GIFT OF
MICHAEL REESE

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THE CHEMISTRY

OF

SOILS AND FERTILIZERS

BY

HARRY SNYDER, B.S.,

Professor of Agricultural Chemistry. University of Minnesota.

and Chemist of the Minnesota Agricultural

Experiment Station.

EASTON, FA.:
THE CHEMICAL FUBLISHIXG COMPANY.

1899.

{All rights reserved.')

.^

Copyright, i?99, by Edward Hart.

PREFACE

For several years courses of instruction have been
given at the University of Minnesota to classes of
young men who intend to become farmers and who
desire information that will be of assistance to them
in their profession. In giving this instruction mimeo-
graphed notes have been prepared, but the increase in
the number of students and the volume of notes have
necessitated the publication of this work. In its prep-
aration, it has been the ahh tdJ^^ive, in condensed form,
the principles of chemistry which have a bearing upon
the conservation of soil fertility and the economic use

of manures.

Harry Snyder.
University of Minnesota,

Coi,I,EGE OF AGRICUI.TURE,

St. Anthony Park, Minn.
April i^, i8gg.

^CAUFOg

CONTENTS

INTRODUCTION

Early uses of manures and the explanation of their action by the
alchemists ; Investigations prior to 1800 ; Work of De Saussure,
Davy, Thaer, and Boussingault ; Liebig's writings and their influ-
ence ; Investigations of Lawes and Gilbert ; Contributions of
other investigators ; Agronomy. Pages 1-9.

CHAPTER I

Physical Properties of Soils. — Chemical and physical properties
of soils considered ; Weight of soils ; Size of soil particles ; Clay ;
Sand ; Silt ; Form of soil particles ; Number and arrangement of
soil particles ; Mechanical analysis of soils. Soil types —
Potato and truck soils ; Fruit soils ; Corn soils ; Medium grass and
grain soils; Wheat soils. Relation of the soil to water ; Amount of
water required for crops ; Bottom water ; Capillary water ; Hydro-
scopic water; Loss of water by percolation, evaporation, and
transpiration ; Influence of cultivation upon the water supply of
crops ; Capillary water and cultivation ; Shallow surface cultiva-
tion ; Cultivation after rains ; Rolling ; Sub-soiling ; Fall plowing ;
Spring plo\nng ; Mulching ; Depth of plowing ; Fertilizers and
their influence upon moisture content of soils ; Farm manures and
soil moisture ; Permeability of soils ; Drainage ; Relation of soils to
heat ; Heat from chemical reactions within the soil ; Heat and crop
growth ; Color of soils ; Odor and taste of soils ; Relation of
soils to electricity ; Importance of physical properties of the soil.
Pages 9-48.

CHAPTER II

Geological Formation and Classification of Soils. — Geological
study of soils ; Formation of soils ; Action of heat and cold ;
Action of water ; Glacial action ; Chemical action of water ; Ac-

Vi CONTENTS

tion of air and gases ; Action of vegetation and micro-organisms ;
Distribution of soils ; Sedentary and transported soils ; Rocks
and minerals from which soils are derived as quartz, feldspar, mica,
hornblende, zeolites, granite, apatite, kaolin, limestone, gypsum ;
Chemical composition of rocks. Pages 49-59.

CHAPTER III

Chemical Composition of Soils. — Elements combine to form
minerals ; Classification of elements ; Combination of elements ;
Forms in which elements are present in soils ; Acid-forming ele-
ments, silicon, double silicates, carbon, sulphur, chlorine, phos-
phorus, nitrogen, oxygen, hydrogen ; Base-forming elements, alu-
minum, potassium, calcium, magnesium, sodium, iron ; Classifica-
tion of elements for plant-food purposes; Amount of plant food in
different forms in various types of soils ; How a soil analysis is
made ; Value of soil analysis ; Interpretation of the results of soil
analvsis ; Use of dilute acids as solvents in soil anah'sis; Distribu-
tion of plant food in the soil ; Composition of typical soils ;
"Alkali" soils and their improvement; Organic compounds
of soil ; Sources ; Classification ; Humus ; Humates ; Humification ;
Humates produced by different kinds of organic matter ; Value
of humates as plant food, amount of plant food in humic forms ;
IvOss of humus by forest fires, by prairie fires, by cultivation ;
Humic acid ; Soils in need of humus ; Soils not in need of humus ;
Composition of humus from old and new soils ; Influence of different
methods of farming upon humus. Pages 60-101.

CHAPTER IV

Nitrogen of the Soil and Air, Nitrification and Nitrogenous Ma-
nures. — Importance of nitrogen as plant food ; Atmospheric
nitrogen as a source of plant food. Experiments of Boussingault,
Ville, and Lawes and Gilbert ; Result of field trials ; Experiments
of Hellriegel and Wilfarth and recent investigators ; Composition
of root nodules ; Amount of nitrogen returned to soil by leguminous
crops and importance to agriculture ; Nitrogenous compounds
of the soil ; Origin ; Organic nitrogen ; Amount of nitrogen in soils ;
Rem jved in crops ; Nitrates and nitrites ; Anunonium compounds ;

CONTENTS vii

Ammonia in rain and drain waters ; Ratio of nitrogen to carbon in
the soil ; Losses of nitrogen from soils ; Gains of nitrogen to soils ;
Nitrification ; Former views regarding ; Workings of an organism ;
Conditions necessary for nitrification ; Influence of cultivation
upon these conditions ; Nitrous acid organisms, ammonia-produ-
cing organisms, denitrification, number and kind of organisms in
soils ; Inoculation of soils with organisms ; Chemical products pro-
duced by organisms ; Losses of nitrogen by fallowing rich prairie
lands ; Deep and shallow plowing and nitrification ; Spring and
fall plowing and nitrification ; Nitrogenous manures ; Sources ;
Dried blood, tankage, flesh meal, fish scrap, seed residue, and uses
of each ; Leather, wool waste, and hair ; Peat and muck ; Legumi-
nous crops as nitrogenous fertilizers ; Sodium nitrate, ammonium
salts ; Cost and value of nitrogenous fertilizers. Pages 102-137.

CHAPTER V

Fixation. — Fixation a chemical change, examples of ; Due to
zeolites ; Humus and fixation ; Other compounds of soil cause fixa-
tion ; Soils possess dififerent powers of fixation ; Nitrates do not
undergo fixation ; Fixation of phosphates ; Fixation a desirable
property of soils ; Fixation and the action of manures. Pages 138-
140.

CHAPTER VI

Farm Manures. — Variable composition of farm manures ; Factors
which influence composition of manures ; Absorbents ; Relation of
food consumed to manures produced ; Bulky and concentrated
foods ; Course of the nitrogen of the food during digestion ; Com-
position of liquid and solid excrements ; Manurial value of foods ;
Commercial valuation of manure ; Influence of age and kind of
animal ; Manure from young and old animals ; Cow manure ;
Horse manure ; Sheep manure ; Hog manure ; Hen manure ; Mix-
ing manures ; Volatile products from manure ; Human excrements •
Preservation of manures ; Leaching ; Losses by fermentation ;
Different kinds of fermentation ; Water necessary for fermenta-
tion ; Composting manures ; Uses of preservatives ; Manure pro-
duced in sheds ; UvSe of manures ; Direct hauling to field ;
Coarse manures may be injurious ; Manuring pasture land ; Small

VIU CONTENTS

piles of manure in fields objectionable ; Rate of application ; Most
suitable crops to apply to ; Comparative value of manure and food ;
Comparative value of good and poor manure ; Summary of ways in
which manures may be beneficial. Pages 141-171.

CHAPTER VII

Phosphate Fertilizers. — Importance of phosphorus as plant food ;
Amount of phosphoric acid in soils, amount removed in crops ;
Source of soil phosphoric acid ; Commercial forms of phosphoric
acid ; Phosphate rock ; Calcium phosphates ; Reverted phosphoric
acid ; Available phosphoric acid ; Manufacture of phosphate fertil-
izers, acid phosphates, superphosphates ; Commercial value of
phosphoric acid ; Basic slag phosphates ; Guano ; Bones ; Steamed
bone ; Dissolved bone ; Bone black ; Use of phosphate fertilizers ;
How to keep the phosphoric acid of the soil available. Pages 172-
185. ^^

CHAPTER VIII

Potash Fertilizers. — Potassium an essential element ; Amount of
potash removed in crops ; Amount in soils ; Source of soil potash ;
Commercial forms of potash ; Stassfurt salts, occurrence of ;
Kainit ; Sulphate of potash ; Other Stassfurt salts ; Wood ashes,
composition of ; Amount of ash in different kinds of wood ; Action
of ashes on soils ; Leached ashes ; The alkalinity of ashes ; Coal
ashes ; Miscellaneous ashes ; Commercial value of potash ; Use of
potash fertilizers; Joint use of potash and lime. Pages 186-195.

CHAPTER IX

Lime and Miscellaneous Fertilizers. — Calcium an essential ele-
ment ; Amount of lime removed in crops ; Amount of lime in soils ;
Different kinds of lime fertilizers ; Their physical and chemical
action ; Action of lime upon organic matter and correcting acidity
of soils ; Ivime liberates potash ; Aids nitrification ; Action of land
plaster on some "alkali" soils; Quicklime and slaked lime ;
Marl ; Physical action of lime ; Judicious use of lime ; Miscel-
laneous fertilizers ; Salt and its action on the soil ; Magnesium
salts ; Soot ; Sea-weed ; Strand plants ; Wool washings. Pages
196-204.

CONTENTS IX

CHAPTER X.

Commercial Fertilizers. — History of development of industry ;
Complete fertilizers and amendments ; Variable composition of
commercial fertilizers ; Preparation of fertilizers ; Inert forms
of matter in fertilizers ; Inspection of fertilizers; Mechanical
condition of fertilizers ; Forms of nitrogen, phosphoric acid,
and potash in commercial fertilizers ; Misleading statements on
fertilizer bags ; Estimating the value of a fertilizer ; Home mixing ;
Fertilizers and tillage ; Abuse of commercial fertilizers ; Proper
use of ; Field tests ; General principles ; Preliminary experiments ;
Verifying results ; Deficiency of one element ; Deficienc}- of two
elements; Will it pay to use fertilizers? Amount to use per acre ;
Influence of excessive applications ; Fertilizing special crops ; Com-
mercial fertilizers and farm manures. Pages 205-224.

CHAPTER XI.

Food Requirements of Crops. — Amount of fertility removed by
crops ; Assimilative powers of crops compared ; Way in which
plants obtain their food ; Cereal crops ; General food requirements ;
Wheat ; Barley ; Oats ; Corn ; Miscellaneous crops ; Flax ; Pota-
toes ; Sugar-beets ; Roots ; Turnips ; Rape ; Buckwheat ; Cotton ;
Hops ; Hay and grass crops ; Leguminous crops. Pages 225-237.

CHAPTER XII.

Rotation of Crops. — Object of rotating crops ; Principles involved
in crop rotation ; Deep and shallow rooted crops ; Humus-consu-
ming and humus-producing crops ; Crop residues ; Nitrogen-consu-
ming and nitrogen-producing crops ; Rotation and mechanical
condition of soil ; Economic use of soil water ; Rotation and farm
labor ; Economic use of manures ; Salable crops ; Rotations advan-
tageous in other ways ; Long- and short-course rotations ; Problems
in rotations ; Conserv^ation of fertility ; Necessity of manures ;
Uses of crops ; Losses of fertility with difi^erent methods of farming ;
Problems on income and outgo of fertility from farm. Pages 238-
254.

References ; Experiments ; Review Questions ; Corrections.
Pages 255-272.

THE CHEMISTRY OF

SOILS AND FERTILIZERS

INTRODUCTION

Prior to 1800 but little was known of the sources
and importance of plant food. Manures had been
used from the earliest times, and their value w^as rec-
ognized, but the fundamental principles underlying
their use were not understood. It was believed that
they acted in some mysterious way. The alchemists
had advanced various views regarding theii action ;
one was that the so-called "spirits" left the decaying
manure and entered the plant, producing more vigor-
ous growth. As evidence, the worthless character of
leached manure was cited. It was believed that the
spirits had left such manure. The terms 'spirits of
hartshorn', 'spirits of niter', 'spirits of turpentine', and
many others reflect these ideas regarding the compo-
sition of matter.

Before the composition of plant and animal bodies
was established, it was believed that one substance,
like copper, could be changed to another substance, as
gold. Plants were supposed to be water transmuted

2. SOILS AND FERTILIZERS

in some mysterious way directly into plant tissue. Van
Helmont, in the seventeenth century, attempted to
prove this. " He took a large earthen vessel and filled
it with 200 pounds of dried earth. In it he planted a
willow weighing five pounds, which he duly watered
with rain and distilled water. After five years he
pulled up the willow and it now weighed one hundred
and sixty-nine pounds and three ounces."' He con-
cluded that 164 pounds of roots, bark, leaves, and
branches had been produced by the direct transmuta-
tion of the water.

It is evident from the preceding example that au}-
thing like an adequate idea of the growth and compo-
sition of plant bodies could not be gained until the
composition of air and water were established.

The discovery of oxygen by Priestley in 1774,
of the composition of water by Cavendish in
1 781, and of the role which carbon dioxide plays in
plant and animal life by DeSaussure and others in
1800, form the nucleus of our present knowledge re-
garding the sources of matter stored up in plants. It
was from 1760 to 1800 that alchemy lost its grip and
the way was prepared for the development of modern
chemistry.

The work of DeSaussure, entitled ^'Recherches
sur la Vegetation,'' published in 1804, was the first
svstematic work showino^ the sources of the com-
pounds stored up in plant bodies. He demonstrated,

INTRODUCTION 3

quantitatively, that the increase in the amount of
carbon, hydrogen, and oxygen, when plants were ex-
posed to sunlight, was at the expense of the carbon
dioxide of the air, and of the water of the soil. He
also maintained that the mineral elements derived
from the soil were essential for plant growth, and gave
the results of the analyses of many plant ashes. He
believed that the nitrogen of the soil w^as the main
source of the nitrogen found in plants. These views
have since been verified by many investigators, and
are substantially those held at the present time re-
garding the fundamental principles of plant growth.
They were not, however, accepted as conclusive at
the time, and it was not until nearly a half century
later, when Boussingault, Liebig, and others repeated
the investigations of DeSaussure, that they were
finally accepted by chemists and botanists.

From the time of DeSaussure to 1835, scientific
experiments relating to plant growth were not actively
prosecuted, but the scientific facts which had accumu-
lated were studied and attempts were made to apply
the results to actual practice. Among the first to see
the relation between chemistry and agriculture was
Sir Humphry Davy. In 181 3 he published his
" Essentials of Agricultural Chemistry", which treated
of the composition of air, soil, manures, plants, and
of the influence of light and heat upon plant growth.
About this same period, Thaer published an important

4 SOILS AND FERTILIZERS

work entitled ^' Principes Raisonnes d' Agriculture".
Thaer believed that humus determined the fertility of
the soil, that plants obtained their food mainly from
humus, and that the carbon compounds of plants
were produced from the organic carbon compounds of
the soil. This gave rise to the so-called humus theory,
wdiich was later shown to be an inaccurate idea re-
garding the source of plant food. The writings of
Thaer were of a most practical nature, and they did
much to stimulate later investigations.

About 1830 there was a renewed interest in scientific
investigations relating to agriculture. At this time
Boussino;-ault became activelv eng^aofed in ao^ricul-
tural research. He was the first to establish a chemical
laboratory upon a farm and to make practical inves-
tigations in connection with agriculture. This marks
the establishment of the first agricultural experi-
ment station. Boussingault's work upon the as-
similation of the free nitrogen of the air is reviewed
in Chapter IV. His study of the rotation of crops
was a valuable contribution to agricultural science.
He discovered many important facts relating to the
chemical characteristics of foods, and was the first to
make a comparative study of the amount of nitrogen
in different kinds, of foods and to determine the value
of foods on the basis of the nitrogen content. His
study of the production of saltpeter did much to pre-
pare the way for later work on nitrification. The

INTRODUCTION 5

work of Boussiiigault covered a \-ariety of subjects re-
lating to plant growth. He repeated and verified
much of the earlier work of DeSaussure, and also
secured man}' additional facts relating to the chemis-
try of crop growth. As to the source of nitrogen in
crops, he states that : "The soil furnishes the crops
with mineral alkaline substances, provides them with
nitrogen, by ammonia and by nitrates, which are
formed in the soil at the expense of the nitrogenous
matters contained in diluvium, which is the basis of
vegetable earth ; compounds in wdiich nitrogen exists
in stable combination, onh- becoming fertilizing by
the effect of time." As for the absorption of the gas-
eous nitrogen of the air b}' vegetable earth, he sa}'s :
" I am not acquainted with a single irreproachable ob-
servation that establishes it ; not onh' does the earth
not absorb gaseous nitrogen, but it gives it off.""

The investigations of DeSaussure and Boussingault,
and the writings of Da\'y, Thaer, Sprengel, and Schiib-
ler prepared the wa}' for the work and writings of
Iviebig. In 1840 he published "Organic Chemistry
in its Applications to Agriculture and PliA'siology".
Liebig's agricultural investigations were preceded by
many valuable discoveries in organic chemistry, which
he applied directly in his interpretations of ao-ricul-
tural problems. His writings were of a forcible char-
acter and were extremely argumentative. They pro-
voked, as he intended, A'igorous discussions upon

6 SOILS AND FERTILIZERS

agricultural problems. He assailed the humus theory
of Thaer, and showed that humus was not an adequate
source of the plant's carbon. In the first edition of
his work he showed that farms from which certain
products were sold naturally became less productive,
because of the loss of nitrogen. In a second edition
he considered that the combined nitrogen of the air
was sufficient for crop production. He overestimated
the amount of ammonia in the air, and underestimated
the value of the nitrogen in soils and manures. A
study of the composition of plant-ashes led him to
propose the mineral theory of plant nutrition. De-
Saussure had shown that plants contained certain
mineral elements, but he did not emphasize their im-
portance as plant food. Liebig's writings on the com-
position of plant-ash, and the importance of supplying
crops with mineral food led to the commercial prepara-
tion of manures, which in later years has developed
into the commercial fertilizer industry. The work of
Iviebig was not conducted in connection wath field
experiments. It had, however, a most stimulating
influence upon investigations in agricultural chemistry,
'and to him we owe, in a great degree, the summari-
zing of previous disconnected work and the mapping
out of valuable lines for future investigations.

Liebig's enthusiasm for agricultural investigations
may be judged from the following extract : '' I shall
be happy if I succeed in attracting the attention of men

INTRODUCTION 7

of science to subjects which so well merit to engage
their talents and energies. Perfect agriadtiire is the
true foundation of trade and industry ; it is the foun-
datiojt of the I'iches of states. But a rational system
of agriculture cannot be formed without the applica-
tion of scientific principles ; for such a system must be
based on an exact acquaintance with the means of
nutrition of vegetables, and with the influence of soils,
and actions of manures upon them. This knowledge
we must seek from chemistry, which teaches the mode
of investigating the composition and of the study of
the character of the different substances from which
plants derive their nourishment." ^

Soon after Liebig's first work appeared the investi-
gations at Rothamsted by Sir J. B. Lawes were under-
taken. The most extensive systematic work in both
field experiments and laboratory investigations which
have ever been conducted have been carried on by
Lawes and Gilbert at Rothamsted, Eng. Dr. Gilbert
had previously been a pupil of Liebig, and his associa-
tion with Sir J. B. Lawes marked the establishment
of the second experiment station. Many of the Roth-
amsted experiments have been continued since 1844,
and results of the greatest value to agriculture have
been obtained. The investiofations on the non-assimi-
lation of the atmospheric nitrogen by crops, published
in 1 86 1, were accepted as conclusive evidence upon
this much-vexed question. The work on manures,

8 SOILS AND FERTILIZERS

nitrification, the nitrogen supply of crops, and on the
increase and decrease of the nitrogen of the soil when
different crops are produced, has had a most important
bearing upon maintaining the fertility of soils.

" The general plan of the field experiments has been
to grow some of the most important crops of rotation,
each separately, for many years in succession on the
same land, without manure, with farmyard manure,
and with a great variety of chemical manures, the
same kind of manure being, as a rule, applied year after
year on the same plot. Experiments with different
manures on the mixed herbage of permanent grass
land, on the effects of fallow, and on the actual course
of rotation without manure, and with different manures
have likewise been made." '^

In addition to Davy, Thaer, DeSaussure, Bous-
singault, Liebig, and Lawes and Gilbert, a great
many others have contributed to our knowledge
of the chemistry of soils. The work of Pasteur, while
it did not directly relate to soils, indirectly had a great
influence upon soil investigations. His researches
upon fermentation made it possible for Schlosing to
prove that nitrification was the result of the workings
of living organisms which have since been isolated
and studied by Warington and Winogradsk}-.

Many of the more recent in\'estigations relating to
the chemistry of soils are reviewed in the following
chapters. Our knowledge regarding the chemistry.

INTRODUCTION 9

physics, geology, and bacteriology of soils is at the
present time far from complete, but many facts have
been discovered which are of the greatest value to the
practical farmer. Of late years investigations relating
to the chemistry of soils and fertilizers have become
so extensive that the term 'agronomy' has been used
to designate that part of agricultural chemistry.

In soil investigations it has frequently happened,
owing to imperfect interpretation of results and to
the presence of man}- modifying influences, that the
results and conclusions of one investigator appear to
be directly contradictory to those of another. This
is well illustrated in the investigations relating to the
assimilation of the free atmospheric nitrogen, in which
seemingly opposite conclusions now form a complete
theorv.

CHAPTER I

PHYSICAL PROPERTIES OF SOILS

1. Soil. — Soil is disintegrated and pnlverized rock
mixed with animal and vegetable matter. The rock
particles are of different kinds and sizes, and are in
varions stages of decomposition. If two soils are
formed from the same kind of rock and differ only in
the size of the particles, the difference is merely a
physical one. If, however, one soil is formed largely
from sandstone, while the other is formed from lime-
stone, the difference is both physical and chemical.
Hence it is that soils differ both physically and chem-
ically. It is difficnlt to consider the physical proper-
ties of a soil withont also considering the chemical
properties. The chemical and physical properties of
a soil, when jointly considered, determine largely its
agricultnral valne.

2. Physical Properties Defined. — The physical
properties of a soil are :

1. Weight.

2. Color.

3. Size, form, and arrangement of the soil particles.

4. The relation of the soil to water, heat, and cold.

5. The relation of the soil to electricity.

6. Odor and taste.

PHYSICAL PROPERTIES OF SOILS II

3. Weight. — Soils differ in weight according to
the composition and size of the particles. Fine sandy
soils weigh heaviest, while peaty soils are lightest in
weight. But when saturated with water, a cubic foot
of peaty soil weighs more than a cubic foot of sandy
soil. Clay soils w^eigh less per cubic foot than sandy
soils. The laro;er the amount of org^anic matter in a
soil the less the weight. Pasture land, for exam-
ple, w^eighs less per cubic foot than arable land.
Weight is an important property to consider when the
total amounts of plant food in two soils are compared.
For example, a peaty soil containing i per cent, of
nitrogen and w^eighing 30 pounds per cubic foot has
less total nitrogen than a soil containing 0.40 per cent,
of nitrogen and weighing 80 pounds per cubic foot.

(i) The weight of soils per cubic foot is approxi-
mately as follows : ^

Pounds.

Clay soil 70 to 75

Fine sandy soil 95 to 1 10

Loam soil 75 to 90

Peaty soil 25 to 60

Average prairie soil • • • 75

Uncultivated prairie soil 65

Figures for the weight per cubic foot or specific
gravity of soils are on the basis of the dry soil. When
taken from the field the weight per cubic foot varies
with the amount of water present.

(2) The volume of a soil varies with the conditions

12 SOILS AND FERTILIZERS

to which it has been subjected. Usually about 50
per cent, of the volume of a soil is air space. A cubic
foot of soil from a field which has been well cultivated
weighs less than from a field where the soil has been
compacted. Hence it is that soils have both a real
and an apparent specific gravity. The apparent spe-
cific gravity of a soil is sometimes less than half of the
real specific gravity. The specific giavity of different
soils as given by Shoen is as follows : ^

specific gravity..

Clay soil 2.65

Sandy soil 2.67

Fine soil 2.71

Humus soil 2.53

4. Size of the Soil Particles. — The size of the soil
particles varies from those hardh- distinguishable with
the microscope to coarse rock fragments. The size of
the particles determines the character of the soil as
sandy, clay, or loam. The term 'fine earth ' is used to
designate that part of the soil which passes through a
sieve with holes 0.5 mm. (0.02 inch) in diameter.
Coarse sand particles and rock fragments which fail
to pass through the sieve are called skeleton. The
amount of fine earth and skeleton is variable. Arable
soils, in general, contain from 5 to 20 per cent, of
skeleton.

The fine earth is composed of six grades of soil
particles. The names and sizes are as follows :

PHYSICAL PROPERTIES OF SOILS 1 3

Millimeters. Inches.

Medium sand 0.5 to 0.25 0.02 to o.oi

Fine sand 0.25 too. i o.oi to 0.004

Very fine sand o. i to 0.05 0.004 to 0.002

Silt 0.05 to O.OI 0.002 to 0.0004

Fine silt o.oi to 0.005 0.0004 to 0.0002

Clay 0.005 and less 0.0002 and less

Soils are mechanical mixtures of various sized par-
ticles. In most soils there is a predominance of one
erade, as clav in lieavv clav soils, and medium sand
in sandy soils. No soil, however, is composed entirely
of one grade. The clay particles are exceedingly
small ; it would take 5000 of the larger ones, if laid
in a line with the edges touching, to measure an inch,
while it would take but 50 of the larger medium sand
particles to measure an inch.

5. Clay. — The term clay used physically denotes
those soil particles less than 0.005 ^^^^^^' (0.0002 inch)
in diameter, without regard to chemical composition.
As used in a physical sense clay may be silica, feld-
spar, limestone, mica, kaolin, or any other rock or
mineral w^hich has been pulverized until the particles
are less than 0.005 mm. in diameter. Chemically,
however, the term clay is restricted to one material,
as will be explained in another part of the work.
The physical properties of clay are well know^n. It
has the power of absorbing a large amount of water,
and will remain suspended in water for a long time.
The roiled appearance of many streams and lakes is

14 SOILS AND FERTILIZERS

due to the presence of suspended clay particles. The
amount in agricultural soils may range from 3 to 50
per cent. Clay soils, if worked when too wet, become
puddled ; then percolation cannot take place, and the
accumulated surface water must be removed by the
slow process of evaporation.

6. Silt. — The silt particles are, in size, between sand
and clay. Many of the western prairie subsoils, clay-
like in nature, are composed mainly of silt. The silt
imparts characteristics intermediate to sand and clay.
While a clay soil is nearly impervious to water, and
w^hen w^et works with difficulty, a silt soil is more
permeable, but is not as open and porous as a sandy
soil. When a soil containing large amounts of clay
and silt is treated wath water, the silt settles slowly,
while the clay remains in suspension. The fine de-
posit in ditches and drains, where the water moves
slowly, is mainly silt.

7. Sand. — There are three grades of sand. The
characteristics, as permeability and non-cohesion of
particles, are so w^ell known that they do not require
discussion. A soil composed entirely of sand would
have little, if any, agricultural value. Sandy soils
usually contain from 5 to 15 per cent, of clay and
silt. The relative sizes of sand, silt, and clay are given
in the illustration.

^8. Form of Soil Particles. — Soil particles are ex-

PHYSICAL PROPERTIES OF SOILS

15

tremely varied in form. When examined with the
microscope they show the same diversity as is observed
in larger stones. In some soils the particles are spher-
ical, while in others they are angular. The shape

Fig. I. Medium Sand X 150. Fig. 2. Fine Sand X 150. Fig. 3.
Very Fine Sand X 150. Fig. 4. Silt X 3?5. Fig. 5. Fine Silt X
325. Fig. 6. Clay X 325-

of the particles is determined by the way in which the
soil has been formed and also by the nature of the
rock from which it was produced.

The form and arrangement of the particles are im-
portant factors to consider in dealing with the water

l6 SOILvS AND FERTILIZERS

content of soils. In the wheat lands of the Red
River Valley of the North, the particles are small and
spherical, being formed largely from limestone rock,
while the subsoil of the western prairie regions is
composed largely of angular silt particles, which are
intermingled with clay, forming a mass containing
only a minimum of inter soil spaces. The silt particles
being angular and imbedded in the clay, the soil has
more the character of clay than of silt. While these
two soils are unlike in physical composition, the form
and arrangement of the particles give each nearly the
same water-holding power. On account of a differ-
ence in the form and arrangement of the soil particles
two soils may have the same mechanical composition,
and yet possess materially different physical proper-
ties. In some soils lo per cent, of clay is of more
value agriculturally than in other soils. Ten per cent,
of clay associated with 60 or 70 per cent, of silt^
makes a good grain soil, while 10 per cent, of clay
associated largely with sand makes a soil poorly suited
to grain culture.

The classification of the soil particles into sand, silt,
and clay is pureh' an arbitrary one. Various authors
use these terms in different ways, and when compar-
ing soils, reported in different works, one may avoid
confusion by omitting the names and noting onh' the
sizes of the particles. A division has recently been
suggested by Hopkins ^ in which the square root is

PHYSIC AI. PROPERTIES OF SOILS 1 7

often taken as the constant ratio between the grades
of soil particles.

9. Number of Particles per Gram of Soil. — It has

been estimated that a gram of soil contains from
2,000,000,000 to 20,000,000,000 soil particles ; soils
which contain less than 1,700,000,000 are unproduct-
ive. The number of particles in a given volume of
soil varies with their size and form. According to
Whitney^ the number of particles per gram of differ-
ent soil types is as follows :

Early truck i ,955,000,000*

Truck and small fruit 3,955,000,000

Tobacco 6,786,000,000

Wheat 10, 228,000,000

Grass and wheat 14,735,000,000

Limestone 19,638,000,000

Assuming that the particles are all spheres, it is es-
timated that in a cubic foot of soil a surface area of
from two to three and one-half acres is presented to
the action of the roots.

10. Methods Employed in Separating Soil Particles.

— Sieves with circular holes 0.5, 0.25, and o. i mm.
are emplo}ed for the purpose of separating the three
coarser grades of sand. The sieve a^ 0.5 mm. size, is con-
nected with the filtering flask c by means of the tube
b^ and the flask is connected at point d with a suc-
tion-pump. Ten grams of soil, after treatment with

"-'•Figures below sixth place omitted and ciphers substituted.

i8

S3ILS AND FERTILIZERS

boiling water, are placed in the sieve. Water is passed
through until the washings are clear. All particles
larger than 0.5 mm. remain in the sieve, and after dry-
ing and igniting, are weighed. The contents of flask r,
containing the particles less than 0.5 mm., are then
passed through a sieve having holes 0.25 mm. in
diameter. Finally a o. 10 mm. diameter sieve is used.
The fine sand and silt are separated by gravity. The
fine sand with some silt and clay are read-
ily deposited and the water containing
the suspended clay is decanted into a
second glass vessel. The residue is treated
with more water and allowed to settle;
this operation is repeated until the micro-
scope shows the soil particles to be nearl)'
all of one grade.

Clay is obtained by
evaporating an aliquot
portion of the washings
or by determining the
total per cent, of the other grades of particles and the
volatile matter and subtracting the sum from 100.
This is the Osborne sedimentation method with modi-
fications. 9 Hilgard's'° elutriator, and the apparatus
of Shoen-Ma}'er are also used for separating the soil
particles.

SOIL TYPES

II. Crop Growth and Physical Properties. —The

FiL'-.

Figs. 8 and 9.

SOIL TYPES 19

preference of certain crops for particular kinds of soil,
as wheat for a clay subsoil, potatoes for a sandy soil,
and corn for a silt soil, is due mainly to the peculiari-
ties of the crop in requiring definite amounts of water,
and a certain temperature for grow^th. These condi-
tions are met by the soil being composed of various
grades of particles which enable a certain amount of
water to be retained, and the soil to properly respond
to the influences of heat and cold. In considering
soil types, it should be remembered that there are so
many conditions influencing crop growlh that the
crop-producing power cannot ahvays be determined l^y
a mechanical analysis of the soil. The foUownnof
types have been found to hold true in a large number
of cases under average conditions, but they do not
represent what might be true of a case under special
conditions. For example a sandy soil of good fer-
tility in which the bottom water is only a few feet
from the surface, may produce larger grainc rops_than
a clay soil in which the bottom water is at a greater
depth. In judging the character of a soil, special
conditions must alw^ays be taken into consideration.
In discussing the following soil types, a normal supply
of plant food and an average rainfall are assumed in
all cases.

12. Potato and Early Truck Soils. — The better
types of potato soils are those which contain about 60
percent, of medium sand, 20 to 25 percent, of silt, and

20 SOII.S AND FERTILIZERS

about 5 per cent, of clay. Soils of this nature when
supplied with about 3 per cent, of organic matter will
contain from 5 to 12 per cent, of water. The best
conditions for crop growth exist when the soil con-
tains from 5 to 7 per cent, of water. In a sandy soil
vegetation may reduce the water to a much lower
point than in a clay soil. On account of sandy soil
giving up its water so readily to growing crops nearly
all is available, while on heavy clay, crops show the
want of water when the soil contains from 7 to 8 per
cent., because the clay holds the water so tenaciously.
When potatoes are grown on soils where there is an
abnormal amount of water the crop is slow in matur-
ing. For early truck purposes in northern latitudes,
sandy soils are the most suitable because they wariti
up more readily, and the absence of an abnormal
amount of water results in early maturity. Excellent
crops of potatoes are grown on many of the silt soils
of the west which have a materially different com-
position from the type given. A soil may have all
of the requisites physically for the production of good
potato and truck crops, and still be unproductive on
account of some peculiarity in chemical composition.

13. General Truck and Fruit Soils. — For fruit grow-
ing and general truck purposes the soil should contain
more clay and less sand than for early truck farming.
Soils containing from 10 to 15 per cent, of clay and not
more than 40 per cent, of sand are best suited for

SOIL TYPES 21

growing small fruits. Such soils will retain from lo
to 1 8 per cent, of water. There is a noticeable differ-
ence as to the adaptability of different kinds of fruit
to different soils. Some fruits thrive on clay land,
provided the proper cultivation and treatment are
given. There is as nuich diversity of soil, required for
producing different fruit crops as for the production of
different farm crops. As a rule, however, a silt soil
is most capable of being adapted to the various con-
ditions required by fruit crops.

14. Corn Soils. — The strongest types of corn soils
are those which contain from 40 to 45 per cent, of
medium and fine sand and about 15 per cent, of clay.
Corn lands should contain about 15 per cent, of avail-
able water. Heavy clays produce corn crops which
mature later than those grown on soils not so close
in texture. JMany corn soils contain less sand and
clay, but more silt than the figures given. If the soil
contains a high per cent, of organic matter, good corn
crops may be produced where there is less than twelve
per cent, of clay. Soils containing a high per cent, of
sand are usually too deficient in available water to
produce a good crop. On the other hand heavy clay
soils are slow in warming up and are not suited to com
culture.

The strongest types of corn soils have the proper
mechanical composition for the production of good
crops of sorghum, cotton, flax, and sugar-beets. How-

22 SOILS AND FERTILIZERS

ever, the amount of available plant food required for
each crop is not the same. The western prairie soils
which produce most of the corn raised in the United
States, are composed largely of silt.

15. Medium Grass and Grain Soils. — For the pro-
duction of grass and grain a larger amount of water
is required than for corn. The yield of both is de-
termined largely by the amount of water which the
soil contains. For an average rainfall of about 30
inches, good grass and grain soils should contain
about 15 per cent, of clay and 60 per cent, of silt.
Such a soil ordinarily holds from 18 to 20 per cent.
of water. Many grass and grain soils have less silt
and more clay. A soil composed of about 30 per
cent, each of fine sand, silt, and clay, would also be
suitable, mechanically, for general grain production.
There are a number of different types of grass and
grain soils, with different proportional amounts of
sand, silt, and clay. Silt soils, however, form the
larger part of the grain soils of the United States.

16. Wheat Soils. — For wheat production, soils of
a closer texture are required than for general grain
farming. There are three classes of wheat soils. The
first (i in Fig. 10) contains from 30 to 50 per cent, of
clay particles, these being mostly disintegrated lime-
stone. The soil of the Red River Valley of the North
belongs to the first class of wdieat-producing soils.
The surface soil contains from 8 to 12 percent, of veg-

soil. TYPES

23

etable matter and the subsoil about 25 per cent, of
limestone in a very fine state of division. For the
production of wheat the subsoil should contain 20 per
cent, of water. A crop can, however, be produced with
less water, but a smaller yield is obtained.

C/ay

f/'ne

Fig. 10. Soil types.

The second type of wheat soil (2 in Fig. 10) con-
tains less clay and more silt. Many prairie subsoils
which produce good crops of wdieat contain about 20
per cent, of sand, 50 per cent, of silt, and from 20 to
30 per cent, of clay. Soils of this class when w^ell
stocked with moisture in the spring are capable of

24 SOILS AND FERTILIZERS

producing good crops of wheat, but are not able to
withstand drought so well as soils of the first class.

To the third class of wheat soils (3 in Fig. 10) belong
those which are composed niainh- of silt, containing
usually 75 per cent., and from 10 to 15 per cent, of clay.
The high per cent, of fine silt gives the soil clay-like
properties. Soils of this class are adapted to a great
variety of crops. For the production of wheat on silt
soils it is very essential that a good supply of organic
matter be kept in the soil so as to bind together the
soil particles. The special peculiarities of the different
grain crops as to soil requirements will be considered
in connection with the food requirements of crops.

17. Sandy, Clay, and Loam Soils. — In ordinary
agricultural literature the term 'sandy,' 'clay,' or
' loam ' is used to designate the prevailing character of
the soil. Sandy soils usually contain 90 per cent, or
more of silica or chemically pure sand. The term
light sandy soil is sometimes used to indicate that the
soil is easily worked, while the term heavy clay
means that the soil offers great resistance to cultiva-
tion. Many soils which are clay-like in character are
not composed very largely of clay. There are sub-
soils in the western states which have clay-like char-
acteristics but contain only about 15 percent, of clay,
the larger part of the soil being silt. A loam soil is a
mixture of sand and clay ; if clay predominates the
soil is a clay loam, while if sand predominates it is a
sandy loam.

RELATION OF THE SOIL TO WATER

i8. Amount of Water Required by Crops. — Ex-
periments have shown that it takes from 275 to 375
pounds of water to produce a pound of dry matter in
a grain crop. In order to produce an average acre of
wheat 350 tons of water are needed. The amount of
water required for the production of an average acre
of various crops is as follows : "

Average amount. IMiiiimum arnount.

Tous water. Tons water.

Clover 400 310

Potatoes 400 325

Wheat 350 300

Oats 375 300

Peas 375 300

Corn 300

Grapes 375

Sunflowers^ 6000

The rainfall during the time of growth is frequently
less than the amount of water required for the pro-
duction of a crop. An average rainfall of 2 inches
per month during the three months of crop growth
would be equivalent to only 369 tons of water per
acre, a variable part of which is lost by evaporation.
Hence it is that the rainfall during an average grow-
ing season is less than the amount of water required,
and in order to produce crops, the water stored up in
the soil must be drawn upon to a considerable extent.
Inasmuch as the soil's reserve supply of water is such
an important factor in crop production, it follows that

26 SOILS AND FERTILIZERS

the capacity of the soil for storing up water and giving
it up as needed is a matter to be considered, par-
ticularly since the power of the soil for absorbing
and retaining water ma}- be influenced by cultivation
'and manuring. Before discussing the influence of
cultivation upon the soil water, the forms in wdiich it
is present in the soil should be studied. Water is
present in soils in three forms : (i) bottom water, (2)
capillary water, and (3) hydroscopic water.

19. Bottom Water is water which stands in the soil
at a general level, and fills all the spaces between the
soil particles. Its distance from the surface can be
told in a general way by the depth of surface wells.
Bottom water is of service to growdng crops when it is

Fig. II. Water films surrounding soil particles.

at such a depth that it can be brought to the plant
roots by capillarity, but when near the surface so that
the roots are immersed, very poor conditions for crop
growth exist. When the bottom water can be brought
within reach of the roots by capillarity a crop
has an almost inexhaustible supply. In many soils
known as old lake bottoms such conditions exist.

RELATION OF THE SOIL TO WATER

27

20. Capillary Water. — The water held in the
capillary spaces above the bottom water is known as
the capillary water. The capillary spaces of the soil
are the small spaces between the soil pat tides in
which w^ater is held by surface tension ; that is, the
force acting between the soil and the w^ater is greater
than the force of gravity. If a series of glass tubes of
different diameters be placed in w^ater it will be ob-
served that in the smaller tubes w^ater rises much
his/her than in the largfer. The w^ater rises in all of

"-r*^

[3 LI

Fig. 12. Comparative height to which water rises in glass tubes.

the tubes until a point is reached w^here the force of
gravity is equal to the force of surface-tension. In
the smaller tubes surface-tension is greater than the
force of gravity, and the water is drawn up into the
tube. In the larger tubes the surface-tension is less
and water is raised only a short distance. There
are present in the soil many spaces which are capable
of taking up water in the same way as the small glass
tubes. The height to which water can be raised by

28 SOILS AND FERTILIZERS '

capillarity depends upon the size and arrangement of
the soil particles. Water may be raised by capillarity
to a height of several feet. Ordinarily, however, the
capillary action of water is confined to a few feet. The
arrangement of the soil particles influences greatly the
capillary power of the soil. Usually from 30 to 60 per
cent, of the bulk of a soil is air space : by compacting,
the air spaces may be decreased ; by stirring, the air
spaces are increased. In some soils of a close texture an
increase in air spaces results in an increase of capillary
spaces and of water-holding capacity, while in other
soils, as coarse sandy soils, increasing the air spaces
decreases the capillary spaces and the water-holding
capacity. The best conditions for crop production
exist when the soil contains water to the extent of
about 40 per cent, of its total capacity of saturation.

21. Hydroscopic Water. — By hydroscopic water is
meant the water content of the soil atmosphere. The
air which occupies the non-capillar}' spaces of the soil
is charged with moisture in proportion to the water in
the soil. Under normal conditions the soil atmos-
phere is nearly saturated. When soils have exhausted
their capillar}- water, the water in the soil atmosphere
is correspondingly reduced. The a\'ailable supply in
other forms being exhausted, the hydroscopic water
cannot contribute to plant growth.'

22. Loss of Water by Percolation. — Whenever a
soil becomes saturated, percolation or a downward

RELATION OF THE SOIL TO WATER 29

movement of the water begins. The extent to which
losses by percolation may occur depends upon the
character of the soil and the amount of rainfall.
When soils are covered with vegetation the losses by
percolation are less than from barren fields. In all
soils which have only a limited number of capillary
spaces and a large number of non-capillary spaces, the
amount of water which can be held above the bottom
water is small. From such soils the losses by perco-
lation are g^reater than from soils which have a largfcr
number of capillary spaces, and a smaller number of
non-capillary spaces. In coarse sandy soils many of
the spaces are too large to be capillary.

