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The Mural Tert=Book Series
Epitep By L. H. BAILEY
SOILS AND FERTILIZERS
The Wural Cext-Book Series
Epitep spy L. H. BAILEY
Carleton, THe SMALL GRAINS.
B. M. Duggar, Pranr Puysiotocy, with
special reference to Plant Production.
J. F. Duggar, SouTHERN FIELD Crops.
Gay, THe Breeps or Live-Srock,
Gay, Tur PRINCIPLES AND PRACTICE OF
Jupeine Live-Strocgk.
Goff, THe PRINCIPLES OF PLANT CULTURE,
Revised.
Harper, ANtmMaAL HusBANDRY FOR SCHOOLS.
Harris and Stewart, THe PRINCIPLES OF
AGRONOMY.
Hitchcock, A Trxt-Book oF GRASSES.
Jeffery, 'TExt-Book oF LAND DRAINAGE.
Jordan, THE Frrpine or ANIMALS, Revised.
Livingston, Firtp Crop PRODUCTION.
Lyon, Sorts AND FERTILIZERS.
Lyon, Fippin and Buckman, Sorts — THEIR
PROPERTIES AND MANAGEMENT.
Mann, Brecinnincs In AGRICULTURE.
Montgomery, THE Corn Crops.
- Morgan, Firip Crops For THE CoTTon-BELT.
Mumford, THe BREEDING OF ANIMALS.
Piper, Foracr PLANTS AND THEIR CULTURE.
Warren, ELEMENTS OF AGRICULTURE.
Warren, Farm MANAGEMENT.
Wheeler, MANURES AND FERTILIZERS.
White, PRINCIPLES OF FLORICULTURE.
Widtsoe, PRINCIPLES OF IRRIGATION PRACTICE.
ae
oath
was
PuaTte I. ‘The earth is perhaps a stern earth, but it is a kindly
earth.’’ — BaI.ry.
SOILS AND FERTILIZERS
BY ce» 4
T LYTTLETON LYON _
\\
PROFESSOR OF SOIL TECHNOLOGY IN THE NEW YORK
STATE COLLEGE OF AGRICULTURE AT
CORNELL UNIVERSITY
Neto Work
THE MACMILLAN COMPANY
1919
All rights reserved
S5a\
L.@2
\A\4
CopyYRigHt, 1917,
By THE MACMILLAN COMPANY.
Set up and electrotyped. Published August, 1917.
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Norwood Yress
J. 8. Cushing Co. — Berwick & Smith Co.
Norwood, Mass., U.S.A.
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PREFACE
In many of the high schools and other secondary schools
into which instruction in agriculture was introduced a few
years ago there has been such a development of the subject
that one general text is no longer adequate. In these schools
some of the more important phases of the subject now re-
ceive a degree of attention that calls for specialized texts.
This is particularly true of the secondary agricultural schools
and the normal schools. It was with the hope of meeting
this need, and also of contributing to the demands of short
courses in agriculture and of summer courses for teachers,
that this book was written.
The attempt has been made so to present the subject that
the pupil who has no knowledge of chemistry or other natural
science will be able to understand it. No chemical symbols
or formule have been used. Use has been freely made of a
limited number of names of chemical substances contained
in commercial ferttlizers which contribute to the nutrition
of plants. These, however, are terms with which the pupil
can familiarize himself as readily as with the geographical
and other names that he has already mastered.
Following each chapter are field and laboratory exercises,
designed to illustrate in a concrete manner the teachings of
the text. There are more of these than any one teacher will
probably find it expedient to have his class perform, but the
considerable number and variety of exercises will make it
possible for any school to afford the. necessary facilities for
performing some of the demonstrations.
V
vl PREFACE
It has not been thought necessary to cite authorities on
which the statements in the text are based. For these and
for more complete discussions of most of the matters treated
in this book, teachers and others who may wish to pursue
the subject further are referred to the college text on soils
by Lyon, Fippin and Buckman.
The author is especially indebted to Dr. H. O. Buckman
for much assistance and advice. He has contributed prac-
tically all of the laboratory exercises.
Ipmaca, N. Y.,
June 1, 1917.
CONTENTS
CHAPTER I
Sor, as A MeEpium For PLANT GROWTH :
Soil as a mechanical support for plants, § i Soil
as a reservoir for water needed by plants, § 2; Uses
of water by plants, § 3; Soil as a source of plete
materials, § 4;. Quantities of plant-food materials in
the earth’s crust, § 5; Soil-forming rocks, § 6; Rock-
forming minerals, § 7; Important minerals, § 8.
Questions on Chapter I
Laboratory Exercises ‘ TINE ‘
Study of soil-forming main ccale. I; Study of soil-
forming rocks, II; To show that plants give off
water, III; Conditions for plant growth, IV; Ef-
fects of different plant nutrients, V.
CHAPTER II
Sor. FoRMATION AND TRANSPORTATION
Agencies concerned in soil formation and pate:
portation, §9; Action of heat and cold, §10; Ac-
tion of frost, § 11; Action of water, § 12; Action of
ice, § 13; Action of wind, §14; Action of gases,
§ 15; Action of plants and animals, §-16; Powdered
rock is not soil, § 17.
Questions on Chapter II . : ‘ ‘ : : :
Laboratory Exercises . ; ‘ °
Soil formation and Sicecce ation: ,
CHAPTER III
Sort ForMATIONS .
Residual soils, § 18; Distribution of eer aie
§ 19; Cumulose soils, § 20; Colluvial soils, § 21;
vii
PAGES
i
7-8
8-10
11-16
16
17
18-28
Vill CONTENTS
Alluvial soils, § 22; Character and distribution of
alluvial soils, § 23; Marine soils, § 24; Distribution
of marine soils, § 25; Lacustrine soils, § 26; Glacial
soils, § 27; AMolian soils, § 28.
Questions on Chapter III .
Laboratory Exercises
Classification of soils, I; tess of a auger in eae
samples, II.
CHAPTER IV
TEXTURE AND STRUCTURE OF SOILS
Shape of particles, § 29; Space oacdiied by oa
cles, § 30; Mechanical analysis of soils, § 31; Me-
chanical analysis of some typical soils, § 32; Soil class,
§ 33; Some properties of the separates, § 34; Chemi-
cal composition of soil separates, § 35; Soil structure
§ 36; Relation of structure to pore space, § 37; Re-
lation of structure to tilth, § 38; Conditions and
operations that affect structure, § 39; Relation of
texture to structure, § 40; Wetting and drying, § 41;
Freezing and thawing, § 42; Effect of organic matter
on structure, § 43; Roots and animals, § 44; Tillage
and structure, § 45; Structure as affected by lime,
§ 46; The soil survey, § 47; Classification of soils,
§ 48; Information furnished by a soil survey, § 49.
Questions on Chapter IV .
Laboratory Exercises
Examination of soil paren: i ierrndienienh of
soil separates, Il; Simple ene Al analysis, III;
Study of soil tines and its determination by examina-
tion, IV; Determination of soil class from a mechani-
eal analysis, V; Soil structure,, VI; Determination
of apparent specific gravity of dry sand and clay,
VII; Calculation of pore space, VIII; A study of the
plow, IX.
CHAPTER V
ORGANIC MATTER
Classes of organic moti § 50: Banefeal effects
of organic matter, § 51; Porosity of organic matter,
PAGES
28
29
30—45
45
46-50
51-57
CONTENTS ix
PAGES
§ 52; Organic matter and drainage, § 53; Organic
matter and soil color, § 54; Organic matter a source
of plant-food material, § 55; Organic matter and
nitrogen, § 56; Organic matter and soil microérgan-
isms, § 57; Organic matter forms acids, § 58; In-
jurious effect of organic matter, § 59; Management
of organic matter in soils, § 60; Sources of organic
matter, § 61.
Questions on Chapter V. ‘ 3 : : : : 57
Laboratory Exercises ‘ 58-60
Examination of soil — perio antiar, he Hxanie
nation of peat and muck, II; Estimation of organic
matter, III; Extraction of decomposed organie
matter, IV; Influence of organic matter on percola-
tion through soils, V; Influence of organic matter on
percentage of moisture held in soil, VI; Influence of
organic matter on percentage of moisture held in soil,
wil.
CHAPTER VI
Som, WATER . : ‘ ; ; : 61-85
Forms of water in esas: § 62; eran the three forms
of water differ, § 63; Fiverncespic water, § 64; Capil-
lary water, § 65; Capillary water capacity, § 66;
Movement of capillary water, § 67; Effect of tex-
ture on capillary movement, § 68; Effect of struc- 2
ture on capillary movement, § 69; Height of water
column and capillary movement, § 70; Gravitational
water, § 71; The water table, § 72; Relations of soil
water to plants, § 73; Ways in which water is useful
to plants, § 74; Water requirements of plants, § 75;
Transpiration by different crops, § 76; Effect of
moisture on transpiration, § 77; Effect of humidity,
wind and temperature of the air, § 78; Effect of soil
fertility on transpiration, § 79; Quantity of water
required to mature a crop, § 80; Capillary move-
ment and plant requirement, § 81; Optimum mois-
ture for plant growth, § 82; The control of soil mois-
ture, § 83; Run-off, § 84; Percolation, § 85; Evap-
x CONTENTS
PAGES
oration, § 86; Mulches for moisture control, § 87;
The soil mulch, § 88; Frequency of stirring, § 89;
Depth of mulch, $90; Effectiveness of mulches,
§ 91; Other devices to prevent evaporation, § 92;
Rolling and subsurface packing, § 93; Removal of
water by drainage, § 94; Benefits of drainage, § 95;
Soil air, § 96; Soil tilth, § 97; Available water dur-
ing the growing season, § 98; Length of growing
season, § 99; Other results of drainage, § 100; Open
ditches, § 101; Tile drains, § 102; Arrangement. of
drains, § 103; Digging ditches and laying tile, § 104.
Questions on Chapter VI . : : ‘ é : , 85
Laboratory Exercises : : 85-89
Determination of the Ae pacstdies of estes in a soil,
I; Capillary movement in different soils, Il; Rate
of percolation of water through soils, III; Water-
holding capacity of soils, 1V; Moisture conservation
by means of a soil mulch, V; Loss of water by tran-
spiration, VI; Review problems Chapter IV and VI,
VII; Tile drainage, VIII.
CHAPTER VII
Puant-Foop MatTsrRIALs IN SOILs © : . 90-110
© Variations in content of plant Se in differant }
soils, § 105; The total supply of plant-food materials,
§ 106; Upward movement of plant-food materials,
§ 107; Plant nutrients compose a small part of the
soil, § 108; Relation of composition to productive-
ness, § 109; Available and unavailable plant-food
materials, § 110; Conditions that influence avail-
ability, § 111; Water-soluble matter in soil, § 112;
Relation of water-soluble matter to productiveness,
§ 113; Chemical analysis of soil, § 114; Absorptive
properties of.soils, § 115; Selective absorption, § 116;
The availability of absorbed fertilizers, § 117; Other
forms of available plant-food material in soils, § 118;
Loss of plant-food material in drainage water, § 119;
CONTENTS xl
PAGES
Quantities of plant-food materials in drainage, § 120;
Effect of crop growth on loss of plant nutrients in
drainage, § 121; Effect of fertilizers on loss of plant-
food materials in drainage, § 122; Drainage water
from different soils, § 123; Absorption of good mate-
rials by plants, § 124; How plants absorb nutrients,
§ 125; Howroots aid in solution of soil, § 126; Pro-
duction of carbon dioxide by microérganisms, § 127;
Solvent action of roots in other ways, § 128; Differ-
ence in absorptive power of crops, § 129; Substances
needed by plants and substances merely absorbed,
§ 130; Quantities of plant-food materials removed
_by crops, § 131; Possible exhaustion of mineral
nutrients, § 132.
Questions on Chapter VII Se see) See ee ae es by 8
Laboratory Exercises : Beaks ai (|
Soluble matter of soil, I: Asospnive Peart of Ai
for dyes, Il; Selective ef, eae by soil, III; Ab-
sorptive power of the soil for gas, IV.
CHAPTER VIII
Acip Sorts AND ALKALI SOILS t . 112-121
Nature of soil acidity, § 133; witive acitlity:
§ 134; Negative acidity, § 185; Ways by which soils
become sour, § 136; Drainage as a cause of acidity,
§ 137; Effect of plant growth on soil acidity, § 138;
_ Effect of fertilizers on soil acidity, § 139; Effect of
green-manures on acidity, § 140; Weeds that flourish
on sour soils, § 141; Crops adapted to sour soils,
§ 142; Crops that are injured by acid soils, § 143;
Litmus paper test for soil acidity, § 144; Litmus
- paper and potassium nitrate, § 145; The Truog test,
§ 146; Alkali soils, § 147; Nature and movements
of alkali, § 148; Effect of alkali on crops, § 149;
Tolerance of different plants to alkali, § 150; Irriga-
tion and alkali, § 151; Removal of alkali, § 152;
Control of alkali, § 153.
Questions on Chapter VIII x : ‘ . . 21-122
Xi CONTENTS
PAGES
Laboratory Exercises : : 5 % - . 122-124
Acid soils in the field, I: Litmus paper with and
without potassium nitrate, Il; Litmus paper test,
III; Test for soil carbonates, IV; Ammonia test for
acidity, V; Zine sulfide test for acidity, VI; Incrusta-
tion of ‘‘alkali’’ by capillary action, VII.
CHAPTER IX
Tue Germ LIFE OF THE SOIL : . 125-140
Microérganisms injurious to crops, Vs ae Gérmé
not directly injurious to crops, § 155; Numbers of
bacteria in soils, § 156; Conditions sffecting bacterial
growth, § 157; Air supply, § 158; Moisture, § 159;
Temperature, § 160; Organic matter, § 161; Soil
acidity, § 162; Bacteria in relation to soil fertility,
§ 163; Action on mineral matter, § 164; Decom-
position of non-nitrogenous organic matter, § 165;
Decomposition of nitrogenous organic matter, § 166;
Ammonification, § 167; Nitrification, § 168; Effect
of soil aération on nitrate formation, § 169; Effect of
temperature on nitrate formation, § 170; Effect of
sod on nitrate formation, § 171; Depths at which
nitrate formation takes place, § 172; Loss of nitrates
in drainage, § 173; Denitrification, § 174; Nitrogen
fixation, § 175; Nitrogen fixation through symbiosis
with higher plants, § 176; Soil inoculation for le-
gumes, § 177; Nitrogen fixation by free-living
germs, § 178. ;
Questions on Chapter IX . , , . i - : 40
Laboratory Exercises : . 140-142
Test for nitrates in aid FS Test for ammonia in
soil, II; Factors affecting nitrate formation, III;
Examination of legume nodules, IV; Examination of
nodule bacteria, V; Soil inoculation, VI.
CHAPTER X
Sor. Arr AND Sort TEMPERATURE : , - 1438-152
Soil air contained largely in noweaniniliee spaces,
§ 179; There may be too much or too little soil air,
CONTENTS Xill
PAGES
§ 180; Movement of soil air, § 181; Movement of
water, § 182; Diffusion of gases, § 183; Composi-
tion of soil air, § 184; Production of carbon dioxide
in soils, § 185; Conditions that affect the quantity
of carbon dioxide in soils, § 186; Usefulness of air in
. soils, § 187; Oxygen, § 188; Nitrogen, § 189; Car-
bon dioxide, § 190; Control of the volume and move-
ment of soil air, § 191; Soil temperature, § 192;
Sourees of soil heat, § 193; Relation of soil tempera-
ture to atmospheric temperature, § 194; Factors that
modify soil temperature, § 195; Control of soil tem-
perature, § 196.
Questions on Chapter X . r ‘ ; ; : ‘ 152
Laboratory Exercises °. . 152-154
Movement of soil air as caipnnineds by faeces and
structure, I; The presence of carbon dioxide in soil
aan EL» Brotuction of carbon dioxide by germs, III;
Temperature and soil color, IV; Slope and soil tem-
perature, V; Drainage and temperature, VI.
CHAPTER XI
NITROGENOUS FERTILIZERS . . . 155-168 :
Relative quantities of the different Paine of eres
gen in soils, § 197; Forms in which nitrogen is ab-
sorbed by plants, § 198; Nitrates as plant-food
materials, § 199; Absorption of ammonia by agri-
cultural plants, § 200; Direct utilization of organic
nitrogen by crops, § 201; Forms of nitrogen in fer-
tilizers, § 202; Nitrate of soda, § 203; Crops mark-
edly benefited, § 204 ; Effect of nitrate of soda on soils,
§ 205; Sulfate of ammonia, § 206; Composition of
sulfate of ammonia, § 207; Action when applied to
soils, § 208; Cyanamid, § 209; Composition of
eyanamid, § 210; Changes in the soil, § 211; Fer-
tilizers containing organic nitrogen, § 212; Vege-
table products, § 213; Animal products, § 214; Fish
waste, § 215; Guano, § 216; Effects of nitrogen on
plant growth, § 217; Availability of nitrogenous
X1V CONTENTS
‘fertilizers, § 218; Relative values of organic and
inorganic nitrogenous fertilizers, § 219.
Questions on Chapter XI . : ; ‘ : ; :
Laboratory Exercises : ,
Influence of nitrogen on meoland nthe pri Exam
nation and identification of nitrogen fertilizers, II;
Comparison of fertilizer effects on plant growth, vie
CHAPTER XII
PuospHoric AcID FERTILIZERS ‘ =,
Bone phosphate, § 220; Mineral phosphates,
§ 221; Basic slag, § 222; Acid phosphate, § 223 ; Com-
position of acid phosphate, § 224; Reverted phos-
phorie acid, § 225; Absorption of acid phosphate by
soll, § 226; Relative availability of phosphorie acid
fertilizers, § 227; Rock phosphate versus acid phos-
phate, § 228; Effect of phosphoric acid on plant
erowth, § 229; Plants particularly benefited by
phosphorie acid, § 230.
Questions on Chapter XII
Laboratory Exercises
Influence of Pcuukuen art on lant cena: ie
Examination and identification of phosphate fer-
tilizers, Il; Comparison of fertilizer effects on
plant growth, ITI.
CHAPTER XIII
PotTasH AND SULFUR FERTILIZERS . f
Stassfurt salts, § 231; Wood ashes, § 232; Thighs
ble potash fertilizers, § 233; Effects of potash on
plant growth, § 234; Sulfur as a fertilizer, § 235;
Experiments with sulfur as a fertilizer, § 236;
Quantities of sulfur contained in crops, § 237;
Quantities of sulfur in soils, § 238; Quantities of sul-
fur in drainage water, § 239; Sulfur contained in se
tilizers,.§ 240.
PAGES
168
168-170
171-176
176-177
177-178
179-185
CONTENTS
Questions on Chapter XIII
Laboratory Exercises
Influence of potash on plait Sh owtihe tie apie tia
tion and identification of potash fertilizers and sulfur,
Il; Comparison of fertilizer effects on plant growth,
LIT.
CHAPTER XIV
LIME ‘ ’ . ‘ : . : ;
Forms of lime, § 241; Absorption of lime by soils,
§ 242; Lime requirement of soils, § 248; Effect of
lime on tilth, § 244; Effect of lime on bacterial
action, § 245; Liberation of plant-food materials,
§ 246; Effect on plant diseases, § 247; The use of
magnesian limes, § 248; Caustic lime versus ground
limestone, § 249; Fineness of grinding limestone,
§ 250; Gypsum or land plaster, § 251.
Questions on Chapter XIV
Laboratory Exercises ; ; :
A study of the fein’ of me I; Fineness of
ground limestone, II; Effect of lime on biological
action, III; Flocculation by lime, IV; Flocculation
by lime, V; Lime and the rotation, VI; Forms of
lime to apply, VII.
CHAPTER XV
Tur PurcHAsE AND MIXING oF FERTILIZERS
Brands of fertilizers, § 252; High- and low-grade
fertilizers, § 253; Fertilizer inspection and control,
§ 254; Trade values of fertilizer ingredients, § 255;
Computation of the wholesale value of a fertilizer,
§ 256; Home mixing of fertilizers, § 257; Fertilizers
that should not be mixed, § 258; Calculation of a
fertilizer mixture, § 259; How to mix the ingredients,
§ 260.
Questions on Chapter XV x : é : :
XV
PAGES
185
185-186
187-192
192
193-195
196-205
205-206
XVl1 CONTENTS
PAGES
Laboratory Exercises : ‘ ; . 206
Fertilizer inspection and Cone I; Laboratory
mixture of fertilizers, II; Home mixture of fertilizers,
III.
CHAPTER XVI
Tue Use or FERTILIZERS : -. 207-219
Fertilizers for different crops, sg 261: Sarai erains,
§ 262; Grass crops, § 263; Leguminous crops, § 264;
Root crops, § 265; Vegetables, § 266; Orchards,
§ 267; Fertilizer mixtures for different crops,
§ 268; Fertilizers for different soils, § 269; Calcula-
tion of results of fertilizer experiments, § 270; Fer-
tilizing the rotation, § 271; Methods of applying fer-
tilizers, § 272; The limiting factor, § 273; The law
of diminishing returns, § 274; Conditions that influ-
ence the effect of fertilizers, § 275; Response of sandy
and of clay soils to fertilizers, § 276; Cumulative
need of fertilizers, § 277.
Questions on Chapter XVI A : : : 2 ‘ 219
Laboratory Exercises : ; . *. 219-220
Fertilization of standard Oe ie SE I; Fertiliza-
tion of home-farms, II; Fertilizer practice in the
community, III; Fertilizer experimentation, IV.
CHAPTER XVII
Farm MANuRES . ? ap etaee ~ 221-232
Solid and liquid manure, 8 278: Chemical compo-
sition of manures, § 279; Farm manure an unbal-
anced fertilizer, § 280; Quantities of manure voided
by animals, § 281; Effect of food on composition of
manure, § 282; Commercial evaluation of manures,
§ 283; Agricultural evaluation of manures, § 284;
Deterioration of farm manure, § 285; Fermentations
of manure, § 286; Leaching of farm manure, § 287;
Protected manure more effective, § 288; Reinforeing
manure, § 289; Methods of handling manure, § 290;
Covered barnyard, § 291; Application of manure to
CONTENTS
land, § 292; Place of farm manure in crop rotation,
§ 293.
Questions on Chapter X VII
Laboratory Exercises
Study of farm manure, 7 Wapstimente pith pact
manure, II; The value of manure produced on the
home farm, III; Reinforcement of farm manure,
IV; Building of a compost pile, V.
CHAPTER XVIII
GREEN-MANURES :
Protective action of green manures, 294: Mate
rials supplied by green manures, § 295; Transfer of
plant-food materials, § 296; Crops used for green-
manuring, § 297; When green-manures may be used,
§ 298; Handling green-manure crops, § 299
Questions on Chapter XVIII
Laboratory Exercises
Study of Pci ida cate in the field, tr Green-
manure and the rotation, II.
CHAPTER XIX
Crop RotTATION é !
Crop rotation aid ei prod@aee onesie, § 300;
Root systems of different crops, § 301; Nutrients re-
moved from soil by different crops, § 202; Some
crops or crop treatments prepare nutriment for
other crops, § 303; Crops differ in effect on soil
structure, § 304; Certain crops check certain weeds,
§ 305; Plant diseases and insects, § 306; Loss of
plant-food material between crops, § 307; Produc-
tion of toxic substances from plants, § 308; Manage-
ment of a crop rotation, § 309
Questions on Chapter XIX
Laboratory Exercises :
Crop rotations, I; Weenlivine the Potion, II.
XVi
PAGES
232
233-234
235-240
240
240-241
242-247
248
248
LIST OF ILLUSTRATIONS
Frontispiece
Rock disintegration by heat and cold . , z facing
Wearing action of water onrock .. . : : facing
Plants as soilformers. ; ‘ : - : facing
Glacial soil and alluvial soil . , : : ‘ facing
Stratification of rock and soil : 3 { 2 facing
Auger for taking soil samples
Relative sizes of soil particles :
Graphic statement of mechanical Salven of ace :
Scheme for determining soil class (after Whitney) .
Ideal arrangement of soil particles .
Section showing structure of loam soil in paod tilth
Plowed land, showing good and poor tilth . f facing
Apparatus for simple mechanical analysis of soil
Apparatus for the determination of the apparent spenitic
gravity of soil .
A walking plow alae its Sealeadrite ;
Cross sections of furrows turned at different biglas
Apparatus for the estimation of organic matter in soil :
Apparatus for estimating rate of percolation and water-holding
capacity .
Soil particles and eri niiiae ins of Beescopic and Sankt
lary water , , :
Erosion of soil by water and by wind ; : : feats
Section of soil with and without a mulch
Systems of laying out tile drains : ;
‘Drain tile outlets . : : fiscina
Sections of land showing locates of tite rains and water
tables
Diagrammatic Bealanation of wake epiieol4 in a hui eine
Apparatus for moisture measurement. , 2 facing
Apparatus for demonstration of effectiveness of mulches in
conserving soil water
Apparatus for observation of Pe teiation Nae eater ets
plants . :
xix
XX LIST OF ILLUSTRATIONS
Surface soil and subsoil . j . . facing
Relative quantities of potash, lime, phosphorie acid and
nitrogen inasoil . é ‘
Equipment for making the ivgias Spee ese. e :
Apparatus for making the zine sulfide test . -
Relative sizes of bacteria and soil particles . . :
Appearance of some soil bacteria (after Léhnis) . ‘
Diagrammatic representation of the nitrogen cycle
Apparatus for estimating the relative rate of air movement
through soils
Apparatus to demonstrate the fiesenee ‘of aaebont fone in
soil air :
Apparatus to jocwonstents thie Parisien of eathin dina in
soil :
Effect of certain fettilcae He Sa a on enlane crdeartle facing
Extent to which fertilizers are used in the several states
Tag representative of the kind often used on bags of fertilizer
Plan for fertilizer experiments j ‘ ; :
Field plat experiments . > Z raping
Influence of soil moisture on the i ere ‘of fertilizers
: : : ; : : ; : . facing
Composition of farm manure . 3 ;
Storage of farm manure . ; ; facing
Movements of plant-food materials eieeen pail air and plant
Cover crops which are also green manures. i facing
PAGE
92
94
123
124
128
131
139
153
153
154
156
197
201
212
212
218
223
226
237
238
SOILS AND FERTILIZERS
/
SOILS AND FERTILIZERS
CHAPTER I
SOIL AS A MEDIUM FOR PLANT GROWTH
Tue farmer’s interest in the soil is due chiefly to what
it contributes to plant production. In this respect it per-
forms several functions: (1) it acts as a mechanical support
for plants by furnishing a foothold comprising many open-
ings through which plant roots ramify and hold the plant
in place; (2) it serves as a receptacle in which water is
held in a convenient way for roots to appropriate; (8) it is
composed, in part, of substances that dissolve in the water
which it holds and are absorbed from solution by roots, and
utilized by plants as food material; (4) its porous nature
allows air to circulate within it, thus supplying plant roots
with air.
These are the contributions that soils make to plant growth.
Before proceeding with a more detailed study of soil it will
be desirable to consider briefly the needs of the plant as
supplied by the soil.
1. Soil as a mechanical support for plants. — Land plants
need anchorage, for they must have some permanent supply
of water and other food material, which is not to be had
from the atmosphere. The soil serves, at once, as anchor-
age and food reservoir. One property of soil that adapts
. B if
2. SOILS AND FERTILIZERS
it especially for the growth of roots is its permeable structure,
which furnishes innumerable channels through which roots
may ramify; another property is its compressibility, which
makes it possible for the roots to grow in thickness by
forcing together the surrounding particles. The compacting
thus effected may be noted in a field of mangels or other
large roots at harvest. The firmness of this anchorage is
illustrated by the resistance that large trees offer to heavy
winds.
2. Soil as a reservoir for water needed by plants. — The
leaves of land plants thrive without being in contact with
water, but their roots must have a nearly constant supply.
This the soil helps to maintain by catching and holding more
or less of the water that falls as rain. The water thus held
is in contact with the small roots and root-hairs of plants,
and may readily be absorbed by them.
3. Uses of water by plants. — Plants require moisture for
several reasons: (1) Water acts as a solvent for substances
that are essential to plant growth, and these substances can
be absorbed by plants only when they are in solution.
(2) Water is itself a plant-food material and it either becomes
a part of the cell without change, or is decomposed and its
component parts are used in forming newsubstances. (3) The |
cells, of which plants are composed, are kept filled and the
plant is more or less firm and erect when its cells are extended
with water. When not so filled, the plant wilts. (4) Nutri-
tive substances and substances formed from them in the
plant tissues are transferred from one part of the plant to
another, as occasion requires, by water in the plant. (5) The
evaporation of moisture from leaves (transpiration) causes a
reduction of temperature in plants, as does evaporation of
perspiration from animals.
4. Soil as a source of plant-food materials. — Plants re-
quire for their growth certain nutrient substances, of which
SOIL AS A MEDIUM FOR PLANT GROWTH 3
some are derived from the air and some from water, but
the larger number must be obtained from soil. They may
be classified thus :
Substances obtained from air or water:
Carbon Hydrogen
Oxygen Nitrogen
Substances obtained from soil:
Nitrogen
Phosphoric acid [phosphorus] !
Potash [potassium]
Lime [calcium]
Magnesia [magnesium]
Iron
Sulfur
All these substances are essential to the normal devel-
opment of farm crops. Carbon, oxygen and nitrogen are
found in air. Hydrogen and oxygen are in water. Plants
obtain their carbon from the air; their oxygen from
both air and water; their hydrogen from water; their ni-
trogen, in the case of certain plants only, from the air. The
other substances are found in all arable soils, from which
plants obtain them after they have become dissolved in the
soil water. While arable soils contain all these substances,
the fact that they must be in solution before plants can use
1This list of plant-food materials gives the names commonly used.
Thus the terms phosphoric acid, potash, and lime are the ones used in con-
nection with fertilizers. Nitrogen is sometimes spoken of as ammonia by
fertilizer manufacturers, but the most general term is nitrogen. The words
in brackets following the unbracketed words indicate other names some-
times found, but not used in this book.
All the substances in this list are capable of uniting with certain other
‘substances to form various combinations. When present in the soil they are
not likely to be in the same combinations as when present in plants. When,
therefore, phosphoric acid in soil or in a plant is spoken of, nothing is implied
regarding the form in which it exists.
4 SOILS AND FERTILIZERS
them sometimes leads to a deficiency in the available
supply. This is either because they are not present in
sufficient quantity, or because they are not readily dissolved
by the liquids with which they come in contact. Many
things tend to influence the quantity of these substances
that plants may obtain. Among these are tillage, decaying
vegetation, drainage and the kind of plant grown. It is
the nitrogen, phosphoric acid, potash and possibly sulfur
that are most likely to be deficient in the solution to which
plants have access, and commercial fertilizers usually con-
tain one or more of these substances.
The kind of fertilizer that it will be desirable to apply
depends, in part, on the so-called availability of each of
the nutrient substances contained in the soil, availability in
this case meaning the readiness with which the plant can
appropriate these food materials. But some plants require
more of certain of these substances than they do of others.
Hence the needs of the plant must also be taken into con-
sideration in deciding what fertilizer to use on a given soil.
5. Quantities of plant-food materials in the earth’s crust.
— As all of the food materials that plants draw from soil,
with the exception of nitrogen, came originally from rocks,
it is of some interest to know what the proportions of these
substances are in the entire crust of the earth. As stated
by Clarke they are present in the following percentages :
OXyZON . 6 eee ete cee! 47.17 > Pate een sy |e
Tirom 3. jee use ie ees AeA) SER ae a
Lime «ete pebee oe, 4.79 Phogolieme acid...) as eee
IMBOneGIA, \cae er ies eey ue.
Nitrogen does not appear in this list because it does not
occur as a constituent of the rocks forming the earth’s crust.
The nitrogen that soil contains is derived from the atmos-
phere by processes that will be described later. Most of
the constituents of soil have, however, been formed from
SOIL AS A MEDIUM FOR PLANT GROWTH Hi
rock, and hence soil may be expected to have a somewhat
similar composition to that of the earth’s crust.
It will be seen that two of the important nutrients, as far
as plants are concerned, namely phosphoric acid and sulfur,
are present in relatively small quantities. Potash, magnesia,
lime and iron are present in much larger proportions. This
is somewhat the relation in which we are likely to find them
in soils, and emphasizes the probable need of phosphoric .
acid and sometimes sulfur for the maximum production of
crops. Potash, in spite of its greater quantity, is often not
available in sufficient amount and must be applied as a
soluble fertilizer.
Lime, being easily soluble in soil water, has frequently
been leached out of soils in such quantities that it must
be replaced. Magnesia is less soluble and hence is rarely
lacking.
6. Soil-forming rocks. — As the earth, which was once
a molten mass, cooled, the crust became solid and this solidi-
fied material formed igneous rocks, so called to distinguish
them from rocks that were formed in other ways. Some
examples of igneous rocks are granite, syenite and basalt.
Other kinds of rocks, called sedimentary, have been formed
from material derived from igneous rock by solution and
sedimentation, and later solidified into rock, often under
pressure. Limestone, dolomite, shale and sandstone repre-
sent some rocks of sedimentary origin. The first two are
quite readily soluble in soil water, having been deposited .
from solution in the process of their formation. Shale
is a more or less hardened clay. Sandstone, as its name
implies, consists of sand grains cemented together.
Metamorphic rocks have been formed by heat, pressure,
solution and other processes acting on either igneous or sedi-
mentary rocks. These forces have frequently produced
rocks quite unlike those originally involved in the process.
6 SOILS AND FERTILIZERS
Gneiss, marble and slate are among the rocks so formed.
Gneiss somewhat resembles granite, from which it is
formed, but unlike granite has a layered structure, the
result of the pressure to which it was subjected. Marble
has been formed from limestone or dolomite by heat and
pressure, which have caused crystallization. It is not,
therefore, so readily soluble as limestone. Slate has been
formed from shale by heat and pressure.
7. Rock-forming minerals. — Most rocks are not homo-
geneous, but are made up of a number of different materials.
An examination will frequently show grains of different
sizes, colors and hardness. The grains are minerals and
they differ from each other in their composition as they
do in their appearance. But each mineral. always has a
more or less well-defined composition, so that when we have
a certain mineral we know something of the quantity of
potash or lime or other base that it contains. The quan-
tity of potash or other plant-food material in a rock will
depend on the proportion of minerals containing those sub-
stances that compose the rock.
8. Important minerals. — There are a few minerals that
it will be well to mention: (1) because they or their products
occur in very large quantity in soil and influence its physical
properties; (2) because of the plant-food material that
they contain. Quartz and feldspar are examples of the class
first mentioned. Quartz is found in almost all soils, and
may form from 85 to 99 per cent of their composition. It
is particularly prevalent in sandy soils. It usually occurs
as a large grain, called sand, is hard and insoluble and con-
tributes no plant-food material. A soil with a great deal
of quartz is usually a light, easily worked soil.
On weathering feldspar contributes to soils a mass of
very finely divided matter known as clay, the smallest of
the soil particles. It, therefore, forms part of the clay in
Prate li. Som Formation. — Heat, cold, and frost have been largely
instrumental in fracturing the rocks in the upper figure, and in produc-
ing the rock débris and soil in the lower. Note that vegetation has
already well started on the slope.
SOIL AS A MEDIUM FOR PLANT GROWTH ‘{
soils and adds to their plasticity, and in addition, this very
fine material is an absorbent, holding the soluble plant-food
materials of fertilizers in a form that prevents them from
leaching from the soil, and yet gives them up to plants rather
easily.
As examples of the second class we again have the feld-
spars as they furnish lime, magnesia and potash; calcite,
which contains lime; hematite, which consists largely of
iron; dolomite, which contains both lime and magnesia;
apatite, which furnishes phosphoric acid and lime, and gyp-
sum, which is a combination of lime and sulfur.
These minerals and the plant-food materials contained
‘in them may be reviewed in tabular form thus:
Mineral Plant-food Material
Feldspars Potash, lime, magnesia
Calcite Lime
Dolomite Lime, magnesia
Hematite Tron
Apatite Phosphoric acid, lime
Gypsum Sulfur, lime
Quartz Silica (not a plant-food material)
As these minerals are widely distributed in rocks from
which soils are formed, they are found in almost all soils,
and thus it is that all the substances required by plants are
to be found in most soils.
QUESTIONS
1. What are the properties of soil that make it well adapted to
furnish a mechanical support for plants?
2. What relation does soil have to the needs of plants for water?
3. Describe the reasons why plants need water.
4. Name the elemental substances that plants derive from soil.
5. What elemental substance do plants obtain from soil that is
not present in rocks from which soil is formed?
6. What two substances necessary to plant growth are contained
in the earth’s crust in the smallest quantities ?
8 SOILS AND FERTILIZERS
7. In what way were igneous rocks formed? Sedimentary
rocks ? Metamorphic rocks ? Name examples of each.
8. Namea mineral containing potash, a mineral containing lime,
a mineral containing magnesia, a mineral containing phosphorie acid,
a mineral containing sulfur, a mineral containing iron.
LABORATORY EXERCISES
The following exercises are designed to suggest possible experi-
ments and demonstrations that may be carried out in connection
with the various chapters. Some may be performed by the student
if adequate facilities are at hand, some are only possible as demon-
strations, while others are field studies and depend on local condi-
tions. Enough suggestions are made with each chapter to give the
teacher a range of choice according to his conditions and facilities.
It is not considered possible or advisable that all the experiments.
and demonstrations listed be carried out.
Exercise I. —Study of soil-forming minerals. (The teacher will
find an elementary text in mineralogy of great aid in this experi-
ment.)
Materials. — Small specimens of quartz, potash-feldspar, mica,
calcite, apatite, gypsum and hematite. Also a piece of a glass, a
knife, dilute muriatic acid, a hand-lens and flame (gas or alcohol).
Procedure. — Study the specimens according to the following
outline, with a view to identifying uke minerals unlabeled. Use
hand lens where possible.
Hardness. — Determine hardness by the following scale.
Hardness Mineral
Scratched by finger. nail . <3 ais Gypsum\ y 4; a8
Cut bynes i, Caleite:
Seratched with Bieculty siti knife . . Apatite
Seratches glass . . . . . . . . Feldspar — Hematite
Scratches glass very Riaily «aac 9 Ae eet
Color. — Observe color and luster of the various specimens and
determine if it is characteristic and useful in identifying the mineral.
Cleavage and fracture. — Do specimens split easily in certain direc-
tions or do they fracture ? What effect do these characters have
upon the appearance of the mineral ?
Form. — Do the specimens seem to have any crystal form that
is characteristic and useful in identification ? .
SOIL AS A MEDIUM FOR PLANT GROWTH i)
Action of acid. — What is the result if the specimen is treated
with a few drops of acid ? Explain.
Flame. — Hold a small fragment of each mineral in the flame.
Observe fusibility and change of color. Is the flame given any
eolor which is characteristic ?
Exercise II. — Study of soil-forming rocks.
Materials. — Small specimens of granite, basalt, shale, slate,
limestone, sandstone and quartzite.
Procedure. — Study the color, texture, and structure of each
sample. Identify the minerals present and from this determine
the plant-food materials carried by each rock. Be prepared to
identify unlabeled samples in laboratory and field.
Exercise III. — To show that plants give off water.
Materials. — Plant growing in small pot, a tumbler.
Procedure. — Place a tumbler over a small plant and observe
the condensation of moisture on the sides. Where does this mois-
ture come from ? What was its original source ? How do plants
give off water? Explain uses of water to the plant.
Exercise IV. — Conditions for plant growth.
Materials. — Small flower pots, rich soil, oat seed.
Procedure. — Fill four small flower pots with a rich garden loam.
Moisten well and plant with oat seeds. When seedlings are a week
old, thin to desired number of plants. Grow for a few weeks under
optimum conditions and then subject them to the following condi-
tions : ,
Pot 1. — Sunshine and optimum water.
Pot 2. — Sunshine and minimum water.
Pot 3. — Cold, shade, and optimum water.
Pot 4. — Dark and optimum water.
Observe results and explain. More pots with other conditions ©
may be tried at the pleasure of the teacher.
Exercise V. — Effect of the different plant nutrients.
Materials. — One-gallon flower pots, very poor sandy soil, nitrate
of soda, acid phosphate, muriate of potash, barley seed.
Procedure. — Fill five flower pots to withia an inch of their tops
with poor sandy soil. It is essential to the success of the experiment
that the soil be poor, and also that it shall be surface soil and con-
10 SOILS AND FERTILIZERS
tain some plant food material. Weigh the soil that is placed in each
pot, mixing with it fertilizer in the following proportions:
Pot 1, nitrate of soda one part to five thousand parts of soil.
Pot 2, acid phosphate, one part to five thousand parts of soil. Pot
3, muriate of potash, one part to ten thousand parts of soil. Pot 4,
all three of these carriers, each at the rate specified above. Pot 5,
no fertilizer. Mix the fertilizer and soil thoroughly before placing
in the pots. Plant a dozen or more barley seeds in each pot. Add
water in sufficient quantity to make the soil moist but not too wet.
‘Place the pots in a place that is moderately warm during the day,
where they will not freeze at night, and where there is abundant
light. When seedlings are a week old, thin to ten. Allow plants to
grow for use in laboratory exercises in Chapters XI, XII and XIII.
Observe growth in each pot.
CHAPTER II
SOIL FORMATION AND TRANSPORTATION
SIDE by side are to be seen rock and soil. On the rock
no vegetation is growing except a few lichens and other
minute plants. On the soil there is a luxuriant growth of
multitudinous plants. Soil is derived from rock. Kvi-
dently there must have been a profound change to cause
such a difference in their relations to plant growth. In
some regions of the earth there is much rock and little
soil, while often on the prairie one sees no large rocks, and
may plow all day and perhaps not strike even a small
boulder. It may be surmised that in connection with the
process of soil formation there has been a large transporta-
tion of material from one place to another. All this was
brought about by natural agencies, most of which are still
operating to form more soil and to increase the productive-
ness of soil already under cultivation.
The process of soil formation is, however, extremely
slow, and it must be remembered that thousands and tens
of thousands of years have elapsed while the operation has
been in progress.
9. Agencies concerned in soil formation and transporta-
tion. — The agencies that have brought about these trans-
formations may be listed as follows:
Heat and cold Tce
Frost * Wind
Water Gases
Plants and animals
it
12 SOILS AND FERTILIZERS
10. Action of heat and cold. — Rocks, as we have seen,
are mixtures of different minerals. These minerals have
different rates of expansion when heated. Exposed rock will
suffer great changes in temperature in twenty-four hours,
especially if it be located in a region of high altitude and
cloudless weather. A block of marble one hundred feet
long will expand one-half inch with a change of 75° Fahren-
heit, and this is frequently of diurnal occurrence in an arid
climate. Because the minerals composing rock expand and
contract at different rates, they tend to tear apart, thus
producing crevices that may fill with water, and this water
acts still further to disintegrate the rock.
11. Action of frost.— One reason that building stones
are more likely to disintegrate in a cold moist climate than
in a dry or warm one is that the small pores and cracks on
their surfaces fill with water, which, when it freezes, exerts
an enormous pressure. The expansive power of freezing
water amounts to about 150 tons to a square foot, which is
equivalent to a column of rock a third of a mile in height.
The rock surface becomes chipped off by repeated freezing
and even great masses of rock are detached by the freezing
of water in larger cracks, as may be seen beneath rock ledges
in the spring of the year.
An interesting example of the effect on rock disintegration
of a cold moist climate as compared with a dry one is found
in the difficulty that has been experienced in preserving
the obelisk, now in Central Park, New York, which had pre-
viously stood for many hundreds of years in the Egyptian
desert without great damage. It has been found necessary
to cover the entire surface of the stone with paraffine in
order to preserve the hieroglyphics carved on its surface.
12. Action of water. — Water has another effect on rock.
Itisasolvent, weak but universal. It acts on all minerals, dis-
solving slight quantities of some, considerably more of others.
Puate II]. Water Erosion. — The wearing action of water is slow
but constant, and is leveling the surface of the earth at the rate of an
inch in several hundred years.
SOIL FORMATION AND TRANSPORTATION 13
It is as a transporting agent that water is most active,
From the time when raindrops beat down on the surface
of the soil, while they are gathering into rivulets and the
rivulets are becoming rivers that discharge into the ocean,
they are engaged in moving particles of rock débris and
soil. It is estimated that the United States is being planed
down at the rate of one inch in seven hundred and sixty
years. This is rapid enough if it were applied at one point
to dig the Panama Canal in seventy-three days.
