Aleu-
rites (A. montana and A.
Fordit)
Seeds of Covepia grandijhra
Seeds of the cotton plant
Embryo of maize kernels
Seeds of soybean
Seeds of flax
Seeds of peanut
Seeds of Perilla frutescens
Seeds of safflower
(Carthamnus tinctorius)
Seeds of Ricinus communis
A pale yellow or colorless oil, solid be-
low 74°F, excellent for food purposes.
A white to yellowish vegetable fat,
edible when fresh, used chiefly in
the soap and candy industries.
A white oil used in the margarine in-
dustry; pleasant odor and nutty
flavor.
Good grades edible, oil golden yellow,
clear, limpid, and odorless; inferior
grades, greenish tinge, used for
soap and lubricants.
Quick-drying oil, extensively used in
the varnish industry; forms a hard
film.
Quick-drying oil, extensively used as
a substitute for tung oil.
Edible after removal of gossypol.
Used as salad, table oil, and in the
manufacture of oleomargarine and
lard substitutes. Lower grades,
various industrial uses.
Clear yellow oil, used in cooking and
baking. Crude oil has many in-
dustrial uses.
A drying oil, edible after refining;
inferior grades used in manufacture
of candles, paints, soap, printing ink.
A drying oil, yellow to brownish in
color, acrid taste and smell; used in
the making of paints, varnishes,
linoleum, and printer's ink.
A nondrying oil, characteristic odor
and taste, edible.
Edible, but used mostly in the manu-
facture of cheap lacquer, Japanese
oil paper, waterproof clothes, arti-
ficial leather, and printer's ink.
A drying oil used in the manufacture
of paints, varnishes, and linoleum.
A nondrying oil, used chiefly as a
purgative in medicine; retains a
high viscosity at high temperatures
and is, therefore, used as a lubricant
in airplane engines.
475
476
ECOLOGICAL CROP GEOGRAPHY
TABLE 50 (Continued).
Oil
Source
Properties and Uses
II. ANNUALS (Continued)
Sesame
Hempseed
Poppy
Rape (Colza)
Seeds of Sesamum indicum
Seed of hemp plant (Canna-
bis saliva)
Seed of opium poppy
(Papaver somniferum)
Seeds of species of Brassica,
particularly B. campestris,
B. naptiSy and B. rapa.
Better grades used as substitute for
olive oil in cooking and medicine
and in Europe, in making mar-
garine and other food products;
poorer grades used for soap, per-
fumery, and rubber substitutes.
Used for edible purposes in some
Asiatic countries, elsewhere chiefly
as a paint oil and for making of soft
soap; semidrying, greenish in color.
Drying oil, pale to golden yellow when
obtained from cold-pressed sound
seed; used chiefly for edible pur-
poses and to some extent in artist's
paints.
Semidrying oil from yellow to dark
brown in color; refined oil edible,
crude oil used in lamps, as a lubri-
cant, in manufacture of soap and
rubber substitutes.
sesame, teaseed, and others, 5; fish, 2; marine mammal, 1 ; and oleo,
oleostearine, fish, liver, and tallow (edible), 3 per cent.
ANIMAL AND VEGETABLE FATS AND OILS
"One-" and "Two-Stage" Production of Fats and Oils. Vege-
table fats and oils are produced directly as the result of the photo-
synthetic process and may in the broad sense be referred to as
resulting from a "one-stage" production. Animal fats and oils, on
the other hand, result from a "two-stage" system of production.
That this reflects on the economy of production is quite evident.
Each of the fats, animal as well as vegetable, has certain charac-
teristics which determine its commercial importance. They can
be and are, however, readily substituted one for the other.
The most important animal fats and oils for both edible purposes
and industrial uses are butter, lard, beef and mutton tallow, oleo
oil and animal stearine, and foots and inedible greases obtained as
residues and by-products of the packing industry. In addition, these
important products of animal husbandry are supplemented by a
considerable supply of fish or marine oils.
OIL PRODUCING CROPS 477
Competition between Vegetable and Animal Fats and Oils.
It is pointed out by Wallace and Bressman (18) that "corn is the
most efficient plant of the temperate zones in fixing the energy of
the sun's rays, and the hog is the most efficient meat animal for
converting that sun energy of corn into a palatable form for human
consumption." This sentence is an expression of the agricultural
philosophy of the American Corn Belt. But, as brought out by
Taylor (16), it is becoming necessary to distinguish between the
production of protein and fat.
The obtaining of animal fats involves the more expensive "two-
stage" production. These fats and oils produced by animals come
in direct competition with vegetable fats and oils obtained from
plants grown under cultivation in the temperate zones, and from
wild nature growths and plantation plantings in the tropics. Vege-
table oils have become of increasing importance in recent years
as substitutes for butter and lard. Technological advances in
refining, purifying, and deodorizing, and especially the widespread
employment of the hydrogenation process have played an important
part in altering the characteristics of vegetable oils to render them
more suitable for human consumption. Vegetable oils are exten-
sively used in human nutrition. The United States is by far the
largest producer and consumer of cottonseed and cottonseed
products in the world. Zimmermann (20) indicates that Europe may
be roughly divided into two parts by the latitude of the Alps with
regard to the type of fats and oils utilized — in the southern portion
liquid oils, obtained mainly from olives and cottonseed, are gener-
ally preferred, lard, lard compounds, margarine, and butter being
relatively unimportant, while in the northern portion of the conti-
nent butter has been waging a losing battle against lard and oleo-
margarine. Vegetable fats and oils have always been of especially
great importance in the densely populated countries of southeastern
Asia. Climatic conditions, religious concepts, and population
pressure have conspired to make animal fats and proteins of but
limited importance in this area.
OIL PRODUCING CROPS
Space does not permit the treatment of all the various oil-pro-
ducing crops. The crops to be discussed are cotton, peanuts, soy-
beans, flax and safflower.
478 ECOLOGICAL CROP GEOGRAPHY
COTTON AND COTTONSEED OIL
Cottonseed Oil a By-product. Cotton is grown primarily for
fiber. The crop produces, however, a series of valuable by-prod-
ucts. The by-products derived from the seed, that is, the cotton-
seed oil, meal, and hull, represent, according to Brown (2), a value
in excess of $200,000,000 in the United States.
According to Westerbrook (19), an average ton of cottonseed
yields approximately 311 pounds of crude oil, 906 pounds of meal,
520 pounds of hulls, and 143 pounds of linters.
Like other valuable agricultural by-products, those of cottonseed
were formerly wasted. The present use of cottonseed is discussed
by Brown in the following paragraph.
"Prior to the advent of the cottonseed-oil mill — some 75 years ago —
cottonseed was considered of little value. Some was used for planting
purposes and a limited amount used for fertilizer and cattle feed, but
the bulk of the seed was thrown away, piled up, and allowed to rot.
Now, all seeds are carefully saved, and all, except about 20 per cent
reserved for planting, are sold to the oil mill. Cottonseed is not now
used as feed or fertilizer to any appreciable extent, but cottonseed meal,
a meal ground from the residue left whfen the oil is extracted from the
crushed seeds, is used very extensively as feed and to a limited extent
as fertilizer. The meal is rich in protein, especially suited to dairy
cattle."
Utilization of Cottonseed Oil. A great variety of products are
made from cottonseed oil. The refined oil is used in the manu-
facture of lard substitutes, oleomargarine, as a cooking oil, and,
when "wintered," as a salad oil. In the manufacture of lard sub-
stitutes, some of the oil is hardened by hydrogenation so that the
finished product will have the desired degree of hardness. Accord-
ing to Jamieson, the approximate percentages of cottonseed oil
used for various purposes in the United States are as follows:
70 per cent for shortening, 16 per cent for salad and cooking oils,
12 per cent for soap, and 2 per cent for oleomargarine. The foots
coming from crude oil are used in making washing powder, grease,
soap, roofing tar, composition roofing, insulating materials, oil-
cloth, waterproofing, cheap paint base, cotton rubber, artificial
leather, and other articles.
Distribution of Production. The distribution of cotton is dis-
cussed in detail in Chapter XXVIII on fiber crops. The production
OIL PRODUCING CROPS 479
of cottonseed is more or less correlated with the production of fiber.
The production of cottonseed oil in the United States has averaged
around 1.5 billion pounds annually. Next in order have been
linseed oil and corn oil. The production of soybean oil has been
of relatively minor importance but has increased rapidly since
1928. The United States is by far the most important producer of
cottonseed oil; other important producers are Egypt and India.
FLAX AND LINSEED OIL
Historical. Flax has long been grown for its fiber and seed.
It is difficult to determine whether it was first grown for food or
fiber. According to Dillman (4), primitive man was probably more
interested in his food supply than in his raiment, and it seems
probable that wild flax was first gathered for its seeds, as a source
of food. Flaxseed, ground with grain or other seeds, is still used for
food in Ethiopia, India, Russia, and to some extent in other coun-
tries.
The making of fine linen is an ancient art. With the advent of the
cheaper cotton goods the importance of fiber flax in world trade
has diminished materially until, at the present time, flax may be
considered primarily as an oil producing crop. Two distinct types
of flax have been developed — the seed flax and the fiber flax.
The first is grown primarily for its seed and oil, the second for fiber
and linen production.
Vavilov (17) considers that "the oldest regions of cultivated flax
are in Asia: India, Bokhara, Afghanistan, Khoresan, Turkistan;
on the coasts of the Mediterranean: Egypt, Algeria, Tunis, Spain,
Italy, Greece, and Asia Minor." Vavilov is inclined to agree with
De Candolle that flax may be of polyphyletic origin, that is, it
developed from two or three species which united into one species,
Linum usitatissimum. Other investigators, however, believe that the
wild flax (L. angustifolium) may be the species from which cultivated
flax originated. This wild species is native to the whole of the
Mediterranean region; furthermore, as pointed out by Tammes
(15), it is the only wild species that crosses readily with cultivated
flax.
Dillman (4) points out that the cultivation of fiber flax was begun
by the colonists in America soon after their settlements had become
established. Seed flax became a crop of some importance in New
480 ECOLOGICAL CROP GEOGRAPHY
York, New Jersey, and Pennsylvania; by 1770 it was a staple article
of export from New York; by 1810 numerous small linseed mills
were in operation in Pennsylvania and New York. The linseed oil
industry developed rapidly with the opening of new lands during
the period 1850-1900. Owing to the ravages of flax wilt, flax be-
came a pioneer crop, moving to the west through the Corn Belt and
into the northern Great Plains as new lands were laid open by the
flow of advancing settlements. It became a staple crop in the Great
Plains area with the development of wilt-resistant varieties. The
classical work of Bolley of North Dakota, showing that" flax wilt
was caused by a parasitic fungus, dispelled the idea that the flax
crop was suitable only to new lands.
The discussion of flax in this chapter is limited to seed flax.
Fiber flax will be considered in Chapter XXVIII.
Uses of Flaxseed. Seed flax is a cash crop; very little is utilized
on the farms where it is grown. The two products of flaxseed are
linseed oil and linseed meal. Various attempts to use the straw for
the making of twine, canvas, towelings, rugs, etc., have not proved
commercially important. At the present time there is some interest
in the utilization of flax straw in the Manufacture of cigarette paper.
Linseed oil has long been the most important source of drying
oil in the paint and varnish industry. The oil is also extensively
used in the manufacture of linoleum, oilcloth, printer's ink, and
patent and imitation leather. According to Dillman (3), flaxseed
yields from 30 to 40 per cent of its weight in oil, or in commercial
crushing about 2\ gallons (7| pounds per gallon) to the bushel
(56 pounds) of seed.
The residue left after the extraction of the oil from the ground,
heated, and pressed flaxseed is known as linseed cake, or if ground,
as linseed meal. It is a highly valued feed, especially for dairy
cattle and young growing animals.
Climatic Relationships. Flax is grown as a spring-sown crop
in northern latitudes. In the mild climates of the Imperial Valley
of California, in southern Texas, Argentina, and in India it is sown
in the fall and grown as a winter crop.
Flax has rather specific moisture and temperature requirements.
Its restricted root development makes the plant highly dependent
on surface soil moisture. This in part accounts for its importance
in the spring and early summer rainfall areas of the northern Great
OIL PRODUCING CROPS 481
Plains of the United States and in the Prairie Provinces of Canada.
The temperature during the vegetative development of the crop
should be moderate. When exposed to conditions of intense sun-
light during its early phases of growth, the crop becomes susceptible
to heat canker. Because of this reaction and its demand for moderate
temperatures, flax is grown as a winter crop in the southern latitudes
and seeded as early as seasonal conditions permit in northern areas.
Even though young flax plants are somewhat more susceptible to
spring frosts than wheat or oats, April 1 to April 15 secdings have
generally produced higher yields in the northern portion of the
United States than later seedings.
Soil Relationships. The soil requirements of flax arc well sum-
marized by Morgan et al. (7) in the following paragraph:
"Flax is not exacting in its soil requirements, its production depend-
ing principally on rainfall and a moderately cool climate. It is tolerant
of a comparatively wide range in /?H values. The crop is well adapted
to the Chernozems of the eastern Dakotas, the Prairie soils of southern
Minnesota, and the Planosols of southeastern Kansas. The crop does
well also on sandy loam soils if the supply of moisture is adequate. In
California, flax is grown very successfully under irrigation on sandy
soils of the Imperial Valley, the so-called soft lands. In the North
Central States the hazard of wilt has been overcome by the develop-
ment of wilt-resistant varieties. Flax diseases are not a factor thus far
in Kansas and California. Weeds are perhaps the greatest hazard to
successful flax production. The control of weeds by means of crop
rotation is an important practice in every area where flax is grown."
World Distribution. Table 51 gives the statistical data on the
world distribution of flax, while Fig. 91 shows the distribution
cartographically.
The Argentine Republic is the world's greatest producer of
flaxseed. According to Bolley (1), flaxseed in Argentina is grown
chiefly within the three great maritime provinces of Buenos Aires,
Santa Fe, and Entre Rios, where both climatic and soil conditions
are exceptionally favorable to flax production. As the interior of the
country is approached, conditions become more hazardous. The
crop is grown on an extensive scale and under conditions of a
highly specialized agriculture. The proximity of the area to navi-
gable waters favors export trade. The Uruguayan flax producing
areas are adjacent to those of the Argentine. Much the same soil
and climatic conditions prevail. For the five-year period of 1930-
482
ECOLOGICAL CROP GEOGRAPHY
31 to 1934-35 Argentina accounted for more than 50 per cent of
the world's flax crop. Uruguay ranked fifth among the important
producers of the crop. Argentine flaxseed is of exceptionally high
quality. Renne (12) reports that Argentine flaxseed contains about
one pound of oil per bushel more than domestic, northern-grown
flaxseed.
TABLE 51. WORLD STATISTICS ON FLAXSEED PRODUCTION — AVERAGES FOR
THE FIVE-YEAR PERIOD OF 1930-31 TO 1934-35
Rank
Country
Total
Acreage, in
1,000 Acres
Yield per
Acre, in Bu.
Production,
in 1,000 Bu.
Percentage of
Total World
Production
1
Argentina
6,636
11.20
74,346
51.14
2
U.S.S.R
6,724
4.44
29,836
20.53
3
India
3,136
5.44
17,064
11.74
4
United States
2,107
5.46
11,501
7.91
5
Urumiav
392
9.01
3,530
2.43
6
Canada
432
5.15
2,225
1.53
7
Poland
253
7.80
1,974
1.36
8
Lithuania
146
6.85
1,000
0.69
9
Latvia
105
1 5.08
533
0.37
10
Morocco
52 '
' 8.46
440
0.30
11
Rumania
55
7.54
415
0.29
All others
2,500
1.71
Total world production
(excluding China) . .
145,364
100.00
Much of the Russian flax crop is grown primarily for fiber. Fiber
production centers around the northeastern portion of the country.
The drier central and southern areas and the Caucasus grow seed
flax. It will be observed from Table 51 that a greater area is de-
voted to flax in the Union of Soviet Socialist Republics than in
Argentina; the seed yield, however, is only 4.44 as compared to
11.20 bushels per acre for the South American republic. Neverthe-
less, Russia ranks next to Argentina as a world producer of flax.
India has long ranked as an important producer of flax. The crop
is grown almost exclusively for seed. For the five-year period cov-
ered in Table 51, India ranked third and the United States fourth
as world producers of flaxseed. The production in the United
States during the period 1930-31 to 1934-35 was, however, con-
siderably below normal owing to a series of drought years in the
northern Great Plains. In the preceding five-year period the pro-
5
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483
484 ECOLOGICAL CROP GEOGRAPHY
duction of the United States amounted to 20,216,000 bushels, that
of India to 16,968,000 bushels. Two regions of flax production of
major importance are found in India — in the Middle Ganges and
the region of the Central Provinces. Flax in India is one of a group
of oil producing crops, including rape, mustard, and sesame, grown
for cooking and lighting purposes.
The important flaxseed producing areas of the world are con-
centrated in rather limited territories. Four countries — Argentina,
Russia, India, and the United States — account for 91.32 per cent
of the world's production of this crop. Add to these the production
of Uruguay, a continuation of the Argentine region, and Canada, a
continuation of the United States flax producing area, and 95.28
per cent of the world's production is accounted for. Likewise, the
Polish, Lithuanian, and Latvian areas may be considered as ex-
tensions of the Russian areas. When these are taken into considera-
tion, it will be found that 97.70 per cent of the world's flax crop is
produced in ten countries.
Production in the United States. Flax in the United States is
primarily a crop of the northern Great Plains area. For the ten-
year period of 1928-1937 the fourjStates of Minnesota, North Da-
kota, South Dakota, and Montana ^produced over 94 per cent of
the flax crop of the country. The crop is of some importance in
eastern Kansas and western Missouri. Flax has also become a crop
of considerable importance in the Imperial, San Joaquin, and
Sacramento Valleys of California during the past ten years. It will
be observed from Table 52 that California produced 1,728,000
bushels of flax in 1939. There is also a considerable recent interest
in flax production in southern Texas and in the Salt River Valley of
Arizona. The California, Arizona, and Texas crops are grown as
winter crops; in the northern areas flax is spring-sown. Table 52
gives the flax statistics for the United States, while Fig. 92 shows
the distribution of the crop cartographically.
The total production of flaxseed in the United States shows wide
fluctuations from year to year. Thus, in 1924 the production was
31,200,000 as compared to the crop of only 5,273,000 bushels during
the drought year of 1936. This great seasonal variability in the
size of the flaxseed crop is accounted for by the centralization of the
producing area in the Great Plains states with their highly variable
grassland climates.
OIL PRODUCING CROPS
485
FIG. 92. Distribution of the flax and soybean producing areas of the United
States in 1939. Since the acreages of these two crops overlap in Minnesota, the
171,000 acres of soybeans for that state are not shown. Each dot represents
10,000 acres.
Flax is one of the few deficiency crops grown in the United States.
The consumption of flaxseed has exceeded the net domestic supply
each year for a period of 30 years. In certain seasons as many as
•
TABLE 52. FLAXSEED: ACREAGE HARVESTED, YIELD PER ACRE, PRODUCTION
AVERAGES FOR THE TEN-YEAR PERIOD 1928-1937 — AND 1939 PRODUC-
TION. ACREAGE AND PRODUCTION EXPRESSED IN THOUSANDS
Production
t
Yield per
Rank
States
Acreage
Harvested
Acre,
in Bu.
Average
1928-1937,
Percentage
of U. S.
1939,*
in Bu.
Total
in Bu.
1
Minnesota . . .
668
7.8
5,245
43.92
12,230
2
North Dakota . .
836
4.8
4,008
33.56
2,055
3
South Dakota . .
265
4.6
1,231
10.31
1,296
4
Montana ....
159
4.0
635
5.32
562
5
California ....
33**
15.6**
515**
—
1,728
6
Kansas ....
45
5.7
257
2.15
735
7
Iowa
18
8.4
151
1.26
945
Other states . . .
23
7.8
179
1.50
779
Total U.S. . . .
2,035
5.9
11,943
—
20,330
* Preliminary.
1 Short-time average.
486 ECOLOGICAL CROP GEOGRAPHY
20 million bushels of seed are imported. Most of the imported
seed originates in Argentina, with some of it coming in from Can-
ada. The tariff act of 1930 provides a duty of 65 cents per bushel
of 56 pounds on imported flaxseed and 4| cents a pound on linseed
oil.
SOTBEANS
A Crop of Many Uses. Soybeans (Soja max) in the United States
are grown to a greater extent as a forage than as an oil and food
crop. However, from the standpoint of world production, the crop
has become of considerable importance as an oil producer since the
first trial shipments of seed to England in about 1908 by Japanese
firms.
The entire plant of this annual legume is utilized for forage,
pasturage, and soil-improvement purposes. The green beans are
used to a limited extent as a vegetable. The dried beans are
used for the manufacture of a great variety of human foods and
livestock feeds. Piper and Morse (10) and Morse (8) present a
detailed outline and discussion of the numerous uses made of the
soybean, especially by the Chinesetand Japanese. It is extensively
utilized by these people in the place*of animal fats and proteins so
generally used by the people of western civilizations.
The main industrial interest in the soybean crop is centered
around the utilization of the oil extracted from the seed. According
to Morse, a ton of beans "containing 19 per cent of oil will yield
by the extraction method about 250 pounds of oil and about 1,600
pounds of meal, and about 150 pounds is lost in cleaning, in milling,
and in moisture." The oil is classified as a drying oil; its iodine
numbers are, however, considerably lower than those of linseed
oil — around 128 as compared to 170 to 204 for linseed oil. The
oil is midway between linseed and cottonseed oil in its charac-
teristics. Raw or crude soybean oil is used in making cores (metal
molding), and for making soft soap. The oil after "boiling" is
used with linseed oil in the manufacture of paints, baking japans,
linoleum, oil cloth, and printing ink. According to Jamieson,
"Some paint makers use ten to fifteen per cent (of the vehicle)
of boiled oil, but a larger proportion of soybean oil can be used with
good results." The refined oil is used in the manufacture of mar-
garine, mayonnaise, and shortening. Soybean meal is a valuable
OIL PRODUCING CROPS 487
feed. Recently both soybean meal and soybean oil have come into
use in the production of plastics.
Historical. The early history of the soybean is lost in obscurity.
Chinese records written over 5,000 years ago referred to the crop.
The culture of the plant in Japan is also very old.
The soybean was first introduced into the United States in 1804.
The crop was tried out by various experimenters both in America
and Europe toward the end of the past century. It did not, how-
ever, become of any great commercial importance until after the
first World War. According to Stewart et al. (14), "before 1917,
fewer than 500,000 acres of soybeans were grown in this country,
including acreages on which soybeans were grown alone as well
as acreages on which they were grown interplanted with other
crops." By 1 924 the acreage of soybeans grown alone had increased
to over \\ million, and by 1938 to over 8 million acres. Preliminary
figures for 1939 indicate in excess of 10 million acres.
Climatic Relationships. The soybean crop as a whole has a
wide range of adaptation. This is in part due to the great differ-
ences found in the characteristics and growth requirements of the
numerous varieties of the crop. Late-maturing varieties can be
grown successfully only in the southern portion of the Cotton Belt,
while early-maturing varieties can be grown for forage purposes
in the northern portion of the Corn Belt. As stated by Morse and
Cartter (9) "in general the climatic adaptations of the crop are
about the same as for corn." The soybean does not, however, have
as distinct a critical period in relation to its moisture demands as the
corn crop. Yet while soybeans are able to withstand short periods
of drought after they are well started, the crop demands a fairly
uniform supply of moisture during the growing season; cool night
temperatures are very effective in slowing up the development of
the plants.
Soil Relationships. Soil conditions favorable to corn are
normally well suited to soybeans. With proper inoculation the
crop can, however, be successfully grown on soils of a lower level
of fertility. The crop is also more tolerant of acid soils than either
alfalfa or red clover. This fact accounts to some extent for the
recent increases in the soybean acreages in the eastern portion of
the United States. The crop demands only fair soil drainage, al-
though best results are obtained on well-drained soils.
488 ECOLOGICAL CROP GEOGRAPHY
World Distribution. The world distribution of the soybean is
discussed by Morse and Cartter in the following paragraph.
"The soybean is grown to a greater extent in Manchuria than in
any other country in the world. It occupies about 25 per cent of the
total cultivated area and is relied upon by the Manchurian farmer as
a cash crop. China, Japan, and Chosen are large producers and the
soybean is cultivated more or less also in the Philippines, Siam, Cochin
China, Netherland India, and India. In other parts of the world,
particularly Germany, England, the Soviet Union, France, Italy,
Czechoslovakia, Rumania, Mexico, Argentina, Cuba, Canada, New
South Wales, New Zealand, Algeria, Egypt, British East Africa, South
Africa, and Spain, various degrees of success have been obtained."
The average production in specified countries for the six-year
period 1931-1936 in millions of bushels of beans was as follows:
China 222.6, Manchuria 155.8, United States 23.7, Chosen 21.2,
Japan 11.7, and Netherland India 6.6. Data for India are not
available.
Distribution in the United States. Table 53 gives the statistics
of soybean production by states. Figure 92 gives the distribution
of the acreage. It will be observed that the crop is of special im-
portance in the central portion of the Corn Belt and the northern
portion of the Cotton Belt. Seed production is centered around
Illinois and Indiana, and also in the eastern portions of North
Carolina and Virginia. Practically no soybeans are produced in
the western portion of the United States. The Great Plains area
is too dry for the crop. In the intermountain and Pacific coast
states the soybean crop is in a poor position to compete with alfalfa
for the production of forage and with the cereals for the production
of concentrates. Furthermore, in much of this area temperatures
are too low for the best development of the crop.
The trend in the production of seed in the United States is sum-
marized by Morse and Cartter in the following paragraph:
"Increase in seed production has been more rapid than the expansion
of acreage. In 1920, 14 states produced 3,000,000 bushels of seed, the
leading states being North Carolina, Virginia, Alabama, Missouri, and
Kentucky; North Carolina alone produced about 55 per cent of the
total. By 1931 seed production had increased to 15,500,000 bushels,
with Illinois, Indiana, North Carolina, and Missouri leading. In 1938,
57,665,000 bushels of seed were produced, of which 51,316,000 bushels
(90 per cent) were harvested in Illinois, Indiana, Iowa, Missouri, and
Ohio; Illinois alone produced 55 per cent of the total."
OIL PRODUCING CROPS
489
TABLE 53. SOYBEANS: TOTAL ACREAGE, ACREAGE HARVESTED, YIELD PER
ACRE, PRODUCTION — AVERAGES FOR THE TEN-YEAR PERIOD 1928-1937 —
AND 1939 PRODUCTION. ACREAGE AND PRODUCTION EXPRESSED IN THOU-
SANDS
Rank
StaUs
Total
Acreage
Acreage
Harvested
for Beans
Yield
per Acre,
in Bu.
Production
Average
1928-
1937,
in Bu.
Percent-
age of
U.S.
Total
1939,*
inBu.
1
2
3
4
5
6
7
8
9
10
Illinois
1,213
566
421
332
202
405
122
254
28
148
1,043
648
199
131
100
66
96
20
28
16
19
106
17.6
15.6
16.0
12.4
16.8
8.0
12.1
8.3
13.5
8.6
8.2
11,678
3,162
2,075
1,247
1,173
757
249
229
222
168
873
53.48
14.48
9.50
5.71
5.37
3.47
1.14
1.05
1.02
0.77
4.01
45,423
13,962
10,227
2,012
9,681
970
375
648
418
484
3,209
Indiana
Iowa
North Carolina . . .
Ohio
Missouri
Virginia ....
Delaware .....
Arkansas . ...
Other states ...
Total U. S
4,734
1,429
14.7
21,833
100.00
87,409
* Preliminary.
SAFFLOWER
A New Oil Crop for the United States. Safflower has been
grown for many years in India and Egypt as a source of oil and red
dye. Its importance as a dye plant has declined greatly since the
introduction of artificial dyestufis; but according to Rabak (11), it
is the most important oilseed crop cultivated in the Bombay Presi-
dency of India, where from 500,000 to 600,000 acres are produced
annually. It is grown extensively also in the dry areas of the Deccan
of India, and to a small extent in China, Japan, Turkestan, and
parts of Europe. In India the oil is used for food and in the making
of soap.
Safflower oil is reported to possess good drying properties. Paints
made with it show good durability and weather resistance. In
addition it has been found to have distinct merits in white paints
and white enamels where non-after-yellowing and permanent
whiteness are desired. The feed value of the oil cakes has not been
determined definitely.
Safflower grows best on deep soils, preferably on clay loams or
490 ECOLOGICAL CROP GEOGRAPHY
sandy loams. Heavy clay and sandy soils are less suitable. Ex-
tremely fertile soils are not desirable as plants on such soils produce
a luxuriant growth but few flowers. The crop demands a fairly
abundant supply of moisture during germination and up to the
flowering period. After that less moisture is desirable. Since the
young plants are frost-resistant, the crop can be grown in northern
areas. Warm weather and an abundance of sunshine are desirable
after the budding stage.
Because of the deficiency of drying oils, considerable interest
has developed in the possibilities of safflower production in the
United States. The crop has been grown experimentally in the
northern Great Plains and western states. In these areas safflower
must compete with flax.
REFERENCES
1. Bolley, H. L., "Flax production in Argentina," N. Dak. Agr. Exp. Sta.
Bull. 253, 1931.
2. Brown, H. B., "A brief discussion df the history of cotton, its culture,
breeding, harvesting and uses," La. IState Dept. Agr. and Immigr., 1939.
3. Dillman, A. C., "Production of seed flax," U. S. Dept. Agr. Farmers'
Bull. 1328, 1924.
4. , "Improvement in flax," U. S. Dept. Agr. Yearbook 1937:745-
784.
5. Hill, A. F., Economic Botany. McGraw-Hill, New York, 1937.
6. Jamieson, G. S., Vegetable Fats and Oils. Chemical Catalog Co., New
York, 1932.
7. Morgan, M. F., J. H. Gourley, and J. K. Ableiter, "The soil require-
ments of economic plants," U. S. Dept. Agr. Yearbook 1938:753-776.
8. Morse, W. J., "Soybean utilization," U. S. Dept. Agr. Farmers' Bull.
1617, 1932.
9. , and J. L. Cartter, "Soybeans: culture and varieties," U. S.
Dept. Agr. Farmers' Bull. 1520, 1927, Revised 1939.
10. Piper, C. V., and W. J. Morse, The Soybean. McGraw-Hill, New York,
1923.
11. Rabak, F., "Safflower, a possible new oil-seed crop for the northern
Great Plains and the Far Western states," U. S. Dept. Agr. Circ. 366,
1935.
12. Renne, R. R., "The flaxseed market and the tariff," Mont. Agr. Exp.
Sta. Bull. 272, 1933.
OIL PRODUCING CROPS 491
13. Sievers, A. F., "Peppermint and spearmint as farm crops," U. S. Dept.
Agr. Farmers' Bull. 1555, 1929.
14. Stewart, C. L., W. L. Burlison, L. J. Norton, and O. L. Whalin,
"Supply and marketing of soybeans and soybean products," ///. Agr.
Exp. Sta. Bull. 386, 1932.
15. Tammes, T., "Das genotypische Verhaltnis zwischen dem wilden
Linwn angustifolium und dem Kulturlein Linwn usitatissimum" Genetica,
5:61-76 (1923).
16. Taylor, A. E., Corn and Hog Surplus of the United States. Food Res. Inst,,
Stanford University, 1932.
17. Vavilov, N. I., Studies on the Origin of Cultivated Plants. Leningrad,
1926 (in Russian with English summary).
18. Wallace, H. A., and E. N. Bressman, Corn and Corn Growing. Wiley,
New York, 1928.
19. Westerbrook, E. C., "Cotton culture in Georgia," Ga. Agr. Ext. Bull.
469, 1939.
20. Zimmermann, E. W., World Resources and Industries. Harper, New
York, 1933.
Chapter XXVIII
FIBER CROPS
INTRODUCTION
Economic Importance of Fibers and Fiber Crops. Next to
food, clothing and shelter represent the primary necessities of life.
Early man made his garments from the skins of animals, but the
need of some form of clothing lighter and cooler than skins and
hides early turned his attention to the use of plant and animal
fibers. The use of fibers is by no means limited to clothing; they
serve a great variety of purposes — cordage, ropes, bagging, canvas,
automobile tires, upholstery, etc.
From the standpoint of value of the total world production, the
fiber crops are outranked by various basic food products. But, in
speaking of the world's most important fiber crop, cotton, Garside
(9) points out that
"most of the commodities that take precedence of it in value of out-
put are, in the large part, used by the producers themselves, marketed
within relatively small territories around the centers of production, or
marketed within the countries of production. ... In contrast, in the
case of cotton, only a very small percentage of the world's crop is used
by the producers, and only a minor portion of the crop is used close to
the areas of production."
This point applies to most of the world's fiber crops. It makes them
one of the great commodities of international trade.
Kinds of Fibers. Three general classes of fibers may be recog-
nized on the basis of their respective origins, namely, vegetable,
animal, and synthetic fibers. Each of these classes may again be
broken down into groups. Thus vegetable fibers may originate as a
covering of seed as in the case of cotton and kapok; from leaves as
in the case of sisal and abac£; from bast as in flax, hemp, and ramie;
or even from the fruit of plants as in the case of coir, the short,
coarse, rough fibers obtained from the husks of the fruits of the coco-
nut palm.
492
FIBER CROPS 493
Perhaps more important than the generic classification of fibers
is a classification based on use. It is not necessary, however, to
become involved here in a lengthy classification. The recognition
of four general classes will suffice. The first and most important
class comprises the soft fibers, of which cotton, flax, and jute are
the most outstanding examples. They are used primarily for mak-
ing cloth and bagging. The second class, the hard fibers — hemp,
abac£, and sisal — are used mainly for twine and rope. The plait-
ing and rough weaving fibers make up a third class. These are
obtained from various species of sedges, rushes, and grasses. The
fourth and final class comprises the filling fibers. Kapok is the
most valuable of these stuffing materials; a considerable number
of surface fibers are commonly used for stuffing pillows, cushions,
mattresses, furniture, and similar articles.
Synthetic Fibers. The development of various synthetic cellu-
lose and even glass filaments, "rayon," and "nylon" has introduced
a new factor in the textile industry. It is impossible to state to what
extent these synthetic fibers will replace the natural fibers. Their
production has shown a significant increase during the past 20
years. All indications point toward their more extensive use. The
partial withholding of American cotton from the markets of the
world has definitely encouraged the use of synthetic fibers.
COTTON
Economic Importance. Cotton is by far the most important of
all fiber crops. Cotton is used all over the world. While the quan-
tity used per person varies greatly in different countries, cotton is
used in one form or another by nearly all people. Huntington et d.
(12) bring out that cotton is more widely employed and hence more
widely sold and bought than any other material. The reasons for
this are quite obvious: cotton goods are cheap; they can be utilized
under a great variety of climatic conditions; and the fiber has
excellent qualities with regard to tensile strength, elasticity, uni-
formity of texture, porosity, and durability.
The use of cotton is by no means limited to the making of cloth-
ing. It is employed in making twine and cordage, for stuffing,
and for the manufacture of a great variety of cotton goods. The
reader is also reminded of the economic importance of the valuable
494 ECOLOGICAL CROP GEOGRAPHY
•••^••^^•••••^••••^•^••••••••^•^^^••••••••••^^•••••^••••••^••••^^•••^•••M^KMMBMi^MIM^^MMilMMMK «T" •
by-products of cotton, namely, cottonseed oil, cottonseed meal,
linters, and cottonseed hulls.