If all of the water which falls on some soils could be
retained and not carried beyond the reach of crops by
percolation, there would be an ample supply for agri-
cultural purposes. To prevent losses by percolation,
the texture of the soil ma\- be changed by cultivation
and by the use of manures. If the soil is of very fine
texture, as a heav}' clay, percolation is slow^, and before
the water has time to sink into the soil, evaporation
begfins; wath o^ood cultivation the w^ater is able to
penetrate to a depth beyond the immediate influence of
evaporation. Compacting an open porous soil by
rolling, checks rapid percolation and pre\'ents the
water from being carried beyond the reach of plant
roots. In order to prevent excessive losses by perco-
lation, the treatment must be varied to suit the re-
quirements of different soils.

30 SOILS AND FERTILIZERS

23. Loss of Water by Evaporation. — The factors
which influence evaporation are temperature, humidity,
and rate of movement of the air. When the air con-
tains but little moisture and is heated and moving
rapidly, the most favorable conditions for evaporation
exist. In semiarid regions the losses of water by
evaporation are much greater than by percolation.
The drv air comes in contact with the soil, the soil
atmosphere gives up its water, and, unless checked by
cultivation, the subsoil water is brought to the surface
by capillarity and lost. In porous soils, a greater
freedom of movement of the air is possible, which in-
creases the rate of evaporation. When the surface of
the soil is covered with a la}'er of finely pulverized
earth, or with a mulch, excessive losses by evaporation
cannot take place, because a material of different tex-
ture is interposed between the soil and the air.

24. Loss of Water by Transpiration. — Losses of
water ma}' also occur from the leaves of plants by the
process known as transpiration. Helriegel obser\'ed
that during some years 100 pounds more water were
required to produce a pound of dr}- matter than in
other years, because of the difference in the amount of
water lost by transpiration. The loss of water b}'
evaporation can be controlled by cultivation, but the
loss by transpiration can be only indirectly influ-
enced. Hot dry winds may cause crops to wilt be-
cause the water lost by transpiration exceeds the amount
which the plant takes from the soil.

INFLUENCE OF CULTIVATION 3 1

The three ways in which crops are deprived of
water are by (i) percolation, (2) evaporation, and (3)
transpiration. With proper methods of cultivation,
losses by percolation and evaporation may be controlled,
and losses by transpiration may be reduced.

INFLUENCE OF CULTIVATION UPON THE WATER SUPPLY

OF CROPS

25. Capillarity Influenced by Cultivation. — The

capillarity of the soil is subject to change with different
methods of cultivation, as rolling and subsoiling, deep
plowing and shallow surface cultivation. The method of
cultivation which a soil should receive in order to secure
the best water supply for crops must vary with the
rainfall, the nature of the soil, and the crop to be pro-
duced. It frequently happens that the annual rainfall
is sufficient to produce good crops, but is too unevenly
distributed. It is possible, to a great extent, to vary
the cultivation to meet the water requirements of
crops.

26. Shallow Surface Cultivation. — When shallow
surface cultivation is practiced, the capillary spaces
near the surface are destroyed and the direct connec-
tion of the subsoil water with the surface is broken.
When the soil particles have been disturbed and a layer
of finely pulverized ea-^tli covers the surface, there is not
that close contact which enables the water to pass
from particle to particle. When evaporation takes
place there is a movement of the subsoil water to the

32

SOILS AND FERTILIZERS

surface, but if the surface is covered with a layer of
fine earth, the subsoil water cannot readily pass
through such a medium, and evaporation is checked.
Hence shallow surface cultivation conserves the soil
moisture.

The means by which surface cultivation is accom-
plished must, of necessity, vary with the nature of the

Fig. 13. With surface cultivation.

soil. If a harrow is used the pulverization should be
complete. If a disk is used the teeth should be set at
an angle, and not perpendicularly, so as to prevent, as

Fig. 14. Without surface cultivation.

suggested by King,'^ the formation of hard ridges
which hasten evaporation. When the disk is set at an
angle, a layer of soil is completely cut off, and the
capillary connection with the subsoil is broken. Sur-
face cultivation should be from two to three inches

INFLUENCE OF CULTIVATION 33

deep, and the finer the condition in which the snrface
soil is left, the better.

Shallow surface cultivation should be resorted to as
a means of conserving soil moisture. It can be prac-
ticed in connection with deep plowing, shallow plow-
ing, subsoiling, or rolling ; in fact, it can be combined
with any method of preparing the land. Shallow sur-
face cultivation does not mean that the soil should not
be previously well prepared by thorough cultivation.
The following example shows the extent to which

shallow surface cultivation mav conserve the soil
water. ^3

Per cent, of water in cornfield.
With .shallow sur- Without shallow
face cultivation. surface cultivation.

Soil, depth 3 to 9 inches 14.12 8.02

Soil, depth 9 to 15 inches 17.21 12.38

27. Cultivation after a Rain. — When evaporation
takes place immediately after a rain, not only is there
a loss of the water which has fallen, but there may
also be a loss of the subsoil water by translocation, if
nothing be done to prevent.'^ The following example
shows the extent to which the subsoil water may be
brought to the surface. '^

Per cent, of water.
Surface soil. Subsoil.

I to 3 inches. 6 to 12 inches.

Before the shower 9.77 18.22

After the shower 22.11 16.70

The rainfall was sufficient to have raised the water
content of the surface soil to 20.77 per cent. The
subsoil showed a loss of 1.52 per cent., while the sur-

34 SOILS AND FERTILIZERS

face soil showed a gain of 1.34 per cent, in addition to
the water received from the shower. If evaporation
begins before the eqnilibrinm is reestablished, there is
lost, not only the water from the shower, bnt also the
water which has been translocated from the snbsoil to
the surface. Hence the importance of shallow surface
cultivation immediately after a rain.

When a subsoil contains a liberal supply of water,
and the surface soil a minimum amount, there is after
an ordinary shower a movement of the subsoil water
to the surface. The soil particles at the surface are
surrounded with films of water which thicken at the
expense of the subsoil water. Surface-tension is the
cause of this movement of the water to the surface,
and under the conditions stated it is temporarily
greater than the force of gravit}'.

A thin hard crust should never be allowed to form
after a rain, because it hastens the losses by evapora-
tion, while a soil mulch formed by surface cultivation
has the opposite effect.

28. Rolling. — The use of heavy rollers for com-
pacting the soil is beneficial in a dry season on a soil
containing large proportions of sand and silt. Rolling
the land compacts the soil and improves the capillary
conditions, enabling more of the subsoil water to be
brought to the surface. Experiments have shown
that when land is rolled the amount of water in the
surface soil is increased. This increase is, however,

INFI.UENCE OF CULTIVATION 35

at the expense of the subsoil water. '^ Unless rolled
land receives surface cultivation excessive losses by
evaporation, due to improved capillarity, may result.
The use of the roller on cla}' land during a wet season
results unfavorably. In man}- localities rolling and
subsequent surface cultivation are not admissible on
account of the drifting of the soil, caused by heav}'
winds.

29. Subsoiling. — By subsoiling is meant pulveri-
zing the soil immediateh' under the furrow slice.
This is accomplished with the subsoil plow, which
simply loosens the soil without bringing the subsoil to
the surface. The object of subsoiling is to enable the
land to retain, near the surface, more of the rainfall.
Heavy clay lands are sometimes improved by occasional
subsoiling, but its continued practice is not desirable.
For orcharding and fruit-growing, it is frequently re-
sorted to, but is not beneficial on soils containing
large amounts of sand and silt. Rolling and subsoil-
ing are directly opposite in effect. Soils which are
improved by rolling are not improved by subsoiling.
The additional expense involved should be considered
when subsoiling is to be resorted to. Experiments
have not as yet been sufficiently decisive to indicate
the conditions most favorable for this practice.

30. Fall Plowing conserves the soil water, by check-
ing evaporation and leaving the land in better condi-
tion to retain moisture. Fall plowing should be fol-

36 SOILS AND FERTILIZERS

lowed by surface cultivation. Evaporation may take
place from unplowed land during the fall, and in the
spring the soil contains appreciably less water than
plowed land. By fall 4)lowing it is possible to carry
over a water balance in "Jihe soil from one year to the
next.

31. Spring Plowing. — When land is plowed late in
the spring there has been a previous loss of water by
evaporation, and the soil has not been able to store up
as much of the rain and snow as if fall plowing had
been practiced. '+ Dry soil is plowed under and moist
soil brought to the surface. This moisture is readily
lost by evaporation if surface cultivation is not em-
ployed ; good capillary connection of the surface soil
and subsoil is not obtained, and the furrow slice soon
becomes dry.

Surface cultivation should immediately follow both
spring and fall plowing.

Per cent, of water ini3
Fall plowed Spring plowed

April 25 land. land.

From 2 to 6 inches 24.7 22.4

" 6 to 12 " 26.6 24.1

" 12 to 18 '• 28.8 26.5

Average difference 2.37 per cent.

32. Mulching. — The use of well-rotted manure or
straw, spread over the surface as a mulch, prevents
evaporation. In forests the leaves form a mulch
which is an important factor in maintaining the water
supply. In order that a mulch be effectual, it nnist

INFLUENCE OF CULTIVATION 37

be compacted, — a loose pile of straw is not a mulch.
In reclaiming lands gullied by water, mulching is
very beneficial. A slight mulch may also be used to
encourage the growth of grass on a refractor^^ hillside.
When land is mulched, evaporation is checked. Sur-
face cultivation and mulchings mav be combined and
excellent results obtained. '3

Per cent, of water in
Mulched straw-
berry patch. Uumulched.

Soil 2 to 5 inches 18.12 11. 17

" 6 to 12 " 22.18 18.14

" 12 to 18 " 24.31 21. II

33. Depth of Plowing. — The depth to which a soil
should be plowed in order to give the best results must,
of necessity, vary with the conditions. Deep plowing
of sandy land is not advisable, particularly in the
spring. On clay land deeper plowing should be the
rule. The longer a soil is cultivated the deeper and
more thorough should be the cultivation. While
shallow plowing is admissible on new prairie land,
deeper cultivation should be practiced when the land
has been cropped for a series of years. The depth of
plowing should be regulated by the season. In the
prairie regions, and in the northwestern part of the
United States, shallow plowing is more generally prac-
ticed than in the eastern states. Deep plowing in the
fall gives better results than in the spring. It is not
a wise plan to plow to the same depth every year.
Prof. Roberts says:'^ "If plowing is continued at one

38 SOILS AND FERTILIZERS

depth for several seasons, the pressure of the imple-
ment and the trampling of the horses in time solidify
the bottom of the furrow, but if the plowing is shallow
in the spring and deep in summer and fall, the objec-
tional hard pan will be largely prevented."

In regions of scant rainfall deep plowing of silt soils
should be done only at intervals of three or five years.,
With an average rainfall, deep plowing should be the
rule on soils of close texture. The depth of plowing
should be varied to meet the requirements of the crop,
of the soil and the amount of rainfall.

34. Permeability of Soils. — The rapidity with
which water sinks into the soil after a rain depends
upon the nature of the soil, and upon the cultivation
which it has received. Shallow surface cultivation
leaves the soil in good condition to absorb water.
When the surface is hard and dry a large per cent, of
the water which falls on rolling- land is lost bv sur-
face drainage. Soils of close texture which contain
but few non-capillary spaces, offer the greatest resist-
ance to the downward movement of water.

The term permeable is applied to a soil when it is
of such a texture that it does not allow the water to
accumulate and clog the non-capillary spaces. Culti-
vation may change the texture of even a cla\' soil to
such an extent as to render it permeable. Deep
plowing increases permeability. In regions of heavy
rains increased permeability is \'ery desirable for good

INFLUENCE OF CULTIVATION 39

crop production on heavy clays. Sandy and loamy
soils have a high degree of permeability, and it is not
necessar}^ that it should be increased.

35. Fertilizers. — When water contains dissolved
salts, it is more susceptible to the influence of surface-
tension, and is more readih' brought to the surface of
the soil. In commercial fertilizers soluble salts are
present. The beneficial effects of commercial fertili-

Sandy soil without manure.

zers Upon the moisture content of soils are liable to
be overestimated, because the fertilizer undergoes fix-
ation when applied, and does not remain in a soluble
condition. Fertilizers containing soluble salts exercise
a favorable influence upon the moisture content of
soils, but the extent of this influence has never been
determined under field conditions.

36. Farm Manures. — Well-prepared farm manures
exercise a beneficial effect upon the moisture content of
soils. When well-rotted manure is worked into a soil,
the coarse soil particles and masses are bound together,

40

SOILS AND FERTILIZERS

and the non-capillar}- spaces are made capillary. The
free circulation of the air which increases evaporation,
is pre\'ented when a sandy soil is manured. When

Fig. 1 6. Sandy soil with manure.

silt and sandy soils are manured they are capable of
retaining more water, as shown b}' the following ex-
ample :'3

Fine sandy

soil.

Per cent.

95 per cent, fine

sandy soil.

5 per cent.

dry mannre.

Per cent.

42

Capacity for holding water 25

The manure enables the soil to retain more water
near the surface and prevents losses by percolation.
The difference in moisture content of manured and un-
manured land is particularly noticeable in a dryseason.'^

Sandy soil

Sandy soil

well niannred.

nnniannred

Water.

Water.

Per cent.

Per cent.

s 10.50

8.10

Soil one to six inches

Coarse leached manure may ha\e just the opposite
effect b}' producing an open and porous condition of
the soil.

INFLUENCE OF CULTIVATION 4I

37. Drainage. — Good drainage is very essential in
order to proper!}- regnlate the water supply. If the
water which falls on the land is allowed to flow over
the surface and is not retained in the soil, there is not
sufficient reserve water for crop growth. The object
of good drainage is to store up as much water as pos-
sible in the subsoil and to prevent surface accumula-
tion and losses. Good drainage is accomplished by
thorough cultivation, and in regions of heavy rainfall
by tile drainage. Well-drained land is warmer in the
spring, has a larger reserve store of water, and is in
better condition for crop growth.

38. Influence of Forest Regions. — The deforesting
of large areas near the source of rivers has an injurious
influence upon the moisture content of adjoining farm
lands. By cutting over and leaving barren large tracts,
less water is retained in the soil. Near forest regions
the air has a higher moisture content, due to the
water given off by evaporation. Farm lands adjacent
to deforested districts lose water more rapidly b}-
evaporation, because the air is so much drier. In
Section 24 it was stated that losses of water by trans-
piration could be indirectly influenced. This can be
accomplished by retaining our forest lands.

Good drainage in agriculture means not only good
drainage for individual farms, but also good storage
capacity in the form of forest lands, for the surplus
water which accumulates near the sources of large
rivers.

RELATION OF THE SOIL TO HEAT

39. The Sources of Heat in soils are (i) solar
heat, and (2) heat resulting from chemical action.
Solar heat is the main source for crop produc-
tion. The action of heat upon soils has been
studied extensively by Schiibler. The amount of heat
a soil is capable of absorbing depends upon its texture
and moisture content. All dark-colored soils have a
greater power for absorbing heat than light-colored
ones. From Schiibler's experiments it appears that
when dry, there may be as great a difference as 8° C,
between light- and dark-colored soils. When one set
of soils was covered with a thin white coat of mag-
nesia, and another set with lampblack, and exposed
under like conditions, the temperatures were:^

White coating. Black coating.

Sand 43 50

Gypsum 43 51

Humus 42 49

Clay 41 48

Loam 42 50

The presence of water in the soil modifies the power
for absorbing heat. A sandy soil for example retains
about 12 percent, of water, while a humus soil retains
35 per cent. The additional amount of water in the
humus soil may cause the soil temperature to be lower
than that of the sandy soil. While the humus soil
absorbs more heat than the sandy soil, the heat is used

RELATION OF THE SOIL TO HEAT 43

Up in evaporating water. A sandy soil readily warms
lip in the spring on account of the relatively small
amount of water which it contains.

The specific heat of a soil is the amount of heat re-
quired to raise a given weight i° C, as compared with
the heat required to raise the same weight of water i°.
The specific heat of soils ranges from 0.2 to 0.4.

The effect of drainage upon soil temperature is
marked. The surface of well-drained land is usually
several degrees warmer than that of poorly drained
land. Water being a poor conductor of heat it follows
that soils which are saturated are slow to warm up in
the spring. At a depth of 2 or 3 feet there is not such
a marked difference in the temperature of wet and dry
soils. It is to be observ^ed that with proper systems of
drainage the surplus water is removed from the sur-
face soil and stored up in the subsoil for the future use
of the crop, and at the same time the temperature of the
surface soil is raised, thus improving the conditions for
crop growth. The relation of drainage to the proper
supply of water and temperature for crop growth is a
matter which generally receives too little consideration
in field practice.

40. Heat from Chemical Reactions within the
Soil. — Heat also results from the slow oxidation of
the organic matter of the soil. When organic matter
decomposes, it produces heat. A load of manure, when
it rots in the soil, gives off the same amount of heat as

44 SOILS AND FERTILIZERS

if it were burned. Manured land is usually i° or 2°
warmer in the spring than unmanured land ; this is due to
the oxidation of the manure. In an acre of rich prairie
soil it has been estimated that the amount of organic
matter which undergoes oxidation produces as much
heat annually as would be produced from a ton of
coal.^^ In well-drained and well-manured land, the
additional heat is an important factor for stimulating
crop growth, particularly in a cold, backward spring.
The production of heat from manure is illustrated in
the case of hotbeds where well-rotted manure is covered
with soil ; this results in raising the temperature of the
soil. When soils are well manured, heat is retained
more effectually. In the case of early frosts, crops on
well-manured land will often escape.

41. Relation of Heat to Crop Growth. — All plant
life is directly dependent upon solar heat as the source
of energy for the production of plant tissue. The
heat of the sun is the main force at the plant's dis-
posal for decomposing water and carbon dioxide and
for producing starch, cellulose, and other compounds.
The growth of crops is the result of the transformation
of solar heat into chemical energy which is stored up
in the plant. When the plant is used for fuel or for
food the quantity of heat produced by complete oxida-
tion is equal to the amount of heat required for forma-
tion.

COLOR OF SOILS

42. Organic Matter and Iron Compounds. — The

principal materials which impart color to soils are or-
ganic matter and iron compounds. Soils containing
large amounts of organic matter are dark-colored.
A union of the decaying organic matter and the
mineral matter of the soil also produces compounds,
brown or black in color. When moist, many soils are
darker than when dry, and soils in which the organic
matter has been kept up by the use of manures are
darker than unmanured soils.'^ When rich, black,
prairie soils lose their organic matter through im-
proper methods of cultivation or when the organic
matter (humus) is extracted in chemical analysis the
soils become light-colored.

The red color of soils is imparted by ferric oxide,
the yellow by smaller amounts of the same material.
The greenish tinge is supposed to be due to the pres-
ence of ferrous compounds, such soils being so close in
texture as to exclude the oxidizing action of the air.
Black and yellow soils are, as a rule, the most produc-
tive. Color may serv^e, to a slight extent, as an index
of fertility. The main reason why black soils are so
generally fertile is because they contain a higher per
cent, of nitrogen. Black soils are occasionally unpro-
ductive because of the presence of compounds injurious
to vegetation.

46 SOILS AND FERTILIZERS

43. Odor and Taste of Soils. — Soils containing
liberal amounts of organic matter have character-
istic odors. The odoriferous properties of a soil are
due to the presence of aromatic bodies produced by
the decomposition of organic matter. In cultivated
soils these bodies have a neutral reaction. Poorly
drained peaty soils give off volatile acid compounds
when dried. The amount of aromatic compounds in
soils is very small.

The taste of soils varies with the chemical compo-
sition. Poorly drained peaty soils usually have a
slightly sour taste, due to the presence of organic
acids. Alkaline soils have variable tastes according
to the prevailing alkaline compound. The taste of
a soil frequently reveals a fault, as acidit}' or alka-
limetry.

44. Power of Soils to Absorb Gases. — All soils pos-
sess, to a variable extent, the physical power of absorb-
ing gases. When decomposing animal or vegetable
matter is mixed with the soil the gaseous products
given off are absorbed. The absorption is both a
chemical and a physical action. The chemical
changes which occur, as the absorption of ammonia,
are considered in the chapter on fixation. The organic
matter of the soil is the principal agent in the physical
absorption of gases ; peat, for example, has the power
of absorbing large amounts. This action is similar
to that of a charcoal filter in removing noxious
gases from water.

COLOR OF SOILS 47

45. Relation of Soils to Electricity. — There is
always a certain amount of electricity in both the soil
and the air. The part which it takes in plant growth
is not w^ell understood. The action of a strong cur-
rent upon the soil undoubtedly results in a change in
chemical composition; a feeble current has either an
indifferent or a slightly beneficial effect upon crop
growth. In order to change the composition of the
soil so as to render the unavailable plant food available,
would require a current destructive to vegetation.
When plants are subjected to too strong a current of
electricity, they wilt and have all of the after-appear-
ance of frost. The slightly beneficial action upon
plant growth is not sufficient to warrant its use^s yet
in general crop production on account of cost. The
action of a weak current of electricity upon plants is
undoubtedly physiological rather than chemical, unless
it be in the slightly favorable influence which it exerts
upon nitrification. The resistance which soils, when
wet, offer to electricity has been taken by Whitney as
the basis for the determination of moisture in soils. ^^

46. Importance of the Physical Study of Soils. —
From what has been said regarding the ph}'sical prop-
erties of soils it is evident that such a study will give
much valuable information regarding their probable
agricultural value. While the physical properties
should always be taken into consideration, they should
not form the sole basis for judging the character of a

48 SOILS AND FERTILIZERS

soil, because two soils from the same locality frequently
have the same general physical composition and still
have entirely different crop-producing powers, due to
a difference in chemical composition.

Attempts have been made to overestimate the value
of the physical properties of soils and to explain nearly
all soil phenomena on the basis of soil physics. Im-
portant as are the physical properties of a soil, it can-
not be said that they are or more importance than the
chemical properties. In fact the four sciences, chem-
istry, physics, geology, and bacteriology, are all closely
connected and each contributes its part to our knowl-
edge of soils.

CHAPTER II

GEOLOGICAL FORMATION AND CLASSIFICATION OF SOILS

47. Geological Study of Soils. — The geological
study of a soil concerns itself with the past history of
that soil, the material out of which it has been pro-
duced, together with the agencies which have taken a
part in its formation and distribution. Geologically,
soils are classified according to the period in the earth's
history when formed, and also according to the agen-
cies which have distributed them. Agricultural geology
is of itself a separate branch of agricultural science.
The principles of soil formation and soil distribution
should be understood, because they have such an im-
portant bearing upon soil fertility. In this work, only
a few of the more important topics of agricultural
geology are treated in a general way.

48. Formation of Soils. — Many geologists believe
the surface of the earth to have been at one time solid
rock. It is now almost vmiversally held that soils
have been formed from rock by various agents; as, (i)
heat and cold, (2) water, (3) gases, (4) micro-organisms
and vegetable life. The disintegration of rock is
usually effected by the combined action of these vari-
ous agents. The process of soil formation is a slow
one and the various agents have been at work for an
almost indefinite period.

50 vSOILS AND FERTILIZERS

49. Action of Heat and Cold. — The cooling of the
earth's surface, followed by a contraction in volume,
resulted in the formation of fissures which exposed a
larger area to the action of other agents. The unequal
cooling of the rock caused a partial separation of the
different minerals, resulting in the formation of smaller
rock particles from larger rock masses. This is well
illustrated by the familiar splitting and crumbling of
many stones when heated. The action of frost upon
rock is also favorable to soil formation. The freezing
of water in rock crevices results in breaking up the
rock masses, forming smaller bodies. The force ex-
erted by water when it freezes is sufficient to detach
large rocks.

50. Action of Water. — Water acts upon soils both
chemically and physically. 'In its physical action,
water has been the most important agent that has
taken a part in soil formation. The surface of rocks has
been worn away by moving water and in many cases deep
ravines and canons have been formed ; the pulverized
rock, being carried along by the water and deposited
under favorable conditions, forms alluvial soil. This
is illustrated in the workings of large rivers where the
pulverized rock masses are deposited along the river
and at its mouth. A large portion of the soil in
valleys and river bottoms has been deposited by water.
The action of water is not alone confined to the forma-
tion of soils along water courses, but is equally impor-

CLASSIFICATION OF SOILS 5 1

tant in the formation of soils remote from streams or
lakes, as in the case of soils deposited by glaciers.

51. Glacial Action. — At one time in the earth's
history, the ice-fields of polar regions covered much
larger areas than at present. '^ Changes of climate
caused a recession of the ice-fields, and resulted in the
movement of large bodies of ice, carrying along rocks
and frozen soil. The movement and pressure of the
ice pulverized the rock and produced soil. This
action is well illustrated at the present time where
mountains rise above the snow line, and the ice and
snow melting at the base are replaced by ice and
snow from above moving down the side of the moun-
tain. When the glacier receded, stranded ice masses
were distributed over the land. These melted slowly
and by their grinding action hollowed out places
which finally became lakes. The numerous lakes at
the source of the Mississippi River and in central Min-
nesota are supposed to have been formed by glacial
action. The terminal of a glacier is called a moraine
and is covered with large boulders which have not
been disintegrated. The course of a glacier is fre-
quently traced by the markings or scratches of the
mass on rock ledges. In glacial soils, the rocks are
never angular, but are smooth because of the grinding
action during transportation. The area of glacial soils
in the northern portion of the United States is quite
large. These soils are, as a rule, fertile because of

52 SOILS AND FERTILIZERS

the pulverization and mixing of a great variety of
rock.

52. Chemical Action of Water. — The chemical
action of water has not taken such an important
part in soil formation as the physical action. While
nearly all recks are practically insoluble in water
there is always some material dissolved, evidenced by
the fact that all spring-water contains dissolved
mineral matter. When charged with carbon dioxide
and other gases, water acts as a solvent upon rocks.
It converts many oxides, as ferrous oxide, into hy-
droxides. The chemical action of water may result in
the formation of new compounds more soluble or
readily disintegrated, as deposits of clay, which have
been produced by the chemical and physical action of
water upon feldspar rock. Limestone is quite readily
disintegrated by water, which produces many chemical
changes in both rocks and soils. The chemical action
of fertilizers known as fixation can take place only in
the presence of water. In fact water is necessary for
nearly all chemical reactions in the soil.

53. Action of Air and Gases. — The part which air
has taken in soil formation has not been as prominent
as that taken by water. By the aid of oxygen, carbon
dioxide, and other gases and vapors in the air, rock
disintegration is hastened. The action of oxygen
changes the lower oxides to higher forms. All rock
contains more or less oxygen in chemical combination.

CLASSIFICATION OF SOILS 53

The carbon dioxide of the air under some conditions
favors the formation of carbonates. The disinte-
grating action of air, moisture, and frost is illustrated
in the case of building stones which in time crumble
and form a powder. The combined action of air,
moisture, and frost is called weathering.

54. Action of Vegetation. — Some of the lower
forms of plants as lichens do not require soil for
growth, but are capable of living on the bare surface
of rocks, obtaining food from the air, and leaving a
certain amount of vegetable matter which under-
goes decay and is incorporated with the rock parti-
cles, preparing the way for higher orders of plants
which take their food from the soil. When this
vegetable matter decays it enters into chemical com-
bination with the pulverized rock, forming humates.'^
The disintegrating action of plant roots and vegetable
matter upon rocks has been an important factor in
soil formation.

55. Action of Micro-organisms. — Micro-organisms,
found on the surface and in the crevices of rocks, are
considered by many as active agents in bringing about
rock decav. The nitrifvino- org^anisms have taken
an important part in rendering soils fertile, and these
with others have without doubt- aided in soil forma-
tion. Some of the organisrns found on the'siirface' of-
rocks are capable of producing carbonac'e6us 'matter
out of the carbon dioxide and other compounds 'of

54 SOII^S AND FERTILIZERS

the air.^° This action results in adding vegetable
matter to the soil.

56. Combined Action of the Various Agents. — In
the decay of rocks the various agents named, — water
acting mechanically and chemically, heat and cold,
air, and vegetation, — have been acting jointly, and have
produced a more rapid disintegration than if each
agent were acting separately. One of the best evi-
dences that soil is derived from rock is that there are
frequently found in fields pieces of rock which are
actually rotten, and, when crushed, closely resemble
the prevailing soil of the field. This is particularly
true of clay soils where fragments of disintegrated
feldspar are found which, when crushed, resemble the
soil in which the feldspar was imbedded.

DISTRIBUTION OF SOILS

57. Sedentary and Transported Soils. — The place
where a soil is found is not necessarily the place w^here
it was produced ; that is, a soil may be produced in
one locality and transported to another. Soils are
either sedentary or transported. Sedentary soils are
those which occupy the original position where they
were formed. They usualh' have but little depth be-
fore rock surface is reached. The stones in such soils
have sharp angles because they have not been ground
by transportation. Transported soils are those
which have been formed in one locality and carried by

ROCKS AND MINERALS 55

various agents as glaciers and rivers, to other locali-
ties, the angles of stones in these soils being ground off
during transportation. Transported soils are divided
into classes according to the ways in which they have
been formed ; as, drift soils produced by glaciers, and
alluvial soils formed by rivers and deposited by lakes.
Other agents which have taken a part in soil
transportation are wind and volcanic action. Many
soils have been either formed or modified by the wind.
The denuding action of heavy wind storms upon many
prairie soils is well known. Soil particles are carried
long distances and then deposited, forming wind-drifted
soils. In some localities volcanic soils are found ; they
are extremely varied in texture and composition — some
are very fertile and contain liberal amounts of alka-
line salts and phosphates, while others contain so little
plant food that they are sterile.
ROCKS AND MINERALS FROM WHICH SOILS ARE FORMED

58. Composition of Rock. — Rocks are composed of
either a single mineral or of a combination of minerals.
Most of the common minerals have a variable range of
composition, due to the fact that one element or com-
pound may be partially or entirely replaced by another.
Most of the common rocks from which soils have been
produced are composed of feldspar, mica, hornblende,
and quartz.

59. Quartz and Feldspar. — Quartz is the principal
constituent of many rock formations. Pure quartz is

56 SOILS AND FERTILIZERS

silicic anhydride (SiOJ. White sand is nearly pure
quartz. A soil formed from pure quartz would be
sterile. Feldspar is composed of silica, alumina, and
potash or soda. Lime may also be present, and re-
place a part or nearly all of the soda. If the mineral
contains soda as the alkaline constituent it is known
as albite, or if mainly potash it is called potash feld-
spar or orthoclase.

The members of the feldspar group are insoluble in
acids and before disintegration takes place are not ca-
pable of supplying plant food. Potash feldspar contains
from 12 to 15 per cent, of potash, none of which is of
value as plant food. When feldspar undergoes disin-
tegration it produces clay. A soil formed from feld-
spar is usually well stocked with potash.

Orthoclase, AlKSi^Og Potash Feldspar.

Albite, AlNaSiyO^ Sodium Feldspar.

60. Hornblende. — The hornblende and augite groups
are formed by the union of magnesium, calcium, iron,
and manganese, with silica. There are none of the
members of the alkali family in hornblende. The au-
gites are double silicates of iron, manganese, calcium,
and magnesium. Quite frequently phosphoric acid is
present in chemical combination with the iron. The
members of this group are readily distinguished by
their color which is black, brown, or brownish green.
The hornblendes are insoluble in acids, hence unavail-

ROCKS AND MINERALS 57

able as plant food, and when disintegrated do not as a
rnle form ver)- fertile soils.

61. Mica. — Mica is qnite complex in composi-
tion, is an abnndant mineral, and is composed of sil-
ica, iron, alumina, manganese, calcium, magnesium,
and potassium. Mica is a polysilicate. The color
may be white, brown, black, or bluish green owing
to the absence of iron, or to its presence in various
amounts. The chief physical characteristic of the
members of this group is the ease with which they
are split into thin layers. It is to be observed that the
mica group contains all of the elements of both feld-
spar and hornblende.

Soils formed from the disintegration of mica are
usually fertile owing to the variety of essential ele-
ments present. Frequently small pieces of undecom-
posed mica are found in soils.

62. Zeolites. — The zeolites form a large group of
secondar}' minerals. They are poh'silicates containing
alumina and members of the alkali and lime fami-
lies, and all contain water held in chemical combina-
tion. They are soluble in dilute hydrochloric acid
and belong to the group of compounds which are ca-
pable, to a certain extent, of serving as plant food. In
color they are white, gray, or red. Zeolites are quite
abundant in clay and are an important factor in soil
fertility. It is this group which takes such an impor-
tant part in the process of fixation. The zeolites, when

58 SOILS AND FERTILIZERS

disintegrated, particularly by glacial action, form very
fertile soils.

63. Granite is composed of quartz, feldspar, and
mica. It is a very hard rock and is slow to disinte-
grate. The different shades of granite depend upon
the proportion in which the various minerals are pres-
ent. Inasmuch as granite contains so many minerals
it usually follows that thoroughly disintegrated granite
soil is very fertile. Pure powdered granite before un-
dergoing disintegration furnishes no plant food. After
weathering, the plant food gradually becomes availa-
ble. Gneiss belongs to the granite series but differs
from true granite by containing a larger amount of
mica. Mica schist contains a larger amount of mica
than gneiss.

64. Apatite or Phosphate Rock. — Apatite is com-
posed mainly of phosphate of lime, Ca (PO )^, together
with small amounts of other compounds as fluorides
and chlorides. This mineral is generall)' of a green
or yellow color. It is present in many soils and is
of little value as plant food unless associated with or-
ganic matter or some soluble salts.

65. Kaolin is chemically pure clay and is formed by
the disintegration of feldspar. When feldspar is de-
composed and is acted upon by water the potash is re-
moved and water of hydration is taken up, forming
the product kaolin, which is hydrated silicate of alu-
mina, Al (SiO ) .H^O. Impure varieties of clay are col-

ROCKS AND MINERALS 59

ored red and yellow on acconnt of the presence of iron
and other impurities. Pure kaolin is white, is in-
soluble in acids, and is incapable of supplying any
nourishment to plants. Clay soils are fertile on ac-
count of the other minerals and organic matter mixed
with the clay and are usually w^ell stocked wnth pot-
ash because of the incomplete removal of the potash
from the disintegrated feldspar. It is to be observed
that the term clay used chemically means alu-
minum silicate, while physically it is any substance, the
particles of which are less than 0.005 mm. in diameter.
66. Other Rocks and Minerals. — In addition to
the rocks and minerals W'hich have been discussed,
there are many others that contribute to soil forma-
tion, as limestone, which is calcium carbonate ; dolo-
mite, a double carbonate of calcium and magnesium ;
serpentine, a silicate of magnesium ; and gypsum, cal-
cium sulphate.

Chemical Composition of Rocks ^"

S i £0" «6 i^c ^6 So -no Hq
■r.tr. << c-^ rr.Z ^u S^ li<fe 5>ffi

Quartz 95-100

Feldspar 55-67 20-29 0-12 i-io i-ii

Kaolin 46 39 14

Apatite 53 •••• {^l^') ""

Mica 40-45 12-37 5-12 1-5

Hornblende.. 40-55 0-15

Granite 60-80 10-15 4^5 2-3 • • •

CHAPTER III

THE CHEMICAL COMPOSITION OF SOILS

67. Elements Present in Soils. — Physically consid-
ered, a soil is composed of disintegrated rock mixed
with animal and vegetable matter ; chemically consid-
ered, the rock particles are composed of a large
number of simple and complex compounds, each
compound in turn being composed of elements chem-
ically united. Elements unite to form compounds,
compounds to form minerals, minerals to form rocks,
and disintegrated rocks form soil. When rocks decom-
pose, the disintegration, except in a few cases, is never
carried to the extent of liberating the elements, but
the process ceases when the minerals have been broken
up into compounds. While there are present in the
crust of the earth between 65 and 70 elements, only
about 15 are found in animal and plant bodies, and of
these but 12 are absolutely essential. Only four of
the elements which are of most importance are at all
liable to be deficient in soils. These four elements
are: nitrogen, phosphorus, potassium, and calcium.

68. Classification of the Elements. — The elements
found most abundantlv in soils are divided into two
classes :

CHEMICAL COMPOSITION OF SOILS 6l

Acid-forming elements Bas^e-forming elements

Oxygen O Aluminum Al

Silicon Si Potassium K

Phosphorus P Sodium Na

Sulphur S Calcium Ca

Chlorine CI Magnesium Mg

Nitrogen N Iron Fe

Hydrogen H

Boron, fluorine, manganese, and barium are usually
present in small amounts, besides others which may
be present in traces, as the rare elements lithium and
titanium.

For crop purposes the elements of the soil may be
divided into three classes :

1. Essential elements most liable to be deficient :
nitrogen, potassium, phosphorus, and calcium.

2. Essential elements usually abundant : iron, mag-
nesium, and sulphur.

3. Unnecessary and accidental elements, usually
abundant, as chlorine, silicon, aluminum, and man-
ganese.

69. Combination of Elements. — In dealing with
the composition of soils the percentage amounts of the
individual elements are not given, except in the case
of nitrogen ; but instead, the percentage amounts of
the various oxides. This is because the elements do
not exist as free elements in the soil, but are combined
with oxygen and other elements to form compounds.
When considered as oxides the acid- and base-forming
elements may form various compounds as :

62 SOILS AND FERTILIZERS

f Silicate
I Phosphate

Calcium \ Chloride

Sulphate
Carbonate

Potassium
Sodium . .
Magnesium ■
Iron

The following reactions will explain some of the
more elementary forms of combinations :

CaO + SiO., = CaSiO, CaO + SO3 = CaSO^

SCaO + P^Oj =Ca3(P0,), K^O + SO3 = K,SO,

CaO + SO3 = CaSO^ Na^O + SO3 = Na,SO,

CaO + CO2 = CaCO. MgO + SO3 = MgSO^

When considered as the oxide, calcium may com-
bine with any of the oxides of the acid-forming ele-
ments, as indicated by the reactions, to form salts.
Each of the compounds formed from the more
common elements may have a separate value as plant
food, hence it is important to consider the combina-
tions of each element separately.

ACID-FORMING ELEMENTS

70. Silicon. — The element silicon makes up from
a quarter to a third of the solid crust of the earth and
next to ox}'gen is the most abundant element found
in the soil. Silicon never occurs in the vSoil in the
free state. It either combines with oxygen to form
silica (SiO^), or with oxygen and some base-forming
element or elements to form silicates. Silica and the
various silicates are by far the most abundant com-

ACID-FORMING ELEMENTS 63

pounds present in the soil. Silicon is not one of the
elements absolutely necessary for plant growth, and
even if it were, all soils are so abundantly supplied
that it would not be necessary to use it in fertilizers.

71. Double Silicates. — When two or more base-
forming elements are united with the silicate radical,
a double silicate is formed. In fact the double sili-
cates are the most common forms present in soils.
There are also a number of forms of silicic acid which
greatly increase the number of silicates, and a study of
the composition of soils is largely a study of these
various silicates.

72. Carbon is an acid-forming element and belongs
to the same family as silicon ; it is found in the soil
as one of the main constituents of the volatile or
organic compounds. Carbon also unites w^ith oxygen
and the base-forming elements, producing carbonates,
as calcium carbonate or limestone. The carbon of the
soil takes no direct part in forming the carbon com-
pounds of the plant. It is not necessary to apply
carbon fertilizers to produce the carbon compounds of
plants because the carbon dioxide of the air is the
source for crop production. It is estimated that there
are 30 tons of carbon dioxide in the air over every
acre of the earth's surface.^' The carbon in the soil is
an indirect element of fertilit}', because it is usually
combined with elements, as nitrogen and phosphorus,
which are absolutely necessary for crop growth. yTp-^

' " OF THK

UNIVERSITY

64 SOILS AND FERTILIZERS

73. Sulphur occurs in all soils mainly m the form
of sulphates, as calcium sulphate, magnesium sul-
phate, and sodium sulphate. It is an important ele-
ment of plant food. There is generally less than one-
half per cent, of sulphuric anhydride in ordinary soils,
but the amount required by crops is small and there
is usually an abundance in all soils.

74. Chlorine is present in all soils, generally in
combination with sodium, as sodium chloride. It may
be in combination with other bases. Soils which con-
tain more than o. 10 per cent, are, as a rule, sterile. Chlo-
rine is present in the soil in soluble forms. It occurs in
all plants, although it is not absolutely necessary for
plant growth, hence its combination in fertilizers is
unnecessary. Chlorine with sodium, as common salt,
is sometimes used as an indirect fertilizer.

75. Phosphorus, one of the essential elements for
plant growth, is combined with both the volatile and
non-volatile elements of the soil. Plants cannot make
use of it in other forms than those of phosphates.
Phosphorus is usually present in the soil as calcium
phosphate, magnesium phosphate, or aluminum phos-
phate, and may also be combined with the humus,
forming humic phosphates. The form in which the
phosphates are present, as available or unavailable, is
an important factor in soil fertility. Soils are quite
liable to be deficient in phosphates, inasmuch as they
are so largely drawn upon by many crops, particularly

ACID-FORMING ELEMENTS 65

grain crops where the phosphates accumulate in the
seed, and are sold from the farm.

76. Nitrogen. — This element is present in soils in
various forms. As a mineral constituent it is combined
with oxygen and the base-forming elements as potassium,
sodium, or calcium, forming nitrates and nitrites, which,
on account of their solubility, are never found in ordi-
nary soils in large amounts. Nitrogen is present
mainly in organic combinations, being associated wdth
carbon, hydrogen, and oxygen as one of the elements
forming the organic matter of soils. Nitrogen may
also be present in small amounts in the form of am-
monia, or of ammonium salts, derived from rain
water and from the decay of vegetable and animal
matter. While nitrogen is present in the air, in a free
state, in large amounts, it can be appropriated indirectly
as food in this form by only a limited number of plants.
For ordinary agricultural crops, particularh' the cere-
als, nitrogen must be supplied through the soil as com-
bined nitrogen. This element is the most expensive
and is liable to be the most deficient of any of the ele-
ments of plant food. No other element takes such an
important part in agriculture or in life processes.

77. Oxygen. — Oxygen is combined with both the
acid- and base-forming elements and is present in
nearly all of the compounds of the soil. It has been
estimated that about one-half of the crust of the earth
is composed of oxygen, which is found in large pro-

66 SOILS AND FERTILIZERS

portions combined with silicon, forming silica. That
which is held in chemical combination in the soil
takes no part in the formation of plant tissue. In ad-
dition to being present in the soil, oxygen constitutes
eight-ninths of the weight of water and about one-fifth
of the weight of air. It also forms about 50 per cent,
of the compounds found in plants and animals. Oxy-
gen in the interstices of the soil is an active agent in
bringing about many chemical changes, as oxidation
of the organic matter, and disintegration of the soil
particles.

78. Hydrogen. — This element is never found in a
free state in the soil, but is combined with carbon and
oxygen as in animal and vegetable matter, with oxy-
gen to form water, and in a few cases with some of
the base elements to form hydroxides. It is not found
in large amounts in the soil, and that which forms a
part of the tissues of plants and animals comes from
the hydrogen in water. Hydrogen in the organic
matter of soils takes no .part directly in producing the
hydrogen compounds of plants. On account of its
lightness, hydrogen never makes up a very large pro-
portion, by weight, of the composition of bodies.