The carrying power of water has resulted in the formation
of the rich river valley soils that have been deposited by
the streams flowing through them. The coastal soils and
lake soils have also been transported by water.
13. Action of ice.— In former times a considerable part of
the northern United States was covered by huge masses of ice,
known as glaciers. These ice masses were of enormous vol-
ume and moved slowly in a southerly direction. The great
thickness of the ice mantles, amounting to several thousand
feet at some places, caused them to cover hills, valleys and
mountains, and their enormous weight ground rock surfaces,
pushed forward heaps of soil and transported huge boulders.
The southern limit of the glaciers corresponded roughly to
the lines now marked by the Ohio and Missouri rivers, and
again extended farther southward along the Pacific coast.
It met the Atlantic coast at about the present location of
New York. Changes of climate caused an alternate reces-
sion and extension of the ice sheets several times, and during
all this period soil was being formed and worked over by
the ice and the water that melted from it. When the glacier
melted, stranded ice masses remained behind. These formed
lakes in which soil was reworked and shifted, and as the
lakes finally drained off, the reworked soil was left behind.
These glacial soils are, as a rule, productive, because of the
thorough pulverization and mixing they have received.
14 | SOILS AND FERTILIZERS
14. The action of wind. — That wind has been an active
factor in the transporation of soil is evident to any one
who has lived in an arid or semi-arid region, where dust
storms are not infrequent. In a humid region the move-
ment of soil by wind is not so patent, but even there, espe-
cially along the seacoast, there is some movement of this
kind. There is also an erosive action produced by wind, but
this has not been very important. However, in arid regions
the sand-bearing wind has been instrumental in wearing
away large surfaces of rock, the eroded portions of which
have helped to form soil.
The most important result of wind action has been the
production of loessial soils, which are found in parts of Wis-
consin, Illinois, Iowa, Missouri, Nebraska and Kansas,
also in the valley of the Rhine and in parts of China. - An-
other result is the production of adobe soils, which are found
in mountain sections of western and southwestern United
States. While these soils do not owe their present location
entirely to the action of wind, that element has played a
large part in removing them from other regions and depos-
iting them where they now are.
15. Action of gases. — Of the gases that compose the
normal atmosphere, oxygen and carbon dioxide are instru-
mental in decomposing rock and soil. They unite chemi-
cally with some of the substances composing rocks, and
when the new compound thus formed is more soluble than
the original substance, the resistance of the rock to water
is decreased. This is a very constant operation, and as air
penetrates deeply into soil and into the pores of rock its
action is widespread.
16. Action of plants and animals. — Some of the lower
forms of plants, of which lichens are a notable example,
are able to live on the bare surfaces of rock, fastening them-
selves to the small crevices and pores and in the process of
SOIL FORMATION AND TRANSPORTATION 15
their growth causing the rock to decay and organic matter
to accumulate in the crevices. These plants are followed by
higher vegetation, the roots of which are larger ; when these
roots extend themselves into cracks in the rock they exert
a prying action when wind gives the plant a swaying motion.
After rock becomes sifficiently pulverized to produce
soil, plants are active agents in decomposing soil particles
by the solvent action of the acid secreted by their roots
and formed by their decay.
Very small plants, included among the microérganisms
because they are too small to be seen without a microscope,
are also concerned in rock decay. Their action is exerted
principally in soil, and is due to the production of acids even
stronger than that secreted by the roots of higher plants.
17. Powdered rock is not soil. — We have seen that in
the process of soil formation the rock is pulverized, but the
process of weathering to which nature resorts is different
in its result from merely grinding rock in a crusher or mortar.
At the same time that the particles are becoming smaller,
certain chemical changes are going on that produce a ma-
terial having a different composition from the original rock.
One result of the transition is the removal of a part or some-
times all of the more soluble constituents of the rock. The
percentage loss of some of the constituents of granite and
of limestone in the process of forming a clay is as follows:
TaBLE 1.— PrerRcENTAGE Loss or PuLaNntT-Foop MATERIALS IN
GRANITE AND LIMESTONE IN Process OF SoIL FORMATION
PERCENTAGE OF Loss
CoNSTITUENTS
Granite Limestone
WEPGEIG ACL)... 5 ec wun eae 0.00 68.78
RI ee. 5s hen eemeeanse 83.52 57.49
2 8 See am ele eT 100.00 — 99.83
i 0 oe a ee 74.70 99.38
16 SOILS AND FERTILIZERS
This table represents merely two cases, and is not meant
to imply that these losses always occur in just these propor-
tions whenever rocks of this type are converted into soil.
It will be noticed that some of the most valuable plant-food
materials are lost in large quantities. For instance, practi-
cally all the lime has been lost, as has also a large propor-
tion of the magnesia and potash. Phosphoric acid shows
great variation in respect to loss.
Other changes that occur in weathering include the forma-
tion of extremely fine particles that give plasticity to soils,
and that have the property of absorbing certain substances,
like fertilizers, from solution and holding them in a condition
in which they do not leach readily from the soil, and yet in
a form in which roots may make use of them. As these
particles are very small, we find a relatively large propor-
tion of them in a clay soil, but a very small proportion in
a sand.
Another operation that accompanies soil formation is
the incorporation of vegetable matter or animal remains —
together called organic matter — with the soil particles.
This adds greatly to the crop-producing power of a soil,
for as the organic matter decays it makes more soluble
the inorganic constituents.
QUESTIONS
1. Name the agencies concerned in soil formation and trans-
portation.
2. In what way do heat and cold act to decompose rock ?
3. What is the action of frost on rock ?
4. How does water aid in the transportation of soil ?
5. What part did the great glaciers play in soil formation ?
6. Has wind been more potent as a soil former or as a trans-
porter ?
7. Describe the ways in which roots aid in the decomposition
of rocks.
8. Explain the difference between powdered rock and soil.
Puate IV. Puants as Sort Formers. — Plants are active agents in
the decomposition of rock. In the upper figure lichens may be seen
beginning the disintegration, and in the lower, large tree roots are forcing
themselves into the cracks in the rock.
SOIL FORMATION AND TRANSPORTATION 17
LABORATORY EXERCISES
Exercise I. — Soil formation and transportation.
This exercise is based on observations in the field and its value
depends on examples available. Use Chapter II as a basis for the
field observations.
If rock outcrops can be found in the neighborhood, a visit to them
would be worth while. Examples of wind action, heat and cold,
frost, and plant and animal influences in forming or transporting soil
should easily be found. The erosive and carrying power of streams
should also be studied in relation to soil formation.
An examination of weathered rock of various kinds should be
made in order to illustrate the chemical phase of soil formation.
The rusting of iron could be used as an example of the effect of
gases. The iron of rocks rusts in the same way. This, together
with the assumption of water and a loss of soluble materials, brings
about the decay of the rock. Remember, however, that the
physical and chemical agencies work hand in hand and that these
agencies are as active upon the soil as upon the original rocks. An
examination in tne spring of fall-plowed land would permit a study
of the effect of weathering on soil structure.
CHAPTER III
SOIL FORMATIONS
From the preceding description of the processes of soil
formation, it will be seen that the operation may involve
the transfer of soil from one place to another, or that it
may take place in one locality, leaving the resulting soil
where the parent rocks stood. The latter soils are called
sedentary, the former transported. These may again be
subdivided as follows:
Residual — formed in place
peeniat Cumulose — plant remains
Colluvial — gravity deposits
Alluvial — stream deposits
Marine — ocean deposits
Lacustrine — lake deposits
Glacial — ice deposits
ALolian — wind deposits
Transported
18. Residual soils. — Soils of this formation are geologi-
cally old, that is, they were formed at an earlier period than
any of the other arable soils. They always bear more or
less resemblance in composition to the rocks underlying
them, although on account of their’great age they have lost
much of the more readily soluble constituents of the original
rock. This is also of agricultural significance, because
many of these soluble constituents are of great importance
18
SOIL FORMATIONS 19
in the growth of plants. The following table shows the
partial composition of an Arkansas limestone and of the
clay soil formed from it, also the percentage of each of the
constituents lost in the process :
TABLE 2.— PARTIAL COMPOSITION OF LIMESTONE Rock AND Its
RESIDUAL CLAY
PERCENTAGE COMPOSITION
CoNSTITUENTS
Rock Soil Lost
Beet So ges Se gt & 0.35 0.96 66.36
Re oe rk ee ee 44.79 3.91 98.93
Magnesia ie eet eens": 0.30 0.26 89.38
Mein Lea ah eae TENSE: 2:35 1.99 89.56
BUM itera ts bc ned bree yay red 4.13 33.69 0.00
It will be seen from the above table that lime, magnesia,
and potash have disappeared in large quantities, as has also
iron, but that silica has lost little or none of what was orig-
inally present, and now constitutes by far the larger part
of the soil. Silica although not of great importance as a
plant nutrient is, nevertheless, of value in crop production,
because it contributes to the formation of the absorptive
compounds before mentioned.
The great age of residual soils has also led to changes in
the composition of iron compounds, producing usually those
of a red or yellow color, these colors being characteristic of
residual soils. The long period of weathering has frequently
resulted in wearing down the particles to such a degree of fine-
ness that heavy soils of the nature of clay, clay loam or silt
are produced.
Analyses of two typical:residual soils from Virginia, that
have been formed from gneiss and limestone respectively,
are given in the following table:
20 SOILS AND FERTILIZERS
TABLE 3. — PERCENTAGE COMPOSITION OF TYPICAL RESIDUAL
SoILs FROM VIRGINIA
ORIGINAL Rock
CONSTITUENTS
Gneiss Limestone
Phosphorie acid Pe oitr mre Gee 8 0.47 0.10
Potash. tite) a eee oe 1.10 4.91
Baas. se ioe Nikoad Me oto ps trace 0.51
Magnesia 5 ibaa," a) oo ott ae 0.40 1.20
Tron Sage os, eet verre eS ew 12.18 7.93
eae. ae toes rai pete ey ae 45.31 bY Ray
A striking feature is their low lime content, which is
characteristic of soils that have been long subjected to
leaching. Such soils would require applications of lime for
the profitable production of most crops. The low content
of lime in the soil derived from limestone illustrates the
fact that such an origin does not insure a satisfactory supply
of lime. .
19. Distribution of residual soils.— These soils are
widely distributed in the United States, being found in four
great provinces — the Piedmont plateau along the eastern
slope of the Appalachian mountains, the Appalachian moun-
tains and plateaus, the limestone valleys and uplands be-
tween and west of these mountains, and the Great Plains
west of the Mississippi and Missouri rivers.
20. Cumulose soils. — Unlike residual soils, cumulose
soils are of very recent origin. They have been formed by
the growth of vegetation in and around lakes, ponds and
marshes, many of which were left by the retreating glaciers.
As the plants die they become immersed in water, which
shuts off the supply of air, and thereby arrests decomposi-
tion. The partly decomposed plant remains accumulate
SOIL FORMATIONS yd
until the surface of the water is reached, when larger plants
take root, and it is not uncommon to find large forests
covering soil formed in this way. Cumulose soils, as may
be expected from their mode of formation, contain a very
large proportion of organic matter. On the basis of the
degree of decomposition of the organic matter they have
been divided into two classes — peat and muck. In peat
the stem and leaf structure of the original plants may still
be detected. Im muck, however, decomposition has gone
so far that the organic matter forms a more or less homo-
geneous mass, and is mixed with a larger proportion of min-
eral matter than in peat.
Peat is used extensively as fuel in some European coun-
tries, but is not of much value for agricultural purposes.
The degree of decomposition reached by the organic matter
determines its usefulness for both these purposes. Muck
eannot profitably be used for fuel, but some muck lands
are highly prized for market-gardening and other of the
more intensive agricultural operations.
The following table shows the composition of some typical
cumulose soils:
TABLE 4. — PERCENTAGE COMPOSITION OF SOME CUMULOSE
SoILs
PERCENTAGE COMPOSITION
ConstTITUENTS
Muck Muck Marsh Mud
Mineralimatter 2) x) 6e. 31.60 24.79 80.40
C(reanie, matter.» a... 68.40 67.63 15.77
SOT Ee aa elie eanmaee 2.63 2.03 Z
Phosphoric acid. -. . . . 0.20 0.19 0.15
Seo Tse or): se A byl 0.17 0.15 0.65
1 Not determined.
22 SOILS AND FERTILIZERS
Many muck soils are underlaid by deposits containing
lime derived from shells of aquatic organisms that inhabited
the bodies of water in which the muck was formed. This
adds materially to the value of the land, as lime is a valuable
soil amendment, particularly on muck land. It is well to
keep this in mind when examining muck land.
The percentage of potash is much lower than in any other
kind of soils, and a potash fertilizer is usually of great benefit
to crops planted on muck. :
21. Colluvial soils. — On all steep slopes there is a gradual
downward creep of soil particles due to the effect of gravity
assisted by rainfall, freezing and thawing, the movements
of animals, in fact any agency that starts the particles in
motion, after which their direction is almost invariably
downward. This soil formation is not extensive, nor in any
sense important. Such soils are confined largely to the
bases of mountains. They are usually shallow and stony.
22. Alluvial soils. — A stream flowing through its valley
will erode its bed if very steep and will deposit sediment
if nearly level, but under most circumstances it both erodes
and deposits soil. As the upper reaches of a river are usually
of steeper grade than the lower, it often happens that con-
siderable material is picked up by the stream near its source,
and as the current becomes slower farther down, this material
is deposited. Alluvial soil is, therefore, found most largely
along rather slowly flowing streams.
It is estimated that water flowing at the rate of three
inches a second will carry only fine clay, but if this rate is
increased to twenty-four inches a second, pebbles the size
of an egg will be moved along the stream bed.
It is quite customary for streams flowing through a flat
region both to erode and deposit soil. Such streams are
likely to be sinuous in their course, the curves gradually
becoming more angular as the current erodes the soil from
SOIL FORMATIONS 23
the concave bank and deposits it on the convex. Finally
the curve becomes so great that the stream breaks through
the banks and straightens its course. In this way a broad
valley may gradually be covered by sediment deposited by
the stream.
Changes in velocity of a stream, as when in flood after
heavy rains or melting snows, cause a change in its carrying
power. Much material will be picked up by a stream in
flood that must be deposited as the flood subsides. A
stream may build up its bed so that the surface of the
water is higher than is the land at some distance on
either side. Such is actually the case in the lower Mis-
sissippi valley.
23. Character and distribution of alluvial soils. — Allu-
vial soils may be sands, loams or clay, depending on the veloc-
ity of the stream and the nature of the eroded material.
It is likely to be the case that the alluvial deposits along the
upper stretches of a stream will be sandy, and that the
material deposited will become finer as the stream proceeds.
Soils of this formation have no very distinctive composition.
Naturally this character depends on the nature of the ma-
terial farther up the stream, and this, of course, varies in
different parts of the country. Even along any one stream
there may be a wide diversity of material picked up and
hence an alluvial soil is likely to be a heterogeneous one.
The content of organic matter is usually high, as this
is carried and deposited with the other matter. Alluvial
soil is generally regarded as rich soil, but there are many
exceptions. When situated along slowly flowing streams,
the land is likely to need drainage.
Alluvial soils are naturally confined £3 the margins of
streams, but they are found along small as well as large
ones, and consequently the aggregate area of alluvial land
is large. The Mississippi valley and its branches contain
24 SOILS AND FERTILIZERS
the largest area of alluvial soil found anywhere in the United
States. Rivers flowing through the coastal plain are all
well lined with alluvial soil adjacent to their banks.
24. Marine soils. — Soils of this formation have been
made by material carried by rivers and deposited in the
ocean, whence they afterwards emerged by elevation of the
sea bottom. They, therefore, resemble alluvial soil that
has been worked and reworked by sea water. They are
generally sandy soils, as the solvent action of water and the
pulverizing force of waves has disposed of most of the min-
erals except quartz. They are light not only in texture, but
also in color. They are nearly always deficient in organic
matter. Their sandy nature fits them particularly well for
trucking, and it is to that industry that a large area of
marine soil is devoted.
25. Distribution of marine soils. — A fringe of land aver-
aging many miles in width along the Atlantic coast from
Long Island southward and including all of Florida is com-
posed of marine soil. This fringe then turns westward
and extends along the Gulf coast in a wide band as far west
as the Rio Grande. The alluvial plain of the Mississippi
river cuts through the belt, but at this point the marine
soil extends as far north as Tennessee. In the aggregate
the marine soils constitute a large area of important
agricultural land producing cotton, corn and other farm
crops, as well as truck crops for which they are especially
adapted.
The following is a statement of the analysis of a typical
marine soil from the coastal plain in Maryland:
TABLE 5.— PERCENTAGE COMPOSITION OF A TYPICAL MARINE
Sorin
Phosphorie acid . . ., 0.05 Magnesia. ... ...«.. (Oia
Pos 2° oo EN ee Te” PRON Se ee ee
Toitme +). 6600 ete SEP OA Silica See: eS
a.
ee mee
FESS
‘
al till
.
7
.s
ial soil.
the lower an alluvi
’
1
Sort Formation. — The upper figure shows a glac
soi
PLATE V.
SOIL FORMATIONS 25
A striking peculiarity of this soil is the high percentage
of silica, due to the fact that quartz is highly resistant
to the constant working to which the particles have been
subjected and which has removed much of the phosphoric
acid, potash, lime and magnesia. Soils of this particular
type contain little fertility, but respond well to fertilization.
26. Lacustrine soils. — These soils have been formed
in the beds of lakes both ancient and comparatively modern.
The older ones were formed in the glacial lakes, and both
are soils that have been worked over by water. They
constitute good agricultural soils and are found from New
England westward along the Great Lakes, and spread out
in a wide area in the Red River valley.
27. Glacial soils. — The tremendous grinding to which
rocks have been subjected by glacial action has resulted in
a large proportion of very fine particles, and consequently
these soils and subsoils are likely to be rather heavy. The
particles are jagged instead of having the rounded appear-
ance found in older soils and soils that have been worked
over by water for longer periods.
Owing to the fact that this process of soil formation has
employed mechanical rather than chemical agencies the
soils resemble the parent rock very closely. Unlike residual
soils, glacial soils when formed from limestone are generally
rich in lime. If, on the other hand, glacial soils are formed
from rocks poor in lime, they have a small lime content.
The hill soils of southern New York (Volusia series) are
derived from shales poor in lime and the soils share this
quality, while certain glacial soils of the Mississippi valley
(Miami series) that are formed from limestone and sandstone
are rich in lime.
In the following table are shown analyses of residual and
glacial soils from Wisconsin, the original rocks from which
they were formed having been largely limestone:
26 SOILS AND FERTILIZERS
TABLE 6. — PERCENTAGE COMPOSITION OF RESIDUAL AND GLACIAL
CLAYS FROM WISCONSIN
RESIDUAL GLACIAL
CONSTITUENTS
1 2 3 4
Phosphoric acid ... . 0.02 0.04 0.05 0.13
Potash .-*, oie oe 161 1.61 2.36 2.60
PAGS sos &, 8. ee en 0.85 1.22 15.65 11.83
Marnesias ioc2 tae 0.38 1.92 7.80 7.95
Peer 2 2 et ey: 5.52 11.04 2.83 2.53
ULE L Es MmeagenyO™: Os Cate 0 ie wala) isa” i Fe 49.13 40.22 48.81
It will be seen that of the substances important for their
plant-food value phosphoric acid and potash are somewhat
more abundant in the glacial soils, that lime and magnesia
are very much more abundant, while the less consequential
substances are present in large quantity in the residual soil.
This is because the residual soil has been subjected to more
leaching.
28. Eolian soils. — Following the retreat of the glaciers
there ensued a period of aridity, especially in the southwest
section of the territory now a part of the United States. Into
these regions there had been washed a large quantity of
fine glacial till, and during the dry period this was blown,
by high westerly winds, into a large area in the Mississippi
and Missouri valleys, where it is now found. It has been
given the name of loess and on account of its wide area and
great fertility it is an important agricultural soil.
These soils are frequently of great depth, their texture
is favorable to the maintenance of good tilth and in prairie
regions their long period in grass, before they were placed
under cultivation, has given them a good supply of organic
matter. The following table contains a statement of
analysis of soils from different sections of the loessal area:
SOIL FORMATION 27
TABLE 7. — PERCENTAGE COMPOSITION OF LOESS
————
————
LocaTION OF SOIL
CoNSTITUENTS
lowa Mississippi! Missouri | Wyoming
Phospuoric acid . . . . 0.23 0.13 0.09 0.11
[Lt PEE Re a ae meer 2.13 1.08 1.83 2.68
ements eS u e Ae 1.59 8.96 1.69 5.88
Pear eee a hE 4.56 1.12 1.24
ee er ae ete ye 3.93 2.61 3.29 2.02
PRPC oM sh ar Ca To | at 2. Be 60.69 74.46 67.10
All of the important plant-food materials, particularly
lime, are abundant in these soils. They rarely need liming,
and up to the present time commercial fertilizers have been
used but little on them.
Adobe is the name applied to another eolian soil similar
to loess in its physical qualities, but differing somewhat
in its mode of formation. It is supposed to be a mixture
of loess with débris from the mountain slopes and has been
formed under arid conditions. The soils thus formed are
extremely fertile when placed under irrigation, which is
usually necessary for their cultivation, because they are
found in Colorado, Utah, southern California, Arizona, New
Mexico and arid portions of Texas. The composition of two
typical soils is given below:
Taste 8.—PrErcenTAGE Composition oF Two ADOBE SoILs
CONSTITUENTS A | B
Phosphoriegacid )...- + ie 0.29 0.94
Potash BN gee te ay a eal bat
eae. pate 2.49 13.91
PE ee ks. ph mre ts 1.28 2.96
Tron 1 oe RR NAY or 8 Ca 4.38 5.12
PEE ON | eal as 66.69 44.64
— ose
28 SOILS AND FERTILIZERS
These soils show a remarkably high content of phosphorie
acid and an abundant supply of the other substances needed
by plants.
Sand dunes and volcanic dust are two other forms of
zolian soils but nowhere are these soils of much agricultural
importance.
QUESTIONS
1. How may soils be divided with respect to the localities in
which they have been formed ?
2. What common plant-food materials have been lost in great-
est quantities by residual soils ? Why are these soils likely to have
a large proportion of clay ?
3. In what four regions of the United States are residual soils
found to be predominant ?
4. What is the characteristic constituent of cumulose soils ?
For what agricultural purposes are muck soils largely used? In
what important plant nutrient are they likely to be deficient ?
5. How is the velocity of a stream likely to affect the nature
of a soil with respect to its proportion of sand and clay ? What
kinds of streams form little alluvial soil ?
6. Why are marine soils characteristically sandy ? For what
agricultural industry are they frequently used ?
7. Are marine soils usually rich or poor in plant-food materials ?
Why?
8. State over what areas in the United States lacustrine soils
are found.
9. Why do glacial soils resemble chemically the rocks from which
they were formed ? What is a characteristic difference between
residual soil and glacial soil when both are formed from rocks rich
in plant-food materials ?
10. Describe the mode of formation of the two principal kinds
of ewolian soils in the United States. Are they characteristically
rich or poor in plant-food materials, and in what one particularly ?
11. Using any map of the United States as a base (preferably a
colorless map showing the state boundaries and river courses), draw
lines tracing roughly the regions occupied by residual, alluvial, marine,
glacial, and zolian soils. These areas may then be shaded or colored
differently and a soil map of the United States thus be made.
PLATE VI. SrrRatrFicaTion. — The upper figure illustrates stratifica-
tion of rock, the lower stratification of soil. This shale rock has at one
time been soil. The soil may sometime be rock.
SOIL FORMATION
LABORATORY EXERCISES
Exercise I. — Classification of soils.
A study of the various kinds of soils must nec-
essarily be made in the field. No one locality
affords examples of all the different kinds of soil
listed in Chapter III. In some places only one or
two classes may be available. In any case make
all possible use of the materials, studying each
soil as to origin, parent rock, color, depth, sub-
soil, organic matter, drainage, general fertility
and crop adaptability.
Exercise II. — Use of the soil auger in taking
soil samples.
Material. — Soil auger and jars or bags for
samples.
Procedure. — Explain the construction of a soil
auger and then proceed with the taking of a sam-
ple of the first eight inches of soil, removing the
soil in two portions. Then clean out a hole
larger than the auger worm to prevent contami-
nation of later samples and take the second eight
inches in the way already described. Place sam-
ples in bags or jars for future reference or exhibi-
tion. Be sure that the samples are representative
of the soils to be studied.
These samples may be used later in the tests
for organic matter, acidity, water retention, and
other demonstrations according to directions in the
laboratory exercises to be found elsewhere in the
book.
Fie. 1. — Au-
ger for taking soil
samples. (A)
handle, (B) joint,
(C) worm with
modified cutting
edge.
CHAPTER IV
TEXTURE AND STRUCTURE OF SOILS
As a result of the grinding to which rock is subjected in
the process of soil formation, there are to be found in soils
particles of all sizes, from gravel and coarse sand down to
particles so minute that they cannot be seen with the highest
power microscope, to say nothing of the unassisted eye.
In all but very sandy soils, particles are generally gathered
into clusters or granules. Texture is a term used in refer-
ence to the size of the particles in a soil; the term struc-
ture refers to the arrangement of particles into granules.
29. Shape of particles. There is no universal shape
for soil particles. They vary from spherical to angular,
and are sometimes rather elongated, but the occurrence of
anything like needle shape is not common. Soils formed
by erosion and wave action are likely to have rounded
particles, as are also soils formed from limestone.
30. Space occupied by particles. —The number of par-
ticles in a given volume of soil can only be estimated, their
minute size precludes an actual enumeration. It has been
estimated that the number of particles in a gram of soil
of certain different kinds is as follows:
Karly truek . . OP eu
Truck and small rant cw Sele eee
Tobacco - a: teeeusas ays. wo oe eens
Wheat <- 225 Se ae el See er ree
Grass and whee nS. 3. SO Eee
Lamestone . <- 6 desks © +s) + eee eo eee
30
TEXTURE AND STRUCTURE OF SOILS 4
If all the particles were spheres, it is estimated that each
cubic foot of soil would have a surface area on its particles
amounting to from two to three and one-half acres.
31. Mechanical analysis of soils. — A separation of the
particles of a soil into groups, each of which comprises
particles whose sizes fall within certain definite limits, is
Fic. 2. — Relative sizes of soil particles in the various grades into which
a mechanical analysis separates a soil. All are enlarged many times. Par-
ticles of fine gravel may vary in size from the largest circle to the next largest ;
coarse sand from the second to the third; medium sand from the third
to the fourth, and soon. The dot in the center represents the largest clay
particles; the smallest cannot be shown in a figure of this magnification.
called a mechanical analysis of the soil. The size limit
of these groups is a purely arbitrary matter, consequently
it is desirable that a universal system shall be adopted.
The classification in general use in this country is one pro-
posed by members of the Bureau of Soils of the United States
Department of Agriculture. It provides for groups of the
following sizes :
Cee SOILS AND FERTILIZERS
DIAMETERS OF PARTICLES
SEPARATES ee eee eee ee ae a eee Sees, Se
Millimeters Inches
Bg ee a a Se ee oe ee ee 2 eee | ee eee
Hie eraweliy isnt. fs 2-1 0.08-0.04
COATS SARA 6k a9 aig 1-0.5 0.04—0.02
MLedIuI Sang: ss 0.5-0.25 0.02-0.01
Fine sand Se eGey Fad 0.25-0.10 0.01—0.004
Very fine sand ... 0.10—0.05 0.004—0.002
SG cee wae eee: 0.05-0.005 0.002—0.0002
Ly. Mi eean et ase Sie less than 0.005 less than 0.0002
32. Mechanical analysis of some typical soils. — When
soils are analyzed according to the mechanical separation
just described, there are shown to be great differences
between some of them, and soils that are adapted to certain
crops are found to have a somewhat characteristic composi-
tion. It must be remembered, however, that such dis-
tinctions are always limited by climate. The following
table, based on the work of the Bureau of Soils and the
Minnesota Experiment Station, contains a statement of the
mechanical analyses of a number of typical soils:
TABLE 9. — MECHANICAL ANALYSES OF SOILS AND SUBSOILS
ADAPTED TO CERTAIN CROPS
CoARSE
Siar SILT CLaY
SAND
Garden truck soil, Norfolk,
Virsimis sie
Garden truck soil, J amaica,
Long Island :
Grass soil, Hagerstown, Ma.
Wheat and grass subsoil,
7.51 | 21.04] 7.15
10.08 | 17.39 | 7.25
10.94 | 23.69 | 51.75
Kentucky 2.34 | 39.92 | 51.77
Corn subsoil, Nebraska .10 | 25.83 | 57.00} 9.49
Potato soil, Minnesota. . : 5.60 28.40! 4.05
Wheat soil, Minnesota. . y 6.18 30.60 | 57.00
TEXTURE AND STRUCTURE OF SOILS By)
PERCENTAGE BY WEIGHT
NE COARSE MEDIUM FINE VERY FINE
GRAVEL SAND SAND SAND SAND SILT CLAY
PERCENTAGE BY WEIGHT
ier
ine
Ry
we
iE
aa
a
ra
FINE COARSE MEDIUM FINE VERY FINE
GRAVEL SAND SAND SAND SAND SILT CLAY
Fic. 3. — Graphic statement of mechanical analyses of two soils. No.1
is a very sandy soil, and it will be noted that the bulk of its particles consist
of medium and fine sand. No. 2 is a heavy clay and its particles belong
mainly to the silt and clay divisions.
33. Soil class. — The terms “sandy soil,’”’ ‘loam soil,”
“ clay soil’”’ and the like have been in such general use and are
so convenient that attempts have been made to devise a sys-
tematic classification on this basis. A soil class is made ©
D
34 SOILS AND FERTILIZERS
up of particles of various sizes, but the proportion of the
large, medium or small particles determines the class to
which it belongs. The following table published by Whitney
will show what percentages of soil separates are contained
in an average sample of each of the soil classes.
TABLE 10. — MECHANICAL COMPOSITION OF VARIOUS SOIL CLASSES
BasEep oN AVERAGES OF Many ANALYSES
Fine |Coarse ~ | Fine
DIUM
GRAVEL SAND Fe
Coarse sands. . .| 12 31 19 20 6 ¥ 5
Sands 2 15 23 37 11 7 5
Fine sands 1 4 10 57 17 7 4
Sandy loams . oa 13 12 25 13 21 12
Fine sandy loams 1 3 t 32 24 24 12
Loam 2 5 5 15 17 40 16
Silt loams . 1 2 1 5 11 65 15
Sandy clays 2 8 8 30 12 13 2d
Clay loams 1 4 4 14 13 38 26
Silty clay loams . 0 2 1 4 a 61 25
Clays : 1 3 2 8 8 36 42
There must be a certain amount of variation in the per-
centages of the separates that go to make up a soil class.
In order to determine the class to which a soil belongs
when its mechanical analysis is known, the diagram in Fig.
4 may be used. If, for instance, a soil contains 40 percent
of silt and 15 percent of clay, lines are drawn from the point
marked 40 percent silt and 15 percent clay, the lines being
parallel to the sides of the right angle formed at O. It will
be found that these lines intersect in the space marked
loam, which is the class to which the soil belongs. If a soil
has 20 percent silt and 10 percent clay, the intersection of the
lines drawn from these points falls in the space marked sandy
loam, and the soil belongs to that class.
TEXTURE AND STRUCTURE OF SOILS BID)
34. Some properties of the separates. — In addition to
differences in their size, there are other distinctions that are
more or less characteristic of these separates. A mechanical
analysis, therefore, tells us something about several of the
properties of asoil.
Clay particles, by
reason of their mi-
nute size, tend to
make a soil plastic
and may cause it to
become hard,com- «
pact and cloddy ,
when dry. Silt
does this toamuch
less degree. The ”
extent to whicha ~
soil exhibits these
propertiesdepends
on its content of
clay or silt. Soils Fia. 4. — Plan by which the soil class may be
ascertained from a mechanical analysis.
CL4aYr
100mhI5-
Rd AT fe
CLAY LOA/T
nt | Ea Sh
JO
LT
70. 2a oO G0 60 70 680 $0 100%6
containing much
clay or silt must not be plowed when wet or they will puddle.
Both clay and silt serve to increase the water-holding power
of a soil, and clay especially increases the difficulty of tillage.
The sand separates have the opposite properties of
clay, and in the order of their greater size of particles.
Sandy soils are more easily worked, are not likely to puddle
or to form clods, and. do not hold a large amount of water,
but on the contrary have a tendency to become dry. Sandy
soils are termed “light ’’ soils because they are easy to till;
clay soils are called ‘‘ heavy” because they make a heavy
draft on the plow.
The absolute specific gravity, or weight of the particles as
compared with the weight of the volume of water which
36 SOILS AND FERTILIZERS
these particles would displace if they were immersed in it,
does not necessarily correspond to these terms. Particles of
greater and less specific gravity are scattered through both
‘“lieht’’ and ‘‘ heavy ” soils and if we are to find the specific
gravity of a soil we must have in the sample to be tested
enough particles to give an average of all in the soil.
35. Chemical composition of soil separates. — The fact
that one kind of mineral wears down to a small particle
more easily than does another indicates that there would be
a preponderance of resistant minerals, like quartz, among
the coarse particles and a large proportion of the more
easily decomposed minerals, like the feldspars, among the
fine particles. This is actually the case, and it indicates
a chemical difference in the separates. Analyses of sepa-
rates made by the Bureau of Soils of the United States De-
partment of Agriculture bring out these differences, as shown
by the following table :
TaBLE 11. — CHEMICAL COMPOSITION OF SOME SoIL SEPARATES
PERCENTAGE OF
PERCENTAGE OF PERCENTAGE OF
i pg me OTASH LIME
SoILs
Sand] Silt | Clay | Sand Silt Clay Sand Silt Clay
Crystalline
residual .| .07 | .22 | .70| 1.60 | 2.37 | 2.86 .5O | > 482: > Sa
Limestone
residual .| .28 | .23 | .37 | 1.46 | 1.83 | 2.62 | 12.26) 10.96| 9.92
Coastal
plain . 2S 4510"..34 | 37") eee") 1.62 JOY, 19° 5
Glacial and
loessial .|.15-} .26°|,.86.| 1.72 | (2.30 | 3.07 | 1,28)2.30) 2.85
Arid . .|.19| .24| .45 | 3.05 | 4.15 | 5.06 | 4.09} 9.22) 8.03
It will be noted from this table that, in general, the smaller
particles are richer in phosphoric acid, potash and lime than
TEXTURE AND STRUCTURE OF SOILS 37
are the larger ones, the only exception being the lime in the
limestone residual. The arid soils do not show as great
differences as do the others, because they have not been
subjected to the same amount of solvent action and tritura-
tion.
36. Soil structure. — By soil structure is meant the ar-
rangement of the particles of which the soil consists. These
particles may be separated so that each is free to move
independently of any other, which is usually true of a dry
coarse sand. Such an arrangement is known as the separate
grain structure. On the other hand the particles may be
arranged in small groups or granules, these being so firmly
combined that the granule acts like a separate particle.
The latter condition is termed the granular or crumbly
structure. When applied to loams and clay soils, these
arrangements of the particles have a relation to the condi-
tion popularly known as tilth. Good tilth in clays and loams
implies a granular structure, poor tilth a separate grain
structure.
The granular structure is not to be confused with a cloddy
condition of the soil. In fact clods have the separate grain
structure, because the soil has been worked when wet until
the granules are broken down and the particles move easily
over each other owing to the lubrication of the moisture.
37. Relation of structure to pore space. — The arrange-
ment of the soil particles determines to a considerable degree
the amount of free or pore space within the soil, especially in
loams and clays. Merely for the purpose of illustrating this
let us suppose that the soil particles are perfect spheres of
equal size, which, of course, they are not. There would be two
arrangements possible, if each sphere were independent of
every other: (1) in columnar order, in which each particle
is touched on four places by its neighbors; (2) oblique
order, in which each particle is in contact with six of its
38 SOILS AND FERTILIZERS
neighbors. ‘The calculated pore space in the first arrange-
ment is 47.64 percent. That in the second case is 25.95
percent. (See Fig. 5.)
It is not actually the case, however, that soil particles
are of the same size in any natural soil. Consequently
small particles fit in between large ones, thus decreasing
greatly the actual pore space. These three cases, of which
only the last may occur in nature, illustrate pore space
Fic. 5.—TIf all soil particles were spheres they could be arranged as
shown above, in which case the pore space would vary in volume as ex-
plained in the text.
when the separate grain structure obtains, as in a dry sand
or a puddled loam or clay.
The granular structure is the one most likely to be found
in nature, although all of the particles may not be in gran-
ules. The granules being of irregular form, with many
angles, there is likely to be a large amount of space between
them. It would be possible under this arrangement for a
soil to have a pore space of 72 percent.
The weight of a given volume of soil, including the pore
space, as compared with an equal volume of water is termed
the apparent specific gravity. This it will be seen is not the
same as the absolute specific gravity because the amount of
pore space is the important factor in determining the ap-
parent specific gravity. Neither do the terms “light” soil
and “heavy ”’ soil bear any definite relation to the apparent
specific gravity. A knowledge of the apparent specific
TEXTURE AND STRUCTURE OF SOILS og
gravity of a soil is useful because it is an indication of the-
amount of pore space.
38. Relation of structure to tilth.— The term “‘tilth”’ is
commonly used to denote the condition of a soil with refer-
ence to plant growth. When the physical condition of a
soil is favorable to plant growth, the soil is said to be in
good tilth ; when the physical condition is unfavorable, it is
said to be in poor tilth. A loam or clay soil to be in good tilth
must have the greater number of its particles in a granular
condition. ‘The more sandy a soil the less the necessity for
a highly granular structure in order that it shall be in good
tilth. The greater the proportion of clay in a soil, the more
necessary is the granular structure. One of the great ob-
jects in soil management is to produce and maintain the
pranular structure.
39. Conditions and operations that affect structure. —
So far as the structure of a soil is concerned, something de-
pends on the inherent quali-
ties of the soil and something
onits treatment by the weather
and by man. These factors
may be enumerated as follows :
(1) texture, (2) wetting and
drying, (3) freezing and thaw-
ing, (4) addition of organic
matter, (5) tillage, (6) roots
and animals, (7) lime.
J Fic. 6. — Structure of a loam soil
40. Relation of texture to in good tilth. (A) sand particle,
structure. — A coarse sand (B) pore space, (C) granule com-
admits only of the separate posed of silt and clay particles.
grain structure. There is not sufficient cohesion to hold
the particles in granules, and there is no plasticity. With a
decrease in the size of the particles, there is a greater tend-
ency to the formation of the granular structure, other con-
— PI
WN
sup
Ly
a
Ss
no/
ey
Rs
OR
ek
A
Ze Vie
\ o,
Wer
ms
TR
ay
40 SOILS AND FERTILIZERS
- ditions being equal. This does not mean that a clay soil is
easier to keep in good tilth than is a loam soil, but under
favorable conditions the small particles have greater plastic-
ity and cohesion and hence form granules more readily.
41. Wetting and drying. — As a soil becomes dry there
is a contraction of volume in which process lines of cleavage
or cracks occur and clods are formed. If these clods be
again wetted and partly dried without working, they will
separate into smaller clods and finally a granular structure
will be produced. ‘This is illustrated by the greater ease
with which clods may be worked down after a rain and
partial drying, than when they remain perfectly dry. Land
in need of drainage is usually in poor tilth, while after drain-
age this condition gradually improves.
42. Freezing and thawing. — The “ heaving” of roots
during winter is an indication that frost has a disrupting
action on the solidarity of the soil. Roots are’ pried out
because the surface of the soil rises when freezing occurs
and sinks when melting takes place. Water that is held
between soil particles freezes when the temperature of the
surrounding soil falls below the freezing point. As water
freezes it expands, the effect of which is to force the particles
farther apart. The pressure applied by the freezing water
is very unevenly distributed. Around the larger water-
holding spaces the particles are moved farther than are
those adjacent to smaller spaces, because the larger the
body of water the greater the expansion when it freezes.
The uneven crowding of the particles causes a breaking up
of the soil into more or less separate masses and as this pro-
ceeds with repeated freezing and thawing there is a pro-
nounced formation of granules in a clay or loam soil.
Fall-plowed land, if left unharrowed, or if too cloddy to
work down to a good tilth, will generally be mellow by spring,
provided there is much freezing weather during the winter.
TEXTURE AND STRUCTURE OF SOILS 41
43. Effect of organic matter on structure. — The quantity
of organic matter in a soil is frequently the deciding factor
in determining its structure. Partially decomposed organic
matter has a loose, spongy structure and at the same time
a plastic quality. The latter causes the soil particles to
cohere, and the former gives to the organic matter the
property of swelling when the soil becomes wet and shrink-
ing when it becomes dry. ‘These changes in volume facilitate
the formation of granules as previously explained.
Large areas of land in this country have deteriorated in
productivity and have become compact and difficult to work
on account of the gradual loss of organic matter. Naturally
clay and heavy loam soils have suffered more in this way
than have lighter soils. Where marked decrease in crop
returns has occurred during the time that soils have been
under cultivation, the difficulty can generally be traced to
loss of organic matter more than to any other factor in plant
growth. Compact soil, with consequent poor tilth, is one
of the most common conditions in poor farming regions,
and is usually associated with a low content of organic
matter.
44. Roots and animals. — In some way not very well
understood roots exert more or less influence on soil struc-
ture. Shallow, fibrous-rooted plants, among which are
the grasses, wheat, barley, millet and buckwheat, have the
most favorable action in granulating soil. More deeply
rooted, and especially tap-rooted plants, have this property
to a less extent. In fact, a crop of beets may help to com-
pact a soil already in bad condition. In establishing a rotation
it is desirable that some fibrous-rooted plants form one or
more of the courses.
Various forms of animal life help to granulate soils. Of
these, earthworms are the most notable. The soil particles
that they excrete from the digestive tract may amount to
42 SOILS AND FERTILIZERS
several tons in an acre in the course of a year, while their bur-
rows ramify through the soil in all directions. The move-
ment of soil particles that results is an appreciable factor
in changing soil structure. Insects and other burrowing
creatures affect soil structure in a similar way.
45. Tillage and structure. — The ordinary operations of
tillage are designed to improve soil structure, and are effective
if these operations are conducted at the proper time and in
the best way. Plowing, which is the most fundamental of all
tillage operations, may improve soil structure or may injure
it, depending on the condition of the soil at the time of
plowing. It is a matter of common knowledge that working
a soil saturated with water will cause it to puddle, or in
other words, to assume the separate grain structure. Plowing
when the soil is very dry may have the same effect, although
not usually to the same extent. However, when a soil is mod-
erately moist, plowing aids greatly in effecting a granular
structure. This it does by the peculiar twisting action that
the curved moldboard gives to the furrow slice. The soil
in immediate contact with the plow surface is retarded by
friction, and the layers above tend to slide over one another
much as do the leaves of a book when they are bent. The
soil is thus broken up into masses of aggregates correspond-
ing to the location of the lines of weakness. If a soil has
been strongly compacted, so that there are few lines of weak-
ness, the clods will be large when the soil is plowed. Plow-
ing helps to improve the tilth of the soil, but it will not over-
come entirely a bad physical condition.
46. Structure as affected by lime. — One of the properties
possessed by lime is that of flocculating clay. This may be
readily observed by stirring a spoonful of clay in a tumbler.
of water and then adding a quarter of a spoonful. of burnt
lime. It will be noticed that the soil settles much more
quickly after the lime has been added than before. Sandy
to good soil manage-
The upper figure is an illustration of poor, the lower of good, tilth.
1s a response
TILuaGce. — Good tilth
Puate VII.
ment.
TEXTURE AND STRUCTURE OF SOILS 43
soils are not flocculated to the same extent by lime, but are thus
affected in proportion to the quantity of clay they possess.
' Of the different forms of lime, quick-lime and water-
slacked lime are more active in producing a granulated struc-
ture of soil than is ground limestone, marl or air-slacked
lime. This is one reason why the burned lime is superior
to ground limestone for use on heavy clay soils, on which
there may be a pronounced difference in the effect of the two
kinds of lime on crop production. Warington reports a
statement of an English farmer to the effect that by the
use of large quantities of lime on heavy clay soil he was
enabled to plow with two horses, while three were necessary
before applying lime.
