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Full text of "Principles of agricultural chemistry"

PRINCIPLES OF AGRICULTURAL CHEMISTRY 



g 

^| Published by ^ 

M The Chemical Publishing Co. >j 

M Easton, Penna. 

Publishers of Scientific Books 

g Engineering Chemistry Portland Cement 

** Agricultural Chemistry Qualitative Analysis g 

g Household Chemistry Chemists' Pocket Manual g 

;; Metallurgy, Etc. f< 



Principles of Agricultural Chemistry 



BY 



G. S. FRAPS, Ph.D. 

Associate Professor of Agricultural Chemistry, Agricultural and 

Mechanical College of Texas. Chemist, Texas 

Experiment Station. State Chemist 



E ASTON, PA. 

THE CHEMICAL PUBLISHING CO. 
1913 



LONDON, ENGLAND 

WILLIAMS & NORGATE 

14 HENRIETTA STREET, COVENT GARDEN, W. C. 



COPYRIGHT, 1913, BY EDWARD HART. 



Preface. 



In this book the author aims to present the fundamental prin- 
ciples of agricultural chemistry. The point of view is that of the 
chemist dealing with agricultural problems; the attempt is made 
to emphasize chemical methods of investigation, and inculcate 
scientific habits of thought. Details are omitted so far as they 
are not necessary to the proper treatment of the subject. Practi- 
cal applications, which are necessarily local, are left out as much 
as possible. The book thus treats of agricultural chemistry 
rather than of chemical agriculture. It attempts to give a com- 
prehensive view of the subject, and to prepare the student for a 
more detailed study of its various phases. 

This book is based upon lectures given for a number of years 
.to students in Agriculture at the Agricultural and Mechanical 
College of Texas. A number of references are given, some of 
which do not refer to the articles in which the facts were first 
published, but to articles of interest or of value to the student, 
which may contain numerous references to the literature of the 
subject. It was not deemed desirable nor was it practical, to 
give references for all the statements made in the text. 

The author is fully aware of the fact that there is room for 
differences of opinion as to what should be treated or omitted in 
a work of this character. He also realizes the difficulty of avoid- 
ing errors, arid will be grateful to the reader who may bring 
errors to his attention, or offer suggestions for the improvement 
of the book. 

Valuable assistance has been received from Mr. S. E. Asbury, 
Assistant State Chemist, and especially Dr. C. P. Fountain, 
Professor of English. 

Agricultural and Mechanical 

College of Texas, 
Aug. 30, 1912. College Station. 



271665 



Contents. 



CHAPTER PAGE 

I. Introduction 7 

II. Essentials of Plant Life 9 

III. The Plant and the Atmosphere 35 

IV. -Origin of Soils 53 

V. Physical Composition and Classes of Soils 79 

VI. Physical Properties of Soils 101 

VII. The Soil and Water 119 

VIII. Chemical Constituents of the Soil 149 

IX. Chemical Composition of the Soil 167 

X. Active Plant Food and Water Soluble Constituents of the Soil 180 

XI. Chemical Changes in the Soil 204 

XII. Soil Deficiencies 244 

XIII. Losses and Gains by the Soil 271 

XI V. Manure 280 

XV. Sources and Composition of Fertilizers 293 

XVI. Purchase and Use of Fertilizers 312 

XVII. Constituents of Plants 346 

XVIII. Composition of Plants 379 

XIX. Digestion 392 

XX. -Utilization of Food 411 

XXL The Maintenance and Fattening Rations 435 

XXII. Feeding Work Animals and Growing Animals 453 

XXIII. Feeding Milk Cows 461 

XXIV. Calculation of Rations 474 

Index 482 



Principles of Agricultural Chemistry 



CHAPTER I. 

INTRODUCTION. 

The object of agriculture is the profitable production of useful 
plants and animals. Agriculture is therefore an art and not a 
science, since an art relates to something to be done, a science 
to something to be known. We may, however, speak of the 
science of agriculture, meaning the body of organized knowledge 
appertaining to this art. 

Success in agriculture depends upon ability to manage men and 
things, to take advantage of markets and local conditions, as well 
as upon a knowledge of how to produce plants and animals, and 
also upon skill in transforming this knowledge into practice. 
That is to say, practical agriculture is a business and business 
methods must be followed in order to succeed in it. 

More than any other pursuit, agriculture is underlaid by a body 
of complex scientific principles, many of which are applied, know- 
ingly or unknowingly, by the practical farmer. 

Agricultural Experiment Stations. The importance of agricul- 
ture has been recognized by civilized governments in the establish- 
ment of agricultural experiment stations and agricultural colleges. 
The oldest, and the most renowned experiment station, that at 
Rothamsted, England, is not a State institution, but was estab- 
lished, conducted, and endowed by Sir John Lawes, the work 
having been begun on a small scale in 1828. Nearly all of the 
experiment stations have been established since 1870; most of 
those in this country date from 1876 to 1882. In addition to con- 
ducting a great variety of experiments along agricultural lines, 
these stations make analyses of soils, fertilizers, feeding stuffs, 
etc. There is at least one experiment station in each State of the 
United States and, in addition, the United States Department of 
Agriculture (U. S. D. A.) ; these agencies are doing a great deal 
of work for the advancement of agriculture. While our knowl- 



2 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

edge of the principles of agriculture is largely due to the work of 
the experiment stations, it is chiefly due, let it be said, to the work 
of chemists. 

Agricultural Chemistry. Agricultural chemistry is the applica- 
tion of chemistry and chemical methods of investigation to 
agricultural problems. It deals, on the one hand, with funda- 
mental causes of phenomena, and, on the other, with practical ap- 
plications to agricultural practice. The chemist was the first of 
the scientists to turn his attention to agriculture, and his results 
were so fundamental, and practically important, and the science 
of chemistry was capable of such broad application to agriculture, 
that for a long time the great body of scientific knowledge re- 
garding agriculture was known as agricultural chemistry. 
The chemist has not hesitated to avail himself of the sciences of 
geology, mineralogy, physics, botany, or such other sciences as 
were needed in the solution of the problems at hand. Many of the 
problems of agriculture are complex, and their solution requires 
the harmonious cooperation of several sciences. Take, for 
example, the transformation of organic nitrogen to nitrates, a 
very important process in the soil. This is a chemical change, 
accomplished by means of micro-organisms, and both chemistry 
and biology are necessary to give a complete explanation of this 
phenomenon, though the explanation has been largely worked out 
by the chemist. 

Scope of the Subject. In a wide sense, agricultural chemistry 
signifies the study of all the scientific laws involved in plant and 
animal growth, whatever the several sciences which may be in- 
volved. We may look at this subject as a fabric in which 
chemistry is so interwoven in warp and woof that, if removed, 
the pattern would be destroyed ; if the other sciences were re- 
moved, the pattern would be very imperfect. 

It shall be our object to deal with the principles ascertained 
in the application of chemistry to agriculture, taking up the sub- 
ject from the view-point of the chemist. In particular we shall 
attempt to indicate the methods which have been followed in 
securing important results. Agricultural science is founded upon 



INTRODUCTION 3 

and grows by experiments. An experiment is a question put to 
nature. It matters not what theories or lack of theories are be- 
hind the experiment, if the question is carefully and skilfully 
put, and if we see with a clear eye, not dazed by prejudgment, the 
answer will advance our knowledge. The knowledge of how ex- 
periments have been planned helps us to plan them for ourselves ; 
the knowledge of how a certain problem has been solved keeps us 
from regarding the knowledge so secured as dogmatic, and gives 
us an opportunity to test it for ourselves if we so desire. The 
scientific investigator cannot accept the conclusions of others at 
their face value; he must examine the evidence offered, and 
satisfy himself that the evidence justifies the conclusion. 

Division of the Subject. Agriculture falls naturally into two 
divisions the production of plants, and the production of 
animals. Usually in the case of plants, only a portion of the 
plant is desired, such as the grain ot wheat or corn, the tubers 
of potatoes, etc. The remainder is considered as a by-product 
and such disposition is made of it as appears feasible. The dis- 
position of the by-product has considerable effect upon the 
fertility of the soil, or the profits of agriculture. In some cases, 
as in the preparation of hay, the entire plant is utilized. In other 
cases, by-products result in the preparation required before the 
product can be placed on the market, such as threshing of wheat 
or rice, husking or shelling of corn, etc. 

The study of plant production involves a study of the condi- 
tions which are favorable to plant life, the composition and prop- 
erties of the atmosphere and the soil, the maintenance of soil 
fertility, fertilizers, methods of soil treatment, etc., as well as 
the composition and properties of the plant products, and a study 
of such chemical changes as are involved in their production or 
preparation for market. 

The study of animal production involves a study of the prin- 
ciples of animal growth and nutrition, the composition and prop- 
erties of feeding stuffs, their preparation or preservation, and the 
methods of feeding for different purposes, such as meat, milk, 
wool, etc. 



4 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

We will begin the study of agricultural chemistry with a study 
of the chemical laws governing the production of plants. We 
must study the conditions best suited to the growth of plants ; 
ascertain how these conditions are filled by the air and soil in 
which they grow ; learn how to overcome unfavorable conditions 
in the soil, and how to maintain and increase its productiveness. 
In addition, we must study the composition of the plant. 

Agriculture Primarily the Production of Organic Matter. 

Agriculture deals primarily with the production of organic mat- 
ter. Organic matter, for the purpose of the agriculturalist, may 
be defined as the compounds of carbon which possess chemical 
energy. In agriculture, inorganic compounds of carbon and other 
bodies are caused to combine with the energy of the sun, so as to 
produce organic compounds containing energy, which may supply 
heat or energy for the use of man or other animals, which may 
serve as fuel, or be used for other purposes. The primary object 
of agriculture is thus to store up the energy of the sun. The 
production of organic matter is accomplished by means of plants. 

Products of Plant Life. The various soil and atmospheric 
agencies, acting upon the life within the seed, produce a plant 
built up by sunshine, water, carbon dioxide from the air, and sev- 
eral mineral substances from the earth. The plant is composed 
mostly of complex organic substances, rich in carbon, and con- 
tains a comparatively small amount of material withdrawn from 
the soil. It is suitable for the food of animals, while the ma- 
terials from which it is built are not. If dried and heated 
sufficiently, the plant burns and gives off heat. 