BASE-FORMING ELEMENTS

79. Aluminum is present in the soil in the largest
quantity of any of the base elements. It is calculated
that from 6 to 10 per cent, of the solid crust of the
earth is aluminum. As previously stated it is one of

BASE-FORMING ELEMENTS 67

the constituents of clay, and furnishes nothing for
plant growth. Physically, however, the aluminum
compounds take an important part in soil fertility.
Aluminum is usually in combination w4th silica or
with silica and some base-forming element, as iron,
potassium, or sodium. The various forms of alumi-
num silicates are the most numerous compounds
present in soils.

80. Potassium is present in the soil mainly in
the form of silicates, and is one of the elements abso-
lutely necessary for plant growth. The term potash
(potassium oxide, K^O) is usually employed when the
potassium compounds are referred to. The amount
and form of the soil potash have an important bearing
upon fertility. Potassium is one of the three elements
of plant food usually supplied in fertilizers. The
form in which it is present in the soil and its economic
supply as plant food, are important factors of crop
growth, and are considered in detail in Chapter VIII.
The amount of potash in soils ranges from 0.02 to 0.8
per cent. In a fertile soil it rarely falls below 0.2 per
cent.

81. Calcium is present in the soil in a variety of
forms, as calcium carbonate, calcium silicate, and
calcium phosphate. The calcium oxide (CaO) of
the soil is generally spoken of as the lime content.
Calcium carbonate and sulphate are important factors
in imparting fertility. A subsoil with a good supply

68 SOILS AND FERTILIZERS

of lime will stand heavy cropping and remain in
excellent chemical and physical condition for crop
growth. In a good soil there is nsnally 0.2 of a per
cent, or more of lime mainly as calcinm carbonate.

82. Magnesium is present in all soils and is usually
associated with calcium, forming the mineral dolo-
mite, which is a double carbonate of calcium and
magnesium. Magnesium may also be present in the
soil in the form of magnesium sulphate or magnesium
chloride. All crops require a certain amount of
magnesia in some form, in order to reach maturity
and produce fertile seeds. There is generally in all
soils an amount sufficient for crop purposes, hence it is
not necessary to consider this element in connection
with soil fertility.

83. Sodium is found in the soil mainly as sodium
silicate, and is present to about the same extent as
potassium which it resembles chemically in many ways;
it cannot, however, replace the element potassium.
Inasmuch as sodium takes such an indifferent part in
plant nutrition it is never used as a fertilizer except in
an indirect way.

84. Iron is an element necessary for plant food and
is found in all soils to the extent of from i to 4 per
cent. Crops require only a small amount of iron,
hence there is always sufficient for crop purposes.
Iron is present in soils in the form of oxides, hy-
droxides, and silicates.

FORMS OF PLANT FOOD

85. Three Classes of Compounds. — For agricul-
tural purposes, compounds present in soils may be
divided into three classes : '^ The first class includes
silicates and other compounds of potash, soda, lime,
magnesia, phosphorus, etc., which are soluble in the

This class

soil-water and in dilute organic acids.

1

^i

V

o/^e/l\ J., ^ Aa?^

[XWVWWv

23

1/me

^/(^/ //?JoM/e /1h//er

Fig. 17. Average composition of soils.
I, Nitrogen ; 2. Potash ; 3. Phosphoric acid.

represents the most soluble and the most active and
valuable forms of plant food. There is only a very
small amount in these forms. In lOo pounds of soil,
rarely more than a few hundredths of a pound of any
one of the important elements is soluble in the soil-
water or in dilute organic acids.

70 SOILS AND FERTILIZERS

The plant food of the second class is in a somewhat
more insoluble form, and consists of all those com-
pounds and silicates which are soluble in hydrochloric
acid of twenty-three per cent, strength, 1.115 sp. gr.
This class of compounds represents the limit of the
solvent action of the stronger solutions of organic
acids, such as are found in the roots of plants.

The third class of silicates includes all of those com-
pounds which require the combined action of the
highest heat and the strongest chemicals and fluxes in
order to decompose them.

The first and second classes of silicates and other
compounds are the only ones which possess any value
as plant food. The third class, after undergoing the
combined action of the various disintegrating agencies
of nature, may be changed into the second class,
called the zeolitic silicates. In this second class are
also included all of the mineral elements combined
with the humus. As a rule, not over fifteen or twenty
per cent, of the total soil is in forms soluble in hydro-
chloric acid ; and of the more important elements only
one to six per cent, form a part of this fifteen. In
two hundred samples of soil, the potash, nitrogen,
lime, magnesia, phosphoric and sulphuric acids,
amounted to 3.5 per cent. (Fig. 17). In many fertile
soils the sum of the nitrogen, phosphoric acid, potash,
lime, magnesia, and sulphuric and carbonic anhydrides
is less than 1.50 per cent. This means that in every 100

FORMS OF PLANT FOOD

71

pounds of soil there are only from 1.5 to 3.5 pounds of
matter which can take any active part in the support
of a- crop, and 96 to 98.5 pounds are present simply as
so much inert material.

86. Acid-insoluble Matter of Soils. — The insoluble
residue obtained after digest-
ing a soil with strong hydro-
chloric acid, contains potash,
soda, and limited amounts of
magnesia, and phosphoric
acid, with other elements
which are of no value as
plant food. If a seed were
planted in soil extracted with
strong hydrochloric acid, it
would make no growth after
the reserve food in the seed
had been exhausted. A plant
grown in such a soil is shown
in the illustration (Fig. 18).

On the other hand it can-
not be said that all of the
plant food soluble in hydro-
chloric acid is equally valu-
able. In fact, the acid repre-
sents more than the limit of
the crop's feeding power.

when there is not enough of

Fig. iS. Oat plant grown in
soil extracted, with hydro-
chloric acid.

72 SOILS AND FERTILIZERS

more soluble forms to aid in the first stages of growth.
In the following table the percentage amounts of
compounds soluble and insoluble in hydrochloric acid
are given : '^

Wheat Heavy clay Grass aud

soil. soil. grain soil.

Solu- Insolu- Solu- Insolu- Solu- Insolu-
ble in ble ble ble ble ble

HCl residue in HCl residue in HCl residue

Insoluble matter. 63.07 84.77 84,08

Potash 0.54 2.18 0.21 3.46 0.30 1.45

Soda 0.45 3.55 0.22 2.95 o.?5 0.25

Lime 2.44 0.36 0.48 0.16 0.51 0.35

Magnesia 1.85 0.25 0.34 0.47 0.26 0.46

Iron 4.18 0.78 3.76 0.72 2.56 1.07

Alumina 7.89 5.54 6.26 5.44 2.99 9.72

Phosphoric acid . 0.38 •.•• 0.12 0.08 0.23 0.05

Sulphuric acid- . . o.ii 0.24 0.09 0.25 0.08 0.02

The insoluble matter after digestion with h}'dro-
chloric acid, was submitted to fusion analysis, and the
figures given under insoluble residue represent the
amounts of potash, soda, etc., insoluble in acids. In
the clay soil 96 percent, of the total potash is in forms
insoluble in hydrochloric acid.

87. Soluble and Insoluble Potash and Phosphoric
Acid. — From the preceding table it is to be observed
that the larger portion of the potash in the soil is in-
soluble in hydrochloric acid. A soil may contain
from 2 to 3 per cent, of total potash, and 90 per cent,
or more may be in such firm chemical combination
with aluminum, silicon, and other elements, as to re-
sist the solvent action of plant roots. The larger

FORMS OF PI.ANT FOOD 73

portion of the phosphoric acid of the soil is soluble in
hydrochloric acid. In some soils, however, from 20
to 40 per cent, is present in the third class of com-
pounds. When a soil is digested with hydrochloric
acid, the insoluble residue is usually a fine gray
powder. Some clay soils retain their red color even
after treatment with acids showing that the iron is in
part in chemical combination with the more complex
silicates.

In order to decompose the insoluble residue obtained
from the treatment with hydrochloric acid, fluxes, as
sodium carbonate and calcium carbonate, are employed
which act upon the complex silicates at a high tem-
perature, and produce silicates soluble in acids.
Plants, however, are unable to obtain food in such
complex forms of chemical combination.

88. How a Soil Analysis is Made. — A sample is
obtained from a field by taking several small samples
to a depth of 6 to 9 inches, from different places, and
uniting them to form one sample. All coarse stones
and roots are removed and a record is made of the
amount of these materials. The soil is air dried, the
hard lumps are crushed, and the materials passed
through a sieve with holes 0.5 mm. in diameter. Only
the fine earth is used for the chemical analysis. Ten
grams of soil are weighed into a soil digestion flask,
and 10 cc. hydrochloric acid of 1.115 sp. gr. are added
for everv o;ram of soil used. The dig^estion flask is

74

SOILS AND FERTILIZERS

provided with a glass stopper which is connected with
a condensing tube. The soil digestion flask is then
placed in a hot water-bath and the di-
gestion is carried on for twelve hours at
the temperature of boiling water. After
the digestion is completed the contents
of the flask are transferred to a filter and
separated into an insoluble part, and the
acid solution which contains the com-
pounds of the various elements. The
following table will give a general idea
of how the different materials are ob-
tained from the acid solution. This table
is not intended as an outline for soil
analysis, but simply to give the stu-
dent of general chemistry an idea of how an analysis
is made.

The second half of the acid solution is divided into
three portions. The first portion is used for the deter-
mination of phosphoric acid. The acid is precipitated
with ammonium molybdate. The second portion is
used for determination of sulphuric acid, which is pre-
cipitated as barium sulphate. The carbon dioxide
is determined on a fresh portion of the original
soil ; the acid is liberated with hydrochloric acid
and the carbon dioxide is retained by absorbents and
weighed. The nitrogen and humus are determined in
separate portions of the original soil.

Fig. 19. Diges-
tion flask.

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C 2 p rtJ ^

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c o 2.

►i 3^ (^ rt' o
3 Crq 2 O S

3 3" !-»•

y O 2"

'"' ^'?
^ fU . .

0) O •— I

crq &• o

r^ " Eli
0 2.S.

3 -O^

c ^

W 3

O P

3-3
p re

J^ CT

hi ^_^.

p s.

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76 SOILS AND FERTILIZERS

89. Value of Soil Analysis. — Opinions differ as to
the value of soil analysis. It is claimed by some that
a chemical anah'sis of a soil is of no practical value
because it fails to give the amount of available plant
food. A soil may have, for example, 0.4 per cent, of
potash soluble in hydrochloric acid and still not
contain sufficient available potash to produce a good
crop, while another soil may contain 0.2 per cent,
of potash soluble in hydrochloric acid and produce
good crops. While these facts are frequently true,
it does not necessarily follow that the chemical
analysis of a soil is of no value because other sol-
vents than hydrochloric acid may be used for soil
analysis. Hydrochloric acid is used because it repre-
sents the limit of the solvent power of plants. The
figures obtained by the use of hydrochloric acid are
valuable inasmuch as they indicate whenever an ele-
ment is present in amounts which are too limited to
admit of crop production. Suppose an ordinary soil
contains 0.05 per cent, of acid-soluble potash, this
would be too small an amount to produce good crops.
The soil might contain 0.5 per cent, and yet not have
a sufficient amount of available potash. Hence it is,
that in interpreting results, the hydrochloric acid sol-
vent may show when a soil is wholly deficient in any
one element, as is sometimes the case, but it does not
necessarily show a deficiency in the case of a soil rich
in acid-soluble potash ; this can, however, be approx-

FORMS OF PLANT FOOD 77

imately indicated, by the use of other solvents, as ex-
plained in section 90.

The character of the soil, as acid, alkaline, or neu-
tral should first be determined, because plant food ex-
ists in a different form in each class of soils. If a soil
contains from 0.3 to 0.5 per cent, or more of lime (as
CaO) and from o.i to 0.4 per cent, of carbon dioxide
(COJ, and is not strongly alkaline, there is a reason-
able content of lime carbonate. If, however, the soil
contains only o.oi or 0.02 per cent, of carbon dioxide,
then the lime is not present as carbonate, but is prob-
ably present as a silicate, in which case the soil may
stand in need of a lime fertilizer. A soil which gives
an alkaline or neutral reaction and contains 0.15 per
cent, of phosphorus pentoxide, and is well supplied with
organic matter and lime, is amply provided with phos-
phoric acid, and under such conditions the exten-
sive use of phosphate fertilizers is not required,
except possibly for special crops. Hilgard states that
should the per cent, of phosphoric acid be as low as
0.05, there is, in all probability, a poverty of this ele-
ment.

Soils containing less than 0.07 per cent, of total ni-
trogen are usually deficient. A soil containing as
high as o. 1 5 or o. 2 per cent, of nitrogen may fail to re-
spond to crop production. Such cases are generally
due to some abnormal condition of the soil, as a lack
of alkaline compounds which are necessary for nitri-

78 SOILS AND FERTILIZERS

fication. The appearance of the crop is the best indi-
cation as to a deficiency of nitrogen.

A soil which contains less than 0.15 per cent, of pot-
ash soluble in hydrochloric acid is quite apt to be de-
ficient. Soils which contain 0.5 per cent, or more of
lime carbonate will produce good crops on a smaller
working supply of potash than soils which are poverty-
stricken in lime. As a rule the best agricultural soils
contain from 0.3 to 0.6 per cent, of potash. Sandy
soils of good depth may contain less plant food than
the figures given, and not be in need of fertilizers.

The term volatile matter is sometimes confused with
the term organic matter. The volatile matter includes
the organic matter and the water which is held in
chemical combination as in the hydrated silicates.
A soil may have a high per cent, of volatile matter
and contain very little organic matter. Indeed all
clays contain from 5 to 9 per cent, of water of hydra-
tion. The per cent, of humus, as will be explained
in the next chapter, does not represent all of the or-
ganic matter.

The best results are obtained from soil analyses
when an extended study is made of the soils of a lo-
cality. Then an unknown soil of that locality can be
compared with a productive soil of known composition.
An isolated soil analysis, like an isolated analysis of
well water, frequently fails in its object because of a
lack of proper normal standards for comparison.

FORMS OF PLANT FOOD 79

When extended series of soil analyses have been made,
much valuable information has been obtained.

Suppose a soil contains 0.40 per cent, of acid-soluble
potash and field experiments indicate that there is a
deficiency of available potash. This may be due to
some abnormal condition of the soil, as an insufficient
amount of other alkaline compounds as calcium car-
bonate to take the place of the potash which has been
withdrawn by the crop, in which case the deficiency
of potash could be remedied without purchasing solu-
ble potash fertilizer, to become insoluble by fixation
processes. If a soil contains only 0.04 per cent, of
acid-soluble potash, the purchasing of potash fertili-
zers would be more necessary, but with 0.40 per cent,
of acid-soluble potash the way is open to render
this potash available for crops. The various ways of
rendering acid-insoluble potash and other compounds
available for crop production, as by rotation of crops,
use of farm manures, use of lime and green manures,
or by different methods of cultivation have not been
sufficiently studied as yet to offer a solution to all of
the problems of how to render inert plant food availa-
ble.

90. Action of Organic Acids upon Soils. — Dilute
organic acids, as a one per cent, solution of citric acid,
have been proposed as solvents for the determination
of easily available plant food. It has been shown in
the case of the Rothamsted soils which have produced

8o vSOILS AND FERTILIZERS

50 crops of grain without manures, and which are
markedly deficient in available phosphoric acid, that
a I per cent, solution of citric acid dissolved only 0.003
per cent, of phosphoric acid while the soil contained a
total of 0.12 per cent. In the case of an adjoining
plot which had received phosphate manures until the
soil contained a sufficient amount of available phos-
phoric acid to produce good crops, there was present
0.03 per cent, of phosphoric acid soluble in a i per
cent, citric acid solution. ^^

Dilute organic acids are, to a certain extent, capable
of showing deficiency of plant food. A soil wdiich
shows 0.03 per cent, of potash or phosphoric acid sol-
uble in I per cent, citric acid is, as a rule, well stocked
wnth available phosphoric acid. Prairie soils of high
fertility yield from 0.03 to 0.05 per cent, of both pot-
ash and phosphoric acid soluble in dilute organic
acids ; soils which are deficient in these elements usu-
ally contain less than o.oi per cent.

The action of a single organic acid of specific
strength cannot be taken as the measure of fer-
tility for all soils and crops alike, because different
plants do not have the same amount or kind of organic
acid in the sap. Of the various organic acids, citric
possesses the greatest solvent action upon lime,
magnesia, and phosphoric acid, while oxalic acid has
the strongest solvent action upon the silicates. Tar-
taric acid appears to be less active as a solvent than

FORMS OF PLANT FOOD Si

either citric or oxalic acid. The coinbined use of
dihtte organic acids, as citric with hydrochloric acid of
1. 1 15 sp. gr., will generally give an accurate idea of
the character of a soil. A fifth-normal solution of
hydrochloric acid has also been proposed as a measure
of the soil's active phosphoric acid, and has given
satisfactory results. ^^

The use of dilute organic acids renders it possible
to detect small amounts of readily soluble phosphoric
acid and potash. It has been stated that when a soil
has been manured a few years with a phosphate fertil-
izer and brought into good condition as to available
phosphoric acid, that a chemical analysis will fail to
detect any difference in the soil before or after the
treatment with fertilizer. In the case of hydrochloric
acid as a solvent, this is true because an acre of soil
to the depth of one foot weighs about 3,500,000 lbs.
and 500 lbs. of phosphoric acid would increase the
total amount of phosphoric acid about 0.015 per cent.
When a dilute organic acid is used, only the more
easily soluble phosphoric acid is dissolved, and this
readily allows fertilized and unfertilized soils to be
distinguished. The use of dilute organic acids and
salts have shown a decided difference between soils
fertilized and unfertilized with potash. ^^

91. Distribution of Plant Food. — In studying the
chemical composition of a soil, the surface soil and
the subsoil both require consideration. It frequently

82 SOILS AND FERTILIZERS

happens that the surface soil and the subsoil have en-
tirely different chemical, as well as physical, properties.
This is particularly true of the western prairie soils,
where the surface soils generally contain less potash
and lime, but more nitrogen and phosphoric acid, than
the subsoils. When jointly considered the surface
and subsoil have strong crop-producing powers, but if
considered separately each would have weak points.

Since crops appropriate their food mainly from the
silt and clay particles, the amount of plant food pres-
ent in these grades of particles determines largely the
reserve fertility of the soil. A soil in which 70 per
cent, of the total potash is present in the silt and clay,
is in better condition for crop production than a sim-
ilar soil with a like amount of potash which is present
mainly in the sand. Because a soil has a given com-
position, it does not follow that all of the different
grades of particles have the same composition. In fact
the different grades of soil particles may have as varied
a composition as is met with among different soils.^^

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84 SOILS AND FERTILIZERS

The figures under i give the composition of the
particles, while under 2 are given the results calcu-
lated on the basis of the total amount of each element.
For example, the clay contains 1.47 per cent, of
potash, while 50.8 per cent, of the total potash of the
soil is in the clay particles.

A soil ma}' contain a comparatively low- per cent, of
potash or phosphoric acid, mainly in the finer particles
and evenly distributed so that the crop is better
supplied with food than if more were present in
the larger particles, unevenly distributed. The dis-
tribution of the plant food in the soil has not been so
extensively studied as the question of total plant food.
Sometimes in judging the character of a soil from a
chemical analysis, a soil fault, as lack of potash in the
surface soil, is corrected by a high per cent, of
the same element in the subsoil. The distribution of
plant food in both surface soil and subsoil, as well
as in the various grades of soil particles, is an im-
portant factor of fertility.

92. Composition of Typical Soils. — A few exam-
ples are given, in tabular form, of the chemical compo-
sition of soils from different regions in the United States.
On account of variations in the same localities, the
figures represent the composition of only limited areas
of soils. There have been made in the United States
a large number of soil analyses, which as yet have not
been compiled nor studied in a systematic way.

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FORMS OF PLANT FOOD 87

93. Alkaline Soils. — When a soil contains such an
excessive amount of alkaline salts as sodium sulphate,
sodium or potassium carbonate or chloride, as to be
destructive to vegetation, it is called an ' alkali '
soil. These soils are found in semi-arid regions, and
wherever conditions have been such that the alka-
line compounds have not been drained from the
soil. Occasionally calcium chloride is the destructive
material. Chlorine in any ordinary combination is
destructive to vegetation when present to the extent
of more than i part per looo parts of soil. Of the
various alkaline compounds potassium carbonate is one
of the most injurious. Sodium sulphate is a milder
form of alkali. When evaporation takes place the
alkaline compounds are deposited as a coating on the
surface of the soil. Many soils supposed to be strongly
alkaline, because a white coating is formed on the
surface, simply contain so much lime carbonate that a
deposit is formed. Many excellent soils have been
passed over as ' alkali ' soils when in reality they are
limestone soils.

94. Improving * Alkali' Soils. ^^ — When a large tract
of alkali is to be brought under cultivation the amount
of prevailing alkaline compounds should be determined
by chemical analysis. It frequently happens that
deep and thorough cultivation are all the treatment
that is necessary. If the prevailing alkali is sodium
carbonate a dressing of land plaster may be applied so

88 SOILS AND FERTILIZERS

as to change the alkali from sodium carbonate to
sodium sulphate, a less destructive form, the reaction
being :

Na CO -f CaSO = CaCO + Na SO .

Many shrubs, as greesewood, and weeds, as Russian
thistle, take from the soil large amounts of alkaline
matter, and it is sometimes advisable to remove a
number of such crops so as to reduce the alkali. A
slightly beneficial effect is sometimes noticed on small
' alkali ' spots where the ashes from straw are used,
forming potassium silicate. As a rule ashes are more
injurious than beneficial, on an ' alkali' soil. Irrigation
and thorough drainage, if continued long enough, will
effect a permanent cure. Irrigation without drainage
may cause a more alkaline condition by bringing to
the surface subsoil alkali. The waters from some
streams and wells are unsuited for irrigation on ac-
count of containing too much alkaline matter. Mildly
alkaline soils will usually repay in crop production all
the labor which is expended in making them pro-
ductive, and when brought under cultivation are fre-
quently very fertile soils. A small amount of alkaline
compounds in a soil is beneficial ; in fact, many soils
would be more productive if they contained more
alkaline matter.

95. Improving Small Tracts of * Alkali' Land. —
When the places are located so that the}' can be under-
drained at comparatively little expense, this should be

FORMS OF PLANT FOOD 89

done, as it will prove the best and most permanent
way of removing the alkali. Good snrface drainage
should also be provided. Quite frequently a quarter
or a third of the total alkali in the soil will, in a dry
time, be found near and on the surface. In such cases,
and if the spots are small, a large amount of alkali
can be removed by scraping the surface and then cart-
ing the scrapings away and dumping them wdiere
they can do no damage.

When preparing an 'alkali' spot for a crop, deep
plowing should be practiced, so as to open up the soil
and remove the excess of alkaline matter from the
surface. Where manure, particularly horse manure,
can be obtained these spots should be manured very
heavily. The horse manure, when it decomposes, fur-
nishes acid products, which combine with the alkaline
salts. The manure also prevents rapid surface evapora-
tion. Oats are about the safest grain crop to seed on
an ' alkali ' spot because the oat plant is capable of thri-
ving in an alkaline soil where many other grain crops
fail.

'Alkali' soils are usually deficient in available
nitrogen. The organism which carries on the work
of changing the humus nitrogen to available forms
cannot thrive in a strong alkaline solution. In many
of these soils, as demonstrated in the laborator}-, nitri-
fication cannot take place. After thorough drainage and
preparation for a crop, a few loads of good soil from a

90 SOILS AND FERTILIZERS

fertile field sprinkled on ' alkali ' spots will do much to
encourage nitrification, by introducing the nitrifying
organisms.

THE ORGANIC COMPOUNDS OF SOILS

96. Sources of the Organic Compounds of Soils.

— The organic compounds of soils are derived from
accumulated vegetable and animal matter which has
been acted upon by micro-organisms. The organic
matter of the soil originally consisted of the same
compounds, as cellulose, proteid bodies, and organic
acids that are found in living plants and animals. By
the action of various micro-organisms the cellulose,
proteid bodies, and other compounds have undergone
chemical changes, and produced the organic com-
pounds of the soil which are mixtures of animal and
vegetable matter in various states of decomposition.
The organic compounds of the soil may exist in
various forms ranging from cellulose to the final oxi-
dation products as carbon dioxide and water. ^7

97. Classification of the Organic Compounds. —

Various attempts have been made to classify the or-
ganic compounds of the soil, but those which have
been described are without doubt mixtures of various
bodies, and not distinct compounds. An old classifi-
cation by Miilder^^ was humic, ulmic, crenic, and ap-
procrenic acids. This classification does not include
any nitrogenous matter containing more than four per
cent, nitrogen, while organic matter with eight to ten

ORGANIC COMPOUNDS OF SOILS 9I

per cent, and in soitie cases eighteen per cent, of
nitrogen is quite frequently met with ; hence this
classification is incomplete as it includes only a part of
the organic compounds of the soil.

98. Humus. — The term humus is employed to
designate what are considered to be the most active
principles of the organic compounds. Humus is the
animal or vegetable matter of the soil in intermediate
forms of decomposition. From different soils, it is ex-
tremely varied in composition : in one soil it may
have been derived mainly from cellulose, while in an-
other it may have been derived from a mixture of cel-
lulose, proteid bodies, and other organic compounds.
The term humus, unless qualified, is a very indefinite
one. The humus given in the analyses of soils is ob-
tained by extracting the soil with a dilute alkali as
ammonium hydroxide, after treating the soil with a
dilute acid to remove the lime which renders the
humus insoluble.

99. Humification and Humates. — When the ani-
mal and vegetable matter incorporated into soils un-
dergoes decomposition there is a union of the organic
compounds and the base-forming elements of the soil.
The decaying organic matter produces organic prod-
ucts of an acid nature. The organic acids and the
base-forming products unite to form humates or or-
ganic salts, which are neutral bodies. This process is
humification. '7

92 SOILS AND FERTILIZERS

Humic acid + calcium carbonate = calcium humate + CO.^.
Humic acid + potassium sulphate =; potassium humate, etc.

The fact that a union occurs between the organic
matter and the soil has been demonstrated by mixing
with soils known amounts of. various organic materials,
as cow manure, green clover, meat scraps, and saw-
dust, and allowing humification to go on for a year or
more. After humification has taken place, the humus
extracted from the soil contains more potash, phos-
phoric acid, and other elements than were present in
the humus of the original soil and humus-forming
material, showing that a chemical union has taken
place between the decaying organic matter and the soil.
The power of various organic substances to produce
humates is illustrated in the following table :^9

Humic phos- Humic

phoric acid. potash.

Cow manure humus : Grams. Grams.

In original manure and soil 1.17 1.06

In final humus product ( after hu-
mification) 1.62 1.27

Gain in humic forms 0.45 0.21

Green clover humus :

In original soil and clover 3.21 5.26

In final hunnis product 3.74 4.93

Gain in humic forms 0.53 (Loss) 0.33

31 eat scrap humus :

In original meat scraps and soil. • 1.07 0.25

In final humus product 1.18 0.36

Gain o. 1 1 o. 1 1

ORGANIC COMPOUNDS OF SOILS 93

Humic phos- Hutnic

, , , phoric acid. potash.

Sawdust humus : Grams. Grams.

In original sawdust and soil 0.85 0.67

In final humus product 0.78 0.70

Oat straw humus :

In original straw and soil 1.02 2.42

In final humus product 1,03 2.41

100. Comparative Value and Composition of Hu-
mates. — The humus produced from nitrogenous
bodies, as meat scraps, is more vahiable than that pro-
duced from celkilose bodies as sawdust, because the
former have a greater power of combining with the
phosphoric acid and potash of the soil. The non-
nitrogenous compounds, as cellulose, starch, and sugar,
undergo fermentation but seem to possess little, if any,
power to form humates. There is also a great differ-
ence in soils as to their humus-producing powers.
Soils deficient in lime or alkaline compounds possess
only a feeble power to produce humates. There is
also a marked variation in the composition of the
humus produced from different kinds of organic matter.
Straw, sawdust, and sugar, materials rich in cellulose
and other carbohydrates, yield a humus characteris-
tically rich in carbon and poor in nitrogen. Materials
rich in nitrogen, like meat scraps, green clover, and
manure, produce a more valuable humus, rich in nitro-
gen and possessing the power to combine with the
potash and phosphoric acid of the soil to form
humates.

29

94 SOILS AND FERTILIZERS

Composition of Humus Produced by

Cow Green Meat Wheat Oat Saw-

manure, clover, scraps, flour. straw. Uust. Sugar,

Carbon 41.95 54.22 4S.77 51.02 54.30 49.28 57.84

Hydrogen 6.26 3.40 4.30 3.S2 2.48 3.33 3.04

Nitrogen 6.16 8.24 10.96 5.02 2.50 0.32 0.08

Oxygen 45.63 34.14 35.97 40.14 40.72 47-07 39-04

Total 100.00 100.00 100.00 100.00 100.00 100.00 100.00

Highest. Lowest. Difference.

Carbon 57-84 Sugar 41-95 Cow manure- . • 15.89

Hydrogen ... 6.26 Cow manure • 2.48 Oat straw 3.78

Nitrogen 10.96 Meat scraps.. 0.08 Sugar 10.88

Oxygen 47.07 Sawdust 34.14 Green clover. . . 12.93

The differences in composition are noticeable. The
humus produced by each material as green clover, oat
straw, or sawdust is different from that produced -by
any other material. The humus from green clover is
undoubtedly very complex in nature, because it con-
tains both nitrogenous and non-nitrogenous cfbm-
pounds, and each class has a different action in humi-
fication processes, hence it follows that the humus
from the green clover must be a complex mixture of
both nitrogenous and non-nitrogenous bodies.

The nature of the humus, whether nitrogenous or
non-nitrogenous, is important. Humus produced from
sawdust and humus from meat scraps may be taken
respectively as types of non-nitrogenous and nitrog-.
enous humus.

loi. Value of Humates as Plant Food. — Various
opinions have been held regarding the actual value,

ORGANIC COMPOUNDS OF SOILS 95

as plant food, of this product from partialh* decayed
animal and vegetable matter. Humus was formerly
regarded as composed only of carbon, hydrogen, and
oxygen, and inasmuch as plants obtain these elements
from water and from the carbon dioxide of the air, no
value was assigned to humus. Later investigators
added nitrogen to the list but stated that the nitrogen,
when combined with the humus and before under-
going fermentation, was of no value as plant food.

Recent investigations have proved that the phos-
phoric acid and other mineral elements combined
with the organic matter of soils are of value as plant
food,'^ and it has been demonstrated that crops grown
on the black soils of Russia obtain a large part of
their mineral food from organic combinations. ^3 Qui.
ture experiments have shown that under normal
conditions plants like oats and rye may obtain their
mineral food entirely from humate sources. Seeds
when planted in a mixture of pure sand and neu-
tral humates from fertile soils, produced normal
plants. In order to secure the best conditions
for growth, a little lime must be present to prevent
the formation of humic acid, and the usual organisms
found in fertile fields must also be introduced. The
following example is given of oats grown under such
conditions :

96 SOILS AND FERTILIZERS

Nitrogen and Ash Elements. ^^

In six oat In six mature

seeds. plants.

Gram. Gram.

Nitrogen 0.0040 0.0556

Potash 0.0013 0.0640

Soda o.oooi -^.0079

Lime 0.0002 0.0249

Magnesia 0.0005 o-oi 10

Iron 0.0064

Phosphoric anhydride 0.0016 0.0960

Sulphuric anhydride o.oooi 0.0090

Silicon 0.0026 0.7300

The fact that plants feed on hiimate compounds,
and that decaying animal and vegetable matter pro-
duce humates from the inert potash and phosphoric
acid of the soil, has an important bearing upon crop
production, because it indicates a way by which inert
plant food may be converted into more active fonns.
It also explains that stable manure is valuable because
it makes the inert plant food of the soil more available.

102. Amount of Plant Food in Humate Forms. —
In a prairie soil containing three and five-tenths per
cent, of hmnus there are present 100,000 pounds of
humus per acre. Combined with this humus there
are from 1,000 to 1,500 pounds each of phosphoric
acid and potash. Soils which have been under long
cultivation without the restoration of any humus
contain from 300 to 500 pounds each of humic potash
and phosphoric acid.'^ A decline in crop-producing
power has in many cases been brought about by the
destruction of the humus.

ORGANIC COMPOUNDS OF SOILS 97

103. Loss of Humus. — The loss of humus from the
soil is caused by oxidation and by fires. Any method
of cultivation which accelerates oxidation reduces the
humus content. In man}- of the western prairie soils
which have been under continuous grain cultivation
for thirty years and more, the amount of humus has
been reduced one-half. Summer fallowing also causes
a loss of humus. When land is continualh' under
the plow, and no manures are used, the humus is
rapidly oxidized, and there is left, in the soil, organic
matter which is slow to decay.

Forest and prairie fires have been very destructive
to the organic compounds of the soil. A soil from
Hinckley, Minn., before the great forest fire of 1893
showed 1.69 per cent, humus and 0.12 per cent,
nitrogen. '7 After the fire there were present 0.41
per cent, humus and 0.03 per cent, nitrogen. The
forest fire caused a loss of 2,500 pounds of nitrogen
per acre. In clearing new^ land, particularly forest
land, there is frequently an unnecessary destruction of
humus materials. Instead of burning all of the vege-
table matter it would be better economy to leave some
in piles for future use as manure. When all of the
vegetable matter has been burned two or three good
crops are obtained but the permanent crop-producing
power of the land is reduced because of the loss
of nitrogen. When the vegetable matter has been
only partially removed the crops at first may be

98 SOILS AND FERTILIZERS

smaller, but in a few years returns will be greater than
if all of the vegetable matter were burned.

104. Physical Properties of Soils Influenced by-
Humus. — The physical properties of a soil may be
entirely changed by the addition or the loss of humus.
The influence of humus upon the weight, color,
water, and heat of soils, is discussed in the chapter on
the physical properties of soils. Soils reduced in
humus content have less power of storing up water
and resisting drought. This fact is illustrated in the
following table :^°

Per Cent. Water.

After 10 hours
exposure iu
In soil. tray, to sun.

Soil rich in humus (3.75 per cent.) 16.48 6.12

Adjoining soil poorer in humus ( 2.50 per cent.) 12.14 3-94

105. Humic Acid. — In the absence of calcium
carbonate or other alkaline compounds, the vegetable
matter may produce acid products destructive to the
growth of some crops. The acidit}- in such cases may
be readily corrected by the use of lime or wood ashes.
Studies conducted by the Rhode Island Experiment
Station indicate that the areas of acid soils are
quite extensive. Acid soils can be distinguished by
their action upon red litmus paper. A soil may, how-
ever, give an acid reaction and contain a fair amount
of lime. The subject of acid soils and liming is consid-
ered in Chapter IX.

ORGANIC COMPOUNDS OF SOILS

99

io6. Soils in Need of Humus. — Sandy and sandy
loam soils that have been cultivated for a number of
years to corn, potatoes, and small grains, without the
use of stable manures or the proper rotation of crops,
are deficient in humus. Clay soils, as a rule, do not
stand in need of humus so much as loam or sandy
soils. The mechanical condition of heavv clavs is.

Fig-. 20. Humus from old soil.

H

%Qx(/<gsn^'^^^-

N

\ Fis:. 21. Humus from new soil.

however, improved by the addition of humus-forming
material. 'x\lkali' soils are usually deficient in humus.
Its addition to loam or sandy soils is beneficial in pre-
venting the soil from drifting because humus binds
together the soil particles. There are but few soils,
under ordinary cultivation, to which it is not safe to
add humus-forming materials. Ordinary prairie soils,
for the first ten vears after breaking, are usually well

lOO SOILS AND FERTII.IZERS

supplied. Swampy, peaty, and muck soils contain
large amounts ; in fact, they are often overstocked
with humus.

107. Active and Inactive Humus. — When soil has
been under long cultivation, and no manures have
been used, the nitrogen and mineral matters combined
with the humus are reduced. The humus from long
cultivated fields contains a higher per cent, of carbon
than that from well-manured or new land ; it is also
less active because of the higher per cent, of carbon
which does not readily undergo oxidation. '^

Humus ironi Humus from

new soil. old soil.

Per ceut. Per cent.

Carbon 44-12 50.10

Hydrogen 6.00 4.80

Oxygen 35.16 33.70

Nitrogen 8.12 6.50

Ash 6.60 4.90

Total humus material ••5.30 3.38

108. Influence of Different Methods of Farming
upon Humus. — The general system of farming has a
direct effect upon the humus content and composition
of the soil. Where live stock is kept, the manure
properly used, and the crops systematically rotated,
the crop-producing power of the land is not decreased,
as in the case of the one-crop system. The influence
of different systems of farming upon the humus con-
tent and other properties of the soil ma)' be observed
from the following table :^°

ORGANIC COMPOUNDS OF SOILS lOl

Phos-
phoric
acid com- Water-
bined holding
Weight Humus. Nitrogen, with capac-
per cu. Per Per humus. ity.

Character of soil. ft. lbs. cent. cent. Per cent. Percent.

, Cultivated thirty-five years ;
rotation of crops and manure;
high state of productiveness. 70 3.32 0.30 0.04 48

, Originally same as i ; con-
tinuous grain cropping for
thirty-five years ; low state of

productiveness 72 1.80 o. 16 o.oi 39

Cultivated forty-two years ;
systematic rotation and ma-
nure ; good state of product-
iveness 70 3.46 0.26 0.03 59

Originally same as 3 ; culti-
vated thirty -five years ; no
systematic rotation or ma-
nure ; medium state of pro-
ductiveness 67 2.45 0.21 0.03 57

CHAPTER IV

NITROGEN OF THE SOIL AND AIR, NITRIFICATION, AND
NITROGENOUS MANURES

109. Importance of Nitrogen as a Plant Food. —

The illustration (Fig. 22) shows an oat plant which has
received no nitrogen, while potash, phosphates, lime, and
all other essential elements of plant food
were liberally supplied. Observ^e the pe-
culiar and restricted growth, with but little
root development. The leaves w^ere yel-
lowish in color.

/^In the absence of nitrogen a plant
makes no appreciable growth. With only
a limited supply, a plant begins its growth
in a normal way but as soon as the avail-
able nitrogen is used up, the lower and
smaller leaves begin gradually to die
down from the tips, and all of the plant's
energy is centered in one or two leaves.
In one experiment when only a small
amount of nitrogen was supplied, the plant
struggled along in this way for about nine
weeks, making a total growth of but six
and one-half inches.'^ Just at the critical point
when the plant was dying of nitrogen starvation,
a few milligrams of calcium nitrate were given. In

Fig. 22. Oat
plant grown
without nitro-
iren.

NITROGEN .AS A PLANT FOOD IO3

thirty-six hours the plant showed signs of renewed
life, the leaves assumed a deeper green, a new growth
was begun, and finally four seeds were produced.
During the time of seed formation more nitrogen was
added, but with no beneficial result. All of the
essential elements for plant growth were liberally pro-
vided, except nitrogen which was very sparingly sup-
plied at first, until near the period of seed formation,
when it was more liberally supplied.

When plants have reached a certain period in their
development, and have been starved for the want of
nitrogen, the later application of this element does not
produce normal growth, as the energies of the plant
have been used up in searching for food. Nitrogen, as
well as potash, lime, and phosphoric acid, are all neces-
sary while plants are in their first stages of growth.

In the case of wheat, nitrogen is assimilated more
rapidly than are any of the mineral elements. Before
the plant heads out, over eighty-five per cent, of the
total nitrogen required has been taken from the soil. 3^
Corn also takes up all of its nitrogen from four to five
weeks before the crop matures. Flax takes up
severity-five per cent, of its nitrogen during the first
fifty days of growth. 37
n Nitrogen is demanded by all crops. It forms the
chief building material for the proteids of all plants.
In the absence of a sufficient amount of nitrogen, the
rich green color is not developed ; the foliage is of a
yellowish tinge. Nitrogen is one of the constituents

I04 SOILS AND FERTILIZERS

of chloroph}'!, the green coloring-matter of plants,
hence with a lack of nitrogen only a limited amount
of chlorophyl can be produced. Plants with large,
w^ell-developed leaves of a rich, green color are not
suffering for nitrogen. Nitrogenous fertilizers have
a tendency to produce a luxurious growth of foliage
deep green in color. .

' ATMOSPHERIC NITROGEN AS A SOURCE OF PLANT FOOD

110. Early Views. — In addition to the carbon, hy-
drogen, and oxygen, which form the organic com-
pounds of plants, nitrogen also, at the beginning of
the present century, was known to be present. The
sources of carbon, h}'drogen, and oxygen, for crop
purposes, were much easier to determine and under-
stand than the sources of nitrogen. Priestley, the dis-
coverer of oxygen, believed that the free nitrogen of
the air was a factor in supplying plant food. De Saus-
sure arrived at just the opposite conclusion. The facts
which led to these beliefs were not convincing because
the methods of chemical analysis had not yet been
sufficiently perfected to solve the question. 3^

111. Boussingault's First Experiments. — Boussin-
gault was the first to make a careful study of the sub-
ject. In a prepared soil, free from nitrogen, and con-
taining all of the other elements necessary for plant
growth, he grew clover, wheat, and peas, carefully
determining the nitrogen in the seed. The plants
were allowed free access to the air, being simply pro-

ATMOSPHERIC NITROGEN

^05

tected from dust, and were watered with distilled
w^ater. But little growth was made. At the end of
two months the plants were submitted to chemical
analysis, and the amount of nitrogen present was
determined.

His first results are mven in the following table :39

Nitrogen.

In seed sown.
Gram.

Clover, 2 mos o. 1 1

Wheat 2

Peas 2 ' '

Boussineault

In plant.
Gram.

0.12

0.156

0.04

0.06

o. 10

Gain.
Gram.

O.OI

0.042

^.003

0.003

0.053

plants, in

a

0.114

0.043

0.057

0.047

^ concluded that when

sterile soil, were exposed to the air, there was with
some a slight gain of nitrogen but
the amount gained from atmospheric
sources was not sufficient to feed the
plant and allow it to reach full ma-
turity. By many these results were
not accepted as conclusive.

112. Boussingault^s Second Ex-
periments.— Fifteen years later
(1853) Boussingault repeated his ex-
periments in a different way. The
plants were grown in a large carboy
with a limited volume of air so as to^ig- 23- Plants grown

rr 11 p . in carboy.

cut Oil all sources of combined nitro-

By means of a second glass vessel

gen, as ammonia.

I06 SOILS AND FERTILIZERS

(^, Fig. 23) the carboy was kept supplied with a
liberal amount of carbon dioxide, so that plant growth
w^ould not be checked for lack of this material. When
experiments were carried on in this way using a fertile
soil, the plants reached full maturity, but when a soil
free from nitrogen was used, plant growth was soon
checked. A general summary of this work is given in
the following table : ^9

Nitrogen.

