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<M No. t&rflVigtl A Acmaon No.^ 


This book should be returned on or before the date last marked betow. 





Prepared under the Auspices of the 



Edited by A. G. NORMAN 

University of Michigan, Ann Arbor, Michigan 








Copyright 19.12, by 

NEW YORK 10, N. Y. 

All Einlits Reserved 

\o part of this book may 'be reproduced rn any 
form, by photostat, microfilm, or any other means, 
without written permission from the publishers. 

Library of Congress Catalog Card Number: (50-5598; 



K. C. BARRONS, Agronomist, The Dow Chemical Company, Midland, 

R. E. BLASER, Professor of Agronomy, Virginia Polytechnic Institute, 
Blacks burg, Virginia. 

T. S. COILE, Professor of Forestry, Duke University, Durham, North 

N. T. COLEMAN, Research Associate Professor, North Carolina Agricul- 
tural Experiment Station, Raleigh, North Carolina. 

F. C. GERRETSEN, Head, Microbiological Department, Agricultural Ex- 
periment Station and Institute for Soil Research, T.N.O., Growing en. 
The Netherlands. 

F. A. GILBERT, Plant Physiologist, Battelle Memorial Institute, Colum- 
bus, Ohio. 

A. MEHLICH, Research Associate Professor, North Carolina Agricultural 
Experiment Station, Raleigh, North Carolina. 

K. G. MULDER, Agronomist, Agricultural Department, Nctherland Nitro- 
gen Fertilizer Industry, stationed at the Agricultural Experiment 
Station and Institute for Soil Research, T.N.O., Groningen, The 

P. V. PEARSON, Chief, Biology Branch, Division of Biology and Medi- 
cine, Atomic Energy Commission, Washington, D. C. 

W. H. SKRDLA, Associate Agronomist, Virginia Polytechnic Institute, 
Blackburg, Virginia. 

T. II. TAYLOR, Assistant Agronomist, Virginia Polytechnic Institute, 
Blacksburg, Virginia,. 

N. E. TOLBERT, Biochemist, Division of Biology and Medicine, United 
States Atomic Energy Commission, Washington, I). C. 

PI. C. TRUMBLE, Waite Professor and TIead, Department of Agronomy, 
Waite Agricultural Research Institute, University of Adelaide, 
South Australia. 

D. J. WATSON, Head, Botany Department, Rothamsted Experimental 
Station, Harpenden, Herts, England. 


Although the duties of an editor often call for him to take decisions 
that may seem to be arbitrary, most editors are susceptible to criticism, 
and are not beyond reading the reviews of their publication that may 
appear in other journals. This editor is no exception. The reviewers 
have in general been generous ; some indeed have provided usable ideas. 
One recent review, however, included the statement that this series, "like 
most other review journals . . . tends to sit uneasily on the edge of two 
stools." The reviewer went on to explain that one type of review con- 
sists of a complete and fully documented account of a specialized topic. 
The other type, the function and appeal of which are quite different, 
"are really essays on the present state of knowledge on a particular 
subject/ 7 and "are of the greatest interest to the non-specialist." 

The only exception that might be taken to these comments is the use 
of the adverb "uneasily, ".and the limitation of the number of stools to 
two. Agronomists have diverse interests, they sit on many stools, and 
some face in different directions. It is the policy of this series to include 
various types of articles of a review or progress report nature, the test 
for inclusion being whether they are likely to be of interest and assistance 
to a substantial group of the profession. Some papers may go beyond 
what is normally considered agronomy ; indeed two such are to be found 
in this volume. Some will be more "specialized" than others, but it 
must be recognized that the definition of what constitutes a specialized 
article may well depend on the personal interests of the reader. The 
editor's position in this matter, therefore, is not uneasy but deliberate. 

In this, Volume IV, the paper by Professor Trumble is in continua- 
tion of the policy announced in Volume III, to include from time to 
time reviews of agronomic developments and trends in particular coun- 
tries or areas. Trumble 's article contrives at the same time to bring out 
the principles upon which the improvement of Australian pastures has 
been based, and is, therefore, more than a narrative essay. Similar 
papers will appear in later volumes. 

Once again the editor feels it incumbent on him to acknowledge the 
counsel and assistance received from the Advisory Board, and to point 
out that it is only through the ready support and co-operation of con- 
tributors that these volumes are possible. 

Ann Arbor, Michigan, 
September, 1952. 




Contributors to Volume 1 IV v 

Preface vii 

Grassland Agronomy in Australia 

BY H. C. TRUMBLK, Waite Agricultural Research Institute, University 
of Adelaide, South Australia 

T. Introduction 3 

II. The Approach to Modern Grassland Improvement 12 

III. Environmental Contiol 23 

IV. Specific Lines of Agronomic Investigation . .... ... 33 

V. Integration 53 

References 63 

Type of Soil Colloid and the Mineral Nutrition of Plants 

BY A. MEIILICH arid N. T. GOLEM AN, North Carolina A f/n cultural 
Experiment Station, Raleigh, North Carolina 

I. Introduction (57 

IT. Approaches to the Study of the Tonic Environment of Plant Boots in Soil 70 

III. Growth and Cation Contents of Plants Grown on Natural and Synthetic- 

Soils 77 

IV. Agronomic Applications 93 

References 96 

The Physiological Basis of Variation in Yield 

BY D. J. WATSON, Rothamsted Experimental Station, Harpenden, 
Herts, England 

I. Introduction 101 

II. Techniques of Growth Analysis 303 

III. Limitations of the Concept of Net Assimilation Bate . . . . . 109 

IV. Experimental Results 113 

V. Discussion 138 

References 144 

Copper in Nutrition 
BY FRANK A. GILBERT, Battelle Memorial Institute, Columbus, Ohio 

I. Introduction 147 

II. Historical 148 

III. Value of Copper to the Plant 151 




IV. Effects of Copper Deficiency in Plants 153 

V. Copper in the Soil 156 

VI. Copper in Animals 165 

VII. Regions of Copper Deficiency 169 

References 173 

Ecological and Physiological Factors in 
Compounding Forage Seed Mixtures 

By R. E. BLASER, W. H. SKRDLA, and T. II. TAYLOR, Virginia Polytechnic 
Institute, Blacksburg, Virginia 

I. Problems with Artificial Seed Mixtures 179 

II. Plant Adaptation as Related to Compounding of Seed Mixtures . . . 182 

III. Compounding Mixtures as Related to Use 212 

References 216 

Soil Manganese in Relation to Plant Growth 

BY E. G. MULDER and F. C. GERRETSEN, Agricultural Experiment Station and 
Institute for Soil Research, T.N.O., Groningen, The Netherlands 

I. Introduction 222 

II. Manganese Determination 224 

III. Manganese in the Soil 228 

IV. The Role of Microorganisms in Transforming Manganese Compounds . 234 
V. Symptoms of Manganese Deficiency in Plants 239 

VI. Manganese Content of Plants 242 

VII. Correcting Manganese Deficiency 244 

VIII. Manganese Nutrition and Fertilizer Interactions 245 

IX. Manganese Toxicity in Plants 249 

X. Function of Manganese in Plants 259 

References 272 

Atomic Energy and the Plant Sciences 

BY N. EDWARD TOLBERT and PAUL B. PEARSON, United States Atomic 
Energy Commission, Washington, I). C. 

I. Introduction 279 

II. Effects of Radiation on Plants 281 

III. Uses of Isotopes in Plant Sciences 293 

References 303 

Vegetation Control on Industrial Lands 
BY KEITH C. BARRONS, The Dow Chemical Company, Midland, Michigan 

I. Scope and Nature of the Problem 305 

II. Chemicals Used for Vegetation Control 306 



III. Special Problems of Various Industrial Lands 320 

References 326 

Soil and the Growth of Forests 
BY T. 8. OOILE, Dukt* University, Durham, North Carolina 

T. Introduction 330 

II. Soil as an Environment for Tree Hoots 332 

III. Northeastern Region 337 

IV. Lake States Region 342 

V. Central Hardwood Region 350 

VI. Prairie-Plains Region 357 

VII. West Coast Region 358 

VIII. Southern Appalachian Region 364 

IX. Southern Region 365 

X. Southeastern Region 368 

XI. Resume of Principal Soil Properties Related to Forest Growth . . . 394 

References 396 

Author Index 399 

Subject Index 411 

Grassland Agronomy in Australia 


Waite Agricultural Ecsearch Institute, University of Adelaide, South Australia 



I. Introduction 3 

1. The Environment 3 

a. Geographical Features . . 3 

I). Factors of Climate and Soil . . .... .... 3 

c. Native Vegetation 4 

2. Historical Aspects of Settlement . ft 

a. Coastal Pockets ... 5 

b. Use of Indigenous Pastures 6 

c. The Impact of Drought 7 

d. Factors of Transport . . 7 

3. Early Constructive Improvement 8 

a. Livestock 8 

b. Plant Introduction 8 

c. Phosphate Application . ... ... 10 

4. Technical Keconiiaissance . 11 

a. Botanical ... . 11 

b. Agricultural 11 

II. The Approach to Modern Grassland Improvement 12 

1. Environmental Analysis .... . . 12 

a. Climatic Factors 12 

b. Soil Factors .... ... 13 

c. Biotic Factors 14 

2. The Contribution of Stapledoii 15 

a. Grazing Influences 15 

b. Ecotypes 15 

c. The Philosophy of the Whole 16 

d. The Personal Equation 16 

3. The Technique of Pasture Investigation 17 

a. The Attitude of Agronomy 18 

b. Grassland Surveys 18 

c. Field Plot Trials 19 

d. Pot Culture Trials 21 

e. Herbage Strain Production . . . . . 21 

III. Environmental Control 23 

1. Climatic Attributes 23 

a. Rainfall 23 

b. Evaporation 23 

c. Drought Frequency 24 

d. Temperature 25 

e. Duration of Light 26 



2. Soils arid Their Fertility 26 

a. Relation of Soils to Climate 26 

b. pH, Nitrogen, and Organic Matter 27 

c. Soil Fertility 27 

d. Soil Building under Pastures 28 

3. Factors of Management 29 

a. Pasture Establishment 29 

b. The Use of Fertilize! 29 

c. Intensity of Grazing 30 

d. Frequency of Grazing 31 

e. The Role of Fodder Conservation 32 

f. Management of Sluub Pastures . 32 

IV. Specific Lines of Agronomic Investigation .... 33 

1. Water Requirements of Pastures 33 

a. Available Water Supply and Its Uptake 33 

b. Evaporation and Transpiration ... 34 

c. Transpiration Ratio Accoiding to Species ... ... 34 

d. The Influence of Defoliation 35 

e. Reduction of Soil Moisture Content 37 

f. Yield in Terms of Available Moisture .... ... 38 

2. Factors Affecting the Mineral Content of Pastures 38 

a. Species 38 

b. Stage of Growth, Defoliation, Management . 39 

c. Soil Factors ... 40 

d. Climatic Factors ... 41 

3. Herbage Plant Improvement ... 41 

a. Plant Introduction .... 41 

b. Use of Locally Adapted Strains .... 42 

4. Soil Deficiencies 43 

a. Phosphate 43 

b. Copper ... 45 

c. Zinc 46 

d. Molybdenum 47 

3. Potassium 48 

f. Sulfur . . . ._ 49 

g. Multiple Deficiencies 49 

5. Associated Growth 50 

a. Compatibility in Herbage Swards .... 50 

b. Competition in Herbage Swards 50 

c. Excretion of Nitrogen from Legumes 51 

d. Control of Botanical Composition by Management 51 

6. Irrigated Pastures 52 

V. Integration 53 

1. The Edaphoclimatic Environment 54 

a. Value and Limitations of the Soil Survey 54 

b. Relevant Climatic Measures .... 54 

c. The Ecological Place of the Field Experiment 55 

2. Integrated Climatic Patterns 56 

a. The Factors Involved 56 


b. Short- and Long- Term Variability 57 

c. Estimation of Possible Production 59 

3. The Eealization of Potential Production 60 

a. Fitting Herbage Plants to the Environmental Pattern ... 60 

b. Scientific Investigation and Field Practice 61 

Keferences 61 


1. The Environment 

a. Geographical Features. The continent of Australia occupies an 
area of three million square miles within the latitudes of 10 and 44S. 
It thus approximates the United States in size, but a major portion is 
located between 15 and 35 connoting an extremely high degree of 
aridity. Conditions of climate comparable to those of the central portion 
are found in northern Mexico, the North Africa Sahara, Saudi- Arabia, 
southern Persia, Pakistan, and northwestern India. Australia may be 
classed as 40 per cent arid, 32 per cent semi-arid, 15 per cent temperate, 
and 13 per cent subtropical to tropical. New Guinea, which slightly 
exceeds in area one-tenth of Australia, lies between the equator and 
11S; it is characterized by conditions that are essentially tropical. 

Hills (1949) describes the land surface as largely of low or moderate 
relief. The highest mountain is 7328 ft. ; only a few peaks exceed 5000 
ft., and most of the country is characterized by low altitude plateau or 
plain. Highlands occur along the eastern margin from Tasmania to 
northern Queensland. Erosion, associated with dissection by intermit- 
tent streams, has etched a variety of rocks from all geological ages. The 
highlands owe their form to warping and block faulting, while differ- 
ential elevation of peneplain has produced a variety of plateaux. The 
residual ridges and mountains are frequently of hard rock masses. 
Tertiary earth movements have yielded volcanic extrusions in eastern 
Australia, while soft strata, frequently of limestone, are common near 
the southern coastline. Extensive artesian basins hold underground 
water that has assured livestock industries under conditions of low and 
infrequent rainfall. Sandplains and lateritic cappings frequently occur 
in the south and west. Schists, gneisses, and granites are common in the 
ranges. Streams flow toward the center at frequent intervals, ending in 
large salt " lakes" such as Lake Eyre, which is approximately 40 ft. 
below sea level, but is almost invariably dry. 

b. Factors of Climate and Soil. Sporadic rainfall and frequency of 
drought naturally characterize a broad land mass of low topography 
located in an arid belt of high atmospheric pressures. Monsoonal rains 


occur in northern Australia during the summer months, and Antarctic 
low pressure systems produce rain over much of the south in the winter 
season. The elevated eastern portion tends to receive all the year-round 
rainfall, because overlapping of the summer and winter low pressure 
systems is augmented by moisture-laden air from the Pacific, which 
brings some rain at all seasons. Precipitation is thus of four major 
types: (a) summer rainfall of the coastal north, (b) winter rainfall of 
the coastal south, (c) all the year rainfall with some snow of the coastal 
east, including most of Tasmania, (d) occasional sporadic rainfall of 
the inland. Leeper (1949) emphasizes (a) the arid center, (b) extensive 
areas with moisture available for one to five successive months, (c) a 
restricted neocoastal region with moisture available for five to nine 
months, and (d) elevated land that is moist for more than nine months 
of an average year. As the rainfall increases above 20 in., on a third 
of the continent, both dependability and the length of the wet period 

Maximum temperatures frequently exceed 100F. in the summer 
months, especially toward the center. Apart from northern and eastern 
Australia, hot conditions are usually accompanied by low relative humid- 
ity. Snow is rare except in the southeastern highlands. Minimum tem- 
peratures of 32F. or slightly less occur in the winter months of June 
to August, but autumn and spring frosts are generally confined to land 
above 1000-ft. elevation, which is also liable to occasional summer frosts. 
Growth is entirely inhibited by low temperatures over the three winter 
months on only a restricted area. 

The soils are mostly associated with aridity, or leaching where sea- 
sonal rainfall is heavy. Low geochemical content of the original rocks 
is reflected in a limited nutrient status; shallow profiles follow incom- 
plete weathering where rainfall is infrequent. Organic matter and 
available nitrogen content "are only rarely high. 

c. Native Vegetation. The vegetation is dominated by arid influ- 
ences, but soil deficiencies also govern the types of flora that have evolved. 
Rainfall increases from the arid center toward the east, north, and north- 
west, southeast, and southwest. Most of the western coast, like the 
center, is arid; practically the entire east coast on the other hand is 
humid. As the rainfall improves, desert gives away to scrub in the 
south and grassland in the north, with woodland and forest occupying 
the wettest regions. The formations are classified by Wood (1949) into 
sclerophyllous grassland and desert steppe, sclerophyllous grass steppe, 
shrub steppe, and various types of scrub ; savannah, mallee scrub, savan- 
nah woodland, and mallee heath; monsoon forest and dry sclerophyll 


forest; rain forest, wet sclerophyll forest, alpine woodland, and high 

The indigenous pastures have been described by Christian and 
Donald (1949) and their location at the same time mapped. Most native 
perennial grasses form small tussocks, characteristically separated by 
bare soil; rhizomatous species are rare. The most common families in 
the south are Aveneae (Danthonia), Agrostideae (Stipa, Sporobolus, 
Agrostis), Festuceae (Eragrostis) . Native pastures of the north are, 
on the other hand, characterized by Andropogoneae (Bothriochloa, Di- 
canthium, Heteropogon, Chrysopoyon, Iseilcma, Themeda), Paniccae 
(Panicum, Brachiaria), Chlorideae (Chloris), Ilordeae (Astrebla) . 
Chenopodiaceae (Atriplcx, Kochia, Bassia) are dominant in shrub 
steppe. Legumes, apart from Acacia species which occur as trees, are 
rare to absent in Australian native pastures. There are no native clovers 
or clover-like plants apart from Trigonella suavissima, which may occur 
on flooded country. 

Some early comments of famous botanists and explorers are of in- 
terest. On the light coastal soils Sir Joseph Banks found the grass "tall 
enough but thin set," with trees far apart. Captain Cook described the 
woods as interspersed "with some of the finest meadows in the world." 
Darwin noted a thin brown pasture "which appears wretched but excel- 
lent for sheep grazing." Early settlers were often misled by transient 
"bright green grass" which on much country soon changed to a thin 
dry stubble. In northern Australia the grass was "tall and rank." 

2. Historical Aspects of Settlement 

a. Coastal Pockets. Settlement proceeded largely from pockets of 
natural fertility located at intervals along the eastern and southern 
coast. Here rivers with their adjoining flats of alluvium ensured the 
successful early settlement of an otherwise inhospitable country. Crops 
and herbage plants from western Europe, together with sheep, cattle, 
and horses, were able to multiply within such favored areas, but the 
coastal soils were of low productivity on the whole; the extension of 
settlement farther inland emphasized problems of decreased moisture 
as regions of moderate to good fertility were discovered. At first a 
major problem was to gain self-sufficiency in food; but the entry of 
Australia into the world wool market about 1820 focused attention on 
the improvement of merino sheep. Vast areas of native pasture invited 
wool production for which the climate was also suitable ; and the capacity 
of wool to be transported and stored over long periods without deteriora- 
tion in the absence of refrigeration enabled a rising world demand for 
wool to be met. Attractive returns from wool between 1820 and 1850 


resulted in a flow of capital for development; the discovery of gold in 
1851, however, stimulated migration most. A certain mental vigor lead- 
ing to resourcefulness arose from the migration, largely but not ex- 
clusively from Britain, of fairly hardy and adventurous settlers whose 
survival depended upon a degree of inventiveness. 

I. Use of Indigenous Pastures. A wide range of grasses and edible 
shrubs provided a natural basis for a livestock industry. Ruminant 
grazing began in 1788; stock numbers expanded most rapidly between 
1850 and 1890. Totals of 106 million sheep and 12 million cattle were 
attained in 1891 and 1894 respectively. After 1940, sheep exceeded 120 
million for a time, falling to 96 million, 1946-47, and rising again to 
11 U million in 1950. Cattle have exceeded 1U million since before 1940, 
rising to above 14 million in 1949-50. In general about eight times as 
many sheep as cattle have been maintained, and the totals thus provide 
comparable grazing equivalents. For a start livestock were supported 
by native pastures in the form of the tufted perennial grasses associated 
with woodland savannah, grass plains of the "prairie" type, and low 
edible shrubs. Davidson (1938) showed that the growth of the sheep 
population in South Australia followed the Verhulst-Pearl logistic curve, 
indicating that the animal population that the native pastures could 
carry was determined by their reserves of food and the regrowth of the 
plants eaten. The livestock in Australia exceeded this value toward 
the end of the nineteenth century, and the carrying capacity of pastures 
throughout Australia subsequently declined greatly. 

Settlement by pastoralists had been opportunist and exploitative, 
frequently leading to denudation through overstocking. The first quar- 
ter of the present century brought a realization of the consequences; but 
constructive pasture improvement has only become a factor of national 
importance within the past two or three decades. Over much of north- 
ern Australia, livestock ar^s still supported by native grasslands; but the 
pastures of southern and eastern Australia are tending largely to be- 
come replaced by introduced species. The native grasses evolved under 
conditions of low or moderate soil fertility, periodic drought, and occa- 
sional light browsing by marsupials, whose numbers were restricted and 
whose migrations were favored by rarity of permanent waters. Under 
this treatment, tall, poorly branched grasses and bushes flourished. The 
introduction of ruminants and permanent fences imposed a type of close, 
persistent grazing to which native herbage plants had not previously 
been subjected. They tended to disappear as a result of close persistent 
grazing and the competition of more aggressive herbage species from 
Europe, Africa, and western Asia; their replacement by more produc- 
tive pastures has been hastened by modern trends of development. 


Marked seasonal incidence of growth is a common feature of both native 
and improved pastures, and this is especially evident in regions with a 
conspicuous winter or summer incidence of the rainfall. 

c. The Impact of Drought. Wheat growing, dairying, and meat 
production all expanded actively from 1880 to 1930. Wool production 
reached a peak about 1893, when virtual saturation of the natural 
pastoral resources with livestock occurred in southern Australia. Factors 
of drought incidence and natural soil fertility governed the distribution 
and form of production which developed; thus dairying grew in close 
proximity to the eastern and southeastern coasts where available moisture 
for most of the year coincided with limited areas of fertile soil ; wheat 
growing was practiced more and more beyond the coastal ranges on 
naturally fertile soils with a high incidence of seasonal drought. The 
use of bare fallow added to the supply of available soil moisture and 
led to specialized cropping; but livestock have become increasingly asso- 
ciated with wheat production. Wool growing has extended into regions 
receiving as little as 7 in. of mean annual rainfall in the southern portion 
of the continent, where high temperatures are only infrequently accom- 
panied by high atmospheric humidities; beef production 011 the other 
hand is a feature of the northern region, where tropical conditions of 
sporadic rainfall and the capacity of cattle to range over long distances 
have favored this form of industry. 

Frequency of drought has been one objective of recent work in agri- 
cultural climatology. A drought period is defined as one in which the 
moisture content of the surface soil (0-4 in.) does not exceed the wilting 
point. The relationship of monthly rainfall to free water surface evap- 
oration from a standard 36-in. lank with guard ring has been employed 
by Trumble (1937, 1945, 1948) to determine drought incidence and its 

d. Factors >/ Transport. The production of food and other materials 
required for the support of a relatively small local population did not 
figure so prominently as wool production in the general development of 
the Australian economy. Although climate, soils, and indigenous pas- 
tures determined this in large measure, no other commodity for which 
the environment was appropriate could have lent itself to particular 
conditions of transport and export demand as they concerned Australia 
and western Europe. The high value of wool per unit of weight, or 
compressed volume, and its durability and keeping qualities under all 
kinds of conditions rendered it appropriate for long-term storage and 
transport over considerable distances. The export of meat and dairy 
products only became a possibility with the development of refrigeration. 
Within Australia, meat is frequently transported long distances on the 


hoof and this, of course, prejudices the quality of the beasts finally 
brought to slaughter. To a lesser extent, living animals are transported 
by rail. High quality beef is produced on improved and sometimes 
irrigated pastures close to the cities. The export of beef, mutton, lamb, 
and dairy products is closely limited by availability of refrigerated 
shipping space. A growing population in Australia and an increasing 
emphasis on high quality home-grown foods is likely to stimulate the 
production of meat and dairy products in contrast to wool in the future. 

3. Early Constructive Improvement 

a. Livestock. The pattern of livestock distribution in Australia was 
described and illustrated by Kelley (1949). Although all progenitors 
of the present day animals were imported, there was little, if any, plan- 
ning. Food for the new settlements was first supplied from overseas, 
and the urgency of local food needs tended to discourage discriminate 
selection. Private agencies were largely responsible for livestock im- 
provement through local selection and cross-breeding. Merino sheep 
were brought from Spain to South Africa and then to Australia in 1797. 
A decade later, a single bale of wool was carried to London from their 
descendants. It was not until fifty years later that the strains of sheep 
which now produce the bulk of Australia's mediumfine wool clip origi- 
nated. The finest quality wool has resulted from rigorous selection of 
the early merinos as maintained in the regions of New p]ngland and 
Canberra-Yass in New South Wales, the western district of Victoria, 
and in Tasmania. Toward the center and in the drier districts of 
Australia the wool tends to be stronger or coarser in character but of 
higher production per sheep. British breeds of sheep, used for meat 
production, and cattle of both beef and dairy types have been frequently 
imported from England to augment local studs. Far more attention 
was devoted to livestock improvement than to pasture improvement in 
Australia until about twenty years ago. 

6. Plant Introduction. The introduction and naturalization of im- 
proved herbage species has been reviewed by Davies (1951). Numerous 
species that are now important were introduced intentionally or acci- 
dentally before the turn of the century, but their use was restricted by 
absence of strain selection, and lack of knowledge concerning their 
ecological requirements or the role of soil improvement through the use 
of artificial fertilizers. Among the earliest introductions were herbage 
plants commonly used in western Europe, including perennial ryegrass 
(Lolvum perenne) and Italian ryegrass (L. multiflorum), cocksfoot or 
orchard grass (Dactylis glomerata), white clover (Trifolwm repens), 
red clover (T. pratense) and lucerne or alfalfa (Medicago sativa). 


Lucerne was favorably reported upon in 1806 and had become the most 
extensively grown forage crop by the end of the nineteenth century 
(Fig. 1). 

FIG. 1. Lucerne at 1% lb- per acre established with a cover crop of wheat on 
fallow. Annual rainfall = 13 in.; South Australian Mallee. 

Paspalum or Dallas grass (Paspalum dilatatum) was introduced 
from South America by von Mueller in 1881 and became valuable as a 
constituent of pastures used for dairying, especially on the northeast 
coast of New South Wales. Prairie or rescue grass (Bromiis unioloides) 
also proved an important pioneer species in eastern Australia. Phalaris 
tuberosa, introduced into Queensland from New York where it had been 
obtained from Italy about 1884, was distributed by Harding, investigated 
in detail later by Trumble (1933), and has now become one of the im- 
portant grasses of southern and eastern Australia (Fig. 2). Rhodes 
grass (Chloris Gay ana) and Kikuyu grass (Pennisetum clandestinum) 
have also become widely used in Australia following their deliberate 
introduction, Rhodes grass by Browne, a New South Wales grazier, about 
the turn of the century from South Africa, and Kikuyu by Breakwell 
(1923) from the Belgian Congo in 1919. Perennial veldt grass (Ehr- 
harta colycina) has been investigated by Rossiter (1947a) ; it apparently 
developed in Western Australia before 1900, from incognizant introduc- 

Subterranean clover (Trifolium subterraneum) is the most important 



economic plant of Australia. It occurs in several outstanding agronomic 
forms, but there is no record of how any of these entered or developed from 
insignificant weeds in southern and western Europe to the status of first 
class herbage legumes, now actively commercialized in Australia and 
exported to several other countries. Hill (1936) has described the dis- 

F\a. ~. Phalaritt tubcrosa with subterranean clover. Annual rain fa 11 24 in., 
Wjiite Institute. 

covery and eventual advocacy of the original Mt. Barker strain by 
Howard. Various species of Medicago, including barrel medic (M. 
tribuloides), have also arisen from accidental and unintentional intro- 
duction, and this applies similarly to cluster clover (Trifolium glomer- 
atum) and woolly clover (Trifolium tomentosum). Strawberry clover 
(T. fragifemm,) is a perennial herbage legume of increasing importance; 
some strains of this species have developed naturally, but the Palestine 
variety was introduced. 

Modern pasture improvement in Australia is based upon the use of 
introduced and selected herbage plants, and the most important of these 
are legumes which have entered Australia by accident, many years before 
their discovery and subsequent economic use. 

c. Phosphate Application. The significance of herbage legumes was 


little recognized until soluble phosphate came to be employed on land 
where they had become established. The use of superphosphate in con- 
junction with wheat growing first emphasized the widespread need of 
Australian soils for available phosphate. Experiments in South Aus- 
tralia toward the end of the nineteenth century demonstrated its value 
for wheat production, and the cultivated area treated with phosphate 
expanded rapidly. The spontaneous development of naturalized legumes 
in the stubbles of the wheat crops increased livestock maintenance and 
soil productivity, thus emphasizing the long-term value of superphos- 
phate in the minds of Australian farmers. Tests of phosphate on grass- 
land were conducted in South Australia and Victoria from 1902 to 1907, 
but it was not until the end of World War 1 in 3918 that interest in 
pasture improvement led to an active expansion in the use of superphos- 
phate for this purpose. The combination of superphosphate and sub- 
terranean clover has rendered unproductive soil highly productive. 
Land that formerly carried a sheep to two acres can now support three 
or four sheep per acre. Commercial clover seed production has yielded 
high financial returns. The nitrogen enrichment of soils, formerly con- 
sidered worthless, by the use of clover species has led to the successful 
establishment and maintenance of associated permanent grasses. 

4. Technical Reconnaissance 

a. Botanical. The work of early botanists laid a foundation for 
the subsequent development of agrostology and grassland agronomy. 
Inquiries by E. Breakwell in New South Wales provided a landmark 
of increasing interest in pasture improvement throughout, Australia. 
Breakwell 's "Grasses and Fodder Plants of New South Wales" (1928) 
brought together information derived from the experiences and obser- 
vations of farmers and pastoral ists, augmenting that arising from offi- 
cial tests. Breakwell 's work as Agrostologist of the New South Wales 
Department of Agriculture was a first attempt to lift from botanical 
treatises and the visual observations of farming practices a popular 
classification and inventory of the forage plants with which practical 
farmers came in contact. 

b. Agricultural. Agricultural practice in many parts of Australia 
has built a fund of experience, supplemented at times by tests and 
demonstrations conducted by State Departments of Agriculture, which 
has led to a philosophy of grassland improvement based upon the ob- 
servations of progressive farmers and technical advisers. Paramount 
among these, especially in South Australia, were the undoubted value 
of superphosphate, applied (a) to sowings of subterranean clover or 
lucerne and (b) to noncultivated land, the natural pastures of which 


had become populated with volunteer clovers, including subterranean 
clover, which had been carried by livestock in wool, hides, or droppings. 
The term "topdressing" has become synonymous with improvement of 
available phosphate status through dressings of superphosphate averag- 
ing for the most part 20 Ib. J^Os per acre. This is contained in half a 
bag (93 Ib.) of Australian superphosphate. Recent investigations indi- 
cate that the three nutrients, phosphorus, calcium, and sulfur, must be 
considered independently as constituents of superphosphate. 

The seeding of subterranean clover, barrel medic, Wimmera ryegrass 
and lucerne with cover crops has become widespread, largely for eco- 
nomic reasons. The practice of sowing legumes has been favored by 
the tendency of sustained cereal cropping to reduce the nitrogen status 
of the soil. This lessens the competitive effects of the crop, and the 
available nitrogen supply has frequently become so low that only legumes 
can actively produce. The ultimate result is nitrogen enrichment, in- 
crease of grazing value, and improved yields of future crops. 

The observations and interest of progressive farmers have done much 
to stimulate agronomic research in Australia, and increasing mechaniza- 
tion has widened the application of increasing scientific understanding 
as in other countries. The foundations for the researches in grassland 
agronomy of the past two decades were thus a synthesis of early botanical 
investigation, practical experience, and commercial encouragement. 
Scientific research, aided in many cases by stimulus from overseas, has 
now built substantially on this foundation. 


1. Environmental Analysis 

a. CUmatic Factors. ^ The annual precipitation has served as the 
main index of moisture available for purposes of pasture development. 
In the south 12 in. is regarded as a minimum for lucerne and Wimmera 
ryegrass, 18 in. for early strains of subterranean clover and Phalaris 
tuberosa, 20 to 24 in. for later strains of subterranean clover, strawberry 
clover, and perennial ryegrass. In the north much higher rainfall is 
associated with the seeding of improved pastures. The seasonal inci- 
dence, reliability, and effectiveness of rains as governed by the rate of 
evaporation are all decisive factors, while the amount of runoff, which 
depends on slope, cover, and general penetrability of the surface soil, 
and the capacity of the soil profile to hold reserves of moisture need 
further to be considered. 

Investigations by Prescott (1931, 1934) on soil formation, by David- 


son (1934) concerning insect ecology, and by Trumble (1937) in 
grassland ecology have led to a better understanding of agricultural 
climatology in Australia generally. Wet and dry bulb temperatures 
enable both relative humidity and temperature to be determined. With 
these values, the saturation deficiency of the air can be read directly 
from appropriate tables, and the loss of water from a standard evapori- 
meter tank estimated with accuracy. 

Studies of evaporation from soil indicated that the top 4 in. lost a 
fifth to one-half the moisture evaporated from a standardized water 
surface over the time between wetting by rain and drying to the wilting 
point. The ratio was highest at a low rate of water loss as in winter, 
and lowest when the rate of evaporation was high, as in summer. For 
the critical months at the commencement and termination of the effective 
rainfall season the evaporation from an exposed soil surface was one- 
third that from a standard evaporimeter, and this ratio has been em- 
ployed by Trumble (1948) for assessing drought frequency. Prescott 


(1949) has employed the ratio as a climatic index of the leach - 

E m 

ing factor in soils, and different values of this ratio indicate varying 
degrees of soil moisture status. 

Climatic data for a single season are appropriately treated on the 
basis of sequential calendar months to form a unit. Monthly rainfall, 
mean air temperature, relative humidity, and standard evaporation, to- 
gether with the mean length of day for each month have been employed 
by Trumble (1949b, 1950a, b) to form integrated climatic patterns which 
tfive a useful picture of the climate over a particular year. The fre- 
quency of occurrence of particular quantitative forms to which the be- 
havior of pastures, as shown by appropriate field experiments, may be 
related provides an inventory of climatic combinations which determine 
the capacity for grassland production from year to year. 

b. Soil Factors. The investigations of Prescott (1944), Taylor 
(1949), Stephens (1949), and their colleagues, embracing surveys over 
more than twenty years, have revealed that Australian soils are ex- 
tremely diverse in both genesis and morphology. Geochemieal poverty 
accounts in part for a general lack of phosphate and certain trace ele- 
ments, hence of available nitrogen; successive cycles of weathering asso- 
ciated with particular conditions of climate have, moreover, led to 
immobilization of some constituents. Much land is characterized by 
what Stephens (1949) has classed as "virtually fossil soils and their 
later derivatives." Podsolization and solonization of calcareous or 
siliceous material account for phosphate and trace element deficiency 
in some areas. 


As conditions become less arid from the center toward the eastern 
coast, brown light soils, gray and brown heavy soils successively occur 
within the semi-arid belt. Red brown earths and black earths follow 
within the subhumid belt, and finally podsolized soils become fairly gen- 
eral in the humid coastal fringe. Skeletal soils occur extensively in 
northern Australia and to a lesser extent in the south. According to 
Taylor (1949) tablelands and ranges of low productivity, desert sand- 
hills, loams, sandplains, and stony deserts account for 56.5 per cent; 
brown soils (light), gray and brown soils (heavy), solonized brown soils, 
and sandhills of the "mallee," and solonetz soils account for 21.0 per 
cent; red loams, red brown earths, terra rossas and black earths 8.3 
per cent; and podsols, residual podsols, and lateritie sandplain 12.4 per 
cent of the total land area. 

The major characteristic of Australian soils is their generally low 
order of natural fertility, to which the indigenous flora and fauna are 
well adapted. The PaOn content of the podsolized and solonized soils 
ranges from less than 0.01 per cent to 0.10 per cent, the K 2 O content 
from less than 0.01 per cent to 1.25 per cent, and the N content from 
0.01 per cent to 0.25 per cent. Corresponding values for red brown 
earths range up to 0.10 per cent, 1.60 per cent, and 0.20 per cent for red 
loams to 0.40 per cent, 0.40 per cent, and 0.70 per cent and for black 
earths to 0.55 per cent, 0.70 per cent, and 0.50 per cent, respectively. 
Soluble salts, largely sodium chloride and sulfate, may exceed 0.2 per 
cent in the south through submergence in the Tertiary and the accession 
of cyclic salt in winds from the sea in Pleistocene and recent periods. 

c. Bivtic Factors. The Australian native grasses tended to be tall, 
sparsely branched, tussock, noncreeping, and incapable of active re- 
growth after ruminant grazing. They wore, on the whole, drought ami 
fire resistant, adapted to low or moderate soil fertility, and capable of 
active regeneration from seed under restricted competition. Under per- 
sistent grazing with sheep, perennial grasses and bushes became elimi- 
nated over extensive areas. Ratcliffe (1936) estimated that at least 80 
per cent of the perennial bush in South Australia had been lost during 
pastoral occupation. Danthonia spp. have survived grazing by sheep 
better than other native grasses. With the sheep came Erodium spp., 
Mcdicago spp., Bromiis, Hordeum, Vulpia and other gramineous species, 
the seeds of which readily adhere to wool. These plants have doubtless 
evolved under the influence of the sheep and accompanied it through 
western Asia and Mediterranean countries to the Americas, South Africa, 
Australia, and New Zealand. The introduced species have steadily re- 
placed the native grasses as these have been eliminated, and there is 
now a trend toward technical synthesis of new pastures. 


2. The Contribution of Stapledon 

a. Grazing Influences. The publications of Stapledon and his col- 
leagues became available from about 1921 onwards and these emphasized 
defoliation as an essential condition of pastures. It was pointed out 
that the mower or hand shears could be employed to simulate grazing 
and provide yields of herbage from swards, and this helped to eliminate 
the mistaken view then held in Australia that grass was a crop. There 
was more to pasture, however, than mere defoliation. The condition of 
grazing included trampling, selective choice, and the return of livestock 
droppings. The need of pastures to withstand close grazing was em- 
phasized from the outset of the grassland investigations which began at 
the Waite Institute in 1925, and the pronounced changes induced in 
native pastures by ruminant grazing gave it added weight. In early 
experiments frequent mowing, cutting for hay, and grazing were em- 
ployed to compare their effects on the same pasture. These tended to 
confirm the thesis of Stapledon (1927) that the grazing animal deter- 
mined the sward. ]n practically all the Australian experiments grazing 
of an appropriate type has benefited pasture considerably, leading to 
improved composition and productivity. This has applied even to shrub 
pastures under an average annual rainfall of 7 to 8 in. Occasional mow- 
ing may also prove advantageous to pastures, in addition to increasing 
animal production. 

~b. Ecotypes. Stapledon (1928) further demonstrated that an end- 
less variety of strains or ecotypes existed within each species of herbage 
plant. The thesis and its application followed logically from Vavilov's 
"Law of Homologous Series in Variation " and Turesson's original work 
with ecotypes. Stapledon 's work on the ecotypes of cocksfoot was a 
classic investigation of strain analysis in a pasture grass according to 
ecological considerations. Frequently variants of a herbage species 
occurred as physiological products of environment. Continued growing 
for seed tended to isolate types with a high proportion of seed but of 
little value for permanent pasture. On the other hand, long-term per- 
sistent stocking tended to encourage low-growing, dense, leafy, and 
persistent forms. Thus suitable pasture types were frequently to be 
found in old grazings or where conditions made for a high degree of 
variability. Modern plant breeding has, of course, built a good deal 
further on these premises, giving particular attention to combining abil- 
ity and hybrid vigor. Stapledon, however, succeeded in establishing one 
criterion at least which is still and always will be vital, namely, physio- 
logical adaptability as the result of long-term environmental selection 
from exceedingly heterogeneous material. 


c. The Philosophy of the Whole. Again, Stapledon (1938) was an 
active proponent of integration in contradistinction to scientific speciali- 
zation. He has spoken with gratitude of one "who seemed intuitively 
to understand the ways of nature and always saw the intricate pattern 
as one majestic whole." Stapledon, himself, spoke freely of the pasture 
complex and the animal complex, which are intimately linked by com- 
mon integrating factors of causation. A knowledge of these has only 
become possible through the progress of modern ecological thought, 
which dates from about 1912. Clements, Tansley, and Cockayne were 
conspicuous among the early plant ecologists, but it was Stapledon who 
revealed in its true light the intimate and essential association of the 
pasture with the grazing animal. 

Grazing is now regarded in Australia as an essential part of the en- 
vironment of all pastures, which even in their simplest form must be 
regarded as associations. These are usually mixtures of plant forms, 
representing widely different families; and the forms may be distinct 
species or varieties of species. Competition between species and varieties 
is an essential feature, and associations become modified by changes in 
the pressure of specific environmental factors, which exercise differential 
effects on the individual plant forms and greatly influence the trend of 
competition. Finally, the evaluation of the pasture is best expressed in 
terms of its capacity for nutrition and the synthesis of animal products. 

Grassland agronomy implies a consideration of pastures in their full 
environmental setting as well as restricted studies of the separated 
parts, the interrelations of which are frequently all important, and can 
assure the completeness of synthesis that characterizes nature. It is per- 
haps a little ironical that although Stapledon tended to distrust statis- 
tics, possibly because the tool rather than the prize at first occupied 
most attention, R. A. Fisher's "Analysis of Variance " has supplied the 
very means by which the interactions common to all processes of inte- 
gration can be assessed with scientific precision. 

d. The Personal Equation. Although methods of science are the 
foundation of modern agronomy and objectivity is necessary for a proper 
scientific attitude, it is impossible to disregard the personal equation in 
work on grassland improvement. Stapledon visited Australia and New 
Zealand in 1926, and the author was fortunate to be associated with 
him and his colleagues at Aberystwyth in 1928. The Welsh Plant 
Breeding Station was already coming to be recognized as a world center 
in grassland improvement, and the atmosphere of the Station then was 
dominated by Stapledon 's personality. Visitors from overseas were 
escorted by Stapledon to trials established in different parts of the Welsh 
countryside. All who met him have received tremendous stimulus which 


prompted new activities on their return to their own countries. J. G. 
Davies, who worked with Stapledon prior to 1928 joined the staff of the 
Waite Institute in that year and later became Australian Agrostologist. 
William Davies began work with B. Bruce Levy on herbage strain im- 
provement in New Zealand the following year and subsequently visited 
Australia in 1931 to 1932. Davies (1933) reported on Australian grass- 
lands as a result of this visit. Cardon, Aamodt, H. L. Ahlgren, Chapline, 
and others of the United States gave active support to the views devel- 
oped at Aberystwyth, and a tremendous impetus was given to grassland 
investigation in America from about 1937 onward. The establishment 
of the Imperial (later Commonwealth) Bureau of Herbage Plants (later 
Pastures and Field Crops) at Aberystwyth was a factor of the greatest 
importance ; the work of R. 0. Whyte enabled grassland workers of the 
British Commonwealth and the United States to come closer together, 
and the results of their investigations to become readily accessible. The 
contacts that arose made for a camaraderie and a common language con- 
cerning grass that has characterized grassland agronomy throughout the 
world. Too much stress cannot be placed upon the personal factors in- 
volved, and Stapledon contributed toward this more than his extensive 
writings can possibly indicate. His ultimate achievements, shared in 
part by William Davies, included grassland survey, the plow-up policy, 
and the temporary ley. These, while applying primarily to the critical 
prewar and wartime condition of England, exercised an influence on 
thought and practice elsewhere. 


a. The Attitude of Agronomy. The term agronomy was not cm- 
ployed in Australia until 1925, but it has now come to be generally 
adopted. Agrostology, employed earlier, connotes a more restricted 
application to grassland problems than agronomy, which covers a wider 
field of plant-soil relationships. A review was made by Trumble (1943) 
to define scope and attitude in Australian agronomy. The term was ap- 
parently derived from the Greek agros field, nomos management, 
which implies, in addition, principle, custom, or law on which the man- 
agement of a field is based. Nom,6s indicates a pasture or district, and 
agronomos means an overseer of public lands. The term nome is an 
ancient one implying the direction, law, or management of an admini- 
strative unit. 

Agronomy in Australia covers the relationships of field crops and 
pastures to climate, soil, and management. Emphasis is toward the 
plant as an integrated expression of environmental influences, and the 


quantitative testing of ecological or physiological hypotheses by direct 
experiment gives the agronomist considerable scope. Practical problems, 
to which economic considerations are attached, are usually involved, but 
fundamental rather than ad hoc investigation is desirable. The agrono- 
mist seeks to establish new facts as well as to apply scientific knowledge 
to practical problems, and original creative thought is as important in 
agronomy as in other sciences. Agronomy is, however, broad in scope 
and may serve as a meeting place for more specialized sciences. Much of 
its ambit is coord inative. Although assisted by field observation and 
depending much upon constructive interpretation, it is required at all 
times to be accurately quantitative, and like any other branch of science 
is based on tested verifiable knowledge. 

Agronomists may need to augment field investigations by researches 
in the laboratory or glasshouse; they learn not to generalize from the 
results of tests conducted under artificial conditions of environment, but 
to rely finally on the results of their own field experience. The agrono- 
mist, invariably appeals to the method of plot testing, and a feature of 
modern agronomy is the competent planning of replicated field experi- 
ments which are accurately executed and sensibly interpreted. A sound 
working knowledge of statistics and of ecological and physiological 
principles is indispensable in the successive stages of planning, analysis 
and interpretation. The scope of agronomy in Australia has been de- 
liberately confined to the plant side, and it has not been extended to 
include work in soil science as it has in some other countries. Moreover, 
genetics and to some extent plant breeding, plant physiology, and some 
aspects of ecology and climatology have progressed in fields other than 
agronomy. Rather has the agronomist sought the cooperation of special- 
ized workers in these specific fields, his major work being based on field 
observation and experiment, together with the integration of plant be- 
havior with environmental changes. Most contributions have been in 
the field of grassland improvement, which presupposes a knowledge of 
climatic and soil factors based on survey and analysis, the building of 
suitable stocks of plant material, and the investigation of field responses 
by direct experiment, which may be supported by farm surveys. 

6. Grassland Surveys. Ecological orientation and detailed scientific 
investigation of specific factors were stimulated at the Waite Institute 
from 1930 onward, and cooperation between the Australian Council for 
Scientific and Industrial Research (C.S.I.R.) and the University of Ade- 
laide was actively fostered by Richardson (1930, 1932). Much of this 
work was directed to soil deficiencies and eventually led to active pro- 
grams concerning the relation of phosphate and trace elements to grass- 
land improvement. The research programs of C.S.I.R. (C.S.I.R.O. since 


1949) were subsequently enlarged to cover a wide range of Australian 
problems, and the federal body has made increasingly important contri- 
butions to Australian grassland improvement, e.g., Riceman, Donald, 
and Piper (1938), Riceman, Donald and Evans (1940), Riceman and 
Anderson (1943), Anderson (1942, 1946, 1948), Riceman (1945, 1948a,b, 
1949, 1950), Anderson and Spencer (1950), Anderson and Neal-Smith 
(1951), Davies (1951). 

Detailed ecological surveys were not attempted until 1945 when a 
comprehensive survey was made by Tiver and Crocker (1951) of the 
pastures of lower southeastern South Australia, covering an area of 
5800 square miles. The region has considerable potentialities for future 
grazing, and the survey, conducted over four years, resulted in the defi- 
nition of the major pasture types and their relationsips to factors of 
climate, soil, and management. The Levy point quadrant technique, 
described by Levy and Madden (1933), was used throughout the survey 
after the reliability and objectivity of the technique was established by 
Crocker and Tiver (1948). Appropriate modification of Levy's original 
methods were made. The field was taken as the unit, or if the field was 
too large, a transect several chains in width was frequently selected. 
Where definable soil and treatment differences occurred within the one 
field, separate analyses were made of each. The past histories of all 
areas examined were obtained as accurately as possible, and because of 
the short developmental period, these were usually good. The changes 
resulting from treatment, on a series of defined soil types, were accu- 
rately assessed, and the survey provided a sound basis for future pasture 
improvement in the region. 

c. Field Plot Trials. The field plot trial is the chief source of new 
information. Davies (1931) investigated the experimental error of the 
yield from small plots of natural pasture at Adelaide and found the 
optimum size of plot under the conditions examined to be 450 square 
links in area and 5 by 90 links in dimensions. The standard error of such 
a plot was 13.75 per cent of the mean yield. The unit of measurement 
in all trials by the Waite Institute has been one link = 7.92 in. ; one 
square link = 0.00001 acre. A long narrow plot was more efficient in 
reducing the standard error on natural pastures than a square or nearly 
square plot of equal area. Investigations of sown pastures, in which 
border effects become more important, have been based largely on repli- 
cated nearly square plots of approximately 0.01 to 0.005 acre. These 
have been found satisfactory for experiments involving comparisons of 
species, strains, mixtures, or fertilizer treatments. Trumble and Donald 
(19,38), in work concerning the development of seeded pasture on 
podsolized sand, employed plots 20 by 25 links (1/200 acre) with ten 



treatments replicated ten times on the basis of a Latin square in the 
original design, resulting in standard error values from 3.74 per cent to 
6.86 per cent over a period of three years of sampling. Sufficient repli- 
cations in the first year enabled differential second and third year treat- 
ments to be imposed, which proved a considerable advantage. 

JTIG. 3. View of productivity trial under grazing. 

The determination of botanical composition, yield of herbage, its 
grazing value, and chemical composition were briefly reviewed for Aus- 
tralian conditions by Davies and Trumble (1934). Methods of sampling, 
botanical analysis, estimation, and the use of the camera are included in 
a general account of the methods adopted at the Waite Institute. Figure 
3 shows a typical grazing experiment. Where major findings from small 
field plots have required substantiation under conditions of practical 
grazing, it has become necessary to employ a small number of treat- 
ments and plots varying in size from an acre to 160 acres according to 
carrying capacity. An absolute minimum of six sheep per treatment 
has characterized these trials. As a general rule a minimum of four 
replications has been employed, and the experiments have been kept as 
simple as possible; randomized blocks have become standard except in 
rare cases. Occasionally where extremely large areas or long transects 


have been used, such replication has been found to be unnecessary, or 
impossible of practical adoption. The technique of pasture experimen- 
tation, including the determination of yield under grazing, as practiced 
in Australia, has been discussed by Donald (1941). 

d. Pot Culture TriaJ,s. Investigations in pot cultures have been nec- 
essary to elucidate with precision factors which cannot be controlled 
under field conditions. Some critics pay little regard to results from 
pot cultures because of an artificial environment, but if conditions are 
standardized and related to parallel field experiments, such criticism is 
redundant. The advantages of pot culture methods include comparisons 
of different soils under standard conditions, the control of soil moisture, 
plant nutrient supply, and other soil factors. Examples of investiga- 
tions regarding chemical composition are available in the work of Kioh- 
ardson, Trumble, and Shapter (1931, 1932), Trumble, Strong, and 
Shapter (1937), and Shapter (1935). 

The need to explore soil fertility problems in a broad regional sense 
led to tests with extremely small pot cultures from 1942 onward. A 
high degree of freedom from contamination, together with the degree of 
control and applicability attained, enabled a useful picture of the prob- 
able widespread incidence of complex deficiencies to be secured fairly 
rapidly (Ferres and Trumble, 1943). 

Pot cultures have proved especially useful in work with molybdenum 
(Anderson and Thomas, 1946; Anderson and Oertel, 1946; Trumble and 
Ferres, 1946). This element is difficult to investigate in field experi- 
ments owing to the readiness with which molybdates wash down a slope, 
or with which molybdenum trioxide is carried by moving air. Extremely 
small quantities of the order of 1/16 oz. to 1 oz, per acre are effective, 
and contamination of untreated plots readily occurs unless exceptional 
precautions are taken. The use of pot cultures eliminates this difficulty 
and has frequently provided precise evidence of deficiency in the field. 
The pot culture technique was used extensively by Richardson and 
Trumble (1928, 1937) to investigate the water requirements of herbage 

e. Herbage Strain Production. Until 1929, little attention was paid 
to the question of strain in herbage plants; the search for new species 
dominated enquiry. Variation in subterranean clover was first recorded 
by Adams, Carne, and Gardner (1927) in Western Australia. Following 
Stapledon's visit to Australia, the Dwalganup, Muresk, Mt. Barker, and 
Wenigup strains were grown at Aberystwyth in 1928. Tests of single 
plants begun at the Waite Institute in 1929 established the capacity of 
the two early-maturing strains, Dwalganup and Muresk, to mature seed 
and regenerate annually where the rainfall season was too short for the 

22 H. 0. TRUMBLB 

later standard Mt. Barker commercial type to succeed. The Wenigup 
variety was later than Mt. Barker. Investigations by Harrison (1932) 
resulted in the discovery of many new varieties of subterranean clover 
in Victoria. All variants of this clover have occurred spontaneously and 
have proved to be fully homozygous; the flowers are cleistogamous and 
hence automatically self-fertilized. It is not known whether these strains 
have entered as separate introductions or have arisen as mutations in 
Australia, but the former hypothesis is more likely. Donald and Smith 
(1937) investigated their behavior under South Australian conditions. 
Bacchus Marsh subterranean clover from Victoria was shown by Smith 
(1942) to be well adapted to extensive areas of South Australia where 
the Mt. Barker strain did not succeed, and this strain has almost entirely 
replaced the earlier Dwalganup strain which was widely sown in the dec- 
ade following 1930. Two other early-flowering types, Seaton and Clare, 
have occurred spontaneously in South Australia, but neither approaches 
the Bacchus Marsh strain in productivity. Barrel medic (Medicayo 
tribuloides) was commercialized for soils above pH 7 after investigation 
by Trumble (1939b). Although much variation occurs, the Noarlunga 
type selected originally for commercialization, has remained superior to 
others. Palestine strawberry clover (Trifalium fragiferum], described 
by Donald and Trumble (1941) was introduced via southern Rhodesia 
by Trumble in 1929; it has proved superior to other strains in South 
Australia, especially for winter production (Fig. 4). Selection of the 

FIG. 4. Variation in strawberry clover. From left, original commercial, Pales- 
tine, and two naturally occurring strains. 

above strains for practical use has followed extensive field testing at a 
variety of centers, first as single plants, then in pure swards, and finally 
in mixtures. Among grasses, Phalaris tuberosa has been extensively 
investigated by Trumble (1933), Trumble and Cashmore (1934), Trum- 
ble (1935), and the Gb81 strain was produced at the Waite Institute by 
hybridization following progeny testing. This proved superior to other 


types in density of sward formation, drought resistance, seed production, 
and recovery after close grazing. Most new seedings in South Australia 
have been made with this strain. Seed certification of important strains 
has come to be adopted by the State Departments of Agriculture, but 
there is still scope for improvement in the services made available. 


1. Climatic Attributes 

a. Rainfall. The rainfall pattern of a particular region is readily 
gained from a study of monthly precipitation over periods approxi- 
mating to fifty years, as recorded at a sufficient number of representative 
centers. The total amount for the year can be regarded as merely a 
provisional index. Herbage plants in most environments can maintain 
growth for a month or more on moisture available in the soil from previ- 
ous rains, and the calendar month is an appropriate unit of time by 
which provisionally to assess the seasonal distribution of rainfall 
throughout a single year. Two-way tables based upon monthly values for 
long enough periods of years reveal after statistical examination the fre- 
quency with which rainfall in selected amounts for any month is likely 
to occur. Examination of the tables indicates the degree of frequency 
with which each month tends to be wet or dry; and treatment can be 
employed in a variety of ways to assess the seasonal incidence of the 
rainfall over the years. It is essential to consider the rainfall pattern 
in conjunction with the capacity for plant growth as controlled by tem- 
perature and light, and this leads to a consideration of integrated cli- 
matic patterns, as described in Sec. V,2a. An example of treatment, in 
terms of monthly rainfall, to provide a picture of the rainfall pattern of 
a country not previously investigated, is given by Trumble (1950b) in 
the Report of the FAO Mission for Nicaragua. 

6. Evaporation. Monthly evaporation was employed in conjunction 
with monthly rainfall by Trumble (1937) to determine the effectiveness 
of rains falling at different times of the year, and the length of the 
effective rainfall season. It was found that provided a suitably stand- 
ardized evaporimeter was utilized and maintained as a scientific instru- 
ment, evaporation from a free water surface was closely related to 
saturation deficiency, as derived from temperature and relative humidity, 
for any given month ; moreover, the evaporation for each month varied 
little from year to year in comparison with rainfall which at Adelaide 
varied widely. Over an initial period of eleven years, 1925-1935, the 
percentage variability as indicated by the standard error was as follows : 


Annual Monthly 

KainfalJ 2.8% 9.8-33.2% 

Evaporation 1.9% 1.8- r>.f)% 

Days taken for an inch of water to be evaporated varied from 4.2 in 
midsummer to 16.8 in midwinter. Jn general, the time taken for this 
quantity of water to be lost by evaporation from bare soil was three to 
four times the above intervals. 

Water is lost from a pasture mainly by transpiration, and so long as 
a cover of pasture is maintained, evaporation from the soil is reduced to 
a minimum. Values for standard free water surface evaporation have 
been used in Australia rather than potential evapo-transpiration because 
the latter combines two quite separate processes which are characterized 
by few compensatory effects. Soil evaporation and transpiration are 
both closely related to free water evaporation as a common controlling 
factor, but the first decreases with the cover, whereas the second in- 
creases with the amount of transpiring leaf surface. Both are affected, 
but in different ways, by management. 

c. Drought Frequency. A drought year in Australia is one char- 
acterized by sufficient persistence of soil desiccation at critical periods 
of the year to preclude any possibility of normal or near normal produc- 
tion. In southern Australia, under conditions of winter rainfall, a 
drought year has been defined by T nimble (1948) as one in which the 
season of continuously effective rainfall is less than five calendar months. 

The three winter months, June, July, and August, are characterized 
in the south by relatively low mean air temperatures (48-53F.) and 
short days (9 1 X>-11 hr.), which do not inhibit growth but restrict it 
decisively. Effective rainfall in April-May, May-September, or Septem- 
ber-October, extends the period over which moisture is available to bring 
two relatively favorable months within this period, making possible suf- 
ficient growth to render supplementary feeding unnecessary. Provided 
the pastures are green for this minimum period, lambs can usually be 
raised and weaned prior to the drying of the feed. For wool or meat 
production the pasture is nutritionally effective when dry, so long as it 
is not deficient in protein and essential minerals. 

Over the agricultural and pastoral areas of South Australia, the per- 
centage drought frequency varies from nil to 95 per cent. The centers 
of highest rainfall, in which pasture development is progressing most 
actively, are associated with values of below 10 per cent. The most pro- 
ductive wheat-growing areas have values of 20 to 30 per cent, and seeded 
pastures are economically feasible to about the 30 per cent limit. Mar- 
ginal wheat-growing areas show drought frequency values of 60 to 70 


per cent. Tables have been prepared by Trumble (1948) for South 
Australia which indicate for 204 centers the mean effective rainfall sea- 
son in months, the probability of effective rainfall for each month, the 
frequency of seasons characterized by drought, and the mean air tem- 
peratures for the coldest month. The tables show the drought risks as- 
sociated with seeding in any month and the wet weather risks at times 
when harvests might be made. 

d. Temperature. The mean monthly value in shade has been taken 
as the most convenient single measure of air temperature in Australia. 
Maps prepared by Leeper (1949) show that January isotherms range 
from 90F. in the northwest, where the rainfall is lighter than elsewhere 
in the north, to 55P\ in the highlands of Tasmania; the July isotherms 
range from 75F. along the northern coast to 45F. in the Tasmanian 
and southeastern continental highlands. 

Maximum temperatures above 100F. are common in the summer 
and occur occasionally throughout the continent except in the south- 
eastern highlands. Physical discomfort is frequently minimized by 
associated low vapor pressures. The mean wet bulb temperature ex- 
ceeds 70F. for six months only within the coastal strip north of the 
Tropic of Capricorn and for ten months at the extreme northern tips of 
the continent. 

Winters are warm in the north, with mean July temperatures exceed- 
ing 60F. above the Tropic; in the south they range from 45 to 50F. 
over the elevated country and 50 to 55 F. at lower elevations, especially 
toward the southwest. Snow is recorded only above 2000 ft. and then 
for a short period of the year within limited areas. Minima of less than 
32F. occur mainly south of the 25S parallel, in the period June- 
August. Earlier or later frosts are mostly confined to land above 1000 
ft. in southeastern Australia. Frosts outside the winter months are rare 
in western Australia. The monthly temperature and moisture status at 
centers in the southern portion of the continent have been employed by 
Trumble (1939a) for agroclimatic classification. 

Changes in atmospheric temperature influence both the rate of photo- 
synthesis and the rate of respiration ; moreover changes in soil tempera- 
ture govern permeability and root respiration, both of which affect 
nutrient uptake. Prescott (1948) has shown that for pasture between 
the temperatures of 46 and 80F. the yield may be expected to increase, 
in general conformity with the Van 't Hoff law, 2.3 to 3.7 times for each 
rise of 18F. in atmospheric temperature, provided soil moisture is not 
limiting. There has been little or no investigation in Australia to 
determine the differential effects of temperature on herbage plants in the 


presence or absence of light as conducted in the United States by Went 
(1943) in studies of thermoperiodicity. 

e. Duration of Light. The length of the daily photoperiod not only 
affects vegetative and reproductive deveJopment and hence survival, but 
also exercises nutritional effects upon herbage plants. At Adelaide 
(35S), the mean daily photoperiod varies from 9.7 hours in June to 
14.3 hours in December. Varieties of herbage plants from high latitudes 
of North America or northwestern Europe frequently fail to flower and 
set seed. Examples are particular samples of Phalaris arundinacea, 
Avena elatior, Agropyron tenerum, Bromus inermis, Dactylis glomerata, 
Phleum pratense, Lolium perenne, and cereals from northern European 
sources. On the other hand, ecotypes from southern Europe or the 
southern United States tend to behave normally. Grasses such as Ki- 
kuyu (Pcnnisetum eland estinum) , from elevated equatorial habitats, 
produce flowers and form seed with readiness at Adelaide. Annuals 
which grow abundantly in southern Australia run to stem and seed 
rapidly with comparatively little vegetative growth in high latitudes of 
the Northern Hemisphere. The limits of yearly day length amplitude in 
Australia are 11.5 to 12.7 hours in the extreme north and 8.9 to 15.f) 
hours in the extreme south. Ferres (1949) has shown that the uptake 
of zinc by subterranean clover is substantially increased by lengthening 
the photoperiod from 10 to 12 hours at mean air temperatures of about 
60F. On the other hand, a similar effect is obtained with red clover 
by reducing the photoperiod from 14 to 12 hours. Owing to the simul- 
taneous operation of changes in light duration, temperature, and mois- 
ture status, it is necessary to employ integrated climatic patterns, as 
described in Sec. V,2, in order to appreciate the combined effects of the 
climatic factors concerned on herbage production. 

2. Soils and Their Fertility 

a. Relation of Soils to Climate. The soils of Australia have been 
related to vegetation and climate by Prescott (1931), and it has been 
shown that leaching, the capillary movements of soil water, seasonal 
temperature effects, and wind have characterized soil formation in Aus- 
tralia. Crocker (1946) has related the major soil types of South 
Australia to Post-Miocene climatic and geological history. Over exten- 
sive areas, solonized, podsolized, terra rossa, and rendzina types of soils 
are considered to have been formed in the Pleistocene and recent ages, 
with consequent fossil morphology. The distribution within the profile 
of water-soluble salts, calcium and magnesium carbonates, oxide of iron, 
and manganese and clay determined in part the physical characteristics 
and nutritional properties of the soils as they now occur. The accession 


of cyclic salt and the control of leaching by the intensity of the daily 
rainfall are also important factors. Mobility and availability of certain 
constituents are affected both by hydrogen-ion concentration and the 
oxidation-reduction potential. The use by Prescott (1931, 1949) of satu- 
ration deficiency and evaporation in conjunction with precipitation has 
facilitated understanding of the derivation and current properties of 
Australian soils. 

1). pH, Nitrogen, and Organic Matter. Prescott (1931) established 
a marked general correlation between the hydrogen-ion concentration of 
the soil and the rainfall. Leaching effects are most marked where high 
rainfall is associated with a low rate of evaporation for specific periods 
of the year. The nitrogen content of the soil has also been shown to 
relate closely to the intensity of rainfall. The association of deficient 
parent material with leaching, surface runoff, and in some cases lateriza- 
tion under previous conditions of climate has established a condition of 
acute and widespread nitrogen deficiency over the greater portion of 
Australia which receives sufficient rainfall to ensure modern pasture 
development. This has emphasized the use of herbage legumes in con- 
junction with fertilizer dressings of available phosphate, together with 
trace element additions according to the soil type and its past history. 
The use of these combinations makes possible fairly rapid soil enrich- 
ment in both nitrogen and organic matter. 

Some deficient soils are relatively high in organic matter derived 
from the native sclerophyll vegetation prior to development, but this 
material is high in lignin and low in nitrogen and the trace elements 
lacking in the soil to which the original vegetation was adapted. This 
organic matter has little if any nutritional value. On the other hand, 
breakdown products of lignin under conditions of deficiency may prove 
adverse to the point of toxicity so far as the rhizobia of herbage legumes 
is concerned. Leaching, or oxidation from repeated plowing, may even- 
tually eliminate this factor. The type of legume grown is closely de- 
pendent upon pH. Subterranean clover is adapted to soils that are acid 
to neutral ; annual species of Mcdicago on the other hand are adapted 
to soils that are neutral to highly alkaline. 

c. Soil Fertility. The status of phosphorus is generally low. In the 
south neither crop production nor pasture improvement is undertaken 
without the application of superphosphate. Copper is extremely low in 
calcareous and siliceous sands and laterized soils on which the most wide- 
spread cases of deficiency occur. Many of these soils are also deficient in 
zinc. Solonized sands of high silica content are particularly low in 
phosphate, copper, and zinc. Molybdenum deficiency has been associ- 


ated, for the most part, with a sloping topography and much older rocks 
or laterite high in total iron and aluminum. 

It has been shown by Piper (1942, 1947) that extremely low concen- 
trations of copper, zinc, and molybdenum will satisfy the needs of 
herbage plants provided these concentrations are maintained. Plants 
secure sufficient copper if the element remains available at 0.1 p.p.m., 
and concentrations as low as 0.001 p.p.m. are capable of increasing 
growth. Availability tends to rise with pll but this element is less 
susceptible to changes of pH than zinc and is much less susceptible than 
manganese or molybdenum. Zinc can also satisfy the needs of the plants at 
extremely low concentrations provided absorption is continuous and utili- 
zation by the plant effective. Availability decreases as the pH of the soil 
rises from 5.6 to 7.5. Molybdenum, on the other hand, becomes increasingly 
available as the pll rises. Tn the absence of applied molybdenum. Piper 
and Beck with (1949) have shown an increase in molybdenum content 
from 0.2 p.p.m. at pll 4.8 to 6.5 p.p.m. at pH 8.3 in the dry material of 
Medicago denticulata. Where molybdates were applied, the concentra- 
tion was 5 p.p.m. at pll 4.8 and 56 p.p.m. at pll 8.3. Symbiotic nitrogen 
fixation appears to be able to supply in full the nitrogen requirements 
of subterranean clover and associated grasses to the limits allowed by 
climate in South Australia provided the supply of available nutrients 
and their balance are satisfactory and restrictive influences are not 

d. Ptw'l Building under Pastures. The need to build soil fertility is 
apparent both on soils that are naturally unproductive and on cultivated 
lands that have rapidly declined in productivity and have reached a 
critically low level of nitrogen and organic matter. Cornish (1949) has 
shown by regression analysis, eliminating the effects of rainfall, that in 
spite of improved crop varieties and technical improvements in farming, 
yields of wheat over extensive areas have fallen substantially and are 
continuing downward. Fertility depletion has been inevitable under the 
methods of exploitative farming practiced in wheat-growing areas. More 
or less continuous cropping with cereals with occasional substitution by 
volunteer weeds or fallow has been characteristic. Frequent cultivation 
of the soil has broken down aggregates, destroying organic matter, ren- 
dering the soil liable to loss of structure and vulnerable to erosion. The 
investigations of recent years have shown that if appropriate legumes 
are utilized and soil deficiencies other than that of nitrogen are over- 
come, striking gains in available nitrogen can be secured under grazing, 
with economic derivation of livestock products during the soil-building 
process. The legumes of greatest value in southern Australia are subter- 
ranean clover, lucerne, annual Medicago species and field peas. As an 


example, seeded pastures for ten years following cropping at the Waite 
Institute resulted in values of 58.85 p.p.ra. of nitrate nitrogen following 
incubation compared with 5.75 p.p.m. on land that had continued under 
cropping for the same period (Woodroffe, 1949). 

3. Factors of Management 

a. Pasture Establishment. The farm machinery available in Aus- 
tralia, apart from importations, has been largely that designed for cereal 
production, and this limitation is further intensified by lack of research 
in agricultural engineering. Most inventions have been the products of 
individuals associated with farming. Active schools of agricultural en- 
gineering in conjunction with the university faculties of agricultural 
science, as fostered in the United States, are badly needed. In the mean- 
while, Australia has persisted with comparatively minor modifications of 
standard wheat-growing machinery, and this has sometimes reduced the 
success of pasture establishment. 

Subterranean clover and lucerne are usually seeded with a cereal 
cover crop which may be harvested for grain or hay or grazed in situ. 
Perennial grasses and legumes are, for the most part, sown on land 
either freshly cleared from scrub or established on fallow following a 
period of cropping. Extremely low seeds rates of the order of ^ to 3 Ib. 
of each constituent have proved successful over a wide range of condi- 
tions. The mixtures most frequently employed consist of one to two 
legumes associated with one to two grasses. The "Majestic" stump- 
jump plow with 26 to 30 in. disks, which are pushed upward out of the 
soil against the tension of extremely strong springs when the disks meet 
an obstruction, has proved a vital factor in the development of poor 
scrublands in South Australia. Two plowings to a depth of 8 to 10 ins. 
are normally employed between the phases of burning and seeding. 
Land has been effectively seeded for pasture within two months of being 
under undisturbed scrub. 

b. The Use of Fertilizers. Practically all phosphate has been added 
as superphosphate. Prom the inception of trace element application in 
South Australia, fertilizer companies have been prepared to mix manga- 
nese sulfate, which is used mainly for cereals, copper sulfate, zinc sul- 
fate, and molybdenum trioxide with superphosphate at the factory. The 
quantities used have been based on amount per bag of superphosphate 
weighing 187 Ib., ranging from 7 to 28 Ib. manganese sulfate 3% to 14 
Ib. copper sulfate, 3^ to 14 Ib. zinc sulfate and 1 to 2 oz. molybdenum 
trioxide. Common quantities per acre in recent years have been 7 Ib. 
copper sulfate, 7 Ib. zinc sulfate, and 1 oz. of molybdenum trioxide 
(Pig. 5). The amount per acre of the trace element mixture has, on 



FIG. 5. Left, pasture on molybdenum- deficient soil. 
molybdenum (Anderson, 1942). 

Eight, top-dressed with 

the whole, varied from 1 to 2 cwt. per acre, for the initial seeding, fol- 
lowed by reduced rates after two or three years. Annual topdressings 
of superphosphate appear to be necessary, but for at least several years, 
one initial application of the trace elements is sufficient. Costs of apply- 
ing the fertilizer are greatly reduced following the seeding year by the 
use of a broadcasting spinner, a South Australian invention, attached 
to and driven by a motor truck which also carries the fertilizer required. 
Some effects of superphosphate are now considered to be attributable in 
part to its content of sulfur (Anderson and Spencer 1950). 

c. Intensity of Grazing. There has been a tendency to undergraze 
rather than overgraze freshly sown pastures. Experience indicates that 
provided establishment is vigorous, some grazing in the first year is an 
advantage, largely in controlling strongly competitive elements such as 
sown or volunteer annual grasses and quick-growing weeds that are eaten 
by livestock. Moreover, once the root system has penetrated sufficiently, 
and the seedling has tillered or branched, the young plant's reserves are 
sufficient for recovery ; as defoliation reduces transpiration, loss of soil 
moisture is retarded, with subsequent advantages. If subterranean 
clover has been seeded with a cereal, stock may be withheld for some 
years, and the clover raked for seed, which at yields of 200 to 400 Ib. per 
acre, has given high financial returns. 

A livestock carrying capacity of at least 1% sheep per acre, equivalent 
to a beast per 5 acres, is regarded as the minimum capacity of the pas- 


ture to support livestock in order to render modern pasture improve- 
ment economically successful. 

d. Frequency of Grazing. Investigations of irrigated pastures at 
Wood's Point on the Murray River in South Australia by Richardson 
and Gallus (1932) and Trumble and Davies (1934) resulted in the estab- 
lishment of pastures capable of maintaining an average of fifteen sheep 
for fattening per acre per annum. This fell to six sheep for a short 
period in midwinter and rose to more than twenty sheep per acre in 
spring and early summer (Fig. 6). The carrying capacity of the best 

FIG. 6. Heavy stocking with sheep on irrigated pastures of perennial ryegrass, 
cocksfoot, and white clover. 

pasturage could be assessed at two head of cattle fattening or l 1 /^ milch 
cows per acre. The question of grazing management arose early and 
stock were rotated on a cycle of three weeks in accordance with the 
findings of Woodman (1928, 1929) in England that frequent defoliation 
resulted in extremely high concentrations of nutrients. This proved a 
disadvantage, neither the carrying capacity nor the condition of the 
stock proving as satisfactory as when the pasture was grazed at longer 
intervals of four to six weeks. Beruldsen and Morgan (1946) reached 
similar conclusions in Victoria. As the growth rate of the pasture is 
much higher in the spring and summer than in winter, it becomes neces- 
sary to develop methods whereby less drastic grazing can be applied 
during the periods of lowest production. One aim has been to graze at 
longer intervals in autumn and winter, with supplementary feeding, and 
to maintain later a higher rate of stocking 1 on a reduced area, supple- 
mented by the use of the mower; during the periods of most active 
growth. Roe and Allen (1945) found continuous grazing of a Mitchell 


grass pasture as satisfactory as winter and summer rotation. Investiga- 
tions by Davies (1946), Moore, Barrie, and Kipps (1946) at Canberra, 
and at the Waite Institute (1950), showed that rotational grazing in no 
case was advantageous, and that a commonsense system involving ma- 
nipulation of livestock numbers supplemented by the use of the mower 
is preferable to a rigid rotational pattern. Under irrigation, of course, 
conformation to a schedule is usually necessary. 

e. The Rale of Fodder Conservation. Investigations at the Waite 
Institute (1950) conducted over the period 1940-45 showed that cutting 
sown pastures for hay yielded comparable or slightly higher yields 
of forage under continuous grazing than under rotational grazing. Live 
weight per head of sheep responded only slightly to feeding back, but the 
capacity of hay, representing surplus production from the pasture, to 
maintain additional livestock was considerable in some seasons, especially 
those characterized by drought. Over a succession of favorable years, 
cutting the surplus spring growth of pastures proved uneconomic, but the 
financial gains in one very unfavorable season more than outweighed 
the cumulative losses from the practice over the four previous seasons. 
The values of cutting and feeding back was greater in the case of sheep 
employed in part for meat production than in the case of merinos used 
entirely for wool production. The results of experiments on pasture 
management involving conservation of some pasture for hay can be 
summarized to indicate that the management of livestock on pastures 
should be along commonsense lines, without the imposition of rigidly set 
schedules, because the seasons cannot be predicted. The aim should be 
to maintain a sufficiently good cover but to prevent excess growth. The 
use of the mower is essential when production greatly exceeds con- 
sumption by livestock and to provide conserved fodder as insurance 
against the inevitable years of reduced productivity. The use of labor- 
saving machinery for fodder conservation is likely to prove of tremend- 
ous value in Australia as it has in the United States. 

/. Management of Shrul) Pastures. Shrub pastures dominated by 
Atriplex, Kochia spp., although greatly depleted by former exploitation, 
are still important sources of wool production in arid southern Australia. 
Investigations were commenced in 1940 by Woodroffe (1941, 1951) on 
pastures of bluebush (Kochia sedi folia) in the northwest of South 
Australia to examine the effects of differential stocking practices on 
such pastures (Fig. 7). The seasons over this period have yielded 
rather better than the long-term average of just under 8 in., and the 
effects of the various grazing treatments may be different in a cycle of 
unfavorable years. Nevertheless, it appears that pastures of this type 
actually benefit from grazing; the pruning effects lead to economies in 



FIG. 7. Bluebush (Kochia sedifolia) with myall (Acacia Sowdenii) undamaged 
by heavy stocking. Annual rainfall 1. 8 in. 

water lost by transpiration. Particularly high rates of stocking, com- 
pared with recognized practical standards, have been imposed without 
deterioration under fairly close subdivision, and it seems evident that 
a major reason for past damage has been insufficient subdivision of the 
holdings and failure to provide sufficient watering points. 


1. Water Requirements of Pastures 

a. Available Water Supply and Its Uptake. The amounts of water 
received and lost by pastures have been considered on the basis of the 
time intervals over which moisture is available near the soil surface in 
conjunction with the capacity of the root zone to store available moisture. 
The pasture mixtures that have corne to be developed tend to be based on 
legumes and grasses which are capable of exploiting both the surface 
horizons and the deeper layers of the subsoil. Deep-rooted herbage 
species such as lucerne and phalaris are valuable where long periods of 
surface soil desiccation occur, but moisture is still held in quantity at 
lower depths. The rate of movement of soil water is controlled by the 
size and continuity of the air spaces within the soil, the suction gradient, 


and the viscosity of the water (Russell, 1950). The downward flow of 
water through sands is thus considerably more rapid than through Joams 
and clays, although it is dependent on the structure of the latter. Deep 
sands have the advantage of being usually free from excess water ; they 
are capable of storing available moisture at considerable depths and also 
retain minimal amounts at the wilting point. Moreover, there is no time 
in the rainfall season when mechanical operations of seeding are pre- 
vented by too wet a surface condition of the soil. Annual Trifolwm and 
MecKcago species exploit the soil to a relatively shallow depth and are 
thus dependent on continuity of available moisture near the surface 
while conditions of temperature and light are favorable. 

b. Evaporation and Transpiration. The evaporation of water from 
bare soil depends upon the amount of water available at the surface and 
the evaporation rate from free water. The loss from saturated level soil 
is comparable with that from water but, as the surface dries, less water 
becomes available for evaporation the surfaces of the particles hold 
less water and suction forces provide increasing resistance. Cover, 
whether it is of dead or growing material, impedes evaporation through 
shading and reduction of surface air movement. 

Most workers on transpiration, for instance Briggs and Shantz 
(1913), Richardson (1923), Maximov (1929), Richardson and Trumble 
(1937), have found a close dependence of transpiration on atmospheric 

Briggs and Shantz obtained correlation coefficients of 0.82 to 0.89 
between transpiration and solar radiation and 0.75 to 0.86 between 
transpiration, air temperature, and wet bulb depression. Richardson 
and Trumble obtained values of 0.91 to 0.95 for correlation between 
evaporation and the transpiration of saltbush, ryegrass, subterranean 
clover, and wheat. Wronger (1934) found increases of from 12 per cent 
to 150 per cent of the transpiration rate in still air due to the influence 
of wind. Plants transpiring actively prior to treatment lost more 
initially but subsequently transpired less than in still air. 

Annual determinations of the transpiration ratio * of ryegrass and 
subterranean clover at the Waite Institute have indicated wide shifts 
due to season. Values for ryegrass varied from 284 to 497 and for sub- 
terranean clover from 478 to 653. Differences in temperature and light 
during the period of active growth, combined with differences in atmos- 
pheric relative humidity, account for major seasonal fluctuations. 

c. Transpiration Ratio According to Species. Rather more than 
two hundred determinations of the transpiration ratio of eighty-five 

* Ratio of water transpired to dry weight of plant. 


species were made at the Waite Institute over the period 1925-39. A 
standard variety of barley was employed in all tests for purposes of 

The transpiration ratio of summer growing grasses, representing 
Astrebla, Cynodon, Eragrostis, Iseilema, Panicum, Paspalum, Sorghum, 
Spinifcx and Sporobolus, ranged from 201 to 508 averaging 328 or two- 
thirds that of barley grown under comparable conditions. Winter an- 
nual grasses, including Hon^denm and Lolium, together with Erodium, 
ranged from 203 to 629 with a mean of 379. Eight Atriplex species 
averaged 459. Annual species of Mcdicago, which grow actively in 
winter and mature early, pave values of 200 to 412 with an average 
of 282, but were 15 per cent higher than barley grown under comparable 
conditions. Perennial winter grasses, Danthonia, Ehrharta, Oryzopsis, 
and tftipa, ranged from 248 to 666 with an average of 480 and were 
higher than barley. The standard midseason strain of Mt. Barker sub- 
terranean clover grew with an average transpiration ratio of 493 and 
was 46 per cent to 50 per cent higher than barley under comparable 
c^iditions. Earlier-maturing strains of subterranean clover had water 
requirements comparable with those of annual Mcdicago species. Culti- 
vated biennial and winter grasses, including Dactylis, Holcus, Lolium, 
and Phalaris, varied from 437 to 619 with a mean of 531 and were 56 
per cent to 87 per cent higher than barley under the same conditions. 
Red, white, and strawberry clover varied from 500 to 601 with a mean 
of 566, and lucerne from 555 to 966 with a mean of 743, 40 per cent 
higher than barley. 

Richardson and Trumble (1937) showed that the transpiration ratio 
of herbage plants tends to rise as the growth stage advances. Most 
herbage plants mature in southern Australia with increasing rates of 
evaporation, and transpiration tends to rise without corresponding in- 
creases in the rate of dry matter production. Symon (1950) found that 
transpiration per unit leaf area in barrel medic rose steadily as maturity 
advanced, becoming steep toward completion of growth. The relative 
growth rate declined throughout when the moisture content was main- 
tained, becoming steady in the later stages when it was reduced. 

Soil factors which reduce the relative growth rate will on the whole 
tend to enlarge the transpiration ratio. This applies to deficiencies of 
soil nutrients and in particular to nitrogen ; it applies also to unfavorable 
structure or tilth restricting soil aeration. Reduction of soil moisture 
on the other hand, by lowering the transpiration rate to a greater extent 
than the relative growth rate, invariably reduces the transpiration ratio. 

d. The Influence of Defoliation. Defoliation, as in grazing, reduces 
transpiration either in proportion to the reduction of total dry matter 



or to a greater degree. The yield of ryegrass was reduced 83 per cent, 
transpiration 89 per cent, and the transpiration ratio 33 per cent, with- 
out loss of protein in experiments by Richardson and Truiuble (1937) 
(Fig. 8). Similarly, the protein production of phalaris was trebled and 
the amount of water transpired reduced 60 per cent as a result of appro- 




> 100 


O 1 


I 100 


| 60 




OF Lo&um fief*&m 




- 24 

12 8 6 5 4 


FIG. 8. Keduehon of yield and transpiration of perennial ryegrass (Lohum 
pcrenne) with increasing frequency of defoliation. 

priate defoliation. The control of pastures by grazing or cutting can 
restrict considerably the amount of water lost by transpiration. The 
root system tends to be reduced by defoliation ; cutting phalaris at five- 
week intervals reduced the weight of the roots to one-fifth of that not 
defoliated. The quantity of nutrients available to livestock tends greatly 
to be increased by defoliation ; maximum quantities of nitrogen were 
gained under ten-week defoliation in the case of phalaris and five-week 
defoliation in the case of ryegrass. Nitrogen absorbed per liter of water 
transpired by phalaris rose from 62 mg. in grass cut once to 468 mg. in 
grass cut five times at five-week intervals. Nitrogen absorbed by rye- 
grass rose from 154 mg. per liter in one cut to 1383 mg. per liter in nine 
cuts at three-week intervals. The amount of nitrogen gained by the 
herbage per unit of water lost by transpiration was thus seven and a half 
times in phalaris and nine times in ryegrass (Fig. 9) that of a single cut, 
as a result of the above frequencies of defoliation. 

The effect of cutting on the economy of water usage depends on the 
capacity of the plant to produce new herbage soon after defoliation, and 
on the succeeding evaporation rate. In twelve comparisons with ryegrass 



and phalaris, increased defoliation in no case increased the transpiration 
ratio significantly. This value either remained unaltered or was reduced 
9 per cent to 32 per cent, and in all cases the percentage of nitrogen was, 
moreover, increased. Pastures heavily defoliated in the spring months 
at Adelaide have invariably responded more actively than those un- 




O 80 

Z 60 

5 40 


2 20 







PIG. 9. Increase of nitrogen yielded per unit of water transpired by Lolium 
pcrcnne with iiicreaaing defoliation. 

grazed or little defoliated. In such cases, the total yield of pasture for 
the year has been greater and the quantity of protein gained consider- 
ably more than where the pastures had received little or no grazing up 
to the period of most active growth. The influence of defoliation is 
closely dependent on the nitrogen available for renewed growth of the 
pasture as this governs the subsequent growth rate. The effect of nitrogen 
on reducing the transpiration ratio has been shown by Ballard (1933) 
to be purely an effect on growth, the transpiration rate itself being un- 

e. Reduction of Soil Moisture Content. Persistent reduction of the 
soil moisture content to the wilting point has lowered the transpiration 
ratio of all herbage species tested on a variety of soil types by from 15 
per cent to 44 per cent. Although restriction of the water supply tends 
invariably to lessen growth, the rate of transpiration is lowered further. 
Increased osmotic pressure probably accounts in part for this. Re- 
duction of the soil moisture content increases the concentration of solu- 
ble salts in the plant and may also raise the content of pentosan colloids 


of high hydration capacity as shown by Wood (1934). Reduced soil 
moisture content under conditions of fairly low evaporation have re- 
sulted in extremely low values for the transpiration ratio. The following 
are examples : Atriplex semibaccata 164, A. vesicaria 174, Medicago tribu- 
loides 176, Ehrliarta calycina 180, Trifolium sub terras cum 255. Ex- 
amination of the moisture content at successive depths of the profile 
throughout the root zone by Cashmore (1934) has shown that perennial 
ryegrass reduces the soil moisture content to the wilting point to a depth 
of 42 in., after effective winter rains have ceased. Phalaris, with a much 
deeper root system, was found to reduce soil moisture to the wilting point 
to a depth of 78 in. Phalaris and lucerne may eventually exhaust the 
soil water available within the root zone, but are able to endure wilting 
for considerable periods. The relative rates of transpiration and pro- 
duction in the field conform to those indicated by determinations under 
open glasshouse conditions, provided significant differences in tempera- 
ture and the evaporation rate are taken into consideration. 

/. Yield in Terms of Available Moisture. Determinations under 
glasshouse and field conditions of water usage at the Waite Institute 
have indicated that the range of production per acre inch of water trans- 
pired by a pasture is from 2 to 12 cwt. Lucerne and irrigated pasture 
under South Australian conditions are likely to produce from 2VL t<> 
4 cwt. dry matter per acre inch of water transpired. Richardson (1923) 
obtained 2.75 to 2.88 cwt. dry lucerne per acre inch of water under field 
conditions in Victoria; the mean transpiration ratio of lucerne under 
glasshouse conditions at Adelaide indicates 2.73 cwt. Seeded pasture 
and natural pasture grown under conditions comparable to those of the 
Waite Institute are likely to average 4 to 5 cwt. per acre inch transpired. 
Oats may produce slightly more, approaching 6 cwt. Under favorable 
conditions seeded pasture has produced 7.33 cwt. per acre inch of avail- 
able moisture at Adelaide. Data submitted by Watkins and Lewy-van 
Severen (1951) show that Napier grass ( Pen-nisei wn purpureum) grown 
under tropical conditions is capable of producing 10 to 12 cwt. per acre 
inch of moisture available, which is probably close to the maximum 
possible. This forage yielded 35 tons of dry herbage per acre in a single 
year in El Salvador, and the figures quoted emphasize the extremely 
large quantities of nitrogen and other essential nutrients required under 
conditions of active growth. 

2. Factors Affecting the Mineral Content of Pastures 

a. Species. Numerous determinations have been made of the mineral 
composition of different herbage species, but many of these are scarcely 
comparable owing to wide differences in the stage of growth at which 


samples have been collected or in the conditions of soil and climate under 
which the plants have been grown. Comparisons of different herbage 
species in regard to chemical composition require to be based on growth 
under identical conditions of soil and climate and harvest of samples at 
the same stage of growth. The results of such comparisons have been 
published by Richardson, Trumble, and Shapter (1931), and by Shapter 
(1935). These investigations indicated the uniformly high protein and 
calcium content of herbage legumes, the high protein and mineral con- 
tent of certain miscellaneous herbs or forbs such as Erodmm, and the 
capacity of most grasses to reflect the nutrient content of the medium 
in which they grow, according to the availability of the particular nutri- 
ents in the region of soil profile explored by the roots, and the total 
amount of growth made by the grass. Native Australian grasses of the 
genus Danthonia, and shrubs of the genera Atriplex, Kochia, on which 
much wool was produced in the earlier phases of settlement, are charac- 
terized by a fairly high protein and mineral content, which is assisted 
by their limited total production per aero. These plants are well adapted 
to the modest soil resources which characterized the Australian wool- 
growing areas in their original condition. Wool production makes small 
demands upon the supply of soil nutrients, especially if meat production 
is not simultaneously involved. The introduction of higher yielding 
herbage species, such as those now employed for pasture improvement, 
involves considerable improvement of the status of available plant nutri- 
ents in the soil. 

fc. Stage of Growth, Defoliation, Management. Stage of growth 
largely determines the protein and mineral content of herbage plants. 
The processes of nitrogen absorption, photosynthesis, and transpiration 
do not proceed at similar rates throughout the growth period; phos- 
phorus, nitrogen, and potash in particular are absorbed most actively in 
the earlier stages of growth, while carbon assimilation and transpiration 
reach a maximum much later. As a consequence of the differential rates 
involved, the protein, phosphorus, and potassium content of most herbage 
plants tends to decrease rapidly as maturity advances. This is especially 
marked in the case of grasses. Herbage legumes show less acute drifts 
and it can be generally said that in mixed pastures the grasses attain 
their maximum nutritive value prior to the appearance of inflorescences, 
whereas legumes have their highest feeding value at or after this stage. 
Subterranean clover is still of higher nutritive value after seeds have 
formed than many grasses prior to flowering. 

The influence of growth stage and frequency of cutting on the com- 
position of Phalaris tuberose, was investigated in detail by Richardson, 
Trumble, and Shapter (1932). It was shown that the protein content 


fell from 33 per cent at an early tillering stage to 3.4 per cent at the 
conclusion of growth in the case of ungrazed herbage. The percentage 
of crude fiber and nitrogen-free extractives increased continuously from 
tillering to the conclusion of growth. The ratio of protein to carbon- 
aceous constituents was 1 to 1.6 at an early tillering stage and rapidly 
widened as growth proceeded, reaching a value of 1 to 26 in the final 
stage. The phosphate and potash content of the herbage was exceedingly 
high at early stages and fell steadily to a minimum at the end of the 
growing season. In this work a loss of 27.8 per cent of the total intake 
of potash was sustained from all portions of the plant, including the 
herbage and the root system, during the final phases of growth. This 
occurred as a migration of potash from the plant to the soil due to pas- 
sive diffusion from the root system at a stage when physiological activity 
was declining. The influence of defoliation was also investigated and 
has been commented upon in Sec. IV,ld in connection with the influence 
of defoliation on transpiration, and in Sec. 111,3 in relation to herbage 

c. Soil Factors. That the mineral composition of mixed herbage 
tends to reflect the available nitrogen supply in the soil was originally 
held by Lawes and Gilbert (1900). There is now much evidence to 
indicate that the nutritive value of a mixed pasture is in large measure 
dependent on the available supply of essential nutrients in the soil as 
determined by initial soil fertility and the application of artificial fertil- 
izers. The evidence accumulated in southern Australia shows that the 
composition of individual species grown on different soils varies accord- 
ing to the available supply or deficiency of nutrients in each soil type. 
In the northern portions of Australia, as in tropical and subtropical 
regions generally, the natural pastures tend to be acutely deficient in 
protein. This is in part due to limited available nitrogen in most soils, 
in comparison with active carbon assimilation at high temperatures. 
Protein deficiency in the north is accentuated by the relative absence of 
legumes in the natural herbage. The problems involved are of consid- 
erable importance in northern Australia as they are in other tropical 
and subtropical regions throughout the world. 

Adverting to the south, the application of soluble phosphate does not 
materially affect the phosphorus content of plants grown on soils high 
in available phosphate, but on phosphate-deficient soils dressings of 
superphosphate increase the phosphate content of introduced herbage to 
a value comparable with that grown on phosphate-rich soil. The major 
effect of phosphate on mixed pastures is to increase the content of pro- 
tein and calcium in addition to that of phosphate due to enrichment of 
the pasture in herbage legumes. Trace element deficiencies are usually 


controlled by the addition of deficient elements to the fertilizer. This 
results in a high enough content of these elements in the pastures to 
overcome animal deficiencies. 

d. Climatic Factors. The nutrition of herbage plants is substantially 
modified by climatic changes. The influences of temperature and light 
on photosynthesis, their direct effects on growth rates, and in the case 
of temperature, on respiration, lead inevitably to shifts in the percent- 
ages of the carbohydrate and nitrogenous fractions as shown by Night- 
ingale (1927). Trumble (1949b) has pointed out that these changes 
may also be associated with modifications in the symptoms of trace ele- 
ment deficiencies or in the uptake of particular nutrients such as phos- 
phorus and zinc. 

Decreases of soil moisture content have been found to decrease the 
percentage of phosphate but to increase the percentage of total nitrogen 
in ryegrass a>s shown by Richardson, Trumble, and Shapter (1931). 
Richardson (1933) emphasized the differences in the chemical composi- 
tion of plants grown in tropical and temperate regions. Under tropical 
and subtropical conditions, the high rate of photosynthesis may be ex- 
pected to produce herbage of low protein and mineral content more 
rapidly than is the case at higher latitudes. The rate of carbon assimi- 
lation is much reduced by the comparatively low temperatures which 
govern the vegetative growth characteristic of temperate regions. The 
summer months of high latitudes are attended by exceptionally long 
days, which compensate in part for the lower temperatures and light 
intensities experienced ; but the very much higher temperatures of the 
tropics are decisive in producing higher growth rates. 

3. Herbage Plant Improvement 

a. Plant Introduction. The value of plant introduction to Australia 
has already been indicated in Sec. I,3b and Sec. II,3e. Davies (1951) 
has pointed out that many of the grasses and legumes now employed in 
Australian pastures were introduced to Australia prior to 1900 although 
only a very small fraction of their present day distribution had by then 
been attained. Nevertheless, importation of new species and strains in 
the past two or three decades has led to valuable results. The introduc- 
tion of nonseeding kikuyu grass from the Belgian Congo by Breakwell 
(1923) and seed-producing forms by Trumble from Kenya in 1940 
(Parker, 1941) has provided raw material of an active sward-forming 
species which associates well with most herbage legumes and can be used 
with considerable advantage for permanent pasture in many parts of 
Australia where sufficient moisture is available over the greater portion 
of the year. This species is proving highly productive in irrigated pas- 


tures devoted to grazing by sheep ; it colonizes the borders of dams, 
channels and waterways generally, maintaining these free from weeds, 
providing additional grazing, and giving strength to banks. Investiga- 
tions by Trumble and Davies (1934) demonstrated the value of New 
Zealand strains of perennial ryegrass, cocksfoot, white clover, and of 
Montgomery red clover, grown in New Zealand, for irrigated pastures in 
South Australia. Morgan (1949), reviewing the development of irri- 
gated pastures in Victoria where much greater areas have been estab- 
lished under irrigation than elsewhere in Australia, indicates that the 
New Zealand strains have been extensively employed, in addition to 
naturally adapted Victorian strains. New Zealand hybrid HI ryegrass 
is characterized by high vigor under Australian conditions and is tend- 
ing to replace Italian ryegrass. 

Palestine strawberry clover, introduced in 1929, proved to be an 
extremely vigorous strain of Trifolium fragiferum. This was com- 
mercialized ten years later and has been sown over increasingly large 
areas in the southeast of South Australia. Its particular advantage over 
other strains of this species lies in the activity of its winter production 
and generally higher yield. Medicago solerolli, M. hispida sardm, Tri- 
folium Balansae, and seed-producing Ehrharta villosa are recent intro- 
ductions of promise. Paspalum scrobiculatum introduced by the 
Australian Division of Plant Industry, C.S.I.R.O., has been shown by 
Paltridge (1942) to be a valuable improved pasture species in the better 
rainfall areas of the southeast of Queensland when properly grown and 
managed. Other species introduced by C.S.LR.O. and the Waite Insti- 
tute in recent years and now under test appear likely to play an im- 
portant part in future pasture improvement. Active overseas explora- 
tion for new herbage plant material was not begun until 1951, although 
persistently advocated by the author since 1928. 

&. Use of Locally Adapted Strains. Despite the undoubted value of 
introduced strains, confidence in selected variants of herbage plant mate- 
rial that have survived in different parts of Australia over long periods 
has been fully justified. Such material has provided the basis for strain 
improvement in subterranean clover (Bacchus Marsh, Tallarook, Yar- 
loop), and barrel medic (Noarlunga), Victorian and New South Wales 
forms of perennial ryegrass, cocksfoot, white clover, and prairie grass 
(Bromus unioloides), the last named investigated by Donald (1939). The 
white Dutch type of white clover, commonly seeded until about twenty 
years ago, has been replaced by New Zealand white and the Victorian 
"Dingee" type, which resembles ladino in growth form. These are now 
widely used for irrigated pastures in southern Australia. Lucerne shows 
regional variation according to climate and management ; environmental 


selection has operated over a period of a century in some cases. Aus- 
tralian lucernes are well able to withstand grazing by sheep. Some types 
have been grown for many years under conditions of extremely low rain- 
fall, and regeneration from seed under grazing has been observed. 
Rhizomatous types are under investigation ; these are based upon deriva- 
tives of natural hybrids which in some cases have been established in 
South Australia for a century. Most progress in the actual breeding of 
improved grasses has been obtained with the Gb81 type of Phalaris 
tttberosa developed at the Waite Institute. This has come into general 
commercial use as an improved drought-resistant, actively tillering, 
permanent form of phalaris which is more productive under conditions 
of hard grazing than most commercial types. It is also lower in stature 
and higher in seed production than standard commercial forms of the 
grass. Interspecific hybrids between Phalaris tuber osa and P. arundi- 
nacea have been produced at Aberystwyth by T. 3. Jenkin, at Adelaide 
by the author, and at Davis, Cal. by R. M. Love. Sterility is evident in 
some of the material, but there is obviously scope for the development 
of extremely valuable new forms. 

4. Soil Deficiencies 

a. Phosphate. A detailed field investigation of changes in phosphate 
and nitrogen status and their effects on the development of seeded 
pasture from an originally unproductive condition was conducted by 
Trumble and Donald (1938). An examination was made of the effects of 
varying dressings of phosphate upon an unproductive podsolized sand 
with 0.006 per cent P20 r >, loss on ignition 1.47 per cent, pH 6.4, and 
yielding only 10 Ib. nitrogen and 1.4 Ib. PoO r , P er a re in sown but un- 
fertilized herbage. This land was characterized by stunted Eucalyptus 
forest and heathlike shrubs. After clearing and seeding to a pasture of 
subterranean clover and Phalaris tuberosa, application of 2 cwt. super- 
phosphate per acre per annum for three years, containing a total applica- 
tion of 150 Ib. P2Os, was found sufficient to develop extremely productive 
pasture. In the absence of applied phosphate, the yield was 6.2 cwt. dry 
herbage per acre, after clearing and seeding down. Application of 2 
cwt. superphosphate per acre per annum for three years produced a 
pasture which averaged 48.5 cwt. dry herbage per acre over three sea- 
sons (Fig. 10). The yield rose from 33.2 cwt. in the first season to 56.6 
cwt. in the third. The average protein production was 796 Ib. support- 
ing five sheep per acre, compared with 81 Ib. protein and a sheep to 
2 acres on unfertilized land. The production through the use of clover, 
associated grasses and phosphate was thus ten times the original and 
was attained at comparatively low cost. The relationship of dry clover 


FIG. 10. Upper, podsolizcd sand seven months after seeding to subterranean 
clover, without phosphate. Below, with 2 cwt. superphosphate (47 Ib. P a O 5 ) per acre 
at seeding. 

production to phosphate dressings followed the logarithmic Mitscherlich 
type in each of the three seasons ; phosphate recovery was directly pro- 
portional to the effective phosphate dressing up to a maximum of 4 cwt. 
superphosphate per acre in any one season (Fig. 11). The percentage 
of nitrogen in the herbage rose with increasing phosphate application 
and the perennial associated grasses developed actively in the third year 



despite the initial low phosphate and nitrogen content of the soil. 
Analysis by partial correlation and multiple regression indicated that 
in the early part of the season nitrogen accumulated previously was 
highly significant in determining the development of associated grass. 
Later in the season residual phosphate assumed an important role in 
determining further development. In addition to the effects on produc- 
tion, the count of soil bacteria was increased tenfold and the general 

a 3 


FIG. 11. Differential increase in nitrogen fixed compared with total yield of sub- 
terranean clover pasture under increasing phosphate application. 

level of soil fertility as indicated by nitrogen level and organic content 
greatly increased. Riceman (1948a, 1949) has produced evidence of 
differential response by herbage plants, e.g., Bacchus Marsh subterranean 
clover, lucerne, phalaris, to varying phosphate applications; lucerne in 
particular requires substantial quantities. Williams (1948) concluded 
that the effects of phosphorus treatment on the protein content of young 
grass were due primarily to variation in nucleoprotein content. 

b. Copper. Riceman, Donald, and Piper (1938) and Riceman, 
Donald, and Evans (1940) revealed the need of calcareous sands, and 
Riceman (1948a) the need of siliceous sands in South Australia for ap- 
plications of copper to ensure pasture development. Variation in the 
response of different herbage species to applications of this element was 
shown in these experiments and in investigations by Trumble and Ferres 


(1946). Lucerne and subterranean clover were both found to respond 
actively to applications of copper on copper-deficient soil. Lucerne, 
which persists through the perenniality of its root system, fails to survive 
on acutely copper-deficient soil in the absence of applied copper. The 
seed production of subterranean clover, on the other hand, under con- 
ditions of copper deficiency, is restricted sufficiently to prejudice sur- 
vival. Applications of copper sulfate to copper-deficient soil thus have 
a marked effect in ensuring the persistence and subsequent productivity 
of these two legumes. As future productivity of the pasture depends 
upon their nitrogen fixation, the application of copper has important 
economic effects on the level of pasture production obtained. Deficiency 
of copper in South Australian soils was established by the investigations 
of Marston and his colleagues (1938). Striking effects of copper on wool 
production and animal health have resulted from both direct administra- 
tion to the animal and application to the pasture. The quantity of 
superphosphate containing copper annually applied to South Australian 
pastures is approximately 15,000 tons, and in all probability, upward of 
a million acres have now been dressed with copper in southern Australia. 
Copper deficiency has also been recorded in Western Australia by Teakle 
and Stewart (1939), Teakle (1942), Rossiter (1951a) ; it occurs ex- 
tensively on sands, frequently associated with Merit ic gravels. 

o. Zinc. Investigations by Biceman and Anderson (1943) revealed 
that deficiency of zinc accompanied copper deficiency on the calcareous 
soils of Robe, in the southeast of South Australia, on which the original 
work of copper deficiency was conducted. Whereas lucerne and sub- 
terranean clover were particularly responsive to copper, barrel medic* 
and, to a lesser extent, subterranean clover on this soil, responded to 
zinc, and it was established that to attain a satisfactory pasture of sown 
grasses and legumes, dressings of both copper and zinc were needed. 
Subsequent investigations by Ricernan (1948a) on deep siliceous sands in 
the upper southeast of Soutfr Australia demonstrated the need for phos- 
phate, copper, and zinc over an extensive region. Subterranean clover, 
lucerne, and phalaris, the three important constituents of the herbage 
mixtures now being used, differed considerably in their response to the 
various fertilizer treatments. The addition of zinc brought about a 
marked increase in the size of individual plants of subterranean clover 
and in the yield of this species per acre. The addition of both zinc and 
copper led to a considerable increase in seed production and rate of 
multiplication, ensuring persistence and continued production of the 
clover. The addition of zinc did not enhance the yield of lucerne. The 
yield of phalaris, which finally becomes the dominant constituent of 
the pastures, depended largely upon the gain by the soil in available 


nitrogen ; it became productive only after several years of legume domi- 
nance. The use of superphosphate at the rate of 1 to 2 cwt. per acre, 
the addition of copper sulfate, 3 to 7 lb. per acre, and zinc sulfate, 7 
to 14 lb. per acre, together with seedings of subterranean clover, lucerne, 
and Phalaris tuber osa, should make possible the economic development 
of at least a million acres of heathland in southern Australia with a 
reasonably good rainfall but formerly regarded as "desert" in view of 
its extremely low natural productivity. Rossiter (1951a.b) has recorded 
fairly extensive zinc deficiency in Western Australia where multiple 
deficiencies of phosphate, copper, zinc, and potash are evident. 

Piw. 12. Kesponse of subterranean clover pasture to molybdenum. 

d. Molybdenum. Molybdenum is concerned primarily in symbiotic 
nitrogen fixation, and direct effects on the host legume (Fig. 12), unlike 
those of copper and zinc, are slight by comparison. Jensen (1948) has 
calculated that 10 to 25 p. p.m. of molybdenum in the nodule are required 
for maximum nitrogen fixation. The rate of fixation decreases with 
concentrations below 10 p. p.m. The plant appears to have a wide toler- 
ance of molybdenum concentration. Adverse effects on grazing animals 
become evident with total plant concentrations above approximately 10 
p. p.m., associated with suboptimal copper. Investigations of laterized, 
podsolized soils related to Archaean crystalline rocks, with sloping topog- 
raphy and high winter rainfall, led to the establishment by Anderson 
(1942, 1946) of molybdenum deficiency in these soils. Anderson and 
Thomas (1946) showed that molybdenum was essential for symbiotic 
nitrogen fixation; in the presence of sufficient molybdenum, phosphate 
also directly increased nitrogen fixation (Fig. 13). Anderson and Oertel 
(1946) found that applications of lime stimulated symbiotic nitrogen 



fixation by increasing the availability of molybdenum to the legume. 
These findings were of unusual interest in explaining the improvement 
of clover production following the burning of logs or stumps. Tradi- 
tionally these effects had been attributed to potash. The South Aus- 
tralian investigations showed that responses to 5 tons of woodash per 
acre were due entirely to the presence of approximately 1 oz. of available 
molybdenum in the ash. Responses to molybdenum have now been 
obtained over a wide range of soils in southern and eastern Australia by 

FIG. 13. Interaction of molybdenum with phosphate on lateritic podsol deficient 
in both elements. 292 - nil. 260 = +P. 81 = +Mo. 122 = P+Mo. (Anderson, 

Trumble and Ferres (1946), Anderson (1948), Rossiter (1951). The 
element is most frequently deficient on leached soils of pH below 7 with 
sloping topography to which subterranean clover is well adapted. 

e. Potassium. Potassium deficiency has been known in Victoria for 
many years under conditions associated with exhaustive cropping and 
especially persistent cutting for hay. Responses to potash fertilizers on 
subterranean clover pastures have been reported for example by Twenty- 
man (1938), Newman (1948), and Hexter (1948), but practical applica- 
tion of the experimental findings has been restricted by the high cost of 
the amounts of potassium fertilizer required per acre and the necessity 
for frequent dressings. Trumble and Ferres (1946) recorded potassium 
deficiency in a series of surface soils collected from different parts of 
South Australia, and positive interactions of potassium with molyb- 
denum were frequent with Mt. Barker subterranean clover in these 
tests. Field tests in South Australia have however not yielded a single 
case in which potassium application could be economically justified, and 
it is assumed that subsoil exploration by the roots of associated grasses 


assures at least for a time, and especially under grazing, an adequate 
potassium supply. Eossiter (1947b, 1951a,b) has obtained marked re- 
sponses to potassium by Dwalganup subterranean clover in Western 
Australia, in pot culture and field experiments. Significant interactions 
were observed with potassium and copper. 

/. Sulfur. Sulfur deficiency has been obscured in Australia for 
many years by the presence of calcium sulfate in all superphosphate 
dressings. Sulfur deficiency has been suspected in New South Wales 
since about 1929, and this deficiency has now been recorded on the basalts 
and granites of the southern tablelands of New South Wales by Ander- 
son and Spencer (1950). It has also been found, according to Davies 
(1951) in several other parts of Australia, including Western Australia 
and southern Queensland. In some cases, including both New South 
Wales and South Australia, a dual deficiency of sulfur and molybdenum 
has been established. 

g. Multiple Deficiencies. All deficiencies so far established in Aus- 
tralia are associated with phosphate deficiency, and responses to one 
or more trace elements cannot be anticipated unless phosphate ceases 
to be limiting. Because nitrogen is almost invariably lacking in the 
soils which respond to phosphate and trace elements, symbiotic nitrogen 
fixation is a first goal and effective legume nutrition becomes essential. 
Apart from a lack of phosphate in available form, and one or more nutri- 
ents other than nitrogen, the presence of (a) toxic derivatives of lignin in 
deficient wet heathlands and (b) high concentrations of soluble salts, may 
inhibit nitrogen fixation, first through an effect on rhizobia and secondly 
through an effect on the host legume. The nutritional aspects involved 
have been dealt with by Anderson (1949). The most frequent examples 
of multiple deficiency, apart from that of nitrogen in South Australian 
soils are: (a) phosphorus, copper, zinc; (b) phosphorus, copper, molyb- 
denum; (c) phosphorus, copper, zinc, molybdenum; (d) phosphorus, 
copper, zinc, manganese. Other cases have occurred in which phosphate, 
copper, zinc, molybdenum, and potash have proved to be deficient, and 
again combined deficiencies of molybdenum and sulfur are now known 
to occur. Potash deficiency appears frequently to be overcome in prac- 
tice through exploration of deeper soil horizon containing abundant 
available potash where the surface horizon may be potash deficient. All 
legumes that have been tested have been found to respond actively to 
molybdenum on molybdenum-deficient soils. Barrel medic, subterranean 
clover, and strawberry clover are especially responsive to zinc where the 
soil status of zinc is low ; lucerne and subterranean clover are among the 
most responsive legumes to copper. Significant interactions occur be- 
tween individual elements. Manganese is most frequently concerned in 


egative interactions, especially as pH falls. Excess manganese has 
een found by Kipps (1947) to reduce lucerne production on an acid 
Dil, although the growth of subterranean clover on the same soil was 
ot similarly affected. 