It has been found that the heat which is secured in the burning 
of plants, or which can be utilized as heat or other forms of 
energy by animals which consume them, comes from the sun. The 
energy of the sun is used to decompose carbon dioxide, water, 
and nitrates, and to form complex organic compounds. These 
bodies then contain stores of energy which can be utilized by 
animals or in other ways. Plants thus store up the energy of the 
sun, and may also be regarded as media for furnishing animals 



INTRODUCTION 5 

with the sun's energy. All energy utilized by plants or animals 
thus comes directly or indirectly from the sun. 

We have used the term ''organic" in connection with the com- 
pounds formed in plants. It was believed in the beginning of the 
1 9th century that organic bodies, such as starch, sugar, urea, etc., 
differed greatly in chemical nature from inorganic bodies, and 
could only be formed under the influence of mysterious life- 
forces. But in 1820 Wohler prepared a product of animal life 
found in the urine, called urea, from a purely inorganic body, am- 
monium cyanate. The supposed barrier between organic and in- 
organic substances was thus broken down; great numbers of 
organic compounds have since, been prepared, some of which 
occur in nature, and the chemist now hardly places bounds to the 
possibilities of organic synthesis in the laboratory. It is well 
known that organic and inorganic bodies obey the same laws, 
though on account of the size and complexity of the subject, 
organic chemistry is still treated separately. 

As far as agricultural chemistry is concerned, there is a wide 
difference between organic and inorganic bodies. Organic com- 
pounds may serve as food for animals, but inorganic do not. On 
the other hand, inorganic bodies serve as food for plants ; but to 
only a very limited extent, if at all, do plants make use of organic 
bodies. With the aid of light, plants build up organic bodies 
which possess chemical energy, from inorganic bodies which do 
not possess chemical energy. For the student of agriculture, 
organic compounds are compounds of carbon which possess 
chemical energy, and they are usually the products of plants or 
animals. 

Conditions of Plant Life. The conditions necessary for the 
production of organic matter by green plants may be summed up 
briefly as follows: 

(1) Light. 

(2) Favorable Temperature. 
' (3) Water. 

(4) Certain elements in certain forms of combination. 
If any of these conditions are unfavorafre, the plant will suffer 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 

and perhaps die. The varying needs of different kinds of plants 
and their varying powers of satisfying these needs, permit plants 
to flourish in nature under a great diversity of conditions, as in 
the tropics, or in arctic regions, in shade or in sunshine, in water 
or in deserts. The conditions of temperature, light, or water 
favorable to cultivated plants are more limited than those of wild 
plants, but still the range is wide. 

The simple conditions we have named are rendered more com- 
plex by the varying degree in which different classes of plants 
require them, and the varying powers they have of supplying their 
needs. The varying powers of soils to supply the needs of the 
plant growth thereon, and the necessity of maintaining the 
fertility of the soil, render the matter still more complex. 

Relation of the Plant to the Atmosphere. The atmosphere has 
its part in supplying some of the conditions for the growth of 
plants, the more important being light, heat, carbon dioxide, and, 
indirectly, water. The atmospheric conditions are less susceptible 
to control than soil conditions; nevertheless, sometimes a partial 
control is established, as temperature and humidity in green 
houses, light in the growth of plants by artificial light or under 
shade, and the prevention of frost by smoke clouds. The 
atmosphere indirectly supplies the plant with small quantities of 
combined nitrogen, through the soil. 

Relation of the Plant to the Soil. The relation of the plant to 
the soil is more complex than its relation to the atmosphere. 
The functions of the soil are primarily to support the plant, sup- 
ply it with water and certain necessary elements, and maintain a 
favorable temperature. These are, however, fulfilled in a very 
complicated manner. 

Methods of Experiment. The methods of studying the problems 
of agricultural chemistry must be varied to suit the end in view. 
At various points we shall bring in experimental evidence in sup- 
port of certain views, thus illustrating by example some of the 
more important methods. The earnest student is advised to study 



INTRODUCTION 7 

the original papers that mark important steps in agricultural 
science. 

The problems of agricultural chemistry are often so complex 
and interrelated as to render their solution very difficult. In the 
study of them, one should endeavor to vary one factor at a time 
and keep the others constant. Let us take, for example, the es- 
sential elements in plants. By chemical analysis we can ascertain 
that plants contain certain elements. Which of these are 
necessary to the plant and which are not? The solution of the 
problem is obtained by growing the plants under the most favor- 
able conditions, with an ample supply of all the elements found in 
the plant except one. If the plant does well, then this one is not 
needed. If it does very poorly, and all the conditions are most 
favorable, then the element is necessary. The difficulties in fol- 
lowing out this method of experiment will be presented later. 

It is obvious that if two variables are present, it would be im- 
possible to tell which one produced a given effect, or what part 
each had in it. The conditions of agricultural experimentation 
are sometimes such that it is difficult to reduce the experiment to 
a variation in one variable, and sometimes proper precautions are 
not taken to eliminate other variables. Take, for example, a field 
experiment on corn, or any other crop. Variables are weather, 
insects, seed, soil, etc. We attempt to eliminate them by sub- 
jecting the entire field to the same conditions, but it is very 
difficult to make all conditions uniform. 

Agricultural investigations must be brought to the test of ac- 
tual conditions. Conditions in the laboratory or in pot experi- 
ments, are often radically different from those which prevail 
in practice. The gap between the two must be bridged by ex- 
periment, rather than by theory. 

Observation and Experience. Agricultural knowledge is 
largely based upon observation and experience. General agricul- 
tural practice is based upon experience, passed on from one 
generation to another. Experience is, indeed, based upon ex- 
periments, though the experiments are not always consciously 



8 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

made, \ery often imperfectly planned and often very expensive. 
Sometimes the trial is made intentionally, and sometimes the 
trials are more or less unintentional and due to ignorance. 
Usually the trials are very limited in scope, and therefore differ 
widely from consciously organized experiments dealing with de- 
finite problems. 



CHAPTER II. 



ESSENTIALS OF PLANT LIFE. 

Prior to 1840, comparatively little was done to apply chemistry 
to the solution of agricultural problems. Much information was 
collected regarding the chemical composition of soils, plants, and 
animals, and a few books discussing the i elation of chemistry to 
agriculture were published, those of Sir Humphrey Davy and 
Thaer being perhaps the most important, but the fundamental 
principles of plant and animal nutrition were not recognized, and 
the books offered little of practical importance to the farmer. 

At that time the prevailing theory was that plants feed upon 
the organic matter, or humus, of the soil, just as animals feed on 
organic matter. According to this theory, the soil should be kept 
full of vegetable matter to feed the plant. The ash or mineral 
matter of the plant, whose presence was known and could not be 
ignored, was thought to act as a stimulant, and not as food. In- 
deed, Thaer, and perhaps others, held that mineral matter could 
be created by plants. 

The great German chemist, Justus von Liebig, in 1840 publish- 
ed a little book entitled "Chemistry in its Application to Agricul- 
ture and Physiology," which developed an entirely new theory of 
plant nutrition. Plants, he said, do not secure their organic mat- 
ter from the soil, but from the air. He showed by calculations 
that there is not enough organic matter in the soil to produce 
average yields of farm crops. The material of importance which 
comes from the soil, he said, is the mineral matter. Supply the 
soil with a sufficiency of mineral matter, and it will remain fertile, 
regardless of its content of organic matter. Such, in brief, was 
Liebig's mineral theory of plant nutrition. This was a practical 
theory and easily tested. Liebig himself, as an object lesson, 
transformed a barren, sandy piece of land near Giessen, Germany, 
into a beautiful garden, by means of his mineral manures. Mr. 
John Lawes was incited to begin field experiments at his manor 
of Rothamsted, England. 

These experiments led to the discovery of the process of mak- 



IO PRINCIPLES OF AGRICULTURAL CHEMISTRY 

ing acid phosphate by treating phosphate rock with sulphuric 
acid. The process, which was patented, became the foundation 
of the fertilizer industry. The Rothamsted experiments, prob- 
ably the most famous field experiments yet instituted, have been 
carried on with the same applications of fertilizers and manure 
since 1852. Sir John Lawes endowed the Rothamsted Ex- 
periment Station, and made provision for continuing its work 
indefinitely. The great fertilizer industries, and the era of 
agricultural experimentation, may be said to date from the ap- 
plication of chemistry to agriculture made by von Liebig in 1840. 

Evidence for the Mineral Theory. As evidence that the organic 
matter of the soil is not necessary to plants, plants have been 
grown to full maturity in soils from which all the organic mat- 
ter had been burned out. Plants were also grown in pure water 
containing no organic matter, or carbon, to which certain mineral 
salts had been added. A prize was offered by the University of 
Gottingen for the solution of the question, whether the ash of 
plants was taken from the soil or created by them. Such prizes 
are still offered in Europe. This prize was won by Weigmann 
and Polstorff. 1 In their first series of experiments, they grew a 
number of plants of different kinds, upon sand from which the 
soluble materials had been removed, as far as possible, by extrac- 
tion with strong acids. One set of plants received only distilled 
water, the other set received a mixture of the mineral salts found in 
the ash of plants, and nitrates. The plants which received distilled 
water hardly grew at all, but the others grew well. This was 
evidence that the mineral matter was necessary for the growth 
of the plants. The plants grown on the sand with distilled water 
alone, when burned, were found to contain slightly more ash than 
was present in the same quantity of seed from which they were 
grown. Weigmann and Polstorff thought that this gain came 
from the sand. They accordingly instituted further experi- 
ments and grew plants in a platinum dish on platinum scraps 
with distilled water, the seed being weighed. Upon incineration, 
the quantity of ash in the plants was found to be exactly equal to 
1 Dissertation, 1842, cited Meyer's Agricultur Chemie. 



ESSENTIALS OF PLANT U?E II 

the quantity of ash in the seed planted. Hence the plants did not 
create any ash, and the ash gained in the previous experiment 
must have come from the sand. This work is an example of the 
importance of continuing experiments until only one possible 
conclusion is indicated, and also shows the danger of formulating 
conclusions upon insufficient data. 

The plants in the platinum dish after reaching the height of 
only two or three inches, began to turn yellow, and died. This 
showed that the ash in the seed was sufficient for only a limited 
development of the plant, and, taken in connection with the pre- 
ceding experiment, showed the mineral matter was necessary 
to the growth of plants. 