In seeds. In plant. Loss.

Gram. Gram. Gram.

Dwarf beans o.icxdi 0.0977 — 0.0024

Oats 0.0109 0,0097 — 0.0012

White lupines 0.2710 0.2669 — 0.0041

Garden cress 0.0013 0.0013

These experiments show that with a sterilized soil,
and all sources of combined atmospheric nitrogen cut
off, the free nitrogen of the air takes no part in the
food supply of the plant.

113. Boussingault's Third Experiments. — In 1854
Boussingault again repeated his experiments; this
time he grew the plants in a glass case so constructed
that there was a free circulation of air from which all
combined nitrogen had been removed. These exper-
iments were similar to his second series ; the plants,
however, were not grown in a limited volume of air.
The results, without going into detail, showed that
the free nitrogen of the air, under the conditions of the
experiment, took no part in the food supply of plants.

ATMOSPHERIC NITROGEN IO7

If anything, there was less nitrogen recovered in the
dwarfed plants than there was in the seed sown.

114. Ville^s Results. — About the same time Ville
carried on a series of experiments of like nature, but
in a different way, and arrived at just the opposite
conclusions. In short, his experiments indicated that
plants w^ere capable of making liberal use of the free
nitrogen of the air for food purposes. The directly
opposite conclusions of Boussingault and Ville, led to
a great deal of controversy. The French Academy of
Science took up the question, and appointed a commis-
sion to review the work of Ville. The commission
consisted of six prominent scientists. They reported
that "M. Ville's conclusions are consistent with his
labor and results." ^^

115. Work of Lawes and Gilbert. — Lawes and
Gilbert, however, carried on such extensive exper-
iments under a variety of conditions as to remove all
doubt regarding the question. Plants were grown in
sterilized soils, in prepared pumice stone, and in soils
with a limited and known quantity of nitrogen beyond
that contained in the seed. Different kinds of plants
were experimented with. The w^ork was carried on
wnth the utmost care and with apparatus so constructed
as to eliminate all controllable factors. The results in
the aggregate clearly indicate that plants, when acting in
a sterile medium, are unable to make use of the free nitro-
gen of the air for the production of organic matter. ^^

I08 SOILS AND FERTILIZERS

1 16. Atwater's Experiments. — Atwater carried on
similar experiments in this country. 4° Some of his
results indicate that when seeds germinate they lose a j
small part of their nitrogen, and when grown in a
sterile soil, they fail to fix any of the free nitrogen of
the air.

In all of the work of the different investigators prior
to 1888, plants were grown in a sterilized medium,
and under these conditions they are unable to make
use^ of the free nitrogen of the air.

/* 117. Field and Laboratory Tests. — Experiments
» with sterilized soils do not represent the normal
conditions of growing crops, where all of the
bacteriological agencies of the soil, the air, and the
plant, are free to act. Experiments have shown that
these agencies have an important bearing upon plant
growth.

In a five years' rotation of clover and other legu-
minous plants, Lawes and Gilbert found that a soil
gained from two to four hundred pounds of nitrogen
in addition to that removed in the crop, while land
which produced wheat continuously had gradually
lost nitrogen. The amount in the subsoil remained
nearly the same. All of these facts plainly indicated
that crops like clover have the power of gaining
nitrogen from unknown sources. The results of
prominent German agriculturists led to the same con-
clusion. It was known that wheat grown after clover

ATMOSPHERIC NITROGEN IO9

gave as good results as the use of nitrogenous manure
for the wheat, but for many years this fact was unex-
plained.

^^118. HellriegePs Experiments. — He grew legu-
— Hiinous plants in nitrogen-free soils. One set of plants
was watered with distilled water, while another had in
addition small amounts of leachings from an old loam
field. The plants w^atered with distilled water alone
made but little growth, while those watered with the
loam leachings reached full maturity and contained
something like a hundred times more nitrogen than
was in the seed sown. The dark green color was also
developed, showing the presence of a normal amount
of chlorophyl. The roots of the plants had well-
developed swellings or nodules, while those that were
watered with distilled water alone had none. The
loam leachings contained only a trace of nitrogen.^'

119. Experiments of Wilfarth. — Experiments by
Wilfarth give more exact data regarding the amount
of nitrogen taken from the air. Lupines were grown
in the same way, and one lot watered with distilled
water, while another lot received in addition leachings
from an old lupine field.

Watered with distilled water. Watered with soil leachings.

Dry matter. Nitrogen. Dry matter. Nitrogen.

Grams. Gram. Grams. Grams.

0.919

0.015

44.72

1.099

0.800

0.014

45.61

I.I53

0.921

0.013

44.48

1. 195

1.021

0.013

42.45

1-337

no SOILS AND FERTILIZERS |

These experiments have been verified by many
other investigators until the fact has been established
that leguminous plants may, through the agency of
micro-organisms, make use of the free nitrogen of the
air. The work of Hellriegel was not accidental but
the result of careful and systematic investigation. As
early as 1863 he observed that clover would develop
along the roadway in sand in which there was scarcely
a trace of combined nitrogen.

120. Composition of Root Nodules. — The root
nodules referred to, are particularly rich in nitrogen.
In one experiment, the light-colored and active ones
contained 5.55 per cent, of nitrogen while the dark-
colored and older ones contained 3.21 per cent. The
entire nodules of the root both active and inactive
contained 4.60 per cent, nitrogen. The root itself
contained 2.21 per cent, nitrogen.^^

The root nodules also contain definite and charac-
teristic micro-organisms, and it was the spores of these
*" organisms that were present in the soil extract in both
HellriegePs and Wilfarth's experiments. In the ster-
ilized soils they were not present. These organisms
found in root nodules, are the essential agents which
aid in the fixation of the free nitrogen of the air, and
^ in its ultimate use as plant food.

121. Nitrogen in the Root Nodules Returned to
the Soil. — Ward has shown that when clover roots
decay, the organisms and nitrogen present in the nod-

NITROGEN COMPOUNDS OF THE SOIL III

ules are distributed within the soil. 3^ Hence when-
ever a legnniinous crop is raised, nitrogen is added to
the soil, instead of being taken away, as in the case of
a grain crop. The amount of nitrogen per acre
returned to the soil b}- a leguminous crop as clover,
varies with the growth of the crop. In the roots of a
clover crop a year old there are present from 20 to 30
pounds of nitrogen per acre, while in the roots and
culms of a dense clover sod, two or three years old,
there may be present 75 pounds or more of nitrogen.
Peas, beans, lucern, cow peas, and all members of the
leguminous family possess the powder of fixing the free
nitrog-en of the air bv means of micro-org-anisms.
The micro-organisms associated with one species as
clover differ from these associated with another as
lucern. The amount of nitrogen which the various
legumes return to the soil is variable. Hellriegel's re-
sults are of the greatest importance to agriculture
because the}' show how the free nitrogen of the air can
be utilized indirectly as food, by crops unable to appro^
priate it for themselves.

THE NITROGEN COMPOUNDS OF THE SOIL

122. Origin of the Soil Nitrogen. — The nitrogen of
the soil is derived chiefl}' from the accumulated re-
mains of animal and vegfetable matter. The orio-inal
source of the soil nitrogen, that is the nitrogen which
furnished food to support the vegetation from which
our present stock of soil nitrogen is obtained, was

112 SOILS AND FERTILIZERS

probably the free nitrogen of the air. All of the
ways in which the free nitrogen of the air has been
made available to plants of higher orders which require
combined nitrogen, are not known. It is supposed,
however, that this has been brought about by the
workings of lower forms of plant life, and by micro-
organisms. Whatever these agencies have been they
do not appear to be active in a soil under high cultiva-
tion, because the tendency of ordinary cropping is to
reduce the supply of soil nitrogen.

123. Organic Nitrogen of the Soil. — In ordinary
soils the nitrogen is present mainly in organic
forms combined with the carbon, hydrogen, and
oxygen; and to a less extent with the mineral ele-
ments forming nitrates. The organic forms of
nitrogen, it is generally considered, are incapable of
supplying plants with nitrogen for food purposes until
the process known as nitrification takes place. The
nitrogenous organic compounds in cultivated soils are
derived mainly from the undigested protein compounds
of manure and from the nitrogenous compounds in
crop residues. When decomposition occurs, amides,
organic salts, and other allied bodies are without
doubt produced as intermediate products before nitrifi-
cation takes place. The organic nitrogen of the soil
may be present in exceedingly inert forms similar to
leather. In fact in many peaty soils there are large
amounts of inactive organic compounds rich in

NITROGEN COMPOUNDS OF THE SOIL II 3

nitrogen. In other soils the nitrogen is present in
less complex forms. The organic nitrogen of the soil
may vary in complexity from forms like the nitrogen
of urea to forms like that of peat.

124. Amount of Nitrogen in Soils. — The fertility
of any soil is dependent, to a great extent, upon the
amount and form of its nitrogen. In soils of the
highest degree of fertility there is usually present
from 0.2 to 0.3 per cent, of total nitrogen, equivalent
to from 7,000 to 10,000 pounds per acre to the depth
of one foot. j\Iany soils of good crop-producing
power contain as low as 0.12 per cent, of nitrogen.
There is usually two or three times more nitrogen in
the surface soil than in the subsoil. In many sandy
soils which have been allow^ed to decline in fertility
the nitrogen may be less than 0.04 per cent. Of the
total nitrogen in soils there is rarely more than 2 per
cent, at any one time, in forms available as plant
food.43 A soil with 5,000 pounds of total nitrogen
per acre would contain about 100 pounds of available
nitrogen of which only a part comes in contact w4th
the roots of crops. Hence it is that a soil may con-
tain a large amount of total nitrogen and yet be defi-
cient in available nitrogen.

125. Amount of Nitrogen Removed in Crops.
— The amount of nitrogen removed in crops ranges
from 25 to 100 pounds per acre depending upon the
nature of the crop. It does not necessarily follow that

114 SOILS AND FERTILIZERS

the crop which removes the largest amount of nitrogen
leaves the land in the most impoverished condition.
Wheat and many grains, while they do not remove
such a large amount of nitrogen in the crop, leave
the soil more exhaused than if other crops were grown.
This, as will be explained, is caused by the loss of
nitrogen from the soil in other ways than through the
crop.37

Pounds of nitrogen
per acre.

Wheat, 20 bushels 25

Straw, 2000 pounds 10

Total '.... 35

Barley, 40 bushels 28

Straw, 3000 pounds 12

Total 40

Oats, 50 bushels 35

Straw, 3000 pounds i 15

Total 50

Flax, 15 bushels 39

Straw, 1800 pounds 15

Total 54

Potatoes, 150 bushels 40

Corn, 65 bushels 40

Stalks, 3000 pounds 35

Total 75

126. Nitrates and Nitrites. — The amount of nitro-
gen in the form of nitrates and nitrites, varies from
mere traces to 150 pounds per acre. Calcium nitrate

NITROGEN COMPOUNDS OF THE SOIL II5

is the usual form met with, especially in soils which
are sufficiently supplied with calcium carbonate to
allow nitrification to progress rapidly. Nitrates and
nitrites are the most valuable forms of nitrogen for
plant food. Both are produced from the organic
nitrogen of the soil. A nitrate is a compound com-
posed of a base element as sodium, potassium, or
calcium, combined with nitrogen and oxygen. A
nitrite contains less oxygen than a nitrate.

Potassium nitrate, KNO , sodium nitrate, NaNO ,
and calcium nitrate, Ca(NO )^, are the nitrates which
are of most importance in agriculture. The nitrites,
as potassium nitrite, KNO^, are met with to a less
extent than the nitrates. Nitrates and nitrites are
present in surface well waters contaminated with
animal and vegetable matter. IMany well waters
possess some material value as a fertilizer on account
of the nitrates, nitrites, and decaying animal and
vegetable matters which they contain.

127. Ammonium Compounds of the Soil. — The
amount of ammonium compounds in a soil is usually
less than the amount of nitrates and nitrites. The
sources of the ammonium compounds are : rain-water
and the ammonia formed from the decay of the
organic matter. Like the nitrates and nitrites, the
ammonium compounds are all soluble and hence can-
not accumulate in soils which receive an average
amount of rainfall. Thev are usuallv found in all

Il6 SOILS AND FERTILIZERS

surface well waters. In the soil, the ammonium com-
pounds may be oxidized and form nitrates. Com-
pounds as ammonium chloride or ammonium carbonate,
if present in a soil in excessive amounts, will destroy
vegetation in a w^ay similar to the alkaline compounds
in alkaline soils.

128. Nitrogen in Rain-water and Snow. — The
amount of nitrogen w^hich is annually returned to the
soil in the form of ammonium compoimds dissolved in
rain-w^ater and snow, is equivalent to from 2 to 3
pounds per acre. At the Rothamsted experiment
station the average amount for eight years was 2)- 2)7
pounds.43 When a soil is rich in nitrogen the gain
from rain and snow is only a partial restoration of that
wdiich has been given off from the soil to the air or
lost in the drain waters. The principal form of the
nitrogen in rain water is ammonium carbonate which
is present in the air to the extent of about 22 parts per
million parts of air.

129. Ratio of Nitrogen to Carbon in the Organic
Matter of Soils. — In some soils the organic matter is
more nitrogenous than in others. In those of the
arid regions the humus contains from 15 to 20 per
cent, of nitrogen, while soils from the humid regions
contain 4 to 6 per cent.^^ In some soils the ratio of
nitrogen to carbon may be i to 6, while in others it
may be i to 18 or more. That is, in some soils there
is I part of nitrogen to 6 parts of carbon, while in

NITROGEN COMPOUNDS OF THE SOIL II 7

others the organic matter contains i part of nitrogen
to 18 parts of carbon. In a soil where there exists a
wide ratio between the nitrogen and carbon, it is
believed that the conditions for supplying crops with
available nitrogen are unfavorable.

130. Losses of Nitrogen from Soils. — When a soil
rich in nitrogen is cultivated for a number of years
exclusively to grain crops there is a loss of nitrogen
exceeding the amount removed in the crop, caused by
the rapid oxidation of the organic matter of the soil.
Experiments have shown that when a soil of average
fertility is cultivated continually to grain that for
every 25 pounds of nitrogen removed in the crop there
is a loss of 146 pounds from the soil due to the
destruction of the organic matter. '^ In general, any
system of cropping which keeps the soil continually
under the plow, results in decreasing the nitrogen.
When a soil is rich in nitrogfen the grreatest losses
occur; when poor in nitrogen there is relatively less
loss. There is a tendency toward the establishment
of an equilibrium as to the nitrogen content of soils.
When a soil rich in nitroofen is g-iven arable culture
the oxidation of the organic matter and the losses of
nitrogen take place rapidly.

131. Gain of Nitrogen in Soils. — When arable
land is permanently covered with vegetation, there is
a gain of nitrogen. Pasture land contains more nitro-
gen than cultivated land of a similar character ; also

Il8 SOILS AND FERTILIZERS

ill meadow land there is a tendency for the nitrogen
to increase. These facts are well illnstrated in the
investigations of Lavves and Gilbert, at Rothamsted.^3

Age of pasture. Nitrogen.

Years. Per cent.

Arable land o. 14

Barn-field pasture 8 o. 151

Apple-tree pasture 18 o. 174

Meadow 21 o. 204

Meadow 30 0.241

After dednctino; the amount of nitrog^en in the manure
added to the meadow land, the annual gain of nitrogen
was more than 44 pounds per acre.

Another source of gain of nitrogen is the fixation of
the free nitrogen of the air by the growth of clover
and other leguminous crops. ■ If a soil is properly
manured and cropped the amount of nitrogen may be
increased. A rotation of wheat, clover, wheat, oats, and
corn with manure will leave the soil at the end of the
period of rotation in better condition as regards nitro-
gen than at the beginning. These facts are illustrated
in the following table :'7

Continuous wheat culture —

Nitrogen in soil at beginning of experiment 0.221 per cent.

Nitrogen at end of 5 years continuous wheat cultiva-
tion 0.193 " "

Loss per annum per acre (in crop 24.5, soil 146.5) . . 171 pounds.

Rotation of crops —

Nitrogen in soil at beginning of rotation 0.221 per cent.

Nitrogen at close of rotation 0.231 " "

Gain to soil per annum per acre 61 pounds.

Nitrogen removed in crops per annum 44 "

NITRIFICATION II9

It is to be reg^retted that in the cultivation of largfe
areas of land to staple crops as wheat, corn, and cotton,
the methods of cultivation are such as to decrease the
nitrogen content and crop-producing power of the soil
when this can be prevented.

NITRIFICATION

132. Former Views Regarding Nitrification. —

The presence of nitrates and nitrites in soils was
formerly accounted for by oxidation. The theory
was held that the production of nascent nitrogen by
the decomposition of organic matter caused a union
between the oxvg-en of the air and the nitroo-en of the
organic matter. The studies of fermentation by
Pasteur led him to believe that possibly the formation
of nitric acid in the soil might be due to fermentation.
It was, however, 15 years later before the French
chemists, Schlosing and ^Miintz, established the fact
that nitrification is produced by a living organism.

133. Nitrification Caused by Micro-organisms.

— Nitrification is the process by which nitrates
or nitrites are produced in soils, by the workings of
org^anisms. Nitrification results in chanmno^ the com-
plex organic nitrogen of the soil to the form of nitrates
or nitrites. It is the process by which the inert
nitrogen of the soil is rendered available as crop food.
The organisms which carry on the work of nitrifica-
tion have been isolated and studied by Warington,
and by Winogradsky.

I20 SOILS AND FERTILIZERS

134. Conditions Necessary for Nitrification are :

1. Food for the nitrifying organisms.

2. A supply of ox\'gen.

3. Moisture.

4. A favorable temperature.

5. Absence of strong sunlight.

6. The presence of some basic compound.

In order to allow nitrification to proceed, all of these
conditions must be satisfied. The process is fre-
quently checked because some of the conditions, as
presence of a basic compound, are unfulfilled.

135. Food for the Nitrifying Organisms. — All

living organisms require a supply of food and one of
the food requirements of the nitrifying organism is a
supply of phosphates. In the absence of phosphoric
acid, nitrification cannot take place. The change
which the phosphoric acid undergoes in serving as
food for the nitrif}'ing organism is unknown, but it
doubtless makes the phosphoric acid more available as
plant food. The principal organic food of the nitrify-
ing organism is the organic matter of the soil.
Organic matter, only when incorporated with soil, can
serve as food for the nitrifying organism. In the pres-
ence of a large amount of organic matter, as in a
manure pile, nitrification does not take place. The
process can take place only when the organic matter
is largely diluted with soil. Under favorable condi-

FiQ. I • Nitric Organism in Potassium Nitrite Solution.

^ «i-:

\y

fe -

A !

% IT

-?

Fig. 2. Bacillus reducing Nitrates to free Nitrogen Gas.
PLATE I.

NITRIFICATION 12 1

tions nitrifying organisms may take all of their food
as inorganic forms ; that is, nitrification may take
place in the absence of organic matter provided the
proper mineral food be snpplied. When growth
under such conditions takes place the organisms assim-
ilate carbon from the combined carbon of the air, and
produce organic carbon compounds. That is, an
organism, working in the absence of sunlight and un-
provided with chlorophyl, ma}' construct organic car-
bon compounds/3 The nitrification which takes place in
the absence of nitrogenous organic matter is of too
limited a character to supply growing crops with all
of their available nitrogen. For general crop produc-
tion the organic matter of the soil is the source of the
nitrogen which undergoes the nitrification process,
and which furnishes food for the nitrifying organisms.

136. Oxygen Necessary for Nitrification. — The
second requirement for nitrification is an adequate
supply of oxygen. The nitrification organism belongs
to that class of ferments (aerobic) which requires oxy-
gen for existence. Oxygen is present as one of the ele-
ments in the final product of nitrification as in calcium
nitrate, Ca(NO )^. In the absence of oxygen the nitri-
fication process is checked. When soils are saturated
with water, the process cannot go on for want of ox}'gen.
In well-cultivated soils, particularly clay soils, the con-
ditions for nitrification are improved b}' aeration be-
cause the supply of oxygen in the soil spaces is increased.

122 SOILS AND FERTILIZERS

137. Moisture Necessary for Nitrification. — Nitri-
fication cannot take place in a soil deprived of mois-
ture. As in all fermentation processes, so with nitri-
fication, moistnre is necessary for the chemical changes
to take place. In a very dry time nitrification is
arrested for the want of water. Water is as necessary
for the growth and development of the living organism
which carries on the work of nitrification, as it is to
the life of a plant of higher order.

138. Temperatures Favorable for Nitrification. —

The most favorable temperatures for nitrification are
between 12° C. (54° F.) and i^f C. (99° F.). It may
take place at as low a temperature as 3° or 4° C.
(37° and 39° F.); at 50° C. (122° F.) it is feeble,
while at 55° C. (130° F.) there is no action. ^^^ in
northern latitudes nitrification is checked during the
winter, while in southern latitudes this change takes
place during the entire year. Crops which re-
quire their nitrogen early in the growing season are
frequently placed at a disadvantage because there is less
available nitrogen in the soil at that time than later.

139. Strong Sunlight Checks Nitrification. — Nitri-
fication cannot take place in strong sunlight; it pre-
vents the action of all organisms of this class. In
fallow land there is no nitrification at the surface but
immediately below where the surface soil excludes the
sunlight, it is most active. In a cornfield it is more
active than in a compacted fallow field.

NITRIFICATION I23

140. Base-forming Elements Essential for Nitrifi-
cation. — The presence of some base-forming element to
combine with the nitric acid prodnced is a necessary
condition for nitrification, and for this pnrpose calcium
carbonate is particularly valuable. The absence of
basic materials is one of the frequent causes of non-
nitrification. In acid soils, the process is checked for
the want of proper basic material. The organisms
which carry on the work cannot exist in a strong acid
or alkaline solution, consequently in strong acid or
alkaline soils the ordinary process cannot take place. '^

141. Nitrous Acid Organisms. — There are at least
two nitrifying organisms in the soil : one produces
nitrates and the other nitrites or nitrous acid. It is
believed that the process takes place in two stages, the
first being performed by the nitrous organism, and the
process completed b}' the nitric organism. Warington
says that "both organisms are present in the soil in
enormous numbers, — and the action of the two organ-
isms proceeds together, as the conditions are favorable
to both."

142. Ammonia-producing Organisms. — There are
also present in the soil organisms which have the
power of producing ammonia from proteid bodies.
The ammonium compounds produced are acted upon
by the nitrifying organisms and readily undergo
nitrification. "^^

143. Denitrification is just the reverse of the nitri-

124 SOILS AND FERTILIZERS

fication process, and is the result of the workings of a
class of organisms which feed upon the nitrates form-
ing free nitrogen which is liberated as a gas. One of
the conditions for denitrification is absence of air, as
the organism belongs to the anaerobic class. Denitri-
fication readily takes place in soils saturated with
water, and wdiere the soil is compacted so that air is
practically excluded. ^^

144. Number and Kinds of Organisms in Soils. —
In addition to the micro-organisms which carry on the
work of nitrification, denitrification, and ammonifica-
tion, there are a great many others, some of which are
beneficial while others are injurious to crop growth.
It has been estimated that in a gram of an average
sample of soil there are from 60,000 to 500,000 bene-
ficial and injurious micro-organisms. ^^ There are pro-
duced from many crop residues, by injurious ferments,
chemical products w^hich may be destructive to crop
growth. Flax straw for example when it decays in
the soil forms products which are destructive to a suc-
ceeding flax crop.

A moist soil, rich in organic matter, and containing
various salts, may form the medium for the propaga-
tion of all classes of organisms. Sewage-sick soils,
clover-sick soils, and flax-diseased lands are all the re-
sults of bacterial diseases. Many of the organisms
which are the cause of such diseases as typhoid fever,
cholera, and diphtheria, may propagate and develop

NITRIFICATION I25

in a moist soil under certain conditions, and then find
their way through drain waters into surface wells, and
cause the spreading of these diseases.

145. Products Formed by Soil Organisms. — In
considering the part which micro-organisms take in
plant growth, as well as in all similar processes, there
are tw^o phases to be considered : (i) the action of the or-
ganism itself, and (2) the chemical action of the product
of the organism. In the case of nitrification, the
action of the organism brings about a change in the
composition of the organic matter, producing nitric
acid which is merely a product formed as a result of
the action of the organism. The nitric acid then acts
upon the soil producing nitrates. In the case of soils
rich in organic matter, the fermentation changes
which take place during humification result in the
production of acid products. This is simply the
result of the action of the ferments. The acids then
act upon the soil bases and produce humates or organic
salts. In many fermentation changes there is first
the production of some chemical compound, and then
the action of this compound upon other bodies. In
rendering plant food available, as in nitrification and
humification, it is the final product, and not the first
product of the organism, which is of value.

146. Inocculating Soils with Organisms . — In grow-
ing leguminous crops on soils where they have never
before been produced, it has been proposed to supply

126 SOILS AND FERTILIZERS

the essential organisms which assist the crops to
obtain their nitrogen. For example, if clover is
grown on new land, the soil is liable to be deficient in
the organisms which assist in the assimilation of
nitrogen and which are present in the root nodules of
the plant. If these organisms are supplied, better
conditions for growth exist. The extent to which it
is necessary to inoculate soils with organisms for the
assimilation of nitrogen, has not yet been determined
by actual field experiments.

147. Loss of Nitrogen by Fallowing Rich Lands.
— Summer fallowing creates conditions favorable to
nitrification. A fallow is beneficial to a succeeding
crop because of the nitrogen which is rendered a^'ail-
able. If a soil is rich in nitrogen and lime, summer
fallowing causes the production of more nitrates than
can be retained in the soil. The crop utilizes only a
part of the nitrogen rendered available, the rest being
lost by drainage, ammonification, and denitrification.
Hence the available nitrogen is increased while the
total nitrogen is greatly decreased. '^

Soil before Soil after

fallowing. fallowing.

Total nitrogen o. 154 o. 1 42

Soluble nitrogen 0.002 0.004

The gain of 0.002 per cent, of soluble nitrogen was
accompanied by a loss of 0.012 per cent, of total
nitrogen. For every pound of available nitrogen
there was a loss of 6 pounds.

NITRIFICATION 1 27

148. Deep and Shallow Plowing and Nitrification.

— In a rich prairie soil nitrification goes on very
rapidly. This is one reason why shallow plowing on
new breaking gives better results than deep plowing.
Deep plowing at first causes nitrification to take place
to such an extent that the crop is overstimulated in
growth. Deep plowing and thorough cultivation aid
nitrification. The longer a soil has been cultivated,
the deeper and more thorough must be the cultivation.

149. Spring and Fall Plowing, and Nitrification.

— Early fall plowing leaves more available nitrogen
at the disposal of the crop than late fall plowing.
Nitrification takes place only near the surface. Hence
when late spring plowing is practiced there is brought
to the surface raw^ nitrogen, while the available
nitrogen has been plowed under, and is beyond the
reach of the young plants when they require the most
help in obtaining food. The various methods of
cultivation as deep and shallow plowing, spring
and fall plowing, and surface cultivation have as much
influence upon the available nitrogen supply of crops
as upon the water supply. The saying that cultiva-
tion makes plant food available is parti cularh' true of
the element nitrogen, the supply of which is capable
of being increased or decreased to a greater extent
than that of an)- other element.

NITROGENOUS MANURES

150. Sources of Nitrogenous Manures. — The

materials used for enriching soils with nitrogen, to
promote crop growth, may be divided into three
classes: (i) organic nitrogenous manures, (2) nitrates,
and (3) ammonium salts. Each of these classes has a
different value as plant food. In fact there are
marked differences in fertilizer value between mate-
rials belonging to the same class. The nitrogenous
organic materials used for fertilizing purposes are :
dried blood, tankage, meat scraps and flesh meal, fish
offal, cottonseed meal, and leguminous crops as clover
and peas. The nitrogen in these substances is princi-
pally in the form of protein. When peat and muck
are properly used they may also be classed among the
nitrogenous manures.

151. Dried Blood. — This is obtained by drying the
blood and debris from slaughter-houses. Frequently
small amounts of salt and slaked lime are mixed with
the blood. It is richest in nitrogen of any of the
organic manures. When thoroughly dry it may con-
tain 14 per cent, of nitrogen. As usually sold, it con-
tains from 10 to 20 per cent, of water, and has a
nitrogen content of from 9 to 13. Dried blood
contains only small amounts of other fertilizer ele-
ments. It is strictly a nitrogenous fertilizer, readily
yielding to the action of micro-organisms and to

NITROGENOUS MANURES 1 29

nitrification ; on acconnt of its fermentable nature, it
is a quick-acting fertilizer, and is one of the most
valuable of the organic materials used as manure.
Dried blood may be applied as a top dressing on grass
land. It gives the best returns when used on an
impoverished soil to aid crops in the early stages of
growth, before the inert nitrogen of the soil becomes
available. It is also an excellent form of fertil-
izer to use on many garden crops, but it should not be
placed in direct contact w4th seeds, as it will cause
rotting, nor should it be used in too large amounts.
Three hundred pounds per acre is as much as should
be applied at one time. When too much is used losses
of nitrogen may occur by leaching and by denitrifica-
tion. It is best applied directly to the soil, as a top
dressing in the case of grass, or near the seeds of
garden crops, and not mixed wnth unslaked lime or
wood ashes, but each should be used separately. As
all plants take up their nitrogen early in their growth,
nitrogenous fertilizers as blood should be applied be-
fore seeding or soon after. An application of dried
blood to partially matured garden crops will cause a
prolonged growth and very late maturity.

Storer gives the following directions for preserving
any dried blood produced upon farms. ^' " The blood
is thoroughly mixed in a shallow box with 4 or 5
times its weight of slaked lime. The mixture is cov-
ered with a thin laver of lime and left to drv out. It

130 SOILS AND FERTILIZERS

will keep if stored in a cool place, and may be applied
directly to the land or added to a compost heap."

The price per pound of nitrogen in the form of
dried blood can be determined from the cost and the
analysis of the material. A sample containing 9 per
cent, of nitrogen and selling for $20 per ton is equiva-
lent to 1 1. 1 1 cents per pound for the nitrogen (2000 X
0.09 = 180. $20.00 ^- 180 = II. II cents).

152. Tankage is composed of miscellaneous refuse
matter as bones, trimmings of hides, hair, horns, hoofs,
and some blood. The fat and gelatin are, as a rule,
first removed b}' subjecting the material to superheated
steam. This miscellaneous refuse, after drying, is
ground and sometimes mixed with a little slaked lime
to prevent rapid fermentation.

Tankage contains less nitrogen but more phosphoric
acid than dried blood. Owing^ to its miscellaneous
nature, it is quite variable in composition, as the fol-
lowing analyses of tankage from the same abattoir at
different times show.'^

First year. Second j'ear. Third year.

Moisture 10.5 9.8 10.9

Nitrogen 5.7 7.6 6.4

Phosphoric acid 12.2 10.6 11.7

As a general rule, tankage contains from 5 to 8 per
cent, of nitrogen and from 6 to 14 per cent, of phos-
phoric acid. It is much slower in its action than
dried blood, and supplies the crop with both nitrogen
and phosphoric acid. Tankage is a valuable form of

NITROGENOUS MANURES 13I

fertilizer to use for garden purposes. It may also be
used as a top dressing on grass lands, and may be
spread broadcast on grain lands. It is best to apply
the tankage, when possible, a few days prior to seed-
ing, and it should not come in contact with seeds.
Two hundred and fifty pounds per acre is a safe dress-
ing, and when there is sufficient rain to ferment the
tankage, 400 pounds per acre may be used. A dressing
of 800 pounds in a dry season would be destructive to
vegetation. On impoverished soil more may be used
than on soils which are for various reasons out of
condition. The cost of the nitrogen, as tankage, may
be determined from the composition and selling price.
If tankage containing 7 per cent, of nitrogen and 12
per cent, of phosphoric acid is selling for $22 per ton,
what is the cost of the nitrogen per pound ? The
market value of phosphoric acid, in the form of bones,
should first be ascertained. Suppose that bone phos-
phoric acid is selling for 4 cents per pound. The
phosphoric acid in the ton of tankage would then be
w^orth $9.60, making the nitrogen cost $12.40. The
140 pounds of nitrogen in the ton of fertilizer would
then be worth $12.40, or 8.8 cents per pound. In
eastern markets the price of tankage is usually much
higher than near the large packing houses of the west.

153. Flesh Meal. — The flesh refuse from slaugh-
ter-houses is sometimes kept separate from the tank-
age and sold as flesh meal, the fat and gelatin being

132 SOILS AND FERTILIZERS

first removed and used for the manufacture of glue and
soap. Flesh meal is variable in composition and may
be very slow in decomposing. It contains from 4 to
8 per cent, or more of nitrogen with an appreciable
amount of phosphoric acid. Occasionally it is used
for feeding poultry and hogs, and cattle to a limited
extent. When thus used the fertilizer value of the
dung is nearly equivalent to the original value of the
meal.

154. Fish Scrap. — The flesh of fish is very rich in
nitrogen. '♦^ The offal parts, as heads, fins, tails, and in-
testines, are dried and prepared as a fertilizer. Many
species of fish which are not edible are caught in large
numbers to be used for this purpose. In sea-coast
regions fish fertilizer is one of the cheapest and best of
the nitrogenous manures. It is richer in nitrogen
than tankage or flesh meal, and in many cases equal
to dried blood. It readily undergoes nitrification and
is a quick-acting fertilizer.

155. Seed Residues. — Many seeds, as cottonseed
and flaxseed, are exceedingly rich in nitrogen. When
the oil has been removed, the flaxseed and cottonseed
cake are proportionally richer in nitrogen than the
original seed. This cake is usually sold as cattle
food, but occasionally used as fertilizer. Cotton-
seed cake contains from 6 to 7 per cent, of nitro-
gen, and compares fairly well in nitrogen content with
animal bodies. Cottonseed cake or meal is not so

NITROGENOUS MANURES I33

quick-acting a fertilizer as dried blood, but when used
in southern latitudes a little time before seeding, the
nitrogen becomes available for crop purposes. Cot-
tonseed or linseed meal containing a high per cent, of
oil is much slower in decomposing than that which
contains but little oil. It is orenerallv considered bet-
ter economy to feed the cake to stock and use the
manure than to apply the cake directly to the land.
Of late years cottonseed-meal has been so reduced in
price that its use as a fertilizer has been, admissible.

A ton of cottonseed-meal costing $20 and contain-
ing 2 per cent, of phosphoric acid and 7 per cent, of
nitrogen would be equivalent to buying the nitrogen
at 1 3. 1 cents per pound, which is frequently cheaper
than purchasing some other nitrogen fertilizer.

156. Leather, Wool Waste and Hair are rich in
nitrogen, but on account of their slow rate of decom-
posing are unsuitable for fertilizer purposes. When
present in fertilizers they give poor field results.

157. Solubility of Organic Nitrogenous Mate-
rials. — The method employed to detect, in fertilizers,
the presence of inert forms of nitrogen as leather, is to
digest the material in prepared pepsin solution. ^9
Substances like dried blood are nearly all soluble in
the pepsin, while leather and inert forms are only par-
tially so. The solubility of organic nitrogen in pep-
sin solution determines, to a great extent, the value of
the material as a fertilizer. 5°

134 SOILS AND FERTILIZERS

Soluble in prepared

pepsin solution.
Per cent, of nitrogen.

Dried blood 94.2

Ground dried fish 75.7

Tankage 73,6

Cottonseed meal 86.4

Hoof and horn meal 30.0

Leather 16.7

158. Peat and Muck. — ]\Iany samples of peat and
muck are quite rich in nitrogen. The nitrogen is,
however, in a very insohible form, and is with diffi-
culty nitrified. When mixed with stable manure,
particularly liquid manure, with the addition of a lit-
tle lime, fermentation may be induced, and a valuable
manure produced. Muck or peat should be dried and
sun-cured, and then used as an absorbent m stables.
Peat differs from muck in being fibrous. If the muck
gives an acid reaction, lime (not quicklime) should be
used with it in the stable, as directed under farm
manures. When easily obtained muck is one of the
cheapest forms of nitrogen.

Composition of Muck Sampe^es.'^

Nitrogen.
Per cent.

Marshy place, producing hay 2.21

Marshy place, dry in late summer 2.01

Old lake bottom 1.81

159. Leguminous Crops as Nitrogenous Manures.

— The frequent use of leguminous crops for manurial
purposes is the cheapest way of obtaining nitrogen.
When the crop is not removed from the land but is

NITROGENOUS MANURES 1 35

plowed under while green, the practice is called green
manuring. This does not enrich the land with any
mineral material but results in changing to humate
forms inert plant food. Green manuring should take
the place of bare fallow, as its effects are in many
respects more beneficial. With green manuring,
nitrogen is added to the soil while with bare fallow
there is a loss of nitrogen. Leguminous crops, as
clover, peas, crimson clover, and cow peas, should be
made to serv^e as the main source of the nitrogen for
crop production.

160. Sodium Nitrate. — The nitric nitrogen most
frequently met with in commercial forms is sodium
nitrate, commonly known as Chili saltpeter. It is a
natural deposit found extensively in Chili, Peru, and
the United States of Colombia. Various theories have
been proposed to account for these deposits, but it is
difficult to determine just how they have been formed.'°
Their value to agriculture may be estimated from the
fact that there are annually used in the United States
about 100,000 tons, and in Europe about 700,000 tons.
The commercial value of nitrogen in fertilizers is reg-
ulated by the price of sodium nitrate which, when pure,
contains 16.49 P^^ cent, of nitrogen. Commercial
sodium nitrate is from 95 to 97 per cent. pure.
An ordinary sample contains about 16 per cent,
of nitrogen and costs from $50 to $60 per ton, making
the nitrogen worth from 15 to 18 cents per pound.

136 SOILS AND FERTILIZERS

Sodium nitrate is the most active of all the nitrogenous
manures. It is soluble and does not have to undergo
the nitrification process before being utilized by crops.
On account of its extreme solubility it should be ap-
plied sparingly, for it cannot be retained in the soil.
As a top dressing on grass, it will respond by impart-
ing a rich green color. It may be used at the rate of
250 pounds per acre, but a much lighter application
will generally be found more economical. Sodium
nitrate may contain traces of sodium perchlorate,
which is destructive to vegetation, if the fertilizer is
used in excess.^' Sodium nitrate, in small amounts,
is the fertilizer most frequently resorted to when the
forcing of crops is desired as in early market garden-
ing. Its use for fertilizing horticultural crops has be-
come equally as extensive as for general farm crops.
Excessive amounts of sodium nitrate may produce in-
jurious results. It stimulates a rank growth of dark
green foliage, and retards the maturity of plants, but
when properly used it is one of the most valuable of
the nitrogenous fertilizers.

161. Ammonium Salts. — iVmmonium sulphate is
obtained as a by-product in the manufacture of illumi-
natino^ gras and is extensivelv sold as a fertilizer. It
usually contains about 20 per cent, of nitrogen, equiv-
alent to 95 per cent, of ammonium sulphate, the re-
maining 5 per cent, being moisture and impurities.
Ammonium sulphate is not generally considered the

NITROGENOUS MANURES 137

equivalent of sodium nitrate. It is, however, a valua-
ble form of nitrogen. The statements made regarding
the use of sodium nitrate apply equally well to the use
of ammonium sulphate. Ammonium chloride and
ammonium carbonate are not suitable for fertilizers on
account of their destructive action upon vegetation.

162. Nitrogen and Ammonia Equivalent of Fer-
tilizers. — Nitrogenous fertilizers are sometimes
represented as containing a certain amount of ammo-
nia instead of nitrogen ; this is so that a higher per-
centage may be made to appear. Fourteen-seven-
teenths of ammonia is nitrogen, and if a fertilizer is
said to contain 2.25 per cent, ammonia, it is equiva-
lent to 1.85 per cent, of nitrogen.

163. Purchasing Nitrogenous Manures. — In pur-
chasing nitrogenous manure, the special purpose for
which it is to be used should always be considered.
Under some conditions, as forcing a crop on an im-
poverished soil, sodium nitrate is desirable. Under
other conditions tankage, cottonseed cake, or some *
other form of nitrogen may be made to answer the
purpose. There is annually expended in purchasing
nitrogenous fertilizers a laro;e amount of monev which
could be expended more economically, if the science
of fertilizing were given a more careful study.

CHAPTER V

FIXATION

164. Fixation, a Chemical Change. — When a fertil-
izer is applied to a soil chemical changes take place
between the soil and the fertilizer. Theie is a general
tendency for the sohible matter of fertilizers to iinderg^o
chemical changes and become insoluble. This pro-
cess is known as fixation. If a solution of potassium
chloride be percolated through a column of clay, the
filtrate will contain scarcely a trace of potassium chlo-
ride, but instead calcium and other chlorides. In its
action upon the soil, the potassium chloride has un-
dergone a chemical change, the element potassium
being replaced by the element calcium. An ex-
change has taken place between the two bases.

165. Fixation Due to Zeolites. — It has been shown
by experiments, particularly by Way and Voechler,
that fixation is due mainly to the zeolitic silicates.^^
Sandy soils containing but little clay have only a fee-
ble power of fixation. Clay soils when digested with
hydrochloric acid to remove the zeolitic silicates, lose
their power of fixation. The fixation of potassium
chloride and the liberation of calcium chloride may be
illustrated by the following reaction :

FIXATION 139

A1,,0, ^ A1,0, 1

^^^^ U.(SiO,)..H,0-r2HCl =p^^o, [x(SiO,)..H,0 -^ CaCl,.
etc. J etc. J

166. Humus May Cause Fixation. — Other com-
pounds of the soil as humus and calcium carbonate
may also take an important part in fixation. In the
case of humus a union takes place between the basic
material and the organic matter of the soil.

167. Soils Possess Different Powers of Fixation. —
All soils do not possess the power of fixation to the
same extent. Heavy clays have the greatest fixative
power while sandy soils have the least. Experiments
have shown that in the first nine inches of soil from
2,000 to 8,000 pounds per acre of potash and phos-
phoric acid may undergo fixation. ^3 Hence it is that
a fertilizer, after being applied to a soil, may be en-
tirely changed in composition, so that the plant feeds
on the chemical compounds formed, rather than on the
original fertilizer.

168. Nitrates Cannot Undergo Fixation. — Nitro-
gen in the form of nitrates or nitrites cannot undergo
fixation. This is because all of the ordinary forms of
nitrates are soluble. If potassium nitrate be added to
a soil, calcium nitrate wili doubtless be obtained as the
soluble compound. The potassium undergoes fixa-
tion, but the nitrate radical does not. Chlorides are
likewise incapable of undergoing fixation.

169. Fixation May Make Plant Food Less Availa-
ble. — If a liberal dressing of phosphate fertilizer be

I40 SOILS AND FERTILIZERS

applied to a heavy clay soil, the phosphoric acid which
is not utilized the first year or two ma}' undergo fixa-
tion to such an extent as to become Unavailable as
plant food. It is not desirable to apply heavy dress-
ings of fertilizers at long intervals because of fixation.
It is always best to make lighter applications and more
frequently.