5. Associated Growth 

a. Compatibility in Herbage Awards. The question of compatibility 
etween species and strains is an important consideration in designing 
peds mixtures. A first principle of modern pasture establishment is 
lie association of grass with legume in any pasture that is to remain 
own for more than one or two seasons. Subterranean clover and lucerne 
astures in Australia in the past have usually been sown as pure stands 
ttth a cereal cover crop, but these have become invaded in due course 
y Hordeum, Vulpia, Bromiw, Cryptotstctnma, and other annuals. The 
alue of phalaris in southern Australia is greatly enhanced by its 
apacity to associate with herbage legumes, and this applies also to kiknyu 
rass. On the other hand, Lolium and EhrJiarta which form dense 
mlti-tillered clumps tend to depress to a greater extent such legumes 
s may be associated with them The competitive effects of Lolium are 
rell illustrated by the investigations of Cashmore (1934) and Trumble, 
Itrong, and Chapter (1937). These species when sown in pastures are 
requently established at extremely low seeds rates. Four-species pas- 
Lires based on phalaris, ryegrass, clover, and lucerne have given good 
esults in South Australian field experiments, affording a 2 by 2 com- 
ination of grass and legume, surface soil and subsoil exploiting in each 
ase. Root distribution of the constituents and the nitrogen status of 
lie soil are major considerations, as emphasized by Trumble (1949b). 
'he type of combination may be employed wherever the supply of mois- 
iire held by the profile is sufficiently liberal. 

b. Competition in Herbage Swards. Competition to which herbage 
igumes are exposed is naturally slight in soils that are low in available 
itrogen, and the dominance of grass or legume in a pasture is frequently 

function of the available nitrogen content of the soil. As the nitrogen 
tatus improves, grasses and other non-legumes tend to become dominant, 
nd their capacity to reduce the intensity of light available to the 
sgumes results in legume depression and eventual suppression, as shown 
y Blackman (1938) and Blackman and Templeman (1938). Reduction 
f the grass by grazing or mowing usually results in a significant im- 
rovement of the legume complement, despite a moderately high nitrogen 
tatus. Numerous field experiments have now confirmed the fact that 
epeated mowing or continuous grazing, as compared with deferred 
otational grazing, greatly increases the amount of herbage legume in 


a pasture. The presence of weeds in pastures frequently follows over- 
grazing or depletion of the soil nutrient supply. This arises from in- 
creased soil moisture through reduced competition from grasses, which 
transpire, shade, and respire less under such treatment. Weeds are 
usually though not invariahly plants of low nutrient content and there- 
fore of low feeding value; they are thus able to survive and dominate 
unproductive pasture through the development of shade volume, based 
largely on high fiber or high water content. Permanent control of weeds 
in such cases must depend largely on the improvement of soil fertility 
through the elimination of soil deficiencies, the establishment of pro- 
ductive pasture, and its maintenance by sound management. 

c. Excretion of Nitrogen from legumes. It was shown by Trumble, 
Strong, and Shapter (1937) that grasses do not derive nitrogen from 
herbage legumes grown in association with them under the conditions 
of South Australia except during the senescent phase of the legume when 
the root nodules are actively breaking down and nitrogen is made avail- 
able from the roots as a consequence of root decomposition. Tinder 
certain conditions, where photosynthesis in a legume is reduced by 
unfavorable conditions of light as shown by Strong and Trumble (1939), 
nitrogen may be actively excreted from the root system to the legumes 
during its active growth. A temporarily high rate of transpiration may 
reduce the water content of the legume, and further increase the amino- 
nitrogen concentration, thus also favoring excretion, but the necessary 
conditions are probably so rare in practice under Australian conditions 
that the phenomenon may be disregarded as being mainly of academic 
interest. The main gains of nitrogen by associated grasses are in the 
return of urea from ingested leguminous material, together with the 
breakdown of legume protein in roots and surface residues. 

d. Control of Botanical Composition by Management. It is evident 
from a wide range of practical experience, in addition to the principles 
outlined in this paper, that the botanical composition of a pasture can 
be closely governed by management. If the practical aim is to develop 
a pasture containing say two-thirds grass and one-third legume, on a 
dry weight basis, such a condition can be attained by selection of legumes 
appropriate to the climatic and soil environment, fertilizer treatment 
that field experimentation indicates, the addition of long-term grasses, 
and finally by grazing management, together with, if necessary, occa- 
sional mowing. It may be argued, and with good reason, that a pasture 
containing two-thirds grass and one-third legume is by no means desir- 
able if the nitrogen status is already high. Purely gramineous pastures 
can be immediately more productive under such conditions than mixtures 
of the same grass with a legume. If, on the other hand, the nitrogen 


status is low, stands of pure legumes are likely to produce more protein 
per acre than mixed associations. If the legume is to be mown for forage 
there is every justification for growing it as a pure stand as, e.g., 
lucerne, red clover, ladino white clover, subterranean clover; but if the 
mixture is to be used for long-term grazing, it is as well to plan from the 
outset according to initial nitrogen status and the ultimate purpose in 
view, developing synthetically according to a definite plan of manage- 
ment, rather than permitting changes to occur fortuitously. 

6. Irrigated Pastures 

Observations of the principles that have governed the development 
of irrigated pastures in Australia have already been made. The prin- 
cipal areas devoted to irrigated pastures in Australia are in proximity 
to the River Murray and its tributaries in Victoria and New South 
Wales. Similar areas are located near the mouth of the Murray in South 
Australia and at Collie and Harvey in Western Australia. These are 
indicated on a map accompanying a brief review of Australian pastures 
by Christian and Donald (1949) and Trumble (1949a). 

Lucerne and mixtures of perennial ryegrass, cocksfoot, and white 
clover have provided the main basis for the development of irrigated 
areas in the south. On the other hand, Wimmera ryegrass and subter- 
ranean clover frequently received supplementary irrigation to extend 
the natural winter rainfall season. This is commonly employed in New 
South Wales to aid fat lamb raising during the winter and spring 
months. Irrigated pastures have extended greatly in Victoria, where 
the early work of Bartels (1928) did much to encourage approved irri- 
gation practices. Commencing with 5 acres established at the State 
Research Farm, Werribee, in 1914, the total was stated by Morgan (1949) 
to have reached a third of a million acres by 1947. 

The available nitrogen content of the soil has often been low to mod- 
erate in the early stages of these developments, and herbage legumes such 
as lucerne, white clover, and strawberry clover have therefore received 
particular emphasis. High yields of perennial ryegrass, cocksfoot, white 
clover with some phalaris, prairie grass, and red clover were recorded at 
Wood's Point in South Australia by Richardson and Gallus (1932) and 
Trumble and Davies (1934). The establishment of lucerne for long 
periods prior to sowing down to pasture is considered to be largely re- 
sponsible for the level of production attained, namely 10.9 tons of dry 
matter per acre, supporting twenty -six sheep per acre for two months, 
and an average of fifteen sheep per acre or better for the full year. 

Many of the areas that have been seeded to pasture under irrigation 
have been characterized by moderate to high salt content which has 


tended, in time, to be completely removed by successive irrigations. 
Morgan (1947) states that over a period of twenty years the acreage of 
visibly salt-affected land in Victoria has been decreased through the 
institution of the border check system of irrigation with suitable grad- 
ing, the sowing of improved pastures, and sound management in regard 
to manuring and grazing. Grading is regarded as especially important 
to make possible uniform application of water for leaching purposes. 
Morgan (1947) found in one case, a decrease from a salt concentration 
of 0.41 per cent at to 6 in. and 1.01 per cent at 12 to 24 in. to 0.0,5 
per cent at to 6 in. and 0.19 per cent at 12 to 24 in. over a period of 
seven years. Moderate irrigations were employed on a basis of twelve 
to nineteen applications totaling approximately 2.44 acre ft. ; and the 
yield of the pasture at the same time increased substantially. Recent 
investigations by the Waite Institute (1950) have demonstrated that a 
high initial content of total soluble salts is a major factor to be consid- 
ered in the reclamation of heavy clay flats adjoining the River Murray. 
Concentrations in this case may vary from 0.5 per cent to above 4.0 
per cent. Rhodes grass and lucerne, both capable of high salt tolerance, 
have proved successful pioneer species; both persist at concentrations of 
0.5 to 1.0 per cent total soluble salts provided irrigations are sufficiently 
frequent and surface cover, which can be rapidly provided by the 
Rhodes grass, is maintained. Surface ridging and the frequent use of 
some excess water to flush the surface, tend to accelerate the removal of 
surface salt. As the surface concentration is reduced, perennial rye- 
grass, barrel medic, subterranean clover, and white clover become im- 
portant constituents of the pastures. Kikuyu grass has also proved to 
be a useful species as development proceeds. Applications of copper, 
zinc, and molybdenum, over and above the basal dressings of 2 cwt. 
superphosphate per acre per annum, improved the mean yields of both 
the pasture mixtures and lucerne by 40 per cent to 60 per cent in the 
above tests. 


Although specialized subfields related to if not forming part of agron- 
omy have developed in Australia as in the United States, the scientific 
investigation of field problems has proceeded for sufficient time to 
make possible the integration of specific lines of approach, leading to a 
certain degree of completeness. An attempt has been made therefore to 
present in this contribution as full an account of interacting principles 
as space permits. Because climate overshadows all other factors in 
Australia, relationships of climatic factors to those of soil, species, strain, 
and management have in particular been emphasized. 


1. The Edaphoclimatic Environment 

a. Value and Limitations of the Soil Survey. The soil survey has 
proved a prerequisite to effectiveness in Australian agronomy. Its value 
lies in the definition of soil boundaries and the separation of categories 
based upon physical and geochemical factors. Its limitations largely con- 
cern an unavoidable failure to assess nutrient properties owing to the de- 
pendence of these upon the plant and the climate in which it is grown. 
Grassland covers a much wider range of topography and soil type than 
any single field crop because the latter depends upon relatively narrow 
limits in regard to soil properties, including usually a fairly high degree 
of soil fertility. 

Pastures on the other hand are frequently employed to utilize soils 
unsuitable for cropping and to create soil fertility. Most field investi- 
gations prior to 1929 were conducted with complete disregard to soil 
type and the applicability to other areas of the field experimental data 
derived. It is now customary to choose experimental sites as represent- 
ing a particular soil type, the distribution of which has been revealed by 
a competent soil survey. The physical characteristics of the profile, 
field capacity, pH, and content of soluble salts are most important. Nu- 
trient status is best determined by field experimentation supported by 
glasshouse investigation. 

6. Relevant Climatic Measures. The climatic environment with which 
any given soil type is associated must be known. This is a complex of se- 
quential changes in temperature, light, and moisture status, but usually 
one or two factors are especially restrictive and call for particular exam- 
ination. Moisture is by far the most important single factor affecting 
production in Australia, and studies of moisture status have character- 
ized investigations of both soil formation and pasture production. The 
degree of leaching closely determines the character of the soil profile and 
its capacity for plant nutrition. As precipitation and the rate of evap- 
oration together determine the leaching factor, it is not surprising that 
ratios of precipitation to evaporation are prominent in the derivation of 
agroclimatic measures under Australian conditions. Prescott (1949) 
has shown as a result of examination of Australian soil boundaries, the 
records of drain gauges, the use of water by field vegetation, and meas- 
urements of transpiration that the most efficient single climatic index of 
leaching in soils is P/E m , where P represents precipitation, E is evapora- 
tion from a free water surface, and m is a constant varying from 0.67 
to 0.80 with a probable mean of 0.73. A value of 0.6 for the index 
corresponds with the margins of Australian deserts ; at 1.1, soil drainage 
is nil and at 1.3 to 1.5 precipitation tends to balance transpiration. At 


1.7 pedocals separate from pedalfers. Determinations of soil moisture 
content in the field by Butler (1950) using electrical resistance gypsum 
blocks indicate that values of this index may be satisfactorily related to 
soil moisture status in the field, but that the value of the index may 
require modification according to the conditions. Despite the over- 
whelming importance of moisture in Australia, the conditions of tempera- 
ture and light while moisture is available closely govern plant behavior, 
and the edaphoclimatic environment can only be given some degree of 
expression when measures of these factors are related to an appropriate 
soil index or indices. 

c. The Ecological Place of the Field Experiment. The field experi- 
ment is coining to be regarded as a sample unit of the particular environ- 
ment that is being investigated. It is now recognized that an experiment 
conducted in a single year will represent only the conditions of climate 
and soil which pertain in that particular year. Climatic analysis, based 
on discernment of the practical agricultural consequences involved, can 
establish the probable frequency of a particular class of season in a long- 
term series. 

Field experiments require thus to be designed not only to cover the 
major soil types that characterize a given region but the major kinds of 
climatic combinations that are likely to occur with significant frequency 
over a long period of years. An example is given of a joint rotation and 
fertilizer experiment at the Waite Institute (1950) in which pasture 
followed four different crops, each after wheat, over a period of years 
involving several cycles of rotation. The experimental design consisted 
of sixteen blocks enabling each course of four rotations to occur every 
year. Each block was divided into 27 plots on a 3 by 3 by 3 factorial 
design. Such an experiment enabled differences between rotations in 
terms of yield of wheat on fallow and the yield of pasture following the 
four different crops to be assessed and, moreover, the interactions of the 
responses with both season and cycle of rotation to be measured. An 
effective climatic measure or picture of each season enables the variations 
of treatment effects with season to be interpreted. 

Australian experiments have tended to emphasize the incorporation 
of pastures for varying periods in crop rotations to regain soil structure 
and nitrogen in overcropped lands. Hodgson (1939) has emphasized 
the new outlook gained by farmers now that the pioneering stage has 
gone, and lucerne, subterraiiean clover, and Wimmera ryegrass have been 
employed for temporary pastures in rotation with wheat in New South 
Wales. The grazing of sown top-dressed pastures for five years or more 
followed by cropping for an approximately equal period is recommended. 
Woodroffe (1949), dealing with the results of South Australian experi- 


ments, emphasizes the value of peas, followed by short-term pastures, on 
the one hand, and perennial pastures maintained for up to ten years, on 
the other, in improving soil organic matter and nitrate content. Forster 
(1950), reviewing the results of field investigations presented at the 
British Commonwealth Specialist Agricultural Conference, Adelaide, 
3949, has emphasized the decline of organic matter in Australian wheat- 
growing soils and further stressed the effect of clover pastures in im- 
proving soil fertility, particularly at the Rutherglen Experimental 
Farm, Victoria. A much cultivated field gave 31 per cent aggregation, 
whereas one under subterranean clover for eight years and then cropped 
gave 53 per cent. There is now in Australia a marked swing toward the 
establishment of long-term leys between intensive periods of cropping. 
This has resulted in a reduction of wheat acreage in recent years, and 
this has also been favored by high world prices for wool. 

2. Integrated Climatic Patterns 

a. The Factors Involved. The concurrent expression of indices of 
temperature, light, and moisture over given intervals of time has rarely 
been attempted. Trumble (1949) presented diagrammatically an analysis 
of twenty-four seasons at the Waite Institute in terms of effective rain- 
fall, air temperature, and the light duration for each month per season. 
The yields of pasture were dependent upon the type of climatic pattern, 
and a study of the patterns concerned enabled variations in production 
from season to season to be understood. The factors employed were (a) 
mean monthly duration of daylight, plotted horizontally for the twelve 
successive months, (b) corresponding mean monthly air temperatures in 
shade in excess of 45 F. plotted vertically to form a rectangular block 
for each month, (c) superimposition of available moisture in units of 
0.25 in. and according to the approximate relation of temperature to 
growth. Such a method of-attempting concurrent expression of light, 
temperature, and moisture values over given intervals of time is doubt- 
less open to refinement, but there are advantages in presenting such pat- 
terns at first in as simple terms as possible. The mean of the patterns 
constructed for Adelaide differs in significant features from each one of 
the twenty-four individual seasons and is thus fictitious. Initial com- 
parisons of contrasting environments, however, can be appropriately 
made on the basis of means, although the final goal should be in terms of 
individual seasons. Trumble (1950a) has employed the method to indi- 
cate probable nutrient requirements of pasture in widely contrasting 
environments such as those of tropical, temperate, and high latitude cli- 
mates. Trumble (1950b) has also in this way described the four major 
climatic types of Nicaragua and compared them with conditions at ex- 


perimental stations in adjoining Central American countries, and the 
southeastern United States, at which agronomic data of possible applica- 
tion to Nicaragua are available. These studies emphasize the high po- 
tential for growth in the tropics and the consequent emphatic need for 
soil improvement. 

l>. Short- and Long-Term Variability. Variation in the shorter term 
includes that between day and night, from day to day, over successive 
phases of the same season, and from season to season within the range 
covered by a short-term experiment of two or more years. Few grassland 
experiments have been conducted for more than a limited number of 
seasons, and the exceptions have usually been affected by upward or 
downward fertility trends, or a treatment such as cutting for hay which 
has departed from accepted grazing practice. Investigation by Trum- 
ble and Cornish (1936) of production for ten seasons of a natural pas- 
ture showed that coincidence of early seasonal rains with favorable 
conditions of temperature and light governed in large measure the total 


1939 vvij:: 1946 :.:;: \94Z \\:\:\\:'" 55 jTrT 



1936 :::[" 

Fio. 14. Integrated climatic patterns showing nature of individual seasons at the 
Waite Institute, 1925-48. The patterns are in order of seasonal production, as closely 
as can fairly be judged. Seasons 1935 and 1947 with effective rainfall commencing 
in March and continuing for eight months were outstandingly high in production. 
Seasons 1944, 1940, 1927, 1930 gave considerably lower yields than all others. Late 
spring drought (1944), low rainfall in autumn and spring (1940), short season 
(1927), short season commencing very late (1930). 



yield for the season. This led to emphasis on the length of the effective 
rainfall season by Trumble (1937) and investigations of its variability in 
the longer term by Wark (1941). 

The amount of moisture required for transpiration will depend upon 
both temperature and the duration of light. Mean monthly values for 
these appear adequate, and only temperature will vary from year to year 
in any month. The differences of temperature which follow changes in 
latitude or altitude are frequently so great as to multiply the rate of 
production several times. Integrated climatic patterns from widely 
separated latitudes suggest that nutrients are required to be absorbed 
from the soil at considerably higher rates in the tropics than in temper- 
ate regions to produce comparable concentrations within the growing 
plant. Copper, for example, needs to be absorbed in the tropics at a rate 
fifteen times that characteristic of temperate conditions ; and a total pro- 
duction of 30 tons of dry material per acre per annum, which is readily 
attained at low altitudes near the equator, requires nitrogen equivalent 
to 3*/> tons of sulfate of ammonia, and phosphate equivalent to 1 ton of 

COLLEGE STN. \LAT jo'4O\ BUENOS AIRES |/.-r j-\w j 
MJ ^o A f^^^ A r u 


BR/SBANE. \LAT fr'M'3 


5 AUSTRAL/A \MJT W \ /TALY U*.r Vjj' 



= : 1P 

\ 6 It 4 OCR MONTH / 




FIG. 15. Comparison of climatic patterns for two Australian centers (Mt. Gam- 
bier winter rainfall, southern Australia; Brisbane summer maximum, sub-tropical, 
north-eastern Australia), with patterns for other centers in middle latitudes. 


superphosphate to provide the minima] requirements of nitrogen and 
phosphorus for satisfactory animal nutrition through herbage alone. 
Such global differences far outweigh variations from season to season at 
one center and could with justification receive greater attention. In- 
creasing distance from the equator leads to reduced growth rates and 
increasing protein concentration, but the marked increase of daily light 
duration in midsummer compensates in part for lowered temperature. 





\ O i 4 PER MONTH / \ - &3" (EST CVAP) / 

FIG. 1C. Climatic patterns for three centers at high latitudes. 

c. Estimation of Possible Production. Trumble (1950a) has em- 
pJoycd a summation index of potential production. This is based on 
transpirational needs in units of one acre inch and is assessed by fitting 
the number of acre inches of moisture available for transpiration to the 
light-temperature pattern (Fig. 14). The ratio of transpiration to 
growth varies with the plant and the environment and should be con- 
sidered in relation to data on the response of particular plants to the 
chief ecological factors of causation. On the basis of the experiments on 
transpiration conducted at Adelaide and the earlier work of Briggs and 
Shantz (1913), transpiration ratios of 300 and 500 have been tentatively 
adopted at mean air temperatures respectively above and below 65F. 
In the patterns so far employed, four dots depict an inch of precipitation 
gained by the soil in the absence of surface runoff, and a single dot 
equivalent to 0.25 in. occupies 25F. mean daily light-hours per month 
decreasing to 12F. mean daily light-hours per month at tempera- 
tures above 65 F. Examination of these patterns has indicated a dry 
herbage potential of 1.8 to 8.0 tons (2240 Ib. per ton) per acre per annum 
within areas of South Australia where the mean wet period exceeds seven 
months and the total rainfall is considered sufficiently high for sown 
pasture production. The potential production in the tropics is probably 
in the order of 35 tons per acre per annum, a value already obtained by 
Watkins and Lewy-van Severen (1951). 



BELIZE |&*r /rjowl MANAGUA. \LAT IX'IO'N \ BROOME t \J.AT ir'sr 






J f M A M J J AS 6 N 






/ - as" ppeciPiTATioN \ 

\ as' (EST CVAP) / 

FIG. 17. Climatic patterns for nine centers at varying altitudes within the 

While there are dangers in oversimplification and the use of gener- 
alized estimates, the principles involved invite ecological examination on 
a world basis, and where suitable records of both production and the 
climatic factors governing yield and composition are available, a fuller 
biological interpretation of regional and seasonal effects should bo pos- 

3. The Realization of Potential Production 

a. Fitting Herbage Plants to the Environmental Pattern. Although 
many successes have attended past trials of new species, there have prob- 
ably been countless failures for every single success, involving a good 
deal of wasted effort under trial-and-error methods. Nowadays new spe- 
cies and strains can be selected for test more efficiently on the basis of 
the fairly effective climatic and edaphic comparisons that can be made, 
and better comparisons are possible than have been the rule. Despite 
this, the agronomist still requires to conduct numerous field tests and 
engage upon comprehensive breeding programs; but the better he is 
equipped with a knowledge of the ecological factors that govern the 
conditions to which the tests are to apply, the more expeditiously will 
new herbage plants be fitted to these conditions. The results of a single 


year's test of a new species or strain should be judged in terms of the 
environmental pattern of that particular season, for the performance of 
the plant material grown is a consequence of both environmental re- 
sources and genetic efficiency, and it is the latter that it is important 
to gain. 

b. Scientific Investigation and Field Practice. The scientific inves- 
tigations required to realize the maximum production possible take nu- 
merous forms, but a first logical step is analysis of environment to define 
those factors that overwhelmingly limit growth, and this stresses a dis- 
criminate survey of practical experience as well as of scientific factors. 
The key to increased production in Australia has so often been found in 
the combination of an appropriate herbage legume with appropriate fer- 
tilizer treatment that this aspect has come to be one of the first examined. 
Sources of existing and possible new herbage material are so extensive 
that few edaphoclimatic situations exist which cannot be met outside the 
arid to semi-arid regions. The field investigations required seem most 
effective in simple randomized blocks, with separate tests numerous 
enough to uncover all possible factors and all possible combinations of 
factors that might matter. Work that is essentially academic can 
quickly lose agricultural significance, and perhaps the deeper lines of 
scientific investigation are best detached in practice from field experi- 
mentation but linked for the purpose of answering specific questions 
that have frequently arisen as a result of interested enquiry. Many new 
principles, once they are fully uncovered, can be related in simple and 
effective economic terms to the farmer or grazier, whose association with 
agronomic enquiry has certainly so far proved an advantage in Aus- 
tralia, and such enquiry can lose much of its value if not persistently as- 
sociated with farming practice itself. Success in this regard appears to 
have been one of the most stimulating results of grassland agronomy as 
carried out so far in both the United States and Australia. 


Adams, A. B., Came, W. M., and Gardner, C. A. 1927. J. Dept. Agr. W. Australia 

4, 524-530. 

Anderson, A. J. 1942. J. Australian Inst. Agr. Sci. 8, 73-75. 
Anderson, A. J. 1946. J. Council Sci. Ind. Research 19, 1-15. 
Anderson, A. J. 1948. J. Australian Inst. Agr. Sci. 14, 28-33. 
Anderson, A, J. 1949. Brit. Commonwealth Sci. Off. Conf. Agr. (Australia) B 

13 pp. 
Anderson, A. J., and Oertel, A. C. 1946. Australia Council Sci. Ind. Research Bull. 

198, 25-44. 
Anderson, A. J., and Smith, C. A. Neal. 1951. Commonwealth Sci. Ind. Research 

Org. Australia Bull. 263. 


Anderson, A. J., and Spencer, D. 1950. Australian J. Sci. Research B, 3, 431-449. 
Anderson, A. J., and Thomas, M. P. 1946. Australia Council Sci. Ind. Research 

Bull 198, 7-24. 

Ballard, L. A. T. 1933. Australian J. Exptl. Biol 11, 161-176. 
Bartels, L. C. 1928. J. J)ept. Agr. Victoria 26, 111-118. 
Beruldsen, E. T., and Morgan, A. 1936. J. Dept. Agr. Victoria 34, 99-108. 
BJackman, 0. E^ 1938. Ann. Botany 2, 257-280. 

Blackman, G. E., and Templeman, W. G. 1938. Ann. Botany 2, 765-791. 
Breakwell, E. 1923. The Grasses and Fodder Plants of New South Wales. Govt. 

Printer, Sydney, Australia. 

Briggs, L. J., and Sliantz, H. L. 1913. U.S. Dcpt. Agr. Bull. 284. 
Butler, P. F. 1950. Thesis. Univ. of Adelaide, Australia. Pt. B. 36 pp. 
Cashmore, A. B. 1934. Australia Council Sci. Ind. Research Bull. 81. 
Christian, C. S., and Donald, C. M. 1949. The Australian Environment. Australian 

Commonwealth Sci. Ind. Research Org. Melbourne, pp. 98-116. 
Cornish, E. A. 1949. Australian J. Sci. Research B 2, 83-137. 
Crocker, R. L. 1946. Australia Council Sci. Ind. Research Bull. 193. 
Crocker, R. L., and Tiver, N. S. 1948. J. Brit. Grassland Soc. 3, 1-26. 
Davidson, J. 1934. Trans. Roy. Soc. S. Australia 58, 33-36. 
Davidson, J. 1938. Trans. Roy. Soc. S. Australia 62, 141-148. 
DuvicR, J. G. 1931. Australia Council Sci. Ind. Research Bull. 48. 
Davies, J. G, 1946. Australia Council Sci. Ind. Research Butt. 201, 97-104. 
Davies, J. G. 1951. J. Australian Inst. Agr. Sci. 17, 54-66. 
Davies, J. G., and Trumble, H. C. 1934. Imp. Bur. Plant Genetics: Herbage Plants. 

Bull. 14, 23-32. 

Davies, W. 1933. Australia Council Sci. Ind. Research Pamphlet 39. 
Donald, C. M. 1939. J. Council Sci. Research Australia 12, 212-226. 
Donald, C. M. 1941. Pastures and Pasture Research. The University of Sydney, 

Donald, C. M., and Smith, C. A. Neal. 1939. J. Council Sci. Research Australia 10, 


Donald, C. M., and Trumble, II. C. 1941. ,7. Australian Inst. Agr. Sci. 7, 124-125. 
Ferres, II. M. 1949. Brit. Commonwealth Sci. Off'. Conf. Australia B 6 pp. 
Ferres, II. M., and Trumble, H. C. 1943. J. Australian Inst. Agr. Sci. 9, 179-182. 
Forster, II. C. 1950. J. Australian Inst. Agr. Sci. 16, 44-52. 
Harrison, J. E. 1932. J. Dept.* Agr. Victoria 30, 505-511. 
Hexter, G. W. 1948. J. Dept. Agr. Victoria 46, 111-120. 
Hill, Rowland. 1936. J. Agr. S. Australia 40, 322-330. 
Hills, E. S. 1949. The Australian Environment. Australian Commonwealth Sci. 

Ind. Research Org. Melbourne, pp. 13-22. 

Hodgson, S. C. 1939. Agr. Gas. of N. S. Wales 50, 407-411, 420. 
Jensen, H. L. 1948. Proc. Lmnean Soc. N. S. Wales 72, 265-291. 
Kelley, R. B. 1949. The Australian Environment. Australian Commonwealth Sci. 

Ind. Research Org. Melbourne, pp. 159-183. 

Kipps, E. H. 1947. J. Council Sci. Ind. Research Australia 20, 176-189. 
Lawes, J. B., and Gilbert, J. II. 1900. Roy. Soc. (London) Phil. Trans. B, 139-210. 
Leeper, G. W. 1949. The Australian Environment. Australian Commonwealth Sci. 

Ind. Research Org. Melbourne, pp. 23-34. 
Levy, E. B., and Madden, E. A. 1933. New Zealand J. Agr. 46, 267-279. 


Marston, H. R., Thomas, R. G., Murnae, D., Lines, E. W. L., McDonald, I. W., 

Moore, H. O., Bull, L. B. 1938. Australia Council Sci. Ind. Research Bull. 113. 
Marston, H. B., et al 1938. Australia Council Sci. Ind. 'Research Bull. 113. 
Maximov, N. A. 1929. The Plant in Relation to Water. Allen and Unwin, London. 
Moore, B. M., Barrio, N., and Kipps, E. IJ. 1946. Australia Council Sci. Ind. Res. 

Bull. 201, 7-69. 

Morgan, A. 1947. ,7. Dept. Agr. Victoria 45, 111-115. 
Morgan, A. 1949. ,7. Dept. Agr. Victoria 47, 97-105. 
Newman, R. J. 1948. J. Dept. A(jr. Victoria 46, 49-57. 
Nightingale, G. T. 1927. Wisconsin Agr. Expt. 81 a. Res. Bull. 74. 
Palt ridge, T. B. 1942. Australia Council Sci. Ind. Research Pamphlet 114. 
Parker, D. L. 1941. J. Agr. S. Australia 45, 55-59. 
Piper, C. S. 1942. J. Agr. Sci. 32, 143-178. 
Piper, C. S. 1947. Prcs. Address, Sec. B. Australian and New Zealand Assoc. Adv. 

Sci., Perth, W. Australia. 
Piper, C. S., and Beckwith, R. 8. 1949. Brit. Commonwealth Sci. Off. Conf. Agr. 

(Australia). Abs. 9 pp. 

Prescott, J. A. 1931. Australia Council Sci. Ind. Research Bull. 52. 
Prescott, J. A. 1934. Trans. Royal Soc S. Australia 58, 48-61. 
Prescott, J. A. 1944. Australia Council Sci. Ind. Research Bull. 177. 
Prescott, J. A. 1948. Australian J. Sci. 11, 24-25. 
Prescott, J. A. 1949. J. Soil Sci. 1, 9-19. 

Ratcliffe, P. N. 1936. Australia Council Sci. Ind Research Pamphlet 64. 
Riceman, D. S. 1945. Australia J. Council Sci. Ind. Research 18, 336-348. 
Riceman, 1). R. 1948a. Australia Council Sci. Ind. Research Bull. 234. 
Riceman, D. S. 19481). J. Council Sci. Ind. Research Australia 21, 236-246. 
Riceman, I). S. 1949. Commonwealth Sci. Ind. Research Org. Australia Bull. 249. 
Riceman, D. S. 1950. J. Agr. S. Australia 54, 132-140. 
Riceman, D. S., and Anderson, A. J. 1943. J. Agr. S. Australia 47, 16-29. 
Riceman, D. S., Donald, C. M., and Evans, S. T. 1940. Australia Council Sci. Ind. 

Research Pamphlet 96. 
Riceman, D. S., Donald, C. M., and Piper, C. 8. 1938. Australia Council Sci. Ind. 

Research Pamphlet 78. 
Richardson, A. E. V. 1923. J. Dept. Agr. Victoria 21, 193-212, 257-284, 321-339, 

385-404, 449-481. 

Richardson, A. E. V. 1930. Australia Council Sci. Ind. Research Pamphlet 17. 
Richardson, A. E. V. 1932. J. Council Sci. Ind. Research Australia 5, 141-151. 
Richardson, A. E. V. 1933. Herbage Revs. 1, 96-99. 

Richardson, A. E. V., and Gallus, H. P. C. 1932. Australia Council Sci. Ind. Re- 
search Bull. 71. 

Richardson, A. E. V., and Trumble, II. 0. 1928. J. Agr. S. Australia 32, 224-244. 
Richardson, A. E. V., and Trumble, II. C. 1937. Waitc Agr. Research Inst. Rept. 

1933-36, 91-106. 
Richardson, A. E. V., TrumbJe, H. C., and Shapter, R. E. 1931. Australia Council 

Sci. Ind. Research Bull. 49. 
Richardson, A. E. V., Trumble, H. 0., and Shapter, R. E. 1932. Australia Council 

Sci. Ind. Research Bull. 66. 

Roe, R., and Allen, G. H. 1945. Australia Council Sci. Ind. Research Bull. 185. 
Rossiter, R. C. 1947a. Australia Council Sci. Ind. Research Bull. 227. 
Rossiter, R. C. 194 7b. J. Council Sci. Ind. Research Australia 20, 389-401. 


Rossiter, R. C. 1951a. Australian J. Agr. Research 2, 1-13. 

Rossiter, R. C. 1951b. Australian J. Agr. Research 2, 14-23. 

Russell, E. J. 1950. Soil Conditions and Plant Growth. Longmans and Green, 8th 

Ed., London. 

Shapter, R. E. 1935. J. Council Sci. Ind. Research Australia 8, 187-194. 
Smith, C. A. Neal. 1942. J. Agr. S. Australia 45, 602-605. 
Stapledon, R. G., Fagau, T. W., Evans, R. E., Milton, W. E. J. 1927. Welsh Plant 

Breeding Sta. Bull. H5. 
Stapledon, R. G. 3928. J. Ecol. 16, 71-104. 
Stapledon, R. G. 1938. Herbage, Revs. 6, 129-145. 
Stephens, C. G. 1949. Brit. Commonwealth Sci. Off. Conf. Agr. (Australia). Ab. 

9 pp. 

Strong, T. 11., and Trumble, IT. C. 1939. Nature 143, 286-287. 
Symon, D. E. 1950. Thesis. Univ. of Adelaide, Australia. 73 pp. 
Taylor, J. K. 1949. The Australian Environment. Australian Commonwealth Sci. 

Research Org. Melbourne, pp. 35-48. 

TeakJe, L. .T. II. 1942. J. Australian Inst. Agr. Sci. 8, 70-72. 

Teakle, L. J. H., and Stewart, A. M. 1939. J. Australian Tnst. Agr. Sci. 5, 50-53. 
Tiver, N. S., and Crocker, R. L. 1951. J. Brit. Grassland Soc. 6, 29-80. 
Trumble, H. C. 1933. J. Agr. S. Australia 37, 400-425. 
Trumble. II. C. 1935. J. Council Sci. Ind. Research Australia 8, 195-202. 
Trumble, II. C. 1937. Trans. Roy. Soc. S. Australia 61, 41-62. 
Trumble, H. C. 1939a. Trans. Roy. Soc. S. Australia 63, 36-43. 
Trumble, II. C. 1939b. J. Agr. S. Australia 42, 953-958. 
Trumble, H. C. 1943. ,/. Australian Inst. Agr Sei. 9, 167-173. 
Trumble, H. C. 1945. Trans. Roy. Soc. S. Australia 69, 16-21. 
Trumble, II. C. 1948. J. Agr. S. Australia 52, 3-27. 
Trumble, II. C. 1949a. The Australian Environment. Australian Commonwealth 

Sci. Ind. Research Org. Melbourne, pp. 116-124. 
Trumble, II. C. 1949b. J. Brit. Grassland Soc. 4, 135-160. 
Trumble, II. C. 1950u. Symposium on Copper Metabolism. Johns Hopkins TJnrvvi- 

sity, Baltimore. 

Trumble, H. C. 1950b. Report of F.A.O. Mission foi Nicaragua. F.A.O. Washing- 
ton Rome. 

Trumble, H. C., and Cashinore, A. B. 1934. Herbage Revs. 2, 1-4. 
Trumble, H. C., and Cornish, E. ^A. 1936. ,/. Council Sci. Ind. Research Australia 

9, 19-28. 
Trumble, II. C., and Davies, I. G. 1934. Australia Council Sei. Ind. Research Bull. 

Trumble, II. C., and Donald, C. M. 1938. Australia Council Sei. Ind. Research Bull. 


Trumble, H. C., and Ferres, H. M. 1946. J. Australian Inst. Agr. Sci. 12, 32-43. 
Trumble, II. C., Strong, T. H., and Shapter, R. E. 1937. Australia Council Sci. Ind. 

Research Bull. 105. 

Twentyman, R. L. 1938. J. Australian Inst. Agr. Set. 4, 210-212. 
Waite Institute. 1950. Waite Agr. Research Inst. Rept. 109 pp. 
Wark, B. C. 1941. Trans. Roy. Soc. S. Australia 65, 249-253. 
Watkins, J. M., and Lewy-van Severen, M. 1951. Agronomy J. 43, 291-296. 
Went, F. W. 1943. Am. J. Botany 30, 157-163. 
Williams, R. F. 1948. Australia J. Sci. Research B 1, 333-361. 


Wood, J. G. 1934. J. Ecol. 22, 69-87. 

Wood, J. G. 1949. The Australian Environment. Australian Commonwealth Sci. 

Tnd. Research Org. Melbourne, pp. 77-96. 

Woodman, II. E., Norman, 1). B., and Bee, J. W. 1928. J. Agr. Sci. 18, 266-296. 
Woodman, H. E., Norman, D. B., and Bee, J. W. ]929. J. Agr. Sci. 19, 236-265. 
Woodroffe, K. 1941. J. Australian Inst. Agr. Sci. 7, 117-121. 
Woodroffe, K. 1949. Brit. Commonwealth *SV?. Off. Conf. Agr. (Australian) D 

16 pp. 

Woodroffe, K. 1951. Private communication. 
Wronger, M. 1934. ZciUchr. f. Bot. 27, 529-564. 

Type of Soil Colloid and the Mineral Nutrition of Plants 

North Carolina Agricultural Experiment Station, Raleigh, North Carolina 



I. Introduction 67 

TT. Approaches to the Study of the Ionic- Envii eminent of Plant "Roots in Soil 70 

1. Ion Exchange 70 

2. Ton Activity 75 

III. Growth and Cation Contents of Plants Grown on Natural and Synthetic 

Soils . . 77 

1. General Considerations 77 

2. Degree of Base Saturation 78 

3. Associated Metal Cations 84 

4. Cation Exchange Capacity 88 

5. The Ecological Array of Plants 91 

IV. Agronomic Applications 93 

References 96 


As has been pointed out by Beeson in his excellent review (Beeson, 
1946), the relation between soils and the mineral composition of crops 
encompasses a host of interrelated factors. Perhaps we are presumptuous 
in attempting to consider one of these factors, the type of soil colloid, as 
though it can stand alone. However, a considerable amount of work has 
shown that plant cation nutrition is definitely related to type of clay, in 
that the ionic environment of plant roots in soils depends to a large 
extent on the amounts and proportions of the various colloidal acids, 
bases, and salts present. 

In contrast to the earlier view that clay minerals could be divided 
into a few discrete groups, it is now well known that large numbers of 
transitional forms exist in soil (Jackson et al., 1948). Nevertheless, for 
the purpose of this review, we wiU consider that soil colloids can be 
divided into the five groups expanding lattice minerals, kaolin minerals, 
hydrous mica minerals, hydrous oxides, and colloidal organic matter. 

The phenomelogical aspects of ion absorption from solution have been 
amply demonstrated by Hoagland et al. (1928); Collander (1941), Becken- 
bach et al. (1938), Beeson et al. (1944), and others (see Iloagland, 1944). 
Such aspects of the absorption process as selective accumulation are out- 



side the scope of this review. Others, such as the effect of ion supply and 
of competition between various cations, are pertinent. 

It is well established that there is a rough proportionality between 
the concentration of a given cation in a plant and that of the nutrient 
solution in which it was grown. Beeson et aL (1944), through the use of 
elegant statistical techniques, have shown that around 80 per cent of the 
variation in Ca, Mg, and K contents of tomato plants grown in nutrient so- 
lutions could be ascribed to variations in the supply of these and other ions. 
Not only was content of a given ion found to be correlated with its own 
supply, but also in some cases positive or negative correlations with the 
supply of a second ion was indicated. Thus, Ca content increased regu- 
larly with Ca supply at a given level of K, but decreased when K supply 
increased and Ca supply was held constant. 

The latter observation is an example of so-called ion antagonism or 
ion competition, which has been noted by many investigators. Hoagland 
et al. (1928) found from studies with Nitella that an increase in the rela- 
tive concentration of one metal cation in a culture solution resulted in 
decreased uptake of the other metal cations present. That this principle 
is applicable to many situations has been shown by Lundegardh (1949), 
Chapman and Brown (1948), Hunter (1943), Hoagland (1944), Matt- 
son (1948), and Leonard et aL (1948). In general, Na and particularly 
K are very effective competitors, and if present in large proportions 
they greatly decrease the Ca and Mg contents of plants. Competition 
between Ca and Mg is usually somewhat less marked, as is the depressing 
effect of Ca and Mg on K content. Collander (1941) noted great competi- 
tion between pairs of chemically similar ions such as K and Kb, Ca and Sr. 
Beeson ct al. (1944) have observed instances in which such ion competition 
was of minor importance. Pierre and Bower (1943) , considering the effect 
of Ca on the absorption of K, conclude that Ca may increase K absorp- 
tion when K is high and the ratio Ca : K is low (the Viets effect, Viets, 
1944) or when Na is high as compared with K, but that Ca reduces K 
absorption when Ca is present in high concentration. 

The effect of hydrogen ion concentration (pll) on ion absorption 
from nutrient solution has been studied thoroughly by Arnon et al. 
(1942) and by Arnon and Johnson (1942). They found Ca absorption 
by tomato, lettuce, and Bermuda grass to be relatively constant between 
pll 5 and 9, but to be significantly lower between pH 4 and 5. In this 
lower pll range, an increase in the Ca concentration of the culture 
solution overcame the deleterious effects of low pll on Ca absorption and 
on the growth of tomato and lettuce. Magnesium and K absorption also 
tended to be less in the pll range 4-5 than in the range 5-9, but the 
differences were not so large as those observed with Ca. De Turk (1941) 


reported much more substantial changes in Ca absorption by red clover 
with changes in pH. Increasing pH from 5 to 7 resulted in a twenty- 
fold increase in Ca absoption from a solution containing 150 p. p.m. Ca. 

Arnon et al. (1942) observed that plants actually lost metal cations 
to culture solutions at pH 3. Recently Jacobson et al. (1950) have 
observed appreciable losses of K from excised barley roots to HC1 
solutions below pH 4.5. Loss of K was very large at pH 3, but loss 
could be decreased and even changed to accumulation by addition of 
high concentrations of KC1 to the IIC1 solution. They interpret this as 
evidence for a reversible chemical reaction involving the exchange of K 
and H in roots. 

While the relationships between ion concentrations and ratios in cul- 
ture solutions and in plants are by no means completely defined, the 
general concepts presented above will serve as reference points in the 
consideration of ion absorption from soils and clays. 

In the study of ion absorption by plants from soils and clays we are 
concerned not only with the effect of ion concentrations and ratios (pos- 
sibly activities and activity ratios) on the plant. We must consider as 
well the problem of defining and measuring the effective ion concentra- 
tions in the soil. The idea of a static soil solution from which plants 
obtain their mineral elements has long been discarded. Regardless of 
the mechanism envisioned to be operative in the transfer of metal cations 
from the soil to the roots of plants, w r e must look upon the exchangeable 
ions as being the immediate source of cationic plant nutrients in most 

To illustrate the problem we will quote some recent observations of 
Mattson (1948). Mattson grew barley plants in three systems, nutrient 
solutions, kaolinite, and bentonite-sand mixtures. K and Ca were added 


Composition of Three-Week Old Barley Plants Grown in Nutrient Solutions, 
in Kaolinite, and Bentonite-8and Mixtures , 


Concentration * 


Content, me. per 

100 g. 








K Ca 







141.0 46.5 







195.5 32.4 







190.2 20.8 






22 2 

200.0 16.3 







208.1 10.5 



* Milhequivalents per liter of cultural solution, or milhequivalents per pot (300 g ) 


as chlorides to the solutions, and as exchangeable ions to the clay systems. 
N, P, Mg, and Fe were constant. Table I shows the quantities of K and 
Ca supplied and the amounts of these ions in the plants grown on each 
substrate. Note that K and Ca delivery from the nutrient solutions and 
from the clays differs, and that there are large differences, particularly 
with respect to Ca delivery, between the two clays. Each clay had a 
distinctive influence on the effective concentrations of Ca and K. As 
Marshall (1944b) has pointed out, in order to define the ionic environ- 
ment of plant roots in soils, we must consider not the total concentrations 
but the effective concentrations of the various ionic species present. 
Two general lines of experimental attack have been followed in attempts 
to delineate the role of the soil or of colloidal clay in influencing the 
effective ion concentrations. The one embodies the study of ion exchange 
reactions, the other the measurement of single-ion activities. 


1. Ion Exchange 

The general nature of the ion exchange process has been thoroughly 
treated elsewhere (Davis, 1945; Kelley, 1948; Gieseking, 1949; Krish- 
namoorthy and Overstreet, 1949, 1950a, 1950b). We shall discuss only 
those aspects which have bearing on the present problem, i.e., those 
which deal with the adsorption and release of cations as related to type 
of clay. 

Jenny (1932) and Giesekirig and Jenny (1936) made an exten- 
sive study of the exchange-adsorption of various ions by Putnam clay 
(beidellite). The order of the common cations for ease of entry was 
Li<Na<K<Mg<Ca<H. Jenny (3932) also observed that relative to 
the metal cations hydrogen was adsorbed less strongly by bentonite than 
by Putnam clay. Jarusov (1937) measured the "mobility" (exchange- 
ability for K+ ) of various metal cations adsorbed on several soils. He 
concluded that the exchangeability of a particular ion was related not 
only to its degree of saturation and the nature of the other exchangeable 
ions, but also depended on the nature of the exchange complex. Thus he 
found the exchangeability of Ca to be much greater in a laterite than in 
a chernozem, and the exchangeability of both H and Ca to be greater in 
a chernozem from which organic matter had been removed than in the 
natural soil. 

A comprehensive study of ion exchange with several minerals and 
with organic soil colloids was reported by Schachtschabel (1940). He 


found relative ion affinities, measured by adding 1 symmetry concentra- 
tion of alkali or alkali earth chlorides to NH 4 clay, to be : 

Montmorillonite Li<Na<K<II<Mg<Ca 
Kaolinite Li<Na<II<K<Mg=Ca 

Ground muscovite Li<Na<Mg<Ca<K<H 

Such series as are listed above are found to vary somewhat with the 
concentration of the salt solution and with the ion initially adsorbed on 
the clay (Jenny, 1932; Schachtsehabel, 1940; Vanselow, 1932), but dif- 
ferences between types of clay are evident, regardless of such effects. 

Schachtschabel was especially impressed with the differences in the 
selective adsorption of NH 4 and Ca by montmorillonite, kaolinite, and 
organic colloids on the one hand and by ground micas on the other. 
After leaching with a mixture of equimolar solutions of NH 4 and Ca 
acetates he found the ratio Ca absorbed: NH 4 adsorbed to be 11.3 and 
10.3 for two samples of organic matter, 1.71 for montmorillonite, 1.42 
for kaolinite, and 0.066 for ground muscovite. Hendricks and Alex- 
ander (1940), however, did not observe such large differences between 
montmorillonite and three micaceous minerals, sericite, glauconite, and 
illite. They did find, in agreement with Schachtschabel, that II is more 
strongly adsorbed by micaceous minerals than by montmorillonite. 

The data considered above show that there are large differences in the 
exchange properties of the several colloidal materials studied. They 
have served as a foundation for subsequent work on the relative affinities 
of the various common cations for the several types of clay. 

Mehlich (1941) presented titration curves of various H clays. The 
pH-degree of base saturation relationships for the different types of clay 
are quite characteristic. Similar observations have been made by Mitra 
ct al. (1943), Muckherjee et al. (1943), and others. Such observations 
may be interpreted as reflecting different relative affinities of the various 
clays for H and for the alkali earth cations employed in the titration. 
Thus, montmorillonite may be inferred to have a relatively high affinity 
for Ca or Ba and kaolinite for II, whereas beidellite, halloysite, and il- 
lite are intermediate. Mehlich (1941) observed that while humic acid 
has a titration curve much like that of montmorillonite, the pH-base 
saturation relationships of a muck soil are similar to those of halloysite 
and kaolinite. 

Elgabaly et al. (1943) observed that addition of 1 symmetry HC1 
released more Zn from Zn-saturated kaolinite than from bentonite. Simi- 
larly, more K was replaced from K-kaolinite than from bentonite. 
Extraction of homoionic clays with C0 2 saturated H 2 O (essentially 
replacement with H 2 C0 3 ) resulted again in greater release of Zn from 



kaolinite than from bentonite, and of K from Aiken clay (kaolinitic) 
than from Yolo clay (montmorillonitic). 

Mehlich and Col well (1943) measured the release by 1 symmetry 
HC1 of Ca and Mg from several soils with identical degrees of Ca and 
Mg saturation. Release was greatest from organic and kaolinitic soils 
and decreased as the proportion of montmorillonite in the soils increased. 
The ratio Ca released : Mg released was higher for kaolinitic and muck 
soils than for montmorillonitic soils, though this may reflect a solution 
of nonexchangeable Mg from the latter rather than a difference in the 
relative affinities of the several colloids for Ca and Mg. 

Allaway (1945) found that addition of HC1 equivalent to exchange- 
able Ca at various degrees of Ca saturation resulted in widely different 
amounts of Ca release from several clays. The order of decreasing re- 
lease was: pea t>kaolinite> Wyoming bentonite >illite> Mississippi ben- 

Differences between clays were marked, as is shown in Fig. 1. 
Allaway also reported results of replacement of Ca from various clays by 
BaClo. Differences between types of clay were small in this case, indi- 










80 20 40 

Per cent Ca saturation 



-i 80 









FIG. 1. Per cent Ca replaced by an equivalent amount of HC1 as affected by type 
of colloid and percentage Ca saturation. (Data on left taken from Allaway, 1945; 
data on right taken from Mehlich, 1946.) 


eating perhaps that it is the affinity for H in which the several clays 
differ most. 

Mehlich (1946) studied the release of Ca from various clays when 
HC1 equivalent to the exchangeable Ca was added. His findings are 
qualitatively similar to those of Allaway (1945). The order of release at 
all degrees of Ca saturation (Fig. 1) was: hall 6ysite> peat >kaolinite> 
illite>beidellite>montmorillonite. This order was unchanged when 
HC1 was added in small but constant amounts to the various clays, 
rather than in amounts equivalent to the exchangeable Ca. 

With reference to the clays used by Mehlich (1946), we have more 
recently found from electron micrographs that the "kaolinite" referred 
to in Fig. 1 is actually halloysite. This finding in no way changes the 
significance of the results. In relation to H, Ca is much more strongly ad- 
sorbed by expanding lattice clays than by kaolinitic clays and organic 

Recently Krishnamoorthy and Overstreet (1949, 1950a, 1950b) have 
propounded a theory which seems to describe satisfactorily ion exchange 
equilibria in a variety of clys and other exchange materials. Experi- 
mentally they found (1950a) that the exchange constant for a given ion 
pair varies considerably from one exchange material to another. For 
K-Ca exchange, as an example, their data gives exchange constants of 
0.057 for bentonite, 0.09] for Yolo clay (montrnorillonitic), 0.098 for 
Hanford clay (micaceous), and 0340 for Aiken clay (kaolinitic). For 
ion exchange involving H, Krishnamoorthy and Overstreet (1950b) 
found the active mass of adsorbed H to vary in a manner suggestive of 
"surface ioriization. " Thus, the effectiveness of II in replacing metal 
cations from various clays would be characteristically affected by the 
degree of base saturation. 

The studies cited above include the most ambitious attempts to de- 
lineate the role of type of clay in cation exchange. It is still pertinent 
to mention a few observations which support the general thesis that type 
of colloid plays a major role in clay-electrolyte interactions. 

Vanselow (1932) compared equilibrium constants for Ca-NH 4 ex- 
change with bentonite and with an oxidized Hawaiian soil and concluded 
that there must be at least two kinds of soil clays, one with a relatively 
greater affinity for Ca than for NH 4 . Bentonite, as compared with the Ha- 
waiian clay, held Ca very strongly against ion exchange [compare with 
Krishnamoorthy and Overstreet (1950a) data for bentonite and Aiken 
clay]. Harward (unpublished data), working in the authors' laboratory, 
has found Ca-K exchange equilibrium constants to be very similar for hal- 
loysite and kaolinite. Montrnorillonite, on the other hand, gives Ca-K 


constants which indicate greater relative affinity for Ca than is the case 
with the kaolinitic clays. 

An interesting approach to the problem of relative ion affinities and 
type of clay has been made by Mattson and his students (Mattson, 1948 ; 
Elgabaly and Wiklander, 1949). They believe that differences between 
the affinities of mono- and divalent ions for different clays depend upon 
the exchange capacity of the clay. They base this belief on a hypo- 
thetical Donnan distribution of ions between an "inside solution/' that 
portion of the clay-water-electrolyte system occupied by the ionic double 
layers, and an "outside solution" consisting of intermicellar liquid. If 
one sets up Donnan equilibrium expressions to describe the distribution 
of mono- and divalent ions between the " inside " and " outside " solu- 
tions, one reaches the conclusion that for a given ion ratio in the "out- 
side solution," the greater the sum of the ion activities in the "inside 
solution" the larger will be the ratio of divalent ion : monovalent ion 
"inside," and the greater will be the proportion of the divalent ion in 
the exchangeable ions. Mattson (1948) cites as an example of this an 
exchangeable Ca: Nil, ratio of 8.4 for bentonite (exchange capacity 
90 me. per 100 g.) as compared with a ratio of 3.3 for kaolinite (exchange 
capacity 3.5 me. per 100 g.), both clays being in equilibrium with a solu- 
tion 0.005 N with respect to both ( 1 a and NII 4 . Mattson concludes, "if 
two soils having different cation exchange capacities (due to different 
acidoid content or strength), contain the same proportion of a monova- 
lent and a divalent ion, then the soil with the higher exchange capacity 
should yield its monovalent ions more readily and its divalent ions less 
readily than the soil having the lower exchange capacity." 

Although the Donnan equilibrium has been used by Mattson and his 
co-workers to explain many ion exchange phenomena in soils, Davis' 
(1942) stand that we are dealing with immeasurable quantities when we 
speak of ion activities, particularly in the "inside solution," should be 
reemphasized. Any conclusions drawn from Mattson 's theory seem to be 
qualitative, at best. 

A second point made by Wiklander (1946) concerns the position of 
II in the lyotropic series for exchange-adsorption. The point is that II 
apparently varies in its ability to replace metal cations, depending on 
whether the ion exchanger in question behaves as a weak or a strong 
acid. This has been pointed out before (Jenny, 1932; Allaway, 1945; 
Mehlich, 1946). Marshall and Krinbill (1942) give the order of increas- 
ing strength of clay acids as: montmorillonite>beidellite>illite> kaolin- 
ite. Their affinity for II would then be in the opposite order. As 
pointed out by Krishnamoorthy and Overstreet (1950b) ; however, affin- 
ity for II depends more on degree of base saturation than does affinity 


for metal cations. Thus, the series quoted above might be modified by 
degree of base saturation. 

From the above cited work we are certainly justified in saying that 
there are major differences in the relative exchangeability of various 
ion pairs when adsorbed on different types of clay. The differences are 
especially pronounced for ions of different valence, i.e., Ca and K, for 
pairs of which II is one member. The extremes are represented by 
kaolinite on the one hand and the expanding lattice clays on the other. 
Quite understandably, there is considerable overlapping between the ex- 
change properties of the expanding lattice clays on the beidellite end of 
the series and the so-called hydrous mica minerals. The lack of quanti- 
tative agreement between the results of different experimenters may be 
attributed in part to differences in experimental techniques and in part 
to the fact that they used different specimens as typical of a particular 

The conclusions reached from consideration of the experiments cited 
above are not in agreement with those of Melsted and Bray (1947), who 
seem to believe that ion exchange in all clays may be described by con- 
sidering concentrations and relative affinities of ions, the relative affini- 
ties being characteristics of the ions alone, and not affected by type of 

2. Ion Activity 

Marshall and his associates (Marshall, 1939, 1942, 1944a, 1944b, 
1948a, 1948b, 1950; Marshall and Bergman, 1941, 1942a, 1942b; Mar- 
shall and Ayers, 1946, 1948; Marshall and Eimo, 1948; Mar-shall and 
Barber, 1949; McLean and Marshall, 1948; McLean, 1949), using clay 
membrane electrodes, have made a number of measurements of single- 
ion activities in clay suspensions. To date they have been able to handle 
systems containing a maximum of two metal cations in addition to the 
omnipresent hydrogen ion. Eecently, Peech and Scott (1950) and 
Schuffelen and co-workers (Schuffelen and Loosjes, 1942; Schuffelen, 
1944, 1948; Schuffelen and Barendregt, 1946), have constructed cells in 
which the alleged Donrian potential between a clay or soil suspension 
and its equilibrium dialyzate could be measured. From the measured 
potential and the analytically determined concentrations of cations in the 
liquid phase they have been able to calculate single-ion activities identi- 
cal with those measured by Marshall. This latter scheme seems more 
flexible and more adaptable to heteroionic systems, though it lacks the 
attractive simplicity of the membrane electrode method. 

Some far-reaching inferences have been drawn between measured ion 
activities and the cationic nutrition of plants (Marshall, 1944, 1948b, 


1950; McLean, 1949; Schuffelen, 1948). Marshall (1948b), for example, 
states, "The differences . . . between the kaolinite and montmorillonite 
groups of clays on the one hand and between monovalent and divalent 
cations on the other, are destined to be of especial importance in soil 
science, plant nutrition, and plant ecology. . . . the uptake of cationic 
nutrients from the soil is a function of the activities of the ions with 
which the growing root is in contact. . . ." 

Most of the measurements of single-ion activities in clay suspensions 
have been made by Marshall and his students. The results which are 
pertinent to the present subject are summarized briefly below. 

Considering first the ion activities in homoionic clay suspensions, at 
constant cation concentration, the activities of the alkali metal cations 
decrease in the order : kaolinite > montmorillonite >beidellite>il lite 
(Marshall, 1950). Differences between the activities of the alkaline earth 
cations are more pronounced, and decrease in the order: kaolinite >illite 
>mortmorillonite>beidellite (Marshall and Ayers, 1948; Marshall and 
Eime, 1948). The above generalizations refer only to clays at the equi- 
valence point. The changes in cation activity when li clays are pro- 
gressively neutralized are distinctive for each clay mineral (Marshall, 

With regard to the difference in activity of various ions associated 
with a given clay mineral, the order at the equivalent point is Na>K> 
NH 4 for kaolinite and montmorillonite, K>NH 4 >Na for illite. For 
the divalent ions above 70 per cent saturation, Ca montmorillonite, kao- 
Jinite, beidellite, and illite ionize more extensively than do the corre- 
sponding Mg clays. Below 70 per cent saturation Ca is more ionized 
from montmorillonite and kaolinite, while the reverse is true for beidel- 
lite. Illite in this range shows almost equal ionization of the two cations 
(Marshall, 1950). 

McLean (1949) and Marshall and Barber (1949) have studied bi- 
ionic clays containing various ion combinations. With montmorillonite, 
substitution of Ca for II greatly increases K activity. Conversely, sub- 
stitution of K for II decreases Ca activity, particularly at low levels of 
Ca saturation. With kaolinite, K activity is also greater when Ca rather 
than H is the complementary ion. In contrast with montmorillonite, 
however, the activity of Ca is considerably increased when K is substi- 
tuted for H. In its Ca-H-K relationships, halloysite is found to be quite 
similar to kaolinite. 

Beidellite and illite are similar in their behavior with regard to ion 
activities in biionic systems. Ca as compared with H, increases the 
activity of K. At high degrees of Ca saturation, Ca activity is greater 


in Ca-K clay than in Ca-H clay, whereas the reverse is true at lower 
degree of saturation. 

Qualitative correspondence between the behavior of Ca-H-K systems 
and Mg-II-K systems has been noted (Marshall, 1950). The activity of 
potassium in K-Mg clay, however, is not so high as that in K-Ca clay 
with the same ion ratios (McLean and Marshall, 1948; McLean, 1949). 

Marshall and Barber (1949) have summarized K-Ca activity ratios 
as related to exchangeable ion ratios for a number of clays. For a given 
ratio of exchangeable ions, montmorillonites have high A K /Ac H ratios, 
kaolinite has low ratios, and illites, beidellite, and halloysite are inter- 
mediate. It is pertinent, perhaps, to note that the differences observed 
by Marshall and Barber between Iwo samples of montmoriJlonite and 
between two samples of illitc are large as compared with the differences 
between mineral species. Perhaps it is unsafe to generalize on the 
basis of the few data we have at hand. 

It is only fair to point out that from strict thermodynamic princi- 
ples it can be argued that measurements made with cells as are used by 
Marshall, Peech, and Schuffelen have no significance (Guggenheim, 
1929). This has recently been emphasized by Low (1951) for the case 
of soils and by Jenny ct aL (1950) for colloidal systems in general. The 
test of the usefulness of single-ion activity measurements in clays and 
soils in making predictions concerning rates of cation absorption by and 
mineral composition of rooted green plants has not yet been made. 


1. General Considerations 

The ability of plants to utilize soil exchangeable cations is no longer 
questioned. This was first established by Nostitz (1925) and was soon 
confirmed by Joffe and McLean (1927), Gedroiz (1930), and Jenny and 
Cowan (1933). A great deal of subsequent work was concerned with 
the effect of the concentration and distribution of exchangeable cations 
on the growth and mineral composition of plants. Growth of plants in 
response to liming and fertilization of different soil types was studied 
as well, and certain broad differences between soil types became appar- 
ent. Thus, Alway and Nygard (1927) found alfalfa to make optimum 
growth on peat soils with pll as low as 4.5, whereas a pH at least as 
high as 5.7 was required for similar growth on mineral soils. Austin 
(1930) found the soil type more influential in determining the composi- 
tion of soybeans growing thereon than the application of moderate 


amounts of fertilizer. Some ten years ago Vandecaveye (1940) sum- 
marized the current status of knowledge concerning plant composition- 
type of soil interactions as follows: ' 4 It is evident that the chemical 
composition of grasses, small grains, and legumes is influenced to a sig- 
nificant extent by certain broad soil properties, but it is obvious also that 
the specific soil factors which are responsible for changes in the composi- 
tion of these crops need further investigation." Since 1940 considerable 
attention has been devoted to the problem of identifying and studying 
the soil factors to which Vandecaveye refers. 

After the discovery that, in addition to organic exchange colloids, the 
clay minerals of the montmorillonite, kaolinite, and hydrous mica groups 
occurred in large amounts in soils, it was a logical consequence that these 
minerals would be studied in relation to inorganic plant nutrition. Of 
course, type of colloid is but one of the variables entering into soil-plant 
nutrition relationships. Intimately associated with type of colloid 
effects are the effects of degree of base saturation, competition of ions 
for adsorption and release, and cation exchange capacity. In addition, 
since this paper is concerned mainly with certain soil factors which 
affect in one way or another the availability of ions to plants, we cannot 
avoid occasional excursions into the realm of the plant physiologists. 
The interactions between different plant species and different soil ex- 
change materials are a very important part of the type of colloid effect. 

2. Degree of Base Saturation 

Degree of base saturation was defined by Hissink (1922) as 100$/T, 
where 8 is the sum of the exchangeable metal cations and T is the 
cation exchange capacity. The most generally accepted definition of 
the latter, due to Bradfield and Allison (1933), is the sum of the bases 
held in exchangeable form by a soil which has reached equilibrium with 
a surplus of CaC0 3 at the- partial pressure of 00 2 existing in the at- 
mosphere and at a temperature of 25 C. The difference between T and 
8 is generally designated as exchangeable H, though considerable evi- 
dence exists (Paver and Marshall, 1934; Muckerjee et al., 1947) that 
exchangeable Al comprises a large part of the ions on base-unsaturated 

Base-saturated soils have pH values in the range 8-8.5. According 
to Radu (1940), kaolinitic clays require a higher pH for complete base 
saturation than do montmorillonites. With decreasing degree of base 
saturation this difference in pH persists, and for a given per cent satura- 
tion, montmorillonitic clays invariably have a lower pH than do kao- 
linitic clays. The consequences of the differences in the pH-per cent base 
saturation relationships in the growth and cation content of plants are 


far reaching. Before considering these relationships more fully an 
examination of the soil-plant root system is in order. 

In discussing inorganic plant nutrition as related to ion uptake from 
soils it is desirable to consider soil and plant together as a system. As 
early as 1928 Kostychew (quoted by Scheffer, 1946, p. 117) suggested 
that in the process of ion absorption two colloidal systems, the soil and 
the plant root, are involved. Scheffer concludes that it is reasonable to 
assume that ion uptake will depend in large measure on the properties 
of the two colloidal systems involved and on the interactions between 
them. Recently Williams and Coleman (1950) and Drake et al. (1951) 
have shown experimentally that plant roots actually have cation ex- 
change capacities of considerable magnitude. 

These findings coincide to some extent with the views of Lundegardh 
(1949, p. 327), who assumes the first step in the absorption of cations 
by plant roots to be exchange adsorption of the ions concerned on the 
surface of the root protoplasm. Such an exchange presumably would 
involve substrate metal cations and metabolically produced H ions. 
Lundegardh obtained evidence that the process thought to be exchange 
adsorption of metal cations by roots follows the mass action law. Re- 
cently Schuffeleri arid Loosjes (1942) have successfully described the 
course of ion absorption by excised barley roots by means of an equa- 
tion based on an adsorption hypothesis. 

To explain some observations with regard to K absorption by, and 
outgo from, excised barley roots, Jacobson et aL (1950) have postulated 
the reaction : 

in which HR is a product of root metabolism and serves as a K-binding 
compound in the absorption of K. Of particular significance is their 
finding that the above reaction is reversible, that is, K is lost from the 
roots in acid media. 

In view of the above current ideas concerning the process of ion 
absorption by plant roots, it is apparent that the effective concentration 
of H ions in the substrate is perhaps as important as the effective con- 
centration of the metal cations whose uptake is being considered. 

In addition to H+ derived from root compounds such as those 
postulated by Lundeg&rdh (1949) and Jacobson et a!. (1950), large 
amounts of metabolically produced CO 2 enter the soil. This CO 2 , when 
dissolved in the soil solution, furnishes further H ions. For root me- 
tabolic activity to continue, this C(>2 and its engendered acidity must be 
removed. In culture solutions this is accomplished by aeration, together 
with the use of salts which buffer the solution against great fluctuations 



in acidity. In soils, the colloids serve as buffers through the exchange 
adsorption of root-produced H ions. 

The amount of II" 1 " produced by the roots of various plant species 
varies greatly. Vageler (quoted by Seheffer, 1946, p. 124) has estimated 
the range to be between 3.6 Ib. of II + per acre produced by small grains 
and 22 Ib. per acre produced by cotton. In most instances root-pro- 
duced 00 2 , on the basis of chemical equivalents, exceeds many fold the 
amount of metal cations absorbed by the plants. This root factor was 
taken into consideration by Truog (1918) in the classification of plant 
species according to their "feeding power." Newton (1923) and 
Mehlich and Reed (1948a) considered the relationship between (/O 2 pro- 
duced by roots and the amounts and proportions of various metal cations 
taken up by different plant species. They concluded that species the 
roots of which produce large amounts of ((_). are high in total metal 
cations and contain a high proportion of divalent cations, as compared 
with species the roots of which produce smaller amounts of (H) L >. 

Mattson (1948) and Drake et al. (1951) have observed that in gen- 
eral the same plant species which evolve large amounts of C0 2 and 
which contain high proportions of divalent cations also have roots of 
high cation exchange capacity. This is shown in Table II. The general 
correspondence between C() 2 production and root exchange capacity, as 

Some Properties of Hoots of Various Plant Species 

Energy for 



CO 2 


Ions from 

Respiration t 

Capacity i 


Minerals * 

mg./g. in 24 hrs. 

me./lOO g. 






Very small 




Fairly high 








Fairly high 




Very high 






Sugar beets 



Field peas 

Very high 



Red clover 





Very high 






* After Rerny; reported by Scheffer (1946), p. 134. 
t After Stoklasa, reported by Scheffer (1946), p. 134. 
t After Drake et al. (1951). 


well as the general agreement of both with the cation absorption proper- 
ties of the various species, is apparent. Not so apparent, however, is 
which factor, (H) 2 production or root exchange capacity, is of more 
significance in affecting the amounts and proportions of metal cations 
absorbed by plants. 

Undoubtedly the fate of root-produced 11+ is intimately related to 
ion absorption. Overstreet and Jenny (1939), for example, measured 
rates of accumulation of Na by excised barley roots from equal concen- 
trations of NaCl, Nai>(JO 3 , and Na clay. At the lower levels of Na, up- 
take increased in the order given. At higher levels of Na, approximately 
the same uptake from each source was observed. Considering the 
exchange of root H + for substrate Na + , the substrate end products are 
completely ionized 1IC1, partially ionized II 2 CO3, and partially ionized 
II clay. From what has been said earlier about the mechanism of ion 
absorption by plant roots, it seems that the greater uptake of Na from 
NallCOa and Na clay than from NaCJ may have been due to the partial 
immobilization of H ( in the former systems, that is, the less completely 
ionized the acid formed in the substrate, the greater the uptake of metal 
cations. This factor is of greatest significance in dilute systems, in 
which the proportion of acid formed to salt present is fairly large. As 
shown by the similar rates of uptake observed by Overstreet and Jenny 
(1939) from the three sources at high levels of Na, it is of little im- 
portance when substrate salt concentrations are high. The idea of 
substrate H + decelerating rates of ion absorption seems valid, in view 
of the previously quoted work of Arnon et al. (1942) and Jacobson et al. 

The various types of soil colloids appear to vary widely in their 
apparent acid strength. Marshall (1944) has given the order of II 
ionization from clay minerals as kaolinite<illite<montmorillonite. 
Organic soil colloids probably belong near kaolinite in this series (Alla- 
way, 1945; Mehlich, 1946). 

The apparent differences in acid strength noted above are reflected 
by very different pH values for the several colloidal materials at a given 
per cent base saturation. As an example, Mehlich (1941) found the plf 
at 25 per cent Ca saturation to be 5.3 for kaolinite, 3.8 for inontmoril- 
lonite, 3.9 for illite, and 4.8 for a muck soil. It is not surprising, then, 
that crops are known to grow successfully at lower degrees of saturation 
on kaolinitic than on montmorillonitic soils. While not discounting the 
possible toxic effects of Al and Mn (Schmehl ct al., 1950) on plants 
grown in acid soils, it seems that high effective concentrations of H + 
may have a serious depressing effect on the rate of uptake of metal 
cations from soils. Jarusov (1938) found the exchangeability of II to 


increase with increase in II saturation (fall in base saturation). The 
yield of mustard also decreased as exchangeable II rose. 

A point related to this subject concerns the failure of CaSO 4 to 
improve plant growth on acid soils where Ca may be presumed to be a 
limiting factor (Fried and Peech, 1946; Lineberry and Burkhart, 
1951; Welch and Nelson, 1950). Since addition of this salt serves to 
replace II ions from the acid clay, its use may make worse rather than 
better the ratio of the effective concentrations of metal cations to that 
of II+. An exception to the generalization that CaSO 4 additions to acid 
soils do not increase Ca uptake is found in work with Oa absorption by 
peanut fruit. In this case CaSO 4 additions are extremely efficacious in 
increasing the Ca content of the fruit (Mehlich and Reed, 1946; Reed 
and Cummings, 1948). Application of gypsum to peanuts is standard 
agricultural practice. A possible explanation for this divergence from 
the ordinary lies in the low metabolic activity and H+ production of 
peanut pegs as compared with plant roots. 

In view of the previous considerations and in light of the fact that 
montmorillonitic clays behave as stronger acids than do kaolinitic clays, 
it seems that the former will be less efficient in lowering the effective 
concentration of root-produced H f and thus will require a higher degree 
of base saturation for optimum cation availability and plant growth 
than will the latter. In addition, Marshall (1948) measures the active 
fractions of exchangeable alkali and alkaline earth cations to be smaller 
in montmorillonitic than in kaolinitic systems, particularly at low de- 
grees of base saturation. It is not surprising, then, that all evidence 
bearing on the subject of cation availability from various types of soils 
and clays is in essential agreement in showing the necessity for a higher 
degree of base saturation with montmorillonitic materials than with 
kaolinites. Mehlich and Colwell (1943, 1946), Allaway (1945), and Chu 
and Turk (1949) have all obtained evidence which agrees in this respect. 
Mehlich and Colwell and Allaway obtained results for Ca uptake by 
plants from various clay systems which closely paralleled the chemical 
release data shown earlier in Fig. 1. That is, Ca uptake by plants, as 
well as growth, increased rapidly as the degree of Ca saturation of 
kaolinitic materials increased to about 40 per cent, but showed only 
small increases with higher percentages of Ca. With montmorillonites, 
on the other hand, growth and Ca content of the plants did not reach 
maximum values until about 80 per cent Ca saturation. 

It has generally been found that organic colloids are more like kaolinitic 
clays than like montmorillonites with respect to degree of Ca saturation 
necessary for optimum plant growth. This similarity to kaolinite has 
already been mentioned with respect to pH-per cent saturation relation- 


ships and with respect to the release of metal cations by II + . However, 
it is not possible to generalize concerning the relative availability of Ca 
from kaolinitic and organic soil colloids. Allaway (1945) found more 
Ca in soybeans grown on peat than in those grown on kaolinite with the 
*ame per cent Ca saturation and the same level of total Ca. Mehiich 
and Colwell (1943) also found soybeans to contain slightly more Ca 
when grown on peat than when grown on a kaolinitic soil when the 
nation exchange capacity was very low (2 me. per 100 g.), but found the 
reverse to be true when the cation exchange capacity was 4 me. per 100 g. 

Mehiich and Reed (1946), working with peanuts, found consistently 
higher fruit quality and a higher Ca content of the shells when the fruit- 
ing medium was kaolinitic than when it was organic. Peanut plants, 
however, contained more Ca when grown in organic rather than in 
kaolinitic media. Water-soluble Ca was found to be higher in the 
kaolinitic systems, and the authors suggested, in line with the effect of 
gypsum on peanut fruiting, that Ca absorption by peanut fruit is pro- 
portional to solution concentration of Ca. 

Mehiich (1952) has suggested that the presence in soils of hydrous 
oxides of Fe and Al may modify Ca availability-per cent base saturation 
relationships for the various clays. 

The evidence we have thus far considered deals largely with the 
influence of degree of base saturation on Ca availability to plants. In 
general, Ca absorption and plant growth increases as the degree of Ca 
saturation rises. The degree of Ca saturation necessary for optimum 
growth varies with plant species, but it is generally higher for montmoril- 
lonitic than for kaolinitic clays. This is in essential agreement with the 
chemical release data and ion activity data cited earlier. According to 
Chu and Turk (1949), soils containing hydrous mica clays may require 
sven higher degrees of Ca saturation than montmorillonite. Chemical 
studies generally have indicated, however, that in this respect illite 
should be intermediate between montmorillonite and kaolinite. 

Data of several investigators have shown that the availability of Mg 
^nd K also increases with degree of base saturation, the soil ratio of 
Ca : K and Ca, : Mg remaining constant as degree of saturation is increased. 
Thus Chu and Turk (1949) found the K and Mg content of oats and rye 
?rown on bentonite-sand mixtures to increase several-fold as degree of 
base saturation rose from 20 to 80 per cent. Raising K and Mg levels 
[>f the substrate by increasing the exchange capacity (adding more clay 
at the same degree of saturation) resulted in much smaller increases in 
the contents of these cations in the plant. It seems, then, that with 
regard to cation availability from montmorillonitic clays, at least, de- 
gree of base saturation is an exceedingly important factor. 


In the case of oats and rye grown on kaolinite-saiid mixtures, Chu and 
Turk (1949) observed no such striking increases in Mg and K contents 
with increase in degree of base saturation. As Mehlich and Colwell 
(1943) have previously stated, cation availability from montmorillonitic 
clays seems dependent on degree of base saturation, whereas in the case 
of kaolinitic clays, though per cent base saturation may still be im- 
portant, cation availability is more nearly proportional to the total 
amounts of the ions present. 

Epstein and Stout (1951) have related the uptake by tomato plants 
of certain bentonite-adsorbed micronutrient cations (Fe, Mn, Zn, Cn) to 
their degrees of saturation. At low percentages of saturation (<0.1 
per cent), the amounts of these elements absorbed by plants were found 
to be nearly proportional to the degree of saturation of the ion in ques- 
tion. It appears, then, that per cent saturation is important when deal- 
ing with the availability of the so-called minor elements, as well as that 
of Ca, Mg, and K. 

The plant experiments cited thus far have been concerned almost 
entirely with cation absorption from partially base-saturated systems. 
The effect of type of colloid has been striking. When dealing with 
completely base-saturated systems, the effect of type of colloid on the 
uptake of cations by plants seems less pronounced and rather incon- 
sistent. Mattson (1948) and Mattson et al. (1949), working with com- 
pletely base-saturated clays in which OH and K were varied reciprocally 
from 10 to 90 per cent saturation of each ion, found pea and barley 
plants to contain consistently more Ca when grown on kaolinitic clay than 
when grown on montmorillonitic clay. This is in agreement with most 
findings. In a subsequent report from the same laboratory (Elgabaly 
and Wiklander, 1949), however, a somewhat similar experiment in which 
excised barley roots were used as cation accumulators showed more Ca 
to be taken up from Ca-Na montmorillonite than from Ca-Na kaolinite. 
Elgabaly et al. (1943) found greater absorption of K and Zn by excised 
barley roots from montmorillonitic clays, though the amounts of these 
ions released by HC1 or H 2 C0 3 were in the reverse order. The reasons 
for these divergent findings are not apparent at present. 

3. Associated Metal Cations 

Although it is generally found that increasing the degree of satura- 
tion of a given ion increases its availability to plants, still a large 
number of studies have shown the availability of one ion to be greatly 
affected by the associated ions on the exchange complex. Thus, Horner 
(1936) found that while the Ca uptake by soybean plants increased 


regularly with degree of Ca saturation in Ca-H, Oa-K, Ca-Ba, and Ca- 
Mg systems, the uptake of Ca was constant when strongly adsorbed 
methylene blue was the reciprocal ion. Also, Wadleigh (1949), citing 
the work of Ratner, stated that in a Ca-Na system in the soil Ca avail- 
ability to plants was reduced. 

The celebrated complementary ion principle was evolved by Jenny 
and Ayers (1939) to account for such findings. According to this, the 
exchangeability, and presumably the availability, of an exchangeable 
ion is greater the more strongly adsorbed are the other exchangeable 
ions, the so-called complementary ions. Thus, a given exchangeable ca- 
tion, K for example, would be considered more available when the 
complementary ion is strongly adsorbed Ca, than when it is weakly 
adsorbed Na. Figure 2, taken from the work of Jenny and Ayers 
(1939), illustrates the effect of the complementary ions Na, N11 4 , and 
Ca on the release of exchangeable K. Jenny and Ayers found good 
agreement between the results of chemical release studies such as those 
summarized in Fig. 2 and the uptake of K by excised barley roots. 

10 20 30 40 50 60 70 80 90 100 
Degree of saturation in per cent 

FIG 2. Effect of complementary ions on the release of K by HC1 in amounts 
equivalent to K on the colloid. (Taken from Jenny and Ayers, 1939.) 

Thus, far more K was absorbed from Ca-K clay than from Na-K clay. 
Results of parallel studies by Jarusov (1938) lead to the same conclu- 
sions with regard to the effect of associated exchangeable ions on the 
availability of a given ion species. 

In considering the complementary ion effect on plant composition, 
one must remember that the complementary ion principle as enunciated 
by Jenny and Ayers (1939) applies to the release of exchangeable 


cations from soil colloids. The effect of one ion in either accelerating 
or retarding the actual root absorption of another ion is a second and 
independent phenomenon. 

In view of the previously discussed different relative affinities of the 
various types of soil colloids for the important metal cations, the com- 
plementary ion principle would lead us to expect different patterns of 
ion availability from the several clays as the complementary ions are 
varied. A more or less classic example of this is the question of changes 
in K availability when an acid soil is limed, resulting in the replacement 
of H by Ca. Jenny and Ayers (1939) found K to be more available to 
excised barley roots from K-Ca montmorillonite than from K-H mont- 
morillonite. Bray (1942), on the other hand, concluded from release 
studies with various Illinois soils, probably containing illite-beidellite- 
organic exchange materials, that substitution of Ca for II on the ex- 
change complex would decrease K availability. The point is (Mehlich, 
1946) that probably both Jenny and Ayers, and Bray are right under 
certain circumstances. The affinities of the exchange materials they used 
for 11 and Ca are very different. Reference to Fig. 1 shows that both 
All away (1945) and Mehlich (1946) found certain bentonites to have a 
greater apparent affinity for Ca than for II, whereas the reverse was true 
for illites and for organic colloids. From this, one would expect K 
availability to increase when certain montmorillonitic soils are limed, 
whereas K availability might decrease when illitic, organic, or kaolinitie 
soils are limed, provided, of course, that the degree of total base satura- 
tion is sufficiently high to avoid per cent base saturation effects such as 
those discussed earlier. These considerations seem to call for some modi- 
fication of Peech and Bradfield's (1943) stand that K availability is 
decreased by liming an acid soil containing neutral salts, while substitu- 
tion of exchangeable Ca for exchangeable II in a more or less salt-free 
soil results in increased K availability. 

Marshal] and Barber (1949) and McLean (]949) found substitution 
of Ca for H to increase K activity in systems containing kaolinite, illite, 
and halloysite, as well as in those containing montmorillonite. These 
findings are somewhat at variance with the results of the chemical release 
studies quoted above, in that they infer that K availability should be 
increased by liming, regardless of type of clay. 

The above considerations do not take into account such factors as K 
fixation by certain clays. This problem has been discussed recently by 
Gieseking (1949). We will merely point out that K fixation of consider- 
able magnitude occurs in montmorillonitic-illitic soils, whereas fixation 
of appreciable amounts of K by kaolinitic or organic soils apparently 
does not occur. Bower (1950) has recently presented evidence to show 


that NH 4 fixation by 2 : 1 clay minerals also takes place. Fixed NH 4 was 
found to be oxidized only slowly to NO S and to be very slowly available 
to plants. 

The results of both ion exchange studies and ion activity measure- 
ments have pointed to great differences in the relative probable availa- 
bilities of mono- and divalent ions from different types of soil colloids. 
Such differences have also been reflected in the composition of plants 
grown on the various types of colloidal materials. 

Most attention has been focused on the K and Ca contents of plants. 
Mehlich (1946) has shown that of plants grown on kaoliiiitic and mont- 
morillonitic soils with identical cation exchange capacities and percen- 
tages of saturation with Ca and K, those grown on the former are 
relatively higher in Ca and lower in K than those grown on the latter. 
Similar results have been obtained by Chu and Turk (1949), Elgabaly 
and Wiklander (1949), and Mattson (1948) (see Table I). From the 
work of Chu and Turk, it would appear that illite behaves much as 
montmorillonite with regard to relative Ca and K availability ; Mehlich 
(1946) has found organic colloids to be more like kaolinite. 

Since the several typos of soil colloidal materials appear to differ with 
respect to relative affinities for K and Ca, one would expect from the 
complementary ion principle that increasing degree of K saturation 
would reduce Ca availability more with certain types of clay than with 
others. For example, Marshall (1950) finds that addition of exchange- 
able K reduces Ca activity markedly in the case of montmorillonite, 
whereas in the case of kaolinite Ca activity is actually increased when 
K is substituted for exchangeable H. Unfortunately, few data by which 
we can judge whether Ca availability also becomes smaller for mont- 
morillonite and larger for kaolinite with increase in exchangeable K are 
at hand. Many data, of which those discussed by Wadleigh (1949) are 
typical, have shown that high levels of exchangeable K decrease Ca 
availability. No type-of -colloid effect, however, is apparent. Chu and 
Turk (1949) found that the amount of Ca taken up by oat and rye 
plants from both bentonite and kaolinite decreased in about the same 
manner with increases in exchangeable K at a constant level of Ca. 
The present authors believe, however, notwithstanding the lack of evi- 
dence in its favor, that kaolinitie soils can be saturated to a larger degree 
with K than can montmorillonitic soils before Ca availability is seriously 

Several papers have dealt with the effect of complementary Mg on 
Ca availability to plants. Vlamis (1949), for example, found the Ca 
content of lettuce and barley to decrease sharply when the degree of 
Ca saturation of Ca-Mg soils fell below 20 per cent. Giddens and Toth 


(1951) also observed Ca availabilty to be decreased by large amounts of 
exchangeable Mg, but observed no effect due to type of soil colloid. Chu 
and Turk (1949) and Mehlich and Reed (1948) reported similar reduc- 
tions in Ca contents of plants when soil levels of exchangeable Mg were 
increased. In general, however, the effect of Mg as a complementary 
ion on the availability of ( 1 a is less pronounced than that of either Na 

The Na ion behaves in a rather erratic manner with regard to its 
effect on plant contents of other metal cations. In general, from ion 
exchange and ion activity considerations, one would expect Na as a 
complementary ion to have a large depressing effect on the availabilities 
of other exchangeable ions. Apparently, however, the well-known dif- 
ferences between plant species with regard to the absorption of Na 
(Collander, 1941) largely overshadow the complementary ion effect. 
Baird and Mehlich (1950), for example, found that Na as a complemen- 
tary ion had a very large effect on the ( -a content of Swiss chard, whereas 
its effect on the Ca content of cotton was very small. Na was absorbed to 
a small extent by cotton, but was found to be present in Swiss chard in 
amounts as high as 207 me. per 100 g. dry weight. Similarly, Lehr 
(1951) found that additions of NaNO a to soils decreased Ca taken up 
by turnips and lupines (species which absorb large amounts of Na), 
whereas its effect on the Ca contents of rye grass and oats (less Na 
absorbed) was much smaller. On the other hand, Itallie (1935) found 
that addition of NaiiS0 4 to soils consistently reduced the Ca and Mg 
contents of various plant species, without regard to the Na contents of 
the plants. 

No type-of -colloid effect has thus far been observed in the interactions 
between soil Na and cation uptake by plants. As was deduced for K, 
Na should depress Ca and Mg availability more in montmorillonitic than 
in kaolinitic soils. 

4. Cation Exchange Capacity 

In general, soils are potentially more productive when the cation 
exchange capacity is high than when it is low. This is well illustrated 
by the work of Bear and Prince (1945) with alfalfa grown on twenty 
New Jersey soils. In view of the previous considerations with regard to 
degree of base saturation and plant growth, it is apparent that this 
generalization is true only when the cation exchange complex is well 
charged with bases, particularly Ca and Mg. Mehlich and Colwell 
(1943) and Mehlich and Reed (1948) found yields of soybeans, oats, and 
turnips to be greater on high than on low exchange capacity soils when 
per cent base saturation was constant for all exchange capacity levels. 



This was true regardless of type of colloid, of which kaolinite, montmoril- 
lonite, and organic were studied. Chu and Turk (1949), however, ob- 
served no large increases in yield of oats and rye as cation exchange 
capacity increased at constant degree of base saturation. 

The effect of soil cation exchange capacity on the cation contents of 
plants is well illustrated by the data presented in Fig. 3. The data are 

, 80 


" 70 

I 60 


White store 




40 80 

Per cent Ca saturation 



FIG. 3. Ca and K in soybean tops in relation to type of colloid and percentage 
Ca saturation at 2 and 4 me. cation exchange capacity. (Taken from Mehlich and 
Colwell, 1943.) 

taken from Mehlich and Col well (1943) and include the contents of Ca, 
Mg, and K in soybeans grown on montmorillonitic, kaolinitic, and or- 
ganic soils, each at cation exchange capacities of 2 and 4 me. per 100 g. 
Ca saturations were 40 and 80 per cent, Mg saturation was 10 per cent, 
and K saturation was 5 per cent. 

In plants grown on the montmorillonitic soil, neither Ca or Mg con- 
tent was influenced by cation exchange capacity, although Ca in the 
plants was much higher at the 80 per cent than the 40 per cent saturation 
level at both exchange capacities. In the case of the kaolinitic soil, Ca 


in the plants increased greatly with increased cation exchange capacity. 
The potassium contents of plants grown on the higher exchange capacity 
soils, both kaolinitic and montmorillomtic, were considerably above those 
of the low exchange capacity series. 

Mehlich and Reed (1948) studied the cation composition of plants 
grown on organic colloid-sand mixtures. Cation exchange capacity was 
varied from 5.2 to 20.8 me. per 100 g. The results with three plant 
species showed little influence of exchange capacity on the total cation 
content of the plants. Again it was observed that an increase in cation 
exchange capacity, at constant per cent base saturation resulted in in- 
creased K contents of the plants. On the other hand, when cation ex- 
change capacity was increased and the degree of Ca and Mg saturation 
and K level were held constant, the Oa and Mg in the plants increased, 
while K in the plants decreased. 

Although the above observations concerning the influence of cation 
exchange capacity on the relative amounts of K and Ca taken up by 
plants may at first sight seem analogous to the considerations by Mattson 
(see Sec. II, ], p. 74) a distinction must be made between this situation 
and the one Mattson has treated. In the above cited experiments cation 
exchange capacity was varied by adding more or less clay to a given 
amount of sand. The concentration of the "micellar solution," the 
hypothetical solution containing the exchangeable ions, would be es- 
sentially constant in all such sand dilutions of a given clay. Thus the 
greater availability of K relative to that of Ca when exchange capacity 
is so increased cannot be ascribed to differences in the concentration of 
the micellar solution. 

In presenting an explanation for this observation, we refer to the 
idea of Marshall (1944b). He has suggested that in considering the re- 
lease of K and Ca from any clay, the smaller the percentage of the 
total exchangeable ions released, the greater will be the proportion of 
K in the displaced ions. This has been confirmed in many ion exchange 
studies. Brown and Albrecht (1951), for example, found relatively 
more Ca than K to be transferred across a collodion membrane from a 
soil to a H-clay suspension when the proportion of H clay : soil was large 
than when it was small. It follows, then, that if plants grown on two 
soils of different exchange capacity remove approximately the same total 
amounts of ions from each, the proportion of K removed from the higher 
exchange capacity soil will be great and that of Ca will be small. 

It is tempting to extend this reasoning in an attempt to explain, in 
part, the differences in K and Ca contents of different plant species 
grown on the same soil with identical levels of soil cations. Reference 
to Table IT shows that plants such as alfalfa and red clover, which con- 


tain large percentages of Ca, are high producers of CO 2 , whereas cereals 
such as wheat and barley, which generally contain small amounts of Ca 
as compared with K, are low producers of C0 2 . It seems possible that 
the release of soil cations accomplished by this root-produced C0 2 , large 
in the former case as compared with the latter, may be such that rela- 
tively great amounts of Ca are made available to alfalfa and red clover 
roots, while less Ca and more K are released in the vicinity of cereal 

5. The Ecological Array of Plants 

An interesting application to the question of the effect of Ca-K ratio 
and P on the ecological array of plants has been proposed by Albrecht 
(1940). He assumes that since N is ultimately derived from the atmos- 
phere, the major portion of soil fertility or plant nutrient supply is rep- 
resented by Ca, P, and K. In view of the variations in these three 
elements in relation to the degree of soil development, a relationship 
between these effects and the ecological array of plants may be antici- 
pated. In experiments with colloid cultures he showed that N and P, 
as well as the Ca-K ratio in the plant, increased with widening Ca-K 
ratio in the culture medium. These data indicate that the plant quality, 
at least in terms of N or protein, is improved with increases in the Ca-K 
ratio. Albrecht then invites the reader to examine the theory in the 
light of possibly wider experiences. Attention should be called in this 
connection to the paper by Parker and Truog (1919), which showed the 
existence of a direct relationship between N and Ca in various plant 
species. The K content of these plant species fluctuated rather widely 
although a trend within certain groups of plant species for the K to 
increase with increasing Ca, is indicated. In an investigation by Homer 
(1936) with soybeans, the percentage N decreased but the total N in- 
creased (due to increased vegetative growth) with increasing Ca-K 
ratios. Similar results are obtained when the complementary ion is H, 
Mg, or Ba. With methylene blue as the complementary ion the degree 
of Ca saturation had no effect on the N content. Data by Marshall 
(1944c) with four pasture species show the N percentages in the crop 
to be negligibly influenced by Ca-K ratios. This applies whether the 
per cent Ca saturation is moderate or whether it is high. 

These data indicate that although Ca-K ratios have some effect on the 
quality of plants, other factors, such as per cent Ca saturation, need to 
be considered. In an experiment with type of colloid and varying degree 
of Ca saturation Mehlich and Col well (1943) found the N content in 
soybeans to be influenced by both of these factors. Figure 4 reproduces 
part of their data and shows increasing N content with increasing degree 



of Ca saturation for the 1:1, 2:1 and organic colloids. For any given 
degree of Ca saturation the N content increased in the above order of 
colloid types. The P supplied was in all cases 5 mg. P 2 05/100 g. soil. 
In a supplementary experiment 10 and 20 mg. P 2 5 were added to the 
1 : 1 type soil. The addition of extra P greatly increased the N content 




5 21 






40 60 

40 60 80 

Per cent Ca saturation 

40 60 80 

FIG. 4. Per cent N in soybean tops in relation to type of colloid and degree of 
Ca saturation. (The rate of PO r , was T> nig. per 100 g. soil. At the 60 per cent 
Ca saturation level of the 1:1 type 2P and 4P is equivalent to 10 and 20 mg. P 2 O & , 
respectively. Data taken from Mehlieh and Col well, 1943.) 

of the plants, as shown in. Fig. 1. It appears, therefore, that other 
factors in addition to the Ca-K ratio, such as degree of base saturation 
and supply of P and N greatly influence the quality of plants. To the 
extent also to which Ca may influence the organic acid content of the 
plant, plant quality may be affected (Schroeder and Albrecht, 1942; 
Wittwer ct al., 1947). 

The mineral content of any plant species may vary so greatly with 
treatment or nutrient level of soil as to render meaningless classification 
of plant species in terms of their "average" quality. An example of 
this is illustrated by some data of Bender and Eisenmenger (1941) in 
Table III. They grew various plant species on an unlimed soil (pH 
4.4) and a limed soil (pll 7.8). The differences in Ca content between 
species, which initially caused them to be classified either as calciphilic 



or calciphobic, were smaller than those produced by liming. Fertiliza- 
tion with K was constant, yet the K content shows no relationship either 
to feeding power for K [which according to Drake and Scarseth (1940) 
is low for oats and high for wheat], or to the exchange capacity of roots, 
[which according to Drake et al. (1951) is lower for wheat than for 


Cation Content of Plants Grown on an Acid (pll 4.4) and a Basic (pH 7.3) Soil 
(From Bender and Eisenmenger, 1941) 











Barley (Calciphile) 







Wheat (Intermediate) 







Oats (Calciphobe) 







Sweet clover (Calciphile) 







Cowpeas (Intermediate) 







Peanuts (Calciphobe) 







Kentucky bluegrass (Calciphile) 







Timothy (Intermediate) 







Redtop (Calciphobe) 







* A, acid soil, ** B, basic soil. 

oats]. IIou and Merkle (1950), also found the K content of "calcifu- 
gous" plants to have as wide a range as "calcicolous" plants. As a 
further example, the data of Blaser and Brady (1950) on the K content 
of different plant species grown in different New York soils may be cited. 
They found the K content of alfalfa to range from 1.0 to 3.71 per cent; 
for Ladino clover from 0.42 to 4.17; and for timothy from 1.5 to 3.71 
per cent, depending on treatment. Equally wide ranges in K content of 
alfalfa were obtained by Hunter et al. (1943). Physiological factors 
influencing the metabolic activity of roots, which in turn influences the 
proportion of cations taken up, need to be taken into account as well 
(Hoagland, 1944; Pepkowitz and Shive, 1944; Cooper et al., 1948). 


Recognition of the type of colloid as one of the factors influencing the 
availability of ions and hence crop yield and quality would be expected 
to have an important bearing on lime and fertilizer practices. In gen- 


sral, in soils predominately of the 1 : 1 type, Ca availability is higher 
than in soils of the 2 : 1 type. Since, in addition, the former have lower 
nation exchange capacities than the latter, smaller amounts of lime are 
needed to bring the soils to a given degree of Ca saturation (Jones and 
Hoover, 1950). Furthermore, the lower availability of Ca in soils con- 
taining the 2:1 types of clay mineral requires that these soils be limed 
to a higher degree of ("a saturation. Under New Jersey conditions of 
igriculture, Bear et al. (1945) and Bear and Toth (1948) stipulated 
:hat in an ''ideal soil" the exchange complex should be made up of 65 
:>er cent Ca, 10 per cent Mg, 20 per cent H, and 5 per cent K. These 
juantities, calculated on the basis of 1 me. per 100 g. soil, correspond to 
260, 24, and 39 Ib. of Ca, Mg, and K per acre, respectively. With each 
nilliequivalent increase in cation exchange capacity these amounts would 
ncrease accordingly. The Ca-Mg and Ca-K ratios in this system are 
5.5 and 13, respectively. The Ca-Mg ratios suggested as "ideal" eor- 
*espond very closely to those calculated as being optimum for several 
ilant species by Mehlich and Reed (1948b). These ratios were found to 
ie between 4 and 6. Since, in addition, the proportionate amounts of 
Ja to Mg taken up by plants were observed to be relatively little in- 
luenced by cation exchange capacity (Mehlich, 1946; and Mehlich and 
ieed, 1948a) the proportions of Ca and Mg suggested by Bear et al. 
nay well be the "ideal" condition to strive for. The exchange complex 
vould then be saturated to the extent of 75 per cent. This should be a 
latisfactory condition for most agricultural crops grown in soils contain- 
ng colloids of the organic-2 : 1 mineral lattice type associations. With 
ncreasing amounts of organic colloid the percentage Ca saturation neces- 
iary for optimum plant growth rnay be lower (Welch and Nelson, 1950). 
With decreasing organic colloid, and with crops having unusually high 
^lg requirement, such as Swiss chard (Baird and Mehlich, 1950), a 
x)mewhat higher degree of -base saturation and narrower Ca-Mg ratio 
vill be required. In soils containing primarily the organic-1 : 1 mineral 
attice type colloid associations good availability of Ca and Mg should 
>e assured at 40 to 60 per cent base saturation with Ca-Mg ratios of 
- to 6. 

The "ideal" of 5 per cent K suggested by Bear et al. corresponding 
o a Ca-K ratio of 13 may require appreciable modification. In contrast 
o the lower order of interaction between Ca and Mg, the interaction be- 
ween Ca and K is great and is influenced by type of colloid, cation ex- 
hange capacity and plant species. In view of the greater release or 
ivailability of Ca from the 1 : 1 than from the 2 : 1 type of colloid, a given 
>ereentage saturation of K will suppress the availability of Ca in the 
\ : 1 type more than in the 1 : 1 type. In consequence of the cation equiva- 


lent constancy in plants (Itallie, 1938; Bear and Prince, 1945; Lucas 
and Scarseth, 1947; Wallace et al., 1948) the suppression of Ca will 
result in a corresponding greater uptake of K. The relative availability 
of K also increases with increasing cation exchange capacity. Since the 
cation exchange capacity of the 2 : 1 clay minerals is greater than that 
of the 1 : 1 type it follows that a constant percentage K saturation in the 
soil will result more readily in " luxury consumption " of K with soils 
of the former than the latter colloid type. The relatively high availa- 
bility of K of organic colloids, together with the high cation exchange 
capacity of this type of colloid will be expected to have the same effect 
as that of the 2 : 1 type. 

In addition to the soil effects referred to, great variability in the 
optimum Ca-K ratios in soil required by different plant species are to 
be taken into account. These ratios, as observed by Mehlich and Reed 
(1948b), range, for example, from 18 to 36 for oats and timothy and 
from 18 to 29 for alfalfa and red clover, whereas the "ideal" soil re- 
quires a Ca-K ratio of 13. 

Using data from the North Carolina Experiment Station, Winters 
(1945) calculated the K requirement for a 90 per cent yield of soybeans 
to be 50 and 155 Ib. per acre when the cation exchange capacities of the 
soils were less than 4 and greater than 6 me. per 100 g., respectively. He 
also found that 90 Ib. of exchangeable K produced 70 per cent and 50 
per cent yields of cotton for the low exchange capacity soils (about 3 
me.) in Georgia, as compared to the higher exchange capacity soils (5 
to 12 me.) in Tennessee, respectively. For a yield of 90 per cent the 
corresponding figures were 160 and 180 Ib of K. In a similar compari- 
son with corn, the K levels were 155 and 180 Ib. for soils at Tennessee 
and Illinois, respectively. The highest amount of K, 220 Ib. was needed 
for Irish potatoes. For yields greater than 70 per cent somewhat higher 
amounts of K are indicated. 

Since, as indicated above, the exchangeable K content at 5 per cent 
saturation corresponds to 39 Ib. per 1 me. cation exchange capacity, the 
amount of 310 Ib. or 0.4 me. (which appears to be in fair excess for 
optimum plant requirements) would be obtained with 8 me. cation ex- 
change capacity. On the basis of the foregoing consideration, it seems, 
then, safe to conclude that the 5 per cent K level would be " ideal " up 
to 8 me., whereas the per cent K may safely decrease with increasing 
cation exchange capacity above this value. 

The problem of the availability of K is complicated by the fact that 
certain members of the 2:1 lattice type, notably vermiculite, fix large 
quantities of K in nonexchangeable form. Fn contrast, certain members 
of the 2 : 1 lattice family and primary minerals contain large quantities 


of nonexchangeable K which becomes convertible into exchangeable and 
plant available forms. 

Studies of the effects of type of colloid on the plant availability of 
cations can obviously not be fully interpreted from measurements of 
their exchangeable cation content. Supplementary measurements, in- 
volving partial release of cations and particularly the determination and 
calculation of "fll" values should be considered useful (Bray, 1942; 
Mehlich, 1946, 1952). Further consideration of the plant factor as in- 
fluencing the proportionate amounts of cations taken up may likewise 
aid in the interpretation of the interaction involved (Mehlich, 1946; 
Mehlich and Reed, 1948b). 

A major influence of type of colloid can be expected also in con- 
nection with the availability of phosphorus and fertilizer practices with 
phosphatic fertilizers. In general, the availability of P diminishes with 
the organic, 2:1, 1:1 and sesquioxide colloids. In view of the associations 
of large amounts of such oxides as gibbsite, goethite, and hematite with 
clay minerals, notably those of the 1 : 1 lattice family, the problem of 
P availability occupies a major portion of soil research activity (for 
further details and literature review, the reader is referred to Dean, 
1949). Theoretically it may be assumed that the greater the anion ex- 
change capacity in relation to the cation exchange capacity the lower 
will be the availability of phosphorus for any given percentage P 
saturation. If this concept should prove to be correct the determination 
of the cation exchange capacity-anion exchange capacity ratio should 
prove to be useful supplementary information to the measurement of 
" available " phosphorus. 


Albrecht, W. A. 1940. J. Am. Soc. Apron. 32, 411-418. 

Allaway, W. II. 1945. Soil Sci. 59, 207-217. 

Alway, J., and Nygard, I. J. 1928. First Intern. Con (jr. Roil Sci. 2, 22-44. 

Arnon, D. I., Fratzke, W. E., and Johnson, (\ M. 1942. Plant Physiol. 17, 515-524. 

Arnon, P. I., and Johnson, C. M. 1942. Plant Physiol. 17, 525-539. 

Austin, ft. II. 1930. J. Am. Soc. Agron. 22, 136-156. 

Baird, G. B., and Mehlich, A. 1950. Soil Sci. Soc. Am. Proc. 15, 201-205. 

Bear, F. E., and Prince, A. L. 1945. J. Am. Soc. Agron. 37, 217-222. 

Bear, F. E., Prince, A. L., and Malcolm, J. L. 1945. New Jersey Agr. Expt. Sla. 

Bull. 721. 

Boar, F. E., and Toth, 8. J. 1948. Soil Sci. 65, 69-74. 

Beckenbach, J. R., Bobbins, W. B., and Shive, J. W. 1938. Soil Sci 45, 403-426. 
Beeson, K. C. 1946. Botan. Rev. 12, 424-455. 

Beeson, K. C., Lyon, C. B., and Barrentine, M. W. 1944. Plant Physiol. 19, 258-277. 
Bender, W. H., and Eisenmenger, W. S. 1941. Soil Sci. 52, 297-307. 


Blaser, R. E., and Brady, N. C. 19/50. Agron. J. 42, 128-135. 

Bower, C. A. 1950. Soil Sri. Soc. A*m. Proc. 15, 119-122. 

Bradfield, R., and Allison, W. B. 1933. Trans. Intern. Soc. Soil Sci. A, 63-79. 

Bray, B. H. 3942. J. Am. Chem. Soc. 64, 954-963. 

Brown, D. A., and Albrecht, W. A. 1951. Missouri Apr. Expt. Sta. Res. Bull. 477, 


Chapman, H. D., and Brown, 8. M. 1943. Soil Sci. 55, 87-100. 
Chapman, H. D., and Liebig, G. F., Jr. 1940. Jlilfjardia 13, 141-173. 
Chu, T. S., and Turk, L. M. 1949. Michigan Agr. Expt. Sta. Tech. Bull. 214, 1-47. 
Collander, R. 1941. Plant Physwl. 16, 691-720. 
Cooper, H. P., Paderi, W R., Garmnn, W. IT., and Page, N. R. 1948. Soil Sci. 65, 


Davis, L. E. 1942. Soil Sci. 54, 199-219. 
Davis, L. R. 1945. Soil Sci. 59, 379-395. 
Dean, L. A. 1949. Advances m Agronomy 1, 391-411. 
De Turk, E. E. 1941. Tnd. EIKJ. Chem. 33, 648-653. 

Drake, M., and Scarseth, G. D. 1940. Soil Sci. Soc. Am. Proc. 4, 201-204. 
Drake, M., Vengris, J., and Colby, W. G. 1951. Soil Sci. 72, 139-147. 
Elgabaly, M. M., Jenny, H., and Overstreet, R. 1943. Soil Sci. 55, 257-263. 
Elgabaly, M. M., and Wiklander, L. 1949. Soil Sci. 67, 419-424. 
Epstein, E., and Stout, P. R. 1951. Soil Sci. 72, 47-65. 
Fried, M., and Peech, M. 1946. /. Am. Soc. Agron. 38, 614-623. 
Gedroiz, K. K. 1930. Second Intern. Congr. Soil Sci. 2, 71-83. 
Giddens, J., and Toth, S. J. 1951. Apron. J. 43, 209-214. 
Giesekmg, J. E. 1949. Advances in Agronomy 1, 159-204. 
Gieseking, J. E., and Jenny, II. 1936. Soil Sci. 42, 273-280. 
Guggenheim, E. A. 1929. J. Phys. Chem. 33, 842-849. 

llcndricks, S. B., and Alexander, L. T. 1940. Soil Sa. Soc. Am. Proc. 5, 97-99. 
Hissink, D. J. 1922. Intern. Mitt. Boclenk. 12, 81-112. 
Hoagland, D. R. 1944. Inorganic Plant Nutrition. Chronica Botanica Co., Waltham, 


Hoagland, D. R., Davis, A. R., and Hibbard, P. II. 1928. Plant Physiol. 3, 473-486. 
Horner, G. M. 1936. Missouri Agr Expt. Sta. Res. Bull 232, 1-32. 
Hou, Hsioh-Yu, and Merkle, F. A. 1950. Soil Sci. 69, 471-486. 
Hunter, A. S. 1943. Soil Sci. 55, 361-369. 

Hunter, A. S., Toth, S. F., and Bear, F. E. 1943. Soil Sci. 55, 61-72. 
Itallie, T. B. van. 1935. Trans. Third Intern. Congr. Soil Sci. 1, 191-194. 
Itallie, T. B. van. 1938. Soil Sci. 46, 175-186. 
Jackson, M. L., Tyler, S. A., Wilhs, A. L., Bourbeau, C. A., and Pennington, R. P. 

1948. J. Phys. Colloid. Chem. 52, 1237-1260. 
Jacobson, L., Overstreet, R., King, H. M., and Handley, R. 1950. Plant Physiol. 25, 


Jarusov, S. S. 1937. Soil Sci. 43, 285-303. 
Jarusov, S. S. 1938. Pedology (U.S.S.R.) 33, 799-828. 
Jenny, H. 1932. J. Phys. Chem. 36, 2217-2258. 
Jenny, H., and Ayers, A. D. 1939. Soil Sci. 48, 443-459. 
Jenny, H., and Cowan, Eu W. 1933. Z. Pflanzenerndhr. Dungung u. Boderik A31, 57- 

Jenny, H., Nielsen, T. R., Coleman, N. T., and Williams, D. W. 1950. Science 112, 



Joffe, J. 8., and McLean, II. C. 1927. First Intern. Congr. Soil Sci. 2, 256-263. 