Finding the Essential Elements. An essential element is an 
element whose presence is absolutely necessary to the full growth 
and maturity of the plant. A useful element, though not essential, 
may be serviceable to the plant. 

The following fourteen elements are invariably present in 
plants : 

The eight non-metals: carbon, hydrogen, oxygen, nitrogen, 
phosphorus, sulphur, silicion and chlorine. 

The six metals: potassium, calcium, magnesium, iron, sodium 
and manganese. 

Other elements are sometimes found in plants. 1 Iodine occurs 
constantly in sea-weeds and sponges, being present as an organic 
compound in the latter. It is prepared from the ash of sea-weeds. 
Fluorine, arsenic, boron, rubidium, bromine, lithium, barium, 
aluminum, thallium, lead, zinc, titanium and copper have also 

Water Culture Experiments. Experiments to ascertain which 
been found in plants, in minute quantities. 

elements are essential or useful to plants are made by growing 
plants in pure water, to which the salts to be tested are added. 
This is known as the water culture method, and is used because it 
is comparatively easy to secure pure water and salts, but almost 
impossible to secure a sand or soil from which plants do not ex- 

1 Jahresber. Agr. Chem., 1864, pp. 94, 99, 159; 1866, p. 121. Exp. Sta. 
Record 3, p. 717; 7, p. 643. 



12 PRINCIPLES OF AGRICULTURAL, CHEMISTRY 

tract some substance. Only the fourteen elements invariably 
found in plants need be considered, and as two of these (hydrogen 
and oxygen) are in the water, and one (carbon) is supplied from 
the air, there remains eleven to be tested. Twelve solutions are 
prepared. One contains all eleven elements, and is used as a 
check. If the plant does not thrive in it, something is wrong 
with the experiment. Each of the other solutions contain salts 
of ten elements, one being left out of each solution. For ex- 




Fig. i. Buckwheat grown in complete nutrient solution (O) 
and with Cl, K, etc., absent. 

ample, sodium is left out of one, potassium left out of another, 
and so on. Seeds are germinated on moist filter paper, and the 
strongest seedlings are supported by a cleft cork in the neck of the 
bottle containing the nutrient solution, so that the roots are im- 
mersed, but the cotyledons are above the surface. The plants 
would probably die if the cotyledons were immersed. The vessel 



ESSENTIALS OF PLANT UFE 13 

is covered with black paper to exclude light and so prevent the 
growth of green algae, which interfere with the success of the 
experiment. The nutrient solution is replaced by a fresh solu- 
tion every few days, to avoid injury to the plants by change in 
the chemical composition of the solution. Absorption of excess 
of acid or basic radicals by the plants, leaves the liquid acid or 
alkaline, according to its previous composition. 

Where the plant grows well, reaches a good size, and produces 
seed, the element absent from the solution is not essential. 
Where the plant makes a very poor and imperfect growth, and 
produces only a few seed, or none at all, the element absent from 
the solution is essential. Since the seed always contain a certain 
quantity of the essential elements, some growth of the plant is to 
be expected. 

The results of one series of experiments, are not, of course, con- 
sidered final. In experimental work, the work of one man has 
usually to be confirmed by that of others, before it receives gen- 
eral acceptance. 

The method of experiment known as "water culture" 1 , is 
suitable for experiments in which the material supplied to the 
roots must be accurately controlled. It is impossible to secure a 
soil or a sand from which plants will not obtain some mineral 
material. Weigmann and Polstorff, as we have seen, found that 
plants extracted ash from sand which had been exhausted with 
strong acids, and other workers have had similar experiences. By 
using pure water and pure salts, we know exactly what material 
is presented to the roots of the plants. The plant may take up a 
small portion of the silica from the glass when the experiment is 
conducted in glass vessels, but this is not usually of importance. 
If necessary, vessels of platinum or of paraffin, can be used. 

The Essential Elements. It has been found by experiments 
such as those described above, that the following elements are, 
without doubt, essential to the life and growth of plants : 

The four metals : potassium, calcium, magnesium, and iron. 

The three non-metals : nitrogen, sulphur, and phosphorus. 
1 Knop, Sachs and others, Jahresber. Agr. Chem., 1861, pp. 126, 136. 



14 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

The non-metals: carbon, hydrogen and oxygen, secured from 
the air and water, as already stated, are essential. A soil, to be 
fertile, must supply to the plant an abundance of potassium, 
calcium, magnesium, iron, nitrogen, sulphur, and phosphorus. 

Plants can be grown to full maturity by means of the follow- 
ing solution: 

One gram calcium nitrate, 

0.25 gram potassium nitrate, 

0.25 gram potassium sulphate, 

0.25 gram magnesium sulphate, 

0.20 gram ferrous phosphate. 

1,000 cc distilled water. 

Chlorine Essential but Unimportant. Experiments to ascertain 
whether or not chlorine is essential to plants were at first con- 
flicting. Three independent investigators grew plants in water 
culture to full and complete maturity without chlorine. Knop 
grew corn, buckwheat and cress ; Wagner grew corn ; and Birner 
grew oats. 

On the other hand, Nobbe and Siegert 1 found that, although 
buckwheat grew- well in water culture without chlorine up to the 
time of flowering, a little later the tips of the stalks died off, the 
leaves became brittle, spotted, and fluffy, starch accumulated in 
the stems and no seed were produced. The diseased condition 
was remedied by the addition of chlorine. Chlorine thus appear- 
ed to be essential to the formation of the seed of buckwheat. 
Leydhecker 2 also found that buckwheat would not seed in absence 
of chlorine, and Nobbe later confirmed previous results by a sec- 
ond series of experiments. 

Thus one group of investigators finds chlorine not essential, the 
other group finds that it is essential. These contradictory results 
are explained by the work of Bayer. 3 Bayer grew oats in water 
culture, with and without chlorine, all the other essential elements 
being, of course, present. With chlorine 12.5 grams seed were 

1 Landw, Vrersuchs-stat. , 1863, p. 116; 1865, p. 377. 

2 Ibid, 1866, p. 177. 

3 Landw. Versuchs-stat., 7, p. 370. 



ESSENTIALS OF PLANT 

secured, without chlorine 7.5 grams of seed. Apparently chlorine 
was not essential. The seed grown in the absence of chlorine 
were found, on analysis, to be nearly free from chlorine. These 
seeds were used in another experiment in water culture as before, 
with and without chlorine. With chlorine, they made seed ; with- 
out chlorine, they failed to produce seed. Chlorine, therefore, 
is essential. The seed used in the first series of experiments con- 




Fig. 2. Pot experiment showing soil deficient in nitrogen 
and in phosphoric acid. Texas Station. 

tained a sufficient quantity of chlorine for the full development 
of the plant, but those used in the second experiment did not. 

There are a number of instances in which apparently con- 
tradictory results of different workers have been reconciled by 
further investigation. 

The opposite results of the investigators referred to above are 
due, in one case, to the presence of sufficient chlorine in the seed 
used; in the other case, to insufficient chlorine in the seed. We 
may conclude that chlorine is essential to the plant, but the min- 
ute quantity required may be present in the seed. Chlorine is 



1 6 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

needed in such small quantity that it need hardly be considered as 
a plant food by the agricultural chemist. 

Silicia not Essential but Useful. Silica is present in all plants 
grown under normal conditions, and makes up- a considerable 
proportion of the ash of some plants. The ash of cereal straws 
contain 20 to 40 per cent. It was formerly thought that silica 
was essential to the strength of cereal straws. Plants have been 
grown to maturity without silica, though they secured traces from 
the glass vessels in which the solutions were contained. 1 The 
plants attained a normal development, and produced seed well. 
Silica is, therefore, not essential to plant life. Though not 
essential, silica is useful. In certain water culture experiments 
by Kreuzhaga and Wolff 2 with oats, the presence of the silica 
increased both the number and the weight of the seed. The 
silica appeared to aid the plant to mature and form seed. The 
following table shows the results of an experiment in which all 
conditions were constant except the silica: 






Number of 
seed 


Weight of seed 
in grams 




71 e 


2T. 


T ittle silica 








1 > u oV 


** 

46 









The silica is supposed to cause the leaves to die off during the 
ripening of the fruit, allowing essential elements to be withdrawn 
and utilized in formation of seed. According to Wolff, if silica 
is absent from the solution, oats will produce empty seed heads 
unless an excess of phosphoric acid is present. The silica thus 
economizes phosphoric acid, and this is a highly useful function. 
Hall and Morison, 3 at the Rothamsted Station, show that silica 
used as a fertilizer causes an increased yield and earlier forma- 
tion of the grain of barley, but causes the plant to take up more 
phosphoric acid from the soil. 

Soda Not Essential. Soda is never absent entirely from any 

1 Sachs, Jahresber. Agr. Chem., 1862, p. 97. 

2 Landw. Versuchs-stat., 1884, P- T 6i. 

3 Proc. Roy. Soc., 1906, p. 445. 



ESSENTIALS OF PLANT UFE I/ 

plant. It has been impossible to exclude soda completely in water 
culture experiments, owing to its presence as impurities in 
reagents, and its entrance into solution by the action of water 
upon glass vessels, but otherwise such experiments show that 
soda is not essential. Soda does not appear to perform any such 
highly useful functions as silica. It may, however, take the place 
of the indifferent essential ash, and so replace potash. 

Definition of Plant Food. Plant food may be defined as any 
substance which contributes to the building of tissue or is other- 
wise essential to the life of plants. Carbon dioxide, which is 
assimilated by the leaves, is plant food, and so is water. But we 
are more concerned in agriculture with the mineral salts which 
enter the roots of plants, since these require control and are more 
or less subject to it, and we have these in mind rather than car- 
bon dioxide or water when we speak of plant food. By plant 
food we usually mean potash, phosphoric acid, nitrogen, sul- 
phates, lime, magnesia, or iron. Often the term is confined to 
nitrogen, phosphoric acid, and potash, for the reason that they 
are the only forms of plant food commonly added to the soil. 

\Ye have spoken of the elements essential to plants, but we must 
bear in mind that the free elements, with two exceptions, are use- 
less to plants. These two exceptions are oxygen, which is given 
off by plants to a much greater extent that it is used, and nitrogen, 
which in the free state can be taken up by leguminous plants, if 
the bacteria which aid in this process are present. All the other 
elements in the free state are either useless or injurious to plants. 
The essential elements must be present in certain forms of com- 
bination ; other combinations are injurious or useless. These 
facts have been ascertained by numerous experiments with water 
cultures and sand cultures. 