The importance of fiber crops in international trade has already
been indicated. In the export trade of the United States the value
of cotton far exceeds that of any other commodity. As stated by
Agelasto et al. (1), cotton "is the chief and often the only source of
income to a large proportion of the farmers in the Southern States."
Social Significance. Cotton is grown in concentrated areas.
Thus Baker (2) points out that 60 per cent of the world's cotton
supply is grown on less than 3 per cent of the world's 'land area.
Vance (22) designates the Cotton Belt of the American South as
one of the most highly specialized agricultural regions in the world.
The economic and social life of the southern states and with it the
social and economic fabric of the entire United States are affected
to a considerable degree by the economic position of cotton. The
three great export crops of the United States are cotton, tobacco,
and wheat. Under "normal" conditions of world trade over 50
per cent of the cotton crop is exported as compared to 33 per cent
in the case of tobacco and 22 per cent of the wheat produced. The
tremendous importance of cotton ta the economic and social well-
being of the country is brought out even more forcefully by means
of actual figures of the acreages devoted to the production of the
net exports of some of the important crops of the United States
than by the above percentages cited. Thus Dowell and Jesness (6)
point out that for the 1 1 -year period 1920-1930 these acreages were:
22,145,000 for cotton; 14,636,000 for wheat; 2,106,000 for rye;
1,505,000 for corn; 1,292,000 for barley; 593,000 for tobacco; and
220,000 acres for rice.
The extent to which cotton affects the economic and social condi-
tions of the South is stated vividly by two journalists, E. V. Wilcox
and Henry K. Webster, in the following two paragraphs cited from
Vance's book, Human Factors in Cotton Production.
"And what does cotton mean to the cotton states? It means life,
health, happiness, and prosperity to them. In fact, nothing else matters
much. If cotton is all right, all's well in the Cotton Belt. And if cotton
is sick the whole South is sick. The physician can collect no bills, the
merchant can sell nothing except on credit; railroads go without freight;
mill operatives languish; children grow pale; every person in the street
is dejected ; and gloom reigns throughout the South. . . . Cotton is the
FIBER CROPS 495
barometer that foretells the industrial fogs, squalls, and fair weather of
the South.
"A good crop and a high price means more than that the farmer's
wife can begin to dream of a new parlor carpet and a piano ; it means
that the preacher's son and the merchant's daughter can go away to
college. The clerk scents a raise and cautiously inquires the price of a
diamond ring for the girl whom for the past two years he has been seeing
home from church. The commercial traveler is lavish with more
expensive cigars than he smoked last year, reflecting that the house
won't mind a bigger expense account, with orders coming in like this."
It is estimated that from 10 to 12 million persons in the United
States, chiefly in the cotton growing states of the South, depend
for their living on the growing, distribution, and manufacture of
cotton and cottonseed, or upon industries and trades otherwise
vitally related to cotton.
Historical. Investigations relative to the origin of cotton lead
to the opinion that there were probably two general centers of
origin of the cotton plant, one in the Old World and one in the
New World. Ware (23) states that
"it is the opinion of some investigators that there might have been
two centers of origin in the Old World, Indo-China and tropical Africa,
and that in the New World cotton might have either originated inde-
pendently in two regions — Mexico or Central America, and the
foothills of the Andes Mountains of South America — or have developed
along different lines in these two regions. . . . the cultivated cottons of
today seem to trace back to cottons grown in ancient times in one or
another of these four world centers. Archeological specimens indicate
very ancient usage of cotton in Mexico and in South America, and
indigenous species in the Old World furnish some evidence of the double
origin in that hemisphere."
American and Asiatic cottons have probably remained distinct
since their origin. They are still so incompatible that crossing
between them is rare, and persisting fertile hybrids are unknown.
American cottons have 26, the Asiatic species only 13 chromosomes.
The probable origin of the three types of cotton grown in the
United States is discussed by Ware in the following paragraph.
"There are many different types and a number of different species
of both Old World and New World cottons, however, and all of the
cultivated forms of New World origin seem to cross readily with each
other, although those that originated in South America are genetically
quite different in many respects from those more recently introduced
496 ECOLOGICAL CROP GEOGRAPHY
from Mexico. While the three types of cotton now grown in this
country — sea island, American-Egyptian, and upland — are all
probably of American origin, it would seem that the sea island and the
American-Egyptian originally came from South America and that all
of the upland varieties either came originally from Mexico or at some
time in the past arose from crosses of Mexican and South American
species. Hybridization of North and South American species especially
may account for some of the upland long staple varieties."
Cotton has long been grown and used for making clothing not
only in South and Central America but also in Asia and especially
in India. Cotton constituted one of the important crops of the
southern states almost from the date that the respective colonies
were founded. It, together with the growing of tobacco and indigo,
was closely correlated with the economic development of these
states. Production of cotton in the southern states increased, ac-
cording to Brown (4), from 73,222 bales in 1800 to 1,061,821 bales
in 1835; 3,220,782 in 1855; 4,302,818 in 1875; 10,266,527 in 1900;
to the record crop of 17,977,374 bales in 1926.
Even a brief history of cotton cannot disregard the effects of
technological improvements made 4n the spinning and ginning of
cotton. The main inventors of cotton machinery may be listed as
John Day, inventor of the flying shuttle in 1732; James Hargreaves,
spinning jenny, 1767; Richard Arkwright, water frame, 1769;
Samuel Crompton, spinning mule, 1779; Edmund Cartwright,
power loom, 1787; and Eli Whitney, cotton gin, 1793. This out-
standing array of developments during the second half of the
eighteenth century had a profound effect on the economic produc-
tion of cotton and on the greater utilization of cotton goods; they
brought cotton goods within the reach of the masses of all lands.
It is interesting to note that American cotton production in-
creased very rapidly throughout the nineteenth century. Produc-
tion was curtailed only temporarily by the Civil War. In 1860
England obtained 2,580,700 bales, or about 80 per cent of her
total cotton supplies, from the southern states. The reduction of
supplies from the South during the Civil War was the chief cause
of the Lancashire cotton famine of 1861-1865. During this period,
British and Continental agencies were active in investigating the
possibilities of cotton production in many tropical areas, but, as
pointed out by Henderson (10), with only temporary success in
FIBER CROPS 497
most of these areas. The shortage of cotton in Europe in the early
sixties greatly stimulated Egyptian and to some extent Indian cotton
production. With the close of the Civil War the United States soon
regained its preeminent position as a producer of cotton. The
phenomenally rapid rise of American cotton production throughout
the nineteenth century is accounted for by the new and rapidly
increasing demands for cotton, by the rapid strides made in the
development and improvements of cotton and textile equipment
and processing machinery, by the large expanses of land available
for agricultural exploitation, by the great improvements in the
means of transportation, and last but not least by the availability
of cheap labor. Labor was available and cheap both before and
after the Civil War. Cotton and cotton culture were the chief
contributing causes for the rapid increases of negro populations
in the southern states throughout the nineteenth century. The
crop provided work for the negro and enabled him to find a place
in American life. Prices of tobacco, rice, and indigo were on the
decline when cotton culture came to the fore. As stated by Vance,
"cotton found the plantation system on the decline; it revived and
pushed this system across the southern map." The economic and
social transformation occasioned by the extensive growing of cotton,
in the words of Frederick J. Turner (cited from Vance), "resus-
citated slavery from a moribund condition to a vigorous and ag-
gressive life."
Classification. Cotton belongs to the genus Gossypium, which is
made up of a number of species. Considerable disagreement exists
with regard to the botanical classification of the crop. Hutcheson
et al. (13) list the seven commonly recognized species as follows:
1 . Gossypium barbadcnsc, the long-staple Barbadoes, Sea Island, Egyp-
tian, and Peruvian varieties.
2. Gossypium herbaceum, the varieties of India, Siam, China, and Italy.
3. Gossypium hirsutum, the American upland varieties.
4. Gossypium arboreum, found in Ceylon, Arabia, and South America.
5. Gossypium pcruvianum, the native varieties of Peru.
6. Gossypium tahitense, found in Tahiti.
7. Gossypium sandwichensty found in the Sandwich and adjacent
islands.
Commercial Types. Many commercial types of cotton are rec-
ognized in the principal markets of the world. A broad grouping
498 ECOLOGICAL CROP GEOGRAPHY
of these types into five general classes according to sources, uses,
and commercial values is as follows:
1. American Upland. This is by far the most important of the
American and of the world's cottons. "American Middling," the
standard short-staple grade, is the basis of price quotations for all
short-staple cottons. Over 99 per cent of the American crop is
upland cotton.1 The American upland varieties have unspotted
white flowers which turn rose, pink, or red on the second day of
blooming. The bolls are four- or five-locked, and the seeds are
usually well covered with white, brown, or green fuzz, in addition
to the lint. The staple length varies from f to 1^ inch, depending on
variety and environmental conditions. In the past this general
class has been broken down into upland short-staple and upland
long-staple cottons with the line of demarcation at the staple length
of If inch. For the five-year average of 1929-1933 only 3.54 per
cent of all the upland cotton produced in the United States had a
staple length of 1 f inch or more. The longer stapled types of this
cotton compete with Egyptian and American-Egyptian cottons.
American upland varieties have been introduced into and are now
extensively grown in other important cotton producing areas of
the world.
2. Sea Island. This cotton is a native of South America. The
plants grow tall and have slender branches, the petals are yellow
with a red spot near the base. The bolls are narrowly ovoid and
three-locked. In contrast to the fuzzy seeds of the upland cotton,
sea-island seeds are naked and black. Fancy sea island cotton has
a fiber length of 2 inches or more. It is the most valuable of the
world's cottons, surpassing all other types in length, strength, and
fineness of lint. Unfortunately, this cotton, because of its late
maturity, is particularly subject to boll weevil damage. It is also
extremely susceptible to the common bacterial blight (angular leaf
spot). As a result, sea island cotton is practically extinct in this
country. Prior to the arrival of the boll weevil in the territories
along the coast of the Carolinas and Georgia, the United States
1 The term "upland" has completely lost its meaning as designating the altitude
or location of the land on which the cotton was produced. The term originated in the
early days of cotton production in the United States when it was applied to that type
of cotton which was grown on the higher land more or less distant from the seacoast,
in distinction from the sea-island cotton which was grown near the coast or on islands
off the coast.
FIBER CROPS 499
produced around 100,000 bales of this high-quality cotton. A
limited quantity is now grown in the West Indies. The fiber is
spun into fine yarns and used largely in the manufacture of laces,
cambric, and fine hosiery.
3. Egyptian. Egyptian cotton, while a distinct type, is similar to
sea island in general appearance of the plants. The fiber is fine,
silky, and strong. It varies from \\ to If inches in length. The fiber
is usually dark-cream or buff in color. It is used especially in man-
ufacturing goods in which great strength is required, such as auto-
mobile tire fabrics, airplane wing and fuselage covers, balloon
cloths, and high-quality hosiery. Egypt furnishes the bulk of the
crop.
4. American-Egyptian. This is Egyptian cotton produced in the
irrigated valleys of Arizona and southern California. The quantity
of this cotton in relation to the total cotton production in the United
States is limited. For the five-year period 1929-1933 an average of
only 16,800 bales of American-Egyptian cotton were produced as
contrasted to 14,044,400 bales of American upland.
5. Asiatic. The Asiatic cottons include Gossypium herbaceum and
several related species, indicum, neglectum, arboreum, and nanking. The
staple is short, often only f to f of an inch in length, but strong and
rather rough. Asiatic cotton is grown in southeastern and southern
Asia. In many districts it is giving way to American upland type».
Climatic Relationships. Cotton is grown over a wide range of
moisture conditions from the humid woodland to the summer dry
grassland climates, or from the Cfa and BB'r to the BSkw and CB'd
climates. In the American Cotton Belt the average annual precip-
itation ranges from 23 inches in western Oklahoma and Texas to
55 inches in eastern North Carolina and 60 inches in southern
Mississippi. Likewise, the spring rainfall ranges from 6 inches in
western Texas to 16 inches in Arkansas and southern Mississippi,
being heavier in the Mississippi Valley states than in Texas or the
South Atlantic states. The summer rainfall is greater in the eastern
and southern portions of the Belt than in the northern and western
portions. Relatively dry autumn months favor harvest and the
production of a cotton of high quality. Fortunately, autumn is the
driest season over practically all of the American Cotton Belt. Rains
at this time of the year interfere with the maturation of the crop and
lead to storm losses and to discolorations of the lint. Furthermore,
500 ECOLOGICAL CROP GEOGRAPHY
as pointed out by Smith (20), an excess moisture of cotton when
ginned, whether due to rain, dew, or "greenness," makes proper
ginning difficult. The ideal distribution of rainfall for cotton is of
the thundershower type with several days of bright, warm weather
between rains.
Moisture relationships seem to be definitely associated with the
shedding, or the abscission of a variable number of the immature
fruits of the cotton plant. Both soil moisture and rates of transpira-
tion constitute, according to Ewing (7), contributing factors deter-
mining the amount of shedding. Ewing points out that a loss of
approximately 60 per cent of the fruit of the plant may be con-
sidered an entirely normal occurrence. He cites data from Ball's
work in Egypt showing that the average rate there is around 40 per
cent; also Harland's figures for St. Vincent which indicate that only
from 10 to 20 per cent of the flowers produced by sea island plants
in the West Indies eventually mature. The amount of shedding
taking place in cotton may also be influenced by insect and disease
factors.
While the cotton crop is able to gain a place of importance in
agricultural regions with considerable ranges in annual and seasonal
precipitations, the crop is far less lenient with regard to variations
in temperature conditions. This is to be expected in view of its
tropical origin. The northern limit of commercial cotton produc-
tion is quite effectively determined by the average summer tem-
perature of 77°F. Production beyond this more or less definite
temperature limit becomes profitable only during a series of years
with supranormal prices. Along the northern margin of the Cotton
Belt the last killing frost in spring occurs on an average around
April 10, and the first killing frost in fall about October 25, so that
the frostless season is about 200 days. In the southern portion of
the Cotton Belt the last killing frost in spring occurs about March 10
on the average, and the first killing frost in fall seldom before
November 25, the frostless season being 260 days or more in length
(Agelasto et al.).
Hazards in Cotton Production. The cotton plant like other
crop plants is subject to certain hazards. From the economic point
of view both environmental and price relationships should be con-
sidered. The discussion of price variation of the commodity is
beyond the scope of this chapter. That violent price fluctuations
FIBER CROPS 501
constitute a factor must, however, be recognized. Since the ravages
of insects and diseases are closely associated with climatic variations,
they will not be discussed separately.
Because cotton is of such vital importance to the commerce of
the world and also no doubt because the great fluctuations in the
prices of the commodity affect the economic status of the cotton
producer, certain writers have tended to exaggerate the natural
hazards encountered in cotton production. These sentiments arc
voiced by such statements as the one taken from Garside: "The
story of the making of a cotton crop is one of successive hopes and
fears, of optimistic expectations and pessimistic forebodings"; also
by the often-quoted saying that "cotton can promise more and do
less and can promise less and do more than any other plant."
The degree of uncertainty attending the production of cotton is
not necessarily greater than found in a good many field crops. As
a matter of fact Marbury (15) points out that
"cotton, though a sensitive plant, is of all summer-growing crops of
the South about the least affected by ordinary changes in the weather.
... Its long period of growth, fruiting and maturity affords it ample
opportunity to recover from a number of temporary set-backs. During
the protracted season from planting in April to the completion of the
harvest in November, it is exposed to many varieties of weather, and it
seems to endure the bad as well as enjoy the good."
Varying hazards are encountered in the different cotton produc-
ing areas of the world. Thus in humid areas the crop may be subject
to damage from excessive precipitation with its associated evils
such as low temperatures, difficulties in obtaining stands, increase
in insect populations, and extra competition from weeds, while the
crop grown in subhumid areas may suffer just as much from lack of
moisture. There may also be compensating risks. Droughts will
cut down the size of the crop, but comparatively dry weather with
moderately high temperatures serves to reduce weevil population
and damage from this and other insects.
Variations in climatic conditions from season to season as well as
within the season determine not only the yield but also to a high
degree the quality of the lint produced. Quality is determined,
however, not by climatic conditions alone; the type and variety
grown, as well as the soil conditions and cultural practices followed,
are of great importance.
502 ECOLOGICAL CROP GEOGRAPHY
The cotton producer has at least in one instance reduced the
risks encountered in his enterprise. The introduction of the boll
weevil for a time threatened the cotton industry of the South.
While this insect is still a factor, the challenge occasioned by its
introduction and rapid spread over the Cotton Belt was met by
plant breeders and producers. The type of cotton produced was
gradually changed by the introduction and breeding of varieties
capable of producing cotton under weevil conditions. Varieties
that had long been noted for high quality were discarded with the
coming of the weevil and were replaced by early-maturing short-
staple sorts. The quality of these early-maturing varieties was in-
ferior, but their early maturity and determinate habits of growth
shortened the fruiting season and with it the period in which they
were subject to weevil damage. The weevil problem was met;
however, the many excellent varieties of long-staple upland cotton
of preweevil days were sacrificed. Another means now widely
employed in an attempt to enable cotton plants to "outrun" the
weevil is the closer spacing of the plants in the row. This leads to
the setting of fewer later squares so that a higher number of early
set squares and bolls may reach maturity earlier in the season and
thus escape damage. The shift in the use of land for cotton in the
southeastern states from the heavier to the less fertile, light-textured
soils of the uplands is also traceable to the need for earlier maturity
to escape severe weevil damage.
Soil Relationships. While the outer boundaries of cotton pro-
ducing areas are determined almost entirely by climatic factors,
the most noticeable differences in the density of cotton acreage and
variations in yield per acre within the American Cotton Belt are
due principally to soil conditions (Stine and Baker, 21). The soil
requirements of cotton are summarized by Morgan et al. (17) in the
following paragraph.
"This long-season southern crop is represented by a number of types
varying considerably in their soil adaptations. It requires a soil of good
moisture-holding capacity, with favorable drainage and aeration. Soils
well supplied with organic matter are the most productive, although
much of the southeastern area is on seriously humus-deficient soil. The
crop is successfully grown at various degrees of acidity, the most favor-
able range being pH 5.2 to 7. The soils east of the Mississippi lowland
are generally so deficient in available nutrients that fertilizers are used
very extensively. The available nitrogen in the soil is rarely adequate,
FIBER CROPS
503
and both phosphorus and potassium must also be supplemented from
fertilizer sources. The rich, dark-colored Rendzina soils of Texas are
much more fertile, and fertilization is not so extensively practiced. The
breeding of cotton types especially adapted to areas of more restricted
rainfall has added extensive acreages in cotton in northern Texas and
western Oklahoma on soils of high mineral fertility and well supplied
with available nitrogen."
World Distribution. The intensive production of cotton is con-
centrated in rather limited areas. It will be observed from Table
54, giving the statistics of world cotton production, that the United
States stands out as by far the most important producer of the com-
modity, producing 56.22 per cent of all the world's cotton. Two
countries, the United States and India, accounted for 73.61 per cent
of the world's cotton for the five-year period of 1925-26 to 1929-30,
and six countries produced 94.47 per cent of all of the world's cotton
crop. Figure 93 gives the geographical distribution of world cotton
production.
TABLE 54. WORLD COTTON PRODUCTION. ACREAGE AND PRODUCTION IN
SPECIFIED COUNTRIES TOGETHER WITH PERCENTAGES OF TOTAL WORLD
PRODUCTION FOR THE TWO FIVE-YEAR PERIODS INDICATED
Rank
Country
Acreage,
in 1,000 Acres
Production,
in 7,000 Bales
Percentage of
Total World
Production
1925-26
to
1929-30
1930-31
to
1934-35
1925-26
to
1929-30
1930-31
to
1934-35
1925-26
to
1929-30
1930-31
to
1934-35
1
2
3
4
5
6
7
8
9
10
11
12
13
United States ....
42,601
26,192
5,563
2,017
1,828
1,492
305
615
472
241
270
495
2,489
34,657
23,625
6,451
4,883
1,743
2,457
328
991
349
436
349
448
2,911
15,268
4,724
2,552
1,021
1,587
504
246
131
253
115
126
138
493
13,343
4,029
2,730
1,775
1,481
772
274
206
195
191
160
132
532
56.22
17.39
9.40
3.76
5.84
1.86
0.91
0.48
0.93
0.42
0.46
0.51
1.82
51.67
15.60
10.57
6.87
5.74
2.99
1.06
0.80
0.76
0.74
0.62
0.51
2.07
USSR ....
Ecrvot
Brazil
Peru
Anglo-Egyptian Sudan .
Chosen* ....
All others
Estimated world total .
84,580
79,628
27,158
25,820
100.00
100.00
1 Includes Manchuria.
504
FIBER CROPS 505
The distribution of cotton in the United States will be discussed
under a separate heading. It will be observed from Table 54 that
disrupted world economic conditions and the institution of cotton
control programs in this country had definite effects on cotton dis-
tribution. The preeminent position of the United States as a world
producer of cotton, however, remains unchallenged even though
production for the second five-year period, 1930-31 to 1934-35,
dropped from 56.22 to 51.67 per cent of total world production.
The acreage of cotton relinquished by the United States was taken
up by Russia, Brazil, Uganda, Argentina, the Anglo-Egyptian
Sudan, and other countries.
India for many years has been surpassed only by the United States
in the production of cotton. According to Bergsmark (3), the
greater part of the Indian cotton is grown on the rolling uplands of
Deccan. Cotton production attains its highest intensity on the
Black Earth Belt of peninsular India. The soils here are fertile and
have good moisture-retaining properties. The importance of this
area as a cotton producer has been a major factor in making Bom-
bay, a center located to the south, west, and northwest of this
region, the principal cotton manufacturing city of India. Stine and
Baker point out that, while the production of cotton in India — as
in the Cotton Belt of the United States — is more concentrated in
certain areas than in others, the crop is grown in nearly all parts
of the country except in regions of very heavy rainfall as on the
Burma coast, in the swampy Ganges lowlands of eastern Bengal,
on the mountainous Malabar coast, and in the desert region of
western Rajputana. The highest grade of Indian cotton, according
to Finch and Baker (8), is produced in southern Madras near
Tinnevelly, Madura, and Coimbatore. In this region the maximum
rainfall comes between June and October, the annual amount being
only 27 to 30 inches. The period of extreme drought occurs in
March.
Rainfall in the cotton as well as in the cereal producing regions
of India is extremely variable. Years of plenty are followed by years
of dearth, and drought frequently injures the crop. Considerable
progress has, however, been made in irrigation developments to
remedy this situation. In the dry areas much of the cotton grown
is of short-staple varieties.
Indian cotton is produced at great expenditures of labor on small
506 ECOLOGICAL CROP GEOGRAPHY
private land holdings. A high percentage of the crop is exported to
Japan and China. Owing to the generally poor quality of the
Indian crop, European importers prefer American to Indian cotton.
India imports a small quantity of raw cotton, mostly American
(see Table 56), and a large quantity of manufactured cotton goods,
chiefly from England.
The future development of India's cotton industry depends
mainly upon the production of more lint per acre and improve-
ments in the crop produced rather than upon the expansion of
cotton acreage.
China has grown cotton since the twelfth century. According to
Cressey (5), the cultivation of cotton spread into China from central
Asia by way of Kansu and Shensi. At present cotton is extensively
grown in the valley of the Wei Ho near Sian (Sianfu). Other im-
portant areas are Shansi and Honan and the valley of the Yangtse
River. The tensile strength of Chinese cotton is good, but the staple
is coarse and short. The position of China in the international
trade of cotton is summarized by Cressey in the following
paragraph.
t
"Although China is an exporter ofxotton, she is also an importer,
buying about twice as much as she sells. This peculiar situation is due
to the fact that China produces short-staple cotton which Japan and
the United States purchase for mixing with long-staple cotton and for
special purposes, such as making blankets. The cotton which China
buys is mostly of the long-fiber variety necessary for the manufacture
of certain cloths. As China increasingly weaves her own cloth, the
export of raw cotton will decline."
The cotton crop of the Union of Soviet Socialist Republics is produced in
Turkestan and Transcaucasia. Cotton is grown farther north in
the first of these regions than elsewhere in the world. The climate
of the Russian areas is of the arid continental type, characterized
by hot summers and cool winters. The increase in Russian cotton
production is accounted for by recent irrigation developments and
economic pressure aimed at self-sufficiency.
Egypt is the world's chief source of long-staple cotton. According
to Norris (18), approximately one-third of the average crop of
1,500,000 bales is of a staple length of 1£ inches and over, and the
staple of the remainder of the crop, known as Uppers, ranges from
to 1^ inches. Less than a century ago Egypt produced little
FIBER CROPS 507
cotton. The Civil War in the United States greatly stimulated
Egyptian production. After the close of that war, Egypt not only
held its place gained as a world producer of high-quality cotton
but continued to increase its production. At the present time cotton
is the leading cash crop and the chief item of export.
Cotton, like all the other crops of the country, is grown under
irrigation. Agriculture is confined to the delta, Lower Egypt, and
the narrow valley of the Nile, Middle and Upper Egypt. The in-
creased importance of cotton production during the past century
is accounted for by the world demand for the high-quality cotton
grown and by the great improvements made in irrigation facilities
and practices. The oldest type of irrigation was of the flood or basin
type. It is still common in Upper Egypt, but much of Middle and
all of Lower Egypt is now under canal irrigation. While the flood
type of irrigation led to the annual "renewal" of the soil by the silt
deposited over the flooded areas, canal irrigation resulted in better
water control and in the intensification of production.
Brazil has possibilities as a producer of cotton. Certain natural
limitations must, however, be considered. The coastal region is
rather wet and the interior is subject to droughts.
Most of the cotton of Peru is grown under irrigation in the alluvial
bottoms of the coastal valleys. Both "smooth" and "rough"
Peruvian cotton is produced. The latter is crinkly, brownish ir
color, and can for that reason be mixed successfully with wool in
the production of expensive fabrics.
Distribution in the United States. The climatic conditions pre-
vailing over the American Cotton Belt and their effects on the
cotton crop have already been discussed. The effects of tempera-
ture and moisture conditions on the limits of cotton production are
apparent from the cartographical view of cotton distribution in
Fig. 94. The northern limits of cotton production are rather well
defined by prevailing summer temperatures, while the western
limits are determined quite definitely by the 23-inch annual pre-
cipitation line. Very little cotton is grown along the Gulf coast
east of Galveston, and practically none in southern Florida. This
is due in part to the greater autumn rainfall in these areas and in
part to the swampy and in places sandy soils in this section. Pro-
duction along the Atlantic coast is also not intense; poor soil con-
ditions interfere with the proper development of the crop.
508
ECOLOGICAL CROP GEOGRAPHY
Throughout the entire Cotton Belt certain areas of concentration
are evident. These are determined primarily by favorable soil
conditions within this broad belt. Such areas of concentration are
found in the Piedmont Plateau, the Upper Coastal Plain, the Black
Prairie of Alabama and Mississippi, the bottom lands along the
Mississippi River and Mississippi-Arkansas and Red River Deltas,
the Black Waxy Prairies of Texas, and on the plains of western
Oklahoma and the lower portion of the panhandle of Texas.
FIG. 94. Distribution of cotton production in the United States. Averages for
the ten-year period 1928-1937. Each dot represents 25,000 acres.
Table 55 gives the cotton statistics of the United States by states.
Cotton is an old crop in the eastern and central portions of the
Cotton Belt. Its production on the dry plains of Oklahoma and
Texas is comparatively recent. These western areas have received
much of the blame of overproduction of cotton during recent years.
The lower yields of Texas and Oklahoma are to a large degree
accounted for by the lower rainfall prevailing in these areas as
compared with the areas to the east. Furthermore, the lint pro-
duced is not as long as for the cotton produced on the fertile soils
in the more humid areas. Nevertheless, cotton not only has estab-
lished itself in these drier areas but is economically well entrenched.
Even though yields are lower and the staple somewhat shorter than
in the areas to the east, the costs of production are also lower. The
FIBER CROPS
509
lower costs are accounted for in part by the more progressive and
extensive methods of production, greater fertility of soil necessitat-
ing smaller outlay for fertilizer, and also by the fact that owing to
the lower precipitation weeds are easily controlled. In much of this
area stands are more readily obtained than in humid sections.
Consequently, "cell-drop planting" is used. This gives the grower
an opportunity to space his plants without the expense of chopping,
that is, thinning down to the desired stand. The high summer
temperatures are also effective in reducing and in places eliminat-
ing weevil damage.
TABLE 55. COTTON: ACREAGE HARVESTED, YIELD PER ACRE, PRODUCTION
OF LINT AVERAGES FOR THE TEN-YEAR PERIOD 1928-1937 AND 1938
PRODUCTION. ACREAGE AND PRODUCTION EXPRESSED IN THOUSANDS. GROSS
WEIGHT OF BALES IS 500 POUNDS
Production
Yield
Rank
States
Acreage
Harvested
per Acre,
in Lbs.
Average
1928-1937,
Percentage
of U. S.
1938,
in Bales
Total
in Bales
1
Texas
13,395
147
4,077
29.54
3,086
2
Mississippi . . .
3,436
225
1,596
11.57
1,704
3
Arkansas ....
2,903
212
1,273
9.22
1,349
4
Alabama ....
2,857
205
1,203
8.72
1,081
5
Georgia ....
2,721
212
1,192
8.64
852
6
Oklahoma . . .
3,098
133
876
6.35
563
7
South Carolina .
1,652
243
827
5.99
648
8
Louisiana ....
1,596
214
711
5.15
676
9
North Carolina .
1,219
281
702
5.09
388
10
Tennessee ....
945
238
466
3.38
490
Other states . . .
1,162
—
877
6.35
1,106
Total U S
34,984
190 8
13 800
1 00 00
11 943
Cotton production in Arizona and California is limited to the
southern irrigated valleys of these states. It will be observed from
Table 55 that ten states of the Cotton Belt account for practically
94 per cent of the cotton produced in the United States. The re-
maining 6 per cent is grown in Missouri, California, Arizona.
Florida, and Virginia.
Table 56 shows the exports of cotton from the United States tc
specified countries. Not all the cotton consigned to a given country
may necessarily be consumed there; some of it may be consigned
to agents at ports, notably Bremen, and hence classified as exports
510
ECOLOGICAL CROP GEOGRAPHY
to Germany rather than to the country where the cotton is actually
consumed or used in the manufacture of goods to be reexported.
Table 56 shows why the cotton industry is so vitally interested in
the economic and political affairs of the four corners of the world.
TABLE 56. EXPORTS OF UNMANUFACTURED COTTON LINT FROM THE UNITED
STATES TO SPECIFIED COUNTRIES. AVERAGES FOR THE FIVE-YEAR PERIOD
OF 1929-30 TO 1933-34
Rank
Country to Which Exported
Amount, in 7,090 Bales
Percentage of Total
United States Export
1
Germany
1,707
21.26
2
Taoan
1,695
21.11
3
United Kingdom
1,332
16.59
4
France
805
10.03
5
Italy
686
8.54
6
China
497
6.19
7
Spain
306
3.81
8
Canada
185
2.30
9
Belgium
160
1.99
10
Netherlands
141
1.76
11
British India
92
1.15
12
Sweden
63
0.78
13
Portugal
61
0.76
14
U.S.S.R
58
0.72
FIBER FLAX
Historical. Until comparatively recent times the nations of
western Europe depended for their textiles chiefly on wool and
flax. Cotton has long been used by the people of eastern Asia.
Marco Polo, the Venetian traveler who visited nearly all the
countries of Asia in the thirteenth century, found that cotton was
then being spun and woven in certain districts in China. Columbus
found the red men in America spinning and weaving cotton. But
through the centuries of Ancient Egypt, Greece, and Rome,
through the long Middle Ages, and well up into modern times,
the use of cotton fiber was confined chiefly to the peoples in the
countries of its early production. It was not until English inventive
genius was applied to the creation of modern cotton manufacturing
machinery and American genius to the creation of the gin that
cotton began to be extensively used in Western civilizations. As
cotton and cotton goods gained in popularity, fiber flax and linen
FIBER CROPS 511
steadily lost ground until it is at present of relatively little impor-
tance in comparison with cotton.
Fiber flax was a comparatively important crop in Colonial
America north of the Carolinas. Many homes had small hand
looms for weaving the homespun yarns. At the close of the eight-
eenth century numerous scutching mills operated in the north-
eastern states. They were dispersed by the advancing cheap cotton.
Fiber and Seed Flax. As the names indicate, fiber flax is grown
primarily for the production of fiber, and seed flax for the produc-
tion of seed and linseed oil. The two types are distinctly different.
Good fiber flax has long and unbranched stems, except for a few
short branches near the top of the stem on which the seed is borne.
Seed flax, on the other hand, is much shorter, and the stems branch
freely. The amount of branching is, however, determined to some
extent in both types by the amount of space available for the de-
velopment of individual plants. Dense stands of seed flax develop
little or no branching (Klages, 14).
Climatic Relationships. Fiber flax is more exacting in its
climatic requirements than seed flax. Climatic and soil conditions
not only affect the yield of the fiber but are definitely correlated
with the quality of the fiber produced. The crop demands moist,
cool weather during the early part of the growing season from
March to June, followed by warm and relatively dry weather
during the early portion of the summer. The absence of storms
that may cause lodging is also important. The fiber obtained from
twisted, lodged plants is of low quality and is used largely for
upholstery tow. Good climatic and soil conditions lead to the
development of plants with the desired length of stems below the
lowest branches and long fiber; short-fiber flax is suitable only
for the making of tow. Cloudy days are much desired during the
growth of fiber flax. If the weather turns warm and dry too soon,
the plants will produce seed and the stems will be short. Under
dry conditions not only will the stems produced be short and woody,
but the fiber will be harsh and dry.
World Distribution. Fiber flax is of importance in but few
areas. The bulk of the world's crop is produced in Russia and in
the countries around the Baltic Sea. According to data presented
by Robinson (19) covering the seven-year period ended June 30,
1937, the Soviet Union produced 574,898 tons of fiber as compared
512 ECOLOGICAL CROP GEOGRAPHY
to 173,080 tons for the production for the remainder of Europe.
The United States produced only 419 tons and all the other countries
8,669 tons of flax fiber. As stated by Robinson, "The Union of
Soviet Socialist Republics, the Baltic countries, and Poland together
produce over 80 per cent of the world's estimated production of
fiber, but the fiber produced in Belgium, the Netherlands, and
Ireland is considered of better quality than that from eastern
Europe." Japan is the only important non-European flax fiber
producing country.
Production in the United States. As the figures above indicate,
fiber flax production is of but minor importance in the United
States. Small acreages are grown in Michigan and in western
Oregon.
The production of fiber flax requires a great deal of hand labor
not only in the harvesting of the crop but also in preparing the
fiber; that is, in retting, drying after retting, breaking, and scutch-
ing. Since labor is cheaper in Europe than in this country, it has
been found economical to import flax fiber rather than to produce
it here. Practically all of the European crop is pulled by hand.
At the present time flax-pulling machines are used in this country.
A satisfactory pulling machine should reduce harvesting costs
materially.
OTHER FIBER PLANTS
Hemp (Cannabis saliva). Hemp is a tall-growing, annual, dioe-
cious plant. Hemp fiber is a white bast fiber that is valuable
because of its length, which varies from three to nine feet, its
strength, and its great durability. The male plants produce the
best grade of fiber. Hemp is also grown in Europe for the oil
extracted from its seeds, used for soap, paints, and varnishes. It
is also cultivated as a drug plant. The flowering tops and leaves
yield the drug known as hashish, a resinous substance containing
several powerful alkaloids.
Hemp requires a mild humid climate and a soil of high fertility.
Calcareous soils are particularly well adapted to its production.