Jones, U. 8., and Hoover, C. D. 1950. Soil Sci. Soc. Am. Proc. 14, 96-100. 

Kollcy, W. P. 1948. Cation Exchange in Soils. Reinhold Publishing Corporation, 

New York. 

Krishnamoorthy, C., and Ovcrstreet, R. 1949. Soil Sci. 68, 307-316. 
Krishnamoorthy, C., and Overstreet, R. 1950a. Soil Sci. 69, 41-54. 
Krishnamoorthy, C., and Overstreet, R. 19, r >0b. Soil Sci. 69, 87-94. 
Lehr, J. J. 1951. Soil Sci. 72, 157-166. 

Leonard, O. A., Anderson, W. 8., and Gieger, M. 1948. Plant Physwl. 23, 223 237. 
Linebcrry, R. A., and Burkhart, L. 195L Soil Sci. 71, 455-466. 
Low, F. 1951. Soil Sci. 71, 409-418. 

Lucas, R. E., and Scarseth, G. D. 1947. J. Am. Soc. Apron. 39, 887-896. 
Lucas, R. E., Scarseth, G. D., and Seeling, D. II. 1942. Indiana Ayr. Expt. Sta. 

Bull. 468. 

Lundegardh, H. 1949. Klima und Boden. Verlag G. Fischer, Jena. 
Marshall, C. E. 1939. J. Phys. Chem. 43, J 155-11 64. 
Marshall, C. E. 1942. Soil Sci. Soc. Am. Proc. 7, 182-186. 
Marshall, C. E. 1944a. J. Phys. Chem. 48, 67-75. 
Marshall, C. E. 1944b. Soil Sci. Soc. Am. Proc. 8, 175-178. 
Marshall, C. E. 1944c. Missouri Agr. Expt. Sta. Res. Bull. 385. 
Marshall, C. E. 1948a. J. Phys. Chem. 52, 1284-1295. 
Marshall, C. E, 1948b. Soil Sci. 65, 57-68. 

Marshall, C. E. 1950. Trans. Fourth Intern. Congr. Soil Sci. 1, 71-82. 
Marshall, C. E., and Ayers, A. D. 1946. Soil Sci. Soc. Am. Proc. 11, 171-174. 
Marshall, C. E., and Ayers, A. D. 1948. J. Am. Chem. Soc. 70, 1297-1302. 
Marshall, C. E., and Barber, 8. A. 1949. Soil Sci. Soc. Am. Proc. 14, 86-89. 
Marshall, C. E., and Bergman, W. E. 1941. J. Am. Chem. Soc. 63, 1911-1916. 
Marshall, C. E., and Bergman, W. E. 1942a, J. Phys. Chem. 46, 52-61. 
Marshall, C. E., and Bergman, W. E. 1942b. J. Phys. Chem. 46, 327-334. 
Marshall, C. E., arid Eime, L. O. 1948. J. Am. Chem. Soc. 70, 1302-1305. 
Marshall, C. E., and Krinbill, C. A. 1942. J. Phys. Chem. 46, 1077-1090. 
Mattson, 8. 1948. Ann. Agr. Coll. Sweden 15, 308-316. 
Mattson, 8., Eriksson, E., Vahtras, K., and Williams, E. G. 1949. Ann. Agr. Coll. 

Sweden 16, 457-484. 

McLean, E. O. 1949. Soil Sci. Soc. Am. Proc. 14, 89-93. 

McLean, E. ()., and Marshall, C.~E. 1948. Soil Sci. Soc. Am. Proc. 13, 179-182. 
Mehlich, A. 1941. Soil Sci. Soc. Am. Proc. 6, 150456. 
Mehlich, A. 1946. Soil Sci. 62, 393-409. 
Mehlich, A. 1952. Soil Sci. 73 (in press). 

Mehlich, A., and Oolwell, W. E. 1943. Soil Sci. Soc. Am. Proc. 8, 179-184. 
Mehlich, A., and Colwell, W. E. 1946. Soil Sci. 61, 369-374. 
Mehlich, A., and Reed, J. F. 1946. Soil Sci. Soc. Am. Proc. 11, 201-205. 
Mehlich, A., and Reed, J. F. 1948a. Soil Sci. 66, 289-306. 
Mehlich, A., and Reed, J. F. 1948b. Soil Sci. Soc. Am. Proc. 13, 399-401. 
Melsted, 8. W., and Bray, R. H. 1947. Soil Sci. 63, 209-225. 
Mitra, R. P., Bagchi, 8. N., and Ray, 8. P. 1943. /. Phys. Chem. 47, 549-553. 
Mukherjee, J. N., Chatterjee, B., and Banerjee, B. M. 1947. J. Colloid Sci. 2, 247- 


Mukherjee, J. N., Mitra, R. P., and Mitra, D. K. 1943. J. Phys. Chem. 47, 549-553. 
Newton, J. D. 1923. Soil Sci. 15, 181-204. 


Nostitz, A. von. 1925. Landw. Vers. Sta. 103, 159-170. 

Overstreet, R., and Jenny, H. 1939. Soil Sci. Soc. Am. Proc. 14, 125-130. 

Parker, F. W., and Truog, E. 1920. Soil flci. 10, 49-56. 

Paver, IL, and Marshall, C. E. 1934. Chemistry <$ Intlustry 12, 750-760. 

Peech, M., and Bradfield, E. 1943. So>l Sci. 55, 37-48. 

Peech, M., and Scott, A. D. 1950. Soil Sci Soc Am. Proc. 15, 115-119. 

Pepkowitz, L. P., and Shive, J. W. 1944. Soil 8ci 57, 143-154. 

Pierre, W. H., and Bower, C. A. 1943. Soil Sci. 55, 23-36. 

Radu, I. F. 1940. Bodcrikunde u. Pflanscncrnlllir. 22, 574-580. 

Reed, J. F., and Cummings, R. W. 1948. Soil Sci. 65, 103-109. 

Rchachtschabel, P. 1940. Kolloid-Bcilicfte 51, 199-276. 

Scheffer, F. 1946. Agrikulturchemie, Teil BrPflanzenernahrung. Verlag Ferdinand 

Enke, Stuttgart. 

Schmohl, W. R., Peech, M., and Bradfield, R. 1950. Soil ScA. 70, 393-410. 
Schroeder, R. A., and Albrecht, W. A. 1942. Torrcy Botanical Club 69, 561-568. 
Schuffelen, A. C. 1944. Lanflbouwkund Tijfochr. 116-124. 
Schuifelen, A. 0. 1948. Agricultural (Louvain) 46, 1-22. 
Schuft'elen, A. C., and Barcndregt, T. 1946. Ere. trav. chim. 65, 807-815. 
Rchuffelen, A. C., and Looses, R. 1942. Proc. Netherlands Acad. ScA. 45, 726-733. 
Truog, E. 1918. Soil Sci. 5, 169-195. 

Vandecaveje, S. E. 1940. Soil Sci. Soc. Am. Proc. 5, 107-119. 
Vanselow, A. P. 1932. Soil Sci. 33, 95-113. 
Viets, F. G., Jr 1944. Plant Physiol. 19, 466-480. 
Vlamis, .T. 1949. Soil Sci. 67, 453-466. 
Wadleigh, 0. H. 1949. Ann. Rev. Biochem. 18, 658-678. 

Wallace, A., Toth, S. J., and Bear, F. E. 1948. J. Am. Soc Agron. 40, 80-87. 
Welch, (\ D., and Nelson, W. L. 1950. Agron. J. 42, 9-13. 
Wiklander, L. 1946. Ann. Agr. Coll. Sweden 14, 1-171. 
Williams, D. E., and Coleman, N. T. 1950. Plant and Soil 2, 243-256. 
Winters, E. 1945. Soil Sci. Soc. Am. Proc. 10, 162-167. 
Wittwer, R. IL, Albrecht, W. A., and Sehroeder, R. A. 1947. Food Research 12, 


The Physiological Basis of Variation in Yield 


Kothamstcd Experimental Station, Uat pcndcn, England 



I. Introduction 101 

IT. Techniques of Growth Analysis 103 

III. Limitations of the Concept of Net Assimilation Rate 109 

TV. Experimental Results 113 

1. Variation of Net Assimilation Rate ... 113 

a. Changes with Time 113 

(1) Smooth Trend 113 

(2) Short Period Deviations from Smooth Trend; the Effect 

of Climatic Factors 116 

b. Variation between Species 120 

c. Effect of Variation in Supply of Mineral Nutrients and Water 121 

d. Conclusion 124 

2. Variation in Leaf Area . 125 

a. Changes with Time ... 125 

b. Tntraspecific Differences ... 128 

c. Effect of Climatic Factors 129 

d. Effect of Variation in Supply of Mineral Nutrients and Water 

3. The Relative Importance of Variation in Net Assimilation Rate and 

in Leaf Area in Determining Yield 135 

V. Discussion ... 138 

References . 144 


The kind of knowledge that can be put to practical use in crop hus- 
bandry consists essentially of relationships established between crop 
yield and variation in the environment, especially variation that can be 
brought about by changing cultural procedures, or in internal factors of 
the crop plant that can be modified by plant breeding. Such knowledge 
has been derived partly from the accumulated experience of farmers, 
but it has been greatly extended and made more precise by scientific field 
experimentation. These empirical relationships describe the connection 
between the end points of a long chain of interdependent processes in 
the environment and the plant, and, broadly speaking, the object of 
agronomic research is to obtain information on all the links in the chain. 
To accomplish this, research is necessary, firstly, on the environment itself, 
to identify and investigate the processes controlling the intensity of 


102 D. J. WATSON 

environmental factors that affect plant growth, and secondly, on the 
growth reactions of the plant that determine yield. On the whole, more 
attention and effort has been devoted to the study of the first aspect of 
the yield-environment relationship than to the second. 

The problem of accounting for variation of yield in terms of growtli 
and development of the crop plant is obviously very complex, for ulti- 
mately it involves the effect of external factors on all the physiological 
processes of the plant, the interrelation between different processes, and 
their dependence on internal factors determined by the genetical consti- 
tution of the plant. Plant physiological research has produced much 
information on many of these processes, but it is difficult to apply the 
results to interpret the behavior of field crops, for the way in which 
different processes interact to determine growth is little understood. 
This has been emphasized by Brooks (1948), who pointed out that "the 
producer of crops is concerned with the integration of all the factors 
which determine plant growth and development, and it is basic knowl- 
edge of this integration which is at present deficient. ' ' The plant mate- 
rial used in laboratory studies may consist of detached organs or tissues, 
and the measurements may be made over short periods of time and in 
conditions that may fall outside the range normally encountered in the 
field. The academic physiologist has no special interest in crop plants, 
but choses species that are experimentally convenient. For all these 
reasons, the application of the results of physiological research to field 
problems may involve wide extrapolation and lead to incorrect conclu- 
sions. Though, theoretically, it should be possible to predict how crop 
yield will vary with environment from a synthesis of known effects of 
variation in environmental factors on individual processes in separate 
organs of the plant, this would demand a far more extensive and detailed 
knowledge of plant physiology than exists at present, and perhaps than 
is ever likely to exist. To discover the physiological basis of variation 
in crop yield it is therefore necessary to supplement laboratory studies 
by direct observations on crops growing in field conditions, measuring 
the simultaneous changes with time throughout the growth period in as 
many growth attributes as possible, and selecting especially those at- 
tributes that are susceptible of a simple physiological interpretation. 

Physiological techniques appropriate for laboratory studies are, in 
general, not suitable for investigations on crops growing in field condi- 
tions. One reason for this is that such techniques may themselves change 
the environment; for example, although it is possible with elaborate 
apparatus to measure directly the gas exchange of plants growing on a 
field plot (Thomas and Hill, 1949), this involves enclosing the plants in 
an airtight chamber or glasshouse, inside which the factors of illumina- 


tion, temperature, atmospheric C() 2 concentration, and water supply 
must differ in intensity in greater or less degree from those outside. A 
more serious difficulty is that the high variability in the plant population 
of a field crop necessitates the repetition of each observation on a large 
number of samples, if accurate estimates of the population means are to 
be obtained. Consequently only simple measurements, easily and quickly 
made, are practicable for field studies. Steps can be taken to reduce the 
labor of sampling by ensuring greater uniformity in the plant popula- 
tion of an experimental plot than is common in practice, for example, 
by accurate spacing of the plants, but there is a danger that such pro- 
cedures may produce results inapplicable to normally variable crops. 


One of the first attempts to analyze yield in terms of antecedent 
growth was made by Balls and Holton (1915) and Balls (1917) on the 
cotton crop in Egypt. They measured the daily growth in height of the 
main stem, the daily rate of flowering, i.e., the number of flowers open- 
ing each day, and the weekly rate of production of ripe bolls throughout 
the later part of the growing period. The flowering and boiling curves 
were used to interpret variations in yield produced by differences in 
spacing and sowing date, water supply, especially the rise of the water 
table, climatic factors, and boll-worm attack. The height measurements 
were used chiefly to account for short-period fluctuations in flowering; 
Balls maintained that these fluctuations, at least in the early part of the 
flowering period, were correlated with fluctuations in the rate of stem 
extension occurring about one month earlier, implying that climatic con- 
ditions at any time " predetermined ' ' the rate of flowering a month later. 

A few years later, Bngledow and his colleagues at Cambridge began 
an investigation of yield in cereals, designed to improve the technique of 
plant breeding by basing selection from the progeny of hybrids on meas- 
ured characters of the plant instead of eye judgment . In the first of a 
series of papers in the Journal of Agricultural Science, Engledow and 
Wadham (1923) outlined the object of their work as follows: "for solv- 
ing the yield problem by raising new hybrid forms . . . the procedure 
should be to find out the plant characters which control yield per acre 
and by a synthetic system of hybridizations to accumulate into one 
plant-form the optimum combination of yield-controlling factors. It may 
be that the best existing forms already embody the optimum combina- 
tions for a succession of seasons, and thus that owing to the vagaries of 
the climate no further improvements can be wrought by raising new 
forms. Only by resolving the cumbersome but economic 'attribute' of 

104 D. J. WATSON 

yield into biological characters can these doubts be probed. The pro- 
cedure for this seems to be a determination of the relation of all accept- 
able * plant characters' to yield and of their inter-relations. To carry 
out the full project for increasing yield by plant breeding, such deter- 
minations would have to be followed by investigations of the mode of 
inheritance of the characters which proved to be related to ' yield ' in 
order that hybridization might proceed on definite constructive lines." 

The experimental procedure followed was to make a censiis of the 
growing crop, recording at intervals the number of plants per unit area, 
number of tillers per plant, shoot height, and, at harvest, number of ears 
per plant, number of grains per ear and weight per grain the ''plant 
characters " assumed to be related to yield. In some cases, more detailed 
studies were made, recording the growth of each of the successive tillers 
and their individual contributions to yield. Many similar investigations 
were subsequently made in Britain, Australia, and New Zealand (e.g., 
Forstcr and Vasey, 1931; Frankel, 1935; Stephens, 1942; the last paper 
includes a review of the literature), and in nearly all field experimen- 
tation on cereals it became the fashion to supplement yield data by so- 
called developmental studies. In Britain a scheme for making similar 
observations on wheat at a number of centers was carried on for several 
years before World War II (Yates, 1936) ; this had a different aim, 
namely, to provide data for forecasting yield from measurements of 
growth made at successive stages prior to harvest. 

The experimental techniques of Balls and Engledow consisted in the 
measurement of morphological characters, or enumeration of organs ; the 
results therefore give a quantitative description of the morphological 
changes that take place during the growth of the crop, but throw little 
light directly on the underlying physiological causes, though they may 
suggest physiological explanations. This was fully realized by Engle- 
dow and Wadham (1923) for they remark: "To plant physiology we 
must look for the final solution of the 'yield problem,' but meantime for 
plant-breeding the only practicable course is to seek an advance by in- 
vestigation of the statistical characters which are more amenable to 
observation than those in terms of which physiology has to proceed. " 

These census studies did not succeed in defining easily measured 
yield-controlling characters that the cereal breeder can use as a basis for 
selection. The reason is that the different yield attributes are not inde- 
pendent expressions of growth. Some of them are inversely correlated; 
circumstances that increase one tend to decrease another. Consequently, 
selection for one attribute, for example, ear number per plant, may in- 
volve counterselection for another, such as number of grains per ear or 
grain size, with little or no improvement in yield, but only a change in 


its morphological constitution. The chief outcome of the work was to 
focus attention on plant density as a factor affecting cereal yield. Engle- 
dow and his colleagues found that the yield of foot-lengths of drill row 
within a cereal crop was positively correlated with plant number, and 
concluded that irregularities in seeding were an important cause of loss 
of yield. Smith (1937) pointed out, however, that the observed corre- 
lation is a result of competition ; foot-lengths of drill row with high plant 
density must on the average be adjacent to less densely planted areas, 
and therefore suffer less from competition, than foot-lengths with low 
plant density. If a uniform distribution of plants were established at 
the higher plant densities found in a normally variable crop, competi- 
tion would be more severe, and the yield of the crop would not neces- 
sarily be increased. Other aspects of this type of analysis of yield, 
applied to the wheat crop, are discussed by Russell and Watson (1940). 
The yield of a field crop is the weight per unit area of the harvested 
produce or of some specific part of it, and it is therefore more logical to 
base an analysis of yield on the weight changes that occur during growth 
than on changes in morphological characters. The first step in develop- 
ing a procedure for analyzing growth in terms of dry weight change was 
made by Blackman (1939). lie pointed out that increase in dry weight 
can be regarded as a process of continuous compound interest, the in- 
crement produced in any interval adding to the "capital" for growth in 
subsequent periods. The rate of interest, or relative growth rate, 

7?- I dW 
K ~W dt 

where W is the dry weight of the plant at any time, represents the 
efficiency of the plant as a producer of new material. This Blackman 
called the efficiency index. The dry matter yield of a plant can then be 
considered as dependent on (1) the initial capital, i.e., the seed weight, 
(2) relative growth rate, and (3) the length of the growth period, and 
variations in yield can be analyzed in terms of these three quantities. 
However, the dry weight of a plant is not all productive capital, for a 
considerable part of it consists of skeletal material not active in growth. 
As dry matter increase is attributable to photosynthesis, apart from the 
small contribution of mineral nutrient uptake from the soil, a better 
measure of the productive capital or "growing material" of the plant 
is leaf size. The rate of increase of dry weight per unit leaf area, 
(1/X) (dW/dt) where L is the total leaf area of the plant, is obviously 
a measure of the excess of the rate of photosynthesis over the rate of dry 
matter loss by respiration. Gregory (1917) was the first to suggest the 
use of this function in the analysis of growth and called it net assimila- 

106 D. J. WATSON 

tion rate (NAR). Briggs, Kidd, and West (1920) preferred the term 
unit leaf rate (symbol E). It is clear that the relative growth rate 
(RGR) is the product of NAR and the ratio of leaf area to total dry 
weight; this ratio (L/W 9 leaf area ratio) may be regarded as an index 
of the amount of ' t growing material ' ' per unit dry weight of the plant. 
A possible method of analysis of change in dry weight, therefore, con- 
sists in the calculation of RGR, and the further analysis of RGR in terms 
of NAR and leaf area ratio. 

Both RGR arid leaf area ratio are complex functions, difficult to in- 
terpret, and a form of analysis is possible which does not involve their 
use. This depends on the fact that the product of NAR arid total leaf 
area gives the* absolute growth rate in dry weight (d\V/dt), and the tot'-il 
dry matter accumulation in any time interval is the integral of this 
product. Consequently, the progress of dry matter accumulation and 
its end point yield at harvest can be completely described in terms of the 
two attributes, NAR and leaf area. The first of them, NAR, is capable 
of relatively simple physiological interpretation, but the second is the 
resultant of many physiological processes, and a deeper analysis of yield 
would involve an examination of the internal and external factors that 
determine leaf area. 

One other attribute that has been used in the analysis of leaf area 
changes should be mentioned, namely, the relative leaf growth rate 
(]/L) (dL/dt). This is useful for comparisons of growth in leaf area 
at different times in the growth period arid for correlation of leaf growth 
rate with external factors, for it provides a means of eliminating the 
effect of varying plant size at different stages of growth. However, it is 
not easy to interpret changes in relative leaf growth rate in physiological 
terms, as the relation between the growth of new leaves and existing 
leaves is obviously very indirect, depending on the provision of material 
by photosynthesis, on cell division in meristems, and on cell extension 
in leaf initials. 

It is convenient to have a name for the technique of investigating 
growth and yield by the use of the growth functions described above, 
and among British plant physiologists the term "growth analysis " is 
commonly used in this special sense. 

It is not practicable to make a continuous record of the changes with 
time in total dry weight and leaf area; instead, they are measured by 
taking samples from a population of similarly treated plants at intervals, 
usually a week or multiples of a week. RGR and NAR are then esti- 
mated as mean rates over the successive intervals. Fisher (1921) showed 
that, if Wj and T7 2 are the total dry weights at times ti and t 2 respec- 
tively, the mean value of RGR for the time interval #2 ^1 is given by 


(log, Ws-loge Wi) , 

-------- --- whatever the form of the growth curve. Following 

(12 fi) 

Gregory (1926) it has been usual to calculate NAR as 

where LI and L 2 are total leaf area at times ti and t 2 respectively, but 
Williams (1946) has pointed out that this expression gives an accurate 
estimate of mean NAR only if the relationship between L and W is 
linear over the interval tz ti. For short intervals (1-2 weeks) it 
appears that this condition is approximately satisfied, and the errors 
introduced are negligibly small, at least for field crops, in comparison 
with those due to sampling variation in W and L. Estimates of NAR 
made by this method for longer sampling intervals may have serious 
positive or negative bias depending on the direction in which the relation 
between L and W deviates from linearity. 

In a field crop the measurements of total dry weight and total leaf 
area are made on random samples of plants, from which mean values 
for the plant population are estimated, and the accuracy of the estimates 
depends on the size and structure of the samples. It is not intended 
to discuss the statistical problems of sampling here; in practice, the size 
and number of the samples is likely to be limited by the labor involved, 
and it is therefore essential to use efficient sampling methods. A pro- 
cedure for improving the accuracy of estimation of growth increments 
designed to eliminate errors due to initial differences between samples 
taken at the beginning and end of an interval was used by Uoodall 
(1945) and has been fully investigated statistically by Mclntyre and 
Williams (1949). Measurements or ratings of a size attribute highly 
correlated with the growth function to be estimated are made on both 
samples at the beginning of the interval (the measurement must not, of 
course, involve destruction or injury of the plants), and the mean values 
of the growth function for the samples taken at the beginning and end 
of the interval are corrected to the mean value of the initial measure- 
ment or rating. This procedure may permit economy of effort in 
sampling, but greatly increases the labor of computation. 

There is no direct method of measuring the leaf area of a plant in 
one operation. If the number of plants in a sample is small the total 
leaf area can be obtained by summing the separately determined areas 
of individual leaves. Various methods are available for this purpose: 
printing the leaf outline on blueprint paper and measuring the area with 
a planimeter, or by cutting out the leaf print and weighing it ; measuring 
appropriate linear dimensions and computing the area from the geometry 

108 D. J. WATSON 

of the leaf shape (Gregory, 1921) ; using an area photometer, which 
measures the reduction in the light falling on a photoelectric cell when 
a leaf is placed in the incident beam (e.g., Kramer, 1937; Milthorpe, 
1942) ; estimating the area of each leaf by matching with one of a graded 
series of standards made by tracing or photographing a suitable set of 
leaves (Bald, 1943). With larger samples of plants such as are neces- 
sary for studies on field crops, it is impracticable to measure the area of 
each leaf, and the total leaf area must then be estimated indirectly from 
total leaf weight and the leaf area to leaf weight ratio. This ratio may 
be determined by weighing and measuring the areas of a small subsample 
of leaves, but in computing the mean ratio for the whole population of 
leaves in the sample, allowance must be made for the fact that the ratio 
varies inversely with leaf weight (Watson, 1937). For plants with large 
undivided leaves, like sugar beet, a less laborious method is to punch out 
disks of known area from the bulked leaf laminas of the sample, taking 
steps to ensure that all parts of the lamina have an equal chance of being 
sampled. By counting the number of disks in a sample of known weight, 
the mean area to weight ratio for the whole population of leaves can 
be estimated. 

The samples taken from a field crop may be based on a fixed number 
of plants or a fixed area of crop. The latter is the only practicable 
method for cereal crops, for after the onset of tillering it is difficult to 
distinguish individual plants. It may also be desirable for widely spaced 
crops, because, in the later stages of growth, interplant competition is 
likely to make dry weight and leaf area per unit area of crop less vari- 
able than per plant. Unit area of crop is also the appropriate basis for 
comparisons between differently spaced crops. 

Much of the remainder uf this article is concerned with the analysis 
of yield in terms of the two attributes NAR and total leaf area, which 
may be regarded, respectively, as measures of the efficiency and of the 
capacity of the photosynthetic system. One advantage of this form of 
analysis is that it effects at least a partial separation of those aspects of 
growth which are controlled by internal factors from those which de- 
pend on external factors, for according to Gregory (1926) "Relative 
leaf growth rate [and hence total leaf area] is largely dependent on 
internal factors and is relatively independent of external conditions; 
whereas, in contrast with this, net assimilation rate has been shown to 
be wholly controlled by external factors." Though other workers main- 
tain that NAR shows time drifts that cannot be accounted for by change 
in external factors, the distinction made by Gregory appears to be 


broadly true. Before discussing experimental results, however, it is 
desirable to consider the significance of NAR in greater detail. 

It may be noted here that agricultural yield usually refers to the 
weight, not of the whole plant, but of particular organs, tissues, or 
chemical constituents that have economic value, such as the grain of 
cereals, the tubers of potatoes, the fiber of flax, the hairs on the seed of 
cotton, or the sucrose of the sugar beet root. Comparisons of agricul- 
tural yield in this sense between crops would be meaningless, for the 
definition of yield varies with the crop. The only suitable basis for such 
comparisons is total dry weight. It is possible for crops of the same 
species to have equal total dry weights at harvest and yet differ in agri- 
cultural yield ; this might occur, for example, with different varieties of 
a species. For a complete analysis of agricultural yield, it would there- 
fore be necessary to examine the causes of variation in the distribution 
of dry matter between organs and tissues as well as in the total weight 
of dry matter. This phase of the yield problem will not be discussed 
hero, though it is obviously an important aspect of the special physiology 
of individual crop species. 


It is important to bear in mind that NAR is not a pure measure of 
photosynthesis, but, as the adjective "net" implies, depends on the excess 
of dry matter gain by photosynthesis over loss by respiration. Conse- 
quently, it is not safe to assume that all changes in NAR originate from 
variation in the rate of photosynthesis. Thomas and Hill (1949) showed 
by direct measurement of the CO 2 exchange of alfalfa grown in sand 
culture, but in conditions otherwise similar to those of a field crop, that 
the loss of CO2 by respiration of the tops and roots, including that of 
the tops during the day, amounted to about 40 per cent of the total C0 2 
uptake in photosynthesis; for successive cuts of alfalfa, the value in- 
creased from 33 per cent to nearly 50 per cent. The total respiration 
of sugar beets was relatively smaller, about 30 per cent of total photo- 
synthesis. Assuming that respiration is of a similar order relative to 
photosynthesis for field crops in general, there is evidently plenty of 
scope for NAR to vary through change in respiration rate independ- 
ently of the rate of photosynthesis. 

When we consider NAR as a resultant of photosynthetic gain and 
respiratory loss, it is apparent that it involves the expression of respira- 
tion rate as the total respiration of the whole plant per unit leaf area. 
Now, respiration of the whole plant per unit leaf area will vary with 
leaf area ratio, independently of change in the respiratory activity of 

110 D. J. WATSON 

the tissues, merely because the respiration of a varying weight of plant 
material is referred to unit leaf area. For example, as leaf area ratio 
falls with advancing age, the rate of respiration per unit leaf area must 
tend to increase, and hence NAR to decrease, independently of any 
change in the rate of photosynthesis or of respiration rate per unit dry 
weight. However, the rate of respiration (per unit dry weight) may 
also fall with age and so offset the direct effect on NAR of change in the 
leaf area ratio. These considerations make it difficult to assess the 
significance of change in NAR with age, or of lack of change, because a 
time drift in NAR, independent of external factors, might originate from 
a drift in the rate of photosynthesis, or in the rate of respiration (per 
unit dry weight), or in leaf area ratio, and absence of a time drift in 
NAR might arise from opposing drifts in these three attributes. 

The same considerations are relevant to the question of what is the 
best basis on which to express NAR. Ideally, the basis of reference 
should be a precise measure of the capacity of the system responsible for 
dry matter accumulation, that is of the "internal factor" or "growing 
material" of the plant. NAR expressed on such a basis would then vary 
only with external factors and would be independent of age, nutritional 
state, and species. Heath and Gregory (1938) maintained that NAR 
shows these characteristics when expressed on the basis of leaf area, and 
this would imply that leaf area is a close approximation to the ideal 
basis. However, as photosynthesis occurs mainly in the leaves, whereas 
respiration proceeds throughout the whole plant, it seems to be impos- 
sible for any one attribute to be a precise measure of the "internal 
factor" for both processes. Since NAR depends on both photosynthesis 
and respiration, it follows that there can be no ideal basis of reference 
for net assimilation that will render NAR wholly independent of the 
internal factors. The best course seems to be to use a basis of reference 
appropriate for photosynthesis, since this must be the dominant process 
whenever increase in dry weight is taking place. 

It is conventional to express photosynthesis on the basis of leaf area; 
textbooks take this for granted and do not explain why leaf area is to 
be preferred to other attributes such as leaf weight. Presumably the 
reason is that both diffusion of C0 2 into the leaf and absorption of light 
are likely to be more closely dependent on leaf area than on any other 
easily measured attribute. During the greater part of the day, photo- 
synthesis of field crops is probably limited by CO 2 concentration, and in 
these conditions the rate of diffusion of CC>2 into the leaf is probably 
not affected by the thickness of the leaf, but depends only on its surface 

There is obviously a need for uniformity in the basis of expression 


of NAR, so that the results of different workers can be compared directly, 
and this is a strong argument for the continued use of leaf area. Some 
workers have expressed NAR on the basis of leaf dry weight, solely to 
avoid the labor of estimating leaf areas. Although this may be satis- 
factory for comparisons between treatments in particular experiments, 
the results lose their value for broader comparisons. 

Williams (1939) preferred to express NAR on the basis of leaf pro- 
tein-nitrogen * instead of leaf area or leaf dry weight. The protein- 
nitrogen content of the leaves was used as a rough measure of the 
content of cytoplasm, and it was assumed that variations in this content 
largely determine the time drift of both respiration and photosynthesis. 
Tn H later paper, Williams (1946) maintained that the time drift of Ep 
in experiments by a number of workers conformed more closely with 
trends in environmental factors than did the time drifts in E A or E w 
and concluded that in a constant environment Ep would be constant 
over a large part of the growth period, implying that leaf protein-nitro- 
gen is a good measure of the "internal factor" for NAR. If so, E P 
should be independent of the nitrogen status of the plant, but, on the 
contrary, Williams found that Ep varied significantly with nitrogen 
supply. To account for this he supposed either that part of the leaf 
protein in plants with a high nitrogen status is present in an inactive 
storage form or that the effectivity of the cytoplasm as a whole decreases 
with increasing nitrogen supply. Assuming the first possibility to be 
correct, Tiver and Williams (1943) suggested that cytoplasmic protein, 
rather than total leaf protein, would be a more adequate basis of com- 
putation though its use would have the practical disadvantage of requir- 
ing elaborate analytical procedures. The second possibility, that the 
effectivity of the cytoplasm varies with nitrogen supply, is merely an 
alternative way of saying that cytoplasmic protein is not a satisfactory 
measure of the "internal factor" for NAR. A priori, neither photosyn- 
thesis in the leaves nor respiration of the whole plant, the two deter- 
minants of NAR, would be expected to depend closely on the amount 
of cytoplasm in the leaves, because photosynthesis is not a property of 
the cytoplasm but only of the chloroplasts, and the total respiration of 
the plant depends on the protoplasmic content of all the organs and not 
merely the leaves. Instead of attempting to devise a basis of reference 

* In the remainder of this paper, NAR will be used to signify net assimilation 
rate on a leaf area basis. Where comparisons are made with other bases of reference, 
the notation of Williams (1939) will be used, as follows: 

JE?4=net assimilation rate on a leaf area basis. 

.EJF net assimilation rate on a leaf dry weight basis. 

Epnet assimilation rate on a leaf protein -nitrogen basis. 

H2 r>. J. WATSON 

for NAR that conforms more closely to the ideal, it is better to continue 
to use the leaf area basis for the sake of uniformity, especially as, for 
reasons already stated, it appears that no single plant attribute can be a 
precise measure of the "internal factor" for NAR. The leaf protein 
basis appears to have no practical advantage, because the estimation of 
total leaf protein or cytoplasmic protein involves even more labor than 
the estimation of leaf area. 

A source of error in the estimation of NAR of field crops is that the 
whole root system cannot be recovered, and often NAR has to be esti- 
mated from the dry weight of the tops of the plant alone. This will 
result in an underestimation of NAR, at times when the root system is 
increasing in dry weight. Williams (1946) has shown that the error 
introduced may be large in the very early stages of growth, later de- 
creasing and becoming negligible. lie concluded that, especially during 
early stages, the exclusion of the root system may obscure or exaggerate 
the real effects of a given treatment on NAR because fertilizer and other 
treatments frequently have differential effects on root and shoot growth ; 
for example, the underestimation of NAR was much greater at a low 
level of phosphate supply than at a higher level. 

Another limitation of the NAR concept arises from the fact that 
photosynthesis is not entirely restricted to the leaf lamina, but occurs 
also in other green parts of the plant, in stems and petioles, and in the 
leaf sheaths and ears of cereals. Consequently NAR is not an exact 
measure of the efficiency of the leaves in producing dry matter, but 
overestimates it to an extent depending on the relative amounts of photo- 
synthesis in the leaf laminas and in the rest of the plant. The error is 
probably small for plants in a vegetative state, but may become serious 
after flowering. Thus, nearly half the dry weight increase of barley 
plants after ear emergence is the result of photosynthesis in the ears 
(Watson and Norman, 1939 Porter, Pal, and Martin, 1950). It should 
be noted here, since the matter will not be referred to again, that 
variation in the amount of photosynthesis in the inflorescence may be 
of some importance in determining variation in cereal yield. Asana 
and Mani (1950) have shown that varieties of wheat differ in the extent 
to which the ears contribute toward dry matter production and have 
suggested that this may have a bearing on varietal differences in loss of 
yield caused by rust infection. 



1. Variation of Net Assimilation Bate 

a. Changes with Time. (1) Smooth trend. Variation of NAR with 
time can, for convenience, be considered as made up of two parts, the 
smooth trend persisting over long periods, and short period deviations 
from smooth trend. 

Tf NAR were wholly determined by external factors, the smooth 
time trend of NAR would follow the seasonal trend in climatic condi- 
tions. But it is possible that NAR may also vary w r ith time independ- 
ently of external factors, in so far as the basis of reference fails to be 
an adequate measure of the internal factor for dry matter accumulation. 
If the magnitude of the internal factor per unit of the basis of refer- 
ence changes steadily throughout the growth of the plant, then NAR 
will show a time drift depending on the age of the plant, even if external 
conditions are held constant. The time drift observed in a varying 
environment will then be determined partly by the smooth trends of 
environmental factors and partly by change in the internal factor with 

Figure 1A shows smoothed curves of EA for four species of crops 
grown in the field at Rothamsted in southeastern England, plotted 
against time throughout the year. Though values for any one species 
cover only part of the year, it is evident that E A undergoes a periodic 
change; from low values in winter it increases through the spring and 
summer to a maximum at the end of June, subsequently falling again 
during the late summer and autumn. The data for only one of the 
four crops, sugar beet, extend over both the rising and falling phases, 
but the results for this crop show a peak in midsummer, and this is evi- 
dence that the rising and falling trends are not characteristic of different 
crops, but represent a response to change in the environment, reflecting 
the seasonal climatic cycle. Though there is no rigid proof, any other 
explanation seems improbable. It follows that if E A varies with age, 
the age effect must be relatively small and insufficient to obscure the time 
trend induced by seasonal change in external factors. Which of the 
possible factors, e.g., temperature, day length, light intensity, are re- 
sponsible for the seasonal variation in NAR cannot be determined from 
the data, because all the factors are highly correlated in their seasonal 

If the time trend of NAR is determined by external factors, the 
curves of the seasonal cycle of NAR for crops in the northern and south- 
ern hemispheres should be opposite in phase. No data exist on NAR of 






FIG. 1. Time trends in net assimilation rate. 

A. Smoothed curves of 7 4 , averaging results of several field experiments on each 
of four crops at Botha mated, England (Watson, 1947a). 

B. E w of field crops of cotton in the Sudan (average of 11 years' data) and in 
Egypt (average of 10 experiments in 2 years) (Crowther, 1944), and of sugar cane 
in North Bihar, India (smooth curve drawn through results of 6 experiments in 4 
years; Asana, 1950). 

0. Ep and ! 4 in single experiments on plants gnmn in pot culture at Adelaide, 
South Australia (experiments 1 to 9) and at Sydney, X. S. W. (experiment 10). 
(1) wheat and (2) Sudan grass (Petrie and Ballard, 1936); (3) and (4) oats 
(Williams, 1936; E P values for experiments ] to 4 taken from Williams, 3939); 
(5) tobacco (untopped plants, Petrie, Watson, and Ward, 1939); (6) flax (high- 
moisture treatment; Tiver, 1941?) ; (7) linseed (high-moisture treatment; Tiver and 
Williams, 1943); (8) tobacco (untopped plants, high-moistuie treatment; Petrie, 
Arthur, and Wood, 1943); (9) -Phalans tuberosa (Williams, 1946); (10) flax (un- 
shaded plants; Milthorpe, 1945). 

D. E w for experiments 1 to 9 at Adelaide. 

field crops grown south of the equator, but Fig. 1C shows the changes 
with time in E P and E A for ton experiments on six species grown in pot 
culture in unseated glasshouses at Adelaide, South Australia (lat. 
35S, compared with 52N for Rothamsted) and at Sydney, N.S.W., 
(lat. 34S). E P and E { increased during November and December to 
high values at the end of December and in January, subsequently de- 
creasing through March and April. There are no records for May, but 
from the end of June onward all the experiments show a rise in NAR 
continuing until November, except that in experiments 3, 4, 6, and 7 the 


final values fall away sharply from the previous rising trend. These 
values refer to very late stages of growth, after the emergence of the 
panicle of oats (experiments 3 and 4) and during the ripening of flax 
and linseed (experiments 6 and 7) when the leaves were in a state of 
senescence. Values of E\ for the corresponding stages for wheat and 
barley were omitted from Fig. 1A. The results plotted in Fig. 1A and C 
thus agree in showing that in both northern and southern hemispheres 
NAR on a leaf area or leaf protein basis follows the seasonal climatic 
trend, fluctuating between high summer values and low winter values. 

By an extension of the same argument, it would be expected that 
crops grown near the equator would show little seasonal trend in NAR. 
The only extensive series of determinations made in the tropics or 
subtropics are those of Crowther (1944) on cotton in the Sudan (lat. 
]4N) and in Egypt (lat. 30N), and of Asana (1950) on sugar cane 
in northern Indian (lat. 25N). Both these workers computed NAR 
on the basis of leaf dry weight. The results, plotted in Fig. IB, show in 
all three cases a steady fall of E w with time, except for a short initial 
rise for cotton grown in Egypt. 

Figure ID shows the time trends of E w derived from the experiments 
at Adelaide, for which the E P and E A data are given in Fig. 1C. Like 
those of Fig. IB all the experiments show a steady fall of NAR with 
time, irrespective of the time of year covered by the growth period. 
The contrast between the time trends of E P (Fig. 1C) and of E w (Fig. 
ID) between July and October is very striking. The fact that, in the 
experiments during this period, the time trend of E f > follows the cli- 
matic trend, while that in E w does not, has already been noted by Wil- 
liams (1946). 

The conclusions to be drawn from Fig. 1 are that the time trend of 
NAR, expressed on the basis of leaf area or leaf protein, is determined 
by seasonal trends in climatic factors and is little affected by age, but 
that NAR on a leaf weight basis is much more dependent on internal 
factors, which cause a marked decline with advancing age, sufficient to 
obscure any time trend induced by change in external factors. 

The existence of an age effect on NAR has long been the subject of 
controversy, which has not yet been settled by critical experiments. 
Gregory (1926), Heath (1937, 1938), and Heath and Gregory (1938) 
maintained that E A and E w are independent of age up to the time of 
maximum leaf area. Williams (1937) held, on the contrary, that the 
leaf dry weight basis gives values that fall steadily with increasing age. 
Williams (1946) also put forward the view that NAR on a leaf area 
basis falls with age except during a short phase early in the growth 
period, but that, on a leaf protein basis, it is independent of age over 

116 D. J. WATSON 

almost the whole of the period of growth, except in conditions of high 
nitrogen supply. 

The crucial test would be to make measurements of NAR on plants 
growing 1 in constant environments. This has not yet been done, presum- 
ably because the elaborate equipment necessary for growing large num- 
bers of plants in controlled conditions has not been available to workers 
interested in the matter. An alternative method is to compare the NAR 
of plants of different ages, i.e., sown on different dates, growing in the 
same conditions. This was attempted by Watson and Baptiste (1938), 
in a field experiment on sugar beet and mangolds, but no significant 
effect of sowing date on EI was established. In another experiment 
(Watson, 1947a) on three varieties of sugar beet, E A of two varieties 
was significantly increased by later sowing, but that of the third was 
unaffected. In both experiments, the average effect of sowing one week 
earlier, that is, of an increase of one week in age, was to decrease 
EA by 0.012 g. per square decimeter per week. The moan E A of all 
sowings fell steadily with time, the mean rate of decrease per week 
being 0.054 g. per square decimeter per week in the first experiment and 
0.043 g. in the second. These experiments support the view that NAR on 
a leaf area basis declines with age independently of external factors, 
though they do not provide conclusive proof, but they also show that 
the age effect was much too small to account for the whole of the time 

Goodall (1945) has determined the time trend in E w for tomato by 
a method that avoids any effect of age. lie measured the dry weight 
change of tomato plants at a constant stage of development (the eight- 
leaf stage) during a twenty-four hour period, and repeated the experi- 
ment at intervals of about two weeks throughout a year. EW increased 
from low values in December to a maximum in midsummer, and then 
decreased again through "the autumn to a winter minimum. These 
results show that E w is subject to a time trend induced by the seasonal 
change in climate, similar to that in E A (Fig. 1A), although as already 
shown, if measurements are made at successive stages of growth of the 
same crop the seasonal trend is obscured by the much greater age effect. 
Leaf area was measured on a few occasions, and for these, approxi- 
mate estimates of E A were made. The mean estimates for the winter 
and for the summer, respectively, were 0.12 and 0.48 g. per square 
decimeter per week, a considerably smaller range than that shown in 
Fig. 1A, presumably because the plants were grown in a glasshouse, 
where the range of external factors, at least of temperature, between 
summer and winter values was not so great as in the field. 

(2) Short period deviations from smooth trend; the effect of climatic 


factors. It is unlikely that internal factors controlling NAR will fluc- 
tuate within short periods of time, and it is therefore reasonable to 
attribute deviations of NAR from smooth time trend to short-period 
changes in climatic factors. Experimental estimates of NAR will, of 
course, also show deviations due to random errors. In so far as the 
deviations in different climatic factors are uncorrelated, it should be 
possible to estimate the independent effects of different factors by the 
method of partial correlation. This has been attempted by Briggs, 
Kidd, and West (1920), Gregory (1926), and Watson (1947a). Briggs 
et al. and Gregory included the whole variation of NAR and of climatic 
factors in their correlations, and did not eliminate time trend, for they 
assumed that over the periods examined by them NAR varied only about 
a mean value and was free from trend. Briggs et al. concluded that 
NAR of maize was correlated more closely with temperature than with 
any other environmental factor. Positive correlations of NAR with 
weekly mean temperature and with mean maximum temperature were 
established. The data for one year provided estimates of the duration of 
light of different intensities relative to full sunlight, and Briggs et al. 
concluded that the best correlation was obtained when light intensity 
was assumed to be limiting up to one-fifth full sunlight. In computing 
these correlations with light intensity, the simultaneous variation in 
other factors was not eliminated. 

Gregory (1926) found that NAR of barley was positively correlated 
with mean day temperature (or mean daily maximum) and negatively 
correlated with mean night temperature (or mean daily minimum). 
His interpretation of this result was that high night temperatures in- 
crease respiration loss and so reduce NAR, whereas high day tempera- 
tures increase NAR by increasing the rate of photosynthesis. It follows 
from these relations to day and night temperature that NAR increased 
with increase in the daily temperature range but was not much affected 
by variation in daily mean temperature. Gregory (1926) also found 
a significant positive partial correlation of NAR with total radiation 
but not with hours of bright sunshine. 

Watson (1947a) obtained similar results for field plantings of pota- 
toes and wheat, though the partial regressions were not significant. 
For sugar beet, however, the signs of the temperature regressions were 
reversed ; NAR was negatively correlated with mean daily maximum 
and positively with mean daily minimum, so that increase in the daily 
temperature range depressed NAR, whereas, as before, change in daily 
mean temperature had little effect. It was considered unlikely that the 
relationship shown by the regressions on maximum and minimum tem- 
peratures represented direct effects of temperature on NAR, and it was 

118 D. J. WATSON 

suggested that they arose indirectly from a dependence of NAK on leaf 
water content. The leaves of field crops of sugar beet often show severe 
wilting on sunny days during the summer, and this might be expected to 
reduce photosynthesis by stomatal closure. The daily range of tem- 
perature tends to be smaller in cloudy and wet periods than when the 
sky is clear ; a small daily temperature range may, therefore, be an index 
of conditions favoring maintenance of turgidity in the leaf, and wide 
daily range of conditions favoring high transpiration rate and wilting. 
Unfortunately, no records of the degree of wilting were kept, and meas- 
urement of leaf water content were made too infrequently to allow a 
critical test of the hypothesis. 

Goodall (1945) attempted to correlate E w , measured on tomato 
plants at a constant stage of development on a number of occasions 
throughout the year, with environmental factors in the glasshouse. The 
partial regression of E w on mean daily light intensity was positive and 
significant, but none of the other factors tested had significant effects. 
The regression coefficients on day and night temperature were both posi- 
tive, and that on night temperature was the greater. 

The results of these four investigations are sufficient to show that 
temperature is an important controlling factor for NAR, but the nature 
of the temperature effects observed is surprisingly variable, suggesting 
that there are important interactions between temperature and other 

The use of partial regression analysis to determine the relation of 
NAR to environmental factors is an insensitive method for several rea- 
sons. The errors of estimation of NAR, especially in field plantings, are 
often high, so that only very large effects of climatic factors can be 
detected. NAR is usually determined over rather long intervals, of two 
weeks or more, and the use of mean values of climatic factors over these 
intervals involves considerable smoothing of the short-term variations. 
To test the possibility of any more complex relationship than a linear 
one involves great labor in computation, nor is it possible to take into 
account the interactions between different factors that certainly exist. 
Another difficulty is that some of the standard meteorological measures 
of climatic factors, e.g., hours of bright sunshine, are not appropriate 
measures of the environment in relation to plant growth. To obtain 
precise information on the effects of climatic factors and their interac- 
tions on NAR it will be necessary to grow plants in controlled environ- 
ments, so that the intensity of each factor can be varied independently 
of the others. 

Blackman and Rutter (1948) made an experimental study of the 
effect of varying light intensity on the growth of bluebell (8 cilia nan- 



script a) and sunflower (Helianthus annuus) by subjecting plants to 
different degrees of shading. They found that NAR increased linearly 
with increase in the logarithm of light intensity, expressed as a fraction 
of full daylight. Blackman and Wilson (1951 a) have confirmed this 
result in nine other species at all stages of growth except late in the 
autumn when the growth rate was very low. The straight line relation- 
ship between NAR and log light intensity was found to hold over a long 
period of the year, (Fig. 2) although NAR in full daylight varied 
widely (between 0.30 and 0.76 g. per square decimeter per week for 
sunflower). It was found that shading had no after effect on NAR; 
plants shaded during April and unshaded plants had the same NAR in 
May, when compared in the same light intensity. Incidentally, this 
result implies that NAR is independent of the thickness of the leaves. 
Shading had little effect on total leaf weight per plant, but increased the 
area of the leaves and reduced their thickness, i.e., increased the leaf 
area to leaf weight ratio. The thinner leaves of the shaded plants were 

0-8 - 






1-0 1-5 

Log light intensity (daylight- 100) 

FIG. 2. The effect of varying light intensity on the net assimilation rate of sun- 
flower seedlings (Helianthus annuus) at different periods in the summer. (Black- 
man and Eutter, 1948.) 

120 D. J. WATSON 

just as efficient in dry matter production per unit area in May as the 
thicker leaves of the plants not shaded in April. This is a strong argu- 
ment in favor of leaf area as a basis of reference for NAR in preference 
to leaf weight. Watson and Baptiste (1938) similarly found that though 
late sowing reduced the thickness of the leaves of sugar beet and man- 
gold it had little effect on NAR. 

Milthorpe (1945), working on flax, has also shown that shading 
reduced NAR, but as his experiment tested only two light intensities it 
gave no information on the form of the relation between NAR and light 
intensity. Monselise (1P51), on the other hand, found that E A of citrus 
(Sweet Lime) seedlings was unaffected when the light intensity was re- 
duced by shading to 30% or less of full daylight, but E w was slightly 
though not significantly decreased. 

Nutman (1937) measured the rate of photosynthesis of coffee leaves 
in natural conditions and found that the rate varied directly with light 
intensity when this was low, soon after sunrise or just before sunset or 
in cloudy periods, but was reduced by the high intensity of full mid-day 
sunlight, through stomatal closure. The total daily assimilation of 
leaves on a coffee tree growing in shade was greater than in the sun. It 
is probable, therefore, that NAR of coffee decreases with increase in 
light intensity in the region near to that of full daylight, showing that 
the relationship found by Blackman and Ruttcr (1948) may not apply 
to all species. 

The sensitivity of NAR to variation of light intensity may play a 
part in determining the effect of spacing on crop yield. Crowther 
(1937) found that closer spacing of cotton decreased E w and attributed 
this to increased shading of the lower leaves. 

b. Variation between tipecies. Heath and Gregory (1938) collated 
results reported by various workers on a number of species of plants 
growing in different environments and concluded that all of them 
showed practically the same mean NAR during the vegetative phase, and, 
therefore, that mean NAR is constant for all species and environments. 
The tabulated values of mean NAR range from 0.12 to 0.72 g. per square 
decimeter per week, and though reasons are given for rejecting some of 
the low values, the remainder still cover a considerable range. The evi- 
dence for the constancy of mean NAR is not convincing, and the results 
can more reasonably be interpreted as showing that mean NAR varies 
with species or environment or both. It has already been shown that 
the NAR of a species varies with the seasonal climatic trend, and it 
therefore seems probable that if measurements were made on the same 
species grown in different places, differences in NAR would be found 


corresponding to the differences between local climates, but this has not 
yet been tested. 

Watson (1947a) determined the mean NAR of several species of 
crops growing in neighboring fields over the same period of the year, so 
that comparisons between species could be made in nearly identical en- 
vironmental conditions. Differences were found that were consistent 
from year to year. The largest was that between wheat and sugar beet ; 
the mean NAR of the latter was nearly twice that of the former. Sig- 
nificant differences were also found between wheat and barley, barley 
and sugar beet, and potatoes and sugar beet. Some of these comparisons 
were not independent of age, but there was almost as great a difference 
in mean NAR between wheat and sugar beet sown within a few days of 
each other as between autumn-sown wheat and spring-sown sugar beet. 
An unpublished experiment at Rothamsted in which wheat, barley, and 
oats sown on the same elate in spring were compared, showed the follow- 
ing differences in mean NAR over the period April 27 to June 21 : 

Mean NAB Wheat Barley Oats S.E. 

Grams per square decimeter per week 0.358 0.312 0.287 0.0065 

Goodall (1950), in West Africa, determined the NAR of cacao seed- 
lings over a period of thirty weeks from planting and obtained values 
that fall much below any of those tabulated by Heath and Gregory 
(1938) ; the mean NAR was only 0.072 g. per square decimeter per 
week. The seedlings were grown under shade trees in about 20 per 
cent of full daylight, but though this may partly account for the low 
values observed, it is probable that cacao has inherently a much lower 
NAR than the other species for which data exist. 

There is also evidence that NAR may vary within a species. Small 
but significant differences have been found between varieties of potatoes, 
and high-sugar content strains of sugar beet appear to have a greater 
NAR than strains bred for high yield (Boonstra, 1939 ; Watson, 1947a). 
Cacao seedlings grown from the progeny of four trees differed in NAR 
during the early stages of growth (Goodall, 1950) ; mean NAR for 
thirty weeks after planting ranged between 0.058 and 0.082 g. per square 
decimeter per week. The existence of interspecific differences in NAR 
is thus well established, and there is also strong evidence of intraspecific 

c. Effect of Variation in Supply of Mineral Nutrients and Water. 
Gregory (1926) found that a fourfold increase in nitrogen supply to 
barley grown in pot culture had no effect on NAR in the period up to 
the attainment of maximum leaf area. Crowther (1934) similarly con- 
cluded that E w of cotton grown in the Sudan was unaffected by nitro- 

122 D. J. WATSON 

gen supply, but his results give some indication of a nitrogen effect, 
and later work (Crowther, 1937) on the same crop in Egypt showed a 
steady increase in E\ v with increasing nitrogen supply. Crowther con- 
sidered that part of this increase may have arisen from branch elonga- 
tion across the spaces between the rows, exposing more leaves to high 
light intensity, but it is difficult to accept the suggestion that the large 
plants receiving high-nitrogen supply were less subject to mutual shad- 
ing than the smaller plants receiving low-nitrogen supply. Ballard and 
Petrie (1936) found that varying nitrogen supply to Sudan grass had 
no effect on E w , but wheat grown with 1 g. NaN0 3 per pot gave values 
of E w consistently less than when the rate of application was 3, 6, or 10 
g., and after ear emergence differences in E w also developed between 
the higher rates. Similarly, Williams (1946) found that nitrogen supply 
had no effect on Ew of Phalaris tuberosa in the early stages of growth, 
but later there was a divergence between the nitrogen treatments, and by 
the end of the experiment, which terminated before flowering and while 
the weight and presumably the area of the leaves was still increasing, in- 
creased nitrogen supply caused a significant increase in EW 

Using material from the long-continued field experiments at Roth- 
amsted, where differences in nutrient supply have been intensified by 
repeated annual applications of varied fertilizer treatments on the same 
plots over many years, Watson (1947b) found that nitrogenous fertilizer 
increased the NAR of barley in the period before maximum leaf area 
and that of mangolds throughout the whole growth period. In an ex- 
periment on sugar beet grown in sand culture (Morton and Watson, 
1948), NAR was unaffected by nitrogen supply, except that, after a 
change from a low to a high water regime, the NAR of high -nitrogen 
plants was considerably greater than that of low-nitrogen plants. 

The conditions in which a nitrogen response occurs are not yet 
defined. It may be that NAR is affected only by severe nitrogen de- 
ficiency and that over a wide range of higher levels of nitrogen supply 
it is nearly constant. Gregory (1937) held that variation of NAR with 
nitrogen supply occurs only in the later stages of growth when leaf 
area is decreasing owing to senescence and death of the leaves and that 
it is attributable to more rapid senescence caused by nitrogen deficiency. 
However, this explanation is inadequate, for several workers have re- 
ported responses to nitrogen occurring at early stages of growth while 
leaf area was still increasing, and when presumably only a small fraction 
of the total leaf area was in a senescent state. 

The data on the effect of phosphate are contradictory. Phosphorus 
deficiency depressed E w of oats in the early stages of growth, but later 
caused an increase (Williams, 1936), attributed in part to delayed se- 


nescence of the plants with low phosphate supply. On the other hand, 
Gregory and Baptiste (1936) reported that phosphorus deficiency had 
no effect on NAR during the first six weeks of the growth of barley, 
but subsequently caused a reduction, and Gregory (1937), in a discus- 
sion of these results, stated that phosphorus deficiency leads to more 
rapid senescence of leaves. However, there is evidence that the rate of 
senescence of leaves may be affected by varying phosphate supply 
without accompanying change in NAR, and this throws doubt on the 
hypothesis that variation in NAR caused by change in phosphorus sup- 
ply is an indirect consequence of effects on senescence. Thus Petrie, 
Watson, and Ward (1939) showed that increased phosphorus supply 
delayed yellowing in the five oldest loaves of tobacco, but hastened it in 
the younger leaves, and topping the plants also delayed senescence, but 
they were unable to detect any effects of phosphorus or topping on NAR. 
Watson (1947b) recorded results similar to those of Williams; the NAR 
of field crops of barley and mangolds was reduced by phosphorus defi- 
ciency in the period before maximum loaf area. 

Information on the effect of potassium on NAR is scanty. Results 
reported by Gregory and Baptiste (1936) for barley show that potas- 
sium deficiency caused a reduction through the whole period of observa- 
tion. This was confirmed by Watson (1947b) for the early stages of 
growth, but in mangolds application of potassium increased NAR only 
at a low level of nitrogen supply. Potassium is generally supposed to 
play a special role in relation to photosynthesis, and it is surprising that 
in these field experiments the effect of potassium on NAR was small 
compared with those of nitrogen and phosphorus. 

Application of farmyard manure increased NAR of barley and 
mangolds in the period before maximum leaf area was attained (Watson, 
1947b) and showed negative interactions with fertilizer applications. 
These interactions may be interpreted as indicating curvature in the 
response to increased nutrient supply, but that between farmyard ma- 
nure and nitrogenous fertilizer may be a consequence of the supply of 
potassium by the farmyard manure, for the N X K interaction was 
also negative, as noted above. With this exception, the interactions 
between mineral nutrients were small and positive; each of the nutri- 
ents increased NAR, the effect of nitrogen being the greatest, and each 
had a greater effect in the presence of the others. In the period after 
maximum leaf area, however, the interactions were large compared with 
the main effects. The significance of these interactions is doubtful, be- 
cause the designs of the old experiments used as source of plant material 
provide no estimate of error, and it is possible that the apparent inter- 
actions resulted from the lower accuracy of estimation of NAR in the 

124 D. J. WATSON 

later stages of growth. However, the results at least suggest that, after 
leaf area ceases to increase, the effect on NAE of variation in one nutri- 
ent becomes more dependent on the supply of other nutrients than in 
the previous growth phase. If the interactions are real, they may reflect 
differences in the rate of senescence of leaves. In the barley experiment 
NAR was low where two of the three nutrients (N, P, and K) were ap- 
plied and the third omitted; these are the conditions likely to produce 
the most severe deficiency symptoms in the leaves and the greatest differ- 
ences in senescence rate. However, it seems that too much emphasis has 
been placed on the possible role of senescence in determining the effect 
of nutrient supply on NAR, and there is no doubt that nitrogen, phos- 
phorus, and potassium can all affect NAR of fully functional leaves. 

Several workers have found that NAR was depressed by reduction 
in water supply (Tiver, 1942; Petrie, Arthur, and Wood, 1943; Tiver 
and Williams, 1943; Morton and Watson, 1948), but there is no trace 
of such an effect in the results of Milthorpe (1945). The reason for the 
discrepancy is not obvious, for the severity of the restriction on water 
supply appears to have been similar in all the experiments. The low- 
water treatments permitted variation in moisture content of soil or sand 
between field capacity and the wilting point, while in the high-water 
treatment the moisture content was held close to field capacity. Drought 
seems to have no cumulative or after effects. The NAR of plants sub- 
jected to drought after a period of high-water supply fell to that of 
plants grown throughout in a low-water regime, and on return from a 
low- to a high-water supply NAR recovered completely and became 
equal to that of plants receiving continuous high-water supply. As the 
fall in NAR lasted only as long as the drought conditions, it seems rea- 
sonable to attribute the decrease of NAR to stomatal closure associated 
with wilting, and not to a change in leaf structure or composition, because 
such changes would persist Jor some time after restoration of full water 
supply. However, Petrie et al. (1943) have suggested other explana- 

d. Conclusion. An earlier review of the literature led Heath and 
Gregory (1938) to conclude that NAR in nature is not a very variable 
quantity, and Gregory (1950) apparently still holds this view. The 
present survey gives a decidedly different impression, for it shows that 
NAR varies between and within species, with mineral nutrition and 
water supply, and, very widely, with seasonal climatic conditions. How- 
ever, the significance of this variation in relation to dry matter accumu- 
lation and yield depends on its magnitude in comparison with the 
variation in leaf area, and this will be discussed in a later section. 


2. Variation in Leaf Area 

Agricultural yield is usually measured in terms of weight of crop per 
unit area of land. In an analysis of the causes of variation in dry matter 
yield, it is therefore appropriate to express the leaf area of a crop on 
the same basis as yield, that is, as the area of leaf surface per unit area 
of land surface, rather than as leaf area per plant, especially if compari- 
sons are to be made between different species of crop. The term leaf 
area index (LAI) has been proposed (Watson, 1947a) for this measure 
of leaf area. If leaf area and land area are expressed in the same units, 
LAI is a pure number independent of the units of area measurement. 
For a single species, grown at approximately constant spacing, variation 
in LAI depends mainly on change in leaf area per plant. The spacing 
of different species, however, varies widely in agricultural practice, 
being adjusted in accordance with experience or the results of field ex- 
perimentation to give maximum yield. Differences between species in 
LAI therefore depend on differences in plant population as well as in 
leaf area per plant. 

a. Changes with Time. The variation with time in LAI has been 
measured in a number of field crops grown at Rothamsted (Watson, 
1947a) ; the results are shown in Fig. 3. For autumn-sown wheat, LAI 
remained very small, less than 0.1, throughout the winter, but began to 
increase in March. The rate of increase in LAI at first increased with 
time, but later decreased, falling to zero in early June when LAI 
reached its maximum. Subsequently, LAI fell steadily until harvest in 
early August. It is evident that LAI of wheat changed continually 
throughout the growth period and did not assume a steady value at any 
stage. The maximum values of LAI ranged from 1.5 to 4 in the three 
wheat crops investigated. 

The prolonged initial phase of low and very slowly increasing LAI 
of autumn-sown wheat was not shown by spring-sown barley; presum- 
ably it was a consequence of winter climatic conditions. The curves for 
barley and wheat were otherwise similar, except that the maximum 
value for barley occurred later, at the end of June. The maximum LAI, 
about 2.5, fell within the range of values found for wheat. 

The graphs of LAI of potatoes show an initial rise and a final fall, 
but the peak was mere flattened than in the cereals, and occurred later. 
There was a period during August and September when almost steady 
values of LAI were maintained, at about 1.5 for the 1937 crop and be- 
tween 2 and 2.5 for the 1938 crop. 

The data for sugar beet are more extensive and give some indication 
of the range of variation in LAI between crops of the same species 



grown in different seasons in the same locality and with similar agricul- 
tural treatment. The graphs for the early phase of increasing LAI are 
concave upward, showing that the rate of increase of LAI tended to 
increase with time as in the cereals. The spread between the results for 






NOV.) DEC. | | MAR | APR | MAY | JUN | JUL | AUG J SEP | OCT. | NOV | 

PIG. 3. Change with time in the leaf area index of field crops grown at Rotham- 
sted. (Data from Watson, 194 7a, replotted.) 

different crops in this stage is accounted for largely by variation in the 
date of sowing. From the end of August onward the graphs flattened 
off to nearly steady values, so that for the whole growth period they 
had an S-shaped form. However, there was a tendency for LAI to fall 
during October and November. This fall was more pronounced in the 
single crop of mangolds for which data are given in Fig. 3 than in 
sugar beet. The maximum values of LAI varied between 2 and 4 and 


occurred still later than for potatoes, in September, October, or No- 

Boonstra (1929, 1937) has published data on the leaf area of field 
crops of oats and sugar beet which show variation with time similar to 
that described above. Other workers on growth analysis have either 
used material grown in pot culture or, if they have used field material, 
have preferred to measure loaf weight instead of area. 

The variation with time in LAI is mainly ascribable to change in 
leaf area per plant, though changes in plant number also play some 
part. The plant population of field crops tends to decrease with time 
through deaths from disease and other causes. In winter wheat, for 
example, the loss of plants between germination and harvest may be as 
high as 25 per cent of the initial population (Russell and Watson, 
1940). In other crops, such as sugar beet, that are thinned to a pre- 
scribed spacing at any early stage, the subsequent losses are usually 

The initial increase of LAI in wheat and barley is associated with 
tillering. During this phase the number of rneristems producing leaves 
increases. Shoot number reaches its maximum when LAI is still small, 
and many of the younger shoots subsequently die. The growing points 
of surviving shoots eventually cease to produce leaves and become in- 
florescence initials. The large increase of LAI that occurs in May for 
wheat and in June for barley (Fig. 3) takes place during the phase of 
stem elongation and is the result of expansion of existing leaves. LAI 
reaches its maximum at about the time when the shoots have attained 
half their final height. The decline in LAI which follows is due to 
senescence and death of the leaves in succession from the base of the 
stem upward. 

In other crops, the developmental sequence that gives rise to changes 
in LAI with time may be much simpler than in the cereals. For exam- 
ple, sugar beet plants remain in a vegetative state in their first season's 
growth and continue to produce new leaves until harvest. The changes 
in leaf area here depend almost entirely on the activity of a single apical 
meristem, and on the growth and longevity of the leaves it produces. 
Lateral buds may also develop, to a varying extent on different plants, 
especially in the late stages of growth, but they produce only small 
leaves, unless the apical growing point is damaged, and contribute little 
to total leaf area. 

General descriptions of the changes in plant population and in the 
morphology of the crop plants, such as those outlined above, can be 
amplified and made quantitative by means of census and developmental 
studies (Sec. II), but they give no information on the physiological 

128 D. J. WATSON 

causes of variation in leaf area. Much of the information derived from 
developmental studies has little relevance to leaf area considerations, be- 
cause the selection of growth attributes for measurement has usually not 
been made with this purpose in mind. 

Variation in the total leaf area of a plant may be brought about 
through change either in leaf number or leaf size. The number of leaves 
present at any time is the difference between the total number of leaves 
produced up to that time and the number which have died; it therefore 
depends on the number of growing points, the length of time during 
which they produce leaves, the rate of leaf production during this 
period, and the length of life of the leaves. Variation in leaf size may 
arise from effects on cell division, resulting in differences in cell number, 
or on cell extension. Physiological analysis of variation in leaf area 
must therefore take account of the effects of internal and external factors 
on the following aspects of leaf growth : 

(1) Those involving meristematic activity; the division of shoot 
meristems, leading to increase in the number of growing points; the 
rate of production of leaf primordia ; induction of flowering, terminating 
the production of leaves at a shoot growing point. 

(2) Those concerned in leaf expansion; the rate and extent of cell 
division and cell extension. 

(3) Those determining senescence and death of leaves. 

It is not yet possible to account for variation of LAI with time or 
between species in these terms. Some rather fragmentary information 
exists on the relative importance of the different aspects of leaf growth 
in determining differences within a species between strains or varieties 
and on the relationships of particular aspects to internal and external 
factors. These will be discussed in the following sections. 

6. Intraspecific Differences. European varieties of sugar beet in- 
clude strains selected for the highest fresh-weight yield of roots con- 
sistent with reasonable sugar content, usually known as E types, and 
others selected for the highest sugar content, known as Z types. E 
types have larger leaves with a higher water-content than Z types. 
Boonstra (1937) compared two such strains (A and Z) of the variety 
Kuhn, and found that the rate of production of leaves was lower in the 
high-yielding strain (A) than in the high-sugar content strain (Z). 
Leaves of A also had a shorter life than corresponding leaves of Z, 
although they continued to expand over a longer period. Consequently, 
Z had more living leaves than A, except in the early stages of growth, 
and the difference tended to increase as growth proceeded. The higher 
leaf number of Z was insufficient to counterbalance the greater leaf size 
of A, so that A had the higher leaf area per plant, but the superiority 


of A over Z decreased from mid-August onward and fell to zero at 
harvest in late October. 

Similar results were found in a comparison between an E type sugar 
beet strain and a variety of mangold (Watson and Baptiste, 1938). The 
mangold had larger leaves, but the sugar beet had a greater leaf number, 
resulting from a higher rate of leaf production and a lower death rate. 
In this case, higher leaf number outweighed smaller leaf size and pro- 
duced a greater leaf area per plant in sugar beet than in mangold. 
These results suggest that, over the range of agricultural varieties of 
Beta vulgarls, leaf size tends to fall and leaf number to rise as sugar 
content and dry matter content increase and that the rise in leaf 
number depends both on more rapid production and on longer life of 
leaves. There is evidence of a similar inverse correlation between leaf 
number and leaf size in comparisons between varieties of wheat and 
potatoes (Watson, 1947a). 

The possible significance of variation in the vitality of leaves in 
relation to yield was first pointed out by Boonstra (1929) ; he used 
"vitality" to signify "continuance of function" or " lebensdauer, " and 
this is probably better described by the term "longevity." lie showed 
that four varieties of oats differed considerably in the length of life of 
corresponding leaves, and found some evidence of an association of long 
life with high yield. Differences in leaf size and in the number of 
leaves produced also contributed to determine the differences in total 
leaf area responsible for the varietal differences in yield, but his data 
are inadequate to determine the relative importance of these and of 
variation in longevity of the leaves. 

c. Effect of Climatic Factors. Gregory (1921) investigated the 
changes with time in total leaf area of cucuimber plants grown in a 
glasshouse at approximately the same temperature at different times of 
year. The rate of expansion of leaf area was greater in summer than 
in spring or winter, and this was attributed to higher light intensity and 
longer photoperiod. The average leaf area over the growth period 
(about thirty days) in the different experiments was found to be pro- 
portional to the total radiation received. The same result was found for 
plants grown in continuous artificial light of intensities comparable to 
daylight in the glasshouse in December, but at a higher temperature. 
Tn the spring and summer glasshouse experiments, relative Leaf growth 
rate (RLGR) was approximately constant throughout the growth period, 
but in the December experiment and in artificial light RLGR fell steadily 
with time, and this was attributed to a detrimental factor associated 
with the low-light-intensity, high-temperature conditions. 

In continuous artificial light, total leaf area increased with increase 

130 D. J. WATSON 

in temperature up to about 25 C., but decreased with further rise in 
temperature (Gregory, 1928). The initial rate of expansion of the 
cotyledons increased with rise in temperature, but their final area was 
reduced at supraoptimal temperatures by inhibition of cell division. At 
temperatures in the suboptimal range, RLGR calculated for the foliage 
leaves alone decreased with time through the operation of a detrimental 
factor associated with low-light intensity, but was independent of tem- 
perature. The effect of temperature in this range on total leaf area was 
therefore wholly determined by the time taken for the first foliage leaf 
to unfold, that is to say, by an effect on development of the apical bud ; 
this effect had a normal temperature coefficient (Qw) of 2.5. RLGR 
decreased with rise of temperature above the optimum, and the rate of 
fall of RLGR with time increased. The accelerated fall of RLGR with 
time was attributed to change in distribution of material between stem 
and leaf and to a check in cell division in the leaf primordia. These re- 
sults led Gregory to postulate that leaf expansion depends on the pro- 
duction of a "leaf forming' 7 substance by a photochemical reaction, 
independent of carbon assimilation, acting on a nitrogenous substrate in 
the leaves or on a precursor stored in the cotyledons. This hypothesis 
would account for the absence of any effect of temperature in the sub- 
optimal range on RLGR and for the observed increase of RLGR with 
increased light intensity and duration. It also implies that RLGR is 
independent of the rate of carbon assimilation. 

Very different conclusions were reached in a study on barley grown 
in pots and exposed to natural summer weather conditions (Gregory, 
1926). The relation of deviations of RLGR from a smooth time trend to 
various climatic factors was examined. In contrast with the results of 
the cucumber experiments it was found that RLGR was correlated posi- 
tively with mean day temperature and negatively with mean night tem- 
perature and with total radiation. The deviations of RLGR from smooth 
trend were found to be independent of NAR. The partial correlation of 
RLGR with evaporating power of the air was not significant though 
fairly large ; contrary to expectation its sign was positive, and this was 
thought to be an indirect effect arising from an association of low evap- 
orating power with waterlogging or leaching caused by high rainfall. 

Blackmail and Rutter (1948, 1950) found that plants of 8 cilia non- 
scripta grown in the open under shades produced a larger total leaf 
area than plants grown with full daylight illumination. The weight of 
leaves was little affected by shading. The ratio of leaf area to leaf 
weight decreased linearly with increase in the logarithm of light inten- 
sity, expressed as per cent of full daylight. The ratio of leaf area to 
total plant weight also showed a linear relation to log light intensity. 


Similar effects of shading on leaf-area ratio were found in experiments 
on other species, including some economic plants (Blackman and Wilson, 
1951b). Monselise (1951) also showed that the leaf area of citrus (Sweet 
Lime) seedlings was increased by shading, and as NAR was unaffected, 
the rate of increase of dry weight was greater in shaded than in un- 
shaded plants. Milthorpe (1945), on the other hand, found that shading 
reduced the leaf area of flax by decreasing both leaf number and leaf 
size. His plants were grown in a glasshouse with a mean day tempera- 
ture about 80F. and a mean night temperature about 70. 

It is reasonable to conclude that growth in leaf area in open-air con- 
ditions is decreased by increase in illumination, whether continuous or 
temporary, and is also affected by temperature. However, the results 
of Gregory and of Milthorpe indicate that in some circumstances, possi- 
bly when temperature is high, leaf area may increase with increase in 

Watson and Baptiste (1938) showed that the rate of leaf production 
from the apical growing point of sugar beet or mangold increased with 
rise in temperature and concluded that both the smooth time trend and 
short-period deviations in the rate were determined chiefly by tempera- 
ture variation. The temperature coefficient (Qw) of the rate of leaf 
production, calculated from the regression of the logarithm of the mean 
rate for sugar beet and mangold on mean temperature for successive 
weekly periods, was 2.4 and was not significantly altered when time trend 
was eliminated. There was evidence of an after effect of low-temperature 
exposure, for on return to a higher temperature the rate of leaf produc- 
tion was temporarily higher than would be expected from the magnitude 
of the temperature rise. The rate of death of leaves could not be shown 
to depend on temperature, except that late in the year it increased as 
the result of injury by frost. There was no obvious seasonal trend in 
the death rate, and this suggests that it was not greatly affected by 
environmental conditions. 

There is evidence from Gregory's experiments on cucumber that 
external conditions at or soon after germination may have a continued 
effect on the subsequent course of leaf area development ; variation of 
temperature in the suboptimal range had no effect on RLGR of the foli- 
age leaves, and the differences in total leaf area between plants grown at 
different temperatures were wholly determined by the time of unfolding 
of the first foliage leaf. The effect of variation in date of sowing on 
the leaf area of sugar beet and mangold (Fig. 4) may have a similar 
explanation. Delay in sowing reduced leaf area per plant (and also 
LAI since the plant populations were similar for all sowings) in July 



and August, but late-sown plants eventually developed a larger leaf 
area than early-sown plants (Watson and Baptiste, 1938; Watson, 
1947a). This was brought about by an increase in leaf size, because the 
late sowings had a smaller number of leaves than the early sowings 
throughout the growth period. The larger leaves of the late-sown plants 




MAY 25 

JUNE 12 







FIG. 4. Effect of date of sowing on leaf area index of sugar beet (Means of 
three varieties. Data from experiments, 1937; Watson, 1947a.) 

were also thinner and had a higher area to weight ratio. Thus, in the 
later stages of growth leaves initiated at the same time attained a much 
larger size in the late-sown plants than in the early-sown. Since the 
climatic conditions during .their growth were identical, the external 
cause of the difference in leaf expansion must have operated at an ear- 
lier stage. The intensity of climatic factors at and soon after germina- 
tion varied with the date of sowing because of the seasonal trend in 
climate, and it seems necessary to assume that this variation in climate 
at the beginning of the growth period induced differences in the internal 
factors controlling leaf expansion that persisted throughout subsequent 
growth. Variation in the date of sowing also affected the relative 
growth of stem and root and the distribution of assimilate between them, 
but whether this was a cause or a consequence of the change in leaf 
expansion is not clear. Nor is it known which climatic factor was the 
operative one. 

Temperature and light may greatly influence the ontogenetic drift in 


leaf area through the control of flowering by vernalization and photo- 
periodism. According to Konovalov (1944) vernalization of wheat ac- 
celerates the rate of production of leaves and shortens their period of 
growth but not their functional life. In consequence the leaf area of the 
plant at any given stage of growth is increased, although the final size 
of individual leaves is little affected. When an inflorescence develops at 
a growing point, production of leaves ceases, and in addition, the pres- 
ence of the growing inflorescence has an inhibitory effect on the expan- 
sion of the young leaves immediately below it. This fact is utilized in 
the commercial practice of topping tobacco plants; removal of the 
inflorescence causes the upper leaves to grow larger than in intact plants 
(Avery, 1934; Petrie, Watson, and Ward, 1939). The inflorescence 
affects cell extension in the upper loaves and not coll division, for the 
increase in leaf area produced by topping is the result of increase in 
coll size, and there is no effect on cell number excopt in the vascular 
tissue. Another consequence of flowering that may affect leaf aroa is 
the breakdown of apical dominance, permitting lateral buds to develop. 

Temperature may affect the leaf area of perennial plants through 
control of bud dormancy. An interesting example of this is found in 
cacao. This species, like many other tropical trees, shows periodic re- 
newal of bud development, leading to the production of new leaves in a 
succession of "flushes," so that growth in leaf area follows a stepwise 
course (Goodall, 1950). In young seedlings, flushing appears to be inde- 
pendent of external factors, but in mature trees it occurs only when the 
daily maximum air temperature rises above 83F. and is inhibited at 
lower temperatures. (Humphries, 1944; Greenwood and Posnette, 

d. Effcci of Variation in Supply of Mineral Nutrients and Water. 
Tt is a familiar fact requiring no documentation that the leaf area of 
plants, in common with other size attributes, is greatly dependent on 
nutrition. The way in which the different aspects of leaf growth listed 
at the end of Sec. IV,2a are influenced by the supply of mineral nu- 
trients is far from being fully analyzed. The following account of some 
of the effects involved is based on observations on material from field 
experiments at Rothamsted (Watson, 1947b), except where other authors 
are quoted. 

Variation in nitrogen supply affects all the phases of leaf growth. 
Increase in leaf area produced by application of a nitrogenous fertilizer 
results from increase in both leaf number and leaf size. The higher 
leaf number may be caused either by an increased rate of production of 
leaves from each growing point, as, for example, in sugar beet or man- 
gold, or by increase in the number of growing points, as in cereal crops, 

134 D. J. WATSON 

the tillering of which is greatly dependent on nitrogen supply. Morton 
and Watson (1948) found that the larger leaves of sugar beet plants 
receiving a high-nitrogen supply had more cells and larger cells than 
corresponding leaves of low-nitrogen plants, showing that nitrogen sup- 
ply affects both cell division and cell extension in the leaf. Because of 
this multiplicity of effects, application of nitrogenous fertilizer tends to 
increase leaf area throughout the whole growth period. 

In contrast with the effect of nitrogen, those of phosphorus and 
potassium appear to be more transitory. Phosphate application was 
found to increase the leaf area of cereal crops mainly by increasing 
tillering, and its effect was greatest near to the time of maximum shoot 
number. Subsequently it declined, falling to zero at about the time of 
maximum leaf area. This suggests that leaf size in cereals is not 
increased by increase in phosphorus supply. Indeed, it may be reduced ; 
Morton and Watson (1948) found that the area of the penultimate leaf 
on the main shoot of barley was consistently less on plots receiving 
phosphate than on plots where phosphate was omitted. Potassium had 
little effect on leaf area of wheat or barley during the tillering phase, 
but increased leaf area during the subsequent phase of shoot extension, 
presumably by increasing leaf size or by delaying senescence. A similar 
difference between phosphate on the one hand and potassium and sodium 
salts on the other was found in experiments on mangold and sugar beet; 
phosphate increased the number of leaves per plant, whereas potassium 
and sodium had no effect on leaf number but caused greater leaf expan- 
sion. However, in mangold phosphate also increased leaf size. Petrie, 
Watson, and Ward (1939) also found that increase in phosphorus sup- 
ply to tobacco increased leaf size, and in this case the effect on leaf 
number was small. 

Information on the effect of nutrition on the length of the functional 
life of leaves is scanty. Application of nitrogenous fertilizer slightly 
increased the death rate of leaves of mangolds, but the increase was 
smaller than that in the rate of production, and this may indicate an 
increase in the longevity of the leaves. As already noted (Sec. IV,lc) 
the evidence on the effects of phosphorus supply on the senescence of 
leaves is contradictory. As the effect of potassium in increasing the leaf 
area of barley was most marked during the period when leaf area was 
decreasing from its maximum, it is possible that increased potassium 
supply delayed senescence of the leaves. 

In general, restriction of the water supply reduces leaf area. Petrie, 
Arthur, and Wood (1943) found, however, that this was true only for 
the earlier part of the growth period of tobacco. Drought conditions 
delayed senescence of the leaves, causing a slower decline of leaf area 


from its maximum, so that plants grown with a continuous high-water 
supply ultimately had a smaller leaf area than plants subjected to 
drought. In experiments on flax (Milthorpe, 1945), drought reduced 
leaf area throughout the whole period of growth, by reducing leaf num- 
ber. This was largely the result of the more rapid death of the lower 
leaves of plants receiving a restricted water supply and partly because 
there were fewer tillers. There was no reduction in leaf size by drought. 
Maximum leaf area was attained earlier in droughted plants, and this 
also was a result of earlier and greater dying off of leaves. The effect 
of drought on senescence of the leaves was thus the opposite of that 
found for tobacco. Variation of water supply had little effect on the 
rates of production or death of leaves of sugar beet, (Morton and Wat- 
son, 1948) ; the reduction in leaf area by drought was therefore the result 
of decreased leaf size, mainly due to a reduction in cell number. The 
effect of drought on leaf area increased with increase in the supply of 

Wadleigh and Gauch (1948) showed that the rate of elongation of 
leaves of cotton decreased with increasing soil moisture stress. Leaf 
growth ceased when the soil moisture stress rose to about 15 atmospheres, 
and the same limiting value was obtained for different irrigation cycles 
during the growth of a given leaf, for different leaves on the same plant 
and for leaves on different plants, although these varied widely in 
growth rate at lower moisture stresses. No data on the effect of varying 
soil moisture stress on final leaf size are given. 

3. The Relative Importance of Variation in Net Assimilation Rate 
and in Leaf Area in Determining Yield 

When Heath and Gregory (1938) put forward their hypothesis that 
mean NAR during the vegetative phase is constant for a wide range of 
species and environments, they also pointed out its implication that, 
since dry matter increase is determined by NAR and leaf area, differ- 
ences in dry matter accumulation must arise mainly from variation in 
leaf area. Although later work has not upheld the constancy of NAR, 
it has confirmed that, in general, dry matter yield does depend more on 
variation in leaf area than in NAR. 

The variation between years in mean leaf area of the same species 
grown in the same situation and between varieties in the same year was 
relatively much greater than the variation in mean NAR (Watson, 
1947a). Throughout the comparisons between years and between vari- 
eties, increase in dry matter yield was associated with increase in mean 
leaf area, but there was no obvious correlation between yield and mean 
NAR. Similarly, varying the supply of nutrients affected dry matter 



production mainly by causing changes in leaf area, and variation in 
NAB was of secondary importance (Watson, 1947b). This is illustrated 
in Fig. 5 which shows the dry matter increment of mangold plants grown 
with a wide range of fertilizer treatments on the Barnfield experiment, 




% 50 


10 20 
LeaF area,( 

30 40 
dm per plant) 




20 40 60 
NAR, (gm pers^dm per week) 

FKJ. 5. The relation of dry weight increase pei plant in the experimental period 
to mean loaf area per plant and to mean net assimilation rate for plants grown on 
plots receiving varied fertilizer treatments in the Barnfield experiment on mangolds, 
Rothamsted (Watson, 1947b). The scales of leaf area and NAR are adjusted so 
that the abscissas of the mean values (represented by crosses) are approximately 
equal. Open circles represent plots which received no nitrogenous fertilizer and black 
circles plots which received sulfate of ammonia (in addition to varying combinations 
of other nutrients). 

Rothamsted, plotted against mean leaf area per plant and mean NAR. 
Dry matter production increased almost linearly with increase in mean 
leaf area over the whole range. Mean NAR was relatively much less 
variable than mean leaf area and showed no consistent trend over the 
greater part of the range of dry weight increase, between 100 and 230 g. 
per plant. The lower values of dry weight increase, below 100 g. per 
plant, on plots receiving no added nitrogen, were associated with a 
marked reduction in NAR, but the effect of nitrogen on leaf area was 
still relatively greater than that on NAR. 

An assessment of the relative importance of variation in leaf area 
and in NAR as determinants of the difference in dry matter yield be- 
tween species must take account of the different lengths of the growth 
period, that is, of variation in the persistence of leaf area in time as 
well as in its mean magnitude. The appropriate measure for this pur- 
pose is the integral of leaf area index over the growth period ; this has 


the dimension of time, and has therefore been termed leaf area duration 
(LAD). The LAD of a crop is a measure of its ability to produce leaf 
area on unit area of land throughout its life and hence of its whole 
opportunity for assimilation. In conditions of constant NAR, dry mat- 
ter production by different crops would be proportional to LAD. 

The mean yields of dry matter for wheat, barley, potatoes, and sugar 
beet grown in several seasons at Rothamsted were found to be approxi- 
mately proportional to mean LAD, so that the ratio of dry matter yield 
to LAD was nearly the same for all crops (Watson, 1947a). This ratio 
is an estimate of dry matter increase per unit leaf area per unit time, 
that is, of mean NAR over the whole growth period, the value of NAR 
at any time being weighted by the magnitude of LAI at that time. The 
ratios for wheat and barley were slightly higher than those for potatoes 
and sugar beet, but the differences were partly attributable to dry matter 
production by photosynthesis in the ears of the cereals. Those results 
indicate that differences in dry matter accumulation between the four 
crops were almost completely accounted for by differences in leaf area. 
At first sight the constancy of the weighted mean NAR for the four 
crops appears to contradict the earlier conclusion (Sec. IV,lb; Fig. la) 
that these crops differ in NAR when compared in the same conditions. 
The reason for the discrepancy is that while wheat and barley produced 
their maximum leaf area in June or early July (Fig. 3), near to the 
time when NAR was also maximal, potatoes and sugar beet failed to 
profit from the high NAR in midsummer because their leaf areas were 
small at this time and did not roach high values until later in the year 
when NAR had fallen to a much lower level, and this was sufficient to 
offset the inherently higher NAR of the potatoes and sugar beet. In 
the estimates of weighted mean NAR, the higher NAR of sugar beet and 
potatoes was counterbalanced by the greater weighting of the high sum- 
mer values of NAR for the cereals, resulting in similar values of the 
weighted mean for all the crops. 

It is evident that variation in dry matter production between differ- 
ent species of annual crops grown in the same situation, liko that between 
varieties of the same crop, between years and between different fertilizer 
treatments, was mainly brought about by variation in loaf aroa, and that 
variation in NAR was relatively unimportant, but this conclusion rests 
on comparison of only four species. 

Some of the factors that influence growth affect leaf area and NAR 
in the same direction ; for example, increase in nitrogen supply or water 
supply in some conditions increases both NAR and leaf area. Other 
factors, of which light is the best example, may have opposite effects on 
NAR and leaf area, and in such cases the resultant variation in dry 

138 D. J. WATSON 

matter production with change in the factor will tend to be small. 
Gregory (1926) noted that "the positive and negative correlations of 
net assimilation rate and relative leaf growth rate respectively with total 
radiation [observed in his experiments on barley] provide a mechanism 
whereby the yield of the plant tends to remain within fairly narrow 
limits, in spite of climatic variation/' Similarly, it follows from the 
linear increase of NAR and linear decrease of leaf weight ratio with 
increase in the logarithm of light intensity, expressed as percentage of 
full daylight, (Blackman and Rutter, 1948; Blackman and Wilson, 
19511)), that RGR increases with increase in light intensity from low 
values to a peak in the neighborhood of full daylight, presumably falling 
again at higher light intensities, so that variation of light intensity in 
the range close to full daylight produces only slight change in RGR 
Consequently, it is likely that yield is little affected by fluctuations in 
natural illumination. Gregory refers to this situation as an example of 
adaptation of the plant to change in its environment, ensuring equal 
facility for growth in a range of climatic conditions, but it is fair to 
point out that as yet there is no evidence of such adaptation to other- 
factors than light. 

The different strains of sugar beet provide another instance of an 
association of increase in leaf area with decrease in NAR; the large- 
leaved E types have a lower NAR than the small-leaved Z types. It is 
unlikely that this inverse correlation is the result of selection for maxi- 
mum yield, for such selection would retain strains that combine large 
leaf area with high NAR, if it were possible for these to occur together, 
though it would eliminate strains having both small leaf area and low 


We may now consider libw far the results reviewed in the preceding 
sections throw light on the efficiency of field crops as producers of dry 
matter and whether they indicate that changes in cultural practice might 
lead to improved efficiency. Much of the following discussion relates to 
crops grown in England, partly because these are the ones with which 
the author is familiar, and also because data for crops in other countries 
are lacking, but the principles involved may have a wider application. 

There appears to be little opportunity for increasing yield through 
increase of NAR. Variation in nutrient supply over a wider range than 
is normal in agricultural practice has only small effects. There is some 
evidence that change in NAR with nutrient supply occurs only at low 
nutrient levels, so that increase in rates of fertilizer application above 
those used at present is unlikely to lead to appreciable increase in NAR. 


The fact that NAR varies between and within species suggests the pos- 
sibility of finding new crops with higher NAR than those now grown, 
or of increasing the NAR of existing crops by plant breeding. However, 
the variation within species so far observed is not great, and the opinion 
of Gregory (1950) that " there is little hope that the efficiency of the 
photosynthetic process can be increased by selection or breeding " is 
probably justified, especially if the association of high NAR with low 
leaf area, shown by the sugar beet strains, occurs generally in other 

It has been shown that the time trend of NAR in natural conditions 
follows the seasonal climatic trend and that short-period deviations from 
smooth trend can be related, to some extent at least, to fluctuations in 
climatic factors. If NAR could be determined more accurately and the 
climate specified precisely by more appropriate meteorological measure- 
ments, it is probable that much more and perhaps most of the variation 
of NAR with time would be accounted for by variation in environmental 
factors. Assuming this to be true, NAR of a field crop at any time is 
determined by the weather conditions at that time and by the genetic 
constitution of the crop plant, but is not much affected by nutrition or 
age. As weather conditions cannot be controlled on a field scale, it fol- 
lows that little can be done by cultural means to improve yield through 
increase in NAR. The factor of water supply must be excepted from 
this statement for it can be controlled by irrigation, and increase of 
yield by irrigation is probably attributable in part to increase in NAR. 
It should be noted here that in places where there is wide seasonal fluctu- 
ation in rainfall, the water supply factor may be an important determi- 
nant of seasonal variation in NAR. For obvious reasons, this is unlikely 
to be true of the changes in NAR (Fig. 1A) of crops grown in England. 

If NAR is fixed by weather conditions and cannot be increased by 
cultural treatment, efficiency in dry matter production must depend on 
making the best use of the period during which the climate favors high 
NAR. From this point of view, barley was the most efficient of the four 
crops for which data are given in Fig. 3, because its maximum LAI 
coincided with the midsummer peak of NAR. Wheat was somewhat less 
efficient ; its LAI attained an earlier maximum, at the beginning of June, 
and decreased rapidly in June and July during the period when NAR 
was greatest. However, photosynthesis in the ears at this time must 
have helped to offset the decline in LAI. Potatoes and sugar beet were 
much less efficient than the cereals, for they produced their greatest leaf 
area too late to profit from the high NAR of the summer months. 

These considerations indicate that the yield of sugar beet could be 
increased by inducing a greater development of leaf area during the 

140 D. J. WATSON 

summer months, and the obvious way of doing this is by earlier sowing. 
Figure 4 shows that early sowing of sugar beet has the desired effect, 
though at the expense of a reduction in leaf area later in the year. How- 
ever, this reduction occurs when NAR has much lower values than in 
midsummer, and so the loss of dry matter production that it causes is 
less than the gain obtained from the increased leaf area in June and 
July. In recent years there has been a steady trend toward earlier sow- 
ing of the sugar beet crop in eastern England, and no doubt this change 
is one of the chief causes of the continuing rise in yield. Previously, 
most of the crop was sown in April or early May, but now much is sown 
in March, and February sowings are not uncommon. The mean date of 
the experimental sowings for which data are given in Fig. 3 was May 7, 
but some of these crops were deliberately sown later than in normal 
practice. Similar arguments suggest that earlier planting of main crop 
potatoes would be advantageous. There is good evidence that delay in 
planting leads to serious loss of yield (Rothamsted Report, 1950) but as 
yet the leaf area changes involved have not been investigated. There 
are, of course, practical limits to earliness of sowing or planting, set 
by the time when the soil becomes dry enough for cultivation and by the 
risk of frost injury to potatoes or of excessive bolting in sugar beet 
caused by prolonged low-temperature exposure. 

There is a possibility that the yield of winter wheat might be in- 
creased by delaying the whole sequence of leaf area development, or at 
least the phase of declining leaf area, so that the maxima in LAT and 
NAR would be more nearly synchronized. The time of onset of the fall 
in leaf area probably depends on the time of formation of the inflor- 
escence, and to delay it would presumably require the temperature and 
photoperiodic responses of the plant to be changed by breeding. The 
same result might be achieved by spring sowing of suitable varieties, but 
hitherto the varieties of spring wheat grown in England have not yielded 
so well as winter wheat. However, new higher-yielding varieties such 
as Atle and Bersee are now available, and the area under spring wheat 
is rapidly increasing. It is possible that spring wheats inevitably have 
a lower LAD than winter wheats and this would offset any advantage 
to be gained from more efficient use of the high NAR of the summer 
months. There is also the practical objection that any change designed 
to make the different cereals more uniform in development would tend 
to make them mature simultaneously and so concentrate the work of 
harvest into a shorter period. 

As the possibility of increasing NAR appreciably by plant breeding 
or cultural means appears to be small, improvement in yield must be 
sought mainly through control of leaf area. The extent to which dry 


matter production could be increased by increase in leaf area depends 
on whether NAR is affected by increase in LAI. If LAI were increased 
indefinitely, at some stage NAR would be expected to decrease through 
reduction in the average light intensity at the leaf surface caused by mu- 
tual shading of the leaves, and possibly through decrease in CO 2 concentra- 
tion of the atmosphere in the neighborhood of the lower leaves due to 
increased uptake of COs in photosynthesis. The value of LAI beyond 
which further increase begins to have an appreciable adverse effect on 
NAR is not known. If it occurred within the range normally found in 
field crops, NAR would be expected to vary with ago, but the results of 
the experiments in which the date of sowing of sugar beet and mangolds 
was varied indicate that the effect of age was small. Comparisons of 
the same species grown in different seasons also suggest that NAR is 
independent of variation in LAI ; variation in the mean LAI of wheat 
in May- June over the range from 1.3 to 3.1, and of sugar beet in July- 
October from 1.3 to 2.5, was not accompanied by any systematic change 
in NAR (Watson, 1947a). This evidence, though far from conclusive, 
suggests that it would be necessary to increase LAI considerably beyond 
the highest values (about 4) shown in Fig. 3 before serious reduction in 
NAR occurred. It follows that if such an increase in LAI could be 
achieved, there would be a corresponding increase in dry matter pro- 

During the greater part of the life of annual crops, LAI has very 
low values. Figure 3 shows that for wheat, barley, and potatoes LAI 
exceeded unity only for ten to twelve weeks of the growing season ; for 
sugar beet the period was longer, but the extension was of little signifi- 
cance for dry matter production because it occurred late in the season 
when NAR was very low. During three-quarters of the growth period 
between sowing and harvest of winter wheat and about half of the 
growth period of the spring-sown crops, LAI was less than unity. So 
long as the leaf area of a crop is less than the area of land on which it 
is growing, that is, when LAI is less than 1, some of the incident solar 
radiation cannot be intercepted by leaves but must fall on bare soil. 
This situation holds for a large part of the life of annual crops and ac- 
counts in part for their very low efficiency of utilization of solar energy. 
An indication of the extent to which dry matter production is limited by 
low LAI can be obtained by calculating from the values of NAR given 
in Fig. 1A (with suitable extrapolation) what the dry matter production 
would be if LAI could be maintained at a value of 4, the maximum in 
the data plotted in Fig. 3, for the six months from April to September. 
The calculated yields are 14 tons dry matter per acre for wheat, and 
24 tons for sugar beet, compared with the maximum yield of 4 to 5 tons 

142 D. J. WATSON 

dry matter that has been obtained at Rothamsted from these crops in 
the most favorable conditions. These figures have a bearing on projects 
to use large-scale cultures of green algae for food production, for they 
indicate the possibility of very high yields of dry matter per unit area, 
if a photosynthetic system equivalent to a field crop with maximal LAI 
could be maintained continuously throughout the period of the year 
when NAR is high. 

In a crop grown from seed, an initial period of very low and slowly 
increasing LAI is inevitable. The length of this period could possibly 
be shortened, and the development of a high LAI hastened, by selection 
and breeding of plants with a high initial RLGR. Application of fertili- 
zers may produce a similar result, and field observations suggest that 
phosphate is particularly effective in hastening leaf growth in the stage 
immediately after germination. Size of the seed, and especially of the 
embryo, is likely to be an important factor determining the initial leaf 
growth rate. Perennial plants are presumably capable of more rapid 
leaf area development in spring than annuals, and an investigation of 
pasture grasses from this point of view would be of interest. 

It has been shown that nutrition has a greater influence on leaf area 
than on NAR, and the beneficial effects of fertilizer applications are 
therefore to be ascribed mainly to increase in LAI. It is probable that 
most agricultural practices designed to increase yield have the same 
physiological basis, and that the development of successful systems of 
crop husbandry largely depends on discovering empirically the optimal 
conditions for leaf area production in a particular environment. In- 
crease of yield through measures taken to control disease, such as the 
rotation of crops or the use of fungicides and insecticides, probably re- 
sults mainly from the prevention of loss of leaf area, though unpublished 
work has shown that some virus diseases cause a reduction in NAR as 
well as in leaf area. Hitherto growth analysis has been applied mainly 
to the investigation of plant growth in relation to environmental factors, 
but the same methods could profitably be used to throw light on the 
physiological effects of attack by pathogenic organisms on crop plants. 

It will be apparent from this review that, though a considerable 
amount of work has been done on growth analysis since the methods 
were outlined by Gregory and by Briggs, Kidd, and West more than 
thirty years ago, only a small part of it relates to field crops, or specifi- 
cally to the physiological basis of variation in yield. Much more attention 
has been devoted to investigation of the causes and significance of vari- 
ation in NAR than in leaf area, though the latter appears to be of far 
greater importance in relation to yield. There is now a need for the 
steady accumulation of data on agricultural crops, covering as wide a 


range of species and environments as possible, to test on a broader basis 
the conclusions already reached, often on slender evidence, and to eluci- 
date the contradictory results, of which several instances have been 
noted. Such data could be obtained without much additional labor, if 
whenever a growth study involving intermittent sampling of a crop is 
undertaken, measurements of leaf area are made in addition to the other 
determinations, for example, of chemical composition, for which the 
investigation may primarily be intended. As Heath and Gregory (1938) 
have pointed out, "much of the information which might have been 
gained [from past growth studies] was not forthcoming owing, pre- 
sumably, to a lack of appreciation of the possibilities of growth analysis. ' ' 

The conclusion of Heath and Gregory (1938) that mean NAR during 
the vegetative phase is constant for all species and environments was 
based on comparisons in which species differences were confused with 
differences in environment. It has been shown not to hold for different 
species grown in the same environment, but a critical test of the con- 
stancy of mean NAR in different environments still requires to be made 
by determining the NAR of the same species grown in a number of situa- 
tions with widely varying climate. This could most conveniently be 
done in a country with a wide latitudinal and climatic range, such as the 
United States; the range available in Britain is too small for this pur- 
pose. Apart from its bearing on Heath and Gregory's hypothesis, in- 
formation on the seasonal trend of NAR in different situations, similar to 
that given in Fig. 1A for southeastern England, would be of great inter- 
est, especially if obtained for the same group of species, for it would 
provide a quantitative basis for comparing the potentiality of the climate 
for dry matter production by crops in different parts of the world. 

Another problem requiring investigation is the dependence of NAR 
of field crops on LAI, and this involves finding a method of varying LAT 
experimentally. The obvious way is by varying the plant population, 
but it is possible that LAI would be limited by nutrient supply and 
would not be greatly affected, except in the early stages of growth, by 
change in plant number. This, rather than a decrease of NAR offsetting 
an increase in LAI, is probably the reason why yield becomes almost 
independent of plant number as the plant population is increased. A 
growth analysis study of the effect of varied spacing on yield would throw 
light on the nature of interplant competition, even if it failed to provide 
information on the effect of NAR of variation in LAI. 

To solve many of the problems which have been discussed, it will be 
necessary to experiment on plants grown in controlled environments. 
The controversy as to the existence of an age effect on NAR can be 
settled only by making measurements throughout the growth period of 

144 D. J. WATSON 

the NAB of plants growing in constant conditions. The effects of 
climatic factors and their interactions on NAR and on leaf growth can 
be fully elucidated only if means of varying the factors independently 
over a wide range are available. Interpretation of the results of growth 
studies on crops growing in natural environments will be made easier if 
comparisons can be made with the same crop grown in a range of con- 
trolled environments, where the climatic factors are held constant or 
made to vary in simple, systematic ways. 

Finally, there is a need for more work on the physiology of leaf 
growth. This aspect of plant physiology has hitherto received too little 
attention. Since it has been shown that leaf area is the major determi- 
nant of crop yield, it is clear that a better understanding of the causes 
of variation in yield depends on a fuller knowledge of the processes that 
control leaf production and leaf expansion and set a limit to leaf size. 


Asana, R. D. 1950. Ann. Botany N.S. 14, 405-480. 

Asana, R. D., and Mani, V. S. 19.10. Phymolofno Plant arum 3, 22-30 

Avery, G. S. 1934. Botan. Gas. 96, 314-329. 

Bald, J. G. 1943. Phytopath. 33, 922-932. 

BaJlard, L. A. T., ami Potno, A. II, K. 193G. Australian J E.rptl Biol MctJ Sci. 

14, 135-103. 

Balls, W. L. 1917. Phil Tianx. Roy. Soc. (London) B208, 157-223. 
Rails, W. L., and Holton, F. 8. 1915. Phil Trans Roy. Soc. (London) B206, 103- 

180, 403-480. 

Blackman, G. E., and Butter, A. .7. 1948. Ann. Botany N.S. 12, 1-20. 
Binckman, G. E., and Ruttcr, A. J. 1950. Ann. Botany N.S. 14, 487-520. 
Blackmail, G. E., and Wilson, G. L. 1951a. Ann. Botany N.S. 15, 03-94. 
Blackmail, G. E., and Wilson G. L. 1951)>. Ann. Botany N.S. 15, 373-408. 
Blackman, V. II. 1919. Ann. Botany 33, 353-300. 

Boonslra, A. E. II. R. 1929. Mcdcdeel Landbouwhoogcschool Wageningen 33, 3-23. 
Boonstra, A. E. II. R. 1937. Mcdcdeel Inst. Suik'crbictcntcelt 7, 79-102. 
Boonstra, A. E. H. R. 1939. Mededccl. Inst. Suikerlietenteelt 9, 161-285. 
Bnggs, G. E., Kidd, F., and West, 0. 1920. Ann. Applied Biol 7, 202-223. 
Brooks, F. T. 1948. Eoy. Soc. Empire Scientific Conf. Ecp. 1, 313. 
Crowther, F. 1934. Ann. Botany 48, 877 913. 
Crowthcr, F. 1937. Jtoy. Agr. Soc. (Cavro) Bull 31. 
Crowther. F. 1944. Ann. Botany N.S. 8, 213-257. 
Englcdow, F. L., and Wadham, S. M. 1923. J. Agr. Sci. 13, 390-439. 
Fisher, R. A. 1921. Ann. Applied Bwl 7, 367-372. 
Forster, H. C., and Vasey, A. J. 1931. J. Agr. Sci. 21, 391-409. 
Frankel, O. H. 1935. J. Agr. Sci. 25, 460-509. 
Goodall, D. W. 1945. Ann. Botany N.S. 9, 101-139. 
Goodall, D. W. 1950. Ann. Botany N.S. 14, 291-306. 
Greenwood, M., and Posnette, A. F. 1950. J. Hort. Sci. 25, 164-174. 


Gregory, F. G. 1917. Third Ann. Rep., Experimental and Eesearch Station, dies- 
hunt, 19-28. 

Gregory, F. G. 1921. Ann. Botany 35, 93-123. 

Gregory, F. G. 1926. Ann. Botany 40, 1-26. 

Gregory, F. G. 1928. Ann. Botany 42, 469-507. 

Gregory, F. G. 1937. Ann. Rev. Bwchem. 6, 557-578. 

Gregory, F. G. 1950. Nature 166, 671-672. 

Gregory, F. G., and Baptiste, E. C. D. 1936. Aim. Botany 50, 579-619. 

Heath, 0. V. S. 1937. Ann. Botany N.S. 1, 565-566. 

Heath, 0. V. S. 1938. Nature 141, 288-289. 

Heath, 0. V. S., and Gregory, F. G. 1938. Ann. Botany N.S. 2, 811-818. 

Humphries, E. C. 1944. Ann. Botany N.S. 8, 259-267. 

Konovalov, I. N. 1944. Sovet. Botan. 3, 21-36. 

Kramer, P. J. 1937. Am. J. Botany 24, 375-376. 

Melntyre, G. A., and Williams, E. F. 1949. Australian J. Sci. Research B2, 319-345 

Milthorpe, F. L. 1942. ,7. Australian Inst. Aor. Sci. 8, 27. 

Milthorpe, F. L. 1945. Ann. Botany N.S. 9, 31-53. 

Monselise, S. P. 3951. Palestine J. Botany, Rehovot Series, 8, 54-75. 

Morton, A. G., and Watson, I). J. 1948. Ann. Botany N.S. 12, 281-310. 

Nutman, F. J. 1937. Ann. Botany N.S. 1, 353-367, 681-693. 

Petrie, A. H. K., Arthur, J. L, arid Wood, J. G. 1943. Australian J. Exptl. Hurt 
Mod. Sci. 21, 191-200. 

Petrie, A. II. K., Watson, K., and Ward, E. 13. 1939. Australian J. Ejrptl Hurt. 
Mcd. Sci. 17, 93-122, 

Porter, H. K., Pal, N., and Martin, R. V. 1950. Ann. Botany N.S. 14, 55-68 

Rotharnsted Experimental Station, Rep. for 1950, 116-118. 

Russell, E. J., and Watson, D. J. 1940. Imp. Bar. Sod Sci. Tech. Commun. 40, 
diap. VII. 

Smith, II. F. 1937. Australia Council Sci. Ind. Research Bull. 109. 

Stephens, S. G. 1942. J. Agr. Sci. 32, 217-254. 

Tiver, N. S. 1942. Australian J. Exptl. Bwl Med. Sci. 20, 149-160. 

Tiver, N. S., and Williams, R. F. 1943. Australian J. Exptl Bwl. Med. Sn. 21, 

Thomas, M. J)., and Hill, G. R. 1949. Photosynthesis in Plants. J. Franck and 
W. E. Loomis, Editors, Iowa State College Press, Ames, pp. 19-52. 

Wadleigh, C. H., and Gauch, H. G. 1948. Plant Physiol. 23, 485-495. 

Watson, IX J. 1937. J. Agr. Sci. 27, 474-483. 

Watson, D. J. 1947a. Ann. Botany N.S. 11, 41-76. 

Watson, D. J. 1947b. Ann. Botany N.S. 11, 375-407. 

Watson, P. J., and Baptiste, E. C. D. 1938. Ann. Botany N.S. 2, 437-480. 

Watson, D. J., and Norman, A. G. 1939. J. Agr. Sci. 29, 321-346. 

Williams, R. F. 1936. Australian J. Exptl. Blol. Med. Sci. 14, 165-185. 

Williams, R. F. 1937. Nature 140, 1099-1100. 

Williams, R. F. 1939. Australian J. Exptl. Biol. Med. Sci. 17, 123-1, i2. 

Williams, R. F. 1946. Ann. Botany N.S, 10, 41-72. 

Yates, F. 1936. J. Ministry Agr. (Engl.) 43, 156-162. 

Copper in Nutrition 


Battelle Memorial Institute, Columbus, Olno 



1. Introduction . ... 147 

II. Historical 148 

TTT. Value of Copper to the Plant 151 

IV. Effects of Copper Deficiency in Plants .... . 153 

V. Copper in the Soil . 156 

1. Amount ... 156 

2. Factors Influencing Availability 156 

3. Effect on Crop Yields 157 

4. Comparison of Different Forms of Copper for Use as a Roil 
Amendment I.")!) 

5. Residual Effects 160 

6. Possible Toxic Effects 161 

7. Effect on Availability of Other Elements 162 

8. Aspcrgillus niger ... 164 

VI. Copper in Animals . ... . . . 165 

1. Use in the Body . . 165 

2. Deficiency Symptoms 166 

3. Use as an Anthelmintie and in Mineral Supplements . ... 168 

4. Toxicity .... 169 

VII. Begions of Copper Deficiency 169 

1. Europe 170 

2. South Africa and the Antipodes 170 

3. America . 171 

References ... 173 


Prom supposed poison to nutrient in twenty-five years. How rapidly 
theories are altered and values changed in the light of advancing scien- 
tific knowledge. This is the story of copper, which, along with cobalt 
and one or two other elements, has quickly leaped from obscurity to 
prominence in the field of nutrition. 