Iron is taken up as ferric compounds; ferrous compounds are 
often injurious. Phosphorus must be present as phosphates, sul- 
phur as sulphates, chlorine as chlorides, silica as silicates or silicic 
acid. Sulphides, sulphites, chlorates, and perchlorates, are 
injurious to plants. Carbon is absorbed as carbon dioxide, 
and as organic bodies to a much less extent. Oxygen 



i8 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



is taken up in water, in carbon dioxide, and as free 
oxygen. Nitrogen enters the plant in nitrates, ammonia, as free 
nitrogen, and to some slight extent in organic bodies. Hydrogen is 
taken up as water and ammonia. Since these elements are pres- 
ent in the soil in the oxidized condition, and are taken up by 
plants in that form, and not as elements, plant food is usually 
referred to and estimated in the form of the oxides. We speak 
of phosphoric acid (P^Og), potash (K 2 O), soda (Na 2 O), lime 
(CaO), magnesia (MgO), oxide of iron (Fe 2 O 3 ) and silica 
(SiO 2 ). These terms are used almost exclusively in agriculture 
and especially in the analysis of soils and fertilizers. We speak 
of nitrogen (N) and chlorine (Cl), for the former may or may 
not be present in the oxidized condition, and the latter is injur- 
ious when oxidized. 

Quantity of Plant Food Required. The method of determining 
the exact quantity of plant food required is tedious and difficult 
and has been applied only to two or three plants. 

To determine the minimum quantity of phosphoric acid re- 
quired by oats, WViff 1 grew eight sets of six oat plants each in 
water cultures. One solution contained an excess of all the 
essential forms of plant food, except phosphoric acid. The other 
solutions received increasing amounts of phosphoric acid. All 
conditions were the same, excepting the varying amounts of phos- 
phoric acid. When the oats were ripe, they were harvested and 
subjected to analysis. The following are some of the results: 



Phosphoric acid in Mgr. 
Per vessel 


Weight of crop 
in grams 


Phosphoric acid 
in dry matter 
per cent. 


Grain 


Straw 




5-8 
3-4 

2-7 

n 

1.8 

I.O 

0-3 


II. 

10.9 
II. I 

10.2 

7-2 

5.2 
3.0 

I.I 


I. II 

0.83 
0-53 
0-33 
0.28 
0.27 
0.27 
0.27 










33- 
24 8 


TA 8 







1 Jahresber. Agr. Chem., 1873, p. 293. 



ESSENTIALS OF PLANT LIFE IQ 

When the plant contained less than 0.33 per cent, of phosphoric 
acid, it was not well developed. When the percentage of phos- 
phoric acid was increased over 0.33 per cent., the quantity of 
straw was little affected, but the quantity of grain increased. In 
the presence of silica, equally as much grain could be produced 
with 0.33 per cent, phosphoric acid. Wolff therefore concludes 
that the minimum quantity of phosphoric acid required by the 
entire oat plant is 0.33 per cent, of the dry material. 

Similar series of experiments were made with potash, lime, 
and other forms of plant food. From these experiments Wolff 1 
concludes that the minimum requirements of the oat plant, based 
on the dry matter of the entire plant, is as follows : 

Per cent. 

Phosphoric acid 0.35 

Potash 0.8 

Lime o. 2 

Magnesia 0.2 

Sulphuric acid 0.2 

Total of the essential constituents 1.75 

Pure ash necessary 3.00 

Nitrogen i.oo 

While the oat plant can get along with 1.75 per cent, of the 
essential ash constituents, a total of 3.00 per cent, of pure ash 
is absolutely necessary. It was impossible to grow a plant with 
less than 3.00 per cent, of ash. The additional 1.25 per cent, 
may consist either of essential elements, or of unessential ele- 
ments, such as silica or soda, but the quantity required must be 
made up in some way or other. We may term the ash in excess 
of the sum of the essential ash ingredients, the indifferent ash. 
The unessential elements can be useful to the plant in making 
up its indifferent ash, which is, however, essential. Various sub- 
stances sometimes added to the soil, such as salt, gypsum, lime, 
etc., may be useful in satisfying the need of the plant for indiffer- 
ent ash. Since 1.25 per cent, of the necessary 3.00 per cent, of 
the ash of oats may be of varying nature, and since plants may 
take up ash in excess of their needs, the ash of the plant is 
subject to considerable variation in composition. 
1 Jahresber. Agr. Chem., 1875, p. 251. 



2O PRINCIPLES OF AGRICULTURAL CHEMISTRY 

Quantity of Plant Food Needed by Plants. The experiments 
by Wolff already cited show the minimum requirements of the 
oat plant, but this method has not been applied to other plants, 
and we are dependent upon other methods for ascertaining the 
needs of the plant. The only other method which has been used 
is to make the analysis of the plant. 

This is not altogether a safe guide: first, because plants may 
take up an excess of plant food; and secondly, near maturity 
material is easily washed from the leaves and other parts of the 
plant by rain, dew, etc., as shown by LeClerc and Breazeale. 1 For 
estimating the draft of the plant on the soil, analysis is of course 
more satisfactory. Such analyses are also used for calculating 
the manurial value of feeds. Most of the estimations of the 
mineral matter in plants have been made by analyses of the ash. 
Nitrogen is determined on a separate sample of the original plant 
material. 

The Ash of Plants. When plant substance is burned, the 
greater portion of it passes off as volatile bodies. The residue is 
termed the ash. The ash is sometimes spoken of as the mineral 
part of the plant, or the inorganic part. These terms are not cor- 
rect. The ash is merely that portion of the plant which forms 
compounds not volatile at the temperature of the combustion. A 
portion of it may have been present in the plant in the form of 
inorganic bodies, and a portion has undoubtedly been in organic 
combination. 

The term crude ash is applied to the ash as secured by burning. 
Pure ash, or carbon free ash, is the crude ash less the free carbon, 
carbon dioxide, and sand contained in it. 

Under ordinary conditions, all of the nitrogen and hydrogen, 
most of the carbon and oxygen, a considerable part of the sul- 
phur, and a small portion of the potash and chlorine pass off dur- 
ing combustion. The ash consists chiefly of carbonates, oxides, 
sulphates, phosphates, silicates, and chlorides of potash, lime, 
magnesia, and soda. Unburned carbon is usually present, and in 
rare cases cyanides and sulphides are found. The fact that a 
1 Yearbook, U. S. Department Agriculture, 1908, p. 389. 



ESSENTIALS OF PLANT 



21 



large part of the sulphur is volatilized was overlooked for a long 
time. For example, the following results 1 were obtained: 





Percentage of SO 3 in 


Cowpeas 


Corn 




0.08 
0.47 
84.0 


O.OI 

o-39 
97-0 









The result has been that the draft of the plant on the sulphur 
in the soil has been decidedly under-estimated, and it is quite 
possible that some soils may be deficient in sulphur. 2 

Variations in Ash. 3 The percentage and composition of the 
ash of plants varies according to the kind of plant, the part of 
the plant, the stage of growth, the variety of the plant, the soil, 
the season, and other conditions. 

Seeds contain plant food stored for the benefit of the young 
plant, and are less variable in composition than any other portion 
of the plant. Although they contain comparatively small quan- 
tities of ash, the ash is rich in the essential plant foods. The 
pure ash is composed largely of phosphoric acid, from 30 to 
50 per cent.; potash, about 30 per cent.; magnesia, about 8 to 
15 per cent. Lime is present in comparatively small quantity, 
and little or no silica is found, except in the case of oats or 
similar plants where the husk or chaff is included in the analy- 
sis. (See table below). Leguminous seeds appear to be richer 
in potash and poorer in lime than the seed of cereals. 

Roots and tubers, which, like seeds, contain a reserve store of 
material for the use of the plant, are also rich in valuable plant 
food, though more variable in composition than seeds. Unlike 
seeds, the ash carries considerably more potash than phosphoric 
acid ; but, like seeds, it contains more magnesia than lime. 

Leaves of plants are very variable in composition. The ash 

1 Fraps, Jour. Am. Chem. Soc., 23, 199. 

2 Jour. Agr. Sci., i, p. 217. 

3 See Wolff, Ashen Analysen. Also Tollens, Exp. Sta. Record 13, 
pp. 207, 303. 



22 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



is rich in potash and lime, but contains much smaller quantities 
of magnesia and phosphoric acid. The quantity of silica is larger 
than in the ash of seeds or tubers, being slightly less than the 
phosphoric acid. 

Cereal straws are variable in ash content, though the ash is con- 
siderably lower than in leaves. The ash is very rich in silica, and 
contains fair amounts of potash. Its content of lime and magnesia 
is comparatively small, and it contains about half as much phos- 
phoric acid as leaves. Like leaves, cereal straws contain more 
lime than magnesia. 

Leguminous straws resemble leaves closely. The ash is rich 
in lime and potash, and contains approximately the same amounts 
of phosphoric acid and magnesia as the ash of leaves. 

AVERAGE AMOUNT OF ASH CONSTITUENTS IN 1000 PARTS BY 
WEIGHT OF THE DRY SUBSTANCE. 



Number 
Aver- 
aged 




Pure 
ash 


Potash 


Ume 


Mag- 
nesia 


Phos- 
phoric 
acid 


Silica 


106 
7 
13 
113 

12 

17 

no 
36 
57 
57 
15 
3 
40 

18 
25 

38 

59 
149 

32 


Hay and Grasses 


69.8 
60.6 
23-6 
68.6 
73-8 
82.3 

19.6 
20.9 
26.1 
31.2 
14.5 
13-7 
27-3 
39-8 

53-7 
44-6 
7^-7 

37-9 

? 