Hemp is an old crop and has long been grown in China. It
was early introduced into Europe, and that continent is the center
of the industry today. Hemp is of special importance in Russia,
Italy, and Hungary. According to Marquart (16), the bulk of
FIBER CROPS 513
the Russian hemp is produced in the region between the Dnieper
and Volga Rivers between the latitudes of 50 and 55°. The Italian
crop is produced in the valley of the Po.
Hemp is of minor importance in the United States; Wisconsin
leads in production. The crop demands a great deal of hand labor.
The fiber is used for ropes, twine, carpets, sailcloth, yacht cord-
age, binder twine, sacks, and webbing.
Jute (Corchorus spp.). Jute, according to Hill (11), is used more
extensively than any other fiber except cotton, although it is less
valuable than either cotton or flax. Jute is a bast fiber obtained
from two species of Corchorus, C. capsularis, an upland, and C. oli-
torius, a lowland, species. These species are tall, slender, half-
shrubby annuals growing to a height of 8 to 12 feet. The crop is
harvested within three or four months after planting, while the
flowers are still in bloom. The fibers are long, quite stiff, and have
a silky luster. They are very abundant but not particularly strong
and tend to deteriorate rapidly when exposed to moisture. In
spite of these disadvantages the fact that jute is cheap and easily
spun makes it valuable. Practically all civilized countries import
some form of Bengal gunny, as it is often called. It is used for
rough weaving and especially for the making of bags and gunny
sacks. The fiber is also used for making twine, carpets, curtains,
and coarse cloth.
Jute is strictly a tropical plant. It demands a warm, humid
climate and docs best on soils of high fertility.
Although probably native to Malaya and Ceylon, jute is now
almost entirely an Indian crop. The bulk of the crop is produced
in the fertile lowlands of the Ganges and Brahmaputra Rivers.
The utilization of jute by Western nations is comparatively recent.
According to Bcrgsmark, the first regular export of raw jute from
India did not begin until 1838. The Crimean War, 1854-1856,
cutting off supplies of Russian flax and hemp fiber to western
Europe, greatly stimulated the demand for Indian jute. The
improvements that resulted from this stimulus caused the Indian
jute to supplant permanently the Russian materials. The Indian
jute manufactures were further stimulated during the first World
War by the demand for sandbags. During the period 1925-1933,
}ute manufactures and raw jute ranked second and third, respec-
tively, among the exports of India.
514 ECOLOGICAL CROP GEOGRAPHY
Ramie (Boehmeria nivea). Ramie is a perennial-rooted plant with
slender stalks reaching a height of three to six feet. The fiber is
obtained from the bast. It is fine, long, strong, and durable.
These qualities and its high luster would make ramie highly desir-
able for textile purposes were it not for the difficulties encountered
during the extraction and cleaning of the fibers. As stated by Hill,
"although it is the strongest fiber known, being three times as
strong as hemp, ramie is not very generally used because the treat-
ment necessary to remove the fibers is so expensive." The fiber has
long been used in southeastern Asia and is used to a limited extent
in Europe for portieres, upholstery, thread, and paper. Ramie is
grown in China, Japan, Formosa, and India. The main producing
area is around Hankow in the Yangtze Valley.
Abaca or Manila Hemp. This excellent fiber is obtained from
several species of wild plantain or banana. Musa textilis is the most
important source. The plant is of greatest commercial importance
in the Philippine Islands. The fibers represent structural elements,
sclerenchyma cells; they vary in color from white to reddish yellow
and are light, stiff, and strong. The chief use of abac^ is in the
manufacture of cordage, especially ^marine cables, for the fiber is
not injured by salt or fresh water. Other uses are for binder twine,
bagging, papier m&ch6, and wrapping paper. The plants require
rich, well-drained soils and a warm, humid climate.
Agave Fibers. Agave fibers are of special importance in the dry
areas of Mexico and Central America. The agaves are stemless
perennials with basal rosettes of erect, fleshy leaves which contain
the fibers. The plants are drought-resistant and are frequently
found on dry, sterile soils. Several species are of importance com-
mercially, the two most important ones being henequen and sisal.
Henequen or Yucatan sisal (Agave Jourcroydes) is a native of Mexico
and is grown chiefly in Tampico. The fiber produced from this
plant is light straw-colored, hard, wiry, and elastic, measuring from
three to five feet in length. Henequen is used chiefly for binder
twine, lariats, and similar products.
Sisal (Agave sisalana) is similar in appearance to henequen except
that the leaves lack the spines of the henequen which makes them
less difficult to handle. This plant, while native to Mexico and
Central America, is now also cultivated in Hawaii, the East and
West Indies, and many sections of Africa, especially in the British
FIBER CROPS 515
possessions. The plants are exceedingly drought-resistant. The
United States imports sisal for the making of binder twine, most
of the supply coming from Mexico and the Dutch East Indies.
REFERENCES
1. Agelasto, A. M., C. B. Doyle, G. S. Meloy, and O. C. Stine, "The
cotton situation," U. S. Dept. Agr. Yearbook 1921:323-406.
2. Baker, O. E., "Agricultural regions of North America, Part II, The
South," Econ. Geog., 3:50-86 (1927).
3. Bergsmark, D. R., Economic Geography of Asia. Prentice-Hall, New
York, 1936.
4. Brown, H. B., "A brief discussion of the history of cotton, its culture,
breeding, harvesting, and uses," La. State Dept. Agr. and Immigr., 1939.
5. Cressey, G. B., China's Geographic Foundations. McGraw-Hill, New
York, 1934.
6. Dowell, A. A., and O. B. Jesness, The American Farmer and the Export
Market. University of Minnesota Press, Minneapolis, 1934.
7. Ewing, E. C., "A study of certain environmental factors and varietal
differences influencing the fruiting of cotton," Miss. Agr. Exp. Sta.
Tech. Bull. 8, 1918.
8. Finch, V. C., and O. E. Baker, Geography of the WorlcTs Agriculture.
Govt. Printing Office, Washington, 1917.
9. Garside, A. H., Cotton Goes to Market. Stokes, New York, 1935.
10. Henderson, W. O., The Lancashire Cotton Famine, 1861-1865. Man-
chester University Press, Manchester, 1934.
11. Hill, A. F., Economic Botany. McGraw-Hill, New York, 1937.
12. Huntington, E., F. E. Williams, and S. von Valkenburg, Economic and
Social Geography. Wiley, New York, 1933.
13. Hutcheson, T. B., T. K. Wolfe, and M. S. Kipps, The Production of
Field Crops. McGraw-Hill, New York, 1936.
14. Klages, K. H. W., "Spacing in relation to the development of the
flax plant," Jour. Amer. Soc. Agron., 24:1-17 (1932).
15. Marbury, J. R., "Relation of weather conditions to growth and
development of cotton," U. S. Dept. Agr. Yearbook 1904:141-150.
16. Marquart, B., Der Hanfbau. Paul Parey, Berlin, 1919.
17. Morgan, M. F., J. H. Gourley, and J. K. Ableiter, "The soil require-
ments of economic plants," U. S. Dept. Agr. Yearbook 1938:753-776.
18. Norris, P. K., "Cotton production in Egypt," U. S. Dept. Agr. Tech.
Bull. 451, 1934.
19. Robinson, B. B., "Flax-fiber production," U. S. Dept. Agr. Farmers9
Bull. 1728, 1940.
516 ECOLOGICAL CROP GEOGRAPHY
20. Smith, G. R., "Gin damage of cotton in relation to rainfall," N. C. Agr.
Exp. Sta. Bull. 306, 1936.
21. Stine, O. C., and O. E. Baker, Atlas of American Agriculture, Part V,
Sec. A, Cotton. Govt. Printing Office, Washington, 1918.
22. Vance, R. B., Human Factors in Cotton Culture. University of North
Carolina Press, Chapel Hill, 1929.
23. Ware, J. O., "Plant breeding and the cotton industry," U. S. Dept.
Agr. Yearbook 1936:657-744.
Chapter XXIX
ANNUAL LEGUMINOUS FORAGE CROPS
INTRODUCTION
Annual legumes are utilized for a variety of purposes. The use
of annual legumes for human consumption was discussed in
Chapter XXIV under the heading, "Edible Legumes." Certain
legumes, as soybeans and peanuts, are grown not only for human
consumption but also for forage and for the production of vegetable
oil. Others are grown strictly for forage and soil improvement
purposes depending on their specific characteristics. Climatic as
well as economic conditions determine to a high degree the special
uses made of certain annual legumes.
SOYBEANS
(Soja max)
The soybean, while being used in the United States primarily
as a forage crop, is of considerable importance as a producer of
vegetable oil. For that reason this crop was discussed in Chapter
XXVII, "Oil Producing Crops."
COWPEAS
(Vigna sinensis)
Historical. The cowpea in reality is not a pea but a bean. It
was commonly cultivated for human food in the Old World before
the discovery of America. According to Piper (16), "it is without
doubt the Phaseolus of Pliny, Columella and other Roman writers,
but this name became applied also to the kidney-bean following
its introduction into Europe from America." In Italy the blackeye
cowpea is still called by the same name as kidney beans, jagiola^
which is the Italian equivalent of Phaseolus.
The cowpea is a native of central Africa. Wild plants differing
but little from cultivated cowpeas occur throughout much of that
517
518 ECOLOGICAL CROP GEOGRAPHY
continent. According to Morse (14), "the large number and great
diversity of cultivated varieties throughout Africa and over the
southern half of Asia and the adjacent islands as well as the Mediter-
ranean region of Europe indicate that the cowpea is of ancient
cultivation for human food."
The cowpea was grown in North Carolina in 1714, coming in all
probability from the West Indies where it was early introduced by
the Spaniards. The first culture of the crop in Virginia was reported
about 1775.
Utilization. The cowpea is generally regarded as a forage and
soil-improvement crop, though the Blackeye and White varieties
are commonly used for human food in the southern states. Thus
Morse (13) in speaking of conditions prevailing in the southern
states britigs out that "the cowpea has been used more as a soil
renovator than any other legume because it is so easily grown,
has such a marked effect upon succeeding crops, and succeeds
under such a great diversity of conditions."
Climatic and Soil Relationships. The temperature require-
ments of the cowpea reflect the tropical origin of the crop. The
crop demands higher temperature^ than corn. This is well illus-
trated in Fig. 95, taken from Morse (14), showing the comparative
distribution of cowpeas in the United States. The crop has greatest
value in the southern states and becomes of decreasing importance
in the North. Cowpeas require higher temperatures than early
maturing varieties of soybeans. The leaves of cowpeas are readily
damaged by late spring and early fall frosts.
After cowpeas are once established, they are able to withstand
relatively dry conditions. Droughts, however, reduce both hay
and especially seed yields. This is also indicated in Fig. 95. The
importance of cowpeas tapers off rapidly as the southern Great
Plains area is approached.
Gowpeas can be successfully grown under a great variety of soil
conditions, the only specific demand being that the soil be well
drained. They do well on sandy and also on heavy clay soils, and
better than clover or alfalfa on thin soils or on soils that are low
in lime. "No other legume," states Morse (14), "can be grown so
successfully on such a variety of soils under adverse conditions
as the cowpea.35 Cowpeas are quite similar with respect to toler-
ance to adverse soil conditions to the annual lespedezas. The ability
ANNUAL LEGUMINOUS FORAGE CROPS
519
of the crop to grow on poor soils together with its great value as a
soil-improving crop accounts in part for the great importance of
cowpeas in the southern states. Where the crop is to be used for
the production of seed, better results are obtained on soils of
moderate than on those of high fertility. A high fertility level
leads to an abundant vine growth to the detriment of seed develop-
ment.
FIG. 95. Outline map of the United States showing the comparative distribu-
tion of cowpeas. (1) Area in which cowpeas are grown most extensively; (2) area
in which cowpeas are grown quite generally; (3) area in which cowpeas are grown
to some extent. (After Morse, 14.)
Distribution. No data on the world distribution of cowpeas are
available. It is known, however, that the crop is of considerable
importance in Asia and particularly in India. Cowpeas are also
grown in the Mediterranean region. In these areas the crop is
grown largely for seed and for human consumption. Only the
Blackeye and White varieties are used for human consumption
in the United States. Their production is of great importance in
the Cotton Belt and in the interior valleys of California. The
California Agricultural Experiment Station has developed a wilt-
resistant Blackeye "pea" that gives promise in the seed producing
areas of that state.
520 ECOLOGICAL CROP GEOGRAPHY
The important cowpea producing states together with the acreage
in 1936 expressed in 1,000 acres are: Texas, 998; South Carolina,
803; Georgia, 625; Arkansas, 517; Mississippi, 423; Alabama, 396;
North Carolina, 290; Louisiana, 216; Illinois, 181; and Tennessee,
163. These tabulated acreages comprise the areas where the crop
is grown alone plus approximately one-half the interplanted acres.
ANNUAL LESPEDEZAS
Varieties and Origin. Since the range of adaptation of the
annual lespedezas is definitely associated with their specific char-
acteristics, it is necessary to call attention to the characteristics of
the several species and varieties. The subdivision of the genus
Lespedeza and the enumeration of the most important varieties
are given by Pieters (15) in the following paragraph.
"The genus Lespedeza includes some 125 species of which only 2 are
annuals. Both of these species L. striata (Thunb.) H. & A. and L.
stipulacea Maxim, have been introduced into the United States from the
Orient. L. striata has been in this country for about 100 years while L.
stipulacea was introduced from Chosen (Korea) in 1919. Named varie-
ties of each species are now more*or less widely distributed. Under
L. striata are to be distinguished th%e common lespedeza, Kobe, and
Tennessee 76, and under L. stipulacea are Korean, Harbin, and the early
Korean U.S.D.A. 19604."
The term "common lespedeza" has been used synonymously
with Lespedeza striata. Pieters recommends that the term "common
lespedeza" be used to designate unselected forms of this species
growing spontaneously throughout its range as distinguished from
selected varieties such as Tennessee 76 and Kobe. Likewise the
term "Korean" should be used to designate the unselected forms of
L. stipulacea; selected forms can then be designated by special
names.
Common lespedeza is a slender plant, usually prostrate in growth
except in dense stands, and has small leaflets and purple flowers.
Kobe is larger, coarser, and somewhat more erect and has larger
leaves and distinctly larger seeds.
Lespedeza stipulacea differs from L. striata in having significantly
broader leaflets and stipules.
Utilization. The annual lespedezas are used strictly for forage
and soil-improvement purposes. Their ability to grow on poor and
ANNUAL LEGUMINOUS FORAGE CROPS 521
even acid soils makes them of special value for soil conservation
and soil improvement.
The ravages of clover anthracnose (Colletotrichum trifolii) have
resulted in marked decreases in the acreages of red clover in Ten-
nessee, Kentucky, and adjacent states; that is, in areas to which
lespedeza is well adapted. As a result large acreages formerly
devoted to red clover production are now used for the growing of
lespedeza. The availability of anthracnose-resistant strains of
red clover may be expected to counteract this trend to some extent.
But the fact remains that lespedeza is more dependable than either
red clover or alfalfa in this area. This dependability of the crop
even under adverse soil conditions has, according to Kinney et al.
(5), contributed much to its popularity. Owing to the tolerance
of lespedczas for soil acidity, the liming of acid soils is not as essen-
tial in the production of leguminous feeds when they are used as
when clovers or alfalfa are grown for the purpose.
Lespedeza as a forage is used especially for the production of
pasturage. While the plant is an annual, it will maintain itself
over a period of years under proper pasture management. Under
favorable climatic conditions the crop is a prolific seed producer.
The larger growing lespedezas, such as Korean and Tennessee 76,
arc also valuable hay crops, especially where soil and other condi-
tions interfere with the production of red clover and alfalfa. The
production of lespedeza hay is, however, more or less limited to
fairly productive soils.
Geographical Range. Some varieties of lespedeza will produce
seed from the Gulf of Mexico to the northern border of Illinois.
Harbin will, according to Picters, produce seed to the northern
limits of the United States. Lespedeza is, however, in a poor com-
petitive position to replace the ordinary clovers to any appreciable
extent in the northern areas of the United States. Lespedezas are
hot-weather and short day plants, most of them will not bloom
and seed under long day conditions. The slow growth of the plants
during the spring months also interferes with the utilization of
lespedeza in northern areas.
"Lespedezas," states Pieters, "are .strongly drought-resistant,
but during prolonged drought little if any growth is made." This
reaction to moisture conditions sets a rather definite limit to the
western distribution of the crop. The lespedezas cease to be a crop
522 ECOLOGICAL CROP GEOGRAPHY
of importance farther west than the eastern tier of counties in Kansas
and Oklahoma.
The varieties of Lespedeza striata are best suited to the area from
northern Tennessee to the Gulf. Kobe and Tennessee 76 are late-
maturing varieties. The range of Kobe extends from southern
Illinois to southern Mississippi and from eastern North Carolina
to western Tennessee. Tennessee 76 is chiefly grown in eastern
and central North Carolina and in western Tennessee. Lespedeza
stipulacea (Korean) matures earlier than L. striata. It reaches its
best development in a zone including Virginia and North Carolina
on the east and eastern Kansas and Oklahoma on the west.
Korean lespedeza is also suited to the Piedmont area of South
Carolina, Georgia, Alabama and extends north to central Illinois
and Indiana.
CRIMSON CLOVER
(Trifolium incarnatum)
Historical. Crimson clover is a native of Europe. It has long
been grown as a forage and soil-improvement crop in the countries
of western and central Europe. The crop was introduced into the
United States as early as 1818, and seed was widely distributed
by the Patent Office in 1855. On account of the showy, bright-
crimson heads the plant was first regarded more for its ornamental
value than as a forage plant. It was not until about 1880 that the
value of the crop for agricultural purposes began to be appreciated
(Kephart, 4).
Utilization and Distribution. Crimson clover is an important
winter annual legume and is used for the production of spring and
early summer pasture, as a cover and green manure crop, and to
some extent for hay. The crop is often seeded for the production
of hay in combination with rye, vetch, and Italian ryegrass.
Crimson clover is frequently seeded in corn and cotton at the last
cultivation of those crops.
Crimson clover is quite tolerant in its soil requirements. It does
well on sandy soils. It is not as dependent on lime as red clover
and alfalfa, being more like alsike clover in that respect. The
crop does not, however, thrive on very acid soils. Furthermore,
good drainage is required.
Crimson clover is adapted to cool, humid areas. It can be used
ANNUAL LEGUMINOUS FORAGE CROPS 323
as a winter annual only where temperatures are not severe or too
variable. Ordinarily it does not survive the winters in latitudes
north of southern Pennsylvania. The crop matures prior to the
advent of high summer temperatures. Dry conditions in the
autumn months sometimes interfere with the establishment of
stands. Crimson clover can be grown as a summer crop in northern
areas, but other clovers may be expected to give better returns in
such sections.
Figure 96, taken from Hollowell (2), gives the location of the
principal crimson clover producing areas of the United States.
FIG. 96. Principal crimson clover producing regions of the United States. (After
Hollowell.)
It will be observed that the crop is grown along the Atlantic Coastal
Plain and the more humid portions of the Cotton Belt. Crimson
clover is also adapted to the western portions of Oregon and Wash-
ington, but it has not become of importance there. Other legumi-
nous plants in this area are generally more productive than crimson
clover.
BUR CLOVER
Species of Bur Clover. Two important species of bur clover
are commonly grown in the United States, namely, the spotted or
southern bur clover (Medicago arabica) and the toothed or California
524 ECOLOGICAL CROP GEOGRAPHY
bur clover (M . hispidd). Two other species are grown to a limited
extent, the Tifton bur clover (M. rigida) and M. minima. The
Tifton bur clover has been grown and distributed from the Georgia
Coastal Plains Experiment Station, located at Tifton, while the
M. minima has been naturally introduced in a number of places
in the southern states and is gradually spreading. According to
McKee (9), M. minima is comparable with spotted bur clover in
winter-hardiness, but Tifton bur clover is the most hardy of all
and usually will survive most winters as far north as Washington,
B.C.
Several species of spotted bur clovers with spineless pods, as
the button clover (M. orbicularis), snail clover (M . scuiellatd), and
tubercled clover (M. tuberculata)^ have been tested. "Experience
has shown, however, that the varieties with large spineless burs
cannot be maintained in pastures except when given special atten-
tion and protection. . . . The seed of spineless varieties with small
burs," continues McKee (9), "escape grazing animals more
readily, and consequently are more persistent and are not uncom-
mon in California."
Utilization. The bur clovers a^e winter annuals ; that is, they
germinate in the autumn, grow during the fall, winter, and early
spring, and mature early in summer. Because they are prolific
seed producers, and also because of the procumbent habits of
growth of the plants and the fact that the burs are protected to
some extent by spines, the plants volunteer readily. Under proper
systems of management the plants may maintain themselves
indefinitely. Sheep are fond of the burs and eat them readily,
especially after they have been softened by rain.
Bur clover is utilized mostly as pasture for cattle, hogs, and sheep.
It is reported that horses will eat the toothed or California bur
clover but will avoid the spotted bur clover. Bur clover is also
used to advantage in combination with bermuda grass in perma-
nent pastures. The bermuda provides pasturage during the summer
months, whereas the bur clover begins to grow with cool weather
in fall and provides pasturage during the winter and spring. Bur
clover may be pastured in North Carolina by the middle of Feb-
ruary, and near the Gulf it furnishes practically continuous winter
pasturage.
Under favorable conditions bur clover can be used for the produc-
ANNUAL LEGUMINOUS FORAGE CROPS
525
tion of hay. However, if the crop is to be used for that purpose
it is best to seed it in mixtures with either winter oats or wheat.
The cereals will tend to support the bur clover.
Bur clover is also used to advantage as a cover and green manure
crop. The habit of the plants to volunteer enhances their value
for this purpose.
Geographical Range. The bur clovers are of value only in areas
where the winters are mild and where moisture is available during
the winter and early spring months. They are extensively grown in
the Mediterranean area and also in Australia, Argentina, and Chile.
] SPOTTED BUR-CLOVER
PARTICULARLY
FIG. 97. Outline map of the United States, showing the regions to which bur
clover is adapted. (After McKee.)
In the United States bur clover is grown in the Cotton Belt and
along the Pacific coast from California to western Oregon and
Washington. On account of temperature limitation the bur clover
producing regions of the South do not extend quite as far to the
north as those producing cotton. The crop is very important in
the lower ranges of California but only of limited importance in
Oregon and Washington. Spotted bur clover is better adapted to
conditions in the Cotton Belt and especially to the northern portion
of the bur clover producing area than the toothed or California
bur clover. McKee (9) reports that California bur clover is
destroyed in winter by temperatures that do little or no harm to
326 ECOLOGICAL CROP GEOGRAPHY
the spotted bur clover. Both the toothed and the spotted bur
clovers are grown in California.
Figure 97, taken from McKee (9), shows the regions of the
United States to which bur clover is adapted.
VETCHES
Species and Varieties. Plants of the genus Vicia are commonly
referred to as vetch. One of the exceptions to this is the horsebean
or broadbean (Vicia Jaba). This species is grown primarily for
seed; it is therefore classified as an edible legume.
The vetches of most importance as listed by McKee and Schoth
(12) are common vetch (Vicia saliva), hairy vetch (V. villosa), smooth
vetch (V. villosa), purple vetch (V. atropurpurea), narrowleaf vetch
(V. angustifolia), woollypod vetch (V. dasycarpa), bitter vetch
(V. Ervilia), monantha vetch (V. monantha), Hungarian vetch
(V. pannonica), and Bard vetch (V. calcarata). With the exception
of bitter vetch, which is grown in the Mediterranean area, these
species are all used in the United States.
The common agricultural species are all viny or weak-stemmed.
The stems attain a length of from tvfq to five feet or more and unless
supported by companion crops assume a procumbent position.
While some of the different species have quite distinctive character-
istics, others are very much alike and sometimes are almost indis-
tinguishable. The various species show great variations with regard
to climatic adaptation, and some differences in regard to soil
tolerances.
Utilization. All of the commercial vetches make good hay,
silage, and pasturage. Since they grow or at least maintain them-
selves during the winter months, they are also of value as cover
and green manure crops. Their ability to grow at moderate tem-
peratures and their rapid development in spring make them of
value as soiling crops. Surplus and waste seed is used in ground
poultry feeds.
Common and Hungarian vetch are most generally used for hay.
For that purpose they are commonly grown with a companion
crop such as winter oats. Narrowleaf vetch may be sown to advan-
tage in Johnson grass-infested bottom lands in the South.
Probably the greatest use of vetch is for green-manuring. Hairy
vetch and smooth vetch are used extensively as cover and green
ANNUAL LEGUMINOUS FORAGE CROPS 527
manure crops in the Cotton Belt. Monantha vetch is used for the
same purpose in the extreme South, and purple vetch is used for
green manure in California. Owing to their tendencies to volunteer
and create objectionable admixtures, the winter-hardy hairy vetch
and smooth vetch should not be grown in strictly winter wheat
producing areas.
Seed Production. Most of the seed of common, Hungarian,
purple, and monantha vetches are produced in the United States.
Western Oregon and western Washington produce most of the
vetch seed of the country. Hairy vetch is also produced in Europe
in the countries bordering the Baltic Sea and south to Hungary,
while the less winter-hardy common vetch is produced in the more
southern European countries and in the British Isles. Bitter vetch
is produced in the eastern Mediterranean region where it is used
as stock feed.
The vetch seed producing areas of the United States are enumer-
ated by McKee and Schoth in the following paragraph.
"In the United States hairy- vetch seed is produced in Michigan,
western Oregon, and western Washington; common and Hungarian in
western Oregon, and western Washington; monantha and purple in
western Oregon, western Washington, and northwestern California;
smooth in western North Carolina; and woollypod vetch in western
Oregon."
Distribution. The distribution of the many species of vetch is
closely related to the abilities of the different types to endure winter
temperatures. Hairy vetch is winter-hardy and is for that reason
extensively grown in northern Europe and in the northern portion
of the United States. The smooth vetch is reported by McKee and
Schoth to be winter-hardy but somewhat less so than hairy vetch.
In turn the woollypod vetch is reported by these same investigators
to be somewhat less hardy than the smooth vetch. Klages (6)
tested the winter-hardiness of the various vetches mentioned in this
discussion, with the exception of smooth vetch, at the Oklahoma
Agricultural Experiment Station. All types except hairy vetch,
woollypod vetch, and Hungarian vetch were not sufficiently winter-
hardy to survive under northern Cotton Belt conditions. The first
two showed no winter injury; the Hungarian vetch showed 14 per
cent of winterkilling; all of the other species were entirely killed
during the more severe of the two years of the test. The non-
528 ECOLOGICAL CROP GEOGRAPHY
winter-hardy species are limited to regions with mild winters,
the Central and Southern Cotton Belt, and the western portions
of the Pacific states. Hairy vetch is the only variety recommended
for fall planting in the North.
The vetches are quite similar to peas with regard to their moisture
and temperature requirements during the growing season in that
they demand moderate temperatures and moisture supplies. None
of the vetches are particularly drought-resistant.
Vetches are rather tolerant with regard to their soil requirements.
They are less affected by acid soil conditions than most legumes.
The soil response of the various species differ. Thus hairy, smooth,
and monantha vetches do well on poor sandy soils, while Hun-
garian vetch succeeds on wet soils where other kinds produce but
little growth.
OTHER ANNUAL LEGUMINOUS PLANTS
Austrian Winter Pea (Pisum sativum). The Austrian winter pea
is the most winter-hardy of the field pea varieties. On account of
its low minimum-temperature growing point it is highly valued
as a winter cover and green manui%jcrop. Next to hairy vetch it is
the most widely used winter legume in the United States. The
Austrian winter pea is not as winter-hardy as hairy vetch. It will
survive the winters only in the humid portions of the Cotton Belt.
The crop is not commonly grown outside of the Cotton Belt. Some
seed is produced from fall plantings in the Pacific Northwest, and
a limited amount from spring seedings in the northern Great Plains
area.
Vclvctbcan (Stizolobium spp.). This vigorous-growing plant
produces vines, with the exception of the bush varieties, usually
attaining a length of 10 to 25 or more feet. The crop is utilized
as a pasture and hay crop and as a summer green manure crop.
The ground beans are also used for feed. Since, however, the pods
are generally picked by hand, harvesting costs run high.
The production of velvetbeans in the United States is found on
the well-drained Coastal-Plains soils of the South Atlantic and Gulf
states. The crop demands high summer temperatures and a fairly
abundant supply of moisture. Up until 1906 the Florida velvet-
bean was the only species grown in the country. This is a late
variety requiring eight or nine months to reach maturity. Since
ANNUAL LEGUMINOUS FORAGE CROPS 529
that time, early-maturing varieties have been introduced from
China and Japan. These early-maturing varieties can, according
to Piper and Morse (17), be grown in the northern portion of the
Cotton Belt. However, as far north as that they have no special
advantage over cowpeas or soybeans.
Crotalaria (Crotalaria spp.). McKee and Enlow (11) report that
the genus Crotalaria contains around 600 species. Only two, Crota-
laria striata and C. spectabilisy are grown commercially in the United
States. The crop demands a long growing season, high tempera-
tures, and fairly abundant supplies of moisture. The principal
use is for green manure. Crotalaria hay is reported to produce
poisoning in cattle. Seeds are poisonous to swine and poultry.
The crop does well on poor sandy soils in the South. Most of the
seed used in the southern United States is imported from Puerto
Rico. Some seed is grown in Florida.
Berseem (Trifolium alexandrinum). Berseem or Egyptian clover
occupies an important role in the agriculture of Egypt, where it is
the foundation of the dairy and beef stock industry. It is also used
as a green manure crop.
Berseem resembles red clover in its habits of growth. The stems
are hollow and very succulent. Most of the roots are found in the
first two feet of the soil. The crop is tolerant of moderate quantities
of white alkali. This annual legume will produce four to five crops
of hay per year under favorable conditions.
Kennedy and Mackie (3) indicate that the crop promises to be of
value as a leguminous crop for winter growing under irrigation in
regions with a climate similar to that of the Imperial Valley of
California. The crop is grown with success in Italy and Australia.
In Australia it is referred to as "winter lucerne" because it amply
fills in the period when alfalfa is dormant.
Subterranean Clover (Trifolium subterraneum). This annual
clover is reported to be a native of Europe, Asia, and Africa. It
is found especially in the Mediterranean regions and in central and
southern Europe. It was introduced into Australia where it is
now being used as a pasture crop. Harrington (1) considers it
as a pasture legume of first importance in the temperate regions of
southern and eastern Australia. Leidigh (8) regards the crop as
valuable in southeastern Texas, but states that it is not especially
drought-resistant. Klages (7) found that the plant's lack of ag-
530 ECOLOGICAL CROP GEOGRAPHY
gressiveness and drought resistance made it unsuitable in central
Oklahoma.
Subterranean clover is quite similar to bur clover in its habits of
growth but is probably less drought-resistant. The plants remain
green farther into early summer than bur clover. The plants reseed
themselves by burying a part of the seed pods in the ground much
like peanuts. It is a prolific seed producer and under humid condi-
tions will maintain itself year after year. Since subterranean clover
is not especially winter-hardy, it can be used only in the central
and southern portion of the Cotton Belt.
Common Sesbania (Sesbania macrocarpa). This annual upright-
growing legume is native to North America and extends as far
north as Alabama, Georgia, and Arkansas. Sesbania, as it is known
in the trade, is used strictly for soil improvement. It is a subtrop-
ical, summer-growing plant, making but little growth in cool
weather. Where moisture is available, it grows rapidly at high
temperatures and under conditions of very low atmospheric
humidity. Sesbania demands fertile soils. According to McKee
(10), the crop is used for green manure in connection with the
production of winter truck crops lip the Imperial and Coachella
Valleys of California and in the Yuma and Salt River Valleys of
Arizona.
Sour Clover (Melilotus indica). Sour clover is an upright-
growing winter annual with much the same temperature growth
requirements as bur clover. It is used as a green manure crop in
the Southwest, the lower Mississippi Delta, and on the black lands
of Mississippi and Alabama.
Serradella (Ornithopus sativus). Serradella is a vetchlike annual
native of the Iberian Peninsula and Morocco. It is cultivated as
a forage and green manure crop in western and central Europe
and is of special importance as a soil-improvement crop on the
sandy soils along the North and Baltic Seas. It has not become of
importance in the United States.
Lupine (Lupinus spp.). Lupines are used in the areas with sandy
soils in western and central Europe, and especially in Germany,
for soil-improvement purposes. They have not become established
commercially in this country.
ANNUAL LEGUMINOUS FORAGE CROPS 531
REFERENCES
1. Harrington, J. E., "Subterranean clover," Jour. Dept. Agr. of Victoria,
34:609-614 (1936).
2. Hollowell, E. A., "Crimson clover," U. S. Dept. Agr. Leaflet 160, 1938.
3. Kennedy, P. B., and W. W. Mackie, "Berseem or Egyptian clover,"
Calif. Agr. Exp. Sta. Bull. 389, 1925.
4. Kephart, L. W., "Growing crimson clover," U. S. Dept. Agr. Farmers'
Bull. 1142, 1922.
5. Kinney, E. J., R. Kenney, and E. N. Fergus, "The lespedezas in
Kentucky," Ky. Agr. Exp. Sta. Circ. 297, 1937.
6. Klages, K. H. W., "Comparative winterhardiness of species and
varieties of vetches and peas in relation to their yielding ability,"
Jour. Amer. Soc. Agron., 20:982-987 (1928).
7 ^ "Comparative ranges of adaptation of species of cultivated
grasses and legumes in Oklahoma," Jour. Amer. Soc. Agron., 21:201-
223 (1929).
8. Leidigh, A. H., "Subterranean clover — a new sandy-land grazing
crop for southeastern Texas," Tex. Agr. Exp. Sta. Circ. 37, 1925.
9. McKee, R., "Bur clover cultivation and utilization," U. S. Dept. Agr.
Farmers' Bull. 1741, 1934.
10. , "Summer crops for green manure and soil improvement,"
U. S. Dept. Agr. Farmers' Bull. 1750, 1939.
11. ? ano» Q R Enlow, "Crotalaria, a new legume for the Soufh,"
U. S. Dept. Agr. Circ. 137, 1931.
12. , and H. A. Schoth, "Vetch culture and uses," U. S. Dept. Agr.
Farmers' Bull. 1740, 1934.
13. Morse, W. J., "Cowpeas: utilization," U. S. Dept. Agr. Farmers' Bull.
1153, 1920.
14 ? "Cowpeas: culture and varieties," U. S. Dept. Agr. Farmers9
Bull. 1148, 1924.
15. Pieters, A. J., "The annual lespedezas as forage and soil-conserving
crops," U. S. Dept. Agr. Circ. 536, 1939.
16. Piper, C. V., Forage Plants and Their Culture. Macmillan, New York,
1937.
17. 9 and w. J. Morse, "The velvetbean" (revised by W. J.
Morse), U. S. Dept. of Agr. Farmers' Bull. 1276, 1938.
Chapter XXX
BIENNIAL AND PERENNIAL LEGUMINOUS
FORAGE CROPS
ALFALFA
(Medicago saliva)
Importance as a Forage Crop. Alfalfa is the most valuable hay
crop produced in the United States. While it is not grown on as
many farms in the country as timothy and clover, the total tonnage
of alfalfa hay is greater than that produced by timothy and clover.
In 1934, alfalfa acreages were reported on 877,453 farms; the total
acreage amounted to 11,669,000 acres; and the total production
of alfalfa hay was 18,742,100 tons. The corresponding data for
timothy and clover, grown either alone or in mixtures, were
1,247,079 farms, 19,978,700 acres* .and 16,346,100 tons of hay.