47. The soil survey. — The purpose of a soil survey is to
classify and map the soils in a given area according to their
crop relations and their physical properties, and to correlate
these soils with those in other areas. The soil unit, or what
may be termed the soil individual, is the type, and on a soil
map each type is given a different color. Every soil type
has a certain peculiar and characteristic appearance and
certain inherent properties that distinguish it from every
other type. When the type is known some practical infor-
mation regarding its texture and its amenability to tillage
and to drainage may be predicted, and something in regard
to its productiveness and the crops to which it is adapted
may also often be inferred.
48. Classification of soils.—In order to distinguish
between soils, and to give a basis on which to separate them
into the types to which reference has been made, a form of
classification has been adopted in this country that takes
into consideration much of what is known of their history
and their properties. Thus the first large division into
which a soil falls is known as the soil province, which is
based, in a general way, on the process of formation. A
44 SOILS AND FERTILIZERS
province may represent residual soil, like the Piedmont
province, or glacial soil, or marine soil, or soils of other
processes of formation.
The next smaller division is the series. A soil series has
been defined as ‘‘ a group of soils having the same range in
color, the same character of subsoil, particularly as regards
color and structure, broadly the same type of relief (topog-
raphy) and drainage, and a common or similar origin.”
The last of these properties is due to the fact that soils of
the same series must fall within the same province.
The final division is the class, which has been described
in paragraph 33. hme 184 A479
erties oh eee. ea ha 270 392
80. Quantity of water required to mature a crop.—A
rough estimate of the quantity of water required to bring
to maturity a crop of wheat may be calculated as follows:
Assuming the yield to be forty bushels or about two tons of
dry matter in straw and grain and the transpiration ratio
to be 400, the quantity of water actually used by the plants
would be 800 tons to the acre, or equivalent to about 7
inches rainfall. In addition to this there would be an equal
or larger quantity of water evaporated directly from the
SOIL WATER 71
soil. The annual amount of rainfall required for crop-
production is brought to a much higher figure by the loss
due to run-off and percolation.
81. Capillary movement and plant requirement. — We
have seen that there is a capillary movement of water from
the more moist to the less moist soil. As water is absorbed
by plants, the moisture content is reduced in the soil sur-
rounding the root-hairs by which the moisture is taken up.
Immediately a movement begins to establish equilibrium
in the water films and during the time the roots continue to —
absorb moisture, the movement of capillary water goes
on. During the blooming period, plants must have very
large quantities of water if they are to develop fully and
produce large yields of grain. Capillary movement is
necessarily slow, especially in heavy loam and clay soils.
It is often impossible for the capillary movement to carry
moisture fast enough, except for short distances, to supply
plants adequately and the crop suffers for want of moisture.
In a dry season the capillary capacity of a soil is likely to
be of more importance than the rate of capillary movement,
as the supply is more easily available. Hence, in time of
drought a loam soil in good tilth is better than a sandy
soil.
82. Optimum moisture for plant growth. — Plants wilt
for want of water at a moisture content somewhat higher
than that represented by hygroscopic moisture. They
show the pale color characteristic of too much moisture
when a soil is saturated. Before either of these well-known
signs of distress is shown, the plant may have too much or
too little water to allow of its maximum growth. The
optimum moisture content lies somewhere within the range
of capillary moisture. It is variously stated by different
experimenters to lie between 60 and 90 percent of the water
capacity of soils. Probably it varies with different soils.
72 SOILS AND FERTILIZERS
The range is doubtless greater for a soil in good tilth than
for one in poor condition, and the wider the range of
optimum moisture content the less likely is a crop to suffer
from either extreme.
83. The control of soil moisture. — Since there may be
too much or too little water in a soil for its most effective
crop production, the problem of moisture control is to remove
the excess and to conserve the remainder, attempting: to
maintain the supply within the range of the optimum mois-
ture content. In heavy soils there is likely to be a surplus
of water in the spring and in sandy soils a deficit in midsum-
mer. The excessive water content in the spring is also
objectionable because it delays plowing, planting, and germi-
nation of seed as well as the early growth of crops. The
ways in which water leaves soil are by (1) run-off over the
surface; (2) percolation; (3) evaporation ; (4) absorption by
plants. The last of these is to be encouraged, at least when
it is economically accomplished. Run-off should generally
be prevented. Percolation and evaporation should be con-
trolled within certain limits.
84. Run-off. — Removal of water in this way is objection-
able because the rivulets carry with them the fine particles,
which are frequently the most valuable part of a soil, and.
gullies are formed that may interfere with the working of
the land. In regions in which the rainfall is large, and
particularly where it falls in torrential showers, more than
half of the precipitation may escape in this way. The
water so removed is, of course, entirely lost so far as its
utilization by plants is concerned. The proportion lost by
run-off is greater on slopes than on level land, and on com-
pact soil than on sandy soil or on soil in good tilth.
The removal of excess water by means of open ditches is,
to some extent, a utilization of run-off to drain land, but
it is not so desirable a method as tile drainage. It is better
Puate VIII. Forms or Erosion. — Erosion of soil by water in
figure. Erosion by wind in lower.
SOIL WATER 759
to have the moisture pass into the soil and this is encouraged
by any of the operations and conditions that favor the main-
tenance of good tilth. Fall plowing and early spring plow-
ing also serve this end. In arid and semi-arid regions run-
off is usually not of any moment. ‘Terracing a hillside is
often resorted to as a preventive of run-off, especially in
the south Atlantic states where the rainfall is often tor-
rential.
85. Percolation. — Water that enters a soil is either
retained by the capillary spaces or eventually percolates
into the subsoil. The percolate is lost to crops, except that
part which remains in the subsoil and is later raised by
capillarity to within reach of roots. The chief consideration
is to maintain the soil in good tilth, which gives a large
capillary capacity, thus storing within easy reach of the
roots a maximum quantity of the descending water. The
more rapidly the gravitational water is disposed of the better,
because its presence prevents aération of the soil together
with those beneficial processes that good ventilation encour-.
ages. One of the most frequent causes of saturation of soil
is lack of facility for the water to escape from the lower
depths. This difficulty is best relieved by tile drainage.
86. Evaporation. — It has been concluded from experi-
ments conducted at Rothamsted, England, that: with an
annual rainfall of twenty-eight inches, one-half is lost by
percolation. The quantity of water required to produce an
average crop in a humid region is about seven inches, which
‘is one-half of the water retained by the soil. The other half
is presumably lost by evaporation. A rough estimate of
the disposition of rain water in a humid region would there-
fore be one-half lost by percolation, one-fourth by evapora-
tion and one-fourth used by the growing crop. The ratio
of quantity lost by evaporation to quantity used by crop
may vary by reason of a number of factors, among which is
74 SOILS AND FERTILIZERS
the ease with which evaporation may take place. Moisture
saved from evaporation is at the immediate disposal of the
crop.
87. Mulches for moisture control.— Any material ap-
plied to the surface of a soil primarily to prevent loss by
evaporation may be designated as a mulch. It may at the
same time fulfill other useful functions, like keeping down
weeds and maintaining a uniform soil temperature. The
mulch ordinarily used for fallow land is produced by stirring
the surface soil. Mulches may be formed of straw, leaves,
flat stones, cloth, sawdust and various other materials, but
the most practical material is soil.
88. The soil mulch. — The soil mulch is made by stirring
the surface of the soil with some one of the ordinary tillage
implements. For fallow land a disk harrow, straight, or
spring tooth harrow may be used. For intertilled crops
numerous forms of cultivators are made for the special pur-
pose of going between the rows of plants. For small grain
_a weeder or spike-tooth harrow, with the teeth slanted back-
ward, is frequently used while the grain is young. This
practice has much to recommend it in an arid or semi-arid
region.
In making a soil mulch the object is to destroy the capil-
larity near the surface soil and thus to prevent the move-
ment to the surface of water from the portion of the soil
below the mulch. Stirring may accomplish this by breaking
up the cohesion of particles to such an extent that moisture
cannot pass from one to the other.
89. Frequency of stirring. — Some kinds of soil re-
quire more frequent stirring than others. For instance,
a sand will maintain a mulch longer than a loam or clay.
The latter becomes moist from below and will gradually
~ allow moisture to reach the surface. Rain will also compact
a mulch and unless it is soon restored there may be more
SOIL WATER 75
moisture lost than was received as rain. While it is not
possible to make a definite rule for frequency of stirring a
mulch, it may be said that a mulch should never be allowed
to remain in a compact condition. However, in arid regions
the surface of the soil sometimes becomes completely dry
so quickly, even when compact, that capillary connection
is destroyed and loss of moisture is prevented.
90. Depth of mulch. — In considering the depth that a
mulch should have, several facts should be kept in mind.
The deeper the mulch the more effective it will be, but as
it must be perfectly dry, roots cannot obtain nourishment in
the zone occupied by the mulch. The surface soil, from
which plants derive a large part of their material, is frequently
only eight to ten inches deep in humid regions and the deeper
the mulch the less top soil remains for roots. In arid regions
plants obtain food materials from greater depths and mulches
may be made deeper, which is fortunate since they need to
be deeper in regions where evaporation is greater. Another
consideration is the disturbance of roots in the process of
cultivation. Here, again, there is less occasion to cultivate
shallow in an arid region, as roots are generally found at
greater depths in such soils.
A good depth for a mulch in humid regions is about three
inches, becoming somewhat less during the last cultivations
of corn. In irrigated regions a mulch of ten to twelve inches
is frequently used, especially in orchards, in which it is often
not necessary to renew the mulch, as the rainfall is usually
light. ;
91. Effectiveness of mulches. —- That mulches are effec-
tive in conserving moisture and increasing crop yield has
lately been called in question by certain writers who claim
that corn is not more benefited by tillage than by the
removal of weeds without tillage, and by some experi-
menters who find that fallow land contains as much moisture
76 SOILS AND FERTILIZERS
when weeds are removed by scraping the surface of the
ground as when the soil mulch is maintained. It seems
possible that the latter result may occur only in those
regions in which conditions are such that a natural mulch is
formed by the rapid drying of the suiface soil, in which
process moisture is removed so quickly that the capillary
column is broken and further loss of moisture is stopped.
This would confine it to semi-arid and arid regions of high
summer temperatures.
The failure of the soil mulch to conserve moisture in corn
land has been explained on the supposition that the corn
roots ramifying through the upper soil absorb so much
water that they cut off the upward movement as effectually
as does a mulch. The results of some experiments in
semi-arid Montana indicate a high degree of usefulness for
the mulch.
TABLE 16. — MoisturE ConTENT oF MuLCHED AND UNMULCHED
EASTERN Montana Soits. AVERAGE OF THREE YEARS
DerprH or SAMPLE PERCENT MOISTURE IN Soin ON Oct 6.
Mulched Unmulched
Hirst 1Gotierreen css), ~ a
x
¢
4 2
‘3 ee
? e
et
evo
%
‘a*
‘
r)
SS *
X
Fie. 14. — The effect of a soil mulch is to break up the capillary spaces
within the mulch itself and thus to prevent the upward movement of water
through it. Water, therefore, remains in the lower soil instead of evaporat-
ing from the surface. This condition is shown in the right-hand column.
When no mulch is maintained the soil dries at the surface and then cracks,
which allows it to dry more rapidly below.
in which grain crops suffer for moisture in the early spring,
it is not uncommon for farmers to harrow the small grain,
following the drill rows with a spike-tooth harrow with its
teeth turned backwards. This practice is likely to be very
beneficial.
78 SOILS AND FERTILIZERS
Windbreaks are effective in decreasing evaporation by
lessening the velocity of the wind. King found that evapora-
tion from a moist soil was twenty-four percent less at a dis-
tance of twenty to sixty feet from a black oak grove than it
was about three hundred feet distant..
93. Rolling and subsurface packing.— These operations
are resorted to in order to bring moisture to the surface or
upper layer of soil. Rolling compacts the superficial layer
of soil and thus establishes capillary connection with the
moist soil below. This may be desirable in order to bring
moisture in contact with seeds, but although germination
is hastened loss of moisture results.
Subsurface packing is designed to make more compact a
naturally loose soil by running wedge-rimmed wheels through
it. If the soil is too loose for capillary movement of water
to proceed effectively, this operation promotes it. Its use
is confined to arid or semi-arid regions.
94. Removal of water by drainage. — Land drainage is
any condition, natural or artificial, that enables the surplus
water to escape from soils. A soil may be highly productive
when drained, but worthless before draining. This is but
another illustration of the many factors affecting soil pro-
ductiveness. Where natural drainage is poor, artificial
drainage is generally a profitable investment. It may be
accomplished either by surface ditches or by underground
drains.
95. Benefits of drainage.— There are many ways in
which good drainage benefits soils and crops. The need of
drainage may be very evident in the yellow color and poor
growth of young plants, or it may be less readily detected, and
yet may be sufficiently needed to make it a profitable invest-
ment. Good drainage is the first requisite in enabling a soil
to reach its maximum productiveness. The principal ways ©
in which drainage benefits the soil and crop are as follows:
SOIL WATER 79
Enlargement in the supply and movement of soil air.
Improvement in tilth.
More available water throughout the growing season.
. Longer growing season.
96. Soil air. — Drainage increases the supply and move-
ment of soil air by allowing the gravitational water to run
off and thus to be replaced by air. With each fall of rain
there is a movement of air through the soil. The increased
air supply is of benefit in the following ways:
1. It furnishes air to roots which require it for the proper
performance of their functions.
2. It facilitates the decomposition of organic matter of
all kinds, thus disposing of the vegetable matter incorporated
with the soil, and permitting the most beneficial kind of de-
composition (see §§ 59, 60).
3. It furnishes the conditions necessary for the trans-
formations of nitrogen in the soil which prepare that sub-
stance to be used by plants (see §§ 116-168).
97. Soil tilth. — Alternate drying and wetting of soil is
one of the processes that causes the formation of granular
structure and consequent improvement of tilth. A_ soil
that is constantly saturated or very wet when worked in
the spring assumes a compact condition. The larger air
space reduces heaving by allowing expansion of freezing
water within the soil, and diminishes the tendency to erosion,
by allowing water to sink quickly into the soil, instead of
running over the surface.
98. Available water during the growing season. — A soil
in need of drainage is often in need of moisture in midsummer,
because when it does dry out its water-holding capacity
is low, on account of its compact condition. Furthermore,
plants form shallow roots in a saturated soil, and if the
weather becomes dry later in the season, the roots do not
then go to the depth necessary to reach the water supply.
oe
80 SOILS AND FERTILIZERS
It frequently happens, therefore, that plants suffer much
from lack of moisture on a soil that has been saturated with
water during the early part of the growing season.
99. Length of growing season.— Drainage increases
the length of the growing season in two ways: (1) The soil
can be worked much earlier than on poorly drained land.
(2) The soil becomes warm earlier, because it is easier to heat
soil particles than it is to heat water. Then too the evaporat-
ing moisture causes a lowering of the soil temperature.
Seeds germinate more quickly and uniformly and plants
make a more rapid growth on account of the warmer soil.
100. Other results of drainage. — All of these improved
conditions unite to produce larger yields of crops and more
uniform growth. Drainage eliminates the continually
wet or swampy portions of fields that interfere with tillage
operations and necessitate working the field in sections.
There is, accordingly, an economy in operation. In meadows
and pastures the kinds of forage plants that grow on a well-
‘drained soil make better feed than those kinds that grow
on wet land.
101. Open ditches. — Excess water is sometimes removed
by means of open ditches of sizé and depth necessary to
drain water from the land and carry it to some waterway.
Such ditches sometimes merely follow a depression or swale
in the land and thus carry off the worst of the excess water,
especially that which comes from higher land, or they are
sometimes laid out in a more systematic way.
Level fields may be plowed in lands with dead furrows
every twelve to twenty feet apart, and with a larger ditch
run through lower ground for the dead furrows to empty
into. This affords only’ surface drainage, but is better
than nothing. Larger ditches should have grass planted
along the sides for several feet from the ditch. Weeds must
be mowed and trash, dirt and stones removed at intervals.
SOIL WATER 81
Open ditches require much labor to keep them in order,
they do not remove the water so thoroughly as do tile drains,
and they not only occupy a considerable area but they inter-
fere with the cultivation of much land on account of the
space along the ditches required for turning the teams in
cultural operations. Only under exceptional conditions may
open ditches be profitably used instead of tile drains.
102. Tile drains. — These drains are composed of baked
clay or hardened concrete cylinders with open ends, their
length being about one foot and their diameter varying
from three inches to eight or more. These tiles are laid
end to end on the bottom of ditches two to four feet in depth,
having a fall sufficient to carry off the water and prevent
the tiles from becoming clogged with soil particles. Tile
should not be made of clay that contains particles of lime, as
the lime when baked is converted into quicklime, which
causes the tile to crumble when buried in the soil.
It is not necessary that tile shall be permeable to water,
as it is through the openings between the ends of the tile
that water enters, and not through the pores. Vitrified
tile may well be used, as they are less likely to be injured
by freezing than are porous tile, because expansion of ab-
sorbed water on freezing causes the latter to disintegrate.
- Concrete tile are often used and these may be made on
the farm, with forms constructed for the purpose.
Silt and fine sand may enter the tiles through the open-
ings between them, and to guard against this collars are
sometimes placed over the joints, but with proper grades
this is not necessary. Sometimes tile are hexagonal on the
outside, for the purpose of preventing settling of the tile
in places, with a consequent stoppage with silt. However,
if the bottom of the ditch is carefully made, round tile are
not likely to deviate from alignment and they are more easily
laid.
G
00
2 SOILS AND FERTILIZERS
103. Arrangement of drains. — In laying out a system
of drains certain rules must be regarded. A main drain
usually follows a depression in the land, rising with the
= [lil
Fig. 15.— The upper drawing illustrates the her-
ring bone system of laying tile drains. The lower
represents the gridiron system.
natural grade, or
if that does not
give a sufficient
rise, becoming
shallower as it
ascends. Some-
times this will be
sufficient to re-
move the surplus
water, but more
often lateral
drains will be nec-
essary. Theseare
of smaller tile and
are usually paral-
lel to each other
and from twenty
to a hundred feet
apart. ‘This ar-
rangement is
called the herring
bone system.
(See Fig. 15.)
There may also be
submains branch-
ing off of the main
drain, and laterals
running into the submains. This is known as the gridiron
system. (See Fig. 15.) Sometimes the laterals are run
across the slope, but usually it is better to run them down.
A lateral should not enter a main drain at a right angle,
PLaTeE IX. Drarnace. — The drain ouilet is often poorly constructed ~
and easily clogged, as shown in the upper figure. The lower one is well
protected.
SOIL WATER 83
but an acute angle should be formed between the two streams
above the point of contact; otherwise the flow of water
will be impeded. For the same reason two laterals should
not enter a main drain opposite to each other.
It is desirable to have as few main drain outlets as possible,
for the outlet is likely to be the weakest point in a drainage
system. If it becomes clogged, the entire system is put
out of action. It is more likely to be injured by freezing
than is the underground tile, and unless well protected it
affords an opening into which small animals may crawl and
clog the system.
The quantity of water removed by tiles of various sizes,
and laid at certain distances and grades as well as other
operations that cannot be treated here, may be ascertained
from the books that deal exclusively with the subject of land
drainage.
104. Digging ditches and laying tile. — The depth of
ditches for tile drainage varies from two to four feet. Three
feet is the usual depth. The closer together the laterals,
the shallower the drains may be laid. A compact soil,
through which water moves very slowly, will require the
use of shallow drains. A lighter soil underlaid by hardpan
will also require shallow drains. The shallower the drains
in any soil, the closer together they must be laid, the cus-
tomary range being from twenty to a hundred or more feet.
Surplus water enters the drains from the soil immediately
surrounding them. As the larger pore spaces become
partly empty, water enters them from surrounding soil,
and in this way drainage gradually extends. The soil mid-
way between the drains is the last to lose its surplus water,
and the water table is always higher between drains than
over them.
The distance between drains must be small enough to
allow the water table to descend promptly to a point where
84 SOILS AND FERTILIZERS
it will not interfere with root growth. The more permeable
the soil and the deeper the drains, the further apart they may
oe
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ch O © L677)
36in a 2
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e Cor) O
TS ee SS See aes eS SS ee LE eS
SANDY LOAM CLAY
Fic. 16. — Cross sections of two soils, a sandy loam and a clay, both of
which have drain tiles laid at right angles to the sections. Owing to the
more rapid movement of water through the sandy loam, the tiles are laid
twice as far apart as they arein the clay. They are also deeper in the former
soil. The water gradient is steeper in the clay. The tiles should be suf-
ficiently close together to keep the water table below the plowing line.
be placed. The position of the water level between drains
is shown in Fig. 16.
Ditches may be dug or partly dug by means of spades,
ditching plows or traction ditchers. The last named, while
THE ELEMENTS OF SOIL WATER CONTROL
WATER CONTROL
MOISTURE CONSERVATION DRAINAGE
(oe. Coe
WILTING PONT CAPACITY.
tr}
UNAVAILABLE AVAILABLE SURPLUS
WATER WATER WATER
Fic. 17. — Diagrammatic explanation of water control in a humid region.
On the one hand we have drainage reducing the surplus water to the maxi-
mum capillary water capacity or below and thus bringing it within the range
of available water. On the other we have moisture conservation by means
of which the moisture is kept above the content of unavailable water or the
wilting point. Somewhere within the limits of available water lies the
optimum moisture content for plant growth.
SOIL WATER 85
expensive in first cost, is economical in operation in many
soils. After the ditch has been opened to its full depth,
it is necessary to go over the entire bottom to remove loose
dirt and to give it the necessary grade. This must be done.
by hand. Either a ditching spade or a drain scoop is the
best implement to use. A fall of at least four inches in a
hundred feet is necessary under most conditions, but in
clay soils less fall is permissible, as there is less danger of
silt entering the drains.
QUESTIONS
1. Name the three forms in which water is present in soils.
2. Explain what is meant by hygroscopic water. Capillary
water. Gravitational water.
3. On what does the content of hygroscopic water depend ?
4. Name six conditions that tend to increase the capillary
water capacity of soil.
5. Explain the relation of soil texture to the movement of
capillary water.
6. How does soil texture affect the rate of movement of
capillary water ?
7. What are the conditions that affect the rate of flow of grav-
itational water ?
8. Explain what is meant by the water table.
9. Describe three ways in which water contributes directly to
plant growth.
10. What is the transpiration ratio ?
11. Name three factors that influence it.
12. Caleulate the number of inches of rainfall transpired by a
three-ton crop having a transpiration ratio of 250.
13. Name four ways in which water leaves soil.
14. What is the principle of the soil mulch ?
15. State four ways in which drainage benefits soils.
LABORATORY EXERCISES
Exercise I. — Determination of the percentage of water in a soil.
Materials. — Samples of moist soil, torsion balance, evaporating
dishes, air oven and flame, desiccator. See Plate IX.
86 SOILS AND FERTILIZERS
Procedure. — Carefully obtain the weight of an evaporating dish
on the balance. Then weigh into the dish 50 grams of the soil to
be tested. Air dry sample in laboratory and then place it in air
oven at 100° C. for two hours. Cool in desiccator and weigh. The
loss in weight is water. Calculate the percentage of moisture
based on absolutely dry soil.
Make this determination in duplibate and on a number of soils.
Calculate the amount of water in an acre foot of the various soils,
considering them to weigh 3,500,000 pounds per acre foot. Note
relation of soil moisture content to bare and cropped soil, kind of
crop, stage of growth and previous rainfall.
Exercise II. — Capillary movement in different soils.
Materials. — Dry samples of pulverized sandy loam, silt and
clay, three long glass tubes 2 inches in diameter, pans for water and
cheesecloth. See Plate [X.
Procedure. — Neatly cover the ends of the three long glass eylin-
ders by tying over them two thicknesses of cheesecloth. Fill eylin-
ders with the respective soils to be studied. Be sure that the
compaction is uniform. Now set the ends of the cylinders in water
one inch deep and observe the height of capillary movement at the
following periods after starting: 1 hour, 2 hours, 12 hours, 1 day,
2 days, 3 days, 4 days, ete. Continue experiment as long as prac-
ticable. Tabulate data and draw curves. Explain the practical
importance of the results obtained.
Exercise IIIT. — Rate of percolation of water through soils.
Materials. — Dry, well-pulverized sand and clay loam, two lamp
chimneys, cheesecloth, torsion balance. See Exercise V, Chapter V.
Procedure. — Prepare two lamp chimneys by neatly tying two
thicknesses of cheesecloth over their bottoms. Place in one a
definite and known amount of sand. In the other place the same
weight of clay loam. Give eacha uniform compaction. Now weigh
each chimney with its content of soil.
Place the chimneys in such a position as to allow free drainage
and add the same amount of water to each, keeping the head of water
constant in each chimney. Observe the rate of the downward
movement of water through the two soils. When percolation has
begun, measure percolate for 15 minutes and express rate in cubic
centimeters per hour.
Explain the reasons for the results obtained and the practical
importance thereof.
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SOIL WATER 87
Exercise IV. — Water-holding capacity of soils.
Materials. — Same as in Exercise III.
Procedure. — When Exercise III is complete, cover chimneys and
allow all the free water to drain away. Then weigh the chimneys
and wet soil. The increased weight is water retained. Calculate
the percentage of water retained by each soil based on the weight
of the original sample.
Write out a full description of the experiment and the points
of importance that it shows.
Exerciss V. — Moisture conservation by means of a soil mulch.
Materials. — Three tumblers, one of which should be one inch
shorter than the other two, moist soil, dry clay loam and dry sand,
torsion balance.
Procedure. — Fill the short tumbler level full with a well-mixed
moist soil. This is to serve as the unmulched treatment. Place
CLAY LOAM MULCH SANDY LOAM MULCH
NO ee
|
MOIST SOIL MOIST SOIL MOIST SOIL
Fie. 18. — Tumblers filled with equal quantities of a moist soil and pre-
pared for a demonstration of the effectiveness of mulches in the conserva-
tion of moisture. Losses of moisture by evaporation are measured by weigh-
ing the tumblers.
exactly the same amount of moist soil in each of the other tumblers
as is used in the shorter one, compacting to within one inch of the top.
On the surface of one place one inch of dry clay loam and on the
other one inch of dry sand. Weigh the tumblers now fully prepared.
Set tumblers in a place of uniform temperature and weigh daily
for a week. The loss of weight each day is moisture. Tabulate
data and draw curves.
Explain the significance of the results obtained.
88 SOILS AND FERTILIZERS
Exercisre VI. — Loss of water by transpiration.
Materials. — Glazed gallon butter jar, oats seed, paraffined paper,
thistle tube, coarse sand and heavy balance.
Procedure. — Filla glazed jar with rich soil, first adjusting coarse
sand and thistle tube as shown in
Fig. 19. Moisten soil with water,
but not too wet, and plant with oat
seed. When seedlings are one week
old, thin to suitable number. Then
cover surface of soil with paraffined
paper, allowing plants to protrude
through small holes cut for that pur-
pose. Paraffine the paper to side of
jar so that all losses of moisture by
evaporation may be _ prevented.
Bring soil up to optimum water con-
tent and weigh. You are now ready
to record losses by transpiration.
73 , Weigh jar each week, replacing
Ra 16. ce Ca erauineadl water lost through the thistle tube.
for observation of transpiration Record data and draw curves. By
of water from plants. (a) thistle changing the jar from sunshine to
scales ee Raw a shade, warm temperature to cold,
parafined paper to prevent eV) high humidity to low, ete. the fac
soil, (e) gravel. tors influencing transpiration may
be studied.
Jars with different crops, different soil or the same soil with differ-
ent fertilizers or different water treatments may be utilized if so
desired.
Exercise VII. — Review problems. Chapters IV and VI.
1. A soil weighs 100 lbs. per cubic foot when dry. The weight
of a cubic foot of water is 62.5 lbs. Calculate its apparent specific
gravity and weight per acre foot. Ans. 1.6 and 4,356,000 lbs.
2. This soil has an absolute specific gravity of 2.7. Calculate
its pore space.
% pore space = 100 — ba ae a ial Ans. 40.7+ %.
3. This soil contains 10 pounds of water a cubic foot. Calculate
percentage of water based on absolutely dry soil. On wet soil.
Ans. 10 % and 9.09 %.
SOIL WATER 89
4. By the following formula, calculate the air space present.
% air space = % pore space — (% water X ap.sp.gr.) Ans. 24.7 %.
5. The wilting point in this soil is 4 percent. What is the per-
centage of available water? Weight of available water per cubic
foot ? Per acre foot ? Ans. 6 %, 6 lbs. and 261,360 lbs.
Exercise VIII. — Tile drainage.
If possible, have the class install a short drainage system. They
should dig at least part of the ditch, grade the bottom, lay the tile
and build the outlet. The explanation of every point involved as
the work proceeds will give such an exercise great practical value.
It will also make the classroom work much more effective.
If drainage operations are being conducted in the near vicinity,
the class should by all means be taken to inspect them. The
general plan of the work, as well as the more detailed phases, should
be explained by the teacher. Materials and illustrations may also
be obtained for later discussion and study in the classroom. If
ditching machinery is being utilized, it also should be given consider-
able study.
Karly in the spring, while the soil is still wet, a field trip might
well be taken. The need of drainage, the movement of water
through soil, the effectiveness of drainage, the entrance of water into
a drainage system, the movement of water through tile, good and
poor outlets and the drainage of roads could be studied with profit.
CHAPTER VII
PLANT-FOOD MATERIALS IN SOILS
PLANTs secure their mineral food materials exclusively
from the soil. In a state of nature plants at death fall
on the surface of the ground and as decay proceeds, their
ash constituents return to the soil. The loss of mineral
matter, under these conditions, is due almost entirely to
its solution and removal in drainage water, or to erosion.
Under ordinary farm practice the procedure is different.
The aboveground portions of plants are removed wholly,
or in part, from the land and the loss of easily soluble min-
eral matter is thus greatly increased.. The soil supply of
those particular elements required for the growth of crops
is a matter of great importance, for it is upon this that man
must depend for his sustenance, and although he may
supplement these elements in. the soil by the use of manures,
the cost of food is thereby materially increased.
105. Variations in content of plant nutrients in different
. Soils. — There are wide differences in the quantities of plant-
food materials in soils from: different localities, although
the localities may be near together. This is illustrated by
the following statement of the analyses of soils from different
parts of the country, the number of pounds of each ingredi-
ent being based on the weight of 2,000,000 pounds of soil,
which is about the weight of the furrow slice of an acre of
land. :
90
PLANT-FOOD MATERIALS IN SOILS 91
TABLE 17. — CoMPposITION OF SoME ARABLE So1Lts BasEep on
ULTIMATE ANALYSES
Pounpbs 1n 2,000,000 Las. or Sorin PERCENTAGE COMPOSITION
LOCATION Bia : Pie
Nitro- phoric Potash Lime Nitro- phoric | Potash} Lime
Ben Aci Be ci
New York | 2,520 1,680 | 40,200 6,600 | 0.126 | 0.084 | 2.010 | 0.330
New York | 2,860 1,620 | 33,400 4,600 | 0.143 | 0.081 | 1.670 | 0.230
New York} 2,800 | 3,280 | 17,200 | 68,400 | 0.140 | 0.164 | 0.860 | 3.420
New York | 4,000 | 3,920 | 39,200 5,400 | 0.200 | 0.196 | 1.960 | 0.270
Ohio!. ./ 1,260 966 | 43,975 | 11,303 | 0.063 | 0.043 | 2.198 | 0.565
Ohio!. .|°3,844 | 14,008 | 67,285 |. 78,772 | 0.192 | 0.700 | 3.364 | 3.938
at es 6.3 186 | 3,106 | 37,214 | 15,478 | 0.009 | 0.155 | 1.860 | 0.773
Ohio!. .| 2,974 1,580 | 37,070 4,480 | 0.148 | 0.079 | 1.853 | 0.224
Illinois? .| 6,480 | 4,145 | 42,493 | 28,644 | 0.324 | 0.207 | 2.124 | 1.432
Illinois? .| 6,020 | 3,710 | 39,165 {104,636 | 0.301 | 0.185 | 1.958 | 5.232
The soils whose analyses are stated in the table given above
are all from arable land and while they represent wide differ-
ences in some of their constituents none of them is so deficient
in any plant nutrient as to prevent it from producing crops.
Comparing the quantities of the constituents of these soils, we
find that in the Illinois soils the lime varies from 28,644
pounds to 104,636 pounds in 2,000,000 pounds of soil. In Ohio
the same constituent ranges from 4480 to 78,772 pounds
with nearly as low a minimum in New York. The nitrogen
in Ohio rises from a minimum of 186 pounds to a maximum of
3844 pounds while the maximum for I]linois is 6480 pounds.
The greatest range of phosphoric acid is from 966 pounds to
14,008 pounds,. both of which soils occur in the same state.
Another fact brought out by this table is that a soil may
be rich in one ingredient and poor in another, also that soils
lying near together may differ more in composition than do
soils that are widely separated.
1 Ohio Experiment Station Bul. 261. 2 Tllinois Soil Report No. 2.
3 Tllinois Soil Report No. 10.
92 - SOILS AND FERTILIZERS
106. The total supply of plant-food materials. — The
statement of analyses in Table 17 shows the quantities of
plant nutrients in 2,000,000 pounds, which represents the
weight of an acre of soil to a depth of only six to eight inches.
There is below this a considerable volume of soil through
which roots ramify, and from which some nutriment is
drawn. ‘The roots of ordinary crops extend to a depth of
three or four feet into the soil, depending on different condi-
tions of soil and climate. In semi-arid and arid regions
roots extend deeper than they do in humid regions, and in
well-drained soils they penetrate deeper than they do in
poorly drained ones. It is, however, from the furrow slice
that plants derive most of their nourishment.
Subsoils sometimes contain more and sometimes less
plant-food materials than do the surface soils. Nitrogen
‘is almost always present in greater quantity in the surface
soil, because. it is a constituent of material that has been
plowed into the furrow slice. Table 18 contains a statement
of the analyses, expressed in percentage composition, of two
soils to a depth of four feet, each foot of which was analyzed
separately.
TaBLe 18. — ULTIMATE ANALYSES OF Two SoILs TO A DEPTH OF
Four Fret, ExpresseED IN PERCENTAGE COMPOSITION
>
DuNKIRK Cray LOAM Vouusia Sint Loam
1st ft. | 2nd ft. | 3rd ft.| 4th ft. | Ist ft. | 2nd ft. | 3rd ft. | 4th ft.
Nitrogen . .| .126| .067 | .064 | .064 | .143 | .052 | .059| .050
Phosphorie
acid .. .} 084) .066 | .103 | .125 |..081. | 039) 018.) Ze
Tame . ....)4800) .270) .520./L-780.) 250ep oneeeeroect) eee
Magnesia .| .160| .150| .150| .320| .560} .390| .290| .400
Potash . . 2.010 |2.480 |2.550 |2.630 |1.670 |1.790 |2.000 | 2.140
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PLANT-FOOD MATERIALS IN SOILS 93
These analyses show in some cases more, and in others
less, of the various constituents below the surface foot,
with the exception of nitrogen, which is always less in the
subsoil. The fact that the greater part of the roots of
most plants is in the surface soil makes the draft greater
on that layer, but the total volume to a depth of four feet,
or even more, may be considered to be the feeding ground
of crops.
107. Upward movement of plant-food materials. — There
is another way in which the soil to a considerable depth
may contribute to the nourishment of crops. This is by
furnishing plant-food materials that are carried upward
by ascending currents of moisture, or that are absorbed by
roots from the lower depths and deposited near the surface
_when the plants die. 'To what extent the upward movement
due to moisture is operative is something of a question;
in humid regions probably very slightly, in semi-arid and
arid regions it is doubtless of considerable moment, as indi-
cated by the existence of alkali crusts.
108. Plant nutrients compose a small part of the soil. —
Another point brought out by Table 17 is the very small
proportion of the soil that is represented by plant-food ma-
terials. For instance, the sum of all of the nitrogen, phos-
phoric acid, lime, magnesia and potash is not much more
than two percent of the total weight of the soil, and it would
be easy to find analyses that would show much less. Some
of the very important substances are present only in tenths
or even hundredths of a percent. The great bulk of the
soil contributes nothing to plant growth other than to furnish
mechanical support and to store air and water for the use
of roots.
109. Relation of composition to productiveness. — The
productiveness of a soil is not necessarily directly propor-
tional to the quantity of plant-food materials that it con-
94. SOILS AND FERTILIZERS
tains. This is because there are so many conditions, to
which soils are subject, that interfere with the ability of
plants to obtain the nutrients.or that, in other ways, inter-
fere with plant growth. It is, however, possible for the
quantity of some substance required by plants to be so small
that it is not sufficient to furnish enough nutriment for prof-
itable crop production. Probably all of the soils, whose
ear
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240.38LB5. PHOSPHORIC ACID
Ea 055LBS. NITROGEN
Fic. 20. — Relative quantities of potash, lime, phosphoric acid and nitro-
gen in a sack containing 200 pounds of dry soil, when the percentages present
are respectively 1.98, 1.64, 0.19 and 0.165.
analysis is stated in Table 17, would be benefited by the
application of some fertilizers, with the possible exception
of the rich prairie soils. This is not because there is not
actually enough plant-food material in the soil, but because
it is not in a form that is available to plants.
110. Available and unavailable plant-food materials. —
The available plant-food materials in soils consist of those
portions of the total supply that plants are able to secure
in their growth. We have seen that it is necessary for all
PLANT-FOOD MATERIALS IN SOILS 95
substances to be in solution in order that they shall be
absorbed by plants. Soil is not readily soluble. The natu-
ral insolubility of soil is modified by various .conditions
of the soil itself and by the plants that grow on it. The rate
of availability of plant nutrients is, therefore, not a constant
quantity for any soil. A soil in good tilth will produce much
better crops than a soil in poor tilth, which means that the
rate of availability of its plant nutrients changes with
the physical condition of the soil.
The available plant-food materials are not necessarily
proportional to the quantities of plant-food materials in a
soil. One piece of land may contain more plant nutrients
than another and yet be less productive. It has been shown
that the addition of four or five volumes of quartz sand to
one volume of a heavy, but highly productive, black clay soil
greatly increased the productiveness, although the conse-
quent dilution of plant-food content reduced the potash to
0.12 percent and the phosphoric acid to 0.03 percent. The
mechanical condition of the soil was better after applying
the sand.
111. Conditions that influence availability. — It is appar-
ent that the immediate availability of the plant-food materials
in a soil is not so much a matter of their total quantity, as
of favorable conditions for the decomposition of both the
organic and the inorganic matter in the soil, and for the growth
of plants. For this reason good tilth, good drainage, warmth,
absence of acidity and the kind and vigor of the plants are
factors that influence availability. When any one or more
of these conditions is unfavorable, the availability of the
plant nutrients may be decreased.
While all of these conditions influence the availability
of the plant-food materials, it still remains true that, other
things being equal, the greater the total supply of each of
these constituents of a soil, the greater will be the total
96 SOILS AND FERTILIZERS
quantity of available plant nutrients, and the greater the
productiveness of the soil is likely to be. Hence, it is
desirable -to conserve the supplies of these substances
and to augment them, if possible, by their judicious ap-
plication in the form of farm manures and other fertilizing
materials, and especially to maintain the store of organic
matter.
112. Water-soluble matter in soil.— Although soil is
very slightly soluble in water, an extract of soil made with
water contains all of the substances required by plants.
The solution obtained by extracting a soil with water is
probably not identical in composition or concentration with
the solution presented to the root-hairs of plants for their
nourishment, because the plant by the excretion of carbon
dioxide, and possibly in other ways, aids in dissolving plant
nutrients. It is probably true, however, that the solution
obtained by water is the nearest approximation that we have
to the solution presented to roots and is, for that reason,
deserving of attention.
113. Relation of water-soluble matter to productiveness.
— It might be expected that there would be a direct relation
between the productive capacity of a soil and the quantities
of plant nutrients in its water extract, and that this relation
would hold between different soils. This would imply that,
as between two or more soils, the plant-food materials dis-
solved by water would, in general, be proportional to the
quantities of the readily available constituents in the soil.
It has been demonstrated that such relations do obtain
between certain soils, but it has not‘been proven that this
is invariably the case. Indeed it is probable that soils which
diffey little in their productivity would not, in every instance,
show such a direct proportional relationship. Experiments
with four good and four poor soils showed the following
averages for their crop yields and water extracts.
PLANT-FOOD MATERIALS IN SOILS 97
TABLE 19.— AVERAGE YIELDS AND ComposITION oF WATER Ex-
TRACTS OF Four Goop anp Four Poor Sorts
Crop: YIELDS PER ACRE Poor Sorrs|Goop Soins
Corn, bushels EE FAS ee eee PPE 33.6 64.3
Potatoes, bushels . . ete ae 78.6 213.2
Water soluble salts in pounds | per acre of surface
four feet . 29) Mar ee eit ee
OS nay RS SEN (ey Oe RR BO Se ae 30 82
POMC SCM (oll ge, weer eae. va cs. |, LOO 192
Potash.) > Pere Nite Cm AR A Ss Seer, aA DG 319
Rratags Petts 4e'.) Suey wba exh Noort A ess gh BBS 1422
1 LOS 2 Be men ee) cea eee en ea ee 82 576
A somewhat similar result was obtained with two soils
contained in large tanks from which drainage water was
collected, and that have been under experiment for a num-
ber of years. Each tank holds about three and one-half
tons of soil. In 1915 tanks filled with soils of different types
were planted to corn. The yields of grain and stalks com-
bined are given in Table 20 and also the number of pounds
to the acre of plant nutrients in drainage water collected
during seven months from the same soil types kept bare
‘of vegetation. As only a trace of phosphoric acid was found
in the drainage that ingredient is not included in the table.
Taste 20.— YIELDS oF Crop AnD PLANT-Foop MaTERIAL IN
DRAINAGE WATER FROM Two Soi. TyprEs
Som Type
Dunkirk Volusia
Clay Loam | Silt Loam
Yield of corn silage (tons per acre) . : 13.4 7.8
* Substances in drainage water (lbs. per acre)
Pepe APE NR 72 59
PCED ate nk) 6s) 4 eters 2 | 438 360
he 2h A a RR Oe $1 57
eee. soe me. tO 52
98 SOILS AND FERTILIZERS
In this case, as in that of the four soils, previously cited,
there is a correlation between the productiveness of the soils
and the composition of the water extract.
114. Chemical analysis of soil.— There have been many
methods devised for the chemical analysis of soil. The
important difference between these is in the solvent used
to bring the soil into solution. Most solvents dissolve only
a part of the soil, in which case the result of the analysis
does not show the entire amount of all the constituents, and
does not, therefore, show the total quantity of the plant-food
materials in the soils. The figures given in Table 17 are
obtained from a complete selution of the soils analyzed and
hence show their ultimate composition.
The advantage of an analysis of this kind is that one can
judge of the lasting qualities of the soil, and if any particular
constituent is present in very minute quantity that fact
is disclosed, and measures can be taken to augment the
supply, but nothing, however, as to immediate productive-
ness can be learned. A collection of rocks may yield to this
analysis as much phosphoric acid, potash, lime, or other
nutrient, as a rich soil. Such an analysis is useful only to
ascertain the ultimate limitations of a soil, or its possible’
deficiency in any essential constituent.
Various solvents have been used with the intention of
finding the quantities of food materials that plants may be
expected to obtain in a reasonable length of time, or in other
words to determine the available plant-food materials.
These methods fail because availability, as we have just
seen, depends on the conditions to which a soil is subjected
in the field, and as these naturally vary from time to time .
it is impossible to find any one solvent that will measure
such a variable quantity as availability.
Chemical analyses of soil are useful in connection with
investigations of questions relating to soils but it is not
PLANT-FOOD MATERIALS IN SOILS 99
always possible, as the result of a chemical analysis, to esti-
mate the degree of productiveness of a soil, or to say that it
should have a certain kind of fertilizer treatment, or that it
is adapted to certain crops.
115. Absorptive properties of soils. —If a solution of
certain substances required by plants be poured on soil they .
will not leach through the soil unaltered, but part will be
held by the soil. On the other hand, the drainage water
_may contain an increased quantity of some other substance
in place of the-one added in solution. As an example of
this we may take the following case. An application of
200 pounds to the acre of a potash fertilizer was made
annually for five years to soil contained in one of the large
tanks previously referred to. The composition of the drain-
age water from the tank so treated, and of the drainage
water from an untreated soil is shown in the following table :
TaBLE 21. — ANNUAL AVERAGE PoUNDS TO THE ACRE oF LIME,
MAGNESIA AND PoTasH IN DRAINAGE FROM SOIL TREATED
with PoTrasH FERTILIZER AND FROM UNTREATED SOIL
CONSTITUENTS IN DRAINAGE WATER
Sorin TREATMENT
Lime Magnesia Potash
ora fertilizer na a) aos 298 81 53
No fertilizer dete 248 56 on
In this case the effect of the ‘application of the potash
fertilizer was to increase the quantities of lime and magnesia
in the drainage water, but not the quantity of potash.