18.6 

21-5 
4.6 

22.2 

17.4 
25-4 

6.1 
6-7 
5-6 
5-6 
4-3 
3-2 
ii. 8 
12.9 

7-3 

IO.I 
20.6 

22.8 
20.4 
36.4 


II. I 
8.3 
i-9 
24.0 
30.0 
33-2 

0.6 
0.6 
0.7 
i.i 

-3 
0.6 

1-3 

2.8 

3-i 
3-7 
5-o 

I.O 

i\ 


4.8 
6-5 

7-5 
3.6 
10.9 

2.4 

2.4 

2-3 

2.2 
2-3 
1-7 
2.2 
6.2 

L3 
1.4 
2.6 

1-9 

3-0 
3-o 


5-0 
6.1 
1.6 
6.6 
6-3 
5.o 

9-3 

10.0 

9.2 
8.0 
6.6 

6.7 
9-8 

13.9 

2.6 

2-9 

3-3 

6.4 

4.7 

10.2 


20.0 
I I.O 
10.3 

i-9 
7.0 

0.9 

0.4 
0.3 
6.7 

12.2 
0-3 
0.3 
0-3 

0.6 

36.3 

22.0 

33-5 

0.8 
0.9 
1-5 


Green corn (in bloom) 




Alfalfa . 




Seeds and Fruits 






Oats 


Corn 


Buckwheat 




Ootton 


Straw 
\Vinter wheat 




Oats 


Roots and Tubers 
Potatoes 









ESSENTIALS OF PLANT 



Effect of the Soil and Season. The character of the soil and 
the weather conditions prevailing during the growth of plants, 
have a great influence upon the composition of their ash. The 
seed is less influenced by these conditions, but the straw of 
cereals is greatly affected. Indeed, it has been proposed to 
determine the needs of the soil for plant food by analysis of 
certain plants grown on it. 

At the Rothamsted Experiment Station, barley has been grown 
on a certain field for over fifty years. Some of the plots receive 
no fertilizer, and others receive various mixtures, but the treat- 
ment has been the same during the entire period. Plots which 
do not receive the complete fertilizer should be depleted of the 
plant food not added in the fertilizer. There is very little varia- 
tion in the composition of the ash of the grain. The phosphoric 
acid and silica in the straw vary slightly, but great changes take 
place in the percentages of potash and soda. 





Percentage composition 
of barley ash, grown 
40 years without potash 1 


Potash 


Soda 


Average 10 years 
Average 10 years 
Average 10 years 
Average 10 years 
Average 40 years 


1852-61 


18.4 
13-3 
9-7 
7-4 
31.0 


6.4 
11.4 

12.7 
11.9 

2.2 


1862-71 


1872-81 


1882-91 







While the yield of grain decreases from 45.62 to 36.63 bushels 
per acre, the composition of its ash is little affected. The potash 
in the ash of the straw decreases from 18.4 per cent, to 7.4 per 
cent., accompanied by an increase in soda, though not in cor- 
responding quantity. The ash in the straw from the plot re- 
ceiving potash fertilizers contains four times as large a per- 
centage of potash as ash of the straw produced without potash 
during the decade 1882-91. Since in the first two ten-year periods 
about 2,700 pounds straw per acre was produced on the no-potash 
plot, while the 40 year average for the potash plot is 2587 pounds, 

1 Agricultural Investigations at Rothamsted, Gilbert, Bulletin 22, Office 
of Exp. Station, U. S. Dept. Agr., page 78. 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



it is evident that the higher percentage of potash did not con- 
tribute to a greater production of straw. That is to say, 
plants may take up a considerable excess of plant food, especially 
of potash. 1 

The influence of the season upon the ash content of plants is 
illustrated by the same series of analyses referred to above, 
namely, barley grown on the experimental plots of the Rotham- 
sted Experiment Station. The differences between the average 
composition of the ash of plants from plots differently manured, 
show the effect of ihe application of plant food. The differ- 
ences between the highest and lowest content of ash for the same 
manure, show the effect of the season. The results in the follow- 
ing table are expressed in terms of the plant instead of the ash as 
in previous tables. 

EFFECT OF MANURES AND THE SEASON ON POTASH AND PHOSPHORIC 
ACID CONTENT OF BARLEY. 





Potash and phosphoric acid in 1000 parts dry matter 
of the plant- 


Potash 


Phosphoric acid 


Highest 


Lowest 


Average 


Highest 


Lowest 


Average 


Grain 


7-7 
8.4 
8.0 

n.8 

22.O 
22.5 


6.0 

5-9 
5-6 

5-3 
6.8 

5-7 


6-5 
6.8 
6.6 

8.6 
13.2 
14.1 


10. 1 
10.5 
10.4 

2.6 

29 
3- 1 


8.9 
9.2 
8.8 

1.2 

MB 

i.i 


9-3 

IO.O 

9.6 

i-7 

2.2 

i-9 


Farm yard manure. . . 
Complete fertilizer. . . 

Straw 


Farm yard manure- . 
Complete fertilizer. . . 



Both fertilizer and season have comparatively little effect upon 
the composition of the grain, as we have observed before. On 
the straw, the season has a greater effect than the fertilizer. For 
example, the average potash in the unmanured straw is to the 
potash in the manured straws as 8.60:14.10 or less than 1 :2, while 
in different seasons the straw grown on the manured plot varied 

1 See also Wilfarth and Wimmer, Exp. Sta. Record 13, 1030. 

2 Bulletin 22, Office of Exp. Station, p. 75. 



ESSENTIALS OF PLANT LIFE 



in potash from 6.8 : 22.00 or over I : 3. Inspection of the table 
shows that phosphoric acid varies in a similar manner, though 
the variations are not so large. In these experiments, at least, 
the effect of the season is greater than the effect of fertilizers or 
the soil. 

Ash of Strong and Weak Plants. Various chemists have select- 
ed strong plants and weak plants growing in the same field at the 
same time, and subjected them to analysis. Some analyses of 
this kind are given in the following table 1 : 

COMPOSITION OF STRONG AND WEAK PLANTS. 







Percentage Composition of ash 




in plant 


PotJish 


Lime 


Mag- 
nesia 


Oxide 
of iron 


Phos- 
phoric 
acid 


Silica 


Winter wheat 
















Strong plants 
Weak plants 


8.04 

7-55 


43.07 
32.89 


6.40 
3-73 


3-60 
2.30 


0.20 
0.20 


7.08 
8.20 


32.82 
48.40 


Oats- 
















Strong plants 


8.03 


43-15 


7.02 


4-5 


0.50 


7.28 


20.86 


Weak plants 


6.48 


39-35 


6.06 


3-30 


O.6o 


7.68 


34.18 


Barley- 
















Strong plants . 


10.83 


43 10 


8.73 


3-83 


O.6o 


7.33 


18.67 


Weak plants . . 


8.39 


38.15 


7-33 


3-77 


O.6o 


8.20 


30.50 



The weak plants contain a smaller percentage of ash than the 
strong plants. The percentages of potash and lime are smaller, 
and the percentages of silica are much larger in the ash of the 
weak plants. 

Effect of Stage of Growth on Ash. The percentage of ash 
shows the relation between the organic matter formed and min- 
eral matter taken up by the plant. The absorption of mineral 
matter from the soil, and the production of organic matter by the 
plant, do not proceed at the same rate, consequently the per- 
centage of ash in the plant varies at different periods of time. 
Changes in the ash content of plants at different periods of 
growth depend upon the kind of plant, and the part of the plant 
under consideration. As a general rule, we find that the ash con- 
tent is greatest in the young plant, and that it decreases with the 
1 Wolff's Ashen Analysen. 
3 



26 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



age of the plant. That is to say, the young plant takes up more 
mineral matter in proportion to the quantity of organic matter it 
elaborates, than the older plant. 

The nature of the soil also affects the changes in the ash of 
a plant during its growth. When an insufficient quantity of plant 
food is supplied by the soil, the plant may withdraw ash ingre- 
dients from its older parts for use in continuing its growth. As 
we have seen, in the presence of an excess of plant food, the 
plant may take up more ash than it needs. These facts should 
be borne in mind in considering the changes in the ash ingre- 
dients during the growth of plants. The composition of the 
plant at different stages on one soil, under one set of conditions, 
may be quite different from the same plant grown on another 
soil under another set of conditions. When the plant approaches 
maturity, ash may be washed out by rain. 

For the reasons just given, the following general statements 
may not apply to individual cases. With the entire plant, the 
percentage of potash in the ash decreases almost invariably, 
while, as a rule, silica increases, magnesia increases, lime de- 
creases, and phosphoric acid decreases in some cases and in 
others increases. 

The above statements are made with respect to the entire plant. 
Exceptions occur with certain parts of the plant, as, for example, 
the ears of oats. 

An example is presented in the following table. Samples of 
the entire wheat plant were collected at different periods of 
growth and subjected to analysis by Pierre: 1 

EFFECT OF STAGE OF GROWTH ON ASH OF PLANTS. 



Stage of growth 


Pure ash 
in plant 
Per cent. 


Percentage composition of ash 


Potash 


Lime 


Mag- 
nesia 


Phos- 
phoric 
acid 


Silica 




74 
6-5 
5-3 
5-1 
48 

4-7 


22.8 
'5-2 
13-5 
13.0 
10.2 
10.2 


20.7 
17-5 
13-7 
II. 5 
12.4 
10. T 


3-8 
4.2 
2.7 
2.7 
2.2 
2.4 


IO.I 

9-i 
6.1 

5-6 
5-3 
5-9 


35-2 
45-0 
55-9 
58-3 
62.5 

64.7 




Beginning of bloom 




Ripe 





1 Wolff's Ashen Analysen. 



ESSENTIALS OF PLANT 



As the grain ripens, and the proportion of seed to husk 
increases, a decrease in the percentage of silica in the ash occurs. 

Ratio of the Essential Elements. The ratio of the essential 
elements affects the development of the plant to some extent. 
Director Hall 1 of the Rothamsted Station states that where 
barley is grown on the plots fertilized with potash and nitrogen 
without phosphoric acid, the grain hardly matures at all, while 
the phosphoric acid in the absence of nitrogen and potash causes 
the grain to ripen early. 

Starting with the fact that lime predominates in leaves while 
magnesia is in excess in seeds, May, under the direction of 
Loew, 2 grew tobacco in sand culture with excess of lime and 
with excess of magnesia, producing in the first experiment a 
large development of leaves, in the second a very small plant. 
According to other experiments of Loew and his pupils, the 
ratio of lime to magnesia is of importance. 

For example, Aso 3 grew rice with various ratios of lime to 
magnesia. The lime and magnesia originally in the soil were 
estimated by extracting the soil for 24 hours with cold 10 per 
cent, hydrochloric acid. Such additions of carbonate of lime 
or carbonate of magnesia were then made to various pots con- 
taining 7 kilograms of the soil as were necessary to secure the 
desired ratios of lime to magnesia. In order to ensure an 
abundance of plant food, each pot also received 15 grams 
ammonium sulphate, 15 grams sodium phosphate, and 15 grams 
potassium carbonate. 