All other tame and wild grasses were grown on 994,619 farms, on
1 7,930,81 3 acres, which produced 1 1 ,798,065 tons of hay. Further-
more, the importance of alfalfa as a hay crop has been increasing.
As stated by Westover (16), in 1919 only one-eighth of the total
hay acreage of the United States was in alfalfa; by 1938 the crop
occupied over one-fifth of the total acreage. In 1938 alfalfa was
grown on 13,462,000 acres in the country and produced 28,858,000
tons of hay. Data dealing with the comparative acreages and
tonnages of alfalfa and other classes of hay do not bring out the
full value of alfalfa as a forage crop. Alfalfa produces not only
higher yields per acre than the other perennial forage crops but
also has a higher feeding value per ton of hay produced. This is
the case especially in comparisons of alfalfa with grass and legume-
grass mixed hays. As a result of its ability to produce a high tonnage
and a hay of exceptionally high quality, alfalfa supports a larger
number of animal units than any other hay produced in the United
States.
The forage uses of alfalfa are not limited to the production of
hay. It has a high carrying capacity as a pasture crop. When
532
PERENNIAL LEGUMINOUS FORAGE CROPS 533
properly handled it produces a valuable silage. In addition to
its energy content, alfalfa is a valuable source of carotene, ribo-
flavin (vitamin G), protein, and calcium. Primarily because of its
high content of these ingredients alfalfa is used not only as a general
feed but also in special feeds such as the laying and growing rations
for poultry.
Importance as a Soil Builder. In areas to which alfalfa is
adapted it provides the cornerstone of systems of crop rotations
designed to maintain or even to increase the fertility of the soil.
In addition, its early and prolific growth makes it valuable in
rotation systems for weed-control purposes, even for the control of
troublesome perennial weeds.
Throckmorton and Salmon (15), in speaking of the merits of
alfalfa, state that "there is no other crop which is so essential in
relation to the live-stock industry, so useful to rotate with other
crops, or so valuable in proportion to the cost of production."
Historical. Alfalfa is one of the oldest of plants cultivated solely
for forage. Media or Persia is in all probability the region of its
original cultivation. Wild alfalfas closely resembling the cultivated
plants are found in this area. The ancient Persians used alfalfa
extensively and carried the plant with them in their military expedi-
tions. Thus the armed forces of Persia carried alfalfa to Greece.
From there it reached northern Africa and thence found its way
to Italy. Early Greek and Roman writers testified their high
esteem for alfalfa, or Medica as they called it. Alfalfa was introduced
into Spain by the Arabs. From there it moved into France, Ger-
many, and England. It seems strange that a plant as valuable as
alfalfa did not become of agricultural importance in western
Europe until the seventeenth century. Lack of knowledge of the
soil requirements of the plant, and failure to inoculate the soils
on which the crop was first sown were no doubt contributing
factors in the slow penetration of alfalfa into the humid area of
western Europe. In this connection it should be kept in mind that
alfalfa has for long periods been regarded as a crop adapted only
to subhumid and relatively dry regions. Its production in tem-
perate humid areas is of comparatively recent origin.
Alfalfa was carried to the western hemisphere by the Spaniards,
probably first to Mexico and thence to South America. Gold
seekers, on their way around Cape Horn, picked up seed of the
534 ECOLOGICAL CROP GEOGRAPHY
plant in Chile and brought it to California in the late forties or
early fifties of the nineteenth century. From there it spread rapidly
to the north and east. Earlier introductions of alfalfa to the eastern
states from southern Europe failed to establish the culture of the
plant there.
Types and Varieties of Alfalfa. Five general groups of alfalfa
are commonly recognized. Since these groups differ materially in
their climatic requirements, and especially in their abilities to
survive under low temperature conditions, they will be discussed
briefly. These groups are the yellow-flowered, the common, the
Turkestan, the variegated, and the nonhardy. All of these alfalfas
with the exception of the yellow-flowered group are classified as
Medicago saliva, or as cultivated alfalfas. The yellow-flowered
alfalfas belong to the species Medicago Jalcata. They are frequently
referred to as "Siberian alfalfas," although not all yellow-flowered
alfalfas come from Siberia.
The yellow-flowered alfalfas are of comparatively little agronomic
importance. They are hardy and able to survive under dry condi-
tions. Their chief value is for hybridizing with the purple-flowered
types.
The common alfalfas are grown extensively over a wide range of
conditions. This group includes the ordinary purple-flowered
smooth alfalfa. Regional strains are designated by their place of
origin such as Kansas-grown, or Idaho-grown, and differ primarily
in their tolerance to low temperatures. Northern-grown common
alfalfas are generally recognized to be more winter-hardy than
southern-grown strains. As a matter of fact, a good many failures
with alfalfa in northern areas can often be attributed to the use
of southern-grown seed. The production of alfalfa seed from fields
seeded with northern-grown seed in southern areas can be utilized
in providing northern regions with an adapted source of seed.
Such a program of seed production would not lead to immediate
reductions in the winter-hardiness of the plants. Common alfalfas
have a rapid rate of recovery after cutting.
The Turkestan alfalfas have been developed in Russian Turkestan.
They are quite similar in appearance and climatic adaptation to
the common alfalfas except that they may be somewhat shorter
and more spreading in habits of growth, and slightly more hairy.
Certain strains of Turkestan alfalfa are highly resistant to bacterial
PERENNIAL LEGUMINOUS FORAGE CROPS 535
wilt of alfalfa (Aplanobacter insidioswri) and are of special value for that
reason. They are winter-hardy in northern areas. The Turkestan
alfalfas are generally characterized by a slow recovery after cutting.
The variegated group includes the alfalfas that have originated
from crosses between common and yellow-flowered species. These
alfalfas exhibit a range of flower colors, hence the name "varie-
gated"; most of the flowers are purple, as are the common alfalfas;
others show a variety of colors from white to yellow or a combination
of colors. The variegated alfalfas are known for their cold resistance.
However, they differ but little in this from northern-grown common
strains. The variegated varieties do not generally recover as
rapidly after cutting as the common alfalfa.
The nonhardy alfalfas, as the name indicates, lack in winter-
hardiness and are for that reason confined to the southern portion
of the United States. In areas with mild winters redeeming features
that make them of value include their long periods of growth, their
ability to make a more rapid growth under short days than the
hardier northern strains, and especially their very rapid recovery
after cutting. For these reasons the nonhardy alfalfas are able to
produce a larger number of crops per season under southern
conditions than the other groups.
Climatic Relationships. Alfalfa is grown over a wide range 0f
temperature and moisture conditions. It is an important crop
from the southern valleys of Arizona and California to the prairie
provinces of Canada, or from BWh to the Dfb and from the EB'd
to the CC'd climates. High summer temperatures alone do not
set limits to alfalfa production, nor do low winter temperatures.
High summer temperatures combined with even moderate humid-
ity, on the other hand, are very effective in excluding the crop since
such conditions favor the development of stem and leaf diseases
and also since a combination of high temperatures and high
atmospheric humidity is favorable to the rapid development of
many weedy plants which serve to smother out the alfalfa.
Alfalfa is not excluded from humid areas. The crop has become of
increasing importance in the eastern portion of the United States
during the past 20 years. However, the production of alfalfa in
such areas is possible only under proper soil conditions, with special
reference to reaction, availability of phosphates, and drainage
features.
536 ECOLOGICAL CROP GEOGRAPHY
The deep and extensive root system of alfalfa gives the crop an
advantage over leguminous crops with comparatively shallow
root systems, such as the true clovers, in areas where surface mois-
ture is deficient. This accounts for the great importance of alfalfa
in areas too dry for the production of red clover. The area of
distribution of the true clovers in the United States ends rather
abruptly as the dry plains are approached, while alfalfa is a crop
of great importance in the plains states. However, in dry areas
yields of alfalfa decrease rapidly upon the exhaustion of the moisture
supply in the subsoil.
Soil Relationships. Alfalfa is very specific in its soil require-
ments. It is especially sensitive to soil acidity and rarely grows to
advantage at ptt levels below 6. On the other hand, it tolerates
alkali and salt concentrations better than most other crops, espe-
cially after the plants are once well established.
Alfalfa is quite adverse to phosphorus deficiencies in soils. Like-
wise, on extremely sandy soils potash may often constitute a
limiting factor.
The crop demands a deep, well-drained soil. Deep soils capable
of storing an abundance of moiftyre are especially desirable when
the crop is grown in subhumid or semiarid areas. Poor drainage
limits root development and provides conditions favoring the
heaving out of plants during the winter and early spring months.
Distribution for Forage Production. Statistical data on the
world distribution of alfalfa, like those on other forage crops, are
scarce, and even when obtainable are subject to rather wide errors.
Statistics of production by countries will not be presented, therefore.
The climatic adaptations of alfalfa make it one of the most impor-
tant of all forages in areas with relatively dry climates, both in
warm and in winter-cold areas. This makes the crop of special
importance in the drier portions of India, in central Asia, Persia,
Turkestan, and Asia Minor; throughout all of the Balkan area
and in southern Russia; in the Mediterranean and adjoining areas;
and in this hemisphere in Argentina, Chile, Peru, Mexico, the
United States, and Canada. In some of these areas, notably in
India and the Mediterranean region, the production of alfalfa is
not as important as the production of cereals. This is to be attrib-
uted, not to any shortcomings of alfalfa as a crop, but to the fact
that these areas do not specialize in the production of livestock.
PERENNIAL LEGUMINOUS FORAGE CROPS
537
The growing of alfalfa and the production of livestock go hand in
hand. The livestock industry in the western portion of the United
States and on the plains of Argentina furnishes notable examples.
The importance of alfalfa in Argentine agriculture is indicated by
the fact that that South American Republic, with a much smaller
area adapted to the production of alfalfa than the United States,
is credited by Spafford (12) with 13,353,907 acres of alfalfa for
the season of 1933-34 as compared with only 11,669,000 acres in
the United States in 1934.
FIG. 98. Distribution of alfalfa hay production in the United States in 1938.
Each dot represents 10,000 tons.
The production of alfalfa is by no means limited to relatively
dry areas; owing to the special merits of the crop its production has
increased rapidly in humid temperate areas both in Europe and in
North America. Prior to 1920, alfalfa, with a few exceptions,
was classed as a crop of the Great Plains and western states. The
crop was grown at that time in but a few favored areas such as in
central New York, south central Minnesota, and northern Missis-
sippi and Alabama, but it was confined in these localities to rela-
tively narrow limits. Since 1920, alfalfa has become, however, a
crop of considerable importance in the Corn Belt and in the north-
eastern dairy regions. Many producers in the intense livestock
producing areas of the northeastern states, after recognizing the
538
ECOLOGICAL CROP GEOGRAPHY
merits of alfalfa, have found it to their advantage to modify their
soil conditions to make alfalfa production possible. This is evident
from Fig. 98, giving the distribution of alfalfa production in the
United States in 1938, and from Table 57, giving the statistics of
alfalfa hay production by states for the ten-year period 1928-1937.
Because of prevailing droughts and prevalence of disease, particu-
larly bacterial wilt, the production of alfalfa has decreased in the
Great Plains area during the past decade. In 1938, nine states
east of the Great Plains area were among the 20 highest alfalfa
producing states of the country. Alfalfa production has also shown
rapid increases in the eastern humid provinces of Canada during
the past 20 years.
The production of alfalfa hay in the western states is concentrated
in the irrigated areas of these states. In many of these areas alfalfa
is not only the most important hay crop produced but is also the
only hay crop. The merits of alfalfa in these areas are so outstand-
ing as to virtually exclude all other possible hay producing crops.
TABLE 57. ALFALFA HAY: ACREAGE HARVESTED, YIELD PER ACRE, PRODUC-
TION AVERAGES FOR THE TEN-YEA^ PERIOD 1928~1937 — AND 1938 PRO-
DUCTION. ACREAGE AND PRODUCTION EXPRESSED IN THOUSANDS
Acreage
/V" U
Production
Rank
States
Harvested
1 928-1937
I let a,
in Tons
Average
1928-1937,
in Tons
Percentage
of U. S.
Total
1938,
in Tons
1
2
California. . . .
Idaho
761
774
3.94
2.44
2,985
,886
12.39
7.83
3,105
1,992
3
4
5
Nebraska .
Minnesota
Iowa
1,132
814
656
1.54
1.72
2.09
,758
,418
,338
7.30
5.88
5.55
1,144
2,715
1,934
6
7
8
9
10
Colorado
Michigan
Kansas
Wisconsin
Montana
Other states
709
818
732
583
686
4,777
1.88
1.54
1.57
1.95
1.57
1.84
,337
,256
,154
,114
,083
8,768
5.55
5.21
4.79
4.62
4.49
36.39
1,388
1,729
690
2,758
1,083
10,341
Total U.S. . . .
12,442
1.94
24,097
100.00
28,879
Alfalfa Seed Production. The production of alfalfa seed is a
highly localized industry. According to Stewart (13) "from 80 to
90 per cent of all of the alfalfa seed produced in North America
PERENNIAL LEGUMINOUS FORAGE CROPS
539
is grown in eleven areas." Even in the specialized seed producing
areas wide fluctuations in yields are experienced from season to
season. In short crop years the seed supply of the United States
is supplemented by imports from Argentina and occasionally from
Turkestan and Italy.
Alfalfa may be designated as being extremely temperamental
with regard to its seed producing habits. Though the plant demands
a considerable amount of moisture for the production of several
crops of hay per season, such stimulation of vegetative growth by
Fio. 99. Distribution of alfalfa and timothy seed production in the United States.
Average for the ten-year period 1928-1937. Each dot represents 2,000 bushels.
the presence of abundant supplies of moisture is unfavorable to
fruiting and seed production. As a result, the major portion of the
seed crop is grown under semiarid conditions or under conditions
where soil moisture supplies can be regulated by means of irriga-
tion. Alfalfa, to produce seed, must have a constant supply of
moisture to draw upon, but this moisture must not be so readily
available as to induce rapid and excessive vegetative growth. The
control of soil moisture alone does not ensure a seed crop. Atmos-
pheric humidity, availability of sunlight, and the presence of
insects — both helpful, facilitating pollination and cross fertiliza-
tion, and harmful, causing the abortion of flowers or destruction of
formed seeds — are other important factors. Rapid drying fre-
540
ECOLOGICAL CROP GEOGRAPHY
quently causes flowers to drop before fertilization can take place.
Bright sunshine probably facilitates the tripping of flowers, which
is necessary before pollination can be accomplished.
TABLE 58. ALFALFA SEED: ACREAGE HARVESTED, YIELD PER ACRE, PRO-
DUCTION — AVERAGES FOR THE TEN-YEAR PERIOD 1928-1937 — AND 1938
PRODUCTION. ACREAGE AND PRODUCTION EXPRESSED IN THOUSANDS
Production
Rank
State
Acreage
Harvested
Yield)
in Bu.
Average
1928-1937,
in Bu.
Percentage
of U. S.
Total
1938,
in Bu.
1
Idaho
37.10
2.8
104.82
11.14
6400
2
Kansas ....
56.40
1.8
104.43
11.10
118.00
3
Arizona ....
19.86
4.9
96.70
10.28
107.00
4
Montana ....
39.80
2.0
81.22
8.63
42.00
5
6
Nebraska ....
Utah
47.00
33.03
1.4
1.9
64.59
6387
6.87
679
92.00
105 00
7
Oklahoma . . .
25.20
2.5
62.97
6.69
138.00
8
Minnesota . . .
40.38
1.4
57.82
6.15
57.00
9
California ....
15.19
3.4
51.54
5.48
60.00
10
South Dakota . .
41.17
1.0
46.68
4.96
4.00
Other states . . .
130.77
t.6
206.10
21.91
247.00
Total U. S . . .
485 90
1 #6
940 74
100 00
1 034 00
Table 58 gives the United States statistics of alfalfa seed produc-
tion by states. Figure 99 shows the seed producing areas carto-
graphically. With few exceptions the alfalfa seed crop of the United
States is produced in the western half of the country. Limited
amounts of seed are produced in northern Michigan, southern
Michigan, and northern Ohio, in Wisconsin, and in occasional
years, in Indiana and Illinois. It is evident from Table 58 that
the relative importance of seed production in the southern Great
Plains area has been increasing in recent years. Compare the
1928-1937 production with the production in 1938. Idaho dropped
from first place to sixth place in volume of production, while
Oklahoma rose from seventh to first place. Kansas and Arizona
maintained their places. In this connection it must, however, be
recognized that the volume of production of alfalfa seed for any
given state is subject to considerable variation from one season to
another.
PERENNIAL LEGUMINOUS FORAGE CROPS 541
THE CLOVERS
The true clovers belong to the genus Trifolium. This genus
contains a large number of species. Hunt (4) estimates around
250 such species. Only a limited number of them are, however,
of great economic importance. The ones to be considered in this
chapter are: red clover, alsike clover, white clover, ladino clover,
and strawberry clover.
RED CLOVER
( Trifolium pratense)
Economic Importance. Red clover is the most widely grown
biennial leguminous forage crop in American agriculture. Prior
to the recent increases in alfalfa production in the northeastern
quarter of the United States, red clover was the leading producer
of leguminous hay. It is now surpassed by alfalfa in total tonnage
produced; however, red clover, grown either in pure stands or in
combination with grasses, is still being grown on a larger number
of American farms than any other leguminous hay crop. The
census reports of the United States do not differentiate between
red, alsike, or crimson clovers. Likewise, no differentiation has
been made between timothy and clover hay, grown alone or in
mixtures. It is therefore impossible to designate the exact acreage
of red clover grown alone. A common practice is to seed red clover
with timothy or other grasses. The first year's crop from such
mixtures consists largely of clover, the second year's crop of a
clover-grass mixture, and if the field is left for more than two years
the hay crop in the third and subsequent years consists mostly of
grasses.
Red clover produces a hay of excellent quality which is valued
especially on account of its high protein and mineral content.
The crop is used to but a limited extent for strictly pasture purposes.
Red clover is extensively employed in crop rotation systems in
humid areas.
Historical. Red clover was apparently first cultivated in Media
and south of the Caspian Sea, in the same general region where
alfalfa was first utilized. But, unlike alfalfa, it was not known as a
crop to the early Greeks and Romans. Its employment in European
agriculture is also comparatively recent, the first mention of its
use being made by Albertus Magnus in the thirteenth century.
542 ECOLOGICAL CROP GEOGRAPHY
According to Piper, there are definite records of its cultivation in
Italy in 1550, in Flanders in 1566, and in France in 1583. It was
not introduced into England until 1645. Red clover was probably
introduced into the United States by the early English colonists.
Jared Elliot wrote of its culture in Massachusetts in 1747.
The importance of the introduction of red clover into European
agriculture is stated by Piper (11) in the following paragraph.
"Its introduction into European agriculture had a profound effect
in that clover soon came to be used in rotations in place of bare fallow.
Its influence there on agriculture and civilization is stated by high
authority to be greater than that of the potato, and much greater than
that of any other forage plant. Clover not only increased the abun-
dance of animal feed and therefore of manure, but also helped greatly
by adding nitrogen to the soil directly."
Merkenschlager (7), however, points out that even red clover with
its outstanding merits as a feed and soil-improvement crop had a
considerable grower resistance to overcome before its culture was
generally adopted in central Europe.
Climatic Relationships. Red clover, like all the true clovers, is
a moisture-loving crop. Its production is strictly limited to humid
areas or to locations where irrigation is practiced. In irrigated
areas it takes a secondary place to alfalfa as a producer of hay,
being grown there mostly for seed production, and in places where
drainage features eliminate alfalfa as a hay crop. Red clover has
been designated as a crop of marine climates; however, Merken-
schlager points out that it does not do well in Europe in the close
proximity of coastal areas where fogs are common. According to
Merkenschlager, serradella is better adapted to such areas, while
red clover occupies the humid areas favored with a greater abun-
dance of sunlight, located between cloudy and foggy coastal regions
and the drier areas in which alfalfa becomes the more important
crop. Lack of sunshine has not been regarded as a limiting factor
to red clover production in any American producing area.
Red clover demands moderate summer temperatures. In the
southern portions of the United States red clover seeded in the
fall behaves as a winter annual. The plants usually die by the
middle of the summer following seeding. Winter temperatures
encountered in the northern portion of the United States are
generally not detrimental to red clover, although winterkilling is
PERENNIAL LEGUMINOUS FORAGE CROPS
543
experienced where the crop is grown on poorly drained soils and
in cases where plants enter the winter in a weakened condition.
Soil Relationships. Red clover is quite specific in its soil re-
quirements, though less so than alfalfa. The crop demands fairly
good drainage. Since it requires an abundance of moisture during
the growing season, soils must have good moisture-holding capac-
ities to produce maximum crops. The crop is not adapted to
extremely light sandy and gravelly soils or to very heavy, imperme-
able clay soils. The former are too droughty, while the latter are
too poorly drained.
Red clover is a lime-loving crop. It does well on heavy soils,
provided such soils contain an abundance of lime and are well
drained. According to Morgan et al. (8), soils more acid than j&H 5.6
rarely produce good clover crops. The chief soil factors that have
restricted success with red clover, state these authors, are heavy,
intractable subsoils, excessive soil acidity, and depleted mineral
fertility. As in the case of alfalfa, the mineral most frequently
lacking is phosphorus.
Distribution. The world distribution of red clover production
is not so extensive as that of alfalfa. Red clover is a crop of humid
regions with moderate temperatures. Alfalfa also does well in these
Fio. 100. Clover and timothy hay distribution in the United States. Average
annual production for the ten-year period 1928-1937. Each dot represents 25,000
tons of hay.
544
ECOLOGICAL CROP GEOGRAPHY
regions when proper attention is given to its very specific soil require-
ments and in addition is used in areas too dry and with summer
temperatures too high for the production of red clover. Its specific
climatic limitations confined red clover production largely to
northwestern Europe, the northeastern portion of the United
States, southeastern Canada, the humid portions of the Pacific
Northwest, and New Zealand.
A glance at Fig. 100 shows that the major production of clover
in the United States, including red, alsike, and mammoth clovers,
and timothy and timothy and clover mixed is practically confined
to the area east of the Great Plains states and north of the Ohio
and Potomac Rivers. Some clover is grown in the very northern
portions of the Cotton Belt. Red clover is also of importance as a
hay crop in the Willamette Valley of Oregon and in western
Washington. Production in Idaho is primarily for seed. Some
clover, and especially timothy and clover mixed hay, is produced
in the intermountain states. Most of the production of these hays
in this region are found in the irrigated valleys and on mountain
meadows, in locations where drainage features are unfavorable to
the growing of alfalfa. The leading clover and timothy hay pro-
ducing states are given in Table 59.
TABLE 59. CLOVER AND TIMOTHY HAY: ACREAGE HARVESTED, YIELD PER
ACRE, PRODUCTION AVERAGES FOR THE TEN-YEAR PERIOD 1928-1937
AND 1938 PRODUCTION. ACREAGE AND PRODUCTION EXPRESSED IN THOUSANDS
t
V JJ
Production
Rank
States
Acreage
Harvested
Yield,
in Tons
Average
1928-1937,
in Tons
Percentage
of U. S.
Total
1938,
in Tons
1
2
3
4
New York . . .
Wisconsin ....
Pennsylvania . .
Iowa
3,282
2,195
2,220
1,910
1.20
1.25
1.16
1.09
3,940
2,816
2,583
2,126
14.82
10.60
9.72
8.00
4,266
3,010
2,686
1 844
5
Ohio
2,056
0.98
2,014
7.58
2,411
6
7
8
Michigan . . .
Missouri . . .
Illinois ....
1,548
1,870
1,286
1.02
0.78
1.08
1,587
1,469
1,401
5.97
5.53
5.27
,735
,071
,688
9
10
Minnesota . .
Indiana
Other states . .
1,013
1,102
5,499
1.20
0.95
1.15
1,220
1,050
6,371
4.59
3.95
23.97
,098
,401
6,575
Total U. S. . . .
23,981
1.10
26,577
100.00
27,785
PERENNIAL LEGUMINOUS FORAGE CROPS
545
Seed Production. Table 60 gives the statistics on red and alsike
clover seed production in the United States for the ten-year period
1928-1937. About three times as much seed of red clover as of
alsike is produced. Both of these clovers are grown in the same
general sections, the red being produced on lands with good and
the alsike clover on soils with poorer drainage. Of the leading seed
producing states listed in Table 60, Minnesota alone produces more
alsike than red clover. Alsike clover seed production approaches
FIG. 101 . Distribution of red clover seed production in the United States. Average
for the ten-year period of 1928-1937. Each dot represents 1,000 bushels.
the amounts of red clover produced in Ohio and in Oregon. How-
ever, in all of the leading seed producing states the acreage devoted
to red clover seed exceeds that devoted to alsike. Figure 101 gives
the red clover seed producing areas of the United States.
Seed production of red and alsike clovers is concentrated in the
eastern and central portions of the Corn Belt. Only two states not
located in the northeastern quarter of the country are important
producers of clover seed, namely, Idaho and Oregon. The crop
is grown under irrigation in the Snake River Valley of Idaho and
in eastern and central Oregon. It is grown under natural rainfall
conditions in the Willamette Valley of western Oregon and in the
northern portion of Idaho. In the Corn Belt an early crop of hay
is generally harvested and the second crop is used for seed produc-
546
ECOLOGICAL CROP GEOGRAPHY
tion. In the irrigated sections of Idaho and Oregon the red clover
fields designed for seed production are commonly pastured until
the end of May or into early June and then allowed to make seed.
TABLE 60. RED AND ALSIKE GLOVER SEED: ACREAGE HARVESTED AND PRO-
DUCTION EXPRESSED IN THOUSANDS AVERAGES FOR THE TEN-YEAR PERIOD
1928-1937
Rank
States
Red Clover
Alsike Clover
Acreage
Harvested
Produc-
tion,
in Bu.
Percent-
age of
U.S.
Total
Acreage
Harvested
Produc-
tion,
in Bu.
Percent-
age of
U.S.
Total
1
Indiana
157.00
149.00
14.91
9.10
11.30
3.37
2
Illinois .
125.00
113.00
11.31
14.00
19.00
5.67
3
Ohio .
112.00
111.00
11.11
59.00
91.00
27.14
4
5
Michigan
Idaho .
103.00
25.00
111.00
111.00
11.11
11.11
22.00
1.90
36.00
10.70
10.74
3.19
6
Iowa
103.00
85.00
8.51
4.60
7.50
2.24
7
Wisconsin
57.00
68.00
6.81
21.00
39.00
11.63
8
Minnesota
35.00
50.00
5.01
29.00
80.00
23.86
9
10
Oregon .
Missouri
19.60
44.00
44.00
42.00
4.40
4.21
9.40
2.10
35.00
3.00
10.44
0.89
Other states
Total U. S. .
93.40
115.00
11.51
1.40
2.80
0.83
874.00
999.00
100.00
173.00
335.00
100.00
Red clover seed is also produced in western Europe. The most
important producing countries are France, Germany, Poland, and
Italy. European clover seed is from time to time imported into the
United States. These European red clovers are, under most condi-
tions, inferior in their performance to domestic strains. Those
originating from southern France and from Italy especially lack
in winter-hardiness when grown in the northeastern portion of
the United States. Aamodt et al. (1) point out that the European
red clovers are decidedly inferior to domestic strains in their ability
to produce good stands during years of seeding when droughts and
high temperatures prevail.
ALSIKE CLOVER
(Trifolium hybridurri)
Historical. Alsike clover is a native of northern Europe. It has
long been cultivated in Sweden; its spread into other agricultural
areas has, however, been relatively recent. The production of
PERENNIAL LEGUMINOUS FORAGE CROPS 547
alsike clover was not recorded in England and Scotland until in
1832. Emigrants from northern Europe no doubt brought seed
with them to the United States. Seed was distributed in the United
States by the Patent Office in 1854.
Utilization. Alsike clover is used for the same purposes as red
clover. Since, however, it is longer lived and more persistent, alsike
clover is used more extensively than red clover in pasture mixtures.
Adaptation and Distribution. Piper ascribes a wider range of
adaptation with regard to temperature and moisture relationships
to alsike than to red clover. This holds true insofar as alsike clover
is able to survive under somewhat lower winter temperatures than
red clover. Alsike will also grow on wet, and even poorly drained,
soils not suited to the growth or survival of red clover. However,
there is little, if any, difference in the drought resistance of these
two crops and in their unfavorable reaction to high summer tem-
peratures. Both red and alsike clovers prefer cool climates and an
abundance of moisture during the growing season.
While alsike clover responds to applications of lime, it is not as
sensitive to soil acidity as red clover. This characteristic, together
with the fact that the crop can be grown in areas with relatively
poor drainage features, gives alsike clover a wider range of adapta-
tion to soil conditions than red clover. This enables the growing
of alsike in areas not adapted to red clover and in places where red
clover culture has dwindled on account of "clover failure," or on
soils commonly designated as being "clover sick."
Alsike clover is a crop of considerable importance in the cool and
relatively moist regions of northwestern Europe. In the United
States and Canada it is grown in the same general areas as red
clover. Table 60 gives the production of alsike clover seed by states.
WHITE CLOVER
(Trifolium repens)
White clover is another leguminous plant native to northwestern
Europe that has been introduced to all moist temperate areas of
the world where it is being made use of extensively in pastures and
lawns. It is a long-lived perennial, a prolific seed producer, and
is normally found growing in association with grasses. On account
of its abundant seed production it occurs naturally in many pastures
548 ECOLOGICAL CROP GEOGRAPHY
without having been included in the pasture mixture sown. In
other words, it is designated as occurring "spontaneously."
White clover has the same general climatic and soil adaptations
and is found in the same general regions as red clover. Where
moisture is abundant it does well, even in sections with relatively
high summer temperatures as in Louisiana and Florida where it
is used for winter pasturage.
According to Hollowell (2) the United States uses between 2
and 3 million pounds of white clover seed annually. Around
95 per cent of it is used in lawn-seed mixtures. About half of the
seed used in this country is of foreign origin, most of it coming from
Poland and from other north European countries and from the
British Isles. Hollowell enumerates three principal seed producing
regions of the United States in order of their relative importance:
(1) Louisiana; (2) Idaho, Oregon, and Washington; and (3) the
northern Corn Belt states, principally Wisconsin.
LADING CLOVER
(Trifolium repels var. latum)
•
Ladino clover is a large form of white clover used primarily for
pasture and to a limited extent for hay. The crop is adapted to
the same general area as white clover, except that, since it is not
so winter-hardy, its region of production does not extend as far
to the north. However, ladino clover is more winter-hardy than
formerly supposed. It is being successfully used in pasture mixtures
in southeastern Idaho at elevations of above 4,000 feet where winter
temperatures occasionally drop down to — 30°F. It is also grown
with success in the central portion of the Corn Belt and to the east.
Ladino clover is adapted to a great variety of soils. It makes
a very rapid recovery after being grazed off. Like white clover
the crop is shallow-rooted and demands an abundance of moisture.
It is ideally adapted to irrigated pastures.
According to Madson and Coke (6), the origin of ladino clover
is not definitely known. It has been grown in the upper valley
of the Po of northern Italy for more than 50 years. It probably
developed there by a process of natural selection from White
Dutch clover. Seed for trial in this country was first secured by
the United States Department pf Agriculture in 1903. The crop,
PERENNIAL LEGUMINOUS FORAGE CROPS 549
however, attracted no great attention until after 1920. In the
past ten years the interest in ladino clover as a pasture plant for
naturally well-watered and irrigated soils has been increasing
rapidly. Most of the seed crop of ladino clover in this country is
produced in southwestern Oregon and in the Snake River Valley
of Idaho.
STRAWBERRY CLOVER
( Trifolium Jragijerum)
Strawberry clover, a native of the eastern Mediterranean area
and of Asia Minor, is another recent introduction to the United
States. It is adapted to the same general region as white clover
and is used for the same agronomic purposes. The special feature
of strawberry clover, as pointed out by Hollowell (3), is its tolerance
to seeped, saline, and alkaline soils containing concentrations of
salts that inhibit the growth of most other crop plants. This char-
acteristic makes strawberry clover of special importance in the
irrigated sections of the western states. The crop thrives, however,
only in places where moisture is abundant.
OTHER BIENNIAL AND PERENNIAL LEGUMINOUS
CROPS
Sweet Clover (Melilotus spp.). The two species of biennial
sweet clover of special agronomic importance are the white
(M. alba) and yellow (M. ojpcinalis). Both are used extensively for
pasture and soil improvement purposes and to a limited extent
for hay production.
Sweet clover offers an interesting example of a plant that has
been elevated from the position of a weed, of common occurrence
along roads, fences, and irrigation ditches, to a field and pasture
crop of considerable importance. Sweet clover, or Bokhara melilot
as it is also called, originated in western Asia, in the same general
territory where alfalfa was first cultivated. Piper indicates that
it was introduced into North America as early as 1739, when it
was reported in Virginia. The extensive utilization of the plant
as a field crop, however, dates back only about 30 years.
Sweet clover has a wide range of climatic adaptation and is also
found on a great variety of soils. It does best, however, on soils
of neutral or slightly alkaline reaction. It thrives well and is made
550 ECOLOGICAL CROP GEOGRAPHY
use of to advantage in both humid and semiarid regions. It with-
stands high summer temperatures and is also winter-hardy. As a
result it is used more or less over the entire area of the United
States. It assumes a place of special importance in the Great
Plains area where it is considered one of the valuable legumes for
increasing the nitrogen and organic matter contents of cultivated
land. The true clovers are excluded from this area by the lack
of a sufficient amount of moisture for their growth requirements;
their places are taken to a large degree by the deep-rooted sweet
clover. Sweet clover is also of considerable importance in the Corn
Belt where it is used to advantage for the production of summer
pasturage and for soil-improvement purposes. The Great Plains
states are also of prime importance from the standpoint of seed
production of the crop, though some seed is produced in the Corn
Belt. The leading seed producing states of the country together
with their production of seed in thousands of bushels for the ten-
year period of 1928-1937 are: Minnesota, 289.3; North Dakota,
139.4; South Dakota, 109.8; Nebraska, 55.1; Kansas, 47.7; and
Illinois, 40.7.
Sericea (Lespedeza sericea). Thi^ perennial lespedeza was intro-
duced into the United States from Japan in 1896 and in 1899.
Sericea produces a fairly woody type of growth, somewhat lacking
in palatability, which may be utilized for pasture and, when cut
early, for the production of hay. The main use of the crop is to
control erosion and provide feed and cover for wild life. According
to Pieters (10), sericea thrives best on clay loams and silt loams but
has made good growth on sands and sandy loams and has done
well on some acid muck soils. It demands good soil drainage.
Since it is not winter-hardy and not particularly drought-resistant,
its culture is confined to the southeastern quarter of the United
States.
Kudzu (Pueraria thunbergiana). Kudzu is a perennial, hot-
weather, leguminous vine native to Japan. Like sericea, it was
introduced into the United States during the latter part of the last
century. It has found a place in the southeastern states as a pasture
and soil-improvement crop and also to some extent as a hay crop.
Its place of usefulness is confined to the humid portions of the
Cotton Belt. While kudzu can be grown in the central portion
of the Corn Belt it cannot be expected to compete successfully
PERENNIAL LEGUMINOUS FORAGE CROPS 551
tfiere with either alfalfa or the clovers. Kudzu, according to
Pieters (9), thrives on many types of soil and has the special merit
of being able to make good growths on soils too acid for alfalfa
and the clovers. Seed production in the United States is rare;
for that reason the crop is generally established vegetatively from
rooted plants.