170. Fixation, a Desirable Property of Soils. — If it
were not for the process of fixation, soils in regions of
heavy rains would soon become sterile. On account
of the plant food being rendered insoluble, it is re-
tained in the soil. The plant food which undergoes
fixation is, as a rule, in an available condition, unless
the soil be one of unusual composition. The fixation
of fertilizers regulates the supply of crop food. Many
fertilizers, if they did not undergo this process, would
be injurious to crops. There would be an abnormal
amount of soluble alkaline or acid compounds which
would be destructive. The process of fixation first
taking place removes, to a great extent, the water-solu-
ble salts, particularly when the reaction is one of
union rather than replacement. Then the plant is
free to render soluble its own plant food in quantities
and at times desired.

Farm manures and commercial fertilizers alike un-
dergo the process of fixation and, in studying fertilizers,
their action upon the soil and the products of fixation
are matters of prime importance.

• CHAPTER VI

FARM MANURE

171. Variable Composition of Farm Manures. —

The term ' farm manure' does not designate a prod-
uct of definite composition. Manure is the most
variable in chemical composition of any of the mate-
rials produced on the farm. It may contain a large
amount of straw, in which case it is called coarse ma-
nure ; or it may contain only the solid excrements and
a little straw, the liquid excrements being lost by
leaching ; then again it may consist of the droppings
of poorly fed animals, or of the mixed excrements of
different classes of well-fed animals.

The term ' stable manure' has been proposed for
that product which contains all of the solid and liquid
excrements with the necessary absorbent, before any
losses have been sustaii^ed.'^ The term ' barnyard
manure' is restricted to that material which ac-
cumulates around some barns and farm vards, and is
exposed to leaching rains and the drying action of the
sun.

172. Average Composition of Manures. — The solid
excrements of animals contain from 6crto 85 per cent,
of water ; when mixed with straw, and the liquid
excrements are retained, the mixed manure con-

142

SOILS AND FERTILIZERS

tairts about 75 per cent, of water. The nitrogen va-
ries from 0.4 to 0.9 per cent. , according to the natnre of
the food and the extent to which other factors have af-
fected the composition. In general, animals consu-
ming liberal amounts of coarse fodders produce manure

-4. 2.1-3. ^.z.m

Fig. 24. Average composition of Fig. 25. Manure after six

fresh manure. months' exposure.

I. Nitrogen. 2. Phosphoric acid.
3. Potash.

with a higher per cent, of potash than of phosphoric
acid. This is because the potash in the food exceeds
the phosphoric acid. The average composition of
mixed stable manure is about as follows :

Average.
Per cent.

Nitrogen 0.50

Phosphoric acid 0.35

Potash 0.50

Range.
Per cent.

0,4 to 0.8

0.2 to 0.5

0.3 to 0.9

In calculating the amount of fertility in manures, it
is more satisfactory to compute the \'alue from the food
consumed and the care which the manure has received,
than to use figures expressing average composition.

FARM MANURE I43

173. Factors which Influence the Composition and
Value of Manure. —

I. Kind and amount of absorbents used.

II. Kind and amount of food consumed.

III. Age and kind of animals.

IV. Methods employed in collecting, preserving
and utilizing the manure.

Any one of the above, as well as many minor factors,
may influence the composition and value of stable
manure.

174. Absorbents. — The most universal absorbent
is straw. Wheat straw and barley straw have about
the same manurial value. Oat straw, however, is
more valuable. The average composition of straw
and other absorbents is as follows :

straw. Leaves. Peat. Sawdust.

Per cent. Per cent. Per cent. Per cent.

Nitrogen 0.40 0.6 i.o o.i

Phosphoric acid 0.36 0.3 .. 0.2

Potash 0.80 0.3 .. 0.4

When a large amount of straw is used the per cent,
of nitrogen and phosphoric acid is decreased, while the
per cent, of potash is slightly increased. Sawdust
and leaves both make the manure more dilute. Dry
peat makes the manure richer in nitrogen. The ab-
sorbent powers of these different materials are about as
follows :'3

144 SOILS AND FERTILIZERS

Per cent, of
water absorbed.

Fine cut straw 30.0

Coarse uncut straw 18.0

Peat 60.0

Sawdust 45.0

The proportion of absorbents in mannre ranges from
a fifth to a third of the total weight of the mannre.

175. Use of Peat and Muck as Absorbents. — On

acconnt of the high per cent, of nitrogen in peat and
the power which it possesses when dry of absorbing
water, it is a vahiable material to use as an absorbent
in stables. As previously explained, peat is slow of
decomposition, but when mixed with the liquid ma-
nure it readily yields to fermentation, particularly if a
little land plaster or marl be used in the stable along
with the peat; Peat has a high absorptive power for
gases as well as liquids, and when used stables are ren-
dered particularly free from foul odors.
RELATION OF FOOD CONSUMED TO MANURE PRODUCED

176. Bulky and Concentrated Foods. — The more
concentrated and digestible the food consumed, the
more valuable is the manure. Coarse bulky fodders
always give a large amount of a poor quality of ma-
nure. For example, the manure from animals fed on
timothy hay and that from animals fed on clover hay
and grain, show a wide difference in composition.
The dry matter of timothy hay is about 55 per cent,
digestible. From a ton of timothy hay there will be

FOOD CONSUMED TO MANURE PRODUCED I45

about 792 pounds of dry matter in the manure. The
nitrogen, phosphoric acid, and potash in the food con-
sumed are nearly all returned in the manure, except
under those conditions which will be noted. The
manure from a ton of mixed feed, as clover and bran,
will be smaller in amount but more concentrated than
that produced from timothy. In a ton of timothy and
in a ton of mixed feed (1500 lbs. clover, 500 lbs. bran)
there are present :

Timothy. Mixed feed.

Lbs. Lbs.

Nitrogen 25.0 40.0

Phosphoric acid 9.0 24.0

Potash 40.0 30.0

The nitrogen, phosphoric acid, and potash in these
tw^o rations are retained in the animal bodies in dis-
similar amounts ; that is, 10 per cent, more of these
elements are retained from the more liberal ration, due
to more favorable conditions for o^rowth. ^Making- al-
lowance for this fact there will be present in the ma-
nure from the mixed feed one-half more nitrogen, and
two and one-half times as much phosphoric acid, as
in the manure from the timothy hay, which, free
from bedding, contains about 792 pounds of indigesti-
ble matter while that from the mixed feed con-
tains 760 pounds, the mixed ration being more digesti-
ble. If both manures contain the same amount of ab-
sorbents, the manure from the ton of mixed clover
and bran will weigh slightly less, but contain more
fertilitv than that from the timothv hav.

146 SOILS AND FERTILIZERS

The value of the manure can be approximately de-
termined from the composition of the food consumed.
Only a small amount of the nitrogen in the food is re-
tained in the body. The larger portion is used for re-
pair purposes. The nitrogen of the tissues which
have been renewed is voided as urea in the liquid ex-
crements. Some of the nitrogenous compounds of the
food are utilized for the production of fat, in which
case the nitrogen is voided in the excrements. The
fact that but little of the nitrogen of the food, under
lYiost conditions, is retained in the body may be ob-
served from the figures of Lawes and Gilbert relating
to the composition of the flesh added to animals while
undergoing the fattening process. ^^

Increase during Fattening.

Dry Nitrogenous

Water. matter. Fat. matter. Ash.

Ox 24.6 75.4 66.2 7.69 1.47

vSheep 20.1 79,9 70.4 7.13 2.36

Pigs 22.0 78.0 71.5 6.44 0.06

The results of numerous digestion experiments
show that when the food undergoes digestion from 5
to 15 per cent, of the nitrogen is, as a rule, retained in
the bod}'. The nitrogen of the food is utilized largely
to replace that which has been required for vital func-
tions. The nitrogen of the food enters the body, un-
dergoes digestion changes, is utilized for some vital
function, and is then voided in the excrements.

The digestion of the food has been compared to the

FOOD CONSUMED TO MANURE PRODUCED 147

combustion of fuel : the undigested products of the
solid excrements represent the ashes, and the urine
represents the volatile products. When wood is
burned the nitrogen is converted into volatile products.
When food is digested and utilized by the body the di-
gestible nitrogen is mainhv converted into urea, while
the undigestible nitrogen is voided in the dung.

177. Composition of Solid and Liquid Excrements
Compared. — In composition the liquid excrements
differ from the solids in having a much larger amount
of nitrogen and less phosphoric acid.^s

Water. Nitrogen. Phosphoric acid. Potash.

Solids. Liquids. Solids. Liquids. Solids. Liquids. Solids.
Percent. Per cent. Percent. Percent. Per cent. Percent. Per cent.

Cows.. 76 89 0.50 1.20 0.35 ... 0.30

Horses. 84 92 0.30 0.86 0.25 ... o.io

Pigs... 80 97.0 0.60 0.80 0.45 0.12 0.50

Sheep . 58 86.5 0.75 1.40 0.60 0.05 0.30

The nitrogen of the food consumed influences the
amount of water in the manure. As a rule, a highly
concentrated nitrogenous ration, produces a higher per
cent, of water in the manure than a well-balanced
ration. There is but little phosphoric acid in the
liquid excrements of horses and cows, while the urine
of sheep and swine contains appreciable amounts of
this element.

The liquid manure is more constant both in compo-
sition and amount than the solid excrements. This
fact may be observed from the following table, which
gives the composition of the solid and liquid excre-

148

SOILS AND FERTILIZERS

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FOOD CONSUMED TO MANURE PRODUCED I49

ments from hog^s when fed on different amounts of

gram

56

The amount of waste matter in the urine is nearly
the same whether an animal be gaining or losing in
flesh, consequently the urine is more constant in both
composition and quantity than the solid excrements.

The amount and composition of the solid excre-
ments vary with the amount and kind of food con-
sumed. If the food is indigestible the solid excrements
contain a larger part of the nitrogen as indigestible
protein. When the body is properh- supplied with
food for all purposes, normal conditions exist, and the
amount of nitrogen voided in the liquid and solid ex-
crements is no more than that supplied in the food
consumed.

178. Manurial Value of Foods. — The manurial
value of fodder is determined by the amount of nitro-
gen, phosphoric acid, and potash present in the material.
Timothy hay, for example, has a manurial value of
$5.30 per ton, which means that if the nitrogen, phos-
phoric acid, and potash in the timothy hay were pur-
chased in commercial forms they w^ould cost $5.30.
Lawes and Gilbert estimate that 80 per cent, of the
fertility in fodders is, as a rule, returned in the ma-
nure.

In the following table are given the pounds of
nitrogen, phosphoric acid, and potash per ton of ma-
terial :"

150 SOILS AND FERTILIZERS

Nitrogen. Phosphoric acid. Potash.

Lbs. Lbs. Lbs.

Timothy hay 25 9 40

Clover hay 45 14 30

Wheat straw 11 4 12

Oat straw 12 4 18

Wheat 45 20 12

Oats 33 16 II

Barley 40 18 il

Rye 42 20 13

Flax 87 32 14

Com 32 14 8

Wheat Shorts 48 31 20

Wheat Bran 54 52 30

Oil meal 100 35 25

Cottonseed meal 130 35 56

Milk 10 3 3

Cheese 90 23 5

Live cattle 53 37 3

Potatoes 7 3 II

Butter I I I

Live pigs 40 17 3

179. Commercial Value of Manures. — When the
value of farm manure is calculated on the same basis
as that of commercial fertilizers it will be found that
stable manure is worth from $2 to $3.50 per ton. The
value of the increased crop resulting from the use of
manure will vary with conditions. It is sometimes
stated that the phosphoric acid and potash in stable
manures is not as soluble as that in commercial fer-
tilizers, and consequently it is w^orth less. While not
so soluble in the form of manure, it frequently hap-

AGE AND KIND OF ANIMAL 151

pens that the phosphoric acid and potash in the com-
mercial fertilizers become, through fixation processes,
less soluble when mixed with the soil than the same
elements in stable manure.

Stable manure is valuable not only for the fertility
contained but also because it makes the inert plant
food of the soil more available and exercises such a
favorable influence on the water supply of crops; hence
it is justifiable to assign the same value to the ele-
ments in well-prepared farm manures as to those in
commercial fertilizers.

If well-prepared stable manure is not worth $2.50
per ton, then too much, accordingly, is paid for com-
mercial forms of plant food.

INFLUENCE OF AGE AND KIND OF ANIMAL

180. Manure from Young and Mature Animals. —

The manure from older animals is more valuable than
that from young animals, even when fed the same
kind of food. This is because more of the phosphoric
acid and nitrogenous matters are retained in the body
of a vounof animal. It is not so much a difference in
digestive power as a difference in retentive power. In
older animals the proportion of new nitrogenous tissue
produced is much less than in young animals, and
more of the nitrogen of the food is used for repair pur-
poses and subsequeptly voided in the manure, while
with younger animals more of the nitrogen of the food
is retained for the construction of new muscular tissue.

152 SOILS AND FERTILIZERS

The difference in composition between the manure of
old and of young animals is not, however, so great as
might appear.

When an animal is neither gaining nor losing in
flesh, and is not producing milk, an equilibrium is
established betw^een the nitrogen in the food supply
and the nitrogen in the manure. Under such condi-
tions practically all of the nitrogen of the food is re-
turned in the manure. ^^

i8i. Cow Manure. — A milch cow when fed a bal-
anced ration, wall make from 60 to 70 pounds of solid
and liquid manure a day, of which 20 to 30 pounds are
liquid excrements. The solid excrements contain
about 6 pounds of dry matter. When a cow is fed
clover hay, corn fodder, and grain, about half of the
nitrogen of the food is in the urine, about one-fourth
in the milk, and the remainder in the solid excre-
ments. Hence, if the solid excrements only are col-
lected, but a quarter of the nitrogen of the food is ob-
tained, while if both solids and liquids are utilized
three-quarters of the nitrogen is secured. Cow manure
is extremely variable in composition, and is the most
bulky of any manure produced by domestic animals.
A well-fed cow will produce about 80 lbs. of manure
per day, including absorbents.

182. Horse Manure. — Horse manure contains less
water than cow manure, and is of a more fibrous
nature, doubtless due to the horse possessing less

AGE AND KIND OF ANIMAL I53

power for digesting cellulose materials. Horse ma-
nure readily ferments and gives off ammonia products.
When the manure becomes dry, fire-fanging results,
due to rapid fermentation followed by the growth of
fungus bodies. Horse manure is generally considered
of but little value. This is because it so readilv de-
teriorates in value and when used it has frequently
lost much of its nitrogen by fermentation. When
mixed with cow manure, both manures are improved,
the rapid fermentation of the horse manure is checked,
and at the same time the cow manure is improved in
texture. It is estimated that horses void about three-
fifths of their manure in the stable. A well-fed horse
at ordinarily hard work will produce about 50 pounds
of manure per day, of which about one-fourth is urine.
A horse will produce about 6 tons of manure per year
in the stable. If properly preserved and used it is a
valuable, quick-acting manure, but if allowed to fer-
ment and leach it will give poor results.

183. Sheep Manure. — Sheep produce a small
amount of concentrated manure, containing less water
than that produced by any other domestic animal. It
readily ferments and is a quick-acting fertilizer.
When mixed with horse and cow manure the mixture
ferments more evenly. Because of the small amount
of water, sheep manure is very concentrated in composi-
tion. It is valuable for general gardening purposes, or
whenever a concentrated quick-acting manure is desired.

154 SOILS AND FERTILIZERS

184. Hog Manure. — The composition of hog ma-
nure is exceedingly variable on account of the varied
character of the food consumed. The manure from
fattening hogs which are well fed compares very fa-
vorably in composition and value with the manure
produced by other animals. It contains a high per
cent, of water, and, like cow manure, may be slow
in decomposing. From a given weight of grain, pigs
produce less dry matter in the manure than sheep or
cows. The liquid excrements of well-fed hogs
are rich in nitrogen, containing, on an average, about 2
per cent. On account of hog manure containing so
much water, losses by leaching readily occur. The
solid excrements when leached and deprived of the
liquid excrements have but little value as a fertilizer.

185. Hen Manure. — Like all other farm manures
hen manure is variable in composition. The nitrogen
is present mainly in the form of ammonium com-
pounds. This makes it a quick-acting fertilizer.
When fowls are well fed the manure contains about
the same amount of nitrogen as sheep manure. Hen
manure readily ferments, and if not properly cared
for losses of nitrogen, as ammonia, occur. It is not
advisable to mix hard wood ashes or ordinary lime
with hen manure because the ammonia is so readily
liberated by alkaline compounds. The value of hen
manure is due to its being a quick-acting fertilizer
rather than to its containing such a large amount of

AGE AND KIND OF ANIMAL 1 55

fertility. A hen produces about a bushel of manure
per year. 55

Composition of Hen Manure.

Per cent.

Water 57-50

Nitrogen 1.27

Phosphoric acid 0.82

Potash o. 28

186. Mixing of Solid and Liquid Excrements. —

The solid and liquid excrements, when properly mixed,
make a well-balanced manure. The urine alone is not
a complete manure, as it is deficient in phosphoric acid
and other mineral matter. The solid excrements and
the urine, when mixed with soil, readily undergo nitri-
fication. The nitrogen in the solid excrements is in
the form of indigestible protein, and is rendered avail-
able as plant food more slowdy. Land which has
been heavily dressed with leached manure has re-
ceived an unbalanced manure, and is deficient in
nitrogen but fairly well supplied with mineral matter.
Such a soil may fail to respond because of the unbal-
anced character of the manure.

187. Volatile Products from Manure. — The fer-
mentation of maniire in stables may cause the pro-
duction of a large number of volatile compounds. The
ammonia and nitrogen compounds are products which
cause losses of value to the manure. Urea, when it
ferments, produces ammonia or ammonium carbonate.
If ammonia is produced it combines with the carbon

156 SOILS AND FERTILIZERS

dioxide, which is always present in stables in liberal
amounts as a product of respiration, and forms ammo-
nium carbonate, a volatile compound. When the
stable atmosphere becomes charged with ammonium
carbonate, some of it is deposited on the walls of the
stable, forming a white coating. The white coating
found on harnesses and carriages stored in poorly ven-
tilated stables, is ammonium carbonate. Accumula-
tions of manure in the stable and poor ventilation are
the conditions favorable to the production of this com-
pound.

188. Human Excrements. — The use of human ex-
crements as manure is sometimes advised, and in some
countries they are extensively used. When fresh, human
excrements may contain a high per cent, of nitrogen
and phosphoric acid ; when fermented, a loss of nitro-
gen occurs. Heiden estimates that in a year 1,000
pounds of excrements per person are made, which con-
tain $2.25 worth of fertility. 5^ For sanitary reasons,
human excrements should be used with great care.
It is doubtful with the abundance and cheapness of
plant food whether their extensive use as manure is
advisable. About 1840, Liebig feared that the essen-
tial elements of plant food would accumulate in the
vicinity of large cities and be wasted, and that in time
there would be a decline in fertility due to this cause.59
Many political economists shared the same fear.
Since that time the fixation of atmospheric nitrogen

PRESERVATION OF MANURE 157

through the agency of leguminous crops, the exten-
sive beds of sodium nitrate, phosphate rock, and Stas-
furt salts, have been discovered, and larger areas of
more fertile soil have been brought under cultivation,
so that it is not now considered so essential to devise
means for utilizing human excrements as manure.

THE PRESERVATION OF MANURE

189. Leaching. — Leaching of manure is the great-
est source of loss. Experiments by Roberts have
shown that when horse manure is thrown in a loose
pile and subjected to the joint action of leaching and
weathering it may lose nearly 60 per cent, of its most
valuable fertilizing constituents in six months. The
tabular results are as follows :^=

April 25. Sept. 28. Loss.

Lbs. Lbs. Per cent.

Gross weight 4,000 i,73o 57

Nitrogen 19.60 7.79 60

Phosphoric acid .. 14.80 7.79 47

Potash 36.0 8.65 76

Value per ton 12. 80 |;i.o6

Cow manure, on account of its more compact nature,
does not leach so readily as horse manure. A similar
experiment with cow manure, conducted at the same
time, showed the following losses :

April 25. Sept. 28. Loss.

Lbs. Lbs. Per cent.

Gross weight 10,000 5,125 49

Nitrogen 47 28 41

Phosphoric acid . . 32 26 19

Potash 48 44 8

Value per ton I2.29 |i.6o

158 SOILS AND FERTILIZERS

When mixed cow and horse manure was compacted
and "placed in a galvanized iron pan with a perfo-
rated bottom" for six months, the losses were as fol-
lows :

March 29. Sept. 30. Loss.

Lbs. Lbs. Percent.

Gross weight 226 222

Nitrogen 1.04 i.oi 3.2

Phosphoric acid • . 0.61 0.58 4.7

Potash 1.20 0,43 35.0

Value per ton $2,38 12.16

190. Losses by Fermentation. — When rapid fer-
mentation takes place in manure, appreciable losses of
nitrogen may occur. When the manure is well com-
pacted and the pile is so constructed as to prevent the
rapid circulation of air through the pile, the losses are
reduced to the minimum. Experiments have shown
that when leaching is prevented, the losses of nitrogen
by the fermentation of mixed manure are very
small. Under unfavorable conditions the losses
by fermentation may exceed 15 per cent. Hen ma-
nure, sheep manure, and horse manure suffer the
greatest losses by rapid fermentation. When extreme
conditions follow each other in succession, as exces-
sive moisture, drought, and high temperature, then
the greatest losses occur.

191. Different Kinds of Fermentation. — The large
number of organisms present in manure all belong to
one of two classes : (i) aerobic, or (2) anaerobic.
The aerobic ferments require an abundant supph' of

PRESERVATION OF MANURE 1 59

air in order to carry on their work. When deprived
of oxygen they become inactive. The anaerobic fer-
ments require the opposite conditions. They become
inactive in the presence of ox}gen and can thrive only
when air is excluded. In the center of a well-con-
structed manure pile anaerobic fermentation takes

Fig. 26. Fermentation of Manure.

place while on the surface aerobic fermentation is act-
ive. The anaerobic ferments prepare the way for the
action of the aerobic bodies. When aerobic fermenta-
tion is completed the organic matter is converted into
water, carbon dioxide, ammonia, and allied gases.
From what has been said regarding the action of these
two classes of ferments it is evident that anaerobic
fermentation is the most desirable.

192. Water Necessary for Fermentation. — In order
to produce the best results in fermenting manure
water is necessary. If the manure becomes too dry
abnormal fermentation takes place. Water is always
beneficial on manure as long as leaching is prevented;

l6o SOILS AND FERTILIZERS

it encourages anaerobic fermentation by excluding the
air. Excessive amounts of water, as that which falls
on piles from the eaves of buildings, is more than is
required for good fermentation. During a dry time it
is beneficial, if conditions admit, to water the compost
pile.

193. Heat Produced during Fermentation. — Dur-
ing the active fermentation of horse manure and sheep
manure, a temperature of 175° F. may be reached by
the fermenting mass. Ordinarily, however, the tem-
perature of the manure pile ranges from 110° to 130°
F. The highest temperature is reached near the sur-
face where fermentation is most rapid. The tempera-
ture of fermentation may be sufficiently high if the
manure is mixed with the proper litter to cause spon-
taneous combustion.

194. Composting Manure May Improve Its Quality.

— When manure is composted so that leaching and
rapid fermentation do not take place the manure may
be improved in quality by becoming more concentra-
ted. Pound for pound, composted manure is more
concentrated than fresh manure, because, if properly
cared for, nearly all of the nitrogen, phosphoric acid,
and potash of the original manure are obtained in a
smaller bulk. A ton of composted manure is obtained
from about 2,800 pounds of stable manure.

PRESERVATION OF MANURE l6l

Fresh Composted

manure. manure.

Per cent. Per cent.

Nitrogen 0.50 0.60

Phosphoric acid 0.28 0.39

Potash 0.60 0.80

In composting manure it should be the aim to in-
duce anaerobic fermentation bv excluding- the air and
retaining the water. This can be best accomplished
by using mixed manure and making a compact pile,
capable of shedding water. The compost pile should
be shaded to secure better conditions for fermentation.
If the pile becomes offensive a little earth on the sur-
face will absorb the odors.

195. Use of Preservatives. — The use of preserv^a-
tives as gypsum and kainit have been recommended to
prevent fermentation losses. Opinions differ as to
their value. ]Moist gypsum, when it comes in contact
with ammonium carbonate, produces ammonium sul-
phate, a non-volatile compound,

(NH ) CO A- CaSO = (NH ) SO 4^ CaCO .

\ 4/2 3 ■ 4 ^ 4-'^2 4 3

Gypsum is used at the rate of about one-half pound
per day for each animal. ^^ Experiments have shown
that it may prevent a loss of 5 per cent, of the nitro-
gen of horse manure. It may be safely sprinkled -in
the stalls as it has no action on the feet of animals.
When gypsum is used as a fertilizer it is very desira-
ble to use it in stables. It is not advisable to use
lime in any other form than the sulphate. Unslaked

l62 SOILS AND FERTILIZERS

lime will decompose manure and liberate ammonia.
Neither kainit nor gypsum should be used when ma-
nure is exposed to the leaching action of rains.
Preservatives cannot be made to take the place of
want of care in handling manure ; they should be used
onh' wdien the manure receives the best of care.

196. Manure Produced in Covered Sheds and Box
Stalls. — Manure produced under cover as in sheds
and box stalls is of superior quality to that produced
in any other way. Losses by leaching are avoided,
the manure is compacted by the tramping of animals,
and the solid and liquid excrements are more evenly
mixed with the absorbents. By no other system is
there such a large percentage of the fertility recovered.
Manure from w^ell-fed cattle, when collected and pre-
pared in a covered shed, will have about the follow-
ing composition :

Per cent.

Water 70.00

Nitrogen 0.90

Phosphoric acid 0.60

Potash 0.70

197. Value of Protected Manure. — Manure that
is produced under cover has greater crop-produ-
cing powers than manure that is cared for in any other
way. Experiments by Kinnard show that such ma-
nure produced 4 tons more potatoes per acre than pile
manure, while 11 bushels more of wheat per acre
were obtained from land which had the previous year

THE USE OF MANURE 163

received the covered manure than from land which
received the uncovered manure. ^^

THE USE OF MANURE

198. Direct Hauling to Fields. — It is always desir-
able, whenever conditions allow, to draw the manure
directly to the field and spread it, rather than to allow
it to accumulate about barns or in the barnyard.
When taken directly to the field from the stable no
losses by leaching occur, and the slight loss from
fermentation and volatilization of the ammonia are
more than compensated for by the benefits derived
from the action of the fresh manure upon the soil.
When manure undergoes fermentation in the soil, as
previously stated it combines with the mineral matter
of the soil and produces humates. The practice of
hauling the manure directly to the field as soon as
produced is the most economical way of caring for it.

With scant rainfall, composting the manure before
spreading is necessary, but with a liberal rainfall it is
not essential. On a loam soil a direct application
of stable manure is more advisable than on heavy clay
or light sandy soils. On sandy soils there is frequently
an insufficient supply of water to properly ferment the
manure. Manure sometimes fails to show any benefi-
cial effects the first year on heavy cla)' land, because
of the slow rate of decomposition, but the second and
third years the beneficial effects are noticeable.

164

SOILS AND FERTILIZERS

199. Coarse Manure May Be Injurious. — The ap-
plication of coarse leached manure may cause the soil
to be SO open and porous as to affect the water supply
of the crop, b)' introducing, below the surface soil, a
layer of straw, which breaks the capillary connection
with the subsoil. Coarse manure and shallow spring
plowing are frequently injurious, when fine or w^ell-
composted manure and fall plowing are beneficial.
The injury resulting from the use of coarse manure is
frequently due to its being allowed to leach before it is
used, so that it does not properly ferment in the soil.

200. Manuring Pasture Land. — In semiarid
regions, where manure decomposes slowly, it is some-
times advisable to spread it upon the pasture land as

IMlUIUxiiiUilliliiL

Fig. 27. Manured land.

a top dressing. The manure encourages the growth
of grass, which appropriates plant food otherwise lost,
and it also acts as a mulch preventing excessive evapo-
ration. Then when the pasture land is plowed and pre-
pared for a grain crop it contains a better store of both

THE USE OF MANURE

l6^

water and available plant food. The manuring of
pasture lands is one of the best ways of utilizing the

Fig. 28. Unmanured land.

manure when trouble arises from slow decomposition.

201. Small Manure Piles Undesirable. — It is

sometimes the custom to make a large number of
small manure piles in fields. This is a poor practice,
for it entails additional expense in spreading the ma-
nure, and the small piles are usually so constructed
that heavy losses occur, and the manure, when finally
spread, is not uniform in composition. Oats grown on
land manured in this way present an uneven appear-
ance. There are small patches of thrifty, overfed
oats, corresponding to the places occupied by the
former manure piles, while large areas of half-starv^ed
oats may be observed.

202. Rate of Application. — The amount of manure
that should be applied depends upon the nature of the
soil and the crop. On loam soils intended for general
truck purposes heavier applications may be made than
when grain is raised. For general farm purposes, 10

l66 SOILS AND FERTILIZERS

tons per acre are usually sufficient. It is better
economy to make frequent light applications than
heavier ones at long intervals. When manure is
spread frequently the soil is kept in a more even state
of fertility, and losses by percolation, denitrification,
and ammonification are prevented.

For growing garden crops 20 tons and more per acre
are sometimes used. It is better, however, not to use
stable manure too liberally for trucking, but to supple-
ment it with special fertilizers as the crop may require.
Soils which contain a large amount of calcium car-
bonate admit of more frequent and heavier applications
of manure than soils which are deficient in this com-
pound. The lime aids fermentation and nitrification.

203. Crops Most Suitable for Manuring. — Soils
which contain a low stock of fertility will admit of
manuring for the production of almost any crop.
Soils well stocked with plant food, like some of the
western prairie soils, which are in need of manure
mainly for the physical action, will not admit of its
direct use on all crops. On a prairie soil of average
fertility an application of well-rotted manure will
cause wheat to lodge. When it cannot be applied di-
rectly to a crop, it may be used indirectly. It never
injures corn by causing too rank a growth, and when
wheat follows corn which has been manured there is
but little danger of loss from lodging.

THE USE OF MANURE 1 67

On some soils stable manure cannot be used for
growing sugar-beets ; on other soils it does not seem to
exercise an injurious effect. Tobacco is injured as to
quality by manure. Crops, as flax, tobacco, sugar-
beets, and wheat, which do not admit of direct applica-
tions of stable manure all require the manuring of
preceding crops. When in doubt as to w^hat crop to
apply the manure to, it is always safe to apply it to corn,
and then to follow with the crop which would have
been injured by its direct application.

The fact that coarse, leached manure may cause
trouble in a dry season, and that well-rotted manure
may cause grain to lodge, are no substantial reasons
why manure should be wasted as it frequently is in
western farming by being burned, used for making
roads, thrown away in streams, or used for filling up
low places.

204. Comparative Value of Manure and Crops. —

The manure from a given amount of grain or fodder
always gives better results than if the food itself were
used directly as manure. The manure from a ton of
bran will give better returns than if the bran itself
were used. This is because so little of the fertilizing
elements is extracted in the process of digestion and
the action of the digestive fluids upon the food makes
the manure more readily available as a fertilizer than
the food which has not passed through any of the
stages of fermentation. It is better economy to use

l68 SOILS AND FERTILIZERS

products as linseed meal and cottonseed meal for feed-
ing stock, and take good care of the manure, than to
use the materials directly.

205. Lasting Effects of Manure. — No other ma-
nures make themselves felt for so long a time as farm
manures. In ordinary farm practice an application of
stable manure will visibly affect the crops for a num-
ber of years. At the Rothamsted Experiment Station,
records have been kept for over fifty years as to the
effects of manures upon soils. In one experiment
manure was used for twenty years and then discon-
tinued for the same period. It was observed that
when its use was discontinued there was a gradual de-
cline in crop-producing power, but not so rapid as on
plots where no manure had been used. The manure
which had been applied for the twenty-year period
prior to its disuse made itself felt for an ensuing
period of twenty years.

206. Comparative Value of Manure Produced on
Two Farms. — The fact that there is a great differ-
ence in the composition and value of manures pro-
duced on different farms may be observed from the
following examples :

On one farm 10 tons of timothy are fed. The
liquid manure is not preserved and 25 per cent, of the
remaining fertility is leached out of the solids, while
5 per cent, of the nitrogen is lost by volatilization.
It is estimated that half of the nitrogen and potash of

THE USE OF MANURE

169

the food is voided in the urine. On account of the
scant amount and poor quality of the food no milk or
flesh is produced.

On another farm 7.5 tons of clover hay and 2.5 tons
of bran are fed. The liquid excrements are collected

Fig. 29. Good manure.

Fig. 30. Poor manure.

and the manure is taken directly to the field and
spread. It is estimated that 20 per cent, of the nitro-
gen and 4 per cent, of the phosphoric acid and potash
are utilized for the production of flesh or milk.

The relative value of the manures from the two
farms is as follows :

Farm No. i.

In 10 tons timothy,
Lbs.

Nitrogen 250

Phosphoric acid 90

Potash 400

Loss in urine.

250 -7- 2 =: 125 lbs. nitrogen
400 -T- 2 = 200 lbs. potash

IJO SOILS AND FERTILIZERS

Loss by leaching.
125 X 0.30 = 37.50 lbs. nitrogen
90 X 0-25 = 22.50 lbs. phosphoric acid
200 X 0.25 = 50 lbs. potash

Total loss.
Lbs. Per cent.

Nitrogen 162.5 65

Phosphoric acid 22.5 25

Potash 250.0 62

Present in final product,

manure from i ton timothy.

Lbs.

"Nitrogen 8,75

Phosphoric acid 6.75

Potash 15.00

Relative money value |;i.oo

Farm No. 2.

In 10 tons mixed feed.
Lbs.

Nitrogen 400

Phosphoric acid 240

Potash 300

Loss, sold in milk and retained in body.
Lbs. Per cent.

Nitrogen, 400X0.20 80 20

Phosphoric acid, estimated 10 4

Potash 12 4

Present in final product,
manure from i ton feed.

Lbs.

Nitrogen 32.0

Phosphoric acid 23.0

Potash 26.0

Relative money value l'3-8o

207. Summary of Ways in which Stable Manure
May Be Beneficial. —

I. By adding new stores of plant food to the soil.

THE USE OF MANURE 171

2. By acting upon the soil, forming huniates and
rendering the inert plant food of the soil more availa-
ble.

3. By raising the temperature of the soil.

4. By making the soil darker colored.

5. By enabling soils to retain more water and to
give it up gradually to growing crops.

6. By improving the physical condition of sandy
and clay soils.

7. By preventing the denuding effects of heavy
wind storms.

CHAPTER VII

PHOSPHATE FERTILIZERS

208. Importance of Phosphorus as Plant Food. —

Phosphorus in the form of phosphates is one of the
essential elements of plant food. None of the higher
orders of plants can complete their
growth unless supplied with this
element in some form. The illus-
tration (Fig. 31) shows an oat plant
which received no phosphates, but
was supplied with all of the other
elements of plant food. As soon as
the phosphates stored up in the
seed had been utilized, the plant
ceased to grow, and after a few
weeks died of phosphate starvation,
having made the total growth
shown in the illustration. All crops
demand their phosphates at an early
stage in their development. Wheat
takes up eighty per cent, of its
phosphoric acid in the first half of
without phosphorus. ^\^q growing period,36 while clover
has assimilated all of its phosphoric acid by the
time the plant reaches full bloom. '^^ Phosphates ac-

Oat plant grown

PHOSPHATE FERTILIZERS 173

cumulate, to a great extent, in the seeds of all grains
and are usually sold from the farm, especially when
grain farming is extensively followed. All crops are
very sensitive to the absence of phosphates; an imper-
fect supply results in the production of light weight
grains. The nitrogen and the phosphates are to a
great extent stored up in the same parts of the plant,
particularly in the seed, which is richer in both
nitrogen and phosphorus than is any other part.
Nitrogen is the chief element of protein, while phos-
phorus is necessary to aid in transporting the pro-
tein compounds through the cell walls of plants.
In speaking of the phosphorus in plants and in fer-
tilizers, as well as in soils, the term phosphoric acid
or phosphoric anhydride is used. This is because
phosphorus is an acid-forming element and, as already
explained, the anhydride of the element is always con-
sidered instead of the element itself.

209. Amount of Phosphoric Acid Removed in
Crops. — The amount of phosphoric acid removed
in an acre of different farm crops ranges from 1 8 to 30
pounds :

Phosphoric acid
per acre.

Lbs.

Wheat, 20 bu 12.5

Straw, 2,000 lbs 7.5

Total 20.0

174 SOILS AND FERTILIZERS

Phosphoric acid
per acre.

Lbs.

Barley, 40 bu 15

Straw, 3,000 lbs 5

Total 20

Oats, 50 bu 12

Straw, 3,000 lbs 6

Total 18

Corn, 65 bu 18

Stalks, 4,000 lbs 4

Total 22

Peas, 3,500 lbs 25

Red clover, 4,000 lbs < 28

Potatoes, 150 bu 20

Flax, 15 bu 15

Straw, 1,800 lbs 3

Total 18

210. Amount of Phosphoric Acid in Soils. — To

meet the demand of growing crops (for 25 pounds of
phosphoric acid per acre), there is present in soils from
1,000, and less, to 8,000 pounds of phosphoric acid per
acre, of which, however, only a fraction is available as
plant food at any one time. The availability of phos-
phoric acid is a factor which has a great deal to do in
determining crop-producing power. INIany soils contain
a large amount of total phosphoric acid, which has be-
come unavailable because of poor cultivation and the

PHOSPHATE FERTILIZERS I 75

absence of stable manure and lime to combine with
the phosphates and render them available.

211. Source of Phosphoric Acid in Soils. — The

phosphates fonnd in soils are derived mainh' from the
disintegration of phosphate rock, and from the remains
of animal life. The phosphate deposits fonnd in various
localities are supposed to have been derived either
from the remains of marine animals or from sea-water
highly charged with soluble phosphates. These de-
posits have been subjected to various geological and
climatic changes which have resulted in the formation
of soft phosphate, pebble phosphate, and rock phos-
phate.^^

212. Commercial Forms of Phosphoric Acid. — The
commercial sources of phosphate fertilizers are (i)
phosphate rock, (2) bones and bone preparations, (3)
phosphate slag, and (4) guano. With the exception
of phosphate slag and guano, the prevailing form of
the phosphorus is tricalcium phosphate. Before be-
ing used for commercial purposes, the tricalcium
phosphate, which is insoluble and unavailable, is
treated with sulphuric acid which produces monocal-
cium phosphate, a soluble and available form of plant
food.

Ca^CPO^X + 2H,SO^ + sno = CaH/PO;, ^ HO +

2CaS0 .2H O.

4 2

In making phosphate fertilizers from bones or phos-

176 SOILS AND FERTILIZERS

pliate rock an excess of the rock is used so that there
will be no free acid to be injurious to vegetation.

213. Different Forms of Calcium Phosphate. —

The usual form in which calcium phosphate is found
in nature is tricalcium phosphate, Ca (PO )^. Unless
associated with organic matter or salts which render
it soluble it is of but little value as plant food. When
tricalcium phosphate is treated with sulphuric acid,
monocalcium phosphate, CaH (PO )^, is formed. This
compound is soluble in water and directly available as
plant food. When tricalcium and monocalcium phos-
phate are brought together in a moist condition, di-
calcium phosphate is produced.

Ca (PO ) + CaH (PO ) = 2Ca H (PO ) .

3\ 4'2 ' 4N 4/2 2 2\ 4/2

Another form of phosphate of lime, met with in basic
phosphate slag, is tetracalcium phosphate, (CaO) P^O..

214. Reverted Phosphoric Acid. — When mono-
and tricalcium phosphate react, the product is known
as reverted phosphoric acid, which is insoluble in
water, but is not in such form as to be unavailable as
plant food. It is generally considered that the re-
verted phosphoric acid is available as plant food : it is
soluble in a dilute solution of ammonium citrate, and
is sometimes spoken of as citrate-soluble phosphoric
acid. Citrate-soluble phosphoric acid may also be
formed by the action upon the monocalcium phos-
phate of iron and aluminum compounds present as

PHOSPHATE FERTILIZERS I 77

impurities in the phosphate rock. This process is a
fixation change, as described in Chapter V. In an old
fertilizer there may be present citrate-soluble phos-
phoric acid in two forms, as dicalcium phosphate and
as hydrated phosphates of iron and aluminum. The
citrate-soluble phosphoric acid in fertilizers is not all
equally valuable as plant food because of the different
phosphate compounds that may be dissolved.

215. Available Phosphoric Acid. — As applied to
fertilizers, the term available phosphoric acid includes
the water-soluble and citrate-soluble phosphoric acid.
These solvents do not, under all conditions, make a
sharp distinction as to the available and unavailable
phosphoric acid when it comes to plant grow^th. Some
forms of bones, w^hich are insoluble in an ammonium
citrate solution are available as plant food, and then
again some forms of aluminum phosphate w^hich are
soluble are of but little value as plant food. The
terms available and unavailable phosphoric acid, as
applied to commercial fertilizers, refer to the solubility
of the phosphates, and as a general rule their value as
plant food is in accord w4th their solubilities. The
more insoluble the less valuable the material.

216. Phosphate Rock. — Phosphate rock is found
in many parts of the United States, particularly in
South Carolina, North Carolina, Florida, Virginia,
and Tennessee. The deposits occur in stratified
veins, as well as in beds and pockets. There are dif-

1 78 SOILS AND FERTILIZERS

ferent types of phosphates as hard rock, soft rock, land
pebble, and river pebble. The pebble phosphates are
found either on land or collected in cavities in the
water courses, and are generally spherical masses of
variable size. The soft rock phosphate is easily
crushed, while the hard rock requires pulverizing with
rock crushers. Phosphate rock usually contains from
40 to 70 per cent, of calcium phosphate, the equiva-
lent of from 17 to 30 per cent, phosphoric acid. The
remaining 30 to 60 per cent, is composed of fine sand,
limestone, alumina and iron compounds, with other
impurities, which often render a phosphate unsuitable
for manufacturing high-grade fertilizer. Raw phos-
phate rock is usually sold at the mines for #1.75 to
$4.50 per ton.