The following are the results of this experiment : 



Ratio of lime to magnesia 


Weight of 
grain in grams 


Weight of 
straw in grams 




2o ^ 


C-y r 


. i ' 


JQ r 


06-0 

CQ C 




. i 


O U O 

A A O 


59-5 
6c e 


2 


<;8 ^ 


05-5 
DQ O 


j 


S'5 
08 ; 


TO? O 


j 2 


84 o 


QC o 


I 1 . . 


7O O 


yo-^ 
106 o 




/y.~ 





1 Rothamsted Experiments, p. 80. 

2 Bulletin No. I, Bureau Plant Industry, U. S. Dept. Agr. 

3 Bulletin Tokyo Imp. Uni., 1904, p. 97. 



28 



PRINCIPLES OF AGRICULTURAL, CHEMISTRY 



According to this experiment, the ratio of i part lime to i part 
magnesia is most favorable to the growth of rice. An increase 
or decrease in the ratio reduces the yield, an excess of lime being 
more injurious than any excess of magnesia. 




Fig. 3. Upper tobacco plant has excess of magnesia, lower plant 
excess of lime. Loew. U. S. D. A. 



In other experiments Loew 1 found the most favorable ratio of 
lime to magnesia for some other plants to be as follows : 

1 Bui. Col. Agr. Imp. Univ. Tokyo, 1902, p. 381. 



ESSENTIALS OF PLANT LIFE 2Q 

Lime : Magnesia : : i : I for oats, 
: : 2 : i for barley, 
1:3:1 for wheat. 

Lime, 1 he says, is required for foliage, and magnesia for seed; 
the greater the proportion of foliage to seed, the greater the ratio 
of lime to magnesia required by the plant. 

Several factors operate to prevent injury by an unfavorable 
ratio of plant food in the soil. The root of the plant exercises a 
certain degree of selection by which it may to some extent de- 
cline to absorb undesirable plant food. In some plants an excess 
of lime is deposited in cells in the form of calcium oxalate, in 
others, it forms a white coating (probably carbonate of lime) 
upon the leaves. There is a difference of opinion as to the 
significance of Loew's work. According to Hopkins' experi- 
ments, 2 the quantity of lime and magnesia are of more importance 
than the ratio. 

The importance of the ratio of lime to magnesia in practical 
farming remains to be decided by field experiments. 

Plant Stimulants. Substances which exert an appreciably 
favorable action upon plant growth and at the same time are not 
essential to the life of the plant, may be termed stimulating com- 
pounds. According to Loew 3 and his pupils, borax and salts of 
lithium, caesium, uranium, manganese, bromine, iodine, fluorine, 
and ferrous iron act as plant stimulants in small doses ; in large 
quantities, they may prove injurious. The more important 
of these stimulants 4 appear to be manganese, iron, and 
fluorine. It is also possible that certain organic substances 
may act as stimulants in small doses, or as poisons in large 
doses. According to Loew, the favorable quantity of the stimu- 
lants named is as follows : Manganous sulphate about 75 pounds 

1 See also Circ. No. 10, Porto Rico Exp. Sta. : Bui. 45, Bureau of Plant 
Industry. 

2 Soil Fertility and Permanent Agriculture, p. 170. 

3 Bui. Tokyo Univ., 1904, p. 163. 

4 Int. Cong. App. Chem., 1912, 15, p. 39. 



3<3 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

per acre; manganous chloride 60 pounds; potassium iodide one- 
third ounce; sodium fluoride one ounce. 

The importance of these stimulating compounds in practical 
agriculture remains to be demonstrated. Such field tests as have 
come to the notice of the writer are contradictory. It has been 
suggested that the copper hydroxide and similar substances used 
for combating certain plant diseases, instead of killing the fungus 
direct, stimulate the plant and increase its vigor sufficiently to 
resist the disease, but we know of no experiments supporting this 
hypothesis. It is also possible that "stimulating" compounds may 
occur in certain soils in quantity sufficient to be injurious. 

Essentials for Plant Life in Addition to Food. Conditions other 
than plant food which are essential to plant life are 
mentioned here for the sake of completeness. The requirements 
of foliage, fruit, or roots are different, but the entire plant suffers 
if a part suffers. 

Water, in considerable quantity, is essential to plant life. Only a 
small portion of the water used by a plant is used as plant food 
and goes to the formation of organic material. Most of it is 
evaporated by the leaves of the plant. 

Light is essential to the formation of organic matter by the 
leaves of plants. Too much or too little light affects the develop- 
ment of the plant. Plants vary in their requirements for light. 

Temperature. Extremes of heat and of cold destroy plants. 
For their best growth a certain temperature is most favorable, 
and it varies with the kind of plant. Temperatures which do not 
destroy the plant may yet interfere with its growth. 

Favorable soil conditions are essential ; the proper degree of 
moisture, of soil atmosphere, absence of deleterious influences, 
etc., are necessary to the best growth. 

The Law of Minimum. In the experiment of Wolff on oats, 
cited previously, the size of the oat crop varied with the quantity 
of phosphoric acid supplied to it, other conditions being favor- 
able. In the following experiment of Hellriegel, 1 various 
1 Exp. Station Record, 1893-4, p. 853. 



ESSENTIALS OF PLANT 



Grams dry matter 
produced 
per pot 



quantities of nitrogen were added to a soil provided with an 
abundance of all other forms of plant food, all other conditions 
being favorable. The harvest of the barley gave the following 
results : 

Grams nitrogen 
supplied 
per pot 

O.OOO 0.50 

0.028 2.99 

0.056 5.32 

O.I 12 I0.8o 

o. 168 16.38 

0.224 21.72 

The size of the crop increases with the quantity of nitrogen at 
the disposal of the plant. The size of the crop thus varies with 
the quantity of the most deficient form of plant food. The plant 
food is the controlling condition in these experiments. Plant 
food, however, is only one requirement of plant life. The 
amount of the crop is profoundly influenced by rainfall, tempera- 
ture, and other weather conditions which are embraced under the 
term season, as well as by the nature of the soil, etc. 




Fig. 4. The growth of oats is proportional to the supply of nitrate 
of soda, other conditions being favorable (after Wagner). 

The law of minimum holds that the size of the crop is regu- 
lated by the condition least favorable to the growth of the plant. 



32 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

For instance, suppose all conditions were favorable to the produc- 
tion of 100 bushels of corn, with the exception of phosphoric 
acid ; then the size of the crop would depend upon the quantity of 
phosphoric acid it could secure; if only enough for 10 bushels, 
then ten bushels it would be. Suppose the soil were very rich, as 
it often is in arid regions, and there were little water, then 
quantity of water would limit the size of the crop. An excess 
of water would also limit decrease the crop. If all conditions 
of soil and water were favorable, the limiting conditions might be 
the quantity of light the plant received, the temperature, or the 
individuality of the plant. 

The conditions which limit plant growth may be kind of seed, 
light, water, space, temperature, total ash, phosphoric acid or any 
other plant food, insects, injurious diseases, or the condition, 
nature or situation of the soil. The size of the crop depends 
upon the least favorable of the conditions which surround it. It 
is exceedingly important in practical agriculture to ascertain the 
limiting conditions, and render them more favorable. 

Mitscherlich 1 gives mathematical expression to the law of 
minimum. Under ideal conditions, a certain maximum yield 
would be obtained. The yield is depressed if some essential 
factor is deficient. If now the deficiency is overcome to a 
certain extent, the yield becomes greater, and is the larger, the 
greater the previous depression. According to Mitscherlich, the 
increase in crop produced by a unit increment of the lacking 
factor is proportional to the decrement from the maximum. 
The mathematical expression is : 

dy 
-fe = (A y}k or log e (A y} = c kx. 

When x is the amount of the factor present, y is the yield, and 
A is the maximum yield possible with an excess of the factor. 

Permanent and Variable Limiting Conditions. The character 

of the soil and the plant food which it supplies are more or less 

permanent during the growth of the crop, but the soil moisture 

and the weather conditions are more variable. The limiting con- 

1 Landw. Versuchs-stat., 1911, p. 231. 



ESSENTIALS OF PLANT 



33 



editions of plant growth are therefore more or less variable, 
according as moisture or weather conditions are more or less 
favorable to growth than are soil conditions. The rate of growth, 
for example, may at one time be controlled by the phosphoric 
acid supply of the soil, and at another by decrease in the rate of 
supply of moisture (drought) or by an excess of water or by too 
cool a temperature, or too little sunlight, etc. The conditions of 
the soil and its supply of plant food are more or less affected by 
soil moisture, weather, or other conditions. 

The varying effect of the season upon plots with different 
fertilizer applications, may be seen by comparing the yield of 
wheat in a wet year and in a dry year, with the average for 51 
years, on the plots at Rothamsted, 1 England. 



Treatment 


Yield of wheat in bushels per acre 


Average 


Wet year 


Dry year 




I3-I 
14.9 

24.0 
33-8 
20.7 
22.7 
35-7 


4-5 
5-6 

10.5 
17.9 
4-3 
4-6 
16.0 


10.7 
14.2 

19.4 
21.9 

8.4 

10.0 

34-2 




Acid phosphate, potash salts, sulphate of 













There is nearly as much difference between the average crop 
on the farm-yard manured plot, and the crop during the wet 
season, as there is between the average yield with no addition, 
and with the farm-yard manure. 

Limiting Conditions are Dependent Variables. The limiting 
conditions are not independent of one another, but to a certain 
extent influence each other so that variation in one may affect 
several. 2 Increase in water in the soil, for example, decreases the 
air content, and may decrease soil temperature. By transpiring 
more water, the plant can take up more plant food. Increase in 
phosphoric acid of the soil may also increase the activity of the 

1 Hall, an account of the Rothamsted Experiments, p. 54. 

' 2 Cameron, Proc. Am. Soc. Agron., 1910, p. 102. 



34 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

soil bacteria, those which convert inert organic matter into 
nitrates included, and thus increase the supply of plant food. 
The phosphate added may affect the physical character of the 
soil. Increase in the soluble plant food in the soil decreases the 
need of the plant for water and its transpiration becomes less. 
Increase in temperature increases the action of soil moisture 
upon plant food constituents, and increases the activity of the 
soil organisms. Thus a change in one condition of plant life 
may, and usually does, affect more than one, and the conditions 
are not absolutely independent. 