Sanfoin (Onobrychus viciaejolia) . Sanfoin, also known as esparcet
or esparsette, is native to the southern half of Europe and eastward
to Lake Baikal. While sanfoin has been grown experimentally in
numerous tests in this country, it has not become commercially
established. According to Kutscher (5), it is grown quite exten-
sively in southern and central Europe where it is considered of
special value on dry, porous, calcareous soils. The crop is slower
to establish itself than alfalfa; full yields are generally not obtained
until the third or even fourth year after seeding.
Lotus. Several species of lotus are of economic importance as
pasture plants. Strecker (14) speaks highly of two species with
regard to utilization under European conditions. Lotus corniculatus,
or birds' -foot trefoil, is designated as being adapted to areas with
severe climatic conditions, both with reference to the moisture
and temperature factors. It also has a wide range of soil adaptation
— from fertile, moist to dry sandy and even stony soils. Birds'-
foot trefoil is being grown to a limited extent in western Oregon
and Washington. Lotus uliginosus is especially adapted to moist
and even to swampy soils.
REFERENCES
1. Aamodt, O. S., J. H. Torrie, and O. F. Smith, "Strains of red and
white clovers," Jour. Amer. Soc. of Agr on., 31:1029-1037 (1939).
2. Hollowell, E. A., "White clover," U. S. Dept. Agr. Leaflet 119, 1936.
3. , "Strawberry clover," U. S. Dept. Agr. Leaflet 176, 1939.
4. Hunt, T. H., The Forage and Fiber Crops in America. Orange Judd Co.,
New York, 1908.
5. Kutscher, H., Wiesenbau. Paul Parey, Berlin, 1909.
6. Madson, B. A., and J. E. Coke, "Ladino clover," Calif. Agr. Ext. Circ.
81, 1937.
7. Merkenschlager, F., "Die Konstitution des Rotklees," Die Ernahrung
der Pflanze, 30:81-89. 1934.
8. Morgan, M. F., J. H. Gourley, and J. K. Ableiter, "The soil require-
ments of economic plants," U. S. Dept. Agr. Yearbook 1938:753-776.
552 ECOLOGICAL CROP GEOGRAPHY
9. Pieters, A. J., "Kudzu, a forage crop for the southeast," U. S. Dept. Agr.
Leaflet 91, 1932.
10. , "Lespedeza sericea and other perennial lespedezas for
forage and soil conservation, U. S. Dept. Agr. Circ. 534, 1939.
11. Piper, C. V., Forage Plants and Their Culture. Macmillan, New York,
1937.
12. Spafford, W. J., "Agriculture in the temperate and sub- tropical
climates of the South," Dept. Agr. So. Australia Bull. 310, Adelaide,
1936.
13. Stewart, G., Alfalfa-growing in the United States and Canada. Macmillan,
New York, 1926.
14. Strecker, W., Die Kultur der Wiesen, ihr Wert> ihre Verbesserung^ Dungung
und Pflege. Paul Parey, Berlin, 1923.
15. Throckmorton, R. K., and S. C. Salmon, "Alfalfa production in
Kansas," Kans. Agr. Exp. Sta. Bull. 242, 1927.
16. Westover, H. L., "The uses of alfalfa," U. S. Dept. Agr. Farmers' Bull.
1839, 1940.
Chapter XXXI
PERENNIAL FORAGE GRASSES
INTRODUCTION
Appreciation of Grasses and Grassland Agriculture. The
term "forage grasses" is used to designate those grasses primarily
grown and utilized for hay or pasturage. Such grasses are either
native to this continent or of foreign origin. With but minor excep-
tions the grasses now extensively cultivated on farms in American
agriculture are of foreign extraction, coming mostly from Europe
and Asia. They are frequently referred to as tame or cultivated
grasses. Species indigenous to North America have long been
utilized in their native habitats, that is, on undisturbed grasslands
and on ranges in the Great Plains and western states. It is, how-
ever, only within recent years that the forage possibilities of these
native grasses have been definitely investigated. While their valfces
have been appreciated, and while they have provided the basis for
the development of a thriving livestock industry in our western
states, but little concerted effort has in the past been put forth to-
ward the improvement of native species of grasses, and toward their
extensive employment in the revegetation of denuded areas and
abandoned crop lands.
Many of our native grasses are better adapted to our environ-
mental conditions than imported or exotic species. Their apparent
neglect is traceable to the regrettable fact that this great native
resource of the grassland areas was definitely exploited rather than
utilized in line with the physiological growth requirements of the
grass crop. The conservation aspects of grassland management are
of recent origin. Since many native species have rather poor seed
habits, seed for reseeding purposes both on the range and on aban-
doned crop lands has been hard to obtain. More recent investiga-
tions regarding the seed producing habits of native grasses have
shown that at least some of them have better seed habits than earlier
553
554 ECOLOGICAL CROP GEOGRAPHY
work indicated. Furthermore, the seed habits of many of them can
be and have been improved upon by the selection and isolation of
strains capable of producing fair to good seed yields. The forage
characteristics of many native grasses have also been definitely
improved upon by selection. The recent interest in the growing of
grasses for soil and water conservation has given a great impetus
to this line of research. Plant breeders up until the present decade
have confined their interests largely to the improvements of food
and fiber crops. The forage grasses, while offering opportunities
for improvement as great as other crop plants, have Been more or
less neglected. This situation can be attributed to the great need
for increased production of food and fiber crops in the past. The
change in attitude, or more correctly the present interest in the
possibilities of grass improvement by the application of those prin-
ciples of plant genetics which have brought about such great
improvements in our general field crops, is traceable to the growing
realization of the value of grasses. Agricultural production in many
areas is being adjusted to a grassland base. Not only is there current
interest in the search for grasses capable of being established and
maintained in dry areas with trying environmental conditions, but
also a real effort is being made toward the improvement of grasses
and their greater utilization in humid areas where their establish-
ment generally does not offer as serious problems as in dry regions.
Grass is the climax vegetation of great expanses of land with the
grassland climate often referred to. In the past, great and at times
unwise expansion of crop production into these important grassland
areas led to the exploitation of these valuable areas. Crop pro-
ducers, and especially the producers of cereal crops, have generally
been regarded as the main exploiters. This is not entirely the case;
producers of livestock have also had a very definite part in this
exploitation as is evident from the present depreciated condition of
many range lands. There is, of course, every justification for the
use of native grassland for crop production purposes in many areas;
as a matter of fact some of our best agricultural lands were formerly
clothed with a protective cover of grass, and such grass covers have,
through the ages, contributed to the development of the very char-
acteristics which make them usable and desirable for crop produc-
tion. The place where the utilization of such grasslands for crop
production cannot be justified is where the plow advanced into
PERENNIAL FORAGE GRASSES 555
grassland areas with highly hazardous climates. This aspect of
land utilization has been referred to in former chapters. It is again
mentioned here to bring out the fact that the necessary and often
painful retrenchment of crop production from such areas not only
has brought material changes in the concepts of proper land use,
but also has resulted in a greater appreciation of the value of grass
on such lands. To the optimist willing to gamble with the hazard-
ous climatic conditions encountered in the dry grassland areas, it
has brought a lesson in plant adaptation, in that it has convinced
many would-be crop producers in these regions that grass is better
adapted to the great extremes in the moisture and temperature
factors than any crop plant that man may substitute. Likewise,
livestock men who have allowed their ranges to be depreciated by
overgrazing are realizing that it is necessary to manage their grass-
lands in a manner compatible with the physiological growth re-
quirements of the plants valued on those ranges in order to prevent
still greater depreciation in the future.
Improvement of these ranges is one of the real needs of western
agriculture. These improvements of the native grasslands must be
based on the physiological growth requirements of the grasses.
While adapted species of grasses are generally tenacious and even
aggressive under favorable conditions, they are unable to withstand
prolonged abuse. The reseeding of such grasslands must be resorted
to in extreme cases, that is, where the desired species have disap-
peared entirely. Usually, however, where some of the desired
species still remain, the most rapid and certain improvement can
be accomplished by alterations in management. Grasses in order
to become established and to be able to maintain themselves must
be given opportunities to produce seed periodically. The seedlings
resulting from periodic seed production must also be given a chance
to establish themselves. Furthermore, if a vigorous growth of
grasses is to be expected, the established plants must be allowed
opportunities to build up their organic reserves. In addition, the
feed to be expected from range areas should be supplemented in
many areas by supplies of feeds produced on nearby crop lands.
Such supplementary feeds may consist of hay, pasturage, or even
of concentrates.
The above offers a few examples of the growing appreciation of
the value of grasses in dry regions. Grassland agriculture also has
556 ECOLOGICAL CROP GEOGRAPHY
its ramifications in humid areas not only from the standpoint of
providing feed for livestock, but also for erosion control and for
providing a crop of value in rotation systems. The fibrous roots of
grasses have a very favorable effect on the structure of the soil.
While leguminous plants have a higher value as producers of hay
on account of their greater protein and mineral contents than
strictly grass hays, the two are often grown to advantage in mix-
tures. This brings out the good features of both of these important
forage crops. Likewise, grasses form a valuable constituent of
nearly all pasture mixtures. The term "grassland agriculture," or
the adjustment of crop and livestock production to a grassland base,
is now used frequently in relation to the establishment of per-
manent systems of agricultural production. It is a good term, and
agriculture has much to gain by making use of the concepts inferred
by it. The adjustments called for in the establishment of a grassland
agriculture have already been made in many of the older agricul-
tural areas of the United States interested in the production of both
cash crops and livestock products. It is the system that has long
been utilized in most of the agricultural sections of northwestern
Europe, and it accounts to no srft^ll degree for their agricultural
stability. The term "grassland" in this connection applies to the
production of both grasses and legumes either in pure stands or in
mixtures.
Many Species of Grasses Available. The members of the grass
family show a great diversity in form, desirable characteristics,
growth requirements, and the manner in which they may be uti-
lized. Some indication of the diversity and numbers of the members
of the grass family is given by the fact that Hitchcock (4) lists 1 59
genera and 1,100 species known to be growing in the continental
United States, excluding Alaska. The range of usefulness of grasses
is given by a classification of their uses. Thus, Hitchcock enu-
merates the various uses to which grasses are put, as food grasses,
hay grasses, pasture grasses, soiling grasses, silage grasses, range
grasses, grasses used in industrial arts, soil-holding grasses, grasses
for lawns and golf courses, and ornamental grasses.
Because of the great number of grasses occurring in native en-
vironments and propagated by man, the distribution of only a
limited number can be discussed in this chapter.
PERENNIAL FORAGE GRASSES 557
GRASSES OF COOL, HUMID REGIONS
Timothy (Phlewn pratense). Timothy is the most widely culti-
vated hay grass in American agriculture. Since it will not stand
close grazing and the trampling by animals incident to grazing, it
is not used to any great extent in pasture mixtures. Timothy is
indigenous to most of Europe, temperate Asia, and parts of northern
Africa. Even though timothy is not native to North America, its
value as a cultivated plant was first recognized in the United States.
The name "timothy" was given to the plant during colonial times,
apparently after one Timothy Hanson, who is reported to have
brought the grass from New England into Maryland. It is now
grown in meadows over wide areas in Europe, but especially in
northern areas and at high elevations. Timothy is regarded as a
valuable grass in the British Isles, in Germany, and particularly in
the Scandinavian countries. Armstrong (1) reports that it has been
found very suitable on good lands in the mountain valleys of Nor-
way, and that it is being grown with success in Sweden, even in the
latitude of the Polar Circle. Timothy is more cold-resistant than
most cultivated grasses. While timothy is considered of value in
Europe on moist, fertile soils, it is not grown as extensively there
as in the United States.
Since timothy has the same general soil and climatic adaptation
as red clover, it is commonly grown in combination with that crop.
The distribution of timothy and timothy-clover mixed hay is shown
in Fig. 100, while the distribution of timothy seed production is
shown in Fig. 99, Chapter XXX. The leading seed producing
states are Iowa, Missouri, Illinois, Minnesota, and Ohio.
The southern limits of timothy production are determined by
its inability to tolerate high summer temperatures. It is very
effectively eliminated by a combination of high summer tempera-
tures and high atmospheric humidity. This accounts for the fact
that the bulk of the timothy crop of the United States is produced
north of the Ohio and Potomac Rivers.
Timothy is a moisture-loving plant. Like red clover, it demands
fair to good soil drainage. The western limits of production in the
United States are definitely determined by the availability of mois-
ture during the growing season; its region of distribution ends
rather sharply in the very eastern portions of the states of the Great
558 ECOLOGICAL CROP GEOGRAPHY
Plains area. The crop is grown to some extent in well-watered
localities in the northern Mountain states and also in the humid
Pacific Northwest. In western Oregon and Washington, however,
it is of less importance than in the northeastern quarter of the
United States.
The Bent Grasses (Agrostis spp.). Several species of Agrostis are
utilized for hay, pasture, and lawn purposes. Redtop (A. alba) is by
far the most extensively used species in this country. However,
creeping bent, designated by Hitchcock as A. palustris and by
Armstrong as A. alba, var. stolonifera, is the most important species
used in the cool, humid portions of Europe.
Redtop is grown in the same general territory as timothy and is
subject to the same climatic limitations in its distribution. Since it
does well on wet and acid soils, it is frequently grown in combina-
tion with alsike clover. Redtop is of special importance in the New
England states and in southern Illinois. Most of the seed of the
United States is produced in the latter area.
Redtop is used for the production of hay and pasturage. It with-
stands close grazing and trampling better than timothy. Redtop,
according to Piper (8), is second onfy%to bluegrass as a pasture plant
in the northeastern part of the United States. It is a vigorous grower
and forms a good turf in a short time.
Piper (8) ascribes a wide range of adaptation to redtop with
respect to the soil and moisture factor, indicating that it is one of
the best of wet-land grasses and also "strongly drought resistant.55
That the grass has a wide range of soil adaptation cannot be denied.
As a matter of fact, its ability to grow on a great variety of soils and
especially in wet places constitutes one of its chief points of merit.
On the other hand, it is evident from the distribution of the grass
that the western limits of redtop production are nearly as effectively
determined by low rainfall in the eastern Great Plains area as are
those of timothy. Redtop, like timothy, is a moisture-loving plant.
It is difficult to establish stands of the grass under low rainfall con-
ditions.
Creeping bent, while regarded of great value as a pasture and
hay grass in northern Europe, is used for that purpose to but a
limited extent in the United States. The grass demands an abun-
dance of moisture and moderate temperatures; its agricultural use
is for that reason largely confined to seaside meadows on the
PERENNIAL FORAGE GRASSES 559
northern Atlantic and Pacific coasts. Creeping bent is highly
valued as a lawn grass in all of the northern portions of the United
States and is extensively used for that purpose in places where an
abundance of moisture is available. In its ability to produce a fine-
textured lawn, it is surpassed only by the still finer leaved velvet
bent (A. canina). While these two bent grasses produce beautifully
textured lawns under favorable conditions and with proper care,
they are more exacting in their environmental requirements than
Kentucky bluegrass. Furthermore, the bent grasses do not start
growth as early in spring or remain green as long in the fall as
Kentucky bluegrass.
Colonial, also designated as Rhode Island bent (A. tennis), is
extensively employed as a pasture grass in the New England states
and in New York. Unlike redtop, the colonial bent demands well-
drained soils; it is similar to redtop in that it thrives on acid soils.
Colonial bent is less tolerant than redtop of high summer tempera-
tures and is for that reason confined in its distribution to northern
areas.
The Bluegrasses (Poa spp.). Kentucky bluegrass (P. pratensis) is
the most widespread pasture and lawn grass of the northern humid
portions of the United States and also occurs in all irrigated areas
in the northern portion of the country. It has been so widely dis-
tributed that it has become a natural component of most humid and
irrigated pastures, so much so that it appears "spontaneously" in
pastures and meadows and often in places where it is not wanted.
Kentucky bluegrass is very aggressive; while this is a desirable
characteristic in pasture grasses, Kentucky bluegrass frequently
crowds out more desirable species in both pastures and meadows.
The greatest point of weakness of the grass is that it languishes
during periods of summer heat. Where species capable of enduring
relatively high summer temperatures, such as orchard grass, brome
grass, and meadow fescue, are replaced by the aggressiveness of
Kentucky bluegrass, the carrying capacities of such pastures are
reduced. Likewise, hay yields of meadows are frequently reduced
by Kentucky bluegrass invasions.
Kentucky bluegrass is markedly resistant to cold. Consequently
its distribution to the north is not limited by severe winter condi-
tions. On the other hand, high summer temperatures determine
its southern range of usefulness. Consequently, it is not utilized to
560 ECOLOGICAL CROP GEOGRAPHY
any great extent farther to the south than timothy. Likewise it is
definitely a grass of humid regions; dry conditions in the eastern
Great Plains area set a rather clear-cut limit to its western range of
distribution. In Europe the grass is valued for its drought resist-
ance. This is a comparative concept in that many of the moisture-
loving grasses extensively employed in European agriculture are
effectively eliminated in our agricultural regions by the significantly
higher summer temperatures prevailing even in the humid portions
of the northeastern quarter of the United States. Piper (10), in
speaking of the prominent places occupied by Kentucky bluegrass,
our most important pasture and lawn grass, and timothy, our most
important hay grass, makes the following worthwhile observation:
"It is difficult to find a satisfactory explanation for the great impor-
tance of this grass and of timothy in America. About all that can
be said is that these two grasses are much better adapted to the
climatic conditions of cold winters and hot summers than are any
other European grasses used for the same purposes." In comparing
the relative distribution of grasses used in European and American
agriculture it is well to keep in mind that northwestern Europe has
marine and littoral climates while \fce climates of the northeastern
quarter of the United States have distinct continental aspects. In
Europe the rough-stalked meadow grass (P. trivialis), a species of
little importance in the United States, is more widely used than
Kentucky bluegrass.
Canada bluegrass (P. compressd) is adapted to the same range of
climatic conditions as Kentucky bluegrass. It is, however, some-
what more resistant to summer heat and drought than Kentucky
bluegrass and will also grow on poorer soils. Kentucky bluegrass
prefers well-drained soils and soils rich in humus. In places Canada
bluegrass may be regarded more as a weedy grass than as a grass of
agricultural importance.
In addition to the three species of Poa indicated above, two native
drought-resistant species of this genus, big bluegrass (P. ampld) and
Sandberg bluegrass (P. secundd), are beginning to be utilized on the
dry lands of the Pacific Northwest. Texas bluegrass (P. arachnifera)
is used to some extent in the southern Great Plains area where it is
valued for its ability to endure high summer temperatures. Fowl
meadow grass (P. palustris), a native of both Eurasia and North
America, is of value only in moist localities of northern areas.
PERENNIAL FORAGE GRASSES
561
Orchard Grass (Dactylis glomerata). Orchard grass is not as
winter-hardy as either timothy or Kentucky bluegrass. Its northern
limit of usefulness coincides quite well with the northern portion of
the Corn Belt. Since, however, the grass is fairly tolerant of high
summer temperatures, it can be grown to advantage to the south,
even in the northern Cotton Belt. Orchard grass is also more
drought-resistant than timothy; however, this difference is not
great enough to affect a significantly greater westward distribution
FIG. 102. Region of distribution of orchard and tall oat grasses, dotted; ber-
muda, single lined; and carpet grass, check lined. The scattered irrigated sections
of the western portion of the United States to which these grasses are adapted in
their respective temperature regions are not indicated.
for orchard grass than has been indicated for timothy. Neverthe-
less, orchard grass can be grown to advantage in the Pacific North-
west on lands too dry to produce timothy profitably.
Orchard grass is used for hay and pasture. It is not as specific in
its soil requirements as timothy. Helm (3) points out that it, like
timothy, is best adapted to fertile loam soils, but orchard grass will
grow also on poorly drained wet land, and on land that is poor and
dry. Orchard grass, however, does not do well on very sandy soils.
It is valued for its early growth in spring and late growth in autumn.
Tall Meadow Oat Grass (Arrhenatherum elatius). Tall meadow
oat grass has the same climatic adaptation as orchard grass and is
562 ECOLOGICAL CROP GEOGRAPHY
used in the same area. It is a relatively short-lived perennial.
Unlike orchard grass, tall meadow oat demands open soils and good
drainage; it is especially adapted to light sandy and even gravelly
soils. Tall meadow oat like orchard grass can be used to advantage
in the irrigated areas of the western states. The regions in the
United States to which orchard grass and tall meadow oat grass are
best adapted are shown in Fig. 102.
Meadow Fescue (Festuca elatior). Meadow fescue finds use pri-
marily as a pasture grass but can also be used to advantage for the
production of hay. It is grown in the same general area as timothy.
The grass, however, is more tolerant of the high summer tempera-
ture than either timothy or Kentucky bluegrass. In irrigated areas
in the western states both orchard grass and meadow fescue are
superior to bluegrass in that their rates of growth are not checked
as much by high summer temperature as those of the bluegrasses.
Meadow fescue prefers rich, moist, or even wet soils; it will not
succeed on sandy areas. It is short-lived on dry soils or under con-
ditions of low summer rainfall.
The Ryegrasses (Lolium spp.). Two species of ryegrasses are used
in the United States, the short-liv&j, usually annual, Italian rye-
grass (L. multifloruni), and the perennial or English ryegrass (L. pe-
renne). In addition, the commercially known common ryegrass,
also designated as domestic, Oregon, and western ryegrass, con-
sisting usually of mechanical and genetic mixtures of the above two
species, is also grown. The ryegrasses are used for pasture, hay,
and to some extent as lawn grasses.
As pointed out by Schoth and Hein (12), the ryegrasses are not
winter-hardy. They are for that reason grown principally in the
Pacific coast states west of the Sierra Nevada and Cascade Moun-
tains and in the southern humid states. In the southern and also
in the northern states, both species behave largely as winter annuals
and as annuals. In the South, they do not withstand the high
temperatures of the summer months and, if seeded too far to the
north, they fail to survive severe winters. Klages (7) reports high
yields for one year of both species from fall seedings in north-central
Oklahoma; owing to their inability to withstand high temperatures
and drought, they did not survive the summer following seeding.
The ryegrasses are highly valued in northwestern Europe, par-
ticularly in England, for their rapid development and fast recovery
PERENNIAL FORAGE GRASSES 565
after grazing or cutting. Their use, however, is confined largely to
soils of high fertility. In western Oregon and Washington they
exhibit a wide range of soil adaptability, being regarded there as
wet-land grasses. The best yields are, however, obtained on fertile
soils with good drainage.
The common ryegrasses should not be confused with the wild
ryegrasses, species of Elymus, which are adapted to quite a different
environment than Lolium. The wild ryes are hardy and drought-
resistant, while the common rye grasses are nonhardy and moisture-
loving.
Reed Canary Grass (Phalaris arundinacea) . Reed canary grass is
a native of the temperate regions of Europe, Asia, and North
America. It is especially valued in low-lying areas subject to over-
flow. According to Schoth (1 1), it does best in moist, cool climates,
and ceases to be of much importance in areas where average mean
minimum temperatures in winter are above 45°, or average mean
maximum temperatures in summer are above 80°F. While the
grass is especially adapted to moist and even swampy soils, selec-
tions of reed canary are being used to advantage on high, well-
drained, productive soils if supplied with ample moisture for spring
and early summer growth. Strecker (13) reports the production of
reed canary on dry, sandy soils in Germany.
Figure 103, adopted from Piper (9), shows the regions of the
United States to which reed canary grass is adapted. While the
whole northern portion of the country is included in the area to
which the grass is adapted, it can be grown in the drier western
portions of the country only in the favored, moist areas or with the
aid of irrigation.
GRASSES OF COOL, DRY REGIONS
Smooth Brome (Bromus inermis). Smooth Brome is a long-lived,
hardy, perennial grass indigenous to a large part of Europe and
Asia. Its chief merit lies in its drought resistance. In Europe it is
used extensively on the Hungarian plains. In the United States
and Canada it is the most important cultivated grass in the central
and northern Great Plains area and in the Prairie provinces to the
north. It is considered of value not only on relatively dry lands but
also as a pasture grass in the irrigated valleys of the intermountain
and Pacific Northwest states. The drought resistance of smooth
564
ECOLOGICAL CROP GEOGRAPHY
brome and its ability to grow on relatively poor, sandy, and even
gravelly soils have attracted attention to this grass in humid areas.
The grass has in recent years been used to some extent in pasture
and meadow mixtures in the Hay and Pasture Region. It is, how-
ever, primarily a grass of the high plains of northern regions.
While smooth brome is able to withstand moderate summer tem-
peratures, it is decidedly adverse to a combination of high summer
temperatures and high humidity. This accounts for its inability to
REEO CANARY
FIG. 103. Regions of adaptation of reed canary grass, upper left; smooth
brome grass, upper right; crested wheat grass, lower left; and slender wheat
grass, lower right. (Compiled from Piper, 9.)
invade the southern part of the Corn Belt. The region of the
United States in which smooth brome grass is most valuable is
shown in Fig. 103.
The Wheat Grasses (Agropyron spp.). Numerous species of
Agropyron, both native to this country and of foreign extraction, have
been found to be of value in dry areas. The one most extensively
grown in the drier portions of the northwestern quarter of the
United States is crested wheat grass (A. crtstatum). This introduc-
tion from the northern regions of the U.S.S.R. has been extensively
employed in reseedings of abandoned crop lands, and depleted
ranges in the northern Great Plains and intermountain regions.
It is well adapted for these purposes on account of its resistance to
PERENNIAL FORAGE GRASSES 565
extreme drought and cold, and on account of its excellent seed
habits. The drought resistance of crested wheat grass, occasioned
by its extensive root system, makes it of special value in dry-land
agriculture in that its introduction has given to these areas a grass
that can be incorporated to advantage into their rotation systems.
High summer temperatures set a southern limit to its distribution.
The regions of the United States to which crested wheat grass is
most valuable are shown in Fig. 103. Crested wheat is used pri-
marily as a pasture and range grass in areas too dry for the success-
ful growing of smooth brome. The forage produced by crested
wheat grass is rather harsh to produce the best type of hay. Dwarf
growing, fine-leaved strains also have merits as lawn grasses in dry
regions.
Slender wheat grass (A. pauciflorum) is a native of this continent.
It has much the same growth habits as crested wheat, but lacks its
extreme resistance to drought. Figure 103 shows that slender wheat
is utilized farther to the east than crested wheat grass. In its western
region of distribution it is used in moister localities than the crested
wheat grass. In its native state it is most abundant on alluvial lands
along streams and is found only occasionally on the higher and
dryer bench lands. It does not withstand flooding. According to
Piper (9), slender wheat "is notable for its ability to grow in all^ali
lands where most other grasses fail." The grass is used for pasture
and for production of hay either where it occurs in native stands or
where it has been seeded. Slender wheat grass was first cultivated
around 1895, and is now grown most abundantly in Manitoba,
Alberta, Saskatchewan, and the Dakotas. It is not, however, of as
great importance as a cultivated grass in this area as smooth brome.
Western wheat grass (A. smithif) is another native of this hemi-
sphere. According to Hoover (5), it is quite generally distributed
throughout the United States, except in the more humid south-
eastern area, but is more at home in the northern Great Plains.
It is a component of many native grassland meadows, and is also
not uncommon in pure stands, especially on heavy gumbo soils of
old lake beds. It is of interest to compare the root systems of the
three wheat grasses mentioned. Crested wheat is a bunch grass;
slender wheat is generally regarded as a bunch grass, but it will
under favorable conditions produce short rootstocks; western wheat
grass, on the other hand, has strongly creeping rootstocks and pro-
566 ECOLOGICAL CROP GEOGRAPHY
duces a tough sod. Like slender wheat, western wheat grass also
lacks the extreme drought resistance of crested wheat.
The list of valuable wheat grasses is by no means exhausted by
the above brief discussion. Before leaving this valuable group of
grasses two native species of great importance to the drier areas of
the Pacific Northwest must at least be mentioned. These are the
bluebunch wheat grass (A. spicatwri) and the beardless bluebunch
wheat grass (A. inerme). They are used not only as range grasses in
their native habitats but have in recent years been employed as
cultivated grasses. Selections of these grasses equal crested wheat
in drought resistance.
Other Native Species for Dry Areas. The list of valuable
native species of grasses is so long that it will be impossible even to
enumerate them here. Some of the more important ones must,
however, be mentioned. Thus in the Great Plains area are found,
just to name a few, the buffalo grass (Buchloe dactyloides) ; the blue-
stem grasses, big bluestem (Andropogon furcatus) and little bluestem
(A. scoparius)\ the grama grasses, blue grama (Bouteloua gracilis) and
side oat grama (B. curtipendula) ; switch grass (Panicum virgatum) and
needle grass (Stipa comata), which a^o extends into the intermoun-
tain area. In the southwest area additional gramas are of impor-
tance, such as black grama (Bouteloua eriopoda)\ rothrock grama
(B. rothrockii)\ and hairy grama (B. hirsuta\ which also extends into
the northern Great Plains in its minor distribution; tobosa grass
(Hilaria mutica); curly mesquite (H. belangerf)\ galleta grass (H.
jamesii)\ and vine mesquite (Panicum obtusum). Other native species
of special importance in the Pacific Northwest besides those indi-
cated in the brief discussion of the Poas and Agropyrons are the wild-
rye grasses such as Canada wild-rye (Elymus canadensis); beardless
wild-rye (E. triticoides)\ and blue wild-rye (E. glaucus).
WILD OR PRAIRIE HAY
Characteristics of Prairie Hay. The hay trade's conception of
wild or prairie hay is that it consists principally of the bluestems
(Andropogons), wheat grasses (Agropyrons), and slough grass (Spartina
michauxiana) that grow either in practically pure stands or in mix-
tures with other grasses or miscellaneous forbs, on the virgin mead-
ows of the Prairie and Great Plains states. These grasses ordinarily
do not develop seed heads prior to cutting, and the hay therefore
PERENNIAL FORAGE GRASSES 567
does not have many distinct stems like that produced from the
cultivated grasses. The exact species represented in the production
of prairie hay are determined by the environmental conditions
under which they are grown. It will be recalled from the discussion
relating to the distribution of the grassland climates in the central
area of the United States, Chapter XX, that the humid eastern por-
tion of this great area is clothed with tall, the central portion with
mixed, and the dry western expanses with short grass covers. This
is primarily a response to the moisture factor of the environment.
Keim et aL (6) bring out that even within confined limits, such as
in an area comprising four counties in north-central Nebraska,
rainfall and subirrigation play an important role in determining
the yields and structures of the native vegetations of grasslands.
Keim et aL present data showing the especially intricate relationship
existing between the depth of the ground-water level and botanical
structure. The most important differences in the botanical com-
position and relative degree of coarseness of the three commercial
classes of prairie hay as recognized by the United States official
standards are traceable to variations in moisture conditions existing
on the upland and bottomland wild hay meadows. The three
classes are upland prairie, upland-midland prairie mixed, and
midland prairie. The first is characterized by an abundance of
short leaves, few distinct stems, and by the fact that the hay is
relatively soft to the touch. Midland prairie hay is made up of
long, stringy, harsh leaves. Upland-midland mixed prairie hay
consists of a mixture of upland and midland (bottomland) grasses.
Since prairie hay is produced over a wide range of climatic and
soil conditions, a great variation in its botanical composition is to
be expected.
In the central and western areas of prairie hay production these
hays are made up almost entirely of native plants. In the more
humid eastern portion of the prairie hay producing region some
of the native grasslands have, however, been invaded by certain
cultivated species, such as timothy, redtop, the bluegrasses, and
smooth brome.
Distribution of Prairie Hay Production. The distribution of
wild grasses cut for hay in the United States is shown in Fig. 104,
taken from Baker and Genung (2). Prairie hay production is of
special importance in the Spring Wheat Belt; in Nebraska, and
568
ECOLOGICAL CROP GEOGRAPHY
especially in the Sand Hills section of Nebraska; in eastern Kansas;
and in northeastern Oklahoma. The demand for land suitable for
cereal production has materially decreased the area devoted to
prairie hay in the past 30 years. To the east of the Great Plains,
prairie hay production has disappeared almost entirely. The acre-
age shown in Wisconsin consists mostly of marsh hay. East of the
Great Plains native grasslands have been forced into the production
of corn and small grains; furthermore, the more favorable moisture
relationships in this area make other forage crops such as the clovers,
WILD GRASSES CUT FOR HAY
Acreage, 1929
FIG. 104. Distribution of wild or prairie hay in the United States. Each dot
represents 2,000 acres. (After Baker and Genung.)
alfalfa, and cultivated grasses more productive than native grasses.
Another factor entering into the situation is that native grasslands
cannot be incorporated into systems of crop rotations like cultivated
legumes and grasses. In the Great Plains prairie hay continues to
provide important supplies of feed. To the west of this area the
climate is so dry that native grasses do not usually grow tall enough
to be cut for hay except in the high mountain valleys.
GRASSES OF WARM, HUMID REGIONS
Bermuda Grass (Cynodon dactylori). Bermuda is the most impor-
tant pasture and lawn grass of the more humid portions of the
Cotton Belt, where it is relatively as important as Kentucky blue-
PERENNIAL FORAGE GRASSES 569
grass is in the North. The grass is a native of India, and of probably
other tropical areas of the Old World. It was introduced into the
United States during the early part of the eighteenth century and
spread rapidly. The points of merit of this grass responsible for
its extensive use are: its ability to make rapid growth under high
temperature conditions; its adaptation to a great variety of soil
conditions; its ability to withstand close grazing or close clipping;
its aggressiveness; its value as a soil binder in erosion control; and
its rather moderate demands for moisture. In addition to these
points the grass is readily established by vegetative means, planting
of sod pieces. It may also be established from seed. While the
grass has a wide range in its soil adaptation, it does best on moist
bottom lands. It grows luxuriantly enough to be utilized for hay
only on the better soils in the central and southern area of its dis-
tribution. Furthermore, soils used for bermuda must be well
drained. The grass is not without certain definite demerits. It will
grow only under conditions of relatively high temperatures; for
that reason it starts growth late in spring and enters into dormancy
with the first drop of temperature in fall. The period over which
it provides pasturage is therefore relatively short in relation to the
length of the thermal growing season. In its northern area of dis-
tribution its growth is not sufficient to make the grass valuable-,
but there it becomes a rather troublesome weed and under some
conditions may be difficult to eradicate.
The bermuda and carpet grass producing areas of the United
States are indicated in Fig. 102. It will be observed that the range
of distribution of bermuda coincides quite well with the distribu-
tion of cotton, except that owing to moisture limitations it does
not extend as far to the west as cotton. It is also utilized in the
irrigated areas of the southwest. The grass is grown in certain areas
north of the line indicated in Fig. 102. Its value in such areas, how-
ever, is questionable on account of temperature limitations.
Carpet Grass (Axonophus compressus). Carpet grass, also known
as Louisiana grass, being more exacting in its temperature and
moisture demands than bermuda, is not as widely distributed.
This is evident from Fig. 102. Its distribution extends neither as
far to the north nor as far to the west as that of bermuda. Carpet
grass is, according to Piper (10), especially adapted to sandy or
sandy loam soils, particularly in places where moisture is near the
570 ECOLOGICAL CROP GEOGRAPHY
surface most of the year. On such areas carpet grass is more val-
uable than any other perennial grass for permanent pastures.
Since carpet grass is less susceptible than bermuda to temperature
depressions in autumn, it can be utilized for grazing over a longer
period of the year than bermuda.
Johnson Grass (Sorghum halepense). Johnson grass is generally
regarded more as a weed than as a forage grass. It is difficult to
eradicate. Large areas of fertile land, particularly river bottoms,
are infested with this grass. On such areas it is utilized to advan-
tage for the production of hay and pasturage. Johnson" grass occurs
more or less in all of the Cotton Belt, except in the drier western
portions. In the northern areas of the Cotton Belt it is killed out
by occasional severe winters.