Formerly, we were apprehensive about the possible toxic effects of 
Bordeaux spray residue, or the harmful consequences we thought might 
occur when we found that the infant son had been mouthing a penny. 
At present, we are more concerned in determining whether our crops 
are getting enough trace elements, our livestock the correct mineral, 



protein, and carbohydrate ratio, and ourselves a balanced diet. Copper 
is now acknowledged to play a very important part in each of these 
nutritional relationships. 

Although the presence of copper was demonstrated in some plants 
and animals early in the nineteenth century, the metal was long believed 
to be carried about passively. For a hundred years, scientists did not 
challenge this assumption. About 1920, however, copper was accepted, 
rather suddenly, as an essential constituent of all living material, and 
interest in determining its necessity and possible nutritive role expanded 
rapidly. The essentiality of copper is now unquestioned, but much re- 
search lies ahead before a complete knowledge of its function in living 
organisms can be obtained. 

Copper compounds are used extensively throughout the world for 
the control of plant disease. Most reports have been on the use of the 
old copper fungicide, Bordeaux mixture. The story of this fungicide, 
starting with its accidental discovery by Millardet, near Bordeaux, 
France, in 1882, makes an intriguing chapter in the history of plant 
disease control, but is outside the scope of this work. 


Copper is believed to be the first metal employed by man. This is 
undoubtedly due to the fact that it occurs in quantity in the free state. 
There is no way of determining, within a period of centuries, when 
copper was first used, but the Copper Age followed the Stone Age, and 
artifacts, weapons, and utensils of the metal were made before the dawn 
of written history. The American Indian worked the copper of the 
Lake Superior region prior to the arrival of the white man. 

The occurrence of the element in plant tissues was reported in 1816 
(Dawson and Mallette, 1#45), and a few years later its presence in ani- 
mal tissues was also demonstrated. For a long time it was generally 
believed that the copper present in biological material was merely acci- 
dental and had no definite function. The amounts in living tissue are at 
best very small, and early analytical methods were not particularly 
sensitive. It is understandable, therefore, why the first reports were 
often conflicting, and occasionally, erroneous. 

Copper research with invertebrate animals developed much earlier 
than with vertebrates. This was perhaps due to the fact that most in- 
vertebrate blood contains relatively larger amounts of copper. The 
metal was detected in the blue blood of snails in 1847 as part of a 
protein complex which was established as a definite respiratory pigment. 


The pigment behaved with oxygen in a manner similar to that of hemo- 
globin, and was given the name hemocyanin. 

About the same time, the presence of copper was demonstrated in the 
human body, but it was considered to be quite accidental. Little inter- 
est was created, and studies of copper in vertebrates languished for 
neaily a century. It was not until after 1920 that copper was accepted 
as a definite constituent of vertebrate as well as invertebrate tissue. An 
important milestone in copper research on vertebrates was the work 
conducted at the University of Wisconsin and initiated about 1924. 
This research revealed the fact that copper plays an important role in 
the formation of hemoglobin. The findings naturally led to a close 
examination of the distribution of copper in all living tissues and food 
and to studies of the relationship of copper to certain enzyme systems. 
The development of research on copper in animals has been covered a 
number of times in recent literature (Elvehjem, 193.5; Rawlinson, 1943; 
Redfield, 1934; Schultze, 1940; Sheldon, 1932). 

Early in the present century it was suspected that copper might be 
essential to plants. Investigations about this time showed that all plant 
material examined contained from three to forty or more parts per 
million of the element, and applications of Bordeaux sometimes increased 
yields even when no disease was present (Lutman, 1911). Lutman 
(1916) and later Cook (1923) reviewed the various reports of the stimu- 
lating effect of copper on plant growth, usually in connection with the 
use of Bordeaux mixture. In these two reviews, however, the essential- 
ity of copper, and therefore, the possibility that the stimulating effect 
might be due to a deficiency of the element in the soil, was apparently 
not considered. 

The success of early experiments was hindered, not only by impurities 
in the nutrient salts used, but also by the traces of copper in water from 
stills with metal condensers (Stout and Arnon, 1939). Thus, Brenchley 
(1914) found only toxic effects when copper was added to solution cul- 
tures. Sommer, in 1931, however, used special purified salts, and \vater 
redistilled in Pyrex, and became the first to demonstrate that, without 
a minute amount of copper, plant growth cannot take place. Her work- 
was corroborated the same year (Lipman and Mackinney, 1931), and the 
status ef copper as a plant nutrient was firmly established. 

The effects of lack of available copper in the soil appear not only in 
vegetation growing on these soils but also in animals feeding on this 
vegetation. The symptoms in both plants and animals may range all the 
way from slightly reduced growth to definite pathological symptoms, 
depending on the severity of the deficiency. Two main groups of plant 
diseases caused by a lack of copper are recognized. The first comprise 


those affecting fruit trees, especially citrus, and are referred to as " die- 
back " diseases or l ' exanthema. " They are widely distributed and have 
been described many times (Andersseii, 1932; Floyd, 1910, 1917; Oser- 
kowsky and Thomas, 1938). The second group affects cereals chiefly 
and is made up of the disorders covered by the term "reclamation dis- 
ease/' Such disorders have been noted for many years in a wide range 
of crops on the heath soils of northwestern Europe. 

Long before a lack of copper in any soil was suspected, a wasting 
disease of cattle, commonly known as " Lechsucht, " was prevalent in 
Europe. It was not until 1933 that it was shown to be caused by a lack 
of copper in the forage eaten (Sjollema, 1933). In the meantime, similar 
bovine troubles were reported from other parts of the world. Symptoms 
were not the same in every case, which suggested that other factors might 
be involved, even though copper therapy always resulted in improve- 
ment. Various sheep troubles were also traced to a lack of copper, but 
here again, symptoms varied somewhat in different countries. 

Soils high in organic matter, particularly newly cultivated peat soils, 
are most frequently discussed in connection with copper deficiency. 
There are many reports of the successful use of copper sulfate or other 
forms of copper on such soils (Allison el aL, 1927; Felix, 1927). 

Recently, it has been found that applications of copper to mineral 
soils increased production even where these soils apparently contained 
enough copper for normal growth (Berger and Truog, 1949; Gilbert, 
1948a; Manns et al., 1937; Swanbaek, 1950). The conclusion was 
reached (Swanback, 1950; Willis and Piland, 1936) that copper, in 
addition to its nutritive value, acts as an oxidation catalyst in rendering 
other elements available. Such results indicate that copper and possibly 
other trace elements have considerably more value as soil amendments 
than is suggested by the slight amount taken up by the plant. 

Because copper is essential to both plants and animals and because 
deficiencies of the element are widespread in the soils of the world, it 
was chosen as the subject of the first symposium of the McCollum-Pratt 
Institute held at Johns Hopkins University, June 14-16, 1950. The 
symposium covered many phases of copper nutrition, including its enzy- 
matic functions, the effect of its deficiency on plants and animals, and 
the interrelationships between copper and other nutritive elements. The 
papers and discussions presented at this symposium have been published 
(McElroy and Glass, 1950). 



All plants contain copper. Early reports were concerned chiefly with 
the possible health danger of an excessive amount in food (Carles, 1917). 
However, this concern gradually disappeared when it was found that 
even fruit with copper spray residue usually contained less of the ele- 
ment than many food materials which had been consumed for years 
without ill effects (Anonymous, 1923). 

The amount of copper in a plant varies, depending on species, soil, 
the amount of fertilizer used, and other factors. However, similar foods, 
under the same circumstances, contain approximately the same amount 
of the element. In descending order of copper content, some different 
classes of plant foods are arranged as follows : nuts, dried legumes, 
cereals, green legumes, roots, leafy vegetables, fruits, and nonleafy vege- 
tables (Lindlow et al., 1929). A summary of the published copper 
analyses of crops has been recorded up to 1941 (Beeson, 1941). 

The amount of copper in a plant may be increased by copper fertili- 
zation (Colman and Ruprecht, 1935; Elvehjem and Hart, 1929; Miller 
and Mitchell, 1931). By this means, in sand culture, the writer in- 
creased the copper content of the corn ear from 5 to 28 parts per mil- 
lion. Bacon and associates (1950) found that copper was taken up by 
the leaves of tobacco plants in amounts varying directly with the 
amounts applied to the soil. However, even when a greater yield results 
from the use of copper, an increase in copper content does not always 
take place. For example, Swanback (1950), in a series of experiments 
covering a period of three years, obtained substantial weight increases 
in tobacco by soil treatments with copper. With one exception, there 
was less copper deposited in leaves with copper sulfate supplied in the 
soil than without it, indicating that active copper in the soil is not al- 
ways synonymous with absorbable copper. 

The methods of determining available copper in soils are not entirely 
satisfactory at present, and can be expected to give only approximate 
results. Therefore, leaf analysis is coming into greater use in an effort 
to indicate the actual amount of soil copper available to the plant. We 
are warned, (Steenbjerg, 1948), however, that leaf analysis of the cop- 
per content of plants is not an infallible guide in the diagnosis of copper 
deficiency. When growth is severely stunted, as it usually is under 
conditions of severe copper deficiency, the copper content of the plant 
material (as per cent of dry matter) may not be unduly low. 

Bordeaux mixture has been found many times to increase the yield 
of potatoes even where the control of disease was not a contributing 
factor (Cook, 1923; Lutman, 1911; Whetzel et al., 1936). This has 


been attributed in part to the lengthened life of the plant, and, in part, 
to a favorable influence on tuber composition. Tubers from sprayed 
vines were usually higher in solids, starch, and nitrogen than tubers 
from unsprayed vines (Cook, 1923). The increased yield and increased 
solids of the tubers apparently depended on the presence of copper in 
the spray, since yields of tubers were decreased when a lime spray con- 
taining no copper was used. In the writer's experiments, tobacco on 
land treated with copper sulfate tended to ripen somewhat later than 
tobacco on land not so treated, and this has been found to be true also 
for other crops (Russell and Manns, 1934). 

Copper has some function in chlorophyll formation, although the 
chlorophyll molecule contains no copper. This function is presumably 
indirect, since plants may cease to grow as a result of copper deficiency 
and still show no signs of chlorosis (Sommer, 1945). Spraying with 
copper has been found to increase the chlorophyll content of wheat 
(Okuntsov, 1946a), cranberries (Bergman and Truran, 1933), citrus 
(Orth et at., 1934), and other plants. A copper treatment may not only 
increase the amount of chlorophyll in a plant, but it may also have a 
protective effect against chlorophyll destruction (Anderssen, 1932; Berg- 
man and Truran, 1937; Okuntsov, 1946b). This would retard the physi- 
ological aging oE the plant and result in a longer life. Chlorophyll is 
extracted with more difficulty from copper-sprayed plants than from 
unsprayed ones (Lutman, 1916). 

From a physiological point of view, copper is important as a con- 
stituent of at least three enzymes : ascorbic acid oxidase, laccase, and 
tyrosinase. The latter may be taken to include monophenol and poly- 
phenol oxidases. Ascorbic acid oxidase catalyzes the oxidation of 
ascorbic acid (vitamin C) in the presence of oxygen (Stotz et al., 1937). 
Laccase will oxidize various phenolic compounds (Keilin and Mann, 
1939, 1940). It is similar-to tyrosinase, but differs in that it does not 
oxidize tyrosine or p-cresol. 

Tyrosinase is the best known of the copper enzymes. In 1937, as 
polyphenol oxidase, it was obtained from potato juice (Kubowitz, 1937), 
and since that time it has been purified from a number of plant sources 
(I)alton and Nelson, 1939; Keilin and Mann, 1938; Parkinson and 
Nelson, 1940). In chard leaves, the enzyme was found to be located in 
the chloroplasts, since the cytoplasm did not show- any appreciable 
oxidase activity, Arnon, 1949). In studying the tyrosinase activity of 
potato tubers in relation to enzymatic blackening, it was found that 
tubers from plants grown on soils poor in copper, although making an 
entirely normal appearance, had a tyrosinase activity less than one-tenth 
that of tubers from plants with a normal copper supply. As a result of 


the low tyrosinase activity, blackening of bruised potatoes deficient in 
copper was slight in comparison with tubers supplied normally with the 
element (Mulder, 1949). 


The effects of copper deficiency in plants range all the way from 
slightly reduced growth to disease symptoms so severe that death eventu- 
ally ensues. In the case of copper deficiency of woody plants, a more 
or less chronic condition known as "dieback" or "exanthema" fre- 
quently occurs. This disease may kill the tree, but more often merely 
results in unthriftiness. "Dieback" occurs in many parts of the world, 
on many kinds of trees. A large number of the published reports have 
been in connection with citrus (Camp and Fudge, 1939; Cipola, 1937; 
Floyd, 1917; Fudge, 1939; McCleery, 1929), but tung (Dickey et al., 
1948; Drosdoff and Dickey, 1943; Gilbert et al., 1946), avocado (Ruehle 
and Lynch. 1940), olive (Smith and Thomas, 1928), apple (Anderssen, 
1932; Dunne, 1938), pear (Oserkowsky and Thomas, 1938), and plum 
(Cahill, 1929) are among other trees affected. 

"Dieback" was first described on oranges in Florida in 1875 
(Fowler). The causal agent, at that time, was believed to be a fungus. 
It was recognized in California in 1896 and is now known to occur in 
most of the citrus-growing areas of the world. Copper was used as a 
corrective for many years before lack of the element was proved to be 
the actual cause. 

An early symptom of copper deficiency is an unusually dark green 
color of the foliage, indicative of a high nitrogen concentration. This 
symptom is characteristic of copper deficiency in other plants also and 
has been observed under controlled conditions in the laboratory. 

In acute copper deficiency of citrus plants, the twigs start to die, 
and the leaves soon turn a yellow-green color, drop quickly, and leave 
the twig denuded (Camp and Fudge, 1939). Gum pockets may form 
between the wood and bark of the twig near the leaf bases, and the twig 
is often covered by a typical, reddish brown, gummy excrescence. Multi- 
ple buds form below the injured twigs, but the growth that develops 
from these buds also dies back. 

The quality of the fruit on copper-deficient trees deteriorates even 
before the appearance of leaf and twig symptoms, and an overly large 
proportion of the crop is thrown into the lower grades. In more severe 
cases, splitting of the fruit is common, and the brown gummy excrescence 
also appears on the rind. Such fruit is usually shed before the period 


of normal maturity. Affected trees may bloom profusely in the spring 
and set a heavy crop of fruit, which is shed hy midsummer. 

In stone fruits, copper deficiency restricts growth considerably, and 
the trees are small and underdeveloped. Vigorous spring growth is 
produced, but the leaves soon turn yellow and drop, and there is serious 
twig dieback. Eruptions of the bark and swollen multiple buds occur as 
in citrus. 

As has been mentioned, herbaceous plants may also be affected by 
copper deficiency and symptoms are even more severe than on woody 
plants. The "reclamation" disease of small grains and other crops, due 
to insufficient amount of available copper in the soil, commonly occurs 
on newly cultivated organic soils (Brandenburg, 1935; Hoffmann, 1939; 
Melchers and Gerritsen, 1944 ; Nicolaisen and Seelbach, 1938 ; Proskura, 
1940; Smith, 1927), but has also been found in alkaline calcareous areas 
(Piper, 1938, 1940). The trouble was originally attributed to the toxic 
action of a contituent of the peat, but Sjollema (1933) showed that the 
disease could be cured by the addition of copper sulfate to the soil, and 
his results were soon confirmed by others (Brandenburg, 1935; Nicolai- 
sen and Seelbach, 1938). 

The disease produces very characteristic and easily recognized symp- 
toms in oats and other cereals, and many descriptive names have been 
given to it, including "yellow tip" and "wither tip." In general, the 
plants make fairly normal growth for several weeks, but with the ap- 
proach of spring, a marginal chlorosis appears and the leaf tips wither, 
droop, and become yellowish gray. The tips of newly emerging leaves 
become chlorotic, wither, and die without unrolling. The lower leaves 
may remain green for a considerable time, and numerous secondary 
tillers develop freely from the base of the plant, but these also show leaf 
symptoms at a later stage. No inflorescence is produced in severe cases, 
although secondary tiller^ continue to form. The withered leaf tips, 
bushy growth, and greenness at the base of such copper-deficient plants 
present a striking contrast to normal plants. 

An inflorescence is formed in less severe cases, but the chaff is whit- 
ish, and practically no grain is produced. Deficient grain formation is 
one of the most characteristic features of the disease in the field, since it 
may result from a copper deficiency, which is not sufficiently severe to 
affect the vegetative growth. This has also been demonstrated in the 
laboratory (Piper, 1940). 

Smith (1927), in studying the reclamation disease in Holland, iso- 
lated an organic substance, which, he claimed, produced symptoms of 
the disease in normal pea and oat plants. He concluded that the bene- 
ficial effect of copper in soils which produced plants with reclamation 


disease was due to the formation of an insoluble compound of copper 
with the organic substance. Other investigators (Brandenburg, 1935; 
Piper, 1942), however, confounded Smith's theory by obtaining symp- 
toms of reclamation disease in copper-free solutions to which no toxic 
substance had been added. 

Copper-deficiency symptoms in tomato plants under greenhouse con- 
ditions have been described several times (Arnon and Stout, 1939; Bailey 
and McHargue, 1943; Gilbert, 1948b; Piper, 1940, 1942; Reed, 1939; 
Sommer, 1931). The dark green color of the somewhat smaller leaves 
whose margins curl upwards and inwards and the permanent wilting of 
the entire top of the plant are characteristic. Similar symptoms are 
shown in tobacco (McMurtrey and Robinson, 1938) and sunflower (Som- 
mer, 1931). The wilting characteristic, even under ample moisture con- 
ditions, seems to be a constant symptom, but others, such as chlorosis 
as found in sugar beets (Van Schreven, 1936), may vary in different 
species and under different conditions. 

Some crops are much more sensitive to copper deficiency in the soil 
than others. For instance, wheat and oats are less tolerant of a lack of 
copper than rye and may fail entirely on a deficient soil which produces 
good crops of rye. 

Tobacco (Gilbert, 1948a; Swanback, 1950), sweet corn (Berger and 
Truog, 1949), and onions (Felix, 1927 ; Knott, 1936), in most cases, make 
much better growth on copper-treated soil than on untreated soil, al- 
though, with the possible exception of onions, copper-deficiency symp- 
toms in these plants have never been noticed in the field. Copper was 
found in at least two cases to increase the duration of burn in tobacco 
(Swanback, 3950; Tisdalo, 1930), but one other experiment reported by 
(). E. Street of the Pennsylvania tobacco experiment station in 1949 
(personal correspondence) was not in accord. It seems safe to assume 
that there is no retarding effect. 

Fertilization not only increases crop yields, but it decreases frost 
damage (Davis, 1950). When trace elements, especially copper, are 
added to the fertilizer, even more protection is afforded (Harris, 1948). 
This point has been well illustrated in Florida citrus orchards after 
certain severe freezes (Lawless and Camp, 1940). Little or no damage 
was done to the completely fertilized trees, but considerable defoliation 
and fruit drop occurred on trees not receiving the minor elements. 



1. Amount 

Copper is generally estimated to range from one to over fifty parts 
per million in normal agricultural soils (McMurtrey and Robinson, 
1938). Holmes (1943) studied the copper contents of a large number 
of United States soils and obtained similar results. His range was from 
two to sixty-seven parts per million. As might be expected, the severely 
weathered, leached, and more acid soils of the South Atlantic states 
averaged much lower in total copper than soils from more western states, 
such as Missouri and Oklahoma. 

The intensity of soil acidity and the composition of the parent mate- 
rial have considerable influence. For example, Cecil and Decatur soils 
from southeastern United States differs widely in copper content, al- 
though they belong to the same great soil groups, and have similar pll 
values, texture, and color. They are, however, derived from different 
parent materials. The Cecil soil is from granite, which was probably 
weathered under more acid conditions than the Decatur, derived from 
limestone. Consequently, since copper is more soluble under acid con- 
ditions, the Cecil soil retained less of the copper of the parent rock than 
the Decatur. It was assumed that the content of the element was nearly 
the same to start with. 

Collington and Norfolk soils are both of coastal plain origin and have 
similar texture and pll values The Collington, however, which is de- 
rived from green-sand marl, contains approximately three times as much 
copper as the Norfolk soil, which is derived from the more common 
coastal plain materials. 

Tt should be understood that the total quantity of copper in a soil 
constitutes an inventory only and does not indicate the amount available 
to plants growing on that Soil. Brun (1945) found that the copper con- 
tained in Norwegian humus soil could be divided into three categories: 
water soluble, absorbed, and fixed. The last could not be removed with- 
out chemical destruction of the soil, and, of course, would be unavailable 
to plants. It is quite possible for a soil to be high in total copper and 
yet be low in available copper. 

2. Factors Influencing Availability 

Many factors influence the degree to which soil copper is available 
to the plant. These include pH value, humus content, nature of the 
previous crop, amount of clay and sand, and effect of other elements 
(Steenbjerg and Boken, 1950). Frequently several factors are effective 


at the same time. Most workers report that copper availability lessens 
with decreased acidity of the soil. Peech (1941) and Piper (1942) 
found that a decrease in acidity for any given level of copper reduced 
the availability somewhat when measured either chemically or by total 
copper absorbed by plants. In soils of high organic content, such as 
peat soils, however, the reverse may be true the more acid the peat, the 
greater may be the relative response to copper, and the greater the 
number of crops that are likely to benefit by the copper application 
(Harmer, 1946). 

The amount of organic matter present in a soil exerts a great in- 
fluence on the availability of soil copper. In fact, many highly organic 
soils can be made profitable only after large amounts of copper have 
been applied to them (Browne, 1950; Comin, 1944; Harmer, 1941, 1946). 
The most striking example, perhaps, is the saw-grass peat of Florida, 
where almost useless soil was made to produce good crops by copper 
fertilization (Allison, 1930; Allison et al., 1927). Truck farmers on the 
Carolina coastal plain usually apply 200 Ib. of copper sulfate per acre 
to newly cleared peat soils and may apply as much as 50 Ib. per acre 
per year thereafter, if justified by results. 

It has been suggested (Steenbjerg and Boken, 1950) that the great 
copper deficiency that appears in newly cultivated peat soils must be 
explained by the original low content of available copper and that this 
is aggravated by dressings of nitrogen, phosphorus, and potassium 
hence the continued use of copper on these soils. 

3. Effects on Crop Yields 

Although copper deficiency occurs, particularly on peats and other 
soils with a very high humus content, it is also common on very sandy 
or gravelly soils with a low humus content (Anderssen, 1932; Riceman 
et al., 1938). It is less common, but sometimes occurs in mineral soils 
with a fair amount of organic matter (Isaac, 1934; Rohrbaugh, 1946). 

A copper deficiency severe enough to cause disease symptoms insures 
remedial measures, but if less severe, usually attracts little attention. 
The result is that maximum growth is not obtained with many crops for 
lack of a pound or two of copper which could be supplied at slight cost 
per acre. Greenhouse and field plot tests have shown that the first slight 
indication of the need for the element is demonstrated by a retardation 
of growth, which occurs long before any visible symptoms are apparent. 
Since areas of marginal deficiency will outnumber areas of acute defi- 
ciency, it is difficult to estimate the amount of potential yield actually 

In addition to the instances where borderline copper deficiences have 


been demonstrated, there are many where applications have resulted in 
marked crop increases, even though the copper content of the soil ap- 
peared to be ample. In the United States, an impetus was given to the 
use of copper on the Atlantic coastal plain soils during the period from 
1934 to 1937. An analysis of twenty-five of these soils demonstrated that 
while none were extremely low in copper, in only four did the copper 
content exceed twenty parts per million (Manns and Russell, 1935). 

Remarkable results were obtained by adding copper sulfate to the 
fertilizer. In field experiments carried out in North Carolina, South 
Carolina, and Virginia in 1935, the average yield of tobacco was in- 
creased 43.9 per cent, and the quality, 10.4 per cent. The yield of cotton 
was increased 20.23 per cent (Churchman ct al., 1936, 1937). In Dela- 
ware, the average values of sweet potatoes, tomatoes, arid lima beans 
were increased 4.45, 9.65, and 43.55 per cent respectively (Manns ct a/., 

In Wisconsin, on Miami silt loam (Berger and Truog, 1949), the 
yields of usable corn ears were 5 to 40 per cent greater when copper 
sulfate was added to the fertilizer. Several investigators have found 
that copper increased tobacco production. In Pennsylvania, 0. E. Street 
of the tobacco experiment station at Lancaster obtained a weight increase 
of 27 per cent in cigar-filler tobacco (personal correspondence, 1949). 
In Florida (Tisdale, 1930), copper increased the percentage of uni- 
formly colored leaves of flue-cured tobacco. In Connecticut (Swanback, 
1950), in experiments with Havana seed tobacco covering a period of 
three years, it was found that copper gave an increase of from 13 to 
more than 26 per cent in crop value. 

F. A. Gilbert (1948a), over a period of eight years, conducted more 
than two hundred field experiments, primarily on tobacco. The purpose 
was to determine the value of copper on soils which were not considered 
to be actually deficient in the element. The tests were made with Burley 
tobacco in four Ohio valley states, and with flue-cured tobacco, in Vir- 
ginia and the Carolinas. Available copper in these soils ran from one 
part per million in a few coastal plain soils to sixteen parts per million 
in some of the Ohio valley soils. The majority were between five and 
ten parts per million. 

In approximately 80 per cent of the tests, an increase in the weight 
of tobacco, in the quality of the leaf, or in the two together, was obtained. 
No satisfactory correlation between available soil copper and increased 
yields were found except at the extreme levels of the soil copper. In 
some cases, identical procedure on the same soil type on near-by farms 
gave quite different results. The greatest increase in production was 
35 per cent, and the average was about 8 per cent, which did not equal 


the results obtained by Churchman and his associates (1936) over much 
of the same territory. 

The only similar set of experiments on copper sulfate was conducted 
in Denmark, primarily on cereals (Steenbjerg and Boken, 1950). Six 
hundred and forty trials were conducted over a period of nineteen years, 
and the results were quite similar to those obtained by Gilbert 87 per 
cent of the copper-treated plots yielded increases as compared to Gil- 
bert's 80 per cent. 

4. Comparison of Different Forms of Copper for Use 
as a Soil Amendment 

Copper sulfate is the form of copper most frequently employed for 
soil-amendment purposes and until recently was used exclusively. Dur- 
ing the past few years, however, continuing experiments have shown that 
copper in other forms, including' finely ground copper minerals, might 
be used to correct deficiencies of the element in the soil. Several of these 
minerals in a comparatively impure state contain more of the metal than 
copper sufate, and it is not difficult to concentrate it even farther by a 
flotation process. 

Among the forms of copper that have been tested are pyrites ash, 
malachite, copper flake, cupric oxide, cuprous oxide, oxide mixtures, 
copper acetate, copper carbonate, copper chloride, and several copper- 
bearing sulfide ores, including chalcopyrite. Pyrite ash, which contains 
from 1 to 2 per cent of copper, is obtained in the production of sulfuric 
acid by roasting pyrite. The ash has been used experimentally as a 
copper fertilizer in Denmark (Steenbjerg and Boken, 1950), but will 
never be of any importance in competition with other forms of copper 
because of transportation costs. 

Teakle and his associates in Australia (1941, 1943a, 1943b) compared 
oxidized copper ore, roaster residues from pyrites burners, and copper 
sulfate as sources of fertilizer copper and found all to be of value. No 
one form was better than others under all conditions. However, the 
sulfate was at a disadvantage in the Australian experiments. It alone 
did not contain zinc and possibly other undetermined constituents, which 
Teakle admitted may have affected the results, since there was evidence 
pointing to a need for zinc on some of the soils used in the tests. 

In Denmark (Steenbjerg and Boken, 1950), finely ground copper 
pyrites containing 12.8 per cent copper and considerable zinc were found 
to be inferior to copper sulfate as a soil amendment, but could be used 
were it economical. No response of the soil to zinc was demonstrated. 
In the United States, copper flake, the copper oxides, and other copper 
salts have compared favorably with copper sulfate as a soil amendment 


in a few experiments which are being continued, but have seldom sur- 
passed the sulfate in effectiveness. 

On peat soils in which soluble copper is quickly "tied up," the small 
crystal form of copper sulfate is preferred to the powdered form, since 
it remains available longer. On such soils, after the immediate copper 
needs have been met, the use of finely ground minerals of high copper 
content, because of their slow solubility, might be preferable to a form 
of copper quickly soluble which has to be applied at frequent intervals. 
Another advantage claimed for the less soluble forms of copper is that 
there is no danger of a toxic effect with very large dressings (Wild and 
Teakle, 1942). 

The application of a soil amendment depends not only on its effect, 
but also on its price. A refined industrial product is more expensive 
than the raw material from which it is produced in this case some 
copper mineral. On the other hand, in fortifying high-analysis fertilizer 
with copper or other trace elements, a high metallic content is of prime 
consideration in order not greatly to change the percentage of NPK. 

5. Residual Effects 

Copper has considerable residual effect in mineral soils much less 
in organic soils. Copper applications must be made more frequently, 
therefore, on heavier soils and on extremely sandy soils subject to exces- 
sive leaching. The residual value of as little as 3 to 10 Ib. of copper 
sulfate on sandy Australian soils was sufficiently substantial so that no 
response was obtained with additional amounts the following year 
(Teakle, 1942). Danish experiments (Steenbjerg and Boken, 1950) 
showed that approximately 40 Ib. per acre was effective for at least three 
years, and the writer, in experiments continuing since 1946 on mineral 
soils, finds that beneficial effects are still obtained from original applica- 
tions of 20 and 40 Ib. of copper sulfate per acre. In Florida (Harris, 
1948), it was found that a 30-lb. application of copper sulfate was ef- 
fective for at least five years, and in California the beneficial effect of 
copper sulfate soil treatments for "exanthema" of pear trees lasted over 
three years (Oserkowsky and Thomas, 1938). 

Copper in organic soils is held tenaciously in the zone of placement 
(Allison, 1931; Lucas, 1948), and preliminary experiments at Battelle 
Institute have shown that a similar tendency exists in a clay loam with 
a fair amount of organic matter. Organic soils collected five years after 
receiving a 50-lb. application of copper sulfate showed that an approxi- 
mate equivalent of 48 Ib. remained in the upper 8 in. This explains why 
shallow-rooted crops are more responsive to copper applications than 
deep-rooted crops and why copper spraying of fruit trees affected by 


"exanthema" is often more effective than soil applications. Although 
the copper in organic and heavy mineral soils is leached slowly, and 
with difficulty, the "fixing" power of such soils is so great as to offset 
this advantage, and such soils usually require more copper than the 
lighter types. 

6. Possible Toxic Effects 

In spite of the many successful experiments on the use of copper, it 
has not been generally accepted as a soil amendment to the extent that 
it is included as a general fertilizer ingredient. In areas of extreme 
copper deficiency, its use is imperative, but in regions where soil treat- 
ments are not 100 per cent successful, little copper is used. In fact, 
there is considerable opposition to its inclusion in general fertilizer 
mixtures on the grounds of its cost, and its possible toxicity over a period 
of years. 

The writer found that the growth of tomatoes in nutrient solution 
was depressed by a concentration of as little as one part per million, but 
some growth was obtained in acid-washed sand when a nutrient solution 
containing five parts per million was applied. Copper toxicity occurred 
on certain extremely sandy western Australian soils with applications 
of as little as 10 Ib. of copper sulfate per acre (Teakle, 1942), but this 
appears to be an exceptional case. 

All agree that there is not the slightest danger of copper toxicity on 
peat soils; in fact, the chief concern is in getting enough of the metal. 
Ten thousand pounds of copper sulfate per acre has been applied to 
plots of Florida peat with but temporary injury (Allison, 1931), while 
in pot tests on peas (Bobko and Panova, 1945), growth was still obtained 
on peat containing 1280 mg. copper per kilogram, or the equivalent of 
10,280 Ib. of copper sulfate per acre. 

Most mineral soils can fix substantial amounts of copper over a period 
of years. In France, Bordeaux mixture has been used yearly on vine- 
yard soils since 1886 without toxic effects. It is estimated that 130 kg. 
of metallic copper per hectare fell on the soil during each ten-year 
period (Rolet, 1934), or the equivalent of approximately 2770 Ib. of 
copper sulfate per acre for a sixty-year period. An average of 80 Ib. 
of copper sulfate per year for thirty-two years has been added as Bor- 
deaux mixture to some Long Island potato soils, but the limit of toxicity 
has not yet been reached (Skaptason, 1940). In one experiment on a 
sandy cranberry bog with a peat subsoil (Bergman and Truran, 1933), 
the equivalent of 2400 Ib. of copper sulfate per acre was applied without 
injury to the vines and with no reduction in yield. Large amounts of 


copper pyrites have been applied to a calcareous soil without injury 
(Smith, 1930). 

In one Ohio experiment, still in progress on Miami soil, the writer 
has added 20 Ib. of copper sulfate per acre per year since 1946. The 
treated vegetable plots thus far have slightly outyielded the untreated 
plots and there is no evidence of toxicity. In a greenhouse experiment, 
tomato plants were set in pots of Miami soil mixed with sand to which 
was added copper sulfate sufficient to injure, and eventually kill, the 
young seedlings. After two weeks, other seedlings planted in the pots 
from which the dead plants had been removed, grew and eventually bore 

In view of the foregoing experiments, there would seem to be little 
possibility that copper toxicity would ever occur on ordinary agricultural 
soils, by accrued copper from fortified fertilizer even if it contained as 
much as 1 per cent of the element. The objection to adding copper sul- 
fate to general fertilizer mixtures because of cost is more valid. Not 
only the cost of the copper but the expense of mixing it with the fer- 
tilizer has to be considered. 

A preliminary survey of eastern fertilizer companies showed that the 
majority contacted did not use copper in their product ; some used it on 
special demand orders, and a minority included it in at least one grade 
or brand. Most companies reasonably follow the recommendations of 
their experiment stations or repeated demands of their customers. The 
use of copper as a soil amendment is increasing, although it is difficult 
to obtain tonnage figures. There are at least five companies advertising 
on a national scale that produce copper-containing trace-element mix- 
tures, where there were none scarcely more than a decade ago. The 
number of independent farmers who use copper as the sulfate or in 
mixtures is increasing also. However, the majority, as yet, give little 
thought to the possible need for any minor elements or do not consider 
that their insurance value is sufficient to warrant their added cost. 

7. Effect on Availability of Other Elements 

It has been proved many times that the absorption and utilization of 
one element is profoundly affected by the concentration of other elements 
present, both in the soil arid in the plant. For example, one element may 
prevent the excessive intake of a second that is toxic in too great an 
amount. On the other hand, it may increase the availability of the sec- 
ond element. 

Copper may function either way. It is known to affect or be affected 
by several other elements. The copper-nitrogen balance is an outstand- 
ing example. As early as 1914 (Lipman and Burgess), it was found 


that copper exerted marked stimulating effects on the nitrifying flora of 
a mineral soil, and frequently more than doubled the normal nitrate 
yield. However, Jensen (1916) obtained a reduction in the amount of 
nitrates with soil applications of copper sulfate at the rate of 100 Ib. 
per acre. It has been suggested that such a high rate kills some of the 
nitrifying organisms. Apparently a low rate does not, since Swanback 
(1950), with applications of 18 Ib. per acre, consistently obtained a 
higher rate of nitrogen production from his test plots than from the 
check plots. 

Where copper deficiency occurs, an increase of the nitrogen level 
increases the severity of the deficiency symptoms (Camp and Fudge, 
1939; Dickey et al., 1948; Gilbert et at., 1946; Hamilton and Gilbert, 
1947). Chemical analyses of tissues (Camp and Fudge, 1939; Fudge, 
1939) from citrus trees exhibiting copper-deficiency symptoms have 
shown a much higher nitrogen content than have analyses of comparable 
tissues from trees which give no indication of the deficiency. A decline 
in nitrogen content has been found following the application of copper 
treatments to deficient trees. This condition might be classified as either 
an excess of nitrogen as compared to copper, or a deficiency of copper 
as compared with nitrogen. The latter point of view is more practical 
since it is quite easy to supply a deficient element, but difficult to remove 
an excess. In most cases, the term "deficiency" must be considered as 
relative, as is brought out not only in the relation of copper to nitrogen, 
but also to several other elements. 

In the past several years, the relation of copper to molybdenum has 
attracted considerable attention, especially since the latter element is 
now considered to be essential to plant life. In 1938, by spectroscopic 
examination, a high molybdenum content was found in the herbage of 
pastures on which sheep and cattle were affected by a " scouring " dis- 
ease, known as "teartness" (Ferguson, 1943; Ferguson et al., 1938, 
1943). It was soon found that copper was a specific remedy for the 
disease (Russell, 1944) and "teartness" could be eliminated by ad- 
ministration of copper sulfate directly to the affected animals or by 
applying it to the pastures. 

Analysis of forage grown in some Florida areas, long recognized as 
copper deficient, show a high molybdenum content (Comar et al., 1948). 
Forage containing five parts per million of copper on a dry matter basis 
has been found to bo adequate for ruminants under certain conditions, 
but up to ten to fifteen parts per million may be inadequate if the 
ration contains considerable molybdenum, lead, or zinc, or if the calcium- 
phosphorous ratio is wide. 

Lucas (1946), among others, has found a copper-zinc relationship. 


Zinc sulfate on organic soil increased plant growth only when copper 
was present, and zinc injury is reduced by the presence of copper. Lab- 
oratory experiments have demonstrated a copper-zinc antagonism in rats 
(Gray and Ellis, 1950; Smith and Larson, 1946). The feeding of ex- 
cessive zinc produced an anemia which was corrected by copper feeding. 
The presence of lead is possibly a factor contributing to copper de- 
ficiency where the lead content of the forage is found to be high and 
copper low, but in most cases is not believed to be of prime importance 
(Shearer and McDougall, 1944). 

Copper has the same effect as potash in correcting excessive absorp- 
tion of iron (Erkama, 1949; Willis and Piland, 1934), and an excess of 
copper can induce iron chlorosis (Chapman et al., 1939; Shkol'nik and 
Makarova, 1950). Corn grown on an unproductive peat soil became 
chlorotic when a large amount of copper sulfate was added to the soil, 
but a green color again developed in the leaves when they were treated 
externally with a 1 per cent solution of ferrous sulfate (Willis and 
Piland, 1936). 

Antagonism of copper and manganese (Schropp, 1948) and of copper 
and boron (Shkol'nik and Makarova, 1949) has also been reported. In 
a South Carolina experiment (Bacon et dl., 1950), no increase in weight 
of tobacco was obtained on Marlboro fine sandy loam by additions of 
copper sulfate. However, when potash deficiency symptoms were ob- 
served and the amount of potash was increased from 48 Ib. to 80 Ib. per 
acre, a pronounced increase in weight was obtained in favor of the 
copper-treated plants over the controls. The variation in the results of 
copper sulfate applications to mineral soils of the same copper content 
may be partly explained by these interrelations or antagonisms between 

8. Aspergillus niger 

By the use of specially purified media, it was found that the fungus 
Aspergillus niger needs copper, zinc, and iron in its nutrition. The black 
pigment in the spores was found to be a mixture of humins dependent on 
copper and iron for their formation (Bortels, 1927). When receiving 
sufficient copper, the spores of this fungus are black ; when receiving no 
copper, they are white ; and with slightly increasing amounts, the color 
ranges from cream through yellow and brown. The fungus has a copper 
sensitivity as low as 0.1 part per million, and, therefore, may be used as a 
criterion of the amount of available copper in the soil (Mulder, 1937, 
1988, 1939). 

On many mineral soils, the amount of available copper determined 
by Aspergillus niger bioassay agrees quite closely with the amount ex- 


tracted by Morgan's "Universal" solution* and determined chemically 
or spectrographically. With organic soils, however, Aspergillus niger 
is much more sensitive and extracts a proportionally greater amount of 
copper than can be obtained by leaching with Morgan's solution. 


1. Use in the Body 

Copper is necessary to animal life, although its essentiality, or even 
its presence in all animal tissues, was questioned for many years (Rose 
and Bodansky, 1920; Willard, 1908). It is now recognized, that for the 
proper utilization of iron, small quantities of copper are needed (Hart 
et al,., 1928; Sheldon, 1932). Without the copper, iron is assimilated 
and stored in the liver, but is not converted into hemoglobin (Elvehjem 
and Sherman, 1932). Such a conversion does take place only in the 
presence of copper. 

Several naturally occurring, animal organic substances contain cop- 
per. One of them, hemocyanin, a copper-protein complex, is found in 
the blood of certain invertebrates. In the crab, spider, and snail, for 
example, the hemocyanin functions as an oxygen carrier, similar to 
hemoglobin in man. A red pigment, turacin, containing 7 per cent cop- 
per, is found in the feathers of the turaco, a South American bird. 
Turacin is a derivative of the normal porphyrin pigments generally 
found in animals and plants. Certain other copper-bearing proteins 
have been isolated, including hemocuprein from the red blood corpuscles 
of mammals and hepatocuprein from liver; but as yet, little is known of 
their physiological significance (Dawson and Mallette, 1945). 

The enzyme tyrosinase is found in animal tissues. This enzyme, in a 
series of changes, converts tyrosin to melanin, a black pigment (Cun- 
ningham, 1931). Thus, copper is claimed to play a role in skin and 
hair pigmentation (Singer and Davis, 1950; Smith and Ellis, 1947). 
Pigmented cat and dog hair, and to a lesser degree, the skin underlying 
pigmented hair, have a higher copper content than white hair and under- 
lying skin (Sarata, 1935). 

Anemia in the rat, accompanying a severe copper deficiency, was 
found to be further accompanied by a decrease in the cytochrome oxidase 
activity of the bone marrow a loss which was offset when copper was 
again fed to the animal (Comar, 1948; Schultze, 1941; Schultze and 
Simmons, 1942). The bone marrow is one of the chief centers of blood 

* One hundred grams of aodium acetate, 30 ml. acetic acid, water to a total vol- 
ume of 1 liter. 


formation from food products (hematopoiesis), and it would seem that 
copper plays an essential part in this reaction. 

Milk produced by cows on a normal ration contains about 0.15 ing. of 
copper per liter (Elvehjem et al., 1929). Efforts have been made to 
increase this ratio by feeding large amounts of the metal (Elvehjem et 
al., 1929; Hamilton et al., 1929). However, the cow, and also the hen, 
with few exceptions, thwart the efforts of man to change the mineral 
composition of their products. 

2. Deficiency Symptoms 

The original Wisconsin work in which anemia was produced in rats 
by means of a diet low in copper has been repeated and confirmed a 
number of times, both with rats and with other animals (Comar, 1948; 
Cunningham, 1931; Elvehjem and Hart, 1932; Teague and Carpenter, 
1951). Symptoms of copper deficiency are anemia, diarrhea, cessation 
of growth, depigmentation of hair, poor reproduction, abnormalities of 
bone formation, nervous disorders, and general debility. In sheep, the 
wool is affected. However, all these symptoms are not always present in 
deficient animals, either in laboratory experiments or in the field. 

Borderline copper deficiency, due either to a low copper intake or 
to a deficiency induced by the addition of molybdenum or other toxic 
elements to the diet, is one of the causes of poor breeding performance 
in cows. If a copper deficiency in the feed of a herd continues for some 
time, the cows may fail to come in heat. If bred, they produce a high 
percentage of dead or weak, sickly calves. 

In copper-deficient cattle, a condition sometimes develops which re- 
sembles X-disease (hyper keratosis) very closely. Many skin sores de- 
velop and fail to heal. There is a loss of hair and a roughening and 
thickening of the skin in more advanced cases. The careful observer 
can distinguish this copper-deficient condition from true hyperkeratosis 
in that the sores in copper deficiency are at the actual sites of injury 
and there are no lesions in the mouth, gullet, or bile duct. Furthermore, 
if the animal is fed small amounts of copper, the condition clears 

Copper deficiencies in domestic animals, especially ruminants, are 
found in many parts of the world. Much of the trouble is complicated 
by various factors including superabundance of other elements, and, 
therefore, the deficiency symptoms vary widely and are known by differ- 
ent names. In Australia, a nervous disorder of cattle is known as the 
"falling disease." Sheep are affected by a staggering disease called 
"enzootic ataxia," and by a wool abnormality as "stringy" or "steely 
wool." In the "falling" disease, the affected animals lack muscular 


coordination, especially of the hind legs, stagger, and frequently fall. 
The disease is usually terminated by sudden death. A positive correla- 
tion was found between hemoglobin and copper values of blood, both in 
copper-deficient, staggering cattle, and those receiving copper supple- 
ments (Bennetts ct al., 1942a). 

"Stringy wool" appears to be the earliest arid frequently the most 
obvious sign of copper deficiency in sheep, occurring even when the dis- 
order is not sufficiently severe to cause manifestations of ataxia (Ben- 
netts, 1942). "Enzootic ataxia" most commonly affects lambs from one 
to two months old. They become unthrifty, stiff in gait, and their 
growth is retarded. The ataxia progresses rapidly, and the lambs usu- 
ally die within a few weeks. Ewes with "stringy" wool always drop 
lambs with ataxia. 

A very low copper status of pastures and animals is constantly asso- 
ciated with these diseases, and optimal response in health and produc- 
tion is obtained by the administration of copper supplements to the 
animals or by topdressing the unhealthy pastures with copper sulfate 
(Bennetts and Beck, 1942; Bennetts ct al., 1941, 1942b). Additions of 
copper to the diet of sheep have also been found to make better wool 
even where the animals were apparently not copper deficient. 

A disease similar to "enzootie ataxia" has been investigated in Eng- 
land. This disease, described in 1932 (Stewart), is called "sway back," 
"swingback, " or "warfa," and was widely distributed throughout Great 
Britain. The disease is confined almost exclusively to young lambs. 
Most are affected at birth and are unable to raise themselves to suckle. 
Others manage to struggle to their feet, but sway and collapse if they 
attempt to walk. The mortality rate of affected animals is nearly 100 
per cent. It was shown that the disease was not due to a copper de- 
ficiency of either soil or herbage (Shearer and McDougall, 1944; Stewart 
et al., 1946), but nevertheless the affected animals suffered from a copper 
deficiency and responded to copper medication (Dunlop et al., 1939). 
Just what conditions prevent the grazing ewes from utilizing the 
natural copper of "swayback" herbage is not yet known, but high levels 
of other elements, such as zinc and lead, may be a contributing factor 
(Gray and Ellis, 1950). The first case of a copper deficiency in cattle 
was reported in England in 1946 (Jamieson and Russell, 1946), and in 
Ireland in 1949 (0 'Donovan, 1949). In both cases, the trouble was con- 
nected with a low copper content of the pasture forage. 

In continental Europe, a copper-deficiency disease of cattle is also 
found, and for years has been known as "Lecksucht" or "licking dis- 
ease." In areas where this disease occurs, the copper content of the 
vegetation is usually very low, unlike conditions in "swayback" areas. 


"Lecksucht" is cured by administration of copper sulfate or by copper 
treatment of pasture soils. 

In the United States, copper deficiency in cattle is known as "salt 
sick," and is most severe in Florida (Becker et al. t 1931; Neal et al., 
1931), where it is frequently complicated by deficiencies of iron and 

The antagonism of copper and molybdenum has already been men- 
tioned. This antagonism, causing the disease known as ' ' teartness, ' ' 
where the copper content of the forage is low in proportion to the mo- 
lybdenum content, is not uncommon in England (Ferguson, 1943; Fer- 
guson et al., 1943; Russell, 1944). A similar condition in cattle was 
described from California and was correlated with forage high in mo- 
lybdenum (Britten and Goss, 1946). 

The effect of copper sulfate as an antidote for molybdenum toxicity 
in cases of "teartness" has been explained as follows (McGowan and 
Brian, 1947) : The activity of bacteria in the gastrointestinal tract is 
believed to be controlled by catechols. Molybdates reduce the effective 
concentration of catechols by formation of complexes. As a result, un- 
controlled bacterial activity becomes excessive and causes the condition 
manifested by extreme diarrhea. The therapeutic effect of copper is 
suggested as being due to its toxic effect on the bacteria. The complete 
story of copper-deficiency diseases to 1944 has been reviewed (Russell, 

The demonstration of disease in animals caused by a mineral unbal- 
ance in the feed emphasizes the necessity for a consideration of the levels 
of all minerals in the diet before determining the requirement of any 
one. A deficiency disease may not reflect merely a low level of a dietary 
essential, but may also indicate an excess of one or more other minerals 
which interfere with the normal metabolism of that essential dietary 

Any attempt to arrive at a conclusive statement regarding the occur- 
rence of copper deficiency in man, or the human requirements of copper, 
would be premature at this time, and would, therefore, be controversial. 
It has been estimated that human daily needs of copper are in the neigh- 
borhood of 2 mg. per day, and the adult body is said to contain from 100 
to 150 mg. of the element (Cuthbertson, 1948) stored, for the most part, 
in the liver (Flinn and Inouye, 1929). 

3. Use as an Anthelmintic and in Mineral Supplements 

Copper sulfate has been used as an anthelmintic for gastrointestinal 
parasites of sheep (Rietz, 1935, 1936; Stewart, 1934; Wood, 1931). 


However, its use has not been uniformly successful, and it has largely 
been replaced by phenothiazene. 

Copper sulfate is one of the important components in most mineral 
supplements for cattle, sheep, swine, and poultry. There is a growing 
use of such supplements. Their prime purpose is insurance against 
possible deficiencies in the regular feed. Granted that such a purpose 
is met, is there any value in the extra amounts of minerals that are con- 
sumed ? Little research has been done on this subject. 

Braude (1945) reported that the addition of five parts per million 
of copper as the sulfate, to the diet of fattening pigs, did not increase 
their weight, although the copper content of the livers was higher in the 
treated pigs than in the controls. However, Carpenter (1949), in a 
series of field trials, found that raising the copper content of the diet of 
growing swine from eleven parts to forty-five parts per million increased 
the average weight of five-month-old pigs 13 to 15 per cent. The growth- 
promoting effect of the copper did not appear to be attributable to any 
effect on the microbial or parasitic populations of the intestinal tract. 

4. Toxicity 

Copper in small amounts is not now considered to be very toxic to 
animals, but on occasion, overdoses have proved fatal. There is one 
report of chronic copper poisoning near a smelter (Bisset, 1934), and 
long ingestion of salt mixtures sold as a preventive for stomach worms 
has also proved fatal to sheep (Bough ton and Hardy, 1934; Rietz, 1936). 

In New Zealand (Cunningham, 1946b), a study was made of the 
poisoning effects of varying amounts of copper in animal feed. Doses up 
to 80 g. of copper sulfate were not poisonous to yearling heifers or to 
adult cows. The lethal single dose ranged between 200 and 400 g. From 
these figures, it has been estimated that the amount of copper sulfate 
that would be fatal to an adult human being in a single dose would 
probably be around 50 g. 

Somers (1947) estimated that a fatal dose of supposedly harmless 
ferrous sulfate would require the ingestion of several hundred 0.2-g 
tablets, or at least 40 g. of the material, although as little as 6 to 10 g. 
have produced death when accidentally swallowed by children. Thus, 
copper, which has been considered poisonous by most people, is scarcely 
more toxic than iron as ferrous sulfate, which is ordinarily thought of as 


Local areas of copper deficiency are widespread throughout the world. 
As has been mentioned, soils high in organic matter, especially newly 


cultivated peat soils, are most likely to be deficient, but very sandy or 
gravelly soils with a low humus content have, in many cases, been re- 
ported to require copper before a satisfactory crop can be grown on 

1. Europe 

The "reclamation disease " of cereals, beets, and leguminous crops 
occurs on reclaimed heath and moorland soils in Denmark, Holland, Ger- 
many, Russia, and other parts of Europe. Sjollema (1933) connected 
this disease with the animal trouble known as "licking disease" or 
"Lecksucht" and demonstrated that the two had a common cause too 
little copper. The "licking disease" also occurs in Sweden (Sandberg 
and Svanberg, 1943) and Norway (Ender, 1942), where it is known as 
"Pica." The location of the copper-deficient soils in Europe has been 
mapped by Rademacher (1937). 

In England, "swayback" of sheep (Dunlop ct al., 1939) and "scours" 
of cattle (Jamieson and Russell, 1946) have been cured by copper treat- 
ments. A soil actually low in the element was not reported until 1946 
(Jamieson and Russell), and the first case of an "exanthema' 7 in fruit 
trees was not recorded until 1950 (Bould ct oL, 1950; Jones, 1950). In 
Ireland, spraying with Bordeaux not only has been of fungicidal value, 
but large crop increases attributed to the correction of copper deficiency 
have been observed over a twenty-year period (Muskett, 1950). There 
has been one record where copper treatments restored to normal, emaci- 
ated cattle which had been fed on poor hay from a peaty soil, or had 
been kept on bare moorland pasture (O 'Donovan, 1949). 

2. South Africa and the Antipodes 

In South Africa, copper deficiencies of sheep similar to "swayback" 
and "cnzootic ataxia" have been reported (Madsen, 1942). A chlorotic 
condition of deciduous fruit Trees also occurs. Analysis of the chlorotic 
material showed a consistent deficiency of copper, and additions of cop- 
per sulfate to the soil around the trees prevented or cured the trouble 
(Anderssen, 1932; Isaac, 1934). Treatments with salts of various other 
elements or with manure had no effect. 

Severe copper deficiencies occur on the geologically ancient soils of 
Australia and New Zealand. In Australia, both "reclamation disease" 
of cereals (Piper, 1940) and "exanthema" of fruit trees occur (Cahill, 
1929 ; Dunne, 1938 ; McCleery, 1929), and copper-deficiency troubles with 
sheep and cattle are prevalent (Bennetts, 1943; Bennetts et al., 1941). 
The low copper content of Australian soils does not appear to be local- 
ized, but is general over the continent, from New South Wales in the 


east, where citrus has been affected for many years (McCleery, 1929), 
through South Australia (Riceman and Donald, 1938; Riceman et al., 
1938), to Western Australia (Beck, 1941 ; Bennetts, 1943; Teakle, 1942). 

Unlike conditions in many other parts of the world, copper troubles 
here are due to the low content of the element in the soil rather than to 
the fact that copper is made unavailable by organic matter. The Aus- 
tralian soils, in which copper deficiency occurs, are leached sands or 
gravels, frequently calcareous, and have a low organic content. 

In New Zealand, reclaimed peat soils are deficient in copper, espe- 
ciallj r peat-pumice and peat-sand mixtures (Cunningham, 1944, 1946c). 
Certain cattle and sheep troubles, such as peat scours, anemia, unthrifti- 
ness, and difficulty in rearing young, all appear to result from this 
deficiency. Top-dressing such deficient areas with 5 Ib. of copper sulfate 
per acre per year is recommended for preventive purposes (Cunningham, 

3. America 

No cattle troubles attributed to a lack of copper are known to occur 
in South America, but conditions similar to "swayback" and "enzootic 
ataxia" in sheep have been reported from Peru (Madsen, 1942). " Ex- 
anthema " of fruit trees also occurs, and copper sulfate is recommended 
for its control (Cipola, 1937). Dr. II Evans, plant physiologist of the 
cocoa research scheme in Trinidad reported at the cocoa industry con- 
ference held in London in 1950 that practically all cocoa growing in 
Trinidad is suffering from faulty trace-element nutrition, and deficien- 
cies of copper are of frequent occurrence. 

In North America, copper deficiency occurs chiefly on high organic 
soils, but heavy soils in California (Oserkowsky and Thomas, 1938), 
light sands in Florida (Dickey ct al., 1948), and sandy loam in North 
Carolina (unpublished report from North Carolina Experiment Station) 
have also been shown to be deficient. 

The largest area of severe copper deficiency in North America is in 
Florida, where the use of copper amendments on the soil is standard 
practice (Allison, 1930a,b). Not only is "exanthema" of citrus* "die- 
back" of stone fruits, and "leaf burn" of tung prevalent, but in some 
locations, the production of any agricultural crop is virtually impossible 
without the use of copper. Cattle restricted to grass forages on certain 
Florida soils suffer from a nutritional anemia known locally as "salt 
sick" (Becker et al., 1931; Neal et al., 1931). This disease, which has 
been mentioned previously, is due primarily to too little copper in the 
forage, although iron and cobalt deficiencies are complicating factors, 
and treatment ordinarily consists of therapy with all three elements. 


The luxuriance of the native vegetation on deficient areas cannot be 
taken as an index of the amount of copper in the soil, since many of these 
plants are adapted to such conditions. Before remedial measures were 
taken, cattle were frequently found to be starving for copper and other 
trace nutrients on native pastures where the thick grass grew knee-high. 
Copper deficiency extends up the Atlantic coastal plain in more or 
less scattered areas, both on organic and mineral soils. Copper is usu- 
ally applied to crops on the organic soils, but is used infrequently on the 
mineral soils, even though results have shown that, in many cases, excel- 
lent results may be obtained by so doing (Manns et al., 1936a,b). Some 
of the deficient coastal plain mineral soils are poor soils in other ways. 
Such marginal soils are occasionally farmed, but are usually in pine 
forest, and the need for trace elements, which may be greater than 
realized, does not attract attention. 

Local areas of copper deficiency occur practically everywhere, where 
peat and muck soils are farmed, for example, in New York (Felix, 1927; 
Knott, 1936), Indiana (Conner, 1933), Ohio (Comin, 1944), and Michi- 
gan (Ilarmer, 1941, 1946). In Michigan, slightly more than 12 per cent 
of the land is classified as organic (Davis, 1950), and is spread over 
every one of the eighty-three counties in the state. The areas range in 
size from less than one to more than 5000 acres. On such land, copper is 
recognized to be just as important as the major plant foods, and the 
recommended application of copper in the form of the sulfate is 25 to 
50 Ib. per acre annually, until a total of 250 to 300 Ib. has been added, 
or until no further benefit is shown. 

On the Pacific coast, areas of copper deficiency have been found in 
California and Washington. In both states, an " exanthema " of pears 
occurs, and in California, other fruit, including citrus, is affected. Cop- 
per has been applied by introducing copper sulfate crystals into holes 
bored in the trunk of the tree a few inches above the root crown (Thomas, 
1931), by spreading the crystals around the base of the tree, and by 
Bordeaux spray. The first method has been the most effective. Spray- 
ing is of value, but must be continued each year, and the action is local- 
ized. Ground treatments result in slight improvement only, and, in 
California at least, are not effective for two or three years after the 
treatment, This is not surprising in view of the fact that the soil in 
many of the treated orchards is very heavy with presumably a large 
capacity for fixing copper (Rohrbaugh, 1946). Furthermore, these 
orchards were not irrigated, and the precipitation is only about 20 in. 
As a result, in most cases, the copper sulfate dissolves very slowly, and 
large crystals of the salt may be found around a treated tree for several 
years after application. In the more humid east, soil applications of 


copper on orchards have been more successful and trunk applications 
are seldom made. 

At the present time, the localities mentioned are recognized as 
being copper deficient. There are other local areas where crops will re- 
spond to copper additions (McLean et al., 1944) even though the total 
amount in the soil is not excessively low. 

There are an increasing number of cases where poor crop growth 
appears to be due to mineral unbalance, rather than to an actual defi- 
ciency of any one element. Additions of pure, highly concentrated salts 
or fertilizer serve to aggravate the condition. The remedy would be, of 
course, to avoid excessive use of such materials or to balance them with 
the lacking major and perhaps minor essentials. 


Allison, R. V. 1930a. Florida Agr. Expt. Sta. Ann. Rept. 122-124. 

Allison, R. V. 1930b. Florida Agr. Expt. Sta. Ann. Eept. 129. 

Allison, R. V. 1931. Florida Agr. Expt. Sta. Ann. Rept. 159-160. 

Allison, R. V., Bryan, O. C., and Hunter, J. II. 1927. Florida Sta. Bull. 190, 33-80. 

Andcrsson, F. G. 1932. J. Pomol. Hort. Sci. 10, 130-146. 

Anonymous. 1923. Calif. Agr. Expt. Sta. Ann. Eept. 160. 

Arnori, D. I. 1949. Plant Physiol. 24, 1-15. 

Arnon, D. I., and Stout, P. R. 1939. Plant Physiol. 14, 371-375. 

Bacon, C. W., Leighty, W. R., and Bullock, J. F. 1950. U.S. Dept. Agr. Tech. Bull. 


Bailey, L. F., and McIIargue, J. S. 1943. Am. J. Botany 30, 558-563. 
Beck, A. B. 1941. J. Dept. Agr. W. Australia 18, 285-300. 
Becker, R. B., Neal, W. M., and Shealy, A. L. 1931. Florida Agr. Expt. Sta. Bull. 


Boeson, K C. 1941. U.S. Dept. Agr. Misc. Pub. 369. 
Bennetts, II. W. 1942. J. Dept. Agr. W. Australia 19, 7-13. 
Bennetts, II. W. 1943. J. Dept. Agr. W. Australia 20, 40-44. 
Bennetts, H. W., and Beck, A. B. 1942. Australia Council Sci. Ind. Research Bull. 

Bennetts, H. W., Beck, A. B., Harley, R., and Evans, S. T. 1941. Australian Vet. J. 

17, 85-93. 

Bennetts, H. W., Harley, R., and Evans, S. T. 1942a. Australian Vet. J. 18, 50-63. 
Bennetts, H. W., Harley, R., and Evans, S. T. 1942b. J. Dept. Agr. W. Australia 

19, 96-104. 

Berger, K. C., and Truog, E. 1949. Proc. Soil Sci. Soc. Am. 1948. 13, 372-373. 
Bergman, H. E., and Truran, W. E. 1933. Massachusetts Agr. Expt. Sta. Ann. Kept. 

1932, 61. 
Bergman, II. E., and Truran, W. E. 1937. Massachusetts Agr. Expt. Sta. Bull. 339, 


Bisset, N. 1934. Vet. J. 90, 405-407. 

Bobko, E., and Panova, E. 1945. DoUady Akad. S.-Kh. NauTc. No. 3, 12-15. 
Bortels, K. 1927. Biochem. Z. 182, 301-358. 


Boughton, I. B., and Hardy, W. T. 1934. Texas Agr. Expt. Sta. Bull 449. 
Bould, C., Nicholas, D. J. D., Tolhurst, J. A. H., Wallace, T., and Potter, J. M. S. 

1950. Nature 165, 920-921. 
Brandenburg, E. 1935. Mededeel Inst. Suikerbietenteelt 9, 245-256. (Rev. Applied 

Mycol. 15, 145). 

Braude, E. 1945. J. Sci. Agr. 35, 163-167. 
Brenchley, W. E. 1914. Inorganic Plant Poisons and Stimulants. University Press, 


Britten, J. W., and Goss, H. 1946. /. Am. Vet. Med. Assoc. 108, 176-181. 
Browne, F. 8. 1950. Progress Rept. for J934-38, Div. of Hort., Central Expt. Farm, 


Brim, Thorrald S. 1945. Bergcns Museums, Arbok, Naturv. Rekke. 
Cahill, V. 1929. J. Dept. Agr. W. Australia II Ser. 6, 388-394. 
Camp, A. F., and Fudge, B. R. 1939. Florida Agr. Expt. Sta. Bull. 335. 
Carles, P. 1917. Eev. sci. 55, 183. 
Carpenter, L. E. 1949. Ann. Ecpt. Hormcl Inst., University of Minnesota, 1948-49, 

Chapman, H. D., Liebig. G. F., Jr., and Vanselow, A. P. 1939. Soil Sci. Soc. Am. 

Proc. 4, 196-200. 
Churchman, W. L., Manns, M. M., and Manns, T. F. 1937. Crop Protection Digest, 

Bull. Ser. No. 63. 
Churchman, W. L., Russell, R., and Manns, T. F. 1936. Crop Protection Digest, 

Bull. Ser. No. 55. 
Cipola, G. 1937. Univ. nac. litoral (Corrientes, Argentina), Inst. Exptl. Agrope- 

cuarias Pub. No. 4. 

Colman, J. M., and Rupreeht, R. W. 1935. J. Nutrition 9, 51-62. 
Comar, C. L. 1948. Nucleonics 3, 34-48. 

Comar, C. L., Davis, G. K., and Singer, L. 1948. J. Bwl. Chem. 174, 905-914. 
Comin, D. 1944. Ohio Agr. Expt. Sta. Bimo. Bull. 29, 144-147. 
Conner, S. D. 1933. Treatment of muck and dark sandy soils. Indiana Agr. Ext. 

Ser. Leaflet 179, 4. 

Cook, F. C. 1923. U.S. Dept. Agr. Bull. 1146. 
Cunningham, I. J. 1931. Biochem. J. 25, 1267-1294. 
Cunningham, I. J. 1944. New Zealand J. Agr. 69, 559-569. 
Cunningham, I. J. 1946a. New Zealand J. Agr. 72, 261. 
Cunningham, I. J. 1946b. New gcaland J. Sci. Tech. 27A, 372-376. 
Cunningham, I. J. 1946c. New Zealand J. Sci. Tech. 27A, 381-396. 
Cuthbertson, W. F. J. 1948. Chemistry & Industry June 19, 391-393. 
Dalton, H. R., and Nelson, J. M. 1939. J. Am. Chem. Soc. 61, 2946-2950. 
Davis, J. F. 1950. Plant Food J. 4, 5-11. 

Dawson, C. R., and Mallette, M. F. 1945. Advances in Protein Chem. 2, 179-24S. 
Dickey, R. D., Drosdoff, M., and Hamilton, J. 1948. Florida Agr. Expt. Sta. Bull. 


Drosdoff, M., and Dickey, R. D. 1943. Proc. Am. Soc. Hort. Sci. 42, 79-84. 
Dunlop, G., Innes, J. M. R., Shearer, G. D., and Wells, H. E. 1939. J. Comp. Path. 

Therap. 52, 259-265. 

Dunne, T. C. 1938. J. Dept. Agr. W. Australia 15, 120-126. 
Elvehjem, C. A. 1935. Physiol. Revs. 15, 471-507. 
Elvehjem, C. A., and Hart, E, B. 1929. J. Biol. Chem. 82, 473-477. 
Elvehjem, C. A., and Hart, E. B. 1932. J. Biol Chem. 95, 363-370. 


Elvehjeni, C. A., and Sherman, W. 0. 1932. J. Biol. Chem. 98, 309-310. 

Elvehjem, C. A , Steenbock, II., and Hart, K. B. 1929. J. Biol. Chem. 83, 27-34. 

Endcr, F. 1942. NorsTc Vct-Tids. 54, 3-27. 

Erkama, J. 1949. Ada Chem. Scand. 3, 850-857. 

Felix, E. L. 1927. Phytopath. 17, 49-50. 

Ferguson, W. S. 1943. J. Agr. Sci. 33, 116-118. 

Ferguson, W. S., Lewis, A. H., and Watson, S. J. 1938. Nature 141, 553. 

Ferguson, W. S., Lewis, A. II., and Watson, S. J. 1943. J. Agr. Sci. 33, 44-51. 

Flinn, F. B., and Inouye, J. M. 1929. J. Biol Chem. 84, 101-114. 

Floyd, B. F. 1910. Florida Agr. Expt. Sta. Ann. Eept. 1910, 70-71. 

Floyd, B. F. 1917. Florida Agr. Expt. Sta. Bull. 140. 

Fowler, J. H. 1875. Proc. Florida Fruit Growers' Assoc. 1875, 62-67. 

Fudge, B. B. 1939. Florida Agr. Expt. Sta. Ann. Eept. 139-141. 

Gilbert, F. A. 1948a. Better Crops with Plant Food 32, 8-11, 44-46. 

Gilbert, F. A. 1948b. Mineral Nutrition of Plants and Animals. University of 

Oklahoma Press, Norman. 

Gilbert, S. G., Sell, H. M., and Drosdoff, M. 1946. Plant Physiol. 21, 290-303. 
Gray, L. F., and Ellis, G. II. 1950. J. Nutrition 40, 441-452. 
Hamilton, J., and Gilbert, S. G. 1947. Proc. Am. Soc. Hort. Sci. 50, 119-124. 
Hamilton, T. S., Mitchell, H. H., and Nevens, W. B. 1929. Illinois Agr. Expt. Sta. 

Ann. Eept. 1929, 120-121, 125-133. 

Harmer, P. M. 1941. Michigan Agr. Expt. Sta. Special Bull. 314. 
Harmer, P. M. 1946. Soil Sci. Soc. Am. Proc. (1945) 10, 284-294. 
Harris, II. C. 1948. Soil Sci. Soc. Am. Proc. (1947) 12, 278-281. 
Hart, E. B., Steenbock, H., Waddell, J., and Elvehjem, C. A. 1928. J. Biol. Chem. 

77, 777-795. 

Hoffmann, W. 1939. Bodenkunde Pflanzenernahr. 13, 139-155. 
Holmes, R. S. 1943. Soil Sci. 56, 359-370. 
Isaac, W. E. 1934. Trans. Eoy. Soc. S. Africa 22, 187-204. 
Jamieson, S., and Russell, F. C. 1946. Nature 157, 22. 
Jensen, C. A. 1916. J. Am. Soc. Agron. 8, 10-22. 
Jones, J. O. 1950. Nature 165, 192. 

Keilin, D., and Mann, T. 1938. Proc. Eoy. Soc. (London) B 125, 187-204. 
Keilin, D., and Mann, T. 1939. Nature 143, 23. 
Keilin, D., and Mann, T. 1940. Nature 145, 304. 
Knott, J. E. 1936. N. Y. (Cornell) Agr. Expt. Sta. Bull. 650. 
Kubowitz, F. 1937. Biochem. Z. 292, 221-229. 

Lawless, W. W., and Camp, A. F. 1940. Florida State Sort. Soc. Proc. 53, 120-125. 
Lindow, C. W., Elvehjem, C. A., and Peterson, W. H. 1929. 7. Biol. Chem. 82, 465- 

Lipman, C. B., and Burgess, P. S. 1914. Univ. Calif. (Berkeley) Pub. Agr. Soc. 1, 


Lipman, C. B., and Mackinney. 1931. Plant Physiol. 6, 593-599. 
Lucas, R. E. 1946. Soil Sci. Soc. Am. Proc. 1945 10, 269-274. 
Lucas, R. E. 1948. Soil Sci. 66, 119-129. 
Lutman, B. F. 1913. Vermont Agr. Expt. Sta. Bull. 162, 
Lutman, B. F. 1916. Vermont Agr. Expt. Sta. Bull. 196. 
McCleery, F. C. 1929. Agr. Gaz. N. S. Wales 40, 397-406. 
McElroy, W. D., and Glass, B., Editors. 1950. Copper Metabolism. The Johns 

Hopkins Press, Baltimore. 


McGowan, J. C., and Brian, P. W. 1947. Nature 159, 373. 

McLean, J. G., Sparks, W. C., and Binkley, A.M. 1944. Proc. Am. Soe. llort. Sci. 

44, 362-368. 
McMurtrey, J. E., and Bobinson, W. (). 1938. U.S. Dept. Agr. Yearbook Agr. 


Madsen, L. L. 1942. U.S. Dept. Agr. Yearbook Agr. 323-353. 
Manns, M. M., Churchman, W. L., and Manns, T. F. 1936a. Trans. Peninsula Hort. 

Soc. 1936, 92-99. 
Manns, T. F., Churchman, W. L., and Manns, M. M. 1936b. Delaware Agr. Expt. 

Sta. Bull. 205, 45-46. 
Manns, T. F., Churchman, W. L., and Manns, M. M. 1937. Delaware Agr. Expt. 

Sta. Butt. 207, 45-46. 

Manns, T. F., and Russell, R. 1935. Delaware Agr. Expt. Sta. Bull. 192, 50-51. 
Melchers, W. J., and Gerritsen, H. J. 1944. Copper as an Indispensable Element 

for Plants and Animals. Maart, Holland. 

Miller, L., and Mitchell, H. S. 1931. J. Am. Dietetic Assoc. 7, 252-257. 
Mulder, E. G. 1937. Chem. WeelcUad 34, 433. 
Mulder, E. G. 1938. Ann. fermentationa 4, 513-533. 
Mulder, E. G. 1939. Arch. Mikrobiol. 10, 72-86. 
Mulder, E. G. 1949. Plant and Soil 2, 59-121. 
Muskett, A. E. 1950. Nature 165, 900-901. 

Neal, W. M., Becker, R. B., and Shealy, A. L. 1931. Science 74, 418-419. 
Nicolaisen, W., and Seelbach, W. 1938. Forschungsdienst 5, 383-387. 
O 'Donovan, J. 1949. Nature 164, 759. 

Okuntsov, M. M. 1946a. Kept. Acad. Sci. U.S.S.E. 54, 645-647. 
Okuntsov, M. M. 19461). Sept. Acad. Set,. U.S.S.K. 54, 837-840. 
Orth, O. 8., Wickwire, G. C., and Burge, W. E. 1934. Science 79, 33-34. 
Oserkowsky, J., and Thomas, II. E. 1938. Plant Physiol. 13, 451-467. 
Parkinson, G. G., and Nelson, J. M. 1940. J. Am. Chem. Soc. 62, 1693-1697. 
Peech, M. 1941. Soil Sci. 51, 473-494. 

Piper, C. S. 1938. Australia Council Sci. Ind. Research Pamphlet 78, 24-28. 
Piper, C. S. 1940. Empire J. Exptl. Agr. 8, 199-206. 
Piper, C. S. 1942. J. Agr. Set. 32, 143-178. 
Proskura, S. 1940. Len i Konoplya, 9, 17-19 (C.A. 37, 4848). 
Rademacher, B. 1937. Fortschr. Landw. Chem. Forsch. 1937, 149-160. 
Rawlinson, W. A. 1943. J. and* Proc. Australian Chem. Inst. 10, 21-30. 
Redfield, A. C. 1934. Biol Revs. 9, 175-212. 
Reed, H. S. 1939. Am. J. Botany 26, 29-33. 
Riceman, D. S., and Donald, C. M. 1938. Australia Council Sci. Ind. Research 

Pamphlet 78, 7-23. 
Riceman, D. S., Donald, C. M., and Piper, C. S. 1938. J. Australian Inst. Agr. Sci. 

4, 41. 

Rietz, J. H. 1935. West Virginia Agr. Expt. Sta. Bull. 264. 
Eietz, J. II. 1936. West Virginia Agr. Expt. Sta. Bull. 271. 

Rohrbaugh, P. W. 1946. Calif. Citrograph 31, (6), 201, 225-228; (7), 250, 258-260. 
Rolet, A. 1934. Vie agr. et rurale 23, 345-346 (Rev. Applied Mycol. 14, 244). 
Rose, W. C., and Bodansky, M. 1920. J. Biol. Chem. 44, 99-112. 
Ruehle, G. D., and Lynch, S. J. 1940. Proc. Krome Mem. Inst. 8, in Proc. Florida 

State Hort. Soc. 53, 152-154. 
Russell, F. C. 1944. Imp. Bur. Animal Nutr. Tech. Commun. No. 15. 


Russell, R., and Manns, T. F. 1934. Trans. Peninsula Hort. Soc. 1934, 97-129. 

Sandberg, O., and Svanberg, M. 1943. Svcnsk Veterinartidslcr. 48, 103-114. 

Sarata, U. 1935. Japan J. Med. Sci. II, Biochem. 3, 79-84. 

Sehropp, W. 1948. Z. Naturforseh. 3B, 381-385. 

Sehultze, M. O. 1940. Physiol. Revs. 20, 37-67. 

Schultze, M. O. 1941. J. Biol Chem. 138, 219-224. 

Schultze, M. O., and Simmons, S. J. 1942. J. Biol. Chem. 142, 97-106. 

Shearer, G. IX, and MeDougall, E. I. 1944. J. Agr. Sci. 34, 207-212. 

Sheldon, J. II. 1932. Brit. Mrd. J. No. 3749, 869-872. 

Shkol'nik, M. Y., and Makarova, N. A. 1949. Dolclady AJcad. Naulc. S.S.S.R. 

(Ecpts. Acad. U.S.S.K.), N. S. V, 68, 185-188. 
Shkol'nik, M. Y., and Makarova, N. A. 1950. DoTclady AJcad. NauJc. S.S.S.E. ( Rcpts. 

Acad. U.S.S.R.), N. S. V, 70, 121-124. 
Singer, L., and Davis, G. K. 1950. Science 111, 472-473. 
Sjollema, B. 1933. Bwchem. Z. 267, 151-156. 
Skaptason, J. B. 1940. Am. Potato J. 17, 88-92. 
Smith, II. V. 1930. J. Am. Soc. Agron. 22, 903-915. 
Smith, B. E., mid Thomas, II. E. 1928. Phytopath. 18, 449-454. 
Smith, S. E., and Ellis, G. H. 1947. Areh. Bwchem. 15, 81-88. 
Smith, S. E., and Larson, E. J. 194G. J. Biol. Chem. 163, 29-38. 
Smith, W. S. 1927. An Investigation Concerning the Presence and Cause of the 

Phenomena Designated as Reclamation Disease. II. Veenman and Sons, Wngen- 

ingen, "Holland. 

Somers, G. F. 1947. Brit. Mcd. J. 2, 201. 
Sommer, A. L. 1931. Plant Physiol. 6, 339-345. 
Sommer, A. L. 1945. Soil Sci. 60, 71-79. 
Steenbjerg, F. 1948. Nature 161, 364-365. 

Steenbjerg, F., and Boken, E. 1950. Plant and Soil 2, 195-221. 
Stewart, J., Farmer, V. C., and Mitchell, R. L. 1946. Nature 157, 442. 
Stewart, W. L. 1932. Vet. J. 88, 133-138. 
Stewart, W. L. 1934. Vet. Eccord 14, 1165-1169. 
Stotz, E. H., Harrcr, C. J., and King, C. G. 1937. Science 86, 35. 
Stout, P. B., and Arnon, D. I. 1939. Am. J. Botany 26, 144-149. 
Swanback, T. R. 1950. Connecticut Agr. Expt. Sta. Bull. 535. 
Teague, II. S., and Carpenter, L. E. 1951. J. Nutrition 43, 389-399. 
Teakle, L. J. H. 1942. J. Australian Inst. Agr. Sci. 8, 70-72. 

Teakle, L. J. II., and Morgan, L. T. 1943a. J. Dept. Agr. W. Australia 20, 119-123. 
Teakle, L. J. H., and Morgan, L. T. 1943b. J. Dept. Agr. W. Australia 20, 123-130. 
Teakle, L. J. H., Thomas, I., and Turton, A. G. 1941. /. Dept. Agr. W. Australia 

18, 70-86. 

Thomas, H. E. 1931. Phytopath. 21, 995-996. 
Tisdale, W. B. 1930. Florida Agr. Expt. Sta. Kept. 1930, 135. 
Van Schreven, D. A. 1936. Phytopath. 26, 1106-1117. 
Whetzel, H. H., Blodgett, F. M., and Mader, E. O. 1936. N. Y. (Cornell) Agr. 

Expt. Sta. 48th Ann. Kept. 1936, 119-120. 

Wild, A. S., and Teakle, L. J. H. 1942. J. Dept. Agr. W. Austutha 19, 71-78. 
Willard, J. T. 1908. J. Am. Chem. Soc. 30, 902-904. 
Willis, L. G., and Piland, J. R. 1934. Soil Sci. 37, 79-83. 
Willis, L. G., and Piland, J. R. 1936. J. Agr. Eeseareh 52, 467-476. 
Wood, W. A. 1931. Univ. Cambridge Inst. Animal Path., Kept. Director 2, 2011- 


Ecological and Physiological Factors in Compounding 
Forage Seed Mixtures* 


Virginia Polytechnic Institute, BlacJcsbvi r/, 



I. Problems with Artificial Seed Mixtures ............ 179 

IT. Plant Adaptation as Related to Compounding of Seed Mixtures .... 182 

1. Climatic Factors ................... 183 

a. Temperature-Plant Relationships . . ........ 183 

b. Light-Plant Relationships . . ....... 186 

2. Soil Factors .................... 190 

a. Moisture and Aeration . ......... 190 

b. Soil Fertility and Soil Reaction . . . .... 194 

3. Biological Factors ................ 198 

a. Morphology of Plants .......... ... 198 

b. Palatability ....... ......... 202 

c. Diseases and Insects ................ 203 

d. Variety .................... 204 

4. Plant Succession Interrelationship of Climat e, Soil, and Biological 
Factors ...................... 205 

a. Grazing Management of Grass-Legume Mixtures ...... 205 

b. Improving Degenerated Kentucky Bluegrass- White Clovei 
Pastures .................... 207 

c. Competition for Potassium ............. 208 

d. Seedling Competition ................ 209 

LIT. Compounding Mixtures as Related to Use ............ 212 

1. Yields and Quality as Influenced by Mixtures ........ 212 

a. Top vs. Bottom Species ...... .... 214 

b. Simple vs. Complex Mixtures ............. 215 

2. Developing a Forage Cropping System ... . . .... 215 

References ..................... 216 


With the advent of livestock enterprises and their incorporation into 
farming systems, the use of artificial mixtures of grasses and legumes 
has been encouraged. A map prepared by Vinall (1935), Fig. 1, shows 
that the forage species used in mixtures in the more humid or in irri- 
gated areas were introduced from other countries. The introduced for- 

* Some of the experiments reported herein were partially financed by The Old 
Dominion Foundation. 




age plants that are adapted to various sections of the United States are 
usually of either northern or southern origin. 

The forage plants used within a region also respond differentially 
to the factors that influence the rate of growth. These differential 
growth responses among species are not well understood, thus it is diffi- 
cult to maintain a balance of grasses and legumes in mixtures. Through 

FIG. 1. On the basis of climate the United States may be divided into five gen- 
eral regions. The kind of plants that furnish most of the pasturage in each region 
are indicated. (Prom TJ.&. Dept. Agr. Misc. Pub. 194, 1934.) 

trial and error and fundamental research much has been learned about 
the behavior of species in mixtures. However, physiological and ecologi- 
cal data needed to interpret the life histories of species in mixtures are so 
limited that cause and effect are often misinterpreted. 

Benedict (1941) conducted an experiment in which dried bromegrass, 
Bromus inermis, Leyss, roots were mixed with sand and sown with the 
same grass. Bromegrass growth was inhibited, and the cause was at- 
tributed to some harmful substance or substances from the dried roots. 
Myers and Anderson (1942) found that bromegrass seedlings grew bet- 
ter in the soil of a four-year-old nitrogen-starved bromegrass sod, if 
nitrogen was added, than in a cultivated soil. The writers concluded 
that the highly carbonaceous organic matter tied up available nitrogen 
and that the toxic substances, if present, were destroyed by nitrogen 

Ahlgren and Aamodt (1939) found that the top and root weights of 
two species used in a mixture were less for both species in the mixture 


than for pure stands. This retarded growth among both species, when 
growing in association, was attributed to harmful root interactions. 
Such a reduction in growth by two species in a mixture was not found 
to exist in other experiments. Stapledon and Davies (1928) grew forage 
species in mixtures to study the influence of one species on another. The 
ryegrasses, particularly Italian ryegrass, Lolium multiflorum, Lam., had 
a depressing effect on the growth of orchardgrass, Dactylis glomerata, 
L., timothy, Pklcum pratcnse, L., and rough stalked meadow grass, Poa 
irivialis, L Tall oatgrass, Arrhcna&herum clatius, (L.) Mert. and Koch., 
also tended to retard the development of certain other grasses. When 
grown with timothy, orchardgrass was the aggressor species. In an- 
other experiment five grasses (Italian ryegrass, perennial ryegrass, Lo- 
lium perenne, L., orchardgrass, tall oatgrass, and timothy) were grown 
with clovers (broad red, Trifolium pratense, L., late flowering red, 
white, Trifolium repcns, L., and alsike, Trifolium hybridum, L.). Or- 
chardgrass and tall oatgrass produced the highest yields in competi- 
tion with clover and retarded the clover the most. Timothy retarded 
the growth of clover the Jeast. Late flowering red clover was retarded 
less by grasses than broad red clover and all red clovers were aggressive 
toward white clover. 

Aberg, Johnson, and Wilsie (IIM.'J) grew rod clover, alfalfa, Mech- 
cayo saliva, L., timothy, and bromegrass in all combinations in a field 
experiment to measure species behavior in different mixtures. They 
found that bromegrass was more aggressive when grown in various mix- 
tures than the other three species. Alfalfa yielded less in a mixture 
with bromegrass and red clover than when grown in pure stands. From 
a greenhouse experiment, these workers reported that bromegrass yielded 
less when grown in mixtures with orchardgrass, timothy, and red clover 
than in pure stands. Orchardgrass and timothy each produced higher 
yields when grown with bromegrass than when grown in pure stands. 
Timothy yields were lower when grown with orchardgrass than in pure 
stands. Alfalfa yields were reduced when grown with orchardgrass 
and increased when grown with bromegrass. The individual plant yields 
of red clover were lower in pure stand than the yields for individual 
plants grown with mixtures of other species. 

Roberts and Olson (1942) measured the yield of individual plants 
of red clover, sweet clover, Melilotus alba, Desr., alsike clover, Wisconsin 
white clover, lespedeza, Lespedeza striata, Thunb., H. and A., and al- 
falfa when grown alone and with each of red top, Agrostis cdba, L., and 
Kentucky bluegrass, Poa pratensis, L. There was no evidence of simul- 
taneous yield decreases of both species in a mixture. 

It should not be denied that there may be plant associations in which 


species in mixtures are mutually harmful to each other because of toxic 
excretions or some antagonistic effect. However, a careful examination 
of literature concerning forage plant mixtures indicates that there is 
generally no gain or loss in the herbage or root yields of all species in a 
mixture. When growing aggressive and nonaggressive species in a mix- 
ture, the increased yields of the aggressive plants were counteracted by 
decreases in yield of the nonaggressive plants. There was a compensat- 
ing rather than a mutually beneficial or antagonistic relationship among 
species grown in association. 

Plant populations resulting from sowing grasses and legumes are 
dynamic; the prominence of a given species in a mixture is depleted or 
augmented, depending upon the relative growth of each species under 
imposed or natural environmental factors. Plants used in forage mix- 
tures vary morphologically, genetically, and physiologically, and thus 
respond differentially to climatic, soil, biological, and other factors. In- 
formation that interprets the variable growth responses of plant species 
under different environmental conditions could be used in designing 
mixtures and imposing desirable management practices. 

Specific data on the relative growth responses of forage plants to 
simple and many interrelated growth factors is fragmentary. In this 
manuscript an attempt is made to piece together the available data on 
growth factors and to discuss their single and combined effects on the 
growth of species in mixtures. This report obviously shows the acute 
need for more fundamental research to gain a better understanding of 
the behavior of plant species and genotypes in mixtures. 



It is difficult to maintain the stands and production of species com- 
ponents in mixtures. New seedings of mixtures of the taller growing 
grasses and legumes often produce the highest yield the year after sow- 
ing, thereafter the productivity declines (Stapledon and Davies, 1930; 
Ahlgren et al., 1944, 1946). The cause of this decline is not well under- 
stood, but is usually attributed to loss of the leguminous associate and 
the concurrent low supply of available nitrogen. Legumes are usually 
more vulnerable to injury and stand depletion than the grasses. 

Although it is not generally acknowledged, grasses alone, when ade- 
quately fertilized, are more productive than grass-legume mixtures. It 
would be much simpler to maintain grasses or mixtures of grasses than 
grass-legume mixtures. However, the utilization of legumes in mixtures 
is of great practical significance because the magnitude of production is 


related to available nitrogen supply. Nitrogen manufactured by well- 
adapted legumes is less expensive than commercial nitrogen fertilizer. 

The growth behavior of species in mixtures can often be interpreted 
by growth factors. The first parts of this section deal with the adapta- 
tion of plant species as influenced by single climatic, soil, and biological 
factors. This was done to simplify the presentation; although the 
growth of plants, alone or in mixtures, is influenced by the combined 
effect of many factors. The last portion of this section deals with some 
competitive effects among plants in mixtures as interrelated to growth 
factors and plant succession. 

1. Climatic Factors 

a. Temperature -Plant Relationships. Temperatures are intricately 
related to the growth behavior of species and strains of forage plants 
and determine, to a considerable extent, their adaptation and amount of 
growth that may be expected at different seasons of the year. Tempera- 
ture is also associated with the sowing date of forage species because of 
its effect on germination and seedling development. 

Species differ in their temperature requirements for germination. 
Chippindale (1949) has shown that a continuous low temperature of 
5 C. to 10 C. did not affect germination of Italian ryegrass, was only 
slightly depressive to perennial ryegrass and orchardgrass, but was 
very depressive to timothy, tall fescue, Festuca elatior, var. arundinacea 
and Kentucky bluegrass. Alternating temperatures (18 C. for 18 
hours; 27 C. for 6 hours) were without effect on the germination of 
Italian ryegrass, perennial ryegrass, and timothy, but were very favor- 
able for germination of orchardgrass, tall fescue, and essential for 
Kentucky bluegrass. 

Field germination of some species of grasses and legumes was com- 
pared with laboratory germination by Stapledon et al. (1927). The 
results indicate that temperatures below 44 F. retard germination. At 
these low temperatures clovers germinated quicker than grasses. Alfalfa 
required higher temperatures for germination than red clover, and night 
frosts retarded alfalfa germination. For optimum germination of al- 
falfa the mean soil temperature should exceed 45 F. for a 30-day 
period after sowing. 

In another experiment the emergence and early seedling growth of 
eight species of forage grasses and legumes were measured under daily 
alternating temperatures of 40-55 F., 55-70 F., 70-85 F., and 
85-100 F. (Sprague, 1943). Sudan grass, Sorghum vulgare, Pers., 
emerged readily at temperatures of 85-100 F., but the emergence of all 
the other species in the test (bromegrass, orchardgrass, meadow fescue, 


Festuca elatior, L., timothy, Kentucky bluegrass, ladino clover, Trifolium 
repens, L., and colonial bentgrass, Agrostis tennis, Sibth.) was reduced. 
The seedling emergence of Kentucky bluegrass, colonial bentgrass, tim- 
othy, orchardgrass, and ladino clover was seriously inhibited at 85 
100 F. Although seedlings of bromegrass and meadow fescue emerged 
at high temperatures, the seedlings died or made little growth during a 
six-week period. The growth rate of seedlings differed with tempera- 
tures. Bromegrass and ladino clover seedlings made the best growth 
at 70-85 P. temperatures. The yields of Sudan grass seedlings wore 
about the same at 70-85 F. and 85-] 00 F. All the other species 
produced the highest yields at temperatures ranging from 55-70 F 

The rate of emergence and development of seedlings, as influenced 
by temperatures, should be associated with planting date The differ- 
ences in responses of species to temperature can enable certain species 
to become aggressive in mixtures at a very early stage of growth. For 
example, tests in Virginia show that alfalfa seedlings (relatively high- 
temperature species) are competitive to orchardgrass seedlings (rela- 
tively low-temperature species) when sown in late summer. The reverse 
occurs with spring sowings. 

Northern and southern forage plants respond differently to tempera- 
tures. E. M. Brown (1939) found that the optimum temperatures for 
herbage production was between 80 and 90 F. for Kentucky and Can- 
ada bluegrass, Poa compressa, L., and 60-80 F. for orchard grass. 
For Bermuda grass, C 'iinodon dwtylon, L., Pers , the herbage yields were 
higher at 100 F. than at other temperatures. The highest root and rhi- 
zome yields for species were obtained at temperatures as follows : Ken- 
tucky bluegrass 60 F., Canada bluegrass 50 F., orchardgrass 60-70 F., 
and Bermuda 100 F. High soil temperatures seemed to be more harm- 
ful than high air temperatures to the cool season grasses. The harmful 
effects from high day temperatures on growth of orchardgrass were 
counteracted by low night temperatures. 

In comparing Dallis grass, Paspalum dilatalum, Poir, Bermuda 
grass, carpetgrass, Axotwpus compresws (Swart/) Beauv., and Kentucky 
bluegrass, Jjovvorn (1945) found that the first three grasses, which are 
used in southern regions of the United States, produced more top and root 
growth at 85 F., than at 65 F. Kentucky bluegrass produced more 
roots at the lower temperature, but herbage yields at the two tempera- 
tures were similar. 

Temperature per se often limits the regional adaptation of plants. 
The pasture plants of southern origin such as the genera, PaspaJiMn, 
Cynodon, Axonopus, Lespcdcza, and Diyilar'w, do riot survive in tem- 
perate regions. The regional adaptation of grasses of northern origin 


is also largely affected by temperatures. For example, orchardgrass is 
used in warmer regions than Kentucky bluegrass and timothy, and tall 
fescue is adapted to warmer regions than orchardgrass. Field plant- 
ings indicate that tall fescue varieties are adapted to a wide range of 
temperature conditions. They are used in latitudes from Florida to 
Maine, however, Alta and Kentucky 31 fescue do not grow vigorously 
during the warm summer months in the lower south. 

Temperatures have a pronounced effect upon the succession of species 
in a mixture. White clover varieties are commonly used in mixtures 
with timothy, orchard, Kentucky bluegrass, or other grasses and during 
the spring months the clover stand is often seriously reduced due to 
grass competition (Johnstone-Wallace, 19:57; A. H. Brown, 19:19; Dodd, 
1941 ; Spragno and (larber, 1950). The grasses of northern origin grow 
at lower temperatures than white clover, hence their early spring 
growth is aggressive toward white clover. In some of northeastern 
states where bromegrass is adapted, it is apparently used with ladino 
clover because bromegrass starts growth later in the spring than orchard- 
grass. For this reason bromegrass is less aggressive toward ladino clover 
than orchardgrass. The species in a mixture that responds similarly to a 
given temperature would be expected to be least aggressive toward each 
other, if other physiological differences are eliminated. 

Injuries due to low temperatures vary with species and strains of 
forage plants. Tysdal and Pieters (19:34) found cold resistance of 
alfalfa and red clover seedlings to be greater than for crown vetch, Cor- 
onilla varia, L., and that of crown vetch to be greater than for lespedeza. 
Of the Icspedezas, Korean, Lespedeza stipulacea, Maxim., was injured 
more than common, Lespedcza stnala, Thunb., H. and A.; perennial 
lespedeza, LcspcAcza scriccu, Thunb Benth., being the most tolerant of 
low temperatures. Cold tolerance differed with stage of growth; red 
clover and alfalfa seedlings were more cold tolerant at stages of growth 
beyond the two-leaf stage than at earlier stages of seedling development. 
Korean lespedeza was more cold tolerant at the two leaf stage than at 
later stages of seedling growth. 

Ruptured plant tissue, encountered during low-temperature periods, 
is often indirectly associated with plant mortality because the injured 
tissue becomes diseased. Jones (1928) described injuries in the phloem, 
xylem, central parenchyma and other injuries in roots and crowns of 
alfalfa due to low temperatures during the winter months. Such severe 
injuries appeared to shorten the life of plants because parasitic disease 
organisms, such as Aplanobacter insidioswm, (L.) McC., which causes bac- 
terial wilt, enter at the points of ruptured tissue. Weimer (1930) iso- 
lated five parasitic strains of Fusaria and three of bacteria at points 


where the phloem was injured by heaving and alternate freezing and 
thawing during the winter. 

Not only do species differ in their temperature adaptation, but Rogler 
(1943) found that strains within a species also differ in this respect. 
For a given species, seedlings of northern origin were found to survive 
in a greater proportion after artificial freezing than seedlings of south- 
ern origin. In another experiment, four clones of bromegrass were 
grown at soil temperatures of 20, 26, and 31 C. (Dibbern, 1947). 
The three clones of northern origin produced the highest herbage yields 
at 20 C., whereas the clone Of southern origin produced the highest 
herbage yields at 26 C. Root growth was retarded more by the higher 
soil temperatures than top growth, and at 31 C. one northern clone did 
not survive. 

The ability of a species to survive under low temperatures (winter 
hardiness) is related to genotypes, grazing or cutting management, and 
other factors. Sprague and Fuelleman (1941) and others report that 
winter hardiness is associated with the degree of dormancy after cutting 
in the fall. Ladak alfalfa, a very winter-hardy variety, recovered much 
more slowly after cutting for hay as compared with less hardy varieties 
such as Grimm, Hardistan, and common alfalfa. 

Some of the combined effects of temperature and other factors on the 
growth and behavior of plant associations are discussed in Sec. II, 4. 

h. Light-Plant Relationships. The light factor, photoperiod arid 
intensity, has a profound influence on the adaptation and growth rate of 
pasture plants and their behavior in mixtures under field conditions. 
Latitude has a great influence on the length of day, the longest day at 
Gainesville, Florida, being 14.1 hours as compared with 16.7 at Saska- 
toon, Saskatchewan, Canada. 

In California, various mixtures of forage species were tested under 
different cutting intensities^ where water was adequate under irrigation 
(Peterson, 1951). The magnitude of the yields was associated with light 
conditions and temperatures (Fig. 2). Even though temperatures were 
favorable for high yields, the productivity of all mixtures decreased in 
the latter part of the growing season because of the shorter days and a 
decrease in light intensity. 

Blackman and Templeman (1938) conducted experiments to measure 
the effect of light intensity upon the growth of red fescue, Festuca rubra, 
L., bentgrass, Agrostis spp., and white clover. In greenhouse and field 
experiments three light intensities were studied : 100 per cent daylight, 
60 per cent of daylight, and 40 per cent of daylight. The yields of herb- 
age of all three forage species were diminished as the light intensity was 
reduced, the effect being approximately linear. In greenhouse experi- 



merits with white clover the relative yields at 40 per cent daylight were 
approximately 40 as compared with 100 for daylight conditions. In a 
field experiment the relative herbage yields of clover under 40 per cent 
daylight intensity ranged from about 60 to 80 per cent of the yields for 
full daylight. A reduction in light intensity on red fescue and bent- 
grass affected leaf production similarly to that reported for white clover. 
The plots were clipped frequently in these experiments. 


Ftb March April 

Aug. Stpt Dot. 


FIG. 2. The effect of light intensity and temperature on the yield of an Alfalfa- 
grass mixture (Peterson, 3951). 

In measuring the effect of light intensity on bromegrass, twenty- 
three clones of different origin were grown under relative light intensi- 
ties of 5, 14, and 46; the light intensity outside of the greenhouse being 
100 (Dibbern, 1947). After about twelve months all the clones died at a 
relative light intensity of 5, more than half of the clones died at a light 
intensity of 14, and about one-fourth of the clones died at a light inten- 
sity of 46. 

Photoperiod was found to have a great effect on the growth rate of 
eight forage seedlings (Sprague, 1943). For every species the dry mat- 
ter production, number of leaves, and plant height were lower under the 
9-hour than the 16-hour day length. The amount of roots produced in 
proportion to the tops was also found to be less for the 9-hour than the 
16-hour day. The higher top-to-root ratio at the short day photoperiod 
was apparently attributed to a slow rate of carbohydrate synthesis under 
short day lengths. In an experiment with three southern grasses, Ber- 
muda, Dallis, and carpetgrass, photoperiod had little effect on the yield, 


but the trend was for higher production with a longer day (Lovvorn, 

Photoperiod influences the vegetative growth development of forage 
plants. During the short photoperiods which occur in the autumn and 
spring the leaves of Kentucky bJue, Canada blue, orchard, brome, and 
other grasses are short and prostrate in habit of growth (Stuckey, 1942; 
Peterson and Loomis, 1948; Evans and Watkins, 1939; Watkins, 1940; 
Keller and Peterson, 1950). As the length of the photoperiod increases, 
the leaves grow longer and more erect. At the end of a test period with 
orchardgrass, the plants were 744 mm. high under a 16-hour day as 
compared with 450 mm. for an 8-hour day (Stuckey, 1942). The internal 
structure of orchardgrass was also altered by light, the walls of fibers 
being noticeably thicker in the long day plants. 

Flower induction and flowering of many forage plants is associated 
with photoperiod and temperature. In a test with perennial ryegrass, 
orchardgrass, bromegrass, timothy, meadow fescue, and Kentucky and 
Canada bluegrass, no flowers developed under a 10-hour day, and 
the best heading was obtained under a 1 H-hour day (Sprague, 1948). 
Flowering was satisfactory when the plants grown under 10 hours of 
daylight received 1 or 2 hours of supplementary light during the middle 
of the night, indicating that the length of the dark period affects flower- 
ing. Increasing the intensity of supplementary light above 75 foot 
candles did not affect flower development of the grasses. Some combined 
effects of temperature and photoperiod are given in Sec. II, 4. 

The local adaptation of strains of a given species is apparently 
greatly influenced by photoperiod. An early maturing strain of brome- 
grass prodiiced about the same number of panicles per plant under 15- 
and 18-hour photoperiods. Of a late maturing strain only HO per cent 
of the plants flowered under a 15-hour day while all the plants flowered 
under an 18-hour day (Evans and Wilsie, 194H). Strains of timothy 
that differed greatly in maturity were tested in different latitudes (Evans 
et al., 1935). A very early maturing strain of timothy bloomed 24 days 
earlier at Washington, D. C., than at the most northerly station at 
Guelph, Ontario, Canada. For the latest maturing selections the dates 
for heading were reversed, i.e., blooming occurred 16 days later at 
Washington, D. C., than at Guelph. Since the temperatures favor 
earlier spring growth at the more southern latitude, the la to blooming 
date of late maturing timothy at more southern latitudes is attributed 
to the comparatively short photoperiod. Early maturing strains are 
those that flower under shorter days than the late maturing strains. 

Temperature alone has been reported to influence the photoperiodic 
response of certain forage plants (Roberts and Struckmeyer, 1938, 1939). 


Alfalfa, typically a long day plant, did not produce flowers at a tempera- 
ture of 70 to 75 F. ; but at an intermediate temperature (63 to 65 F.) 
flowered only in the long day environment. Jn the cool environment 
(55 F.) the temperature induced flowering under short day conditions, 
but the typical photoperiodic response occurred under the long day con- 

Red clover and white clover did not flower under short day conditions 
at any temperature, but produced a few flowers at 63 to 65 F. under 
long day conditions and showed a typical photoperiodic response at 
nf> F. and long day. Louisiana white clover flowered under all condi- 
tions except warm temperatures and short days. 

The potential yielding capacity of a timothy variety is apparently 
associated with photoperiod (Evans, 3939). Late maturing varieties 
grown at more southern latitudes in North America will not produce 
high yields because the culms will remain short and dwarfed as coin- 
pared to earlier maturing varieties. Wry early maturing (short day) 
varieties, \\ould be expected to mature so early in the northern latitudes 
that low temperatures would retard growth. The productivity would be 
low unless such strains excel in aftermath growth. 

The dry matter production and maturity of strains and species as 
influenced by photoperiod will influence their aggressiveness in a mix- 
ture. Early maturing grass and legume varieties are those that produce 
elongated leaves and flower under shorter photoperiods than the later 
maturing plants. If an early maturing grass variety is sown with a 
later maturing variety, the early one will become the aggressor because 
the culms and erect leaves will shade and retard growth of the late vari- 
eties Keller and Peterson (1950) measured the growth behavior of 
strains of timothy and red clover that differ in maturity when grown in 
pure stand and various mixtures. The dry matter production of red 
clover was not altered by photoperiod. Timothy yields were increased 
as the length of day was increased. When timothy-red clover mixtures 
were grown under a 10-hour day, the timothy in the mixture was not 
benefited ; however, with a 14-hour day the yield of timothy in the mix- 
ture increased by 47%. The proportion of timothy to red clover growing 
in a mixture increased with increasing day lengths, thus making timothy 
more aggressive or better able to compete with red clover under long 

Ladino clover and other white clover genotypes of northern origin 
flower under long photoperiods and fail to flower under the shorter 
photoperiod in Florida (Blaser and Boyd, 1940). Since white clover 
generally behaves as a winter annual in Florida, ladino is not used in 
that region, because it does not produce seed. The white clover geno- 


types of southern origin flower readily under the shorter photoperiod 
encountered in that region. Genotypes of other annual legumes from 
northern and southern origin such as black medic, Medicago lupulina, 
L., and annual sweet clover, Melilotus spp., responded similarly to white 
clover genotypes to photoperiod, (Blaser and Stokes, 1946, and unpub- 
lished results). 

Certain legumes, such as Korean lespedeza, fruit readily under a 
short photoperiod, but a photoperiod of more than 14 hours will prevent 
fruiting (Smith, 1941). In Missouri, Korean lespedeza is apparently 
better adapted to southern Missouri than to the northern part of the 
state. In northern Missouri the rate of seedling growth is slower than 
in southern Missouri during early spring because the short days and 
low temperatures retard vegetative growth. In the fall of the year, long 
days delay flowering; hence plants are often killed by frost before re- 
seeding (Smith, 1941). 

In experiments conducted in Florida, Korean lespedeza made very 
poor vegetative growth when compared with common lespedeza (Warner 
and Blaser, 1942). Under the short day lengths during January and 
February, when lespedeza germinated, Korean lespedeza plants were 
dwarfed and matured seed in spring. Because of this dwarfness and 
early maturity, Korean lespedeza not only made poor growth, but it was 
not able to compete with other species in the mixture. 

2. Soil Factors 

a. Moisture and Aeration. Deficiencies and excesses in soil moisture 
are acute agricultural problems because these factors are difficult and 
often impossible to regulate. Grasses are generally less vulnerable to 
injury from excesses and deficiencies in soil moisture than legumes. 
The natural grasslands in the United States are devoid of legumes 
(Weaver and Clements, 1938). Grasses survive serious droughts because 
the axillary buds are below the soil surface where they apparently escape 
extreme xeric conditions and because they assume a dormant condition 
during dry periods. Grass species in the prairie region differ in their 
adaptation to soil moisture. The taller grass species, such as big blue- 
stem, Andropagon fur cat us, MuhL, are dominant in prairie regions 
where soil moisture is most favorable ; the short grasses such as buffalo 
grass Buchloe dactyloides, Nutt., are predominant where moisture is less 

According to investigations by Dillman (1931), the drouth tolerance 
of plant species is not associated with water requirements (pounds of 
water required to produce a pound of dry matter). The range of water 
requirements varied widely for crop plants, sorghums and millets having 


a low water requirement as compared with alfalfa and perennial grasses. 
To manufacture 1 Ib. of dry matter, bromegrass, crested wheatgrass, 
Agropyron cristatum (L.) Beau., and western wheatgrass, Agropyron 
smithii, Rydb., required 784, 853, and 1183 Ib. of water, respectively. 
Water requirements varied with season, for example Grimm alfalfa har- 
vested at three dates required 469 Ib. of water per pound of dry matter 
for the early summer cutting, 817 Ib. for the mid-summer cutting and 
1115 Ib. for the late summer crop. The use of alfalfa, in the dry land 
regions, is attributed to the growth that is made during the early season 
when water requirements are apparently at their lowest point. 

Since the water requirements of plants adapted to regions of low 
rainfall are not necessarily low, it appears that the root volume and 
depth is important. The capillary water movement in soils to roots of 
plants is too slow to meet water requirements for growth, hence root 
growth is important in supplying the water needs of the plants (Baver, 
1948). Burton (1943) found that the maximum root depth of seven 
southern grasses did not differ greatly, but the distribution of roots 
within the rooting zone was very great. Three-fourths of the roots of 
carpet and vaseygrass, Paxpalum urvillci, Steud., known to be adapted 
to wet soils, were found in the upper 8 in. of soil. With strains of 
Bahia grasses, Paspahim spp., throe-fourths, of the roots were found in 
the upper 20 in. of soil. The root weights in the upper 16 in. of soil 
amounted to 10.97 g. of roots per 100 sq. in. of surface soil for common 
Bahiagrass, Paspalutn natatum, Fliigge, as compared with 3.77 g. for 

Bahia grasses were much more drouth tolerant and more productive 
during dry periods than carpetgrass in Florida (Blaser, unpublished 
results). Stephens (1942) found that Dallis grass and carpetgrass re- 
quire moist soils as compared to Bermuda grass, and Lovvorn (1945) 
and Mayton (1935) report that Dallis grass is less susceptible to drouth 
injury than carpetgrass. 

Gist and Smith (1948) measured the root mass and depth of pene- 
tration of grasses of northern origin. For the 0- to 3-in. depth they 
found the root weights in pounds per acre for various grasses to be : 
Kentucky bluegrass, 1126; orchardgrass, 1247; bromegrass, 718; timo- 
thy, 680. At the 12- to 18-inch soil layer the root weights for grasses 
were as follows : Kentucky bluegrass, 3 Ib. ; orchardgrass, 30 Ib. ; timo- 
thy, 6 Ib. ; and bromegrass, 106 Ibs. per acre. The data indicate that the 
expected productivity of these grasses during dry periods, from highest 
to lowest yields, would be in the following order : bromegrass, orchard- 
grass, timothy, and Kentucky bluegrass. Lamba et &Z. (1949) studied 
root growth of timothy, red clover, alfalfa, and bromegrass. The average 


root weights of seedling plants increased steadily during the first year, 
but increases were much larger during the second year. Alfalfa and 
bromograss produced more root growth than timothy and red clover. 
These investigators report that timothy obtains most of its water and 
nutrient supply from the upper 8-in. layer in silty loam soils. 

During dry periods the reserve supply of soil moisture is utilized 
readily and growth is subsequently retarded. Ohamblee (1951 ) found 
that the depth at which moisture was depleted was associated with plant 
species and root characteristics. The moisture supply in the upper 12 
in. of soil was depleted as fast by orchardgrass as by alfalfa, but at 
lower depths the moisture was much lower and often at the wilting point 
for alfalfa. 

In dry years the highest herbage yields are obtained from species 
that have deep and extensive root systems. During 1951 the summer 
and fall seasons were very dry in Virginia. At Blacksburg an orchard - 
grass-ladino clover mixture produced 3405 Ib. of dry herbage as com- 
pared to 6891 Ib. for an alfaifa-orchardgrass-ladino clover mixture 
The herbage yields for an orchard grass-alfalfa mixture was 74H9 Ib. as 
compared to 6812 for alfalfa without a grass (Table 1). A mixture of 
birdsfoot trefoil-white clover-Kentucky bluegrass produced a yield of 
3690 Ib. per acre. Mixtures with alfalfa and birdsfoot trefoil produced 
more herbage during the summer months than mixtures with ladino 
clover during this dry year. In two grazing experiments in Virginia a 
Kentucky 31 fescue-ladino clover mixture was more productive than a 
ladino elover-ordiardgrass mixture during the drier summer months 
Kentucky 31 fescue pastures in pure stand were more productive than 
orchardgrass pastures. In plot experiments orchardgrass and Kentucky 
31 fescue were more productive than Kentucky bluegrass during the 
deficient rainfall period. 