217. Superphosphate. — Pulverized rock phosphate
known as phosphate flour, is treated with commercial
sulphuric acid and soluble monocalcium phosphate
obtained. The amount of sulphuric acid used is de-
termined from the composition of the rock. Impuri-
ties as calcium carbonate and calciinn fluoride react
with sulphuric acid and caUvSe a loss of acid. Ordi-
narily, a ton of high-grade phosphate rock requires a
ton of sulphuric acid. The mixing is usually done in
lead-lined tanks. A weighed amount of phosphate
flour is placed in the tank, and the sulphuric acid
added, through lead pipes, from the acid tower. The
mixing of the acid and phosphate is done with a me-

PHOSPHATE FERTILIZERS 179

chanical mixer, driven by machiner}-. From the
mixer the material is passed into large tanks, where
two or three days are allowed for the completion of
the reaction. When the mass solidifies, it is ground
and sold as superphosphate. In the manufacture of
superphosphate, gypsum (CaSO .2H^0) is always pro-
duced. A ton of superphosphate prepared from high-
grade rock in the way outlined will contain about 40
per cent, of lime phosphates, equivalent to 1 8 per cent,
phosphoric acid. If a poorer quality of rock is used a
proportionally smaller amount of phosphoric acid is
obtained. A more concentrated superphosphate is ob-
tained b}' producing phosphoric acid from the phos-
phate rock, and then allowing the phosphoric acid to
act upon fresh portions of the rock, the reactions be-
ing as follows :^3

Ca^CPO^X + 3H,S0^ = 3CaS0, - 2H^(P0;,
C^iJiPOX + 4^P0^ ^ 3HP = 3[CaH (POJ^.H O].
Ca/PO^X + aH P0^ + i2H O = 3[Ca H,(PO;,.4H O].

The phosphoric acid is separated from the gypsum be-
fore acting upon the phosphate flour. In this way,
superphosphate containing from 35 to 45 per cent,
of phosphoric acid is produced. When fertilizers are
to be transported long distances this concentrated prod-
uct is preferable. The terms 'acid' and 'superphosphate'
are generally used to designate both the first product
formed by the action of sulphuric acid and that pro-

l8o SOILS AND FERTILIZERS

duced by the phosphoric acid but of late there is a ten-
dency to restrict the term 'acid phosphate' to the
product formed by the action of sulphuric acid, and
the term 'super-phosphate' to the concentrated product
formed by the action of phosphoric acid.

218. Commercial Value of Phosphoric Acid. — The
commercial value of phosphoric acid in fertilizers is
determined by the value of the crude phosphate rock,
cost of grinding and treating with sulphuric acid, and
cost of transportation. The price of phosphoric acid
in superphosphates usually ranges from 5 to 6 cents
per pound. The field value, that is the increased
yields obtained from the use of superphosphates, may
not be in accord with the commercial value because so
many conditions govern its use. The phosphoric acid
obtained from feed-stuffs is usually considered worth
about a cent a pound less than that from superphos-
phates. Water-soluble phosphoric acid is generally
rated a half cent per pound higher than citrate-soluble
phosphoric acid.

219. Phosphate Slag. — In the refining of iron ores
by the Bessemer process, the phosphorus in the iron is
removed as a basic slag. The lime, which is used as a
flux, melts and combines with the phosphorus of the
ore, forming phosphate of lime. The slag has a varia-
ble composition. The process by \vhich the phos-
phorus of pig iron is removed and converted into basic
phosphate slag is known as the Thomas process, and

PHOSPHATE FERTILIZERS l8l

the product is sometimes called Thomas' slag. At the
present time but little basic slag is produced for fer-
tilizer purposes in this country. In Germany and
some other European countries the amount used is
nearly equal to the amount of superphosphate. Phos-
phate slag is ground to a fine powder and is applied
directly to the land, without undergoing the sulphuric
acid treatment. Phosphoric acid is present mainly in
the form of tetracalcium phosphate, (CaO) P^O..

220. Guano is the Spanish for dung, and is a concen-
trated form of nitrogenous and phosphate manure of
interest mainly on account of its historic significance.
It is a mixture of sea-fowl droppings which have ac-
cumulated along the seacoast in sheltered regions.
The mixture of dung, dead animals, and debris, has
undergone fermentation, and is concentrated in both
nitrogen and phosphoric acid. The introduction of
guano into Europe marked an important period in agri-
culture, inasmuch as its use demonstrated the action
and importance of concentrated fertilizers. All of the
best beds of guano have been exhausted and only a
little of the poorer grades are now found on the mar-
ket. The best qualities of guano contained from 12
to 15 per cent, of phosphoric acid, 10 to 12 per cent,
of nitrogen, and from 5 to 7 per cent, of alkaline salts.

BONE FERTILIZERS

221. Raw Bones contain, in addition to phosphate
of lime, Ca (PO ) , org^anic matter which makes them

' 3^ 4'2' o

162 SOILS AND FERTILIZERS

slow in decomposing and slow in their action as a fer-
tilizer. Before being used as fertilizer they should be fer-
mented in a compost heap with wood ashes in the fol-
lowing way : A protected place is selected so that no
losses from drainage will occur. A layer of well-com-
pacted manure is covered with wood ashes, the bones
are then added and well covered with manure and
wood ashes. From three to six months should be al-
lowed for the bones to ferment. The large, coarse
pieces may then be crushed and are ready for use.
The presence of fatty material in a fertilizer retards its
action because fat is so slow in decomposing. Bones
from which the organic matter has been removed are
more active as a fertilizer than raw bones. Bones
contain from i8 to 25 per cent, of phosphoric acid and
from 2 to 4 per cent, of nitrogen. The amount and
value of the citrate-soluble phosphoric acid in bones
are extremely variable.

222. Bone Ash is the product obtained when bones
are burned. It is not extensively used as a fertilizer
because of the greater commercial value of bone-black.
It contains about 36 per cent, of phosphoric acid, and
is more concentrated than raw bones.

223. Steamed Bones. — Raw bones are subjected to
superheated steam to remove the fat and ossean which
are used for making soap and glue; they are then pul-
verized and sold as fertilizer imder the name of bone
meal, which contains from 1.5 to 2.5 per cent, of nitro-

BONE FERTILIZERS 183

gen and from 22 to 29 per cent, of phosphoric acid.
Steamed bones make a more active fertilizer than raw
bones. Occasionally, well-prepared bone meal is used
for feeding pigs and fattening stock in the same way
that flesh meal is used.

224. Dissolved Bone. — When bones are treated
with sulphuric acid as in the manufacture of super-
phosphates the product is called dissolved bone. The
tricalcium phosphate undergoes a change to more
available forms, as described, and the nitrogen is ren-
dered more available. Dissolved bone contains from
2 to 3 per cent, of nitrogen and from 15 to 17 per
cent, of phosphoric acid.

225. Bone-black. — When bones are distilled bone-
black is obtained. It is extensively employed for re-
fining sugar, and after it has been used and lost its
power of decolorizing solutions, it is sold as fertilizer.
It contains about 30 per cent, phosphoric acid and is a
concentrated phosphate fertilizer.

226. Use of Phosphate Fertilizers. — The amount
of phosphoric acid advisable to apph' to crops, varies
with the nature of the soil and the kind of crop to be pro-
duced. On a poor soil 400 pounds of superphosphate
per acre is an average application. It is usually ap-
plied as a top dressing just before seeding, and may be
placed near the hills of corn or potatoes, but not in
contact with the seed. It is not advisable to make
heavy applications of superphosphates at long inter-

184 SOILS AND FERTILIZERS

vals, because the process of fixation ma}- take place to
such an extent that crops are unable to utilize the fer-
tilizer. Lighter and more frequent applications are
preferable. Phosphates should not be mixed with
lime carbonate or with loam before spreading.^' It is
best to apply the fertilizer directly to the land. Phos-
phates may be used in connection with farm manures.
Many soils which contain liberal amounts of total
phosphoric acid are improved with a light dressing of
superphosphates. Such soils, however, should be more
thoroughly cultivated, and manured with farm ma-
nures, to make the phosphates available. There is
frequently an apparent lack of phosphoric acid in the
soil when in reality the trouble is due to other causes,
as lack of organic matter to combine with the phos-
phates or to a deficiency of lime. Before using phos-
phate fertilizers, careful field tests should be made to
determine if the soil is in actual need of available
phosphoric acid. Directions for making these tests
are given in Chapter X.

227. How to Keep the Phosphoric Acid Available.

— Phosphoric acid associated with organic matter in
a moderately alkaline soil, is more available than that
in acid soils. Soft phosphate rock may be mixed with
manure or materials like cottonseed meal and made
slowly available for crops. Soils which have a good
stock of phosphoric acid, when kept well manured,
and occasionallv limed if necessarv, contain a lib-

BONE FERTILIZERS 185

eral supply of available phosphoric acid. As an illus-
tration, the following example of two soils from ad-
joining farms, which have been cropped and manured
differently, may be cited :^°

Soil well manured No manure and

and crops continuous wheat

rotated. raising.

Per cent. Per cent.
Total phosphoric acid ••• . 0.20 0.20

Humus 4.25 1.62

Humic phosphoric acid . . 0.06 0.02

It is more economical to keep the insoluble phos-
phoric acid of the soil in available forms by the use of
farm manures than it is to purchase superphosphates.

CHAPTER VIII

POTASH FERTILIZERS

228. Potassium an Essential Element of Plant
Food. — Potassium is one of the three elements most

essential as plant food. When it is
removed from a soil plants are un-
able to develop. Oats seeded in a
soil from which the potash only
had been extracted made the total
growth shown in the illustration
(Fig. 32). When potash is present
in the soil in liberal amounts vig-
orous plants are produced. Potash,
like phosphoric acid and nitrogen,
is utilized by crops in the early
stages of growth. Potassium does
not accumulate in seeds to the same
extent as phosphoric acid and nitro-
gen, but is present mainly in stems
and leaves, consequently when
straw crops are utilized in pro-
grown without potash, ducing manure the potash is not
lost or sold from the farm. But with ordinary grain
farming excessive losses of potash do occur, particu-
larly when the straw is burned and the ashes are wasted.

Fig. 32. Oat plant

POTASH FERTILIZERS 187

229. Amount of Potash Removed in Crops. — In

grain crops from 35 to 60 pounds of potash per acre
are removed from the soil. For grass crops more pot-
ash is required than for grains, while roots and tubers
require more than grass. The approximate amount of
potash removed in various crops is given in the fol-
lowing table :37

Potash per acre.
Ivbs.

Wheat, 20 bu 7

Straw, 2,000 lbs 28

Total 35

Barley, 40 bu 8

Straw, 3,000 lbs 30

Total 38

Oats, 50 bu 10

Straw, 3,000 lbs 35

Total 45

Corn, 65 bu 15

Stalks, 3.000 lbs 45

Total 60

Peas, 30 bu 22

Straw, 3,500 lbs 38

Total 60

Flax, 15 bu 19

Straw, 1 ,800 lbs 8

Total 27

l88 SOILS AND FERTILIZERS

Mangels, lo tons 150

Meadow hay, i ton 45

Clover hay, 2 tons • • 66

Potatoes, 150 bushels 75

230. Amount of Potash in Soils. — In ordinary
soils there are from 3,500 to 12,000 pounds of potash
per acre to the depth of one foot. Many soils with
apparently a good stock of total potash give excellent
results when a light dressing of potash salts is applied.
The amount of available potash in the soil is more
difficult to estimate than the available phosphoric
acid. There is also a great difference in crops as to
their power of obtaining potash. Some require
greater help in procuring this element than others. A
lack of available potash is sometimes indirectly due to
a deficiency of other alkaline matter in the soil, which
prevents the necessary changes taking place in order
that the potash may be liberated as plant food.

231. Sources of Potash in Soils. — The main
source of the soil potash is feldspar, which, after dis-
integration, is broken up into kaolin and potash com-
pounds. Mica and granite also, in some localities,
contribute liberal amounts. The most valuable forms
of potash are the zeolitic silicates. The amount of
water-soluble potash, except in alkaline soils, is ex-
tremely small. By the action of many fertilizers the
potash compounds undergo changes in composition.
For example, the gypsum which is always present in

STASSFURT SALTS 1 89

acid phosphates, liberates some potash. The potash
compounds of the soil are in various degrees of com-
plexity from forms soluble in dilute acids to insoluble
minerals as feldspar.

232. Commercial Forms of Potash. — Prior to the
introduction of the Stassfurt salts, wood ashes were
the main source of potash. Since the discovery and
development of the Stassfurt mines, the natural prod-
ucts as kainit, and muriate and sulphate of potash have
been extensively used for fertilizing purposes. A
small amount of potash is also obtained from waste
products as tobacco stems, cottonseed hulls, and the
refuse from beet-sugar factories.

STASSFURT SALTS

233. Occurrence. ^3 — I'he Stassfurt mines were first
worked with the view of procuring rock salt. The
presence of the various compounds of potash, soda, and
magnesia, associated with the layers of rock salt, were
regarded as troublesome impurities, and attempts were
made by sinking new shafts to avoid them, but with
the result of finding them in greater abundance.
About 1864 their value as potash fertilizers was es-
tablished. The mines are now owned and worked by
a syndicate. It is supposed that at one time the
region about the mines was submerged and filled with
sea-water. The tropical climate of that geological period
caused rapid evaporation, which resulted in forming
mineral deposits, the less soluble material as lime sul-

190 SOILS AND FERTILIZERS

phate being first deposited, then a layer of rock salt,
and finally layers of potash and magnesium salts in
the order of their solubility.

234. Kainit is a mineral composed of potassium
sulphate, magnesium sulphate, magnesium chloride,
and water of cr}'stallization. As it comes from the
mine it is mixed with gypsum, salt, potassium chlo-
ride, and other bodies. Kainit contains from 1 2 to 1 2. 50
per cent, of potash, and is one of the most important
of the Stassfurt salts. It is extensively used as a pot-
ash fertilizer, and is also mixed with other materials
and sold as a commercial fertilizer. The magnesium
chloride causes it to absorb water, and the presence of
other compounds results in the formation of hard
lumps, whenever kainit is kept for a long time.
Kainit is soluble in water, and can be - used as a top
dressing at the rate of 75 to 200 pounds or more per acre.

235. Sulphate of Potash. — High-grade sulphate
of potash is prepared from some of the crude Stassfurt
salts, and may contain as high as 97 per cent. K^SO .
Low-grade sulphate of potash is about 90 per cent,
pure. High-grade sulphate of potash contains about
50 per cent, of potassium oxide (K^O), and is one of
the most concentrated forms of potash fertilizer. It
is particularly valuable because it can be safely used on
crops as tobacco and potatoes which would be injured
in quality if muriate of potash were applied, or if
much chlorine were present.

STASSFURT SALTS 191

236. Miscellaneous Potash Salts. — Carnallit, 9
per cent. K^, — composed of KCl.MgC1^.6Hp.
Polyhalit, 15 per cent. K^O, — composed of K^SO .Mg
SO^.(CaSOJ^.Hp. Krugit, 10 per cent. K^,— com-
posed of K^s6^.MgS0^.(CaS0J^.Hp. Sylvinit, 16
to 20 per cent. K^O, — composed of KCl.NaCl and
impurities. Kieserit, 7 per cent. K^O, — composed of
MgSO and carnallit.

237. Wood Ashes. — For ordinary agricultural pur-
poses, wood ashes are the most important source of
potash. Ashes are exceedingly variable in composi-
tion. When leached the soluble salts are extracted
and there is left only about i per cent, of potash. In
unleached ashes the amount of potash ranges from 2
to 10 per cent. Soft wood ashes contain much less
potash than hard wood ashes. Goessmann gives the
following as the average of 97 samples of ashes :^^

Average composition. Range.

Per cent. Per cent.

Potash 5.5 2.5 to 10.2

Pho.sphoric acid 1.9 0.3 to 4.0

Lime 34.3 18.0 to 50.9

In 10,000 pounds of wood. Potash. Phosphoric acid.

Lbs. Lbs.

White oak 10.6 2.5

Red oak 14.0 6.0

Ash 15.0 I.I

Pine 0.8 0.7

Georgia pine 5.0 1,2

Dogwood 9.0 5.7

192 SOILS AND FERTILIZERS

238. Action of Ashes on Soils. — In ashes, the pot-
ash is present mainly as potassinni carbonate. Ashes
are nsnally regarded as a potash fertilizer only, but
they also contain lime and phosphoric acid, and may
be very beneficial in supplying these elements. They
are valuable too because they add alkaline matter to
the soil, which corrects acidity and aids nitrification.
A dressing of ashes improves the mechanical condi-
tion of many soils by binding together the soil parti-
cles. This property is well illustrated in the so-called
"Gumbo" soils, which contain so much alkaline mat-
ter that the soil has a soapy taste and feel, and when
plowed the particles fail to separate.

239. Leached Ashes. — When ashes are leached the
soluble salts are extracted, and the insoluble matter
which is left is composed mainly of calciinn carbonate
and silica. ^5

Uuleached ashes. Leached ashes.

Per cent. Per cent.

Water 12.0 30.0

Silica, etc 13.0 13.0

Potassium carbonate 5.5 i.i

Calciiuii " 61.0 51.0

Phosphoric acid 1.9 1.4

240. Alkalinity of Leached and Unleached Ashes.

— A g^ood wav to detect leached ashes is to deter-
mine the alkalinity in the following way : Weigh
out 2 grams of ashes into a beaker, add 100 cc. dis-
tilled water, and heat on a sand-bath nearly to boiling,

STASSFURT SALTS I93

cool, and filter. To 50 cc. of the filtrate add about 3
drops of cochineal indicator, and then a standard solu-
tion of hydrochloric acid from a burette until the solu-
tion is neutral. If a standard solution of acid cannot
be procured, one containing 15 cc. concentrated hydro-
chloric acid per liter of distilled water may be used for
comparative purposes. Leached ashes require less than
2 cc. of acid to neutralize the alkaline matter in i gram
while unleached ashes require from 10 to i8cc. In pur-
chasing wood ashes, if a chemical analysis cannot be
secured, the alkalinity of the ash should be determined.

241. Coal and Other Ashes. — Since the amount of
phosphoric acid and potash in coal ashes is very small,
they have but little fertilizer value. Soft-coal ashes con-
tain more potash than those from hard coal, but it is held
in such forms of combination as to be of but little value.

The ashes from sawmills where soft wood is burned
and the ashes are unprotected, are nearly worthless.
When peat-bogs are burned over, large amounts of ashes
are produced. If the bogs are covered with timber,
the ashes are sometimes of sufiicient value to warrant
their transportation and use.

Phosphoric
Potash. acid.

Per cent. Per cent.

Hard coal o. 10 o. 10

Soft coal 0.40 0.40

Sawmill ashes'^ 1.20 i.oo

Peat-bog ashes'^ 1.15 0.54

Peat-bog ashes (timbered)'^ 3.68 2.56

Tobacco stems 4.00 7.00

Cottonseed hulls 20.00 7.00

194 SOILS AND FERTILIZERS

242. Commercial Value of Potash. — The market
value of potash is determined from the selling price of
high-grade sulphate of potash and kainit. Ordinarily,
the price per pound of potash varies from 4 to 5 cents.
As in the case of both nitrogen and phosphoric acid,
the market and the field values may be entirely at
variance. Before potash salts are used, careful field
tests should be made to determine the actual condi-
tion of the soil as to its needs in potash.

243. Use of Potash Fertilizers. — Wood ashes, or
Stassfurt salts, should not be used in excessive
amounts. Not more than 300 pounds per acre should
be applied unless the soil is known to be markedly de-
ficient, and previous tests indicate that larger amounts
are safe and advisable. Potash fertilizers should be
evenly spread and not allowed to come in contact with
plant tissue. They should be used early in the spring
before seeding or before the crop has made much
growth. Wood ashes make an excellent top dressing
for grass lands, particularly where it is desired to en-
courage the growth of clover. There are but few
crops or soils that are not greatly benefited by a light
application of wood ashes, and none should ever be
allowed to leach or waste about a fann.

When a potash fertilizer is used, a dressing of lime
will frequently be beneficial. The potash undergoes
fixation, and when it is liberated there should be some
basic material as lime to take its place. Goessmann

STASSFURT SALTS I95

obsen-ed that land manured for several years with
potassium chloride finally produced sickly crops, but
that an application of slaked lime restored a healthy
appearance to succeeding crops. ^^ If the soil is well
stocked with lime its joint use with potash fertilizers
is not necessar}'.

CHAPTER IX

LIME AND MISCELLANEOUS FERTILIZERS

244. Calcium an Essential Element of Plant Food.

— Calcium is present in the ash of all plants, and is
usually more abundant in soils than phosphorus or

potassium. It takes an essential
part in plant growth, and when-
ever withheld grow^th is checked.
The effect of removing calcium
from the soil is shown in the illus-
tration (Fig. 1,^,)^ wdiich gives the
total growth made by an oat plant
under such a condition.

Plants grown on soils deficient
in calcium compounds, lack hard-
iness. They are not so able to
withstand drought, or climatic
changes, as plants grown on soils
well supplied wath this element.
Calcium does not accumulate
in the seeds of plants, but is pres-
ent mainly in the leaves and
stems where it takes an impor-
tant part in the production of new
tissue. The term lime is used in
speaking of the calcium oxide content of soils and crops.

>'ig- 33-
Oat plant grown with-
out lime.

LIME AND MIvSCELLANEOUS FERTILIZERS 197

245. Amount of Lime Removed in Crops. ^^ —

Pounds per acre.

Wheat, 20 bushels i

Straw, 2000 pounds 7

Total 8

Corn, 65 bushels i

Stalks, 3000 pounds 11

Total 12

Peas, 30 bushels 4

Straw, 3500 pounds 71

Total 75

Flax, 15 bushels ' 3

Straw, 1800 pounds 13

Total 16

Clover, 4000 pounds 75

Clover and peas remove so much lime from the soil
that they are often called lime plants. The amount
required by grain and hay is small compared with that
required for a clover or pea crop.

246. Amount of Lime in Soils. — There is no ele-
ment in the soil in such variable amounts as calcium.
It may be present from a few hundredths of a per cent,
to twenty per cent.; soils which contain from 0.4 to
0.5 per cent, are usually well supplied. The lime in
a soil takes an important part in soil fertility ; when
deficient, humic acid may be formed, nitrification
checked, and the soil particles will lack binding material.

198 SOILS AND FERTILIZERS

247. Different Kinds of Lime Fertilizers. — By the

term 'lime fertilizer' is usually meant land plaster
(CaSO .2IIO). Occasionally quicklime (CaO) and
slaked lime (Ca(OH)^) are used on exceedingly sour
land. In general a lime fertilizer is one which sup-
plies the element calcium ; common usage, however,
has restricted the term to sulphate of lime.

248. Action of Lime Fertilizers upon Soils. — Lime
fertilizers act both chemically and physically. Chem-
ically, lime unites with the organic matter to form
humate of lime and prevent the formation of humic
acid. It aids in nitrification and acts upon the soil,
liberating potassium and other elements of plant food.
Physically, lime improves capillarity, precipitates clay
when suspended in water, and prevents losses, as the
washing away of fine earth.

249. Action of Lime upon Organic Matter. — When
soils are deficient in lime, an acid condition may de-
velop to such an extent as to be injurious to vegeta-
tion. In fact nitrogen, phosphoric acid, and potash
may all be present in liberal amounts, but in the
absence of lime poor results will be obtained. Ex-
periments at the Rhode Island Experiment Station
indicate that there are large areas of acid soils in the
Eastern States which are much improved when treated
with air-slaked lime.^^ There is a great difference in
the power of plants to live in acid soils. Agricultural
plants are particularly sensitive, while many weeds

LIME AND MISCELLANEOUS FERTILIZERS 1 99

have such strong power of endurance that they are
able to thrive in the presence of acids. The charac-
ter of the weeds frequently reflects the character of the
soil as to acidity, in the same way that an "alkali"
soil is indicated by the plants produced.

250. Lime Liberates Potash. — The action of lime
upon soils well stocked with potash results in the fixa-
tion of the lime and the liberation of the potash ; the
reaction takes place in accord with the well-known
exchange of bases. The extent to which potash may
be liberated by lime depends upon the firmness with
which the potash is held in the soil. Boussingault
found that when clover was limed there was present
in the crop three times as much potash as in a similar
crop not limed. His results are as follows : ^^

Kilos per hectare.
In crop not limed. In limed crop.

First Second First Second

year. year. year. year.

Lime 32.2 32.2 79.4 102.8

Potash 26.7 28.6 95.6 97.2

Phosphoric acid, ii.o 7.0 24.2 22.9

The indirect action of land plaster upon Western
prairie soils in liberating plant food, particularly
potash and phosphoric acid, is unusually marked.
Laboratory experiments show^ that small amounts of
gypsum are quite active in rendering potash, phos-
phoric acid, and even nitrogen soluble in the soil
water. 5

200 SOILS AND FERTILIZERS

251. Quicklime and Slaked Lime. — When it is de-
sired to correct acidity slaked lime is used. Air-
slaked lime is not as valuable as water-slaked lime.
Quicklime cannot be used on land after a crop has
been seeded. Both slaked lime and quicklime
should be applied some little time before seed-
ing and not to the crops. The action of quicklime
upon organic matter is so rapid that it destroys vege-
tation. Slaked lime is less injurious to vegetation.

252. Pulverized Lime Rock. — In some localities
pulverized lime rock is used. It may be applied as a
top-dressing in almost unlimited amounts. It is most
beneficial on light, sandy soils, where it performs the
function of fine clay as well as being beneficial in its
chemical action. Not all soils are alike responsive to
applications of limestone, and before using, it is best
to determine to what extent it will be beneficial.
There are no conditions where limestone is injurious
to soil or crop.

253. Marl. — Underlying beds of peat, deposits of
marl are occasionally found. Marl is a mixture of
disintegrated limestone and clay, and contains varia-
ble amounts of calcium carbonate, phosphoric acid,
and potash. When peat and marl are found together
they may be used jointly with manure as described in
Section 175. Many sandy lands in the vicinity of peat
and marl deposits would be greatly improved, both
physically and chemically, by the use of these materials.

LIME AND MISCELLANEOUS FERTILIZERS 20I

254. Physical Action of Lime. — The addition of
lime fertilizers to sandy soils improves their general
physical condition. Heavy clays lose their plasticity
when limed ; the fine clay particles are cemented
and act as sand, which improves the mechanical
condition of the soil. The physical action of lime
upon soils is well illUvStrated in the case of 'loess soils,'
which are composed of clay and limestone. The
lime cements the clay particles and forms compound
grains, making the soil more permeable, and more
easily tilled. The improved physical condition alone
which follows the application of lime fertilizers, is fre-
quently sufficient to warrant their use.

255. Application of Lime Fertilizers. — Lime is
generally used as a top-dressing on grass lands at the
rate of 200 to 500 pounds per acre. Excessive appli-
cations are undesirable. Lime as gypsum is particu-
larly valuable when applied to land where crops are
grown which assimilate large amounts of lime. It
should be remembered that it is not a complete, but
mainly an indirect, fertilizer.

If used to excess it may get the soil in such a con-
dition that no more plant food can be rendered avail-
able. A common saying is " Lime makes the father
rich but the son poor."" This is true, however, only
when lime is used in excess. When used occasion-
ally in connection with other manures, it has no inju-
rious effects upon the soil and is a valuable fertil-

202 SOILS AND FERTILIZERS

izer, especially where clover is grown w4th difficulty.
MISCELLANEOUS FERTILIZERS

256. Salt is frequently used as an indirect fertilizer.
Sodium and chlorine, the two elements of which it is
composed, are not absolutely necessary for normal
plant growth. When salt is applied to the soil and
the sodium undergoes fixation, potassium may be
liberated. An early experiment of Wolff illustrates
this point : a buckwheat plot fertilized with salt pro-
duced a crop with more potash and less sodium than
a similar unfertilized plot.

Salt may be used to check the rank grow^th of straw
during a rainy season, and thus prevent loss of the
crop by lodging. It should not be used in excessive
amounts, as it is destructive to vegetation ; 200 pounds
per acre is a fair application. Salt also improves the
physical condition of the soil by increasing the surface-
tension of the soil water. Salt should not be used on
a tobacco or potato crop, because it injures the quality
of the product.

257. Magnesium Salts. — Magnesium is present in
the ash of all plants, and is an essential element of
plant growth. Usually soils are so well stocked with
this element that it is not necessary to apply it in
fertilizers. Some of the magnesium salts, as the
chloride, are injurious to vegetation, but when associa-
ted with lime as carbonate, magnesia imparts fertility.
In many of the Stassfurt salts magnesium is present.

MISCELLANEOUS FERTILIZERS 203

258. Soot. — The deposits formed in boilers and
chimneys when wood and soft coal are burned contain
small amounts -of potash and phosphoric acid. They
are valuable mainly as mechanical fertilizers impart-
ing the properties of organic matter. There is but
little plant food in soot, as shown by the following
analysis :

Soft-coal soot. Hard-wood soot.

Per cent. 13 Per ceut.69

Potash 0.84 1.78

Phosphoric acid 0.75 0.96

259. Seaweeds. — Seaweeds are rich in potash
and near the sea coast are extensively used for fer-
tilizers.

Composition of

mixed seaweed.

Per cent ^9

Water 81 .50

Nitrogen 0.73

Potash 1.50

Phosphoric acid o. 18

260. Strand Plant Ash. — Weeds and plants pro-
duced on waste land along the sea are in many Euro-
pean countries burned, and the ashes used as fertilizer
on other lands. By this means waste land is made to
produce fertilizer for fields which are tillable. The
amount of fertility removed in weeds is usually greater
than that in agricultural plants, because weeds have a
greater power of obtaining food from the soil. When
wheat or other grain is raised, and a small crop of
grain and a large crop of weeds are the result, there
is more fertility removed from the soil than if a heavy

204 SOILS AND FERTILIZERS

stand of grain were obtained. The ashes of strand
plants and weeds are extremely variable in composition.
261. Wool Washings and Waste. — The washings
from wool contain snfficient potash to make this
material vahiable as a fertilizer. In wool there is a
high per cent, of potash, which is soluble, and readily
removed in the w^ashings. Wool waste may contain
from I to 5 per cent, of potash and from 4 to 7 per
cent, of nitroeen in somewhat inert forms.

CHAPTER X

COMMERCIAL FERTILIZERS AND THEIR USE

262. Development of the Commercial Fertilizer
Industry. — The commercial fertilizer industry owes
its origin to Liebig's work on plant ash. The first
superphosphate was made by Sir J. B. Lawes, about
1840, from spent bone-black and sulphuric acid. His
interest had previously been attracted to the use of
bones by a gentleman who farmed near him, " who
pointed out that on one farm bone was invaluable for
the turnip crop, and on another farm it was useless. "^^
Since i860 the commercial fertilizer industry in this
country has developed rapidly, until now the amount
of money expended in purchasing commercial fer-
tilizers and amendments is estimated at $60,000,000
annually. Nearly all of this sum is expended in less
than a quarter of the area of the United States.

263. Complete Fertilizers and Amendments. — The

term commercial fertilizer is applied to those materials
which are made by the mixing of different substances
which contain plant food in concentrated forms.
When a commercial fertilizer contains nitrogen, phos-
phoric acid, and potash, it is called a complete fer-
tilizer, because it supplies the three elements which are
liable to be most deficient. Materials as sodium nitrate

2o6 SOILS AND FERTILIZERS

which supply only one element are called amend-
ments. It frequently happens that a vSoil requires only
one element in order to produce good crops. In such
cases only the one element needed should be sup-
plied. Complete fertilizers are sometimes used when
the soil is only in need of an amendment.

264. Variable Composition of Commercial Fer-
tilizers.— Since commercial fertilizers are made by
mixing various materials which contain different
amounts of nitrogen, phosphoric acid, and potash, it
follows that they are extremely variable in composi-
tion and value. No two samples are the same,
hence the importance of knowing the com-
position of every separate brand purchased. The
composition of fertilizers is varied to meet the require-
ments of different soils and crops. Some fertilizers
are made rich in phosphoric acid, while others are
rich in nitrogen and potash.

265. How a Fertilizer is Made. — The most com-
mon materials used in making complete fertilizers
are : Nitrate of soda, kainit, and dissolved phosphate
rock. These materials have about the following com-
position :

Nitrate of soda 15.5 per cent, nitrogen.

Kainit 12.5 per cent, potash.

Dissolved phosphate . • • 14.0 per cent, phosphoric acid.

The fertilizer may be made rich or poor in any one
element. Many fertilizers contain about twice as

COMMERCIAL FERTILIZERS 209

example could be made from feldspar rock, apatite
rock, and leather. The leather contains nitrogen,
the apatite contains phosphoric acid, and the feldspar,
potash. Such a fertilizer would have no value when
used on a crop, because all of the plant food elements
are present in unavailable forms. Hence, in purchas-
ing fertilizers, it is necessary to know not only the
percentage composition, but also the nature of the
materials from which the fertilizer was made.

267. Inspection of Fertilizers. — In many states
laws have been enacted regulating the manufacture
and sale of commercial fertilizers, and provision is made
for inspection and analysis of all brands offered for
sale. The label on the fertilizer package must specify
the percentage amounts of nitrogen, available phos-
phoric acid and potash. Inspection has been found
necessary in order to protect the farmer and the honest
manufacturer.

Occasionally a fraud is revealed like the following : 7°

Natural plant food $25 to I28 per ton.
Composition, Per cent.

Total phosphoric acid 22.21

Insoluble " " 20.81

Available " " 1.40

Potash soluble in water o. 13

Actual value per ton, $1.52.

268. Mechanical Condition of Fertilizers. — When
a fertilizer is purchased, the mechanical condition
should also be considered. The finer the fer-

2IO SOILS AND FERTILIZERS

tilizer, as a rule, the better it is for promoting crop
growth. Some combinations of plant food produce
fertilizers which become so hard and lumpy that it is
difficult to crush the lumps before spreading. The
mass must be pulverized so as to be evenly distributed,
otherwise the plant food will not be economically
used. A fertilizer that passes through a sieve with
holes 0.25 mm. in diameter is more valuable and can
be used to better advantage than one of the same com-
position that requires a 0.5 mm. sieve.

269. Forms of Nitrogen in Commercial Fertilizers.

— Nitrogen is present in commercial fertilizers in three
forms : (i) /Vmmonium salts,(2) nitrates, and (3) organic
nitrogen. The organic nitrogen is divided into tw^o
classes: [a) soluble in pepsin solution, and (d) insolu-
ble in pepsin solution. The relative values of these
different forms of nitrogen are discussed in Chapter
IV. Three fertilizers may have the same amount of
total nitrogen and still have entirely different crop-
producing powers.

. No. I. No. 2. No. '^.

Nitrogen as : Per cent. Per cent. Per cent.

Ammonium compounds ... 1.75 0.25 o. 10

Nitrates 0.15 0,15 o. 10

Organic nitrogen :

Soluble in pepsin o. 10 1.25 0.55

Insoluble in pepsin 0.35 1.25

Total 2.00 2.00 2.00

In purchasing fertilizers it is important to know not
only the amount of nitrogen, but also the form in

COMMERCIAL FERTILIZERS 211

which it is present. In No. 3 the nitrogen is in inert
forms like leather, while in No. 2 it is largely in the
form of dried blood, and No. i has mainly ammonium
compounds. Each of these fertilizers, as explained in
the chapter on nitrogenous manures, has a different
plant food value.

270. Phosphoric Acid. — There are three forms of
phosphoric acid in commercial fertilizers: (i) Water-
soluble, (2) citrate-soluble, and (3) insoluble. The
water- and citrate-soluble are called the available phos-
phoric acid. In most fertilizers the phosphoric acid is
derived from dissolved phosphate rock, and is in the
form of monocalcium phosphate. The citrate-soluble
is mainly dicalcium phosphate with variable amounts
of iron and aluminum phosphates in easily soluble
forms. The insoluble phosphoric acid is tricalcium
and other phosphates which are soluble only in strong
mineral acids. The insoluble phosphoric acid in fer-
tilizers is considered as having but little value. As
in the case of nitrogen three fertilizers may have the
same total amount of phosphoric acid and yet have
entirely different values.

Water-soluble phosphoric acid
Citrate-soluble " "

Insoluble

Total 10.00 10.00 10.00

No. 3 is of but little value; the fertilizer contains in-

No. I.
;r cent.

No. 2.
Per cent.

No. 3.
Per cent.

8.00

0.25

0.25

1.50

8.00

0.75

0.50

1-75

9.00

212 SOILS AND FERTILIZERS

soluble phosphate rock or some material of the same
nature. No. i is the most valuable, because it con-
tains the least insoluble phosphoric acid. This fer-
tilizer contains dissolved phosphate rock or dissolved
bone. No. 2 is composed of such materials as the best
grade of basic slag or roasted aluminum phosphate
or fine steamed bone.

271. Potash. — The three forms of potash in fer-
tilizers are: (i) water-soluble, (2) acid-soluble, and (3)
insoluble. Materials as sulphate of potash, kainit, and
muriate of potash, which are soluble in water, be-
long to the first class. In some states the fertilizer
laws recognize only the water-soluble potash. In the
second class are found materials like tobacco stems
and the organic forms of potash. Substances like
feldspar, which contain insoluble potash, are of no
value in fertilizers. As a rule, the potash in commer-
cial fertilizers is soluble in water; in only a few cases
are acid-soluble forms met with. Insoluble potash
would be considered an adulterant.

272. Misleading Statements on Fertilizer Pack-
ages. — Occasionally the percentage amounts of nitro-
gen, phosphoric acid, and potash are stated in mis-
leading ways as annnonia, sulphate of potash, and
bone phosphate of lime. Inasmuch as 14/17 of am-
monia is nitrogen, the percentage figure for ammonia
is proportionally greater than the nitrogen. And so
with sulphate of potash which contains about 50 per

COMMERCIAL FERTILIZERS 213

cent, potash. This method of stating the composition
can be considered in no other way than a fraud,
especially when the fertilizer contains no sulphate of
potash, but cheaper materials, and the phosphoric acid
is not derived from bone.

273. Estimated Commercial Value of Fertilizers,

— The estimated value of a commercial fertilizer is
obtained from the percentage composition and the
trade value of the materials used. Suppose that two
fertilizers are selling for $25 and $30, respectively,
each having a different composition, the estimated
values would be obtained in the following way :

Composition of Fertilizers.

No. I. No. 2.

Selling ptice $25. Selling price $30,

Percent. Percent.

Nitrogen as nitrates 1.50 2.10

Pho.sphoric acid, available 8.00 lo.co

" " insoluble 2.00 0.50

Potash ( water-soluble) 2.00 3.50

Pounds per Ton.

No. I. No. 2.

Nitrogen 1.50 X 20 = 30 2. 10 X 20 ^= 42

Phosphoric acid . 8.0 X 20 = 160 lo.o X 20 =^ 200

Potash 2.0 X 20 ^ 40 3.5 X 20 = 70

Estimated Value.

No. r. No. 2.

Nitrogen 30 X o. 145 = I4.35 42 X o. 145 = $6.09

Phosphoric acid 160 X 0.06 = 9.60 200 X 0.06 = 12.00

Potash 40X0-045=^ i-8o 70X0.045= 3.15

I15.75 121.24

214

SOILS AND FERTILIZERS

Difference between estimated value and selling
price, No. i, $9.25; No. 2, $8.76.

274. Home Mixing. — At the New Jersey Experi-
ment Station it has been shown that " the charges of
the manufacturers and dealers for mixing, bagging,
shipping, and other expenses are on the average $8,50
per ton, and also that the average manufactured fer-
tilizer contains about 300 pounds of actual fertilizing
constituents per ton. These figures are practically

,> ^

Fig. 34. Composition of P'ertilizers.

true of other states where large quantities of commer-
cial fertilizers are used.'^^i ii;^ states where smaller
amounts are used the difference between the estimated
cost and selling price is greater than $8.50.

These facts emphasize the economy of home mixing.
The difference in price between the raw materials
and the product sold is frequently so great that it is an
advantage for the farmer to purchase the raw mate-
rials, as sulphate of potash, nitrate of soda, and acid

COMMERCIAL FERTILIZERS 215

phosphate, and mix them as desired. By so doing a
fertilizer of any composition may be prepared and
there is less danger of securing an inferior article.
Of course it is not possible by means of shovels and
sieves to accomplish as thorough mixing of the ingre-
dients as with machiner^^

Formula No. i.

Pounds.

Nitrate of soda 500 containing nitrogen • .

Acid phosphate 1200 containing phos. acid

Sulphate of potash • . 300 containing potash 150.0

0

Pounds.

Percenta|;^e

composition

fertilizer.

77-5

3-87

16S.0

8.40

150.0

7.50

Total 395.5

Formula No. 2,

Nitrate of soda 250 containing nitrogen 38.7 1.99

Acid phosphate 900 containing phos. acid- • 126.0 6.3

Sulphate of potash . . 450 containing potash 225.0 11. 5

Plaster, etc 400

Total 389.7

Formula No. 3.

Nitrate of soda 200 containing nitrogen 31.0 1.55

Acid phosphate 1500 containing phos. acid..- 210.0 10.50

Sulphate of potash . . 150 containing potash 75.0 5.75

Plaster, etc 150

Total 316.0

275. Fertilizers and Tillage. — Commercial fer-
tilizers cannot be made to take the place of good
tillage, which is equally as important when fertilizers

2l6 SOILS AND FERTILIZERS

are used as when they are omitted. Scant crops are
as frequently due to the want of proper tillage as to
the absence of plant food. Poor cultivation results in
getting the soil out of condition ; then instead of thor-
oughly preparing the land, commercial fertilizers are
resorted to, and the conclusion is reached that the soil
is exhausted, when in reality it is suffering for the want
of cultivation, for a dressing of land plaster, for farm
manures, or for a change of crops. There is no ques-
tion but what better tillage, better care and use of
farm manures, the culture of clover and the systematic
rotation of crops would result in greatly reducing the
$60,000,000 annually spent for commercial fertilizers,
without reducing the yield of crops. The better the
cultivation, the less the amount of commercial fer-
tilizer required.

276, Abuse of Commercial Fertilizers. — When a
soil produces poor crops, a complete fertilizer is fre-
quently used when an amendment only is needed.
Restricted crop production in long cultivated soils is
due to deficiency of available nitrogen. If the nitro-
gen were supplied, improved cultivation would gen-
erally furnish the available potash and phosphoric
acid, but instead of providing the one element needed,
others which may already be present in the soil in
liberal amounts, are often supplied at a great expense.
Another abuse of fertilizers is their application to the
wrong crop. A heavy application of potash fertilizer

FIELD TESTS WITH FERTILIZERS 217

to a wheat crop grown on a clay soil, or an application
of nitrate of soda on land seeded to clover, or of land
plaster to flax grown on a limestone soil, would be a
useless waste of money.

277. Proper Use of Fertilizers. — In order to make
the best use of commercial fertilizers, both the soil and
the crop must be carefully considered. All crops do
not possess the same power of obtaining food from the
soil ; turnips, for example, have very restricted powers
of phosphate assimilation, hence they require special
manuring wdth phosphates. Wheat requires help in
obtaining its nitrogen. A wdieat crop will starve for
the want of nitrogen, while an adjoining corn crop will
scarcely feel its need. Wheat has strong power of
assimilating potash compounds, while clover has less.
Hence in the proper use of fertilizers the power of the
plant to obtain its food must be considered. An
application of potash to clover, nitrogen to wheat, and
phosphoric acid to turnips, would be a judicious use of
these fertilizers, while if a mixture of the three ele-
ments were applied to each crop alike, the clover
would not be particularly benefited by the nitrogen
or the wheat by the potash. Before commercial fertili-
zers are used, careful field trials should be made with
different crops.