116. Selective absorption. — Some substances are retained
by soils only in small part. Among these are nitrates,
which, as we shall see later, are very important forms of
nitrogen, and sulfates, which are also required by plants.
100 SOILS AND FERTILIZERS
When sulfate was added annually to soil in one of the tanks
already mentioned, for a period of five years, as much as
two-thirds of the quantity applied was removed in the drain-
age water, in addition to what would have been removed if
the soil had received no sulfate. The potash previously
mentioned as having been applied to this soil, and the sulfate
here spoken of were one substance called sulfate of potash.
The latter was held by the soil and the sulfate largely leached
through. It is evident that the substance was decomposed
in part or in whole.
It is thus apparent that there are certain soluble fertilizers
that may be applied to soils without much danger of loss
by leaching and other fertilizers that are likely to be partly
carried out of the soil in this way.
117. The availability of absorbed fertilizers. — When a
soluble fertilizer is absorbed by a soil, a part of it, at least,
is held in a condition in which it is more readily available
to plants than is the large mass of plant-food material origi-
nally in the soil. Thus there may be in a soil several
thousand pounds to an acre of nitrogen, phosphoric acid or
potash in the three or four feet through which roots ramify,
and yet the yield of crops on this soil may be materially
increased by the application of less than a hundred pounds
of one or more of these substances.
The ability of soil to hold fertilizers in a readily available
form is strikingly illustrated by an experiment at the Rotham-
sted Experiment Station in which soil from plats that had
been treated with certain fertilizers for many years was
thoroughly extracted with water and the extracts analyzed.
Complete analyses of the soil from the several plats were
also made. The yields of crops on these plats had been
recorded for many year's and the annual average of these,
together with the Ae data, is given in the accompany-
ing table:
PLANT-FOOD MATERIALS IN SOILS 101
TABLE 22.— YIELDS OF CROPS AND COMPOSITION OF SOIL AND
WatveR Extract or SOIL
ComMPpLeTE ANALY-| Water Extract
pane sis PERCENTAGES |PArRTS PER MILLION
Som, TREATMENT ACRE Phos- fe Pie et dn. Gat tek,
Beads pigs Potash pone Potash
Dnemanured:) ->s. 4.2) 1,276 7 O.089' + 0.183" 0.525 3.40
Nitrogen and phosphoric |
Pee ee SE ee tra reer Olid | Oe | 3.000 3.88
Nitrogen and potash . .| 2,985 | 0.102 | 0.257 | 0.808 | 30.33
Complete fertilizer. . .| 5,087 | 0.182 | 0.326 | 4.025 | 24.03
Harry manure... soe eo 2 6 Rt 0.176: | - O46F »|:-4-46351- 26.45
It may be observed that the water extract of the soil from
the plats treated with any fertilizer ingredient was much
richer in that constituent than were the plats not so treated,
while the total quantities found in the soil were not propor-
tionately increased. ive
118. Other forms of available plant-food materials in soil.
— The natural weathering of soil that goes on continually
makes soluble a part of the originally insoluble mineral mat-
ter and this is absorbed just as are the fertilizer salts. When
land is cropped each year, this soluble matter is used by
plants about as quickly as it is formed, but when land is
bare fallowed the dissolved matter is largely absorbed, and
thus a bare fallow increases the quantity of available nutri-
ents for the following crop.
Another, and very important supply of available plant
nutrients, is that combined with the organic matter in soils.
When organic matter is incorporated with soil, decomposi-
tion begins, acids are formed and these unite with mineral
matter previously in a difficultly soluble condition. The
result is a compound, partly organic and partly inorganic.
These compounds decay still further until all the organic
matter passes off as we have already seen (§ 50), and the
102 SOILS AND FERTILIZERS
inorganic matter that remains is either used directly by plants
or is absorbed in the same way as the soluble fertilizers.
In an experiment several organic substances were mixed
with soil, the quantities of phosphoric acid and potash com-
bined with organic matter being determined before mix-
ing and after standing for a year or more. The results of
some of these experiments are given in the following table:
TABLE 23.— CoMBINATIONS OF PHosPpHORIC ACID AND PoTasH
with Organic Matrer Propucep By MIXING ORGANIC
MATTER WITH SOIL
PHOSPHORIC PorTasH
Acip GRAMS GRAMS
Experiment with cow manure and soil
if ofizinal Manure and saw .: 350.0 “om Ey . 1.06
In anixtore alter standing, .)..))0. 0.6 T0547) Ge Lae
(ain am orranic farm pd.) 65.60 ye eee eee 0.21
Experiment with green clover
In original soil-and clover... 29s =) sae 5.26
In'’mixturée after standing); ef a.) qe Set 4.93
Cami organic form <.. Roe he te,” 6 oh oss 0.33
Experiment with meat scrap
In original soil and meat scrap . . . .| 1.07 0.25
In‘mixture aiter standing) '-2" oe oY Ta 0.36
Gain in oreanie Form: * 13056 ies sa Cs OEE 9
When the organic compounds thus formed undergo further
decay the inorganic plant-food materials become available.
119. Loss of plant-food material in drainage water. —
The drainage water from cultivated fields in humid regions,
and to a less extent in semi-arid and arid regions, except
where irrigation is practiced, carries off very considerable
quantities of plant-food material. When it is considered
that soil is constantly subjected to leaching by rainwater
passing through it, that this amounts to many tons of water
in the course of a year on every acre of land, and that a water
extract of soil always contains some of each of the substances
PLANT-FOOD MATERIALS IN SOILS 103
required for plant growth, it is not hard to realize that there
must result a constant and significant loss of fertility. The
plant-food materials lost in largest quantity are lime, mag-
nesia, potash, nitrogen and sulfur. Phosphoric acid is
not removed in large quantity from any soil and appears
only in traces in the drainage water of most soils.
120. Quantities of plant-food materials in drainage. —
The quantities of. plant-food materials that are removed
from soil in the course of a year will depend on a variety of
conditions and, to some extent, these and the total losses
that may be expected are indicated by the following table,
which is based on the annual average loss for a period of
five years from a Dunkirk clay loam soil contained in tanks
four feet deep and four feet two inches square.
TaBLE 24.— NuMBER OF PouNpbs or Puiant-Foop MATERIALS
REMOVED IN DRAINAGE WATER FROM ONE ACRE OF LAND
TANK Mac- | Pot- | Nirro-| Sut-
Mo Crop FERTILIZER LIME cereal phe! aan stk
3 | Rotation No fertilizer | 281 50 64 7 32
4 | No vegetation |} No fertilizer | 519 | 99 88 102 45
11 | Rotation Sulfate of
Potash 298 | 81 53 5 56
121. Effect of crop growth on loss of plant nutrients in
drainage. — It will be seen that the loss of lime is very large,
amounting to several hundred pounds to the acre. The soil
with no vegetation has suffered much more in this respect
than has the soil that was planted. The soil that was
fertilized with sulfate of potash lost somewhat more lime
than did the unfertilized soil. The loss of magnesia followed
the same course as did the lime. More potash was lost
from the unplanted soil than from the cropped, but the use
of a potash fertilizer did not increase the removal of potash.
In the case of nitrogen, the effect of not cropping the soil
104 SOILS AND FERTILIZERS
is astonishing. The loss from the cropped soil is moderate,
but from the unplanted soil it is excessive. The loss of sulfur
is decreased by cropping, and much increased by fertilizing
with sulfate of potash.
The loss of lime and nitrogen in the uncropped soil as
compared with the one that was cropped is greater than
the quantity that would have been removed by ordinary
crops. Consequently there is an actual saving of these
plant-food materials when crops are produced.
122. Effect of fertilizers on loss of plant-food materials
in drainage. — We have seen that the effect of sulfate of
potash was to increase the loss of lime, magnesia and sulfur.
In general, the result of fertilizer applications is similar to
that shown above. This is borne out by experiments con-
ducted at the Rothamsted Experimental Station in which
drainage was collected from. plats treated with different
fertilizers. The total flow of drainage water from these
plats was not measured, but the composition of the water
indicates the effect of the fertilizers.
TaBLE 25.— CoMPposITION OF DRAINAGE WATER FROM WHEAT
PLATS, ROTHAMSTED EXPERIMENT STATION
Parts PER MILLION
Pat Manures APpiuieD, RATE
a Bee CRE Lime |Magnesia| Potash | Nitrogen
2 Farm manure, 14 tons ..| 147.4 | 4.9 5.4 16.3
2 and 4) Ne tmanure: 2? 2 S0GG 2 98.1 ye i ie f 4.0
+5) Minerals only . . 124.3 6.4 5.4 5.2
6 Minerals + 200 lbs. am-
monium salts. 143.9 7.9 4.4 8.7
8 Minerals + 600 lbs. am-
monituaersalte®~*.2 5° . 1/1973 8.9 ae 2
9 Minerals + 550 lbs. ni-
trate. Gree os eee 5.9 4.1 18.6
13 Ammonium salts + super-
phosphate + sulfate of
potash )..3% ; .| 201.4 9.3 3.3 17.6
PLANT-FOOD MATERIALS IN SOILS 105
Without going over this table in detail, it may be noticed
that the effect of both farm manure and commercial fertiliz-
ers is to increase the percentage of plant-food materials in
the drainage water.
123. Drainage water from different soils. — The composi-
tion of the drainage water varies with different soils.
Table 20 in which the composition of the drainage water
from Dunkirk clay loam and Volusia silt loam is given, is
an illustration of the very considerable differences that
may occur in this respect. The more productive soil has
lost the greater quantity of plant-food material. The rates
of loss, however, are not proportional to the amounts of
plant nutrients that the soils contain. The Dunkirk soil
contains less nitrogen than the Volusia, but has lost more in
the drainage water.
124. Absorption of food materials by plants. — It is only
when substances are in solution that they may be absorbed
by agricultural plants. This means that the soil from which
plants draw their nourishment must contain water. Plants
absorb both water and nutrient salts through their roots,
more especially through the root-hairs, as these have very
delicate walls through which solutions may readily pass.
The movements of water and of salts through the walls of the
root-hairs are independent of each other. When the weather
is very hot and dry, a larger proportion of water to salts will
pass into the roots than when the weather is cool and moist.
125. How plants absorb nutrients. — When a solution
of plant nutrients is brought in contact with roots, there is
a tendency for the solution in the inside of the root and that
on the outside to become of the same strength for each par-
ticular substance in the solution. Thus, if there is much
available nitrogen in the solution, it will be absorbed in
greater quantity than if there were very little. Then, when
the nitrogen in the plant juice is utilized by the plant to
106 SOILS AND FERTILIZERS
form tissue, it is removed from the juice and more nitrogen
is absorbed to reéstablish equilibrium.
The substances that are used by plants in large amounts
are absorbed in greater quantity than those that are not
required in making tissue, or in other ways removed from
solution in the plant juices. The unused substances that
remain in the plant juices prevent, by their presence, the
further absorption of those particular substances from the
soil water. It is important that substances like nitrogen,
phosphoric acid, potash and lime shalt be present in abundant
quantities in the solution from which ir draw their
nourishment.
126. How roots aid in solution of soil. — In addition to
their function in the absorption of plant nutrients, there
can be no doubt that roots aid in the solution of these nutri-
ents from the soil. One way is by the excretion of carbon
dioxide, which when dissolved in water is an excellent solvent
for such substances as lime, potash and even phosphoric
acid when present in certain forms. The following table
shows the percentage of carbon dioxide in air drawn from
_ the bottom of the large soil tanks that have previously been
mentioned. One of these tanks produced a crop of corn
during the summer when the analyses were made, the other
tank was kept bare of vegetation.
TABLE 26. — PERCENTAGE OF CARBON D10xIDE IN AIR OF SOIL
PLANTED TO CoRN AND OF Bare SOIL
DaTE oF ANALYSIS PLANTED Soin UNPLANTED SOIL DIFFERENCE
Aue 19+ 5° 0 aaa 3.42 2.45 .97
IE. 23" Ne aS ee o.00 2.00 1.53
Aue. 26.005 2 ae 3.44 280 1.07
Ae. 30) oo ee 3.03 2.04 .99
Bent 2°" ore 3.28 Pe 1.11
PLANT-FOOD MATERIALS IN SOILS 107
It is apparent that the effect of the growth of plants has
been to increase the amount of carbon dioxide in the soil
air. The figures represent the period of the greatest pro-
duction of carbon dioxide by the corn plant.
127. Production of carbon dioxide by microérganisms.
—In addition to the carbon dioxide excreted from roots,
there are large quantities produced by microérganisms that
exist in soils. These organisms are concerned in the decom-
position of organic matter, and one final product of such
action is carbon dioxide. It has been estimated that in
one acre of soil to a depth of sixteen inches, there are sixty-
eight pounds of carbon dioxide produced by bacteria and
fifty-four pounds excreted by roots during the growing
season.
128. Solvent action of roots in other ways. — Many in-
vestigators think that the large quantities of mineral matter
that plants remove from soils could not be obtained from
the water solution even with the aid of carbon dioxide.
Several different ways have been suggested by which plants
may assist in rendering soluble the nutrients contained
in soils. It will not be necessary to discuss these as there
has been no definite and conclusive outcome to the investi-
gation of the subject. The indications are, however, very
strong that the plant aids in obtaining its food material in
some way or ways other than by the excretion of carbon
dioxide.
129. Difference in absorptive power of crops. — Crops
differ greatly in their ability to draw nourishment from the
soil. The difference between the quantities of nitrogen,
phosphoric acid and potash taken up by a corn crop of
average size and a wheat crop of average size is very
striking. In Table 27 it may be seen that two tons of
red clover contain three times as much potash, nearly ten
times as much lime, and somewhat more phosphorie acid
108 SOILS AND FERTILIZERS
than does a crop of thirty bushels of wheat, including the
straw.
The ability of any kind of plant to secure nutriment from
the soil depends on a number of factors which need not be
discussed here. According to their ability in this direction,
plants have been popularly classified as ‘‘ weak feeders ”’
and ‘strong feeders.’’ To the former belong such crops
as wheat and onions, which require very careful soil prep-
aration and manuring. In the latter class are maize,
oats and cabbage which demand relatively less care. In
the manuring and rotating of crops, this difference in ability
to obtain nutriment must be considered, in order not only
to secure the maximum effect on the crop manured, but
also to get the greatest residual effect of the manure on suc-
ceeding crops.
130. Substances needed by plants and substances merely
absorbed. — Some substances found in soils and absorbed
by plants are used for the formation of plant tissue, and
hence are indispensable. Other soil constituents, although
absorbed by plants to sufficient extent to be found in their
ash, are not essential to a normal growth of crops. The
substances that are essential are generally present in plants
in considerable quantities, because they constitute a part
of the plant tissue.
131. Quantities of plant-food materials removed by crops.
— When crops are removed from the land, they carry in
their tissues considerable quantities of plant-food materials.
The drain on the total supply may be serious if the soil is
not well supplied with these substances. The larger the
yield of crops the greater the quantities of plant nutrients
they are likely to contain. The following table shows the
quantities of nitrogen, potash, phosphoric acid and lime
removed from an acre of land by some of the common crops.
The entire harvested crop is included :
PLANT-FOOD MATERIALS IN SOILS 109
TABLE 27.—- NuMBER OF PouNDs or NITROGEN, Potasn, LiME
AND PHospHoRIC AcID REMOVED FROM ONE ACRE OF SoIL BY
CERTAIN Crops
Crop YIELD Nirrocen | Portas Lime Rear sony
CID
Wheat . . .{| 380 bushels 48 28.8 9.2 ps ee |
Barley . . .| 40 bushels 48 35.7 9.2 20.7
Wats... 2... | 45 pushels 55 46.1 11.6 19.4
torn, 2) 3 bushels 43 36.3 = 18.0
Meadow hay .| 13 tons 49 50.9 32,3 12.3
Red clover .| 2 tons 102 83.4 90.1 24.9
Potatoes .. .| 6 tons AT 76.5 3.4 215
TWuraips boo oa tens | 192 148.8 74.0 33.1
While these are only a few of the cultivated crops, they
give some idea of the quantities of plant-food materials
removed from soils by ordinary cropping. The nitrogen
removed by red clover is partly taken from the air and conse-
quently the draft on the soil supply is not so great as would
be indicated by the figure here given.
132. Possible exhaustion of mineral nutrients. — Com-
paring the figures given above with those in Table 17
it is evident that there is a supply in most arable soils
that will afford nutriment for average crops for a very long
period of time. On the other hand, when it is considered
that the soil must be depended on to furnish food for hu-
manity and domestic animals as long as they shall continue
to inhabit the earth, at least so far as is now known, the
very apparent possibility of exhausting, even in a period
of several hundred years, the supply of plant nutrients
becomes a matter of grave concern.
The visible sources of supply to replace or to supplement
the nutrients in the soil now cultivated are, for the mineral
substartces, the subsoil and the natural deposits of phosphates,
potash salts and limestone; and for nitrogen, deposits of
nitrates, the by-product of coal distillation and the nitrogen
110 SOILS AND FERTILIZERS
of the atmosphere. The last of these is inexhaustible,
and the exhaustion of the soil nitrogen supply, which a few
years ago was thought by some to be a matter of less than
half a century, has now ceased to cause any apprehension.
The conservation or extension of the supply of mineral
nutrients is now of supreme importance. The utilization
of city refuse and the discovery of new mineral deposits
are developments well within the range of possibility, but
neither of these promises to afford more than partial relief.
The utilization of the subsoil through the gradual removal
by natural agencies of the topsoil will, without doubt, tend
to constantly renew the supply. The removal of topsoil
by wind and erosion is, even on level land, a very considerable
factor. The large amount of sediment carried in streams im-
mediately after a rain, especially in summer, gives some idea of
the extent of thisshifting. This affects chiefly the surface soil,
and thereby brings the subsoil into the range of root action.
There is little doubt that a moderate supply of plant-
food materials will always be available in most soils, but for
progressive agriculture manures must be used.
QUESTIONS
1. How does the total quantity of plant-food materials in soils
compare with the total weight of soil ?
2. Are the percentages of nitrogen, phosphoric acid and potash
uniform in different soils, or do they differ ?
3. Is there a direct relation between the productiveness of a soil
and its content of plant-food materials ?
4. What is meant by available and unavailable plant nutrients ?
5. Name some of the factors that influence the availability of
plant nutrients in soils.
6. Why is it not always possible to determine by chemical analy-
sis the degree of productiveness of a soil ?
7. Explain what is meant by the absorptive properties i soil for
soluble fertilizers.
8. Explain what is meant by selective absorption.
PLANT-FOOD MATERIALS IN SOILS rh
9. Explain the availability of absorbed fertilizers.
10. What two constituents are removed in greatest quantity
by drainage water from an unplanted soil ?
11. Explain how roots aid in the solution of soil.
LABORATORY, EXERCISES
Exercise I. — Soluble matter of soil.
Materials. — A very rich soil, filter paper and funnel, evaporat-
ing dish, flame, dilute hydrochloric acid.
Procedure. — Place a small amount of a rich soil on a filter paper
held in a funnel and leach with distilled water, catching percolate
in an evaporating dish. Evaporate percolate to dryness and exam-
ine residue. Is it large or small in amount? Treat with a few
drops of dilute acid. Finally heat over a flame. Explain results.
This soluble matter is the most valuable portion of the soil.
Exercise IJ. — Absorptive power of soil for dyes.
Materials. — Soil, filter paper, funnel, solution of gentian violet.
Procedure. — Place a small amount of soil on a filter paper ina fun-
nel and treat with a solution of gentian violet. Note that the water
comes through clear for a considerable period indicating the high ab-
sorptive power of the soil for this dye. The capacity of the soil to
absorb soluble matter prevents heavy losses of plant-food materials.
Exercise III. — Selective absorption by the soil.
Materials. — Soil, filter paper and funnel, solution of gentian
violet and solution of eosin.
Procedure. — Proceed in the same way as Exercise II, comparing
the absorptive power of portions of the same soil for the two dyes.
Note the difference. The soil varies in its absorptive power with
different materials. For instance, the soil absorbs acid phosphate
much more strongly than sodium nitrate.
Exercise IV.— Absorptive power of the soil for gas.
Materials. — A moist loam rich in organic matter, a flask or
bottle, concentrated ammonia.
Procedure. — Place in a flask or bottle a quantity of moist soil.
Pour in a few drops of ammonia. Note strong odor. Stopper
bottle and shake. Allow to stand for half an hour with several shak-
ings. Open and note odor.
The absorptive power of the soil for ammonia, oxygen and other
gases isa very important function. Explain why this is true.
CHAPTER VIII
ACID SOILS AND ALKALI SOILS
Some soils are termed acid, or sour soils. They are so
called because they give the same tests with certain chemi-
cals that are obtained with vinegar and other acids. A
common test for acids is to bring them in contact with blue
litmus paper, and if the material is acid the paper is colored —
red. Soils that are strongly acid will also do this. Another
property of acid materials is that, if sufficient quick-lime
is brought in contact with them they will no longer color
blue litmus paper red. This may be tried by slowly stirring
quick-lime into vinegar and testing it occasionally with
litmus paper. If sufficient quick-lime be added to an acid
soil, it will no longer turn blue litmus paper red.
Whether a soil is acid or not is a matter of practical im-
portance, because some plants do not grow so well on sour
soils as they do on soils that are neutral or alkaline; on the
other hand some crops prefer an acid soil.
133. Nature of soil acidity. There are two kinds of
soil acidity (1) when acids are present that have been formed
by fermentation of organic matter in the soil, (2) when there
is a deficiency of such material as lime or potash. In either
case the soil will color blue litmus paper red.
134. Positive acidity. — The condition of soil first men-
tioned above has been termed positive acidity. It arises
from the decomposition of organic matter when soil condi-
tions are not favorable to the proper breaking down of the
intermediate substances. An insufficient air supply caused
112
ACID SOILS AND ALKALI SOILS 113
by saturation or compaction of the soil, or a lack of lime, may
lead to the formation of these acids. Acid soils to which —
certain organic acids have been added were found to be
unfavorable to the growth of plants like wheat, while the
same soil, to which lime had been applied, produced a much
better growth. Lime overcomes the injurious effect of this
kind of acidity.
135. Negative acidity.— When a soil contains no free
acids but is sour in its relations to plant growth, it may be
said to possess negative acidity. Negative acidity is coun-
teracted by the application of lime just as is positive acidity.
The condition that renders the soil acid is a lack of sub-
stances like lime, magnesia, soda and potash. Any one of
these four substances is called a base. Lime, being the cheap-
est of these to apply, is the usual corrective. The injurious
action of soil acidity on plant growth has been attributed
to one or more of the following causes: (1) lack of lime to
overcome organic acids when they are formed; (2) absence
of sufficient carbonate of lime; (3) great absorbent properties
that cause the soil to compete with plants in their attempt
to draw plant-food materials from the soil.
136. Ways by which soils become sour. — In regions of
ample rainfall there is always a tendency for soils to become
sour, and unless they originally contain large quantities
of lime, or are of recent formation, they are likely to be in
need of lime. This tendency may be due to any one or more
of the following causes: (1) removal of lime and similar
substances in drainage water; (2) removal of these sub-
stances by plants; (3) accumulation of acids contained in
fertilizers applied to the soil; (4) formation of organic acids
from plant remains.
137. Drainage as a cause of acidity. — The chief cause of
soil acidity is doubtless the removal of lime, magnesia, soda
and potash from soil by the water that percolates through
1 Bg :
114 SOILS AND FERTILIZERS
the soil and passes off as drainage. The quantities of these
materials that are annually lost from an acre of soil, as found
by lysimeter experiments, are shown in Table 24.
It will be noticed that there is a much greater loss from the
unplanted soil than from the planted. The quantities of
these materials taken up by some crops is much less than the
difference between the quantities in the drainage in the
planted and unplanted soil, hence the growth of these crops
on land is really a means of saving lime.
138. Effect of plant growth on soil acidity. — Plant growth
may promote soil acidity in the following ways: (1) by re-
moval of the bases in the ash of the plants; (2) by leaving
in the soil the acids with which these bases were combined ;
(3) by formation of organic acids during decomposition of
plant remains.
It will be seen from Table 27 that the quantities of
potash and lime removed in crops of average size vary
considerably and in some cases are very large. When,
as ina state of nature, the vegetation on the land is returned
to it after life ceases, and its organic material is again
incorporated with the soil, there is no loss in this way, but
in ordinary farming most of the above ground portion of
the crop is removed from the land. The manure of growing
animals returns to the soil only a small proportion of the
lime that was originally in the plants because the animal
has used it, and the potash is likely to be leached from the
manure unless it is carefully handled.
Crops in growing remove more potash and other bases
from the soil than they do the acid-producing substances,
which latter are left in the soil and contribute still more to
its tendency to assume an acid condition.
139. Effect of fertilizers on soil acidity. —It has been
shown very conclusively that the continued use of considerable
quantities of sulfate of ammonia on land may result in bring-
ACID SOILS AND ALKALI SOILS is
ing about an acid condition. In the case of this fertilizer
the ammonia is absorbed either directly or indirectly and
most of the sulfate, which is an acid, remains in the soil.
Probably no other fertilizer is so active in producing acidity,
but it is possible that sulfate of potash or muriate of potash
or gypsum may, in less degree, have the same tendency.
The use of free sulfur for combating fungous diseases may
also lead to the formation of a sour soil.
140. Effect of green-manures on acidity. — In soils defi-
cient in lime the incorporation of green-manure crops has
been thought to produce temporarily an acid condition.
It is during the early stages of fermentation in the soil that
the acids are formed. When further decomposition pro-
ceeds, the acids are broken up and acidity disappears. This
condition has been noticed mainly in the South Atlantic
states. Where it has been found to occur, there is some ad-
vantage to be gained from plowing under the green-manure
as long as possible before planting the next crop.
141. Weeds that flourish on sour soils. — Whether a soil
is acid or not will make a great difference in the kinds of
plants that will thrive on it. Certain weeds will generally
be found growing on sour soil and the presence of these in
large numbers may be taken as evidence that the soil needs
lime. Weeds that appear to flourish on acid soils may do
so either because they are physiologically adapted to an
acid condition, or because other vegetation does not thrive,
and hence these particular weeds have less competition on
this soil. The weeds that in one part of the country or
another may be considered to indicate an acid soil are as
follows :
Sheep sorrel Corn spurry
Paintbrush Wood horsetail
Daisy Plantain
Horsetail rush Goose-grass
116 SOILS AND FERTILIZERS
142. Crops adapted to sour soils. — There are a consider-
able number of plants, other than weeds, that grow well on
sour soils, some, in fact, thriving better when the soil is
acid than when it is not so. The following is a list of those
that have been found to be adapted to soils of this kind:
Blueberry Rhode Island bent-grass Rye
Cranberry Cowpea Millet
Strawberry Soy bean Buckwheat
Blackberry Castor bean Carrot
' Raspberry Hairy vetch Lupine
Watermelon Crimson clover Serradella
Turnip Potato Radish
Redtop Sweet potato Velvet bean
This list affords a sufficient number of plants to permit of
a largely diversified cropping system on sour soil, should it
be undesirable, or very expensive, to put lime on the land.
The considerable number of legumes in the list would admit
of soil improvement through their use.
143. Crops that are injured by acid soils. — While there
is a considerable number of agricultural plants that are
adapted to sour soil, it is true that the greater number of
the most important crops is injured by such soil. General
farming can best be conducted on soil that is not greatly
in need of lime. One reason for this is that the great soil-
improving crops — red clover and alfalfa—are very un-
certain crops on acid soils. The following plants are injured
by sour soil:
Alfalfa Pumpkin Cucumber
Red clover Salsify Lettuce
Saltbush Spinach Onion
Timothy Red beet Peanut
Blue-grass Sorghum Okra
ACID SOILS AND ALKALI SOILS 117
Maize Barley Tobacco
Oats Sugar beet Kohlrabi
Pepper Currant Eggplant
Parsnip ~ Celery Mangel-wurzel
Cauliflower Cabbage -
Some of these plants will grow well on soil that is too sour
for other crops. For example, red clover will grow fairly
well on soil that is too acid to raise alfalfa.
144. Litmus paper test for soil acidity. — This test is
made with blue litmus paper, which is brought in imme-
diate contact with wet soil. A rapid and decided change
to red is taken to indicate an acid condition of the soil.
Carbonic acid, which is always present in soils, but
which is not injurious to plant growth, is supposed to give
_ only a faint pink color to the litmus paper. Various ways
of bringing the paper into contact with the soil have
been proposed, among others the placing of filter paper or
blotting paper between the soil and the litmus paper.
It has also been pointed out that the acid perspiration of
the fingers may lead to a mistaken conclusion that the soil
is acid.
Much litmus paper is sold that is of very poor quality,
and an effort should be made to obtain a good article. When
good paper is uséd and the test is carefully made, the general
experience has been that it is a fairly good, although not an
infallible, guide to the need of a soil for lime.
145. Litmus paper and potassium nitrate. — This is per-
formed in the same manner as the former litmus paper test,
except for the substitution of a saturated solution of potas-
sium nitrate instead of water for moistening the soil. It is
a more delicate test than the one with litmus paper alone.
The operation consists in working a small soil sample to a
thick paste with a saturated solution of potassium nitrate
118 SOILS AND FERTILIZERS
and applying the paper directly to the soil. If the soil is
acid, the potassium will be absorbed and an acid or acid salt
set free, which will act on the litmus paper, giving it a decided
pink color. .
146. The Truog test. — In this test solutions of calcium
chloride and zine sulfide are brought in contact with the
soil to be tested and the mixture is boiled. If the soil is
acid, a gas called hydrogen sulfide is formed and driven off
with the steam. The presence of this gas may be detected
by placing a strip of moist lead acetate paper over the mouth
of the flask in which the soil and solutions are boiled. The
lead acetate paper is rapidly darkened by the hydrogen
sulfide gas as it passes out of the flask. Detailed descrip-
tions of the methods for making these tests for soil acidity
will be found in the laboratory exercises.
147. Alkali soils. — We have seen that every soil is
constantly undergoing decomposition, by which process a
very minute fraction becomes soluble every year. Ordi-
narily, in humid regions, this soluble matter is leached out
by the rain water that percolates through the soil. In
those parts of the world where the rainfall is very slight,
and yet where decomposition of soil proceeds, there is a
tendency for the soluble matter to accumulate in the soil
where there is no drainage, or for it to move to places where
seepage accumulates. A strong accumulation of such soluble
matter is known as alkali because it usually has an alkaline
reaction, 7.e. it turns red litmus paper blue.
148. Nature and movements of alkali. — Because of its
easy solubility, alkali may move from place to place or up-
ward and downward in soils. During periods of drought
it is carried upward by the capillary rise of the soil water,
while during periods of rainfall it may move downward,
where it is out of range of roots. The composition of alkali
varies greatly in different regions. The main distinctions
ACID SOILS AND ALKALI SOILS 119
are between white and black alkali. The former gets its
name from the fact that when it accumulates on the surface
of the ground, as is very common in a dry time, it has a white
appearance. The latter, on the other hand, is black, because,
owing to its caustic nature, it dissolves organic matter from
the soil, which gives it a black color.
149. Effect of alkali on crops. — Both white and black
alkalis are injurious to plant growth when present in large
quantity, but black alkali is much more active in this re- ©
spect, as it attacks plant tissue just as it does the organic
matter in soils. White alkali injures plants by withdraw-
ing water from the plant cells and causing the plant to
wilt. The nature of the salts contained in the alkali, and
the species and even the individuality of the plant, de-
termine the amount of alkali that is required to destroy a
crop.
150. Tolerance of different plants to alkali. — Some plants
are better able to endure the presence of alkali in soil than
are others. This is due, in part, to the natural resistance
of the plant to the injurious effect, and in part to the rooting
habit of the plant. Deep-rooted plants are, in general,
better able to resist alkali than are shallow-rooted ones,
probably because some part of the root is in a less strongly
impregnated part of the soil.
Of the cereals, barley and oats are the most tolerant. Of
the forage crops, a number of valuable grasses are able
to grow on soil containing a considerable quantity of
white alkali. Timothy, smooth brome-grass and alfalfa
are among the cultivated forage crops most tolerant of
alkali, although they do not equal the native grasses in this
respect.
The resistance of a number of plants to white alkali, ex-
pressed in pounds to the acre to a depth of four feet, is as
follows:
120 SOILS AND FERTILIZERS
TABLE 28. — RESISTANCE OF Crops TO ALKALI
Crop Tota ALKALI Tota, ALKALI
Peaches ... 11,280 Barley os nike 25,520
MMIII PTGS cbc ita?! te 12,480 Gag 13) ae ee 45,760
POS 755 wel te 16,120 Sugar beets. 59,840
Pears. sy tty 20,920 Sorghum .. 81,360
Q¥ane OR coli. 21,840 Alfalias "3.208 110,320
Saltbush . . 156,720
151. Irrigation and alkali.— Frequently the injurious
presence of alkali in an irrigated region has been discovered
only after irrigation has been practiced for a number of years.
This is due to what is termed “ rise of alkali,’ and comes
about through the accumulation, near the surface of the
. soil, of salts that were formerly distributed throughout
a depth of perhaps many feet. Before the land was irrigated,
the alkali was distributed through a great depth of soil, but
after water was turned on, this was dissolved, and later
brought to the surface, as the soil was allowed to dry out.
The upward movement in such cases exceeds the downward
~ because the descending water passes largely through the
non-capillary pore spaces, while the ascending water passes
entirely through the capillary spaces. The alkali accumu-
lates principally in the capillary spaces and hence is swept
to the surface in large quantities by the upward movement
of capillary water.
152. Removal of alkali.— There are several ways in
which alkali may be removed from soil, among which are
the following: (1) leaching with underdrainage ; (2) correc-
tion with gypsum; (8) scraping; (4) flushing.
The first of these consists in laying tile drains, much as is
done for draining land in humid regions, then flooding the
land with large quantities of water, which dissolves the alkali
ACID SOILS AND ALKALI SOILS 121
and carries it out through the drains. This is, by all means,
the most effective way of removing alkali.
Gypsum has been used for converting black alkali into
white alkali, which it does by inducing chemical changes in
the alkali. This may well be used when black.alkali land
is to be drained.
Scraping consists in allowing alkali to accumulate at the
surface of the soil and then removing it with a scraper. This
is never a very effective treatment.
Flushing is accomplished by removing the surface incrusta-
tion with a rapidly moving stream of water instead of a
scraper. Like the former method it is not usually an
adequate treatment.
153. Control of alkali.— Instead of actually removing
alkali its injurious action may often be kept in check by keep-
ing it well distributed through the soil and not allowing it
to accumulate near the surface. This may be done by con-
trolling evaporation and by the cultivation of alkali-tolerant
_ plants. The methods usually employed for retarding evap-
oration of moisture are generally applicable for controlling
alkali.
Cropping with alkali-tolerant plants naturally suggests
itself as a means of combating alkali where it does not exist
to such an extent as to interfere with all crop production.
As these plants remove considerable quantities of alkali in
their ash, they also serve as a means of alkali removal.
QUESTIONS
1. Distinguish between positive and negative acidity in soils.
2. Describe three ways in which soil acidity may be injurious to
plant growth.
3. State three ways by which the growth of plants on soil tends
to make it become sour.
4. What is the effect on soil acidity of a continued use of am-
monium sulfate ?
122 SOILS AND FERTILIZERS
5. If green-manures are found to produce acidity on a particular
soil, what precaution should be taken in using them ?
6. Name three or four weeds whose presence in large numbers
indicates that a soil is acid.
7. Name six or eight crops that are adapted to growth on sour
soils, and an equal number that are injured by a sour soil.
8. Deseribe the litmus paper test for the detection of a sour soil.
9. Describe the test with litmus paper and potassium nitrate
solution.
10. State what is meant by an alkali soil.
11. Explain the difference between white and black alkali, and
the effect of each on crops.
12. Name some of the crops most tolerant of alkali.
13. Describe four ways by which alkali may be removed from soil.
LABORATORY EXERCISES
Exercise I. — Acid soils in the field.
Plan a field trip to a soil known to be distinetly acid. Observe
structure of soil, organic content, character of crop and, particularly,
character of other vegetation. It might be well to make a collec-
tion of the plants which are supposed to indicate acidity. Take
samples of this soil for future tests for acidity in the laboratory.
Exercise JI.— Litmus paper with and without potassium ni-
trate.
Materials. — Litmus paper, acid soil, evaporating dish, a neutral
potassium nitrate solution.
To prepare litmus paper boil litmus powder (1 part) with aleohol
(2 parts) for five minutes. Allow to settle and pour off the alcohol,
thus carrying away certain dyes of low sensitiveness. To the
powder now add five parts of water. Boil 10 minutes and allow
to stand overnight. Decant liquid and filter it. This gets rid of
most of the carbonates. Now make acid with sulfuric acid and bring
back to required tint with barium hydrate. Dip narrow strips of
filter paper into the solution and dry on glass. When dry cut into
strips of the required size. :
Procedure. — Mix one portion of a distinctly acid soil to a thick
paste in an evaporating dish with distilled or rain water. Allow
to stand for a few minutes, then pat to a smooth surface and apply
to it one end of a strip of litmus paper, leaving the other end free for
comparison. Press paper closely in contact with soil.
ACID SOILS AND ALKALI SOILS 123
Treat another small portion of this soil in the same way, using
a neutral potassium nitrate solution instead of distilled water.
Observe the rate of change of color of the litmus paper with and
without potassium ni-
trate.
Exercise ILl.—
Litmus paper test.
Materials. — Same
as Exercise II.
Procedure. — Test
a number of different Fic. 21. — Procedure in the litmus paper test.
soils. The students (@) small evaporating dish, (b) soil worked to a
should be encouraged thin paste with pure water or a neutral potassium
irene in’ (hemor nitrate solution, (c) the litmus paper in position,
with one end free for comparison.
samples. Note whether
there appears to be a difference in degree of acidity of these soils
as indicated by the quickness with which the litmus paper turns red
and the shade of red produced.
Exercise IV. — Test for soil carbonates.
Materials. — Soil, evaporating dish, dilute hydrochloric acid.
Procedure. — Treat a small portion of the soil to be tested with
dilute hydrochloric acid. Effervescence indicates the presence of
carbonates. A soil so reacting needs no lime. If no reaction oc-
curs, test with litmus paper, as the soil may be alkaline, neutral
or acid.
Exercise V. — Ammonia test for acidity.
_ Materials. — Soil, 8 oz. bottle, concentrated ammonia.
Procedure. — Place about 25 grams of soil in an 8 oz. bottle and
add 10 c.c. of ammonia. Fill two-thirds full with distilled or rain
water. Shake well and allow to stand overnight. A darkening
of the supernatant liquid is an indication of the lack of lime.
This method is not a quantitative one because the degree of
darkening of the liquid depends on the amount of organic matter
present rather than the degree of acidity.
Exercise VI. — Zine sulfide test for acidity. (See Fig. 22.)
Materials. — Soil, 250 to 300 ¢.c. Erlenmeyer flask, tripod and
wire gauze, flame, calcium chloride-zine sulfide solution, lead ace-
tate paper.
The calcium chloride-zine sulfide reagent is made up as follows:
50 grams of neutral calcium chloride plus.5 grams of zine sulfide
124 SOILS AND FERTILIZERS
is added to 250 e.c. of distilled water. The solution should be
shaken well each time before using as the zine sulfide is insoluble and
tends to sink to the bottom of the vessel.
The lead acetate paper is made by dipping strips of filter paper
into a saturated solution of lead acetate and drying.
Procedure. — Place in a 250 or 300 c.e.
Erlenmeyer flask a 10 gram sample (well
pulverized) of the soil to be tested. Now
add 5 ¢.e. of the calcium chlo ide-zine sulfide
reagent, the former being in solution and
the latter in suspension. Add 75 e.c. of dis-
tilled water. Place on a wire gauze over a
flame and bring to boiling. Boil exactly one
minute, being careful not to allow the sample
to froth over.
The boiling having become constant and
the CO, being driven off, lay over the mouth
of the flask a strip of lead acetate paper
moistened in distilled water. Allow it to
remain there exactly three minutes. The test
, , is now complete and acidity is indicated by
Fic. 22.— Apparatus the blackening of the paper.
for the zinc sulfide test ExercisE VII. — Incrustation of “ al-
for soil acidity. (a) lead kali”? -b a :
acetate paper in posi- %# Mest aes ary action. .
tion, (b) flask, (c) soil Materials. — Sandy loam, lamp chimney,
treated with calcium pan, salt.
chloride and zine sulfide, Procedure. — Prepare a lamp chimney by
(d) tripod, (e) Bunsen : J
barter. neatly tying over the end two thicknesses of
cheesecloth. Fill with sandy loam. Set the
chimney now prepared into a solution of common salt. The salt
solution will soon rise through the column by capillary action and
evaporation will take place from the soil. This will soon cause
an incrustation of ‘‘ white alkali’”’ on the surface of the soil.
Explain this experiment in relation to irrigation practice and
moisture conservation under arid conditions.
CHAPTER IX ;
THE GERM LIFE OF THE SOIL
Tuus far we have been engaged in considering soil as
lifeless material, on which plants are to be grown, but which
in itself is inert and inanimate. Such a conception of soil
is inadequate, for there is to be found in all arable land a
vast number of forms of microscopic life that really consti-
tute a part of the soil itself. From the standpoint of crop
production they are of great importance, as we probably
should not be able to maintain soil fertility without them.
Under germ life, as used in this chapter, are included
bacteria, fungi, alge, and some of the molds, but we shall in
the main, dispense with these distinctions and use the term
“germs” or ‘‘ microérganisms ” to cover all or any of them.
In spite of what has just been said about the importance of
germs in plant production, there are many that are injurious
to plants both directly in the causation of disease, or indi-
rectly by contributing to processes in soils that are detri-
mental to the conditions favorable to plant growth. In dis-
cussing the subject it will be convenient to take up first
the soil germs that are directly injurious to plants. After
that the subject will be discussed according to the processes
in the soil with which microérganisms are concerned.
154. Microérganisms injurious to crops. — The soil germs
that injure crops do so by attacking the roots. Those that
attack other parts of plants may live in the soil during their
spore stage but they are not strictly microérganisms of the
soil. Some of the more common diseases produced by soil
125
126 SOILS AND FERTILIZERS
germs are: wilt of cotton, cowpeas, watermelon, flax, tobacco,
tomatoes, and other plants; damping-off of a large number
of plants, root-rot and galls.
Some of the germs causing these diseases may live in the
soil for many, years. Some of them will die within a few
years if the plants on whose roots they live are not grown on
the soil, but others are able to maintain existence on almost
any organic substance. Infection is carried in the soil, or by
the roots of the plants themselves, consequently farm imple-
ments or manure may often be a means of spreading the germs.
For combating the difficulties caused by the germs, many
methods have been tried with more or less success. Rota-
tion of crops is successful in some cases, but in others entire
discontinuance is the only remedy. The use of lime has been
beneficial in the case of some diseases. Steam sterilization
for greenhouse soils will hold in check a considerable number
of diseases. Strains of cowpeas and cotton plants have been
bred that are immune to the effects produced by some germs.
155. Germs not directly injurious to crops. — The part
played by the microérganisms that affect the growth of
crops may be roughly listed as follows: (1) action on mineral
matter; (2) decomposition of non-nitrogenous organic
matter; (3) decomposition of nitrogenous organic matter ;
(4) fixation of nitrogen from the air and its incorporation
in the soil. Most of the processes involved in these trans-
formations bring about conditions favorable to crop growth,
but some of them are injurious, as, for instance, the forma-
tion of substances poisonous to plants and the liberation
of nitrogen which escapes into the air. These injuries are,
however, not direct effects of the germs on the crops, but
indirect ones caused by the products of the organisms.
Bacteria, fungi, alge and certain molds all play a part
in these processes, but none of them so actively as do the
bacteria. On account of the dominant part that bacteria
THE GERM LIFE OF THE SOIL 12%
take in soil fertility some further description of their oc-
currence in soils will be given.