The application of supplemental moisture during dry summer periods 
has increased yields by as much as eightfold in Pennsylvania (Robinson 
and Sprague, 1947). Other experiments also show that low summer 
yields are augmented by water supply. 

The root and top growth of forage plants is intricately related to soil 
environment; soil drainage and aeration being critical factors in soils in 
the humid section of the United States. Sprague (1933) and Farris 
(1934) studied root development of various grasses and crop plants in 
New Jersey. It was found that the root systems of plants grown in soils 
in this humid region were decidedly less extensive than in soils of mid- 
western states. Boynton and Reuther (1938) found that the oxygen in 
the soil air was as low as 0.1 per cent in the second foot of a silty clay 
loam during early spring. Carbon dioxide was found to be much higher 


Seasonal Yields of Various Forage Mixtures in Virginia, 1951 

Yields in Pounds per Acre Total for 

Mixtures in Pounds per Acre May 7 29 July 10 Aug. 20 OIL 9 Season 

Alfalfa 20 orelundgrasslT 3459 2389 945 696 7489 
A]f;j]f:i 10, ladmo clover 1, 

orclmrdgrass 3 3658 2165 546 522 6891 

A If a If ;i 20 3322 1881 1030 579 6812 

Ladmo clover 2, orchard grass 8 1927 1001 477 3405 

Kentucky hluegrass 30, Virginia white 

clover 'l, and birdsfoot trefoil 10 1003 2264 423 3690 

Hoot find Herbage Growth of Leguminous Plants as Influenced by Soil Moisture 

Moisture Black Medic California Bur White Clover Persian Clover 

Level * (Medwago (Mvdicago (Trifolium (Trifolium 

(Per cent) lupulina) hi^pida) rcpens) resupinatwm ) 

Herbage Roots Herbage Koots Herbage Itoots Herbage Roots 

25 32 75 33 53 Ts 48 30 46 

5(1 108 88 75 77 82 113 69 91 

75 100 300 100 300 300 100 100 100 

100 15 ]5 74 69 92 74 106 94 

1 One hundred per cent equals moisture level after a IJPOII fine sand A\HS saturated with 
\MiU'T and permitted to drain 10 hours 

in the soil atmosphere than in the above-ground atmosphere. Lamba d 
al. (1949) found that root growth of alfalfa, timothy, red clover, and 
bromegrass was better in a sandy soil than in a silty loam soil. Artificial 
aeration of a silt loam stimulated the depth of penetration and amount 
of root growth of alfalfa and bromegrass. 

The root development of plants is dependent upon the combined 
effects of soil environment and genetic characteristics of species (Farris, 
1934; Burton, 1937; Weaver and dements, 1938; Baver, 1948; Lamba 
el al., 1949, and others). 

In an experiment conducted by Volk and Blaser (unpublished results, 
University of Florida) legume species displayed differential responses 
when grown at four moisture levels, approximately 25, 50, 75, and 100 
per cent of field capacity (Table II). The relative yields of black medic 
were 32, 108, 100, and 15 as the moisture increased from a low to a high 
level. White clover growth was not retarded by high moisture levels; 
the relative yields being 18, 82, 100, and 92, respectively, for low to 


high water levels. The yields of tops were associated with root growth. 
For black medic clover the relative root yields were 75, 88, 100, and 15 
as compared with 48, 113, 100, and 74 for white clover when the soil mois- 
ture ranged from 25, 50, 75, and 100 per cent field capacity, respectively. 
The adaptation of Persian clover was similar to white clover, but yields 
of California bur clover, Medicayo kispida, Gaertn., were slightly dimin- 
ished by high moisture levels. 

White and Persian clovers produced numerous short, fine, surface 
roots under the highest moisture level, but black medic had short coarse 
roots (Fig. 3). The development of many fine surface roots in Persian 
and white clovers apparently increased the surface area of roots which 
increased the oxygen availability to the plant at high moisture levels 
where lack of oxygen usually limits metabolic activity. 

Burton (1937) crossed alfalfa species with inherent tap- and branch- 
ing-tap root systems. The alfalfa genotypes with the more branching 
roots were found to produce higher herbage yields than the less branch- 
ing genotypes when grown in a poorly aerated soil. 

Since soil moisture and aeration are difficult to control, the plant 
species that are best adapted to these localized soil conditions should be 
used in mixtures. In general, forage plants are most productive on 
reasonably well-drained soils, but certain species, such as redtop, meadow 
fescue, tall fescue, tall oatgrass, carpetgrass, birdsfoot trefoil, alsike, 
white, and red clovers, will grow on imperfectly drained soils. 

&. Soil Fertility and Soil Reaction. Perhaps the earliest work in the 
United States which associated plant population changes in pastures with 
the fertility status of soils was reported by Carrier and Oakley (1914). 
They reported that fertile soils had fewer weeds and better stands of 
cultivated grasses than poor soils. Experimentally, they treated small 
plots with manure and various combinations of mineral fertilizers in 
1909. A marked decrease 4n broom-sedge, Andropogon virginicus, L., 
and an increase in Kentucky bluegrass and white clover were associated 
with superphosphate or nitrate of soda treatments. The white clover 
population was increased the most on plots which received superphos- 
phate without nitrogen. Cooper (1932) reported various degrees of 
degeneration of Kentucky bluegr ass-white clover pastures in New York. 
The best pastures were made up of Kentucky bluegrass-white clover 
mixtures and the poorest pastures were made up of poverty grass, Dan- 
thonia spicata, (L.), Beauv. There was little correlation between pH 
and species components in various stages of succession, and the degenera- 
tion of desirable species was attributed to depletion of soil nutrients. It 
has been clearly established that the productivity and maintenance of 
cultivated grasses and legumes in the humid area of the United States 



cannot be attained without applying mineral nutrients ( Johnstone- Wal- 
lace, 1937; Dodd, 1941; Brown and Munsell, 1943; Mott, 1943; Blaser 
et al., 1945; MacDonald, 1946; Sprague et al, 1947, and many others). 
Information on the relative growth responses of species components 
to the mineral nutrient status of soils should be useful in compounding 
seed mixtures. It is generally assumed that leguminous plants require 

FIG. 3. Effect of soil moisture level on roots of clover. Upper, black medic 
clover; lower, white clover. Left to right: approximately 25, 50, 75, and 100 per 
cent of field capacity. White clover produced many fine surface roots and made 
good growth under high moisture conditions. Black medic had short coarse roots 
under high moisture conditions and made poor growth. 


higher nutrient levels than grasses. Grasses and certain legumes respond 
quite differently to the nutrients sulfur, boron, and molybdenum. Under 
sandy soil conditions in Florida, the leguminous plants red clover, black 
medic, and white clover growing with grass mixtures were stunted and 
yellowish in the absence of sulfur supplements (Bledsoe and Blaser, 
1947; Neller ct al., 1951). Sulfur influenced the rate of grass growth 
indirectly through improving the available nitrogen supply. Data re- 
ported in various annual reports in Virginia show that ladino clover does 
not respond to borax applications whereas alfalfa induces pronounced 
responses on certain Virginia soils. In the absence of boron supplements, 
alfalfa cannot compete with associated grasses and weeds, hence the 
stand of alfalfa degenerates. Grasses ha\e not been found to respond to 
supplemental applications of borax in field experiments. Experiments 
conducted in Florida (Killinger ct al., 1943, and unpublished results) 
showed that under very similar soil conditions leguminous plants in tho 
genera, Mcdicago and Me Hiatus responded to boron, whereas Trifolium 
spp. did not respond. However, the seed production of crimson clover, 
Trifolium incarnatum, TJ., was increased when soils were supplemented 
with borax in Alabama (Naftel, 1942). Experiments on certain soils 
show that legumes such as subterranean cloxer, TrtfvltHHi subtcrrancinni 
L., and alfalfa often respond in growth when molybdenum is applied 
(Anderson and Thomas, 1946; Evans and Purvis, 1951). 

Robinson (1944) found that seedlings of grasses and legumes pro- 
duced more dry matter as increments of phosphorus were added. The 
leguminous seedlings made relatively better growth at low levels of phos- 
phorus than the grass seedlings. Tn a field experiment with an orchard 
grass-ladino clover mixture grown on a soil low in phosphorus, the rela- 
tive phosphorus absorption from phosphate fertilizers containing P 3 - 
was measured by Blaser and McAuliffe (1949). During the first four 
weeks more than 22 per cent of the phosphorus absorbed by orchard 
grass and ladino clover seedling plants came from the fertilizer. Ap- 
proximately two weeks later 15 and 25 per cent of the phosphorus in 
orchardgrass and ladino clover, respectively, came from the fertilizer. 
The herbage from a second harvest also showed that orchardgrass uti- 
lized more soil phosphorus than ladino clover. 

Tn experiments in Virginia, phosphorus absorption was measured 
among species for two plant associations (alfalfa-orchardgrass and la- 
dino clover-orchardgrass mixtures) in two locations (Rich unpublished 
data). Superphosphate at the rate of 53 Ib. per acre containing P 32 
was applied in spring on replicated plots treated the previous year 
with 0, 100, 200, and 400 Ib. of P 2 5 per acre. For all species the 
amount of phosphorus absorbed from the fertilizer increased as the 


residual phosphate applications decreased (Table III). For alfalfa- 
orchardgrass mixtures the orchardgrass absorbed as much phosphorus 
from the fertilizer as alfalfa. Ladino clover absorbed more phosphorus 
from the fertilizer than the orchardgrass component in the mixture. 
These results with P 32 suggest that orchardgrass and alfalfa species are 
better adapted to absorb phosphorus from the less available sources of 
soil phosphorus than ladino clover. Yields of the grass and legume frac- 
tions of mixtures in these experiments indicate that the leguminous asso- 
ciate is more competitive to the grass associate under the higher levels of 
phosphorus fertilization. 


FMioxphoriiK Absoi hod by Forage Components in Two Glass-Legume Mixtures under 
Four Levels of Fertilization in Virginia, 1951* 

53 lb. per acre of Kadioactive PaO-, Broadcast in Spring 

A If a If a -orchard- Ladino-orchard- 

Pounds pc-i Acre of RrnMjnixture__ grass mixture 

PaO-, Applied in 1950 Orchard- Ladino Orchard- 

and Disked in Alfalfa, grass clover grass 

Per Cent P Alsorbcfl from Fertilizer 

400 24.0 26.2 29.2 16.0 

200 31.5 32.7 42.0 22.1 

100 32.7 32.9 48.8 25.9 

38.6 42.9 45.1 37.5 

Mean 31.7 33.6 41.2 25.3 

PCI Cent P in Plant 

400 0.31 0.40 0.31 0.36 

200 0.28 0.37 0.29 0.37 

100 0.28 0.36 0.29 0.36 

0.26 0.38 0.29 0.35 

Mean 0.28 0.37 0.29 0.36 

* Average of two locations. 

In experiments conducted in North Carolina, Woodhouse (1947) 
found that the increases of Korean lespedeza due to liming ranged from 
1 to 226 per cent during a three-year period (Table IV). Lime was 
more beneficial to alfalfa than to lespedeza; the yield increases for al- 
falfa ranged from 212 to 802 per cent. Growth of both alfalfa and 
lespedeza was improved with phosphate fertilizer. The yield increases 
ranged from 36 to 43 per cent for alfalfa as compared with 2 to 24 per 



Relative Growth Responses of Alfalfa and Lospedeza to Lime, Superphosphate, and 

Potash at North Carolina 

Percentage Yield Increases 







Yield increases due 





to phosphorus (%) 
Yield increases due 





to potassium (%) 
Yield increases 






due to lime (%) 

- 1 



cent for lespedeza. When treated with potassium fertilizer, alfalfa yields 
were increased from 6 to 16 per cent as compared with 12 to 17 per 
cent for lespedeza. 

The effect of nitrogen and potassium on plant succession due to differ- 
ential absorption and growth rate of species components in mixtures is 
given in Sec. ll-4c. 

Plant species also respond differently to soil acidity. In a green- 
house experiment, York (1947) found that alfalfa and perennial les- 
pedeza responded quite differently to levels of liming and pH. A soil 
was limed to approximately pH 5.0, 6.0, 7.0, and 8.0. The yield of 
alfalfa was 5.1 g, per pot at pll 5.0 and 8.8 g. at pll 6.0, beyond which 
there was no further yield increase. With lespedeza the yield was 9.3 
g. for the unlimed soil at pH 5.0, as compared with a decrease in yield 
to 6.9, 4.5, and 0.4 g. when the soil was limed and the pH values were 
about 6.0, 7.0, and 8.0 respectively. 

On a sandy acid soil in Florida the production of six Trifolium 
species and four species in the genera Medicago and Melilotus were tested 
at two levels of lime (Blaser et aL, 1941). The yield of the Trifolium 
species was increased slightly by liming whereas the yields of Medicago- 
McHlotus species were increased greatly when the rate of lime was raised 
from 1 to 2 tons per acre. When growing white clover and California 
bur clover in a mixture, the proportion of bur clover in the forage was 
increased by adding lime and that of white clover was reduced. It was 
concluded that the Trifolium species remained productive under a lower 
lime and pH level than Medic ago-Melilotus species. 

3. Biological Factors 

a. Morphology of Plants. The establishment, maintenance, and 
propagation of species in mixtures is related to morphological character- 


istics. Plants that grow erect, such as many grasses of northern origin, 
are generally aggressive to plants with a prostrate habit of growth, such 
as white clover. It is generally more difficult to maintain short prostrate 
strains than taller prostrate strains of white clover in an association 
with erect growing grasses unless very close or intensive clipping or 
grazing is practiced. In an experiment at Middleburg, Virginia, four 
varieties of white clover were grown alone and separately in mixtures 
with each of two grasses, Kentucky bluegrass and orchardgrass. From 
the standpoint of size, the strains of white clover may be classified from 
tallest to shortest in the following order: ladino, S-100, Virginia, and 
Kent wild. Ladino clover was the most productive clover when grown 
either in pure stand or in a grass mixture, and Kent wild was the least 
productive (Table V). In 1950 the mean yields of mixed herbage 
(legumes and grasses) for one harvest were: ladino clover, 2496 lb., and 
Kent wild clover, 1237 lb. per acre. In 1951 the yields were relatively 


Herbage Yields and Botanical Composition as Influenced by Four Varieties of White 
Clover Grown in Different Mixtures, Middleburg, Virginia * 

Herbage Yields 1950 Herbage Yields 1951 

White Clover Varieties Total Clover Clover Weeds Total Clover Clover Weeds 
and Grass Mixture Lb. Lb. % % Lb. Lb. % % 










Ladino-Ky. bluegrass 









Ladino alone 



























S-100-Ky. bluegrass 









8-100 alone 



























Virginia-Ky. bluegrass 









Virginia alone 


















Kent wild-orchardgrass 









Kent wild-Ky. bluegrass 









Kent wild alone 


















* Yield data include last harvest in 1950 and first harvest in 1951. 


the same. S-100 clover was somewhat more productive than Virginia 
white clover in both years. 

Botanical composition data show that the growth of clover varieties 
is influenced by grass association. During 1950 in ladino clover-orchard 
grass and ladino clover-bluegrass mixtures, the herbage was made up of 
53 and 58 per cent of ladino clover, respectively. When Kent wild clover 
was grown witli orchardgrass only 11 per cent of the yield was made up 
of clover as compared with 11) per cent clover for the bluegr ass-white 
clover mixture. In 1951, S-100, Virginia white clover, and Kent wild 
clover were less productive and constituted a lower percentage of the 
mixture when grown with orchardgrass than when grown with blue- 
grass, whereas the ladino cL>ver yields were of similar magnitude when 
grown with either of these two grasses. 

It may be concluded that shorter growing clover varieties such as 
Kent wild, Virginia, and S-100 are less competitive when grown in 
mixtures with tall aggressive orchardgrass than with short arid less 
aggressive bluegrass Species grown in mixtures that are similar in 
height would be expected to be reasonably compatible if they respond 
similarly to other physiological factors. 

Competition among plants is probably not influenced by root mor- 
phology. Davies (1928) found that Italian ryegrass was aggressive 
toward rough stalked meadow grass (shallow roots), meadow fescue, 
(deeper roots), red clover (deep roots), and alfalfa (very deep roots). 
Competition was attributed to aerial shading. 

Rate of aftermath growth is influenced by morphological characteris- 
tics of plants. Orchardgrass, which produces much higher aftermath 
yields than does timothy, also produces numerous lateral shoots at the 
base of each culm even before the first spring growth is grazed or mowed 
(Fig. 4). These lateral shoots develop quickly after the spring growth 
is removed. In timothy there are only one to three buds per corm, and 
these buds do not usually develop into shoots until the spring growth is 
removed. The differential rate of aftermath development of these two 
species is also influenced by temperature and moisture (See Sec. II, 

Stoloniferous or rhizomatous grasses generally form dense sods which 
are more aggressive toward legumes than are bunch grasses. When 
bunch grasses are seeded heavily, they are also competitive and legumi- 
nous species do not usually survive in the bunchy grass growths. With 
sparse stands of bunch grass, associated species grow in the open areas. 
Bunchy growth habits are very undesirable when palatability among 
species differs. With ladino clover, a palatable species, and Kentucky 31 
fescue, an unpalatable species, cattle overgraze the palatable clover and 


undergraze the unpalatable fescue. Selective grazing of fescue is encour- 
aged because of its bunchy growth. 

FIG. 4. Comparative shoot development of orchard grass and timothy. Upper, 
timothy; lower, orchard grass. Owing to the development of many shoots at the base 
of each culm, orchard grass produces high aftermath yields. 

Some stoloniferous grasses, such as carpet and centipede, Eremochloa 
ophiuroides, Munro., Hack., form an extremely dense sod. It is very 
difficult to maintain other grasses and clovers in mixtures with such 
sods, even under close grazing management practices. In the southern 
region where seedlings of winter or spring annual legumes volunteer, 
seedling mortality is often high because of the dense grass sods, (Hollo- 


well, 1938; Blaser et al., 1945; Stewart and Rogers, 1947). Stephens 
(1942) and Lovvorn (1944) report that it is easier to grow legumes 
with Dallis grass (a bunch grass) than carpet grass (a stoloniferous 
grass), because the latter has a more open sod. The reconstruction of 
pasture species as related to morphology is given in Sec. II, 4b. 

The degeneration of pastures from three to five years after seeding 
has been reported by Bates (1948), Pollitt (1947), and others. No great 
changes in botanical composition of the herbage occur, but the yield, 
protein, and carotene content sharply decreases. This has been associ- 
ated with the formation of a mat of roots immediately under the surface 
of the soil. Under grazing conditions, the grasses developed more but 
smaller tillers, as they became older. 

b. Palatability. In general, the palatability of a forage species is 
primarily associated with growth stage, i.e., mature herbage is decidedly 
less palatable than young leafy herbage (Watson, 1951). Likewise, the 
differences in palatabiHty due to differential growth stage within a spe- 
cies are usually larger than the differences in palatability among forage 
plants when growth stage is similar. Palatability varies with animals; 
cattle usually prefer orchard grass in a vegetative stage of growth to 
Kentucky bluegrass herbage in a similar growth stage, yet the reverse 
usually occurs with sheep. 

From the viewpoint of herbage quality, mixtures should be made up 
of forage plants that are highly nutritive and palatable. According to 
Garrigus (1950), the dry matter intake from palatable species is appar- 
ently higher than from less palatable ones. With a fecal bag technique, 
he found that sheep and steers consumed less herbage when grazing Ken- 
tucky 31 fescue than when grazing other grasses and legumes. The dry 
matter intake when grazing leguminous species was higher than grass 
species. No data were reported for mixtures. 

In Virginia, the palatability of species and mixtures was measured 
with beef animals. Small areas of the experimental plots were sampled 
immediately before and after grazing. The animals were removed before 
any species or mixture was grazed too closely so as to avoid a confound- 
ing of availability and palatability. During a two-year period, when 
animals had access to all species or mixtures, 48 per cent of a pure stand 
of orchardgrass herbage was consumed as compared to 27 per cent for 
herbage from a pure stand of Kentucky 31 fescue (Table VI). When 
ladino clover was grown with the grasses, 44 per cent of the mixed herb- 
age from Kentucky 31 fescue-ladino clover was consumed as compared 
with 64 per cent of the available herbage of a ladino clover-orchardgrass 
mixture. Orchardgrass was more palatable than Kentucky 31 fescue, 
and ladino clover improved the palatability of both grasses. 


In the palatability experiment the clover population in the clover- 
grass mixtures was maintained with palatable orchardgrass, and the less 
palatable fescue because the plots were mowed closely after each grazing 
trial (Table VI). In an adjacent grazing experiment with beef cattle, 
the ladino clover population was high in both mixtures for the first year. 
During the second year ladino clover made up 40 per cent of the herbage 
in the orchardgrass-ladino clover mixture as compared with only 16 
per cent ladino clover in the Kentucky 31 fescue-ladino clover mixture. 
At Blacksburg, Virginia in an experiment with dairy cattle, the ladino 
clover population is also much lower when grown with Kentucky 31 
fescue than with orchard grass. 


Yields, Relative Palatability, and Botanical Composition of Four Pasture Mixtures 

(Middleburg, Virginia, J 950-51) 

Mixtures* Means for 1950 arid 1951 Ladino Clover in Mixtures 

TT T_ 1950 1951 
Herbage ___ 

Yields consumed Grazed Clipped Grazed Clipped 
Lb./acrc % % % % % 




Ky. 31 fescue 



Orehardgrass and 

ladino clover 




Ky. 31 fescue and 

ladino clover 




49 26 53 

44 16 33 

* Seeding rates in pounds per acre grasses in pure stand 34 lb., with clover 8 Ib and 
clover at 2 lb. The experiments were sown in September, 1949. 

In grazing experiments, the low population of ladino clover in rela- 
tively unpalatable fescue herbage as compared with Orehardgrass is at- 
tributed in part to selective grazing, but is more directly attributed to 
closeness of grazing. Cattle refused to graze Kentucky 31 fescue closely, 
unless pasturage was scarce. Kentucky 31 fescue also produces more 
herbage during the late summer and fall and this competitive effect also 
is thought to be harmful to ladino clover. 

c. Diseases and Insects. Insect and disease injuries often reduce the 
stand, productivity and/or longevity of forage plants. Disease and 
insect pests may attack and injure plants during seedling development 
or after establishment (Graber and Jones, 1935; Chilton and Garber, 
1941; Dickson, 1947; Hanson and Allison, 1951; and others). 

When growing mixtures of forage plants, the species that are highly 


susceptible to prevailing diseases or insects are retarded and consequently 
the resistant species becomes dominant. The differential susceptibility 
of strains within forage species to disease and insects offers much induce- 
ment for developing disease and insect-resistant strains (Painter and 
Grandfield, 1935; Hermann and Eslick, 1939; Burton, 1948; and others). 

Although a plant that is resistant to a disease or an insect usually 
becomes aggressive to an associated plant that is susceptible to the pest, 
Burton ei al. (1946) found an inverse relationship. On sandy soils of 
the Southeast annual lespedezas often disappear because they are very 
susceptible to injury from root-knot nematode, Heterodera marioni 
(Cornu). Among twenty-eight strains of lespede/a grown on a nema- 
tode-infestod soil, all strains died at the end of the first summer. Out of 
]47 Bermuda grass selections certain strains were found to be both highly 
susceptible and resistant to nematodes. Root-knot susceptible lespedeza 
grew well and was found to be practically free of nematodes when grown 
with five root-knot resistant strains of Bermuda grass. 

d. Variety. Crop varieties are plants within a species that differ in 
genetic constitution. The adaptation of varieties differ because of the 
differential response between genotypes and environmental factors. An 
ideal variety would be one that is superior in yield, longevity, and qual- 
ity when considering all climatic, soil, and biological factors. 

Varieties and strains were often considered in the previous sections 
when discussing plant adaptation, and hence those relationships will not 
be repeated. The previous reviews suggest that all factors which affect 
yield and quality should bo carefully considered in formulating a breed- 
ing program which is directed toward the improvement of varieties. If 
this is done the isolation of varieties that are superior with respect to 
some growth factors and inferior to others can be avoided. 

The voluminous data pointing out the superiority of certain varieties 
for local or regional conditions will not be given. In the evaluation of 
varieties, yields are often overemphasized and information on the life 
history is neglected. The improved strains of grasses developed at 
Aberystwyth are apparently very superior in longevity arid leafiness 
under close grazing, but seedling vigor arid productivity during the early 
life were apparently sacrificed in comparison with commercial varieties 
(Stapledon and Davies, 1930; Davies, 1939). 

Experiments conducted in Virginia show that Virginia commercial 
orchardgrass produced more aggressive seedlings than the S-143 Aberys- 
twyth) variety (Table VII). By expressing the relative yield of Vir- 
ginia commercial seedlings as 100, the yield of S-143 seedlings was 36 
when seeded on September 4 and sampled 38 days later. When seeded 



"Relative Rate of Seedling Development of Two Orchardgrass Varieties, Virginia 


Sowing date 

Days after 

Weight of 25 Seedlings 

Relative Seedling 





September 4 
March 35 
April 15 







on March 15 and April L5 and sampled 65 days later, the relative yields 
of S-143 were 86 and 74, respectively. 

Seedlings of forages that become established quickly are more likely 
to survive than seedlings which grow slowly, under common hazards of 
field conditions. Since slow developing seedlings are subjected to more 
hazards than rapid growing seedlings, it becomes apparent that higher 
seed rates to obtain stands are required for the species that develop rela- 
tively slowly. This may account for the high rates of seeding orchard 
grass recommended in England as compared to the United States. 

4. Plant Succession An Inter relationship of Climatic, Soil, 
and Biological Factors 

In mixed plant associations, the differential growth responses of 
species to artificial and natural environmental factors determine plant 
succession. The processes of plant succession are exceedingly complex, 
because of the interacting relationships among factors that affect growth 
Tn spite of insufficient fundamental data, a description and interpreta- 
tion of several examples of plant succession as influenced by various 
growth factors is given in the subsequent sections. 

a. Grazing Management of Grass-Legume Mixtures. The kind of 
grazing management practices used are dependent upon the morpho- 
logical characteristics of species (Klapp, 1937; Jones, 1939; Moore et al.< 
1946). Species with tall and erect habits of growth, such as alfalfa- 
bromegrass mixtures, can be almost completely defoliated under heavy 
continuous grazing. Frequent and rather complete removal of foliage 
causes a drastic reduction in yield because of depleted organic food 
reserves in the roots, stolons, rhizomes and/or stubble (Graber et a/., 
1927; Graber, 1931; Rather and Dorrance, 1938; McCarty and Price, 
1942 ; Smith and Graber, 1948 ; Dotzenko and Ahlgren, 1950 ; Tesar and 
Ahlgren, 1950). Tall erect growing species may be maintained under 
rotational grazing where grazing periods are of short duration and are 


followed by long rest periods. Close grazing is not especially injurious 
to stand and yield if the period of grazing is short. With grasses that 
store food reserves in the stubble close grazing may be more injurious to 
the grasses than to the legume in mixtures (Sullivan and Sprague, 
1943; Sprague and Sullivan, 1950). 

Mixtures made up of short, erect, and/or prostrate species have sur- 
vived and produced as high or almost as high yields under continuous as 
under rotational or intermittent grazing (Carrier and Oakley, 1914; 
Comfort and Brown, 1933; Ilein and Cook, 1937; Hodgson et al., 1934; 
Woodward et al., 3938; Moore et (il., 1946; Peterson, 1947; Mayton ct al., 
1947). With the shorter and/or prostrate species complete defoliation 
does not usually occur, even under close intensive grazing; hence, pro- 
duction can be maintained under either rotational or continuous grazing. 

During the spring season there is usually a critical period of competi- 
tion among grass-clover associations because of temperature and light 
interrelationships. In Sec. II, la. it was pointed out that grasses of 
northern origin start active competitive growth earlier in the spring 
than clover because of their adaptation to lower optimum temperatures. 
White clovers are further retarded by the erect reproductive growth of 
grasses during spring months, which is attributed to the combined effects 
of temperature and photoperiod. With grasses, like Kentucky bluegrass, 
orchardgrass, and bromegrass, a short photoperiod accompanied by cool 
temperatures has been found to stimulate flower induction. After the 
flower primordia are laid down, the combined effect of long days with 
cool temperatures, encountered during the spring, stimulates shoot 
elongation and flowering of grasses (Peterson and Loomis, 1948 ; Gard- 
ner, 1950; Newell, 1951). Since flower primordia are laid down during 
the fall of the year under short day low temperature conditions, most 
grasses of northern origin usually flower only once during the growing 

Because of the combined effects of temperatures and photoperiod, 
the grass blades and culms elongate rapidly as the days lengthen in 
spring, making grasses aggressive toward white clover. When tempera- 
tures become optimums for clovers, their growth is usually restricted 
because of the low light intensity. The species in mixtures also compete 
for moisture or nutrients, Sec. II, 4c. 

Nitrogen fertilization also augments grass competition. The earli- 
ness of grass growth is often limited because of a low level of available 
nitrogen. By adding nitrogen the earliness and magnitude of grass 
growth relative to the clover in the mixture is accentuated, thereby mak- 
ing the grasses even more aggressive toward prostrate white clover 


The aggressiveness of grass associates can be offset by imposing early 
spring grazing. Early grazing apparently favors the predominance of 
white clover in the sod because of the improved light intensity and higher 
soil and air temperatures at the clover level. By grazing to remove the 
insulating herbage, higher soil temperatures and better clover growth 
would be anticipated. 

1). Improving Degenerated Kentucky Bluegrass-White Clover Pas- 
tures. Permanent pastures in the more humid northern and northeastern 
states that are poorly managed and not given proper cultural treat- 
ments are often composed of broom-sedge, povertygrass, hawkweed, 
Hieracium pratense, Taush., dwarf white clover, and Kentucky blue- 
grass plants. By fertilization, an environment is created whereby the 
desirable species are encouraged and the undesirable ones are discour- 
aged. Fertilizers are not toxic to undesirable species. This was shown 
by MacDonald (1939), who found that the growth of certain undesirable 
plants found in degenerated pastures was stimulated by fertilizers. 

At this stage where the soil has been supplemented with needed nutri- 
ents, species respond differently to temperatures. Bluegrass and white 
clover grow at lower optimum temperatures than do most of the unde- 
sirable plants, hence, these desirable plants become aggressive because 
of their spring growth. This early spring growth of the desirable species 
as compared with the undesirable plants brings into effect the growth 
factor, light. The early spring herbage of the desirable plants reduces 
the light intensity and photosynthesis at the growth level of the unde- 
sirable plants. When temperatures in late spring become optimum for 
growth of undesirable plants, their rate of growth is restricted because 
of the low light intensity and its effect on organic foods. 

At this stage morphology and palatability become factors. Hawk- 
weed, with its prostrate leaves, begins to grow erect as the sod thickens. 
This erect habit of growth restricts light aWtorption and some hawkweed 
foliage is also consumed with the palatable herbage of desirable species 
which further retards its growth. 

Morphologically broom-sedge is a robust, erect-growing species with 
a bunchy growth habit. Carrier and Oakley (1914) found that mowing 
and close grazing shifted the plant population from broom-sedge to 
bluegrass and white clover. Under close grazing and rather complete 
defoliation, the growth rate of broom-sedge is retarded more than that 
of desirable species components. As the rate of growth of undesirable 
species diminishes, white clover and bluegrass encroach because these 
species are propagated vegetatively by stolons or rhizomes. 

This type of plant succession, without nitrogen fertilizer, requires 
some two to five years because the growth of grass is dependent upon a 


legume for nitrogen. The succession to desirable plants may be realized 
in a much shorter time by applying nitrogen fertilizer with lime and 
minerals. This stimulates the growth of bluegrass which is usually lim- 
ited by soil nitrogen. 

Unproductive permanent pasture areas where the population of 
desirable species is very low can be brought into a productive status 
much faster by renovation and reseedirig with suitable mixtures than by 
surface broadcasting of fertilizer and regenerating the stoloniferous spe- 
cies (Sprague et al., 1947). Obviously, unproductive pastures and mead- 
ows can be reconstructed without renovation or reseeding only when the 
desirable species are propagated by rhizomes or stolons. 

c. Competition for Potassium. Plants grown in mixtures often com- 
pete for potassium. Blaser and Brady (1950) found that weeds absorbed 
higher percentages of potassium than grasses and that grasses absorbed 
higher percentages of potassium than clover. Bear and Wallace (1950) 
found that certain weeds growing in alfalfa were higher in potassium 
content than alfalfa. In Virginia experiments, the mean potassium con- 
tent of species fractions of seventeen grass-legume mixtures grown on 
five fertilized soils was 3.28 per cent for grasses as compared with a mean 
of 2.32 per cent for legumes. 

The critical percentage, at which potassium affects rate of grass 
growth, has not been established, but it is thought that grasses have a 
lower potassium requirement than legumes and yet the luxury consump- 
tion of potassium is higher for grasses than for legumes. Drake et al. 
(1951) found that plant species, such as grasses, with roots of a low base 
exchange capacity absorbed more potassium than plants with roots high 
in base exchange capacity. 

Temperature, as related to growth of species, influences competition 
for nutrients. Since grasses of northern origin grow at lower tempera- 
tures than legumes, grassed are aggressive competitors for potassium 
during the spring season. Ladino clover is often potassium deficient and 
stunted because of the low available potassium when grown with grasses. 
Alfalfa and ladino clover populations have been almost eliminated in 
one year in grass association where potassium fertilizer was not supplied. 

Nitrogen fertilization is also intricately associated with potassium 
competition among grasses and legumes. The earliness of grass growth 
is often limited by available nitrogen rather than by temperature. By 
supplying nitrogen fertilizers in early spring, the augmented grass 
growth and concurrent high absorption of potassium reduces the supply 
of potassium for the leguminous associates. Consequently, on soils low 
in potassium, the clover population and growth diminishes. 

Further evidence of nutrient competition among grasses and legumes 


as related to nitrogen and potassium fertilization was obtained from an 
experiment in Virginia (unpublished). In a soil rather low in available 
potassium, ladino clover was grown in pure stand and with several 
grasses. The ladino clover yields in pure stand were not retarded by 
nitrogen fertilizer, and the responses from potassium fertilization were 
low. When ladino clover was grown with grasses, the clover stand and 
growth was very poor when treated with nitrogen alone, but quite satis- 
factory when both potassium and nitrogen fertilizers were applied. 
Ladino clover in grass mixtures made the best growth when potassium 
was used in the absence of nitrogen. Even though high levels of potas- 
sium were supplied with nitrogen to ladino clover-grass mixtures, the 
ladino clover population and yields were smaller where nitrogen fertili- 
zer was applied than in its absence. This suggests the presence of other 
competitive factors, such as light and water. 

Evidence of competition for potassium between grasses and legumes 
suggests that grass-legume mixtures may require higher levels of potas- 
sium than pure stands of legumes. On soils low in potassium, applica- 
tions of potassium after the flush spring growth of grasses would 
probably encourage the leguminous associate in the aftermath growth. 

d. Seedling Competition. When a mixture of seeds of forage species 
arc seeded together, a struggle for survival develops immediately after 
the first seeds germinate. At this stage the mixture of plants enters into 
a dynamic biological community because of the differential reaction and 
responses among species to various environmental growth factors. 

The influences of germination on seedling growth and competition can 
have an important bearing on seedling competition because the early 
plants will have a definite advantage over the later ones. Ohippindale 
(1949) showed that seeds of grass species differ in the time required for 
germination. Under identical environmental conditions, Italian rye- 
grass germinated in five days, while orchard grass required fourteen 
days. In the field, Stapledon et al. (1927) found that the percentage 
establishment of orchardgrass seeds sown was 39 to 44 per cent while for 
Italian ryegrass, it was 52 to 70 per cent. The rate and time of germi- 
nation of seed of different species is influenced by the combined effect of 
the factors, temperature, moisture, and light. Some viable seeds fail to 
germinate readily because seed coats are impermeable to water or oxygen, 
or because the seed contain dormant or rudimentary embryos (Meyer 
and Anderson, 1939). Some seeds, such as common Bahia grass, will 
not germinate rapidly regardless of environment because their tough 
waxy seed coats restrict water absorption (Burton, 1940). With sulfurio 
acid scarification quick germination is attainable. 

The combined effect of moisture and temperature influences the rate 






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and degree of germination of some species. Blaser and Killinger (1950) 
found that alternating temperatures in a moist environment stimulated 
germination of hard white clover seeds. Scarified seeds germinated 
readily without alternating temperatures. Chippindale (1949) deter- 
mined the moisture requirements of various grass seeds by placing seeds 
in a soil at different levels of available moisture. The data indicate that 
the moisture requirements of orchardgrass are very high, those of peren- 
nial ryegrass and Kentucky bluegrass are high, and those of timothy and 
tall fescue are low. 

Light in the presence of optimum temperatures improved the per- 
centage germination of Kentucky bluegrass and tall fescue. Anderson 
(1931) reported that light improved the germination of Canada blue- 
grass, but a combination of light and nitrate resulted in additional 

Although the rate and time of germination, as related to environ- 
mental factors, is an initial phase that may determine the aggressiveness 
of species in mixture toward each other, other factors also become opera- 
tive. The rate of seedling growth after emergence is often associated 
with size of seed or caryopsis. Seeds of ryegrasses have a large caryopsis 
as compared with redtop which may partially account for the rapid 
development of ryegrass seedlings as compared with redtop. Redtop 
has a very small caryopsis as compared to Kentucky bluegrass and chew- 
ings fescue; yet Erdmann and Harrison (1947) showed that redtop is 
aggressive in relation to the other species. In several experiments con- 
ducted in Virginia with white clover varieties, ladino clover seedlings 
developed faster than S-100 clover, which in turn developed more 
quickly than Kent wild clover. Stapledon ct al. (1927) associated the 
rate of tillering with aggressiveness of species. Perennial ryograss til- 
lered more profusely than other grasses included in the study. 

Apparently rate of seedling growth after emergence is partially de- 
pendent upon stored food reserves in seeds, and also on genetic factors 
which determine the various rates of growth of species under different 
environments. An approximate classification of the aggressiveness of 
forage seedlings during establishment, which is based on observations 
and experiments in Virginia and New York and data reported by Staple- 
don and Davies (1930), is given on page 212. The species with the 
lowest numbers are the most aggressive. 

Information as to the relative rate of seedling development can be 
quite useful in compounding seed mixtures. An experiment was estab- 
lished in Virginia to measure the adaptation of varieties of birdsfoot 
trefoil. The trefoils were seeded with grass and/or legume mixtures at 
two locations (Table VIII). When birdsfoot trefoil (slow seedling de- 


Rank Grasses Rank Legumes 

1. Italian ryegrass, Lolmm multiflorum 1. .Red clover, Tnfolium pratcnac 

12. Perennial ryegrass, Lolium percnnc 1. Sweet clover, M el i lot us alba 

3. Tall oat grass, Arrhenatherum 2. Alfalfa, Medicago sativa 

claims 3. Alsike clover, Tnfolium hybridum 

4. Orchardgrass, Dactylis glomerata 4. Ladmo white clover, Tnfolium 
r>. Tall fescue varieties, Alta and Ken- tepentt 

tucky 31, Festuca elatior var. arun- f>. Birdsfoot trefoil, Lotux corniculalns 

dwacea Seed sources from Italy, France, 

(5. Bromegrass, Bromus inermis and Germany 

7. Meadow fescue, Fesluca elatior S-100, white clover 

7. Orchardgrass, S-143 7. Birdsfoot trefoil, Empire (New Vork) 

8. Timothy, Phleum pratense H. (Common white clovor 

8. Meadow foxtail, Alopecuru* pratenmfi 

9. Bedtop, Agrostis alba 

10. Red fescue, Fetftuca rubui 

11. Canada bluegrass, Poa compressa 

11. Kentucky bluegrass, Poa pratcnms 

12. Bent grass, Agro&tis spp. 

velopment) was sown with a liglit rate of orchard^rass (fast s<vdlin' de- 
velopment) the relative yield the subsequent year was 47 as compared 
with 100 when birdsfoot trefoil was sown with Kentucky bluegrass (slow 
seedling development). Kentucky 31 fescue seedlings are more aggres- 
sive than Kentucky bluegrass; hence the relative yield of birdsfoot 
trefoil varieties was less with fescue than for seedlings grown with Ken- 
tucky bluegrass. When the trefoils were sown with a complex mixture of 
aggressive species (alfalfa, Orchardgrass, red clover, and ladino clover) 
the relative yield was only 10. With this complex mixture the aggressive 
species reduced the stand and yield of trefoil even though seeding rate 
adjustments were made. The birdsfoot trefoil produced a relative yield 
of 83 when grown with a complex mixture made up of species compo- 
nents that develop comparatively slow during seedling development. 


1. Yields and Quality as Influenced by Mixtures. 

The yields of several species grown in mixtures are generally higher 
than the yields of individual species. Stapledon and Da vies (1928) con- 
ducted an experiment to test the yields of forage plants due to associa- 
tion. The first year after sowing, the relative yield of legumes grown 
alone was given a value of 110. With perennial ryegrass-legume mix- 
tures the relative yield was 133 as compared with 139 for Orchardgrass- 
legume mixtures. In another experiment, Stapledon and Da vies (1930) 


report that two grass-legume mixtures produced a mean yield of 82.8 
cwt. as compared with an average of 39.4 cwt. for seventeen grass species 
grown in a pure stand. The yields of the legumes in pure stand were 
also less than the yields of the grass-legume mixtures. At Ottawa, 
Canada, the yield of herbage from ten cultivated grasses grown sepa- 
rately for a period of three years varied from 1077 to 2415 Ib, of 
herbage per acre, as compared to yields ranging from 4016 to 5712 Ib. 
per acre for the ten grasses in legume mixtures (Kirk, ]937). Other 
work conducted in more humid areas of the United States shows that 
the use of legumes with grass in mixtures resulted in increases in dry 
matter production (Fergus, 1935 ; Johnstone-Wallaee, 1937 ; Brown and 
Munsell, 1943 ; Blaser et al., 1948 ; Sprague et a/., 1947 ; and others) . 

Wilsie (1949) conducted experiments with alfalfa-grass mixtures in 
a region where alfalfa is well adapted. During a period of five years, 
alfalfa seeded in pure stand produced as much herbage as alfalfa-grass 
mixtures. Toward the end of the experimental period, the stand of 
alfalfa was depleted by bacterial wilt and the alfalfa-grass mixtures be- 
gan to produce higher yields than pure alfalfa. 

In the above experiments the soils were supplemented with minerals 
other than nitrogen so as to create a reasonably favorable mineral nutri- 
ent status for the legumes. By supplying minerals other than nitrogen, 
legume-grass mixtures would be expected to produce higher yields than 
grass mixtures, the growth of which would be limited by the low level of 
nitrogen. With liberal nitrogen applications very high yields can be 
obtained for mixtures with or without legumes (Johnstone-Wallaee, 
1937; Robinson and Pierre, 1942; Fink, 1943; Robinson and Sprague, 
1947; Blaser and Brady, 1950; Burton and DeVane, 1951). It is also 
possible to regulate seasonal growth by nitrogen fertilization (Frankena, 
1937;Giobel, 1937). 

If the utilization of grass mixtures supplemented with nitrogen fer- 
tilizer was economically sound, management practices would be greatly 
simplified since leguminous plants in mixtures are much more vulnerable 
to stand depletion than are grasses (Davies, 1928; Brown, 1939; Dodd, 

High quality herbage may be characterized by low fiber and lignin 
contents and high digestibility, and high contents of protein, minerals, 
and vitamins (Morrison, 1949; Watson, 1951). The quality of a given 
species is best when in a leafy vegetative growth condition and poorest 
when in a stemmy growth condition (MacDonald, 1946; Watson, 1951). 
There is usually a greater difference in quality between the extreme 
growth stages of a single species than between species at the same stage 


of growth. Herbage quality depends primarily on management and 
secondly on species components in mixtures. 

a. Top vs. Bottom Species. Morphologically forage plants may be 
classified into either top or tall and bottom or short species. Bottom 
species, such as Kentucky bluegrass, bent grasses, rough stalked meadow 
grass and the shorter white clover phenotypes, become dominant under 
hard and continuous grazing. 

Whether the sod should be made up of short, dense herbage of bottom 
species or of taller less dense herbage of top species, has been a much 
debated topic. The choice between bottom and top species depends quite 
largely upon the method of utilization and use. For heavy continuous 
grazing, bottom species may be superior to top species when considering 
longevity and yield. A reverse relationship would be expected under 
rotational grazing or hay management practices. 

Stapledon and Davies (1928) conducted an experiment to measure 
the influence of species on each other. With various mixtures of top 
grasses and legumes, it was found that the yields of herbage declined 
each year during a four-year period. The decline in production was 
associated with the encroachment of bottom species such as bent grass. 
Ahlgren et al. (1946) also attributed declining yields of tall species to an 
increase in bottom grasses such as redtop and Kentucky bluegrass. 

In Pennsylvania, an unproductive bluegrass-white clover pasture 
was top-dressed with lime and fertilizer and renovated (limed, fertilized, 
and sown with top grasses and legumes). After the bottom species 
(bluegrass and white clover) were well established, this mixture pro- 
duced 3700 Ib. as compared w ? ith a yield of 5200 Ib. of herbage per acre 
for the top species (Sprague et al., 1947). 

R. B. Musgrave of Cornell University (unpublished data) tested the 
productivity of mixtures with top species, bottom species, and mixtures 
of top and bottom speciesr The yields of mixtures witli ladino clover 
were higher than the yields with Kent wild clover in the mixture. Mix- 
tures with top grasses (tall oats, orchard, or timothy) produced higher 
yields than mixtures with bottom grasses (redtop, Kentucky bluegrass, 
or red fescue). Nowosad and Stevenson (1947) found that a mixture of 
three top grasses (brome, timothy, and slender wheat) with three bot- 
tom grasses (Kentucky blue, Canada blue, and redtop) with legumes, 
gave a yield of 4440 Ib. of herbage per acre. When the bottom grasses 
were excluded from the mixture the yield was 4413 Ib. of herbage per 

It may be concluded that top species have a greater capacity for 
production if favorable grazing or cutting management practices are 


b. Simple vs. Complex Mixtures. The number of species compo- 
nents to use in mixtures has been a controversial issue. In European 
countries and England rather complex mixtures have been used in com- 
parison to those recommended in the United States. Johnstone- Wallace 
(1927) and Stapledon and Davies (1928) concluded that mixtures 
should be reasonably complicated the whole aim being to combine 
early and late species and strains so as to obtain a long and reasonably 
uniform herbage supply. Stapledon and Davies (1928) suggested a 
type mixture made up of six grass and three leguminous species ; within 
this mixture a total of eight strains was also suggested. 

In a more recent publication Milton (1939) showed that yields of 
mixtures composed of two or six grasses with given legumes were of 
similar magnitude. Willard (1951) suggested that forage seedings 
should be made up of at least one grass and one legume and that the 
employment of more species is good insurance against failure. Results 
obtained during the last two years in Virginia indicate that the yields 
of mixtures with ladino clover can be improved during the first harvest 
year by adding alfalfa or red clover to the mixture. 

The compounding of mixtures with many species, with the idea of 
obtaining both high yields and a good distribution of herbage, has ap- 
parently not been successful in practice. The writers were unable to 
find a publication which showed that complex mixtures were superior to 
simpler ones. The trend, in compounding mixtures, has been altered 
toward using a few species that are particularly well adapted to local- 
ized environments and imposing specialized management utilization prac- 
tices, such as cutting for hay and then grazing, cutting for silage and 
then grazing or grazing alone (Stapledon and Davies, 1930; Willard 
et al., 1947; and Cornell University, unpublished data). When consid- 
ering plant adaptation as related to growth factors, it is obviously much 
easier to manage simple mixtures, hence, the employment of special man- 
agement and utilization practices with special purpose, simple mixtures 
seem to be practical. 

2. Developing a Forage Cropping System 

Hein and Cook (1937) found that over one-half of the total herbage 
was produced during the first one-third of the grazing season at Belts- 
ville, Maryland. In northern as well as southern latitudes, a flush 
growth of herbage is invariably produced in early spring which is fol- 
lowed by seasonal periods of low herbage yields, (Brown and Munsell, 
1936; Blaser et al., 1945). High herbage yields during the spring season 
are attributed to favorable temperature, rainfall, and light conditions. 

In practice a reasonably uniform supply of herbage, with some re- 


serve pasturage, should be available throughout the grazing season. If 
a given acreage and mixture is used only for pasture, there will either 
be an excess of herbage which will be wasted at one season or an acute 
shortage at another season. 

Since many of the growth factors cannot be controlled, it seems logi- 
cal to manipulate mixtures and management practices with the objective 
of developing a more uniform herbage supply during the grazing season. 
Instead of using one mixture solely for grazing, and other mixtures 
entirely for silage or hay ; mixtures might be managed flexibly for com- 
binations of hay, silage, and grazing uses. 

For such flexible forage cropping systems, mixtures can be com- 
pounded: (1) for grazing; (2) for silage and aftermath grazing; (3) 
for silage, hay, and aftermath grazing; (4) for early, mid, late season, 
and/or winter grazing. The acreage used for grazing or preserved 
crops can be varied so as to use the mixtures to furnish the feed supply 
that is most needed. 

The employment of several mixtures in cropping system seems logical 
because the relative growth of forage species varies with seasons. This 
is true because species respond differentially to environmental factors. 
When considering morphological characteristics, species are best suited 
for certain uses, i.e., for grazing, hay, or silage. However, the productive 
status of species, when utilized flexibly, can be maintained under ap- 
propriate grazing or cutting management. 


Aberg, Ewert, Johnson, T. J., and Wilsie, C. P. 1943. J. Am. Soc. Agron. 35, 357- 


Ahlgren, II. L., and Aamodt, O. S. 1939. J. Am. Soc. Agron. 31, 982-985. 
Ahlgren, II. L., Wall, M. L., Miutkenhirn, R. J., and Burcalow, F. V. 1944. J. Am. 

Soc. Agron. 36, 121-131. 
Ahlgrcn, H. L., Wai], M. L., Mnckenhirn, R. .T., and Sund, J. M. 1946. J. Am. 

Soc. Agron. 38, 914-922. 

Anderson, Alice M. 1931. Am. J. Botany 18, 889. 
Anderson, A. J., and Thomas, M. P. 1946. Auslralia Council Sci. Ind. Research 

Bull. 198, 5-25. 

Bates, G. H. 1948. J. Brit. Grassland Soc. 3, 176-184. 
Baver, L. IX 1948. Soil Physics. John Wiley and Sons, New York. 
Bear, Firman E., and Wallace, Arthur. 1950. New Jersey Agr. Expt. Sta. Bull. 

748, 1-32. 

Benedict, H. M. 1941. J. Am. Soc. Agron. 33, 1108-1109. 
Blackman, G. E., and Templeman, W. G. 1938. Ann. Botany 2, 765-791. 
Blaser, B. E., and Boyd, F. 1940. Florida Agr. Expt. Sta. Bull. 351, 1-29. 
Blaser, B. E., and Brady, N. C. 1950. Agron. J. 42, 128-135. 


Blnser, E. E., Glasseock, E. S., Killinger, 0. B., find Stokes, W. E. 1948. Florida 

Agr. Expt. Sta. Bull. 453. 

Blnser, E. E., and Killinger, G. B. 1950. Agron. J. 42, 235-220. 
Blaser, B. E., and McAuliffe, Clayton. 1949. Soil Sci. 68, 145-150. 
Blaser, E. E., Stokes, W. E. 1946. J. Am. Soc. Agron. 38, 325-331. 
Blaser, R. E., Stokes, W. E., Glassoock, E. S., and Killinger, G. B. 1948. Soil Set. 

Soc. Am. Proc. 8, 271-275. 
Blaser, E. E., Stokes, W. E., Warner, J. I)., Eitehey, G. E., and KilHnger, G. B. 

1945. Florida Agr. Expt. Sta. Bull 409. 
Blaser, E. E., Volk, G. M., and Smith, F. B. 1941. Soil Sci. Soc. Am. Proc. 6, 29S- 


Bledsoe, Eoger W., and Blaser, E. E. 1947. J. Am. Soc. Agron. 39, 14(5-152. 
Boynton, Damon, and Eeuther, Walter. 1938. Soil Sci. Soc. Am Proc 3, 37-42. 
Brown, B. A. 1939. J. Am. Soc. Agron. 31, 322-332. 

Brown, B. A., and Munsell, E. I. 1936. Connecticut State Coll. Ball 209. 
Brown, B. A., and Munsell, E. 1. 1943. Storrs (Connecticut) Agt. Expt. Sta Bull 


Brown, E. Marion. 1939. Missouri Agr. Expt. Sta. Research Bull. 299. 
Burton, Glenn W. 3937. J. Am. Soc. Agron. 29, 600-606. 
Burton, G. W. 1940. J. Am. Soc. Agron. 32, 545-549. 
Burton, G. W. 1943. J. Am. Soc. Agron. 35, 192-196. 
Burton, Glenn W., McBeth, C. W., and Stephens, J. L. 1946. J. Am Soc. Agron. 

38, 651-656. 

Burton, Glenn W. 1948. Georgia Coastal Plmn Expt. Sta. Circ. 10. 
Burton, G. W., and DeVane, Earl H. 1951. J. Am. Soc. Agron. Soil Sci. Soc. Am 

Abs. 23. 

Carrier, Lyman, and Oakley, E. A. 1914. Virginia Agr. Expt. Sla Bull 204. 
Chamblee, D. S. 1951. Abs. Am. Soc. Agron. Soil Sci. Soc. Am. 23-24. 
Chilton, S. J. P., and Garber, E. J. 1941. J. Am. Soc. Agron. 33, 75-83. 
Chippindale, H. G. 1949. J. Brit. Grassland Soc. 4, 57. 
Comfort, James E., and Brown, E. Marion. 1933. Am. Soc. Animal Prod. Proc 26, 


Cooper, H. P. 1932. Plant Physiol 7, 527-532. 

Davies, William. 1928. Welsh Plant Breeding Sta. Bull. Ser. II, No. 8, 82-144. 
Davies, William. 1939. Welsh Plant Breeding Sta. Bull. Ser. II, No. 15, 1-24. 
Dibbern, John C. 1947. Botan. Gas., 109, 44-58. 
Dickson, James G. 1947. Diseases of Field Crops. McGraw-Hill Book Co., New 


Dillman, Arthur C. 1931. J. Agr. Besearch 42, 187-238. 
Dodd, D. E. 1941. Soil Sci. Soc. Am. Proc. 6, 288-297. 
Dotzenko, Alex., and Ahlgren, Gilbert H. 1950. Agron. J. 42, 246-247. 
Drake, Mack, Venqris, Jonas, and Colby, William G. 1951. Soil Sci. 72, 139-147. 
Erdmann, Milton H., and Harrison, C. M. 1947. J. Am. Soc. Agron. 39, 682-689. 
Evans, H. J., and Purvis, E. E. 1951. Agron. J. 43, 70-71. 
Evans, Marshall, and Wilsie, C. P. 1946. J. Am. Soc. Agron. 38, 923-932. 
Evans, Morgan W. 1939. Am. J. Botany 26, 212-218. 

Evans, Morgan W., Allard, H. A., and McConkey, O. 1935. Sci. Agr. 15, 573-579. 
Evans, Morgan W., and Watkins, James M. 1939. J. Am. Soc. Agron. 31, 767-774. 
Farris, Nolan F. 1934. Soil Sci. 38, 87-111. 
Fergus, E. N. 1935. J. Am. Soc. Agron. 27, 367-373. 


Fink, Delmar S. 1943. Soil Sci. Soc. Am. Proc. 8, 265-267. 

Frankena, H. J. 1937. Fourth Intern. Grassland Congr. Kept. 339-343. 

Gardner, Frank P. 1950. M.S. Thesis, Iowa State Coll., Ames, Iowa. 

Garrigus, W. P. 1950. Kentucky Agr. Expt. Sta. Mimeo. Kept. 

Giobel, G. 1937. Fourth Intern. Grassland Congr. Kept. 330-338. 

Gist, George R., and Smith, B. M. 1948. J. Am. Soc. Agron. 40, 1036-1042. 

Graber, L. F. 1931. Plant Physiol. 6, 43-72. 

Graber, L. F., and Jones, F. R. 3935. J. Am. Soc. Agron. 27, 364-366. 

Graber, L. F., Nelson, N. T.. Leukel, W. A., and Albert, W. B. 1927. Wisconsin 

Agr. Expt. Sta. Bull. 80. 

Hanson, Clarence H., and Allison, J. Lewis. 1951. Agron. J. 43, 375-379. 
Hein, M. A., and Cook, A. C. 1937. U.S. Dept. Agr. Tech. Bull 538. 
Hermann, Wilford, and Eslick, Robert. 1939. J. Am. Soc. Agron. 31, 333-337. 
Hodgson, R. E., Grander, M. S., Knott, J. C., and Ellington, E. V. 1934. Wash- 
ington Agr. Expt. Sta. Bull. 294. 

Hollowell, E. A. 1938. J. Am. Soc. Agron. 30, 589-598. 
Johnstone-Wallace, D. B. 1927. Agr. Progress 4, 92-97. 
Johnstone-Wallace, D. B. 1937. J. Am. Soc. Agron. 29, 441-455. 
Jones, Fred Rueuel. 1928. J. Agr. Eesearch 37, 189-211. 

Jones, lowerth. 1939. Welsh Plant Breeding Sta. Butt. Ser. II, No. 15, 40-129. 
Keller, Ernest R., and Peterson, Maurice L. 1950. Agron. J. 42, 598-603. 
Killinger, G. B., Blaser, R. E., Hodges, E. M., and Stokes, W. E. 1943. Florida 

Agr. Expt. Sta. Bull. 384. 

Kirk, L. E. 1937. Fourth Intern. Grassland Congr. Kept. 90-96. 
Klapp, E. 1937. Fourth Intern. Grassland Congr. Sept. 108-115. 
Lamba, P. S., Ahlgren, H. L., and Muckenhirn, R. F. 1949. Agron. J. 41, 451-458. 
Lovvorn, R. L. 1944. /. Am. Soc. Agron. 36, 590-600. 
Lovvorn, R. L. 1945. J. Am. Soc. Agron. 37, 570-582. 
MacDonald, H. A. 1939. M. S. Thesis, Cornell Univ., Ithaca, New York. 
MacDonald, H. A. 1946. Agr. Eng. 27, 117-120. 
MacDonald, H. A. 1946. Cornell Univ. Agr. Expt. Sta., Mem. 261. 
Mayton, E. L. 1935. Alabama Agr. Expt. Sta. Bull. 243. 
Mayton, E. L., Grimes, J. C., and Rogers, H. T. 1947. J. Am. Soc. Agron. 39, 584- 


McCarty, Edward C., and Price, Raymond. 1942. U.S. Dept. Agr. Tech. Bull. 818. 
Meyer, Bernard S., and Anderson, Donald, B. 1939. Plant Physiology. D. Van 

Nostrand Co., New York. 

Milton, W. E. J. 1939. Welsh Plant Breeding Sta. Bull. Ser. H, No. 15, 25-39. 
Moore, R. M., Barrie, Nancy, and Kipps, E. H. 1946. Australia Council Sci. Ind. 

Research Bull. 201. 
Morrison, Frank B. 1949. Feeds and Feeding. The Morrison Publishing Co., 

Ithaca, N. Y. 

Mott, G. O. 1943. Soil Sci. Soc. Am. Proc. 8, 276-281. 

Myers, H. E., and Anderson, Kling. 1942. J. Am. Soc. Agron. 34, 770-773. 
Naftel, James A. 1942. J. Am. Soc. Agron. 34, 975-985. 
Neller, J. R,, Killinger, G. B., Jones, D. W., Bledsoe, R. W., and Lundy, H. W. 1951. 

Florida Agr. Expt. Sta. Bull. 475. 
Newell, L. C. 1951. Agron. J. 43, 417-424. 

Nowosad, F. S., and Stevenson, T. M. 1947. Sci. Agr. 27, 86-96. 
Painter, Reginald, and Grandneld, C. O. 1935. J. Am. Soc. Agron. 27, 671-674. 
Peterson, Maurice L. 1947. J. Am. Soc. Agron. 39, 412-422. 


Peterson, Maurice L. 1951. Am. Soc. Agron. Soil Sci. Soc. Am. Abs. 21-22. 

Peterson, Maurice L., and Loomis, W. E. 1948. Plant Physiol. 24, 31-43. 

Pollitt, Richard. 1947. ,7. Brit. Grassland Soc. 2, 119-126. 

Rather, H. C., and Dorrance, A. B. 1938. ,/. Am. Soc. Agron. 30, 130-134. 

Roberts, James L., and Olson, Frank R. 1942. J. Am. Soc. Agron. 34, 695-701. 

Roberts, R. H., and Struckmeyer, Esther B. 1938. J. Agr. Research 56, 633-647. 

Roberts, R. H., and Struckmeyer, Esther B. 1939. J. Agr. Research 59, 699-710. 

Robinson, R. R. 1944. Soil Sci. Soc. Am. Proc. 9, 147-150. 

Robinson, R. R., and Pierre, W. IT. 1942. J. Am. Soc. Agron. 34, 747-764. 

Robinson, R. R,, and Sprague, V. G. 1947. J. Am. Soc. Agron. 39, 107-116. 

Rogler, George A. 1943. J. Am. Soc. Agron. 35, 547-559. 

Smith, Dale, and Graber, L. F. 1948. J. Am. Soc. Agron. 40, 818-831. 

Smith, George E. 1941. J. Am. Soc. Agron. 33, 231-236. 

Sprague, Howard B. 1933. Soil Sci. 36, 189-207. 

Sprague, M. A., and Fuelleman, R. F. 1941. J. Am. Soc. Agron. 33, 437-447. 

Sprague, V. G. 1943. Soil Sci. Soc. Am. Proc. 8, 287-294. 

Sprague, V. G. 1948. J. Am. Soc. Agron. 40, 144-154. 

Sprague, V. G., and Garber, R. J. 1950. Agron. J. 42, 586-593. 

Sprague, V. G., Robinson, R. R., and Clyde, A. W. 1947. J. Am. Soc. Agron. 39, 


Sprague, V. G., nd Sullivan, J. T. 1950. Plant Physwl. 25, 92-102. 
Stapledon, R. G., and Davies, Win. 1928. Welsh Plant Breeding Sta. Bull. Ser. H, 

No. 8, 150-162. 
Stapledon, R. G., and Davies, Win. 1928. Welsh Plant Breeding Sta. Butt. Ser. H, 

No. 8, 7-81. 
Stapledon, R. G., and Davies, Wm. 1930. Welsh Plant Breeding Sta. Bull. Ser. H, 

No. 11, 5-42. 
Stapledon, R. G., Davies, Wm., and Beddows, A. R. 1927. Welsh Plant Breeding 

Sta. Butt. Ser. H, No. 6. 

Stephens, J. L. 1942. Georgia Coastal Plain Expi. Sta. Bull. 27. 
Stewart, E. II., and Rogers, H. T. 1947. J. Am. Soc. Agron. 39, 830-831. 
Stuckey, Irene H. 1942. Am. J. Botany 29, 92-97. 
Sullivan, J. T., and Sprague, V. G. 1943. Plant Phy^oL 18, 656-670. 
Tosar, Milo B., and Ahlgren, H. L. 1950. Agron. J. 42, 230-235. 
Tysdal, H. M., and Pieters, A. J. 1934. J. Am,. Soc. Agron. 26, 923-928. 
Vinall, H. N. 1935. J. Am. Soc. Agron. 27, 161-172 

Warner, J. D., and Blaser, R. E. 1942. Florida Agr. Expt. Sta. Bull. 375. 
Watkins, James M. 1940. /. Am. Soc. Agron. 32, 527-538. 
Watson. Stephen J. 1951. Grassland and Grassland Products. Edward Arnold and 

Co., London. 
Weaver, John E., Clements, Freddie E. 1938. Plant Ecology. McGraw-Hill Book 

Co., New York. 

Weimer, J. L. 1930. J. Agr. Research 40, 121-143. 
Willard, C. J. 1951. Forages. Iowa State Coll. Press, 431-447. 
Willard, C. J., Lewis, R. D., Thatcher, L. E., Dodd, D. R., and Jones, Earl. 1947. 

Ohio Agr. Ext. Ser. Bull. 261. 
Wilsie, C. P. 1949. Agron. J. 41, 412-420. 

Woodhouse, W. W. 1947. Ph.D. Thesis, Cornell Univ., Ithaca, New York. 
Woodward, T. E., Shepherd, J. B., and Hem, M. A. 1938. U.S. Dept. Agr. Tech. 

Bull. 660. 
York, E. T. 1947. Ph.D. Thesis, Cornell Univ., Ithaca, New York. 

Soil Manganese in Relation to Plant Growth 


Agricultural Experiment Station and Institute for Soil Research, T.N.O., Grownpen, 

The Netherlands 



I. Introduction .... 222 

II. Manganese Determination . . . . . ... 224 

1. Colorirnetric Methods . . . . 225 

2. Speetrocheinieal Methods . .... 227 

3. Polarographic Methods ... ... 227 

4. Biological Procedures . .... 227 

III. Manganese in the Soil .... . 228 

3. Effect of pH on Soil Manganese 228 

2. Availability of Soil Manganese and Its Estimation by Chemical 
Analysis ... 230 

3. Occurrence of Tnvalent Manganese in Soil 232 

4. Effect of Organic Matter on Soil Manganese ... .... 233 

5. Manganese in Calcareous Soils 234 

IV. The Hole of Microorganisms in Transforming Manganese Compounds . 234 

1. Oxidation of Manganous Compounds .... 234 

2. Soltibilization of Manganic Oxides 237 

3. Microorganisms in Relation to Leaf Spots of Manganese-Deficient 
Oats 238 

4. Resistant Oat Varieties . . 239 

V. Symptoms of Manganese Deficiency in Plants ... 239 

VI. Manganese Content of Plants 242 

1. Normal Plants Growing undei Natural Conditions 242 

2. Manganese Content of Healthy and Manganese-Deficient Plants . 243 
VII. Correcting Manganese Deficiency 244 

1. Application of Manganese Sulfate to the Soil 244 

2. Spraying the Foliage with a Dilute Solution of Manganese . . . 244 

3. Treating the Soil with Acidifying Substances 245 

4. Flooding 245 

VIII. Manganese Nutrition and Fertilizer Interactions 245 

1. Nitrogen Applications 245 

2. Effect of Phosphate Fertilization 247 

3. Effect of Copper on Manganese Nutrition 247 

4. Iron-Manganese Relationships 248 

IX. Manganese Toxicity in Plants 249 

1. Manganese Toxicity in Relation to the Supply of Some Nutrient 

Elements 253 

a. Effect of Nitrogen Compounds 253 

b. Effect of Phosphorus 253 

c. Effect of Calcium 253 



d. Manganese Excess in Relation (o Iron Deficiency 254 

e. Manganese Toxicity in Relation to Molybdenum Supply . . 255 
2. Symptoms of Manganese Toxicity in Some Crop Plants .... 257 

X. Function of Manganese in Plants 259 

1. Manganese in Relation to Carbohydrate Breakdown 260 

a. Glycolysis 2(50 

b. Organic Acid Metabolism 260 

2. Manganese in Relation to Nitrogen Metabolism 262 

3. Manganese Nutrition and Ascorbic Acid Content of Plants and 
Animals 266 

4. The Role of Manganese in Photosynthesis 26H 

References 272 


Among the earlier workers who studied the so-called stimulating 
effect of manganese on plant growth the names of Loew (1903), Bertram! 
(1905), and particularly Maze (1914) must be mentioned. The last 
named carried out nutrient solution experiments with corn (Zen 
mays L.). 

Of much importance was the discovery by Sjollema and Hudig 
(1909) (see also Hudig, 1911), that oat plants suffering from an un- 
known "soil disease " could be cured by the addition of 50 kg. of man- 
ganese sulfate per hectare. This "disease" was found to occur in the 
northern part of the Netherlands, particularly on reclaimed peaty soils 
which had become neutral or slightly alkaline through liming or appli- 
cation of Chilean nitrate as a nitrogen fertilizer. Hudig was unable to 
decide whether the beneficial effect of manganese had to be attributed to 
neutralization of some unknown injurious soil constituent or to its 
"stimulating influence" on plant growth. 

A number of papers, mostly by Western European authors, appeared 
subsequently to Hudig 's paper. It was shown that the " Dorrflecken- 
krankheit" ("Gray Speck disease," as the oat disease was called first by 
Clausen, 1910), was common on many neutral sandy and peaty soils. 
One of the most remarkable of these papers was published by Hiltner 
(1924). He showed that the "Dorrfleckenkrankheit" is not limited to 
oats growing on neutral or alkaline soils, but may also be found in plants 
growing* in acid nutrient solutions. In both cases it was cured by man- 
ganese. These experiments were very important for they demonstrated 
that the disease was not primarily caused by organic substances or by 
an alkaline reaction. Although these results may be considered as evi- 
dence that the gray speck disease is brought about by manganese de- 
ficiency, this conclusion was not drawn by Hiltner. Since carbon dioxide 
treatment of oat plants suffering from gray speck disease was found to 


have a similar effect as supplying manganese to the nutrient medium, 
lliltner (1924) attributed the beneficial effect of manganese to improved 
carbon dioxide assimilation by the plants, so that the disturbed equi- 
librium C0 2 assimilation-mineral substance uptake, which was supposed 
to be the cause of the disease, thereby would be corrected. 

The essentiality of manganese as a micronutrient element for green 
plants became apparent shortly after 1920 (McIIargue, 1922). The first 
authors who recognized that the symptoms of gray speck disease are 
essentially the symptoms of manganese deficiency were Samuel and Piper 
(1928). They carried out culture solution experiments with oats in 
comparison with pot and field experiments with "sick" soils. Very low 
values for manganese were found in diseased plants in comparison with 
healthy plants from sterilized "sick" soil or from "healthy" soil. Al- 
though clear differences in soil manganese were found, the methods used 
were inadequate for determining the plant-available manganese in soil, 
so that no explanation was given of the fact that plants growing on 
soils which contain large amounts of total manganese are unable to 
absorb the small quantities of this element that are required for normal 
development. Apparently Samuel and Piper were unaware of the im- 
portant investigations by Beijerinck and Sohngeu, who as early as 
1913 and 1914, respectively, carried out a number of microbiological 
experiments concerning the oxidation of manganous salts to manga- 
nese dioxide. From his investigations Sohngen (1914) concluded that 
the unavailability of manganese in neutral or alkaline soils was due 
to the conversion of Mn 4 + to insoluble manganic oxides. In a later 
paper Piper (1931) demonstrated the importance of both soil reaction 
and oxidation-reduction equilibrium in rendering manganese unavailable 
to plants. The papers of Beijerinck and Sohngen were overlooked by 
soil scientists until their experiments were repeated and extended by 
Gerretsen (1936, 1937). Since that time a considerable number of 
papers have appeared dealing with the various aspects of soil manganese. 
Some of the investigators, for example, Gerretsen (1937), Leeper (1947), 
Quastel et al. (1948) are of the opinion that the conversion of available 
Mn++ to insoluble Mn + + + or Mn+ + + + is brought about by soil micro- 
organisms; others believe that this is not the case because of the great 
rapidity with which this process takes place (Pujimoto and Sherman, 

The fact that manganese, when supplied to plants in excessive 
amounts may cause toxic symptoms, has appeared to be of great im- 
portance in agriculture and horticulture. It has been shown, particu- 
larly during the last decade, that many acid soils may contain amounts 
of plant-available manganese large enough to bring about manganese 


toxicity of the plants growing on it. In fact, manganese injury has been 
shown to be one of the main causes of soil acidity damage in many plant 
species on many acid soils. Since many papers deal with this subject, 
a relatively large portion of this review is devoted to the topic of manga- 
nese toxicity. 

Many authors have considered the function of manganese in living 
organisms, plants, bacteria, and fungi, as well as animals. It appears 
that manganese plays the role of an activator in many enzymatic re- 
actions. Practically all these investigations have been carried out in 
vitro so that it is as yet impossible to decide which enzymatic reactions 
are involved when manganese deficiency occurs in vivo. There is in- 
creasing evidence that manganese plays an important role in the photo- 
synthetic apparatus of green plants and together with iron controls the 
oxidation-reduction potentials in the cells during illumination and in 
the dark. 


Manganese in soils and plants can be determined by colorimetric, 
spectroscopic, polarographic, and biological methods Plant material is 
generally ashed or wet-digested, though in some cases spot tests are used, 
which aim to estimate the manganese content of leaves, stems, fruits, 
etc., directly. The determination in soils is complicated by the fact that 
the several manganese compounds differ widely in availability, which to 
a great extent depends on the pH and the redox potential of the soils. 
Moreover, microorganisms take a very active part in transforming solu- 
ble manganese compounds into insoluble oxides and vice versa; conse- 
quently the manganous-manganic equilibrium in the soil depends largely 
on the activity of the soil flora, a fact which often has been overlooked 
by soil chemists. 

Microbiological transformation may affect the amount of available 
manganese in a very short time, so storage of wet samples has to be 
avoided. Also purely physical treatments, such as drying or sterilizing, 
can effect drastic changes in the available manganese content of a soil ; 
these facts should be born in mind when taking soil samples for manga- 
nese determination. Sherman and Harmer (1942) stress the point that 
samples should be analyzed immediately and in their natural field con- 
dition, especially because some soils release larger amounts of exchange- 
able manganese if they are air-dried before extraction. Boken (1952) 
showed that not only the amount of exchangeable manganese increases 
considerably when wet soil samples are dried at higher tempera- 
tures, but also that this is the case during storage of air-dried soil 
samples even at room temperature. The increase in the manganese 


values is a function of both the length of the storage period and of the 
storage temperature. 

1. Colorimetric Methods 

In many cases the original method of Willard and Qreathouse (1917) 
as modified by Richards (1930) is still used; it involves the destruction 
of the organic material by ashing, the removal of the chlorides by digest- 
ing with sulfuric acid, the elimination of the disturbing effect of iron 
by addition of phosphate and finally the oxidation of the manganese to 
permanganate by means of periodate. The red color of the permanga- 
nate is measured photometrically. Strickland and Spicer (1949) have 
made an extensive study of the kinetics of the formation of permanganate 
using periodic acid as an oxidant and give a detailed account of the 
probable mechanism of the oxidation, at the same time recommending 
suitable conditions for an effective absorptiometric method. 

According to de Wael (1941) Richards' method does not give correct 
results; digestion with sulfuric acid causes errors (up to 18 per cent) 
due to evaporation, whereas the ash retains some manganese because of 
the formation of insoluble manganic oxides. Coppenet (1949) showed 
that the silicic acid in the ash of cereal straw combines with manganese 
causing 27.4 to 40.5 per cent of the manganese present to escape deter- 
mination. To avoid this the author dissolves the silicate in 2-3 ml. 
hydrofluoric acid. Strickland and Spicer (1949) found permanganic 
acid in the distillate from boiling sulfuric acid containing manganese 
solutions. This error can be avoided by the substitution of 85 per cent 
HaPO* for the 12 N H 2 SO4 commonly used. 

Smith (1950) emphasizes the point that the oxidation to permanga- 
nate by means of periodate is less rapid than is generally believed. He 
recommends holding the temperature of the solution near the boiling 
point for at least thirty minutes after the addition of KI0 4 . Nydahl 
(1949) claims that by using ammonium peroxidisulfate instead of perio- 
date the oxidation is completed in a few seconds, whereas with periodate 
no more than 86 per cent of 1 //,mol manganese is converted into per- 
manganate after boiling for one hour. 

As the accuracy of the colorimetric determination of permanganate 
diminishes markedly at very low concentrations, several authors at- 
tempted to revise existing methods or to perfect new ones. Sideris 
(1937) uses the formaldoxime reagent (H 2 C : NOH) of Deniges, (1932) 
which instantaneously develops a wine red color directly proportional 
to the amount of manganese in the solution. After some improvements 
with regard to the interfering ions of iron and phosphate (Sideris, 1940), 
amounts of manganese varying from 0.005 to 0.01 mg. in a 10-ml. sample 


can be determined with an accuracy of approximately 2 per cent. The 
same reagent is used by Waldbauer and Ward (1942) and Kniphorst 
(1946), whereas Wiese and Johnson (1939) prefer benzidine (NH 2 - 
CH 4 -CeH 4 -NH 2 ) which gives a blue color with permanganate, quickly 
changing into a stable yellow-green color. 

The most sensitive reaction for manganese is the oxidation of 4,4'- 
tetramethyldiaminodiphenylmethane by KMn() 4 . According to Gates 
and Ellis (1947) the organic material is ashed at 600 C., dissolved in 
a HN0 8 -H 3 P0 4 mixture, oxidized with KI0 4 , and methane base 
added. Chlorides, vanadium, and cerium interfere ; recoveries of manga- 
nese added to various materials ranged from 90-112 per cent. The 
sensitivity range according to these authors lies between 0.05 and 0.5 
fig. Mn. According to Cornfield and Pollard (1950) this method is 300 
times as sensitive as the permanganate method; they were able to deter- 
mine the manganese content in the ash of 0.05-0.1 g. oven-dried plant 

In the widely used Morgan soil testing system (Lunt et a/., 1950) 
manganese is determined in the soil extract either with benzidine and 
NaOH or with KI() 4 and methane base (tetra-base) ; the resultant blue 
color is compared with a standard color chart, rating from 5 to 40 
p.p.m. in soil. 

Chemical tissue tests are very useful to reflect the nutrient status 
of the plant. Leaf analysis for practical diagnostic purposes was intro- 
duced by Lagatu and Maume (1932). Roach (1944, 1946) at the East 
Mailing Research Station in England applied the method for the detec- 
tion of manganese deficiency : 25 mg. of dried leaf were burned directly 
in an acetylene flame, and the line intensity was determined with a flame 
spectrometer. Roach and Roberts (1945) used an ingenious method for 
diagnosing manganese deficiency in leaves by injecting or spraying a 
growing leaf with a solution gf MnS0 4 (0.025 per cent) . Deficient leaves 
respond by improving the chlorotic color of the tissues in a few days. 

Nicholas (1948) has developed a quick and more-or-less precise quan- 
titative determination of the manganese content of crop plants which 
may be used for the diagnosis of deficiencies in the field, as well as for 
the detection of cases where excess may be expected. With Morgan's 
acetate-acetic acid buffer at pH 4.8 0.5 g. of leaf is extracted. The 
reagents used for the test are trioxymethylene sulfate and NaOH, 
when manganese is in excess, or KI0 4 with methane base for deficiency 
levels. In the latter case the sensitivity ranges from 1 to TOO parts per 
1000 million. 


2. Spectrochemical Methods 

The desirability of greater rapidity, permitting analyses of large 
numbers of soil samples, has resulted in the development of spectro- 
chemical procedures for manganese. Flame spectrography has been 
perfected by Lundegardh (1951) to such an extent that a number of 
important elements can be quantitatively determined by means of an 
automatic robot machine of very ingenious construction. Of biological 
interest is the high sensitivity in the flame of heavy metals, e.g., manga- 
nese. The manganese line (4030 A) can be separated from the near-by 
potassium line (4044, 2 A) by means of a spectrographic slit with a 
width of 0.005 mm. The accuracy of the determination in leaves is 
approximately 3 per cent, and the error is in general definitely less than 
5 per cent. Ileidel (1946) also uses a spectrochemical procedure for the 
determination of manganese. 

3. Polar ographic Methods 

A promising method seems to be the polarographic determination 
which has been used by Zak (1942) in an investigation of the fluctuation 
of the manganese content of lucerne during the season. Manganese 
shows a pronounced step in the polarographic curve at 1.53 v. and 
may be determined in this way with an accuracy of 0.01 mg. per cent. 
Zak shows that the silicic acid of the ashed plant material binds up to 
20 per cent of the manganese present, and repeated evaporation to dry- 
ness with HC1 is necessary to avoid these losses. The polarographic 
method has the advantage that in a single polarogram different ions can 
bo determined one after another. 

Riches (1946) proposes to isolate different trace elements from a 
mineral acid digest by the use of synthetic resins. With a small column 
packed with granules of Amberlite 1 R 100 it was possible to retain 
quantitatively copper, cadmium, zinc, nickel and manganese. Recovery 
after elution with N HC1 followed by polarographic determination 
amounted to 87-96 per cent. 

4. Biological Procedures 

The objection that the crude ways in which soils are generally ex- 
tracted for chemical determinations differ very much from the progres- 
sive mild extraction exercised by the plant roots does not hold true for 
biological tests, which come much nearer to natural conditions. 

As early as 1912 Bertrand and Javillier demonstrated the favorable 
influence of manganese ions on the growth of Aspergttlm niger. Niklas 
and Toursel (1941) showed that 0.001 per cent of MnSO 4 increased the 


weight of the mycelium as much as 83 per cent. Steinberg (1936) 
obtained an increase in weight of the mycelium of Aspergillus niger of 
approximately 30 per cent by the addition of manganese. He showed, 
however, that the optimal heavy metal concentration varies with the acid- 
ity of the solution, being approximately twentyfold in the solution at pH 
8.01 as compared to that at 7.35. Lohnis (1944-45), who made a very 
thorough investigation of the influence of manganese on yield and sporu- 
lation of Aspcrgillus niger, came to the conclusion that, though Asper- 
gillus is quite sensitive to traces of manganese under highly acid 
conditions, an Asperg&lus standard will not be suitable for soil tests. 
Nicholas (1950), however, uses the Aspergillus method for the determi- 
nation of manganese in soils, but adjusts the basal solution to pH 7.5 
with dilute ammonia before addition of the soil sample. The effective 
range per 50-ml. culture solution lies between 0.01 and 10 /*g. 

An interesting microbiological method has been developed by Bentley, 
Snell, and Phillips (1947). Lactobacillits arabinosus responds to manga- 
nese by producing more lactic acid, which is measured by titration. 
The basal medium is freed from traces of manganese by preabsorption 
with the test organism. Within 73 hours 0.3 ju,g. manganese causes an 
increase in acid production of 6 ml. 0.1 N acid. Recovery of added 
manganese was quantitative within the experimental error of approxi- 
mately 10 per cent. 


Manganese occurs in the soil in different forms with widely divergent 
solubilities. Therefore one has to distinguish between total manganese 
and available manganese. The former, which may be determined by 
treating the soil with strong acids (Alten and Weiland, 1933, even use 
aqua rcgia], is of secondary importance for plant growth. Of much more 
significance is the available or "active" manganese as it is called by 
Leeper (1935, 1947). It includes water-soluble and exchangeable Mn + + 
and those forms of manganic oxide which are easily reducible by hydro- 
quinone at pH 7. Those oxides which oxidize hyposulfite at pH 7 and 
hydroquinone at pH 2, but not at pll 7 are considered by Leeper mod- 
erately active, whereas the rest of the manganic oxides, which require 
more drastic treatment for solution may be considered inert and of no 
value for plant growth. 

1. Effect of pH on Soil Manganese 

The occurrence of manganese in various forms depends on a number 
of factors of which pH and organic matter content are the most im- 


portant. Soils with pH values lower than 5.5 may contain a large 
amount of their manganese in water-soluble or exchangeable form. With 
increasing pH Mn ++ will be converted into manganic oxides (Mn+ + + 
and Mn + + + + ), as a result of which it becomes far less available to 
plants so that under certain circumstances manganese deficiency may 
occur. This conversion presumably depends largely either directly or 
indirectly on the activity of microorganisms. The oxidation of Mn + + 
which in the test tube takes place at pH values above 8, proceeds in the 
soil at much lower values probably owing to the presence of hydroxy 
acids and perhaps pyrophosphate (Sdhngen, 1914; Heintze and Mann, 
1947). Mattson et al. (1948) wore unable to observe a stimulating effect 
of hydroxy acids on Mn+ ~ f oxidation. Since the experiments of Sohn- 
gen have been confirmed by the present authors a more detailed investi- 
gation of this problem seems urgent. Microorganisms appear to be able 
to oxidize Mn ++ at pH values of the soil above 5.5. 

Fixation of added manganese in an unexchangeable form in many 
neutral or alkaline soils proceeds rapidly. Wain et al. (1943) observed 
fixation of the bulk of the added manganese within a few days after its 
application. Similar results have been obtained by Sherman and Harmer 
(1942). The rapidity with which the exchangeable manganese content 
of a soil can fall after liming is clearly shown in Table I derived from 
Heintze (1946). Increasing amounts of lime were added to a clay loam 
and after one week's incubation pH values and exchangeable manganese 
were determined. 


Exchangeable Manganese of a Clay Loam after One Week's Incubation with Lime 

(After Heintze, 1946) 

Treatment pH Manganese (mg. %) 

Control 4.5 10.2 

1 ton lime per acre 5.5 10.0 

3 tons lime per acre 6.3 8.4 

8 tons lime per acre 7.5 5.0 

12 tons lime per acre 7.9 2.0 

In the light of these facts it becomes intelligible that the application 
of manganese sulfate to manganese-deficient soils generally has only a 
transitory effect, unless at the same time measures are taken to reduce 
the pH of the soil. 

In this connection it is of interest to note that the application of 
lime, not as CaC0 3 but as CaO, to manganese-deficient clay soils rich 
in organic matter may result in a temporary improvement and even in 


a complete recovery (Maschhaupt, 1934; Popp et al., 1934). The former 
author even used from 15,000 to 20,000 kg. CaO per hectare which fully 
suppressed the deficiency symptoms on a so-called Roodoorn soil, a sea 
clay soil, devoid of CaCO, with a pIJ of 5.7 and a humus content of 
12.5 per cent. In a couple of years, however, on this soil wheat showed 
severe manganese-deficiency symptoms. A similar beneficial effect of 
treating manganese-deficient soils with high amounts of Ca() on growth 
and health of oats was noted by Gisiger and Hasler (1948). At high 
pIJ values soil organic matter apparently may reduce higher manganese 
oxides to Mn++ (Mattson et al., 1948). 

The reduction of manganic oxides to Mn 4 * , may proceed either by 
direct reaction with organic matter or by biological processes. Reduc- 
tion by organic matter is more likely at low pll values since the oxidizing 
power of the higher oxides increases rapidly with acidity. Hydroxy 
acids again play an important part in this reduction (see below). Bio- 
logical reduction can take place in acid as well as in alkaline soils if the 
oxygen tension is low through waterlogging. 

2. Availability of Soil Manganese and Ls Estimation by 
Chemical Analysis 

Initially it was thought by Leeper (1935, 1947) as well as by Sherman 
and Harmer (1942) that the active manganese brought into solution 
by 0.2 per cent hydroquinone in normal ammonium acetate of pH 7.0 
would be a reliable measure of plant-available manganese and thus for 
distinguishing between healthy and deficient soils. In alkaline soils 
easily reducible manganese should be at least 100 p. p.m. in order to 
maintain an adequate level of exchangeable manganese for plant growth. 
In such soils the quantity of exchangeable manganese should be > 3 

Ileintze (1946) in an extensive study of "marsh spot" in peas failed 
to distinguish between soil samples from healthy and diseased parts in 
the same fields when using Steenbjerg's method (1935) for the determi- 
nation of exchangeable manganese or Leeper 's method with hydro- 
quinone and calcium nitrate. 

Dion, Mann, and Heintze (1947) investigated the factors controlling 
the reducibility of higher manganese oxides. Estimation of the easily 
reducible manganese appeared to be dependent on the pH of the system, 
the nature of the salt solution, the nature of the reducing agent, the 
time of contact in addition to the amount and nature of the higher oxides 
of manganese present. Pyrolusite (MnO L >) and a synthetic preparation 
of Mn(OH)a were found to be easily reducible. Manganite (MnO(OH) ) 
and hausmannite (MnMn 2 4 ) are apparently difficultly reducible forms. 


The substitution of hydroxylamine hydrochloride for hydroquinone in 
beeper's procedure was found to avoid the troublesome destruction of 
hydroquinone prior to the colorimetric manganese determination. 

Jones and Leeper (1950, 1951a), investigating the availability of 
manganese in various synthetic manganese oxides, could not correlate 
the response of oats and peas obtained in pot experiments with the 
quantities of manganese in the soil as determined by means of a solu- 
tion of hydroquinone in normal ammonium acetate. With this reagent 
the amounts extracted from manganite, hausmannite, and pyrolusite 
were of the same order. Yet the manganite and pyrolusite when added 
to manganese-deficient soils gave healthy plants, whereas hausmannite 
failed. The combined action of a concentrated electrolyte and a reduc- 
ing agent seemed to be too drastic. Much better results were obtained 
with 0.0f> per cent watery hydroquinone solutions (one-hour contact). 
The method as adopted by these authors includes stirring of the soils 
with 50 per cent alcohol containing 0.05 per cent hydroquinone, the 
alcohol being used to flocculate the colloids Hydroquinone is removed 
by washing with 50 per cent alcohol, and the manganese now present as 
the exchangeable ion is replaced with a semimolar calcium nitrate solu- 
tion at pll 7. The results obtained by this method by Jones and Leeper 
(1951a) have given the best correlation with plant response. 

Electron microscope photographs of a number of synthetic manga- 
nese oxides showed that all the beneficial manganese oxides consisted of 
very small particles. Obviously a large specific surface is needed to 
ensure activity. This was found to be true of several highly oxidized 
forms: manganite, pyrolusite, cryptoinelane, and manganous manganite; 
hausmannite, however, was found to be inert and unavailable to oats 
even when the particles were as minute as those of the active forms. 
X-ray analysis showed that the latter was highly crystalline, whereas 
in the others the degree of crystallinity was low. Difference in crystal- 
Unity was suggested by Jones and Leeper (1951a) to be also the cause of 
the divergent results with respect to manganite, for which Dion, Mann, and 
Heintze (1947) reported a low reducibility in hydroquinone solutions. 

Curing manganese-deficient soils with active oxides did not increase 
the content of exchangeable manganese of the soils. This shows clearly 
that a reserve of the bivalent manganese is not needed for healthy plant 

Tn experiments with Australian soils active manganese oxides were 
found to preserve their activity for a considerable number of years 
(Jones and Leeper, 1951b). Presumably they have to be reduced to 
Mn+ + at the root surface before the manganese can be absorbed. Re- 



version of active oxides to a less available form is thought to be due 
mainly to aging, i.e., the surface becomes more ordered and less active. 

3. Occurrence of Trivalent Manganese in Soil 

An important contribution to our knowledge of the different states 
in which manganese may be present in the soil comes from Dion and 
Mann (194G). They showed that in alkaline soils a significant part of 
the soil manganese may be present in the trivalent state, which exists as 
the^nore or less highly hydrated manganese oxide Mn 2 8 -#H 2 0. This 
is considered to be the first product of oxidation of divalent manganese 
in soils. According to these authors the following manganese cycle may 
be represented : 


Exchangeable Mn 

MnO 2 


Autoxidation of divalent manganese to Mn0 2 will probably be of 
significance only at pll values above 8. In less alkaline soils oxidation 
of divalent manganese is assumed to result in the production of trivalent 
manganese. In a percolation experiment with three soil samples 80.3 
to 98.5 per cent of the added manganese sulfatc which had been circu- 
lated for two weeks through the soil was recovered as trivalent manga- 

In acid solutions manganic hydroxide dismutes to give an ion of 
divalent manganese and a molecule of MnO 2 , according to the following 
equation : 

2Mn(OH), + H 2 SO 4 -> MnSO 4 -f-MnO 2 

Under soil conditions Dion and Mann (1946) expect the same dismu- 
tation to take place. To show the effect of pH on this process they car- 
ried out an experiment to measure the amount of Mn+ + produced in one 
week as a result of storage of Mn(OII) 3 at different pH values. At pH 


7.50, 10.7 per cent dismutation was observed after one week, whereas at 
pll 6.18 a value of 82 per cent was found. 

With sodium or potassium pyrophosphate the trivalent manganese 
may be extracted from the soil forming a stable complex to which the 
formula Na3(Mn(H 2 P20 7 )3) may probably be ascribed. 

The results of Mattson et al. (1948) confirm the concept of Dion and 
Mann as to the occurrence in alkaline soils of a large part of the soil 
manganese in the trivalent state. 

4. Effect of Organic Matter on Roil Manganese 

The role which organic matter plays in the conversion of the Mn + + 
to insoluble manganese compounds in the soil is not clear. That the 
presence of a certain amount of organic matter is required for the ap- 
pearance of manganese deficiency of the plants has been shown by many 
workers. In the Netherlands manganese deficiency will be found on 
sandy soils containing a certain amount of organic matter and on re- 
claimed peaty soils when the pH becomes higher than 6 or 6.5. On 
neutral or alkaline clay soils, however, manganese deficiency is seldom 
found, unless they contain a certain amount of organic matter. 

It may be possible that the effect of organic matter is due to the 
presence of hydroxy acids which according to Sohngen (1914) and 
lleintze and Mann (1946) play an important part in the conversion of 
soil manganese. 

Heintzc and Mann (1949) advance the hypothesis that manganese 
deficiency of plants on neutral and alkaline soils of high organic matter 
content and of adequate total manganese content is due to the formation 
of complexes of Mn + + with the organic matter which are dissociated 
only to such a slight extent that the available manganese in the soil is 
insufficient for the needs of the plants. The formation of such complexes 
was shown by these authors. Jones and Leeper (1951b) found no evi- 
dence for the existence of such complexes in their experiments. 

Hudig (personal communication) made the interesting observation 
that in the northern part of Holland, on the borderline between acid 
sandy peat soil and clay soil, gray speck disease of oats was a common 
phenomenon, whereas on both sides of this line oats were perfectly 
healthy. The most plausible inference is that in the diseased area the 
pH of the peaty soil had been raised by the clay to a level at which 
manganese is made insoluble. The question, however, as to why on 
alkaline clay soils manganese is much more available than on sandy soils 
of the same pH needs further elucidation. 


5. Manganese in Calcareous Sails 

The French workers Boischot and Durroux (1949) have studied the 
fate of manganese in calcareous soils ; manganese was found to be fixed 
by adsorption on the surface of the calcium carbonate particles. In 
contact with a 0.1 per cent neutral solution of ammonium humate the 
adsorbed manganese was set free in a form accessible to plants. This 
uould explain why crops growing on calcareous soils generally do not 
suffer from manganese deficiency ; if it does occur on such soils it is not 
caused by adsorption of the manganese on the calcium carbonate, but, 
according to these authors, has to be ascribed to biochemical oxidative 



1 . Oxidation of Manganous Compounds 

The oxidation of manganous compounds to brown manganic oxides 
by bacteria and fungi was first shown by Beijerinck (1913). A small 
micrococcus and motile rods were isolated, forming small brown colonies 
on agar with 0.05 per cent manganous lactate as sole carbon source 
( Bacillus manganica). Amongst the fungi were representatives of Bo- 
trytis, Mycogone, Tricholadium ; one of the most active fungi was Papu- 
lospora manganica, which feeds on traces of organic substances present 
in plain agar and which is able to oxidize manganous carbonate at rela- 
tively large distances from the mycelium. 

Sohngen (1914) made a very valuable contribution to the problem 
and showed that a great variety of microorganisms, including Pseudo- 
mona>s fluorescent, Azotobacter cliroococcum, Escherichia coli, Oidium 
lactis and different species of Saccharomyces were able to transform 
soluble manganous compounds into insoluble, brown manganic oxides, 
when grown on agar media containing neutral salts of hydroxy acids 
(gluconic, malic, citric, lactic, and tartaric acids). However, the same 
oxidation could be performed by applying a drop of a sterile Na2CO a 
or NallCOa solution to the surface of these agar media. 

On the other hand, it was shown by this author that in agar plates, 
containing sugars or cellulose and Mn0 2 , the latter compound is trans- 
formed into soluble manganous salts through the intermediary of the 
hydroxy acids produced by different cellulose or sugar-decomposing 
microorganisms. Whether manganous salts will be converted into man- 
ganic oxides or the reverse reaction will take place largely depends on 
the pll of the medium. 


The agricultural aspect of the problem rested for a quarter of a 
century until Gerretsen (1936, 1937), by using soil agar plates in the 
center of which agar with 1 per cent MnSO 4 was placed, showed that 
brown rings of Mn0 2 were formed, which consisted of numerous small 
colonies of bacteria and of fungi in which MnO 2 had been precipitated. 
The intensity of the precipitation rapidly diminished when the pll of 
the agar was raised or lowered, the limits lying between pll 6.3 and 7.8. 

Leeper and Swaby (1940) using Gerretsen 's technique, slightly modi- 
fied, confirmed his results. Though brown spots generally developed 
most rapidly in plaques of pll between 6 and 7.5 they also observed 
brown spots due to microbial oxidation on plaques of which the final 
pH ranged from 4.8 to 8.9, the initial pll being 5.5. MacLachlan (1941) 
by means of the same soil agar plaque method was able to isolate a 
greater number of manganese oxide-precipitating bacteria from a manga- 
nese-deficient soil than from a normal soil and attributed manganese 
deficiency in the soil in question to the activity of microorganisms. Ac- 
cording to Bromfield and Skerman (1950) neither the agar used by 
Beijerinck nor that by Gerretsen to isolate the active bacteria was 
satisfactory for the purpose, because pure cultures of bacteria isolated 
from Gerretsen 's medium failed to oxidize Mn j 4 on plain soil agar 
media. Bromfield and Skerman, however, used meat infusion agar as 
an intermediate culture medium when isolating these bacteria and over- 
looked the fact that according to different authors most manganese 
oxidizing bacteria either do not thrive on such media or lose their ability 
to oxidize rnanganous compounds (Beijerinck, 1913; von Wolzogen 
Ruhr, 1927). Bromfield and Skerman (1950) isolated two bacteria which 
were unable to oxidize manganous compounds separately, but did so in 
association on soil agar plaques. In contrast to these statements Timonin 
(1950a) isolated several microorganisms on Gerretsen 's calcium citrate- 
manganous sulfate agar which were capable of oxidizing manganous 
salts on artificial media as well as on soil agar manganese sulfate plaques 
without further addition. 

The present situation with regard to the microbiological oxidation 
of manganous compounds to insoluble manganic oxides is not yet suffi- 
ciently cleared up. There is positive evidence that microorganisms of 
widely divergent origin are able to produce hydroxy acids from cellulose 
and other substrates of vegetable origin and that the manganous salts 
of these acids are readily oxidized chemically by the oxygen from the 
air when the pll is above 7. In accordance with this fact the application 
of organic material may result in inducing manganese-deficiency symp- 
toms or in aggravating them, with lower yields of grain than on un- 
treated soil. Hudig and Meyer (1919) in their fundamental experiments 


on gray speck disease incorporated different organic materials in their 
sand cultures (cotton, glucose, filter paper, etc.) which resulted in the 
appearance of severe manganese deficiency symptoms which could be 
prevented in some cases by applying MnS0 4 , indicating that by the 
addition of organic material available Mn + + had been immobilized. 
Timonin (1946) using straw mulch obtained similar results and tie la 
Lande Cremer (Agricultural Experiment Station, Groningen, private 
communication) using aqueous extracts of wheat straw observed distinct 
symptoms of manganese deficiency in his pot cultures. 

However, the nature of the organic material incorporated in the soil 
seems to be of great importance. When Hudig and Meyer (1919) added 
oat leaves instead of cellulose to their pot cultures, the plants remained 
healthy; extracting the leaves with sodium hydroxide or with acids 
annulled the effect, and the disease symptoms were as heavy as with 
cellulose. Fujimoto and Sherman (1948) observed a considerable in- 
crease in available manganese of Hawaiian soils after treatment with 
sucrose, ground pineapple leaves, and sugar cane leaves with a high 
carbon nitrogen ratio. Hurwitz (1948) in studying the effect of apply- 
ing oat straw and alfalfa meal at a carbon-nitrogen ratio of 30:1 to 
a soil observed a considerable increase in exchangeable manganese which 
after three days 7 incubation at 37 and 47C. reached a maximum value. 
Thereupon it decreased to about the initial value after about two weeks' 
incubation. The increase in exchangeable manganese as described by 
these authors apparently has to be attributed to the very rapid break- 
down of the organic matter as a result of which the oxygen supply be- 
came limited and the redox potential was lowered. In the case of sucrose 
a decrease in pH may also have occurred. 

Mann and Quastel (1946) percolating neutral or slightly alkaline 
soils with 0.02 M MnSO 4 showed that the manganese usually disappears 
at an increasingly rapid -rate and is found in the soil in an oxidized 
form. Biological poisons such as sodium azide (0.001 M) inhibit the 
oxidation. They concluded that oxidation under the given experimental 
conditions is wholly or almost wholly accomplished by proliferating 

Though the oxidation of manganese compounds is exothermic, there 
is as yet no evidence of the existence of true autotrophic manganese 
oxidizing bacteria. The precipitation of the manganic oxides has been 
observed inside the bacterial and fungal cells as well as outside (Beijer- 
inck, 1913; von Wolzogen Kiihr, 1927; Gerretsen, 1936). Whether in 
all cases oxidation takes place through the intermediary of hydroxy 
acids and an accompanying rise of the pll or that a more direct oxida- 
tion by mans of special enzymes occurs as well is still to be investigated. 


As manganese-oxidizing microorganisms of the former class require only 
small quantities of organic materials and representatives are to be found 
among the most common groups of soil microbes, it is evident that in 
most soils the conditions for microbial immobilization of manganese will 
be fulfilled as soon as the pH rises above neutrality. Moreover organic 
compounds excreted by the roots may favor the development of manga- 
nese-precipitating microorganisms in the rhizosphere. Timonin (1946) 
showed that a susceptible variety of oats harbored in its rhizosphere five 
to thirteen times as many manganese-oxidizing bacteria as a resistant 
variety. The application of cyanogas as a soil disinfectant reduced the 
numbers of bacteria in the rhizosphere to about 7 per cent of their 
original value and tripled the yield of the plants. 

It is interesting to note that according to von Wolzogen Kiihr (1927) 
the removal of manganese from dune water in the filter beds of the 
waterworks is essentially a bacteriological process, analogous to that 
described above for the soil. This author attributes to the precipitated 
manganic oxide the property of absorbing immganous compounds on 
its surface which are readily oxidized by microorganisms; in this way 
manganic concretions of increasing size are built up. It is alluring to 
suppose that a similar process takes place in the soil by which manganese 
deposits grow in size and gradually become less available to the plants. 
The formation of iron-manganese concretions in the A 2 horizons of cer- 
tain poorly drained prairie soils which are waterlogged for a considerable 
part of the year, perhaps may be attributed to a similar process. These 
concretions which may have diameters from 0.1 to 15 mm. contain from 
fifteen to seventy-five times as much manganese and from two to more 
than four times as much iron as the surrounding soil in which they are 
found ; the manganese is present as the higher oxides (Drosdoff and 
Nikiforoff, 1940). 

2. Solubttization of Manganic Oxides 

The solubilization of unavailable manganic oxides can be accom- 
plished by microorganisms in different ways: by changing the redox 
potential or the oxygon tension of the soil, or eventually by producing 
reducing organic substances which cause the manganic-manganous equi- 
librium to shift in the direction of the latter compounds. The favorable 
effect of waterlogging on manganese-deficient soils is to be ascribed to 
these activities of microorganisms. In addition to a high water content 
which greatly limits the entrance of oxygen from the air, a certain 
amount of assimilable organic matter is necessary for the growth of the 
microorganisms to enable them to accomplish their diverse metabolic 
activities. Sohngen (1914) has convincingly shown that precipitated 


brown Mn0 2 may be brought into solution by hydroxy acids, produced 
by microorganisms, e.g., from cellulose, but not by fatty acids, such as 
acetic, propionic, or butyric acids. Similar results have been obtained 
by Heintze and Mann (1947). They found, however, a sharp difference 
between Mn(OH) 3 and MnO 2 , the former being dissolved to a large 
extent by various hydroxy acids whereas the latter was practically un- 

The pll may influence manganese availability in different ways. The 
reduction of higher manganic oxides by organic matter is more impor- 
tant at low pll values, since the oxidizing power of these oxides increases 
rapidly with acidity. The production of strong inorganic acids espe- 
cially sulfuric acid by the sulfur-oxidizing bacteria and nitric acid and 
sulfuric acid by nitrifying bacteria favorably influences the amount of 
manganese available to the plants. 

3. Microorganisms in Relation to Leaf Spots of Manganese- 
Deficient Oats 

Microorganisms may play another important role in connection with 
the development of the typical symptoms of manganese deficiency. Ger- 
retsen (1937) carried out extensive studies with sterile cultures of oats, 
in soil, sand, and nutrient solutions containing inadequate quantities 
of manganese for normal growth and showed that, when these cultures 
were kept sterile, the plants did not show typical symptoms of gray 
speck disease, though generally they remained smaller than normal 

Infection of those cultures, either with a small quantity of the origi- 
nal diseased soil (5 per cent) or oven with a diseased root tip of a 
diseased plant resulted in tho appearance of the typical symptoms. 
Alkaline products produced in tho decaying roots by tho infecting sapro- 
phytic microorganisms are carried in the transpiration stream to tho 
leaves, where they produce the gray spots. 

According to Oerretsen it is necessary to distinguish between the 
direct physiological effect of manganese deficiency (etiolation, reduced 
photosynthesis, necrosis) and the typical leaf spots related to the in- 
fection of the roots. 

In the light of these facts one aspect of the distinction between sus- 
ceptible and resistant varieties of oats might be traced back to an 
increased unspecific resistance of tho roots toward invading microor- 
ganisms, hereditary "axeny," as Gauinann (1946) calls it, which is a 
common quality of resistant varieties in general. On the other hand, 
diminished photosynthesis is the reason why manganese-deficient plants 
contain less carbohydrates than normal plants (see Sec. X,4), and it 


is to be expected that in consequence the roots not only remain smaller 
but also have a lower degree of resistance to invading microorganisms. 
In accordance with this view Timonin (1946) succeeded in growing 
healthy susceptible oats on a diseased plot which had been treated with 
cyanogas, a soil fumigant. He ascribes the improvement, however, to 
the eradication of the manganese-oxidizing bacteria in the soil. Hasler 
(1951) showed that the dry weight of the roots of a number of grasses 
was much more depressed than that of the leaves on manganese-deficient 
soils, the ratio of the dry weights of the roots of the diseased plants as 
compared to those of the healthy ones being 1 : 5, whereas that of the 
leaves was 1:2.5. 

4. Resistant Oat Varieties 

The fact that the resistant varieties do not show the typical gray 
speck disease symptoms may point to an increased resistance of the roots 
toward invading saprophytie microorganisms. 

There is no doubt that the resistant varieties need manganese too for 
normal growth, though they might be adapted to a lower level of this 
element than the ordinary varieties. Accordingly the yield of the re- 
sistant varieties is also unfavorably affected by manganese deficiency. 
Kademacher (1935) growing a resistant variety on a manganese-deficient 
soil obtained a lower yield (45 per cent) than on a healthy soil. Though 
in Timonin 's experiments (1946) the resistant variety ACTON produced 
40 per cent more grain than the susceptible variety on a diseased plot, 
the yield of the former was doubled by fumigating the soil with cyanogas. 
It is supposed that in this case the oat plants have had more manganese 
at their disposal, as, according to Timonin, the greater part of the 
manganese-oxidizing bacteria had been killed by the soil disinfectant. 
It is the impression of the authors that there is as yet insufficient evi- 
dence to draw a definite conclusion with regard to the real causes of the 
resistance of certain oat varieties to manganese deficiency. 


Cereals, oats (Wallace, 1944; Samuel and Piper, 1929). Among 
cereals, oats is the most susceptible crop. Marginal gray-brown colored 
necrotic spots and streaks appear first on the third highest leaves, par- 
ticularly on the basal half. The streaks tend to elongate and coalesce. 
At the distal ends of the affected basal part the necrotic spots may 
soon extend across the blades so that the upper half or two-thirds of 
the leaf falls over with a sharp kink at the collapsed portion. The distal 
ends of the leaves remain green for a considerable time. On older leaves 


the collapse may be confined to the lower quarter, and oval spots of 
necrotic tissue may appear irregularly on the leaf blade, though less 
frequently toward the tip end. Streaks of tissue collapsing at the 
margins of the leaves are also very characteristic. The root system is 
poorly developed and is more affected by microorganisms than is the 
case with an adequate manganese supply. 

In wheat and barley the symptoms are not so characteristic as in 
oats. The leaves are somewhat pale green and may show only faint 
chlorotic streaking and yellowing. In severely affected barley irregular 
brown necrotic spots occur on the leaves running especially between the 
veins. In some cases these necrotic spots may be situated on the middle 
parts of the leaves with falling over of the distal halves similar to oats. 
In other cases the spots are located on the basal half and sometimes on 
the distal half. In wheat interveinal white lesions and streaks may 
develop. In rye and maize the necrotic tissues are also white colored. 
In severely attacked rye large parts of the leaves may collapse. The 
general appearance of manganese-deficient cereals is very limp. In the 
field rye is considerably less susceptible than the other cereals. Of ten 
varieties of winter and spring wheat tested by Gallagher and Walsh 
(1943) three appeared to be nearly immune to manganese deficiency, 
six others were particularly sensitive, and one was intermediate. Similar 
large differences were noted in oats. 

Grasses. Grasses growing on soils where oats showed severe symp- 
toms of manganese deficiency did not exhibit the typical leaf symptoms 
(Hasler, 1951). Some leaves had brownish tips while grayish spots 
were situated on the leaf blades. Of the fifteen species tested by Ilasler, 
Alopecurus pratensis, Arrhenatherum clatius, and Bromus erectus gave 
the highest increases in yield upon manganese treatment. Anthoxan- 
thum odoratum, Cynosures cristaius, Festuca pratensis and Trisetum 
flavescens gave intermediate responses. The following species responded 
slightly or not at all to added manganese. Agrostis alba, Dactylis 
glomerata, Festuca rubra, Lolium italicum, Lolium perenne, and Poa 
pratensis. The root systems of manganese-deficient grasses were poorly 

Beans (Phaseolus vulgaris) (Townsend and Wedgworth, 1936). At 
first the trifoliate leaves show a faint mottled pattern, the tissue near 
the veins remaining green longer than that between the veins. The 
cotyledonary leaves remain green until late in the development of the 
disease. A few days after the appearance of the first mottling the entire 
leaf blade may turn golden yellow. Small necrotic brown spots can be 
seen parallel to each side of the midrib and principal veins which may 
extend to the tips and margins of the leaves. Subsequently, the under- 


surface of affected leaves appears to be cupped between the veins, while 
the upper surface of the same areas appears water-soaked and soon 
breaks down. New growth from the apical bud becomes slower as the 
disease progresses, and the buds eventually die. All leaves become brown 
and withered by the time the bud dies. Frequently there is secondary 
growth from lateral buds. 