Johnson grass is frequently grown in combination with other
crops such as winter oats or vetch. In such cases the infested areas
are often plowed and seeded to winter annuals. Since such treat-
ment relieves the sodbound condition of the Johnson grass, it
stimulates rather than injures the grass.
Other Southern Grasses. A great variety of grasses of tropical
origin can be used in the very southern portion of the United States.
Space does not permit the discussion of these grasses in detail. Dallis
grass (Paspalum dilatatum), a native of Argentina, is utilized from
North Carolina to Florida and west to Texas. Klages found it
exceedingly drought-resistant in north-central Oklahoma but
unable to survive winter temperatures. Vasey grass (Paspalum
urvillei), also a native of Argentina, is a close relative of Dallis grass
and adapted to the same area in the United States. Guinea grass
(Panicum maximum) , a native of Africa, is adapted only to the very
southern portion of the United States. Bahia grass (Panicum nota-
turn), a native of Cuba and Mexico, is grown in the same region as
Guinea grass. Natal grass (Tricholaena rosed) was after its introduc-
tion into the United States first grown as an ornamental. It has
merits as a forage grass in Florida, along the Gulf coast, and in the
very southern portion of California.
REFERENCES
1. Armstrong, S. F., British Grasses and Their Employment in Agriculture.
University Press, Cambridge, England, 1937.
PERENNIAL FORAGE GRASSES • 571
2. Baker, O. E., and A. B. Genung, "A graphic summary of farm crops,"
U. S. Dept. Agr. Misc. Pub. 267, 1938.
3. Helm, G. A., "Orchard grass in Missouri," Mo. Agr. Exp. Sta. Circ.
172, 1934.
4. Hitchcock, A. S., "Manual of grasses of the United States," U. S. Dept.
Agr. Misc. Pub. 200, 1935.
5. Hoover, M. M., "Native and adapted grasses for conservation of soil
and moisture in the Great Plains and Western States," U. S. Dept. Agr.
Farmers' Bull. 1812, 1939.
6. Keim, F. D., A. L. Frolik, and G. W. Beadle, "Studies of prairie hay
in north-central Nebraska," Nebr. Agr. Exp. Sta. Res. Bull. 60, 1932.
7. Klages, K. H. W., "Comparative ranges of adaptation of species of
cultivated grasses and legumes in Oklahoma," Jour. Amer. Soc. Agron.,
21:201-223 (1929).
8. Piper, C. V., "Important cultivated grasses," U. S. Dept. Agr. Farmers'
Bull. 1254, 1934.
9. ^ "Cultivated grasses of secondary importance," U. S. Dept.
Agr. Farmers' Bull. 1433, 1934.
10. , Forage Plants and Their Culture. Macmillan, New York, 1937.
11. Schoth, H. A., "Reed canary grass," U. S. Dept. Agr. Farmers' Bull.
1602, 1938.
12. , and M. A. Hein, "The ryegrasses," U. S. Dept. Agr. Leaflet
196, 1940.
13. Strecker, W., Die Kultur der Wiesen, ihr Wert, ihre Verbesserung, Diingurtg
und Pflege. Paul Parey, Berlin, 1923.
Chapter XXXII
MISCELLANEOUS CROPS
TOBACCO
Historical. The position of tobacco is unique in that it repre-
sents one of the most recent additions to the list of crops of world
importance. Tobacco is a native of America. Linton (13) desig-
nates it as one of the most important gifts from the New World to
the Old. The antiquity of tobacco and its use on this continent are
indicated by Linton in the following paragraph.
"In spite of the attempts of various authors to prove its Old World
origin there can be no doubt that it was introduced into both Europe
and Africa from America. Most species of Nicotiana are native to the
New World, and there are only a fe^v species which are undoubtedly
extra- American. The custom of smoking is also characteristic of
America. It was thoroughly established throughout eastern North and
South America at the time of the discovery; and the early explorers, from
Columbus on, speak of it as a strange and novel practice which they
often find hard to describe. It played an important part in many re-
ligious ceremonies, and the beliefs and observances connected with it
are in themselves proof of the antiquity of its use."
At the time of the discovery of America, tobacco was in general
use over the greater parts of North and South America. The In-
dians of Central and South America were mostly cigar and ciga-
rette smokers. The Spaniards, coming in contact mostly with these
inhabitants of the New World, adopted the methods of the Indians
by using tobacco in the form of crudely constructed cigars and
cigarettes. The Spaniards in turn became the promoters of the
cigar in Europe; they were slow, however, in making their product
known to the other nations of Europe. According to Laufer (12),
the cigar spread in Europe only in the first part of the last century.
The cigarette was not introduced into England until the Crimean
Campaign of 1854-1856, when it was brought back by British
officers who had learned this new method of using tobacco from
572
MISCELLANEOUS CROPS 573
their French and Turkish allies. The British had long been pipe
smokers. Unlike the Spaniards, the British, in their early expedi-
tions to the New World, contacted mostly the pipe-smoking Indians
of North America. They, in turn, took up the use of tobacco in
this form and became the most active propagators of pipe smoking.
As stated by Laufer, "English sailors and soldiers, students and
merchants carried the pipe victoriously wherever they went." The
English also soon gained a reputation for the making of good pipes,
a reputation and distinction that they hold to this day.
The rapid spread of the use and the culture of tobacco to nearly
all sections of the world was amazing. England, Portugal, and
Spain received tobacco directly from America. During the period
of rapid expansion of commerce following the discovery of the
Americas they, in turn, carried the plant and its products over all
the world.
Tobacco was first introduced into Spain as an ornamental, and
was later valued for its alleged medicinal values. Tobacco was
grown in Portugal in 1558. The plant was first brought and made
known in England by Sir John Hawkins around 1565. Here, as in
Spain, the plant was apparently grown as a curiosity for some time
before it was actually used. The smoking of tobacco in pipes in all
probability originated with sailors who returned from America
It fell to the lot of Sir Walter Raleigh to popularize tobacco in Eng
land. Tobacco culture began to spread in France from 1560.
Thcvet and Nicot are credited with the introduction of tobacco into
France. It was after the latter, Jean Nicot, that the generic name
of the plant, Nicotiana, was coined. The plant made its entrance
into Italy in 1561 under the sponsorship of two churchmen, the
Cardinal Santa Cruce, who brought it from Portugal, and by the
papal nuncio and ambassador of Toscana at the court of France,
Nicolo Tornabuoni. Laufer brings out that tobacco was cultivated
during the sixteenth century in many parts of Germany, chiefly
around Nuremberg, in Saxonia, Thuringia, Hessen, the Palatinate,
and Mecklenburg. Tobacco was first introduced into Norway in
1632. Peter the Great of Russia (1689-1725) became an adept
smoker during his sojourn in England. He followed the custom
earlier established in other countries, namely, to introduce tobacco
into his country, not only for the pleasure it would afford to smokers,
but also for the sake of the revenue it would yield. Jean Nicot, for
574 ECOLOGICAL CROP GEOGRAPHY
instance, was highly praised for having increased the revenue of
the French government by the introduction of tobacco into the
kingdom.
The use and culture of tobacco spread rapidly, not only in
Europe, but also in the other continents. It was introduced into
Turkey around 1605, and about the same date into Japan and
China. Even early travelers in Africa report the cultivation and
the use of tobacco among the natives of that continent.
The early rapid dissemination of tobacco may be accounted
for in part by the many and novel virtues credited to it, such as
allaying hunger, dispelling fatigue, and a great variety of medicinal
uses. It was for a time regarded as a potent and benevolent drug
"for the cure of many maladies." William Barclay (Edinburgh,
1614), writes of tobacco as having "much heavenlie vertue in
store" and describes America as "the countrie which God hath
honoured and blessed with this happie and holie herbe."
There was, however, definite opposition to the use of tobacco.
Thus, King James of England in 1 604 in his famed Counterblaste of
Tobacco refutes, in the physiological terminology of his time, the
medicinal virtues of the drug, and #he absurdities written in praise
of its alleged healing powers. JameS, after a long tirade, describes
the use of tobacco as "a custome lothsome to the eye, hatefull to
the nose, harmfull to the braine, dangerous to the lungs, and in
the blacke stinking fume thereof, neerest resembling the horrible
Stigian smoke of the pit that is bottomelesse." James's choice of
words in the condemnation of tobacco makes rather refreshing
reading. "It is a great contempt of God's good gifts that the sweet-
ness of man's breath, being a gift of God, should be willfully
corrupted by this stinking smoke. Moreover, which is a great
iniquitie, and against all humanitie, the husband shall be ashamed,
to reduce thereby his delicate, wholesome, and cleane complex-
ioned wife, to that extremitie, that either shee must also corrupt
her sweete breath therewith, or else resolve to live in a perpetual
stinking torment."
The early importations of tobacco into England were in all
probability of Nicotiana rustica, a small-leaved variety with a high
percentage content of nicotine. It was the species in common use
among North American Indians. This fact may also account for
the ire of King James in condemning the crop. Nicotiana rustica
MISCELLANEOUS CROPS 575
is not now cultivated as a smoking tobacco, excepting in por-
tions of India. Its primary use is for the production of nicotine.
The broad-leaved, low-nicotine species N. tabacum was commonly
grown by the Indians of the West Indies and of Mexico. It is the
type that entered world trade through the commerce of the Span-
iards and Portuguese traders. Nicotiana tabacum was not introduced
into Virginia until about 1610, coming there from Trinidad.
In spite of James's counterblast and other attempts to limit its
use, consumption increased rapidly. The early history of tobacco
production in the United States is summarized by Garner et al. (7)
in the following paragraph.
"From the small beginning at Jamestown, the production of tobacco
in Virginia and Maryland increased rapidly, for it was about the only
commodity the colonists could produce to exchange for the many manu-
factured products they required from Europe. From the crop of 20,000
pounds in 1618 at Jamestown, exports in 1627, only 9 years later, had
increased to 500,000 pounds. In fact, although the foreign market
rapidly expanded, production increased at an even greater rate. The
total exports from Maryland and Virginia were 1,500,000 pounds in
1639, but the value per pound had declined from nearly 55 cents in
1619 to about 6 cents. At the outbreak of the Revolutionary War,
exports of tobacco had increased to about 100,000,000 pounds, nearly
all of which was produced in Virginia and Maryland. After the close
of the Revolution, culture was extended into North Carolina, Ken
tucky, Tennessee, Ohio, and Missouri, and later to several other States.
Domestic manufacture of tobacco first assumed importance after the
Revolution and has continued progressively to absorb an increasing
portion of the crop, until at present more than half of the total produc-
tion is utilized for this purpose."
Utilization of Tobacco. Hill (9) discusses tobacco under the
novel heading of "Fumitories and Masticatories." These two
terms are well chosen to designate the utilization of tobacco. The
leaf is either smoked in a pipe, in the form of cigarettes or cigars,
or is "masticated" in the form of chewing tobacco or snuff. All
of these uses are old. There is some difference of opinion as to
whether the natives of the Americas chewed tobacco; however, the
taking of the leaf in the form of snuff is a European innovation.
The relative use of tobacco in different forms has undergone
change. This is evident from the per capita consumption of tobacco
in various forms in the United States, expressed in pounds at five-
year intervals, 1900-1935, Table 61 (2). The most spectacular
576
ECOLOGICAL CROP GEOGRAPHY
phase of the tobacco industry has been the amazing increase in
cigarette consumption. As late as 1880, only a few cigarettes were
made in the United States. In 1894, the Egyptian cigarette
appeared and slowly made headway even though it was expensive.
Soon American manufacturers began to add Turkish tobacco to
improve the burning qualities of their product. In 1 900, the per
capita consumption of small cigarettes was only 34.9, by 1910 it
was 93.7, by 1920, it was 418.8, ten years later 972.0, and in 1935
it amounted to 1,055.6. The production of small cigarettes in the
United States increased from 532,719,000 in 1890; 3,254,131,000
in 1900; 47,430,105,000 in 1920; 123,802,186,000 in 1930 to
164,476,300,000 in 1938 (2 and 3). The cigarette came into great
demand during the first World War and has consistently gained
in popularity since that time.
TABLE 61. PER CAPITA CONSUMPTION OF TOBACCO PRODUCTS IN THE UNITED
STATES AT FIVE-YEAR INTERVALS, 1900-1935, EXPRESSED IN POUNDS OF
VARIOUS FORMS OF CONSUMPTION
Year
Forms of Consumption
Total
Cigars*
Ciga-
rettes *
Ohewing
Tobacco
Smoking
Tobacco
Snuff
1900
1.33
1.59
1.59
1.58
1.87
1.39
1.17
0.97
0.14
0.15
0.34
0.67
1.56
2.07
2.73
3.04
2.39
2.09
2.17
1.77
1.43
1.10
0.80
0.55
1.31
1.92
2.30
2.36
1.98
2.14
1.87
1.84
0.20
0.25
0.34
0.33
0.34
0.33
0.33
0.28
5.37
6.00
6.74
6.71
7.18
7.03
6.90
6.68
1905
1910
1915
1920
1925 . . . . .
1930
1935
* Pounds of cigars and cigarettes represent unstemmcd equivalent of tobacco used
in the manufacture of these products.
Nicotine is another product of tobacco of considerable value,
being used extensively as an insecticide. The present supply is
obtained almost exclusively from the by-products of the tobacco
industry, that is, from the stems, waste, and low-grade leaves.
The nicotine content of the commonly used Nicotiana tabacum is
relatively low. Nicotiana rustica, on the other hand, has a high
percentage content of nicotine. Under favorable conditions,
JV. rustica has produced yields of 150 pounds of nicotine per acre.
MISCELLANEOUS CROPS 577
The species is being grown to some extent for the production of
nicotine in Mexico.
Climatic Relationships. A comparison of Fig. 105, showing the
world distribution of tobacco, with the various climatic maps of
the continents, presented in Chapter XX, brings out that tobacco
is grown over a wide range of climatic conditions. The extremes
of the climatic regions of tobacco production are illustrated by the
fact that the crop is of importance from the moist tropical, Af or
AA'r, to the boreal and dry, Df, DW or BC'r, CB'd climates.
Tobacco production extends from the tropics, East Indies, and
West Indies, to the temperate areas as in Wisconsin, Connecticut,
Ontario, and Russia.
While tobacco can be grown over a wide range of climatic
conditions, the production of a product of quality demands rather
specific soil and climatic conditions. The user of tobacco demands
a leaf with a good flavor, a good aroma, and a good burn, or
ability to hold a fire. The exact specifications of quality are
influenced by the use to be made of the leaf. Thus, different
qualities are stressed for pipe tobacco than for cigar or cigarette
tobaccos, and still different features for chewing tobacco or leaf
intended for the manufacture of snuff. Even the leaf intended for
the different parts of a cigar, the filler, binder, and wrapper, must
meet different specifications. As with many other agricultural
products, growers of tobacco, forced by economic considerations
to use their own product, often utilize a grade not acceptable to
general commercial outlets. This is the case especially in areas
where an artificial social environment has been created. With
the operation of an exchange economy, products entering com-
mercial outlets must be of a quality enabling them to compete
with the products of other producing areas. Consequently, areas
producing on an export basis tend to stress quality. Finch and
Baker (5) bring out that the commercial value of tobacco "is more
affected by the soil and climatic conditions under which it is
grown than that of any other important farm crop." Since this
is the case, tobacco producing areas, growing more of the crop
than the domestic markets of their respective producing countries
can absorb, must produce a product with qualities to attract
purchasers. Only a relatively small number of areas of the many
tobacco growing sections of the world are favored with climatic
578 ECOLOGICAL CROP GEOGRAPHY
and soil conditions enabling them to produce a leaf of quality.
It must also be kept in mind, as pointed out by Garner (6), that
the tobacco industry has become highly specialized, and that the
trade regularly looks to certain well-defined areas of production
for its supply of the various kinds of leaf required. Each commer-
cially important district produces a tobacco of certain well-known
characteristics which make it desirable for special purposes.
The above discussion brings out that it is difficult to state the
characteristics of an optimum climate for tobacco culture. Certain
general statements, however, can be made. Tobacco, unlike some
of its users, is a plant of moderation in that it requires fairly uniform
conditions with respect to temperature and moisture during its
period of growth. Since the plant has a rather limited root system,
it is easily damaged by drought. Dry seasons tend not only to
reduce the size of the plants but also to produce abnormally thick
leaves having poor combustibility. A constant supply of water
during the growing season is, therefore, a prime necessity. On
the other hand, excessive moisture is undesirable. Wet seasons
result in the production of large, thin, tender leaves, having free-
burning properties, but susceptiBlp to injury through decay in the
processes of curing and fermenting. Where the crop is grown in
humid areas, good soil drainage is essential. Likewise, in order to
produce a leaf of quality, a section must have uniform and fairly
high temperatures during the growing season; extremes are
decidedly detrimental. Atmospheric humidity is also of impor-
tance—so much so that oceanic influences are often considered
as affecting quality. Thus, the excellence of the cigar leaf of the
Vuelta Abajo district of Cuba, famed for its flavor and aroma, is
accounted for by a combined influence of climatic and soil condi-
tions. The district producing the highest quality of leaf embraces,
according to Finch and Baker, only about 25 square miles, lying
south of the mountains in western Pinar del Rio province, in the
westernmost extremity of the island. The climate is definitely
modified by oceanic influences. Likewise, some of the world's
finest cigarette tobaccos are produced under climatic conditions
modified by proximity to water. This is the case in southern
Macedonia, around the port of Kavalla, and in the Smyrna district
bordering the Aegean, also in the Trebizond and Samsun districts
on the southeastern shore of the Black Sea. The outstanding
MISCELLANEOUS CROPS 579
tobacco producing districts of the United States are also character-
ized by having a rather high atmospheric humidity during the
growing season. Good tobacco regions should also be free from
high winds and hail, which may do considerable damage to the
tender leaves.
In addition to the natural climatic conditions, the tobacco crop
is also produced under shade in the production of special types,
as cigar wrapper leaves. Reductions of light produce thin, fine-
textured leaves.
Soil Relationships. The soil relationships of tobacco must be
discussed with reference to quality effects as was done in the case
of the climatic responses of the plant. As stated by Morgan et aL
(15), "The soil requirements of tobacco are somewhat unique, in
that in addition to the needs for normal growth, there are certain
rather special correlations between soil type and characteristics
of quality in respect to each of the various types of tobacco."
Plant physiologists have given a lot of thought to these "special
correlations" in attempting to throw light on the many and inter-
esting relationships of soil characteristics to quality in tobacco.
The general soil requirements for tobacco are stated by Morgan
et aL in the following three paragraphs.
"In general, tobacco is a crop making very rapid growth during a
short season. It requires large amounts of available soil moisture within
reach of its comparatively shallow root system, but, at the same time,
it is relatively sensitive to poorly drained conditions. Carefully ad-
justed, though relatively large, amounts of readily available nitrogen
must be supplied. Bright-leaf tobacco may be somewhat of an excep-
tion as to its need for large amounts. The phosphorus needs of the
plant are not great, although soils with low levels of available phos-
phorus permit little growth until corrected by phosphatic fertilizers.
Potash is utilized by the tobacco plant in especially large amounts, and
the crop has little or no ability to obtain potassium from the 'non-
exchangeable' potassium of soil minerals. Hence, liberal potash fertili-
zation is ordinarily practiced, except in rotations on land receiving a
supply of available potash from large amounts of animal manures.
The relative proportions of basic constituents (calcium, magnesium,
and potassium) capable of ready assimilation by the plant are impor-
tant in determining the burning qualities and ash characteristics, espe-
cially in cigar types. Chlorides in the soil solution are undesirable
because of the objectionable burning effects. In Puerto Rico, there is
apparently sufficient sodium chloride brought in as a fine spray by the
580 ECOLOGICAL CROP GEOGRAPHY
northeast trade winds for the atmosphere to have a deleterious effect
upon the quality of tobacco for a distance of approximately 4 miles
from the coast.
"Tobacco is capable of normal growth over a wide range of soil
acidity. Excessive acidity, however, atpH levels below 5.0, is often harm-
ful to quality or yield, as it results in low supplies of calcium and mag-
nesium, low phosphorus availability, and excessive solubility of man-
ganese and aluminum. As the soil reaction approaches the alkaline
range, the black root rot disease is favored, especially in areas like the
Connecticut Valley where the crop is grown year after year on the
same fields.
"It is interesting to note that the high-quality cigarette tobacco, the
flue-cured bright tobacco, is grown on the light-colored and light-
textured soils of the Piedmont and Coastal Plain, which are low in
organic matter and in nutrients. The significant thing about these
soils is their physical condition, which permits them to serve as a
medium to which proper amounts of nutrients may be added. In other
words, they are responsive to management because of inherent physical
characteristics."
World Distribution. Tobacco is produced to some extent in
practically every country of the world. Finch and Baker designate
the area in which tobacco is gr^wn commercially, including the
areas where the crop is grown for home consumption, as extending
from 55° N. latitude in Europe and 45° in North America to 40°
South. While the crop is widely distributed, it must nevertheless
be recognized that only a comparatively limited number of areas
are favorably situated with respect to climatic and soil conditions
to produce a leaf of superior quality. The major production of
commercial tobacco is found in warm areas, or at least in regions
with relatively warm growing seasons. In many areas the crop is
grown in an artificial social environment in that production is
fostered by government support of the industry. Indirectly the
heavy taxation of tobacco and its products has stimulated the
production of quality in the crop.
Table 62 gives the statistics of world tobacco production for the
five-year period of 1930-31 to 1934-35. Data for production in
China are available for only two years of this period. Chinese
production was nevertheless included in the percentage tabulation
presented in Table 62. Figure 105, taken from the historical series
of the Bureau of Agricultural Economics (4), shows the world
distribution of tobacco production cartographically.
2 3
•8
_o J« fib
N en J2r
8 S
581
582
ECOLOGICAL CROP GEOGRAPHY
The bulk of the crop, 65.21 per cent, is grown in three countries,
namely, India, China, and the United States. The percentage
data presented in Table 62 are based on production. The Bureau
of Agricultural Economics of the United States Department of
Agriculture credits the United States with 23, and India and China
each with 19 per cent of the world's tobacco acreage for the five-
year period of 1931-1935, year beginning with July. According
to this tabulation 62 per cent of the world's tobacco acreage is
found in the above three countries.
TABLE 62. WORLD TOBACCO STATISTICS BY IMPORTANT PRODUCING COUN-
TRIES FOR THE FIVE-YEAR PERIOD 1930-31 TO 1934-35
Rank
Country
Acreage, in
1,000 Acres
Yield, in
Lbs. per Acre
Production
In 1,000
Lbs.
In Percent-
age of Esti-
mated
World Total
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
India
1,285
1,299,
1,706 *
459
86
97
195
179
50
124
41
53
120
67
1,066
1,046
783
742
1,685
1,097
530
515
683
1,720
1,259
417
793
1,369,670
1,357,813
1,336,559
340,805
216,164
145,330
117,094
106,218
103,615
92,249
89,572
84,740
71,259
67,145
56,447
53,527
613,606
22.01
21.82
21.48
5.48
3.47
2.34
1.88
1.71
1.67
1.48
1.44
1.36
1.15
1.08
0.91
0.86
9.86
China*
United States
U.S.S.R
Brazil
Taoan
Java and Madoera . . .
Italy
Greece
Philippine Islands . . .
Germany
Turkey
France
Hunararv ......
Cuba
Bulgaria
All other countries . . .
Estimated world total . .
—
—
6,221,813
100.00
* Two-year average only.
The tobacco producing regions of the world may for convenience
be grouped into eight main areas: The eastern portion of the
United States; Cuba and the West Indies; Brazil; the Mediterranean
and Asia Minor area; the Balkan and southern Russian area; India;
China; and the Philippine Islands and the East Indies. Areas of
lesser importance are found in Germany, France, and Hungary.
MISCELLANEOUS CROPS 583
The United States is by far the most important exporting coun-
try, exporting for the five-year period 1930-1934 in excess of
479 million pounds annually. Other important exporting coun-
tries, with their exports stated in rounded figures of millions of
pounds for the same period, are: Netherland India, 144; Greece, 88;
Brazil, 67; Turkey, 67; Bulgaria, 49; the Philippine Islands, 45;
Cuba, 38; British India, 36; Algeria, 26; and Hungary, 23. The
countries of northwestern Europe are the outstanding importers
of the commodity.
It will be impossible to discuss here the conditions under which
tobacco is grown in its many areas of production. The areas pro-
ducing tobacco of exceptional quality must, however, at least be
mentioned. The quality of American tobacco varies in the different
areas of production but is generally good and under normal condi-
tions enjoys a good export demand. Cuba produces cigar tobaccos
of exceptional quality. Sumatra and Java produce a fine light
tobacco particularly useful for cigar wrappers. Turkey and Greece
produce a high type of cigarette tobacco which is extensively used
for blending purposes. According to Lippincott (14), American
companies buy 65 to 70 per cent of the output of the Smyrna and
Samsun districts of Asia Minor. Two other important producing
areas in Asia Minor and the Levant are the Trebizond and Latakii
districts. According to Finch and Baker, "Samsun and Smyrna
tobaccos are strong and highly aromatic; Trebizond tobacco is light
and mild; while Latakia is artificially flavored with certain herbs in
the process of curing." The Xanthe, Kavalla, and Salonika areas of
Greece produce cigarette tobaccos of quality. The leaf produced
in these areas of Asia Minor and Macedonia bears, according to
Finch and Baker, the same relation to the cigarette industry that
Cuban tobacco bears to the cigar industry.
Distribution in the United States. The production of tobacco
in the United States is highly localized. This holds true not only
for the crop as a whole but especially for the production of each
principal type of leaf demanded by the increasing specialization
in tobacco manufacturing. According to Hutcheson et al. (11),
the tobacco crop of the United States occupies only 0.40 per cent
of the total acreage in crops. Yet, in 1932 the crop ranked seventh
in value of the crops grown in the country. In 1935 the value of
the tobacco crop was exceeded only by the values of the corn,
584
ECOLOGICAL CROP GEOGRAPHY
all hay, wheat, cotton, and oats crops. The farm value of the
tobacco crop for that season was estimated at $237,389,430, while
the farm value of the potato crop dropped slightly below that
figure, namely to $230,668,860.
Three main classes of tobacco are generally recognized: (a) cigar
tobacco; (b) manufacturing tobacco; and (c) export tobacco.
These classes are further divided into types according to special
characteristics and appropriate use. The three principal types
of cigar tobacco correspond to the three parts of the cigar, namely,
wrapper leaf, binder leaf, and filler leaf. The principal* commercial
manufacturing and export types are the fire-cured, dark air-cured,
flue-cured, the Maryland, and Burley. Manufacturing and export
types of tobacco are used for cigarette, pipe-smoking, and chewing
mixtures.
Table 63 gives the statistics of tobacco production in the United
States by states for the ten-year period of 1928-1937 and the pro-
duction for 1938. It will be observed that two states, North Caro-
lina and Kentucky, account for almost 60 per cent of the production
of the country. Six states produce in excess of 85 per cent of the
total crop.
TABLE 63. TOBACCO: ACREAGE HARVESTED, YIELD PER ACRE, PRODUCTION
AVERAGES FOR THE TEN-YEAR PERIOD 1928-1937 AND 1938 PRO-
DUCTION
Production
Average
\r L
Rank
States
Number
of Acres
Harvested
Yield,
in Lbs.
Average
1928-1937,
Percentage
nf IT <\
1938, in
J928-1937
in 1,000
Lbs.
ui u. o.
Total
1,000 Lbs.
\
North Carolina
645,830
766
493,927
36.31
517,210
2
Kentucky . .
411,820
780
321,370
23.62
289,115
3
Tennessee . .
129,770
838
108,818
8.00
98,687
4
Virginia . .
141,890
701
98,075
7.21
98,906
5
South Carolina
102,500
779
79,624
5.85
98,800
6
Georgia . .
79,080
816
66,787
4.91
90,950
7
Pennsylvania
31,050
1,228
37,923
2.79
32,110
8
Ohio . . •
37,640
891
33,294
2.45
23,885
9
Wisconsin . .
24,910
1,316
32,098
2.36
32,710
10
Maryland . .
35,740
704
25,217
1.85
29,250
Other states .
60,030
1,054
63,267
4.65
64,200
Total U.S. . . .
1,700,260
803.2
1,360,400
100.00
1,375,823
MISCELLANEOUS CROPS
585
TOBACCO-GROWING DISTRICTS
FLUE CURED TYPES
YFI CLASS I
II* OLD tfLT FLUf-CURfO
Ilk MIDDLE »£LT FLU£-CUR£0
12 tASTfRN NORTH CAROLINA FLVt-CURtd
13 SOUTH CAROLINA FLU£-CUR£tf
14 CfORGIA FLU£-CUR£0
FIRE-CURED TYPES •
Tm CLASS 2
, J 22 £ASTC*N n*l.C(JI>CO (CLAUKSVlLLf AND HOPKIHSVILLt)
I S 29 WfSTfRH FI*£-CU*CD 1PADVGAM AND MAYFtCLD)
|j!4 H£ND£*SON FIHf-CURtD
AIR-CURED TYPES
CLASS 3
ji"
J2 SOUTH£*N MA*YLAMD
as one- s vent it
!• CRf£N»IYHI
37 VIRGINIA SUN-CUR f*
CIGAR-FILLER TYPES
CLASS 4
41 PENNSYLVANIA SftDLfAF
42 CffHARDT
43 ZIMMfR 0* SPANISH
44 OtfrCM
45 CfORCIA AND FLORIDA SUN-CROWN
CIGAR-BINDER TYPES
TtfC CLASS 5
51 CONMCCriCUr VXtlfr »ROAOLfAF
52 CONNECTICUT HAVANA SCSD
53 WCIT rOffff AND PfUNSYLVANIA HAVANA
54 SOUTHF.RN WISCONSIN
55 *ORTH£RN WISCONSIN
CIGAR-WRAPPER TYPES
me CLASS «
• I CONNfCTICUT Miter SNADl-CROWN
<2 CCOffCM 4NO FLORIDA SHADt-GROWN
FIG. 106. Locations of the tobacco-growing districts of the United States. (After
Morrow and Smith.)
Table 64, taken from Garner *f a/. (7), lists the principal com-
mercial types of tobacco, indicates the areas in which they are
grown, gives their chief uses, and shows the varieties used in their
production. Figure 106, taken from Morrow and Smith (16),
9
O
5^
*
!B
•S
Q
o
u
I
o
6
*
586
Cfl
:• JT
MISCELLANEOUS CROPS 587
shows the tobacco producing districts of the United States together
with the types produced in each district. Baker and Genung (1)
give the distribution of the tobacco acreage in the United States.
The United States is the world's greatest exporter of tobacco.
But the country is also an importer of quality leaf. Cigar leaf is
imported from Cuba and Puerto Rico, wrapper leaf from Sumatra
and the East Indies, and Turkish cigarette tobaccos from Asia
Minor and Greece. However, exports far exceed imports. In
1934 the United States exported 440,866,000 pounds of leaf and
imported 57,786,000 pounds.
The United States is also a great consumer of tobacco, being
surpassed in per capita consumption only by the Netherlands.
The per capita consumption of all tobacco products in various
countries for 1932 were as follows: Netherlands, 7.80 pounds; the
United States, 6.00 pounds; Belgium, 5.49 pounds; Denmark,
4.43 pounds; United Kingdom, 3.32 pounds; Germany, 3.24 pounds;
Sweden, 2.98 pounds; and France, 2.90 pounds.
Hill makes an interesting observation regarding the import
demands of various nations, "England, a great pipe-smoking
country, demands the best and strongest grades. Germany prefers
a thick leaf, rich in oil and reddish in color. Switzerland demands
the best quality, Italy and Austria a good grade, while France and
Spain are satisfied with the poorer grades."
HOPS
(Humulus lupulus)
Historical. Nothing is known concerning the date at which the
hop plant was first brought under cultivation. The hop was known
to the early Greeks, even if only in its wild stage. It is described
by Pliny in his Natural History as lupulus, lupulus salictarius, an
appetizer and salad.
Gross (8) discusses the earliest report of the hop as a cultivated
plant in the following paragraph.
"The earliest reports on the hop as a cultivated plant date from the
Carlovingian epoch, King Pepin le Bref having donated homularias
(hop gardens) to the monastery of St. Denis about the year 768. As it
would be straining a point to assume that hops would be extensively
grown for any other purpose at that period, it may be reasonably sup-
posed that they were used as an aromatic for the malt liquor cerevista
588 ECOLOGICAL CROP GEOGRAPHY
then in general repute. Weaker malt beverages biera, canum and oel
were also manufactured."
During the Middle Ages, hop gardens were cultivated to a
limited extent as adjuncts to monasteries in central Europe. Hops
are mentioned in connection with the Freising monastery around
the year 850. However, hopped beer apparently did not become
general in Germany until the fourteenth century. The crop became
of importance in Flanders during the fourteenth century. Hops
were introduced into England toward the close of the fifteenth
century. Henry VII and Henry VIII prohibited their use in beer.
Edward VI, however, formed a better opinion of hops, and granted
numerous privileges in connection with their cultivation. Hops
have been grown in central Europe for centuries. Bohemia soon
gained a reputation for the production of hops of high quality, a
distinction that this area has held up to the present time.
According to Smith (18), hop growing in North America began
in New Netherlands as early as 1629 and in Virginia in 1648,
although it did not become important until about 1800. In 1849
the New England states and New York produced nearly 1,500,000
pounds, of which New York produced 70 per cent. After the Civil
War the industry developed in Wisconsin. In 1879 the state of
New York produced an all-time maximum crop of 21,629,000
pounds. The growing of hops on the Pacific coast was started
between 1858 and 1869. Production there increased gradually
until at the present time the production of the crop in the eastern
areas is negligible. The harvested hop acreage in the United
States declined from more than 40,000 to less than 20,000 acres
during the period of national prohibition. Since the legalization
of beer in 1933, there has been a general increase in acreage and
even a revival of hop production in the state of New York.
Utilization. Hops are grown for the production of lupulin,
consisting of resins and essential oil, which imparts the character-
istic flavor to beer, ale, and other malt beverages. The essential
oil also contributes to the aroma and keeping qualities of beer
and ale. Furthermore, the tannins occurring in the scales (or bracts)
and stems of the cone of the hop aid in the clarification of the brew
after boiling. The amount of hops required in the brewing industry
is rather small. Each 31 -gallon barrel of beer brewed in the United
States requires only | to f pound of hops, though in some countries
MISCELLANEOUS CROPS 589
beer is more heavily hopped so that the figures sometimes reach
\\ pounds.
Climatic and Soil Relationships. The hop plant is somewhat
similar to tobacco in that the quality of the product is rather
markedly influenced by environmental factors. The hop is a plant
of the central temperate zone. It does best under temperature
conditions without sharp and often repeated fluctuations. Accord-
ing to Gross, the plant develops more satisfactorily when the tem-
perature rises slowly and constantly from early spring up to the
middle of summer, and then gradually and uniformly recedes.
The hop plant demands a fairly abundant supply of moisture.
Ideal moisture conditions are provided where the plant has an
abundant supply accumulated during the winter months to draw
upon. After growth starts, cold spring rains are harmful. An
abundance of moisture is desirable during late spring and during
early summer, that is, during the period of rapid growth. The
latter part of the summer should be dry. Excessive moisture in
late August and in September frequently leads to severe losses from
various fungus diseases and plant lice.
The hop plant is a long-lived perennial. Long severe winters
frequently result in the killing out of many of the plants. This
offers another reason for the location of the crop in rather moderate
areas.