156. Numbers of bacteria in soils. — It is naturally to
be expected that soils differ greatly in the number of bac-
teria that they possess. Where there is a large amount of
easily decomposable organic matter, the number is great,
and consequently in rich garden soils that have been heavily
manured, or where the carcasses of animals have been buried
the bacterial flora is dense. On the other hand, in very
sandy soils, desert soils and water-logged soils, bacteria are
few in number.
While there are usually many bacteria in fertile soil, it is
not always the case that there are more in such soils than
in less productive ones. The number of bacteria that a
soil may contain cannot be considered a measure of its pro-
ductiveness. The numbers of bacteria found in one gram
of soil of different kinds and treated in different ways are
given in the following table:
TaBLE 29. — NuMBER OF BacTERIA TO A GRAM oF Sort DurRING
SomE PERIOD OF THE GROWING SEASON
Sort | DEPTH . | Crop pe sees
Sli Gliay ..- . . «| &inches |-Orehard ‘in’ high | 2,200,000
state of cultiva-
tion. In cover
crops
Adjoining soil above} 3 inches | Meadow for twelve| 450,000
and of same char- years
acter
Of same type as| 3inches | Vegetables and | 1,800,000
ae A. ee heavily manured
Same type as above|. ... .|]Searlet clover | 3,360,000
plowed under and
alternated with
maize for ten years
128 SOILS AND FERTILIZERS
157. Conditions affecting bacterial growth. — The en-
vironment is a controlling influence in the development of
bacteria as it is of all organisms. Among the important
environmental influences are the supply of air and moisture,
the temperature, the presence of organic matter, and the
presence or absence of
acidity in the soil.
158. Air supply. —
While all bacteria require
some air for their growth,
certain of them are able
to get along with much
less than others. Those
requiring an abundant.
supply of air have been
— ¢alled aérobie bacteria
se a inmam showing herelstve and those that thrive
(A) a fine sand particle, (B) a large clay better on a small air sup-
eee Seas a ie All'are ply are termed anaérobic.
The bacteria that are of
the greatest benefit to the soil are, in the main, aérobes, and
those that are injurious in their action are chiefly anaérobes.
Bacteria, however, have more or less ability to adapt them-
selves to a larger or smaller air supply. The fact that struc-
ture, texture and drainage are so largely instrumental in
regulating the quantity of air in the soil makes them im-
portant factors in determining the kinds of bacterial processes
that take place in a soil.
159. Moisture. — Like other forms of plant life, bacteria
require moisture for their growth. A soil may become so
dry that the number of bacteria is decreased, but owing to
their rapid multiplication the number soon increases with
a replenished moisture supply. An excess of water may
decrease the number or change the character of the flora
THE GERM LIFE OF THE SOIL 129
by cutting off the air supply. A well-drained soil in good
tilth affords the best moisture conditions for the develop-
ment of desirable bacteria.
160. Temperature. — It is seldom that soil temperatures
become sufficiently high to interfere with bacterial activity,
and then it is only near the surface. Freezing does not
kill most soil bacteria, but it renders them inactive during
the frozen period. It is in the early spring that temperature
is an important factor so far as its effect on bacteria is con-
cerned. At that season it is desirable to warm the soil
as rapidly as possible.
161. Organic matter.—- Many forms of bacteria utilize
the organic matter of the soil as a source of food supply.
Others thrive without any organic matter. For the proper
functioning of a normal bacterial flora there should be a
good supply of organic matter in the soil.
162. Soil acidity. — Most of the useful bacteria make
their best growth in a soil that shows no acidity. This is
notably true of those bacteria that assist in the process
of making organic nitrogenous matter suitable for use by
plants, and also the symbiotic bacteria of alfalfa and red
clover. One of the important effects of lime is the increased
activity of beneficial soil bacteria.
163. Bacteria in relation to soil fertility. — We have now
discussed the conditions under which. soil bacteria grow.
The next step will be to describe the various processes by
which they increase soil fertility and also, to some extent,
by which they unfavorably influence soil productiveness. To
do this they will be discussed in the order stated in § 155.
The reader must, however, bear in mind that there are doubt-
less many bacteriological processes in the soil regarding
which nothing is known.
164. Action on mineral matter.— There are, without
doubt, microérganisms that act on mineral matter in soil,
K i
130 SOILS AND FERTILIZERS
attacking the insoluble substances and rendering them more
soluble. The phase of this subject that is of most apparent
agricultural importance is the effect of microdrganisms
on the very difficultly soluble rock or bone phosphoric acid,
converting it into phosphoric acid available to plants.
In laboratory experiments with pure cultures of bacteria
these changes have been found to occur. There has also
been found to take place a reverse process by which the more
easily soluble phosphoric acid is converted into the less
soluble one. . There is, at present, no way by which man can
control this operation in the soil. It has been held that the
presence of a large quantity of organic matter will make the
phosphoric acid of rock readily available. The results of
experiments with raw rock phosphate and farm manure do
not always confirm this idea. Under some conditions the
dominant process may be the conversion of difficultly soluble
into readily soluble phosphoric acid, while under other
conditions the reverse may take place.
165. Decomposition of non-nitrogenous organic matter.
— There is much organic matter on the surface or in the
plowed soil that contains no nitrogen. The cell walls of
plants, and the sugars, starch and fats of plants contain no
nitrogen. These substances are broken down by bacteria,
passing through different stages among which acids occur,
and finally being resolved into carbon dioxide and water.
We have seen that the plant uses carbon dioxide as food
material, and we may now understand the cycle through
which the carbon of this gas goes. Plants absorb carbon
dioxide through their leaves, decompose it and use the carbon
in their tissues. After the plant is dead, the tissues decom-
pose and carbon dioxide is again formed and passes into the
air. Just as higher plants live and grow by using carbon
from carbon dioxide, so bacteria live and grow by using ok:
carbon of plant tissues.
THE GERM LIFE OF THE SOIL 131
166. Decomposition of nitrogenous organic matter. —
The main difference between the decomposition of non-
nitrogenous and nitrogenous organic matter is that in the
latter nitrogen and usually sulfur play a part. The sulfur
is not of so much importance, but it is very necessary that
we should follow the various processes through which nitro-
gen is transformed from organic substances into the final
forms in which it is again used by plants or returned to the
air. These processes will be treated under the following
Fie. 24. — Appearance of some soil germs under'the microscope. (A) free
living nitrogen-fixing bacteria (Azotobacter), (B) bacteria that cause one
step in the production of nitrates from ammonia (Nitrosomonas), (C) nitro-
gen-fixing bacteria from the nodules of leguminous plants (Radicicola),
(D) ammonia-forming bacteria (Proteus vulgaris).
heads: (1) ammonification; (2) nitrification; (3) denitri-
fication. |
Organic nitrogenous matter when it first enters the soil
as plant or animal remains or as solid farm manure or green-
manure is largely in the form of what are known as proteids.
As soon as such material is incorporated in any normal
soil, decomposition begins and the rate at which it proceeds
depends on the character of the soil in which the process
is going on. There are several different forms of bac-
teria that are capable of decomposing proteins and there
are always enough of these in any arable soil to do the work
if the soil has the proper moisture, ventilation and heat and
is not acid.
¥s2 SOILS AND FERTILIZERS
167. Ammonification. — Various intermediate products
occur in the breaking down of proteids, but we are concerned
chiefly with the product known as ammonia. This is the
nitrogenous substance contained in many fertilizers, and ~
it may be used by some crops directly as food material.
Rice, for instance, and probably other swamp plants can
use ammonia better than any other form of nitrogen. Even
some upland crops like corn, peas, barley and potatoes can
use it, but not as well as they can the form of nitrogen into’
which ammonia is transformed by the next. fermentation,
namely nitrification.
It may be well to say, in passing, that there are some other
products intermediate between proteids and ammonia that
are directly used by plants, and it is altogether likely that
farm manure owes part of its great fertilizing value to some
of these substances that it may possess.
168. Nitrification. — This is the final step in the prepara-
tion of nitrogen for use by most agricultural plants, for it is
in the form produced by nitrification that nitrogen is most
useful to most crops. This form is called nitrates. Like
ammonification this fermentation goes on in any normal
soil if the ammonia is there for it to work on, and also like
ammonification the conditions of temperature, air supply,
moisture and lime must be satisfactory or the process will
be so slow that plants will suffer for nitrogen.
There has been some question as to whether heavy manur-
ing with organic manures results in a decreased nitrification.
While this may be the case where farm manure is used in
very heavy dressings of as high as fifty to a hundred tons
to the acre, as is sometimes done in truck crop gardening,
it is not likely to be the case in soils in which ordinary field
crops are grown.
169. Effect of soil aération on nitrate formation. — One of
the most important conditions that must obtain, if ammon-
THE GERM LIFE OF THE SOIL 133
ification and nitrification are to proceed rapidly, is an ade-
quate supply of air in the soil and this can only be secured
by thorough tillage. This is illustrated by an experiment
in which columns of soil eight inches in diameter and eight
inches high were removed from a field of clay loam and car-
ried to the greenhouse without disturbing the structure of
the soil as it existed in the field. At the same time vessels
of similar size were filled with soil dug from a spot near by.
These represented unaérated and aérated soils respectively,
because one had been undisturbed, while the other had
been thoroughly exposed to the air. Both were kept at the
same temperature and moisture content in the greenhouse
but no plants were grown in them. The production of
nitrates was as follows:
TABLE 30. — ForMaTION oF NITRATES IN UNABRATED AND IN
AERATED SOIL
NITRATES IN Dry Soin, Parts PER
ILLION
Times oF Maxine ANALYSES
Unaérated soil Aérated soil
When taken from field . . . . 3.2 3.2
After standing one month .. . 4.2 17-6
After standing two months ie 9.0 45.6
170. Effect of temperature on nitrate formation. — There
is a considerable range of temperature through which the
process of nitrate formation proceeds with more or less
intensity. Freezing stops the fermentation, but does not
kill the bacteria, whose activity is resumed when the tempera-
ture rises to about 40° F. and increases until a temperature
approaching 75° to 85° F. is reached, after which the in-
tensity gradually diminishes. At 110° F. and above, there
is little formation of nitrates. |
134 SOILS AND FERTILIZERS
The more rapidly a soil becomes warm in the spring, the
sooner will nitrates be formed. Crops like winter wheat
will often begin growth before the soil is sufficiently warm
to admit of the rapid formation of nitrates and, as winter
rains will have leached from the soil nitrates that accumu-
lated during the preceding year, the plants often suffer
seriously from lack of nitrogen.
It is not often that the soil for several inches below
the surface becomes hot enough, even in midsummer, to
interfere with nitrate formation. Crops that make their
growth in late spring or summer are not likely to suffer
for nitrates unless the total supply of nitrogen is deficient.
171. Effect of sod on nitrate formation. —In soil on
which there is a good stand of grass very little nitrate is
ever found. Sod apparently has a depressing influence on
nitrate formation. On the same type of soil as that used in
the experiment last described, the average quantities of
nitrates for each month of the growing season in the surface
eight inches of sod land, as compared with corn land under
the same manuring, were as follows:
TaBLeE 31.— Nitrates 1n Sort UnpER Sop ann UNDER CORN
NITRATES IN Dry Soit, PARTS PER
ILLION
Monta a
Sod Land Corn Land
ee eee ss S| a a ee 8.9 —
i Oe a... Oa aS 3.0 19:1
Sainie 2a LS) Ree es PA 2.4 40.3
TAD) ct sh 1c Ey ca OR 4.0 194.0
PAUIEORG.. “SC ome EE ee as 5.4 186.7
There was more nitrogen contained in the corn crop than
there was in the timothy crop, so that the larger quantity
THE GERM LIFE OF THE SOIL 135
of nitrates in the corn land cannot be attributed to failure
_ of the plants to remove it. Grass appears to have a decidedly
depressing effect on the process of nitrate formation, and
this may be one reason why grass is generally a detriment
to the growth of young orchards.
172. Depths at which nitrate formation takes place. —
It is probable that the processes by which nitrates are formed
are, in humid regions, confined largely to the furrow slice
of soil. Nitrates found below that point have probably
been, in large measure, washed down from above. The sub-
soil in such a region is not a very favorable medium for these
processes. In arid and semi-arid regions, however, the case
is different. Here the distinction between surface soil and
subsoil is not so marked, and owing to the rich and porous
nature of these subsoils nitrification may proceed at con-
siderable depths. }
173. Loss of nitrates in drainage. — It has already been
shown that there is a large removal of nitrates in drainage
water (§ 121). As nitrogen is the most expensive of fer-
tilizer constituents every effort should be made to prevent
this loss. A very effective way to do so is to have a crop
growing on the land during all of the growing season. A
comparison of the loss from the planted and unplanted soil,
in the paragraph referred to, will show how effective a crop
is as a means of preventing loss of nitrates in drainage
water.
Hall states that nitrates formed during the summer or
the autumn of one year are practically all removed from the
soil of the Rothamsted fields before the crops of the following
year have advanced sufficiently to use them.
174. Denitrification. — After nitrates have been formed
by the processes that have just been described, there are
other bacteria or some of the same bacteria acting under
different conditions that attack the nitrates and convert
136 SOILS AND FERTILIZERS
them into other substances. There are three different pro-
cesses and three distinct products that may result. These
are: (1) reduction of nitrates to ammonia; (2) reduction
of nitrates to free nitrogen; (3) conversion of nitrates into
organic nitrogenous substances. All of these fermentations
result in a conversion of the more easily available forms of
nitrogen into less available, and in the case of the production
of free nitrogen there is a loss of nitrogen from the soil, as
the free nitrogen is a gas and passes off into the air.
Most of the bacteria that effect these changes do so only
when there is a limited supply of air, so that a thorough aéra-
tion of the soil practically prevents denitrification. Straw
apparently induces denitrification when conditions are at
all favorable for that process.
The addition of a nitrate fertilizer to ‘a well-drained soil
receiving farm manure is not likely to result in a loss of
nitrates unless the dressing of manure has been extremely
heavy. At the Rothamsted Experiment’ Station, where
large quantities of nitrate of soda are used every year in
connections with annual dressings of farm manure, the nitrate
produces nearly as large an increase when applied to the
manured as when added to the unmanured plat.
Very heavy applications of farm manure, of fifty tons to
the acre or more, may temporarily interfere with formation
of nitrates. The plowing under of large quantities of straw
and even, under some conditions, green-manures may have
this effect.
175. Nitrogen fixation. — Another and very important
bacteriological process is the transfer of nitrogen from the
atmosphere to the soil. This process is termed “ nitrogen
fixation’ and it may occur either with the assistance of higher
plants, or without. The first of these is called nitrogen
fixation through symbiosis with higher plants, the second
nitrogen fixation by soil organisms not associated with plants.
THE GERM LIFE OF THE SOIL 137
The importance of this process to soil productiveness may
be realized when it is considered that nitrogen is the most
expensive of all the ingredients of commercial fertilizers,
and that many pounds to the acre may be secured by en-
couraging the growth of the bacteria concerned in the op-
eration. .
176. Nitrogen fixation through symbiosis with higher
plants. — The value of certain plants as soil improvers has
long been recognized, and within the last half century their
ability to improve soil has been traced to their property of
taking nitrogen from the air and leaving it in the soil. ‘The
plants that do this belong, with a few exceptions, to the
family of legumes.
The method by which nitrogen is transferred from the air
to the soil is not perfectly understood, but it appears to
be somewhat as follows:
On the roots of leguminous plants are found nodules or
tubercles, which are large enough to be seen with the naked
eye, and in which live the bacteria that remove the nitrogen
from the soil air and convert it into nitrogenous organic
matter, that then becomes a part of the host plant. As a
consequence legumes are very rich in nitrogen, and the
tubercles contain an especially large quantity. When the
roots and nodules decay and when the aboveground part of
the plant is plowed under, the nitrogenous matter they con-
tain becomes a part of the soil.
If the nitrogen-fixing bacteria are not present in the soil
or other medium in which the legumes grow, no nodules
will be formed and no atmospheric nitrogen will be fixed.
The plant must then live on the combined nitrogen of the
soil just as other plants do and consequently it does not
serve to increase the store of soil nitrogen. In fact, the
reverse occurs, for on account of the high nitrogen content
of legumes, they withdraw, under these conditions, large
138 SOILS AND FERTILIZERS
quantities of nitrogen from the soil. Even when the nitro-
gen-fixing bacteria are present, leguminous plants may draw
much of their nitrogen from the nitrates in a soil that is
rich in these substances. As a result, less nitrogen is taken
from the air and if the crop is removed the quantity of nitro-
gen remaining in the soil may be no greater than before the
legume was planted.
177. Soil inoculation for legumes. — After it had been
discovered that leguminous plants acted as hosts for bacteria
that draw nitrogen from the soil air, the idea at once pre-
sented itself that soils not containing these bacteria could be
inoculated with them, and thus be made much more suitable
to the growth of legumes. It has been found to be practi-
cable to accomplish this inoculation by spreading on the land
soil from a field on which the kind of legume it is proposed
to plant has grown successfully. The fact that inoculation
by means of soil from other fields may possibly transmit
weed seeds and fungous diseases, and that it also necessitates
the transportation of a great bulk and weight of material has
led to numerous efforts to inoculate soil by means of pure
cultures of bacteria. This has been fairly successful in re-
cent years, but the surest way is by the use of soil. However,
pure cultures may be obtained from most of the agricultural
experiment stations and from the U. 8. Department of Agri-
culture, Washington, D. C.
It must be borne in mind that when soil is used for inocula-
tion it must come from a field that has produced a good crop
of the same kind of legume that is to be planted on the inoc-
ulated field, also that the soil must not be allowed to become
very dry, as that is likely to kill the bacteria. The inoculat-
ing soil is applied after plowing and is harrowed in.
If inoculation is to be successful, the soil on which the
legume is to be planted must be of a nature favorable to the
legume, otherwise growth will not be normal in spite of
THE GERM LIFE OF THE SOIL 139
inoculation. The conditions favorable for legumes are the
same as for most upland crops, namely good drainage and
good tilth, while for red clover, peas or alfalfa the soil should
have an abundant supply of lime.
Not only is the yield of an alfalfa crop greatly increased
by the presence of the nitrogen-fixing organisms and also
ey
Q oo
> 7,
SS ne (Ii At j
& 2 ———" 6 antmal
Peet a A on :
= MTERIIEOTE PRODUCTS .
carbon Hoxide, ete.
Free 77) ven CX fee as * :
D NIT RIFICA SLs
Fig. 25.— The cycle through which nitrogen passes in its movements
among soil, plant, animal and atmosphere. Solid lines in the diagram indi-
cate the usual transformations of nitrogen. Dotted lines indicate the occa-
sional transformations.
of lime, but the percentage of nitrogen that the crop contains
is thereby increased.
178. Nitrogen fixation by free living germs. — In addi-
tion to the nitrogen-fixing bacteria described above, there
exist in many soils germs that are able to take nitrogen from
the atmosphere and convert it into nitrogenous organic mat-
ter without the aid of a host plant. How extensively these
organisms operate is difficult to say. In poor land they are
often effective in recouping the supply of soil nitrogen, but
it is doubtful to what extent they function in rich soil. At
the Rothamsted Experiment Station one of the fields had
been allowed to lie unused for many years because it was too
140 SOILS AND FERTILIZERS
poor to cultivate. It grew up mainly to grass, with a very
few legumes, and in the course of twenty years it had gained
nitrogen at the rate of twenty-five pounds to the acre an-
nually. With the exception of about five pounds to the acre
that was brought down by rain, dust and the like, the accu-
mulation was doubtless due to the free-living germs.
QUESTIONS
1. Explain the difference between the directly injurious and the
indirectly injurious effect of soil germs on plant growth.
2. Are the numbers of bacteria in«soils rather uniform, or do
they vary greatly in different soils ?
Describe the relation of soil bacteria to the air supply.
Their relation to moisture.
Their relation to temperature.
Their relation to organic matter.
Their relation to soil acidity.
Their relation to soil fertility.
. Describe the cycle: through which carbon passes from plant
to soil and back to air again.
10. Explain the fermentation known as ammonification.
11. Describe what is meant by nitrification.
12. How do soils of arid and humid regions differ in respect to
the depths at which nitrate formation occurs ?
13. Why does nitrate formation not take place in early spring ?
14. Describe three fermentations by which the nitrogen of ni-
trates is converted into other forms.
15. Describe the two processes by which atmospheric nitrogen
is fixed in the soil by germs.
16. Describe the cycle through which nitrogen passes frou the
plant to soil and back to plant again.
eee ee So eee ee
LABORATORY EXERCISES
Exercise I. — Test for nitrates in soil.
Materials. — A rich garden loam, a 500 c.c. vessel for mixing
the soil and water, wooden stirrer, funnel and filter paper, hydrate
of lime, water bath, ammonium hydrate solution, evaporating dish,
phenoldisulphonie acid.
THE GERM LIFE OF THE SOIL 141
The phenoldisulphonic acid is prepared as follows: To 37 grams
of concentrated sulphuric acid add 3 grams of pure crystalline phenol.
Heat for six hours in a lightly stoppered flask set in boiling water.
Procedure. — To 50 grams of soil in the 500 c.c. container add
250 c.c. of distilled water. Add 1 gram of hydrate of lime to flocecu-
late the soil. Stir three minutes and allow to stand 20 minutes.
Pipette off 25 or 30 c.c. of the clear supernatant liquid and filter it.
Evaporate 10 c.c. of the filtrate to dryness over a water bath in an
evaporating dish. Moisten with a few drops of phenoldisulphonic
acid and stir well. Allow to stand a few minutes. Dilute with a
few cubic centimeters of water and neutralize with ammonia. The
development of a yellow color is an indication of the presence of
nitrates and its intensity is a measure of the amount.
Exercise II. — Test for ammonia in soil.
Materials. — A small portion of the soil solution obtained in
Exercise I, and Nessler’s solution.
The Nessler’s solution is made as follows: To a 250 e.ce.
solution of potassium iodide (made by dissolving 63 grams in 250
c.c. of ammonia-free water) add a saturated solution of mercuric
chloride until the precipitate nearly all redissolves. *Now add 250
e.c. of a solution of potassium hydrate (150 grams to 250 e.ce. of
water). Make up the whole solution to one liter. Allow to stand
until any precipitate has settled before using. Keep in well-stop-
pered bottle in the dark.
Procedure. — To ten cubic centimeters of the soil extract add a
few cubic centimeters of Nessler’s solution. The development of a
light yellow is an indication of ammonia.
Exercise III. — Factors affecting nitrification.
Materials. — Same as Exercise I plus four 100 ¢c.c. graduated ecyl-
inders. Use moist acid soil from beneath sod.
Procedure. — Place four 50-gram portions of a moist soil from
beneath sod in 8-ounce wide-mouth bottles. Bring soil of bottle:
No. 1 to optimum moisture. Saturate soil of bottle No. 2 to give
poor aération. Thoroughly mix one gram of carbonate of lime to
bottle No. 3 and one gram of lime plus one-tenth gram of ammonium
sulfate with soil of bottle No. 4. Raise both to optimum moisture.
Stopper all bottles lightly with cotton and allow to stand in a warm
room for a week or ten days.
Develop nitrates from these samples as directed in Exercise [.
Pour developed solutions into 100 c.c. graduates and dilute to a con-
142 SOILS AND FERTILIZERS
venient mark. Compare the intensity of color from the various
treatments and explain the results obtained. How may the results
be applied to field practice ?
Exercise IV. — Examination of legume nodules.
Visit fields of red clover,vetch, alfalfa, peas, etc., and with a spade
carefully uproot some of the plants and search for nodules. Note
the number, size and location of the nodules on the various legumes.
If suitable specimens of roots bearing nodules are found it might be
feasible to preserve them for exhibition purposes. They may be
satisfactorily preserved in glass cylinders filled with water to which
a few drops of formalin have been added. The cylinders should be
tightly stoppered to prevent evaporation.
Exercise V. — Examination of nodule bacteria.
If the instructor has an oil immersion microscope available, with
staining mixtures and other facilities for preparing slides of bacteria,
this would be a desirable demonstration. The pupil would then
gain a first hand knowledge of bacteria. Other soil organisms might
also be mounted for class use.
Exercise VI. — Soil inoculation.
If the instructor could arrange in some way to codperate with a
near-by farmer in inoculating his soil by some of the means available
for the purpose, this would be a valuable demonstration for the pupils
to attend. Actually seeing a thing done is worth much more than
mere class room study.
CHAPTER X
SOIL AIR AND SOIL TEMPERATURE
Tue volume of soil air depends on the volume of pore space
that is not filled with water. It is, therefore, evident that
ordinarily the non-capillary or larger spaces are the ones
that contain air. It will be remembered that the most im-
portant conditions that favor a large pore space in soils are:
(1) granular structure, (2) presence of organic matter. In
any soil the pore space may change from time to time with
the structure and the application of organic matter.
179. Soil air contained largely in non-capillary spaces. —
The removal of water allows more space to be filled with
air. Immediately after a heavy rain much of the pore space
of the surface soil is filled with water. After this has had
time to drain away only the capillary spaces remain filled,
but capillary water is lost much more slowly. It is the non-
capillary pore space that, during the greater part of the time,
constitutes the air space of the soil. As a compact condition
of soil results in smaller pore spaces and consequently in
more capillary spaces, it causes a decrease in the volume of
air.
180. There may be too much or too little soil air. — Soil
air is a necessary constituent of a productive soil, as will be
explained later, but it is not always the case that the more
air space in a scil the better it is for crop production. Very
large air spaces, like those found in a cloddy soil, allow the soil
to dry out too readily. Up to a certain limit a good supply
143 |
144 SOILS AND FERTILIZERS
of soil air is desirable, but there can be too much. On the
other hand, there may be too little. It may be assumed
that when a soil is in a compact condition it has an insuffi-
cient supply of air.
181. Movement of soil air. — The rate at which air moves
through a soil depends largely on the size of the pore spaces,
rather than on their aggregate volume. Movement of air
is necessary to ventilate the soil, just as it is to freshen the
air in a house in which many persons live, or a public hall
in which people congregate. Among the factors concerned
with the movement of soil air are (1) movement of water,
(2) diffusion of gases, (8) some minor conditions, like dif-
ferences in temperature between atmospheric air and soil
air, periodic changes in atmospheric pressure and suction
produced by wind.
182. Movement of water.— The movement of soil air
caused by water is probably the most important of any.
When rain falls, the surface soil first receives the water,
which usually fills all of the spaces between the particles.
As the water descends, air is driven from the pore spaces
to make room for the water, the air escaping upward as the
water goes downward, or else being forced out through the
drainage channels below. The movement of air proceeds
to the depth of the water table. Fully one-fourth of the
air in a soil may be forced out by a normal change in the
moisture content of a soil. As the soil dries out air returns.
183. Diffusion of gases. — Owing to the difference in com-
position between the atmospheric air and soil air, there is a
tendency for them to mix, and this process would go on until
the two had the same composition, were it not for the fact
that gases are continually being formed in the soil and thus
prevent the soil from attaining the same composition as the
atmospheric air. The process of diffusion is, therefore, con-
tinuous. :
SOIL AIR AND SOIL TEMPERATURE 145
The rate of diffusion depends on the total volume of the
pore spaces and not on their average size. A soil in good
tilth is therefore in suitable condition for permitting dif-
fusion of atmospheric and soil air.
184. Composition of soil air.— The greater part of the
soil air, like atmospheric air, is composed of nitrogen and
oxygen. The principal difference between soil air and
atmospheric air, in respect to composition, is that the former
contains more moisture and more carbon dioxide. The
moisture comes from evaporation of water in the soil.
The carbon dioxide is produced for the most part by the
germs in the soil and by roots. The following table shows
how soils may vary in their content of carbon dioxide.
TABLE 32.— PERCENTAGE OF CARBON DIOXIDE IN AIR OF DIFFER-
ENT Sorts aT SAME DeEpTH
PERCENTAGE COMPOSITION
CHARACTER OF SOIL
Diowile Oxygen | Nitrogen
Peemawbterilciis, Uw titeries so vraiicse le 0.87 19.61 79.52
RRC fk etree ce wee | OLGB 19.99 79.35
Asparagus bed not manured for one
year 2 A heen ies” ness Sah nae OE a 0.74 19.02 80.24
Asparagus bed freshly manured . . 1.54 18.80 79.66
Sandy soil six days after manuring .| 2.21 -— a
Vegetable mold compost. . . . .| 3.64 16.45 79.91
Soils that are high in organic matter and in which decom-
position goes on readily, usually have a large quantity of
carbon dioxide.
185. Production of carbon dioxide in soils.—It has
already been shown that plant roots give off a considerable
quantity of carbon dioxide throughout the growth of the
L ;
146 SOILS AND FERTILIZERS
plant (§ 126). This, however, does not account for the
gas that is formed in soils on which no plants grow. For
this the germ life of the soilis responsible. These organisms
consume fresh air and give off carbon dioxide in the process
of their growth. In soils that contain a large and active pop-
ulation of microédrganisms there is more carbon dioxide formed
than in a more nearly sterile soil.
It has been estimated that in an acre of ordinary soil to a
depth of four feet the germs produce between sixty-five and
seventy pounds of carbon dioxide a day for two hundred
days in the year, and that, during the growing period, the
roots of oats or wheat would give off nearly as much in an
acre.
186. Conditions that affect the quantity of carbon dioxide
in soils. — As carbon dioxide is heavier than air, the quantity
increases with depth. In warm weather more carbon dioxide
is formed than in cold because the germs are more active.
The soil moisture exerts an influence by furnishing the
necessary moisture for the germs. A very dry or a very
wet soil is not favorable to the production of the gas. More
carbon dioxide is given off by roots during the blossoming
period than at other stages of plant growth, consequently
the carbon dioxide content of soil air is highest about the
time the plants are in blossom.
187. Usefulness of air in soils. — The three gases, oxygen,
nitrogen and carbon dioxide, that go to make up practically
all of the soil air are useful in bringing about those processes
that make soils fertile. Each one of these gases has its
function in contributing to plant growth either directly, or
by taking part in processes that render the soil more habitable
to plants. The functions of each gas will be discussed sep-
arately.
188. Oxygen. — This constituent of soil air serves the
following uses: (1) As a direct food material for plants,
SOIL AIR AND SOIL TEMPERATURE 147
and as a means of promoting in the plant the processes
necessary to its growth. Roots of most crops must have
access to a supply of oxygen.
(2) Decomposition of plant residues and other organic
matter in soils requires the presence of oxygen, and without
decomposition these materials would accumulate in the soil
to the exclusion of higher plant life. Decomposition is
also of use in the production. of carbon dioxide, the function
of which will be discussed later, and in the formation of
compounds of organic matter with mineral matter, decom-
position serves to increase the availability of mineral sub- —
stances (see § 118).
(3) The process by which the nitrogen of organic matter is _
converted into nitrates can proceed only in the presence of
oxygen.
189. Nitrogen. — Although not so essential as oxygen,
there is at least one important service that is rendered by
the nitrogen of soil air. This is to furnish the nitrogen-fixing
organisms with a supply on which they may draw to produce
the nitrogenous compounds that become incorporated in
leguminous plants, or that are formed directly in the soil by
the free-living nitrogen fixers.
190. Carbon dioxide. — The principal service that carbon
dioxide renders is in acting as a solvent for the mineral matter
of the soil. For this purpose it is itself first dissolved in
soil water, in which condition it is a weak acid, but although
weak, its universal presence and constant action make
it an effective solvent. It dissolves from the soil more or
less of all the nutrient substances required by plants in dis-
tinctly greater quantities than does pure water.
A number of experiments in which carbon dioxide was
artificially brought in contact with soil on which plants were
growing have resulted in producing larger crop yields than
were obtained from soil not so treated. It cannot be. con-
148 _ SOILS AND FERTILIZERS
cluded from this that an artificial supply of carbon dioxide
will always be beneficial, but it does indicate that carbon
dioxide assists in making the plant nutrients more available,
although in many soils the natural supply is sufficiert for its
maximum effect.
191. Control of the volume and movement of soil air. —
It will be gathered from the preceding paragraphs that a
good supply of air in soil with opportunity for its exchange
with atmospheric air is desirable for a number of reasons.
These conditions can be controlled by man to some extent.
In fact those operations that usually promote tilth serve at
the same time to effect a desirable condition of the soil with
respect to air. The operations by which man may control
soil air are as follows:
1. Tillage of all kinds, when properly done and at the
right time, increases the volume of air in most soils by help-
ing to form the crumbly structure, and by disposing of
excess water.
2. Both farm manure and lime cause an increase in the
carbon dioxide content of soil air, the former by contribut-
ing organic matter that finally decomposes, the latter by
hastening decomposition processes.
3. Underdrainage by removing water from the pore
spaces increases the volume of air and causes its movement.
4. Cropping produces channels through the soil where
roots have decayed, and these openings, on account of their
large number and ramifications through the soil, aid greatly
in increasing the volume of soil air.
192. Soil temperature. — The temperature of the soil
may influence plant zvrowth both directly and indirectly.
The direct effect is to be found in the plant itself, the roots
of which require a certain degree of heat before they begin
to function. A temperature somewhat above the freezing
point is necessary for this purpose, some common plants
SOIL AIR AND SOIL TEMPERATURE 149
beginning growth slightly above.that point, while others
need several degrees higher temperature. ‘This is also true
of the germination of seeds. The optimum temperatures
for both plants and seeds are considerably higher. A tem-
perature may be reached at which both plant growth and
seed germination may be inhibited, but soils rarely reach
such a degree of heat, except at the immediate surface.
The problem with soils usually consists in bringing them to
a sufficiently high temperature in the spring.
The indirect influence of temperature is exerted through
the germs that affect plant growth. These, like higher
plants, require a certain degree of warmth before growth
begins and a still higher temperature before they reach their
full activity. It often occurs that crop growth is well under
way before the soil is sufficiently warm for germs to function
actively, and consequently growth is checked by the need
of nitrates, which have not been formed in sufficient quantity
on account of the low temperature. This condition is often
demonstrated by the yellow color of the leaves.
193. Sources of soil heat. — The greater part of the heat
that enters the soil comes directly from the sun. The other
possible sources are the organic matter in the soil and heat
from the interior of the earth. Heat produced by the de-
composition of organic matter may sometimes be a factor
when the proportion is large, as is the case in hotbeds and
some gardens, but ordinarily it may be left out of considera-
tion, as may also the heat transmitted from the center of
the earth.
194. Relation of soil temperature to atmospheric tem-
perature. — Changes in temperature of the atmosphere are
transmitted to the soil, although the extremes are never so
great in the soil as in the atmosphere, except at the im-
mediate surface, and the extremes become less as the depth
increases. In summer the temperature of the surface soil is
150 SOILS AND FERTILIZERS
sometimes higher than the average temperature of the at-
mosphere, or even than the maximum air temperature. The
soil below is cooler and continues to decrease in temperature
as the depth increases. For that reason a cellar is usually
cooler in summer than is the outside air. On the other hand,
the soil does not become as cold as does the atmosphere in
winter, and below a few feet, in temperate regions, the soil
does not freeze. The following table gives the mean atmos-
pheric temperatures, and the soil temperatures, at different
depths by months throughout an entire year.
TABLE 33. — AVERAGE MontTHLY TEMPERATURE READINGS TAKEN
AT LINCOLN, NEBRASKA
AVERAGE OF TWELVE YEARS
was 3 Inches | 12 Inches | 36 Inches
Deep Deep Deep
A ELL 2 Se? hh ae 252 27.8 Fi 38.5
Pela ae ise! hi. WS & 24.2 27.3 30.2 35.9
Phim Pee 2 oa ed 35.8 31.2 35.4 30.9
URS Rt dls si ike nee HAs 56.0 49.3 43.8
Sh CN, giled ies «SPR I ae 61.9 67.5 60.7 50.0
Sime eee. Sa Sp 71.0 78.0 69.9 615
el, Mic een sie) eg 76.0 83.6 veanre 67.4
AueteGhe ts Oo 74.5 $1.3 iOuk 69.8
Benpuemimer wares. se 67.6 73.4 69.2 67.6
Octobet ewe wees OT. 55.5 58.4 57.8 61.3
Woyomber Samiagi) fs. 3 38.7 40.9 44.7 62.2
Decent pers. sage se 28.3 31.4 BE Bee 43.3
AVERAGE 1 (ye ia a 50.9 55.3 52.9 52.5
LANGE.) tee eh 51.8 56.3 45.5 34.3
195. Factors that modify soil temperature. — There are
a number of conditions that exert an influence on the tem-
perature of the soil, important among which are (1) the
moisture content, (2) the color of the soil, (3) the slope of
the land.
SOIL AIR AND SOIL TEMPERATURE L5l
A wet soil is always a cold soil, because it requires about
five times as much heat to raise the temperature of a pound
of water through one degree of temperature as it does to
heat a pound of dry soil to the same extent, and also because
when the water becomes warm it evaporates and in so doing
removes much heat from the soil. The evaporation of a
pound of water from a cubic foot of soil will reduce the tem-
perature of the soil about ten degrees Fahrenheit. Provision
for having the water drain away from the land in the spring
rather than evaporate will make a great difference in the
warmth of the soil. A dark soil absorbs more heat than a
light colored one. This is enough to make some practical
difference in a region having a short growing season.
Land that slopes to the south absorbs more heat, in the
North Temperate zone, than does land having any other
slope, and the nearer the slope comes to making a right
angle with the sun’s rays the more heat it will absorb.
An east or west slope receives more heat than does a north
slope. For this reason a north slope is especially favorable
for grass land, because grass is more injured by midsummer
heat than by lack of sunshine.
196. Control of soil temperature.— As water is the
substance in the soil most difficult to heat, it is evident that
good drainage, that will remove the excess water derived
from melted snow and ice, is the most effective means of
warming land in the spring, in order that it shall be fitted
for planting. If water can pass out of the soil by under-
drainage it then becomes desirable to curtail evaporation,
and this may be done by surface tillage. Evaporation of
water removes, as we have seen, large quantities of heat.
If water can be removed in any other way much heat is
saved. In regions having hot spring days the loss by evapo-
ration may be so large that more water is removed than is
desirable and yet the soil may lack the necessary warmth,
152 SOILS AND FERTILIZERS
Sandy soils are less likely to be cold in spring than are
‘elay soils, because the former usually hold water less tena-
ciously. In, vineyards a covering of stones on the soil
has been found to facilitate the warming of the soil in the
spring, but it is doubtful whether, in view of their other dis-
advantages, stones are desirable.
Good tilth is, next to drainage, the best aid to warming soil
in spring, as it allows the water to pass down into the lower
soil and thus decreases evaporation from the surface. Har-
rowing in the spring produces this result, while rolling, by
compacting the surface, increases evaporation and cools the
soul.
QUESTIONS
1. Describe the conditions that govern the volume of air in soils.
2. State the two principal factors that affect the movement
of soil air.
3. How does the composition of soil air differ from that of
atmospheric air ?
4. What are the sources of carbon dioxide in soil air ?
5. What are the functions of the oxygen of soil air ?
6. What are the functions of the nitrogen of soil air ?
7. What are the functions of the carbon dioxide of soil air?
8. In what ways may the volume and movement of soil air
be controlled ?
9. Describe the direct and the indirect effect of temperature
on plant growth.
10. What are the sources of soil heat ?
11. Describe three factors that modify soil temperature.
12. By what means may soil temperature be controlled?
LABORATORY EXERCISE
Exercises I.— Movement of soil air as influenced by texture and
moisture.
Materials. — Dry sand, dry clay loam, 6’ funnels, cotton, aspi-
rating bottles (10 liter).
Procedure. — Place a large funnel through the cork of an aspi-
rating bottle, fill to the mark with water, as shown in Fig. 26.
Place a small piece of cotton in the bottom of the funnel and fill with
SOIL AIR AND SOIL TEMPERATURE 153
a definite volume of sand. Now start as-
piration by opening the water-cock of the
bottle. When aspiration has become con-
stant, note time necessary to draw one liter
of air through the sand.
Using clay loam in place of sand, run
the experiment again, bringing the water in
the aspirating bottle up to its original mark
before starting. The time necessary to pull
a liter of air through each soil serves as a
measure of the comparative rate of possible
air movement through them.
Without removing the clay loam from the
funnel, add enough water to bring it to
optimum moisture condition. Repeat the
test above. Explain results. Fic. 26.— Apparatus
for studying the relative
rate of air movement
Exercise II. — The presence of carbon
dioxide in soil air. through soils. (A) soilin
Materials. — Box of rich soil in good mois- funnel, (B) cotton sup-
ture condition, flask, limewater, tubes. port, (C) aspirating bot-
Procedure. — Equip a flask or bottle as tle, (D) water.
shown in Fig. 27 so that air from the soil may be sucked into the
limewater. The turbidity of the limewater indicates the presence
of carbon dioxide.
Tube for wilhdrawing
YX soll air
Wicks
12a
Coarse cae
Fic. 27. — Apparatus prepared for the demonstration of the presence of
carbon dioxide in soil air.
154 SOILS AND FERTILIZERS
First pull atmospheric air into the limewater for five minutes.
Note results. Now connect flask to tube extending into the soil and
draw in soil air. What conclusions do you come to regarding the
relative carbon dioxide content of soil air and atmospheric air ?
What is the function of carbon dioxide in the soil ?
Exercise III. — Production of carbon dioxide by bacteria.
Materials. — Flask, limewater and moist
rich soil.
Procedure. — Place a small amount of
limewater in a flask and then suspend in
the flask over the limewater a bag of rich,
moist soil. Stopper tightly and allow to
stand fora week. Note the turbidity of the
limewater. Explain the results.
Exercise [V.— Temperature and color.
Materials. — Coal dust and a hy-
drate. Thermometers.
Procedure. — Divide a small plat of
smooth, level soil into three portions.
Fic. 28. — Production Leave one part untouched, cover one witha
of carbon dioxide by thin coating of coal dust and the other with
Fe mA ak tei a coating of calcium hydrate. On a warm,
Sere limewater, (C) Sunny afternoon take the temperatures of
small bag containing each at one, three and six inches deep.
moist soil suspendedfrom Tabulate and give a practical explanation
stopper, (D) limewater. oF the data obtained.
Exercise V.— Slope and temperature.
Materials. — Thermometers.
Procedure. — On a warm, sunny day take temperature at one,
three and six inch depths on a south slope, north slope and level
land, being careful to select for the observations soils having the
same texture and moisture contents. Tabulate data and explain
the practical relationships between temperature and slope of land.
Exercise VI. — Drainage and temperature.
Materials. — Soil, two jars, thermometer.
Procedure. — Prepare two large jars of moist soil. Stir one until
two or three inches of the top soilis dry. Add water to the other
until it is saturated. Set these jars of soil in the sunshine out of
doors on a warm day. After two hours take the temperaturé of
the two soils at one inch and three inchesin depth. Tabulate data.
CHAPTER XI
NITROGENOUS FERTILIZERS
WE have seen that nitrogen exists in soils in several differ-
ent forms, as organic matter, ammonia and nitrates, and that
it may be transformed from one to another of these, depend-
ing on the conditions that obtain in the soil itself. Ferti-
lizers used for their nitrogen may have this nitrogen present
in any one or more of these forms, and when incorporated
with the soil, transformation will proceed according to the
same laws that govern the soil nitrogen. This is important
because nitrogen is more readily used by crops in some
forms than in others.
197. Relative quantities of the different forms of nitrogen
in soils. — One would naturally expect to find the greater
part of the supply of soil nitrogen in the most stable forms,
and this is, in fact, the case. The uncombined nitrogen of the
air constitutes the largest supply because of its diffusibility
with the atmospheric air. Next in quantity is the nitrogen
of organic compounds, ranging from 0.05 to 0.3 percent or
1000 pounds to 6000 pounds to the acre in the furrow slice
of ordinary arable land and slightly, but appreciably, soluble
in water. In upland cultivated soils the nitrogen of nitrate
salts forms the next largest supply, but rarely exceeds 20
percent of the total combined nitrogen of the soil.
In inundated soils, the nitrogen of ammonia salts and
nitrites forms a larger proportion of the soil nitrogen than
does the nitrate nitrogen, but in well-aérated soils these com-
pounds exist in very small quantities.
155
156 SOILS AND FERTILIZERS
198. Forms in which nitrogen is absorbed by plants. —
The utilization of atmospheric nitrogen by leguminous plants
and by a few others that have nodule-bearing roots has been
established beyond question; but the extent to which this
form of nitrogen may be utilized by other plants, or the kinds
of plants that have the ability to use it, are subjects on which -
opinions differ. It is sufficient to say that such plants as
red clover, alfalfa, peas, beans, vetch, and so on, are able to
use atmospheric nitrogen. It must be remembered, however,
that they also use nitrogen that is in the soil itself and that
they may remove large quantities of this material.