Peas (Wallace, 1944). The plants may appear quite healthy or, with 
a severe deficiency, may show a somewhat chlorotic condition in the 
foliage. In the seeds a very characteristic condition of the seed occurs, 
known as marsh spot. When the seed coat is removed and the two 
cotyledons are separated, small brown specks or larger circular brown 
areas are seen on the flat surfaces. The areas may become hollowed out 
in very severe conditions. 

More severely affected plants show a brownish discoloration of the 
young tendrils and the youngest intern odes at the top of the stem 
(Samuel and Piper, 1929). The youngest leaves fail to expand, becom- 
ing yellowish with small discolored areas between the veins. Slightly 
older but not fully expanded leaves acquire a characteristic mottled 
appearance due to the mesopliyll between the small veins becoming yel- 
low, whereas the veins themselves remain green. The lower leaves retain 
their normal green color. The growing tips and the youngest leaves 
will be completely dead in a short time. 

Potato (Wallace, 1944). The tip leaves lose their luster and turn 
pale. They tend to be small and rolled toward the upper surfaces. 
Small blackish brown spots may be developed on the leaves along the 
veins, and although these are more numerous on the pale leaves near the 
tips of the shoots, they may also be present on older leaves which are 
still green. In severe conditions the plants show much browning and 
yellowing, especially in the young foliage. 

Tobacco (McMurtrey, 1944). The first visible symptom is a loss of 
color in the young leaves. Between the veins the tissue is light green to 
almost white while the veins themselves remain darker. The leaf has 
a checkered appearance, because of the contrast between the green veins 
and the tissues that have lost their color. In the latter tissues necrotie 
spots may develop which may drop out giving the leaf a ragged appear- 
ance. Usually this spotting is not confined to the tip and margins, as 
in the case of potassium deficiency, but involves parts scattered over the 
entire leaf. The plant as a whole may be considerably dwarfed. 

Tomato (Skinner, 1944). The earliest symptom is a lightening of 
the green color, which gradually turns to yellow in the leaf areas farthest 
from the major veins. As the condition progresses the yellow becomes 
more marked and extensive. The veins remain green, which gives a char- 


aeteristic mottled appearance to the leaf. Eventually the foliage may 
become completely yellow, and in many cases necrosis sets in, appearing 
at first as small brown pinpoints centering in the yellow areas farthest 
from the veins and expanding until larger dead areas indicate complete 
breakdown of the tissue. Growth is spindling, little or no blossoming 
takes place, and no fruits form. 

Sugar beet and mangold (Wallace, 1944). The leaves tend to be 
more upright than usual and somewhat triangulate in outline, due to 
curling of the margins toward the upper surfaces The intervcinal tis- 
sue becomes chlorotic. Brownish spots may appear in the mterveinal 
areas and the brown tissue may die and fall out leaving small holes. 

In Brassica crops (Wallace, 1944), the symptoms first appear as an 
interveinal chlorotic marbling With severe deficiencies the whole of 
the leaves may bo practically bleached, only the veins remaining green 
(kale) or some necrosis may develop in the mottled tissue, when it takes 
on a dull brownish gray appearance (savoy cabbage). 

Other vegetable crops. The general foliage symptoms are a chlorosis 
between the veins, in many cases extending from the margin inward. 
The tissue along the veins and midrib remains green much longer. 

Ornamental plants. Dickey and Reuther (1938) describe manganese 
deficiency symptoms in a great number of ornamental plants. In most 
cases the affected leaves show a yellow green chlorosis extending inward 
from the margins between the primary veins, the tissue immediately 
surrounding the midrib and primary veins remaining green. 

Fruit plants (apples) (Wallace, 1944). The leaves develop an inter- 
veinal chlorosis which begins near the margins and extends toward the 
midrib, and finally only the veins remain green Strongly growing 
young shoots may be only little affected, which is a point of difference 
from iron deficiency, in which the chlorotic condition is always most se- 
vere in the young tip foliage. In pears, plums, peaches, and cherries the 
symptoms are similar to or only slightly different from those of apple 
(see Wallace, 1944). In citrus the leaf pattern is also that of a network 
of green veins on a lighter green background (Camp et aL, 1944). 


1. Normal Plants Growing under Natural Conditions 

The manganese content of plants grown under natural conditions 
varies enormously. This is mainly due to the fact that the availability 
of soil manganese varies in much the same way. Since the latter has 
been shown to be dependent to a large extent on soil pH and oxidation- 


reduction potential (see Sec. Ill), it may be expected that plants grow- 
ing on acid soils and 011 waterlogged soils are rich in manganese. 

Olsen (1934) determined manganese in leaf blades of Hot cm lanatus, 
Oxalis acetosella, Asperula odorata, and beech (Fagus silvatica) grow- 
ing on Danish soils at a wide range of pH values. A close correlation 
was found between soil pH and manganese content of these plants. 
Above pH 7 values lower than 100 p.p.m. were found, whereas on the 
most acid soils the leaves contained more than 1600 p.p.m. in the dry 
matter. Plants growing on swampy soils contained high manganese 
values even at pH values higher than 7. The uptake of manganese by 
different plant species growing under the same conditions may differ 
widely. This appears from the extensive investigations of Erkama 
(1947), who analyzed a great number of naturally occurring plant 

The analytical data of Mayer and Gorham (1951) show that the 
manganese content of naturally occurring plants varies with the individ- 
ual species, the pll of the soil, and the water content of the soil. The 
correlation with pll, as observed by these authors was less pronounced 
than was the case in the investigation of Olsen (1934). 

2. Manganese Content of Healthy and Manganese- Deficient 


There is little agreement in the literature as to the critical amount 
of manganese in plants below which deficiency symptoms may be found. 
Samuel and Piper (1929), Piper (1931), and Leeper (1935) found 
14 to 15 p.p.m. in the whole plant at the flowering stage to be the lowest 
value in healthy cereals. Rye, ryegrass, and a tolerant barley variety 
were found to be healthy when containing only 10 to 11 p.p.m. manga- 
nese on the dry basis. Gerretsen (1937) succeeded in growing healthy 
oat plants in sterile culture media very low in available manganese. 
Values as low as from 5 to 10 p.p.m. Mn in such plants were found. 

In manganese-deficient winter wheat (tops) analyzed in early spring 
Coi'c and Coppenet (1949) found values of 20.3 and 22.5 p.p.m. and in 
healthy plants 34.5 and 48.5 p.p.m. Goodall (1949) determined manga- 
nese in various parts of wheat plants at different growing stages. He 
found no response to manganese treatment when the manganese content 
of the older leaf blades at the beginning of shooting was higher than 
34 p.p.m. 

Nicholas (1949) determined manganese in the leaves of a number of 
crop plants grown on a soil poor in available manganese. Oats with 7 
p.p.m. Mn had the lowest value and showed pronounced deficiency symp- 
toms; wheat and barley containing 14 and 12 p.p.m. of Mn respectively 


were slightly deficient, whereas maize on the same soil containing 15 
p. p.m. Mn in the dry leaves was healthy. From the other plants investi- 
gated, peas with 8 p. p.m. and sugar beet and mangold both with 10 
p.p.m. showed moderate deficiency symptoms. In flax, radish, carrot, 
and lucerne with 15 p.p.m. or over, visual signs of the deficiency were 
absent. These values are much closer to those of the Australian workers 
than to those of Goodall and Coic and Coppenet. 

Hasler (1951) found the following concentrations of manganese in 
manganese-deficient grasses: Arrhcnatherum claims, 87 p.p.m.; Festaca 
pratensis, 44 p.p.m. A large variation in the manganese content of 
various grass species grown on the same soil has been recorded by Beeson 
et al. (1947). Under the conditions of their experiments Agrostis alba 
contained 815 p.p.m. Mn whereas Poa pratensis had values of 108 and 
164 p.p.m. Seekles (1950) determined manganese contents of grass 
grown on different soils in the Netherlands. Grass from clay soils had 
the lowest manganese content viz. 114 p.p.m. in the dry matter that 
from peaty soils had 152 p.p.m. and that from sandy soils 191 p.p.m. 
These values are averages of a great number of analyses in samples 
originating from different parts of the country. 

Manganese deficiency can be corrected in a number of ways. 

1. Application of Manganese Sulfate to the Soil 

Amounts from 50 to 100 kg. per hectare are being recommended by 
various authors, although on alkaline peat soils larger amounts may be 
required for obtaining healthy plant growth. Since on many manganese- 
deficient soils the added manganese sulfato will be readily converted into 
practically unavailable oxides, the duration of the improvement is often 
very short. This was already noted by Iludig (1911), who had to apply 
manganese sulfate simultaneously with the sowing of oats in order to be 
sure that the plants did not suffer from gray speck disease. 

2. Spraying the Foliage with a Dilute Solution of Manganese 

This method is more economical since much smaller amounts can be 
employed. From 0.2 to 0.5 per cent manganese sulfate solutions are 
being used (from 500 to 1000 1. per hectare). Gallagher and Walsh 
(1943) employed 1 per cent manganese sulfate sprays in correcting 
manganese deficiency in oats. Harmer and Sherman (1943) added 
manganese sulfate to Bordeaux mixture at the rate of 1 kg. MnS0 4 per 
500 1. Bordeaux mixture. Manganese deficiency in fruit trees was cor- 


reeled by Thompson (1944) by injecting a solid manganese salt into 
the trunk. 

3. Treating the tfoil with Acidifying 

The beneficial effects of treating the soil with acidifying substances 
such as sulfur or sulfate of ammonia are often due to the formation of 
pockets of relatively high acidity in which the manganese becomes 
much more soluble than in the bulk of the soil. That this statement is 
true may be concluded from the experiments of Hudig (1911) in which 
mixing of a peaty soil with sulfuric acid or acetic acid in amounts equi- 
valent to those present in ammonium sulfate had no effect on the defi- 
ciency symptoms of oats, whereas a treatment with sulfate of ammonium 
gave practically healthy plants. Similar results have been obtained by 
Gerretsen in an unpublished experiment with sulfur of a different 
degree of fineness. The best results were obtained with coarse particles. 

Treating the soil with acid peat may also give good results. 

A method which has given perfect results is mixing the applied 
manganese sulfate with one of the above mentioned substances. 

4. Flooding 

The flooding of soils sometimes may give a much improved manga- 
nese supply to the plants due to the reduction of part of the manganic 
oxides to available manganese. Under certain circumstances, however, 
flooding may have the reverse effect This has been demonstrated in the 
Dutch and Belgian sea polders which were inundated during World War 
II. After the flooding manganese deficiency was more frequently ob- 
served than before. 


The effect of compounds which bring about considerable changes 
in pH (lime, sulfur) will not be considered here, since their effect has 
been discussed in detail in Sec. 111,1. 

1. Nitrogen Applications 

The beneficial effect of ammonium sulfate as contrasted to the harm- 
ful influence of nitrate, particularly sodium nitrate, on the availability 
of soil manganese is well known. This effect is entirely indirect and re- 
sults from the changes in pll which accompany the uptake of NHV 1 " and 
N0a~~ by the plants. Since the shift in pH is greater with sodium ni- 
trate than with calcium nitrate, the former affects the availability of 
soil manganese more strongly. 


It may be expected, however, that the nitrogen compounds will exert 
a direct effect on the uptake of manganese. Furthermore the change in 
pH of the nutrient medium may also affect the uptake of manganese ions. 
Several authors have observed that nitrate nitrogen may favor the 
manganese uptake by plants. Olsen (1934) growing barley in nutrient 
solutions of pH 6-7 found 90 p. p.m. in the dry matter of the leaf when 
the plants had been supplied with nitrate and 23 p. p.m. when ammonium 
nitrogen had been employed. Co'ic et al. (1950) studying manganese 
deficiency in cereals in Brittany obtained much more healthy plants 
when the crop was treated with calcium nitrate than in the absence of 
added nitrogen. The manganese content of the grain from manganese- 
deficient plants was 14 p. p.m. without nitrogen fertilization and 19.4 
p.p.m. when treated with a moderate amount of calcium nitrate. When 
treated with manganese the values were 15.5 and 21.3 p.p.m. of man- 
ganese respectively. 

Timonin (1950b) reports a beneficial effect of calcium nitrate in 
correcting manganese deficiency under field conditions. 

The favorable effect of nitrates on manganese uptake by plants is 
also apparent from papers reporting on studies of manganese excess 
(Millikan, 1950; Lohnis, 1951 ). 

Manganese uptake in relation to pll of the nutrient medium was 
studied by Olsen (1934) in culture solution experiments with barley, 
mustard (Sinapis alba), Zea may 8, and Lemna polyrrhiza. An optimal 
uptake was found to take place at pll 6 and 7. Similar results were 
obtained by Burstrdm and Boratynski (1936) in nutrient solution ex- 
periments with wheat. From pll 3.5 to 6.5 a clear increase in manganese 
uptake was observed. 

The increased uptake of Mn 4 + (or other cations) at decreasing hy- 
drogen-ion concentration of the nutrient medium may be explained by 
an enhanced affinity of Mir^ + for the rool surface as a result of the 
increased Ca/H ratio on the root surface exchange complex (complemen- 
tary ion effect). If under similar conditions of decreased hydrogen-ion 
concentration a base-adsorbing solid substrate, e.g., clay, is present, two 
systems are operating with opposite effects on the availability of Mn+ + . 
The release of Mn ++ from the surface of the solid exchange material 
will be diminished, whereas the affinity of Mn + + for the root surface is 
enhanced. Epstein and Stout (1951) studying the uptake of manganese 
from bentonite-containing suspensions observed an increased absorption 
of manganese with increasing Ca/II ratio on the bentonite. Apparently 
the increased affinity of Mn+ + toward the root surface at increased 
Ca/H ratio outweighed the diminished exchangeability of manganese on 


the bentonite. Under soil conditions the complementary ion effects will 
be obscured by changes in the concentration of available manganese. 

2. Effect of Phosphate Fertilization 

A beneficial effect of superphosphate on uptake of applied manganese 
was observed by Steckel et al. (1948) when both fertilizers were mixed 
together. The beneficial effect is stated to be due to the precipitation of 
the manganese as the manganous phosphate, which would retard the 
oxidation of the manganese and would provide a constant though small 
supply of divalent manganese. The somewhat increased acidity caused 
by the superphosphate surrounding the manganese would also be of some 
importance in preventing rapid oxidation of the added manganese. 

On the sandy soils of central Florida which are almost exclusively 
composed of siliceous sand, application of large amounts of phosphate 
at pll values from 5.5 to 6.0 may give rise to the accumulation of calcium 
phosphate, presumably "hydroxy apatite" which retains applied man- 
ganese and magnesium so that they are not so readily leached by high 
rainfall as is the case from these soils without the presence of accumu- 
lated phosphate. Both manganese and magnesium thus adsorbed are 
available to citrus (Wander, 1950) 

Albrecht et al. (1941) in studying the effect of calcium carbonate 
and phosphate applications to a well-weathered prairie soil of pll 5.5 
found that calcium carbonate when mixed throughout all the soil lowered 
the manganese content of sweet clover, lespedeza, Poa pratensis, and 
notably Agrostis alba, as might be expected. Mixing the carbonate into 
the surface one-fourth of the soil and leaving three-fourths untreated 
gave a considerably higher manganese content of the crop as compared 
with the untreated plants. Phosphate dressings were found to exert a 
beneficial effect on manganese uptake of the plants. 

3. Effect of Copper on Manqanese Nutrition 

Iludig et al. (1926) have stated that copper treatment of neutral 
soils on which the crop suffered from copper deficiency would correct 
the copper deficiency but would promote the occurrence of manganese 

Mulder (1938) studying the phenomena related to copper nutrition 
of plants and copper treatment of soils has carried out a few experi- 
ments, the results of which tend to confirm the above statement of Iludig 
et al. (1926). The microbiological oxidation of manganous salts to 
Mn0 2 by fungi was found to be clearly stimulated by the addition of a 
trace of copper to the nutrient medium of the microorganisms. The 
copper-manganese relationship in green plants was studied in nutrient 


solution experiments with cereals. In one experiment with rye an 
increased demand for manganese was observed with increased copper 
supply. In a similar experiment with barley such a copper-manganese 
interaction did not occur. In the presence of an excessive amount of 
manganese, however, the barley roots of copper-supplied plants showed 
an intensive browning presumably due to Mn(>2, particularly in the 
upper parts, which was absent when the plants suffered from copper 
deficiency. Although the plants were not growing under sterile condi- 
tions, the browning occurred so uniformly that it was improbable that 
microorganisms were involved. The results of these experiments show 
that copper may activate the biological oxidation of manganous com- 
pounds by fungi and probably by root cells from barley plants. 

Kenten and Mann (1949) were able to extract from horseradish roots 
an enzyme system which may oxidize manganese in the presence of 
hydrogen peroxide to Mn + + + or Mn + + + + . The system consists of per- 
oxidase and peroxide substrate (Ken ten and Mann, 1950). Although it 
is unknown whether the system may accumulate Mn0 2 in vivo, it is 
probable that at a high concentration of Mn + + this may be the case. ]t 
is unknown whether this system may be less active in copper-deficient 
plant roots. 

The effect of copper sulfate on the oxidation of manganese in acid 
soils treated with calcium carbonate was studied by Sherman et al. 
(1942). In contrast to the biological oxidation reported above, a retard- 
ing effect of copper on manganese oxidation was demonstrated, as a 
result of which oat plants were suffering much less from manganese defi- 
ciency than in the absence of applied copper sulfate. Both soils used by 
Sherman et al. (1942) were clay soils which presumably were not defi- 
cient in copper. The results of 0delien (1948), working on copper- 
deficient soils are in agreement with those of lludig ct aL (1926). 

4. Iron-Manganese Rela-1 ion ships 

According to Shive (1941), Somers and Shive (1942), Soniers, Gil- 
bert, and Shive (1942), and Stiles (1946), the ratio of iron to manga- 
nese in the nutrient medium of soybean plants and presumably also of 
other plant species should lie between l.f) and 2.5 to assure optimal 
plant growth. If the ratio is above 2.5, symptoms of iron toxicity 
( = manganese deficiency) would occur; if it is below 1.5, the plant 
would suffer from manganese toxicity ( iron deficiency). Since the 
values for active (soluble) manganese and iron within the plant tissues 
associated with good growth covered about the same range of values as 
did those in the external medium, the observed phenomena were thought 


to be due to the existence of a close interrelationship between iron and 
manganese within the living cell. 

In a large number of papers either published earlier than those of 
Shive and collaborators, or later, the existence in plants of a more or less 
pronounced iron-manganese interdependency has been reported (see the 
review by Twyman, 1946). According to most authors, however, the 
range of iron-manganese ratios of the nutrient medium at which normal 
plant growth is possible is much wider than that mentioned by Shive et al. 
In contrast to the statement of these authors that more importance 
should be attached to the ratio of manganese to iron than to their abso- 
lute concentrations in the nutrient medium, Hewitt (1948c) found that 
the growth of oats and sugar beet was affected by absolute levels of these 
elements rather than by their ratios. Similar results were obtained by 
Morris and Pierre (1947) in nutrient solution experiments with lespedeza. 
Increase of the concentrations of both iron and manganese caused pro- 
nounced symptoms of manganese toxicity notwithstanding that the 
ratio of iron to manganese in the nutrient solution was unchanged. 
Ouellette (1951) found both the concentration of iron and manganese 
in the culture solution and their ratio of importance in attaining optimal 
growth of soybeans. Although iron chlorosis due to manganese excess 
is reported by many authors, there is sufficient evidence available in the 
literature to state that manganese excess is not identical with iron defi- 
ciency and that iron excess is not identical with manganese deficiency 
(see Sec, IX). 

Some authors have presented clear evidence that an increased iron 
supply to the plants may depress the uptake of manganese (Somers and 
Shive, 1942, for soybeans; Morris and Pierre, 1947, for lespedeza; Bur- 
strom, 1939, for wheat). An increased manganese supply may also 
depress the uptake of iron, but the effect is less clear than the reverse 
(Somers and Shive, 1942). Friederichsen (1944) studied the effect of 
increasing manganese concentration of the nutrient solution on the iron 
content of roots and leaves of spinach and barley plants. With nitrate 
as the nitrogen source high concentrations of manganese did not affect 
the iron content of the leaves. The roots, however, were much lower in 
iron. When the plants were supplied with ammonium nitrogen, manga- 
nese depressed not only the iron content of the roots but also that of the 


It has been shown, mainly during the last decade, that excess of 
manganese in the nutrient medium may cause toxicity symptoms. Since 
the concentrations of manganese at which the toxicity symptoms become 


visible are relatively low, many acid soils may be found on which the 
manganese supply to the plants is high enough to bring about some crop 
injury. From the results of several investigations which will be dis- 
cussed below, it has appeared that manganese toxicity is one of the 
main causes of soil acidity injury to plants. Aluminum toxicity and lack 
of available calcium, magnesium, or molybdenum may also affect plant 
growth on certain acid soils. 

Before excess of available manganese was recognized as the cause of 
injury to plants growing on certain acid soils (Jacobson and Swanback, 
1932 ; Bortner, 1935 ; Wallace et al, 1945 ; Hewitt, 1945 ; Hale and lleintze, 
1946; Lohnis, 1946, 1951), manganese toxicity of plants had been 
studied by soil scientists working on manganiferous soils, i.e., soils rich 
in manganese. Such soils have been described as early as 1909 by Kelley 
(see Sherman et al., 1949; Jacobson and Swanback, 1932) in the drier 
regions of the Hawaiian Islands. Manganese contents ranging from 1 
to 4 per cent may be found in such soils. Kelley (1909) indicated the 
relationship between the poor growth of pineapple in these regions and 
the high manganese content of the soils. Extensive pot experiments with 
similar soils have been carried out in Puerto Rico by Hopkins ct al. 

That manganese toxicity may be the cause of injurious effects ob- 
served on acid soils was shown by Jacobson arid Swanback (1932) 
working with tobacco on Connecticut soils, and Bortner (1935) studying 
abnormally growing tobacco in Kentucky. Extensive investigations have 
been carried out by workers of the Long Ashton Research Station in 
England (Wallace et al., 1945; Hewitt, 1945, 1946, 1947, 1948a). They 
compared the visual symptoms of acidity injury of different plant spe- 
cies growing in the field with those of sand cultures at different levels 
of certain added micronutrient elements. A striking resemblance was 
found to exist between field symptoms of acidity and excess of manganese 
in the sand cultures, particularly at low calcium levels. This was found 
to be true of several agricultural and horticultural crops (including run- 
ner bean (Phaseolus vulgaris), cauliflower, savoy cabbage, swede, and 
kale). In potato, calcium deficiency was also frequently seen as an 
acidity symptom. Oats, barley, celery, carrot, beet, and particularly 
sugar beet and mangold appeared to be much more sensitive to excess of 
aluminum than to excess of manganese so that acidity injury to these 
crops may resemble aluminum toxicity. Hale and lleintze (1946), 
studying cases of field acidity from various parts of England came to 
conclusions similar to those of Wallace et al. (1945). 

The poor growth of legumes on many acid prairie soils in the United 
States appeared to be due to high amounts of soluble manganese in these 


soils (Morris and Pierre, 1947, 1949; Morris, 1948). On certain 
acid soils of northern Wisconsin potatoes may suffer from "stem streak 
necrosis/' a disease which Berger and Gerloff (1947a,b) showed 
to be due to excess of available manganese. Schmehl et al. (1950) 
growing alfalfa in an acid soil from New York observed symptoms 
of manganese toxicity According to these authors the poor growth 
of their plants was only partly due to manganese excess. Aluminum 
toxicity apparently was of more importance. Similarly Heslep (1951) 
found phosphorus deficiency, manganese toxicity and presumably a third 
factor as the causes of poor growth of lettuce in two acid Californian 

Although magnesium deficiency is often found to be the cause of 
acidity damage of cereals and potato on sandy and peaty soils in the 
Netherlands (Smit and Mulder, 1942), manganese toxicity may also 
occur (Lohnis, 1946, 1950, 1951). Tn 1940 the disease was observed for 
the first time in Phaseolus vulgaris growing on a sandy soil which had 
been fertilized with ammonium sulfate for a number of years as a 
result of which the pH had dropped to a very low value. Its cause 
remained unknown until 1943 when visual symptoms identical with 
those noted in the field were induced by the addition of excess manga- 
nese to plants growing in nutrient solutions or in neutralized soil. To 
obtain more evidence as to the cause of the disease, young full grown 
lea,ves of Phaseolus vulgaris from both injured and normal plants, grown 
on the same soil treated with limp, were analyzed for manganese. The 
values found in a large number of samples from injured plants, collected 
during three successive years, ranged from 1104 to 4216 p.p.m. Mn in 
young foliage and from 40 to 904 p.p.m. in healthy plants of the same 
age. Although in different years apparently owing to different climatic 
conditions widely varying concentrations of manganese were found, the 
threshold values above which the foliage was always visibly affected was 
almost constant in the successive years, that is approximately 1200 p.p.m. 
on a dry weight basis. This value depends on a number of various 
factors, and it may be expected that changing the circumstances under 
which the plants are growing also will change the amount of manganese 
at which toxicity symptoms become visible. Temperature was found by 
Lohnis to have an important effect. Bean plants containing manganese 
in such amounts that severe symptoms of injury might be expected at 
moderately high temperature remained healthy at a high temperature. 
Millikan (1951) in nutrient solution cultures of peas found a remark- 
able difference in tolerance between older and younger leaves of the 
same plant. Manganese concentrations much higher than those which 


were found in the affected younger leaves did not cause injury to the 
lower leaves. 

Of further plant species tested by Lohnis (1951), vetch and lucerne 
appeared to be very susceptible to excess of manganese. The minimum 
amount of manganese in affected plants (field experiments) was for 
vetch 500 p.p.m. in 1948 and 1117 p p.m. in 1949 and for lucerne 477 
p.p.rn. in 1948 and 1083 p.p.m. in 1949. White and red clover and flax 
were found to be slightly susceptible. Mangold was depressed in growth 
in acid soils but appeared to be insensitive in nutrient solutions. This 
agrees with the results of Hewitt (1948a) that the injury by acidity in 
sugar beet and mangold is often due to aluminum toxicity. Potatoes, 
tobacco, mustard, oats, and strawberry appeared insensitive in field tests. 
In contrast to the results of Lohnis potatoes have been found to suffer 
from manganese toxicity on certain northern Wisconsin soils [stem 
streak necrosis, Berger and Gerloff (1947a,b)], while tobacco growing on 
certain acid soils in Kentucky was found to show typical manganese 
toxicity symptoms (Bortner, 1985). Whether these different results in 
potatoes and tobacco have to be attributed to the different environmental 
conditions under which the plants were growing or to varietal differences 
is unknown. 

Morris and Pierre (1949) working with nutrient solutions found 
lespedeza and sweet clover to be much more sensitive to manganese tox- 
icity than peanuts. Gowpeas and soybeans held intermediate positions. 
Since the peanuts contained much lower amounts of manganese than 
the other plant species supplied with the same amount of manganese, the 
tolerance of this plant apparently is due to a limited absorption of 
manganese. Lespedeza absorbed large amounts of manganese, whereas 
the sensitiveness of sweet clover apparently was due to its inability to 
endure relatively low amounts of manganese. 

In accordance with these results Jjohnis concluded from the manga- 
nese contents of the various plants tested for manganese toxicity that 
a tolerance for a high level of available manganese in the soil may be 
due (1) to a weak absorption of manganese (oats, mustard, mangold) 
and (2) to a strong tolerance within the plants (tobacco, flax, straw- 
berry, potato, and presumably broad bean). Striking examples were 
found to be oats, which contained only 325 p.p.m. of Mn when growing 
in an acid soil, and tobacco, which contained nearly 3000 p.p.m. Both 
plant species showed no visual symptoms of manganese toxicity. Jacob- 
son and Swanback (1932) recorded values of 5250, 6470, and 11670 
p.p.m. of manganese in affected tobacco grown on acid soils. 


1. Manganese Toxicity in Relation to the Supply of Some 
Nutrient Elements 

a. Effect of Nitrogen Compounds. The effect of nitrogen nutrition on 
manganese toxicity was studied in detail by Millikan (1950) in nutrient 
solution experiments with flax. With nitrate and urea as the nitrogen 
sources severe symptoms of manganese injury were noted which were 
absent in the case of ammonium nitrate and ammonium sulfate and in 
plants subjected to nitrogen deficiency. Toxicity symptoms were af- 
fected by these treatments in the following range of increasing severity 
nitrate>urea>NH 4 NO 3 > (NH 4 ) 2 S0 4 >nitrogen deficiency. Although 
the manganese content of the plants was much higher in the case of 
nitrate nutrition than when supplied with ammonium compounds, it was 
presumably not the only cause of the large difference in toxicity symp- 
toms. The beneficial effect of the presence of ammonium ions in the 
nutrient solutions on the appearance of manganese toxicity symptoms was 
also observed by Lohnis (1951). The foliage of beans treated with nitrate 
alone contained five times as much manganese as in the presence of 
ammonium nitrate. 

1). Effect of Phosphorus. A beneficial effect of phosphate fertiliza- 
tion of acid soils on tobacco plants suffering from manganese toxicity 
was found by Bortner (1935). In nutrient solutions with high man- 
ganese, phosphate gave a similar effect. These results were not con- 
firmed by Morris and Pierre (1947), who found a greater depression of 
growth of lespedeza owing to excessive manganese in culture solutions 
with a higher phosphate concentration. Walsh ct al. (1950) observed a 
favorable effect of applications of superphosphate arid basic slag in pre- 
venting manganese toxicity of swedes. 

c. Effect of Calcium. There is no agreement in the literature as to 
the effect of calcium ions on manganese injury. Hewitt (1945) considers 
calcium as an element that clearly antagonizes the intake of manganese 
under sand culture conditions. With increasing calcium supply (as the 
sulfate) the symptoms of manganese toxicity became less severe. 

Morris and Pierre (1947) in culture solution experiments with les- 
pedeza were unable to show an alleviation of manganese toxicity by the 
addition of calcium. Jf acid soils were treated with calcium sulfate, the 
symptoms of manganese deficiency in lespedeza and sweet clover were 
found to be aggravated (Morris, 1948). This was shown to be due to a 
lowering of the pH as a result of which the content of water-soluble 
manganese in the soil increased. Water-soluble rather than exchange- 
able manganese of the soil was found to be a reliable indicator of manga- 


nese toxicity. A similar unfavorable effect of calcium sulfate application 
on soil pH and manganese toxicity was found by Berger and Gerloff 
(1947a) with potato and by Schmehl et al. (1950) in pot experiments 
with alfalfa. 

The well-known beneficial effect of liming (increase of pH) on man- 
ganese toxicity is due to the conversion of soluble manganese to un- 
soluble manganese oxides (see Sec. III). The uptake of Mn++ by the 
plants is favored, however, as was shown by Olsen (1934) in nutrient 
solution experiments with barley, Zea mays, mustard, and Lemna polyr- 
rhiza. Optimal absorption was found to occur at pH 6 to 7. 

d. Manganese Excess in Relation to Iron Deficiency. If the state- 
ment of Somers and Shive (1942) that normal plant growth depends on 
a certain iron-manganese ratio within the plant would appear to be true, 
it may be expected that manganese toxicity is identical with iron de- 
ficiency. Several authors have discussed this problem; some of them 
agree to a certain degree with Somers and Shive, others do not give 
support to their views. 

Evidence that excess of manganese may produce symptoms of iron 
deficiency comes from those authors who have studied manganese excess 
in pineapple on manganiferous soils in Hawaii and Puerto Rico. On 
these soils growth of pineapple is very poor apparently owing to a large 
absorption of manganese. The plants become very chlorotic, and they 
respond clearly to sprays of ferrous salt solutions. (Johnson, 1917 ; 
Hopkins et al., 1944; Sideris and Young, 1949). When Phaseolus beans 
were planted in such soils, they showed severe chlorosis within ten days, 
and no further growth of the plants took place (Hopkins et al., 1944). 
Applications of iron as humate or liming the soil to pH 6.2, which pre- 
cipitated a great deal of the soluble manganese, gave normal plant 
growth. In addition to these experiments with soil, Hopkins and col- 
laborators carried out extensive investigations with beans, tomato, and 
pineapple, growing in culture solutions in order to elucidate the iron- 
manganese relationship. They presented substantial evidence that under 
the conditions of their experiments the injurious effect of excessive man- 
ganese might be counteracted by iron. This was found to be true not 
only of the chlorosis but also of necrotic spotting which occurred on the 

Similar results were obtained by Millikan (1947, 1949), who studied 
the effect of a number of heavy metals, including manganese, on the 
growth of flax in nutrient solutions. Although his main interest lay with 
the antagonizing effect of molybdenum on manganese toxicity, Millikan 
carried out treatments with iron salts to show that the chlorosis and top 


necrosis of his flax plants were due to iron deficiency. Other symptoms 
of excessive manganese, such as the dwarfed growth and the lower leaf 
necrosis were not prevented by iron. Warington (1951) confirmed 
Millikan 's results with flax in foliage painting tests with dilute ferrous 
sulfate solutions. 

The results of Hopkins et al. (1944), Millikan (1947, 1949), and 
Warington (1951) indicate that at least part of the symptoms of man- 
ganese toxicity may be considered as manganese-induced iron deficiency. 

Morris and Pierre (1947) were unable to confirm these results with 
lespedeza. Symptoms of iron deficiency were found to differ widely 
from those of manganese toxicity. Nevertheless they observed a consid- 
erable alleviation of manganese toxicity by addition of iron. This was 
found to be due to an approximate 50 per cent reduction in the manga- 
nese content rather than to an increase of total iron in the plant. In a 
further set of experiments (Morris and Pierre, 1949) it was shown that 
the symptoms of manganese toxicity in soybeans, cowpeas, and peanuts 
were entirely different from those of iron deficiency. 

Manganese toxicity of potato (stem streak necrosis) was found by 
Berger and Gerloff (1947a), to be entirely different from iron deficiency, 
and it was unaffected by treating the plants with dilute ferrous sulfate 

Although Hewitt (1948b) in a single case reports the occurrence of 
iron deficiency (in sugar beet) upon treatment with several heavy ele- 
ments, including manganese, he was unable to obtain any response to 
ferric citrate when painted on the leaves of Phaseolus showing manga- 
nese toxicity symptoms (1945). Similarly, Lohnis (1951) in her exten- 
sive studies on manganese toxicity did not observe a beneficial effect of 
ferrous sulfate treatments of manganese-injured plants. Symptoms of 
iron deficiency in beans when grown in an iron-deficient nutrient solu- 
tion appeared to be entirely different from those of manganese toxicity. 
In a single experiment, however, in which the manganese injured bean 
plants grew at a high temperature, a clear response to iron treatment 
was found. The appearance of the plants was whiter than usual. Since 
Hopkins et al. (1944), who obtained a very clear response of manganese 
injured Phaseolus to ferrous sulfate, were working under tropical condi- 
tions, it may be possible that the temperature factor can explain the 
controversy between various workers as to the relation between iron 
deficiency and manganese toxicity. 

c. Manganese Toxicity in Relation to Molybdenum Supply. In a 
large number of nutrient solution experiments Millikan (1947, 1949, 
1950, 1951) has investigated the effect of molybdenum on toxicity symp- 


toms caused by excess of some heavy metals, including manganese. In 
flax plants a marked reduction in the severity of the injury was observed. 
Ammonium molybdate appeared to be more effective than sodium inolyb- 
date (Millikan, 1947, 1949). 

In a further set of experiments Millikan (1951) studied the effect of 
sodium and ammonium molybdates on manganese uptake from high and 
low manganese solutions by flax, peas, cabbage, and tomato and its dis- 
tribution in the plant tissues, using a tracer technique. A marked ac- 
cumulation of manganese in the tops of the leaves of flax at both 
manganese levels was observed. This concentration corresponds with the 
lower leaf necrosis which commences at or near the tip of the leaf. The 
presence of excess of molybdenum appeared to have a marked effect not 
only on the total manganese content, which was much reduced, but also 
upon its distribution in the leaves. The manganese content of the leaf 
ends was relatively much more depressed than that of the base of the 
leaves. In peas, cauliflower, and tomato similar relationships were found 
to exist between manganese content, manganese distribution in the 
leaves, occurrence of toxicity symptoms, and addition of molybdates. 

From the results of his experiments and from the similarity of visual 
symptoms of manganese excess and molybdenum deficiency, Millikan con- 
cludes that a narrow relation exists between both phenomena. It should 
be stressed, however, that comparatively large amounts of molybdenum 
are required to affect manganese toxicity in Millikan 's experiments, 
whereas in molybdenum studies extremely small amounts of this micro- 
nutrient element have been found to give normal plant growth, In 
contrast to Millikan 's results with flax, Hewitt (1948c) found that molyb- 
denum may accentuate chlorosis caused by excess of manganese in sand 
cultures of sugar beet. Lohnis (J951) was unable to show any effect of 
molybdenum on manganese toxicity of flax growing in nutrient solutions. 
Warington (1951) showed* that molybdenum in amounts similar to those 
employed by Millikan may intensify the chlorosis induced by manganese 
excess in flax and soybean. These results are in agreement with those of 
Hewitt with sugar beet. In contrast to molybdenum, vanadium was 
found to be able to alleviate the symptoms of manganese toxicity. 

To test Millikan 's hypothesis as to the relation between manganese 
toxicity and molybdenum deficiency the senior author carried out the 
following experiment (unpublished). Manganese determinations were 
carried out in white clover grown in acid soils in a number of which the 
plants responded clearly to small amounts of added molybdenum. If a 
relation between manganese toxicity and molybdenum deficiency exists, 
it would be expected that plants which responded to added molybdenum 


would have higher manganese contents than those which did not so re- 
spond. This appeared not to be the case. 

2. Symptoms of Manganese Toxicity in Some Crop Plants* 

Beans (Phaseolus vulgaris) (Lohnis, 1951; Hewitt, 1945). The 
first symptoms in younger leaves appear as marginal and later smooth 
interveinal chlorosis between major veins. When older, the leaves be- 
come somewhat crinkled and are spotted with small yellowish and later 
whitish areas. Finally minute brown necrotic spots appear. Petioles 
of the seed leaves and of the first trifoliate leaves are speckled with small 
superficial purple brownish spots. Severely injured plants remain 
stunted and produce hardly any flower or seed. Less injured plants may 
recover later in the season, when only traces of the initial injury still 
occur in the older leaves. 

Peas (Millikan, 1951). First symptoms, necrosis along the edges of 
the third or fourth leaflets in the form of small grayish spots in the inter- 
veinal tissues. These marginal spots soon coalesce, and the necrotic 
edge may inroll. The tendrils of the affected leaves show a necrosis at 
the tips. The upper leaves of the plant may show symptoms like iron 
deficiency chlorosis followed by necrosis. 

Vetch (Lohnis, ]951). The young leaves are chlorotic and a very 
marked dark purplish discoloration occurs along the margins of tho full 
grown leaves. Sometimes small orange-red sunken spots may be found 
in the leaf margins, and the upper surface of the leaves may be speckled 
with minute dark spots. The plants remain small and spindly. 

Soybeans and cowpeas (Morris and Pierre, 1941). In soybeans pale 
green irregular areas occur between the main veins of the leaves. Most 
of the affected areas become brown. In cowpeas small reddish purple 
spots are distributed uniformly over the leaf area. In both plant species 
growth is markedly decreased. 

Alfalfa (Hewitt, 1948a). Growth is reduced and there is marginal 
paling of midstem leaves, followed by pale brown or buff spotting near 
margins; younger leaves are distorted at tips, with wavy margins or 
twisting of lamina. Later a yellow-green or gray-green paling at leaf 
tips occurs ; margins become brown or bronzed and irregularly speckled. 

Red clover (Hewitt, 1946). Marginal chlorosis of leaves. When 
older, leaflets show marginal crinkling and forward curling, slightly 
cupped; paling becomes yellow-green, spreading interveinally ; light 
brown necrotic spotting appears between veins around inner border of 
pale marginal regions. 

* This list covers only the most important agricultural and horticultural crops of 
which a rather clear-cut description has been found in the literature. 


Sweet clover (Morris and Pierre, 1949). The distal leaf margin 
shows marked chlorosis, usually accompanied by a definite crimping of 
the leaf; no spotting. 

Lespedeza (Morris and Pierre, 1949). Dark reddish brown leaf 
spots, very distinct on the underside of the leaves, cover in more severe 
cases as much as 50 per cent of the leaf area. Leaf margins are chlorotit*. 
Considerable shedding may occur. 

Potato (Berger and Gerloff, 1947b). First symptoms are the appear- 
ance of dark brown streaks on the lower stem at the base of the petioles. 
A pale yellow chlorosis develops in areas between the veins on the lower 
leaves although the veins themselves remain green. Quite often small 
brown necrotic areas, irregular in shape, appear between the veins near 
the midrib on the leaflets. As the necrosis becomes more severe, many 
long, narrow brown streaks are found on the lower portions of the stem 
and even on the petioles. The necrotic streaks also affect the inner tissues 
of the stem. The affected parts become very brittle, the petioles break 
off with a slight touch, and the chlorotic leaves finally dry and fall from 
the plant. The streaking of the stem and subsequent leaf dropping 
progress upward on the plant until the terminal bud becomes necrotic 
and the plant dies prematurely. 

Cauliflower (Hewitt, 1946). There is marked forward cupping of 
margins of middle and older leaves. A marginal paling occurs, spread- 
ing interveinally between major veins, followed by dark brown spotting 
in pale areas. There is also severe marginal and interveinal crinkling 
and distortion. 

Savoy cabbage (Hewitt, 1946). Growth is stunted. Expanding 
leaves show a marked paling in a narrow marginal zone ("rim effect"), 
becoming cream or dull white. Occasionally a slight mottling spreads 
inward interveinally for a short distance. Slight forward cupping of 
first affected older leaves may occur, but is absent in later leaves. Older 
leaves later develop indigo or black tinting along margins and in veins 
in marginal zone, and there is interveinal dark brown necrotic spotting. 

Flax. Although this plant may tolerate relatively large amounts of 
manganese without any harmful effect, severe damage is affected by ex- 
cessive amounts. The growth of the plants is stunted, and a severe 
apical chlorosis occurs. A brown necrosis may develop at the middle 
of one or both edges of the second lowest pair of leaves. This necrosis 
soon involves the whole of the distal half of the leaf. Other lower leaves 
will also become damaged, the necrosis mostly commencing at the tips 
of the leaves and extending downward, so that soon the top half of the 
leaf will be involved. The lower halves of the leaves will remain normal 
green in color. Sometimes numerous dark brown necrotic spots may be 


found on the lower leaves. On the stems sometimes numerous small 
brown spots may be found, which may coalesce to form larger areas. 

Carrot (Hewitt, 1948a). Growth is slightly reduced ; chlorosis of leaf 
margins is followed by bronze necrotic speckling along leaf margins and 

Lettuce (Hewitt, 1948a). Growth is reduced. Foliage is pale and 
dull yellow around leaf margins. 

Peach (Thornberry, 1950). Excessive manganese causes "inter- 
nal bark necrosis/' i.e., occurrence of necrotic lesions localized inter- 
nally without any observable change on the surface. These lesions may 
converge into necrotic areas which tend to advance until the trunk or 
bark is girdled. At later stages of the disease there is surface darkening 
and subsequent splitting of the outer bark along with the production of 


Manganese plays an important role as a cofactor in various enzymatic 
reactions. Many of these reactions have been studied in vitro with more 
or less purified enzymes obtained from normal organisms, plants as well 
as animals. Control experiments employing tissues or enzymatic prep- 
arations derived from organisms deficient in manganese are missing in 
most of these investigations. 

In several enzyme studies concentrations of manganese far higher 
than those required in nutrition experiments with plants or microorgan- 
isms have been employed. Another fact which deserves more attention 
is the specificity of the metals. In many enzymatic reactions in vitro 
manganese may be replaced my magnesium, cobalt, nickel, or still other 
metallic ions. Although it may be possible that in the living organisms 
this replacement also occurs, little is known of it so far. The fact that 
manganese deficiency of green plants occurs mainly on neutral or alka- 
line soils in which the magnesium supply is ample and magnesium 
deficiency on acid soils in which available manganese is present in large 
amounts is not in favor of the replaceability of both metals in their 
major functions in higher plants. Whether a tendency in that direc- 
tion occurs in any "natural" enzymatic reaction may only be decided 
by experiments in which different combinations of manganese, mag- 
nesium, cobalt, etc., have been supplied. The tissues of such plants will 
have to be used for enzymatic studies. 

The only experiments of this type of which the authors are aware 
are those of Nilsson et al. (1942), who studied the replacement of magne- 
sium by manganese in a number of enzymatic reactions and in some 
growth studies with three species of bacteria, namely, Azotobacter chroo- 


coccum, Bacterium radiobacter, and Bacterium prodigiosum. Although 
the results obtained demonstrate that under the conditions of these ex- 
periments manganese may be substituted for magnesium in Azotobacter 
M nd presumably also in B. radiobactcr and B. prodigiositm, the time 
during which the rate of growth of these bacteria was ascertained was 
so abnormal, that is, two and five months respectively, that the conclu- 
sions have only limited value A further objection to these experiments 
is that no cultures with both manganese and magnesium added were 
included, so that it cannot be concluded to what extent the growth in 
the solution with either magnesium or manganese may be considered 
as normal. 

Although it is not the purpose of the authors to give a detailed re- 
view of all the enzymatic reactions described in the literature in which 
manganese may function as a cof actor, some of the reactions which arc 
of fundamental importance in higher and lower plants will be reported 
here. In addition an attempt will be made to connect the results of 
these enzymatic studies with those of plant physiological and bacterio- 
logical investigations 

It has been shown that manganese catalyzes not only various reactions 
of carbohydrate breakdown and organic acid metabolism but also a 
number of important conversions involved in nitrogen metabolism and 
phosphorus metabolism 

1. Manganese hi Relation lo Carbohydrate Breakdown 

a. Glycolysis. The breakdown of carbohydrates to tricarbonic acids 
(glycolysis) by the cells of higher plants, microorganisms, and anim-il 
cells occurs in a number of graded steps, each of which is catalyzed by 
different enzymes. Some of these reactions are activated by manganese, 
magnesium, or cobalt ions, namely, phosphoglucomutasc, which catalyzes 
the interconversion of glucnse-1-phosphate and glucose-6-phosphate, and 
enolase, which catalyzes the formation of phosphoenolpyruvate from 
D-2-phosphogly cerate. Mg+ + , Mn + + , or Zn + + are active as a cof actor 
in this case (see the review of Lardy, 1949). Tn fermentation experi- 
ments with purified apozymase from Raccharamyces ccrcvisiae, Nilsson 
et al. (1942) observed practically no breakdown of glucose to ethanol 
and carbon dioxide in the absence of either manganese or magnesium. 
Both metals gave about the same activation Optimal activity was ob- 
tained with 0.01 M MnClo. 

b. Organic Acid Metabolism. It is a well-known fact that organic 
acids play an important role in cell respiration as well as in the reverse 
process, carbon dioxide assimilation. The former process, the breakdown 
of the end products of glycolysis to carbon dioxide and water, proceeds 


through a number of enzymatic reactions involving different organic 
acids known as the Krebs cycle (Green, 1949; Bonner, 1950). Although 
these reactions have been studied in detail mainly in animal tissues and 
tissue extracts and in microorganisms, there is both direct and indirecl 
evidence available that similar reactions occur in higher plants. 

One of the important enzymes of the tricarboxylic acid cycle of Krebs, 
isocitric dehydrogenase, which catalyzes the transformation of isocitric 
acid to a-ketoghitaric acid, requires either Mn' 1 j ' or Mg++ (von Euler 
ct al., 1989; Adler ct al., 1939; Ochoa, 1948). This conversion proceeds 
in two steps : 

isocitrio dpliydrogcMiaso 
i> Tsocitric acid-fTPNox < ^_ Oxalosuce-imc acid-f- r JTN ro ,i ( 1 ) 

oxaloNurcmir cjirboxylase 

Oxalosuccinic acrid < ^ a-Kctoglutaric acid-j-C() 2 (2) 


Reaction (1 ) depends on the presence of triphosphopyridine nucleotide 
CTPN). According to Ochoa, Mn + + is required for reaction (2) and 
not for d). Since both reactions (1) and (2) are reversible, this sys- 
tem perhaps can play an important part in the biological fixation of 
carbon dioxide as a first step in photosynthesis. 

The experiments of Ochoa have been carried out with extracts from 
animal tissues. Yon Euler el nl. (1939) have found the isocitric dehy- 
drogenase system in animals, yeasts, and higher plants. In the absence 
of Mg ++ or Mn++ the reaction does not proceed. The activity of Mg + + 
was found to be less than that of Mn + + . The optimal concentration of 
Mn + + is 5.10- 4 M, and that of Mg++ is 2.5.10- 3 M (extract of animal 
tissues). Berger and Avery (1944) investigated the isocitric dehydro- 
genase of the Avena coleoptile. It was shown to be activated by Mn, 
Mg, and Co ions and to a lower extent by Zn and Ni. In accordance 
with von Euler ct al. (1939) a Mn concentration of 5.10~ 4 M was found 
to be optimal. 

A further example of a carboxylase depending for its activity on 
manganese is the oxalacetic carboxylase studied in detail by Vennesland 
et al. (1949). This enzyme, which splits oxalacetic acid in pyruvate and 
carbon dioxide has been found in parsley root. Its activation by various 
cations has been studied by Speck (1949). In the absence of metal ions 
oxalacetic carboxylase from parsley roots was found to be nearly in- 
active. The optimal effect was obtained with Mn+ + at a concentration 
of 0.01 M. Ca + +, Co++, Cd++, and Zn++ showed also a notable effect 
while Pb++, Ni++, Fe++, Mg++, Cu++, and Ba++ acted only slightly. 

The preparation of oxalacetic carboxylase from a number of different 


plants (wheat germ, carrot, beet, spinach, parsley, parsnip, peas) in- 
variably showed the capacity of catalyzing the reversible reaction : 

L-Malate-{-TPN ox ^ x Pyruvate-f- CO 2 -f-TP]Sr rfld (3) 

an activity referred to as "malic enzyme." This reaction, which may 
be of great importance in the fixation of carbon dioxide, is catalyzed by 
Mn++ as well as Co+ + (Conn, Vennesland, and Kraemer, 1949). 

A manganese-activated "malic enzyme" system in animal tissues has 
been described by Ochoa et al. (1948; see also Salles et aL, 1950). 

The malic enzyme system has recently been studied in connection 
with carbon dioxide assimilation of green plants (Vishniac and Ochoa, 
1951; Tolmach, 1951; Arnon, 1951). It was shown that illuminated 
isolated chloroplasts may greatly enhance the carbon dioxide fixation in 
the malic enzyme reaction (3). This effect apparently is due to the 
photochemical reduction of TPN by the illuminated chloroplasts as a 
result of which reaction (3) is shifted to the left. It is questionable, 
however, whether this reaction represents a true model of photosynthesis 
since the photochemical reduction of TPN or DPN may also be coupled 
with other reactions which require the presence of the reduced pyridine 

In addition to the enzymatic reactions described above many more 
dealing with organic acid metabolism which are activated by manganese 
may be found in the biochemical literature. 

2. Manganese in Relation to Nitrogen Metabolism 

The activity of manganese as a cof actor in enzymatic reactions is not 
limited to the carbohydrate and organic acid metabolism, but is of similar 
importance in the nitrogen metabolism of plants and animals. Many of 
the simple peptidases of plants, microorganisms, and animals do not 
operate in the absence of metallic ions. These may be manganese ions 
but also cobalt, ferrous, or magnesium ions. L-Leucine-aminoexopepti- 
dase, a peptidase which splits L-leucylglycine and other L-leucine con- 
taining di- and tripeptides is activated by manganese and magnesium, 
(Smith and Bergmann, 1944; Smith, 1951). Apparently high concentra- 
tions of these cations are required to give full operation of the reaction. 
It was observed that the effect of manganese on the activity of peptidase 
was considerably greater when enzyme and cations were incubated to- 
gether for some time before the substrate was added. This indicates that 
the metal reacts with the enzyme protein in forming the active enzyme. 

The peptidase which hydrolyzes glycylglycine is specifically activated 
by cobalt and to a much smaller degree by manganese (Maschmann, 


1941; Smith, 1951). In this case, however, no time lag in the activation 
of glycylglycine dipeptidase by cobalt has been observed. It was found 
that cobalt formed a complex with the dipeptide. From these and a 
number of similar observations it was suggested (Smith, 1951) that the 
role of the metal ion in the enzyme system could be explained by assum- 
ing an interaction of this ion with the substrate on one hand and with 
the protein on the other. 

Very interesting is the observation by Bamann and Schimke (1941a, 
b) that the "L-peptidase" activity of animal and plant tissues may be 
increased by both Mn and Mg ions whereas the "D-peptidase" reaction 
is activated by Mn++ but not by Mg++. In their experiments the au- 
thors tested seedlings of lentil, peas, oats, wheat, barley, and rye ; leucyl- 
glycine was used as the substrate in the enzyme reactions. (For a 
review of the literature on metal activated peptidases see Smith, 1951 
and also Hewitt, 1951). 

Further manganese-activated enzymes which play a part in the nitro- 
gen metabolism of plants are arginase and glutamyl transphorase. Argi- 
nase splits the amino acid arginine into ornithine and urea. It may be 
activated by Mn+ + , Co+ + , Ni++, or Fe" 1 j (Hellermari and Perkins, 
1935; Stock, Perkins, and Hellerman, 1938; Anderson, 1945; Folley and 
Greenbaum, 1948; Greenberg, 1951). 

Glutamyl transphorase plays a part in the amide metabolism of 
plants. It has been found to catalyze the reaction : 

Glutamine -f- Hydroxylamine >- Glutamohydroxamic acid -f- Ammonia 

ATP (adenosinetriphosphate) or ADP (adenosinediphosphate), 
phosphate or arseriate, and manganese (not replaceable by magnesium, 
zinc, copper, ferrous iron, aluminum, or cobalt) are essential compo- 
nents of the complete system. The enzyme has been isolated from seed- 
lings of Cucurbita pepo (Stumpf et al., 1951). It has been found 
present in a wide variety of algae and plants, particularly in nodules 
of clover and lupine. The same enzyme system has been found to cata- 
lyze the exchange of isotopic ammonia with the amide group of gluta- 
mine (Delwiche et al., 1951). 

The question may be raised whether the observed effect of manganese 
on the above-mentioned enzymatic reactions may explain the results of 
those investigations in which the relation between manganese nutrition 
and nitrogen metabolism has been studied in vivo. In experiments with 
excised roots of wheat plants and with macerated roots, Burstrom 
(1939, 1940) has shown that the rate of nitrate assimilation may be 
increased considerably by addition of small amounts of manganese to 
the nutrient solution. Since manganese has an activating effect on the 


so-called basal respiration of wheat roots (Luiidegardh, 1939), the 
beneficial effect of added manganese on both nitrate assimilation and 
basal respiration of roots may be a result of a manganese-activated 
enzymatic reaction of the glycolysis or tricarboxylic acid system. 

Nance (1948), in experiments with wheat roots, failed to demonstrate 1 
a stimulating 6ftV<t of manganese on nitrate reduction. This may have 
been due to a higher manganese content of the seed than was the case 
in the experiments of Burstrom (1939). Jones ct aL (1949) in culture 
solution experiments with soybeans observed an accumulation of nitrite 
in the nutrient solution when 110 manganese was added. The plants 
developed yellow leaves, ascribed by the authors to nitrogen deficiency. 
Supplied with small amounts of manganese, no nitrite accumulated, and 
the plants were green and healthy. These results would indicate that 
manganese activates the reduction of nitrate to nitrite. The presence of 
nitrite in culture solutions of plants deficient in manganese has also been 
observed by Evemnami and Aberson (1927) and Gerretsen (3937). 
The latter author, however, ascribes its presence to the fact that the roots 
and especially the root tips of manganese-deficient plants are easily at- 
tacked by microorganisms which in the presence of decaying organic 
material easily reduce nitrate to nitrite. 

From the fact that spinach plants, growing in nutrient solutions with 
either ammonium or nitrate nitrogen, showed no substantial difference in 
manganese deficiency, Friederichsen (1944) concluded that manganese 
plays no part in nitrate reduction of this plant. Alberts-Dietert (1941) 
studied the effect of manganese on growth of Chlorella in culture solu- 
tions with different nitrogen compounds. In the absence of added man- 
ganese, nitrate and ammonium nitrogen gave the same effect when 
Chlorella was grown under autotrophic conditions. In the presence of 
glucose, however, nitrate was found to be inferior to ammonium salts, 
apparently owing to a poorjiitrate reduction. Supplied with manganese 
this difference was not observed. These results would indicate that 
under autotrophic conditions the effect of manganese deficiency on 
nitrate reduction was overshadowed by its effect on carbon dioxide 

High concentrations of nitrate in manganese-deficient plants have 
been recorded by Leeper (1941) and Hewitt et aL (1949). Although 
these results in accordance with those of Burstrom (1939) may indicate 
a possible function of manganese in nitrate reduction, it may also be 
explained by assuming a reduced carbohydrate content in manganese- 
deficient plants as a result of a poor carbon dioxide assimilation (see 
Gerretsen, 1949). 

Hewitt et al. (1949) in the case of manganese-deficient cauliflower 


found an accumulation of nitrate as well as of amino acids, particularly 
aspartic and glutamic acids, in young leaves. These results are hard to 
reconcile with the postulated role of manganese in nitrate reduction. 
They may indicate, however, that the function of Mn may be sought in 
catalyzing some reaction in the chain between amino acids and protein, 
e.g., the above-mentioned activity or the glutamyl transphorase 
The accumulation of nitrate possibly might result from the accumulation 
of amino acids. The results of Hewitt ct al. (1949) are in agreement 
with earlier investigations by Friederichsen (1944) who showed that 
manganese-deficient spinach leaves had a considerably higher ammonia 
and amino acid content than leaves from normal plants ; nitrate was also 
higher in manganese-deficient leaves, but the difference was much less 
pronounced than in the roots. The protein content was slightly lower 
in manganese-deficient plants Gerretsen (1936, 1937) found also a 
higher ammonia content in manganese-deficient leaves of oats than in 
normal plants. 

The effect of manganese in comparison with that of iron and molyb- 
denum on the assimilation of nitrate in excised wheat roots has been 
studied recently by Burstrorn (1949) in inhibition experiments with 
di-n-amylacetie acid This substance in concentrations as low as 1()~ M 
was found to be able to inhibit nitrate assimiliation almost completely. 
Addition of manganese or iron in amounts of 5 p.p.m. restored the ni- 
trate assimilation, whereas molybdenum had no effect. From these experi- 
ments it may be concluded that manganese activates a reaction in wheat 
roots essential for the nitrate assimilation which may be blocked by 
di-n-amylacetic acid These results need not to be in conflict with the 
view of the senior author that molybdenum has to be considered as an 
essential element in the reduction of nitrate by AspcrgMus niger, denitri- 
fying bacteria, and green plants (Mulder, 1948). Molybdenum which 
exerts its activity in concentrations a thousand times smaller than those 
employed for manganese has undoubtedly been present in adequate 
amounts in the roots employed by Burstrom. At least two views exist : 
(a) both manganese and molybdenum are essential for nitrate assimila- 
tion in roots of wheat ; (b) the mechanism of nitrate assimilation of 
roots is different from that of leaves of higher plants and that of micro- 
organisms. The latter concept apparently holds for Aspergillus niger, 
which according to unpublished experiments by the senior author does 
not require Mn for nitrate reduction. 

The view that at least two different mechanisms of nitrate assimila- 
tion exist in green plants is in accordance with the results of recently 
published investigations by Mendel and Visser (1951). These authors 
demonstrated that the nitrate reduction which occurs in tomato leaves 


in the dark is dependent upon respiration for a source of energy, while 
in the light the reduction may well be independent of respiratory proc- 
esses with the necessary energy supplied by light. This was concluded 
from the fact that iodoacetate, a well-known inhibitor of cell respiration, 
almost completely inhibited nitrate reduction in the dark, whereas it 
was completely without effect in the light. 

3. Manganese Nutrition and Ascorbic Acid Content 
of Plants and Animals 

The question whether manganese may affect the formation of ascorbic 
acid in plants and animals cannot be answered definitely. In a number 
of investigations pronounced differences in ascorbic acid content between 
manganese-deficient and normal plants have been found. Several other 
workers, however, were not able to confirm these results. 

The first observation of a beneficial effect of manganese on the 
ascorbic acid content of plants was made by Rudra (1939a) lie investi- 
gated the effect of dilute solutions of manganese sulfate and manganese 
chloride on germinating seeds of Cicer arietinum, Phaseolus mungo, 
wheat, barley, and oats. After six days germination considerably higher 
values for ascorbic acid were found in the manganese-treated seedlings 
of Cicer and the cereals than in those germinated in water. The optimal 
concentration of manganese was found to be 0.001 per cent in the case 
of Cicer and 0.01 per cent with the cereals. In a further paper the same 
author (1939b) claims that the inability of guinea pigs to synthesize 
ascorbic acid may be attributed to insufficient manganese in the tissues 
of these animals. Simultaneous injection of mannose and manganese 
was found to increase the ascorbic acid content of some tissues, particu- 
larly liver and jejunum. Without manganese, mannose would not affect 
the ascorbic acid content (see also Rudra, 1944). These experiments 
have been repeated by Skinner and McHargue (1946) with scorbutic as 
well as normal guinea pigs. No effect of injections of mannose and 
manganese on the scorbutic condition of the animals nor on the amount 
of indophenol-reducing substances of their livers was observed by these 

In another paper Rudra (1943) described on slender evidence the 
occurrence of a manganese-activated hexose dehydrogenase in the small 
intestines of animals, which would be able to produce ascorbic acid from 

In experiments with tomatoes growing on manganese-deficient soils 
Hester (1941) observed an increased content of ascorbic acid in the 
fruits from plants treated with manganese. These results have not been 
confirmed by Lyon et al. (1943), who in carefully controlled nutrient 


solution experiments found manganese-deficient tomatoes as rich in 
ascorbic acid as fruits from control plants. A similar negative effect 
was obtained by Gum et al. (1945). The ascorbic acid contents of 
neither the foliage nor the fruit of tomatoes, growing in nutrient solu- 
tions, showed any consistent differences with manganese treatment. In 
contrast to these results, von Bronsart (1950) in Germany obtained 
consistently higher values for ascorbic acid (sum of reduced and oxidized 
forms) in tomatoes from manganese-treated plants than in the fruits 
from untreated control plants. 

A positive effect of manganese additions or sulfur treatments of 
manganese-deficient soil on growth and ascorbic acid content of spinach, 
Sudan grass, and oats has been reported by Harmer and Sherman 
(1943). In Sudan grass and oats the reduced form of ascorbic acid 
was affected mainly, whereas in spinach the oxidized form was increased 
to a very large extent by an improved manganese supply. Rangnekar 
(1945) found a notably higher concentration of ascorbic acid in the 
leaves of manganese-treated Amaranihus gangcticus than in the leaves 
of control plants. 

Maton (1947), working in Hoagland's laboratory, found a remark- 
able effect of the manganese supply to some plants growing in culture 
solutions on the ascorbic acid content of their leaves. In sunflower 42 
ftg. ascorbic acid per gram fresh weight of leaves was found in the 
absence of manganese against 74 /u,g. in leaves of plants supplied with 
0.125 p.p.m. of Mn. In tobacco the differences were even more pro- 
nounced : 20 /Ag. per gram fresh weight of Mn -deficient leaves against 
145 /Ag. in leaves of manganese-supplied plants. Tomatoes on the other 
hand did not show any difference in ascorbic acid content of the leaves 
at different manganese levels notwithstanding the occurrence of great 
differences in total yield. 

No correlation was found by Hivon et al. (1951a) between manganese 
nutrition of soybeans grown in the field and ascorbic acid content of 
the leaves. In an extensive nutrient solution experiment with green pod 
beans the same authors (1951b) determined ascorbic acid (reduced 
form) in the leaves of manganese-deficient and normal plants at 27, 34, 
41, 48, 55, 62, and 69 days from planting. At 30 days the plants with 
restricted manganese showed definite chlorosis which became increasingly 
severe at later sampling date. No effect of manganese supply on ascorbic 
acid content occurred. 

The discussion of the above-mentioned papers clearly demonstrates 
the great lack of uniformity in the results obtained by the various au- 
thors. Although several workers have reported definitely negative 
results, the number of papers in which a positive effect has been shown 


is too large to deny the effect which, under certain circumstances, man- 
ganese may have on the ascorbic acid content of green plants. Since 
weather conditions, notably illumination, have been shown to be of great 
importance in controlling ascorbic acid content of plants, it may be pos- 
sible that they play an important part in affecting the manganese- 
ascorbic acid relationship. This point is also stressed by Hamner (1945) 
in a discussion of minor element-vitamin relationships in plants. The 
fact that some authors are working under field conditions and others 
under greenhouse conditions, either with nutrient solution cultures or 
with soils, may also be considered as a point which deserves more 

The relationship between manganese and the content of some other 
vitamins or vitaminlike substances has been studied in a few cases only. 
Gum ci al. (l!)4f>) found lower concentrations of carotene in manganese- 
deficient tomato leaves than in those from normal plants. The fruits of 
these plants showed no differences For riboflavin slightly lower values 
were found in the leaves and fruits from manganese-deficient tomato 
These results are in accordance with those of Burger and Hauge (1951), 
who analyzed manganese-deficient and normal soybean plants for caro- 
tene, choline, and tocopherol (vitamin E). Plants from manganese- 
deiicient soil which exhibited symptoms of chlorosis and necrosis were 
found to be notably lower in carotene and tocopherol, but higher in 
choline. A similar beneficial effect of manganese treatment on carotene 
content of the leaves was found in wheat and oats. 

i. The Hole of Manganese in Photosynthesis 

The evidence is increasing that manganese is an essential Constituent 
of the photosynthetic apparatus in green plants. In this connection it 
is interesting to note that as early as 3924 Ililtner in his extensive in- 
vestigations on gray speck .disease of oats relates two remarkable experi- 
ments, which hitherto received little attention. (1) Increasing carbon 
dioxide assimilation of oat plants by enriching the surrounding atmos- 
phere with carbon dioxide was found to prevent the outbreak of the 
gray speck disease on a manganese-deficient soil ; reducing the carbon 
dioxide content of the air aggravated the symptoms (see Table II). (2) 
Reducing the carbon dioxide assimilation by shading the plants also inten- 
sified the Mn-deficiency symptoms, whereas the effect of manganese 
additions was much more pronounced on the shaded plants than on the 
plants grown in normal daylight. Both experiments point to an inti- 
mate connection between carbon dioxide assimilation and manganese 
activity in the plant. 

A quarter of a century later Gerretsen (1949) showed that CO 2 


(After Hiltner, 1924) 


Number of 
Treatment Grains 

Total Dry 
Weight, g. 


O Mn, no CO 2 added * 


Pronounced Mn- 
deficiency symptoms 

-f Mn, no CO 2 added * 



No symptoms after 
the appearance of 
the fourth leaf 

() Mn, CO 2 added 



No symptoms at all 

-f Mn, CO 2 added 



No symptoms at all 

* Reduced COr content ot the air. 

assimilation of leaves from oat plants, grown on manganese-deficient 
soil or in culture solutions poor in manganese, is reduced to 25-40 per 
cent of the normal rate. As special care had been taken not to use 
leaves which were chlorotic or which showed any pronounced outward 
signs of manganese deficiency, it is unlikely that in this case chlorosis 
had been the cause of a reduction of the photosynthetic activity by 60-75 
per cent. 

To investigate the role manganese eventually plays in photosynthesis, 
Gerretsen (1950a, 1951) used cell-free watery suspensions of crushed 
oat leaves in which he determined the redox potential in the dark and 
during illumination. 

It was shown that the change of the E h upon illumination was much 
more pronounced with normal leaf material than was the case with 
manganese-deficient leaves. The addition of small amounts of manga- 
nese as MnS0 4 in the latter case restored the E h changes to normal 
values. Addition of manganese to normal leaf extracts in the dark had 
no effect, but upon illumination the potential rose with 100 to 150 mv. 
to values which make the formation of peroxides and in particular 
hydrogen peroxide highly probable. 

Addition of trivalent iron had the opposite effect the equilibrium 
Fe + + + ^ Fe ++ was shifted to the right by illumination and to the 
left in the dark. Gerretsen concluded that in the plant a photosensitive 
oxidation-reduction system exists in which manganese and iron act as 
complementary oxidation-reduction agents. They keep each other in 
equilibrium at a fixed potential during illumination and at another 
potential in the dark. As the potential of such a combination is deter- 
mined in the first place by the ratio of the components and much less 
by the absolute quantities, it is evident that an excess of one element 
over the other is likely to disturb the oxidation-reduction equilibrium 


in the plant. As early as 1930 Hopkins suggested that manganese tends 
to control the ratio Fe+ + + z Fe+ + in the cell, and in a more recent 
paper he and his co-workers are led to believe that the interaction of 
manganese, iron, and light controls to a large extent the oxidation- 
reduction potential of green plants (Hopkins et a/., 1944). Thatcher 
(1934) grouping the elements according to their function in the plants 
placed Mn and Fe amongst the oxidation-reduction regulators and called 
them "mutually coordinating catalysts for oxidation-reduction re- 

In this connection the observation of Shive (1941), Somers, Gilbert, 
and Shive (1942), and Somers and Shive (1942) that the dry weight of 
their soybean plants was related to the iron-manganese ratio and not 
so much to the absolute concentrations of the elements seems to fit very 
well into this scheme. 

Although several workers repeating the experiments of Shive and 
his collaborators were unable to confirm their results as to the narrow 
ratio of iron to manganese required for optimal growth, most of them 
observed an antagonizing effect of manganese on iron (see Sec. VIII). 

The scope of this review does not permit us to go into details of the 
complicated photochemical reactions which constitute photosynthesis. 
It will suffice to say that by virtue of his experiments Gerretsen (1950a) 
assumes that in the dark manganese and iron exist respectively in the 
divalent and trivalent forms. Owing to illumination, under absorption 
of light energy, the situation becomes reversed and now Mn+~ h ~ f and 
Fe+ + cooperate in the photolysis of water, which is regarded as the 
first step in photosynthesis. The ultimate effect is that Mn+ + + accepts 
one electron from OII~, (H 2 ?= Oil" +H 4 ) which becomes a OH 
radical. The manganese ion is reduced to Mn + +, whereas the OH 
radical finally gives rise to the evolution of oxygen (2OII ^O 2 + II^O). 
At the same time, by light induced electron transfer, Fe++ cedes an 
electron to H+ , which becomes a highly reactive H atom, the iron being 
oxidized to Fe+ + +. The H atom immediately combines with an inter- 
mediate acceptor to a more stable HX reduction product, which will be 
used in the formation of carbohydrates. Manganese and iron are now 
back in their original valency states, and the process can start anew. 

It should be stressed that other workers demonstrated the importance 
of manganese in the fixation of carbon dioxide in certain light-induced 
reactions. Apparently the reduced carbon dioxide assimilation as ob- 
served by Gerretsen in manganese-deficient oat leaves may be due to 
reduced primary photochemical reactions or to reduced activity of en- 
zymes of the tricarboxylic acid cycle or to both. 

The fact that manganese deficiency, iron deficiency, and manganese 


toxicity are all accompanied by chlorosis does not imply that the cause 
of this chlorosis is the same in all these cases. In the latter two cases 
the junior author is inclined to ascribe the chlorosis to photooxidation 
of chlorophyll, which is a secondary effect of the rapid destruction of 
the protective protein substances surrounding the chloroplasts, in con- 
sequence of the high redox potentials which are characteristic for the 
illuminated Mn-Fe redox systems in the plant, when Mn is in excess 
(Gerretsen, 1950b). 

This view is supported by the fact that injury due to manganese 
excess is greater in more intense light, which has been observed by dif- 
ferent workers, McCool (1913, 1935), Hopkins d al. (1944), Morris and 
Pierre (1949), whereas Qericke (1925) reports that wheat plants grow- 
ing in solutions deficient in iron showed excellent growth and normal 
green color in the shade and little growth and chlorosis in bright sun- 

Accepting reduced carbon dioxide assimilation as one of the main 
consequences of manganese deficiency enables us to interpret a number 
of divergent characteristic symptoms from a central point of view. 

1. The reduced content of sugar and starch in the leaves of oat plants 
(McHargue, 1926) and of tomatoes (Eltinge, 1941) deficient in manga- 
nese is a direct result of reduced photosynthesis. 

2. The same holds true for the retardation of growth, the smallness 
and slackness of the leaves, the weakness of the leaf ribs which causes 
the leaves to drop over with a kink. 

3. Reduced frost resistance (Gerretsen, 1949; Lloyd Frisbie, 1947) 
is closely related to the turgescence of the cells and the latter to the 
content of sugars in the cell sap. 

4. The presence of large quantities of nitrates in the leaves of manga- 
nese-deficient oat plants and canary grass as observed by Leeper (1941) 
fits well into the scheme, as it is obvious that accumulation of inorganic 
nitrogen must take place in leaves, in which insufficient carbohydrates 
are synthesized to combine with the nitrogen to build up proteins. 

5. The entrance of toxic substances into the cells of manganese- 
deficient oat leaves (Gerretsen, 1937) with subsequent loss of turgescence 
and poisoning of the protoplasts is closely linked with increased permea- 
bility of the cell walls and the reduced size of the protoplasts due to lack 
of assimilates. 

6. The reduced volume of the root system (Gerretsen, 1937; Hasler, 
1951) and the susceptibility to invading saprophytic microorganisms 
can also be traced back to shortage of carbohydrates, the multiplication 
of the cells in the meristematic zone being much slower, as well as the 


rejuvenation of the root cap tissue, which determines its protective 

7. By increasing the carbon dioxide content of the surrounding air 
gray speck disease symptoms may be reduced or even disappear (Hilt- 
ner, 1924) ; in this case the increase of carbon dioxide assimilation 
neutralizes the decrease due to manganese deficiency. 

8. Manganese-deficiency symptoms are aggravated by shading the 
plants ; in this case reduced photosynthesis is further reduced by dimin- 
ishing light intensity, which inevitably leads to a change for the worse. 


Adler, E., Euler, II. v., Giinther, G., and Plans, M. 1939. Biochem. J. 33, 1028-1045. 
Alberts-Dietcrt, F. 1941-42. Planta 32, 88-117. 

Albrocht, W. A., and Smith, N. 0. 1941. Bull Torrcy Botan. Club 68, 372-380. 
Alton, F., and Woiland, H. 1938. Z. Pflanzeneriuihr. Ihmgung u. Bodenk. A 30, 


Anderson, A. B. 1945. Biochem. J. 39, 139-142. 
Arnon, D. I. 1951. Nature 167, 1008-1010. 
Bamann, E., and Schimke, O. 1941a. Bwchcm. Z. 310, 119-130. 
Bamanii, E., and Schimke, O. 19411). Bwchem. Z. 310, 131-151. 
Beeson, K. C., Gray, L., and Adams, M. B. 1947. J. Am,. Soc. Agron. 39, 356-362. 
Beijerinck, M. W. 1913-14. Proc. Set. Sect. Koninll. Alcad. Wetenschap. Amsterdam 

16, 397-401. 

Bentley, O. G., Snell, E. E., and Phillips, P. H. 1947. J. Biol Chem. 170, 343-350. 
Berger, J., and A very, G. 8. 1944. Am. J. Botany 31, 11-19. 
Berger, K. C., and Gcrloff, G. C. 1947a. Soil Set. Soc. Am. Proc. 12, 310-314. 
Berger, K. C., and Gerloff, G. C. 1947b. Am. Potato J. 24, 156-162. 
Bertrand, G. 1905. Compt. rend. 141, 1255-1257. 
Bertrand, G., and Javillier, M. 1912. Ann. Inxt. Pasteur 26, 241. 
Boischot, P., and Durroux, M. 1949. Compt. rend. 229, 380-381. 
Boken, E. 1952. Plant and Soil 4, 154-163. 

Bonner, J. 1950. Plant Biochemistry. Academic Press, New York. 
Bortner, C. E. 1935. Soil Sci. 39, 15-33. 

Bromfield, S. M., and Skerman, V. B. P. 1950. Soil Set. 69, 337-348. 
Bronsart, H. v. 1950. Z. Pflanzenernahr. Dungung u. Bodenk. 61, 153-157. 
Burger, O. J., and Hauge, S. M. 1951. Soil Sci. 72, 303-313. 
Burstrom, H. 1939. Planta 29, 292-305. 
Burstrom, H. 1939-40. Planta 30, 129-150. 
Burstrom, H. 1949. Arch. Biochem. 23, 497-499. 

Burstrom, H., and Boratynski, K. 1936. Lanfbruks-Hbgslcol. Ann. 3, 147-168. 
Camp, A. F., Chapman, H. D., Bahrt, G. M., and Parker, E. E. 1944. In Hambidge, 

G., Hunger Signs in Crops. Am. Soc. Agron. and Natl. Fertilizer Assoc., 

Washington, D. C. 

Clausen, H. 1910. Mitt. deut. Landw. Ges. 25, 631-639. 
Coic, Y., and Coppenet, M. 1949. Compt. rend. 228, 1379-1381. 
Coi'c, Y., Coppenet, M., and Voix, 8. 1950. Compt. rend. 230, 1610-1611. 
Conn, E., Vennesland, B., and Kraemer, L. M. 1949. Arch. Biochem. 23, 179-197. 


Coppenet, M. 1949. Ann. Agron. 19, 798-800. 

Cornfield, A. H., and Pollard, A. S. 19.10. J. Sci. Food Agr. 1, 107-109. 

Dclwichc, C. C., Loomis, W. D., and Stumpf, P. K. 1951. Arch. Biochcm. Bwphys. 

33, 333-338. 

Deniges, G. 1932. Compt. rend. 194, 895-897. 

Dickey, R. D., and Reuther, W. 3938. Florida Apr. Expt. Sta. Bull. 319. 
Dion, H. O., and Mann, P. J. G. 1946. J. Agr. Sci. 36, 239-245. 
Dion, F. G., Mann, P. J. G., and Ileintze, S. G. 1947. J. Agr. Sci. 37, 17-22. 
Drosdoff, M., and Nikiforoff, C. C. 1940. Soil Sot. 49, 333-345. 
Eltinge, E. T. 1941. Plant Physiol. 16, 189-195. 
Epstein, E., and Stout, P. R. 1951. Soil Sci. 72, 47-65. 
Erkama, J. 1947. Uber die Eolle von Kupfor und Manga n im Leben der hoheren 

Pflanzen pp. 105. Thesis, Univ. of Helsinki. 

Euler, II. v., Adler, E., Gunther, G., and Elliot, L. 1939. Ensymologia 6, 337-341. 
Eversmann, F., and Aberson, J. A. 1927. Landbouwkund. Tijdschr. 39, 270-293. 
Folley, S. J., and Greenbaum, A. L. 1948. Biochcm. J. 43, 537-549. 
Friederichsen, I. 1944. Planta 34, 67-87. 

Fujimoto, C. K., and Sherman, G. D. 1948. Soil Sci. 66, 131-145. 
Gallagher, P. H., and Walsh, T. 1943. J. Agr. Sci. 33, 197 203. 
Gates, E. M., and Ellis, G. II. 1947. J. Biol. Chcm. 168, 537-544. 
Gaumann, E. 1946. Pflanzliche Infektionslehve. Basel, pp. 611. 
Gericke, W. F. 1925. Botan. Gaz. 79, 106-108. 
Gerretsen, F. C. 1936. Verslagen Landbouwk. Oiiderzockingen R. L. P. &., 

Groningen 42a, 1-67. 

Geiretsen, F. C. 1937. Ann. Botany 1, 207-230. 
Gerretsen, F. C. 1949. Plant and Soil 1, 346-358. 
Gerretsen, F. C. 1950a. Plant and Soil 2, 159-193. 
Gerretsen, F. O 1950b. Plant and Soil 2, 323, 343. 
Gerretsen, F. C. 1951. Plant and Soil 3, 1-31. 
Gisiger, L., and Hasler, A. 1948. Plant and Soil 1, 18-50. 
Goodall, I). W. 1949. Ann. Applied Biol. 36, 26-39. 
Green, D. E. 1949. In Lardy H. A., Respiratory Enzymes. Burgess Publishing Co., 

Greenberg, D. M. 1951. In Rummer, J. B., and Myrback, C. K., The Enzymes. 

Academic Press, New York. Vol. T, Pt. 2, pp. 893-921. 

Gum, O. B., Brown, H. D., and Burrell, R. C. 1945. Plant Phyftiol. 20, 267-275. 
Hale, J. B., and Heintze, S. G. 1946. Nature 157, 554. 
Hamner, K. C. 1945. Soil Sci. 60, 165-171. 

Harmer, P. M., and Sherman, G. D. 1943. Soil Sci. Soc. Am. Proc. 8, 346-349. 
Hasler, A. 1951. Schwnz. landw. Monatsh. 29, 300-305. 
Heidel, R. H. 1946. Proc. Iowa A cad. Sci. 53, 211-223. 
Heintze, S. G. 1946. J. Agr. Sci. 36, 227-238. 
Heintze, S. G., and Mann, P. J. G. 1946. Nature 158, 791-792. 
Heintze, S. G., and Mann, P. J. G. 1947. /. Agr. Sci. 37, 23-26. 
Heintze, S. G., and Mann, P. J. G. 1949. J. Agr. Sci. 39, 80-95. 
Hellerman, L., and Perkins, M. E. 1935-36. J. Biol. Chcm. 112, 175-194. 
Heslep, J. M. 1951. Soti Sci. 72, 67-80. 
Hester, J. B. 1941. Science 93, 401. 
Hewitt, E. J. 1945. Ann. Kept. Agr. Hort. Research Sta. f Long Ashton, Bristol, 



Hewitt, E. J. 1946. Ann. Kept. Agr. Hort. Research Sta., Long Ashton, Bristol, 

Hewitt, E. J. 1947. Ann. Kept. Agr. Hort. Research Sta., Long Ashton, Bristol, 

Hewitt, E. J. 1948a. Ann. Kept. Agr. Eort. Research Sta., Long Ashton, Bristol, 


Hewitt, E. J. 1948b. Nature 161, 489-490. 
Hewitt, E. J. 1948c. Ann. Rept. Agr. Hort. Research Sta., Long Ashton, Bristol, 


Hewitt, E. J. 1951. Ann. Rev. Plant Physiol. 2, 25-52. 

Hewitt, E. J., Jones, E. W., and William, A. H. 1949. Nature 163, 681-682. 
Hiltner, E. 1924. Landw. Jahrl). 60, 689-769. 

Hivon, K. J., Doty, D. M., and Quackenbush, F. W. 1951a. Soil Sci. 71, 353-359. 
Hivon, K. J., Doty, D. M., and Quackenbush, F. W. 1951b. Plant Physiol. 26, 832- 


Hopkins, E. F. 1930. Science 72, 609-610. 
Hopkins, E. F., Pagan, XL, and Ramirez-Silva, F. J, 1944. J. Agr. Umv. Puerto 

Rico 28, 43-101. 

Hudig, J. 1911. Landw. Jahrl). 40, 618-644. 

Hudig, J., and Meyer, C. 1919. Vcrslag. Landbouwk. Onderzonk. 23, 128-158. 
Hudig, J., Meyer, C., and Goodijk, J. 1926. Z. Pflanzenernahr. Dungung u. Bodenk. 

A 8, 14-52. 

Hurwitz, C. 3948. Soil Set. 66, 267-272. 

Jacobson, H. Q. M., and Swanback, T. K. 1932. J. Am. Soc. Agron. 24, 237-245. 
Johnson, M. O. 1917. /. 2nd. Eng. Chem. 9, 47. 
Jones, L. H. P., arid Leeper, G. W. 1950. Science 111, 463-464. 
Jones, L. H. P., and Leeper, G. W. 1951n. Plant and Soil 3, 141-353. 
Jones, L. H. P., and Leeper, G. W. 1951b. Plant and Soil 3, 154-159. 
Jones, L. II. P., Shppardsoii, W. B., and Peters, C. A. 1949. Plant Physiol. 24, 


Kelley, W. P. 1909. J. Ind. Eng. Chem. 1, 533-538. 
Kenten, H. H., and Mann, P. J. G. 1949. Biochem. J. 45, 255-263. 
Kwiten, K. II., and Mann, P. J. G. 1950. Bwchem. J. 46, 67-73. 
Kniphorst, L. C. E. 1946. Chem. Weekblad 42, 328-334. 
Lagatu, H., and Maume, L. -1932. Compt. rend. 194, 933-935. 
Lardy, H. A. 1949. In Lardy, H. A., Respiratory Enzymes. Burgess Publishing 

Co., Minneapolis. 

Looper, G. W. 1935. Proc. Roy. Soc. Victoria 47, 225-261. 
Leeper, G. W. 1941. J. Australian Inst. Agr. Sci. 7, 161-162. 
Leeper, G. W. 1947. Soil Set. 63, 79-94. 

Leeper, G. W., and Swaby, R. J. 1940. Soil Sci. 49, 163-169. 
Lloyd-Friable, 8. 1947. Citrus 2nd. 6, 15. 
Loew, 0. 1903. Landw. Jahrb. 32, 437-448. 
Lohnis, M. P. 1944-45. Antonie van Leeuwtnhoek 10, 101-122. 
Lohnis, M. P. 1946. Tijdschr. Plant enziekt en 2, 157-160. 
Lohnis, M. P. 1950. Lotsya 3, 63-76. 
Lohnis, M. P. 1951. Plant and Soil 3, 193-222. 
Lundegardh, H. 1939. Planta 29, 419-429. 
Lundegardh, H. 1951. Leaf Analysis. (Trans, by R. L. Mitchell) London, pp. 176. 


Lunt, H. A., Swanson, C. L. W., and Jacobson, H. G. N. 1950. Connecticut Agr. 

Expt. Sta. Bull. 541. 

Lyon, 0. B., Beeson, K. C., and Ellis, C. H. 1943. Botan. Gaz. 104, 495-514. 
McCool, M. M. 1913. Cornell Univ. Agr. Expt. Sta. Mem. 2, 171-198. 
McCool, M. M. 1935. Contrib. Boyce Thompson Inst. 7, 427-437. 
McHargue, J. S. 1922. J. Am. Chem. Soc. 44, 1592. 
McIIargue, J. S. 1926. J. Ind. Eng. Chem. 18, 172-175. 
McLachlan, J. I). 1941. Sci. Agr. 22, 201-207. 
McMurtrey, J. E. 1944. In Hambidge, G., Hunger Signs in Crops. Am. Soc. 

Agron. and Natl. Fertilizer Assoc. Washington, D. C. 
Mann, P. J. G., and Quastel, J. H. 1946. Nature 158, 154-156. 
Maschhaupt, J. G. 1934. Z. Pflamenernahr. Diingung u. Boderik. B 13, 313-320. 
Maschmann, E. 1941-42. Biochem. Z. 310, 28-41. 
Maton, J. 1947. Biologisch Jaarb. Koninklijlc. Natuurw. Genootsch. Doflonaea, Gent. 

14, 109-115. 

Mattson, S., Eriksson, E., Vahtras, K. 1948. Lanfbruks-Hogskol. Ann. 15, 291-307. 
Mayer, A. M., and Gorham, E. 1951. Ann. Botany 15, 248-263. 
Maz6, P. 1914. Ann. Inst. Pasteur 28, 21-46. 

Mendel, J. L., and Visser, D. W. 1951. Arch. Biochem. Biophyx. 32, 158-169. 
Millikan, C. R. 1947. J. Australian Inst. Agr. Sci. 13, 180-186. 
Millikan, C. R. 1949. Proc. Roy. Soc. Victoria 61, 25-42. 
Millikan, C. R. 1950. Australian J. Sci. Research B 3, 450-473. 
Millikan, C. R. 1951. Australian J. Sci. Research B 4, 28-41. 
Morris, H. D. 1948. Soil Sci. Soc. Am. Proc. 13, 362-371. 
Morris, H. D., and Pierre, W. H. 1947. Soil Sci. Soc. Am. Proc. 12, 382-386. 
Morris, H. IX, and Pierre, W. II. 1949. Agron. J. 41, 107-112. 
Mulder, E. G. 1938. Over de betekenis van koper voor de groei van planten en 

microorganismen. pp. 133 (Doctoral Thesis, Agricultural Univ. Wageningen, 


Mulder, E. G. 1948. Plant and Soil 1, 94-119. 
Nance, J. F. 1948. Am. J. Botany 35, 602-606. 
Nicholas, D. J. D. 1948. Chemistry & Industry 707-712. 
Nicholas, D. J. D. 1949. J. Hort. Sci. 25, 60-77. 
Nicholas, D. J. D. 1950. Proc. Fertilizer Soc. 10, 13-43. 

ISTiklas, H., and Toursel, O. 1941. Bodenk. u. Pflamenernahr. 23 (68), 357-360. 
Nilsson, R., Aim, F., and Burstrom, D. 1942. Arch. MicroUol. 12, 353-376. 
Nydahl, F. 1949. Ann. Chem. A eta 3, 144-157. 
Ochoa, S. 1948. J. Biol Chem. 174, 133-157. 

Ochoa, S., Mehler, A. H., and Kornberg, A. 1948. /. Biol. Chem. 174, 979-1000. 
0delien, M. 1948. Nord. Jordbr. ForsJc. 4, 711-721. Cited in Bibliography on 

Minor Elem. Chilean Nitrate Educ. Bur. N. Y., Vol. 2, 1951. 
Olsen, C. 1934. Biochem. Z. 269, 329-348. 
Ouellette, J. 1951. Sci. Agr. 31, 277-285. 
Parbery, N. H. 1943. Agr. Gas. N. S. Wales 54, 14-17. 
Piper, C. S. 1931. J. Agr. Sci. 21, 762-779. 
Popp, M., Contzen, J., arid Gericke, 8. 1934. Z. P flans enernahr. Dungung u. 

Bodenk. B 13, 66-73. 

Quastel, J. H., Hewitt, E. J., and Nicholas, D. J. D. 1948. J. Agr. Sci. 38, 315-322. 
Rademacher, B. 1935. Z. Ziicht. A 20, 210-250. 
Rangnekar, Y. B. 1945. Current Sci. (India) 14, 325. 


Richards, M. B. 1930. Analyst 55, 554-560. 

Riches, J. P. R. 1946. Nature 158, 96. 

Roach, W. A. 1944. Ann. Ecpt. East Mailing Research Sta. 43-60. 

Roach, W. A. 1946. J. Soc. Chem. Ind. 65, 33-39. 

Roach, W. A., and Roberts, W. O. 1945. Imp. Bur. Hort. Plantation Crops. No. 16, 

Rudra, M. N. 1939a. Bwchcm. Z. 301, 238-244. 

Rudra, M. N. 1939b. Nature 144, 868. 

Rudra, M. N. 1943. Nature 151, 641-642. 

Rudra, M. N. 1944. Nature 153, 743-744. 

Salles, J. B. V., Harrary, I., Banfi, R. F., and Ochoa, S. 1950. Nature 165, 675-676. 

Samuel, G., and Piper, C. S. 1928. J. Agr. South Australia 31, 696-705 and 789-799. 

Samuel, G., and Piper, C. S. 1929. Ann. Applied Biol. 16, 493-524. 

Schmchl, W. R., Peech, M., and Bradfield, R. 197)0. Soil Sci. 70, 393-410. 

Seckles, L. 1950. Lotsya 3, 119-141. 

Sherman, G. D., and llarmer, P. M. 1942. Soil Sci. Soc. Am. Proc. 7, 398-405. 

Sherman, G. D., McHargue, J. S., and Hodgkiss, W. S. 1942. J. Am. Soc. Agron. 
34, 1076-1083. 

Sherman, G. D., Tom, A. K. S., and Fujimoto, C. K. 1949. Pacific Sci. 3, 120-123. 

Shive, J. W. 1941. Plant Physiol. 16, 435-445. 

Sideris, C. P. 1937. Ind. Eng. Chem., Anal. Ed. 9, 445-446. 

Sideris, C. P. 1940. Ind. Eng. Chem., Anal. Ed. 12, 307. 

Sideris, C. P., and Young, II. Y. 1949. Plant Physiol. 24, 416-440. 

Sjollema, B., and Iludig, J. 1909. Verslag. Landbouwk. Onderzoek. 5, 29-157. 

Skinner, J. J. 1944. In Hambidge, G., Hunger Signs in Crops, Am. Soe. Agron. 
and Natl. Fertilizer Assoc. Washington, 1). C. 

Skinner, J. T., and McHargue, J. S. 1946. Am. .7. Physiol. 145, 566-570. 

Smit, J., and Mulder, E. G. 1942. Mededecl. Landbouwhoogc school Wagemngcn 46, 

Smith, E. L. 1951. In Edsall, J. T. ? Enzymes and Enzyme Systems. Harvard 
Univ. Press, Cambridge, Mass. 

Smith, E. L., and Bergmann, M. 1944. J. Biol. Chem. 178, 315-324. 

Smith, J. B. 1950. .7. Assoc. Offic. Agr. Chemists 33, 284-287. 

Sohngen, N. L. 1914. Zentr. Bakt. II 40, 545-554. 

Somers, I. I., Gilbert, S. G., and Shive, J. W. 1942. Plant Physiol. 17, 317-320. 

Somers, I. L, and Shive, J. W. 1942. Plant Physiol 17, 582-602. 

Speck, J. F. 1949. J. Biol -Chem. 178, 315-324. 

Steckel, J. E., Bertramson, B. R., and Ohlrogge, A. J. 1948. Soil Sci. Soc. Am. 
Proc. 13, 108-111. 

Steenbjerg, F. 1935. Tids. Planteavl. 40, 797-824. 

Steinberg, R. A. 1936. Am. J. Botany 23, 227-231. 

Stiles, W. 1946. Trace Elements in Plants and Animals, pp. 178, Univ. Press, Cam- 

Stock, C. C., Perkins, M. E., and Hellerman, L. 1938. J. Biol. Chem. 125, 753-769. 

Strickland, J. D. H., and Spicer, G. 1949. Ann. Chim. Acta 3, 517-542. 

Stumpf, P. K., Loomis, W. D., and Michelson, C. 1951. Arch. Bwchem. 30, 126-137. 

Thatcher, R. W. 1934. Science 79, 463-466. 

Thompson, S. G. 1944. Ann. Kept. East Mailing Research Sta. 119-123. 

Thornberry, H. H. 1950. Phytopath. 40, 419-429. 

Timonin, M. I. 1946. Soil Sci. Soc. Am. Proc. 14, 131-136. 

Timonin, M. I. 1950a. Sci. Agr. 30, 324-325. 


Timonin, M. I. 1950b. Trans. Intern. Congr. Soil Sci., 4th Congr. Amsterdam 3, 


Tolmach, L. J. 1951. Nature 167, 946-948. 

Townsend, G. E., and Wedgworth, H. H. 1936. Florida Agr. Expt. Sta. Bull 300. 
Twyman, E. 8. 1946. New Phytologist 45, 18-24. 

Vennesland, B., Gollub, M. C., and Speck, J. P. 1949. J. Bwl. Chem. 178, 301-314. 
Vishniac, W., and Ochoa, S. 1951. Nature 167, 768-769. 
Wael, J. de 1941. Rec. trav. chim. 60, 260-266. 

Wain, R. L., Silk, B. J., and Wills, B. C. 1943. J. Agr. Sci. 33, 18-22. 
Waldbauer, L., and Ward, N. M. 1942. Ind. Enp. Chem., Anal. Ed. 14, 727-728. 
Wallace, T. 1944. The Diagnosis of Mineral Deficiencies in Plants. His Majesty's 

Stationery Office, London. 

Wallace, T., Hewitt, E. J., and Nicholas, D. J. D. 1945. Nature 156, 778-782. 
Walsh, T., Golden, J. D., and Fleming, G. A. 1950. Trans. Intern. Congr. Soil ScL, 

4th Congr. Amsterdam 3, 115-119. 

Wander, I. W. 1950. Proc. Am. Soc. Eort. Sci. 55, 81-91. 
Warington, K. 1951. Ann. Applied Bwl. 38, 624-641. 
Wiese, A. C., and Johnson, C. B. 1939. /. Biol. Chem. 127, 203-209. 
Willard, H., and Greathouse, L. H. 1917. J. Am. Chem. Soc. 39, 2366-2377. 
Wolzogen Kuhr, C. A. H. von. 1927. /. Am. Water Worlcs Assoc. 18, 1-31. 
Zak, J. 1942. Biedcrmanns Zentr. B 14, 301-316. 

Atomic Energy and the Plant Sciences * 


United States Atomic Energy Commisvionj Washington, D. C. 



I. Introduction 279 

II. Effects of Radiation on Plants 281 

1. External Radiation and Plant Development 281 

2. Internal Radiation Effects 28f> 

3. Genetic Effects and Plant Breeding 287 

4. Biochemical Effects of Radiation 289 

5. Biological Chains 291 

111. Use of Isotopes in Plant Sciences 293 

1. Soil, Fertilizer, and Mineral Nutrition 293 

2. Plant Metabolism 29f> 

References 303 


The Atomic Energy Commission supports research in the plant 
sciences along three broad lines: (1) The effects of radiation on plant 
growth, both physical effects and biochemical effects, are of primary 
concern to the Commission. (2) Of equal importance are the uptake of 
fission products and other radioactive material, their movement and 
distribution in the soil, their uptake by plants and utilization by ani- 
mals. (3) The AEC is also responsible for applying atomic energy 
products and techniques to fundamental research with plants. 

In the implementation of this program the AEC carries on a consid- 
erable amount of work in the plant sciences at its national laboratories, 
particularly on plant genetics, radiation effects, uptake of fission prod- 
ucts, and biosynthesis. This paper discusses only the unclassified part 
of the AEC program in the plant sciences. In addition, the AEC has 
forty-one cost-sharing contracts for plant science research at twenty-nine 
universities, colleges, and research institutions. Apart from such direct 
support, the AEC produces isotopes at incentive prices and sponsors 
courses in the use of isotopes in research. 

In this review of AEC-supported research in plant sciences there is 

* A major portion of the AEC Semiannual Report to Congress dated January, 
1952, is a less technical and moie detailed discussion of this same subject. The report 
is available from the Superintendent of Documents, U.S. Government Printing Office, 
Washington 25. D. C. 


not always a distinction made between work in a national laboratory 
and that supported in universities and colleges. Although much of the 
work in the AEG national laboratories is fundamental in nature, it is 
directed specifically toward the determination of effects of radiation 
from the piles, accelators, and fission products upon plant and animal 
life. Research projects at institutions that receive AEC assistance are 
carried out under cost -sharing agreements with the institutions. Several 
factors are considered in granting allotments from AEC's available re- 
search funds: (1) the relation of the proposed work to AEC's statutory 
purpose; (2) how the work will supplement the research at the AEC 
national laboratories; and (3) projects which give promise of developing 
new techniques in the use of isotopes. 

The atomic energy program, involving plants and soils, includes stud- 
ies of the effects of both internal radiation (absorbed radioisotopes and 
fission products) and external radiation upon the development, growth, 
yield, and biochemical changes in plants. In addition, fundamental, 
cytological, and plant genetic studies are applicable to plant science and 
the possibility of plant breeding. The first part of this report is pri- 
marily concerned with the more programmatic aspects while the latter 
part will describe more general and fundamental work supported by the 
AEC, most of the latter being done at universities and colleges. 

To make clear how a great diversity of projects fit into an overall 
scheme two tables listing the various AEC research projects in the plant 
sciences have been prepared. All the work which is largely supported 
by the AEC is listed in Table I. University research agreements dealing 
more with the use of isotopes in plant sciences are outlined in Tables II 
and III. To get a complete picture of the research in some areas it will 
be necessary to look at two tables at once. For instance the Soil, Fer- 
tilizer, and Mineral Nutrition research at AEC laboratories and major 
projects is listed in Table I while in Table II are listed other projects in 
this same field which are partially supported at universities and colleges. 
Many of the projects listed in the tables are not mentioned in this short 
review, but the tables by themselves should furnish an overall picture of 
AEC support in plant sciences at this time. Other plant science projects 
in the United States also get indirect aid from the AEC by being able 
to purchase radioisotopes at a nominal cost, but none of this work is 
mentioned here. Portions of the review have been taken from the AEC 
national laboratories quarterly progress reports, and some of this work 
has not been completed and published. 



The effect of radiation on biological material depends upon (1) type 
of radiation internal, external, gamma, alpha, beta, or neutrons, (2) 
rate of exposure, and (3) variable species resistance. In general, it takes 
several thousand roentgens (r) of external radiation to cause visible 
plant damage but only several hundred roentgens to injure animals. It 
is a universal observation that the higher forms of life are more sensitive 
to radiation damage than the lower forms. However, plants are affected 
by low levels of radiation such as that from P 32 because of the facts that 
P 32 accumulates in the growing tips and that the dividing cells there 
are the most sensitive to radiation. 

External radiations may be administered in a variety of ways. Using 
the same source, the dose may be given slowly or rapidly, continuously 
or intermittently. Using different sources one may vary the character of 
the radiation (different energies, charges, or masses) or compare the effect 
of different radiations given simultaneously with that of each radiation 
type used alone. Increase in effectiveness with increased specific ioniza- 
tion is usually seen in studies of higher forms seed plants, mammals, 
and insects. Such a complex system might be expected to consist of 
many similiar units (cells), many of which must be destroyed before a 
whole effect can be seen. 

1. External Radiation and Plant Development 

The principal work in this field has been done at Brookhaven Na- 
tional Laboratory by A. II. Sparrow and W. R. Singleton. For three 
years various plants, especially corn and potatoes, have been grown in 
concentric circles around a 16-curie source (in 1951, 200 curies) of Co 60 
placed in the center of a three-acre field (Fig. 1). The gamma rays 
from this source are similar to x rays except that the gamma radiations 
are harder and more penetrating. The source is raised and lowered 
through a steel pipe into a lead "pig" in the ground by means of a 
remote control mechanism 70 meters away. The source was in the " up " 
position all the time, except when necessary to enter the field for culti- 
vation, note-taking, hand pollination, etc. 

The intensity of radiation is varied by the distance of the various 
rows from the source. Since the intensity of radiation is inversely pro- 
portional to the square of the distance from the source, extreme differ- 
ences in radiation are obtained. For example, plants at 1 meter from 
the 16-curie source received 500 r per day while those at 10 meters re- 
ceived only 5 r per day. At 60 meters only 0.084 r per day was received. 

Most plants can tolerate a very high level of external radiation con- 



tinuously without visible damage as compared to the higher forms of 
animal life. Although plants vary in radiation sensitivity, all plants are 
affected by sufficiently high exposure. It is important to note that no 
stimulation has been observed at any radiation intensity. At high radia- 
tion intensities hypertrophic growth in certain structures was frequently 
noted in some species; in others tumor-like growth, as well as somatic 

FIG. 1. Genetic stocks of corn growing in the 200 curie Co 80 radiation field. 
Signs mark distance in meters from the radiation source in the center of the field. 
Plants in 3M row killed by radiation of approximately 700 r/day. Plants in 4M row 
very abnormal (approximately 400 r/day). Plants in 5M circle (250 r/day) almost 
normal in appearance but produced few seeds and small amount of pollen. Many 
mutations induced in pollen from this row. Photo taken August 21, 1951, 

mutations, were observed. Tomato plants that received 20,000 r at a 
rate of 150 r per hour decreased in chlorophyll content and were re- 
tarded in development. Removed from the radiation, they resumed 
normal growth. Spider wort was allowed to grow in a field varying from 
5 r to 128 r per day. Growth was normal at 10 r per day, but at higher 
exposures growth declined but was accompanied by physical abnormali- 
ties until at 128 r per day there was no growth. Corn produced appar- 
ently normal growth at 125 r per day, and the growth was almost normal 
at 250 r per day, but at this level very few seeds were produced on each 
ear. At 390 r per day the plants were severely stunted. 


Growth and flower development of lily plants were inhib- 
ited if exposed to more than 60 r per day, but no structural ab- 
normalities were obvious. In the broad bean, growth and fruiting 
seemed normal under exposures of 5 r per day; at 22 r per day the 
plants flowered but bore no fruit, and at 34 r per day the seeds germi- 
nated, but growth and flowering were inhibited. 

Dosages which cause extensive morphological changes also produce 
a considerable number of chromosomal aberrations. Since recovery to a 
normal growth pattern occurred in many plants which had previously 
shown severe radiation damage, it would seem that most of the morpho- 
logical aberrations were not of a genetic nature. 

Potatoes have been used to study the effects of acute doses of x rays 
and fast neutrons and of continuous chronic gamma irradiation from 
cobalt-60 upon germination and growth of plants (Sparrow and Chris- 
tensen, 1950). For the potato tuber various dosages of radiation to the 
tuber before planting resulted in a decrease in the yield. Continuous 
gamma radiation at equivalent levels had no adverse effect on growth. 
Tubers were cut into seed pieces and given x ray doses before planting 
from 75 r to 38,400 r. The date of emergence and consequently height of 
young plants were adversely affected by 300 r or higher (Fig. 2). Yield 
was significantly reduced by 1200 r, and 4800 r was near the lethal dose. 
At 1200 r and above the leaves in young plants seemed to be unusually 
thick and glossy with an uneven or slightly wrinkled appearance. 

One as-yet-unexplained phenomenon was revealed when, during the 
harvest, seed potatoes that failed to sprout were dug up. Those tubers, 
heavily exposed to radiation, had not rotted as would ordinarily have 
occurred but were still fairly firm. 

Recovery of the tubers from x ray irradiation occurred when F] 
tubers were planted the second year. Yield data indicated no apparent 
relationship to the original dosage. These plants included both high- 
and low-yielding lines that are being studied further. Thus, one may 
speculate that the radiation effect on the first year's yield and growth 
may be due in large part to physiological effects, and the effect observed 
on the F 2 crop could be attributed to long-lasting or permanent genetic 

In comparison with the acute x ray irradiation of the potato seed, 
the field cobalt-60 source was used for chronic gamma irradiation studies 
over the whole growing season by planting potatoes at varying distances 
from the cobalt source. Dosage rates were 0.26, 1.15, 4.8, 19.5, and 
79.7 r per day to give accumulated season totals of approximately 28, 
123, 516, 2086, and 8529 r. No consistent relationship between dosage 
and yield was observed. Plants near the center of the field averaged as 



high yields of potatoes as those planted at greater distances from the 
source of radiation. There was no visible difference in size or apparent 
vigor of the plants. The biological destructiveness of continuous gamma 
irradiation would thus appear to be much lower (not greater than 14 


" ** *** 
4fc *Swi> " '. " . 

'? ;f^/'4 % : --' 

":;*, ^, 

r & ' , 
f. . vr. - 

s * 
' ..-*& .' 

FIG. 2. Thirteen pieces of potato tuber were irradiated by x ray at each dosage 
of 0, 75, 150, 300, 600, 1200, 4800, 9600, 19,200, and 38,400 r and planted in rows 
as shown; 4800 r is a near lethal dose. 

per cent) than acute irradiation of the potato tuber. No evidence of 
stimulation was obtained. 

These observations in the cobalt field indicate that potatoes are rela- 
tively resistant to ionizing radiation. Two possibilities suggest them- 
selves. One is the fact that cultivated potatoes are polypoid (4w-48) 
and hence should be more resistant than diploid plants. The other is 
the small size of their chromosomes which may make them less radio- 
sensitive. Work with plants with large chromosomes, such as Trillium, 
Tradescantia, and Lilium, show that these are much more sensitive to 
radiation than plants with small chromosomes, such as tomatoes, sun- 
flower, most grasses, corn, marigolds, snapdragon, and various weeds 
(Sparrow, 1950). 


That chronic radiation is much less damaging physiologically than 
the same amount of radiation delivered in a short exposure is well estab- 
lished with animals. Several explanations are possible, but they all stem 
from the basic fact that density of ionization does not reach a very high 
level in the chronic exposure. Thus, the plant has a much better chance 
to recover from the damage than if given a single heavy exposure. This 
is true not only of physiological effects but for "2-hit" chromosome 
aberrations as well. It would not be expected to hold for mutations 

A third type of irradiation damage is that from neutrons. Potato 
tubers have been exposed to neutrons from a pile with dosages similar to 
the x ray treatments described earlier. A tentative estimate is that fast 
neutron acute irradiation of plants is probably at least four times more 
effective than acute x irradiation. The more severe effect of fast neu- 
trons supports the hypothesis of the importance of ionization density, 
since fast neutron irradiation produces very dense ionization tracks. 
The passage of a single track through or very near a chromosome would 
therefore be expected to cause a serious, if not a lethal effect. 

2. Internal Radiation Effects 

Although heavy radiation is damaging to plant life, there have been 
claims that radioactive fertilizers would increase crop yields, but these 
have not been confirmed (Alexander, 1951). Even the lowest levels of 
internal and external radiation appear to cause adverse changes in the 
plant, histologically and biochemically. Fortunately, at the levels nor- 
mally used in radioactive isotope tracer experiments in vivo, such low 
levels of radiation result that the physiological effect is essentially nil. 
However, it has been necessary to determine under what conditions the 
damage produced from isotopes is serious enough to affect the validity 
of the conclusions. 