FIELD TESTS WITH FERTILIZERS

278. Experimental Plots, — A piece of land w^ell

2l8 SOILS AND FERTILIZERS

tilled and of uniform texture, should be used for field
trials with fertilizers. After preparation for the crop,
small plots, 1/20 of an acre, are staked off. A con-
venient size is, leiio;th 204 feet, width 10 feet 8 inches,
area 2176 square feet. Between each plot a strip 3
feet wide should be left. In these experiments the
plan is to apply one element or a combination of
elements to a plot and compare the results with other
plots treated differently.^^

279. Preliminary Trials. — It is best to make pre-
liminary trials one year and verify the conclusions the
next. In making- the tests the first year eight plots
are necessary and fertilizers are applied in the follow-
ing way :

The first plot receives no fertilizer and is used as the
basis for comparison.

The second plot receives a dressing of 8 pounds of
nitrate of soda, 16 pounds acid ]>hosphate, and 8
pounds sulphate or muriate of potash.

The third plot receives nitrogen and phosphoric
acid.

The fourth plot receives nitrogen and potash.

The fifth plot receives nitrogen.

The sixth plot receives phosphoric acid and potash.

The seventh plot receives potash.

The eighth plot receives phosphoric acid.

FIELD TESTS WITH FERTILIZERS

219

No fertilizer.
I.

N

K,0
2.

N
P.O5

3-

N
K,0

4-

N
5.

P.O.,
K,0

6.

K,0

7-

P.O5
8.

Should good results be obtained on plot No. 3, the
indications are that there is a deficiency of the two
elements nitrogen and phosphoric acid. An increased
yield from No. 4 indicates deficiency of nitrogen and
potash. Under such conditions the use of a complete
fertilizer would be unnecessary. If No. 5 gives an
additional yield the soil is in want of nitrogen. From
the eight plots it will be possible to tell which of the
various elements it will be advisable to use. The fer-
tilizers should be applied after the land has been thor-
oughly prepared and before seeding. Corn is a good
crop for the first trials. The number of plots may be
increased by using well-prepared stable manure and
gypsum on plots 9 and 10 respectively. The second
year the results should be verified.

280. Deficiency of Nitrogen. — If the results indi-
cate a deficiency of nitrogen, select two crops, one as
wheat which is particularly benefited by dressings of
nitrogen, and another as corn which has no difficulty in
obtaining this element. The cultivation of each crop
should be that which experience has shown to be the

220 SOILS AND FERTILIZERS

best. On one wheat, and one corn plot, 8 pounds of
nitrate of soda should be used, a plot each of wheat
and corn being left unfertilized. If both the corn and
the wheat are benefited by the application of nitro-
gen, the soil is in need of available nitrogen. If, how-
ever, the wheat responds and the corn does not, the
soil is not in great need of nitrogen but does not con-
tain an abundance in available forms.

281. Deficiency of Phosphoric Acid. — In experi-
menting with phosphoric acid, turnips are grown on
two plots and barley on two plots. To one plot of
each 16 pounds of acid phosphate are applied. If both
crops show marked additional yields the soil is in need
of available phosphoric acid. If only the turnips re-
spond while the barley is indifferent the soil contains
a fair amount of available phosphoric acid. Barley
and turnips are used because there is such a marked
difference in the power of each to assimilate phos-
phoric acid.

282. Deficiency of Potash. — In order to determine
the condition of the soil as to potash, potatoes and oats
may be used as the trial crops, and 8 pounds of sul-
phate of potash should be applied to one plot of each.
Marked additional yields indicate a poverty of availa-
ble potash ; an increased potato crop and an indiflfer-
ent oat crop indicate potash not in the most available
forms. If no additional yields are obtained the soil
is not in need of potash.

FIELD TESTS WITH FERTILIZERS 221

283. Deficiency of Two Elements. — If the prelim-
inary trials indicate a deficiency of two elements as
nitrogen and phosphoric acid, both elements are used
together, in the same way as described for deficiency
of nitrogen, with additional plots for the separate ap-
plication of nitrogen and phosphoric acid.

284. Importance of Field Trials. — While it seems a
troublesome matter to determine the actual needs of a
soil, it will be found that both time and money are
saved by a systematic study of the question. Suppose
fertilizers are used in a " hit or miss" way year after
year on a soil, deficient only in phosphoric acid. It
would take 8 years to find out what the soil was
deficient in, if a different fertilizer were used each year,
and during all this period, either the soil has failed to
receive its proper fertilizer, or expensive and unneces-
sary plant food has been provided.

285. Will it Pay to Use Commercial Fertilizers?

— This question can be answered only by trial. If a
soil is in need of available plant food, the additional
amount of crop produced should pay for the fertilizer
and the expense of using it. Some fertilizers have an
influence on two or three succeeding crops, and only
partial returns are received the first year. When large
crops must be produced on small areas, as in truck
farming, commercial fertilizers are generally neces-
sary. In the production of large areas of staple crops
as wheat and corn, in the western prairie states,

222 SOILS AND FERTILIZERS

they have never been used. If the soil is properly
tilled and there is a good stock of natural fertility, the
use of commercial fertilizers can be avoided. With
poor cultivation and a soil that has been impoverished
by injudicious cultivation their use is more necessary.

286. Amount of Fertilizer to Use per Acre. — When
commercial fertilizers are used, it should be the aim to
apply just enough to produce normal yields. Heavy
applications at long intervals are not as productive of
good results as light applications more frequently.
From 400 to 600 pounds per acre is as much as should
be used at one time unless previous trials have shown
that heavier applications are necessary. The way in
which the fertilizer is to be applied, as broadcast or
otherwise, must be determined by the crop to be
grown. The fertilizer should not come in direct con-
tact with seeds, neither should it be worked into the
soil to such a depth that it may be lost by leaching
before it can be appropriated by the crop.

287. Excessive Applications of Fertilizers Injuri-
ous. — An overabundance of plant food has an inju-
rious effect upon crop growth. Plants take their
food from the soil in dilute solutions, and when
the solution is concentrated abnormal growth results.
Potatoes heavily manured with nitrate of soda make a
luxuriant growth of vines but produce only a few
small tubers. When a medium dressing is used along
with potash and phosphoric acid, a more balanced

FIELD TESTS WITH FERTILIZERS 223

growth is obtained, and a better yield is the result.
Heavy applications of nitrate of soda produce a rank
o^rowth of straw, with a low yield of grrain. The ex-
cessive amount of nitrogen causes the mineral matter
to be utilized for straw production and leaves only a
small amount for grain production. When applica-
tions of commercial fertilizers are too heavy, plants
take up unnecessary amounts of food and fail to make
good use of it. In fact crops may be overfed the
same as animals. Hence in the use of fertilizers ex-
cessive applications are to be avoided.

288. Fertilizing Special Crops. — There are crops
which need special help in obtaining some one ele-
ment, and in the use of fertilizers it should be the rule
to help those crops which have the greatest difficulty
in obtaining food. When the soil does not show a
marked deficiency in any one element, light dressings
of special purpose manures may be made to the follow-
ing crops :

Wheat. — Nitrogen first ; phosphoric acid to a less
extent.

Barley^ oats^ and rye require manuring like wheat,
but to a less extent. Each crop has a different power
of obtaining nitrogen. Wheat requires the most help
and barley and rye the least.

Corn. — Phosphoric acid first ; then nitrogen and
potash.

224 SOILS AND FERTILIZERS

Potatoes. — General manuring ; reenforced with pot-
ash.

Ma ngels. -^ N i tr ogen .
Turiiips. — Phosphoric acid.
Clover. — Lime and potash.
Timothy. — General manuring.

289. Commercial Fertilizers and Farm Manures.

— ' Commercial fertilizers should not replace farm ma-
nures, but simply reenforce them. Although com-
mercial fertilizers are called complete manures, they
fail to supply organic matter. It is more important in
some soils than in others, that the organic matter be
maintained because in some soils the organic matter
takes a more important part in crop production than
does the food applied in commercial forms. For
example, when a rich prairie soil is reduced by grain
cropping and is allowed to return to pasture, heavier
yields of grain are afterwards obtained than from sim-
ilar soils which received applications of commercial
fertilizers.

CHAPTER XI

FOOD REQUIREMENTS OF CROPS

290. Amount of Fertility Removed by Crops. —

From an acre of soil, producing average crops, the
amount of fertility removed varies between wide lim-
its. For example, an acre of mangels removes 150
pounds of potash, while an acre of flax removes 27
pounds ; an acre of corn removes about 75 pounds of
nitrogen, while an acre of wheat removes about 35
pounds. Crops w^hich remove the most fertility do
not always require the most help in obtaining their food.
This is because the amount of plant food assimilated,
and the power of crops to obtain this food, are not
the same. An acre of corn, for example, takes over
twice as much nitrogen as an acre of wheat, but wheat
will often leave the soil in a more impoverished con-
dition than corn, because corn has greater power for
procuring nitrogen and for utilizing that formed by
nitrification after the wheat crop has completed its
growth. The available nitrogen if not utilized by a
crop may be lost in various ways. IVIangels require
about twice as much phosphoric acid as flax, but are
a strong feeding crop and require less help in obtain-
ing this element.

It was formerly believed that the amoimt of plant

226 SOILS AND FERTILIZERS

food present in the matured crop indicated the kind
and amount of fertilizing ingredients to apply, and
that a correct system of manuring required a return
to the soil of all elements removed in the crop. Ex-
periments have shown that both of these views are in-
correct. The composition of plants cannot be taken as
the basis for their manuring. For example an acre of
wheat contains 35 pounds of nitrogen while an acre of
clover contains 70 pounds. If 70 pounds of nitrogen
were applied to an acre of clover and 35 pounds to an
acre of wheat, poor results would follow, because clo-
ver can obtain its own nitrogen while wheat is nearly
helpless in obtaining it, and the 35 pounds would not
necessarily come in contact with the roots so that it
could all be assimilated. While the amount of plant
food removed in crops cannot serve as the basis for their
manuring, valuable results are obtained from the study
of the different elements of fertility removed in crops,
and in making use of the following figures, other fac-
tors, as the influence of the crop upon the soil and the
power of the crop to obtain its food, must also be con-
sidered.

FOOD REQUIREMENTS OF CROPS 227

Pi^ANT Food Removed by Crops''^

Pounds per acre.
Phos-
Gross Nitro- phoric Pot- Sil- Total

Crops. weight. gen. acid. ash. Lime. ica. ash.

Wheat, 20 bus 1200 25 12.5 7 i i 25

straw 2000 10 7.5 28 7 115 185

Total 35 20 35 8 116 210

Barley, 40 bus 1920 28 15 81 12 40

Straw 3000 12 5 30 8 60 176

Total 40 20 38 9 72 216

- Oats, 50 bus 1600 35 12 10 1.5 15 55

Straw 3000 15 6 35' 9.5 ' 60 150

Total 50 18 45 II. o 75 205

Corn, 65 bus 2200 40 18 15 i i 40

Stalks 3000 35 2 45 II' 89 160

Total 75 20 60 12 90 200

Peas, 30 bus 1800 .. 18 22 4 i 64

Straw 3500 .. 7 38 71 9 176

Total . . 25 60 75 10 240

Mangels, 10 tons.. 20000 75 35 150 30 10 350

Meadow hay, i ton 2000 30 20 45 12 50 175

Red Clover Hay,

2 tons 4000 .. 28 66 75 15 250

Potatoes, 150 bus.. 9000 40 20 75 25 4 125

Flax, 15 bus 900 39 15 83 0.5 34

Straw 1800 15 3 19 13 3 53

Total 54 18 27 16 3-5 87

291. Plants Render Their Own Food Soluble. — It

was supposed at one time that plants obtained all of
their mineral food from the mineral matter dissolved
in the soil water. Experiments by Liebig demonstra-
ted that plants have the power of rendering their own
food soluble, provided it does not exist in forms

228 SOILS AND FERTILIZERS

too inert to undergo chemical change. Liebig grew
barley in boxes so constructed that all of the water-
soluble plant food could be secured. Two of the boxes
were manured and two left unmanured. In one box
which received manure and one which received none,
barley was grown. One each of the manured and
unmanured boxes was left barren. He collected all of
the drain waters and determined the soluble mineral
matter present, also weighed and analyzed the crop.
His results showed that 92 per cent, of the potash in
the crop was obtained from forms insoluble in water. ^^

In the roots of all plants there are present various
organic acids. Between the rootlet and the soil there
is a layer of water. The plant sap and the soil water
are separated by plant tissue which acts as a membrane.
All of the conditions are favorable for osmosis. The
acid sap from the roots finds its way into the soil in
exchange for some of the soil water. This acid, excre-
ted by the roots, acts upon the mineral matter, render-
ing it soluble, when it is taken up by the plant.
Different plants contain different kinds and amounts
of organic acids as well as present different areas of
root surface to act upon the soil, and the result is that
agricultural crops have different powers of assimila-
ting food.

Plants not only possess the power of rendering their
food soluble but they are also able to select their own
food and to reject that which is unnecessary. For ex-

CEREAL CROPS 229

ample, wheat grrown on prairie soil containing soda in
equally abundant and soluble forms as the potash, will
contain relatively little soda compared with the potash
in the crop.^^

CEREAL CROPS

292. General Food Requirements. — Cereal crops con-
tain a high per cent, of silica and evidently possess
the power of feeding upon some of the simpler silicates
of the soil, 73 liberating the base elements which are
utilized as food, while the silica is deposited in the
outer surface of the straw. As previously stated, cer-
eal crops although they do not remove large amounts
of total nitrogen from the soil require special help in
obtaining this element. There is, however, a great
difference among the cereals as to power of assimila-
ting nitrogen. Next to nitrogen these crops stand
most in need of phosphoric acid. The humic phos-
phates are utilized by nearly all of the cereals.

293. Wheat. — This crop is more exacting in its
food requirements than barley, oats, or rye. Wheat
is comparatively a weak feeding crop, and the
soil should be in a higher state of fertility than for
other grains. The extensive experiments of Lawes
and Gilbert have given valuable information regard-
ing the effects of manures on wheat. The results are
given in the following table -J"^

230 SOILS AND FERTILIZERS

Average Yiei^d of Wheat per Acre.

Bushels.

No manure for 40 years 14

Minerals alone for 32 years 15^

Nitrogen " " " " 23^

Farmyard manure for 32 years 32|

Minerals and nitrogen for 32 years' 36^^

0-^4

The food requirements of wheat are such that it should
be given a favored position in the rotation. Wheat may
follow clover provided the clover sod is light and is
fall plowed. On some soils, however, wheat does not
thrive following a sod crop. It takes nearly a year
for a heavy sod residue to get into suitable food forms
for a wheat crop. Under such conditions, oats should
first be sown, then wheat may follow. On average
soil a medium clover sod, plowed late in summer or in
early fall, and followed with surface cultivation, leaves
the land in good condition for spring wheat. It is not
advisable to have wheat follow barley, because the
soil will be too porous, and barley being a stronger
feeding crop leaves the land in poor condition as to
available plant food. When a corn crop is well ma-
nured, wheat may follow. The food requirements of
wheat are best satisfied following a light, w^ell cultiva-
ted clover sod, or following oats which have been grown
on heavy sod, or following corn that has been well
manured.

1 86 pounds of nitrogen as sodium nitrate.

2 86 " *' " " ammonium salts.

CEREAL CROPS 23 I

294. Barley. — While wheat and barley belong to
the same general class of cereals, they differ greatly in
their habits and food requirements. Barley is a
stronger feeding crop, has a greater root development
near the surface, and can utilize food in cruder forms.
In many of the western states, soils which produce
poor wheat crops, from too long cultivation, give ex-
cellent yields of barley. This is due to changed con-
ditions, of both the chemical and mechanical composi-
tion of the soil. Long cultivation has made the soil
porous and reduced the nitrogen content. Barley
thrives best on a rather open soil and has greater ni-
trogen assimilative powers than wheat. Barley, how-
ever, responds liberally to manuring, particularly to ni-
trogenous manures. The experiments of Lawes and
Gilbert on the growth of barley are briefly summa-
rized in the following tablets

Average Yield of Barley Per Acre for 34 Years.

Bushels.

No manure 17I

Superphosphate alone 23I

Mixed minerals 2\\

Nitrogen alone 3o|

Nitrogen and superphosphate 45

Farmyard manures 49I

295. Oats. — Oats are capable of obtaining food un-
der more adverse conditions than either barley or
wheat. They are also less exacting as to soil require-
ments. The oat plant will adapt itself to either sandy

232 SOILS AND FERTILIZERS

or clay soil, and will thrive in the presence of alkaline
matter or humic acid where wheat would be destroyed.
In a rotation, oats usually occupy a position less favored
by manures. They are, however, greatly benefited by
fertilizers particularly by those of a nitrogenous na-
ture.

296. Corn. — Experiments with corn indicate that
under ordinary conditions it requires most help in ob-
taining phosphoric acid. Corn removes a large amount
of gross fertility but its habits of growth are such that
it generally leaves an average soil in better condition
for succeeding crops. Corn is not injured as are many
grain crops by heavy applications of stable manure.
It does not, like flax, produce waste products which
are destructive to itself. Rich prairie soils when
newly broken give better results for wheat culture
after one or two corn crops have been removed. The
food requirements of corn are satisfied by applications
of stable manure, occasionally reenforced with a little
phosphoric acid. After clover, corn gives excellent
returns, and when corn is the chief market crop it
should be favored by having the best position in a ro-
tation.

MISCELLANEOUS CROPS

297. Flax is very exacting in food requirements
and for its culture the soil must be in a high state of.
fertility. It is a type of a weak feeding crop. There
are but few roots near the surface and consequently it

MISCELLANEOUS CROPS 233

has restricted powers of nitrogen assimilation. 37 Flax
does not remove a large amount of fertility but if
grown too frequently the tendency is to get the land
out of condition rather than to exhaust it. Flax
should be indirectly manured. Direct applications of
stable manure produce poor results, but when the ma-
nure is applied to the preceding crop excellent results
are obtained. The best conditions for flax culture re-
quire that it should be grown on the same land only
once in five years. Dr. Lugger has demonstrated
that there are produced, when the roots and straw of
ilax decay, products which are destructive to succeed-
ing flax crops. 7^ The food requirements of flax are
met when it follows corn which has been well manured,
or a sod which has been given the cultivation described
for wheat. Flax and spring wheat are much alike in
food requirements.

298. Potatoes. — Potatoes are surface feeders and
when grown continually upon the same soil without
manure, the yield per acre decreases more rapidly than
any other farm crop. Experiments with potatoes by
Lawes and Gilbert using different manures gave the
following result r^^

Average Yield per Acre for 12 Years.

Tons. Cwt.

No manure i 19I

Superphosphate 3 5

Minerals alone 3 7|

Nitrate of soda alone 2 4|

Mixed manures and nitrogen 5 lyf

Farm manures, alternate years 4 3|

234 SOILS AND FERTILIZERS

Potatoes require liberal general manuring reenforced
with wood ashes or other potash fertilizers. In the
rotation they should follow grain or pasture land, pro-
vided the fertility of the soil is kept up.

299. Sugar-beets. — This crop is more exacting in
its food demands than other root crop. Excessive
fertility is not conducive to a high content of sugar.
Soils in a medium state of fertility usually give the
best results. 7^ Sugar-beets should not receive heavy
dressings of stable manure, because an abnormal
grow^th results. Nitrogenous fertilizers can be ap-
plied only in limited amounts, heavier dressings of
potash and phosphoric acid are more admissible.
When sugar-beets follow^ corn which has been manured,
or grain which has left the soil in an average state of
fertility, the food requirements are well met.

300. Roots. — Mangels are gross feeders and re-
move a larger amount of fertility from the soil than
any other farm crop." When fed to stock and the
manure is returned to the soil they materially aid in
making the plant food more available for delicate
feeding crops. Mangels are better able to obtain their
phosphoric acid than are turnips and need the most
help in the way of nitrogen. Turnips are surface
feeders with stronger power of nitrogen assimilation
than the grains but with restricted power of phosphate
assimilation. Manures for turnips should be phos-
phatic in nature.

MISCELLANEOUS CROPS 235

301. Rape is a type of a strong feeding plant capa-
ble of obtaining its food under conditions adverse to
grain culture. When grown too frequently upon the
same soil it does not thrive. On account of its great
capacity for obtaining food, it is a valuable crop to
use for green manuring purposes. ^9

302. Buckwheat is a strong feeding crop and its
demands for food are easily met. On rich soil, a rank
growth of straw results, with poor seed formation.
Buckwheat is usually sown upon the poorest soil of
the farm. Being a strong feeder it is frequently used
as a manurial crop, being plowed under while green to
serve as food for weaker feeding crops.

303. Cotton. — On average soils cotton stands in
need first of phosphoric acid, second of nitrogen.^ It
is most able to obtain potash, but soils deficient in pot-
ash require its use. Organic nitrogen as cottonseed
meal and stable manure appear equally as effective as
nitric nitrogen. Phosphoric acid must be applied in
the most available forms. In fertilizing cotton,
the use of green manuring crops as cow peas with an
application of marl gives beneficial results. Marl, how-
ever, should not be applied alone because of the forma-
tion of insoluble phosphate of lime. Lime combines
with the decaying organic matter in preference to
phosphates, a result which is beneficial to both soil
and crop.

304. Hops. — The hop plant is peculiar in regard

236 SOILS AND FERTILIZERS

to its food requirements. An excess of easily soluble
plant food is injurious while a lack is equally so. An
abundance of food in organic forms is most essential.
Heavy dressings of farm manures may be applied.
Where hops are grown there is a tendency to use all
of the manure on the hops while the rest of the farm
is left unmanured. Very light applications of com-
mercial fertilizers may be used in connection with sta-
ble manure, but such use should be made only after a
preliminary trial on a smaller scale.

305. Hay and Grass Crops. — Most grass crops have
shorter roots than grain crops ; they are surface feed-
ers and not so able to secure mineral food. When a
number of crops have been removed the soil may stand
in need of available mineral matter. Farm manures
are particularly well adapted for fertilizing grass. Ap-
plications of nitrogenous manures result in discoura-
ging the growth of clover. Heavy manuring of grass
land has a tendency to reduce the number of species
and one kind is apt to predominate.^' On some soils
ashes, and on others lime fertilizers, have been found
very beneficial. The manuring of grass lands must
be varied to meet the requirements of different soils.
Permanent meadows require different manuring from
meadow simply introduced as an important crop in the
rotation.

306. Leguminous Crops. — For leguminous crops pot-
ash and lime fertilizers have been found of most value.

MISCELLANEOUS CROPS 237

Analyses of leguminous crops, as clover and peas, show
large amounts of both potash and lime. Many crops
as clover fail when grown too frequently upon the
same soil, not because the soil is exhausted but because
of the development in the soil of organic products
which are destructive to growth. When the inexpen-
sive food requirements of leguminous crops are sup-
plied, the soil is enriched with nitrogen and phos-
phoric acid which have been changed to more availa-
ble forms.

CHAPTER XII

ROTATION OF CROPS AND CONSERVATION OF SOIL
FERTILITY

307. Object of Crop Rotation. — The object of the
systematic rotation of crops is to conserve the fertility
of the soil, and at the same time to produce larger
yields. In order to accomplish this, the food require-
ments of different crops must be met by good cultiva-
tion and proper manuring. Rotations must be planned
according to the nature of the soil and the system of
farming that is to be followed. For general grain
farming a different system must be practiced than for
exclusive dairying. Whatever the nature of farming
the whole farm should gradually undergo a systematic
rotation. If the farm is uneven in soil texture, differ-
ent rotations must be practiced on the various parts.
There is no w^ay in which soils are more rapidly de-
pleted of fertility than by the continued culture of one
crop. In exclusive wheat raising for example the
losses w^hich occur are not confined to the fertilit}' re-
moved in the crop but may take place in other ways
as described in the chapter on nitrogen. When wheat
is properly grown in alternation with other crops,
losses of nitrogen are reduced to the minimum.

When remunerative crops can no longer be produced
the soil is said to be exhausted. Soil exhaustion may

ROTATION OF CROPS 239

be due either to a lack of fertility or to getting the
soil out of condition because of the "one-crop system"
and poor methods of cultivation.

308. Principles Involved in Crop Rotation. — In
the systematic rotation of crops there are a few funda-
mental principles with which all rotations should be
made to conform. Briefly stated these principles are :

1. Deep and shallow rooted crops should alternate.

2. Humus-consuming and humus-producing crops
should alternate.

3. Crops should be rotated so as to make the best
use of the preceding crop residue.

4. Crops should be rotated so as to secure nitrogen
indirectly from atmospheric sources.

5. Crops should be rotated so as to keep the soil in
the best mechanical condition.

6. In arid regions crops should be rotated so as to
make the best use of the soil water.

7. An even distribution of farm labor should be se-
cured by a rotation.

8. Farm manures and fertilizers should be used in
the rotation where they will do the most good.

9. Rotations should be planned so as to produce fod-
der for stock, and so that every vear there will be some
important crop to be sold.

309. Deep and Shallow Rooted Crops. — When
deep and shallow rooted crops alternate, the draft upon
the surface soil and subsoil is more evenly distributed.

240 SOILS AND FERTILIZERS

In many soils nitrogen and phosphoric acid are more
abnndant in the surface soil while potash and lime
predominate in the subsoil. When such a condition
exists, the alternating of deep and shallow rooted
crops is very beneficial, because the surface soil is re-
lieved of continuous heavy drafts upon the elements
present in scant amounts.

310. Humus-consuming and Humus-producing
Crops. — When grain or hoed crops are grown con-
tinuously, oxidation of the humus occurs, and the
chemical and physical properties of the soil may be
entirely changed by the loss of the humus. The ro-
tating of grass and grain crops and the use of stable
manure serve to maintain the humus equilibrium. On
some soils lime may be required along with the humus
to prevent the formation of humic acid, and in such
cases the best conditions exist when both lime and hu-
mus materials are supplied. The alternation of hu-
mus-producing and humus-consuming crops is one of
the essential matters to consider in a rotation.

311. Crop Residue. — Crop residues should always
be placed at the disposal of weak feeding crops. For
example, after a light clover and timothy sod, wheat
or flax should be grown in preference to barley or
mangels. The weak feeding crop should then be fol-
lowed by a strong feeding crop, and each is properly
supplied with food. It would be poor economy, on an
average soil, to follow clover and timothy with mangels,

ROTATION OF CROPS 24 1

then with barley, and finally with flax, because the
flax would be placed at a serious disadvantage follow-
ing two strong feeding crops. If reversed, the crops
would be placed in order of assimilative pow^r, and the
best use w^ould be made of the sod crop residue.
When crops of dissimilar feeding habits follow each
other in rotation not only are the crop residues used to
the best advantage, but the soil is relieved of excessive
demands on special elements. For example, wheat
and clover take different amounts of potash and lime
from the soil. Wheat has the power of feeding upon
silicates of potash which clover cannot assimilate,
hence wheat and clover in rotation relieve the soil of
excessive demands on the potash.

312. Nitrogen-consuming and Nitrogen-producing
Crops. — It is possible in a five-course rotation to main-
tain or even increase the nitrogen of the soil without
the use of nitrogenous manures. In Section 131 an ex-
ample is given of a rotation which has left the
soil with a better supply of nitrogen than at the begin-
ning. W^hen a soil produces a good clover crop once
in five years, and stable manure is used once during
the rotation, the soil nitrogen is not decreased. By
means of rotating nitrogen-producing and nitrogen-
consuming crops it is possible to sell nitrogenous grain
products from the farm without purchasing nitroge-
nous manures. The conservation of the nitrogen of
the soil is the most important point to consider in the

242 SOILS AND FERTILIZERS

rotation of crops, because it is the most expensive ele-
ment and is the most liable to be deficient.

313. Influence of Rotation upon the Mechanical
Condition of Soils. — With different kinds of crops,
the mechanical conditions of soils are constantly under-
going change. Grain crops and hoed crops tend to
make the soil open in texture. Grass crops have the
opposite effect. All soils should undergo periodic
compacting and loosening. Some require more of one
treatment than of the other. In a good rotation the
mechanical action of the crop upon the soil should be
considered, otherwise the soil may get into poor condi-
tion to retain water or become so loose that heavy
losses occur through wind storms. Sandy soils are
improved by those methods of cropping which compact
the soil, while heavy clays require the opposite treat-
ment. The rotation should be made to conform to
the requirements of the soil.

314. Economic Use of Soil Water. — The rotation
should not be of such a nature as to make excessive
demands upon the soil water. For example, after a
grain crop has been produced, it is best in regions of
scant rainfall to plow the land and get it into condi-
tion to conserve the water for the next year's crop,
rather than to attempt to raise a catch crop the same
year. Crops removing excessive amounts of water
should not be grown too frequently. Sunflowers, for
example, remove twenty times more water than grain

ROTATION OF CROPS 243

crops. Cabbage removes from the soil more water
than many other crops. With a good rotation it is
possible to carr\' the water balance in the soil from
year to year, so that crops will be supplied in times of
drought.

315. Rotation and Farm Labor. — The rotation of
crops should be planned so that an even distribution
of farm labor is secured. The importance of this
principle is so plain that its discussion is unnecessary.
It is a topic outside of the domain of chemistry,
but is nevertheless one of the most important to con-
sider in economic farming, and should not be lost
sight of in planning rotations.

316. Economic Use of Manures. — Farm manure
should be applied to those crops which experience has
shown to be the most benefited bv its use. At least
once during a five years' rotation the land should receive
a dressing of stable manure. If commercial fertilizers
are used, they should be applied to the crops which
require the most help in obtaining food. With the
growing of clover and the use of farm manures, only
the poorer kinds of soil will require commercial fertil-
izers for general crop production. It is more econom-
ical to reenforce the farm manures with fertilizers
especially adapted to the soil and crop than to purchase
complete fertilizers.

317. Salable Crops. — In all farming, something
must be sold from the farm. It should be the aim to

244 SOILS AND FERTILIZERS

sell products which remove the least fertility, or if
those are sold which remove large amounts, to return
in cheaper forms the fertility sold. In a good rotation
it is the plan to have at least one salable crop
each year. The whole farm need not undergo the
same rotation at the same time and the rotation may
be subject to minor changes as circumstances require.
To illustrate, wheat and flax occupy about the same
position in a rotation. If when the crop is to be
seeded the indications are that wheat will be a poor
paying crop and flax sell well, flax should be sown.
The rotation should be such that one of two or three
crops may be grown as circumstances require.

318. Rotations Advantageous in Other Ways. — A
good rotation will be found advantageous in many
ways. With one line of cropping, land becomes foul
with special kinds of weeds which are unable to
thrive when crops are rotated. Frequently the rota-
tion must be planned so as to reclaim the land from
'Vv^eeds.

Relief from insect pests is often secured by a proper
rotation. Many insects are capable of living only on
a special crop and when this crop is grown continually
on the same land the best conditions for insect ravages
exist.

319. Long- and Short-course Rotations. — Rota-
tions vary in length from 2 to 1 7 years. Long-course

ROTATION OF CROPS 245

rotations are more generally followed in Enropean
countries. The length of the rotation can only be de-
termined bv the conditions existing; in different local-
ities. As a general rule long-course rotations should
be attempted only after a careful study of all the
conditions relating to the system of farming that it is
desired to follow. For northern latitudes a rotation
of four or five years ogives excellent results. In some
localities three-course rotations are the most desirable.

A rotation that is suitable for one locality or kind
of farming may be unsuited for other localities or con-
ditions. Because of variations in soil, climate, and
rainfall, no definite standard rotation can be pro-
posed that will be suitable for all conditions.

320. Example of Rotation. — In dealing with the
subject of rotations it is best to take actual problems
as they present themselves and plan rotations that will
best meet all conditions. For example, a farm of
160 acres is to be rotated with the main object of pro-
ducing fodder for live stock, and a small amount of
grain for sale. The following rotation has been pro-
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248 SOILS AND FERTILIZERS

The farm is divided into eight fields of 20 acres
each ; seven fields are brought under the rotation,
while one field is left free for miscellaneous purposes.
Each year there are produced 20 acres of corn, 20
acres of timothy and clover hay, 10 acres each of
wheat and flax, 20 acres of barley, and five acres each
of corn fodder, rye, peas, and potatoes, while 20 acres
are reserved for pasture. The main income is derived
from the sale of live stock and dairy products.

Problems on Rotations

1. Plan a rotation for general fanning ( 160 acres), using the fol-
lowing crops: clover, timothy, barley, oats, potatoes, and corn. The
soil is in an average state of fertility. Twenty-five head of stock
are kept.

2. Plan a three-course rotation for a sandy soil, the main object
being potato culture.

3. Plan a seven-year rotation for grain farming, using manure
and sodium nitrate once during the rotation. The soil is a clay
loam in a good state of fertility.

4. Plan a rotation for general farming on a sandy loam.

5. How would you proceed to bring an old grain farm from a low
to a high state of productiveness? Begin with the feeding of the
stock.

6. Using conmiercial and special-purpose manures, how would
you proceed to raise wheat, potatoes, and hay, each continuously?

7. Plan a rotation for a northern latitude, where corn cannot be
grown, and where clover and timothy fail to do well; wheat and all
small grains thrive ; also millet, peas, rape, and some of the root
crops. The soil is a clay loam, resting on a marl subsoil. Manure
is very slow in decomposing. The rotation should be suited to
general farming, wheat being the important market crop.

CONSERVATION OF FERTILITY

321. Manures Necessary for Conservation of Fer-
tility. — In order to conserve the fertility of the soil,
not only must a systematic rotation be practiced, but
a proper use must be made of the crops produced.
When they are sold from the farm and no restoration
is made soils are gradually depleted of their fertility.
No soil has ever been found that will continue to pro-
duce crops without the use of manures. Many prairie
soils give large yields for long periods without manur-
ing, but they are never able to compete in productive-
ness with similar soils that have been systematically
cropped and manured. With a fertile soil the decline
of fertility is so gradual that it is not observed unless
careful records are kept of the 3'ields from year to year.

322. Use of Crops. — The use made of crops whether
as food for stock or sold directly from the farm, deter-
mines the future crop-producing power of the soil.
With different systems of farming different uses are
made of crops. When exclusive grain farming is fol-
lowed no restoration of fertility is made, while in the
case of stock farming, the manure produced contains
fertility in proportion to the crops consumed. If
good care is taken of the manure, and in place of the
grains sold, mill products are purchased and fed, there
is no loss of fertility. Between these two extremes,
exclusive grain farming and stock farming, there are
found in actual practice, different systems of farming,

250 SOILS AND FERTILIZERS

which remove various amounts of fertility from the
soil.

323. Two Systems of Farming Compared. — The
losses of fertility from farms are determined by the
crops and products sold, the care of the manure, and
the fertility in the products purchased and used on the
farm. If an account were kept of the income and
outgo of the fertility of farms it would be found that
with some systems, the soil is gaining in fertility, while
with others a rapid decline occurs. In studying the
income and outgo of fertility, it is necessary to calcu-
late the amount of the three principal elements, nitro-
gen, phosphoric acid, and potash in the crops and
products sold. For making these calculations tables
are given in Sections 178 and 290. In the handling of ma-
nure it is impossible to prevent losses, but it is possible
to reduce them to very small amounts. Hence in the
calculations, a loss of 3 per cent, is allowed for mechan-
ical waste, and for uneven distribution of the manure;
that is, in addition to the fertility sold from the farm a
loss of 3 per cent, is allowed for all crops raised and
consumed as food by stock.

On one farm the crops raised and sold are : Flax 40
acres, wheat 50 acres, oats 20 acres, barley 50 acres ;
no stock is kept, the straw is burned, and the ashes
are w^asted.

CONSERVATION OF FERTILITY 25 1

Exci^usivE Grain Farming.
Sold from the Farm

Phosphoric
Nitrogen. acid. Potash.

Pounds. Pounds. Pounds.

Flax, 40 acres 1600 600 800

Flax straw 600 120 320

Wheat, 50 acres 1250 625 350

Wheat straw 500 375 1400

Oats, 20 acres 700 240 200

Oat straw 300 1 20 700

Barley, 50 acres 1400 750 400

Barley straw 600 250 1500

Total 6950 3080 5670

In addition to the nitrogen removed in the crops
other losses mnst be considered. Experiments have
shown that when exchisive grain farming is practiced,
for every pound of nitrogen removed in the crop, four
pounds are lost from the soil in other w^ays. This
w^ould make the total loss of nitrogen over 28,500
pounds or 177 pounds per acre, w-hich large as it may
seem is the actual loss from the soil when grain only
is raised and sold. Experiments at the Minnesota
Experiment Station have shown that after a soil had
been cultivated 40 years, the annual loss per acre of
nitrogen in exclusive wheat raising was 25 pounds
through the crop and 146 pounds due to the oxidation
of the nitrogenous humus of the soil.'^

When exclusive grain farming is followed, the
annual losses of fertility from a farm of 160 acres are
28,500 pounds of nitrogen, 3000 pounds of phosphoric
acid, and 5500 pounds of potash.

252 SOILS AND FERTILIZERS

On a similar farm of 160 acres the crops are rotated

as described in Section 320. The amounts of fertility

in the products sold, the crops raised and consumed

as fodder, and the food and fuel purchased, are given
in the following table:

Stock Farming
Sold from the Far in

Phosphoric

Nitrogen. acid. Potash.

Pounds. Pounds. Pounds.

Butter, 5000 pounds 5 5 5

Young cattle, 10 head 200 190 16

Hogs, 20 of 250 pounds each- 100 40 10

Steers, 2 48 38 4

Wheat, 10 acres 250 125 70

Flax, 10 acres 390 150 190

Rye, 10 acres 285 128 85

Total 1278 676 380

Raised and Consumed on the Farm

Clover, 20 tons 66 270 600

Timothy. 20 tons 600 180 8cK)

Corn, 20 acres 1500 300 800

Corn fodder, i acre 75 15 60

Mangels, 2 acres 150 70 300

Potatoes, I acre 40 20 75

Straw, 40 tons 400 200 1000

Peas, 5 acres 85 200

Oats, 20 acres 700 240 200

Barley, 20 acres with straw- • 800 400 760

4265 1780 4795
Mechanical loss of food con-
sumed, 3 per cent 128 53 144

CONSERVATION OF FERTILITY 253

Food and Fuel Purchased

Phosphoric

Nitrogen. acid. Potash.

Pounds. Pounds. Pounds.

Bran, 5 tons 275 260 150

Shorts, 5 tons 250 150 100

Oil meal, 2 tons 100 35 25

Hard-wood ashes 25 100

625 470 375

Sold from farm 1278 676 380

Ivoss in food consumed, etc .. . 128 53 144

Total 1406 729 524

Food and fuel purchased 625 470 375

Balance lost from farm 781 259 149

The manure produced and used on this farm results
in the production of larger crop yields than is the
case with exclusive grain culture. The clover and
peas more than balance the loss of nitrogen. Ex-
periments have shown that a rotation similar to
this caused an increase in soil nitrogen. Manure,
meadow and pasture all tend to increase the soil
humus and nitrogen. The losses of phosphoric acid
and potash are exceedingly small, averaging less
than a pound per acre of each. The action of manure
on this farm is continually bringing into activity the
inert plant food of the soil so that every year there is
a larger amount of active plant food, which results in
producing larger yields per acre.

The increase or decrease of fertility on farms has
a marked effect upon crop yields. For example the

254 SOILS AND FERTILIZERS

averagfe yield of wheat in those counties in Minnesota
where live stock is kept, is 7 bushels per acre greater
than in similar counties where all grain farming is
followed.

Problems

Calculate the income and outgo of fertility from the following
farms :

1. Sold from the farm : wheat 40 acres, oats 40 acres, barley 40
acres, rye 20 acres, flax 10 acres. The straw is burned and no use
is made of any manures.

2. Sold from the farm : wheat 20 acres, barley 20 acres, flax 5
acres, 1000 pounds of butter, 10 hogs, and 10 steers. Purchased :
Bran 3 tons, shorts 2 tons, oil meal i ton. Crops produced and fed
on farm : Clover and timothy hay 40 tons, corn fodder 3 acres, corn
10 acres, oats and peas 10 acres, roots i acre, millet i acre, and bar-
ley 5 acres.

3. Sold from the farm : Wheat 10 acres, sugar beets 5 acres, milk
100,000 pounds, butter 500 pounds, 20 pigs, 6 head of young stock,
2 acres of potatoes. Purchased : 5 tons of bran, 2 tons of oil meal,
T ton of cottonseed meal, 15 cords of wood, i ton of acid phosphate,
1000 pounds of potassium sulphate, and 500 pounds of sodium ni-
trate. Raised and consumed on the farm : Corn fodder 15 acres,
mangels i acre, peas and oats 5 acres, clover 20 tons, timothy 10
tons, straw from grain sold, oats, 10 acres, corn 20 acres.

REFERENCES

1. Venable : Histon* of Chemistry.

2. Gilbert : Inaugural Lecture, University of Oxford.

3. Liebig : Cheniistr\- in Its Applications to Agriculture and
Physiology.

4. Gilbert: The Scientific Principles of Agriculture (Lecture).

5. Minnesota Agricultural Experiment Station, Bulletin No. 30.

6. Stockbridge : Rocks and Soils.

7. Association of Official Agricultural Chemists, Report 1898.
Note : — This sentence should read : A division has recently

been suggested by Hopkins in which the square root of ten is
taken as the constant ratio between the grade of soil particles.

8. Maryland Agricultural Experiment Station, Bulletin No. 21.

9. Osborne : Journal of Analytical Chemistry, Vol. II, Part 3.

10. Wiley : Agricultural Analysis, Vol. I.

11. Hellriegel : Calculated from Beitrage zu den Natunvissen-
schaft Grandlagen des Ackerbaus.

12. King : Wisconsin Agricultural Experiment Station, Report
1889.

13. Unpublished results of author.

14. King : Soils.

15. Roberts : Fertility of the Land.

16. Minnesota Agricultural Experiment Station, Bulletin No. 41.

17. Minnesota Agricidtural Experiment Station, Bulletin No. 53.

18. Whitney : Division of Soils, U. S. Department of Agriculture,
Bulletin No. 6.

19. Merrill : Rocks, Rock-weathering and Soils.

20. Miintz : Comptes Rendus de I'Acadeinie des Sciences, CX
(1890).

21. Storer : Agriculture, Vol. I.

22. Dyer : Journal of the Chemical Society, March, 1894.

23. Goss : Association of Official Agricultural Chemists, Report
1896.

256 SOILS AND FERTILIZERS

24. Peter : Association of Official Agricultural Chemists, Report

1895.