199. Nitrates as plant-food material.— Most upland
plants used in agriculture appear to absorb most of their
nitrogen in the form of nitrates. This it will be remem-
bered is the final form in which nitrogen appears when ni-»
trogenous substances undergo normal decomposition in soil.
The nitrogen of the various nitrogen carrying fertilizers is
finally converted into nitrate in the soil.
200. Absorption of ammonia by agricultural plants. —
Ammonia is rarely found in soils, except when they are
saturated with water. Plants like rice, that grow on water-
covered soil, can utilize ammonia ; in fact, rice has been found
to make a better growth on ammonium compounds than on
nitrates. This is a case in which the plant has evidently
adapted itself to its surroundings, for upland rice presumably
uses nitrate nitrogen. However, some dry land plants can
also use ammonia. It. has been found, for instance, that
peas obtained nitrogen as readily from ammonium salts as
from sodium nitrate. On the other hand wheat plants, while
able to secure some nitrogen from ammonia, have been found
to grow much better when they could obtain nitrates.
201. Direct utilization of organic nitrogen by crops. —
One of the early beliefs in regard to plant nutrition was
that organic matter was directly absorbed by plants and that
7
i
t
ad TO iy
FERTILIZER TESTS. — Some soils. respond best to one
PuLatTEe XII.
fertilizer constituent
In the
ote that the best growth of
lower figure the best growth is in the vessel that received phosphoric acid.
N
others to another.
oats in the upper figure is in the vessels that received nitrogen.
’
NITROGENOUS FERTILIZERS 15?
it furnished their chief supply of food. Opinion afterwards
swung to the opposite extreme, and it was generally held
that no organic matter is absorbed by agricultural plants.
Lately, however, it has been shown that many crops can use
nitrogenous organic matter, and an organic compound called
creatinin, that has been isolated from soil, was found to
produce a better growth of wheat seedlings than did sodium
nitrate. This may account in part for the high fertilizing
value of farm manure. Many crops, especially among
garden vegetables, are most successfully grown only when
supplied with organic nitrogenous materials.
202. Forms of nitrogen in fertilizers. — There are many
different kinds of material used to provide nitrogen in com-
mercial fertilizers. Their value varies considerably, because
the nitrogen in some is not so readily available as it is in others.
In some the nitrogen is in the form of nitrate, in others am-
monia, but most of the mixed fertilizers contain some or all
of their nitrogen in the form of organic matter.
203. Nitrate of soda. — This material is found in natural
deposits in northern Chili, where it is mined in enormous
quantities and shipped to most of the European countries
and to the United States. It is refined before shipment,
reaching this country nearly 96 percent pure. Between 15
and 16 percent of the total material is nitrogen. The im-
purities are not of a kind to be injurious to plants.
This fertilizer is easily soluble in water and is readily ab-
sorbed by most farm crops. It is the most active form of
nitrogen. Because it does not need to be acted on by soil
organisms before being used by plants, it is of great value in
starting growth in the early spring, before the soil is warm
enough to cause a conversion of the nitrogen of soil organic
matter, or of farm manure into nitrates. It will be remem-
bered that nitrates are largely washed out of the soil during
the fall and winter and that there is not usually enough
158 SOILS AND FERTILIZERS
of this form of nitrogen to start plant growth early in the
spring.
204. Crops markedly benefited by nitrates. — Winter
grain 1s usually benefited by an application of 25 to. 50
pounds to the acre of nitrate of soda about the time that
growth begins in the spring. The phosphoric acid and potash
fertilizers may be applied in the fall.
Timothy meadow responds wonderfully to a top dressing
of nitrate when the plants first show signs of life. Not only
is the yield of hay increased, but the sod is thickened, which
increases its value as a manure for succeeding crops. Phos-
phoric acid and potash fertilizers should be applied at the
same time. The following table shows the increased yield
of hay and succeeding grain crops obtained from applications
of nitrate fertilizer applied only to the grass crops. Note
the increased yield of hay and grain from larger applications
of nitrate when the other fertilizers are not increased, and
also the striking effect of the better sod on the yield of corn,
which crop was not fertilized. This offers a rational method
for producing organic manure from mineral fertilizers.
TABLE 34. — YIELDS oF Hay AND GRAIN ON UNFERTILIZED SOIL
AND ON Soiu FERTILIZED FOR Hay BUT NOT FOR GRAIN
| YIELDS OF CROPS PER ACRE
Pounpbs FERTILIZER PER ACRE
BS a? Corn Oats | Wheat
720 | No fertilizer PPA Mm (ode: Sig es sy Sd) es oe
160 lbs. nitrate of soda
80 lbs. muriate of potash
320 lbs. acid phosphate
320 lbs. nitrate of soda
80 lbs. muriate of potash
320 Ibs. acid phosphate |
726 | No fertilizer DC rem mmm nk 7905 0 5-7: Bat ee
NITROGENOUS FERTILIZERS 159
By the time the wheat crop was raised the beneficial effect
of the timothy sod had disappeared.
Many kinds of garden vegetables must have a rapid
growth in order to have the succulence upon which their
value largely depends. To secure this quick growth nitrate
of soda gives an excellent form of nitrogen on account of its
ready availability. As previously noted, however, it is not
an adequate substitute for organic nitrogen for all kinds of
garden crops.
205. Effect of nitrate of soda on soils. — Nitrates are
easily leached from soils, and for that reason nitrate of soda
should not be applied in the autumn as it will be lost, in large
part, during the fall and winter. Even when applied pre-
paratory to planting, it should not be used in excessive quan-
tities at one time, but if large applications are necessary
apply part after the plants have made some growth.
It has been found that the continued and abundant use of
nitrate of soda causes some soils to become deflocculated,
resulting in a puddled condition when the soil is worked wet
and a cloddy condition when dry. This, however, is not
likely to occur with any ordinary use of the fertilizer. On
acid soils it serves a double purpose, for it tends to correct
acidity.
206. Sulfate of ammonia. — The source of supply of this
fertilizer is coal, which when distilled, as is done in the man-
ufacture of illuminating gas, or in the production of coke,
yields among other products ammonia from which sulfate
of ammonia is made. The industry has grown enormously
in recent years, but has by no means reached its maximum,
as of the hundreds of thousands of tons of coal burned an-
nually for the manufacture of coke in this country barely
more than one-half is used for the production of ammonia.
There are still great possibilities for obtaining nitrogen from
this source. :
160 SOILS AND FERTILIZERS
207. Composition of sulfate of ammonia. — There is more
nitrogen in a ton of this fertilizer than in any other. The
commercial material usually contains about 20 percent of
nitrogen, which is from eighty to one hundred pounds more
than is contained in a ton of nitrate of soda. It is easily
soluble in water, but when applied to soils the ammonia is
absorbed, and probably very little of it is taken up directly
by plants. On the other hand, the absorbed ammonia
nitrifies readily, especially if there is plenty of lime in the
soil, and the nitrates thus formed may readily be used by
plants.
208. Action when applied to soils. — A pound of nitrogen
in the form of sulfate of ammonia has slightly less value than
the same quantity in the form of nitrate. If the soil to which
it is applied is in need of lime, the value of the fertilizer will
be less than if sufficient lime be present. It also tends to
make a soil acid when used in large quantities for a long
period. These two facts make it apparent that lime should
be abundantly supplied to soils on which this fertilizer is
used. Lime, whether it is applied to the soil or is naturally
present, serves to neutralize the acid formed when the am-
monia is converted into nitric acid by soil bacteria, which is
the process by which nitrates are formed, and also to neutral-
ize the sulfuric acid left in the soil when the ammonia is
changed by this process. |
The nitrates resulting from the fermentation of sulfate of
ammonia are quickly leached out of the soil when no plants
are growing on it; therefore sulfate of ammonia should not
be applied at that time. In England the following losses
of nitrogen occurred from plats on which nitrate and am-
monium salts were used, and on which crops were grown.
The term ‘‘ minerals ”’ is here used to mean phosphoric acid
and potash fertilizers.
NITROGENOUS FERTILIZERS 161
TABLE 35.— Pounps or NITROGEN IN DRAINAGE WATER FROM
Soin TREATED wiITH NITRATE AND AMMONIA FERTILIZERS
1879-1880 1880-1881
TREATMENT Spring | Harvest| Spring | Harvest
Sowing to Sowing to
to Spring to Spring
Harvest | Sowing | Harvest | Sowing
Unmanured , ft AA iat Peas Aa 10.8 0.6 174
Mineral fertilizers only. EES 1.6 13.3 0.7 Lie
Minerals + 400 pounds ammonium
Salts) 9% 18.3 12.6 4.3 21.4
Minerals + 550 pounds Ae of
soda... . SO) 15.6 15.0 41.0
Minerals + 400 puande ammonium
salts applied in autumn... 9.6 {| 59.9 3.4 | 74.9
400 pounds ammonium salts alone. | 42.9 | 14.3 1,4, 8D2
400 pounds ammonium salts + sul-
PaenevOr potash ese | A OL ot |} oe
Estimated drainage in inches . .. 11.1°'| 4.7 | 1.8 | 188
These figures show a very considerable loss of nitrogen
from the nitrogen-fertilized plats, with a somewhat greater
loss from the nitrate-treated plats than from those receiv-
ing ammonia. Neither of these fertilizers is well designed
to add to the total supply of nitrogen in the soil, for which
purpose a less easily nitrifiable fertilizer must be used.
209. Cyanamid. —- Within recent years it has been found
possible to take nitrogen from the atmosphere and combine
it with lime for use as a fertilizer. Two different materials
are manufactured. One is called cyanamid, the other
nitrate of lime. Both are produced by the use of powerful
currents of electricity, but the processes are essentially dif-
ferent and only the cyanamid is now being manufactured in
the United States, and it alone will be discussed in this book.
210. Composition of cyanamid. — The word cyanamid is
M
162 SOILS AND FERTILIZERS
merely a trade name. Another name that has been used is
lime nitrogen. The latter is good because it emphasizes the
fact that the fertilizer contains lime, which is a point in its”
favor, as the lime helps to overcome soil acidity. There is
about 26 percent of caustic lime in the fertilizer. How-
ever, in the quantities in which fertilizers are used the
sweetening effect of the lime would not go very far. The
fertilizer usually contains between 15 and 16 percent of nitro-
gen, which puts it on a par with nitrate of soda in this
respect.
211. Changes in the scil.— Cyanamid must be decom-
posed in the soil before its nitrogen becomes available to
plants. It is, therefore, not as rapid in its effects as is nitrate
of soda, but resembles sulfate of ammonia in this respect.
Under some conditions products may be formed during its
decomposition that are more or less injurious to plants.
This is said to be true when the fertilizer is incorporated
with water saturated soil or very acid soil. As decomposi-
tion proceeds these injurious substances are destroyed. In
order to be sure that no injury will be done to plants, cyan-
amid should be applied at least a week before planting.
It is not well adapted to use on very sandy soils, nor does
it give its best results when used as a top dressing, as it re-
quires incorporation with the soil for its proper decomposi-
tion. Ordinarily its fertilizing value is not greatly below that
of sodium nitrate, and is about equal to that of sulfate of
ammonia.
212. Fertilizers containing organic nitrogen. — There are
a great many materials containing organic nitrogen that
are used as fertilizers. As many of them are of little or no
value for other purposes they would be wasted if not used to
benefit the land. There is very great diversity as to their
fertilizer value, but in general the availability of the nitrogen
to plants is less than that of nitrate of soda. In order that |
NITROGENOUS FERTILIZERS 163
their nitrogen shall become available, the substances them-
selves must decompose in the soil, the nitrogen undergoing
the usual transformations.
Many of the organic fertilizers contain phosphoric acid,
or potash, or both. These ingredients add to the value of
the fertilizer. They will be discussed under the heads of
(1) vegetable products, (2) animal products, (8) guano.
213. Vegetable products. — Among these are cottonseed
meal, linseed meal and castor pomace together with other
materials that are less used and that will not be discussed
here.
The meals here mentioned are primarily stock-foods and
are more profitably fed to live-stock, the resulting manure
being applied to the soil, than used directly as fertilizer.
Nevertheless, cottonseed meal is used extensively as a fer-
tilizer and linseed meal to a less extent. The former is much
used for tobacco of better grades and as a top dressing for
lawn grasses, as 1t does not have the offensive odor that char-
acterizes many of the organic fertilizers.
Cottonseed meal contains between 6 and 7 percent of nitro-
gen when free from hulls, and 4 percent when these are pres-
ent. It also contains about 2.5 percent of phosphoric acid
and 1.5 percent of potash.
Linseed meal contains about 5.5 percent of nitrogen, and
_ between | and 2 percent of phosphoric acid and of potash.
Castor pomace, which is the residue after the extraction
_ of castor oil from the beans, has a nitrogen content of between
5.5 and 6 percent, and a rather variable amount of phos-
phoric acid and potash.
214. Animal products. — These include the slaughter house
products among which are red dried blood, with about 13
percent of nitrogen; black dried blood, with 6 to 12 percent
nitrogen; dried meat and hoof-meal, with 12 to 13 percent
nitrogen; tankage, of which the concentrated product has
164 SOILS AND FERTILIZERS
a nitrogen content of from 10 to 12 percent, and crushed
tankage, that has from 4 to 9 percent nitrogen. Leather
meal and wool and hair waste may also be mentioned but
they have only a small fertilizer value. Ground fish or fish
waste is also sold as a fertilizer and usually contains about
8 percent of nitrogen.
Dried blood is the most readily decomposed of these
products, and its nitrogen is in the most available form.
It also contains a small quantity of phosphoric acid. It is
slower in its action than either nitrate of soda or sulfate of
ammonia. With this, as with all the animal products, the
soil should be in a condition favorable to decomposition of
organic matter and to the formation of nitrates.
Dried meat contains a high percentage of nitrogen, but
does not decompose so easily as does dried blood, and is not so
desirable a form of nitrogen. It may be fed to hogs or poultry
to advantage, and the resulting manure is very high in nitro-
gen.
Hoof-and-horn meal is high in nitrogen, but decomposes
slowly. Its nitrogen is less active than dried blood or meat.
It is useful to increase the store of nitrogen in a depleted soil.
Tankage is highly variable in composition. The concen-
trated tankage, being more finely ground, undergoes more
readily the decomposition necessary for the utilization of its
nitrogen.
. Leather meal and wool and hair waste when watnehel
are in such a tough and undecomposable condition that they
may remain in the soil for years without losing their structure.
They are not to be recommended as manures.
215. Fish waste. — The material sold under this name is
usually waste from canning factories, and consists of the
heads, tails, bones, entrails and all other discarded portions
of the fish that are canned. As a fertilizer it acts very slowly
and is not at all adapted to crops that make their growth in
NITROGENOUS FERTILIZERS 165
the early spring. It is better adapted to sandy soils than to
heavy ones.
216. Guano. — This was formerly a very important fer-
tilizing material, but there is comparatively little of it im-
ported into this country at present, because the world’s
supply is nearly exhausted. It consists of the excrement and
carcasses of sea fowl. The composition of guano depends
on the climate of the region in which it isfound. Guano from
an arid region contains much more nitrogen and potash than
that from a region of more rainfall, because these constituents
hagre been leached out of the latter. All of the plant-food
materials contained in guano are in a readily available con-
dition, and its fertilizing value is high.
217. Effects of nitrogen on plant growth. — The all impor-
tant part that nitrogen plays in plant growth is that of an
indispensable constituent of protein, which is the basic sub-
stance in every cell of every plant. It is therefore concerned
in the formation of every part of the plant. If the supply
of nitrogen is inadequate, the effect is to decrease the yield
of the crop, especially the leaves, stems, stalks or straw,
while the quantity of grain produced is not curtailed to the
same extent. On the other hand, an excess of available nitro-
gen causes an abundant growth of the vegetative parts of the
plant rather than of the seed or grain. As a result, in
cereals the straw becomes so long and weak that the plants
fall down or ‘“ lodge.’’ Grass crops are less likely to suffer
from an excess of nitrogen than are cereals, and nitrogen
is particularly beneficial to the grasses. Many vegetables
that are grown for their vegetative parts can utilize to good
advantage a large quantity of nitrogen. If nitrogen is not
present in sufficient quantity for cereals, the kernels are
shriveled and light. There can be no doubt that the lack of a
readily available supply of nitrogen at critical periods in the
growth of plants is a frequent cause of curtailed crop yields.
166 SOILS AND FERTILIZERS
Another effect of excess nitrogen supply is to delay the
ripening of crops. This is often seen in orchards that receive
clean cultivation throughout the summer. The large supply
of nitrogen thus made available, as well as the moisture re-
tained in the soil, serves to retard ripening and the immature
wood is likely to be injured by winter temperatures. In
regions having short, but usually hot seasons, cereals are
sometimes delayed in ripening until injured by frost.
Sometimes the quality of crops may be injured by an ex-
cess of nitrogen. Barley deteriorates in its malting qualities,
and peaches in flavor when too much nitrogen is supplieds
The percentage of nitrogen may be increased in some crops
by supplying a large quantity of available nitrogen. Tim-
othy hay responds in this way, as do many vegetables, and the
straw and even the grain of cereals.
Resistance to disease is often decreased when nitrogen is
abundant. ‘This is familiarly exhibited in the ease with which
a crop of wheat or oats on very rich soil will succumb to rust.
There are numerous cases of this kind, probably due to a
change in the physiological resistance of the plant to the
diseases to which it is exposed.
218. Availability of nitrogenous fertilizers. — It has been
pointed out that nitrates are the form in which nitrogen is
most acceptable to the larger number of agricultural plants,
and this being the case fertilizers having nitrates offer a very
readily available form of nitrogen. Ammonium salts not
being so readily appropriated by most plants require at
least partial conversion into nitrates. Ammonia is ab-
sorbed by soil, but in its absorbed condition readily
undergoes nitrification. However, there is apparently some
loss or conversion into an insoluble condition, for experiments
have generally shown that there is rarely quite as much nitro-
gen recovered by crops from sulfate of ammonia as from ni-
trate of soda. The organic nitrogenous fertilizers must un-
NITROGENOUS FERTILIZERS 167
dergo ammonification and nitrification in the soil. Some
of them decompose much more readily than others.
In order to ascertain the relative degree of availability of
the nitrogenous fertilizers, experiments have been conducted
by numerous investigators in which they have used one of
these fertilizers on one or more plats of land, or in one or more
vessels of soil, and other nitrogenous fertilizers in a similar
way. It is, of course, always necessary that there shall be
an abundance of all the other plant-food materials. These
experiments were repeated for several years with different
crops, at the end of which time a comparison was made of the
yields of the crops on the soil treated with the different fer-
tilizers. In Table 36 the results of some of these experiments
are stated, with the yields obtained with nitrate of soda
taken as 100 in each case.
TABLE 36. — RELATIVE EFFECTIVENESS OF NITROGENOUS FERTI-
LIZERS
W AGNER JOHNSON | VOORHEES
NITROGEN CARRIERS AND AND AND
DorscH# OTHERS LIPMAN
es, GL. Sta 22 oh SES! Ue, 100 100 100
Saline, animonias See oo al). 90 79
ies, Ost sien ig) 7. 70 3 64
rms thea © pitta! Lyehih es ei cidette cg [is 60 LZ
Sa STO a a ee a a 45 53
ASS ES Eee eee eee er a 49
Horn-and-hook meal: . ...... 70 68
Dyn) 03's WWirra= -4/G 2 Sr aati tai 69 x
SntoHiseed tesle es 5 ee ke 65
ete OMA nels (ep ah oe 65
era 5 ethene te ef.) Sein 30
See ES ATO. Lee eee cd ea 20
Wireeeroune eh ov ek ek ve 64
While these experiments are helpful in giving an idea
of the relative values of these fertilizers, they do not necessa-
168 SOILS AND FERTILIZERS
rily hold for every soil. It will be noticed that there is con-
siderable discrepancy in these results, but that is always to
be expected. A fertilizer may have a more rapid rate of am-
monification or nitrification than another fertilizer in one
soil and less rapid in another soil.
219. Relative values of organic and inorganic nitrogenous |
fertilizers. — In the experiments cited the organic fertilizers
were, in every case, less effective than the inorganic ones.
However, the cost of a pound of nitrogen is generally more in
the better class of organic fertilizers, like dried blood, than it
is in the inorganic fertilizers, like nitrate of soda and sulfate
of ammonia. This may be because of the demand of fer-
tilizer manufacturers for a dry material for their goods, but
the beneficial effect of the organic matter it contains may
also be a factor in creating the demand for dried blood.
QUESTIONS
1. Name the forms in which nitrogen occurs in soils.
2. State what forms of nitrogen are absorbed by crops, and what
differences exist between plants in this respect.
3. Name the fertilizer materials that contain nitrogen, and spec-
ify the form in which nitrogen occurs in each.
4. What crops are particularly benefited by nitrate fertilizers?
5. How is the nitrogen of nitrate and ammonia fertilizers likely
to be lost from soils, especially if no crop is on the land?
6. How may danger arising from formation of poisonous products
in the decomposition of cyanamid be avoided ?
7. Describe the effects of nitrogen on plant growth.
8.° State the order of availability of nitrogen in nitrate of soda,
sulfate of ammonia and dried blood.
LABORATORY EXERCISES
Exercise I. — In Exercise V, Chapter I, an experiment designed
to show the importance of the plant-food materials to plant growth
was described. If this test has been properly conducted the infiu-
ence of nitrogen upon plant growth will be clearly shown.
NITROGENOUS FERTILIZERS 169
Exercise II. — Examination and identification of nitrogen
fertilizers.
Materials. — Set of fertilizers (comprising sodium nitrate, am-
monium sulfate, cyanamid, dried blood and tankage), evaporating
dish, phenoldisulphonie acid, ammonia, funnel and filter paper,
litmus paper, hand lens, flame.
Procedure. — It is well for the student to be able to identify
the common fertilizers and to know a few practical tests when the
identity is in doubt. The following outline is given with this end
in view.
Sodium Nitrate
This fertilizer appears in clouded light yellowish crystals, soluble
in water and rather deliquescent. It has no marked odor.
Hold a erystal in the flame. Note the brilliant yellow color.
This is a test for the element sodium.
Test for the nitrate part of the fertilizer by moistening a crystal
in an evaporating dish with a drop of phenoldisulphonie acid.
Allow to stand a few minutes and then dissolve in a little water.
Now neutralize with ammonia and obtain the yellow color charac-
teristic of nitrates.
Ammonium Sulfate
This fertilizer is a light grayish colored salt, finely ground and
soluble in water. Heat a little in an evaporating dish and note the
odor of ammonia. ;
Cyanamid
Cyanamid is a fine, dry, black powder which carries besides its
nitrogen compound, carbon and lime. The carbon may be tested
for by rubbing the fertilizer between the fingers. Dissolve as much
of the fertilizer as possible in water, filter and test the filtrate with
litmus paper. It should be intensely alkaline on account of the
lime it contains. The physical characters of the fertilizer are such
as to make it easily recognized.
Dried Blood and Tankage
These materials can be easily identified and distinguished by
their physical properties, especially if a hand lens is used. Consid-
erable hair and bone is likely to be found in tankage. The odor of
both is characteristic. Study each fertilizer until identification is
easy.
170 SOILS AND FERTILIZERS
Exercise III. — Comparison of fertilizer effects on plant
growth.
Materials. — Fertilizers, flower pots, poor sandy soil, oat seed.
Procedure. — It may be of advantage to compare two or more
of the nitrogen fertilizers with reference to their effect on plant
growth. Fill flower pots with the same amount of a poor
sandy loam after thoroughly mixing the fertilizer with the soil.
Apply nitrogen fertilizers at the rate of 250 pounds per acre (1 of
fertilizer to 10,000 of soil). Alsoadd at the same time acid phosphate
and muriate of potash at the rate of 1 to 5000 of soil respectively. ©
One gram of lime per pot is also necessary. Leave one pot untreated
with the nitrogen fertilizers as a check. Now plant oat seeds and
bring the soil to optimum moisture content. When seedlings are
a week old thin to proper number. Keep pots in suitable place and
observe relative development of the plants under the different treat-
ments.
~
CHAPTER XII
PHOSPHORIC ACID FERTILIZERS -
FERTILIZERS commonly used in this country for their phos-
phorie acid may be divided into two classes, natural phos-
phate fertilizers and acid phosphate fertilizers. The former
are in the condition in which they are found in nature, and —
are very difficultly soluble. The latter are merely the phos-
phate fertilizers that have been treated with strong acid,
after which process they are readily available to plants.
There is an intermediate form present in basic slag, which is
not quite so available as the acid phosphate, but more
readily available than the natural phosphate fertilizers.
Natural phosphates, when in organic compounds, like bone,
are more readily available than when in purely -inorganic
compounds, like rock.
220. Bone phosphate. — Most of the bone now used in
fertilizers has been steamed or boiled, which removes the fat,
and also the nitrogen that fresh bones contain. Fresh bones
have a content of about 22 percent phosphoric acid and
4 percent nitrogen. Steamed bones have from 28 to 30 per-
cent phosphoric acid and 1.5 percent nitrogen. Bone tankage,
which has already been spoken of as a nitrogenous fertilizer,
contains from 7 to 9 percent of phosphoric acid. Bone should
always be finely ground, as it is then more readily available.
It is a slow acting form of phosphoric acid.
221. Mineral phosphates. — These are found as natural
deposits of rock in various parts of the world, some of the
ize
Via SOILS AND FERTILIZERS
most extensive being in the United States. When ground
these are often called ‘ floats.”” South Carolina phosphate
contains from 26 to 28 percent of phosphoric acid. Florida
phosphate exists in the forms of soft phosphate, pebble phos-
phate and boulder phosphate. Soft phosphate contains from
18 to 30 percent phosphoric acid, and because of its being —
more easily ground than most of these rocks it is often applied
to the land without being first converted into an acid phos-
phate. The other two forms, pebble phosphate and boulder
phosphate, are highly variable in composition, varying from
20 to 40 percent in phosphoric acid content.
Tennessee phosphate contains from 30 to 35 percent of phos-
phoric acid. In addition to these deposits, which have been
extensively mined since their discovery, there have been found
much larger deposits in the states of Idaho, Wyoming and
Montana, but these have not yet been worked.
Apatite and coprolites are other forms of natural phosphate
that are used as fertilizers. The former is found in Canada
and the latter in England and France. They are not of much
importance in the fertilizer business of this country.
222. Basic slag. — This is also called Thomas phosphate.
It is a by-product in the manufacture of steel from pig iron
rich in phosphorus. The phosphoric acid in this material is
more readily available than that in the mineral phosphates,
and when used as a fertilizer it does not require treatment
with acid. It should be finely ground. It is not extensively
used in the United States.
223. Acid phosphate. — The very difficultly soluble phos-
phates may be rendered more easily soluble by treatment
with sulfuric acid. The product is called acid phosphate.
When applied to soils it is much more available to plants
than are any of the natural phosphates. Acid phosphates
contain gypsum or land plaster as well as phosphoric acid.
The proportion of the total quantity of phosphoric acid
PHOSPHORIC ACID FERTILIZERS 4173
originally present that is rendered soluble depends on the
quantity of sulfuric acid added. In practice there is usually
part of the phosphoric acid that is left in an insoluble form.
224. Composition of acid phosphate. — Acid phosphate
made from animal bone is called dissolved bone and contains
about 12 percent of available and from 3 to 4 percent of
insoluble phosphoric acid. It also contains some nitrogen.
When made from South Carolina rock, acid phosphate con-
tains from 12 to 14 percent of available phosphoric acid,
including from 1 to 3 percent of what is called reverted
phosphoric acid. The best Florida acid phosphate contains
as high as 17 percent, and the Tennessee acid phosphate 14
to 18 percent of available phosphoric acid.
225. Reverted phosphoric acid.—- A change sometimes
occurs in acid phosphate on standing, by which some of the
phosphoric acid becomes less easily soluble, and to that extent
the value of the fertilizer is lessened. This change is known
as reversion. It is much more likely to occur in acid phos-
phate made from rock than in that made from bone. The
quality of the material affects this change. The presence of
iron and aluminum is supposed to increase reversion. Re-
verted phosphoric acid is probably not so available as the
original acid phosphate.
226. Absorption of acid phosphate by soil. — Like many
soluble substances acid phosphate, when applied to soil,
is in part absorbed and held in a form in which it will not be
leached out by the drainage water, but on the other hand,
remains in a condition in which it is available to plants.
Part of the soluble phosphoric acid may unite with iron or
aluminum in the soil to form insoluble combinations. The
richer a soil is in lime the less is the danger of forming these
insoluble combinations. The availability of acid phosphate
may continue for a second year, or even longer, after being
applied to the soil.
174 SOILS AND FERTILIZERS
227. Relative availability of phosphoric acid fertilizers.
— The availability of these fertilizers has been casually men-
tioned as each was discussed, but a brief résumé will serve
to make the matter more definite. Acid phosphate, including
dissolved bone, is the most readily available of the phos-
phoric acid fertilizers. The reverted portion is more or less
available, depending on the character of the original rock,
and on the kind of soil to which it is applied. It is not as
valuable as the soluble phosphoric acid. The insoluble por-
tion has no greater availability than the rock from which the
acid phosphate was made.
Next to acid phosphate in availability comes basic slag,
then steamed bone and finally the rock phosphates.
Acid phosphate and basic slag may be used for top dressing
grass or winter grains, but the other fertilizers must be in-
corporated in the soil in order to become available. It is
necessary that they shall be acted on by the soil water having
carbon dioxide in solution and possibly by other acids formed
by the decomposition of organic matter.
228. Rock phosphate versus acid phosphate. — The ques-
tion has frequently been raised in the last few years regarding
the use of ground rock phosphate or floats as a substitute for
acid phosphate. Which of these practices is the better must
be largely determined by practical experiment, and by a study
of the conditions under which floats become available.
It is urged in favor of floats that the price of phosphoric acid
is much less in this form than in the form of acid phosphate,
which is made by a more or less expensive process. It is
further argued that even if much more material must be used
in order to get a pound of available phosphoric acid the re-
mainder stays in the soil to increase the total supply, and that
‘gradually it will become available, finally perhaps reaching
a point where no more need be applied.
On the other side is the well-established practice of using
PHOSPHORIC ACID FERTILIZERS 175
acid phosphate, which dates back more than half a century,
and has been accepted during that time as an improvement
over the use of untreated bone, which was largely super-
seded when the.process of making acid phosphate was in-
vented.
On most soils acid phosphate apparently gives the more
profitable immediate returns. On some of the rich soils of
the Middle West, however, there is an indication that
ground rock is a more economical source of phosphoric acid.
Except in those regions where the superiority of floats has
been demonstrated it is probably safer to use acid phosphate.
229. Effect of phosphoric acid on plant growth. — As has
been previously stated, phosphoric acid is essential to the
growth of plants. It is absorbed by plants at a fairly uniform
rate throughout the period of their active growth, while nitro-
gen is largely taken up during the early stages of growth.
Nitrogen and phosphoric acid are closely associated in plant
development.
One very apparent effect of phosphoric acid is to hasten
ripening. Cereal plants that receive an ample supply of
available phosphoric acid reach the heading stage and final
maturity sooner than do plants having an insufficient supply.
This may be an advantage in a climate having a cool short
season as it may help the crop to avoid frost in the fall. On
the other hand this rapid ripening may limit the yield
in a dry season, when there is a tendency for the crop to
shorten its growing periods sufficiently to curtail the quan-
tity of nutrients it absorbs and the food it elaborates.
Root development is always stimulated by available phos-
phoric acid. Young plants send their roots more deeply
into the soil, which is an advantage in dry regions, where the
top soil dries out quickly. Under any circumstances it in-
creases the absorbing surfaces and benefits growth.
The quality of many crops, particularly of pastures, is
improved by phosphoric acid. Animals reared on pastures,
176 SOILS AND FERTILIZERS
fertilized with phosphoric acid have been found, in a number
of experiments conducted in Great Britain, to be more vigor-
ous and to develop faster than when no phosphoric acid was
applied. |
By balancing the effect of nitrogen, phosphoric acid pre-
vents an undue formation of straw, at the same time making
it stronger ; on the other hand, it increases the production of
grain in cereal crops. In the same way it increases resistance
to disease, probably by producing a more normal develop-
ment of the plant cells.
An insufficient supply of phosphoric acid is less easy to de-
tect than is an inadequate supply of nitrogen, because its ef-
fect is exercised on the production of grain or other seeds,
rather than on the height and color of the plants. It re-
quires some care, therefore, to detect a lack of phosphoric
acid.
230. Plants particularly benefited by phosphoric acid. —
The crops that respond particularly well to applications of
phosphoric acid are turnips, barley, cabbage and other plants
of that family, beets, spinach, radishes and lettuce. Corn is
said to be well qualified to secure its phosphoric acid from the
natural phosphates, as are also some of the legumes.
QUESTIONS
1. Name the natural phosphate fertilizers.
2. Why should natural phosphates be finely ground, when ap-
plied to the soil ?
3. How does basic slag compare in availability with rock phos-
phate ?
4. How is acid phosphate made, and how does it compare
in availability with the natural phosphates ?
5. What is reverted phosphorie acid ?
6. Why is soluble phosphoric acid not readily leached out of soil
after being applied as a fertilizer ?
7. What phosphoric acid fertilizers may be used for top dressing
grass or other crops ?
PHOSPHORIC ACID FERTILIZERS A WP
8. Compare floats and acid phosphate as sources of phosphoric
acid when fertilizing land.
9. Describe the effects of phosphoric acid on plant growth.
10. Name the plants that are particularly benefited by fertili-
zation with phosphorie acid.
LABORATORY EXERCISKS -
Exercise I.—In Exercise V, Chapter I, an experiment was
described that was designed to show the importance of some plant-
food materials to plant growth. If this test has been properly con-
dueted it should now be ready to show the actual effects of the
phosphorie acid on crop development.
Exercise IJ. — Examination and identification of phosphate
fertilizers.
Materials. — Set of fertilizers (consisting of ground bone, raw
rock phosphate, basic slag and acid phosphate), hydrochloric acid,
nitric acid, litmus paper, flame, test tubes, funnel and filter paper,
ammonium molybdate solution.
The ammonium molybdate solution is made as follows:
Dilute 50 ¢.c. of ammonia (sp. gr. .9) with 75 c.c. of distilled water.
Dissolve in this 25 grams of molybdic acid. Pour this into a solu-
tion consisting of 175 c.c. of nitric acid (sp. gr. 1.42) diluted with
250 c.c. of water. Make the addition slowly with constant stirring.
Allow to stand in a warm place for two days and then decant the
clear supernatant liquid for use.
Procedure. — The fertilizers should be tested as described below
and examined until their identification is easy and positive.
Ground Bone
Bone is usually ground to a coarse powder. It is dry and has a
decided and characteristic odor. It is light gray in color, insoluble
in water and has a characteristic appearance under the hand lens.
Its physical characters are sufficient for identification.
Ground Phosphate Rock
Floats appear on the market as a light gray powder, insoluble
in water and with little odor.
Dissolve a small amount in hydrochloric acid, heat and filter. Add
ammonia until a precipitate appears. Dissolve it with a small
amount of nitric acid. Thenadd ammonium molybdate. Heat gen-
tly. A yellow precipitate indicates the presence of phosphoric acid.
N
178 SOILS AND FERTILIZERS
Basie Slag
This form of phosphoric acid appears as a dry, dark gray powder
with a slight odor. If differs from cyanamid in that it does not
stain the fingers upon handling. It is alkaline to litmus paper.
Test for phosphates as under phosphate rock.
Acid Phosphate
This fertilizer is a slightly deliquescent salt, brownish gray in
color, and finely ground. Its odor is characteristic and serves to
distinguish it from ground rock. Unlike floats it is partially soluble
in water.
Dissolve a small amount in water. Filter and test the filtrate for
phosphoric acid as described above.
Exercise IIJ.— Comparison of fertilizer effects on plant
erowth.
Materials. — Fertilizers, flower pots, poor sandy soil, oat seed.
Procedure. — The comparison of the various phosphorus fer-
tilizers upon crop growth, especially acid phosphate and raw rock, is
a valuable experiment. Fill the required number of flower pots
with the same amount of a poor sandy loam after thoroughly
mixing the fertilizer with the soil. Apply the phosphorus ferti-
lizers at the rate of 250 pounds per acre (1 of fertilizer to 10,000
of soil). Also add at the same time sodium nitrate and muriate
of potash at the rate of 1 of fertilizer to 5000 of soil respectively.
Apply one gram of lime per pot. Leave one pot untreated with the
phosphorus fertilizers as a check.
Now plant the oat seed and raise the soil to optimum moisture.
When seedlings are a week old, thin to required number. Keep
pots under suitable conditions and observe relative development of
the various treatments.
CHAPTER XIII
POTASH AND SULFUR FERTILIZERS
THE materials used as potash fertilizers, with a very
few exceptions, are soluble in water. The matter of their
relative availability is, therefore, of minor importance.
When applied to soil, the potash salts are absorbed and held
in a condition in which they leach out only in moderate quan-
tities, but to a greater extent than does phosphoric acid. In
the absorbed condition, however, they are readily available
to plants. |
It seems strange that with the many thousand pounds of
potash contained in an acre of ordinary land, as may be
seen by consulting Table 17, there should be any benefit
derived from the few pounds of potash that are contained
in a fertilizer. The fact that the fertilizer is effective gives
emphasis to two facts: (1) the great insolubility of the
soil potash; (2) the availability of the absorbed potash.
231. Stassfurt salts. — Most of the potash fertilizers used
in the United States come from Germany, where there are
extensive beds varying from 50 to 150 feet in thickness, lying
under a region of country extending from the Harz mountains
to the Elbe river and known as the Stassfurt deposits.
There are two forms in which potash is found in‘the Stass-
furt beds. These are the sulfate of potash and the muriate
of potash. It is necessary to distinguish between these two
because the muriate, when used in large applications, has an
injurious effect on certain crops, among which are tobacco,
179
180 SOILS AND FERTILIZERS
sugar beets and potatoes. On cereals, legumes and grasses
the muriate may be used without causing any injury, provided
it is not brought in contact with the seed.
Comparatively pure forms of both muriate and sulfate of
potash are on the market. The former contains about 50
percent of potash, and the latter about 48 to 50 percent. The
sulfate is more expensive, but the muriate is equally good,
except on the rather small number of crops that are injured
by it.
The mineral produced in largest quantity by the Stass-
furt mines is kainit, consisting of sulfate of potash and
muriate of magnesia. It contains from 12 to 20 percent
of potash. It has the same effect on crops as has the muri-
ate of potash.
Kainit should not be drilled with the seed of any crop
for when placed in direct contact with the seed injury
may result. It is a wise precaution to apply the kainit a
week or more before planting, if a heavy application is to
be made. ‘
232. Wood ashes. — The principal supply of potash in this
country at one time was wood ashes. With the diminished
consumption of wood as fuel, this source of potash has fallen
off. Now wood ashes are only an occasional supply. In
addition to potash, wood ashes furnish considerable lime and
a little phosphoric acid. There is no muriate present and
hence no injurious effect on plants, but it should not be
brought directly in contact with seeds.
_ Unleached wood ashes contain 5 to 6 percent of potash,
.2 percent of phosphoric acid and 30 percent of lime. Leached
_ wood ashes have only about 1 percent of potash, 1} percent
of phosphoric acid and 28 to 29 percent of lime. The un-
leached ashes are the more valuable.
Wood ashes are not only an excellent potash fertilizer,
but are also useful to counteract acidity in soils, for which
POTASH AND SULFUR FERTILIZERS 181
purpose the lime in the ashes is even more effective than the
potash because there is more of it.
233. Insoluble potash fertilizers. —- Many rocks contain
potash ; for this reason there is a large quantity in soils. It
has been proposed to grind the rocks that are richest in pot-
ash and to use them for fertilizer. Experiments with finely
ground feldspar have been conducted by a number of investi-
gators, but have given little encouragement for the successful
use of this material. An insoluble form of potash is not
given any value in the rating of a fertilizer.
234. Effects of potash on plant growth. — Plants require
potash in order to make a normal growth. If no available
potash is present, the elaboration of sugar and starch in
plants is curtailed. Crops like potatoes and sugar beets, that
produce much starch and sugar, are greatly benefited by an
abundant supply of potash. It also has other functions in
plants that make it indispensable. The grain of cereals fills
out better and weighs more to the bushel and the straw is
stronger, when a good supply of potash is available. Leg-
umes are usually greatly benefited by potash. The large
formation of sugar and starch affords the nitrogen-fixing
bacteria the kind of food which they need, and to obtain
which they live in symbiosis with the legume. If part of
a clover and timothy field be well fertilized with potash,
and another part receive none, it is likely to be the case that
the proportion of clover to timothy will be much greater on
the fertilized part of the field than on the unfertilized part,
unless the natural supply of available potash is unusually
large.
Potash tends to delay ripening of plants, but not to the
same extent as does nitrogen. It also has an influence
similar to that of phosphoric acid, in that it helps to overcome
the tendency of nitrogen to make plants less resistant to dis-
ease.
182 SOILS AND FERTILIZERS
235. Sulfur as a fertilizer. — It has been pointed out that
sulfur is one of the substances essential to plant growth,
but it has generally been considered that a sufficient quantity
is contained in arable soils to supply the needs of crops,
and that its application as a fertilizer is unnecessary. In
spite of this there have been occasional experiments con-
ducted from time to time in which sulfur, usually in the form
of flowers of sulfur, has been applied to soils to ascertain its
effect on plant growth.
236. Experiments with sulfur as a fertilizer. — Most of
the experiments with sulfur have been conducted in Europe.
In some cases the application of sulfur to the soil was found to
be beneficial to plant growth, in other cases there was no ef-
fect. Where no result was produced, it is reasonable to be-
lieve that there was sufficient sulfur in the soil to supply
the needs of the plants, and that any further addition was un-
necessary. In those experiments in which sulfur was found
to exert a beneficial action we cannot be certain that the in-
creased plant growth was due to the larger quantity of sulfur
obtained by the plants. Sulfur has been found to influence
the action of the germs in soils, and it is possible that the
plants grew better because the soil nitrogen was converted
more rapidly into an available form by the stimulating ef-
fect of sulfur on the bacteria concerned in that process. Sul-
fur sometimes has other beneficial effects on plant growth.
These secondary reactions sometimes lead to erroneous con-
clusions regarding the effect of a fertilizer.
‘237. Quantity of sulfur contained in crops. — It has been
computed from the analyses of various plants that the
quantity of sulfur, when figured as sulfur trioxide, that is
removed from the soil by crops of ordinary size is sometimes
greater, and sometimes less, depending on the kind of crop,
than is the quantity of phosphoric acid removed by the same
crop. This may be seen in the following table.
POTASH AND SULFUR FERTILIZERS 183
TABLE 37. — PouNDS OF SULFUR TRIOXIDE AND PHospHoRIC ACID
REMOVED FROM AN ACRE OF SOIL BY AVERAGE CROPS
CONTENT IN POUNDS TO THE
ACRE
Crop AND YIELD TO THE ACRE
Sulfur Trioxide| Phosphoric Acid
Ps eae VB Ey Yi his We hrs Re oe alae ik CEB 21.1
ReROECR SUSE) DUE!) a in a EN ORO 14.3 20.7
Rene er cae Paths Wiss): Manis erhivin uate Reece oho by One 19.7 19.7
orn(50 bu)... i" % Heathen eS ee 12.0 18.0
Alfalfa (9000 lb. dry wt. bt Re FF eT a ae 64.8 39.9
Dupaips (465 (cbs dry Wt.) -) «: 6 ss 92.2 33.1
ag DAre (ASO ie dry Wa) oo...) Ned 98.0 61.0
Potsoes,.(os00 Ih. ary whe) .)).66 US 11.5 21.5
Meadow hay (2822 1b. dry wt.) . . . 1 12.3
238. Quantities of sulfur in soils. — Analyses of virgin
and cultivated soils have shown that there has been a de-
pletion of sulfur in cropped soils. It also appears that the-
quantity of sulfur trioxide is probably not greater than the
quantity of phosphoric acid in many soils, as may be seen
from the following table, which is based on the analyses of a
considerable number of soils.