Probably the most extensive use of tagged elements in plant science 
research has been with phosphorus-32. In the case of P 82 it is concen- 
trated in the meristematic regions such as the growing root and stem 
tip where its radiation effect is thus concentrated and where the newly 
forming cells are more sensitive both biochemically and genetically. In 
animals the accumulation of P 32 , Ca 45 , and fission products in the bone 
and their effect on the hematopoietic system is an analogous situation. 
In plant sciences the effects of internal radiation have not been studied 
extensively and there has been no utilization of this tool in plant bio- 
chemical studies. For instance, the production of plant tumorous 
growth by radiation is unexplored. The exact mechanism which operates 
in the damage of living tissue by radiation is not completely understood. 


It is known that cell division is affected and that irradiation injury may 
be accompanied by chromosome breakage. 

Gross determination of internal radiation damage has been carried 
out under a joint USDA-AEC project. Plants (barley and alfalfa) are 
grown in nutrient solutions containing various amounts of the radio- 
isotope, i.e., P 32 . The length and dry weight of the tops and roots are 
used as the criteria of injury caused by radioactive material (Fig. 3). 

FIG. 3. Barley grown in nutrient solution 2xlO~ 6 molar in phosphate and con- 
taining left to right: 0, 2, 4, 8, 16, 32, and 64 microcuries P 32 per liter. 

Damage to the tops is more severe than damage to the roots, and the 
injury is primarily due to radiation from the P 32 accumulated within 
the plant. Injury is associated with a high specific activity of the iso- 
tope in the nutrient solution, i.e., ratio P 32 /P 31 . This condition allows 
a higher specific activity of the isotope to accumulate in the plant, or 
in reverse one might say the plant can be partially protected from a 
radioactive isotope by abundance of the inactive form. Blume, Hagen, 
and Mackie (1950), using barley growing in nutrient solution, found 
that the lowest level at which any damage was produced was at 5.6 
millicuries P 32 per grain of l-^O.v When plants were grown in soils 
with surface application of P 32 from to 12.5 millicuries P 32 per gram 
of P 31 , the damage was too small to be statistically significant (Blume, 
1952). These and similar results indicate that concentrations of isotopes 
much higher than those usually used in plant nutrition studies are neces- 
sary to get visible damage to plant growth. 

Histological changes induced in barley plants by radiation from P 32 
can be detected at much lower levels than amounts causing a decrease in 
plant growth (Mackie, Blume, and Hagen, 1952). The size of the outer- 


most cells of the terminal meristem of barley growing in P 32 nutrient 
solutions were measured and related to the specific activity of the P 32 . 
The cells of barley growing in nutrient solution containing as little as 2 
microcuries P 32 and 2 x 10~ 5 mole P 31 per liter were larger in the epider- 
mal layer of the stem apices compared to the nonirradiated controls. 
Measurement of these apex cells of the growing points of the stem gave 
no indication of the existence of a threshold value which divides dam- 
aging from nondamaging doses of radiation It does not follow that 
this injury would be reflected in a permanent symptom of abnormality, 
and at the lowest radiation levels apparent injury to the root tip was not 
followed by damage to the apical meristem. At levels of radiation where 
there was apparent injury to the root tip, histological examination 
showed that cell division ceased, the cells of the growing points enlarged, 
the cytoplasm became less dense, and the cell walls thickened. 

3. Genetic Effects and Plant breeding 

Radiation has served as a useful adjunct in the study of genetics, not 
only because it has afforded more mutations for study, but also because 
the frequency of an otherwise extremely rare event can be increased to 
the point where the processes or mechanisms of the mutational change 
can be conveniently studied under various conditions. In addition, the 
analysis of genetic and cytogenetic effects of radiation has given valuable 
data from which general theories on the mechanism of radiation effect 
have been postulated. 

The frequency of spontaneous mutation varies considerably, but 
is generally of the order 10"~ r> or 10 ~ 7 for any particular gene (10~ H for 
bacteria). Data now being gathered at Brookhaven indicate that the rate 
in corn may be much higher, in the order of 10~ :J to 10 * ({ . In spite of 
this, when all types of mutation for all genes borne by any one individual 
are considered, mutation becomes almost commonplace. Muller (1950) has 
estimated that approximately one in every twenty germ cells contains a 
new mutation that has arisen during the life of the organism. The 
application of any mutagenic agent, even in small amounts, will obvi- 
ously increase the frequency of mutation. If an estimate of a doubling 
of mutation rate with every 50 r is assumed (this is the figure for Droso- 
phila; estimates range from 3 r to 300 r for man), it is apparent that a 
dosage of 200 r would increase the frequency of new mutations to 
roughly one in every four gametes. Fortunately, however, a fair pro- 
portion of these would be so minute as to be almost undetectable although 
most of them would be undesirable. A few might be useful, or poten- 
tially so, under somewhat changed environmental conditions. Thus, a 


long-range possibility of actual benefit lies in the genetic effects of 
radiation on the heredity of plants and animals. 

The AEO is conducting genetic research at three of its national 
laboratories, Brookhaven, Oak Ridge, and Argonne, and twenty-one 
genetic research projects at cooperating universities throughout the coun- 
try are directly supported by the AEC. Most of these projects are 
designed to reveal the mechanisms by which radiations cause genetic 
changes. In Table III is a list of university projects specifically con- 
cerned with agricultural genetics. 

In a fundamental study of radiation genetics, Brookhaven is growing 
corn under continuous radiation in its gamma-ray field. Corn is being 
studied intensively because more is known about the genetics and cytol- 
ogy of corn than of any other farm crop plant. The mutation rate of 
four endosperm characters 8u, Pr, Sh, and R has been studied in both 
megaspore and microspore (Singleton, 1950a,b). At the highest radia- 
tion given in 1950 (125 r / day) slightly more than 1 per cent of muta- 
tions were obtained from 6400 seeds studied. Lower intensities of 
radiation produced fewer mutations. No increase over the spontaneous 
mutation rate was found with intensities less than 5 r per day. A total 
of 275,000 seeds were examined through 1950. Although endosperm 
characters were studied primarily, there is reason to suppose other plant 
characters will respond similarly to radiation. Attempts are being made 
to induce such plant characters as the short stalk rd, and the shorter 
stalk br< 2 . Pollinations made in the radiation field in 1950 gave sufficient 
seed for about 10 acres of corn which is being examined for short types 
this year. It seems likely that such induced plant characters can be 
inbred and isolated in a hybrid within two or three years, which is much 
less than required by a crossing and backcrossirig program. It is this 
feature of the gamma radiation that is of interest to plant breeders. 
There is a good chance that a greater diversity of genes responsible for 
hybrid vigor may be induced by radiation, thus giving the plant breeder 
many more genes with which to work. Such an eventuality might make 
it unnecessary to comb various parts of the world for specific genes of 
disease resistance and drought resistance. 

At the University of Minnesota the effects of radioactive substances 
on plant pathogens and other microrganisms are being investigated in 
an attempt to determine the biological significance and usefulness of 
changes induced by radioactive materials. In the corn smut fungus, 
Ustilago zeae, many mutants have been obtained by growth on media 
containing uranyl nitrate. Detailed comparative studies of such mu- 
tants have shown that they differ from the parental lines in morphology, 
physiology, and pathogenicity. 


A similiar project on the physiology and genetics of plant pathogenic 
microorganisms grown in the presence of various radioisotopes is being 
supported at the Ohio Experiment Station. Corn breeding experiments 
and effects of atomic bomb exposures on corn seed is a continuing project 
at the California Institute of Technology. 

In a series of experiments somewhat similar to the Brookhaven proj- 
ect, 75,000 peanut seeds were exposed to x rays at dosages of 10,000 r, 
16,000 r, and 18,500 r at North Carolina State College. One major 
plant breeding objective was to produce a mutant resistant to leaf spot 
disease which causes serious loss in peanut crops. In the summer of 
1951 there were raised 13,600 progenies of the X 3 generation. The 
peanut plants range from normal or slight variability to plants of varia- 
bility of every description as a result of the radiation in 1949. 

Although the X 3 progeny has not been completely analyzed at the 
time of this report, mutants of a wider range of variability in resistance 
to leaf spot have been obtained. There are also many other variants 
which may be of economic importance. 

4. Biochemical Effects of Radiation 

The nature of radiation damage in plant tissue is probably as com- 
plex as that in animal tissue, but with plant material few investigations 
have been made. Cytogenetic investigations of radiation effects have 
been made on plant material, but relatively few biochemical studies have 
been reported. Much more work is needed in all fields before an ade- 
quate understanding of the mechanisms of radiation damage can be 

Fundamentally the initial physical, chemical, and biochemical effects 
should be the same in all biological systems. lonizations, excitation, and 
the production of activated molecules, H 2 2 , H0 2 , and Oil radicals 
should lead to a wide array of unusual chemical by-products and actual 
destruction or inactivation of many molecules, leading to a general dis- 
turbance of the more sensitive metabolic processes. 

It is possible that important labile enzymes are easily destroyed 
even in the presence of the usual complex cell constituents which should 
exert a considerable protective influence. Although enzymes are not 
found in dilute pure solution in vivo, Dale (1943) believes that enzyme 
inactivation plays a large role in radiobiological injury. It is not defi- 
nitely known which systems are the critical ones in plant metabolism, 
although it is known that certain enzymes and plant hormones are sus- 
ceptible to radiation damage (Skoog, 1935). 

Physiological and cytological consequences of irradiation of plants 
and plant materials are being carried on at Brookhaven National Labora- 


fory and in collaboration with investigators at other institutions. For 
example, at the University of Pennsylvania investigations are in progress 
on the tyrosinase activity in potato tubers, and in preparations of the 
enzymes from the tubers. 

The phytoradiology work at Argonne National Laboratory under 8. 
Gordon was initiated to study the effects of radiation on higher plants 
and has developed into a major project on biochemical effects of ionizing 
radiation. A number of the observed effects of high-energy radiations 
on plants are similar to those caused by changes in auxin level, and thus 
the effect of such radiation on auxin (indoleacetic acid) and auxin 
economy becomes pertinent to research upon the mechanisms of radia- 
tion effects. One of the major controlling factors of plant growth and 
development are the growth hormones or auxins and the chief site of 
auxin synthesis is the growing terminal bud of the higher plant. 

Investigation at Argonne Biology Laboratory has dealt with the effect 
of ionizing radiation (1) on auxin in in vitro and m vivo systems, (2) 
on the biosynthesis of auxin in the living plant tissues, and (3) on 
physiological processes controlled by auxin. 

In aqueous solutions x-ray irradiation inactivates auxin with apparent 
first order kinetics. Added organic compounds are able to protect free 
auxin against inactivation by ionizing radiation. Such protective action 
was shown by ethanol, glucose, ascorbate, cysteine, glutathione, and ci- 
trate all possible components of a plant cell. 

Auxin levels have been determined immediately after various single 
doses of x-ray irradiation Were given to kidney bean, cocklebur, and cab- 
bage plants. Radiation doses as low as 25 to 100 r cause an immediate 
drop in free auxin levels. As the radiation dose is increased, the absolute 
amounts of free auxins in the tissue progressively decrease. Depending 
on the plant material, it takes from 50 to 1000 ionizations produced in 
the tissues to inactivate one moleciile of auxin. Auxin is present in 
very minute amount in the cell and when one considers the tremendous 
excess of molecules in the cell which could compete with indoleacetic 
acid for the radiation-induced oxidizing groups, the efficiency of free 
auxin inactivation by ionizing radiation is surprisingly high. 

Continued production of auxin after irradiation is likewise inhibited 
by low radiation doses. Kidney bean and cocklebur plants were irradi- 
ated in single doses from 25 to 10,000 r, their auxin levels being followed 
by periodic sampling after irradiation. Auxin formation is inhibited in 
the kidney bean by as little as 25 r, with progressive inhibition by higher 
doses. Recovery of the capacity to synthesize auxin after irradiation is 
attained in from several days to two weeks, depending on the dose. Doses 


of 10,000 r result in increasingly depressed biosynthesis, with no re- 

The effectiveness of low doses of ionizing radiation can be interpreted 
as being due to its action upon molecules which affect multiniolecular 
turn over, i.e., the enzymes. If the enzyme system involved in auxin 
supply is radiosensitive, the free auxin reservoir would be rapidly low- 
ered and made manifest by reduced auxin level. 

Biochemical investigations are underway dealing with the effect of 
ionizing radiation directly on the system involved in growth hormone 
synthesis. Exposure of the plants to radiation causes decreased growth 
and auxin concentration. The effect of the low radiation doses can be 
reversed by applying synthetic growth hormone to the plant following 
irradiation. The effect of higher radiation doses cannot be reversed, 
implying that a more profound biochemical injury has taken place such 
as on the enzymes. 

Morphological changes due to irradiation can likewise be shown to 
be due, in part, to radiation sensitivity of the hormone system. Plant 
workers are familiar with the phenomenon of apical dominance. The 
terminal growing point, or bud, suppresses the growth of lateral buds. 
When the terminal meristem is cut off, or severely injured, the lateral 
buds immediately leave their "dormant" state and begin growing. This 
process was shown to be specifically controlled by the auxin produced by 
the terminal bud. Thus, when the stem tip is removed and auxin alone 
is applied to the stump, the laterals stay suppressed as long as the auxin 
source is allowed to remain. If the applied source is in turn removed, 
normal grow r th of the laterals is immediately initiated. 

Terminal growing points of the cocklebur were irradiated with single 
low doses of x-ray irradiation ; the remainder of the plant being shielded 
with lead. Lateral bud growth ensued, the buds increasing over 100 per 
cent in size within two days. When auxin was applied to the tips imme- 
diately after irradiation, lateral buds stayed suppressed. 

Argonne investigators have concluded that these apical dominant 
responses to irradiation are chiefly, if not wholly, due to radiation sensi- 
tivity of the auxin supply system. Apparently the process of auxin 
formation is relatively sensitive to radiation, and this provides an 
explanation, in part, for changes in growth and development of higher 
plants exposed to relatively intense, low doses of ionizing radiation. 

5. Biological Chains 

The purpose of such programs are to determine the extent and 
manner of concentration of radioactive materials in plants and in aquatic 
organisms of our rivers. This function is necessary in order to deter- 


mine (1) why certain forms concentrate particular isotopes to such a 
high degree, (2) how the concentration of radioactivity in these organ- 
isms can affect higher forms of life such as animals and fish, which ingest 
them, and (3) whether the concentration of radioactive isotopes present 
on the land and in the rivers can be decreased in order to reduce possible 

Several projects are specifically designed for this purpose. At the 
Hanford Laboratory the concentration of radioactive materials in 
the aquatic organisms of the Columbia River is monitored at frequent 
intervals as a check on the safety of Hanford operations. More than 
500 samples of vegetation, soil, and mud are assayed each month for 
radioactivity. In addition, the organisms occupying important links in 
the food chain of the river as well as fish are reared in pile effluent or 
subject to individual isotopes which may contaminate the river. The 
organisms are then fed to higher forms which would normally consume 
them. The pattern of deposition of the activity in both of the forms is 

Radiobiological ecological surveys of the Columbia River project 
have disclosed the particular biological chains in need of continuing 
study. Ecological surveys of the Savannah River Project Area are to 
be undertaken with support from the AEC by universities and colleges 
in the states most directly concerned. 

It has been found that in the Columbia River radioactive phosphate 
is taken up extensively by both the fauna and flora and constitutes a 
greater biological hazard than other radioactivity in the river. It is 
produced from the natural phosphates in the river water when the water 
is used for cooling the pile. Algae in the river have the ability to build 
up phosphorus concentrations thousands of times that present in the 
river water. The fish feed on the algae and over 85 per cent of the activ- 
ity deposited in trout is assimilated from food organisms. Thus, the 
longer-lived isotopes deposited in the fish originate principally from the 
food while shorter-lived isotopes are accumulated directly from the water. 
Activity concentrated in animal forms is therefore dependent upon feed- 
ing habits as well as upon the activity density of the surrounding water. 
These studies designed to measure biological chains indicate that the level 
of activity in the Columbia River has been maintained at levels that have 
no adverse effects on the fauna and flora of the river. The levels in the 
water below the piles and in the fish are far below tolerance for man and 
are entirely safe for food. 

Hanford has operated a small experiment station in which a variety 
of fruits and vegetables were irrigated with water drawn from the Co- 
lumbia River below the reactor cooling outlets. At no time has any 


significant or, in fact, measureable amount of radioactive material ap- 
peared in the soil and crops. 

Annual surveys have been made of the soil, plants, and animals col- 
lected in the area of the first atomic bomb detonation site at Alamogordo, 
New Mexico, in order to obtain some concept of what role the low level 
contamination of the soil may play in the metabolism and life cycles of 
the plants in this area. The data may serve to indicate what can be 
expected from bomb areas of much higher activity. 


Although the changes that radiation causes in living matter are of 
great scientific interest, the AEC also sponsors fundamental research in 
the broad fields of soil science, plant nutrition, plant biochemistry, and 
physiology, and plant genetics. Generally these projects involve the use 
of radioactive isotopes in their research programs. In Table I Part II 
are listed the projects at AEC national laboratories and AEC univer- 
sity projects which receive a major part of their support for this type 
of research from the AEC. In Tables II and III are listed forty-one 
projects in plant sciences which are partially supported by the AEC at 
universities and colleges. It is impossible to discuss these diversified 
projects in a single review, but the descriptive titles in the tables will 
serve as a guide, and in many cases publications of the investigators will 
provide further information. 

1. Soil, Fertilizer, and Mineral Nutrition 

The AEC has a broad field of interest in soils and fertilizers, mineral 
metabolism, and plant nutrition. Table II lists research projects which 
the AEC is partially supporting in this field at universities. Various 
processes of the atomic energy industry create radioactive materials that 
might become available to growing plants. Research topics associated 
with the soil and plants are but a segment of a diversified group of 
research projects built around the theme of fission products in the life 
cycle from soil, to plants, to animals or man. It is necessary for the 
AEC in its research to evaluate (1) the state and availability of minerals 
(fission products) in the soil, (2) the absorption of minerals by the roots 
and thus the physiology of the root, (3) translocation and deposition of 
various elements in plants, and lastly (4) the role of minerals in plant 
biochemistry. That much fundamental research must precede the com- 
pletion of this Herculean task is obvious, and the AEC Act provides for 
some of the support of this research. 

Many of the AEC research projects in soil and plant nutrition in- 


volve work in more than one of the three divisions indicated in Table II. 
Most of the projects utilize radioisotopes, and it is hoped they will 
stimulate research in fields beyond that supported directly by the AEC. 

The AEC is interested in the movement in the soil and uptake by 
plants of radioactive bomb debris and fission products such as strontium, 
yttrium, cesium, columbium, ruthenium, tellurium, ionium, barium, 
sodium, potassium, lanthalum, cerium, plutoniurn, and uranium as well 
as some nonradioactive elements used in its program such as beryllium. 
All these minerals are taken up by plants, but many do not present a 
problem because they are either not taken up in significant quantities 
or else their half life is too short to make them much of a hazard. 
Strontium and yttrium are potentially the most biologically hazardous 
of the fission products. Strontium-90 has a 25-year half life and stron- 
tium-89 a 55-day half life. Both are beta emitters, are absorbed and 
concentrated out of the soil by plants as if they were an isotope of 
calcium, and they are likewise absorbed and utilized by man and animals 
in lieu of calcium. 

Strontium -yttrium absorption by both plants and animals has been 
the subject of numerous investigations (Table I and II), such as those of 
Jacobson and Overstreet (1948). Tests by the Hanford botany group 
have shown that red kidney bean plants take up strontium in proportion 
to its concentration in a nutrient solution over a broad range of 0.0001 
to 100 parts per million. Plants build up concentrations of strontium in 
their leaves five to ten times as great as that present in the nutrient so- 
lution. Abnormally high concentrations of calcium in the soil will 
partially prevent strontium uptake by plants. 

Strontium likewise is readily translocated to the leaves and all other 
parts of the plant including edible fruits. In one experiment 1.6 per 
cent of the initial dose of strontium applied to the soil appeared in leaves 
of barley and peas, whereas only 0.00045 per cent of a dose of trivalent 
plutonium was translocated to the leaves. 

Radioiso topes are proving to be of greatest value in fertilizer research. 
A major effort has been a joint AEC-U.S. Department of Agriculture 
project in the Bureau of Plant Industry, Soils, and Agricultural Engi- 
neering for developmental work on the safe and extensive use of radio- 
isotopes in the field. There are several phases of this program such as 
(1) development of procedures for use of radioisotopes in general soil 
and plant research, (2) development of procedures for preparing and 
handling labeled fertilizers and ascertaining levels of possible injury to 
the plant from radioactive fertilizers, (3) investigation of the role of 
trace elements, particularly in relation to chlorosis, (4) performance of 
basic soil research with P 32 , Ca 45 , Zn 65 , K 42 , S 85 . 


2. Plant Metabolism, 

Radioactive tracers can be successfully utilized in almost all phases 
of plant biochemistry and physiology, but the number of investigators 
and the amount of work in these fields are surprisingly small compared 
to animal biochemistry. The projects listed in Table III cover a rather 
broad range of subjects in plant metabolism. 

Research in photosynthesis is an excellent example of an old problem 
being attacked with successful results with a radioisotope, C 14 . A major 
AEC project in this field at the Radiation Laboratory of the University 
of California has used the two tools C 14 labeled CO 2 and paper chroma- 
tography in the study of the mechanism of the utilization of light energy 
in carbon dioxide reduction (Calvin et al., 1951). 

Experiments with C 14 2 of high specific activity have allowed a great 
number of observations on this hitherto almost impenetrable system of 
reactions. The advantages of such a method lie first in its sensitivity; 
intermediates of concentrations of less than 10~ 6 M may be readily deter- 
mined in a few milligrams of plant material. Secondly, when labeled 
carbon dioxide is added the reservoirs, the intermediate products are 
consecutively labeled with C 14 . Analysis of the products of photosyn- 
thesis in C 14 2 by two-dimensional paper chromatography has allowed 
separation of most of these compounds. 

As the length of exposure of an actively photosynthesizing plant to 
C 14 2 was shortened, the labeled carbon fixed by the plant was found in 
fewer and fewer compounds. Thus by rate curves, it was found that 
the C 14 2 was first incorporated into the carboxyl group of phospho- 
glyceric acid. It was further confirmed that this carbon dioxide reduc- 
tion is accomplished entirely by dark reactions and that the reducing 
power formed during photosynthesis in the light had a half life of sev- 
eral minutes in the dark. 

Present investigations by the University of California group are 
concerned with the sequence of organic intermediates on the pathway to 
sugars in the photosynthesis process. In addition progress is being made 
upon elucidation of a photosynthesis organic cycle necessitated for con- 
tinuous generation of the two-carbon compound which is carboxyl ated 
by the C0 2 to give phosphoglyceric acid. 

Biochemists are using radioisotopes to study the action of the well- 
known weedkillers, such as 2,4-D. Much is known of the practical use of 
2,4-D ; little is known of its biochemical action. Radioactive labeled 2,4-D 
is being used to study its rate of absorption by susceptible and resistant 
plants, its translocation in various species, its destruction and break-down 
products, and the specific biochemical steps blocked by its action. 


In Table II are listed several projects dealing with mineral move- 
ment and metabolism in plants which bear upon various mineral de- 
ficiencies. Chlorotic plants are found in all parts of the country and 
occur when trace minerals such as iron, zinc, copper, and manganese are 
not absorbed by the plant or are naturally deficient. In one of these 
projects at Washington State College, studying the mechanism of mineral 
translocation in plants, it has been found that movements of the minerals 
can be easily influenced by pH and concentration of phosphates. Iron 
is absorbed best under more acid conditions, and its mobility in the 
plant decreases at higher phosphate concentrations and pH. It appears 
to be precipitated as ferric phosphate and hence metabolically becomes 


AEG Research in Plant Sciences at Its National Laboratories and Totally Supported 

University Projects 

T. Effects of Radiation on Plants 

1. External Radiation Effects 

a. Brookhaven National Laboratory 

(1) Genetics and Physiological Effects of Ionizing Radiation on Plants: 
Killing, Stunting of Growth, Abnormal Growth Patterns, Change Yields 

W. R. Singleton 

2. Internal Radiation Effects 

a. Argonne National Laboratory 

(1) Growth and Development of C 14 -Labeled Plants N. J. Scully 

b. Han ford National Laboratory 

(1) Levels of Radioactive Elements Which Will Cause Damage to Plants 
and Microorganisms J. W. Porter 

c. USDA Bureau of Plant Industry, Soils, and Agriculture Engineering 

(1) Radiation Injury to Plants Grown on Nutrient Solutions Containing 

3. Genetic Effects 

a. Brookhaven NationaJ Laboratory 

(1) Cytological and Cytochemical Effects of Radiation in Plants 

A. H. Sparrow 

(2) Genetic Effects of Ionizing Radiation (Corn Breeding Program) 

W. R. Singleton 

4. Biochemical Effects 

a. Argonne National Laboratory 

(1) Radiosensitivity of Growth Hormone and Its Biogenesis S. A. Gordon 

5. Biological Chains 

a. University of California at Los Angeles Medical School 

(1) Radiological Survey of Soil and Biological Material from Continental 
Atomic Bomb Detonations K. H. Larson, S. Warren 

b. Hanford Biology Laboratory 

(1) Concentration of Radioactive Materials in Aquatic Organisms of the 
Columbia River R. F. Foster 


(2) Radiobiological Ecological Survey of the Columbia Eiver E. F. Foster 

(3) Radioactivities of Soil and Plants Irrigated with Columbia River Water 
below the Reactors at Hanford 

c. Oak Ridge National Laboratory 

(1) Ecological Survey of Oak Ridge Pile and Processing Wastes on Plants 
and Animals in the Immediate Vicinity 

d. Washington University, Applied Fisheries Laboratory 
(1) Bikini iind Eniwetok Biological Surveys 

II. Use of Isotopes in Plant Sciences 

1. Soil, Fertilizer, and Mineral Nutrition 

a. USD A Buieau of Plant Industry, Soils, and Agricultural Engineering 
(3) Improvement of Soil Management and Crop Production through In- 
vestigations with Isotopes 

(Furnishes Inboled fertilizers to 25 state agricultural stations) 
1). University of California at Los Angeles 

(1) Uptake of Ce, Cs, Sr, and Pu by Various Crops from Representative 
Soils K. H. Larson 

ft. liaiifoid Biology Laboratory 

(3) Absorption and Translocatioii of Radioelements (Y* 1 , Sr 90 , Cs, P* 1 , Pu) 
by Plants J. W. Porter 

(2) Mechanisms Involved in Retention and Release of Radioactive Isotopes 
by Soils 

d. Scheriectady Area 

(1) Permeability and retention of Radioactive Materials in Local Soils 

e. University of Tennessee AEC Project 

(1) Tiicoiporation of Ca. 4B into Soil and Relation of Soil Types to Avail- 
ability of Nutrients C. L. Comar 

2. Plant Biochemistry and Physiology 

a. Argonne Biology Laboratory 

(1) Synthesis of C 14 Labeled Indolacetic Acid R. Stutz 

b. Brookhaven National Laboratory 

(1) Metabolism and Photosynthesis in Plants M. Gibbs 

c. University of California Radiation Laboratory 

(1) Path of Carbon in Photosynthesis M. Calvin, A. A. Benson 

d. Hanford Biology Laboratory 

(1) Plant Metabolism of Radioelements J. W. Porter 

e. Oak Ridge Biology Laboratory 

(1) Biochemical and Biophysical Investigations in Photosynthesis with 
Particular Attention to the Light Reaction W. A. Arnold 

(2) Nucleic Acid Metabolism of Plant Tissue G. R. Noggle 

3. Biosynthesis 

a. Argonne National Laboratory 

(1) Biosynthesis of C 14 -Plant Products Labeling of Plant Species and 
Isolation of Sugars, Dextran, Organic Acids, Alkaloids, etc. 

N. J. Scully 

b. Brookhaven National Laboratory 

(1) Biosynthesis with Plants M. Gibbs 

c. Oak Ridge 

(1) Separation, Identification, and Role of Sugars and Saccharides in 
Plant Tissue G. R. Noggle 





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mining the Mechanism of Protecting Plants from 
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Alexander, L. T. 1951. Agron. J. 42, 252-255. 

Blume, J. M., Hagen, C. E., and Mackie, R. W. 1950. Soil Set. 70, 415-426. 

Blume, J. M. 1952. Soil Sci. 73, 299-303. 

Calvin, M., Bassham, J. A., Benson, A. A., Lynch, V. II., Ouellet, C., Schow, L., 

Stepka, W., and Tolbert, N. E. 1951. Symposia Roc. Exptl. Biol. 6, 284-30.1. 
Dale, W. M. 1943. J. Physiol. 102, 50-54. 
Jacobson, L., and Overstreet, R. 1948. Soil Sci. 65, 129-134. 

Mackie, R. W., Blume, J. M., and Hagen, C. E. 1952. Am. J. Botany 39, 229-237. 
Muller, H. J. 1950. Am. Scientist 38, 33-59, 126. 
Skoog, J. 1935. J. Cellular Comp. PJiynwl 7, 227-270. 

Singleton, W. R. 1950a. Maize Genetics Cooperation New* Letter 24, 3-4. 
Singleton, W. R. 1950b. Eec. Gen. Soc. Am. 19, 125. 
Spjirrow, A. H. 1950. Genetics 35, 135. 
Spnrrow, A. H., and Christensen, E. 1950. Am. J. Botany 37, <507. 

Vegetation Control on Industrial Lands 


The Vow Chemical Company, Midland, Michigan 



1. Scope and Nature of the Problem 305 

II. Chemicals Used for Vegetation Control 306 

1. Chlorophenoxyacetie Acids 307 

a. Derivatives and Formulations 307 

b. Some Physiologic Aspects 307 

c. Compound Specificity 308 

d. Application Methods . . 309 

e. Application 1*1 ecaut ions 311 

2. Sodium Chlorate 312 

3. Sodium Trichloroacelate 313 

4. Substituted Phenols 314 

5. Ilerbicidal Oils . 315 

6. Boron Compounds 317 

7. Sodium Arsenite 318 

8. Ammonium Sulfamate ... . 319 

9. CMU 3-OChlorophenyl)-], 1 -dimethyl Urea 319 

10. Mixtures of lleibicides 320 

111. Special Problems of Various Industrial Lands 320 

1. Some Ecological Considerations 320 

2. Utility Right-of-Ways 321 

3. Highways 322 

4. Railroads 323 

f). Miscellaneous Problems 325 

References 326 


Agronomists generally recognize that the control of weeds by one 
means or another constitutes a major portion of the effort involved in 
crop production. The magnitude of the job of controlling vegetation 
on nonagricultural land is not so well appreciated. Until recently this 
has been largely accomplished by manual or mechanical methods with 
scythes, brush hooks, and mowing machines. During the past decade 
there have been many developments in killing or suppressing plant 
growth by chemical means. This chapter will be largely devoted to 
advances in the use of herbicides for the control of unwanted vegetation. 

Lands may be divided into five groups for the purpose of considering 
problems related to the control or eradication of plant growth : (a) crop 



land, (b) pasture and range, (c) forests, (d) recreational areas includ- 
ing home lawns, and (e) industrial lands. 

It is with group (e), industrial lands, that this discussion will deal. 
Among the lands that may be considered as industrial in nature are the 
following : 

railroad right-of-ways and switch- drainage and irrigation ditches 

ing yards canals and waterways 

highway right-of-ways grounds surrounding factories, 
pipeline right-of-ways mills, and refineries 

electric line right-of-ways lumber and pole yards 

telephone and telegraph right-of- oil tank farms 

ways airfields 

transmitter and transformer sta- parking lots 

tions water reservoirs 

Military lands may be included in the above list for purposes of this 
review. Problems of vegetation control at arsenals, ammunition dumps, 
and firing ranges are often very similar to those encountered on indus- 
trial property. 

The needs of industry for vegetation control vary with the use to 
which the land is to be put. The vegetation control objectives peculiar 
to railroads, highways, and other industrial lands will be discussed under 
various headings in Sec. III. 

Each situation presents its own problems. Species composition is an 
important consideration, and a plant census is essential to efficient vege- 
tation control by chemical means. Ecological factors must be studied in 
determining practical objectives. Only by a working knowledge of plant 
taxonomy and ecology in addition to the new technology related to herbi- 
cides can the most efficient vegetation control be accomplished. 


Herbicide research is being undertaken on such an extensive scale at 
the present time that it is difficult, if not impossible, to mention in a 
review of this nature all the compounds referred to in the literature as 
showing promise for one or another industrial vegetation control prob- 
lem. Discussion will be confined to those herbicides that have already 
found a place. 

Knowledge of a chemical tool is as essential to its proper use as 
knowledge of a mechanical device. Understanding of the nature of the 
physiological effect of an herbicide on the plant, variation in species 
response, the importance of the condition of the plant and various soil 


and climatic factors constitute the basic information needed for efficient 
use of an herbicide. 

1. Chlorophenoxyacetic Acids 

Two members of this family of plant growth regulators have come 
into wide use for industrial vegetation control, 2,4-dichlorophenoxyacetic 
acid (hereafter called 2,4-D) and 2,4,5-trichlorophenoxyaeetic acid 
(hereafter called 2,4,5-T). 

a. Derivatives and Formulations. The acids themselves are seldom 
employed because certain salts and esters are more readily formulated. 
Early in the development of 2,4-D it became evident that under ordinary 
conditions its alkyl esters were more effective herbicides than its salts. 
The alkyl esters of both 2,4-1) and 2,4,5-T came into use for industrial 
vegetation control and particularly for control of woody plants. 

Recently esters of higher molecular weight have virtually replaced 
the alkyl esters in the United States for industrial vegetation control 
purposes. The lower vapor pressure of such materials reduces the likeli- 
hood of sufficient volatilization occurring from sprayed surfaces to result 
in damage to unsprayed vegetation (Allen, 1950). Mullison et al. 
(1951) have shown that the hcrbicidal activity of certain glycol ether 
esters of 2,4-D is greater on many plant species than the common alkyl 
esters of 2,4-D. 

Commercial formulations are generally emulsifiable, although they 
may be diluted with straight oil for certain uses. Many formulations 
have an acid equivalent concentration per gallon of 4 Ib. of either 2,4-D, 
2,4,5-T or a fifty-fifty mixture of these two. 

b. Some Physiologic Aspects. The physiology of the action of 2,4-D 
and the influence of various environmental factors has been discussed 
in an earlier review in Advances in Agronomy (Crafts and Harvey, 
1949) and also by Mitchell (1948). 2,4,5-T appears to operate by much 
the same mechanism and is probably subject to the same internal and 
external influences (Linder et al., 1949). A few points bear emphasis 
because of their relationship to successful use of these compounds. 

Spraying operations must necessarily extend over as long a season 
as possible to make industrial use of herbicides a practical proposition. 
There is often a tendency to begin spraying brush and rapidly elongating 
herbaceous perennials at an early date, but experience has shown this 
practice to result in relatively poor kill. This phenomenon appears to be 
related to the transport of the herbicide from leaves to stems and roots, 
which Mitchell and Brown (1946) have found occurs in association with 
organic food materials within the plant. Spraying foliage of woody plants 
before it is fully developed and is providing excess products of photosyn- 


thesis for movement downward frequently gives inferior results in terms 
of root and crown kill. Likewise applications early in the growth of an 
herbaceous perennial frequently result in a poor kill of underground 
parts, apparently because it is still drawing on underground reserves 
and has not yet begun to return an excess of food materials to storage 

Experiments with perennial weeds, such as Canada thistle, indicate 
that as maturity approaches poor results are obtained, again probably 
because of limited transport. Such principles should be considered in 
spraying mixed vegetation on industrial grounds. Late growing season 
treatments of herbaceous weeds are generally profitable only where 
earlier mowing has induced resumption of vegetative growth. 

Tree saplings or suckering growth of woody plants that have previ- 
ously been cut off do not reach physiological maturity in the sense that 
an herbaceous plant does at time of seed formation. Spraying opera- 
tions on woody vegetation have proved successful throughout the summer 
(Durr, 1950). 

The effects of atmospheric and soil conditions on the performance 
of an herbicide is an important consideration in planning the continuous 
spraying operations essential for many industrial uses. Weaver et al. 
(1946) found that 2,4-D in oil solution was not removed from foliage by 
simulated rain. Rainfall soon after spraying with emulsions appears to 
have no adverse effect when esters of chlorophenoxyacetic acids are used. 
Once the water has evaporated the residual ester is removed from the 
leaf with difficulty. 

The herbicidal effectiveness of chlorophenoxyacetic acids has been 
observed in the field to be correlated to some degree with growth rate 
(Marth and Davis, 1945). Lee (1949) reports that corn is most likely 
to suffer injury from 2,4-D applications when moisture and temper- 
ature conditions are favorable to good growth. The more tolerant 
weeds and woody plants appear to be influenced in their response in a 
similar manner. Low temperatures, such as may occur in the early 
spring, are not conducive to good weed kill apparently because of re- 
tarded growth. Kill of the more tolerant species, for example white ash 
and cattail, has been observed to be much more complete during hot 
weather than when cool weather follows spraying. Soil moisture de- 
ficiencies that materially retard growth appear to inhibit the kill of 
woody as well as herbaceous species (Durr, 1950). 

c. Compound Specificity. Both woody and herbaceous plants are 
being controlled with these compounds on industrial lands. The use of 
2,4-D for control of herbaceous weeds is too well known by agronomists 
to call for extensive discussion in this review. In general the principles 


of herbaceous weed control on roadsides, mill and factory grounds, etc., 
are similar to those established for perennial weed control in cultivated 

Hainner and Tukey (1946) were among the first to point out the 
possibilities of killing a variety of woody species with 2,4-D. The use 
of 2,4-D for woody vegetation control on electric utility right-of-ways 
dates from 1945. From the beginning of this work certain woody species 
appeared resistant to 2,4-D, and the success of the chemical for control- 
ling right-of-way brush growth appeared very much in doubt. Thus 
Ashbaugh and Barrens (1946) listed hickory, maple, oak, and members 
of the genus Rubus as being difficult to kill. Early in 1947 the writer 
observed that highway right-of-way plots sprayed with an ester of 2,4-D 
in 1945 and again in 1946 were becoming increasingly populated with 
blackberry. Elm, willow, sumac, and elderberry had been eliminated. 
Although blackberry may be acceptable on some industrial grounds it is 
generally considered undesirable. 

The specific action of derivatives of 2,4,5-T on many plants that are 
tolerant to 2,4-D was first reported by Tain (1947) who found it to be 
more active than 2,4-D on a number of species in Hawaii including 
eucalyptus and lantana, and also by Barrons and Coulter (1947a), who 
found it very active on blackberry and other members of the genus 
Rubus. Subsequently 2,4, 5-T has been observed to be more active than 
2,4-D on a number of woody plants including mesquite, osage orange, 
maples, and poison ivy. 

Mixtures of esters of 2,4-D and 2,4,5-T containing one-third to one- 
half of the latter were soon placed on the market, frequently under the 
name of "brushkillers." Such mixtures have been widely used for 
woody plant control since 1948. Where the objective is the control of a 
single species, known to be susceptible to one or the other component, 
2,4-D or 2,4,5-T may be used alone. For mixed woody populations, so 
prevalent on right-of-ways, mixtures of the two compounds have proved 
best. Most species appear to be at least as susceptible to a mixture of 
2,4-D and 2,4,5-T as to 2,4-D alone, willow being one established excep- 
tion (Butler, 1950). 

Where control of herbaceous weeds is the primary objective, 2,4-D 
formulations generally prove adequate or even superior to 2,4-D-2,4,5-T 
mixtures. Some herbaceous species, such as horsenettle and ground 
cherry, are considerably more susceptible to 2,4,5-T than to 2,4-D. Re- 
gardless of the objective there is much to recommend a careful species 
census prior to a choice of spray material. 

d. Application Methods. Five methods are being employed for the 
application of chlorophenoxy acetic acid weed killers to woody growth. 


1. Foliage spraying during the season of active growth in relatively 
large volume of water from ground equipment. 

2. Low volume foliage application with ground equipment using oil 
or water as a carrier. 

3. Low volume foliage application by aircraft with oil or oil-water 
emulsions as a carrier. 

4. Application to bark at the base of the plant (basal application) 
during either the dormant or growing season using oil as a carrier. 

5. Application in oil to cut stumps at any season of the year. 
Smith (1946) found that 2,4-D was absorbed and translocated when 

applied as a coarse discontinuous spray thus permitting low volume 
application. Although low volume spraying is now almost a universal 
practice in agriculture, high volumes are commonly utilized in applying 
chlorophenoxyacetic acids for industrial vegetation control. High vol- 
ume spraying minimizes risk from drift and provides maximum coverage 
of dense vegetation often growing at different levels. This method is 
by far the most important at the present time and constitutes the basis 
of most control programs, particularly where plant populations are large 
(Ashbaugh, 1950). Other methods may be employed to meet specialized 
problems and conditions. 

Much foliage spraying is done with a concentration of 3 to 4 Ib. 
acid equivalent per 100 gallons of spray applied in a volume adequate 
to wet the foliage. The experience of many operators indicates the im- 
portance of wetting all sides of a woody plant and driving the spray into 
dense growth in order to wet the stems (Suggitt, 1950). The relative 
importance of stem vs. leaf wetting by high volume aqueous sprays has 
not been clearly established, although the work of Mullison (1952) on 
beans has shown that absorption of lethal doses can take place through 
succulent stems. 

Low volume spraying l>y airplane or ground equipment has a definite 
place where water is difficult to procure or on land inaccessible to spray 
trucks. Low volume treatment is most successful where vegetation is 
not dense. There is inherently more drift hazard from a low volume, 
highly concentrated spray than from a high volume spray, and the 
sensitivity of crops adjacent to areas to be treated should be carefully 

Hamner and Tukey (1946) first reported experiments in which 2,4-D 
was applied to cut surfaces. Early field results on stump treatment 
were promising (Anonymous, 1946). Barrens and Coulter (1948) re- 
ported good results with stump treatment at all times of the year, and 
pointed to preliminary results on application to uncut bark. Subse- 
quently a number of workers have reported experiments on stump and 


basal application (Barrens and Coulter, 1947; Egler, 1949; Coulter, 
1950, 1951; Beatty, 1950). 2,4,5-T has given superior results on most 
species for basal or stump treatment. Applications during summer and 
at varying times during the dormant season have proved successful; 
however, Coulter (1950) points to the field experience of a number of 
users who have obtained best results in late winter and spring. 

Oil is used as a carrier for 2,4,5-T or 2,4-D in stump and fcasal ap- 
plication. Fuel oils and kerosene have proved as effective as other oils 
(Barrens and Coulter, 1947c). The concentration of 2,4,5-T generally 
recommended by manufacturers for stump and basal spraying varies 
from 12 to 20 Ib. per 100 gallons. Coulter (1950) states that 16 Ib. per 
100 gallons of oil is the most practical concentration. Adequate volume 
must be applied thoroughly to saturate the bark from the ground line 
to the cut surface of the stump or up about 2 ft. when uncut brush is 
being treated. 

Certain species, including red maple, appear more susceptible to basal 
or stump treatment than to foliage sprays (Beatty, 1950). Klingman 
(1950) has listed a number of additional advantages of basal treatment. 
Currently basal bark treatment seems to be desirable under the following 
circumstances : 

1. Where original stands are thin or where earlier spraying has 
greatly reduced stands. 

2. Where adjacent sensitive plants make blanket foliage spraying 

3. Where lack of suitable power equipment precludes conventional 
foliage application. 

4. Where labor is lacking during the summer or where it is desirable 
to extend the season of operations to reduce seasonal variations in labor 

5. Where species such as red maple predominate which may be more 
readily controlled by a basal treatment. 

Stump treatment appears to be profitable wherever trees must be cut 
before building new lines or where, for esthetic reasons, visibility, or 
fire breaks it is not desirable to leave dead trees or brush standing. 

e. Application Precautions. Spray operators must exercise due 
caution in using chlorophenoxyacetic acids because of the hypersensitiv- 
ity of certain crop and ornamental plants which may be growing adjacent 
to treated areas. Cotton, grape, tomato, and papaya are plants that 
have most often shown responses when growing near treated land. Mal- 
formed leaves do not necessarily indicate a reduction in productivity 
of these crops; however, sound public relations policy dictates great 
caution on the part of spray operators. 


Three ways in which chlorophenoxyacetic acids may reach unsprayed 
areas are recognized. 

1. Drift of spray particles. 

2. Blowing of dust from soil and plant surfaces following spraying. 

3. Drift of vapor volatilizing from sprayed surfaces. 

In the writer's opinion the likelihood of their occurrence is in the 
order named. 

(Hose observation will reveal very tiny droplets arising from spray 
guns or booms and moving vertically in thermal currents as well as 
laterally in the wind. Reduction of pressure to ensure large droplets, 
careful handling of spray guns and booms, and due consideration for 
wind direction and velocity will materially aid in avoiding trouble from 
drift. Dormant basal treatment or late season foliage spraying may 
often be safely practiced on areas that must be skipped during the regu- 
lar season of operations. Drift from oil solutions as used for dormant 
spraying must not be overlooked when hypersensitive woody plants such 
as grapes are growing nearby. 

Salts of 2,4-D and 2,4,5-T are so low in volatility that it is unlikely 
that vapor drift can cause foliar effects on the most sensitive plants 
(Mullison, 1949). The alkyl esters are considered to be sufficiently 
volatile to account for some of the responses that have occurred on uu- 
sprayed areas (Tafuro et al , 1950). The higher molecular weight esters 
are of very low volatility and it appears unlikely that they vaporize suffi- 
ciently to cause trouble out-of-doors when, even in closed containers, the 
biological effects of their vapor is negligible (Allen, 1950; King and 
Kramer, 1951). Blowing of chlorophenoxyacetic acid derivatives ad- 
hering to soil dust, leaf hairs, and other particles undoubtedly occurs 
and can account for effects on plants that were upwind at the time of 
spraying. The prevalence of this mode of movement as a source of 
trouble is difficult to ascertain. Airplane spraying presents special 
hazards, and Raynor (1950) has offered suggestions for safe use. 

2. Sodium Chlorate 

The use of sodium chlorate for the eradication of noxious perennial 
weeds on crop land is well known to agronomists. It has also been 
widely used for many years for roadbed spraying on railroads in the 
United States and Canada. 

Sodium chlorate kills top growth by contact action and is system - 
ically toxic following root absorption. It is a powerful oxidizing agent 
and presumably kills by some oxidizing action. It is nonselective, al- 
though some species require higher dosages than others for a lethal effect. 
Moderate dosages may give a contact kill of all top growth of herbaceous 


vegetation, but fail to kiJl underground parts of tolerant species. It is 
a common observation on railroad beds following a few years spraying 
with the dosages frequently used that many herbaceous non-grasses are 
eliminated whereas perennial grasses such as quack, Johnson, and 
Bermuda grass persist. Woody plants, such as Virginia creeper and 
trumpet vine that invade the roadbed, and certain herbaceous broad - 
leaved perennials, such as bouncing bet, are difficult to eradicate with 
economic rates of application. Vegetation control, through contact 
foliage burning and limited systemic stunting, is the most common ac- 
complishment on the more tolerant plants. Higher doses than commonly 
employed will result in eradication. 

The success of a particular rate of application of sodium chlorate 
varies with soil moisture. Excessive rainfall leaches the compound read- 
ily. Crafts (1935) found no evidence of adsorption by soil colloids. 
His studies indicated that chlorate distribution in soils is largely deter- 
mined by the amount of water that passes through the soil following 
application of the chemical. 

Soil fertility factors in relation to chlorate absorption by roots have 
been studied extensively. Crafts (1939) found that for the same degree 
of plant kill on fertile soils higher dosages were required than on soils 
low in fertility. Nitrate ions were found by Crafts to inhibit absorption 
of chlorate. Even on railroad beds, where soil fertility is not ordinarily 
considered, because of stone or cinder ballast, it is frequently observed 
that poorer results are obtained where the underlying soil is of a fertile 

3. Sodium Trichloroacetate 

Among the most recently developed herbicides to come into wide use for 
industrial vegetation control is sodium trichloroacetate, often called sodium 
TCA. This compound, which has a growth-suppressing and at suitable 
dosages a lethal effect on many grasses, is widely used as a component 
of mixed sprays for railroad beds and other areas where complete vegeta- 
tion control is desired. Special problems such as control of phragmites 
grass, cattail, and Johnson grass are currently being handled with 
sodium TCA or with a mixture of this herbicide with other compounds. 

Sodium TCA enters plants primarily through the root system al- 
though under some conditions limited foliar translocation may take place 
(Haygood, 19.51; Barrens and Hummer, 1951). The compound, which 
is very soluble in water, is subject to leaching and decomposition in the 
soil (Loustalot and Ferrer, 1950). 

Barrens and Hummer (1951) have discussed the various plant re- 
sponses to sodium TCA. Buds of many perennial grasses exhibit a pro- 


found dormancy which is followed by death or recovery, depending on 
dosage and various other factors. Many non-grasses are tolerant of 
sodium TCA while others are inhibited in growth. 

Rates found useful for perennial grass control vary from 50 Ib. per 
acre upward, depending on species and various external factors. Be- 
cause sodium TCA has little effect on many non-grasses, it is frequently 
applied in combination with other herbicides. In some instances, in- 
vestigators have observed superior results when the grass was in a weak- 
ened condition as a result of prior mowing or spraying. Barrens and 
Hummer (1951) presented data indicating a relationship between low- 
ered carbohydrate reserves and good grass kill. When combined with 
a phenolic contact herbicide which burned grass foliage to the ground 
the writer has, in some instances, observed a better kill than when sodium 
TCA was applied alone. Barrons and Hummer (1951) found that 
sodium TCA was absorbed by all plants tested but the limited amount 
present in grass foliage compared with that in foliage of TCA-tolerant 
plants suggests that it may be decomposed readily within the susceptible 
species. These authors suggest that a reduction in grass top-growth, by 
mowing or by a contact herbicide, insures a greater concentration of 
TCA in the cambial regions where it apparently has its greatest effect. 

Sodium TCA is sold in dry form to be made into a spray or, in some 
instances, to be mixed with a suitable diluent for dry application. A 
concentrated solution is also available for railroads or other users of 
tank car quantities. It presents no particular hazards to warmblooded 
animals, does not support combustion and, although corrosive to certain 
metals on long exposure, it appears to present no corrosion problem to 
rails or fences that may be wet with a spray. Furthermore, a corrosion 
inhibitor is usually incorporated in commercial sodium TCA powder and 
concentrated solutions. 

Soil moisture is the important external factor governing the effective- 
ness of sodium TCA. Moisture is needed to put the chemical in the soil 
solution. Excess rainfall may promote leaching below the zone of active 
root absorption. 

4. Substituted Phenols 

Many chloro and nitro substituted phenols are acutely phytotoxic. 
Pentachlorophenol is now widely used as a fortifying agent for herbi- 
cidal oils (Sherwood, 1950). Crafts (1945) found dinitro-ortho-second- 
ary butyl phenol (called DNOSBP) to be the most phytotoxic of the 
substituted phenols, and this compound is now used in formulating gen- 
eral contact sprays. According to Crafts and Reiber (1948), DNOSBP 
is approximately four times as phytotoxic as pentachlorophenol. It is 


now available under proprietary names as a general contact weedkiller. 

The nature of the effect of DNOSBP has recently been reviewed by 
Barrens (1951). Little if any translocation of the toxicant occurs 
within most plant tissues. Where sufficient oil is present in the spray to 
move through plant tissues, DNOSBP will also be moved in oil solution. 
The effect of pentachlorophenol is also largely confined to tissues wet 
with a spray or reached by the oil component (Barrons, 1949). 

Although these phenolic compounds may be used to fortify straight 
oil sprays they are more frequently applied as oil water emulsions with 
the phenolic toxicant in the oil phase. According to Sherwood (1950) 
pentachlorophenol-fortified oil may be used at one-fifth the volume of a 
straight oil with equivalent results. Crafts and Reiber (1948), who in- 
vestigated the quantitative relationships of oil and phenolic fortifying 
agents, concluded that for broadleaved weeds there was little advantage 
in using more than 3 per cent oil as a carrier for DNOSBP in the final 
spray. Increasing the oil content to around 10 per cent improved the 
kill of grasses. It is a common practice in preparing contact sprays 
either of pentachlorophenol or DNOSBP to use about 20 per cent oil 
in order to ensure adequate penetration to the growing points of grasses. 

DNOSBP is very soluble in oil and the commercial formulations 
available may be mixed with most oils in any proportions. Oils in the 
boiling range of the fuel oils, diesel oil, and kerosene are commonly em- 
ployed. Pentachlorophenol is considerably less oil soluble and an oil 
solvent high in aromatics is essential for the preparation of a satisfactory 
spray. There are on the market concentrated emulsifiable pentachloro- 
phenol formulations to which additional oil must be added. 

The use of phenolic herbicides in fortified oils or oil emulsions is limited 
to specialized vegetation control problems because of their temporary 
contact or " chemical mowing " effect. Where perennial vegetation pre- 
dominates and rainfall is prevalent repeated applications are required 
for continued control. Annual plants may be killed with phenolic sprays 
especially when young. In semi-arid sections where annuals predominate 
and dry soil prevents emergence of more seedlings, one spraying will 
have a lasting effect. Thus in California, much roadside vegetation 
control for fire protection and also ditchbank weed control is accom- 
plished with emulsions containing pentachlorophenol or DNOSBP. 

5. Herbicidal Oils 

Various petroleum fractions have been used for many years for the 
control of herbaceous vegetation particularly in the western United 
States. Creosote oil and other coal by-product oils have occasionally 
been used. 


Straight oils, like phenolic-fortified emulsions, are contact herbicides. 
Only tissues actually wet by an oil spray or reached as a result of in- 
ternal movement are affected. Most plants are susceptible to the action 
of herbicidal oils; however certain species, notably members of the 
UnibclUferae family, are quite tolerant. 

Minshall and Helsori (1949), in a study of the effects of herbicidal 
oils on the physiology of plants, confirmed earlier reports that internal 
movement is largely through intercellular spaces. Using a dye dissolved 
in oil they failed to find evidence that oil moved into living cells. Crafts 
(1946) suggests that plants differ in the manner in which their proto- 
plasm reacts to oil, thus postulating cellular absorption. Dallyn and 
Sweet (1951) report that aromatic oils actually penetrate cells of oil- 
susceptible plants, but in tolerent species the oil remains in intercellular 

Crafts and Reiber (1948) distinguish between the acute oil toxicity 
resulting in a rapid burning of foliage and chronic toxicity resulting in 
a yellowing of leaves, stunting, and subsequent death. The lower boiling 
aromatic fractions are responsible for acute plant responses, whereas 
higher boiling components which persist within plant tissues often have 
a chronic effect. Minshall and llelson (1949) found that a cessation of 
photosynthesis and transpiration followed oil treatment. Oil-tolerant 
plants later resumed these processes whereas the susceptible plants died. 
Greene (1936) found that in most instances respiration was lowered fol- 
lowing* oil spraying. Minshall and Ilelson (1949) postulate that oils kill 
by disrupting internal water relations which in turn affect transpiration 
and other processes. 

The observations of early users of oils as herbicides indicated thai 
crude fractions were more toxic to plants than refined fractions. Treat- 
ments that removed unsaturates and aromatics reduced toxicity. Gray 
and de Ong (1926) found that the sulfonation test, which indicates the 
proportion of unsaturated compounds present, may be used as an index 
of phytotoxicity. However, ('rafts and Reiber (1948) have shown that 
certain unsulfonatable residues are often toxic. 

In recent years a number of highly phytotoxic petroleum oils have 
been placed on the market especially for weed control purposes. Crafts 
and Harvey (1949) list fourteen proprietory weed oils for general con- 
tact weed control on sale in California in 1948. These special oils vary 
to some degree although all are high in aromatics. 

The choice of straight oil or a phenolic-fortified oil emulsion where 
contact killing of weeds is desired is largely a question of economics. 
Crafts and Harvey (1949) express the view that since the use of fortified 


oil emulsions greatly extends the service of a given volume of oil they 
will probably become widely used as their properties become known. 

Emulsifiable aromatic petroleum fractions high in xylenes are cur- 
rently used for the control of submerged plants in irrigation canals and 
ditches. (Anonymous, 1949). They have essentially a contact action on 
aquatic vegetation, and regrowth from roots of anchored aquatics occurs 

6. Boron Compounds 

The phytotoxic effects of excesses of boron in the soil have been 
recognized for many decades and much experimental work on the subject 
has been conducted by plant nutrition and fertilizer investigators. The 
use of borax, a hydrated sodium tetmborate, and other boron compounds 
for vegetation control was apparently an outgrowth of such work. 

Unlike sodium chlorate and the organic compounds used as herbicides, 
chemicals in this group owe their herbicidal effect to a phytotoxic ele- 
ment, boron, rather than to a particular molecular structure of other- 
wise nontoxie elements. The borate ion is absorbed by the roots and 
becomes systemically toxic. 

A coarse grade of sodium borate sold under the proprietary name 
Borascu has been used for several years for soil sterilization of areas to 
be kept free of vegetation such as parking lots and driveways. Recently 
a form higher in boron content, designated as concentrated Borascu, has 
become available. 

Boron compounds have a low level of toxicity to warmblooded ani- 
mals and do not support combustion. They are relatively cheap, but 
large quantities are required for effective control of vegetation. As most 
boron -carry ing ores are mined in California, transportation is a major 
cost factor when used in eastern or midwestern United States or Canada. 

Soil properties and rainfall are the important factors in the success 
of boron compounds for soil sterilization. Crafts (1939), who studied 
the response of plants to borax in three soils at two nutrient levels, con- 
cluded that it was most effective in the lighter and more porous soils, 
lie found that soil fertility per se had no effect on borax toxicity as it 
does with sodium chlorate. 

Crafts and Raynor (1936) found that the toxicity of borax applied 
at herbicidal dosages on a given soil varies with the rate of fixation and 
leaching. Soil moisture is essential to move the slightly soluble borax 
into the zone or root growth. Fixation tends to hold the borax near the 
surface particularly in clay soils, but on porous soil it may be leached 
below the zone of maximum root growth. That fixation accounts for loss 
of toxicity was shown by Crafts and Raynor (1936), who observed a 


gradual decrease in the toxic properties of soil in cans even though no 
boron was lost from the cultures. The rate of toxicity loss was greatest 
in clay soil high in lime and was lowest in a sandy loam. 

During a season of high summer rainfall the writer has observed 
complete failure of two ton of borax per acre on a clay loam while the 
same dosage on an adjacent sandy soil gave a complete kill of existing 
herbaceous vegetation. Boron compounds appear to have the greatest 
initial effect and to give the longest period of control on light soils in 
areas of moderate to light rainfall. 

Plants vary considerably in their boron tolerance. Grasses as a group 
are relatively tolerant, however, certain broadleaved species also require 
very heavy dosages for effective control. 

7. Sodium Arsenite 

For many years sodium arsenite was used for soil sterilization of rail- 
road beds and other industrial grounds; however, its high degree of 
toxicity to animals has been a cause of considerable livestock loss. It is 
considered safe only on well-fenced areas where there is no chance of 
stock eating sprayed vegetation or drinking water that may be contami- 
nated by leaching from sprayed areas. Great care must be exercised in 
handling arsenite solutions to avoid contact by the operator or inadvert- 
ent spillage where stock may have access to it. 

Like borax, sodium arsenite owes its herbicidal properties to a toxic 
element, in this instance arsenic. Solutions sprayed on foliage have a 
contact herbicidal effect; however, the killing of established plants re- 
sults from systemic poisoning following absorption of the arsenite ion 
from the soil. 

As the highly soluble sodium arsenite must be present in the root 
zone to be absorbed, rainfall and the textural grade of the soil are im- 
portant factors in toxicity*. (Crafts and Eosenfells, 1939). In addition 
to the kaolinitic colloids of the soil, the presence of red iron oxide was 
found by these authors to reduce arsenic toxicity. Like borax, sodium 
arsenite tends to be most successful on light soils in areas of moderate 
to light rainfall. 

As with other herbicides, plant species vary in their tolerance. Deep- 
rooted perennials growing on soils where much of the arsenite may be 
fixed in the surface layer are often difficult to kill. Certain summer an- 
nuals that are natives of arid or semi-arid regions show considerable 
physiologic tolerance (Bobbins et al., 1942). 

Dosages of sodium arsenite required for soil sterilization vary from 
about 4 to 8 Ib. per square rod, depending on soil and rainfall factors. 


Lower rates applied as a foliage spray will kill top growth by contact 
but root kill may be limited. 

8. Ammonium Sulfamate 

This herbicide has a systemic effect on most plants and is translocated 
from foliage to the stems and underground parts of many species. The 
use of ammonium sulfamate on industrial lands is primarily for woody 
plant control. Grasses and other herbaceous plants adequately wet with 
the spray will be killed. 

Jacobs (1950) has reported extensive commercial scale comparisons 
between ammonium sulfamate and esters of the chlorophenoxyacetic 
acids for brush control on utility right-of-ways. He reports that at a 
somewhat higher initial cost ammonium sulfamate gives a more complete 
kill of mixed woody species than the chlorophenoxyacetic acids, and less 
frequent applications thus need to be applied. Jacobs points out that 
ammonium sulfamate gives a superior kill of oaks, hickories, maples, and 
wild cherries, whereas certain other species are more sensitive to 2,4-D 
and 2,4,5-T. He suggests the use of ammonium sulfamate on mountain- 
ous and relatively inaccessible right-of-ways where cost of application 
is high and where the most effective killer will lengthen the period be- 
tween sprays. Greco (1951) has reported successful eradication of a 
variety of marshland woody species with ammonium sulfamate. 

9. CMU 3-(p-chlorophcnyl)-l,2-dimethyl urea 

A discussion of the many new experimental herbicides now being 
investigated for various industrial vegetation control problems is beyond 
the scope of this review. One of particular note is 3-(p-chlorophenyl)- 
1,1-dimethyl urea, called by its manufacturers CMU. 

Bucha and Todd (1951) and Wolf (1951) have presented data on the 
nature of the herbicidal effect of this compound. It is toxic to most 
plants. It is absorbed from the soil by the roots and appears to be trans- 
ported to above-ground parts. CMU is very persistent in the soil. 

Young and Loomis (1951) reported that effective vegetation control 
was obtained for one season on railroad cinder ballast with the use of 
20 Ib. of CMU per acre. The vegetation controlled included quackgrass 
and miscellaneous annual and perennial plants. Comparable results 
were obtained when 10 Ib. of CMU were applied in combination with 80 
Ib. of sodium chlorate or 30 Ib. of sodium TCA. Viehmeyer et al. (1951) 
reported successful control of mixed vegetation along an irrigation ditch 
with CMU. Further work will be required before the place of CMU in 
various vegetation control programs can be determined. 


JO. Mixtures of Herbicides 

Because of variation in response of plant species to different herbi- 
cides many vegetation control problems must be handled with mixtures. 
The common use of 2,4-D and 2,4,5-T esters for control of woody plants 
has already been described. 

Mixtures of sodium chlorate and boron compounds are being used 
for killing existing vegetation and providing a germination-preventive 
residue. Chlorax and Polybor-chlorate are proprietary products of this 
type. Taylor (1951) found a mixture of sodium chlorate and sodium 
TCA to be among the most successful treatments for railroad beds, and 
this combination is now used on some railroads. 

A mixture of borax and sodium T( -A has shown promise for complete 
vegetation control and sodium 2,4-D added to this combination has im- 
proved the kill of deep-rooted perennials In the mixtures referred to 
above sodium TCA serves primarily as a grass-controlling agent. When- 
ever employing sodium TCA for grass control another herbicide such as 
2,4-D must also be used if non-grasses are present. An effective mixture 
for the control of established vegetation consists of a phenolic-fortified 
oil emulsion with a 2,4-1) ester in the oil phase and sodium TCA in the 
water phase. 


So many industrial vegetation control problems have only recently 
been attacked with chemical tools, that further experience must be gained 
before the most efficient and economic methods for each type of problem 
will be fully known. Variations in soil, rainfall, length of growing sea- 
son, and species composition all have their influence on choice of chemicals 
as well as methods and timing of application. Supply and cost of labor 
is another vital factor. No blanket programs can be suggested in a re- 
view of this type, however certain problems and their solution will be 

1. Some Ecological Considerations 

The old saying "nature abhors a vacuum" is never more evident 
than following certain herbicide applications. The most persistent soil 
sterilants are eventually leached or inactivated below the phytotoxic 
level. Reinvasion then takes place and plant successions may be ob- 
served influenced by species tolerance to the chemical and prevailing 
ecological factors. 

The continual elimination of all vegetation essential for certain lands 
such as railroad beds is difficult and expensive, particularly in humid 


regions. Before deciding on the need for a vegetation-free condition in 
any situation one should consider the practicability of a grass cover 
maintained relatively free of non-grasses by chlorophenoxyacetic acid 
sprays. Many people have killed all existing vegetation only to find 
reinvasion occurring sooner than anticipated, frequently with species 
more objectionable than those which occupied the area before treatment. 
Wherever a cover of a short-growing perennial grass will serve the pur- 
pose, it is generally less expensive to maintain than a sterile soil. Mow- 
ing soon after flowering will keep most grasses at a reasonable level. 
Where mechanical mowing is impractical a contact spray of a penta- 
chlorophenol or DNOSBP-fortified oil emulsion will provide a "chemical 
mowing" as required. Modest dosages of sodium T( 1 A may be used for 
suppressing grass growth. When using a selective grass suppressing 
agent, snch as sodium TO A, it is very necessary to include an herbicide, 
such as 2,4-D, to control the non-grasses; otherwise they may grow 
rampant because of reduced grass competition. 

Although grassland is usually considered the most desirable cover 
for right-of-ways, Egler (1951) has pointed out that reinvasion with 
certain woody plants will readily occur in grass communities in New 
England. He further reports that several types of shrub communities 
have persisted for many years without reinvasion with tree species. 
Where tall woody plants cannot be tolerated but a shrub cover is ac- 
ceptable, the studies of Egler (1951 ) may have particular significance. 
He proposes conversion from a mixed tree-shrub community to a shrub 
or a shrub-grass community by spot treatment with chlorophenoxyacetic 
acids rather than a blanket spray. 

The ease of establishing and maintaining grassed land in humid areas 
where woody plants are normally present varies with soil factors. In 
poor acid soils, where grass has difficulty in becoming established, rein- 
vasion with woody plants and non-grass herbaceous species may occur 
qiiite readily. Where a thick turf develops, as competitive plants are 
eliminated reinvasion is frequently rather slow 

2. Utility Right^Ways 

Potential savings by the use of chemical brush control methods as 
compared with repeated hand cutting have been estimated by a number 
of right-of-way maintenance engineers with whom the writer has dis- 
cussed the subject to vary from 50 to 75 per cent. Costs during the first 
year or two while the area is being converted from brush to grassland 
are not necessarily higher than the cost per annum for cutting. Savings 
are realized during ensuing years when only an occasional maintenance 
treatment is required. 


Many of the factors one must consider in deciding on a program for 
brush control on right-of-ways have already been discussed. Foliage 
applications of a chlorophenoxyacetic acid brush killer are generally 
used for the conversion program to eliminate the bulk of the woody plant 
population. Basal dormant treatment may be desirable where risks 
from summer spraying are great or where woody plant populations are 
relatively small. Ammonium sulfamate may have a place on inaccessible 
land, as suggested by Jacob (1950). The choice of basal vs. foliage 
spraying for maintenance of an area after much of the brush has been 
eliminated is a subject currently being investigated by a number of 
public utilities. Stump treatment has proved especially useful when 
new lines are being established through wooded areas. 

Ashbaugh (1950) has discussed a program for brush control on util- 
ity right-of-ways which has proved successful in the mountains of west- 
ern Pennsylvania. Two foliage sprays of a chlorophenoxyacetic acid 
brush killer at yearly intervals have reduced the number of woody plants 
from between 4000 and 8000 per acre to less than 1000. During ensuing 
years basal spraying is employed for adequate maintenance. Ashbaugh 
reports that the West Penn Power Company with which he is associated 
has converted 5000 acres of right-of-way from brush land essentially to 
grassland. The frequency with which a maintenance spray is required 
will depend on many environmental factors that influence rate of growth 
and rate of reinvasion. 

Alternating herbicides in the maintenance program as suggested by 
Jacob (1950) may prove desirable. 

3. Highways 

Much roadside spraying has been aimed at woody plants, the prime 
vegetation control problem in humid areas. In general the problems of 
woody plant control along.highways are similar to those on utility right- 
of-ways. Accessibility with power equipment makes a high volume 
foliage spray highly practical in most situations. Basal applications 
have proved desirable in some instances for maintenance once the mass 
of woody vegetation has been eliminated. This method may also prove 
valuable where foliage spraying would jeopardize sensitive plants. Syl- 
wester (1950) has pointed out that brush control is essential on highways 
to improve visibility, to provide good drainage, and to minimize drifting 
snow. He reports considerable savings by the use of chemicals as con- 
trasted to hand cutting which permits rapid regrowth. 

In many instances highway maintenance authorities are responsible 
for the eradication of noxious perennial weeds growing in the right-of- 
way. Local weed control research has established the best methods for 


each species under varying environmental conditions. Bruto (1950) has 
discussed the use of herbicides for noxious weed control in Missouri. In 
areas where agricultural land is relatively free of ragweed, roadside 
spraying to kill this species is now practiced as a public health measure. 
(Anonymous, 1950; Vintinner, 1951). 

Vegetation near guard rails and traffic signs where mowing cannot 
be accomplished mechanically presents a special problem. The objective 
here is to eliminate tall-growing non-grasses and retard grass growth. 
Complete elimination of vegetation in such situations is not desirable in 
areas of high rainfall because of erosion and the inevitable reinvasion 
with weeds. No proved chemical program is being used, however lurka 
and Pridham (1950) have reported progress with several herbicide mix- 
tures. In arid sections where annuals predominate, contact sprays of 
oil or fortified oil emulsions are widely used around signs and guard rails 
as a fire preventive measure. 

Overall weed control for the sake of beautification is not a primary 
objective on most highways, but there are areas where it is being prac- 
ticed, particularly along parkways in metropolitan areas. In this con- 
nection 2,4-D is the most useful herbicide. By eliminating tall growing 
weeds with this herbicide a single mowing after grass flowering is often 
adequate to keep the vegetation short for the balance of the season. 

In humid areas where elimination of non-grass vegetation is desired, 
late spring and early summer spraying will often provide maximum kill 
of tall growing perennials such as golden rod, wild aster, and thistles. 
The same spray may fail to control other species which are low in growth 
at this time of the year, i.e., wild carrot, because grass and taller herba- 
ceous plants protect them from spray interception. Mowing after grass 
flowering followed by spraying after some weed regrowth has occurred 
is a recognized method of providing maximum kill. 

4. Railroads 

Complete elimination of vegetation on the roadbed is the universal 
objective of maintenance engineers. The width of this strip usually 
extends from 4 to 6 ft. beyond the edge of the ballast. Vegetation in 
this area causes slippage if it should lodge on the tracks. It impedes 
good drainage, shortens tie life, and endangers train crewmen who must 
often mount and dismount moving cars. 

For many years some spraying of roadbeds has been practiced and 
today a large proportion of the heavily traveled track in the United 
States and Canada is treated with herbicides. At one time sodium 
arsenite was widely employed, but livestock losses have discouraged its 
use by most railroads. Sodium chlorate is widely used for railroad 



spraying. Because this compound renders sprayed vegetation highly 
flammable calcium chloride is frequently included in the spray solution 
as a fire preventive measure. Several of the mixtures as discussed earlier 
are also employed (Rake, 1950). 

Much special equipment has been built by railroads and by contract 
spray operators for roadbed treatment. Rapid sectional controls that 
permit heavy application where vegetation requires and which may be 
quickly shut off where there is no vegetation are common to good equip- 
ment. When 2,4-1) is to be included in the spray, an injection system 

FIG. 1. Koadbed sprayer in operation. This is the lead car of a spray train 
consisting of tank cars and a locomotive. Note the series of valve handles in front 
of the operators used to control the various boom sections. 

FIG. 2. A railroad brush sprayer in operation. Ahead of this spray car are sev- 
eral tank cars all being pulled by a locomotive. 


which permits introduction of this herbicide into a mixture where safe 
to use and quick shutoff where hazards to adjacent plants dictate has 
been found useful. 

The control of vegetation between the roadbed and the fence by 
mowing or other mechanical means has long been a major section crew 
task. Railroads are taking an increasing interest in adapting the woody 
plant control methods so widely used on utility right-of-ways. Several 
special pieces of on-track equipment that permit spraying brush from a 
moving spray train have been constructed and are now in use. Foliage 
application of chlorophenoxyacetic acid brushkillers are employed. Gil- 
lingham (1951) has discussed such equipment and its use. 

Certain areas where fire hazard is great, such as under wooden 
trestles, are often treated with borax at high rates to provide a relatively 
vegetation-free condition for as long a period as possible. 

,7. Miscellaneous Problems 

Only a portion of the many programs now employed for vegetation 
control on various industrial lands have been reported in the literature. 
A few that have come to the writer's attention will be mentioned. 

For adequate fire protection oil tank farms require sparce vegetation 
throughout the area with bare soil near tanks. Grazing by cattle or 
sheep has proved useful for large areas while various chemical treat- 
ments are often used adjacent to the tanks. Herbicides may also be used 
for the elimination of unpalatable species in the grazed area. 

Problems of complete vegetation control are handled with various 
herbicides frequently in combination (Rake, 1950). Pole yards, trans- 
former stations, lumber storage areas and grounds near wooden build- 
ings are examples. Such areas should be covered with crushed rock, 
gravel, or cinders to prevent water and wind erosion. Contact sprays of 
phenolic herbicides have been used to keep vegetation at a minimum 
in ammunition storage areas without creating an erosion problem. 

Egler (1950) has reported the successful use of a chlorophenoxyacetic 
acid brushkiller for vegetation control on transmitter sites. By selective 
basal application species especially valuable for wildlife food or cover 
were preserved while less desirable species were eliminated. 

Both submersed and emergent aquatic plants may be a problem in 
irrigation ditch and canal channels and terrestial plants must be prop- 
erly managed on the banks. Methods of vegetation control on irrigation 
systems in the western United States have been thoroughly discussed in 
a recent bulletin (Anonymous, 1949). Burning, mowing, controlled graz- 
ing, and herbicides are all employed. The injection of emulsifiable 


petroleum fractions high in xylenes for the control of submerged aquatics 
in irrigation ditches is one of the more recent developments. 

Cattail in irrigation ditches of the Imperial Valley have been suc- 
cessfully killed with a spray containing an amine salt of 2,4-D, sodium 
TCA, and a wetting agent. Other emergent aquatic weeds being success- 
fully controlled with 2,4-D are lotus and alligator weed (Hess, 1946). 
This herbicide is now employed for the control of water hyacinth in 
canals and waterways in Florida and Louisiana (Hitchcock et al., 1949). 


Allen, W. W. 1950. Proc. Third Annual Southern Weed Control Conf. 7-12. 

Anonymous, 1946. Down to Earth 2 (3), 2-6. 

Anonymous, 1949. Control of weeds on irrigation systems. U.S. Dept. of Interior, 
Bureau of Eeclamation, 1-140. 

Ashbaugh, F. A. 1950. Down to Earth 6 (3), 2-4. 

Ashbaugh, F. A., and Barrens, K. C. 1946. Elec. Light and Power 24 (11), 56-60. 

Barrens, K. C. 1949. Proc. Third Annual Northeastern Weed Control Conf. 219-224. 

Barrens, K. C. 1951. Down to Earth 7 (3), 10-12. 

Barrens, K. C., and Coulter, L. L. 1947a. Proc. Fourth Annual North Central Weed 
Control Conf. 255. 

Barrens, K. C., and Coulter, L. L. 1947b. Proc. Fourth Annual North Central Weed 
Control Conf. 254-255. 

Barrons, K. C., and Coulter, L. L. 194 7c. Proc. Fourth Annual North Central Weed 
Control Conf. 254. 

Barrons, K. C., and Coulter L. L. 1948. Research Eept. North Central Weed Con- 
trol Conf. 

Barrons, K. C., and Hummer, R. W. 1951. Agr. Chemicals 6 (6), 48-50, 113-121. 

Beatty, R. H. 1950. Proc. Seventh Annual North Central Weed Control Conf. 123. 

Bruto, F. R. 1950. Down to Earth 6 (3), 9-10. 

Bucha, H. C., and Todd, C. W. 1951. Science 114, 493-494. 

Butler, C. C. 1950. Proc. Seventh Annual North Central Weed Control Conf. 125- 

Coulter, L. L. 1950. Proc. Seventh Annual North Central Weed Control Conf. 123- 

Coulter, L. L. 1951. Agr. Chemicals 6 (8), 34-36, 99. 

Crafts, A. S. 1935. Eilgardia 9, 437-457. 

Crafts, A. S. 1939. J. Agr. Research 58, 637-671. 

Crafts, A. S. 1945. Science 10, 417-418. 

Crafts, A. S. 1946. Plant Physiol 21, 345-361. 

Crafts, A. S., and Harvey, W. A. 1949. Advances in Agronomy 1, 289-315. 

Crafts, A. S., and Raynor, R. N. 1936. Hilgardia 10, 343-374. 

Crafts, A. S., and Reiber, H. G. 1948. Hilgardia 18, 77-156. 

Crafts, A. S., and Rosenfells, R. S. 1939. Hilgardia 12, 177-200. 

Dallyn, S. L., and Sweet, R. D. 1951. Proc. Fifth Annual Northeastern Weed Con- 
trol Conf. 13-17. 

Durr, B. 1950. Telephony Magazine 139 (5), 13-16; 139 (6), 18-20. 

Egler, F. E. 1949. Botan. Gaz. 112, 76-85. 

Egler, F. E. 1950. Down to Earth 5 (4), 9. 


Egler, F. E. 1951. Proc. Fifth Annual Northeastern Weed Control Con/. 251-254. 

Ewart, G. Y. 1951. Agr. Eng. 32, 152-158, 160. 

Gillingham, W. P. 1950. Compressed Air Mag. 56 (6), 150-154. 

Gray, G. P., and de Ong, E. B. 1926. Ind. Enff. Chem. 18, 175-180. 

Greco, E. C. 1951. Proc. Fourth Southern Weed Control Conf. 97-101. 

Greeve, J. E. 1936. Plant Physiol. 11, 101-113. 

Hamner, C. L., and Tukey, H. B. 1946. Botan. Gaz. 107, 376-385. 

Haygood, E. S. 1951. Proc. Fourth Annual Southern Weed Control Conf. 27-30. 

Hess, A. D. 1946. Proc. Third North Central Weed Control Conf. 119-120. 

Hitchcock, A. E., Zimmerman, P. W., Kirkpatrick, H., and Earl T. T. 1949. Contrib. 
Boyce Thompson Inst. 15, 363-401. 

lurka, H. H., and Pridham, A. M. S. 1950. Proc. Fifth Annual Northeastern Weed 
Control Conf. 329-332. 

Jacobs, H. L. 1950. Proc. Seventh Annual North Central Weed Control Conf. 113- 

King, L. J., and Kramer, J. A. 1951. Proc. Fifth Annual Northeastern Weed Con- 
trol Conf. 31-34. 

Klingman, D. L. 1950. Proc. Seventh Annual North Central Weed Control Conf. 

Lee, O. C. 1949. Proc. Sixth Annual North Central Weed Control Conf. 65-66. 

Linder, P. J., Brown, J. W., and Mitchell, J. W. 1949. Bot. Gaz. 110, 628-632. 

Loustalot, A. S., and Ferrer, R. 1950. Agronomy J. 42, 323-327. 

Marth, P. C., and Davis, F. F. 1945. Bot. Gae. 106, 463-472. 

Minshall, W. H., and Helson, V. A. 1949. Proc. Third Annual Northeastern Weed 
Control Conf. 8-13. 

Mitchell, J. W. 1948. Agr. Chemicals 3 (3), 28-30, 81. 

Mitchell, J. W., and Brown, J. W. 1946. Botan. Gaz. 107, 393-407. 

Mullison, W. R. 1949. Proc. Am. Soc. Hort. Sci. 53, 281-290. 

Mullison, W. R., Coulter, L. L., and Barrens, K. C. 1951. Proc. Fifth Annual 
Northeastern Weed Control Conf. 87-94. 

Mullison, W. R. 1952. Unpublished Data. 

Rake, D. W. 1950. Proc. Seventh Annual North Central Weed Control Conf. 116-117. 

Raynor, R. N. 1950. Proc. 1950 Meeting Agr. Aircraft Assoc. 27-30. 

Robbins, W. W., Crafts, A. S., and Raynor, R. N. 1942. Weed Control. McGraw- 
Hill Book Co. New York. 

Sherwood, L. V. 1950. Proc. Fourth Annual Northeastern Weed Control Conf. 85-87. 

Smith, H. H. 1946. Botan. Gaz. 107: 544-551. 

Suggitt, J. W. 1950. Chemistry in Canada 2, 197-200. 

Sylwester, E. P. 1950. Down to Earth 6 (2), 4-5. 

Tafuro, A. J., Van Geluwe, J. D., and Curtis, L. E. 1950. Proc. Fourth Annual 
Northeastern Weed Control Conf. 31-35. 

Tarn, R. K. 1947. Botan. Gas. 109, 194-203. 

Taylor, J. P. 1951. Proc. Fifth Annual Northeastern Weed Control Conf. 267-276. 

Viehmeyer, G., Hervert, F., and Rathke, C. 1951. Research Kept., North Central 
Weed Control Conf. 145. 

Vintinner, F. J. 1950. Proc. Fourth Annual Northeastern Weed Control Conf. 

Weaver, R. J., Minarik, C. E., and Boyd, F. T. 1946. Botan. Gaz. 107, 540-544. 

Wolf, D. E. 1951. Proc. North Central Weed Control Conf. 104. 

Young, I. W., and Loomis, W. E. 1951. Research Rept., North Central Weed Con- 
trol Conf. 145. 

Soil and the Growth of Forests 


DuLc Uiiwt'ttsity, Duihain, North Carolina 



T. Introduction .... . . . 330 

1. The Problem 331 

2. Measures of Forest Growth ... 331 

3. Soil Properties Related to Forest Giowth ... 332 

11. Soil as an Environment for Tree Roots 332 

1. Climate: Effectiveness and Distribution of Precipitation . . . 333 
"2. Soil Properties- Texture, Permeability, Aeration, Infiltration, 

Stonmess, and Organic Matter Content 334 

3. Topography: Slope, Subsurface Irrigation, and Water Table . 336 

4 Inheient Hooting Habits of Forest Trees . . 33(5 

III. Northeast em Region 337 

1. Comfei Types . . ... ... 337 

2. Hardwood Types . . 340 

IV. Lake States Region . . 342 

1. Aspen Type . . ... . .... 342 

2. Other Hardwood Types . . 346 

3. Conifer Types 348 

V. Central Hardwood Region .... . . 3.10 

VI. Prairie-Plains Region 357 

VI 1. West Coast Region 358 

1. Pacific Northwest . 358 

2. Culifoiuia 362 

VIII. Southern Appalachian Region 364 

IX. Southein Region 365 

1. Loblolly and Shortleaf Pines in Arkansas .... ... 365 

2. Black Locust HI Mississippi .... 365 

3. Redcedar in Arkansas 365 

X. Southeastern Region 368 

1. Piedmont Plateau Region 368 

a. Loblolly and Shortleaf Pine on Residual Soils 368 

b. Young Loblolly and Shortleaf Pine Stands on Residual Soils . 380 

c. Loblolly Pine, Yellowpoplar, and Redcedar on Alluvium . . 381 

d. Young Redcedar on Residual Soils 382 

2. Southeastern Coastal Plain 383 

a. Loblolly Pine in Virginia, North Carolina and Northeastern 
South Carolina 383 

b. Loblolly Pine in South Carolina, Georgia, Florida and Alabama 384 

c. Longleaf Pine in the Coastal Plain 385 

d. Slash Pine in the Coastal Plain 390 

e. Pond Pine in the Coastal Plain 392 

f. Sand Pine in Central Florida 394 


330 T. S, OOILE 

XI. R6sum6 of Principal Soil Properties Belated to Forest Growth .... 394 

1. Soil Factors 394 

2. Other Factors 395 

Beferences 395 


In the humid parts of the United States the area occupied by forests 
is greater than that occupied by field crops. Most of the mountain land 
in both the East and the West will be in forests or grass indefinitely 
because of topography and climate. Many other geographic units are 
committed to forest use because of poor drainage or extreme soil proper- 
ties such as sandiness which preclude their use for field crops in the 
foreseeable future. 

Agronomic research here and abroad has resulted in the accumulation 
of a vast amount of information on the relationship between soil proper- 
ties and the growth and yield of field crops. In contrast, most of the 
significant research in this country on the relation between soil and the 
growth of forests has taken place during the last 15 to 20 years. Results 
that can be used in the field, in the estimation of land quality for forests, 
have been obtained only in very recent years. 

Soil characteristics which affect the growth and yield of field crops 
can be greatly modified and improved by artificial drainage, cover crops 
and green manure crops, appropriate crop rotation, tillage, and the 
proper use of fertilizers. Irrigation has long been practiced to make 
fertile dry-land soils productive for field crops, and it is being used 
more and more in humid climates. In contrast, little can be done in the 
way of increasing the productivity of the vast acreage of soils support- 
ing forests. The rotation, or time that an individual forest occupies an 
area, may vary from 30 years for pulpwood to over 100 years for saw 
logs. Even if appreciable increase in growth could be obtained from the 
application of fertilizer, it would not ordinarily be economically feasible. 

In this review significant contributions to our knowledge of the rela- 
tion between soil profile features and the growth of various forest types 
or tree species will be presented on a regional basis. This seems neces- 
sary because the economic range of various tree species is limited region- 
ally as are also soil groups and the climates under which both the soils 
and the forest vegetation have developed. Soil properties which may be 
significantly correlated with forest growth in one region may not be sig- 
nificant in another region because of differences in tree species, climate, 
length of growing season, length of day, or action of other limiting soil 


1. The Problem 

If all forest land was covered with well-stocked stands of sufficient 
age for the entire solum and the upper substratum to have affected their 
growth, there would be little practical need for studying the relation 
between soil properties and growth because the volume of wood per acre 
at a given age would be a direct measure of productivity. However, this 
situation obtains only in isolated cases east of the Great Plains, and in 
some second-growth and virgin forests in the West. Moreover, most of 
the accessible virgin forests of the West will eventually be cut and sub- 
sequent stands will be managed on a much shorter rotation than at 
present ; hence, even for these lands, information on the productivity of 
the soil for various species is needed. 

Most forest land does not support stands of such stocking and age as 
to reflect soil productivity in terms of height, growth, or yield. The 
principal object of studies of soil properties and the growth of forests 
should be the development of methods for evaluating the productive po- 
tential for various tree species of non-forest land (abandoned crop land), 
cut-over, partially cut timberlands, or land that supports very young or 
very old decadent stands. 

2. Measures of Forest Growth 

Measures of forest growth include annual and periodic volume in- 
creases in cords, cubic feet, and board-foot units per acre. Yield at a 
given age is also expressed in these units. However, in evenaged stands, 
the total height of trees in the dominant crown canopy is the best meas- 
ure of soil productivity because it is least affected by stand density or 
the number of trees per acre at any given age. Stand density is usually 
expressed as basal area (the sum of the cross-sectional areas of the tree 
stems 4.5 ft from the ground expressed in square feet per acre), or 
stocking in milacres (Chisman and Schumacher, 1940). 

In forestry a site may be defined as an area of land with a charac- 
teristic combination of soil, topographic, climatic, and biotic factors. 
Site quality refers to the productive capacity of an area of land for a 
tree species or a mixture of species (a forest type). It may be expressed 
in terms of total height of trees in the dominant crown canopy at an 
index age (50 years for many species). When site quality is expressed 
in terms of height of trees at a given age, it is called site index. Typical 
site index curves are shown in Pig. 1. 



/O 10 50 40 SO 6O 70 60 90 /OO HO 

FIG. 1. Typical site index curves. 

,?. Soil Properties Related to Forest Growth 

Numerous studies have been conducted to test the relationship be- 
tween physical, (Jiemical, and biological properties of soil and the 
growth of forests. Site quality is largely determined by soil properties, 
or other features of site, which influence the quality and quantity of 
growing space for tree roots. Success or failure in demonstrating sig- 
nificant relationships between soil properties and plant growth depends 
largely on the investigator's ability to select for measurement and sta- 
tistical tests the independent variables that are initially limiting or most 


The factors that affect root distribution in forest stands may be listed 
as climate, soil, topography, and inherent rooting habits of different 
tree species. 


1. Climate: Effectiveness and Distribution of Precipitation 

A considerable amount of the total precipitation occurring over for- 
ested land never reaches the mineral soil. In the pine and hardwood 
forests of the Southeast approximately 0.25 in. of precipitation is inter- 
cepted by the tree crowns and is lost through evaporation, and as much 
or more is absorbed by the unincorporated organic matter (A horizon). 
Hence, any individual rain must be in excess of approximately 0.5 in. 
before it may contribute to the moisture supply in the upper mineral 
soil. Tinder climatic conditions characterized by periodic precipitation 
during the growing season the uppermost part of the mineral soil is 
repeatedly moistened to the field capacity and dried to near the wilting 
point. In contrast, the soil below this zone may be at or near the wilting 
percentage for longer periods of time because the water retention ca- 
pacity of the upper zone must be satisfied before water will move under 
the force of gravity to lower depths. If the total annual precipitation oc- 
curs mostly as snow or as rain during the winter months, the entire soil 
mass will start the growing season at the field capacity, and its moisture con- 
tent will be gradually reduced during the growing season. In the 
former case, small tree roots will be concentrated in the upper part of 
the soil which is repeatedly moistened, whereas in the latter case the 
roots will be more uniformly distributed in depth. 

Roots will grow whenever conditions of temperature, aeration, mois- 
ture, and fertility are favorable. In the South, lateral roots of pine 
trees grow throughout the year with intermittent periods of dormancy 
whenever the soil moisture content approaches the wilting percentage 
or when soil temperature drops to the freezing point (Reed, 1939). 
Granted that the fertility level of any soil is sufficient to support tree 
growth, then the distribution of tree roots and their concentration verti- 
cally in stands will be influenced by water availability and aeration. 
Soil aeration decreases markedly from the surface downward in well- 
differentiated soils; hence, a high concentration of small roots, the tips 
and relatively young tissue near the tips of which represent most of the 
absorbing area, is not to be expected at great depths below the surface. 
Under conditions where subsurface irrigation is not a factor and precipi- 
tation is uniformly distributed throughout the year, as in humid tem- 
perate climates, small roots tend to be concentrated in the uppermost 
part of the mineral soil as well as in the F and H layers of the A hori- 
zon if they are present. These zones afford maximum aeration and are 
the first to benefit by the average rain of 0.75 to 1.50 in. during the 
growing season. The penetration of precipitation of this magnitude is 
limited and conditioned primarily by the water-holding capacity of the 

334 T. S. COILE 

soil which is determined by texture and organic matter content. Within 
a given climatic regime, the average penetration of moisture from peri- 
odic rains is greater in coarse-textured than in fine-textured surface soils, 
and this is reflected in the vertical distribution of small roots. 

In regions where the annual precipitation occurs largely as snow, 
factors of soil, substratum, and topography that influence moisture in- 
filtration, storage, and subsurface flow determine the relative position of 
roots in the soil profile. 

2. Soil Properties: Texture, Permeability, Aeration, Infiltration, 
Stonincss, and Organic Matter Content 

Small roots are uniformly distributed to greater depths in coarse- 
textured soils than in fine-textured soils where the amount and distribu- 
tion of rainfall is of the same order. For example, on Lakewood sand 
in the Ocala National Forest in Florida, roots less than 0.1 in. in diam- 
eter in stands of sand pine (Pinus clausa, Engelm. Vasey) are rather 
uniformly distributed in the mineral soil to a depth of 17 to 20 in. In 
contrast, roots of this size class in mature pine stands or oak-hickory 
forests on fine-textured soils (silt loams and clay loams) in the Pied- 
mont Plateau region are concentrated in the top 3 in. of mineral soil. 
In both cases, this depth indicates the average penetration of 1.5 in. of 
rain when consideration is given to interception, absorption by surface 
organic matter, and the water-holding capacities of the mineral soils. 
Water penetrates deeper into soils which contain an appreciable amount 
of stone than it does into those of the same textural grade without stone. 

Permeability of soil to water and air is correlated with other soil 
properties and affects root growth markedly. Coile and Gaiser (1942a) 
found that the foliation and subsequent growth of black locust (Robmia 
pseudoacacia L.) seedlings growing in a heavy plastic impermeable clay 
were markedly increased by the presence of a screen cylinder containing 
sand. This device improved soil aeration. 

Soil aeration, difficult to measure directly, is highly correlated with 
other soil properties such as volume changes (swelling and shrinking) 
that occur with changes in moisture content. Soils which exhibit large 
changes in volume with moisture changes tend to be poorly aerated 
when they contain adequate amounts of water for root growth, the non- 
capillary pore space (air space) being greatly reduced by internal 
swelling. Coile (1942), Slade (1949), and McClurkin (1951) have 
found that volume changes of fine-textured soils measured as shrinkage 
from a saturated state to the oven-dry state are highly correlated with 
the moisture and xylene equivalents of the soil. On the basis of 31 ob- 


servations on the subsoils of 16 widely different soil series of the Pied- 
mont region, Slade developed the following equation for shrinkage : 

r(Shrinkage in % vol.) - -0.413+ (0.1790.040) (M.E.+X.E.) + (0.951 
0.153) (M.E.-X.E.) (1) 

where M.E. = moisture equivalent, weight basis 

X.E. = xylene equivalent, weight basis, corrected to specific grav- 
ity of water 
M.E.-X.E. = imbibitional water value (I.W.) (Fisher, 1924) 

Both variables are significant at the 1 per cent level. 

McClurkin's data were based on 21 observations on 11 different soil 
series in the same region. The following relationship between volume 
shrinkage and other physical properties of the soil was developed: 

Y (Shrinkage in % vol.) =11.265+1.021 (I.W.) -0.0575 (2 sand %-silt 
plus clay %) (2) 

The first independent variable (I.W.) is significant at the 1 per cent 
level, whereas the second, mechanical composition, is significant at the 5 
per cent level. The former is correlated with the amount and the crystal 
structure of clays, whereas the latter is a direct measure of amount of 
various particle size classes. 

Soil permeability, expressed in terms of pore space drained under 
60 cm. tension, can be estimated if the imbibitional water value and me- 
chanical composition of the soil are known (Diamond, 1951). Analysis 
of 116 observations of permeability paired with the two independent 
variables yielded the following equation : 

Y (Permeability) =23.15-11.23 (log. I.W.) -0.07 (silt plus clay %) (3) 
A similar study of permeability pore space drained under 60 cm. tension 
in 15 hours, made by Maple (1951) on 113 samples from 53 profiles, 
yielded the following equation : 

Y (Permeability) =11.23 -6.17 (log. I.W.) (4) 

Curie (1951) found root and shoot growth of slash pine (P. canbaea 
Morelet) seedlings to be lower in subsoil of low permeability and high 
imbibitional water value, such as the Orange series, in comparison with 
contrasting soil series such as Davidson, Georgeville, and Cecil whose 
permeability is higher and whose imbibitional water values are relatively 
low. In this study the Orange subsoil was water-logged for 18 months 
and consequently was poorly aerated. 

Humus, either unincorporated and in the form of an H-layer or 
incorporated in the mineral soil as an AI horizon, exhibits favorable 
characteristics for holding water that is available to plants. Thick 

336 T. S. COILE 

H-layers are associated with a high concentration of small roots, which 
condition may be attributed in part to the high water-holding capacity 
of the humus coupled with the fact that in an ordinary rain the humus 
may absorb all the water, thus leaving little or none for gravitational 
flow to the mineral soil below it (Coile, 1938a). 

Organic matter increments in coarse- and medium -textured soils in- 
crease the moisture equivalent or field capacity more than they increase 
the wilting percentage ; hence, they increase the amount of water available 
for root growth in the A 5 horizon as compared to the A 2 horizon. This 
tends to cause the development of a concentration of small roots in the 
AI horizon if rainfall occurs intermittently during the growing season 
(Coile, 1938b; Coile and Gaiser, 1942b). 

3. Topography: Slope, Subsurface Irrigation, and Water Table 

Degree of slope and extent of slope influence both surface and subsur- 
face movements of water. Lower slopes have a greater potential supply 
of water than upper slopes and ridges with the same precipitation. 

Subsurface irrigation is an important source of soil moisture and 
hence influences root distribution in steep mountain soils when relatively 
impervious rock formations approach the surface of the land. This is 
especially significant in areas such as the Northern Rocky Mountain 
region where most of the annual precipitation may occur as snow. Fol- 
lowing the snow melt, water in excess of the water-holding capacity of 
the soil and substratum tends to move down the slope along relatively 
impermeable rock strata and may be observed as seepage where the 
impermeable material approaches the surface. Thus an important source 
of moisture for root growth under such conditions of climate and terrain 
is a subsurface supply which entered the soil at some distance from and 
above the place where it is finally absorbed by roots. Under such condi- 
tions small roots of trees tend to be uniformly distributed to a greater 
depth than is the case in soils on gentle slopes that receive appreciable 
quantities of water directly on the surface during the part of the year 
when temperatures are sufficiently high for plant growth both above and 
below ground. 

A permanent water table close to the surface of the ground causes 
tree roots to be concentrated above the saturated zone. This condition is 
often seen in coastal regions. 

4. Inherent Rooting Habits of Forest Trees 

A considerable volume of material has been written into textbooks 
of forest ecology and silvics in attempts to classify the root systems of 
trees into deep-rooted, shallow-rooted, with or without tap roots, and 


intermediate classes. This has been done without much quantitative 
evidence. The position in three-dimensional space of the root systems 
of most forest trees is subject to great modification by the root environ- 
ment i.e., physical properties of the soil, water availability, and aeration. 

In young well-stocked forest stands a concentration of roots near the 
surface becomes evident at about the time a closed canopy has been 
formed and competition for growing space above the ground (light) be- 
comes marked. This appears to be between 18 and 24 years for southern 
pines. This condition may be considered the beginning of a forest soil 
root profile which culminates in the greatest amount of absorbing root 
surface in the A and upper A horizon under the climax forest (Coile 
1937, 1940). 

The root patterns of seedlings are relatively distinct by groups of 
seedlings. Large seeded species tend to develop relatively deeply pene- 
trating root systems before shoot growth becomes significant. For ex- 
ample, the tap roots of the oaks, hickories, and walnuts may grow a foot 
in length before the cotyledons appear above the surface of the soil. In 
contrast, most of the pines other than longleaf pine have a more bal- 
anced ratio of roots to shoots. As young trees develop to maturity, their 
root systems are more and more modified by their environment, i.e., the 

A great many of the controlling factors in forest succession, which 
culminates in a stable and perpetuating forest community, hinge upon 
the development of a zone of high root concentration near the surface, 
which precludes the reproduction of species whose juvenile root system 
is inherently superficial or whose reduced photosynthetic efficiency under 
a closed forest canopy results in the manufacture of insufficient food for 
adequate root development extending below the zone of greatest compe- 
tition from established vegetation. 


1. Conifer Types 

Haig (1929) reported a study of the relation between the site index 
of young red pine (Pinus resinosa Ait.) plantations in Connecticut and 
the " colloidal M content of the various soil horizons. He found that the 
site index of red pine increases as the percentage of the finer fractions 
(silt plus clay) increases in the A horizon. Presumably the textural 
grades of the A horizons studied ranged from sands to loams, and the 
textural profiles of the soils were not greatly differentiated. Haig's data 
indicate that red pine has higher site index values on sandy loam and 



loam soils than on loamy sand or sands (Fig. 2). This generality also 
holds in the Lake States region, where it has been found that jack pine 
(P. banksiana Lamb.) does better on the coarser soils than either red 
pine or white pine (P. strobus L.). Another study of the relationship 
between soil properties and the site index of young red pine plantations 
in Connecticut was made by Ilickock et al. (1931). The plantations were 

tO 30 40 


FIG. 2. Eelation of site index of red pine plantations to amount of fines in the 
surface soil (Haig, 1929). Correlation index is 0.580.07; standard error of esti- 
mate is 1.32. 

from 12 to 30 years of age and occurred on a rather wide range of soil 
types. They found a low degree of correlation between site index and 
individual soil attributes such as soil series, texture, and the character 
of the AQ horizon and of the subsoil. No relation was found between the 
acidity of any soil horizon and site index of red pine. Silt plus clay 
content of the A horizon showed a fairly good correlation with site index 
for values of silt plus clay up to 25 per cent, which is in line with Haig's 

Total nitrogen content of the A horizon showed a better correlation 
with site index than did any other factor analyzed (Hickock et al., 
1931). With respect to total nitrogen content of the surface soil in 
this study, it should be appreciated that other factors of the soil-site and 
vegetation complex affect it; for example, soil nitrogen should increase 
with increasingly favorable moisture conditions for the growth of vege- 
tation and the subsequent decay of organic matter formed by the vegeta- 

It is believed that the absence of stronger correlations between site 


index of red pine and soil characteristics was due to the age of the plan- 
tations, which was under 30 years. It is probable that subsoil character- 
istics, parent material, and the moisture regime as influenced by 
topography are most effective in conditioning growth of forest stands 
after they have reached the developmental stage when competition for 
growing space, moisture, and nutrients becomes marked. Unless forest 
stands are greatly overstocked when they start, they do not develop a 
conspicuous concentration of small roots near the surface until they are 
20 to 25 years old. When this concentration of surface roots occurs, 
which can be called a forest soil root profile, competition for moisture and 
nutrients obtains in the surface zone, and trees must depend partly on 
roots at lower -depths in the soil and substratum for the absorption of 
water. If subsoil or substratum characteristics are unfavorable for root 
growth, then the growth of the trees is reduced when the roots in the 
surface-soil zone compete strongly for available water and nutrients. 

Remarkable response in growth of young red pine to application of 
slash and humus on deep sands in Warren County, New York, has been 
reported by Heiberg and White (1950). The plantings, made in 1928, 
showed retardation of growth when only 5 or 6 years old. The stagnated 
trees were characterized by general chlorosis, dying of needles, decrease 
in the number of years that the needles persist on the tree, shortening of 
the needles, and decreased height and diameter growth. Application of 
fresh slash in the spring of 1934, obtained from nearby white pine (P. 
strobus L.) stands on good soils, resulted in immediate response in the 
form of improved color and needle length followed by increased height 
growth the next year. In control plots glass wool was used to obtain 
the same mulching effects as slashing, but no response in tree vigor oc- 
curred. The effect of a 2 in. application of the H-layer from a 
white pine-hemlock (Tsuga oanadensis, L. Carr.) stand, which was 
spaded into the soil, on the growth of red pine, white pine, white spruce 
(Picea glauca, Moench Voss.) and red spruce (P. rubra Link.) was 
striking. In 15 growing seasons the average heights by species for 
humus-treated and control plots were : red pine 14.7 and 7.2 ft. ; white 
pine, 9.9 and 5.2 ft. ; white spruce, 6.6 and 4.4. ft. ; and red spruce, 6.1 
and 1.8 ft. The tree spacing was 2 ft. by 2 ft. 

Studies were later made of the effects of various applications of 
mineral fertilizer on the growth of red pine. The amount and kind of 
fertilizer applied per acre were : 500 Ib. 5-10-5, 100 Ib. ammonium sul- 
fate, 500 Ib. calcium oxide, 200 Ib. potassium chloride, 200 Ib. tricalcium 
phosphate, and 300 Ib. sodium nitrate. Increase in tree vigor and re- 
sponse in height growth occurred only in the treatments containing po- 
tassium and sodium. Mean annual height growth for the seven growing 

340 T. S. COILE 

seasons of these two treatments was 104 per cent and 41 per cent over 
the control respectively. The entire fertilizer experiment was repeated 
in 1946 with increased amounts applied and with potassium sulfate 
added. Results again indicated a marked growth response to potassium. 
The effect of fertilization on potassium content of the youngest foliage 
(one year old) and growth of the trees was still evident after 16 years. 

Ileiberg (1941) indicated that height growth of forest trees com- 
monly planted in New York is greater on mull than on more humus 
types. This relationship can be partly attributed to favorable soil-site 
factors, such as good physical soil properties and favorable moisture con- 
ditions, which are conducive to mull formation as well as to rapid tree 

The inherent productivity of the wind-blown sandy soils derived 
from water-deposited sands of glacial origin in parts of the Northeast 
is extremely low. These soils are comparable in some respect to those 
of the sandhills of the Southeast and the deep sands of Michigan. 
When such soils were cleared, for either cultivation or pasturage, wind 
erosion frequently became severe and their productivity for forest plan- 
tations was further decreased by reduction in organic matter. Altpeter 
(1941), working in Vermont, has found mulches of organic matter such 
as manure, straw, hay, weeds, or tree slash to increase both survival and 
growth of conifers on these windblown sands. His observations are in 
accordance with those of Heiberg (1941), and Ileiberg and White 
(1950), in the Adirondacks, and those of Wilde and Patzer (1940) in 

2. Hardwood Types 

Hickock et al. (1931) also studied the relation between the composi- 
tion of natural mixed hardwoods and soil properties in Connecticut. 
They found no strong correlation between the occurrence of the various 
species and the soil factors. In the case of lesser vegetation they found 
that both the frequency and total numbers of plants were higher on 
moist soils than on drier soils. They did not find any plants that were 
good indicators of soil types. 

More recently Lunt (1939) reported on the relation between certain 
chemical characteristics of the surface soil to a depth of f> in. and the site 
index of evenaged stands of oak in Connecticut. Essentially no cor- 
relation was discovered between site index of the oak and various soil 
characteristics associated with fertility, namely, total nitrogen, exchange- 
able calcium, available potassium, available phosphorus, and total ex- 
changeable bases. This lack of correlation between the fertility factors 
and site index would be expected if no great difference between inherent 


chemical composition of the soils occurred. Under such circumstances 
the composition of the surface soil would he conditioned primarily by the 
stand composition of the oak forest. In this study no observations were 
made on soil profile characteristics or physical properties. Although ap- 
parently no quantitative data were obtained on topography, Lunt con- 
cluded that there was a relationship between site index and topography, 
the best sites being on lower slopes. Lower slopes generally afford better 
growth conditions than upper slopes or ridges, for tree species that grow 
in well-drained soils, because of better moisture relations. 

McKinnon et al. (1935) made a survey of the composition and stock- 
ing of cutover old field white pine lands in central New England and 
concluded that very light soils should be planted (presumably to pine) 
or allowed to grow hardwoods for cordwood, whereas bettor sites should 
be managed for hardwood sawlogs. 

Diebold (1935) observed the relationships between soil types and 
forest site quality in the Northeastern Appalachian Plateau of east-cen- 
tral and south-central New York. The soils of the region are derived 
from glacial deposits; they are genetically young and strongly influenced 
by the nature of the parent material, which may be acid or alkaline. 
Sugar maple and beech were found throughout the area along with 
other species. On the basis of types of humus layers and occurrence of 
wind-throw, Diebold concluded that deep, well-drained soils with an 
alkaline influence in the subsoil were best for the natural hardwood 
forests, whereas shallow soils and those with poor internal drainage (as 
evidenced by subsoil mottling) were of low quality for the local hard- 
woods. Donahue (1939) observed that poor internal drainage was re- 
lated to failures or to poor growth in coniferous plantations. 

Studies of the relationship of depth to water table in various soils in 
south-central New York as it was influenced by kinds of soil were made 
by Diebold (1938) and later reported by Spaeth and Diebold (1938). 
Although they observed that occurrence of roots was markedly affected 
by the presence of a water table in the poorly drained soils, the few data 
they had on heights of trees showed no apparent correlations with pres- 
ence of high water tables. On the basis of soil conditions in that area it 
appears likely that had proper data been obtained on height, age, volume, 
and stand composition, the expected relations between poor subsoil 
drainage characteristics and stand composition and site quality would 
have been revealed. 




1. Aspen Type 

The growth of aspen (Populus tremuloides Michx.) as affected by 
soil properties and fire has been studied by Stoeckeler (1948). Aspen 
is the most widespread type in the Lake States. There are nearly 20 
million acres of this type which represent 39 per cent of the commercial 
forest area. Management of aspen in the Lake States is a problem of 
considerable importance to foresters in the region. As in the case of 
other forest types elsewhere, a significant amount of the area of the 
present or potential type is not made up of stands of such character that 
site index can be determined in the conventional manner; hence, the 
desirability of being able to estimate site quality from the soil is ap- 
parent. Stoeckeler (1948) measured several soil properties in 30 rea- 







10 40 60 90 



FIG. 3. Effect of soil properties and burning on site index of quaking aspen 
(Stoeckeler, 1948). 



sonably well-stocked stands of aspen which ranged from 20 to 69 years 
of age. Soil texture, as measured by the amount of silt and clay in the 
A and B horizons combined, was found to be an important factor affect- 
ing site quality of aspen. Productivity increased with a rise of silt plus 
clay content to an optimum of 50 to 55 per cent and then dropped off 
somewhat in the finer-textured soils such as the poorly aerated clays. 
This relationship, along with the effect of burning on site index, is shown 
in Fig. 3. 

Data from 29 plots were grouped on the basis of textural classes and 
abundance of calcium carbonate in the subsoil. The water table in the 
soils of these plots was too deep to affect tree growth. The texture of 
the soils ranged from coarse sands to silt loams. Volumes of the stands 
increased with increases in the amount of fines in the soil and the great- 
est volumes were found on medium-textured soils with limy substrata 
(Pig. 4). Stoeckeler suggested that site classes I, II, III be managed for 

FIG. 4. Influence of soil properties on site class and yields of quaking aspen 
(Stoeckeler, 1948). Eolation of site class to average site index is: 1=86; 11 = 77; 
111=68; IV=57; and V=45. 

aspen, whereas the better soils of class IV might be converted to white 
pine, and the remainder of class IV and class V could be converted to 
jack and red pines. Aspen is replaced naturally on the first three site 
classes by hardwood, spruce, and fir. A relationship between former 
forest cover and the site index of aspen was found in the case of 37 plots 
which had not been seriously affected by repeated fires. Poor growth of 
aspen was found on land which previously supported jack pine or a poor 
growth of red pine. Areas which formerly grew good white pine pro- 
duced fair aspen, and land which once supported the birch-beech-maple 
type is in site classes I or II for aspen. The height of mature bracken 



fern is a fairly good indicator of site quality for aspen. Where bracken 
is only 1 to 2 ft. high, site quality for aspen is low, whereas land which 
will grow bracken to a height of over 3 ft. is of good quality for aspen. 