CHAPTER III. 



THE PLANT AND THE ATMOSPHERE. 

Although the atmosphere is equally as important as the soil for 
the production of plants, yet, since atmospheric conditions are 
little subject to control and are less complex in relation to the 
plant than soil conditions, much less attention need be given to it. 
We have already found that the carbon of the plant comes from 
the air. The atmosphere receives and transports water vapor, 
and precipitates it in the form of rain or snow. The amount, 
kind and period of rainfall which are dependent on atmospheric 
conditions are highly important to agriculture. The atmosphere 
moderates the variations in temperature. It tempers and stores 
the heat of the sun. If there were no atmosphere, the tempera- 
ture would be very hot in the direct sunshine and freezing in the 
shade. 

The soil atmosphere is also of importance. The air penetrates 
the soil, supplies the roots of plants with the oxygen they need, 
and oxidizes deleterious substances. It aids in the preparation 
of plant food so that the plant can take it up. It also aids in the 
formation of soil from rock. 

Composition of the Air. The air consists chiefly of nitrogen 
and oxygen. It contains, in addition, a small amount of carbon 
dioxide, some water vapor, small quantities of argon and allied 
rare gases, besides minute quantities of ammonia, nitric acid, 
hydrogen peroxide, and marsh gas. It also contains suspended 
solid matter, some of which consists of micro-organisms. 
In towns, the air contains some sulphuric acid and hydrogen sul- 
phide. The moisture in the air varies considerably. 

The composition of dry air varies but slightly, even when 
sampled at widely distant localities. Its average composition by 
volume is as follows : 

Oxygen 20.90 parts. 

Argon 0.90 parts. 

Nitrogen 78. 15 parts. 

Carbon dioxide 0.03 parts. 

Hydrogen 0.02 parts. 

100.00 parts. 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



Carbon Dioxide. If a vessel of clear lime water is exposed to 
the air, the lime water after a time becomes cloudy, and a white 
precipitate or a crust of calcium carbonate is formed. The 
formation of this precipitate is a test for carbon dioxide, and it is 
due in this case to the carbon dioxide of the air : 



Ca(OH) 



CO 2 = CaCO 3 



HO. 



Since plants can be grown to full maturity in water containing 
certain mineral salts, and the plant contains much more carbon 
than the seed, while the water does not contain any, it follow r s 
that the plant must have taken carbon from the air. 

The following is an example of an experiment showing that 
plants can assimulate carbon dioxide in the presence of light. 
Boussingault placed a sprig of leaves in a vessel containing 86.5 cc. 
of a mixture of oxygen and carbon dioxide and exposed it to the 
sun. After nine hours exposure, the gas was measured and sub- 
jected to analysis. The results of the experiment follow: 





Carbon dioxide 


Oxygen 




31.9 cc. 
12.3 cc. 


11.5 cc. 
3I.4CC. 






Loss 


19.6 cc. 


Gain 19.9 cc. 





This shows that the leaves absorbed carbon dioxide and re- 
placed it with a nearly equal volume of oxygen. 

Another experiment consists in enclosing the plant in an air- 
tight vessel, through which air is passed. A known amount of 
carbon dioxide is added to the air, and the carbon dioxide in the 
air which passes out is determined. The quantity which dis- 
appears is absorbed by the plant. Numerous experiments give 
the same results. 7'he green leaves of plants absorb carbon 
dioxide in the presence of light, and replace it with an equal or 
nearly equal volume of oxygen. 

The amount of carbon dioxide in the air can be estimated by 
drawing a known volume of air first through calcium chloride to 
remove water, and then through a solution of caustic potash to 



THE; PLANT AND THE: ATMOSPHERE: 37 

absorb the carbon dioxide. The potash bulb is weighed before 
and after the experiment, and the gain in weight is carbon dioxide. 
The carbon dioxide may also be absorbed by soda-lime, or by 
barium hydroxide. Water lost from the absorbing tube is col- 
lected in a small tube containing calcium chloride, and weighed 
with the absorbing tube. 

While the percentage of carbon dioxide in the air is small, and 
is continually depleted by plants during the day, yet the total 
quantity is large. The income and outgo of the carbon dioxide of 
the air appear so nearly to balance that no great variation in the 
amount takes place. The following are the chief processes which 
restore carbon dioxide to the atmosphere : - 

(1) The respiration of animals. Animals absorb oxygen and 
give off carbon dioxide. The oxidation of organic material de- 
rived from food or body substances produces the carbon dioxide. 

(2) Combustion. All processes of combustion of organic ma- 
terials produce carbon dioxide. 

(3) Fermentation and decay. These are changes which occur 
in organic materials, and are usually accompanied by production 
of carbon dioxide. 

(4) Decomposition of calcium bicarbonate by shell fish. The 
calcium bicarbonate dissolved in the sea water is decomposed, 
setting carbon dioxide free, and the calcium carbonate is used by 
the animal to form its shell. 

Ca(HCO 3 ) 2 = CaCO 3 + H 2 O + CO 2 . 
This carbon dioxide was originally derived from the air. 

(5) Dissociation of carbonates by heat, as in the burning of 
lime. This is a matter of small importance, especially as the 
lime takes up the carbon dioxide again sooner or later. 

CaCO 3 = CaO + CO, 2 

Carbon dioxide is also emitted from some volcanoes, deep 
springs, and other subterranean sources. 

Quantity Present. Country air contains on an average 0.029 
per cent, carbon dioxide, or, in round numbers, 3 volumes to 
10,000 volumes of air. City air contains larger quantities. Angus 



38 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

Smith found the air in Glasgow to contain 0.05 per cent, and in 
London 0.044 per cent. More carbon dioxide is present in the 
air at night than in the day. For example, Armstrong 1 found 
the air to contain 0.0296 per cent, carbon dioxide in the day, and 
0.330 per cent, at night. 



CARBON D/OX/DE OF Am 



Off&AN/C 

GARBONOF 
PLANTS 




Fig. 5. Circulation of carbon. 

These variations are easily explained. In cities more carbon 
dioxide is evolved by respiration and combustion than in the 
country, and less is absorbed by plants. At night the production 
of carbon dioxide by animals continues, but plants give it off 
instead of absorbing it, hence the larger amount at night. 
1 Proc. Roy. Soc., 1880, p. 343. 



THE; PLANT AND THE: ATMOSPHERE; 39 

Carbon dioxide is soluble in water, and is brought to the earth 
with rain. It exerts a solvent action on constituents of soils and 
rocks, especially on carbonate of lime. The amount of carbon 
dioxide dissolved by water varies according to temperature and 
pressure. Carbon dioxide is usually found in springs, wells, and 
river water, as well as in dew or rain. 

Circulation of Carbon. Carbon circulates from the air to 
plants, from plants to animals, and from plants and animals back 
to the air. The oxidation of carbon in decay of organic matter 
is due to bacteria. The diagram on page 38 illustrates the cir- 
culation of carbon. 

Effect of Light on Plants. The energy stored by plants comes 
for the most part from the sunlight. In the presence of light, 
green leaves absorb carbon dioxide and give off oxygen. This 
can be demonstrated by a simple experiment. Some fresh green 
leaves are placed in a funnel filled with water containing carbon 
dioxide, inverted in a vessel of water, and placed in the sunlight. 
Bubbles of gas begin to rise, which may be collected in a small 
test-tube attached to the stem of the funnel, and tested with a 
spark on a splinter. This bursts into flame, and so proves the 
gas to be oxygen. 

In darkness, plants take up oxygen and give off carbon dioxide, 
though the amount is small in comparison with the reverse action 
in the light. For example, Corenwinder 1 ascertained that three 
pea plants exhaled 24 cc. carbon dioxide during an entire night, 
while they absorbed 86 cc. carbon dioxide during an hour of 
direct sunshine. 

The amount of light most favorable to the growth and develop- 
ment of the plant, depends on the kind of plant. Some plants 
grow better in the sunshine, while others thrive only in the 
shade. In the diffused light of cloudy days, or the softened light 
of a forest, plants may exhale either carbon dioxide or oxygen, 
according to the kind of plant, the intensity of the light, and the 
stage of development of the plant. 

Chlorophyll, the green coloring matter of the leaf, seems to 
1 Jahresber Agr. Chem., 1858, p. 106. 



40 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

be an essential agent in the decomposition of carbon dioxide and 
the production of organic matter. Only those parts of the plant 
which contain chlorophyll are able to assimilate carbon dioxide. 
If, for any reason, chlorophyll is not formed, assimilation 
cannot take place. The green color of chlorophyll is sometimes 
disguised by the presence of other pigments. 

Effect of Color of Light. The effect of light depends upon its 
color and intensity. The following are outlines of methods for 
studying the effect of color of light on plants. 

(i) Plants may be grown in boxes of different colored glass. 1 
This method allows the experiment to be continued any desired 
length of time. The plants can be then subjected to analysis or 
otherwise examined. The light which passes through colored 




Fig. 6. Tent for shading tobacco. Pennsylvania station, 
glass, is not, however, usually a single color, but is admixed with 
white or other colors, as can be easily seen by analysis of it with 
a spectroscope. This is an objection to the method. 

(2) A ray of sunlight is decomposed with a prism and the 
spectrum thrown upon a screen with a slit in it, allowing the 

1 Weber, Jahresber. f. Agr. Chem., 1875-6, p. 336. Flammarion, Exp. 
Sta. Record 10, p. 103. 



THE: PLANT AND THE: ATMOSPHERE 




Fig. 7. Tobacco, (A) shaded; (B) not shaded. Pennsylvania Station. 



42 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

passage of only one kind of light. This falls upon a leaf placed 
in water containing carbon dioxide. All the colors except the one 
to be tested are excluded by the screen. 1 The number of bubbles 
of oxygen liberated from the leaf in a given time is taken as a 
measure of the action of the light in producing organic matter by 
the decomposition of carbon dioxide. More accurate results are 
secured if the volume of oxygen is measured. 