25. Loughridge : American Journal of Science, Vol. VII (1874).

26. Hilgard : Year-book U. S. Department of Agriculture, 1895.

27. Houston : Indiana Agricultural Experiment Stalion, Bulle-
tin No. 46.

28. Miilder : From Mayer : Lehrbuch der Agrikulturchemie, 2.

29. Journal of the American Chemical Society, Vol. XIX, No. 9.

30. Year-book U. S. Department Agriculture, 1895.

31. Loughridge : South Carolina Agricultural Experiment Sta-
tion, Second Annual Report.

32. Association of Official Agricultural Chemists, Report 1893.

33. Washington Agricultural Experiment Station, Bulletin No.

13-

34. Association of Official Agricultural Chemists, Report 1894.

35. California Agricultural Experiment Station, Report 1890.

36. Minnesota Agricultural Experiment Station, Bulletin No. 29.

37. Minnesota Agricultural Experiment Station, Bulletin No. 47.

38. Lawes and Gilbert : Experiments on Vegetation, Vol. I.

39. Boussingault : Agronomic, Tome I.

40. Atwater : American Chemical Journal, Vol. VI, No. 8 and
Vol. VIII, No. 5.

41. Hellriegel : Welche Stick stofF Quellen stehen der Pflanze zu
Gebote?

42. Minnesota Agricultural Experiment Station, Bulletin No. 34.

43. Warington : U. S. Department of Agriculture, Office of Ex-
periment Stations, Bulletin No. 8.

44. Hilgard : Association of Official Agricultural Chemists, Re-
port 1895.

45. Marchal : Journal of the Chemical Society (abstract), June,
1894.

46. Kiinnemann: Die Landwirthschaftlichen Versuchs-Stationen,
50(1898).

47. Adametz : Abstract, Biedermann's Centralblatt fiir Agrikul-
turchemie, 1887.

48. Atwater: American Chemical Journal, Vol. IX (1887).

REFERENCES 257

49. Stutzer : Biedermann's Centralblatt fiir Agriciilturchemie,
1883.

50. Jenkins : Connecticut State Agricultural Experiment Sta-
tion, Report 1893.

51. Wagner : Biedermann's Centralblatt fiir Agrikulturchemie,
1897.

52. Journal of the Royal Agricultural Society, 1850.

53. From Sachsse : Lehrbuch der Agrikulturchemie.

54. Lawes and Gilbert : Experiments with Animals.

55. Beal : U. S. Department of Agriculture, Farmers' Bulletin
No. 21.

56. Minnesota Agricultural Experiment Station, Bulletin No. 26.

57. Mainly from Armsby : Pennsylvania Agricultural Experi-
ment Station, Report 1890. Figures for grains calculated from
original data.

58. Heiden : Dungelehre.

59. Liebig : Natural Laws of Husbandry.

60. Cornell University Agricultural Experiment Station, Bulle-
tins Nos. 13, 27, and 56.

61. Kinnard : From Manures and Manuring by Aikman.

62. Wyatt : Phosphates of America.

63. Wiley : Agricultural Analysis, Vol. III.

64. Goessmann : Massachusetts Agricultural Experiment Station,
Report 1894.

65. Connecticut (State) Agricultural Experiment Station, Bulle-
tin No. 103.

66. Goessmann: Massachusetts Agricultural Experiment Station,
Report 1896.

67. Wheeler : Rhode Island Agricultural Experiment Station,
Reports 1892, 1893, etc.

68. Boussingault : From Storer : Agriculture.

69. Handbook of Experiment Station Work.

70. New York (State) Agricultural Experiment Station, Bulle-
tin No. 108.

71. Voorhees : U. S. Department of Agriculture, Farmers' Bulletin
No. 44.

258 SOILS AND FERTILIZERS

72. Liebig : Die Chemie in ihrer Anwendung auf Agrikultur
und Physiologic.

73. Warington : Chemistry of the Farm.

74. Lawes and Gilbert : Growth of Wheat.

75. Lawes and Gilbert : Growth of Barley.

76. Lugger : Minnesota Agricultural Experiment Station, Bulle-
tin No. 13.

77. Lawes and Gilbert : Growth of Potatoes,

78. Minnesota Agricultural Experiment Station, Bulletin No. 56.

79. Shaw : L^. vS. Department of Agriculture, Farmers' Bulletin
No. II.

80. White : U. S. Department of Agriculture, Farmers' Bulletin
No. 48.

81. Lawes and Gilbert : Permanent Meadows.

82. Thompson : Graduating Essay, Minnesota School of Agricul-
ture.

83. Nefedor : Abstract, Experiment Station Record, Vol. X, No. 4.

EXPERIMENTS

1. Pulverized Rock and Soil. — Pulverize in an iron mortar,
pieces of feldspar, mica, granite, and limestone. Examine each
with a lens. Finally mix all of the pulverized material, and com-
pare the mixture with samples of soil.

2. Weight of Soils. — Weigh a cubic foot of air-dried sand, clay,
and peat. For this purpose use a box holding ^ of a cubic foot of
soil. Do not compact the soil.

3. Form of Soil Particles. — Examine under a microscope soil
particles and distinguish the various grades of sand and silt. Ob-
serve the form of the soil particles and make drawings of them.

4. Separation of Soil Particles. — By means of sieves, with holes,
I, ^, and % mm. in diameter, separate these three grades of parti-
cles as described in Section 10. To what type does the soil
examined belong?

5. Capillarity. — Place small glass tubes of various sizes in a
vessel of water and note the height to which water rises by capil-
larity.

6. Capillarity of Soils. — Fill glass tubes 2 inches in diameter
w4th clay and fine sand, respectively. Support the tubes so that
one end will touch the water in a cylinder. Observe the rate and
height to which the capillary water rises, making daily measure-
ments for a week.

7. Hydroscopic Moisture. — Places grams of air-dried soil on a
watch-glass, in a water-oven, and after two hours reweigh and de-
termine the loss of weight. Calculate the per cent, of hydroscopic
moisture.

8. Influence of Cultivation on Soil Water. — Fill four boxes, each
a foot square and a foot deep, with air-dried loam soil. Weigh the
boxes and soil used. Each box is to be treated separately as fol-
lows : Measure one-half gallon of water into a watering-pot. Allow
the water from the watering-pot to flow on the soil, regulating the
flow so that it is all absorbed. The soil should be saturated, but

26o SOILS AND FERTILIZERS

there should be no dripping. Measure or weigh any water left in
the watering-pot. One box is to receive shallow surface cultivation,
using for the purpose a small gardener's tool. Another box is to
be left without receiving any treatment. The third is to receive
treatment imitating that of the disk harrow, having the disks set per-
pendicularly. A sharj) knife may be used for this purpose. In the
fourth box the disk cuttings are to be made at an angle. Leave
each box exposed to the sun or in a heated room, and determine
the loss of weight every day for a week. From the loss of weight,
determine the per cent, of water lost and the per cent, left in the
soil.

9. Capacity of Soil to Absorb Water. — Weigh 100 grams of dry
soil. Fit a medium-sized filter-paper in a funnel. Moisten the
paper so that it will not absorb an}- more water. Then place the
soil in the filter and add slowly from a beaker, containing exactly
100 cc. of water, enough to thoroughly saturate the soil. Collect
all of the drippings from the funnel. Measvire the drippings and
the unused water in the beaker. Calculate the per cent, of water
absorbed b\- the soil.

10. Capacity of Sand for Holding Water. — Repeat Experiment 9,
using sand.

11. The Influence of Manure upon the Water-holding Power of
Soil. — Repeat Experiment 9, using 95 grams of sand and 5 grams
of dry and finely pulverized manure. The sand and manure
should be thoroughly mixed before performing the experiment.

12. Action of Heat upon Soils. — Expose to the sun's rays samples
of dry clay, peat, and sand ; after two hours' exposure, obtain the
temperature of each. The bulb of the thermometer is simply cov-
ered with soil. All of the observations should be made under sim-
ilar conditions.

13. Influence of Manure upon Soil Temperature. — Expose to the
sun's rays, moist clay soil, and mixed cla3'and fresh horse manure.
After two hours observe the temperature of each.

14. Odor and Taste of Soils. — Observe the odor of dry, peaty
soil that has been kept in a corked bottle. Note the taste of

EXPERIMENTS

261

peaty and of alkaline soils ; test each wdth moistened litmus paper.

15. Absorption of Gases. — Put 50 grams of soil into a wide-
mouthed bottle, add 50 cc. of water and i cc. strong ammonia.
Note the odor. Cork the bottle, shake, and after twenty-fqur
hours again observe the odor.

16. Insoluble and Soluble Products of Soil. — Digest in a covered
beaker 10 grams of soil with 100 cc. hydrochloric acid (50 cc.
strong hydrochloric acid and 50 cc. water). After two hours' diges-
tion, cool and filter, using 25 cc. water to wash the acid from the
insoluble residue. Note the quantity and appearance of the insol-
uble matter. To one-half the filtrate add ammonia until alkaline.
What is the precipitate ? Remove it by filtering, and to this second
filtrate add ammonium oxalate. What is the precipitate ?
Evaporate the remainder of the original filtrate nearly to
dryness. Add 20 cc. water, 3 cc. nitric acid, and 5 cc. of
ammonium molybdate. After shaking the test-tube con-
taining the mixture, it is placed in a beaker of water and
heated to about 65° C. W^hat is the yellow precipitate ?

17. Testing Soils for Combined Carbon Dioxide. — One
gram of soil is placed in a test-tube (Fig. 35) and 5 cc. of
water and 3 cc. of hydrochloric acid added. A small
looped tube a, containing a drop of lime-water, is then
inserted into the test-tube. The test-tube is warmed.
Observe the precipitate formed in the loop. What is it ?

18. Humus from Soils. — Five grams of soil are placed
in a glass-stoppered bottle, 100 cc. water and 3 cc. hydro-
chloric acid added. After shaking, the contents of the
bottle are left twenty-four hours to subside. The acid
is then poured off and 100 cc. of water added. The soil
is left until the next day, when the water is poured off and V^__^/
100 cc. of water and 5 cc. of ammonia are added. After Fig- 35-
shaking and allowing a little time for the soil to settle, the ammo-
nia solution is filtered off.

To a portion of the filtrate add hydrochloric acid until the solu-
tion is just acid. Observe the precipitate. Evaporate another por-
tion of the solution to drvness. What is the black residue ?

a

6

262 SOILS AND FERTILIZERS

19. The nitrogen of soils. — Place in a strong test-tube a mixture
of 5 grams of soil and an equal bulk of soda-lime. Connect the
test-tube wdth a delivery-tube which leads into another test-tube
containing distilled water. Heat the test-tube containing the soil for
five or ten minutes. Then test with litmus paper the liquid in the
second test-tube, neutralize with standard acid as in Experiment 30.

20. Nitrates. — Examine laboratory samples of the following
nitrates: Potassium, calcium, and sodium. Place in separate test-
tubes Yz gram of each, add 10 cc. of water, and heat gently. To
each when cool add a few drops of sulphuric acid, then a few drops
of an indigo solution.

21. The Nitrogen of Blood. — Repeat Experiment 19, using 100
milligrams of dried blood in place of the soil.

22. Organic Nitrogen Soluble in Pepsin. — Prepare a pepsin solu-
tion by dissolving 5 grams of commercial pepsin in a liter of water,
adding i cc. of strong hydrochloric acid. Place in separate test-
tubes 5 grams each of dried blood, tankage, and horn meal. Add
25 cc. of pepsin solution and place the test-tubes in a cylinder con-
taining water at a temperature of 40° C. Shake the test-tubes occa-
sionally, and at the end of one-, two-, and five-hour periods observe
the amounts of insoluble matter remaining in the test-tubes.

23. Testing for Nitrates. — Dissolve some sodium nitrate, not
exceeding 100 milligrams, in 10 cc. water. Add 2 cc. of a dilute
solution of ferrous sulphate, and place the test-tube in a cylinder
of water. Sulphuric acid is then added by means of a long stemmed
funnel. Observe the dark ring formed.

24. Water in Manure. — Dr}' 100 grams of fresh manure in a
water-oven for four hours. Determine the loss of weight and the
per cent, of water.

25. Leaching Manure. — Place 5 kilos of manure, the same as
used in Pixperiment 24, in a box provided with small holes in the
bottom, so that the manure can be leached. Place the box over a
sink or a receptacle for receiving the leachings. Percolate 3 gallons
of water through the manure, daily, for five days. Finally weigh
the manure, determine the per cent, of water, and the total loss of
dry matter.

EXPERIMENTS 263

26. Volatilizing Ammonium Salts. — In separate test-tubes place
about 100 milligrams each of ammonium carbonate and ammonium
sulphate. Apply heat gently and observe the results. Place a cold
glass rod in the test-tube when the white fumes are being given off.

27. Testing for Phosphoric Acid. — Dissolve a small piece of bone
(5 grams) in 20 cc. nitric acid (10 cc. strong nitric acid and 10 cc.
water). Filter. To the filtrate add 3 cc. of ammonium molybdate,
warm, and shake. In a second test-tube dissolve 100 milligrams of
sodium phosphate in 10 cc. water and add 3 cc. ammonium mo-
lybdate. Compare the result with that obtained with the bone.

28. Testing for Water-soluble and Acid-soluble Phosphates. —
Place I gram of tricalcium phosphate in a test-tube with 10 cc.
water. Boil. Filter through a close filter. To the filtrate add 3 cc.
of ammonium molybdate. Repeat the experiment, using dilute
nitric acid in place of water. Repeat the experiment, using mono-
calcium phosphate and water.

29. Preparation of Acid Phosphate. — Place 100 grams of pow-
dered tricalcium phosphate in a large lead dish. Add slowly and
with constant stirring 100 grams of commercial sulphuric acid,
using an iron spatula for the purpose. Transfer the mixture to a
wooden box and allow it to act for about three days. Then pul-
verize and examine. The material is saved for Experiment 34.
The mixing of the acid and phosphate should be Hone in a place
where there is a good draft.

30. Testing Ashes. — Test samples of leached and of unleached
ashes in the way described in Section 240.

31. Flocculation of Clay. — Ten grams of clay soil are placed in
a tall beaker or cylinder, 1000 cc. of water added, and the material
triturated. The water containing the suspended clay is divided
into two portions. To one portion i gram of calcium carbonate is
added and the mixture stirred. After two or three hours compare
the two portions.

32. Action of Lime on Acid Soil. — In a flask place 100 grams
of acid peaty soil, add 5 grams of recently slaked lime and 200 cc.
water ; connect the flask by means of a delivery-tube with a wash-
bottle containing lime-water and observe the results.

264 SOILS AND FERTILIZERS

33. Mad. — Test a sample of marl for lime and carbon dioxide,
as directed in Experiments 16 and 17. Observe the nature of the
insoluble residue. Test the marl with litnms paper.

34. Testing Land Plaster. — Test for carbon dioxide as directed
in Experiment 17. There should be but little carbon dioxide in
the best grades of land plaster. Digest i gram of gypsum in a test-
tube with 10 cc. dilute hydrochloric acid. Observe the nature and
the amount of insoluble matter.

35. Mixing Fertilizers. — Mix in a large box

200 grams acid phosphate (saved from 28),
50 grams kainit,
50 grams sodium nitrate.
Calculate the approximate composition of this fertilizer and its
trade value.

36. Testing Fertilizers. — Test the above fertilizer for water-
soluble phosphoric acid, as directed in Experiment 27. Test for
nitrogen pentoxide, as directed in Experiment 19.

37. Calculating Results. — A fertilizer is said to contain 3.1 per
cent, ammonia, 12 per cent, bone phosphate of lime and 6 per cent,
potassium sulphate ; calculate the equivalent amounts of nitrogen,
phosphoric acid, and potash.

REVIEW QUESTIONS

I. From what are soils derived ? 2. What are the physical prop-
erties of soils ? 3. Why do soils differ in weight? Arrange clay,
sand, loam, and peat in order of weight per cubic foot. 4. When
wet, what would be the order ? 5. What is the absolute and what the
apparent specific gravity of soils ? 6. Define the terms : Skeleton, fine
earth, fine sand, silt, and clay. 7. What are the physical properties
of clay ? 8. What are the forms of the soil particles ? 9. How do
different t3'pes of soil vary as to the number of soil particles per
gram of soil ? 10. How is a mechanical analysis of a soil made ?

11. Why do certain crops thrive best on definite types of soil?

12. W^hat factors must be taken into consideration in determining
the type to which a soil belongs ? 13. Explain the mechanical
structure of a good potato soil. 14. How does a wheat soil differ in
mechanical structure from a truck soil? 15. A good corn soil is
also a good type for what other crops? 16. How much water is re-
quired to produce an average grain crop, and how do the rainfall
and the water removed in crops during the growing season compare ?
17. In what forms may water be present in soils ? 18. What is bot-
tom water and when may it be utilized by crops ? 19. What is capil-
lary water? 20. Explain the capillar}' movement of water. 21. Ex-
plain how the capillary and non-capillary spaces in the soil ma}- be
influenced by cultivation. 22. What is hydroscopic w^ater and of
what value is it to crops ? 23. What is percolation ? 24. To what
extent may losses occur by percolation ? 25. What are the factors
which influence evaporation ? 26. What is transpiration ? 27. In
what three ways may water be lost from the soil ? 28. Why does
shallow surface cultivation prevent evaporation ? 29. Why is it
necessary to cultivate the soil after a rain ? 30. Explain the move-
ment of the soil water after a light shower. 31. What influence
has rolling the land upon the moisture content of the soil ? 32.
What is subsoiling and how does it influence the moisture content
of soils ? 33. What influence does early spring plowing exert upon
the soil moisture? 34. What is the action of a mulch upon the soil?
35. Why should different soils be plowed to different depths? 36. What
is meant by the permeability of a soil ? 37. How may cultivation
influence permeability? 38. How may commercial fertilizers influ-
ence the water content of soils ? 39. Explain the physical action
of well-prepared farm manures upon the soil and their influence
upon the soil water. 40. What is the object of good drainage ?
41. Why does deforesting a region unfavorably influence the agri-
cultural value of a country ? 42. What are the sources of heat in
soils ? 43. To what extent does the color of soils influence the tem-

266 SOILS AND FERTILIZERS

perature ? 44. What is the specific heat of soils ? 45. To what ex-
tent does drainage influence soil temperature ? 46. How do
manured and unmanured land compare as to temperature ? 47.
What relation does heat bear to crop growth ? 48. What materials
impart color to soils? 49. What is the effect of loss of organic
matter upon the color of soils ? 50. What materials impart taste to
soils? Odor? 51. What effect does a weak current of electricity
have upon crop growth ? 52. Do all soils possess the same power
to absorb gases? Why? 53. What is agricultural geology? 54.
What agencies have taken part in soil formation? 55, How does
the action of heat and cold aid in soil formation? 56. Explain the
action of water in soil formation. 57. What is glacial action, and
how has it been an important factor in soil formation? 58. Ex-
plain the action of vegetation upon soils. 59. How has the action
of micro-organisms aided in soil formation ? 60. Explain the
terms : Sedentary, transported, alluvial, colluvial, volcanic, and
windformed soils. 61. What is feldspar and what kind of soil
does it produce ? 62. Give the general composition of the follow-
ing rocks and minerals and state the quality of soil which each
produces: Granite, mica, hornblende, zeolites, kaolin, apatite, and
limestone. 63. What elements are liable to be the most deficient
in soils ? 64. Name the acid- and base-forming elements present
in soils. 65. What are the elements most essential for crop growth ?
66. State some of the different wa^-s in which the elements present
in soils combine. 67. Why is it customary to speak of the oxides of
the elements and to deal with them rather than with the elements ?
68. Do the elements exist in the soil in the form of oxides? 69.
What are double silicates ? 70. In what forms does carbon occur
in soils? 71. Is the soil carbon the source of the plant carbon ?
72. What can you say regarding the occurrence and importance of
the sulphur compounds ? 73. What influence would o. 10 per cent,
chlorine have upon the soil? 74. In what forms does phosphorus
occur in soils? 75. What is the principal form in which the nitro-
gen occurs in soils ? 76. What can be said regarding the hydrogen
and oxygen of the soil? 77. State the principal forms and the
value as plant food of the following elements : Aluminum, potas-
sium, calcium, sodium, and iron. 78. For plant food purposes,
what three divisions are made of the soil compounds ? 79. Why
are the complex silicates of no value as plant food ? 80. Give the
relative amounts of plant food in the three classes. 81. How is a
soil analysis made ? 82. What can be said regarding the economic
value of a soil analysis ? 83. What are some of the important facts
to observe in interpreting results of soil analysis ? 84. Under what
conditions are the results most valuable ? 85. Do the terms volatile
matter and organic matter mean the same ? 86. How may organic

REVIEW QUESTIONS 267

acids be employed in soil analysis ? 87. Why are dilute organic
acids used ? 88. Is the plant food equally distributed in both surface
and subsoil ? 89. Do different grades of soil particles, from the
same soil, have the same composition? 90. What are "alkali
soils"? 91. Why is the alkali sometimes in the form of a crust?
92. Are all soils with white coating strongly alkaline? 93. Give
the treatment for improving an alkali soil. 94. How may a small
" alkali spot " be treated? 95. What are the sources of the organic
compounds of soils? 96. How may the organic compounds of the
soil be classified ? 97. Explain the term humus. 98. How is the
humus of the soil obtained ? 99. W^hat is humification ? What is
a humate ? How are humates produced in the soil ? 100. Explain
how different materials produce humates of different value. loi.
Arrange in order of agricultural value the humates produced from
the following materials : Oat straw, sawdust, meat scraps, sugar,
clover. 102. Of what value are the humates as plant food ? 103.
How much plant food is present in soils in humate forms? 104.
What agencies cause a decrease of the humus content of soils ?
105. To what extent does humus influence the physical properties of
soils? 106. What is humic acid ? 107. What soils are most liable
to be in need of humus ? When are soils not in need of humus ?
108. In what ways does the humus of long-cultivated soils differ
from that of new soils ? 109. How may different methods of
farming influence the humus content of soils ? no. What may be
said regarding the importance of nitrogen as plant food? in.
W^hat are the functions of nitrogen in plant nutrition? 112. How
may the foliage indicate a lack or an excess of this element ? 113.
In what three ways did Boussingault conduct experiments relating
to the assimilation of the free nitrogen of the air? 114. What were
his results ? 115. What conclusions did Ville reach? 116. Give
the results of Lawes and Gilbert's experiments. 117. How did
field results compare with laboratory experiments? 118. In what
ways were the conditions of field experiments different from those
conducted in the laboratory? 119. Give the results of Hellriegel's
and Wilfarth's experiments. 120. What is noticeable regarding
the composition of clover root nodules ? 121. Of what agricultural
value are the results of Hellriegel ? 122. What is the source of the
soil's nitrogen ? 123. How may the organic nitrogen compounds
of the soil vary as to complexity ? 124. To what extent may the
nitrogen in soils var>^ ? 125. To what extent is nitrogen removed
in crops ? 126. To what extent are nitrates, nitrites, and ammo-
nium compounds found in soils? 127. To what extent is nitrogen
returned to the soil in rain-water. 128. How may the ratio of
nitrogen to carbon vary in soils ? Of what agricultural value is this
ratio? 129. Under what conditions do soils gain in nitrogen con-
tent? 130. What methods of cultivation cause the most rapid de-

268 SOILS AND FERTILIZERS

cline in the nitrogen content of soils? 131. What is nitrification?
132. What are the conditions necessary- for nitrification? and
what are the food requirements of the nitrifying organism? 133.
Why is oxygen necessary for nitrification ? 134. How does tem-
perature, moisture, and sunHght influence this process? 135.
What part does calcium carbonate and other basic compounds take
in nitrification ? 136. How is nitrous acid produced? 137. What
is denitrification ? 138. What other organisms are present in soils
besides those which produce nitrogen pentoxide, nitrogen trioxide,
and ammonia? 139. What chemical products do these various or-
ganisms produce ? 140. Why are soils sometimes inoculated with
organisms? 141. Why does summer fallowing of rich lands cause
a loss of nitrogen? 142. What influence have deep and shallow
plowing, and spring and fall plowing upon the available soil
nitrogen ? 143. Into what three clavSses are nitrogenous fertilizers
divided? 14.4. How is dried blood obtained ? What is its compo-
sition, and how is it used? 145. What is tankage? How is it
used, and how does it differ in composition from dried blood ?
146. What is flesh meal ? 147. What is fish scrap fertilizer, and
what is its comparative value ? 148. What seed residues are used
as fertilizer ? What is their value ? 149. What method is em-
ployed to detect the presence of leather, hair, and wool waste in
fertilizers? Why are these materials objectionable? 150. How
may peat and muck be used as fertilizers? 151. What is sodium
nitrate ? How is it used, and what is its value as a fertilizer? 152.
How does ammonium sulphate, as a fertilizer, compare in value
with nitrate of soda ? 153. What is the difference between the
nitrogen content and the ammonia content of fertilizers? 154.
What is fixation ? Give an illustration. 155. To what is fixation
due? 156. What part does liunnis take in fixation ? 157. Why do
soils differ in fixative power ? Why are nitrates not fixed? 158.
Why is fixation a desirable property of soils? 159. Why is it
necessary to study the subject of fixation in the use of manures ?
160. Why are farm manures variable in composition? 161. What
is the distinction between the terms stable manure and farm-yard
manure? 162. About what ])er cent, of nitrogen, phosphoric acid,
and potash is present in ordinary manure? 163. Coarse fodders
cause an increase of what element in the manure? 164. What four
factors influence the composition and value of manure? 165.
What influence do absorbents have upon the composition of
manures? 166. What advantages result from the use of peat and
muck as absorbents? 167. Compare the value of manure produced
from'clover with that from timothy hay. 168. How may the value of
manure be determined from the nature of the food consumed ?
169. To what extent is the fertility of the food returned in the
manure? 170. Is much nitrogen added to the body during the

REVIEW QUESTIONS 269

process of fattening? 171. Explain the course of the nitrogen of
the food during digestion and the forms in which it is voided in
the manure. 172. Compare the solid and liquid excrements as to
constancy of composition and amounts produced. 173. What is
meant by the manurial value of food ? 174. Name five foods with
high manvirial values; also five with low manurial values. 175.
What is the usual commercial value of manures compared vnth
commercial fertilizers? 176. How does the manure from young
and from old animals compare as to value? 177. How much
manure does a well-fed cow produce per day? 178. What are the
characteristics of cow manure? How do horse manure and cow
manure differ as to composition, character, and fermentability ?
179. What are the characteristics of sheep manure? 180. How
does hen manure differ from any other manure ? 181. Why should
the solid and liquid excrements be mixed to produce balanced
manure? 182. What volatile nitrogen compound may be given off
from manure ? 183. What may be said regarding the use of humar-
excrements as manure ? 184. Is there any danger of an immediate
scarcity of plant food to necessitate the use of human excrements
as manure ? 185. To what extent may losses occur when manures
are exposed in loose piles and allowed to leach for six months ?
186. What two classes of ferments are present in manure? 187.
Explain the workings of the two classes of ferments found in
manures. 188. How much heat may be produced in manure dur-
ing fermentation ? 189. Is water injurious to manure? 190. How
should manure be composted ? What is gained? 191. How does
properly composted manure compare in composition with fresh
manure? 192. Explain the action of calcium sulphate in the pre-
servation of manure. 193. How does manure, produced in open
barnyards, compare in composition with that produced in covered
sheds? 194. When may manure be taken directly to the field and
spread? 195. How may coarse manures be injurious to crops?
196. What is gained by manuring pasture land? 197. Is it econom-
ical to make a number of small manure piles in a field ? Why ?
198. At what rate per acre may manure be used? 199. To
what crops is it not advisable to add stable manure? 200. How
do a crop and a manure produced from that crop compare in
manurial value? 201. Why do manures have such a lasting effect
upon soils? 202. Why does manure from different farms have
such variable values and composition ? 203. In what seven ways
may stable manures be beneficial ? 204. What may be said regard-
ing the importance of phosphorus as plant food ? What function
does it take in plant economy ? 205. How much phosphoric acid
is removed in ordinary farm crops ? 206. To what extent
is phosphoric acid present in soils? 207. What are the sources
of the soil's phosphoric acid ? 208. What are the commer-

270 SOILS AND FERTILIZERS

cial sources of phosphate fertilizers ? 209. Give the four cal-
cium phosphates and their relative fertilizer values. 210. Define
reverted phosphoric acid. 211. Define available phosphoric acid.
212. In what forms do phosphate deposits occur? 213. State the
general composition of phosphate rock. 214. Explain the process
by which acid phosphates are made. Give reactions. 215. How
is the commercial value of phosphoric acid determined? 216.
What is basic phosphate .slag and what is its value as a fertilizer ?
217. What is guano? 218. How do raw bone and steamed bone
compare as to field value ? As to composition ? 219. What is dis-
solved bone? 220. How is bone-black obtained, and what is its
value as a fertilizer? 221. How are phosphate fertilizers applied to
soils? In what amounts? 222. How may the phosphoric acid of
the soil be kept in available condition ? 223. What is the function
in plant nutrition of potassium? 224. To what extent is potash
removed in farm crops ? 225. To what extent is pota.sh present in
soils? 226. What are the sources of the soil's potash ? 227. What
are the various sources of the potash used for fertilizers? 228.
What are the Stassfurt salts, and how are they supposed to have
been formed? 229. What is kainit ? 230. How nuich potash is
there in hard-wood ashes ? 231. In what ways do ashes act on soils ?
232. How do unleached ashes differ from leached ashes? 233.
What is meant b}^ the alkalimetry of an ash? 234. Of what value,
as fertilizer, are hard- and soft-coal ashes ? 235. What is the fer-
tilizer value of the ashes from tobacco stems ? 236. Cottonseed
hulls? 237. Peat-bog ashes? 238. Saw-mill ashes? 239. Lime-
kiln ashes? 240. How is the commercial value of potash deter-
mined? 241. How are potash fertilizers used? 242. Why is it
sometimes necessarv' to use a lime fertilizer in connection with a
potash fertilizer? 243. What can be said regarding the importance
of lime as a plant food ? 244. To what extent is lime removed in
crops? 245. To what extent do soils contain lime ? 246, What are
the lime fertilizers ? 247. Explain the phy.sical action of lime fer-
tilizers. 248. Explain the action of lime on heavy clays. 249. On
sandy soils. 250. In what ways, chemically, do lime fertilizers
act? 251. How may lime aid in liberating potash? 252. What is
marl ? 253. How are lime fertilizers applied ? 254. What is the
resiilt when land plaster is used in excess? 255. Explain the
action of salt on soils ? 256. When would it be desirable to use
salt as a fertilizer? 257. Is soot of any value as a fertilizer? Ex-
plain its action. 258. Are sea-weeds of any value as fertilizer? 259.
What is a commercial fertilizer ? An amendment ? 260. To what
does the commercial fertilizer industry owe its origin? 261. Why
are commercial fertilizers so variable in composition ? 262. Ex-
plain how a commercial fertilizer is made. 263. Why are the
analysis and inspection of fertilizers necessary? 264. What are the

REVIEW QUESTIONS 27 I

usual forms of nitrogen in commercial fertilizers ? 265. Of phos-
phoric acid and potash ? 266, How is the value of a commercial fer-
tilizer determined ? 267. What is gained by home mixing of fer-
tilizers ? 268. What can be said about the importance of tillage
when fertilizers are used? 269. How are commercial fertilizers
sometimes injudiciously used? 270. How may field tests be con-
ducted to determine a deficiency in available nitrogen, phosphoric
acid, or potash? 271. To determine a deficiency of two elements?
272. How are the preliminary results verified? 273. Why is it
essential that field tests with fertilizers be made ? 274. Under Avhat
conditions does it pay to use commercial fertilizers? 275. What is
the result when commercial fertilizers are used in excessive
amounts? 276. Under ordinary conditions, what special help do
the following crops require : Wheat, barley, corn, potatoes, man-
gels, turnips, clover, and timothy? 277. In what ways do commer-
cial fertilizers and farm manures dififer ? 278. Does the amount of
fertility removed by crops indicate the nature of the fertilizer re-
quired? In what ways are plant ash analyses valuable ? 279. Ex-
plain the action of plants in rendering their own food soluble. 280,
Why do crops differ as to their power of procuring food? 281.
Why is wheat less liable to need potash than nitrogen? 282. What
position should wheat occupy in a rotation? 283. In what ways do
wheat and barley differ in feeding habits? 284. What can be said
regarding the food requirements of oats? 285. Corn removes from
the soil twice as much nitrogen as a wheat crop, yet a wheat crop
usually thrives after a corn crop. Why? 286. What help is corn
most liable to need in the way of food? 287. What position should
flax occupy in a rotation? 288. On what soils does flax thrive best?
289. What is the essential point to observe in the manuring of po-
tatoes? 290. What kind of manuring do sugar-beets require? 291.
Why should the manuring of mangels be different from that of tur-
nips? 292. What may be said regarding the food requirements of
buckwheat and rape? 293. What kind of manuring do hops and
cotton require? 294. What kind of manuring is most suitable for
leguminous crops? 295. What is the object of rotating crops? 296.
Should the whole farm undergo the same rotation system? 297.
W^hat is meant b}- soil exhaustion? 298. What are the nine impor-
tant principles to be observed in a rotation? 299. Explain why it
is essential that deep and shallow rooted crops should alternate.
300. Wliy is it necessary that the humus be considered in a rota-
tion? 301. What is the object of gro\\-ing crops of dissimilar feeding
habits? 302. How may crop residues be used to the best advantage?
303. In what ways may a decline of soil nitrogen be prevented by
a good rotation of crops? 304. In what ways do different crops and
their cultivation influence the mechanical condition of the soil?
305. How may the best use be made of the soil water? 306. How

272 SOILS AND FERTILIZERS

may a rotation make an even distribution of farm labor? 307. How
are manures used to the best advantage in a rotation? 308. In what
other ways are rotations advantageous? 309. What may be said re-
garding long- and short-course rotations? 310. How is the conser-
vation of fertilitv best secured? 311. Why does the use made of
crops influence fertility? 312. W'hat are the essential points to be
observed in the two systems of farming compared in Section 323?
313. Is it essential that all elements removed in crops should be re-
turned to the soil in exactly the amounts contained in the crops?
Why? 314. How does manure influence the inert matter of the
soil? 315. What general systems of farming best conserve fertility?
316. Under what conditions may farms be gaining in reserve fer-
tility? 317. Why in continued grain culture does the loss of nitro-
gen from a soil exceed the amount removed in the crop?

CORRECTIONS

Page 25, line 19, for "three months," read "two months."

Page 28, line 18, after soil, add : "absorbed from the air."

Page 28, line 26, add : "when reduced below 4 per cent."

Page 64, line 5, for "one-half," read "one-tenth."

Page 72, line 18, read"94," not "96."

Page 150, line 2, read "clover hay nitrogen, 35," not "45."

Page 187, under Flax, transpose "19" and "8."

INDEX

Absorbents 143

Absorption of heat by soils 42

Absorptive power of soils 46

Acids in plant roots 228

Aerobic ferments 121, 158

Agricultural geology 49

Agronomy 9

Albite 56

Alkaline soils 87

Aluminum of soils 66

Amendments 205

Ammonium compounds 115

salts 136

Anaerobic ferments 159

Analysis of soil, how made-. 73, 74

of soil, value of 76, 80

Apatite rock 58

Application of fertilizer 222

of manures 163, 165

Arrangement of soil particles 16

Ashes 191

action of, on soils 192

testing of 193

Assimilation of nitrogen 102

of phosphates 173

Atmospheric nitrogen 104

Atwater . . ■■ 108, 132

Availability of plant food 79

Available phosphates 177, 184

nitrogen 113, 133

Barley, fertilizers for 223

food requirements of • • • ■ 231

Blood, dried 1 28

Bone, dissolved 183

fertilizers 181

Boneash 182

Bone-black 183

Boussingault's experiments

4, 104, 105, 106

Calcium an essential element ..196
carbonate and nitrific'on • 123

compounds of soils 67

phosphate 58, 1 75

Capillarity 27

and cultivation 31

Carbon of soil 63

sources for plant growth . -63

Chlorine of soil 64, 87

Clay, formation of 58

particles 13

Clover as manure 134

nitrogen returned by

108, 118, 253

root nodules no

manuring of- 194, 199, 224,237

Coal ashes 193

Color of plants, influenced by

nitrogen 104

of soils 45

Combination of elements in soils- 61

Commercial fertilizers 205, 225

and tillage 216

abuse of 216

extent of use 205

field tests with 218

home mixing of 214

inspection of 209

mechanical condition of -210

nitrogen of 210

phosphoric acid of 211

potash of 212

proper use of 217

valuation of 213

Composition of soils 83, 85

Composting manures 160

Corn , fertilizers for 223

food requirements of - ■ - • 232

and manure 167

Cotton, fertilizers for 235

274

INDEX

Cottonseed meal 132

Cow manure 152

Crop residue 239

Cultivation after rains 33

shallow surface 31

Davy, work of 3

Dissolved bone 1 83

Distribution of soils 54

Denitrification 123

De Saussure, work of 3, 104

Drainage 41, 43

Dried blood 128

Dyer 80

Early truck soils 19

Electricity of soil 47

Evaporation 30

Excessive use of fertilizers 222

Experiments 259

Fallow fields 126

Fall plowing 35

Farm manures 141, 171

Farm manures and commercial

fertilizers 224

Feldspar 55, 209

Fermentation of manures 158

Fertility, conservation of 249

removed in crops 227

Fertilizers, amount to use 222

influence upon soil water. 39

on barley 231

on wheat 230

Field tests wath fertilizers 218

Fine earth 12

Fish fertilizer 132

Fixation 1 38

Flax, food requirements of 233

soils 20

Flesh meal 131

Forest fires 97

Formation of soils 49, 54

Form of soil particles 14

Fruit soils 20

Gains. of humus 100

of nitrogen 117

Glaciers, action of 51

Grain soils 22

Granite 58

Grass lands, fertilizers for 236

Grass soils 22

Guano 181

Gypsum and manure 161

Heat and crop growth 44

produced by manures 160

of soil 42, 43

Heiden 156, 161

Hellriegel 25, 30, 109

Hen manure 154

Hog manure 154

Hops, fertilizers for 236

Horse manure 152

Human excrements 156

Humates 91

as plant food 95

Humification 92

Humic acid 98

Humic phosphates 92, 184

Humus 91

active and inactive 100

causes fixation 139

composition of 94

Income and outgo of fertility..

250, 253

Injury of coarse manures ••40, 164

Insoluble matters of soils 70, 71

Iron compounds of soil 68

Kainit 190, 206, 212

Kaolin 58

King 32, 35, 36

Lawesand Gilbert.. 7, 107, 229. 230

Leached ashes 192

Leaching of manure 157

Leather 133

Leguminous crops,fertilizers for, 237
as manure 134

INDEX

275

Liebig 6, 7, 156, 227

Liquid manure 147

Lime, action on soils 198

amount of, in soils 197

amount removed in crops • 1 97

excessive use of 201

fertilizers 196

indirect action of 199

physical action of 201

use of 20 r

and acid soil 198

and clover 1 99

Loam soils 24

Loss of fertility in grain farming, 252

Loss of humus 97

of nitrogen 117, 126

Losses from manures 157, 158

Magnesium compounds of soils • . 68

salts as fertilizers 202

Mangels, fertilizers for 224

Manure from cow 152

hen 154

hog 154

horse 152

sheep 153

Manures, farm 141

influenced by foods 144

use of, in rotations 243

value of J 70

and soil water 39, 98

Manurial value of foods 149

Manuring of crops 166

pasture land 164

Marl 200

Mechanical analysis of soils 17

condition of fertilizers. • -210
Methods of farming, influence

of, upon fertility 100

Mica 57

Micro-organisms and soil for-
mation 49. 53

Mixing manures 155

Movement of water after rains.. 33
Mulching 36

Nitrate of soda 135

Nitric nitrogen 136

Nitrification 119

conditions necessary for 120

and sunlight 122

and plowing 127

Nitrogen assimilation 104

as plant food 102

compounds of soil 65

deficiency of, in soil 219

losses of, from soil 117

ratio of, to carbon 116

removed in crops 114

of commercial fertilizers. 210

amount of, in soils 113

as organic forms 112

as nitrates 114

availability of 113

forms of 112

origin of 1 1 1

Nitrogenous manures 128

Number of soil particles 17

Odor of soils 46

Organic acids, action of, upon

soils 79, 80

Organic compounds of soil,

classification of 90

source of 90

Organic nitrogen 128, 133

Organisms, ammonia-producing, 1 23

of soil 124

nitrifying 1 20

products of 125

Osborne 1 8

Orthoclase 56

Oxidation in soil 43

Peat 134, 144

Percolation 28

Permeability of soils 38

Phosphate fertilizers 172

use of 183

rock 177

slaar 180

276

INDEX

Phosphoric acid of commercial

fertilizers 211

acid in soils 174

acid, deficiency of 220

acid removed in crops 173

Phosphorns compounds of soils. .64

Physical property of soils 10, 47

modified by farming lor

Plant food, classes of 69, 70

ash and fertilizers 226

Plowing, depth of 37

fall 35

spring 36

influences nitrification. . . 127

Potash fertilizers 186

fertilizers, use of • . • • .... 194
of commercial fertilizers . 2 1 2

in soils 188

in soils, sources of 188

removed in crops 187

and lime, joint use of 194

Potassium compounds of soil ... 67

Potato, fertilizers for 224

food requirements of 233

soils 19

Questions 265

Rainfall and crop production ... 25

Rape, food requirements of 235

References 255, 257

Reverted phosphoric acid 176

Roberts 37, 157

Rocks, composition of 55, 59

Rock disintegration 49

Rolling 34

Roots, action on soil 228

Rotation of crops 238, 254

of crops, principles in-
volved 239

length of 244

problems 248

and farm labor 243

and humus 241

and insects 244

and soil nitrogen 241

Rotation and soil water 242

and weeds 244

Salt as a fertilizer 202

Sand, grades of 13. H

Seaweeds as fertilizers 203

Sedentar}' soils 54

Seed residues 132

Sheep manure 153

Silicon and silicates 163

Silt particles 14

Size of soil particles 12

Skeleton of soils 12

Small manure piles 165

Sodium compounds of soil 68

Soil, composition of 83, 85

exhaustion 238

types 19

Soot 203

Specific gravity of soil 12

Spring plowdng 36

Stockbridge 12, 25

Stock farming and fertility 254

Storer 63, 1 29

Stutzer 133

Sub-soiling 35

Sugar beets, fertilizers for 234

beet soils 21

beets and farm manures. .167

Sulphate of potash 190

Sulphur compounds of soil 64

Superphosphates 178

Tankage 130

Taste of soils 46

Temperature of soils 42

Tests with fertilizers 218

Thaer, work of 3

Tobacco, manuring of 167

Tobacco stems 193

Transported soils 54

Truck farming and fertilizers ..221
Turnips, fertilizers for 224

Ville 107

Volcanic soils 55

INDEX

277

Volume of soils 12

Voorhees 214

Water, action of, upon rocks and

soils 50

bottom 26

capillary 27

capillary, conservation of

31, 32, 33

hydroscopic 28

losses by evaporation 30

losses by transpiration 30

of soil 26, 41

of soil influenced —

by drainage 41

plowing.. 35, 36
forest regions, 4 1
manures. .39, 98

Water of soil influenced —

by mulching. • • .36

rolling ... 34

subsoiling • • -35

required by crops 25

W^arington 119,121, 123, 229

Weeds, fertility in 203

Weight of soils 11

Wheat, fertilizers for 223

food requirements of - . • . 229

soils 22, 23

Whitney 17, 47

Wilfarth 109

Wood ashes 191

Wool waste 204

Zeolites 57, 139

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