TABLE 38. —‘Pounps or SuLFuR TRIOXIDE AND PHospHoric AcID
IN SANDY AND CrLaAy SOILS
PouUNDS PER ACRE
Sulfur Trioxide Phosphoric Acid
Sen metis Perea, Pe Oe, 1650 2610
Reemeeenntse 3.) a a eta uerhicthes 2250 4230
239. Quantities of sulfur in drainage water. — Sulfur
suffers a much greater removal in drainage water than does
phosphoric acid. In lysimeter experiments this has been
184 SOILS AND FERTILIZERS
shown to amount to from 31 to 56 pounds to an acre in one
year, depending on whether the soil was limed or unlimed,
cropped or bare, as shown in the following table.
TABLE 39. — PounpDs oF SULFUR IN DRAINAGE WATER FROM ONE
ACRE OF SOIL
SULFUR
TREATMENT Crops GROWN (POUNDS PER
ACRE)
: 1911— | Annual
Lime Fertilizer 1910 {1911} 1912 1913-14 14 Aver-
age
None None Maize |Oats | Wheat |Timothy 127.2 |e
None None None |None} None None 176.1 | 44.0
None None Maize |Oats | Wheat |Timothy and clover | 126.2] 31.5
None None Maize |Oats | Grasses |Grasses 172.8 | 43.2
Lime None Maize |Oats | Wheat |Timothy 175.7 | 43.9
Lime None None |None| None’ |None 912.6 seek
Lime None Maize |Oats | Wheat |Timothy and clover | 164.2 | 41.0
Lime None Maize |Oats | Grasses |Grasses 1510 aed
None! Sulfate of potash | Maize |Oats | Wheat ;Timothy 225.7 | 56.4
. Lime | Sulfate of potash | Maize |Oats | Wheat |Timothy 248.1 | 62.0
.
With the rather large removal of sulfur in crops and drain-
age water, and a somewhat meager supply in the soil, it would
appear likely that a deficiency might ultimately arise if there
were no way in which sulfur could be added fo soils. To
offset the loss there is a certain quantity of sulfur, amounting
to 6 or 8 pounds an acre, washed down by the rainfall each
year. There is also a variable quantity of sulfur contained
in some of the commonly used fertilizers.
240. Sulfur contained in fertilizers. — It has been rather
fortunate perhaps that many of the fertilizers that are used
because they contain other plant-food materials, also con-
tain sulfur. This is true of farm manure and other animal
and bird excrements, residues of crops, animal offal, gypsum
or land plaster, acid phosphate, sulfate of ammonia, kainit,
sulfate of potash and all the slaughter house products.
POTASH AND SULFUR FERTILIZERS 185
Whether, under ordinary methods of farming, it is desir-
able to use any fertilizer for the sulfur it contains has not yet
been ascertained. It would appear, however, to be a subject
worthy of consideration.
~- QUESTIONS
1. What occurs to a soluble potash fertilizer when applied to
soil ?
2. With thousands of pounds of potash in an acre of soil, why
do a few pounds of fertilizer increase the supply available to plants ?
3. Where are most of the potash fertilizers obtained?
4. Name the potash fertilizers.
5. Describe the effects of potash on plant growth.
6. Name some crops that are particularly benefited by potash.
7. Is there any indication that the use of sulfur as a fertilizer
may be desirable ?
8. In what manures and fertilizers is sulfur contained ?
LABORATORY EXERCISES
Exercise I. — In Exercise V, Chapter I, an experiment designed
to show the importance of three plant-food materials. to plant
growth was described. If this test has been properly carried out it
should now be available to show the effects of potash on plant de-
velopment.
Exercise IJ. — Examination and identification of potash fer-
tilizers and sulfur.
Materials. — Set of fertilizers (consisting of muriate of potash,
sulfate of potash, wood ashes and sulfur), nitric acid, hydrochloric
acid, silver nitrate, filter paper and funnel, flame, litmus paper.
. Procedure. — The fertilizers should be studied and tested until
identification is sure.
Muriate of Potash
This salt is placed on the market as opaque crystals, soluble in
water.
Dissolve a small portion of the fertilizer in water and filter.
Add a drop of nitric acid and then silver nitrate. A white curdy
precipitate indicates the presence of muriate.
186 SOILS AND FERTILIZERS
Sulfate of Potash
This salt appears as a light yellowish powder, soluble in water and
non-deliquescent.
Dip a crystal in hydrochloric acid and then place in the flame.
The violet color is a test for potash.
Wood Ashes
Wood ashes are so characteristic as to need but little description.
Leach a small portion with water and test the percolate with litmus
paper.
Sulfur
Sulfur is a yellowish gray powder. It melts readily and burns
with a bluish flame, giving a characteristic odor. It is insoluble in
water.
Exercise IIJ.— Comparison of fertilizer effects on plant
growth.
Materials. — Fertilizers, flower pots, poor sandy soil, oat seed.
Procedure. — The study of the effect of the various potash fer-
tilizers as well as of sulfur might be of value. Fill the required
~ number of flower pots with the same quantity of a poor sandy loam
after thoroughly mixing the fertilizer with the soil.
If the effects of the various potash fertilizers are to be compared
add them respectively at the rate of 250 pounds per acre (1 of fer-
tilizer to 10,000 of soil). Apply at same time sodium nitrate and
acid phosphate at the rate of 1 of fertilizer to 5000 of soil respec-
tively. Add one gram of lime to each pot. Leave one pot un-
treated with potash fertilizers as a check.
If sulfur is to be used apply it at the rate of 250 pounds per acre.
Leave one pot with no treatment, have one to which only sulfur is
applied, prepare a third with a complete fertilizer only (mixture
of equal parts of sodium nitrate, acid phosphate and sulfate of
potash applied at the rate of 1 of fertilizer mixture to 5000 of soil),
and a fourth pot with sulfur plus the complete fertilizer.
Carry out the experiment as explained in Exercise III, Chapter
XI, and observe results.
CHAPTER XIV
LIME
In the chapter on acid soils, reference was made to lime
as a corrective of acidity. Lime is not a fertilizer in the
same sense as are the substances that have been discussed
in the last three chapters. It is, to be sure, an indispensable
ingredient of plant tissue, but as it is generally present in
sufficient quantity in arable soils, and as it is rather soluble,
there is usually enough lime to fully supply plant growth, and
this in spite of the fact that the soil may be greatly in need
of liming. It is because of its effect on the soil, rather than
directly on the plant, that lime is used as a soil amendment.
241. Forms of lime. — The forms in which lime is used
on soils are (1) ground limestone, (2) marl, (3) air-slaked
lime, (4) quick-lime and (5) water-slaked lime. The first
three of these are similar in their effects, and are chemically
alike, being what is termed carbonate of lime. Quick-lime
and water-slaked lime have much the same action on soils,
and are called caustic lime.
Quick-lime is made by burning limestone ina kiln. Quick-
lime, when treated with water, forms water-slaked lime.
Air-slaked lime is quick-lime that has been exposed to dry
air until it has lost its caustic properties. Marl is found in
beds in the earth, as is limestone, but it is softer than lime-
stone. Like limestone it is ground before being used.
Owing to the combinations of the lime itself with water
and gases in these various forms, there is required a greater
weight of some forms than of others to give the same quantity
187
188 SOILS AND FERTILIZERS
of lime. When the materials are fairly pure, the number of
pounds of each required to give approximately equivalent
quantities of lime are as follows:
Qiiekolimiceiore for. |. oe GARR ee hh aeorteE
Water-slaked lime 2.0. «4. ow ts 74 pounds
Air-slaked lime, marl, ground limestone. 100 pounds
When applying lime to land, these relationships should be
kept in mind. Ifit isa question of using quick-lime or ground
limestone one must provide nearly twice as much limestone
as quick-lime in order to apply an equal quantity of lime.
242. Absorption of lime by soils. — In the forms in which
it is applied to soils, lime is not so soluble as potash fertilizers.
When brought in contact with soil, the lime is absorbed and
rendered still less soluble. It is, however, somewhat more
soluble than soil potash, and drainage waters usually con-
tain several times as much lime as potash. It is the soluble
part of the lime that has the beneficial effect on crops and
soils. The ways in which the benefit accrues are numerous
and will be described in a number of the following para-
graphs. Lime is usually applied in much greater quantities
than are fertilizers, but the treatment is given only at inter-
vals of four or five years.
243. Lime requirement of soils. — It is possible, by means
of chemical methods, to ascertain how much lime a soil will
absorb before it shows alkalinity due to the presence of an
excess. Such a test is useful to indicate the quantity of lime
that should be applied to a soil in order that it shall be at
least temporarily adapted to the production of lime-loving
plants.
The results of such a test are usually expressed in pounds
of lime required to satisfy the absorptive properties of a
certain number of pounds of soil, as for instance, 2,000,000
pounds. This will vary in different soils from none to several
thousand pounds.
LIME 189
244. Effect of lime on tilth. — A clay or loam soil when in
acid condition tends to become compact and difficult to till.
The addition of lime to soil helps to bring about a granular
formation of the small particles, and to give the soil better
tilth. This effect has previously been noted in § 46.
245. Effect of lime on bacterial action. — Some of the
most beneficial bacteriological processes are greatly favored
by an abundant supply of lime in the soil. Important among
these are the various processes involved in the formation
of nitrates from organic forms of nitrogen. It seems also
to be associated with the operation by which some legumes,
for instance alfalfa, secure nitrogen from the air. The in-
creased supply of easily available nitrogen is often reflected
in the yield and nitrogen content of the crops, as well as in
the percentage of nitrates in the soil. This is illustrated by
an experimert in which alfalfa was raised on plats of land
one of which was limed liberally and the other not limed.
The hay was weighed when cut, and was then analyzed,
as were also the weeds growing with the alfalfa. The soil
was sampled and the nitrates determined. The soil was also
allowed to stand for ten days at an optimum water content
and a temperature suited to the production of nitrates,
at the end of which time the quantities of nitrates formed
were determined. The results are shown in Table 40.
Taste 40.— Tue Errect or Limine SoILt ON THE YIELD AND
CoMPOSITION OF ALFALFA RaIseD ON IT, AND ON Its NITRI-
FYING POWER
t | LIMED Not Limep
YViela-or hay, pounds on plat ~:" . 3. | 103 75
Percentage of protein in alfalfa. . . . 20.63 15.88
Percentage of protein in weeds. . . . 10.67 8.79
Nitrates in dry soil, parts per million. 8.10 4.30
Nitrates produced in ten days,
ER 376100 92.00
190 SOILS AND FERTILIZERS
The effect of the lime was not only to increase the yield of
alfalfa hay, but also its protein content, as well as that of the
weeds growing with it. The rate of nitrate formation in the
soil was also greater when limed.
246. Liberation of plant-food materials.—It has gen-
erally been held that the application of lime to soils renders |
some of the other plant nutrients more soluble by reason
of the exchange of lime for these substances in the insoluble
combinations found in soils. This has been discussed in
section 115. There is little doubt that magnesia is thus
rendered more available, but magnesia is rarely lacking.
Potash is often said to be made soluble, but although such may
be the case with some soils it is probably not true of all, and
there is really little evidence to substantiate the claim in any
case. The use of lime, under some soil conditions, may render
phosphoric acid more available, probably by supplying a base
more soluble than iron or alumina, with which, in soils defi-
cient in lime, the phosphoric acid might otherwise be combined.
247. Effect on plant diseases. — The presence of abun-
dance of lime retards the development of certain plant diseases,
such as the “ finger-and-toe ’’ disease to which cabbages
and some root crops are subject. On the other hand, it
may promote some diseases, as, for example, potato scab.
248. The use of magnesian limes. — Some limestone
contains a considerable proportion of magnesia. When
grown in water cultures, many agricultural plants are injured
when the proportion of magnesia is greater than that of |
lime. In soil, however, magnesia is not nearly as soluble
as lime and consequently there may be many times more
magnesia than lime present without as much actually being
in solution. Hence it is seldom that magnesia is injurious,
and magnesian lime may be used to overcome soil acidity
except possibly in the few soils in which the ratio of magnesia
to lime is already very high. .
LIME 191
249. Caustic lime versus ground limestone. — As lime
helps to correct soil acidity no matter in what form it is
applied, there is little advantage in one form over another
so.long as it is remembered that 100 pounds of ground lime-
stone are equivalent to 56 pounds of freshly burnt lime, and
provided the cost, hauling included, is in that ratio. The
greater ease with which ground limestone may be handled
would, under these circumstances, give it the preference.
In respect to its effect on tilth, lime, in the caustic form,
is apparently more effective than when in the form of ground
limestone. For heavy clay soil, the compact and cloddy
condition of which presents a serious difficulty, caustic lime
is preferable. A comparison of these two forms of lime on a
heavy clay soil is shown in the following table in which the
average percentage increase in crops from the limed over the
unlimed plats for a period of five years is stated.
‘
TABLE 41. — AVERAGE PERCENTAGE INCREASE IN YIELD DUE TO
Caustic LIME AND GROUND LIMESTONE
PERCENTAGE
Form or Lime Appiiep eee pe acer ape
PER ACRE Pisce
NRT TANNR Eee go a ie higd?) ls, vey vw 3000 20.9
SARMTOIMGSLONG .. . s,s 2 8 ba 6000 14.8
MreMRAME k) ye es le Re 1000 3.9
Ground, limestone.) (6.660 0 2000 3.7
Calistic Masncsian ime, . .. «2... 2000 6.7
Ground magnesian limestone ... . 3225 3.3
250. Fineness of grinding limestone.— The greater
solubility of finely ground material, as compared with coarse,
makes it desirable that limestone be at least fairly well
pulverized before it is used. If it is so ground that all of the
particles will pass through a sieve having 50 meshes to the
192 SOILS AND FERTILIZERS
inch, it will probably be just as effective as if ground much
finer.
251. Gypsum or land plaster. — In the early agriculture
of this country, before ordinary commercial fertilizers were
used, gypsum was a popular soil amendment. Its effective-
ness has apparently decreased as the soils on which it was
used have been longer under cultivation. It has generally
been credited with liberating potash, and possibly as the
soils have become more acid it has been less effective in this
respect. At any rate, it is rarely used at present.
Gypsum has little effect on tilth and is not in any sense
a substitute for caustic lime for that purpose, nor is it of
any value to overcome soil acidity, as it contains a strong
acid. 5
QUESTIONS
1. How does the need of,a soil for lime differ, in principle, from
its need for the other fertilizers we have studied ?
2.. Name the forms in which lime is applied to soils.
3. Which of these are similar chemically and in their effect on
soils ?
4. Howis quick-lime made? Water-slaked lime? Air-slacked
lime ?
5. How does the solubility of lime compare with that of potash,
when both are absorbed by soil ?
6. What is shown by a chemical determination of the lime
requirement of a soil ?
7. What is the effect of lime on some of the bacteriological pro-
cesses in soil ?
8. How does lime affect the availability of certain other plant
nutrients in soil ?
9. What is its effect on certain plant diseases ?
10. Discuss the use of magnesian limes.
11. Discuss the use of caustic lime as compared with ground
limestone.
12. How does the fineness of grinding limestone affect its imme-
diate usefulness ?
13. How does gypsum affect soil ?
LIME 193
LABORATORY EXERCISES
Exercise I. — A study of the forms of lime.
Materials. — Set of lime samples (ground limestone, marl, quick-
lime, hydrate of lime and gypsum), hand lens, muriatic acid, litmus
paper.
Procedure. — Study the various forms of lime until identifica-
tion is easy.
Ground Limestone and Marl
Ground limestone can be detected by its physical condition, es-
pecially if a hand lens is used. It is practically insoluble in water.
Its color varies from white to gray. The presence of carbonates
may be detected by a few drops of dilute muriatic acid.
Mar! is a soft powdery form of calcium carbonate. Its texture
and the presence of shells and organic matter serve to distinguish
it from ground limestone.
Quick-lime
Quick-lime appears on the market either in lumps or as a fine.
powder. It is very caustic and intensely alkaline to litmus paper.
When in contact with water it heats and slakes, becoming hydrate
of lime. This characteristic distinguishes it from the other forms
of lime. )
Hydrate of Lime
This form of lime is a white powder, soluble in water. Its sour
taste serves to distinguish it from marl and limestone. It is alka-
line to litmus paper.
Gypsum
This amendment is marketed as a grayish to white powder, in-
soluble in water. Itis calcium sulfate. It does not react with acid
as does the limestone nor with water as does the lump lime. Its
lack of taste distinguishes it from hydrate of lime.
Exercise IT. — Fineness of ground limestone.
Materials. — Samples of limestone, 10, 20, 40, 60 and 100 mesh
sieves, balance and weights.
Procedure. — The fineness of ground limestone has a marked
effect on its value. Weigh out 100-gram portions of the various
samples of limestone and pass them through the sieves. Weigh
fe)
194 SOILS AND FERTILIZERS
the resulting grades and calculate the proportion of the original
sample passing through the different mesh sieves. Try to makea
relative estimate of the value of the various samples on this basis.
Exercise III. — Effect of lime on biological action.
Materials. — An acid soil from under sod, two 8-ounce, wide-
mouth bottles, hydrate of lime, large vessel for mixing soil and
water, funnel and filter paper, evaporating dishes, water bath,
phenoldisulphonie acid, ammonia, flame, two 100 c.c: graduated
cylinders.
Procedure. — Place 50-gram samples of the acid soil in each of
two 8-ounce bottles. Add and mix well with one gram of carbonate
of lime. Bring the soils in each bottle up to optimum moisture
content. Plug mouths lightly with cotton and set aside at opti-
mum temperature for a week.
Now estimate nitrates in manner described in Exercise I, Chap-
ter IX. A comparison of the results will show the influence of lime
on nitrification. Apply these results to practical problems.
Exercise IV. — Flocculation by lime.
Materials. — Ground limestones and hydrate of lime; large
bottle for preparing soil suspension, two 100 c.c. graduated cylinders.
Procedure. — Prepare a soil suspension by shaking a heavy
clay soil for 15 minutes in a bottle partially filled with water (one
of soil to ten of water) after adding a few drops of strong ammonia.
Allow to stand for two or three hours and then pour suspension into
the cylinders. Fill to 100 mark. Now add to one a pinch of hy-
drate of lime and to the other the same amount of ground lime-
stone. Shake well and allow to stand.
Watch closely and explain results. Apply the principle involved
here to actual field practice.
Exercise V. — Flocculation by lime.
Materials. — Clay soil and hydrate of lime.
Procedure. — Prepare from one portion of clay soil a well-puddled
ball. Add hydrate of lime to another portion of the clay soil (rate,
1 of lime to 500 of soil), and work into a ball after adding sufficient
water. Allow the two samples to dry thoroughly. Crush each one.
Note difference in crushing resistance and the structural character
of each soil. Apply results to actual field practice.
Exercise VI. — Lime and the rotation.
The place of lime in a rotation depends on a number of factors.
Discuss these with the student. Take a number of standard rota-
LIME 195
tions and decide where in the rotation the lime should come and
why.
Encourage the pupils to obtain the rotations used on their home
farms and discuss lime in relation to such rotations. It might also
be well to visit some good farmer and discuss with him the form of
lime he buys, how he applies it, what amounts he uses and where in
the rotation he adds it to the soil. The practical phases of the use
of lime are what the pupil should understand.
Exercise VII. — Problems — Forms of lime to apply.
In buying lime the form that will give the greatest amount of
calcium for the money is usually purchased unless the flocculating
effect of burnt lime is necessary. The relative value of the lime, the
cost per ton, the freight and the cost of application must be con-
sidered. For a rough calculation 50 pounds of burnt lime is con-
sidered equal to 75 pounds of hydrate and to 100 pounds of ground:
limestone.
Problem 1.— A farmer located on land already sufficiently fri-
able, wishes to apply one ton of burnt lime or its equivalent in other
forms. Burnt lime costs him $5.00 per ton f. o. b., hydrate lime
$4.00 and ground limestone $2.25 per ton. Freight is 25¢ per ton,
as is also hauling and application together. Which form of lime
should the farmer buy ?
_ Problem 2.— The next year the f. o. b. price of lime changed to
$4.90, $3.00 and $2.00 for the burnt lime, the hydrate and the
limestone, respectively. Considering freight and cost of haul and
application the same as before, what form should be purchased ?
Problem 3. — This same farmer can purchase marl at $1.00 per
ton, but he must load it himself and haul it three miles over a dirt
road. It is impure, carrying only two-thirds the calcium that the
limestone has. From conditions in your locality how would you
consider the desirability of purchasing this form of lime as com-
pared with those forms mentioned in Problem 2?
CHAPTER XV
THE PURCHASE AND MIXING OF FERTILIZERS
Ir is hardly three-quarters of a century since the fertilizer
industry began its development. In that time the use of
commercial fertilizers has spread to all the important agri-~
cultural states of this country. Their sale amounts to
more than $110,000,000 annually, of which fully one-half
is expended by the farmers of the South Atlantic states,
in an area lying within three hundred miles of the seaboard.
Nearly one-half of the remainder is purchased in the Middle
Atlantic and New England states, while only about five
percent is used west of the Mississippi river.
A large utilization of fertilizers in a region is atical but
not always, an indication of an intensive agriculture. The
importance of fertilizers in farm practice and the large
expenditure that their use involves, together with the possi-
bilities for profit, when they are properly used, make it de-
sirable that those who utilize fertilizers should thoroughly
understand the commercial, as well as the agricultural,
values of these products.
252. Brands of fertilizers. — The various fertilizer con-
stituents or‘carriers that have been described are purchased
oy fertilizer manufacturers, who mix them into various
vombinations, each of which is called a brand. Each of
these brands usually contains nitrogen, phosphoric acid
and potash, in which case it is called a complete ferti-
196
197
THE PURCHASE AND MIXING OF FERTILIZERS
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198 SOILS AND FERTILIZERS
lizer, although occasionally a brand of fertilizer will have
only two carriers. Each brand is given a trade name, fre-
quently implying the usefulness of the fertilizer for some
particular crop, but without reference to the character
of the soil on which it is to be used. It is better, how-
ever, to purchase a fertilizer on the basis of its composi-
tion rather than because of its name. The composition
of fertilizers for different crops will be discussed later (see
§ 261).
If, in compounding a fertilizer, those carriers are used
that are difficultly soluble, the fertilizer is not so valuable
as if composed of easily soluble substances. The solubility
as well as the percentage of each ingredient should be known
to the purchaser.
253. High-grade and low-grade fertilizers. — A fertilizer is
known on the market as high-grade or low-grade, depending
on the percentage of fertilizing constituents that it contains,
or on the availability of its plant-food materials. Low-grade
fertilizers cost less than high-grade because they contain
less plant-food material or because they are less soluble,
although the price of a pound of the plant nutrients may be no
less, and, in fact, is usually more. The low-grade product
is encumbered with a large amount of inert material, that
adds to the cost of transportation and handling, without
adding to the value of the fertilizer. For these reasons the
cost of a pound of any one of the plant nutrients is usually
less in high-grade than in low-grade goods. A ton of low-
grade fertilizer may contain 500 or 600 pounds more inert
material than a high-grade fertilizer, upon which freight
must be paid, and which must be hauled from the station
and spread on the field.
The following figures were obtained by tabulating one
hundred and thirty brands of fertilizers analyzed at the
Vermont Experiment Station.
THE PURCHASE AND MIXING OF FERTILIZERS 199
TABLE 42. — COMPARATIVE VALUES OF Low-GRaDE, MEDIUM AND
HicuH-GRADE FERTILIZERS
Fa Sa Cosr in Cents oF|%
3 Sai ONE POUND oFf |Ng@
a wo 38a
& Zz o Ha Bea
@ | 8s leas 2 sag
Q ° Moe "3 iS
oa me Ee < FS &
FERTILIZER ae ao As BO BH
HS Ay 6 Ai & op 2 He
me a8 4 Q | A ow
a & 1} ie} ns Bow & o a a
ss 448 > OB Ga| w a a |pa<
s8 | deg | 85 |seme| 2 | 2 | 2 208
le} yo < ial OS Ms “rat q io} eet)
OF nH Go |OR4s | 4 | & | .a& IP dA
High grade . | $26.30 | $38.93 | $12.63 | $0.48 | 28 | 5.
Medium grade} 18.22] 30.00] 11.78} 0.65 | 31 | 6.3 | 7.0 | 60.6
Low grade .| 13.52| 27.10| 13.58| 1.00 | 38 | 7.
In mixing fertilizers in a factory, it is customary to incor-
porate with the carriers of plant nutrients more or less material
that has no influence on plant growth, but that serves to di-
lute the mixture and to prevent it from becoming damp by
the absorption of moisture, and also to prevent the chemical
interaction of the constituents. This material is called a filler.
254. Fertilizer inspection and control.— Most of the
states have enacted legislation providing for the inspection
and control of the sale of commercial fertilizers. Each
brand of fertilizer, that sells for $5.00 or more a ton, must
pay a state license fee and each bag must bear a tag stating
the guaranteed percentage of nitrogen, phosphoric acid and
potash that the fertilizer contains, and giving some informa-
tion in regard to their solubility.
There is little uniformity in the requirements of the dif-
ferent states. In some states a very detailed statement of
the composition of the fertilizer and the solubility of its
constituents is required. The following information is
called for by some of the states.
Percentage of nitrogen in the following forms:
200 SOILS AND FERTILIZERS
In nitrates and ammonium salts. These are generally
present in nitrate of soda and sulfate of ammonia. Their
_ availability has already been discussed (see § 218).
Water-soluble organic nitrogen. This is probably not
so readily available as the two former Kinds, but differs little
from them in this respect.
Active water-insoluble organic nitrogen. Although not
directly available this becomes so quickly enough for the
crop to which it is applied to obtain part of it.
Inactive water-insoluble organic nitrogen is that part of
the organic nitrogen that is of little value for immediate
plant growth.
Percentage of phosphoric acid in the following forms :
Water-soluble phosphoric acid, which is readily available
(see § 227).
Reverted phosphoric acid. Not so readily available
(see § 227).
Available phosphoric acid. This usually consists of the
sum of the two forms mentioned above. Sometimes when
this term is used no distinction is made between the water-
soluble and the reverted, but this is not so satisfactory.
Insoluble phosphoric acid. This is slowly available, but
in animal products, such as bone, tankage and other slaughter
house waste, it becomes available more quickly than if present
in rock phosphate. However, the analysis does not distin-
guish between the organic and inorganic carriers.
Percentage of potash in the following forms:
Soluble in water.
Present as chloride.
255.. Trade values of fertilizer ingredients.—In the
states having fertilizer inspection laws, it is customary for
the officers in charge of the inspection to adopt each year a
schedule of trade values for nitrogen, phosphoric acid and
potash in each of the carriers ordinarily found in fertilizers.
THE PURCHASE AND MIXING OF FERTILIZERS 201
These values are based on the wholesale market reports
for six months preceding March 1 of each year, to which is
added about 20 percent of the price, to cover cost of handling.
Potato Manure ‘‘A”’ without Potash 1916
ANALYSIS:
Nitrogen . - . ; - 4.11 to 4.94 pat cent.
Equal to Ammonia - - : a to
Soluble Phosphoric Acid -. - ay a es tas
Reverted Phosphoric Acid : ate =
Available Phosphoric Acid . 4
Insoluble Phosphoric Acid - - BES
Total Phosphoric Acid - - js to 12.
MANUFACTURED BY
xX. YW. Z. FERTILIZER COMPANY
Fic. 30.— Tag representative of the kind often used on bags of fertilizer
to state the percentages of their constituents.
The following values are for the year 1914.
TrapE VALUES OF PLANT NUTRIENTS IN Raw MATERIALS
Nitrogen in nitrates ‘
Nitrogen in ammonium salts :
Organic nitrogen in dried and finely round fish, meat and
blood :
Organic nitrogen in 1 finely ground bone ‘and tankage ,
Organic nitrogen in coarse bone and tankage ,
Org anie nitrogen in castor pomace and cottonseed meal
Phosphorie neil water soluble
Phosphoric acid, reverted : :
Phosphoric acid in fine bone, fish ‘and tankage : :
Phosphoric acid in cottonseed meal and castor pomace .
Phosphoric acid in coarse fish, bone, tankage and ashes .
Phosphorie acid in mixed fertilizers, insoluble
Potash as high-grade sulfate, in forms free from muriate,
in ashes, ete.
Potash as muriate
Potash as castor pomace ‘and cottonseed meal
VALUE PER
PouND
IN CENTS
18.5
18.5
202 SOILS AND FERTILIZERS
These values may be used by the consumer to calculate
the wholesale cost of a fertilizer of guaranteed composition,
which he can then compare with the retail price asked by
the retail dealer. He may also compare the relative values
of brands of similar composition offered for sale by different
manufacturers.
256. Computation of the wholesale value of a fertilizer. —
Suppose that we have the following statement of the analysis
of a fertilizer.
Per CENT
Natrosen in mibrate:of soda frre’ 2, a) Oe eee 1
Nitrogen in dried blood oa” A ee Bel ae 2
Phosphorie acid. water solubléjace. 2)... ci 8 6
Phospinieseid reverted: i. 0 0554) 5 Ran Pe 2
Migiaalre eer rian: 2 33. Be sale Bed, ios ge aE ta ee 10
The number of pounds of each constituent to a ton of
fertilizer is then found by multiplying the weight of a ton
of fertilizer by the percentage of the constituent, thus :
Nitrogen, as nitrate .01 x 2000 = 20 pounds per ton.
Nitrogen in dried blood .02 x 2000 = 40 pounds per ton.
Phosphoric acid, water-soluble .06 x 2000 = 120 pounds per ton.
Phosphorie acid, reverted .02 x 2000 = 40 pounds per ton.
Potash, muriate .10 x 2000 = 200 pounds per ton.
The trade values, as published by the fertilizer inspection
officers, are then applied to the several constituents.
Nitrogen as nitrate 20 x $.185 =$ 3.70
Nitrogen in dried blood 40x $20 = 8.00
Phosphoric acid, water-soluble 120 x $.045 = 5.40
Phosphoric acid, reverted 40x $.04 = 1.60
Potash, muriate 200 x $.0425 = 8.50
$27.20
Such a fertilizer will cost the consumer more than the fig-
ure derived in this way, because the entire cost of mixing
and retailing must be added to it. It may serve as a basis
for ascertaining whether it would not be more profitable
THE PURCHASE AND MIXING OF FERTILIZERS 203
for a group of consumers to purchase the fertilizer ingredients
in car-load lots and do the mixing themselves.
It must also be remembered that this is the commercial
value and not necessarily the agricultural value, which latter
is determined by the profits from its use, and will depend on
many factors.
257. Home mixing of fertilizers. — There is a large margin
between the trade value of fertilizer ingredients and their
retail price as sold by the dealer. The cost of the raw ma-
terials often doubles in the process of mixing and retailing,
with the necessary transportation. It has been demon-
strated that the raw materials may be purchased from the
wholesale dealer and mixed by the consumer at a consider-
ably lower cost than if purchased mixed from the retail dealer,
and that the results are fully as satisfactory.
Other advantages from home mixing are that it permits
the farmer to use exactly the proportion of the several con-
stituents that he desires, and that it makes unnecessary
the handling of a large amount of inert materials frequently
contained in mixed fertilizers. It is thus possible for him
to ascertain, by field tests, the best proportions of the various
fertilizer constituents to use on his own land for each of the
crops he is growing. This knowledge makes it possible to
decrease greatly the expenditure for fertilizers.
258. Fertilizers that should not be mixed. — Because
fertilizers consist of chemicals, some of which react on each
other to form compounds different from those in the original
substances, it is unwise to mix certain of these carriers.
The result may be to convert soluble nutrients into insoluble
ones, or to cause the loss of some constituent in the form
of gas. If one is to mix his own fertilizers he must know
what materials should not be brought in contact. The fol-
lowing are some of the common carriers that should not
be mixed :
204 SOILS AND FERTILIZERS
Caustic lime ;
Wood ashes it aa UE
Dissolved bone
Basic slag
Cyanamid Sulfate of ammonia
Caustic lime |_.,, | Slaughter house waste containing ni
Wood ashes trogen
Basic slag Farm manure
The following mixtures should be applied immediately :
Nitrate of soda
Muriate of potash
Kainit
Acid phosphate with Nitrate of soda or ground limestone.
Caustic lime | with
Cyanamid should not be mixed with acid phosphate if
there is more than one part of the former to ten of the latter.
259. Calculation of a fertilizer mixture. — In deciding
on the composition of fertilizers the best and simplest way
is to consider them according to the percentage of each of
the three constituents, nitrogen, phosphoric acid and potash,
they contain. If we decide to use a 3-8-5 fertilizer, the
next step is to calculate how many pounds of each of the
earriers of these substances must be used for each ton of the
complete fertilizer, and how much filler must be added.
Suppose we have on hand the following carriers :
Nitrate of soda containing 15 percent nitrogen
Acid phosphate containing 14 percent available phosphoric acid
Muriate of potash, containing 50 percent potash
The first step is to calculate the number of pounds of
nitrogen, of phosphoric acid and of potash in a ton of a
3-8-5 fertilizer. To do this we merely multiply the num-
ber of pounds in a ton by the percent of each plant-food
material.
THE PURCHASE AND MIXING OF FERTILIZERS 205
2000 x .03 = 60 pounds nitrogen per ton
2000 x .08 = 160 pounds phosphoric acid per ton
2000 x .05 = 100 pounds potash per ton
The next step is to calculate the number of pounds of the
carrier required to furnish the quantity of plant-food material
that has just been found. This is done by dividing the
weight of the plant-food material required by the percent
of this particular plant-food material in the carrier that is
to be used.
60 + .15= 400 pounds nitrate soda
160 + .14 = 1143 pounds acid phosphate
100 + .50 = _200 pounds muriate of potash
1748 pounds of the three carriers
The weights of the different carriers are then added, giving
in this case 1743 pounds needed for every ton of fertilizer.
The remainder of the ton (2000 — 1743 = 257 pounds)
is then made up with a filler, consisting of sand, dry earth,
muck, peat, sawdust or something of the kind.
260. How to mix the ingredients. — A smooth tight floor
is needed on which each carrier is spread in turn to break
down the lumps. It is then passed through a coarse screen.
A weighed quantity of the filler or principal carrier is then
spread out in uniform depth and on top of it another carrier,
until all are represented. Then the pile is shoveled over and
over, and finally leveled and the process repeated until the
ingredients are thoroughly mixed. This lot of fertilizer
is then put in sacks and the operation repeated with another
quantity until a sufficient amount is prepared. There
should always be two hundred pounds or more of filler in
each ton to give a more uniform distribution of the carriers.
QUESTIONS
1. In what parts of the United States are fertilizers used in
greatest quantities ?
2. What is meant by a eh of fertilizer ?
206 SOILS AND FERTILIZERS
3. Whatisa high-grade in distinction from a low-grade fertilizer ?
4. Explain what is meant by a filler.
5. What, in a general way, does a report on the inspection of a
fertilizer show ?
6. How are trade values of plant nutrients evaluated ?
7. What are the advantages to be derived from the home mixing
of fertilizers ?
LABORATORY EXERCISES
Exercise I. — Fertilizer inspection and control.
Fertilizer laws are designed to protect the honest manufacturer
as well as the farmer. Obtain the laws of your state which have to
do with fertilizer inspection and control. Analyze them step by
step with this point always in mind. Decide whether or not the
law does really regulate and protect in the way that it should. oy! ease 40 7.3
Walle. baa ee Sloe iw 85 15.5
SHOR 5%). = 1 Mae, co eR 34 6.2
(282. Effect of food on composition of manure. — The
richer the food in nitrogen and other plant-food materials,
the more of these there will be in the manure. This has
FARM MANURES 225
been demonstrated by a number of experiments, from which
the following have been selected.
TABLE 47. — Errect oF Foop oN CoMPOSsITION OF ANIMAL AND
Pouuttry MANURE
—————=
Pounps PER TON OF MANURE
weet 3 Nitrogen Eee Potash
Fed to steers
Corn and mixed hay . . . ..| 29.80 10.53 26.64
Corny oil: meal and hay... «|. 3b.00 10.99 24.48
Corn, oil meal and clover . . .| 33.60 11.91 24.96
Fed to fowls.
Nitrogenous ration Pree a Ae ee 18.78 6.48
Garaonaceous ration. .....° <<. ~~, La:20 14.65 5.04
283. Commercial evaluation of manures. — As a means
of comparing manures, they may be evaluated in a manner
similar to that used with commercial fertilizers. This,
however, fails to place any value on the organic matter,
which is undoubtedly of much benefit to the soil. In the
following table are given the values of manures produced
by different animals based, in part, on the composition given
in Table 45 when the nitrogen is considered to be worth ten
cents a pound, the phosphoric acid two and one-half cents
and the potash four cents.
TaBLe 48.— VaLur or Excreta PRODUCED BY SEVERAL
Farm ANIMALS
ANIMAL VALUE PER TON
ERs Os AOS ee Gt $1.50
CEE gs ok ge mweta ar yh costes 1.64
(PrarMeEM sg EO nee Ae? a a oe, 1.97
Wee hg eee ne pad 2.87
NTE, 2) ae, ws wt eee acs. . s 4.80
Q
226 SOILS AND FERTILIZERS
If the mixed horse and cow manure together with litter,
similar to that referred to in section 280, be made the
basis of the calculation, the evaluation would be $1.60. Dilu-
tion of the plant-food materials due to the litter tends to.
reduce the value.
284. Agricultural evaluation of manures.— The com-
mercial value may be quite different from the agricul-
tural value, which is calculated from the increased crop
production resulting from the use of the manure. -This
will vary with different soils, but even on similar soils it
will vary with different manures. The following table gives —
the results of an experiment in which treated and untreated:
manures were evaluated commercially and were then applied
to the land. The value of the increased crops in a three
years’ rotation was then calculated in terms of financial
return to the ton of manure applied:
TaBLE 49.— COMMERCIAL AND AGRICULTURAL EVALUATION OF
MANURES
eae CoMMERCIAL AGRICULTURAL
VALUE VALUE
Yard manure untreated . . . . $1.41 $2.15
Yard manure plus floats . . . . 2.04 3.31
Yard manure plus acid phosphate . 1.65 5.67
Yard manure plus kainit RS = 1.45 2.79
Yard manure plus gypsum .. . 1.48 2.46
285. Deterioration of farm manure. — There is always a
loss in the value of farm manure on standing. The ways
in which this is brought about are: (1) fermentation; (2)
leaching. The first of these is a natural process, common
to all farm manure on standing, and not occasioned by any
outside agencies. The second is due to the running off of
PLate XV. Manures. — Farm manure is becoming relatively more
scarce every year. Its protection is becoming more essential to success-
ful farming.
FARM MANURES AIA |
the liquid portion of the manure, and to the exposure of the
manure to rain.
286. Fermentations of manure. — The mixture of solid
and liquid excreta together with litter used as bedding con-
stitutes a wonderfully favorable material for the growth of
bacteria, the number of which frequently amounts to many
billion in a gram of manure. This is many times more
than are found in soil. It is then small wonder that fer-
mentations proceed at a prodigious rate in a manure heap.
These fermentations are produced both by bacteria requiring
oxygen for their activity and by those that need little. The
fermentations on the outside of the heap are different from
those on the inside, where air does not readily penetrate,
but as fresh manure is thrown on the pile from day to day,
most of the manure first undergoes fermentation in the pres-
ence of air and afterwards without air.
It is through the action of germs on the nitrogenous com-
pounds of manure that loss of value through fermentation
occurs. In the presence of air ammonia is formed, and this
being in a volatile form, is likely to escape. The drier the
heap, the more likely the ammonia is to escape.
The fermentations in the interior of a moist manure heap
are, in the main, favorable to the production of readily
available plant-food material. It is desirable to keep the
heap as compact as possible, and to prevent it from becom-
ing dry by the application of water in amounts sufficient to
keep the heap moderately moist without leaching it. In
the arid and semi-arid parts of the country, this is an im-
portant precaution to be taken in the preservation of farm
manure. :
287. Leaching of farm manure. — When water is allowed
to soak through a manure heap and to drain away from it,
there is carried off in solution, and to some extent in sus-
pension, more or less of the organic matter and plant-food
/
228 SOILS AND. FERTILIZERS
materials that are soluble in water and that consequently
represent the most valuable part of the manure. As about
one-half of the nitrogen and two-thirds of the potash of farm
manure is in a soluble condition, the possibility of loss by
leaching is very great. Even phosphoric acid may thus
be removed.
‘It is rather difficult to distinguish between the losses due
to fermentation and those caused by leaching. In an experi-
ment conducted in Canada a carefully mixed quantity of
farm manure was divided into two parts, one of which was
placed in a bin under a shed, the other was exposed to the
weather outside, in a similar bin. After-a year the two por-
tions were analyzed and the losses thus computed are stated
in the following table.
TasBuLE 50. — Losses BY FERMENTATION ALONE AND BY FERMEN-
TATION AND LEACHING COMBINED
PERCENTAGE Loss
CoNSsTITUENT Lost
Protected Unprotected
Oreanic matter es 2 a 60 69
Witwomen Wie eas) RE 23 40
Phosphoric agigraule:... < tei. 4 +f 16
Potsen:.. oun... soul kee 3 36
288. Protected manure more effective. — Over a period
of fourteen years, in a three year rotation of corn, wheat
and hay at the Ohio Experiment Station, stall manure gave
an average yield of 30 percent more than did equal quantities
of yard manure. This gives a fair basis on which to cal-
culate whether it would pay to protect the manure when the
expense of doing so,:and the quantity of manure produced,
are considered.
FARM MANURES 229
289. Reinforcing manure. — Various substances are in-
corporated with animal manures, either in the stall or in
the heap, for the purposes of: (1) curtailing loss by leaching
and fermentation, and (2) balancing the manure in order to
better adapt it to the needs of most crops. The latter has
been mentioned in section 280. The materials commonly
used for these purposes are gypsum, kainit, acid phosphate
and floats. |
Experiments at the Ohio Experiment Station indicate that
the conserving effect is slight, but that the benefit due to
reinforcing is considerable when acid phosphate or floats
are used. ‘To ascertain the conserving properties of several
substances, each was mixed with the manure at the rate of
40 pounds to the ton, and the loss of fertilizing value was
computed from analyses after the mixtures had stood from
January to April. The results are shown in the following
table :
TABLE 51. — Errect oF REINFORCING MATERIALS ON CONSERVA-
TION OF FERTILITY IN FaRM MANURE
VALUE OF TON OF MANURE
MATERIALS USED ee ey
In January In April
MI ty eS i, $2.19 $1.41 36
RemenemeTh: ole sigyth ie... 2.05 1.48 38
Lon tc ti Sere 2.24 1.45 35
TV e DE ile? GOR 5 a ae ede y k 2.04 24
med phosphate. .° . .. 2.34 1.65 29
The actual agricultural value of the reinforced manure was
ascertained from tests covering a period of fourteen years
in a rotation of corn, wheat and hay, of which the results
were as follows:
230 SOILS AND FERTILIZERS
TABLE 52. — FINANCIAL RESULTS OF REINFORCING FaRrM MANURE
VALUE OF NET In-
CREASED YIELD TO
THE TON OF MANURE
Manure alone =O 2 SEI TSI, Aah" th $3.04
Miamiire pli eyes ok eae es wen ae 3.56
Wiingre pis Kenia) ra? ee eee o.¢1
Manure plus floats . . AEs ae) ir ae IL 4.49
Manure’plus acid phosphate sli oo el Tod by 4.82
It has already been remarked that farm manure is deficient
-in available phosphoric acid, and this experiment demon-
strates the benefit to be gained by reinforcing it with a phos-
phoric acid fertilizer.
290. Methods of handling manure. — The least oppor-
tunity for deterioration of farm manure occurs when it is
hauled directly to the field from the stall and spread at once.
Manure may even be spread on frozen ground or on snow,
provided the land is fairly level and the snow is not too deep.
However, it is not always possible to follow this method and
manure must sometimes be stored. In the storage of ma-
nure the two important conditions are a sufficient but not .
an excessive supply of moisture, and a well-compacted mass.
Water draining away from a manure heap, and a fermenta-
tion producing a white appearance of the manure under the
surface of the pile (“‘ fire fanging ’’), are both sure indications
of unnecessary loss in its fertilizing value.
291. Covered barnyard. — The best method of storing
manure is in a covered yard in which the cattle are allowed to
exercise and thus to trample and compact the mixed manure
from the barn. The advantage to be gained from the tram-
pling is brought out by some Pennsylvania experiments in
which the losses of fertilizing constituents were compared
when the covered manure was trampled and when it was not.