Being a deep-rooted plant, the hop requires a deep, well-
drained soil. Alluvial soils, or deep sandy or gravelly loam soils,
are most desirable. Heavy clay soils, especially if wet, must be
avoided.
Distribution. Table 65 gives the world statistics on hop pro-
duction for the five-year period 1930-31 to 1934-35. Data on
production in the Union of Soviet Socialist Republics are not
available. It is known, however, that the crop is of some impor-
tance in Russia. It will be observed that only two non-European
areas — the United States, Australia, and New Zealand — produce
hops extensively. The crop is of special importance in Germany.
Most of the production there is found in the southern part of that
country, in Bavaria, Wurttemberg, and in Bohemia, that is, in
areas where rather moderate climates prevail. England and Wales
have long been important hop producers; again, the climate is
moderate.
590
ECOLOGICAL CROP GEOGRAPHY
TABLE 65. WORLD STATISTICS ON HOP PRODUCTION FOR THE FIVE- YEAR
PERIOD 1930-31 TO 1934-35
Rank
Country
Acreage
in Acres
Production
In 1,000 Lbs.
In Percentage
of World
Total *
1
2
3
4
5
6
7
8
Germany
56,060
26,000
18,198
5,351
6,198
5,291
1,546
1,931
1,433
37,584
31,566
24,304
3,637
3,450
3,116
2,688
2,009
1,459
34.23
28.75
22.13
3.31
3.14
2.84
2.45
1.83
1.32
United States
England and Wales ....
France
Poland
Yugoslavia
Australia and New Zealand
Belgium
All others *
World total *
122,008
109,813
100.00
* Excluding the U.S.S.R.
The United States is an important producer and exporter of hops.
According to Hoerner and Rabak (10), hops were at one time grown
in many areas of the United Statesf i>ut they have never been of
commercial importance except in New York and on the Pacific coast.
Powdery mildew and prohibition
practically eliminated the crop
from New York until very recent
years, when the industry revived
in the western and central por-
tions of the state. Nearly the
entire crop is produced on the
Pacific coast. For the ten-year
period of 1928-1937 Oregon
produced 18,352,000 pounds or
nearly 51 per cent of the
country's total crop. California
produced 8,695,000 and Wash-
ington 7,032,000 pounds. Figure
107 shows the distribution of the
hop acreage in 1938. The im-
\
/
/
FIG. 107. Hop production in the
United States in 1938. Each dot rep-
resents 1 ,000 acres. Nearly the entire
crop is produced on the Pacific Coast.
portanceof the Willamette Valley
of western Oregon is evident.
MISCELLANEOUS CROPS 391
BUCKWHEAT
(Fagopyrum spp.)
Importance of the Crop. Buckwheat, except in limited regions,
is a crop of minor importance both in world agriculture and in the
United States. Quisenberry and Taylor (17) bring out that for
every bushel of buckwheat grown in the United States there are
produced about 300 bushels of corn, 100 bushels of wheat,
150 bushels of oats, 35 bushels of barley, and 5 bushels of rye.
Buckwheat probably originated in the mountains of central and
western China. It was brought to the United States from Europe
by early colonists. Buckwheat cakes seem to have fallen off in
favor since more and more heavy manual labor is performed by
means of machinery. Around 1866, buckwheat was grown on
nearly 800,000 acres; more than a million acres were grown in the
United States in 1918. Since that time the crop has decreased in
importance.
Three species of buckwheat are recognized: (a) common (Fago-
pyrum esculentum); (b) Tartary or Siberian (F. tartaricum); and
(c) notch-seeded buckwheat (F. emarginatttm). The three varieties
of buckwheat — Japanese, Silverhull, and Common Gray —
generally grown in the United States belong to the F. esculentwn
species. Tartary buckwheat is recommended for its superior hardi-
ness. Zavitz (19) records high yields of this species in Ontario.
Outside of its main areas of production, buckwheat is frequently
grown as a catch crop. Since it requires but a short period to
complete its cycle of development, it fits well into a cropping
program to replace a crop that may have been destroyed earlier
in the season. Buckwheat is able to produce a crop in from 10 to
12 weeks. The crop also has merits as a honey plant and can be
used to advantage for soil-improvement purposes.
Climatic and Soil Relationships. Buckwheat is a crop of moist,
cool climates. It will grow at rather low temperatures. This,
together with its short growing season, makes it a good crop at high
latitudes and at high elevations. Buckwheat has a distinct critical
period at flowering time. High temperatures and dry weather,
and also hot weather with frequent rains at that time, are often
disastrous to the crop. Such conditions lead to a poor set of seed,
because of the blasting of the flowers. This makes buckwheat a
592
ECOLOGICAL CROP GEOGRAPHY
rather hazardous crop. Seeding is often delayed in spring so that
the principal growth may take place during relatively warm portions
of the year and seed formation during the cooler months of late
summer and early autumn. In the western areas of its production
in the United States the crop is often seeded early enough to bring
it into bloom late in July, that is, before temperatures get too high.
Buckwheat is extremely tolerant of poor soil conditions. It
will produce a better crop on infertile, acid, poorly tilled lands
than any other grain if the climatic conditions are favprable. Like
other crops, buckwheat responds to good treatment with increased
yields. It is well adapted to light, well-drained soils such as sandy
loams and silt loams. The crop will not do well on heavy, wet soils.
High fertility is not required; as a matter of fact, the crop lodges
rather readily on such soils. Buckwheat is ideally adapted to poor
lands in that it can compete successfully there with other grain
crops. Other crops are usually more profitable on fertile soils,
except where buckwheat may be used as a catch crop.
Distribution. Among the countries of the world, the Soviet
Union has the largest production of buckwheat, with France ranking
second, Poland third, Canada fourth, and the United States fifth.
Other producing countries are Japan, Germany, and Rumania.
TABLE 66. BUCKWHEAT: ACREAGE HARVESTED, YIELD PER ACRE, PRODUC-
TION AVERAGES FOR THE TEN- YEAR PERIOD 1928-1937 AND 1938
PRODUCTION. ACREAGE AND PRODUCTION EXPRESSED IN THOUSANDS
Production
Rank
States
Acreage
Harvested
Tield,
in Bu.
Average
1928-1937,
in Bu.
Percentage
of U. S.
Total
1938,
in Bu.
1
2
3
Pennsylvania . .
New York . . .
Ohio
149
152
23
17.7
17.1
16.8
2,620
2,586
384
32.90
32.47
4.82
2,170
2,496
210
4
5
6
7
8
West Virginia . .
Minnesota . . .
Michigan ....
Indiana ....
Maine
20
32
22
16
12
17.2
9.1
11.7
13.6
18.0
354
306
264
215
209
4.45
3.84
3.31
2.70
2.62
256
172
243
168
130
9
10
Wisconsin ....
Virginia ....
Other states . . .
17
14
51
11.0
12.8
12.9
187
180
659
2.35
2.26
8.28
150
162
497
Total U.S. . . .
508
15.8
7,964
100.00
6,654
MISCELLANEOUS CROPS
593
Table 66 gives the buckwheat statistics for the United States
by states, while Fig. 108 shows the distribution of the crop. New
York and Pennsylvania produce in excess of 65 per cent of the crop.
It will be observed from Fig. 108 that the crop is of greatest
importance in south-central New York, northwestern and north-
central Pennsylvania, in the western counties of Maryland, and in
>KIAMOM* ^-MBS»---7/S»»ia
i
Fio. 108. Distribution of buckwheat in the United States in 1938. Each dot
represents 2,000 acres.
north-central West Virginia. In general these areas of high produc-
tion follow the higher and rougher topographies. Because of its
inability to compete successfully with other crops, buckwheat is of
little agricultural importance outside of these areas. Its use in other
sections of the United States is confined to special purposes such
as a honey crop, or catch crop. The growing of the crop for these
special purposes accounts for the scattered appearance of buck-
wheat over much of the northeastern quarter of the United States.
REFERENCES
1. Baker, O. E., and A. B. Genung, "A graphic summary of farm crops,"
U. S. Dept. Agr. Misc. Pub. 267, 1938.
594 ECOLOGICAL CROP GEOGRAPHY
2. Bureau of Agricultural Economics, "First annual report on tobacco
statistics," U. S. Dept. Agr. Statistical Bull. 58, 1937.
3. 9 "Annual report on tobacco statistics, 1938," U. S. Dept. Agr.
Statistical Bull. 67, 1938.
4. ^ "World acreage and production of tobacco by countries,"
U. S. Dept. Agr. Historical Series, 1938.
5. Finch, V. C., and O. E. Baker, Geography of the World's Agriculture.
Govt. Print. Office, Washington, D. C., 1917.
6. Garner, W. W., "Tobacco culture," U. S. Dept. Agr. Farmers9 Bull. 571,
1936.
7. , H. A. Allard, and E. E. Clayton, "Superior germ plasm in
tobacco," U. S. Dept. Agr. Yearbook 1936:785-830.
8. Gross, E., Hops, Trans. German by Charles Salter. Scott, Greenwood,
London, 1900.
9. Hill, A. F., Economic Botany. McGraw-Hill, New York, 1937.
10. Hoerner, G. R., and F. Rabak, "Production of hops," U. S. Dept. Agr.
Farmers9 Bull. 1842, 1940.
11. Hutcheson, T. B., T. K. Wolfe, and M. S. Kipps, The Production of
Field Crops. McGraw-Hill, New York, 1936.
12. Laufer, B., "Introduction of tobacco into Europe," Field Museum of
Natural History Anthropology Leaflet t\9, Chicago, 1924.
13. Linton, R., "Use of tobacco among North American Indians," Field
Museum of Natural History Anthropology Leaflet 15, Chicago, 1924.
14. Lippincott, I., Economic Resources and Industries of the World. Apple ton,
New York, 1930.
15. Morgan, M. F., J. H. Gourley, and J. K. Ableiter, "The soil require-
ments of economic plants," U. S. Dept. Agr. Yearbook 1938:753-776.
16. Morrow, J. V., and D. Smith, "Tobacco shrinkage and losses in weight
in handling and storage," U. S. Dept. Agr. Circ. 435, 1937.
17. Quisenberry, K. S., and J. W. Taylor, "Growing buckwheat," U. S.
Dept. Agr. Farmers9 Bull. 1835, 1939.
18. Smith, D. C., "Varietal improvement in hops," U. S. Dept. Agr. Year-
book 1937:1215-1241.
19. Zavitz, C. A., "Farm crops," Ont. Agr. Col. Bull. 228, 1915.
AUTHOR INDEX
Aamodt, O. S., 203, 204, 546
Abbe, C., 229
Abbot, J. S. C., 20
Ableiter, J. K., 357, 395, 397, 437, 456,
481, 502, 543, 579
Ackermann, A., 227
Adams, R. L., 466
Agelasto, A. M., 494, 500
Albert, W. B., 227
Albright, W. D., 277
Alexander the Great, 454
Alexander II of Russia, 20
Ailard, H. A., 97, 277, 278, 575, 585
Anderson, A., 78
Andrew, J., 167
Archard, C. F., 463
Aristotle, 31
Arkwright, R., 496
Armstrong, S. F., 557, 558
Arner, L., 451, 456
Arnin-Schlangenthin, 225
Babcock, £. B., 86
Bacon, C. W., 278
Bacon, Francis, 20
Baker, G. O., 207
Baker, O. E., 7, 26, 39, 40, 156, 216, 345,
378, 389, 390, 393, 405, 427, 441, 451,
462, 494, 502, 505, 567, 577
Baldwin, M., 326
Ball, C. R., 3, 5, 406
Balls, W. L., 500
Barclay, W., 574
Bartel, A. T., 203
Barulina, £. I., 226
Bayles, B. B., 203
Beadle, G. W., 567
Beattie, J. H., 448
Beattie, W. R., 448
Becker, A., 403
Beijerink, M. W., 24
Bellaire, R., 321
Belz,J. O., 159
Benecke, W., 101
Bennett, £. R., 431
Bennett, M. K., 343, 344
Bensin, B. M., 7
Berger, A., 425
Bergsmark, D. R., 352, 403, 505, 513
Black, A. G., 58
Black, J. D., 58
Blackman, F. F., 105, 271
Blair, T. A., 146, 154, 194
Blakenburg, P., 383
Bolley, H. L., 480, 481
Bonar, J., 28
Bornmuller, 363
Boussingault, J. B., 23
Bouyoucos, G. J., 230
Bowen, E., 28, 32, 39
Bowman, I., 50, 63
Boysen-Jensen, P., 271
Brandes, E. W., 451, 456
Brandon, J. F., 364
Bressman, E. N., 329, 394, 477
Bretschneider, 413
Briggs, I.J., 174, 175, 184
Briggs, L. F., 334
Briggs, L.J., 159
Brody, S., 91
Brown, E. M., 371
Brown, H. B., 478, 496
Brown, L. A., 190, 192
Brown, W. H., 144
Buchanan, J. H., 397
Buechei, F. A., 7
Buffon, G. L. L., 221
Buhlert, 225, 226
Burgerstein, A., 148
Burlison, W. L., 224, 487
Bushnell, J., 435
Burtt, Davy, J., 392, 393
Caldwell,J. S., 145
Call, L. E., 25, 292
Capalungan, A. V., 334
Garden, P. V., 58
Carleton, M. A., 202, 357, 363
Carrier, L., 12
Carr-Saunders, A. M., 28
Cartter, J. L., 487, 488
Cartwright, E., 496
Chapman, W. R., 40
Chilcott, E. C., 77, 195, 196
595
596
AUTHOR INDEX
Chittenden, F. H., 451, 456
Chung, H. L., 444
Clark, C. F., 433
Clark, J. A., 131
Clausen, R. £., 86
Clayton, E. E., 575, 585
Clements, F. E., 7, 8, 96, 111, 275, 300,
306
Clusius, C., 433
Coffman, F. A., 364, 380
Coffman, W. B., 206
Cohen, E., 240
Cokc,J. E., 548
Cole,J. S., 191, 192, 194
Conklin, E. G., 85
Costantin, J., 94
Coulter, M. C., 86
Crampton, H. E., 126
Cressey, C. B., 506
Crist, J. W., 119
Crocker, W., 106
Cruce, Santa Cardinal, 573
Gushing, S. W., 16, 51
Dachnowski, A., 143
Dalton,J.J., 397
Daniel, H. A., 292
Darwin, C., 87
Day, J., 496
DeCandolle, A. P., 8, 356
Delf, M., 141
De Martonne, E., 167
Deming, G. W., 364
Derick, R. A., 375
Dettweiler, 14
De Vries, H., 87, 94, 125
Dickson, R. E., 78
Dillman, A. C., 175, 479, 480
Dorno, C., 270
Dowell, A. A., 494
Dowling, R. N., 463
Doyle, C. B., 494, 500
Drake, Sir. F., 444
Drude, O., 8
Duhamel, H. L., 221
Duley, F. L., 78, 202
Dungan, G. H., 154
East, E. M., 28, 86
Edward VI of England, 588
Elcock, H. A., 470
Eldredge,J. C., 154
Engelbrecht, T. H., 356, 373
Enlow, C. R., 529
Etheridgc, W. C., 371
Eucken, R., 18, 21
Evans, M. W., 262
Ewing, E. C., 500
Faris,J. A., 219
Farnsworth, H. C., 343, 344
Fergus, E. N., 521
Finch, V. C., 7, 350, 378, 393, 505, 577
Finnell, H. H., 291
Fischer, H., 96
Fisher, R. A., 194
Fitch, C. L., 431, 436
Fitting, H., 57, 75, 143
Fordham, M. A., 18
Forster, H. C., 279
Frankenfield, H. C., 156, 259, 267, 301
Franzke, C., 154
Frederick the Great, 19
Free, E. E., 200
Frolik, A. L., 567
Frost, H. B., 86
Fucss, W., 433, 434
Funk, S., 304, 306
Gaines, W. L., 90
Garber, R. S., 154
Garner, W. W., 97, 277, 278, 575, 578,
585
tGarside, A. H., 492, 501
Oenung, A. B., 354, 389, 405, 427, 441,
447, 462, 567
Gilbert, J. H., 23, 179
Glinka, K. D., 324
Geoppert, H. R., 222
Gorke, H., 222
Gourley, J. H., 357, 395, 397, 437, 456,
481, 502, 543, 579
Graber, L. F., 227
Grafe, V., 101
Gras, N. S. B., 18
Gray, L. C., 26, 39, 40
Gregg, W. R., 156, 267, 301
Gregory, H. E., 31, 62
Griesebach, A., 7, 8
Gross, E., 587
Haberlandt, F., 100, 148
Haeckel, E., 4
Haecker, V., 87
Hahn, E., 14
Hall, F. H., 425
Hann, J., 48, 136, 153, 270, 295, 298
Hansen, A., 4
Harndenburg, E. V., 417, 418
Harder, R., 106, 271
Hargreaves, J., 496
Harlan, H. V., 122, 370
AUTHOR INDEX
597
Harland, S. C., 500
Harrington, J. E., 529
Harris, F. S., 183
Harvey, R. B., 218, 228
Harvey, W., 86
Hawkins, Sir J., 573
Hawthorn, L. R., 425
Hayek, A., 124, 301, 304
Hayes, C.J.H., 20
Hedrick, U. P., 15, 425
Hedlund, T., 226
Hein, M. A., 562
Hellriegel, H., 23, 179
Helm, G. A., 371, 561
Henderson, W. O., 496
Hendry, G. W., 418
Henney, H.J., 195
Henry, A. J., 156, 259, 267, 301
Henry VII of England, 588
Henry VIII of England, 588
Hensen, E. R., 58, 175, 356, 402
Hesse, R., 5
Hcrtwig, O., 240
Hildebrandt, F., 77, 94
Hill, A. F., 472, 513, 514, 575, 587
Himmel, W. J., 305
Hirth, P., 166
Hitchcock, A. S., 556
Hoerncr, G. R., 590
Holbert, J. R., 224
Holloweil, E. A., 523, 548, 549
Holtz, H. F., 182, 197
Holzman, B., 147
Hooker, H. D., 106, 227
Hoover, M. M., 154, 565
Hopkins, A. D., 258, 260, 262
Hughes, H. D., 58, 175, 356, 402
Humboldt, A. von, 7, 8
Hume, A. N., 154
Hunt, T. E., 231,541
Huntington, E., 16, 47, 48, 51, 104, 381,
493
Hutcheson, T. B., 117, 426, 497, 583
Jacobs, P. B., 391
James, King of England, 574
James, P. B., 391
Jamicson, G. S., 474, 486
Jasny, N., 7
Jefferson, Thomas, 17
Jenkins, J. M., 381
Jenkins, M. T., 389
Jenkins, T.J., 279
Jenny, H., 164, 327, 328
Jesness, O. B., 494
Jevons, W. S., 4
Johannsen, W., 86
Johanson, H., 227
Johnston, W. H., 204
Jones, E., 332
Jones, J.W., 381
Jones, S. B., 321
Jost, L., 101
Kadel, B. G, 160
Kameriing, Z., 141
Kearney, T. H., 140, 206, 332
Keim, F. D., 567
Keller, A. G., 30, 31, 62
Kellogg, E. C., 138, 323, 324, 326
Kendrew, W. G., 285, 295
Kennedy, P. B., 529
Kenney, R., 521
Kephart, L. W., 522
Kezer, A., 202, 364
Kiesselbach, T. A., 78, 178, 180, 182, 228
Kincer, J. B., 156, 159, 239, 259, 267, 301
Kinney, E. J., 521
Kipps, M. S., 426, 497, 583
Kirsche, P., 360
Kish,J. F., 40
Klages, K. H. W., 4, 63, 64, 78, 79, 91, 95,
103, 111, 119, 129, 154, 198, 207, 225,
226, 227, 228, 231, 511, 527, 529, 562,
570
Klebs, G., 96
Koeppe, C. E., 195
Kokkonen, P., 230
Koikunov, V. R., 199, 200, 204
Koonce, D., 364
Koppen, W., 169, 289, 295, 307
Kornicke, F., 95, 363
Kraus, E. J., 97
Kraybill, H. R., 97
Krzymowski, R., 69, 203
Kuster, E., 96
Kutscher, H., 551
Kunz,J.,275
Lamarck, J. B. P. de, 124
Lamb, C. A., 229, 230
Lang, R., 140, 165
Langworthy, C. F., 451, 456
Lawes,J. B., 23, 179
Leather, J. W., 182
Lefevre, G., 87
Lehenbauer, P. A., 246, 249
Leidigh, A. H., 529 '
Leighty, C. E., 390
Lepkovsky, S., 465
Leukel, W. A., 227
Lidfors, B., 227
598
AUTHOR INDEX
Licbig,J., 23
Link, K. P., 465
Linton, R., 572
Lippincott, I., 583
Livingston, B. E., 8, 73, 75, 76, 82, 142,
160, 200, 243, 245, 246, 248, 250, 252,
255, 256
Livingston, Grace J., 243, 246
Loeb,J., 97
Loew, O., 96
Lundegardh, H., 103, 125, 126, 144, 148,
184, 221, 269
Luther, M., 32
Macfarlane, J. M., 227
Mackie, W. W., 374, 529
MacDougal, D. T., 269
Madson, B. A., 548
Malthus, T. R., 24, 34
Mangelsdorf, P. C., 391
Marbury,J. R., 501
Marbut, C. F., 79, 138, 324, 352
Margraff, 463
Maria-Theresa, 19
Marquart, B., 512
Marschner, F. J., 40
Martin, J. H., 128, 142, 205, 224, 228,
407,410,411
Martin, L., 80
Martin, M. L., 122
Marvin, C. F., 276
Mathews, O. R., 190, 192
Matthaei, G. L. C., 239, 271
Mattice, W. A., 63
Maximov, N. A., 137, 140, 146, 175, 185,
199, 227
Maze, W. H., 167
McClure, M. T., 21
McCormick, C., 25
McDougal, E., 136
McGee, W. J., 87
McKee, R., 95, 524, 525, 526, 527, 529,
530
McLane,J. W., 143
Mead, D. W., 160
Meloy, G. S., 494, 500
Merkenschlager, F., 542
Merriam, C. H., 263
Meyen, F. J. F., 7
Meyer, A., 164
Michael, L. G., 402
Middendorff, A. T., 290
Middlendorff, 17
Miller, E. C., 113, 206, 232
Miller, F. E., 446
Miller, M. F., 78, 202
Mitcherlich, E. A., 199, 200
Morgan, M. F., 357, 395, 397, 437, 456,
481, 502, 543, 579
Morgan, T. H., 84
Mobius, M., 96
Molisch, H., 219, 222, 226
Montgomery, E. G., 180
Moreillon, M., 275
Morrow, J. V., 585
Morrow, W. H., 470
Morse, W. J., 486, 487, 488, 518, 529
Muenscher, W. C., 94
Muller-Thurgau, H., 222, 226, 227,
228
Mun, Thomas, 33
Munichdorfer, F., 230
Munro, R., 15
Munns, E. N., 156, 259, 267, 301
Murphy, H. F., 334
Napoleon I, 20, 463
Neger, F., 124
Nelson, M., 381
Nelson, N. T., 227
Nelson, R., 220
Nevens, W. B., 90
Newton, H. P., 391
Newton, R., 142, 227
Nichols, G. E., 57, 76, 80
Nicot, J., 573
Nightingale, G. T., 278
Nilson-Ehle, H., 225
Norris, P. K., 506
Norton, L. J., 487
Nourse, E. G., 67
Ohlweiler, W. W., 227, 228
Olbricht, K., 46, 49, 51
Overpeck, J. C., 470
Palmer, T. G., 452
Passarge, S., 13, 314
Pavlov, K., 204
Pearl, R., 28, 39, 40
Pearsall, W. H., 89
Pearson, G. A., 249
Peltier, G. L., 224, 228
Penk, A., 164
Percival,J., 341,343
Perrin, H., 167
Peter the Great, 573
Pfeffer, W., 101, 141, 229
Pfeiffer, T., 180
Photenhauer, C., 180
Piemeisel, L. N., 175
Pieters, A. J., 520, 521, 550, 551
AUTHOR INDEX
599
Piper, C. V., 486, 517, 529, 542, 547, 549,
558, 560, 563, 565, 569
Piston, D. S., 287
Plato, 31
Pond, R. K., 422
Pope, M. N., 122
Prescott, J. A., 164
Priestley, J. H., 89
Pickett, V. G., 61
Pulling, H. E., 270
Quantz, K. E., 117
Quesnay, F., 22
Quiscnbcrry, K. S., 224, 591
Rabak, F., 489, 590
Raleigh, Sir W., 434, 573
Ratzel, F., 44
Raunkiacr, C., 266
Redway,J. W., 214
Reed, C. D., 63
Reed, G. M., 405, 409
Reed, L.J., 40
Reed, W. G., 214
Reeves, R. G., 391
Renne, R. R., 482
Renner, G. T., 304
Reuter, E. B., 29, 41
Rippel, A., 91, 180
Robbins, W. W., 135
Robertson, B. R., 90
Robertson, D. W., 202, 364
Robertson, C. J., 452, 457, 460, 461
Robinson, B. B., 511
Rosa, T. J., 226
Rose,J. K., 188
Ross, E. A., 37
Rotmistroff, W. G., 122, 146
Rufener, W. W., 425
Russell, E. J., 23, 200
Russell, J. C., 78
Sachs, J., 219, 222
Salmon, S. C., 216, 219, 224, 225, 226,
228,230,381,533
Sande-Bakhuyzen, H. L. van de, 128
Saunders, A. R., 232
Schander, R., 154, 223
Schaffnit, E., 223, 225, 228
Scharfetter, R., 92, 94
Schimper, A. F. W., 7, 8, 76, 96, 102, 124,
135, 143, 225, 266, 290, 303
Schindler, F., 345, 357, 413
Schliephacke, K., 225
Schmidt, O., 93, 226
Schoth, H. A., 526, 527, 562, 563
Schouw,J. F., 7, 8
Schroter, C., 144
Schubler, G., 23
Schulz, E. R., 465
Scofield, C. S., 332
Seelhorst, C. von, 183, 201
Seeley, D. A., 240
Seely, C. I., 197, 198
Segelken,J. G., 275
Selschop J. P. F., 219
Shantz, A. L., 79, 119, 140, 174, 175, 184,
191, 206, 300, 334
Sharp, L. W., 87
Shelford, V. E., 275
Shepard, W., 40
Shepherd, G., 397
Sherwood, S. F., 451, 456
Shirley, H. L., 269, 271
Shollenbcrger.J. H., 355
Shreve, E., 142
Shreve, F., 8, 73, 76, 82
Sieglinger,J. B., 128
Sievers, A. F., 473
Sievers, F. J., 197
Simons, E. C., 454
Sinz, E., 225
Smith, A., 80
Smith, Adam, 33
Smith, A. M., 232
Smith, B. B., 156, 259, 267, 301
Smith, D., 584
Smith, D. C., 588
Smith, G. R., 500
Smith, J. R., 432
Smith, J. W., 146, 156, 193, 434
Smith, O. F., 546
Sorouer, D., 183
Sorouer, P., 231
Spafford, R. R., 69, 80, 106, 129
Spafibrd, W.J., 401, 537
Spann, O., 21
Spencer, H., 87, 124
Sprengel, K., 23
Stahl, E., 126
Stanton, T. R., 380
Steinmetz, F. H., 228
Stephens, J. C., 407, 410
Stevens, F. C., 451
Stevenson, E. J., 433
Steward, C. L., 487
Stewart, G., 538
Stewart, Geo. R., 9
Stine, O. C., 390, 494, 500, 502, 505
Strecker, W., 551, 563
Strong, A. L., 351
Strowbridge, J. W., 441, 443
600
AUTHOR INDEX
Stroud, R., 470
Stuart, W., 430, 432, 442
Summerby, R., 226
Sumner, W. G., 30, 31
Suncson, C. A., 224, 228
Supan, A., 259
Sweeney,}. S., 38
Szymkiewicz, D., 164
Taggart, W. G., 453
Talma, 101
Tammes, T., 479
Tansley, A. G., 4, 57, 76, 80
Tarr, R. S., 80
Taylor, A. E., 389, 390
Taylor, C. C., 107, 403
Taylor, G., 46, 52, 53, 54, 108
Taylor, J. W., 203, 591
Thaer, A. D., 357
Thorn, C. C., 182
Thompson, H. C., 416, 438
Thompson, W. R., 136, 160
Thompson, W. S., 29
Thornthwaite, C. W., 140, 167, 168, 240,
295, 314, 321
Thorp, J., 326
Throckmorton, R. K., 533
Thuenen, J. H. von., 60
Timoshenko, V. P., 351, 352
Tincker, M. A. H., 279
Tingey, D. C., 364
Tippett, L. H. C., 272
Tornabuoni, N., 573
Torrie,J. H., 546
Tottingham, W. E., 465
Townsend, C. O., 451, 456
Tozzer, A. M., 13
Transeau, E. N., 163
Trumble, H. C., 165, 279
Truog, E., 330
Tucker, M., 183, 202
Turner, F. J., 497
Tysdal, H. M., 224
Ursprung, A., 232
Vaile, R. S., 61
Valkenburg, R. B., 104, 493
Vance, R. B., 494, 497
Van Royen, W., 308, 314
Vasey,A.J.,279
Vauban, S. L. P. de, 33
Vavilov, N. I., 479
Velosa, G. de, 454
Venn, J. A., 18
Vilmorin, P. L. L. de, 463
Vinall, H. M., 406, 407, 413
Visher, S. S., 49, 298
Wade, B. L., 424
Wadham, S. M., 279
Walker, H. B., 25
Wallace, H. A., 63, 329, 394, 477
Wall6n, A., 226
Waller, A. E., 112
Walster, H. L., 117
Warburton, C. W., 390
Ward, R. D., 154, 287, 296, 297, 307
Ware, J. O., 495
Warming, E., 4, 7, 8, 9, 125, 135, 140,
268, 290
Washburn, G. B., 451, 456
Washburn, R. S., 411
Waterman, W. G., 80
Wattal, P. K., 37
Weaver, J. E., 7, 113, 119, 183, 275, 305,
306
Webster, H. K., 494
Weibel, R. O., 224
Weismann, A., 87
Weitz, B. O., 40
Werneck, H. L., 85, 104
Werner, H. O., 435
Westerbrook, E. C., 478
Westover, H. L., 532
Widtsoe,J. A., 179, 182
Wiessmann, H., 272
Wilcox, E. V., 494
Wilfarth, H., 23
Willcox, W. F., 33
Willcox, O. W., 108, 208
Williams, F. E., 104, 493
Wissler, C., 30
Whalin, O. L., 487
Whitbeck, R. H., 350
Whitney, E., 496
Wolfe, T. K., 426, 497, 583
Woodward, R. W., 364
Wright, H., 24, 29, 37
Wyche, R. H., 381
Yarnell, D. L., 159
Yoder, P. A., 451, 456
Young, H. N., 420
Young, R. A., 447
Zade, A., 372, 373
Zavitz, C. A., 591
Zimmermann, E. W., 7, 24, 36, 44, 341,
352, 382, 383, 452, 477
Zon, R., 119, 300
SUBJECT INDEX
Abac*, 514
Absolute humidity, 152
Acid soils,
formation of, 330
plant tolerance to, 331
Adaptation,
adverse, 126
biversale, 126
characteristics, 124
classification of, 126
converse, 126
defined, 124
direct or indirect, 124
economy of energy in, 126
evolution and, 84
external factors in, 84
internal factors in, 84
range of, 74, 1 30
varieties of crops in, 85
vegetation and climatic rhythm in, 127
Agave fibers, 514
Agave Jour croydes^ 514
sisalana, 514
Age of plants and cold resistance, 228
Agriculture,
commercial, 24
scientific, 23
self-sufficient, 18, 26
transition from local to world industry,
35
westward movement in United States, 6
world concept of, 4
Agricultural Adjustment Administration,
10
Agricultural and industrial regions, 53
Agricultural areas,
transportation relation to, 55
United States, of, 217
world, of, 55
Agricultural boundaries of continents, 107
Agricultural competition, 6
Agricultural development,
early stages in, 1 3
modern philosophy effects of, 20
population pressure effect of, 28
recent stages in, 23
sciences and research effects of, 21
Agricultural economics, 58
Agricultural policies, ecological basis tor,
9
Agricultural practices, origin of, 12
Agricultural problem, urgency of, 10
Agricultural production,
curtailment of, 9
labor costs in, 60
specialization in, 24
stages in, 13, 23
world outlook of, 4
Agricultural progress, motivating forces
in, 12
Agricultural regions of the United States,
217
Agrobiology, 200
Agrochoras, 7
Agroecology, 7
Agronomic curriculum, 4
Agronomic investigations, 4
Agronomy defined, 3
Agropyron cristatum, 564
inerme, 566
pauciflorum, 565
smithii, 565
spicatum, 566
Unerum, 279
Agrostis alba* 558
alba var. stolonifera, 558
cardna^ 559
palustris, 558
tenuisy 559
Air drainage, 216
Air movement,
local significance of, 286
regional significance of, 285
relation to climate, 284
Alcohol, 451
Alfalfa,
bacterial wilt of, 538
climatic relationships of, 535
distribution, forage, 536
distribution, seed, 539, 540
Great Plains, in, 78
heaving damage of, 230
historical, 533
importance of, 532
root system of, 536
seed production, 538, 540
601
602
SUBJECT INDEX
Alfalfa (Continued)
soil builder, as a, 533
soil relationships of, 536
subsoil moisture depletion by, 78
southern grown seed, 534
types of, 534
varieties of, 534
whiter-hardiness and organic reserves,
227
Alkali-clay pans, 331
Alkaline soils,
formation of, 330
plant tolerance to, 332
Alpine plants, 270
Alsike clover,
adaptation of, 547
distribution, hay, 547
distribution, seed, 545, 546
historical, 547
Alternate freezing and thawing, 329
Altitude and climate, 335
composition of light, 270
American-Egyptian cotton, 499
upland cotton, 498
Anabiosis, 205
Andropogon furcatus, 566
scoparius, 566
Anemometers, 289
Animal fats and oils, 476, 477
Animate energy, 35
Anticyclones, 287
dplanobacter insidiosum, 535
Arachis hypogaea, 426
Arctic plants, 276
Aridity index of, 167
Arrhenatherum elatius, 561
Artificial freezing of plants, 224
Artificial illumination, 279
Artificial social environment, 9, 58, 452
Arts in relation to population, 31
Asiatic cotton, 499
Atmometers, 161, 276
Atmospheric conditions and quality of
light, 269
Atmospheric drought, 144
Atmospheric humidity and development
of trees, 303
Atmospheric moisture, 151
Australia, restricted agricultural areas
of, 108
Austrian whiter peas, 528
Avena byzantina, 372
elatior, 279
grtuca, 372
saliva, 372
Axonojnis compressus, 569
Bahia grass, 570
Bagasse, 452
Bard vetch, 526
Barley,
climatic relationships of, 363
commercial importance of, 362
distribution, United States, 369
distribution, world, 366
export of, 494
feed, as, 364
historical, 363
malting, 362, 364
soil relationships of, 365
utilization of, 362, 371
winter, 365, 371
yields and variability, 116, 122
Barometric gradient, 283
Barriers, economic and political, 59
Beans,
climatic requirements of, 417
distribution, United States, 418
distribution, world, 418
historical, 417
production trends of, 422
soil relationships of, 418
types of, 416
Beardless wild-rye grass, 566
Beaufort wind scale, 289
Beet sugar, see "Sugar Beet"
Beets, 448
Beet tops and pulp, 452
Bengal gunny, 513
Bent grasses, 558
Bermuda grass, 568
Berseem, 529
Big bluegrass, 560
Big bluestem, 566
Bioclimatics, 258
Bioclimatic zones, 262
Biological health of populations, 39
Birds-foot trefoil, 551
Birth-death ratio, 38
Birth rates, downward trends of, 40
Bitter vetch, 526
Black grama grass, 566
Blackeye peas, 519
Blue grama grass, 566
Blue wild-rye grass, 566
Bothmeria nivca, 514
Bog soils, 144
Bokhara melilot, 549
Bouteloua eriopoda, 566
curtipendula, 566
gracilis, 566
hirsuta^ 566
rothrockii, 566
SUBJECT INDEX
603
Bread crops, 341
Broomcorn, 408, 411, 412
Bromus inermis, 279, 563
Buchlof dactyloides, 566
Buckwheat,
climatic relationships of, 591
distribution of, 592
importance of, 591
soil relationships of, 592
special uses of, 593
species and varieties, 591
Buffalo grass, 566
Bur clover,
geographical range of, 525
species of, 523
utilization of, 525
Cacti,
physiological peculiarities of, 142
California bur clover, 523
Canada bluegrass, 560
Canada wild-rye grass, 566
Cannabis saliva, 512
Cane sugar,
historical, 453
production of, United States, 461
production of, world, 456
See "Sugar Cane"
Cardinal points,
environmental factors, effects of, 101
for light, 269
for temperature, 100
stage of development in relation to,
102
water, for 199
Carpet grass, 569
Carrots, 448
Cassava, 448
Cereals,
northern limits of production, 48
phases of development of, 93
relative winterhardiness of, 216
Chewing tobacco, 575
Chick pea, 418
Chill bands in plants, 220
Chilling of plants, 219
Chorotypes, 7
Cicer arietum, 418
Cigarettes,
origin of, 572
increase in use, 576
quality leaf for, 583
Cigars,
origin of, 572
type of leaf for, 577
Civilization, early centers of, 31
Classification of climates,
basis for, 294
Koppen's, 307
limitations of, 295
objectives of, 294
Thornthwaite's, 314
Climate,
classification of, 294
land and water, effects on, 296
transitions of, 296
local altitude effects on, 335
variability of, 295
Climates,
continental, 298
forest-steppe, 304
grassland, 305
littoral, 298
marine, 296
mountain, 300
savanna, 304
transitional, 298
woodland, 301
See "Classification of"
Climatic energy, 46, 51
Climatic rhythm, 94, 127
Climax vegetations, 301
Climographs, 104
Clover,
anthracnose, 521
failure, 547
sick soils, 547
species, number of, 541
timothy mixed hay, 544
Cold resistance in relation to
age of plants, 228
anatomical feature, 226
bound water, 226
chemical factors, 227
habit of growth, 227
morphology of plants, 224
rate of growth, 226
parts of plants, 228
Colletrichum trifolii, 521
Colonial bent grass, 559
Commercial agriculture, 24
Commercial fertilizers, 328
Common alfalfa, 534
Common vetch, 526
Communal farming, 17