Aspen stands growing on sandy loam containing 35 to 50 per cent 
silt-plus-clay contain much more reproduction of other hardwoods and of 
conifers than do stands on coarser-textured soils. 

The prospects of profitable management of quaking aspen on various 
soils as affected by intensity of repeated burns is indicated in Table I 
(Stoeckeler 1948). 

Management of Quaking Aspen as Affected by Soil and Fires (Stoeckeler, 1948) 

Soil Per Cent Si: 
Class plus Clay i 
Top 24 ii 
of Soil 

It Class of 
n Product 
i. Expected 
of the Site 

Prospects of Profitable Management 
Intensity of Burning 


Light Moderate 
burn burn 


Poor sands 0-10 

Better sands 
and loamy 10-20 




No No 

not* N 


Pulp \\ood 

L,gl,t sandy 



Yt ' s not*' 


Good sandy 35 ^ 



Yes Yes 



Loams, silt 
loams, and Over 
heavier t .~0 



Yes Yes 




* May produce u light pulpwood cut if there is a permanent water table within 3 to 7 ft of 
the surface. 

t Excludes heavy clay soils whose growth potential is appioximutely the same as that indi- 
cated for light sandy loams 

The effect of the distance from the soil surface to the prevailing 
ground water table, measured as the upper limits of the deoxidized zone 
(gley horizon), and the organic matter content of the upper 7 in. of soil on 
average annual height growth and site index of quaking aspen has been 
reported by Wilde and Pronin (1949). Working with poorly drained 


siliceous gley sands in central Wisconsin they obtained conventional 
data on 22 stands that ranged in age from 22 to 27 years. Height 
growth and site index increased with increases in organic matter content 
between 1.5 and 4.5 per cent. Growth increased with increasing depth 
to the ground water table when it was between 16 and 32 in. Further 
increases in depth were associated with decreasing site quality. 

A comprehensive study of the interrelationships of soil and site index 
of aspen was conducted by Kittredge (1938) in Minnesota and Wisconsin. 
The relation between site index of aspen and the following factors was 
studied: soil texture groups; geological formation groups; combined 
texture and geological formation groups ; soil profile groups ; and natural 
community plant indicator groups. Site index of aspen was found to be 
most closely related to soil profile groups, to natural community plant 
indicator groups, and to combinations of these two. 

Conventional soil types were grouped by Kittredge into various 
classes on the basis of the character of the C horizon, extent of develop- 
ment of the A 2 horizon (leached zone) and the moisture regime under 
which it was developed, textural class of the A horizon, presence or ab- 
sence of a gley zone, and the development of the AI and A horizons. 
The correlation ratio was used as a measure of the relation between 22 
soil profile groups and site index of aspen. Observations were made on 
230 sample plots. No one profile feature alone had sufficient weight to 
enable prediction of habitat productivity. A correlation ratio of 0.795 
was found for the relationship between site index and the 22 soil profile 
groups. The mean site indices of many of the groups were, however, not 
significantly different from each other. Xeric conditions tended to be 
unfavorable for the growth of aspen, especially if they were intensified 
by sandy surface soil and subsoil and associated with a poor development 
of the A 2 horizon. Mesic conditions tended to be favorable. Hydric 
conditions tended to be favorable except where they were accompanied 
by deficient drainage. Strong development of the A 2 horizon was associ- 
ated with good growth and a weak A 2 with poor growth. A calcareous 
subsoil tended to be more favorable than a noncalcareous subsoil. Sandy 
C horizons combined with sandy surface horizons were unfavorable in 
xeric habitats but generally were favorable in hydric habitats. A clayey 
subsoil was favorable for the growth of aspen except when associated 
with deficient drainage. Rock substratum at shallow depths was gener- 
ally imfavorable for the growth of the species. 

Kittredge (1938) concluded that the site index of aspen is a more 
reliable measure of site quality than volume growth, and may be used 
satisfactorily for the evaluation of the differences and relative productiv- 
ity of the aspen habitats. Conversely, the habitat groups, which may be 

346 T. S. COILE 

established most effectively on the basis of soil profiles, may be used 
within limits for prediction of the average growth. Individual plants of 
the aspen community do not indicate, with sufficient reliability, differ- 
ences either in the habitats or growth rates of aspen. Groups of plant 
indicators, of which the most satisfactory were those based on maximum 
frequencies in natural communities other than aspen, together with the 
soil profile groups, are the most useful classifications for the differentia- 
tion and for the prediction of the productivity of the different aspen 

2. Other Hardwood Types 

The relation of soil characteristics to forest growth and composition 
in unevenaged northern hardwood forests of northern Michigan has been 
studied by Westveld (1933). No really satisfactory methods have been 
devised to estimate site index of unevenaged stands. In this study the 
heights of dominant trees, regardless of age, were taken as the site index. 
The 83 one-acre plots examined occurred on 25 soils types. Three site in- 
dex classes, 70, 80, and 90 ft. were recognized, and 92 per cent of the plots 
were in the 80- or 90-ft. site index classes. It may be assumed that site 
index was based on height at maturity rather than height at some base 
age, such as 50 years in the case of eastern conifers. The narrow range 
in site index from the poorest to the best is not in accordance with the 
usual range in evenaged stands of other species. For example, site 
indices for various species have been found as follows: (basis 50 years) 
red spruce, 30 to 70; southern pines, 30 to 120; and (basis 100 years) 
Douglasfir, 80 to 210. In attempting to account for the narrow range 
of site indices, Westveld (1933) observed that in an oak yield study in 
Connecticut the range in site index was from 60 to 100, but 86 per cent 
of plots were in the 70- to 90-ft. classes. On the basis of this he sug- 
gested that hardwoods may have more exacting site requirements than 
conifers, and that the poor sites in these regions are usually not occupied 
by hardwood forest types. It is doubtful that such a generalization 
should be attempted, although it is agreed that certain hardwood types 
have relatively high site requirements. However, it is probable that in 
most of the earlier yield studies, extremely poor sites were not sampled 
because of such factors as apparent subnormal stocking. Furthermore, 
certain scrub oak types are typical of land of low site quality for any 

The relation between soil characteristics and site index found by 
Westveld (1933) may be summarized as follows: 

SOILS OF GROUP 1. Loams, sandy loams, and loamy sands with yellow 
sand substratum 15 to 30 in. below the surface. Ordinarily occur as site 


class 80, although locally they may occur as class 90. Shallow or stony 
phases of any of these soils may occur as class 70. 

SOILS OF GROUP 2. Loams and sandy loams with a sandy clay till, 
or drift, substratum 25 to 30 in. below the surface. Occur as site class 
90, except where stony when they will occur as class 80 and where shal- 
lowness is combined with stoniness they may occur as class 70. 

SOILS OF GROUP 3. Silt loams and loams with clay, or sandy clay, 
subsoils. Occur as site class 90 except in the case of very stony soils. 

SOILS OF GROUP 4. Silt loams and loam with open coarse sand, gravel, 
and cobbles below 40 in. Occur as site class 90 except in cases of shal- 
low or stony soils. 

SOILS OF GROUP 5. Shallow soils resting on bedrock. Site class 80. 

In 1941 Locke reported on the relation between soil conditions and 
other site factors and the annual growth of upland oak in the upper 
Mississippi Valley region. He concluded that the depth of soil horizons 
and their permeability, slope, and aspect were most important in deter- 
mining the rate of growth under various conditions of stocking. 

Einspahr and McComb (1951) studied the site index of oak in rela- 
tion to soil and aspect in northeastern Iowa. Total depth of soil to im- 
permeable subsoil or to bedrock was correlated with site index. The 
influence of soil depth on growth was greater on southerly slopes than 
on northerly slopes. Site index increased with increasing depth of soil. 
Site index of oak stands decreased with increasing slope per cent, and 
it was greater on southerly than on northerly aspects. The site index of 
white pine growing with the oaks averaged 8 ft. higher than that of the 
oaks, and the greatest difference was found on the poorer oak sites. 

A subdivision of a part of the Upper Peninsula Experimental Forest 
in Michigan on the basis of soils and vegetation was made by Wilde and 
Scholz (1934). They indicated that classification of forest tracts on 
the basis of cover types, for management purposes, may not be entirely 
satisfactory because the cover types often represent a temporary condi- 
tion and thus do not give a true expression of forest productivity. They 
recognized the following five soil conditions and associated forest types : 
(1) slightly podsolized loam with upland hardwood type (high produc- 
tivity) ; (2) loam podsol with hemlock hardwood type (medium to high 
productivity) ; (3) swampy podsol with lowland hardwoods and some 
conifers (low productivity) ; (4) muck with hardwood conifer swamp 
type (low productivity) ; and (5) woody peat with cedar swamp type 
(very low productivity ) . 

Youngberg and Scholz (1949) disclosed an apparent relationship 
between total replaceable bases in the upper 7 in. of soil and the growth 
of mixed oak stands in the unglaciated region of southwestern Wiscon- 

348 T. S. COILB 

sin. Growth or yield was expressed in rather arbitrary terms as volume 
of average dominant tree in cubic feet at 100 years. Growth increased 
on the average from 30 cu. ft. to 135 cu. ft. as the total replaceable bases 
increased from 2 to 10 me. per 100 g. When the latter values increased 
between 18 and 26 me. per 100 g. the growth was less than 30 cu. ft. 
Qualitative data on soil types and probable stand composition suggest 
that stand composition and physical properties of the soil (texture and 
depth) may be confounded with exchangeable bases and growth re- 

3. Conifer Types 

The importance of soil moisture in the occurrence and growth of 
black spruce has been emphasized by Westveld (1936). Black spruce 
will tolerate wet soils, but its growth there is inferior. Westveld found 
that on poorly drained mineral soils (fine sandy loams) where spruce 
constituted about 53 per cent of the stand and 10 species were repre- 
sented, the 10-year diameter and height growth was 0.9 in. and 7.0 ft. 
respectively. On well-drained sandy loam soils where spruce consti- 
tuted only about 5 per cent of the stand, the 10-year diameter and height 
growth was 1.6 in. and 12 ft., respectively, with 13 species represented. 
On poorly decomposed peat (Spaulding peat) the growth of spruce was 
only 0.4 and 3.0 ft. in 10 years, whereas on muck soil the 10-year growth 
was 2.4 in. and 13 ft., respectively. Because of the superior growth of 
spruce on soils where it constituted only a small percentage of the stand, 
Westveld suggested silvicultural treatment to favor spruce, especially 
when the associated species are of inferior commercial value. 

A broad ranking of pine soils of northern Michigan into three classes 
was made by Donahue (1936). Conventional soil types, important in 
area, were ranked as follows : 

1. FIRST-CLASS PINELAND. Ogenaw sandy loam : low-lying, smooth, 
moist, sandy loam surface soil underlain at 2 to 4 ft. with red clay. 
Roselawn sandy loam: sandy morainic deposits. Lenses of sandy clay 
or clayey sand in B horizon and in the parent material. 

2. SECOND-CLASS PINELAND. Koselawn sand : coarse-textured surface 
soil and few clayey lenses in the subsoil. Rubicon sand: flat, well- 
drained, with yellow B horizon 6 to 22 in. from surface. Bridgeman fine 
sand : windblown deposits. Pine sand. 

3. THIRD-CLASS PINELAND. Saugatuck sand : hardpan 6 to 12 in. from 
surface averaging 18 in. thick. Wallace fine sand: wind-blown with 
hardpan. Grayling sand : practically no fine sand, silt, or clay. Low 
water table, 




1 | 








173 o 
c g 


4J O 







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. i 

3 o 




O ,d 












p3 J 






d "o 




* ft 
5 * 






^ &D rH 

(H O 










r2 A 


o +3 


bcommittee ( 
oc. Bull 9, 









"o ^ 

O ' C 

' O ' rrt ' 




' 4J 

"C v " 



00 o N 

^ B | | 

'I g 







3 'oo 


^J rrt t O 



Compactness When 

Very compact. Brea 
lumps, very difficult 
possible to pulver 

Moderately compac 
duced only by eonsi< 
pressure to coarse 
ules which are pul 
only by considerabl 

Friable. Pulverize 
moderate pressure* t 

of moderately res 

Mellow. Pulverizes 










Slightly coherent, 
izes completely witt 


Noncoherent, loose. 

f sources: J. C. Russell 
iociation. Ames, Iowa. 


'S 6 







1 fc 


1 I 


OD - 



<p fl 






2 | 

o> 3 tj 



"^ 1 





I 1 



d d 
W rt 


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* a 

Plasticity When 

"** fl 
'"S -2 J 

C8 ^ * 

^"s .s 

a. 5 
3 T, 

fc*13 o 

0, 4-J 

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S .2 S 

Moderately plastic. 
Kneads stiffly. 





"53 'S 
rt ^ 

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.1 1 

Very slightly plasti 
barely formable 











Nonplastic. Crum 

cannot be rolled 

ity and compactness a 
annual meeting, Ameri 


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Q * 


350 T. S. COILE 


On the basis of a study of physical and chemical soil properties and 
the growth of 135 black locust plantations and 120 black walnut (Jug- 
lans nigra L.) plantations, Auten (1936) concluded that the physical 
properties of the subsoil were most influential in determining site index. 
Plasticity, compactness, and structure of the subsoil gave the highest 
correlations with site index. Both species appeared to act similarly and 
unfavorably to insufficient or excessive drainage. Generally both species 
made their best growth on medium-textured soils such as sandy loams 
and silt loams. But little relationship was found between acidity, or 
chemical composition of the soil, and growth of either species. 

In a re-examination of the 1936 data on site features and the growth 
of black locust and black walnut, Auten (1945a) found that physical 
properties of the subsoil and depth to the subsoil were correlated with 
height growth. Ratings were assigned to each subsoil by code number 
for drainage, plasticity, compactness, and color according to the de- 
scription given in Table II. Thickness and texture of the A and B 
horizons were measured in the field. The following laboratory measure- 
ments were made: plasticity index, total nitrogen, organic carbon, and 

Excessively dry sites were excluded from Auten 's general analysis. 
Examples of these sites include excessively drained sandy soils, shallow 
soils over bedrock, and severely eroded soils with tight subsoils. 

The relation between subsoil properties and site index is given in 
Table III. 

Eelation of Subsoil Properties to Site Index * (Auten, 1945a) 

Black locust 



Subsoil Property 

































































* Coded subsoil properties are given in Table II. 

t Subsoil plasticity 6 is not represented here because all plasticity 6 subsoils were in the 
excessively drained group that was removed as explained in the section on dry sites. 

The relation between site index of the two species and depth to the 
subsoil (least permeable horizon) is shown in Fig. 5. 

No real difference was found between high and low sites with re- 



spect to nitrogen and organic matter content of the soil. Similarly, no 
relationship could be demonstrated between soil reaction and site quality. 
In 1937 Auten reported a study of the site requirements of yellow- 
poplar in the Central States. Seventy-eight sample plots in stands be- 
tween 23 and 61 years of age were examined. Soil and other site features 
examined included : drainage of the land ; soil texture ; color of subsoil ; 


Y* 99.** 0.99 

5y* * tl.8 





2 TO 



i* 9O 





* 49, 4*0.1 

99 (bPTH 

9 11 19 *4 30 31 


FIG. 5. Average relation between site index and depth to subsoil. A. black 
locust; B. black walnut. Plotted points are site index residuals (Auten, 1945a). 

depth of horizons; depth of organic matter penetration (thickness of AI 
horizon); replaceable calcium; available magnesium; soluble phos- 
phorus; available potassium; reaction; total nitrogen; exposure; topog- 
raphy; and aspect. Growth of trees was measured as average annual 
height growth for the most part. Many of Auten 's results are of inter- 
est from the standpoint of the influence of yellowpoplar on the chemical 
properties of the surface soil. Yellowpoplar was found to make the best 
growth on deep, medium-textured, well-drained soils. An interesting 
relation between the depth of AI horizon and average annual height 
growth was found. The range of depths of AI horizons was 1 to 12 in., 
and the range of the height-age ratio was 0.64 to 4 ft. Auten (1937a, 










^ P 





j Charact 






9 i> i 

J" ^ 


^ 00 













^ ^ 









( __ l 





k 1 








gj ep^ 






^ ^03 e 

| * 






^ K 

"~T CD 






'g' 2 

d fl 
















C\J CO ^f 









^3 o 

H pq 





CO ^H 









O O 




^ S 




,2 *03 'S 




GO fe S 

O O 










ci co T^ 

\O CO 










H .M 00 








Subsoil Character 


Blue-gray or drab 
Mottled below 8 i 

T*< O > 

| M | 

!l 1 1! 

C) s^ TJ 

s 173 ^* ij 

rt cv fe cp i ^ 

2 12 ^ s 

2 o ^ o go 
ft S h S PQ 





o bo 

jH a P 

t-, f 3 

o o J3 

^ rO g 

S *S o 
^ w ^ 

te: Horizontal rows do 








1937b) concluded that "yellowpoplar will not grow successfully on sites 
whose original AI horizon is less than one inch deep." It appears, 
however, that yellowpoplar will become established and grow rapidly in 
old field coves whose soil has no Aj horizon if the soil has good physical 
properties and is well drained. If a soil has properties such that a lux- 
uriant growth of yellowpoplar develops, the large annual fall of litter 
high in calcium results in the incorporation of humus so that a deep AI 
horizon is formed. The writer has observed AI horizons of up to 12 in. 
in depth under yellowpoplar of site index 120 in northern Georgia. 
Auten found no clear-cut relationships between fertility attributes of 
the soil and the growth of yellowpoplar. Exposure, topography, and 
aspect as they influence precipitation, temperature, and evaporation 
were related to its annual growth. 

A method for predicting site quality of land for yellowpoplar on the 
basis of soil and topography was developed by Auten (1945b). This 
was based on a reanalysis of data from his earlier reports (1937a, 1937b). 
Chemical and physical properties of the soil as well as topographic 
features of aspect and exposure were either measured or described. 
Aspect referred to slope-facing direction, and exposure to absence of 
protection from drying winds. 

Descriptive terms used to judge some features of soil or topography 
are given in Table IV. 

Large differences in quantity of replaceable mineral nutrients were 
found among the soils studied. Calcium content per unit weight of soil 
in the AI horizon was higher on good sites than on poor sites. However, 
this may be a reflection of the large amount of litter, high in calcium, 
produced on such sites. No relation could be demonstrated between site 
index and the amount of nitrogen, magnesium, phosphorus, or potassium 
in the soil. 

Site index averages for the subsoil color groups 1 to 6 in Table IV 
were respectively 57, 59, 90, 84, 91, and 84. Most of the yellowpoplar 
stands (65 out of 77) were on well-drained soils. Average site indices 
for combinations of drainage groups 1 and 2 ; 3, 4, and 5 ; and group 6 
were 56, 83, and 95 respectively. Since 66 of the 77 soils were either 
sandy loams or silt loams little could be concluded about soil texture and 
site index. Depth to a tight subsoil rather than the thickness of the 
morphological A horizon was found to be correlated with site index (Pig. 
6). An interesting relationship between the depth or thickness of the AI 
horizon (Pig. 7) and site index of yellowpoplar was demonstrated. This 
relationship is valid only on areas of undisturbed soil. Depth of organic 
matter incorporation was correlated with soil moisture conditions. 



The regression is : 

Height of trees = 1.125 (age) + 2.62 (Ai) + 23.06 


and, the standard error of an estimate is 12.12 ft. 

Average site indices for exposure classes 1 to 6 were 101, 94, 89, 77, 
72, and 65, respectively. Southerly facing slopes had an average site 



70 o 


If /0 14 



FIG. 6. Average relation between site index of yellowpoplar and depth to subsoil. 
Each plotted point is the average of site index residuals accumulated by 6-in. inter- 
vals of depth to subsoil from 0-36 in. (Auten, 1945b). 



24 e a 10 



FIG. 7. Eelation of site index of yellowpoplar to thickness of the A x soil horizon 
(Auten, 1945b). 

index of 89, whereas northly facing slopes had an average site index of 
72. Upper slopes and ridges were of lower site quality than lower slopes 
and coves. 

The influence of topographic features of site index are shown in 
Table V. 



Site Index Points to Subtract from 100 for Aspect, Exposure, and Position in Hilly 
to Steep Terrain (Auten, 1945b) 












The effects of soil and topography on site index of yellowpoplar are 
summarized in Table VI. 

In a study of the relation between soil, topography, and the site index 
of white oak (Quercus alba L.) in southern Ohio, Gaiser (1951) found 
topographic position, exposure, and depth of surface soil to be correlated 
with height growth. The data consisted of tree and site measurements 
on 51 plots in evenaged oak stands. Variables tested were: (1) distance 
from ridge line (per cent), expressed as 

1 "~ per cent distance from ridge line 

(2) exposure as the sine of the azimuth taken clockwise from southeast 
and adding one 

X2 = sine (azimuth from SB) + 1 

(3) depth of the A horizon in inches 


depth A in inches 

The dependent variable, site index, was taken, as its logarithm to the 
base 10, T = log S.I. Slope per cent and available moisture in inches in 
both the A and B horizons were also tested. The independent variables 
correlated with site index of white oak are given in the following equa- 
tion whose error of estimate is 9 per cent : 











I 2 



.s >^ 

"w O O 

1 CO , 


^* >- ^ J2 


O tO oS 


'3 M S 












WiS^ W) 






_ IO lO 

1 ? 5 







CO **** 






X C efl 











WH - 


~ * -i ^ 



** d 

'd e >.^ 
efl a3 


-*- 1 




W x 


ft -S| 



i S ? * 





ce oe 



5 1! 

cs "S 



* 2 ^ 







G & 

?" ' 



i S>*3 

SS 80 



^ S~ ^ 

k * d 



2 d 

** *~s>2* 


2 ^ 

rH 1 


'aJ >i t*>^ 

I " S 

1 I 1 

*o *-> 

T! O 


-* ^ S 


a S 








02?^ 2 


S 02 




2; ** 




K^*- je^i 





"^ !fc bO t> 


- "o 



"- 1 







1 10 


o O 

~ rt K'2 

73 eo 

rH | 10 ^ 


t- "35 *o 

d ^ 15 

d o 








3 ^ .^f"* | 

'w < K 

. a> 

3 m M a 


*" *** 

^ o 

co ' ** 

t! "*"* "^ 


d d "5 ^ 


.f'3 ^^ 


"d ' 



*''O .."^ 

"as ^ 

"" JQ K " 



f* fe C 

d ce 

** b^ ti' 



.25 o 

H O 

10 t to 'Sr" 1 

S | * P 



rH 1 CO J? 01 






P 1 5 

OQ rt efo.S 

02 1) 

s ^ ^ 



o o> al * 



* * "Llf 


5 1 '& . 


ft ^ ^ ft 

'S 2 

S G 1 w 


Q) p . CO -t2 


5 d J 
> > 

]M I | 

0> 2 '*S K 

"o PH 02 * 





- 2 ^ ^ 00 'B CO 

"3 "2 S 8 ** ^S *J 
g ^ O 6C.5 bfi.g p 

: 3t||| 




T = 1.837 - 0.036Xi - 0.020X 2 - O.OSlXa (6) 

Site index of white oak increases with distance from the ridge line 
and with increasing depth of the A horizon. It was higher on northerly 
and easterly exposures than on southerly and westerly exposures. Site 
index increased with available water-holding capacity in inches of the A 
horizon; this was confounded with soil depth since the textures of the 
surface soils were similar. 


Studies of the relation between soil characteristics and the growth of 
trees in semi-arid regions have been undertaken largely because of inter- 
est in establishing and maintaining shelter belts. The Shelterbelt Project 
of the mid-thirties, in the Prairie-Plains region from Texas to North 
Dakota, required information on soil features that were advantageous to 
the successful establishment of trees. Stoeckeler and Bates (1939) con- 
cluded that porous soils, coarse-textured ones, were most favorable for 
trees in regions of limited rainfall because: (1) a given amount of rain- 
fall will penetrate to a greater depth in such soils than in finer-textured 
ones; (2) during periods of abnormal rainfall water is stored to consid- 
erable depths where it may subsequently be available to tree roots but 
is not susceptible to loss through evaporation; and (3) runoff during 
heavy rainfall is minimized in coarse-textured soils. The presence of 
natural growth of trees on sands in areas of low precipitation in the 
Great Plains is attributed to the periodic replenishment of moisture to 
great depths in the sands. Roots have been found in such soils to depths 
of over 20 ft. 

Harper (1940) found that trees adapted to the climatic environment 
in central Oklahoma make good growth on upland soils when the surface 
layer does not contain more than 25 per cent of clay and the subsoil 
does not contain more than 30 per cent of clay. In western Oklahoma 
satisfactory growth of trees obtains where the soil is coarser textured 
than that indicated above. Fine-textured soils or shallow soils over un- 
weathered rock preclude successful establishment of trees in central and 
western Oklahoma. 

The relation between soil properties and the natural occurrence of 
forest and grassland communities in Colorado has been reported by 
Livingston (1949). In the Great Plains of central Colorado, ponderosa 
pine (P. ponderosa Laws.) occurs on coarse-textured soils with a con- 
glomerate substrate, whereas mixed prairie communities occur on adja- 



cent fine-textured soils. The former soil conditions ordinarily contain 
more available moisture than the latter. 


Relatively little work has been done west of the Great Plains on forest 
soil properties as they affect tree growth. 

1. Pacific Northwest 

The most important tree species and forest type in this region is 
Douglasfir (Pseudotsuga taxifolia, Lamarck. Britt). The relation be- 
tween certain soil profile characteristics and Douglasfir site quality in 
Lewis County, Washington, has been studied by Hill et at. (1948). 
Stands of Douglasfir and the soils which produced them were studied 
in that part of the county where the annual precipitation ranged from 
45 to 55 in. The altitude varied from 150 to 1000 ft. The winter pre- 
cipitation, in the form of rain, is heavy. One hundred forty-eight stands 


C fffi- 












FIG. 8. Standard soil profiles (S.O.S., Washington). 


which were mostly between 40 and 60 years of age were examined. Soil 
profiles recognized were 13 of the 16 basic profiles recognized by the Soil 
Conservation Service in Washington. Surface soil textures were grouped 
as coarse (C), light (L), medium (M), or heavy (H) and were used 
with the following profiles to form mapping units : 

1. Deep soils, undifferentiated to a depth of several feet, allowing 
maximum water storage and root penetration. 

2. Deep soils with subsoils or soil horizons which are slightly im- 

3. Soils with heavy, tight, impermeable subsoils. 

4. Soils with hardpan subsoils, impervious to water and roots. 

Of the four classes of profiles indicated above which differ in the 
permeability of the subsoil, each had four possible kinds of substrata: 
unconsolidated soil materials, hardrock, gravels, and semi-consolidated 
materials. Thus there were 16 basic profiles with four textural grades 
of surface soil possible in each. However, the 148 stands examined 
occurred on only 13 different soil profiles, or units. The basic soil pro- 
files are shown diagrammatically in Fig. 8. 

The relationship between the soil units and site quality for Douglasfir 
is shown in Table VII. 

The results given in Table VII can be simplified as shown in Table 
VIII in which the soil and other site conditions are listed according to 
site quality classes. 

It is evident from this work that the greatest growth of Douglasfir 
occurs on deep, permeable, medium-textured soils. 

Gessel (1949) reported a study of soil profile features as they are 
related to site index of Douglasfir in northwestern Washington. Soil 
and site index measurements and methods of analysis were similar to 
those of Hill et al. (1948). Profiles with coarse-, light-, and medium- 
textured soils over open gravel in the 35 to 45 in. annual rainfall belt 
represented average site indices of 125, 150, and 176, respectively, at 100 
years of age. The same types of profiles in the 45- to 60-in. rainfall belt 
supported stands with average site indices of 117, 143, and 170, respec- 
tively. Profiles with a hardpan or an impermeable zone were of higher 
site quality when the surface soil was medium textured than when it was 
light textured ; also site quality was greater when the impermeable zone 
was more than 24 in. from the surface than when it was less than that. 
Gessel (1949) suggested that since most of the precipitation occurs when 
the trees are dormant, it may be assumed that an annual rainfall of 35 
to 40 in. is sufficient to bring the profile to the field capacity, and any 
greater amount has little value for tree growth because it cannot be held 
in the porous substratum. For such profiles, the data appear to indicate 









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Soil Groups Listed by Site Quality Classes for Douglasfir in Lewis and Grays Harbor 

Counties, Washington 

Site Class III Site Class II Site Class I 

Site Index 

130 140 150 160 170 180 190 

(1), L 3H (1)M, 1L, 2H,(6) HI 1H, 1M, 2M, 6Hb-North 

61Ia-South 3M, 6H2, 6Ha-North 6Hb-South Grays Harbor 

Grays Harbor 

6Hb-South 6Hb-South (1) GM 

(1) GL 

a lower site quality with 55 in. of rainfall than obtains where the precipi- 
tation is 40 in. The former occurs at slightly higher elevations. Perhaps 
the picture is confused by subsurface irrigation in the soils which occur 
in the lower topographic position and concurrent lower precipitation belt. 

The relationship between Douglasfir site quality and soil fertility was 
studied in five localities in Oregon and Washington by Tarrant (1949). 
One plot in each site class from I to IV (site index 200, 170, 140 and 
110 at 100 years) was examined in each locality making a total of 20 
plots. Two soil pits were dug in each plot or stand and the various hori- 
zons were sampled and later analyzed. Physical and chemical properties 
of the soils measured were : silt-plus-clay, pH, total N, available P, avail- 
able K, base exchange capacity, replaceable calcium, replaceable magne- 
sium, and organic matter content. No significant relationships between 
these characteristics and Douglasfir site quality were demonstrated. The 
author suggests that the nutrient content of forest soils of the Douglasfir 
region appears to be too high to constitute a limiting factor in tree 

Acidity of the various soil horizons was between 5.0 and 6.0 pH units. 
Silt-plus-clay content of the soil was between 40 and 50 per cent. Total 
N ranged from 0.09 to 0.55 per cent. Available phosphorus in p.p.m. 
ranged from 10 to 44. Available potash in p.p.m. ranged from 105 
to 572. 

Base exchange capacity, replaceable calcium, and replaceable magne- 
sium expressed in milliequivalents per 100 g. of soil ranged from 7 to 
36 ; 1.0 to 12.0 ; and 0.6 to 2.1, respectively. Organic matter contents of 



the Ai, A 2 , and B horizons were approximately 15.0, 6.5, and 3.5, re- 

2. California 

Of the 100 million acres in California, over 45 per cent has been 
classified as commercial or noncommercial forest land. Soil site studies 

Timber Bating Chart for California (Storie and Wieslander, 1948) 

Factor A : Depth, Texture 

Bating in 

Per Cent 


Over 72 in. deep 



60-72 in. deep 



48-60 in. deep 



36-48 in. deep 



24-36 in. deep 



12-24 in. deep 



0-12 in. deep 



Factor B: Permeability 

Profile groups 

Permeable profiles 



Slowly permeable profiles 



Very slowly permeable profiles 



Factor C: Chemical (alkalinity, salinity, etc.) 

None 100 

Slight effect 80-90 

Moderate effect 20-80 

Strong effect 0-20 

Toxicity class 


Factor D : Drainage, Bunoff 

Drainage symbol 

Well drained 



Excessive runoff 



Imperfect drainage 



Poor drainage 



Factor E: Climate 

CF Coastal Fog 

CB Coast Bange 

WS Westside 

ES Eastside 






Pine (P.J.) 

Ppt. Bating 

Ppt. Bating 

Ppt. Bating 

Ppt. Bating 

45 in. 120% 

45 100% 

45 100% 

40 90% 

40 110 

40 95 

40 95 

35 80 

35 100 

35 90 

35 90 

30 70 

30 90 

30 60-70 

30 50-60 

25 60 

25 80 

25 30 

25 20 

20 50 

20 . . 30 

15 40 



incident to the resource survey of California have been made by Storie 
and Wieslander (1948). Observations on forest stands and the soils 
which produced them were made at 163 locations in the Coast Range and 
Sierra Nevada areas. The elevations ranged from a few feet above sea 
level to 8000 ft. 

Timber site quality at each location was determined by measuring 
the height and age of a dominant tree over 70 years of age and by read- 
ing the site class from appropriate site class curves based on height and 
age. In California, the customary curves used are those of Dunning 
(1942) which intercept 25-ft. height intervals at 300 years. 

According to Storie and Wieslander (1948), four main soil factors 
appear to govern or limit the growth of conifers in California. These 
are: (a) depth and texture characteristics; (b) permeability; (c) 
chemical properties; (d) drainage and runoff. Table IX is a timber 
rating chart for sites and forests in California expressed under these 

The product of the factors A X B X C X D X E in per cent gives 
the site rating. 

Examples: Use of rating chart. 

1. Hugo loam ; 60 in. to bedrock, permeable, no toxic conditions, well 
drained, CR region, 50-in. annual rainfall. 

Factor Factor Factor Factor Factor 

90 100 100 100 100=90% high site 

2. Gleason stony loam; 33 in. to bedrock, permeable, no toxic condi- 
tions, well drained, ES region, 25-in. annual rainfall. 



no too 

00 SO 





FIG. 9. Eolation between site index and timber site rating based on soil and 
other factors in California (Storie and Wieslander, 1948). 

364 T. S. COILE 

70 X 100 X 100 X 100 X 60 = 42 % low site 

3. Maymen loam, 8 in. to bedrock, permeable, no toxic conditions, 
excessive runoff, CR region, 50-in. annual rainfall. 

20 X 100 X 100 X 80 X 100 = 16% nontimber site 

The relationship between timber site rating and height-age index is 
shown in Fig. 9. 


The relation between soil site characteristics and the survival and 
early growth of plantations on old fields in the Great Applachian Valley 
of Tennessee has been reported upon by Minckler (1941a, 1941b, 1941c). 
Soils of this area are derived from limestone, dolomitic limestone, shale, 
and sandstone. Steep slopes are characteristic of the shale areas, and in 
general the soils have been eroded and sometimes have a cover of briars 
or sassafrass (Sassafrass variifolium, Salis. Kuntze). Minckler observed 
that yellowpoplar, black walnut, and white ash (Fraxinus americana L.) 
make the best growth on the relatively steep and heavily vegetated 
northerly shale slopes, with northerly dolomite slopes second for yellow- 
poplar. White pine and shortleaf pine (Pinus echinata L.) did best on 
dolomite soil, with limestone and shale next in that order. However, he 
found that local differences in site, and especially in soil profile, influ- 
enced growth more than the general differences between soil types as a 
whole. On the basis of early observations, Minckler compiled a chart 
showing recommended species for different soil sites (Table X). 

With respect to survival and growth, Minckler found that on site B 
yellowpoplar made a mean height growth in 2 years of 2.4 ft. as con- 
trasted with 1.3 ft. on site G. Shortleaf pine had a survival of 43 per 
cent on sites A, C, and E, and 93 per cent on sites F, G, and H. Black 
walnut had reached heights of 3 to 6 ft. on sites A, B, and I, whereas on 
other sites its growth was negligible. 

The importance of the condition of the B horizon was illustrated by 
the mean height growth of yellowpoplar in 2 years in sites A, B, C, and 
D. On friable, plastic, and stiff B horizons the growth was 2.5, 1.5, and 
0.8 ft., respectively. A similar response was shown by white ash. 

It is likely that the relatively poor response of shortleaf pine to good 
quality sites was related to the greater competition of native vegetation. 

Minckler (1941c) found soil moisture to be related to aspect and 
slope position with a 1.5 per cent increase for each 190-ft. descent on 
slopes of 30 per cent. Depth of the A horizon on 82 old field areas was 
related to aspect, slope per cent, and slope position, with northerly, 


gentle, and lower slopes having a deeper topsoil than the opposite con- 


1. Loblolly and Shortleaf Pines in Arkansas 

Turner (1938) studied the growth of loblolly and shortleaf pines as 
influenced by soil properties on 222 plots in 22 soil types of the Coastal 
Plain region of southern Arkansas. His field data were adequate in 
number of plots and the stand data were sufficient. However, soil meas- 
urements were confined to thickness of horizons in the profile, mechanical 
composition, and acidity. Statistical treatment of the data was limited 
to simple correlation analysis and scatter diagrams. Thus the net effects 
of each soil property on site index and the interactions of various soil 
features were not tested. The various site classes can be described 
qualitatively as follows : 

1. Superior sites. Site index 96 to 115. Located in flood plains of 
small streams. Fine sandy loam or silt loam soils without marked profile 
development and with good internal drainage. 

2. Intermediate sites. Site index 76 to 95. Distinct profile develop- 
ment. Surface soil shallower than for superior sites. Some series are 
imperfectly drained. 

3. Inferior sites. Site index 56 to 75. Shallow surface soils associ- 
ated with previous accelerated erosion on slopes from 5 to 20 per cent 
and shallow surface soils on flat topography. Both of the above condi- 
tions of shallow surface soil were ordinarily associated with subsoils (B 
horizons) having a relatively high clay content. Some soil profiles with 
excessive internal drainage (sands) belong in this group. 

2. Black Locust in Mississippi 

The height growth of black locust 4 years old was found to be corre- 
lated with the depth of the surface soil by Roberts (1939) in Mississippi. 

The relationship was curvilinear and the data may be summarized 
as follows : 

Depth of surface soil (in.) 1 5 10 15 20 25 30 35 
Av. height of trees (ft.) 2.2 3.6 5.4 7.0 8.4 9.7 10.8 11.7 

3. Redccdar in Arkansas 

The site index and diameter growth of eastern redcedar (Juniperus 
virginiana L.) has been correlated with total depth of soil to unconsoli- 
dated parent rock material in the Ozark region of Arkansas by Arend 
and Collins (1948). Diameter growth, total and merchantable height, 




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368 T. S. COILE 

and ages of 30 to 40 trees were measured in each of 91 different stands. 
The soils were classified as to parent material (limestone, dolomite, 
cherty limestone, mixtures of limestone and sandstone, sandstone, and 
first bottom alluvium) soil depth, topographic position, direction and 
degree of slope, and acidity of samples from to 3 in. and 3 to 6 in. 
measured in pH units. Total depth of the soil was the only site feature 
found to be correlated with height growth. Understocked stands were 
shorter by about 5 ft. site index than well-stocked stands. Acidity in pll 
units was not related to rate of growth within the range of 4.7 to 7.8. 
Surface soil in redcedar stands was approximately one pll unit higher 
(6.6) than in adjacent open areas. This is in line with the observations 
of Coile (1933) in the Piedmont region of North Carolina. Site class, 
soil depth, and site index were summarized by Arend and Collins as 
follows : 

Site I. Alluvial soils, deep and well drained. Site index 55-60. 

Site II. Upland soils, 24 in. and over in depth. Site index 45-50. 

Site III. Upland soils, 12 to 24 in. in depth. Site index 35-40. 

Site IV. Upland soils, less than 12 in. in depth. Site index 25-30. 


1. Piedmont Plateau Region 

a. Loblolly and Shortleaf Pine on Residual Soils. In a study of soils 
with highly differentiated profiles derived from sedimentary rocks of 
Triassic age in the lower Piedmont Plateau of North Carolina, Coile 
(1935) found that site index of shortleaf pine was related to the texture- 
depth index of a soil profile. The texture-depth index is the ratio of the 
silt plus clay content of the B horizon to the thickness of the A horizon. 
Texture-depth indices less than 2 or greater than 8 indicated poor sites. 
Highest site indices were found where the texture-depth index of the 
soil was between 4 and 6. On the average this would represent a soil 
with 12 in. of A horizon and a B horizon containing 60 per cent silt and 
clay. On such soils shortleaf pine usually had a site index of 80 ft. 
Should the same kind of subsoil be covered with only 4 in. of A horizon, 
the texture-depth index would be 15 and the site index relatively low. 
The reasoning behind the development of the texture-depth index was based 
on the belief that site quality was a function of the amount and favor- 
ableness of growing space for tree roots in the soil. In the case of soils 
which have highly differentiated profiles with respect to texture, struc- 
ture, and consistence, the depth of the surface soil and certain physical 


properties of the subsoil become pertinent factors in determining the 
volume and quality of growing space for tree roots. 

Because subsoils of the same textural class may have greatly different 
internal drainage, aeration, consistence, and structural characteristics, 
all of which affect root growth, the texture of the subsoil alone, or in 
conjunction with the depth of the surface soil, is not closely correlated 
to site quality for a wide variety of soil series. 

An intensive study was made by Coile (1948) of the relation between 
soil features and the site index of loblolly and shortleaf pines in the 
lower Piedmont Plateau of North Carolina. The data consisted of 53 
plots in loblolly pine, 75 plots in shortleaf pine, and 23 plots in mixed 
stands of the two species. The stands occurred on 27 soil types derived 
from sedimentary rocks of Triassic age, acidic and basic igneous rocks, 
the Carolina Slate formation, and alluvium and colluvium. On the basis 
of previous investigations of tree root distribution in these soils, only 
stands over 30 years of age were measured because competition for 
growing space in the soil is not particularly important in younger stands 
of average stocking. 

Site index was assigned to each plot using the conventional total 
height and age relationships and appropriate curves in U. S. Dcpt. Agr. 
Misc. Pub. 50, 1929. The contribution to site index (the dependent 
variable) of four primary soil variables, their joint effects, and their 
deviations from linearity were tested. The soil variables were : 

Xi thickness (or depth) of the A horizon in inches. 

X% = ratio of silt plus clay to the moisture equivalent of the B 


X 3 = product of Xi and A\>, hence (XiX 2 ) 
X4 second power of X<2, hence (X%) 2 
X 5 = product of Xi and X 4 , hence (X^X 4 ) 
X fi = total depth of soil to the C horizon in inches. 
Xi product of X>2 and A", hence (X 2 Xc t ) 
X& = product of X 4 and JT r) , hence (X 4 X$) 
XQ imbibitional water value of the B horizon. 

Imbibitional water value is the difference between the moisture equiv- 
alent and xylene equivalent of a soil when the latter value is adjusted 
to a water equivalent on the basis of its specific gravity (0.86). The 
imbibitional water value is highly correlated with the properties of 
clayey soils which affect their permeability to water and air and hence 
their quality for the growth of roots. 

The data were first classified and analyzed by three topographic posi- 
tion classes, i.e., ridges, middle slopes, and lower slopes and bottoms. No 



significant differences in site were found between topographic position 
classes that were independent of the soil variables. Site index increased 
from ridge through slopes to lower slopes and bottoms but this was con- 
founded with increasing depth of the surface soil (Xi). 

Four soil variables, all significant at the 1 per cent level, were found 

16 20 22 24 26 26 30 32 34 

FIG. 10. Relation between site index and the depth in inches of the surface soil 
when the imbibitional water value of the subsoil is at the mean value for the group 
of plots involved. Curve A is for loblolly pine and was calculated from the regression 

F L =100.04 1.39Tg 


Curve B is for shortleaf pine and was calculated from the regression 


F 8 =:77.32 l.OOJT,, 


The broken lines connect the mean residuals from regression; the number of plots 
upon which each is based is indicated by the number adjacent to the point. 



to be correlated with site index and the following regression equations 
were developed : 

S.I.L = 38.71 - -!} + 40.27X 2 - 6.58X 4 - 1.17X 9 (7) 

S.I.s = 80.67 - - - 2.50X 2 - 1.08X 4 - 1.19X 9 


Although soil variables X^ and X 4 were statistically significant, esti- 
mates of site index using equations (7) and (8) did not differ appreci- 

X 70 


FIG. 11. Belation between site index and the imbibitional water value of the sub- 
soil when the depth of the surface soil is at the mean value for the group of plots 
involved. Curve A is for loblolly pine and was calculated from the regression 

r L= 100.04 -1.39X, 

Curve B is for shortleaf pine and was calculated from the regression 

r s= 77.32 ^ 100X, 
X x 

The broken lines connect the mean residuals from regression; the number of plots 
upon which each point is based is indicated by the adjacent number. 



ably from those obtained by the use of equations (9) and (10) below in 
which these variables were omitted. Moreover, the inclusion of X 2 and 
AT 4 required an additional laboratory measurement. 

= 100.04 - 7 J* - 1.39A' 


S.l.s - 77.32 - -'- - 1.0(LY 


The error of estimate of a single observation in these equations is 
between 10 and 12 per cent of the estimated site index. 

The net effects of depth of surface soil and imbibitional water value 
of the subsoil are given in Figs. 10 and 11. 

It is of practical importance to note that the variable AT 9 is charac- 
teristic of a soil series within rather narrow limits. Furthermore, soil 
series may be classified into relatively few groups according to their 

FIG. 12. Block diagram for the site index of loblolly pine as affected by the 
depth of the A horizon (.YJ and the imbibitional water value of the B horizon (-Y). 
The base of the three-dimensional figure can be considered as made up of soils with 
varying properties, while the curved upper surface can be visualized as the heights 
at 50 years of trees which the soils would produce. Calculated from the regression 

SJ. L r=100.04 __ 1.39Z 8 



average X 9 values. Also, this value is highly correlated with soil con- 
sistence when moist and can be expressed in terms of relative plasticity. 
Hence, in estimating site quality of soil in the field, it is necessary only 
to measure the depth of the surface soil with an auger and to assign the 
XQ value of the subsoil which is the average for the series or consistence 

Figures 12 and 13 show the effects of both surface soil depth and 
subsoil properties on the site index of the two species. 

Frequent fires in loblolly and shortleaf pine stands of the Piedmont 
Plateau reduce height growth of the trees (Stoehr, 1946). On the basis 
of soil and tree measurements on unburned versus frequently burned 
stands of loblolly and shortleaf pines in the Carolinas and Georgia it 
was found that burning lowered the apparent tree site index. The data 
consisted of 36 unburned and 21 burned stands of shortleaf pine and 
21 unburned and 11 burned stands of loblolly pine. It was found that 
Coile's original equations (9) and (10) could be applied with confidence 
in the Carolinas and Georgia in unburned stands. However, tree site 

FIG. 13. Block diagram for the site index of shortleaf pine as affected by the 
depth of the A horizon (XJ and the imbibitional water value of the B horizon (Z 9 ) . 
Calculated from the regression 

S.L 8 =77.32 =1.00X8 

374 T. S. COILE 

index of recurrently burned stands was significantly lower than soil-site 
index as estimated from equations (9) and (10). Results of statistical 
tests showed that the effects of depth of surface soil (Zi) and physical 
properties of the subsoil (Xg) were not influenced by geographic location 
or burning, but the equation constant or level of the regression was 
significantly reduced by recurrent fires. Hence, new equation constants 
and their standard deviations were calculated for burned stands. They 
are given in equations (11) and (12) that follow: 

S.I.L (burned) = (74.50 3.1) - -^ - 1.39-Y,, (11) 



SJ.s (burned) = (57.12 3.1) - ^ - 1.00X (12) 


It is believed that a large part of the reduction in tree site index 
associated with frequent fires is due to direct injury to the tree, such as 
defoliation and injury to the living tissues, rather than to changes in 
soil properties. In other words, if new stands were grown on previously 
burned areas their site indices would follow equations (9) and (10). 

A revision of the earlier work of Coile (1948) on soil and the growth 
of loblolly pines in the Piedmont Plateau region has been made by Coile 
and Schumacher (1952). One hundred and sixty-one additional soil- 
site plots were measured in this physiographic region from North Caro- 
lina to Alabama. These new data were combined with the old, and new 
tests were made. Because of the appreciable latitudinal range in the 
Piedmont region and the possible effect of climate as well as past land 
use on height growth of pine, the data were classified as northern and 
southern Piedmont. The dividing line was on an east-west extension of 
the northern boundary of Stanley County, North Carolina. 

Number of Soil-Site Plots by Species, Geographic Location, and Fire History 

" North 





Not burned 



Not burned 


Loblolly pine 








Shortleaf pine 















* Plots from which equations (9) and (10) were developed. 


Whereas all of the old data (Coile, 1948) were from stands that had 
not been burned in recent years, the new data included some stands that 
had been burned frequently. The distribution of plots according to 
species, geographic location, burning, and "old" or "new" data is given 
in Table XI. 

The combined data furnished 123 plots in loblolly pine and 199 plots 
in shortleaf pine. Soil factors tested were the following: 
I/Xi where X\ = depth of A horizon in inches. 
XQ imbibitional water value of the B horizon. 
I/XQ where X 9 = imbibitional water value of the B horizon. 

Non-soil factors tested were burning (B) and geographic location 

Analysis of data for loblolly pine showed depth of surface soil (Xi) 
and imbibitional water value of the subsoil (X 9 ) both to be highly signifi- 
cant; but neither geographic location (L) nor the effects of burning (B) 
were of any significance. 

The final regression equation for estimating site index of evenaged 
loblolly pine in the Piedmont region is as follows : 

log (S.I.)L = 2.0188 - ~ - 0.00843X 9 - (13) 

AI A 9 

Although the last variable on the right is not significant, it has been 
retained because a large amount of soil site data from the southeastern 
Coastal Plain indicates that if Piedmont and Coastal Plain data were 
combined, the net effects of imbibitional water values of the subsoil on 
site index would be curvilinear as indicated. 

The standard error of estimate for loblolly pine was 11 per cent of 
the calculated site index. 

Figure 14 is the graphic presentation of the net relationship between 
site index and the two significant variables for loblolly pine. The plotted 
points connected with broken lines represent residuals or average devia- 
tion of observed site index from computed site index. 

Depth of the surface soil (Xi) and physical properties of the subsoil 
expressed as imbibitional water value (X 9 ) were highly correlated with 
the site index of shortleaf pine. 

The equation for estimating site index of shortleaf pine throughout 
the Piedmont region is : 

log (S.I.) S = 1.8878 - r - 0.00859X 9 - + 0.0053(L) (14) 

AI A 9 

where L is +1 if in the "North" and L is -1 if in the "South." 







I' 7 



6 12 16 20 





12 - 16 




FIG. 14. Relation between site index of loblolly pine, expressed logarithmically, 
and the depth of the surface soil and the imbibitional water value of the subsoil. 
Broken lines connect the mean residuals from regression; the number of plots upon 
which each point is based is indicated by the adjacent number. 



The standard error of estimate was 12 per cent of the calculated 
site index. 

The net effects on site index of each of the two significant soil factors 
for shortJeaf pine when one of the soils factors is held at its mean value 
is shown in Fig. 15. 

Fortunately, for field application of results, the imbibitional water 
values of subsoils can be identified by broad classes on the basis of soil 
consistence when moist. For example, friable soils have relatively low 

4 8 13 16 20 24 


fc 1.9 





12 16 




FIG. 15. Relation between site index of shortleaf pine, expressed logarithmically, 
and two important soil variables. Broken lines connect the mean residuals from the 
regression ; the number of plots upon which each point is based is indicated by the 
adjacent number. 



imbibitional water values whereas very plastic soils have high values. 
In the former case this characteristic is independent of the amount of 

Subsoils of the same series in the Piedmont are relatively constant 
with respect to their X 9 values, and hence, if a field man can estimate 
soil consistence or identify the soil series, he can assign the proper 
average -Y 9 value to a soil. 


Interrelations of Consistence, Texture, and Imbibitional Water Values 
of Piedmont Subsoils 




of Soil 




Consist nice 
When Moist 






of Mean 

Very friable 

Loamy sands and 
sandy loams 







Loams to clays 






Semi plastic 

Sandy clay loams 
to clays 







Sandy clays 
to clays 






Very plastic 






Consequently, the subsoils of the Piedmont may be classified accord- 
ing to their X 9 values, as in Table XII. Analysis of variance of these 
data showed that the variation among classes was so great that the 
standard error of the difference between neighboring class means based 
upon the fewest samples, classes 3 and 4, is 0.85, or less than one-fifth 
of the class difference. * 

The soil series and series variations which occur in the five subsoil 
classes are as follows : 

Subsoil Class 1. Very friable when moist. 
Durham, Altavista, Granville (very friable). 
Subsoil Class 2. Friable when moist. 

Georgeville, Ilerndon, Alamance (friable), Tirzah, Efland, Goldston, 
Durham, Appling, Cecil, Madison, Lockhard, Worsham, Wilkes, David- 
son, Mecklenburg, Lloyd, Tatum, Congaree, Chewacla, White Store 
(azonal), Mayodan, Penn, Granville, all colluvium. 
Subsoil Class 3. Semiplastic when moist. 
Alamance, Colfax, Enon, Creedmore, Wehadkee. 


Subsoil Class 4. Plastic when moist. 
Helena, White Store. 

Subsoil Class 5. Very plastic when moist. 
Iredell, Orange, White Store (red phase). 

Estimates of site index made with equations (9) and (13) and (10) 
and (14) have a maximum difference of only 3 ft. for each species. Be- 
cause of this, Table XIII, based on the original equations (9) and (10), 
was developed and has been used throughout the Piedmont region. 


Site Index Values for Loblolly and Shortleaf Pines in the Piedmont Plateau 
as Influenced by Soil (Coile, 1952) 

Rub- Subsoil 

soil Consistence Depth to Subsoil (Inches) 


When Moist 










Very friable 








































































Very plastic 

















Numerous field tests of the soil site data given in Table XIII have 
been made in North Carolina and in parts of South Carolina. This 
table is based on equations (9) and (10). The field tests compared 
' ' tree site" index with "soil site" index. The former was obtained in 
the regular manner by measuring the total height and age of six to eight 
dominant trees in a well-stocked evenaged stand over 30 years old and 
by extrapolating site index from appropriate curves in U.S. Dept. Agr. 
Misc. Pub. 50. A similar number of observations of surface soil depth 
and subsoil class (consistence) were made and their mean values used 
to assign soil site index from Table XIII. When several stands and 
soils are thus examined there is no significant difference between the 
average of the estimates obtained by the two methods. 

The principal use for the indirect or soil method was originally vis- 
ualized for land not supporting stands of suitable age, stocking, or 
species for direct site determination. Examples of this are cutover, 
abandoned fields, very young stands, unevenaged or partially stocked 

380 T. S. COILE 

stands, or land which presently supports other tree species. However, 
field tests with the soil method of estimating site potential show that it 
is just as precise as the direct method and requires only about one-third 
of the time needed to measure accurately total heights and ages and then 
obtain site index from curves or tables ; hence, it is recommended for use 
even when stands suitable for tree measurements exist. 

Many who use the direct method of site determination do not fully 
recognize the sources and magnitude of errors or inaccuracies involved 
therein. Common inaccuracies in measurement of total heights of trees 
with an Abney level are due to: (1) base line not properly measured, or 
riot as long or longer than the height of the tree; (2) Abney level is not 
in adjustment; (3) tip of tree and its base are difficult to see because of 
understory or density of the stand; (4) total age of a tree cannot be 
obtained accurately because (a) tree center is not encountered, or (b) 
ring counts may be confused by "false" rings when a core is taken with 
an increment borer, or (c) when age is taken at 4.5 ft. the time required 
for the tree to reach that height may be misestimated. 

Conventional site index curves contain errors of unknown magnitude 
because of certain basic assumptions with respect to the form of the 
curves and the relation of the distance between curves to age. This 
error is known to exist but it is not measurable from site index data 

Tests of the relation between site index as estimated from the soil 
and tree site index for stands 10 to 30 years of age have indicated that 
site curves for loblolly and shortleaf pine give overestimates for young 

It is suggested that those who wish to use the soil site method for 
estimating land quality would benefit by testing both methods (tree vs. 
soil measurements) in several existing stands on soils that are widely 
different. It should give the observer confidence when the soil method 
is applied to areas where suitable trees for direct site estimation do not 

1). Young Loblolly and Shortleaf Pine Stands on Residual Soils. 
An interesting application of the relation between soil profile features 
and site index of loblolly and shortleaf pines has been made in adjusting, 
or correcting, existing site curves (U.S. Dept. Agr. Misc. Pub. 50, 1929) 
in the lower age classes, i.e., stands under 50 years of age (Coile and 
Schumacher, 1952). Using total height and ages of trees in the domi- 
nant canopy in conjunction with conventional site class curves for the 
species, site index estimates for young stands (10 to 30 years old) have 
been found to be much higher than site estimates for older stands on the 
same kinds of soil. This led to the conclusion that existing site curves 


for southern pines give overestimates of site quality in young age classes. 
A correction factor for existing site curves was desired that would in- 
clude the effect of age of stands on changes in the ratio of tree site index 
to soil site index. Equations for the two species were developed having 
the form 

y 7 

where \t 

~Y = correction factor to be applied to existing curves 

y = site index estimated from curves 
Y = site index estimated from soil 

-= reciprocal of age 


Since the index age is 50 years then log y = log Y at that age. The 
equation for the ratio of tree site index (y) to soil site index (Y) for 
loblolly pine, based on 69 plots in stands 12 to 18 years of age and on 11 
different soil series in the Piedmont region is the following : 

log |r = 1.2892 (~ - 0.02\ (15) 

I \/L / 

the standard error of 1.2892 is 0.1867. Thus for a stand 10 years of age 
gy] = (0.1 - 0.02) (0.1867) = 0.0149 

which is equivalent to 3.4 per cent of the ratio y/Y at this age. 

The relation between conventional site curves and curves adjusted 
according to equation (15) is shown in Fig. 16. It is evident that the 
former type gives overestimates in young stands. 

Twenty well-stocked evenaged stands of the shortleaf pine type were 
examined. Their ages ranged from 12 to 29 years and they occurred on 
10 different soil series of widely different properties. 

Analysis of the shortleaf pine data, parallel to that of loblolly pine, 
provided the following ratio of tree site index to soil site index : 

log 4 = 3.1746 (~ - 0.02^ (16) 

The standard error of 3.1746 is 0.1467. 

c. Loblolly Pine, Yellowpoplar, and Redoedar on Alluvium. Studies 
of the properties of well -drained first bottom alluvial soils and the hori- 
zontal distance to the stream channel as well as the vertical distance 
above the stream bed have been made with respect to the growth of 
loblolly pine (Ralston, 1947), and yellowpoplar and redgum (Liquid- 



amler styraciflua L.) (Metz, 1947). Results showed site index values 
for loblolly pine and yellowpoplar were not dissimilar from estimates 
made by the use of the equation developed by Coile (1948) for loblolly 
pine in lower slopes and bottoms. This equation is : 

(S.L) L = 110.11 - - - ---- _ L98 (LW .) 

depth surface soil 


MISC puas 

20 30 


FIG. 16. Relation between conventional site index curves and adjusted site index 

The effect of distance to the stream channel on the site index of yel- 
lowpoplar was significant at the 5 per cent level. The equation express- 
ing this relationship is : 

(S.I.)YP = 86.91 + 0.102 (distance to stream in feet) (18) 

Site index of redgum was not found to be correlated with the soil 
characteristics or position with respect to the stream channel in these 
studies. The data for the three species studied were gathered from 75 

d. Young Redcedar on Residual Soils. Ledford (1951) found that 


the depth of the surface soil was highly correlated with the height 
growth of young redcedar (Juniperus virginiana L.) 10 to 14 years of 
age in the Duke Forest, Durham, North Carolina. On the basis of 73 
observations of height growth of the species as related to the depth of the 
surface soil in inches (depth) and the imbibitional water value (I.W.) 
of the subsoil, he found that height growth was a function of age and 
depth of surface soil. Apparently, properties of the subsoil do not ma- 
terially affect height growth in such young stands. Actually, however, 
subsoil properties measured as imbibitional water value are confounded 
with surface soil depth. Subsoils with high imbibitional water values 
would tend to be associated with shallow surface soils because of the low 
permeability to water of such very plastic soils and hence high rate of 
erosion under past cultivation. 

The growth equation for young redcedar growing on seven different 
soil series is : 

i. i.x i /.coir 5.3514 1.9518 /1QN 

log height = 1.6525 --- ^ ,-- r-, , ., (19) 

fe b age + 1 depth to subsoil 

2. The Southeastern Coastal Plain 

a. Loblolly Pine in Virginia, North Carolina, and Northeastern South 
Carolina. Gaiser (1948, 1950) reported on the relation between soil 
characteristics and drainage and the site index of loblolly pine in the 
Coastal Plain region of Virginia, North Carolina, and the northeastern 
part of South Carolina. Results were based on 202 plots in stands over 
30 years of age. Drainage classes based on surface drainage were: 
good, imperfect, and poor (Lee, 1946). The soils were sampled to a 
depth of 4 ft. or more, and the following variables, all significant at the 
1 per cent level, were found to affect site index : depth in inches of soil 
from the surface to the least permeable subsoil layer (depth) and the 
imbibitional water value (I.W.) of the subsoil. Equations for estimating 
site index were developed which have an error of estimate of 10 per cent. 
They are given below. 

Good or imperfectly drained soils: 

log (S.I.) = 1.692 + 0.110 (log depth + log I.W.) (20) 

Poorly drained soils with plastic subsoils: 

log (S.I.) = 1.715 + 0.110 (log depth + log I.W.) (21) 

Poorly drained soils with friable subsoils: 

log (S.I.) = 1983 - (22) 



Equations (20) and (21) differ only in the equation constant, the 
effect of soil variables not being unlike. 

Tables XIV and XV have been developed for field use by Coile 
(1951) from equations (20), (21), and (22) and other information on 
the interrelations of soil consistence when moist, texture, and imbibi- 
tional water values. 


Site Index of Loblolly Pine in the Coastal Plains of Virginia, North Carolina, and 

Northeastern South Carolina as Influenced by the Characteristics 

of Poorly Drained Soils (Coile, 1952) 

Subsoil Characteristics 

Depth to Subsoil in Inches 




water value 







Sandy loams to 


sandy clays 


7.J 81 







to plastic 

Sandy clays 


81 88 






Very plastic 



8.1 92 







Site Index of Loblolly Pino in the Coastal Plains of Virginia, North Carolina, and 

Northeastern South Carolina as Influenced by the Characteristics of 

Well and Imperfectly Drained Soils (Coile, 1952) 

Subsoil Characteristics 

Depth to Subsoil (Inches) 



when moist 


water value 







Very friable 










Loamy sands to 
light sandy loams 









Sandy loams 


















Sandy clay loams 
to clay loams 









Sandy clays 








&. Loblolly Pine in South Carolina, Georgia, Florida, and Alabama. 
On the basis of stand and soil observations in 217 areas of evenaged 
loblolly pine over 20 years of age in the Coastal Plain regions of South 
Carolina, Georgia, Florida, and Alabama, Metz (1950) found the follow- 


ing soil and topographic features to be significantly correlated with 
height growth of loblolly pine : 

1. Product of depth of A horizon and the imbibitional water value 
of the B horizon. 

2. Product of depth of A horizon and the silt content of the B 

3. Product of depth of A horizon and the clay content of the B 

4. Degree of surface drainage, i.e., well, imperfectly, or poorly 

The net effect of increasing imbibitional water value, silt content, 
and depth to B horizon was positive with respect to height growth, 
whereas increased clay content alone retarded height growth. Height 
growth increased with decreasing surface drainage. In this analysis the 
B horizon refers to the least permeable or finest-textured horizon, and 
the depth of the A horizon refers to the distance from the surface to the 
least permeable horizon. This was usually the B2 horizon. 

The general equation for estimating site index was : 

log (total height) = C - 6.97 /age + [0.000420 (I.W. of B) + 0.000021 
(silt of B) - 0.000077 (clay of B)J (depth of A) (23) 

where C = 2.0605 for well drained soils 

C = 2.0729 for imperfectly drained soils 

C = 2.0887 for poorly drained soils 

To calculate site index for loblolly pine with equation (23) the age 
to be used is 50 years, and the appropriate constant (C) for drainage is 
entered in the equation. Direct measurements of subsoil characteristics 
shown within the brackets may be employed, or mean values of these 
variables may be calculated for standard textural grades. The depth 
of the A horizon (actual distance in inches to the least permeable sub- 
soil horizon) may be made in the field or calculated by convenient classes. 
The error of estimate for a single observation is 10 per cent. 

Table XVI gives estimates of site index for loblolly pine in the 
Coastal Plain from South Carolina to Alabama as derived from equations 
for standard textural grades of subsoils, depth to the least permeable 
subsoil horizon, and surface drainage classes (Coile, 1952). 

c. Longleaf Pine in the Coastal Plain. The height growth of long- 
leaf pine (P. palustris Mill.) as influenced by soil properties and other 
factors was studied by Ralston (1949, 1951). Soil and mensurational 
data were analyzed from 303 plots in well-stocked evenaged stands of this 
type in the Carolinas, Georgia, and Florida. 




Site Index of Loblolly Pine as Influenced by Depth to Least Permeable Horizon 

(Subsoil), Texture of Subsoil, and Drainage, Coastal Plain of South Carolina, 

Georgia, Florida, and Alabama, Based on 231 Plots (Coile, 1952) 

Texture of Subsoil 


Depth to Subsoil 
















Sand and loamy sand 

















Sandy loam and sandy 
clay loam 

















Loam, clay loam, sandy 
clay, and light clay 










Silty clay and heavy 


















Silty clay loam and 
silt loam 

















The equation for estimating height growth of 115 plots on imperfectly 
and poorly drained soils was : 

log (total height) = 1.886 - lL20*j + 136.0**! + 0.00244* 2 + 
0.00191*3 + 0.000384*4 - 0.00072* 5 (24) 


where Xi = 

at 1.0 ft. 


* 2 = moisture equivalent of the subsoil in per cent 
* 3 = depth to mottling in inches 
* 4 = stand density in number of stocked milacres 
* 5 = +1 for plots in the Carolinas and 1 for those in Georgia 
and Florida 

The latitudinal constant (x5) was significant at the 5 per cent point, 
whereas the other variables were significant at the 1 per cent level. The 
error of estimate for a single observation was 7.9 per cent. Tests of the 
effects of turpentining and turpentining latitude interaction did not re- 
veal any significant relationships with growth. 

Analysis of data from 188 plots on well-drained soils using the same 
independent variables that were tested for the imperfectly and poorly 



drained soils, with the exception of depth to mottling, resulted in the 
following growth equation : 

log (total height) = 1.915 - ll.lLri + 136.0^ + 0.00118^ + 
0.000374x 3 - 0.014^4 - 0.022z 5 + 0.00fcc (23) 

where Xi, x 2 , and x 5 are as stated in equation (24) 
#3 = number stocked milacres 

Xi = +1 for turpentine trees and 1 for " round " trees 
x 6 = +1 for stands turpentined in the North or round in the 
South, and 1 for stands that are round in the North or 
turpentined in the South 

The variables, x*i and X Q , were significant at the 5 per cent level ; 
all other factors were significant at the 1 per cent point. The error of 
estimate of a single observation is 9.3 per cent for equation (23). 
Graphic illustration of the effects of turpentining and latitudinal distri- 


SO 60 70 

FIG. 17. Growth curves for longleaf pine on well-drained soils showing the ef- 
fects of turpentining and latitudinal distribution. 




fO 2O 50 40 


FIG. 18. Site index of longleaf pine on well-drained soils as influenced by mois- 
ture equivalent and latitudinal distribution. 

/O ZO JO 40 


FIG. 19. Site index of longleaf pine on imperfectly and poorly drained soils as 
affected by moisture equivalent and depth to mottling. 



bution on height growth when stand density and moisture equivalent of 
the subsoil are at their mean values is shown in Fig, 17. 

Well-drained soils supporting longleaf pine tend to have rather uni- 
formly deep surface soils hence the only soil factor related to growth 
was the physical nature of the subsoil measured as the moisture equiva- 
lent. The effect of this soil property and of latitudinal distribution on 
site index is illustrated in Fig. 18. In the case of imperfectly drained 
and poorly drained soils the properties related to height growth are the 
depth to mottling and the moisture equivalent of the subsoil (Fig. 19). 

Analysis of the relation between silt plus clay content and the mois- 
ture equivalent (M.E.) of subsoils from 147 plots showed that these 
values were so highly correlated that either could be used for estimating 
site index (Fig. 20). The equation for the regression in Fig. 20 is: 

Y (silt + clay of B horizon) = 2.34 (M.E. of B horizon) (26) 

On the basis of established relationships between the moisture equiva- 
lents and textural grades of subsoils supporting longleaf pine, Coile 

FIG. 20. The relationship between silt plus clay content and the moisture equiv- 
alent of the B horizon. 

590 T. S. COILE 

(1951) developed Tables XVII and XVIII for field use in estimating 
site quality of land for longleaf pine in the region. 


Site Index of Longleaf Pine on Well-Drained Soils in the Southeastern Coastal Plain 
as Influenced by the Texture of the Subsoil 







Poorly stocked 









Loamy sand 




Sandy loam 




Sandy clay loam 




Sandy clay 




Light clay 




Heavy clay 





Site Index of Longleaf Pine on Poorly and Imperfectly Drained Soils in the South- 
eastern Coastal Plain as Influenced by Soil Characteristics 

Subsoil Characteristics 









Loamy sand 



Sandy loam 



Sandy clay loam 



Sandy clay 



Light clay 



Heavy clay 



Depth to Mottling (Inches) 

30 48 

Site Index 

62 67 

63 69 
66 71 
68 74 
70 76 
72 78 
74 81 

d. Slash Pine in the Coastal Plain. The effect of soil properties and 
other factors on the growth of natural slash pine (P. canbaea Morelet) 
stands over 20 years of age was studied by Knudsen (1950a). Soil and 
stand measurements were made on 231 plots in South Carolina, Georgia, 
Florida, and Alabama. Twenty independent variables were tested as to 
their effects on height growth. The soil variables included imbibitional 
water value of the B horizon, moisture equivalent of the B horizon, 
depth of the A horizon, mechanical composition of the A and B horizons, 
acidity (pH) of the A 2 and B horizons, and depth to mottling. Other 
independent variables were age of stands and turpentining. Appropri- 
ate tests of curvilinearity and interactions were also made. The only 



soil property found to be correlated with site index of slash pine was the 
nature of the subsoil as reflected, in its imbibition al water value. The 
net effects of turpentining were to reduce site index by 3 ft. The regres- 
sion for slash pine site index is : 

log (S.I.) = 1.89153 + 0.0024423 (I.W.) + 0.0071144 (T) 
where I.W. = imbibitional water value of the B horizon 

T = +1 for " round " trees and 1 for turpentined trees 

Equation (27) is shown graphically in Fig. 21. 




6 10 12 14 

ivy ore HORIZON 

FIG. 21. Belation between site index of slash pine and imbibitional water value 
of B horizon as affected by turpentining. 

Knudsen (1950b) examined the interrelation of some physical prop- 
erties of Coastal Plain soils from 448 locations in the Southeast. One 
equation developed makes it possible to express imbibitional water value 
(I.W.) of the B horizon in terms of its silt and clay content (Si and C). 
The relationship is : 

392 T. 8. COILE 

I.W.B = 0.28470 + 0.06936 (Si) B + 0.23610 (C) B (28) 

Both independent variables are highly significant. 

Coile (1952) used arbitrary mean values of silt and clay for four 
broad classes of subsoil texture (Table XIX) to calculate their imbibi- 
tional water values with equation (27) and subsequently calculated site 
index for slash pine with equation (28). Table XIX gives estimates of 
site index for slash pine on the basis of subsoil texture which can be 
estimated in the field. 

Site Index of Slash Pine Based on Texture of Subsoil (Coile, 1952) 

Site Index 
Texture of Subsoil (Bound Trees) 

Sands and loamy sands 75 

Sandy loam and sandy clay loam 80 

Loam, clay loam, sandy clay, and light clay 85 

Silt loam, silty clay loam, silty clay, and heavy clay 90 

e. Pond Pine in the Coastal Plain. Soils supporting stands of pond 
pine (P. serotina Michx.) have a wide range of profile characteristics. 
It occurs on mineral soils, organic loams, mucks, and peats. Hofmann 
(1949) studied the relation of soil properties to height growth of pond 
pine on 130 plots in the Carolinas, Georgia, and Florida. One hundred 
and one of these observations were on mineral soils, imperfectly and 
poorly drained ; 29 observations were on organic loams, mucks, and peats 
all of which were poorly drained. The equation developed for estimating 
site quality of mineral soils is as follows: 

log (S.I.)p - 1.6775 + 0.00347 (M.E.) - 0.000276 (depth Aj X O.M.) 
+ 0.00071 (depth mottling) + 0.000312 (length growing season) (29) 
where M.E. = moisture equivalent of the subsoil 

depth AI X O.M. = product of depth of AI horizon and its or- 
ganic matter content 
depth mottling distance from surface to a zone of conspicuous 


length of growing season = average number of frost free days per 

In equation (29) the moisture equivalent of the subsoil was significant 
at the 2 per cent level, and the other independent variables were signifi- 
cant at the 5 per cent level. 

Analysis of data from 29 organic soils (O.S.) indicated that stand 



density, organic matter content of the surface soil, and the product of 
depth of A! and organic matter content affected height growth of pond 
pine. Equation (30) shows this relationship when "stand density is at 
its mean level. 

log (S.l.)p(os ) - 1.7917 - 0.00283 (depth A! X O.M.) (30) 

The relation between site index of pond pine and soil properties is 
shown in Table XX. This can be used for making estimates of site 
quality in the field. 


Site Index of T'ond Pine in the Southeastern Coastal Plains 
as Influenced by Soil Characteristics (Ooile, 1952) 



Muck and 


Mineral Soils * 







(A 1 XOM)=20t 

(AiXOM )r=200 

(A 1 XOM.)=r400 

(A^OM )rrlOOO 












Loamy sand 












Sandy loam 











Sandy clay 












Sandy clay 






















* Mineral soils* less than 15 per cent organic matter in the surface soil. 

Organic loams. 35 to 115 per cent organic matter in the surface soil. 

Organic soils: over 35 per cent organic matter in the surface soil (murks and peats). 
t Product of the depth of organic matter incorporation (Aj) and percentage of organ it- mat- 
ter (O.M.) in the surface soil. 

Zahner (1951) re-examined the data for 20 plots in organic soils 
previously studied by Hofmann (1949) and included some new vari- 
ables; pH of surface soil, moisture equivalent, and imbibitional water 
value of the A 2 horizon, and its mechanical composition. Only the 
organic matter content of the surface soil was significantly related to site 
index. This relationship was expressed as : 

394 T. S. COILE 

log (S.I.)p(OB) = 1.8278 - 0.0035 (per cent organic matter) (31) 

The error of estimate of a single observation using equation (31) is 
approximately 14 per cent. 

Table XX shows estimates of site index for pond pine based on equa- 
tions (29) and (30). 

/. Sand Pine in Central Florida. The growth of sand pine on deep 
sands, mostly of the Lakewood series, in the Ocala National Forest in 
north-central Florida was studied by Barnes (1951). The data were 
based on sample plots in 54 evenaged stands. The soil was sampled and 
described to a depth of 9 ft. Mechanical analysis, separation of sands, 
and moisture equivalent determinations were made on all soil zones that 
appeared to differ in color or mechanical composition throughout the 
entire 9-ft. profile. In addition, the water-holding capacity of the soil 
to a depth of 9 ft. was calculated in inches of rainfall. None of the soil 
properties measured was found to be significantly correlated with height 
growth. Classification of the plots into two topographic position classes, 
(1) low flats and lower slopes and (2) upper slopes, high flats, and 
ridges, showed a difference in height growth that was significant at the 
7 per cent level. Height growth of trees was greatest on the lower topo- 
graphic position classes. This would indicate that data on depth to 
water table may be a useful measurement for deep sands in gently roll- 
ing topography. However, position of water table could not be deduced 
from profile observations to a depth of 9 ft. 

The growth equation developed for the dominant stand in sand pine 

10 r >77 

log (total height) = 1.9797 - (32) 



The productivity of soil for forest growth is conditioned by the 
quantity and quality of growing space for tree roots. Soil properties 
that may be classed under these two categories may have direct effects on 
growth, both direct and indirect effects (interaction), or only indirect 

The principal soil features and other factors related to forest site 
quality are : 

1. Soil Factors 

a. Depth of surface soil (A horizon), depth to least permeable layer, 
or depth to mottling. These measures of quantity of growing space 


imply effective root depth for trees (small roots). The relationship of 
growth to these measurements is generally curvilinear. The net effects 
of increments of depth being great when depth is low. The effects of 
increasing depth on growth decreases beyond a certain point. 

b. Total depth soil, and soil material functions as a measure of 
quantity of growing space in the case of immature or poorly differenti- 
ated profiles. 

c. Physical nature of the subsoil, least permeable layer, or sub- 
stratum as it influences water movement, water availability to roots, 
aeration, and mechanical hindrance to root growth. This factor may 
exhibit with either a or 6 above significant joint effects or interactions 
with tree growth. Physical properties of the subsoil that may be directly 
correlated with forest growth include texture, pore space distribution, 
imbibitional water values, water-holding capacity, and changes of 
volume with moisture content (shrinkage and swelling). 

d. Physical properties of the surface soil, notably pore space dis- 
tribution and texture may under certain conditions influence water 
infiltration and storage which is especially important to tree growth in 
semi-arid regions. 

e. Organic matter in the form of either incorporated or unincor- 
porated humus influences the moisture regime of soils as well as their 
structure and porosity to air. It serves as a direct source of energy for 
soil organisms and as a reservoir of nitrogen and other essential plant 
nutrients. In excessive amounts, organic matter may reflect poor drain- 
age and be associated with low productivity. 

/. Chemical characteristics involving nutrient supply may be a 
limiting factor in forest growth on deep excessively drained silicious 
sands in humid climates. In such cases the fertility factor is usually 
confounded with adverse physical soil properties and a low water table. 

2. Other Factors 

a. Climate and Length of Day. These two factors are confounded 
for tree species that have a wide latitudinal range. The relatively rapid 
growth of certain species of trees in northern latitudes can be attributed 
in part to long days during the frost-free period which offsets the short 
growing season. Climate, expressed as inches of rainfall, number of 
frost-free days per year, or defined indirectly by latitude and longtitude, 
has been found to be correlated with growth of forests independent of 
soil factors. 

b. Aspect and Exposure. In regions or areas of marked relief, 
aspect of land (compass direction that a slope faces), and exposure 
(susceptibility of land surface to drying winds) greatly affect the local 

396 T. S. COILE 

climate as it is characterized by precipitation and temperature, wind 
movement (direction and rate), and evaporation. Northerly facing 
slopes (NW, N, and NE) are cooler and more moist than southerly 
facing slopes. A convenient way to express aspect is with an azimuth 
scale of 360 from North. Exposure may be stated in terms of the 
position of an area of land with respect to adjacent land as for example 
ridge vs. cove or draw. 

c. Topography and Water Table. The relation of topographic 
position of land to forest productivity is primarily indirect. Relative 
topographic position and distance from the soil surface to the water table 
both influence water supply to the soil and tree roots. This moisture 
supply, modified by climate and soil properties may range from excessive 
to insufficient. 

Subsurface irrigation resulting from seepage on mountain slopes and 
from fluctuating water tables in the alluvial flood plains of streams is 
an important factor in productivity that may be independent of soil pro- 
file features alone. 

d. Surface Geology The permeability to water of rocks, rock 
formation, or unoonsolidated geologic material may influence land pro- 
ductivity independent of the soil proper if the latter is shallow. Pene- 
trability of substratum to tree roots may have an effect on tree growth 
independent of both its permeability to water and the properties of the 
overlying soil. 


Altpeter, L. S. 1941. J. Forestry 39, 705-709. 

Arerid, J. L., and Collins, B. F. 1948. Soil Set. Soc. Am. Proc. 13, 510-511. 

Auten, J. T. 1936. Central States For. Expt. Sta. Note 31. 11 pp. mimco. 

Auten, J. T. 1937a. Central States For. Expt. Sta. Note 32. 13 pp. mimeo. 

Auten, J. T. 1937b. Central States For. Expt. Sta. Note 33. 5 pp. mimeo. 

Auten, J. T. 1945a. J. Forestry 43, 592-598. 

Auten, J. T. 1945b. J. Forestry 43, 662-668. 

Barnes, R. L. 1951. M. F. Thesis. School of Forestry, Duke University, 46 pp. 

Ohisman, H. II., and Schumacher, F. X. 1940. /. Forestry 38, 311-317. 

Coile, T. S. 1933. Ecology 14, 323-333. 

Coile, T. 8. 1935. J. Forestry 33, 726-730. 

Coile, T. S. 1937. J. Forestry 35, 247-257. 

Coile, T. S. 1938a. Soil Sci. Soc. Am. Proc. 3, 274-279. 

Coile, T. S. 1938b. Soil Sci. Soc. Am. Proc. 3, 43. 

Coile, T. S. 1940. Duke University, School of Forestry Bull. 5, 85 pp. 

Coile, T. S. 1942. Soil Sci. 64, 101-103. 

Coile, T. S. 1948. Duke University, School of Forestry Bull. 13, 78 pp. 

Coile, T. S. 1952. Forest Farmer 10(7), 10, 11, 13; 10(8), 11-12. 

Coile, T. S., and Gaiser, R. N. 1942a. J. Forestry 40, 660-661. 


Coile, T. S., and Gaiser, E. N. 1942b. Unpublished manuscript. Duke University 
School of Forestry. 

Coile, T. S., and Schumacher, F. X. 1952. Unpublished manuscript. Duke Univer- 
sity School of Forestry. 

Curie, L. D. 1951. M. F. Thesis. School of Forestry, Duke University, 31 pp. 

Diamond, S. 1951. M. F. Thesis. School of Forestry, Duke University, 31 pp. 

Diebold, C. H. 1935. Ecology 16, 640-647. 

Diebold, C. H. 1938. Ecology 19, 463-479. 

Donahue, E. L. 1936. Am. Soil Survey Assoc. 17, 79-80. 

Donahue, E. L. 1939. Cornell University Agr. Expt. Sta. Mem. 229. 44 pp. 

Dunning, D. 1942. Calif. Forest and Range Expt. Sta Research Note No. 28, 
Dec. 1. 21 pp. 

Einspahr, D., and McComb, A. L. 1951. J. Forestry 49, 719-723. 

Fisher, E. A. 1924. J. Agr. Sci. 14, 204-220. 

Gaiser, E. N. 1948 Ph.D. Thesis. Duke University, 61 pp. 

Gaiser, E. N. 1950. J. Forestry 48, 271-275. 

Gaiser, E. N. 1951. Central States For. Expt. Sta. Tech. Paper No. 121. 12 pp. 

Gessel, S. P. 1949. Soil Sci. Soc. Am Proe. 14, 333-337. 

Haig, I. T. 1929. Yale University, School of Forestry Bull. 24. 33 pp. 

nail, E. C. 1935. J. Forestry 33, 169-172. 

Harper, H. J. 1940. Soil Sci. Soc. Am. Proc. 5, 327-335. 

Heiberg, S. O. 1941. Soil Sci. Soc. Am. Proc. 6, 405-408. 

Heiberg, S. O., and White, D. P. 1950. Soil Sci. Soc. Am. Proc. 15, 369-376. 

llickock, H. W., Morgan, M. F., Lutz, 11. J., Bull, II., and Lunt, H. A 1931. Con- 
necticut Agr. Expt. Sta. Bull. 330. 73 pp. 

Hill, W. W., Arnst, A., and Bond, E M. 1948. J. Forestry 46, 835-841. 

Hofmann, J. G. 1949. D. F. Thesis. School of Forestry, Duke University. 66 pp. 

Kittredge, J., Jr. 1938. Ecol. Monographs 8, 153-246. 

Knudsen, L. L. 1950a. Ph.D. Thesis. Duke University. 45 pp. 

Knudsen, L. L. 1950b. M. F. Thesis. School of Forestry, Duke University. 27 pp. 

Ledford, E. H. 1951. M. F. Thesis. School of Forestry, Duke University. 29 pp. 

Lee, W. D. 1946. Soils of the Coastal Plain of North Carolina. N. C. State College. 
16 pp. mimeo. 

Livingston, E. B. 1949. Ecol. Monograph 19, 123-144. 

Locke, S. S. 1941. Soil Sci. Soe. Am. Proc. 6, 399-402. 

Lunt, H. A. 1939. /. Agr. Research 59, 407-428. 

McClurkin, D. C. 1951. M. F. Thesis. School of Forestry, Duke University. 21 pp. 

McKinnon, F. S., Hyde, G. E., and Cline, A. C. 1935. Harvard Forest Bull. 18, 
80 pp. 

Maple, W. E. 1951. M. F. Thesis. School of Forestry, Duke University. 27 pp. 

Minckler, L. S. 1941a. J. Forestry 39, 685-688. 

Minckler, L. S. 1941b. Appalachian Forest Expt. Sta., Tech. Note 45. 6 pp. 

Minckler, L. S. 1941c. Soil Sci. Soc. Am. Proc. 6, 396-398. 

Metz, L. J. 1947. M. F. Thesis. School of Forestry, Duke University. 31 pp. 

Metz, L. J. 1950. Ph.D. Thesis. Duke University. 51 pp. 

Ralston, C. W. 1947. M. F. Thesis. School of Forestry, Duke University. 25 pp. 

Ralston, C. W. 1949. Ph.D. Thesis. Duke University. 61 pp. 

Ralston, C. W. 1951. J. Forestry 49, 408-412. 

Reed, J. F. 1939. Duke University, School of Forestry Bull. 4. 

398 T. S. COILE 

Roberts, E. G. 1939. J. Forestry 37, 583-584. 

Slade, R. S. 1949. M. F. Thesis. School of Forestry, Duke University. 35 pp. 

Spaeth, J. N., and Diebold, C. H. 1938. Cornell University Agr. Expt. Sta. Mem. 

213. 76 pp. 

Stoeckeler, J. H. 1948. J. Forestry 46, 727-737. 
Stoeckeler, J. H., and Bates, C. G. 1939. J. Forestry 37, 205-221. 
Stoehr, H. A. 1946. M. F. Thesis. School of Forestry, Duke University. 47 pp. 
Storie, R. E., and Wieslander, A. E. 1948. Soil Sci. Soc. Am. Proc. 13, 499-509. 
Tarrant, R. F. 1949. J. Forestry 47, 716-720. 
Turner, L. M. 1938. Arkansas Agr. Expt. Sta. 'Bull. 361, 52 pp. 
Westveld, R. II. 1933. Michigan Agr. Expt. Sta Bull. 135, 52 pp. 
Westveld, R. H. 1936. Am. Soil Survey Assoc. 17, 45-47. 
Wilde, S. A. 1933. Ecology 14, 94-105. 

Wilde, S. A., and Patzer, W. E. 1940. J. Am. Soc. Agron. 32, 551-562. 
Wilde, S. A., and Pronin, D. T. 1949. Soil Sci. Soc. Am. Proc. 14, 345-347. 
Wilde, S. A., and Scholz, H. F. 1934. Soil Sci. 38, 383-400. 
Youngberg, C. T., and Scholz, H. F. 1949. Soil Sci. Soc. Am. Proc. 14, 331-332. 
Zahner, R. 1951. M. F. Thesis. School of Forestry, Duke University. 21 pp. 

Author Index 

Numbers in italics refer to the pages on which references are listed in bibliogra- 
phies at the end of each article. 

Aamodt, O. 8., 180, 810 

Aberg, Ewert, 181, 810 

Aberson, J. A., 264, 278 

Adams, A. B., 21, 61 

Adams, M. B., 272 

Adler, B., 261, 272, 278 

Ahlgren, Gilbert H., 205, 817 

Ahlgren, H. L., 180, 182, 191, 193, 205, 

214, 816, 218, 219 
Albert, W. B., 205, 2 8 
Alberts-Dietert, F., 264, 272 
Albrecht, W. A., 90, 91, 92, 96, 97, 99, 

247, 272 

Alexander, L. T., 71, 97, 285, SOS 
Allard, H. A., 188, 817 
Allaway, W. H., 72, 74, 81, 82, 83, 90 
Allen, G. H., 31, 68 
Allen, W. W., 307, 312, 326 
Allison, J. Lewis, 203, 218 
Allison, R. V., 150, 157, 160, 161, 171, 


Allison, W. B., 78, 97 
Aim, F., 259, 260, 275 
Alten, F., 228, 272 
Altpeter, L. S., 340, 896 
Alway, J., 77, 96 
Anderson, A. B., 263, 272 
Anderson, Alice M., 211, 216 
Anderson, Donald B., 209, 218 
Anderson, A. J., 19, 21, 30, 46, 47, 48, 49, 

61, 68, 63, 196, 216 
Andersson, F. G., 150, 152, 153, 157, 170, 


Anderson, Kling, 180, 218 
Anderson, W. S., 68, 98 
Arend, J. L., 365, 396 
Arnon, D. L, 68, 69, 81, 96, 149, 152, 155, 

173, 177 f 262, 878 
Arnst, A., 358, 359, 360, 397 
Arthur, J. I., 114, 124, 134, U5 

Asana, R. D., 112, 115, 144 
Ashbaugh, F. A., 309, 310, 322, 326 
Auten, J. T., 349, 350, 351, 352, 353, 354, 

355, 356, 396 
Austin, R. H., 77, 96 
Avery, G. S., 133, 144, 261, 272 
Ayers, A. D., 75, 76, 85, 86, 97, 9S 

Bacon, C. W., 151, 164, 173 

Bagchi, S. N., 71, 98 

Bahrt, G. M., 242, 272 

Bailey, L. F., 155, 173 

Baird, G. B., 88, 94, 96 

Bald, J. G., 108, 144 

Ballard, L. A. T., 37, 68, 114, 122, 144 

Balls, W. L., 103, 144 

Bamann, E., 263, 272 

Banerjees, B. M., 78, 98 

Banfi, R. F., 262, 276 

Baptiste, E. C. D., 116, 120, 123, 124, 

129, 131, 132, 145 
Barber, S. A., 75, 76, 77, 86, 98 
Barendregt, T., 75, 99 
Barnes, R. L., 394, 896 
Bartels, L. C., 52, 62 
Barrentine, M. W., 67, 68, 96 
Barrie, N., 32, 63 
Barrie, Nancy, 205, 206, 218 
Barrons, K. C., 307, 309, 310, 311, 313, 

314, 315, 326, 327 
Bassham, J. A., 295, 303 
Bates, C. G., 357, 398 
Bates, G. H., 202, 216 
Baver, L. D., 191, 193, 216 
Bear, F. E., 88, 94, 95, 96, 99, 208, 216 
Beatty, R. H., 311, 826 
Beck, A. B., 167, 170, 171, 173 
Beckenbach, J. R., 67, 96 
Becker, R. B., 168, 171, 173, 176 
Beckwith, R. S., 28, 63 




Beddows, A. R., 183, 209, 211, 819 
Bceson, K. C., 67, 68, 96, 151, 173, 266, 

272, 275 
Boijerinck, M. W., 223, 234, 235, 236, 

3)iy a) 

Bender, W. H., 92, 93, 96 

Benedict, H. M., 180, 216 

Bonnets, H. W., 167, 170, 171, 173 

Benson, A. A., 295, SOS 

Bentley, 0. G., 228, 272 

Beiger, J., 261, 272 

Berger, K. C., 150, 155, 158, 17$, 251, 

252, 254, 255, 258, 272 
Bergman, II. E., 152, 161, 178 
Bergman, W. E., 75, 98 
Bergmann, M., 262, 87 G 
Bertramson, B. R., 247, 876 
Bertrand, G., 227, 272 
Beruldsen, E. T., 31, 62 
Buikley, A. M., 173, 176 
Bisset, N., 169, 173 
Blackman, G. E., 50, 68, 118, 119, 120, 

130, 138, 144, 186, 816 
Blackmail, V. II., 105, 144 
Blaser, R. E., 93, 97, 189, 190, 191, 195, 

196, 198, 202, 208, 211, 213, 215, 816, 

217, 218, 219 

Blodsoe, R. W., 196, 817, 218 
Blodgett, F. M., 151, 177 
Blume, J. H., 286, SOS 
Bobko, E., 161, 173 
Bodansky, M., 165, 176 
Boischot, P., 234, 272 
Boken, E., 156, 157, 159, 160, 177, 224, 


Bond, R. M., 358, 359, 360 r 3S7 
Bonner, J., 261, 272 
Boratynski, K., 246, 272 
Boonstra, A. E. H. R., 121, 127, 128, 129, 


Bortels, K., 164, 17S 
Bortner, C. E., 250, 252, 253, 272 
Boughton, I. B., 169, 174 
Bould, C., 170, 174 
Bourbeau, C. A., 67, 97 
Bower, C. A., 68, 86, 97, 99 
Boyd, F., 189, 216 
Boyd, F. T., 309, 387 
Boynton, Damon, 192, 217 
Bradfield, R., 78, 81, 86, 97, 99, 251, 254, 


Brady, N. C., 93, 97 9 208, 213, 816 

Brandenburg, E., 154, 155, 174 

Braude, R., 169, 174 

Bray, R. H., 75, 86, 96, 97, 98 

Breakwell, E., 9, 41, 68 

Brenchley, W. E., 149, 174 

Brian, P. W., 168, 176 

Briggs, G. E., 106, 117, 142, 144 

Briggs, L. J., 34, 59, 68 

Britten, J. W., 168, 174 

Bromfield, S. M., 235, 272 

Bronsart, H. V., 267, 272 

Brooks, F. T., 102, 14 i 

Brown, B. A., 184, 185, 195, 213, 215, 


Brown, D. A., 90, 97 
Brown, E. Marion, 206, 213, 817 
Brown, II. D., 267, 268, 873 
Brown, J. W., 307, 327 
Brown, S. M., 68, 97 
Browne, F. S., 157, 174 
Brun, Thorrald 8., 156, 174 
Bruto, F. R., 323, $86 
Bryan, O. C., 150, 157, 17$ 
Bucha, H. C., 319, 326 
Bull, H., 338, 340, 397 
Bull, L. B., 46, 63 
Bullock, J. F., 151, 164, 173 
Burge, W. E., 152, 176 
Burger, O. J., 268, 878 
Burgess, P. S., 162, 175 
Burkhart, L., 82, 98 
Burrell, R. C., 267, 268, 273 
Burstrom, D., 246, 259, 260, 878, 275 
Burstrom, H., 249, 263, 264, 265, 272 
Burton, Glenn W., 191, 193, 194, 204, 

209, 213, 817 
Butler, C. C., 309, $86 
Butler, P. F., 55, 62 

Cahill, V., 153, 170, 174 

Calvin, M., 295, 303 

Camp, A. F., 153, 155, 163, 174, 175, 

242, 272 

Carles, P., 151, 174 
Carne, W. M., 21, 61 
Carpenter, L. E., 166, 169, 174, 177 
Carrier, Lyman, 194, 206, 207, 217 
Cashmore, A. B., 22, 38, 50, 68, 64 



Chamblec, D. S., 192, 217 

Chapman, H. D., 68, 97, 164, 174, 242, 


Chatterjee, B., 78, 98 
Chilton, S. J. P., 203, 217 
Chippiiidale, H. G., 183, 209, all, 817 
Chisman, II. H., 331, 396 
Christensen, E., 283, SOS 
Christian, C. S., 5, 52, 68 
Chu, T. S., 82, 83, 84, 87, 88, 89, 97 
Churchman, W. L., 150, 172, 176 
Cipola, G., 153, 171, 174 
Clausen, H., 222, 272 
Clements, Frederic E., 190, 193, 219 
Cline, A. C., 341, 396 
Clyde, A. W., 195, 208, 213, 214, 219 
Coic, Y., 243, 246, 272 
Coile, T. S., 334, 336, 337, 368, 369, 374, 

375, 379, 380, 382, 384, 385, 386, 

392, 393, S9(i, 397 
Colby, W. G., 79, 80, 93, 97 
Colby, William G., 208, 817 
Coleman, N. T., 77, 79, 97, 99 
Collander, E., 67, 68, 88, 97 
Collins, E. F., 365, 89G 
Colman, J. M., 151, 174 
Colwell, W. E., 72, 82, 83, 84, 88, 89, 91, 

92, ,9cV 

Comar, C. L., 163, 165, 166, 174 
Comfort, James E., 206, 217 
Comin, D., 157, 172, 174 
Conn, E., 262, 272 
Conner, S. D., 172, 174 
Contzen, J., 230, 275 
Cook, A. C., 206, 215, 31$ 
Cook, F. C., 149, 151, 152, 174 
Cooper, H. P., 93, 97, 194, 217 
Coppenet, M., 225, 243, 246, 878, 273 
Cornfield, A. H., 226, 273 
Cornish, E. A., 28, 57, 62, 64 
Coulter, L. L., 307, 309, 310, 311, 386, 


Cowan, E. W., 77, 97 
Crafts, A. S., 307, 313, 314, ;U5, 316, 317, 

318, 326, 327 
Crocker, E. L., 19, 26, 68 
Crowther, F., 114, 115, 120, 121, 122, 144 
Cummings, B. W., 82, 99 
Cunningham, L J., 165, 166, 169, 171, 


Curie, L. D., 335, 397 
Curtis, L. E., 312, 327 
Cuthbertson, W. F. J., 168, 174 

Dale, W. M., 289, 303 

Dallyn, S. L., 31(5, tttf 

Dalton, N. D., 152, 174 

Davidson, J., 6, 13, 62 

Davies, .1. G., 8, 17, 19, 20, 31, 32, 41, 42, 

49, 52, 62, 64 
Davies, Wm., 181, 182, 183, 200, 204, 209, 

211, 212, 213, 214, 215, 817, 219 
Davis, A. E., 67, 68, 97 
Davis, F. F., 308, 327 
Davis, G. K., 155, 163, 165, 174, 177 
Davis, J. F., 172, 174 
Davis, L. E., 70, 74, 97 
Dawson, C. E., 148, 165, 174 
Dean, L. A., 96, 97 
Delwiche, C. C., 263, 273 
Deniges, G., 225, 273 
de Ong, E. E., 316, 387 
De Turk, E. E., 68, 97 
De Eose, H. E., 310, 327 
DC Vane, Earl H., 213, 817 
Diamond, S., 335, 397 
Dibbern, John C., 186, 187, 217 
Dickey, E. D., 153, 163, 171, 174, 242, 


Dickson, James G., 203, 217 
Diebold, C. II., 341, 397, 398 
Dillman, Arthur C., 190, 217 
Dion, H. G., 230, 231, 232, 233, 273 
Dodd, D. E., 185, 19.5, 213, 215, 217 1 219 
Donahue, E. L., 341, 348, 397 
Donald, C. M., 5, 19, 21, 22, 42, 45, 52, 

68, 63, 64, 157, 171, 176 
Dorrance, A. B., 205, 219 
Doty, D. M., 267, 274 
Dotzenko, Alex., 205, 217 
Drake, M., 79, 80, 93, 97 
Drake, Mack, 208, 217 
Drosdoff, M., 153, 163, 171, 174, 175, 

237, 273 

Dunlop, G., 167, 170, 174 
Dunne, T. C., 153, 170, 174 
Dunning, D., 363, 397 
Durr, E., 308, 326 
Durroux, M., 234, 278 




Earl, T. T., 326, 827 

Egler, F. E,, 311, 321, 325, 32(>, 327 

Eime, L. O., 75, 76, 98 

Einspahr, 1)., 347, 897 

Eisenmenger, W. S., 92, 93, 96 

Elgabaly, M. M., 71, 74, 84, 87, 97 

Ellington, E. V., 206, 18 

Elliot, L., 261, 273 

ElhH, C. H., 266, 275 

Ellis, G. H., 164, 165, 167, 175, 177, 226, 


Eltinge, E. T., 271, 87$ 
Elvehjem, C. A., 149, 151, 166, 174, 175 
Ender, F., 170, 175 
Englcdow, F. L., 103, 104, 105, 144 
Epstein, E., 84, 97, 246, 273 
Erdmann, Milton H., 211, 217 
Eriksson, E., 84, 98, 229, 230, 275 
Erkama, J., 164, 175, 243, 273 
Eslick, Robert, 204, 218 
Euler, II. V., 261, 272, 273 
Evans, H. J., 196, 217 
Evans, Marshall, 188, 217 
Evans, Morgan W., 188, 189, 17 
Evans, S. T., 19, 45, 63, 167, 170, 17$ 
Eversmann, F., 264, 273 
Ewart, G. Y., 327 

Farmer, V. C., 167, 177 
Farris, Nolan F., 192, 193, 17 
Felix, E. L., 150, 155, 172, 175 
Fergus, E. N., 213, 17 
Ferguson, W. S., 163, 168, 175 
Ferrer, R., 313, 327 
Ferres, II. M., 21, 26, 45, 48, 62, 64 
Fink, Delmar S., 213, 18 
Fisher, E. A., ,197 
Fisher, R. A., 106, 144 
Fleming, G. A., 253, #77 
Flinn, F. B., 168, 175 
Floyd, B. F., 150, 153, 17 S 
Folley, S. J., 263, 273 
Forster, H. C., 56, 62, 104, 144 
Fowler, J. H., 153, 17,5 
Frankel, O. H., 104, 144 
Frankena, H. J., 213, 218 

Fratzke, W. E., 68, 69, 81, 96 
Fried, M., 82, 97 

Friederichsen, I., 249, 264, 265, 272 
Fudge, B. R., 153, 163, 174, 175 
Fuelleman, R. F., 186, 219 
Fujimoto, C. K., 223, 236, 250, 273 

Gaiser, R. N., 334, 336, 355, 383, $96, 


Gallagher, P. H., 240, 244, 273 
Gallus, H. P. C., 31, 52, 63 
Garber, R. J., 185, 203, 17, 219 
Gardner, C. A., 21, 61 
Gardner, Frank P., 206, 18 
Garmaii, W. H., 93, 97 
Garrigus, W. P., 202, 218 
Gates, E. M., 226, 273 
Gauch, H. G., 135, 145 
Gaumann, E., 238, 273 
Gedroiz, K. K., 77, 97 
Geiger, M., 68, 98 
Gericke, S., 230, 275 
Gericke, W. F., 271, 273 
Gerloff, G. C., 251, 252, 254, 255, 258, 

Gerretsen, F. C., 223, 235, 236, 238, 243, 

264, 265, 268, 269, 270, 271, 273 
Gerritsen, H. J., 154, 176 
Gessel, S. P., 359, 397 
Giddens, J., 87, 97 
Gieseking, J. E., 70, 86, 97 
Gilbert, F. A., 150, 155, 158, 175 
Gilbert, J. H., 40, 62 
Gilbert, S. G., 153, 163, 175, 248, 270, 


Gillingham, W. P., 325, 827 
Giobel, G., 213, 218 
Gisiger, L., 230, 273 
Gist, George R., 191, 18 
Glass, B., 150, 175 
Glasscock, R. S., 213, 17 
Golden, J. D., 253, 77 
Gollub, M. C., 261, 77 
Goodall, B. W., 107, 116, 118, 121, 133, 

144, 243, 273 

Goodijk, J., 247, 248, 274 
Gorham, E., 243, 75 
Goss, H., 168, 174 



Graber, L. F., 203, 205, 218, 219 

Grandfield, C. O., 204, 218 

Gray, G. P., 316, 327 

Gray, L., 272 

Gray, L. F., 164, 167, 175 

Greathouse, L. H., 225, 277 

Greco, E. C., 319, 327 

Green, D. E., 261, 273 

Greenbaum, A. L., 263, 273 

Greenberg, D. M., 263, 273 

Greene, J. E., 316, 327 

Greenwood, M., 133, 144 

Gregory, F. G., 105, 108, 110, 115, 117, 
120, 121, 122, 123, 124, 129, 130, 
135, 138, 139, 142, 143, 144, 145 

Grimes, J. C., 206, 218 

Grunder, M. S., 206, 18 

Guggenheim, E. A., 77, 97 

Gum, O. B., 267, 268, 273 

Giinther, G., 261, 272, 273 

Hagen, C. E., 286, SOS 

Haig, I. T., 337, 338, 897 

Hale, J. B., 250, 273 

Hall, E. C., 897 

Hamilton, J., 153, 163, 171, 174, 175 

Hamilton, T. S., 166, 175 

Hamner, C. L., 309, 310, 327 

Hamner, K. C., 268, 272 

Handley, E., 69, 79, 81, 97 

Hanson, Clarence H., 203, 218 

Hardy, W. T., 169, 174 

Harley, E., 167, 170, 173 

Harmer, P. M., 157, 172, 175, 224, 229, 

230, 244, 267, 273, 276 
Harper, H. J., 357, 397 
Harrary, I., 262, 276 
Harrer, C. J., 152, 177 
Harrison, C. M., 211, 217 
Harrison, J. E., 22, 62 
Harriss, H. C., 155, 160, 175 
Hart, E. B., 151, 165, 166, 174, 175 
Harvey, W. A., 307, 316, 326 
Hasler, A., 230, 239, 240, 244, 271, 273 
Hauge, 8. M., 268, 272 
Haygood, E. S., 313, 327 
Heath, O. V. 8., 110, 115, 120, 121, 135, 

143, 145 

Heiberg, S. O., 339, 340, 397 

Heidel, E. H., 227, 273 

Hein, M. A., 206, 215, 218, 219 

Heintze, S. G., 229, 230, 231, 233, 238, 

250, 27S 

Hellermann, L., 263, 27S t 276 
Helson, V. A., 316, 327 
Hendricks, S. B., 71, 97 
Hermann, Wilford, 204, 218 
Hervert, F., 319, 327 
Heslep, J. M., 251, 273 
Hess, A. D., 326, 387 
Hester, J. B., 266, 273 
Hewitt, E. J., 223, 249, 250, 252, 253, 

255, 256, 257, 258, 259, 263, 264, 

265, 274, 275, 277 
Hexter, G. W., 48, 62 
Hibbard, P. H., 67, 68, 97 
Hickock, H. W., 338, 340, 397 
Hill, G. E., 102, 109, 145 
Hill, Eowland, 10, 62 
Hill, W. W., 358, 359, 360, 397 
Hills, E. S., 3, 62 
Hiltner, E., 222, 223, 268, 272, 2?4 
Hissink, D. J., 78, 97 
Hitchcock, A. E., 326, 327 
Hivon, K. J., 267, 274 
Hoagland, D. E., 67, 68, 93, 97 
Hodges, E. M., 196, 2 18 
Hodgkiss, W. S., 248, 276 
Hodgson, E. E., 206, 218 
Hodgson, S. C., 55, 62 
Hoffmann, W., 154, 175 
Hofmann, J. G., 392, 393, 397 
Hollowell, E. A., 202, 218 
Holmes, E. S., 156, 175 
Holton, F. S., 103, 144 
Hoover, C. D., 94, 98 
Hopkins, E. F., 250, 254, 255, 270, 271, 


Homer, G. M., 84, 91, 97 
Hou, Hsioh-Yu, 93, 97 
Hudig, J., 222, 223, 235, 236, 244, 245, 

247, 248, 274, 276 
Hummer, E. W., 313, 314, 326 
Humphries, E. C., 133, 145 
Hunter, A. S., 68, 93, 97 
Hunter, J. H., 150, 157, 173 
Hurwitz, C., 236, 274 
Hyde, G. E., 341, 396 



limes, J. M. R., 167, 170, 174 
Inoyc, J. M., 168, 175 
Isaac, W. E., 157, 170, 17 S 
Itallie, T. B. van, 88, 95, 97 
lurko, H. II., 323, 827 

Jackson, M. L., 67, 97 

Jacobs, II. L., 319, 322, 827 

Jacobson, II. G. N., 226, 250, 252, 274, 


Jacobson, L., 69, 79, 81, 97, 294, SOS 
Jamieson, S., 167, 170, 175 
Jarusov, S. S., 70, 81, 85, 97 
Javillier, M., 227, 272 
Jenny, H., 70, 71, 74, 77, 81, 84, 85, 86, 

97, 99 

Jensen, C. A., 163, 176 
Jensen, H. L., 47, 62 
Joffe, J. S., 77, 98 
Johnson, C. B., 226, 77 
Johnson, C. M., 68, 69, 81, 96 
Johnson, I. J., 181, 216 
Johnson, M. O., 254, 274 
Jolmstone-Wallace, D. B., 185, 195, 213, 

215, 218 

Jones, D. W., 196, 218 
Jones, Earl, 215, 219 
Jones, E. W., 264, 265, S74 
Jones, F. R., 185, 202, 218 
Jones, Towerth, 205, 218 
Jones, J. 0., 170, 175 
Jones, L. H. P., 231, 233, -264, 274 
Jones, IT. S M 94, 98 

Keilin, I)., 152, 175 

Keller, Ernest R., 188, 189, 218 

Kelley, R. B., 8, 62 

Kelley, W. P., 70, 98, 250, 274 

Kenten, R. II., 248, 274 

Kidd, P., 106, 117, 142, 144 

Killinger, G. B., 195, 196, 202, 211, 213, 

215, 217, 218 
King, C. G., 152, 177 
King, H. M., 69, 79, 81, 07 
King, L. J., 312, 827 

Kipps, E. H., 32, 50, 68, 205, 206, 218 
Kirk, L. E., 213, 218 
Kirkpatrick, H., 326, 827 
Kittredge, J., Jr., 345, 897 
Klapp, E., 205, 218 
Klingman, D. L., 311, 327 
Kniphorst, L. C. E., 227, 274 
Kuott, J. C., 206, 218 
Knott, J. E., 155, 172, 175 
Knudsen, L. L., 390, 391, 397 
Konovalov, I. N., 133, 145 
Kornberg, A., 262, 75 
Kramer, J. A., 312, 327 
Kramer, P. J., 108, 145 
Kraemer, L. M., 262, 272 
Krinbill, C. A., 74, 98 
Krishnamoorthy, C., 70, 73, 74, 98 
Kubowitz, F., 152, 175 

Lagatu, H., 226, 271 
Lamba, P. 8., 101, 193, tfM* 
Lardy, II. A., 260, 874 
Larson, E. J., 164, 177 
Lawes, J. B., 40, 62 
Lawless, W. W., 155, 175 
Ledford, R. H., 382, 397 
Lee, O. C., 308, SS7 
Lee, W. T)., 383, 397 

Leeper, G. W., 4, 2o, 62, 223, 228, 230, 
231, 233, 235, 243, 264, 271, 214 
Lehr, J. J.