FARM MANURES ea
TABLE 53.— Loss or FERTILIZING CONSTITUENTS FROM FARM
MANURE IN COVERED SHEDS WHEN TRAMPLED AND WHEN
Not TRAMPLED
PERCENTAGE Loss oF
TREATMENT OF MANURE
Nitrogen ee oa Potash
Covered and trampled .§. .. . 5.0 5:5 8.5
Covered and not trampled . . . .| 34.1 19.8 14.2
292. Application of manure to land. — In applying farm
manure to the field, it is customary either to throw it from
the wagon in small heaps, from which it is distributed later,
or to scatter it as evenly as possible immediately on hauling
it to the field. The use of the automatic manure-spreader
accomplishes the latter procedure in an admirable manner. ~
As between these two methods, the advantage, so far as the
conservation of fertility is concerned, is with the practice of
spreading immediately. When piled in small heaps, fer-
mentation goes on under conditions that cannot be controlled,
and that may be very unfavorable. The heaps may dry
out, and thus lose much of their nitrogen, or they are likely
to leave the field not uniformly fertilized because of the
leaching of some of the constituents of the manure into the
soil directly under and adjacent to the heap. On the other
hand, when spread immediately, little fermentation takes
place, as the manure does not heat, and the soluble sub-
stances are leached quite uniformly into the soil. Plowing
should follow as closely as possible the spreading of the
manure, except when it is intended for a top dressing.
293. Place of farm manure in crop rotation. — When a.
crop rotation includes grass or clover as one of the courses,
the application of farm manure may well be made at that
time as a dressing. It can thus be spread at times when
cultivated land would not be accessible, and the crop of hay
232 SOILS AND FERTILIZERS
will profit greatly. Sod, when plowed under, is frequently
planted to corn — a crop that is rarely injured by farm ma-
nure. Experiments in Illinois indicate the great response
of clover to farm manure, as compared with oats and corn.
TABLE 54. — INCREASED Crop YIELDS AND VALUES WHEN MANURE
Was APPLIED TO CORN AND OATS AND TO CLOVER
PERCENTAGE INCREASE| PERCENTAGE VALUE
IN YIELD oF INCREASE
TREATMENT
ee Clover eae Clover
Manure . . : 11 92 $ 7.53 | $10.08
Manure, lime and phosphate 30 141 12.21 15.48
QUESTIONS
1. What plant nutrients does farm manure contain, and what
indirect fertilizing material ?
2. In what ways is the organic matter of farm manure beneficial
to soils ?
3. Which is richer in plant-food materials, liquid or ‘salt
manure ?
4. What constituent should farm manure have added to it in
order that it should be a well-balanced fertilizer ?
5. What farm animal produces the largest quantity of manure
for every 1000 pounds of live weight ?
6. Which produces the more valuable manure, a ration rich
in plant-food materials, or one poor in these substances ?
7. Which of the farm animals furnishes a manure having the
greatest commercial value a ton ?
8. In what two ways does farm manure suffer loss on standing ?
9. How is nitrogen likely to be lost by fermentation, and what
. condition is likely to bring this about ?
10. What substances are lost by the leaching of manure ?
11. What materials are used for conserving manure ?
12. Isit better to store manure, or to haul it directly to the land ?
Why ?
13. Discuss the place of manure in the crop rotation.
FARM MANURES 233
LABORATORY EXERCISES
Exercise I. — Study of farm manure.
In one or more trips through the community the class may study
in a practical way the following points regarding farm manure and
its utilization.
1. Enter a horse stable where fresh manure is lying in the stalls.
Observe the odor of ammonia. Explain the reason for such an odor
and its significance.
2. Compare horse manure and cattle manure as to weight, struc-
tural condition and amount of water. What relation may these
characteristics have to fermentation and to the handling of the
manures ?
3. In the same way compare swine, sheep and poultry manures.
4. Examine the leachings from an exposed manure pile. What
is the color of such liquid and what plant-food materials does it prob-
ably contain ?
5. Study the various ways of handling manure that are in vogue
in the community. List and discuss their good and poor points,
remembering that the method that would entail the least loss of
plant-food material may not always be practicable, due to lack of
capital or to the press of the season’s work. The common ways
of handling manure are : hauling directly to the field and either
(1) spreading or (2) leaving in piles for later distribution, (3) stor-
ing in a covered barnyard, (4) storing ina manure pit, (5) allowing
manure to be tramped down behind the animals or (6) storing in
piles either under cover or exposed. |
6. Study the mechanism and operation of a manure-spreader.
An efficient spreader should run easily and yet distribute the manure
evenly and in a finely divided condition.
Exercise IJ. — Experiments with farm manure.
Plat experiments similar to those suggested in Exercise IV, Chap-
ter XVI might be carried out with profit with farm manure. The
effect of different amounts of manure, the relative returns of manure
from different classes of animals, the influence of lime on the return
from the application of manure, and the residual influence of manure»
are only a few of the possible tests that might be made.
Tests as described in Exercise III, Chapter XI might be carried
out with manure as well as with commercial fertilizers and lime if
plats of soil are not available.
234 SOILS AND FERTILIZERS
Exercise II]I.— The value of manure on the home-farm.
From the data in the text, have each student calculate the
probable quantity of manure produced on his home-farm. Have
him calculate the commercial value of this manure. Then from the
way in which the manure is handled have him estimate the loss
which occurs to this manure. Now discuss the probable agricultural
value of the manure as compared with its original commercial value.
Exercise IV. — Reinforcement of farm manure.
In codperation with some near-by farmer, reinforce some farm
manure, allowing the pupils to aid not only in the actual work, but
in the determination of the kind and amount of reinforcing materials
to use. Calculate from the quantities used and their composition
as given in the text, the probable composition of the manure after
the treatment and determine whether it has become a properly
‘balanced material. The reinforced manure should be spread in
the field so that its influence on the succeeding crop may be com-
pared with untreated manure. Reinforcements with different ma-
terials may even be compared under actual field conditions.
Exercise V. — Building of a compost pile.
Farm manure in a compost pile supplies the organisms which
bring about the decay of the sod, leaves or other plant materials
which are. to be reduced to simple compounds. Composted mate-
rials are of especial value in greenhouses and gardens in supplying
organic matter to the soil, that a good structure may be maintained.
Choose a level spot on which to locate the compost pile. First
put down a layer of sod, moistening if necessary until optimum con-
ditions are attained. Next apply a thin layer of fine, well-rotted
manure, then sod and so on till the pile is complete. The pile may
be as large as necessary or convenient and should be level on top to
prevent the rainfall from running off the surface. If the interior of
the pile is moist to begin with, it will stay moist through the period
given to fermentation. Six months or a year are necessary for
effective composting.
Other materials than sod may be placed in a compost heap,
such as leaves, vines of all kinds, rotted vegetables, garbage, small
sticks, ete. It isa good practice also to add lime to the pile to keep
it sweet. If the material is to be used as a fertilizer as well as to
condition the soil, acid phosphate may also be added.
CHAPTER XVIII
GREEN-MANURES
Crops that are grown primarily for the purpose of being
plowed under to improve the soil are called green-manures.
They may benefit the soil in one or more of four ways: (1) By
utilizing soluble plant-food material that would otherwise
leach from the soil; (2) by incorporating vegetable matter
with the soil; (8) leguminous crops, when used, add to the
available nitrogen of the soil; (4) plant-food materials from
the lower soil may be brought to the surface soil.
A large number of crops may be used for this purpose,
while the climate determines to some extent which crops
should be used. Crops that.can be planted in the fall to
grow during the cool weather may be utilized when otherwise
the land would frequently lie bare. Leguminous crops have
the great advantage of acquiring nitrogen from the air. Deep-
rooted crops usually accumulate a large amount of nutriment
from the soil and considerable from the lower depths. They
are therefore useful in bringing plant-food material to the
upper layers of soil. Succulent crops decompose easily, and
dry out the soil less, when plowed under, than do woody crops.
Crops with extensive root-systems prevent loss of soluble
matter more thoroughly than do plants with small root
systems.
294. Protective action of green-manures. — It has been
shown in section 121 that the growth of crops on land may
prevent a large loss of plant-food material, especially nitrogen
235
236 SOILS AND FERTILIZERS
and lime, indrainage water. If, therefore, green-manure crops
cover the soil, when otherwise nothing would be growing on it,
they exercise a protective action. In the case of orchards a
green-manure crop saves much nutriment as compared with
clean cultivation. A catch-crop, like rye, that is sown in the
fall after a summer crop has been harvested and is plowed
under in the spring, saves some plant-food material.
295. Materials supplied by green-manures. — Probably
the most beneficial effect exerted by green-manures is the ad-
dition of organic matter to soil. Practically the only source
of organic matter is in the form of farm manure or of plant
residues. Farm manure is yearly becoming more scarce
and expensive. Some substitute must be found. In an
average crop of green-manure, from five to ten tons of
material is turned under. Of this, from one to two tons is
dry matter, and from four to eight tons is water. This would
correspond to a dressing of four to eight tons of farm manure,
so far as the organic matter alone is concerned.
Legumes add nitrogen as well as organic. matter. The
nitrogen contained in a ton of the green crop, when in a con-
dition to plow under, is as follows:
TABLE 55. — QUANTITIES OF NITROGEN IN SOME LEGUMINOUS
GREEN-MANURE CROPS
NITROGEN | PROBABLE | NITROGEN
Crop PER TON, | YIELD’ PER| PER ACRE,
Pounps /|AcrE, Tons} Pounps
Red.ok mammothicloyer. . . << 10 6 60
Crimson Gloverjmeesk. . <2. ges 9 6 54
Wide elayer seer yh Ga, 10 5 50
702109 Fie i |: °c ee cs 14 8 Li2
SCOOAS ) cc og A 8 6 48
Bey DESHS 7 Sree a ee 10 6 60
GVasinda field pasa e202). (6 Rk 11 5 55
GREEN-MANURES 237
Not all of the nitrogen contained in these crops is taken
from the air. On soils rich in nitrogen, a considerable pro-
portion may be obtained from the soil. On poor soils, the
proportion derived from the atmosphere is considerably
larger. Soils needing nitrogen most are those that benefit
most largely from its application.
296. Transfer of plant-food materials. — There is a trans-
fer of plant nutrients in a double sense: (1) removal of these
ANIMAL TO MARKET
LOSS LARGELY ORGANIC ~ | eae
Vad
WITH SOME NITROGEN }
AND PHOSPHORIC ACID \ Yl
\ |
LARGE Loss oF onannic <> YANURE \
MATTER, NITROGEN, PHOS-
PHORIC AGID AND POTASH
GREEN MANURE
Fic. 34. — Movements of plant-food materials. After absorption by the
plant they may be returned in whole or in part to the soil. If grain and
straw or hay are sold nothing but the stubble and roots are returned. If
fed to animals, part may be returned in the manure. If plowed under as
green-manure, all are returned.
substances from combination with other minerals and their
conversion into combinations with organic matter; (2) re-
moval from lower soil by absorption by roots and the deposi-
tion of this material in the upper layer of soil when the plant
dies and is plowed under. The first of these transfers results
in an improved condition of the plant nutrients, because in
the combinations with organic matter they are in general
more available to plants than when in combinations with
238 SOILS AND FERTILIZERS
inorganic matter. By the second form of transfer the nutri-
ents in this available form are deposited in the upper soil from
which most crops draw the larger part of their nutriment.
297. Crops used for green-manuring. — The following table
contains a list of the plants commonly used as green-manures
both in cultivated fields and in orchards, together with some
information as to the season of the year when they may be
used and whether adapted to northern or southern conditions.
TABLE 56. Crops UsEp AS GREEN-MANURES
SEASON
Legumes (annual)
Canada field pea
Hairy vetch
Crimson clover
Peanut
Velvet bean
Soy bean
Cowpeas
Legumes (biennial or perennial)
Red or mammoth clover .
Alsike clover .
Alfalfa .
Sweet clover .
Non-Legumes
Rye .
Oats
Buckwheat
Cowhorn turnips
Mustard
Rape
summer
winter
winter
summer
summer
summer
summer
one year at least
one year at least
one year at least
one year at least
winter
. | fall or early spring
fall and summer
summer
summer
summer and fall
REGION
Northern states
Northern and southern states
Middle and southern states
Middle and southern states
Middle and southern states
Middle and southern states
Southern states
Northern states
Northern states
Northern and southern states
Northern and southern states
Northern and middle states
Northern and middle states
Northern states
Northern states
Northern states
Northern states
A soil that has become less productive under cultivation,
and that must be improved before profitable crops can be
grown, receives more benefit from the use of legumes than
from any other crop. The legume to use is naturally the one
best adapted to the region in which the soil is located.
The perennial or biennial legumes are too slow of growth
really to be considered green-manure crops. They are like
Puate XVI. Sort Covers. — Cover-crops may consist merely of
weeds allowed to grow voluntarily, as shown in the upper figure, or of
grain or other planted crops, as shown in the lower.
ein”
Bs’
“
ae
GREEN-MANURES 239
timothy and other grasses and can well be grown for hay, only
the sod being plowed under. Only in the case of very much
run down soils are these crops plowed under. Crimson
clover is an annual, and in the central and southern states
may be sown in the fall and plowed under in the late spring,
thus making use of a period of the year when the ground is
least likely to be occupied by a crop. Cowpeas, soy beans
and field peas must be raised during the summer months.
Vetch promises to be a satisfactory green-manure for winter
use in the northern states, when the cost of seed becomes
less than ‘it is at present.
Where it is desired to keep a crop on the soil during the
autumn, winter and spring, for the purpose of utilizing the
soluble plant-food material, the cereals, especially rye, are
useful. Buckwheat, on account of its ability to grow on poor
soil, is adapted to use as a green-manure, but it must be
grown in the summer or early fall.
298. When green-manures may be used. — The most
economical way to use green-manures is between the regular
crops, rather than to lose a crop for the purpose of applying
green-manure. Between a small grain crop and a spring-
planted crop, there is usually opportunity for some green-
manure to be raised, even in the northern states. This crop
may be rye, vetch, buckwheat or rape and in the southern
states may be added crimson clover, which is perhaps best
for that region. In the South, however, there is much
more opportunity for the use of green-manure crops on ac-
count of the longer season. Where timothy and red clover
grow successfully, it is probably best to rely on the sod of
these crops to furnish green-manure rather than to attempt
any system that would necessitate dropping a crop from the
rotation. By a judicious fertilization of the hay crops, a
heavy sod may be produced, thus utilizing the inorganic
matter of the fertilizer to produce organic matter in the sod.
240 SOILS AND FERTILIZERS
It is probably where special crops are produced that green-
manures will reach their greatest usefulness. Their use in
orchards is well established. For this purpose they are
plowed under in the spring and planted in midsummer.
Potato-growers and even market-gardeners are using green-
manures in increasing quantity.
299. Handling green-manure crops.— The stage of growth
at which green-manures should be plowed under has a rather
important bearing on their effect on the soil. In order that
they shall decompose readily, they should be succulent when
incorporated with the soil. If plants that have fully ripened
are plowed under, they decompose very slowly and interfere
with the formation of nitrates. An acid soil is unfavorable
to the decomposition of green-manures and to the formation
of nitrates ; hence it is desirable that lime be applied before
planting the manure crops unless the soil is already well
supplied with lime.
QUESTIONS
1. Describe what is meant by green-manure crops.
2. State four ways in which they may be beneficial to the soil.
3. What two substances are prevented from being leached from
soil in large quantities by the growth of green-manure crops ?
4. How do legumes differ from other green-manures in con-
tributing to soil fertility ?
5. In what two ways is there a transfer of plant nutrients brought
about by the use of green-manures, and how do they benefit the soil ?
6. Name five leguminous green-manure crops and state the time
of year in which they are generally planted in your locality.
7. Give the same information regarding five non-legumes.
8. What is the disadvantage of plowing under green-manure
crops when they are fully ripe ?
LABORATORY EXERCISES
Exercise I. — Study of green-manure in the field.
Plan a field trip to some farm where a crop is being turned under
for green-manure. Determine whether the time is most favorable
GREEN-MANURES 241
for the operation. Study the action of the plow which is being
used and see if the depth of the plowing, the inclination of the
furrow slice, and the covering of the green material is as it
should be.
Calculate the weight of the crop being turned under and with
this as a basis, figure the pounds of water, dry matter, nitrogen,
phosphoric acid and potash being placed in the soil per acre. If
the crop is a legume, make a guess as to the probable gain of the soil
‘In nitrogen. Is this nitrogen available or unavailable ?
ExercisE IJ. — Green-manure and the rotation.
Take a number of good practical rotations and indicate where,
in the succession of crops, a green-manure might be introduced.
Encourage the pupils to bring data from their home farms for this
study. Tabulate such material and study it in the class room.
Also bring up the question in relation to gardening and trucking.
Discuss the necessity, advisability and ways of introducing a green-
manure under such conditions.
CHAPTER XIX
CROP ROTATION
Ear ty in the development of agriculture, it was understood
that a succession of different crops on any piece of land
gave better returns than did one crop raised continuously.
The practice of changing the crops raised each year thus
became customary, and the prevalence of the method among
European peoples shows that its benefits are widely appre-
ciated. In Great Britain and some of the countries of
Kurope, crop rotations have been most systematically
and effectively developed. Such development has been stim-
ulated by the diminishing productiveness of the soil, con-
sequent upon long-continued cultivation, coupled with an
increasing and progressive population. Regions having
undepleted and uninfested soil, as was formerly the case in
the prairie region of the United States, and countries that
have an unprogressive people, like those of India, have done
little with crop rotation.
Another condition that discourages the use of crop rotation
is the suitability of a region to the production of some one
erop of outstanding value, combined, perhaps, with a rela-
tively cheap supply of fertilizing material. These conditions
obtain in the cotton belt of the United States. The abun-
dant use of fertilizers may postpone for a long time the
recourse to crop rotation.
300. Crop rotation and soil productiveness. — There
are many benefits to be derived from a proper rotation of
242
CROP ROTATION 243
crops that are not directly concerned with soil productive-
ness, and of these this book does not treat. In a number
of ways crop rotation may directly affect the soil, and these
will be discussed under several different heads.
301. Root systems of different crops. — Some crops have
roots that penetrate deeply into the subsoil, while others are
only moderately deep-rooted and still others very shallow-
rooted. Arong the deeply rooted plants are alfalfa, clover,
certain of the root crops and some of the native prairie
grasses. Among those having moderately long roots are
oats, corn, wheat, meadow fescue and a few other grasses,
and among those having shallow roots are barley, turnips
and many of the cultivated grasses.
As plants draw their nourishment from those portions of the
soil into which their roots penetrate, the deeper soil is not
called upon to provide food material for the shallow-rooted
crops, and the deep-rooted crops remove relatively less of
their nutrients from the surface soil. It, therefore, happens
that a rotation involving the growth of deep and shallow-
rooted plants effects, by utilizing a larger area of the soil,
a more economical utilization of plant nutrients than would
a continuous growth of either kind.
302. Nutrients removed from soil by different crops. —
Some crops require large amounts of one fertilizing constit-
uent, while others take up more of another. For instance,
wheat crops are able to utilize the potassium and phosphorus
of the soil to a considerable degree, but have less ability to
secure nitrogen. They are usually much benefited by the
application of a nitrate fertilizer and leave in the soil a con-
siderable residue of nitrogen that may be available to other
plants. A number of other crops, as, for example, beets and
carrots, can utilize this residual nitrogen.
Grasses remove comparatively little phosphoric acid.
Potatoes remove very large quantities of potash. A rota-
244 SOILS AND FERTILIZERS
tion of crops is, therefore, less likely to cause a deficiency
of some one constituent than is a continuous growth of
one crop, and it utilizes more completely the available
nutrients.
303. Some crops or crop treatments prepare nutriment
for other crops. — It is quite evident that leguminous crops
not only leave in the soil an accumulation of organic nitrogen
transformed by bacteria from atmospheric nitrogen, but that
they leave part of the nitrogen in a form readily available
for use by other plants. The presence of a grass crop on the
land for several years favors the action of non-symbiotic
nitrogen-fixing bacteria. The grass crops also leave a very
considerable amount of organic matter in the soil, which
by its gradual decomposition contributes both directly and
indirectly to the supply of available nutrients.
Stirring the soil at intervals during the summer greatly
facilitates decomposition, and leaves a supply of easily avail-
able food material. The introduction of intertilled crops in
the rotation thus serves to prepare nutriment for those that
receive no intertillage.
304. Crops differ in their effect on soil structure. — Plants
must be included among the factors that affect the arrangement
of soil particles. The result of root growth is usually to im-
prove the physical condition of soil. In general, crops with
rather shallow and very fibrous roots are most beneficial, at
least to the surface soil. Millet, buckwheat, barley and to a —
less extent, wheat leave the soil in a friable condition. Itis on
heavy soils that this property is most beneficially exercised.
Tap-rooted plants, and others with few surface roots, do not
exhibit this action. Alfalfa and some root crops are likely
to leave the soil rather compact as compared with the crops
mentioned above. The effect of sod is nearly always bene-
ficial to heavy soils, and this is one of the reasons for using
a grass crop in a rotation.
CROP ROTATION 245
305. Certain crops check certain weeds. — By rotating
crops the weeds that flourish during the presence of one crop
on the land may be greatly checked by succeeding crops.
Some weeds are best destroyed by smothering, for which
purpose small grain, and notably corn or sorghum grown for
fodder are effective. Other weeds are most injured by til-
lage, to accomplish which the hoed crops are needed; while
others can best be checked by the presence of a thick sod on
the ground for a number of years. In the warfare against
weeds that must be waged wherever crops are raised, the use
of different crops involving different methods of soil treat-
ment is of great service.
306. Plant diseases and insects. — Many plant diseases
and many insects spend their resting stages and larval exist-
ence in the soil. A continuous growth of any one crop on the
soil favors the increase of these species by providing each
year the particular plant on which they thrive. A change of
crops, by removing the host plants, causes the disappearance
of many diseases and insects through their inability to reach
their host plants. A long rotation, such as is frequently
used in Great Britain, is particularly effective in eradicating
those diseases that persist in the soil for a number of years.
In the case of diseases that affect more than one species
of plant, as does the beet and potato scab, there is need for
special care in arranging the rotation. Such considerations
may make it desirable to change the plan of a rotation.
Another feature of the relation of crop-rotation to plant dis-
eases is that the more thrifty growth obtainable under rota-
tion assists the crop to withstand many diseases.
307. Loss of plant-food material between plantings.— Many
systems of crop rotation permit a more constant use of the
land than is possible with continuous growth of most annual
crops. As a soil bearing no crop on it always loses more
plant-food material in the drainage water than does one on
246 SOILS AND FERTILIZERS
which plants grow, it is thus possible, by a well-chosen
rotation, to save plant-food material that would otherwise
be lost.
308. Production of toxic substances from plants. — That
soil sometimes contains organic substances that exert an
injurious effect on the growth of certain plants is indicated by
recent experiments and was surmised by some early writers
on the subject. De Candolle was probably the first to ad-
vance the idea in 1832. He suggested that at least some
plants excrete from their roots substances that are injurious
to the growth of the plants themselves and others of their
species, although the excreta may be harmless or even bene-
ficial to other plants. This he considered one of the reasons
for the failure of many crops to succeed when grown contin-
uously, while the same soil may be productive under a rota-
tion of crops.
Of recent years this subject has been investigated exten-
sively in the United States and to some extent in Europe.
There appears to be no doubt that toxic substances of an
organic nature sometimes occur in soils, and there is evi-
dence that some of them are connected with the growth of
certain crops to which they are injurious. In most soils
containing toxic substances the injurious effect is exerted on a
large number of plants rather than only on those that have
been previously grown. It is still a question to what extent
excretion from roots or partial decomposition of plant residues
are responsible for the poor growth that results from the
continuous growth of crops on the same soil.
309. Management of a crop rotation. — The advantages
of a crop rotation are so apparent and are connected so closely
with the profits to be derived from farming that there can be
no doubt regarding the advisability of practicing a rotation,
even when some one crop may be much more profitable than
any others that can be grown. Thus even in regions and on
CROP ROTATION O47
soil particularly favorable to the production of any one crop,
like tobacco, cotton, hay, corn or wheat, it will seldom be ad-
visable to raise one crop to the exclusion of others, but the
most rational practice will generally provide for some system
of crop rotation.
There are three classes of crops that should, so far as possi-
ble, have a place in any rotation. These are legumes, sod
crops or grasses and intertilled crops. The value of legumes
as nitrogen gatherers has already been discussed. It is partic-
ularly on poor land that legumes are of most benefit, and if
some of the tops, as for instance, the second growth of clover,
be plowed under, their value will be greater.
Sod crops are of great value in furnishing organic matter
to the soil. The larger the hay crop, the more sod produced,
which is a double incentive to the use of fertilizers and
farm manure on this crop (see § 204). Sod also forms
a favorable condition for the fixation of nitrogen. Legumes
appear to have one advantage over sod crops as nitrogen
gatherers, in that the nitrogenous matter remaining in the soil
is more available to some crops, at least, and is more readily
converted into nitrates.
In each course of a rotation there should be, if possible, one
intertilled crop, like corn, cotton, potatoes or cabbage. The
intertilled crop should follow the sod crop, or the legume,
because the cultivation given the soil throughout the summer
produces a condition favorable to the decomposition of the
organic matter furnished by the sod. Except where the con-
servation of moisture is an important factor, the use of an
intertilled crop is preferable to a clean fallow, as it is more
economical of the nitrogen and lime supply, and appears to
result in better crops the year following.
Other crops to be used in the rotation will be determined by
the climate, soil, market and convenience in handling.
Fertilization of the rotation is discussed in section 271.
248 SOILS AND FERTILIZERS
QUESTIONS
1. What advantage is gained by alternating deep-rooted with
shallow-rooted plants in a rotation ?
2. Why is a rotation of crops less likely to cause a deficiency in
some one constituent of the soil than is; the continuous growth of
one crop ?
3. In what ways do some crops and some crop treatments pre-
pare available nutriment for other crops ?
4. How may soil structure be affected by crop rotation ?
5. Explain the relation of crop rotation to weeds.
6. Explain the relation of crop rotation to plant diseases and
insects.
7. Hew may plant nutrients be prevented from leaching by the
use of the proper rotation ?
8. What three classes of crops should have a place in any rota-
tion and why ?
LABORATORY EXERCISES
' Exercise I. — Crop rotations.
Study standard crop rotations from different parts of the United
States as to crops grown, climate, markets, fertility of the soil,
fertilization, ete. Try to find the reason for the use of each rotation
under its particular conditions.
With the aid of the pupils, obtain a number of the rotations used
in the community or county. Study these from all standpoints,
and, if possible, suggest improvements. A rotation survey of the
community might be made in ordef that data valuable to the
farmers, as well as to the pupils, shall be obtained. The students
should aid in this as well as in the tabulation and interpretation of
the data.
Exercise II. — Fertilizing the rotation.
Under given conditions have the pupil work out the fertilization
of a standard rotation for the locality. This means not only the
kinds and quantities of fertilizer to apply, at what point in the
rotation to add them and at what time of year to put on the soil,
but also the use of lime, green manure and farm manure. Such a
study should be a summation of many of the practices and principles
of good soil management.
INDEX
Absolute specific gravity, of soil Air of soil, oxygen in, 146.
particles, 35.
and ‘‘heavy’’ soil, 35.
and ‘“‘light”’ soil, 35.
Absorbed fertilizers, 100.
Absorption, of lime by soils, 188.
of gases, test for, 111.
selective, 99.
selective, test for, 111.
Absorptive power of different crops,
107.
Absorptive properties of soils, 99.
Acid phosphate, absorption by soil,
‘7a.
manufacture and composition, 172.
vs. rock phosphate, 174.
Acid soils, described, 112.
causes of, 113.
crops adapted to, 116.
crops injured by, 116.
effect of drainage on, 113.
effect of fertilizers on, 114.
effect of green manures on, 115.
effect of plant growth on, 114.
litmus paper test for, 117.
relation to bacteria, 129.
tests for, 122, 123.
Truog test, 118.
weeds that flourish on, 115.
Adobe, composition of, 27.
distribution of, 27.
AXolian soils, described, 26.
adobe, 27.
loess, 27.
Air of soil, composition, 145.
control of movement, 148.
control of volume, 148.
demonstration of movement, 152.
in relation to drainage, 79.
movements, 144.
nitrogen in, 147.
quantities present, 143.
relation to pore space, 143.
relation to water, 144.
usefulness of, 146.
Alkali and irrigation, 120.
control of, 121.
effect of crops on, 119.
movements of, 118.
removal of, 120.
tolerance of different plants to,
119.
Alkali soils, nature of, 118.
Alluvial soils, character of, 23.
described, 22.
distribution of, 23.
formation of, 22.
Ammonia, absorption by plants, 156.
test for, in soil, 141.
Ammonification, 132.
Animals, effect on structure, 41.
Apatite, plant-food materials in, 7.
Apparent specific gravity, and
“heavy’”’ soil, 38.
and ‘‘light’’ soil, 38.
of soil particles, 38.
Auger for sampling soil, 29.
Available plant-food materials, 94.
Availability, conditions that in-
fluence, 95.
of nitrogenous fertilizers, 166.
Bacteria, action on mineral matter,
129.
ammonification caused by, 132.
conditions affecting growth, 128.
decomposition of nitrogenous
organic matter, 131.
decomposition of non-nitrogenous
organic matter, 130.
examination of nodules for, 142.
249
250
INDEX
Bacteria, in relation to air supply, 128.| Drainage, and length of growing
in relation to lime, 189.
in relation to moisture, 128.
in relation to organic matter, 129.
in relation to soil acidity, 129.
in relation to soil fertility, 129.
in relation to temperature, 129.
nitrification caused by, 132.
numbers in soils, 127.
Basic slag, 172.
Calcite, plant-food material in, 7.
Capillary capacity, test for, 87.
Capillary movement, test for, 86.
Capillary water, 63.
Carbon dioxide, conditions that affect
quantity, 146.
demonstration of formation in soil,
154.
demonstration of presence in soil,
158.
functions in soil, 147.
percentage in bare and planted
soil, 106. f
percentage in soil air, 145.
production by microérganisms, 107.
production in soils, 145.
Chemical analysis of soil, 98.
Chemical composition, of various
soils, 91.
relation to productiveness, 93.
Class, the soil, defined, 33.
in soil survey, 44.
method for determination, 34.
Classification of soils in survey, 43.
Colluvial soils, described, 22.
formation of, 22.
Compaction of soil due to root
growth, 2.
Compost, building of a pile, 234.
Crop rotation, 242.
Crops, relation to soil texture, 32.
Cumulose soils, composition of, 21.
described, 20.
formation of, 20.
Cyanamid, changes in the soil, 162.
composition of, 161.
manufacture of, 161.
Denitrification, 135.
Dolomite, plant-food materials in, 7.
season, 80.
and available water, 79.
benefits from, 78.
by open ditches, 80.
defined, 78.
in relation to soil air, 79.
in relation to tilth, 79.
Drainage water, composition of,
103, 104.
Drains, arrangement of, 82.
concrete, 81.
tile, 81.
Evaporation, prevention of, 74-77.
proportion of rainfall lost by, 73.
Feldspars, plant-food materials in, 7.
Fertility of soil in relation to bac-
teria, 129.
Fertilizer constituents, trade values,
200.
experiments, plan for, 212.
formulas for different crops, 210.
ingredients, how to mix, 205.
mixture, calculation of, 204.
Fertilizers, brands of, 196.
computation of wholesale value,
202.
conditions that influence effect of,
aT.
consumption of, in U. S., 196.
cumulative need of, 218.
- effect on soil acidity, 114.
for different crops, 207.
for different soils, 211.
for grasses, 208.
for leguminous crops, 208.
for orchards, 209.
for root crops, 209.
for small grains, 207.
for vegetables, 209.
high and low grade, 198.
home mixing of, 203.
inspection and control, 199.
law of diminishing returns, 215.
methods of applying, 214.
nitrogenous, 155.
nitrogenous, forms of nitrogen in,
157.
phosphoric acid, 171.
INDEX
251
Fertilizers, phosphoric acid, tests for, | ‘‘ Heavy”’ soil, and apparent specific
Lia
potash, 179.
potash, tests for, 185.
response of soil to, 218.
tests for nitrogenous fertilizers, 169.
that should not be mixed, 203.
* the limiting factor, 215.
the purchase and mixing of, 196.
_ use of, 207.
Fertilizing the rotation, 213.
Formation of soil, agencies concerned,
#1.
Formations of soil, 18.
Freezing and thawing of soil, effect
on structure, 40.
Frost, effect on rock disintegration,
12.
Gases, diffusion of, 144.
effect on rock disintegration, 14.
Germs, injurious to crops, 125.
in soil, kinds of, 125.
not directly injurious to crops, 126.
Glacial soils, composition of, 26.
described, 25.
distribution of, 26.
formation of, 25.
Glaciers, effect on rock disintegra-
tion, 13.
Grains, fertilizers for, 207.
Granite, losses during soil formation,
15:
Grasses, fertilizers for, 208.
Gravitational water, 67.
Green manures, crops used for, 238.
effect on soil acidity, 115.
handling, 240.
materials supplied by, 236.
nature of, 235.
protective action of, 235.
when to use, 235.
Guano, 165.
Gypsum, plant-food material in, 7.
use on land, 192.
Heat and cold, effect on rock disin-
tegration, 12.
Heat of soil, sources of, 149.
““Heavy”’ soil, and absolute specific
gravity, 35.
gravity, 38.
Hematite, plant-food material in, 7.
Hygroscopic water, 61.
Ice, effect on rock disintegration, 13.
Igneous rocks, 5.
Inoculation of soil for legumes, 138.
Iron, proportion in earth’s crust, 4.
Irrigation for removal of alkali, 120.
Lacustrine soils, described, 25.
formation of, 25.
Law of diminishing returns, 215.
Legumes, fertilizers for, 208.
Leguminous plants as nitrogen fixers,
137.
“Light’’ soil, and absolute specific
gravity, 35.
and apparent specific gravity, 38.
Lime, absorption by soils, 188.
as a soil amendment, 187.
caustic vs. ground limestone, 191.
demonstration of flocculation by,
194.
effect on bacterial action, 189.
effect on plant diseases, 190.
effect on tilth, 189.
fineness of grinding limestone, 191.
forms of, 189.
in relation to structure, 42.
liberation of plant-food materials,
190.
magnesium, 190.
proportion in earth’s crust, 4.
requirements of soils, 188.
tests for, 193.
Limestone, effect of fineness of grind-
ing, 191.
ground vs. caustic lime, 191.
losses during soil formation, 15.
Limiting factors in plant growth, 215.
Loess, composition, 27.
distribution, 26.
Magnesia, proportion in earth’s crust,
Manure, cow, partial composition of,
222.
_ effect of food on composition of,
224.
252
Manure, farm, 221.
farm, agricultural evaluation of,
226.
farm, an unbalanced fertilizer, 223.
farm, application to land, 231.
farm, chemical composition of, 222.
farm, commercial evaluation of,
225.
farm, covered barnyard for,.230.
farm, deterioration of, 226.
farm, experiments with, 233.
farm, fermentations of, 227.
farm, leaching of, 227.
farm, methods of handling, 230. ~
farm, place in crop rotation, 231.
farm, protected more effective, 228.
farm, reinforcing, 229.
farm, solid and liquid, 221.
green, crops used for, 238.
green, materials supplied by, 236.
green, handling, 240.
green, nature of, 235.
green, protective action, 235.
green, when to use, 239.
horse, partial composition of, 222.
quantities voided by animals, 224.
sheep, partial composition of, 222.
swine, partial composition of, 222.
value from different animals, 225.
Marine soils, composition of, 24.
described, 24.
distribution of, 24.
formation of, 24.
Mechanical analysis of soil, 31.
determination of class from, 34.
method for, 46.
of some typical soils, 32.
relation of crops to, 32.
size of separates, 32.
INDEX
Mulch, effectiveness of, 75.
frequency of stirring, 74.
of soil, nature and use, 74.
Mulches, for moisture control, 74.
test for conservation of water by,
87.
Nitrate formation, depths of occur-
rence, 135.
effect of aération on, 132.
effect of lime on, 189.
effect of sod on, 134.
effect of temperature on, 133.
Nitrate of soda, effect on soils, 159.
sources and composition, 157.
Nitrates, as plant-food material, 156.
crops markedly benefited by, 158.
loss in drainage water, 135.
test for, in soil, 140.
Nitrification, 132.
Nitrogen, animal products contain-
ing, 163.
availability in fertilizers, 166.
effects on plant growth, 165.
fixation, nature of, 136.
fixation by free living germs, 139.
fixation by plants, 137.
forms in fertilizers, 157.
forms in which used by plants, 156.
in fertilizers, 155-170.
in soils, quantities of different
forms, 155.
organic, direct utilization by
plants, 156.
organic, fertilizers containing, 162.
vegetable products containing, 163.
Nodules, examination for, 142.
on leguminous plants, 137.
Mechanical composition of various| Orchards, fertilizers for, 209.
soil classes, 34.
Metamorphic rocks, 5.
Minerals, from which rocks are
formed, 6.
soil-forming, laboratory exercise, 8.
plant-food materials in, 7.
relation to soil, 6.
Moisture, see water.
Muck, origin, 21.
relation to lime and potash, 22.
Mulch, depths of, 75.
Organic matter, and drainage, 53.
and formation of acids, 55.
and nitrogen, 54.
and plant-food material, 54.
and soil color, 53.
and soil organisms, 54.
benefits of, 52.
effect on structure, 41.
effect on availability of plant nu-
trients, 102.
estimation of, 58.
INDEX
253
Organic matter, examination of soil| Plant growth, conditions of, labora-
for, 58.
extraction of, 59.
influence on rate of percolation, 59.
influence on water held by soils, 60.
injurious effect, 55.
in soil, description, 51.
in soil management, 55.
kinds of, 51.
porosity of, 53.
sources of, 57.
Oxygen, proportion in earth’s crust, 4.
Packing, subsurface, 78.
Particles of soil, examination, 46.
number per gram, 30.
relative sizes, 31.
shape of, 30.
space occupied by, 30.
Peat, origin, 21.
Percolation, test for rate of, 86.
Plant constituents, obtained from air
or water, 3.
obtained from soil, 3.
Plant-food materials, available and
unavailable, 94.
essential to growth, 3.
absorption by plants, 105.
in apatite, 7.
in calcite, 7.
in drainage water, 102.
in dolomite, 7.
in farm manure, 222.
in green manures, 236.
in gypsum, 7.
in hematite, 7.
in liquid excreta, 222.
in minerals, 7.
in soils, 90.
in solid excreta, 222.
laboratory exercise, 9.
liberation by lime, 190.
movement of, 93.
obtained from air or water, 3.
obtained from soil, 3.
possible exhaustion, 109.
proportion in soils, 93.
quantities in earth’s crust, 4.
removed by crops, 108.
total supply in soils, 92. °
variations in soils, 90.
tory exercise, 9.
Plant nutrients, laboratory exercise,
9.
Plant roots, aid in solution of soil
constituents, 106.
solvent action, 107.
Plants, effect on rock disintegration,
14.
substances essential to growth, 3.
uses of water by, 2.
Phosphate, bone, 171.
mineral, 171.
Phosphoric acid,
growth, 175.
Phosphoric acid, plants benefited by,
176.
proportion in earth’s crust, 4.
reverted, 173.
Phosphoric acid fertilizers, 171.
availability of, 174.
Pore space, its determination, 49.
relation to structure, 37.
Potash, effect on plant growth, 181.
proportion in earth’s crust, 4.
Potash fertilizers, sources, 179.
wood ashes, 180.
Province, the soil, in soil survey, 44.
effect on plant
Quartz, substance of which composed,
ve
Residual soils, composition, 20.
described, 18.
distribution of, 20.
loss during formation, 19.
Rock, changes in soil formation, 15.
disintegration by heat and cold, 12.
disintegration, effect of gases on,
14.
disintegration, effect of glaciers on,
13:
disintegration, effect of ice on, 13.
disintegration, effect of plants on,
14.
erosion by wind, 14.
expansion by heat, 12.
relation to soil, 15.
Rocks, from which soil has been
formed, 5.
igneous, 5.
254
INDEX
Rocks, losses during soil formation, 15. | Soils, residual, 18.
metamorphic, 5.
sedimentary, 5.
sedentary, 18.
transported, 18.
soil-forming, laboratory exercise, 9. | Specific gravity, apparent, its deter:
Rolling land, 78.
Root crops, fertilizers for, 209.
Root systems of different crops, 243.
Roots of plants, effect on structure,
41.
Rotation of crops, 242.
and soil productiveness, 242.
management of, 246.
nutrients removed by, 248.
Sedentary soil, 18.
Sedimentary rocks, 5.
Separates of soil, 32.
chemical composition of, 36.
examination, 46.
properties of, 35.
Series, the soil, in soil survey, 44.
Soil, as a mechanical support for
plants, 1.
as a reservoir for water, 2.
as a source of plant-food material,
2.
changes during formation from
rock, 15.
Soil class, in classification for surveys,
44,
method for its determination, 47.
Soil formation, agencies concerned,
Li
and _ transportation, laboratory
exercise, 17.
Soil formations, 1, 18.
Soil-forming minerals, laboratory
exercise, 8.
Soil-forming rocks, laboratory exer-
cise, 9.
Soil mulch, nature and use, 74.
Soil province, in classification for
surveys, 44.
Soil, relation to rock, 15.
Soil series, in classification for sur-
veys, 44.
Soil survey, described, 43.
classification of soil for, 43.
information furnished by, 44.
Soil type, in classification for surveys,
44,
mination, 48.
of soil, apparent, 38.
of soil particles, absolute, 35.
of soil particles, apparent, 38.
Structure, of soil, as affected by freez-
ing and thawing, 40.
as affected by lime, 42. .
as affected by organic matter, 41.
as affected by plant roots and
animals, 41.
as affected by tillage, 42.
as affected by wetting and drying,
AO.
conditions that affect, 39.
granular or crumbly, 37.
defined, 37.
relation to pore space, 37.
relation to texture, 39.
relation to tilth, 39.
operations that affect, 39.
separate grain, 37.
Subsurface packing, 78.
Sulfate of ammonia, action when
applied to soils, 160.
composition, 160.
sources, 159.
Sulfur, as a fertilizer, 182.
contained in crops, 182.
contained in drainage water, 183.
contained in fertilizers, 184.
contained in soils, 183.
proportion in earth’s crust, 4.
Temperature, control of, 151.
demonstration of effect of slope on,
154.
factors that modify, 150.
of soil and atmosphere, 149.
of soils, relation to plant growth,
148.
Texture, of soil, described, 30.
relation to crops, 32.
relation to structure, 39.
Tile, concrete, 81.
drains, 81.
laying, 83.
Tillage in relation to structure, 42.
Vegetables, fertilizers for, 209.
INDEX ARS)
Tilth, as affected by lime, 189. Water, expansive power in freezing,
in relation to drainage, 79. 2:
yelation to structure, 39. forms in soils, 61.
Toxic substances and crop rotation, gravitational, definition, 62.
246. gravitational, movement, 67.
Transpiration, as affected by soil gravitational, properties of, 66.
moisture, 69. hygroscopic, definition, 61.
by different crops, 69. hygroscopic, properties of, 62.
conditions affecting, 70. in soil, determination of per cent,
ratio, 69. 85.
relation to soil fertility, 70. optimum content for plant growth,
test for loss by, 88. Cle
Transported soil, 18. percolation through soil, 73.
Type, the soil, in soil survey, 44. quantity required to mature a crop,
70.
relation to plants, 67.
requirements of plants, 68.
run-off, 72.
Water, as a soil transporting agent, solvent action on rock, 12.
is. test for capacity of soil for, 87.
capillary, capacity of soils, 63. test for capillary movement, 86.
capillary, definition, 62. test for conservation by mulch, 87.
capillary, effect of structure on test for loss by transpiration, 88.
movement of, 65. test for rate of percolation, 86.
capillary, effect of texture on uses by plants, 2.
movement of, 65. ways in which useful to plants, 68.
capillary, height of column and | Water-soluble matter in soil, 96.
movement, 66. test for, 111.
capillary movement and plant re-| Water table, 67.
quirement, 71. Weeds that flourish on acid soils, 115.
capillary, movement of, 64. _ | Wetting and drying soil, affect on
capillary, properties of, 63. structure, 40.
carrying power for rock débris, 13. | Wind, action in transporting soil, 14.
control of soil content, 72. erosive action on rocks, 14.
effect on rock disintegration, 12. Windbreaks, to decrease evaporation,
evaporation from soil, 73. woe '*
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