Comparative advantage, principle of, 22,
59
Cor chorus capsularis, 513
olitorius, 514
Corn,
adaptation characteristics in relation
to moisture in, 136
604
SUBJECT INDEX
Corn (Continued)
climatic relationships of, 393, 395
commercial importance of, 389
critical period at tasselling, 205
distribution, United States, 404
distribution, world, 397
drought reactions of, 204
ecological optimum for, 113, 395
exports of, 494
feed crop, as a, 389
fodder, 389, 393
food crop, as a, 390
heat units required for, 240
industrial uses of, 390
livestock industry, relation to, 389
moisture relationships of, 394
oil and fat producing crop, as an, 477
physiological growing season for, 394
pod, 391
pop, 405
production trends, 397
silage, 389, 393
soil-nitrogen-yield relationship of, 328
soil relationships, 396
spread of culture of, 392
sweet, 405
temperature relationships of, 393
variability of yields, 112
yield-climate correlations, 112
yields and summer precipitation, 194
yields, factors limiting in South, 329
Cotton,
American^ 495
Asiatic, 495
bacterial blight of, 498
boll weevil, 498, 501, 502
botanical classification of, 507
Brazil, 507
cell-drop planting of, 509
China, 506
Civil War, effects on, 497, 507
climatic relationships of, 499
commercial types of, 497
distribution, United States, 507
distribution, world, 503
economic importance of, 493
Egypt, 506
export of, 494, 509, 510
famine, Lancashire, 496
hazards in production, 500
historical, 495
India, 505
oil producing crop as an, 478
Peru, 507
plantation system in production of, 497
products of, 478
Russia, 506
shedding of, 500
soil relationships of, 502
spinning of, 496
Cotton seed oil,
production of, 478
utilization of, 478
Cowpeas,
Blackeye variety, 519
climatic relationships of, 518
distribution of, 519
historical, 517
human food, as, 417
seed production of, 520
soil relationships of, 518
utilization of, 518
white varieties of, 519
wilt resistance in, 519
Creeping bent grass, 558
Crested wheat grass, 564
Crimson clover,
distribution of, 522
historical, 522
utilization of, 523
Critical periods in crop production,
defined, 128
drought in relation to, 147
excessive moisture and, 147
minimum factors in, 129
moisture relationships and, 201
shifting of, 128
transpiration in relation to, 184
varieties, choice of, in relation to, 128
Crop distribution,
ecological optimum, in relation to, 103
favorable and adverse areas, 107
minimal, moderate, and optimal areas,
in, 104
Crop ecology, 5
Crop improvement,
environmental factors in, 9
technological advances in, 63
variability of crops and, 64
wild species, value in, 85
Crop production, hazards in, 129
Crop risks,
adjustments of enterprise in relation to,
129
diversification and, 129
Crop rotations, biotic factors in, 81
Crop season, 212
Crop statistics, 8
Crop yields,
calculated limits of, 109
ecological optimum and, 111
means of improving, 108
SUBJECT INDEX
605
medieval, 18
precipitation at stated periods and, 193
secular trends of, 63
variability of, 111
eastern Great Plains, 119
central Great Plains, 120
Crops grown by primitive people, 15
Crotalaria, 529
Crotalaria spectabilis, 529
striata, 529
Curly mcsquite grass, 566
Cyclones, 287
Cynodon dactylon^ 568
Dactylis glomerata, 279, 561
Dallis grass, 570
Dasheen, 448
Desert, boundary of, 170
Determinate growth, 90
Development,
early theories of, 87
limiting factors to, 95
Mendelian inheritance in, 87
rhythm in, 92
stages of, in cereals, 93
units of heredity in, 86
Dewpoint, 151
Diminishing returns, law of, 29
Dioscorea alata, 447
Distribution of crops,
economic forces in, 3
historical influences, 7
physiological forces in, 73
political forces in, 7, 58
social forces in, 3, 57
technological influences on, 65
Diversification of cropping, 1 29
Dolichocs lablab, 417
Dormancy in plants,
drought, induced by, 205
external factors and, 96
Drought,
atmospheric and soil, 1 46
critical periods in relation to, 147
defined, 146, 147
dormancy, 205
escape, 140
minimal and optimal areas in relation
to, 146
phenological mean and, 147
physiological, 225
reactions of corn, 204
of sorghums, 205
of wheat, 203
Drought resistance,
breeding for, 186
efficiency of transpiration in relation
to, 184
physiological limits of, 186
Dry areas,
cost of production in, 67
limitations in utilization of, 67
power equipment, use in, 66
Ecads, 300
Echnichloa Jrumcntacca, 412
Ecological crop geography, 5
Ecological optimum,
broad concept of, 111
crop distribution, and the, 103
defined, 103
physiological and social environment,
and the, 118
Ecological plant geography, 7
Ecology defined, 4
Econograph, 53
Edaphic factors, 138, 323
Edible legumes in nutrition, 416
Efficiency of transpiration, 163, 174, 175,
178-184
See "Transpiration"
Egyptian clover, 529
Egyptian cotton, 499, 506
Electrical illumination, 279
Elymus canadensis, 566
glaucus, 566
triticoides, 566
English ryegrass, 562
Environment,
denned, 57
factors of the, 77-81
genetic segregation and the, 88
growth curve configurations and the,
92
human, the, 44
internal conditions, and the, 96
interrelationship of factors, of the, 267
longevity of plants, and the, 94
Epharmony, 9
Ephemerals, 141, 143
Epigenesis, theory of, 85
Epiphytes, 143
Euchlaena, 392
Eugenics, 29
Evaporation,
measurement of, 160
moisture efficiency and, 159
rates of, 160
soil, from, 159
variability of, 160
Evaporimeters, 160
Ever-blooming plants, 277
606
SUBJECT INDEX
Excessive moisture and humidity,
critical periods and, 147
curing and storage of crops and, 147
soil effects, 147
transpiration rates and, 148
Exponential temperature index, 243
Export crops of the United States,
494
Exploitation, tempo of, 24, 29
Extensive production, 68
Fagopyrum cmarginatum, 591
esculcntum, 591
tartaricum, 591
Fallows, 207
Paris band, 220
Farm Security Administration, 10
Fatty oils, 472, 474
Fertilizers, early use of, 1 7
Festuca elatior, 562
Fiber crops,
economic importance of, 492
kinds of, 493
Fiber flax,
climatic relationships of, 511
distribution, United States, 512
distribution, world, 511
historical, 479, 510
Russia, 482
seed flax, relation to, 511
Fibers,
kinds and uses of, 492
synthetic, 493
Flax,
climatic relationships of, 480
distribution, United States, 484
distribution, world, 481
heat canker, 481
historical, 479
moisture relationships of, 122
nurse crop, as a, 274
soil relationships of, 481
uses of, 480
wilt, 480
yields and variability of, 122
See "Fiber Flax"
Floristic plant geography, 8
Foot-candle, 267
Forest-steppe climates, 304
Fowl meadow grass, 560
Freezing injuries of plants,
early concepts of, 221
sequences of events in, 223
theories regarding, 219, 222
Frost injuries affected by,
alternate freezing and thawing, 229
hardening, 228
heaving, 229
protection, 231
rate of freezing, 228
rate of thawing, 229
soil moisture and type, 230
Fumitories, 575
Furrow drills, 231
Galleta grass, 566
Garbonza bean, 418
Gasolene culture, 63
Glaze, 156
Glycine max, 417
Gossypium arbor cum, 479, 499
barbadensc, 497
herbaceum, 498
hirsutum, 497
indicum, 499
nanking, 499
neglectum, 499
peruvianum, 497
sandwichense, 497
tahitcnse, 497
Gram-calorie, 267
Grasses,
American and European, 560
exploitation of, 553
growth requirements of, 555
improvement of, 554
species of, 556
uses of, 556
value of, 553
Grassland agriculture, 553
Grassland climates, 305
Grassland regions,
bunch-grass and short-grass, 305
climatically dry, 50
crops in, 306
Great Northern beans, 421
Graupel, 156
Growing season,
defined, 213
index of temperature efficiency, as an,
238, 254
length of, in United States, 215
thermal, 214
physiological, 214
Growth,
determinate and indeterminate, 90
height and weight relationships, 89
Growth curves,
mathematical formulation of, 90
phases of, 89
supplementary to yield data, 91
symmetry of, 91
SUBJECT INDEX
607
Guinea grass, 570
Gur, 452, 454
Habitat,
actual and potential, 73
factors of, 75
growth of crops beyond potential limits
of, 74
interaction of factors of, 76
physiological environment, in relation
to, 73
time factor in the, 82
Hail,
damage, 153
distribution of, 154
formation of, 1 54
Hairy grama grass, 566
Hairy vetch, 526
Harbin lespedeza, 520
Hardening of plants, 223
Hardiness of plants,
correlations with field tests, 224
evaluation of, 223
limitations of standards of, 224
Hardpans, 331
Heat damage to crops, 233
Heaving of plants, 229
Hekistotherms, 259
Hemp, 512
Henequen, 514
Hereditary units, 86, 87
Hilaria belangeri, 566
jamesii, 566
mutica, 566
Hoe-culture, 15
Homularias, 587
Hops,
climatic relationships of, 589
distribution of, 589
historical, 587
soil relationships of, 589
utilization of, 588
Hordeum distichon, 15
hexastichon, 15
ithaburcnsc, 363
sanctum, 15
spontantum, 363
Humid and dry areas, boundaries of, 170
Humidity,
absolute and relative, 152
temperature range and, 298
Humidity provinces,
annual precipitation and, 158
basis for determination of, 163
meteorological and vegetative features
in relation to limits of, 171
Humulus lupulus, 587
Hungarian vetch, 526
Hunting and fishing stage, 13
Hurricanes, 288, 456
Hybrid corn, 63
Hydrophytes, 140
Hydrothermal index,
formulation of, 250
irrigated areas, use in, 257
limitations of, 250
winter precipitation and the, 252
Hygrometers, 152
Inanimate energy, 36
Incipient drying, 144
Indeterminate growth, 90
Index value of plants, 111
Indian contributions to agriculture, 15
Industrial revolution,
exchange economy established, 35
specialization in production and the, 34
Intensive production, 68
International trade, 9
Interregional competition,
power equipment and, 66
transportation costs and, 62
trucking and, 62
Ipomoea batatas, 444
Irrigation,
advancement of civilization and, 16
India, in, 37
temperature of water, in, 220
Isobars, 283
Isohythes, 160
Isoiketes, 54
Isonotides, 166
Isophanal map, 261
Isophanes, 260
relation to life zones, 262
Isopleths, 104
Isotherms, world mean, 259
Italian ryegrass, 562
Japanese sugar cane, 463
Johnson grass, 570
Jute, 513
Kafir, 408
Kaoliang, 409
Kentucky bluegrass, 559
Kobe lespedeza, 520, 522
Koppen's classification of climates,
basis of, 307
formulation of, 31 1
maps of continents,
Africa, 312
608
SUBJECT INDEX
Kdppens classifications of climates, maps
of continents (Continued)
Asia, 311
Australia, 314
Europe, 310
North America, 308
South America, 309
zonal subdivisions, 307
Kudzu, 550
Ladino clover, 548
Land tenure, early forms of, 18
Land utilization, policies for, 9
wind erosion, and, 292
Laterites, 139
Legumes, annual, 517
perennial, 532
Length of day,
bioclimatics, in, 262
development of plants and, 277
distribution of plants, and, 278
latitude and, 276
sugar beets, effects on, 465
Lens esculenta, 425
Lentils, 425
Lepidium sativum, 102
Lespedeza,
geographical range of, 521
origin of, 520
perennial, 550
utilization of, 520
varieties of, 520
Lespedeza , sericca, 550
stipilacca, 520, 522
striata, 520, 522
Life zones, Merriam's, 263
Light,
action on plants, 268
development and structure, 272
altitude and composition, 270
atmospheric conditions and composi-
tion, 269
cardinal points for, 269
chemical and heating effects of, 267
competitive plant cover and, 273
distribution of plants, as a factor in, 266
intensity and development of cereals,
273
length of day and, 276
measurement of, 267
duration, 276
intensity, 275
quality of, 271
quantity of, 268
wave lengths, effects of, 269
Lima beans, 421
Limiting factors, axiom of, 105
relation to law of the minimum, 106
Linen, 510
Linseed cake, 480
Linum angustifolium, 15, 479
usitatissimum, 479
Little bluestem grass, 566
Littoral climates, 298
Lodging of plants, 273
Lolium multiflorum, 562
perenm, 279, 562
Long day plants, 277
Longevity of plants in relation to environ-
ment, 94
Lotus, 551
Lotus corniculatus, 551
uliginosusy 551
Low night temperatures, favorable effects
of, 221
Lupine, 530
Machine civilizations, 35
Maize, see "Corn"
Mangels, 448, 449
Manila hemp, 514
Man-land ratio, 29, 39
Manorial system, 18, 19
Marginal lands, 74
Marine climates, 296
Marl, early application of, 17
Masticatories, 575
Meadow fescue, 562
Mechanized agriculture, 25
replacement of acreage by, 26
Medicago arable a, 523
Jalcata, 534
hispida, 524
minima, 524
orbicularis, 524
rigida, 524
sativa, 532, 534
scutellata, 524
tubcrculata, 524
Medieval crop yields, 18
Medieval to modern period, transition
from, 20
Megatherms, 259
Melilotus alba, 549
indica, 530
officinalis, 549
Mentha piperascens, 473
pfperita, 473
viridis, 473
Menthol, 473
Mercantile system, 21
Mesophytes, 140
SUBJECT INDEX
609
Mesotherms, 259
Midland prairie hay, 567
Millets,
climatic relationships of, 41 3
commercial importance of, 412
distribution, United States, 414
historical, 413
types of, 412
Milling technology, 342
Milo, 408
Mint, 474
Moisture,
absorption of, factors interfering with,
143
cardinal points for, 199
classification of plants in relation to,
140
climatic and cdaphic factor, as a, 138
conservation of, 207
critical periods and, 201
crop hazards in relation to, 191
development of cereals and, 201
dominant factor, as a, 136
ecological optimum, relation to, 188
excessive effects of, 147
general aspects of, 135
losses of, 158-161
minimal areas, importance in, 189
physiological significance of, 137
provinces, Thornthwaite's," 168
social factor, as a, 189
soil, excess in, 200
temperature relationships and, 136
types of cropping, and, 207
yield correlations, 198
Moisture-temperature index, 250
Molasses, 451
Monantha vetch, 526
Mountain climates, 300
Mountain ranges, effects on climate, 297
Musa textilis, 514
Mustard, 484
Narrowleaf vetch, 526
Natal grass, 570
Nationalism, 22, 461
Native vegetations,
distribution of, 301
index value of, 7, 300
soil effects of, 301
Natural selection, 125
Needle grass, 566
Nicotiana tabacum, 575
rustica, 574
Nicotine production, 576
Nitrogen applications in dry areas, 182
Nonhardy alfalfa, 535
Northern limits, cereal production, 216
N-S ratio, 164
Nurse crops, light and moisture relation-
ships, 273, 274
Oats,
climatic relationships of, 373
commercial importance of, 372
distribution, United States, 378
distribution world, 374
ecological optimum for, 115
hay, 372
historical, 372
soil relationships of, 374
stcrilis or red type, 373, 380
winter, 373, 381
yields and variability, 114, 121
Offshore winds, 297
Oil,
cottonseed, 478
linseed, 480
producing crops, 472, 474, 477
safflower, 489
soybean, 479, 486
Oils,
competition, vegetable and animal, 477
consumption, United States, 474
essential, 472
fats, and, 472
kinds of, 472
refinement of, 477
Onobrychus viciacfolia, 551
Onshore winds, 297
Ontogeny, 85
Optima, 103, 106
Orchard grass, 561
Oregon ryegrass, 562
Ornithopus sativa, 530
Ortstein, 139
Oryza spp., 382
Panicum italicum^ 15
maximum, 570
miliaceum, 15, 412
notatum, 570
obtusum> 566
virgatum, 566
Paspalum dilatatumy 570
wrmllei, 570
Pastoral stage, 14
Pasture mixtures, biotic factors in, 81
Patriarchal family, 14
Pea beans, 420
Peanuts,
climatic relationships of, 426
610
SUBJECT INDEX
Peanuts (Continued)
distribution, United States, 427
origin of, 426
soils for, 426
utilization of, 426
world trade in, 428
Peat soils, 144
Pedalfers, 138, 324
Pedocals, 138, 324
P-E index, 167
Penntsctum glaucum, 413
Peppermint, 473
Perennial lespedeza, 550
Perfume oils, 472
Periodicity, choice of crops in relation
to, 77, 78, 94
Permanent wilting, 145
Perennial grasses, 553
Peruvian cotton, 507
Phalaris arundinacca^ 279, 563
Phaseolus acowtifolius, 417
acutifolius, 416
apgularis, 417
aureus, 417
calcaratus, 417
coccineuSy 417
limensisy 417
lunatusy 417
metcalfeiy 416
multiftoruSy 417
mungOy 417
vulgar is, 416
Phenological mean, 128, 147
Phenology, 85
Phletan pratense, 557
Photoelectric cells, 275
Photocritical periods, 277
Photoperiodism, 97
Phylogeny, 85
Physiocratic system, 22
Physiognomy of plants, 300
Physiographic factors, 334
Physiological drought, 143, 219, 225, 290
Physiological environment, 57, 73
Physiological growing season, 214
Physiological index,
application of, 248
calculation of, 246
limitations of, 249
Physiological limits, 100, 146, 246, 346
Pinto beans, 422
Pipe smoking, history of, 573
Pisum arvenscy 423
sativum, 423, 528
Plains, agricultural significance of, 334
Plastics, 487
Plant culture stage, 14
Plant distribution and photoperiodum,
278
Plant distribution and wind, 290
Plant ecology, 5
Plant geography, 8
Plant physiognomy and climate, 300
Plow-culture, 300
Plow, introduction of, 19
Poa ampla, 559
arachniferay 559
compressa, 559
palustrisy 559
pratensiSy 559
secunddy 559
trivialis, 559
Podzols, 139
Polar boundaries of agriculture, 260
Polar limits of trees, 303
Population,
biological health of, 39
centers, and food production, 54
resources of, 47, 51, 54
soil fertility and, 52
temperature in relation to, 48
checks, medieval Europe in, 33
Orient, in, 30
psychoeconomic factors and, 30, 39
^Christianity, influences on, 32
increases, availability of food, 30
culture, state of, and, 30
force for progress, as a, 28
industrialism, effects of, 34, 40
nineteenth century, during, 36
twentieth century, early part, during,
37
medieval Europe in, 32
mercantilism, effects on, 33
negro, in United States, 497
optimum density for, 41
potatoes, effects of, on, 431
potential world centers, 46
primitive societies, in, 30
problem, aspects of, 29
stationary, possibilities of, and effects
on agriculture, 40
theories, Greek and Roman, 31, 32
world, of, 44
world centers of, factors determining,
44,47
Potatoes, sweet,
climatic relationships of, 444
distribution of, 445
historical, 444
production, United States, 446
propagation of, 445
SUBJECT INDEX
611
soil relationships of, 445
storage of, 444
Potatoes, white,
climatic relationships of, 434
distribution, European, 439
United States, 439, 442
world, 438
early crop, of, 440, 442
efficiency of, as food producer, 431
food crops as, relative importance, 430
historical, 433
importance of, in Europe and America,
431, 432
industrial uses of, 432
moisture relationships of, 436
late crop of, 440, 441
photoperiodism of, 277
population, effects on, 431
production trends of, 443
seed production of, 443
soil relationships of, 437
temperature relationships of, 435
utilization of, 432
Power machinery and inter-regional
competition, 66
Prairie,
ecological aspects of, 306
mixed, 301
short grass, 306
tall grass, 306
Prairie hay,
botanical composition of, 567
characteristics of, 566
distribution of, 567
Precipitation,
annual, 156
efficiency of, 159
forms of, 153, 156
measurement of, 1 56
provinces, based on annual, 158
seasonal distribution of, 158
United States, 157
world, 155
yield correlations, 192, 196
Precipitation effectiveness index,
calculation of, 167
comparisons with other indices, 168
seasonal distribution of, 168
utilization of, 169
Precipitation-evaporation ratio, 163
Precipitation-saturation deficit quotient,
164
Precipitation-temperatures ratio, 165
Preformation, theory of, 85
Pressure belts, 284
Primitive society, 12
Production,
artificial basis for, 9
hazards in dry areas, 67
intensity of, 68
physiological limits of, 130
Production zones,
physiological limits of, 61
population in relation to, 60
transportation and refrigeration in rela-
tion to, 60
Proso millet, 412, 414
Protection and winter damage, 231
Psychrometers, 152
Public domain, 9
Pucraria thunbcrgiana, 550
Purple vetch, 526
Radiant energy, 267
Rain factor, 165
Rain gauges, 156
Rainfall intensity, 159
Rainfall ootima for human occupation, 50
Range lands, exploitation and improve-
ment of, 554, 555
Ramie, 514
Rape, 476, 484
Red clover,
climatic relationships of, 542
distribution, hay, 543
distribution, seed, 545, 546
economic importance of, 541
foreign seed, 546
historical, 541
soil relationships of, 543
Rcdtop grass, 558
Reed canary grass, 563
Relative humidity, 152
Remainder index, 239
Respiration and temperature, 221
Rhode Island bent grass, 559
Rice,
civilizations, 47, 381
climatic relationships of, 382
commercial importance of, 381
distribution, United States, 385
distribution, world, 383
exporting countries, 385, 494
food crops, as, relative importance of,
341, 430
historical, 382, 386
importance in humid areas, 147
Orient, in, 381, 383
soil relationships of, 383
subsistence economy hi production of,
383
upland, 383
612
SUBJECT INDEX
Root crops, 448
Roots, extensibility of, 230
Rothrock grama grass, 566
Rough-stalked meadow grass, 560
Rum, 451
Runoff, 158
Rutabagas, 448
Rye,
climatic relationships of, 356
commercial importance of, 355
distribution, United States, 361
distribution, world, 360
export of, 494
historical, 356
soil relationships of, 357
stabilizing effects of, 362
utilization of, 356
yields and variability, 117
Ryegrasses, 562
Saccharum officinarum, 463
sinense, 463
Safflower, 489
Sandberg bluegrass, 560
Sanfoin, 551
Saturation deficit, 153
Savanna climates, 304
Scientific agriculture, 23
Sea Island cotton, 498
Secalc anatolicum, 356
cerealC) 356
Sericea, 550
Serradella, 530
Sesame, 476, 484
Sesbarda macrocarpa, 530
Setaria italic a ^ 412
Shade plants, 272
Short-day plants, 277
Sisal, 514
Side oat grama, 566
Sirup, 453, 461, 462
Sleet, 156
Slender wheat grass, 565
Slough grass, 566
Small White beans, 421
Smooth brome grass, 563
Smooth vetch, 526
Smothering of plants, 229
Snow cover, protective effects of, 231
Snuff, 575
Social environment, 5, 57, 58
Soil,
aeration, 200
blowing, 291
carbon: nitrogen ratio of, 327
chemical aspects of, 326
Conservation Service, 9
deficiencies of elements, in, 326
drainage and heaving, 231
erosion, 207
rainfall intensity and, 159
runoff in relation to, 158
topography in relation to, 335
exploitation, 41
factors, local aspects of, 336
fertility, improvement of, 53, 328
genesis, 138, 323
improvement in humid and semiarid
regions, 65
leaching, 328
major groups of, 323
microbiological activities in, 327,
330
moisture, 138, 333
excessive amounts, effects of, 200
frost damage, relation to, 231
mulches, 207
nature of, 323
nitrogen content of, 327
nitrogen-temperature relations in, 327
nitrogen-climate relations of, 328
physical aspects of, 326
profile, 326
reaction, 329
"toxins, 144
water relations of, 333
zonal troups in relation to moisture
and temperature, 139, 324
Soja max, 417, 486
Solarium toberosum, 430
Solar energy, losses of, 270
Solonchak soils, 330
Solonetz soils, 330
Sorghum halepense, 570
Sorghums,
adaptation characteristics of, in rela-
tion to moisture, 136
classification of, 405
climatic relationships of, 406
commercial importance of, 405
distribution, United States, 410
distribution, world, 409
drought reactions of, 204
dwarf types of, 407
historical, 406
root systems of, 206
sirup from, 406
soil relationships of, 408
standard types of, 407
utilization of, 405, 409
xerophytic structures of, 205
Sorgos, 406, 408, 411
SUBJECT INDEX
613
Sour clover, 530
Soybeans,
climatic relationships of, 487
historical, 487
human consumption, for, 419
distribution, United States, 488
distribution, world, 488
oil production, from, 479, 486
production trends of, 488
soil relationships of, 487
utilization of, 486
Spartina michauxiana, 566
Spearmint, 473
Specific heat, water and soil, 230
Spotted bur clover, 523
Steppes, boundaries of, 170, 306
Stipa comatay 566
Stizolobium Deeringianum, 417, 528
Strawberry clover, 549
Subterranean clover, 529
Succulents in American and European
agriculture, 448, 449
Sudan grass, 406, 408, 413, 414
Sugar,
beet and cane, competition in, 452
by-products in production of, 451
food, as a, 451
historical, 453, 463
interzonal competition in, 452
political factors in production, 452,
460, 461, 463
sources, for the United States, 468
use of, 451
See '"Sugar Beet" and "Sugar Cane"
Sugar beet
climatic relationships of, 464, 467
curly top of, 470
feed crop as a, 448, 449
historical, 463
distribution, United States, 468
distribution, world, 466
seed production of, 469
soil relationships of, 465
Sugar cane,
climatic relationships of, 455
diseases of, 455
distribution, world, 456
historical, 453
production, United States, 461
ratoon crop, 455
soil relationships of, 456
Sun plants, 272
Sunflowers, moisture used by, 208
Sunlight, composition of,
altitude effects, 270
atmospheric conditions and, 269
seasonal variation in, 270
Sunshine duration transmitter, 276
Surplus commodities, utilization of, 433
Surpluses and carry-overs, 41
Sweet clover, 78, 549
Sweet corn, 405
Sweet potatoes, see " Potatoes, sweet "
Switch grass, 566
Tall meadow oat grass, 561
Taro, 448
Technological advances in,
crop breeding, 63
soil management, 65
power equipment, use in, 66
Teleological concept of nature, 125
Temperature,
death of plants due to high, 233
diurnal range of, 298
efficiencies of, 238
efficiency indices,
correlations of, 254
efficiency index, 240
exponential index, 243
growing season, 238
hydrothermal index, 250
interrelationships of, 252
physiological index, 246
relation to crop distribution, 252
temperature summation, 239
high, effects of, 233
humidity, effects on range, 298
inversion, 216
limits in crop production, 216
low night, and respiration, 220
maxima, 211
means, 211
means for world, 299
minima, 211
normals, 211
optima for white race, 48
plants, of, 232
provinces, based on efficiency index,
242, 258
recording of, 211
requirements for plants of southern
origins, 220
seasonal range of, 298
sensibility of, 48, 49
summations, 239
working conditions, provides, 21 1
zones, astronomical, 259
bioclimatic, 260, 263
isothermal, 260
Tennessee 76 lespcdeza, 520, 522
Tcosinte, 392
614
SUBJECT INDEX
Tcpary beans, 418
Texas bluegrass, 560
Thermal belts, 216
Thermal efficiency, provinces, 242
summer concentration, of, 242
Thermal growing season, 214
Thermographs, 211
Thornthwaite's classification of climates,
basis of, 314
formulation of, 319
maps of continents,
Africa, 319
Asia, 318
Australia, 320
Europe, 317
North America, 315
South America, 316
Tifton bur clover, 524
Timothy, 557
Tobacco,
ceremonial use of, 572
classes of, 584
climatic relationships of, 577
commercial types of, 585, 586
consumption, per capita, 576, 587
early American culture of, 575
export of, 494
exporting countries of, 583
distribution, United States, 583
distribution, world, 580
districts, United States, 585
fertilizer requirements of, 579, 580
forms of use, 572, 576
historical, 572
import demands by countries, 587
importance of, as crop, 583
nicotine production from, 576
quality of, 577, 579
quality leaf producing areas, 583
shade grown, 579
specialization in production, 578
spread of use, 573
soil relationships of, 579
utilization of, 57 £
varieties of, 586
Tobosa grass, 566
Toothed bur clover, 523
Topography, relation to land use,
erosion and drainage, 334
Tornadoes, 288
Transient wilting, 145
Trade barriers, 9
Transitional climates, 298
Transpiration,
coefficient,
crops of, various, 175
defined, 174
seasonal variations in, 179
daily march of, 184
efficiency of,
atmospheric humidity, effects on, 175
availability of moisture,
effects on, 180
climatic factors, effects on, 178
defined, 175
drought resistance, relation to, 184
185, 186
edaphic factors, effects on, 179
evaporation rates, and, 178, 179
plant characteristics, effects on, 182
soil fertility, effects on, 180, 181, 182
temperature, effect on, 175, 219
low soil temperature and rates of, 219
rates of corn and sorghums, 206
ratio,
determination of, 174
index of ecological status, as an, 185
relation to transpiration coefficient,
and efficiency of transpiration, 174,
175
seasonal march of, 184
wilted leaves, of, 232
Trees, drying winds, effects on, 303
polar limits of, 303
upper limits of, 290
Tricholaena rosea, 570
Trifolium alexandrinum, 529
fragiferum, 549
hybridum, 546
incarnatum, 522
pratense, 541
repens, 547
repens var. latum, 548
subterraneum, 529
Tripsacum, 391
Triticum durum, 15
monococcum, 15
turgidum, 15
vulgar fy 341
vulgar e antiquorum, 15
vulgare compactum, 1 5
Tropism, theory of conduct, 97
Turkestan alfalfa, 534
Turnips, 448
Types of cropping and moisture, 207
Typhoons, 288, 456
Upland prairie hay, 567
Upland-midland mixed prairie hay, 567
Vapor pressure, 151
Variability of climate and human occupa-
tion, 51
SUBJECT INDEX
615
Variegated alfalfa, 535
Varieties in adaptation, 85
Vasey grass, 570
Vegetable civilizations, 35, 47
Vegetable fats and oils, 474, 477
Vegetation as an index of moisture condi-
tions, 171
physiognomy of, 300
rhythm, 94, 127
light effects on, 275
temperature range, effects of, on, 298
Velvet bent grass, 559
Velvetbean, 528
Vernalization, 95
Vetch, 526, 527
Vicia angustifolia, 526
atropurpurca, 526
calcarata, 526
dasycarpa, 526
ervilia, 526
Jaba, 416, 526
monantha, 526
pannonica, 526
saliva, 526
villosa, 526
Vitamins, 448
Vigna scsquipcdalis, 417
sinensis, 417, 517
Vine mesquite grass, 566
Want and scarcity in human history, 41
Water, see "Moisture"
Water relations of soils, 333
Water requirement, 174
See "Transpiration"
Water-use-yield correlations, 191
Weather, variability and migratory cy-
clones and anti-cyclones, 288, 289
West, settlement of, 6
Western wheat grass, 565
Wheat
black stem rust of, 291
bread crop, as a, 341
characteristics of, determined by en-
vironment, 119
climatic relationships of, 343
commercial importance of, 341
distribution, United States, 354
distribution, world, 347
drought reactions of, 115, 203
durum, yields and variability, 121
export of, 348, 494
feed crop, as a, 342
frontier crop, as a, 342
hazards in production of, 115
historical, 342
moisture relationships of, 195, 346
physiological limits of, 346
producing potentialities of world, 346
Russian production of, 352
soil relationships of, 347
spring, yields and variability, 120
temperature relationships, of, 194, 345
water-use-yield correlations of, 191
winter, abandonment of acreage, 130
winter and spring,
genetic constitution of, 95
hazards, differences in, 115
light reactions, differences in, 95,
279
yield-moisture relationships in optimal,
moderate, and minimal areas, 194,
197
yields and variability of, 115
Wheat grasses, 564
White clover, 547, 548
White settlement, northern limits of, 48
Wild ryegrasses, 563
Wilting coefficient, 143, 334
Wilting of plants, 144, 145
Wind,
disease dispersion by, 291
distribution of plants, effects of, 290
erosion, 283, 284, 291
hot, effects of, 233
mechanical effects of, 291
offshore and onshore, 297
physiological effects of, 291
soil moisture losses and, 291
systems, 285
velocity, measurement of, 289
Winter hardiness, see, "Temperature"
Woodland climates, 301
Woodland regions, crops in, 304
World agricultural areas, 55
World outlook on agricultural pro-
duction, 3
Xerophytes, 141, 142, 143
Yams, 447
Yucatan sisal, 514
%ea mays, 391
Zero of vital temperature point, 239
Zwinga sugar cane, 463
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