Control of Light. Only in isolated cases is control of light of 
practical significance in agriculture. Forcing of early vegetables 
by artificial light has been tried but has not proved successful 
enough to be generally adopted. Cigar wrapper tobacco is grown 
under the shade of cheesecloth or slats. 2 Reduction of light by 
shading makes the plant grow taller and produce thinner leaves 
than under ordinary conditions. The thin leaves bring high 
prices for use as wrappers in making cigars. The shading, how- 
ever, also modifies moisture and temperature conditions. 3 

Oxygen. Oxygen is necessary to both animal and plant life. 
Without oxygen, animals quickly die from suffocation. The 
oxygen is required by animals for processes of oxidation 
necessary to life, such as the production of animal heat. The 
oxygen consumed is replaced by carbon dioxide in the respired 
air. Oxygen is also consumed in the decay of organic matter, in 
combustion, and in other processes of oxidation. 

The oxygen lost from the air by oxidation is restored by green 
plants, which, as we have seen, absorb carbon dioxide and evolve 
oxygen. On account of diffusion and air currents, the quantity 
of oxygen in the air varies but slightly. In analyses made in 
widely separated parts of the world, the minimum and maximum 
amounts of oxygen in pure dry air are 20.53 an< ^ 2I -3 parts by 
volume. 

Oxygen is necessary for the germination of seeds, for the 
development of buds, for the roots of certain plants, and for 

1 Pfeffer, Jahresber Agr. Chem., 1870-2, p. 179. 

2 Report No. 62, U. S. Dept. Agr. 

3 Stewart, Bui. 39, Bureau of Soils. 



THE: PLANT AND THE ATMOSPHERE 43 

flowers. De Saussure 1 found that buds require oxygen by the 
following experiment. He enclosed woody twigs cut in the spring 
just before the time for buds to unfold, in jars containing various 
gases. In hydrogen or nitrogen the twigs decayed, but in the air 




Fig. 8. .Experiment to ascertain the effect of gases 
on the roots of plants. 

the buds opened and, on analysis of the air, oxygen was found 
to have disappeared. It thus became evident that the buds require 
oxygen for their development. 

In similar experiments with flowers, De Saussure found that 
they consume several times their volume of oxygen in 24 hours. 
De Saussure 2 tested the effect of different gases upon roots of 

1 Johnson, How Crops Feed, p. 23. 

2 Johnson, How Crops Feed, p. 24. 



44 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

plants by cementing the plant in a bell jar, so that the stem and 
leaves were in the outer air, while the roots were within the 
vessel and exposed to any gases that might be placed therein. 
The horse chestnut died in 7 to 8 days when its roots were placed 
in carbonic acid gas, in from 13 to 14 days in nitrogen, or hydro- 
gen, while the plant remained healthy to the end of the experi- 
ment (21 days) when the roots were in contact with air. The 
experiment shows that the roots of this plant require oxygen, 
though it lived for some time without oxygen. Other experi- 
ments show that roots absorb oxygen and give off carbon dioxide. 
The roots of some plants, which prefer heavy, wet soils, probably 
do not require oxygen. The difference in the root requirements 
of plants for oxygen is probably one factor in their adaptation to 
various types of soil. 

Nitrogen. The nitrogen of the air, which makes up four-fifths 
of its volume, is in the free state, and enters into combination 
only with difficulty. So far as animals and the majority of plants 
are concerned, the nitrogen of the air serves only as a dilutant 
for the oxygen, which would have too energetic an oxidizing 
action if in the pure state. 

To be of value to animals or to most cultivated plants, nitrogen 
must be in combination. This store of combined nitrogen is com- 
paratively small. Plants and the bodies of animals contain some 
combined nitrogen ; there is some in the soil, coal contains a small 
percentage, and there are some deposits of nitrate of soda. 
Combined nitrogen is lost when organic matter is burned, any 
nitrogen present being evolved in the free state. Explosives are 
rich in nitrogen, which is set free when they are used. In certain 
processes of decay, free nitrogen is evolved. 

The supply of combined nitrogen in the soil is comparatively 
small, and it is constantly drawn upon by crops. Under our 
present system of agriculture, the stores of nitrogen in the soil 
are exploited and depleted. A considerable quantity of nitrogen 
is washed from the soil by water. Maintaining the fertility of 
the soil is largely a question of maintaining its store of combined 
nitrogen. Fortunately, we have now obtained the means for 



THE PLANT AND THE ATMOSPHERE 45 

causing the free nitrogen of the air to enter into combination. 
The ways at present in which this is accomplished are as 
follows : 

1 i ) One process is the assimilation of free nitrogen by bacteria 
in symbiosis with leguminous plants. This method is the most 
promising for practical agriculture. The energy of the sun is 
utilized and the nitrogen is converted directly into organic matter. 
Some bacteria appear to be able to assimilate nitrogen without the 
aid of plants. 

(2) Another process is the electrical production of 
nitric acid or nitrates. An electrical discharge is passed 
through air or through a mixture of nitrogen and 
oxygen, and the oxides of nitrogen produced thereby are 
absorbed by water or sodium carbonate or caustic soda. When 
water is the absorbing medium, nitric acid is produced ; if caustic 
soda or lime is used, nitrates are produced, which may be used 
as a fertilizer. Since nitric acid is more valuable than nitrate of 
soda, nitric acid is made when practicable. This method is 
practicable only when electricity can be produced cheaply, such 
as is accomplished by water power. 

(3) Production of Calcium Cyanamid. 1 Air, freed from 
oxygen by passing over heated metallic copper, is passed into a 
mixture of calcium carbonate and carbon heated in the electric 
furnace. The first product is probably calcium carbide: 

2CaCO 3 + 50 = 2CaC, + 3CO 2 . 

This is then converted by absorption of nitrogen into calcium 
cyanamid : 

CaC 2 + 2N = CaCN 2 + C. 

The product contains 15 to 25 per cent, nitrogen and is used 
directly as a fertilizer. A cheap source of electrical energy is 
required. 

Circulation of Nitrogen. The circulation of nitrogen is some- 
what more complicated than that of carbon. The diagram shows 
the various processes which it undergoes. 
1 Bulletin 63, Bureau of Soils. 



46 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

Argon, which is found in the air, is a gas related to nitrogen 
and is apparently incapable of entering into chemical combination. 
It has no agricultural importance. Associated with argon in the 
air, in very small quantity, are the other gases of similar char- 
acter, namely, neon, helium, krypton, and zenon. 



A TMO 5PHE7VC NITROGEN 




Fig. 9. Circulation of nitrogen. 

Ammonia. The air contains about one part of ammonia in 
fifty million. The column of air resting on an acre weighs about 
41,300 tons, which would contain about 1.5 pounds ammonia. 
Country air contains less ammonia than town air. The ammonia 
in the air probably comes from the decay of organic nitrogenous 
bodies, especially urine. The exhalations of volcanoes and 



THE PLANT AND THE ATMOSPHERE 47 

fumeroles also contain ammonia, which may be due to the action 
of water on nitrides. 

Ammonia gas is absorbed by the foliage of plants, as has been 
shown by experiments such as the following of Peters and Sachs. 1 
The stem of a bean plant was cemented under a bell jar. The 
leaves and foliage were within the jar, while the roots and soil 
were outside. The plant was supplied through tubes with air 
mixed with 4-5 per cent, carbon dioxide. Another plant in a 
similar apparatus was supplied with the same gases, but they 
were passed through a dilute solution of carbonate of ammonia, 
which gives off ammonia. After two months, the plant supplied 
with ammonia weighed, when dried thoroughly, 6.74 grams, and 
contained 0.208 gram nitrogen; the other plant weighed 4.14 
grams, and contained 0.106 gram nitrogen. The gain of nitrogen 
must have been caused by the absorption of ammonia by the 
foliage of the plant. If the entire plant and the soil in which it 
grew had been placed in the bell jar, ammonia would have been 
absorbed by the soil and presented to the roots. But the arrange- 
ment of the experiment eliminated this possibility, since the soil 
and roots did not come in contact with the ammonia at all. 

The ammonia of the atmosphere is in such small quantity that 
it has practically no effect upon plants. This has been shown by 
experiments such as the following: Hellriegel 2 grew lupines in 
sterilized sand supplied with all plant food except nitrogen. The 
nitrogen content of both seed and sand had been previously ascer- 
tained by analysis. After the plants had reached their full 
development, both plants and soil were subjected to analysis, and 
the amount of nitrogen found was .007 gram less than was present 
in the seeds planted and in the original soil. The plants, there- 
fore, had lost a small amount of nitrogen, instead of gaining any 
from the free nitrogen, or from the ammonia of the air. 

Nitric Acid. Nitric acid occurs in the air, probably in com- 
bination with ammonia. It is formed by electrical discharges 
(lightning). The quantity of nitric acid in the air is very small, 

1 Johnson, How Crops Feed, p. 56. 
- Exp. Sta. Record, 5, 844. 



4 8 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



however, and the plants are unable to absorb any appreciable 
quantity directly from the atmosphere. 

Combined Nitrogen in Rain Water. The atmospheric ammonia 
and nitric acid are chiefly of importance from the fact that they 
are brought to the soil in rain, dew or snow, and thereby afford 
nourishment for plants. 

The quantity of combined nitrogen in the rain has been ascer- 
tained at a number of Experiment Stations, 1 by determining the 
quantity and composition of each rainfall. The results of a 
number of series of observations, each extending over a period of 
a year or longer, are summarized in the following table : 

COMBINED NITROGEN IN RAINFAU, PER YEAR IN POUNDS PER ACRE. 





(a) 

Nitrogen 
as ammonia 


(b) 

Nitrogen as 
nitric acid 


(a + b) 
Total 
combined 
nitrogen 


Temperate Zone 


5-72 
12 95 
0.50 

3-38 
2-95 
2.62 

4.26 
14.05 

I-I3 


2.27 
6.97 

I.I3 

0.24 

I.I3 
1.04 

3-33 

6.24 
0-75 


7-99 
19-93 
1.6 3 
3.62 
4.08 
3-66 

7-59 
19-25 

1.88 






Minimum ( Ploty ) 


Rothauisted lintjlaiid 


Kansas 


Tropical Zone 











There appears to be considerable variation in the quantity of 
combined nitrogen brought to the earth by the rain; the average 
for the temperate zone is 8 pounds per acre. This is sufficient 
to produce approximately 5.3 bushels of corn, leaves and stalk 
included. But it is probable that the water which percolates 
through the soil, in humid regions, takes out more combined 
nitrogen than is brought down by the rain. 

Hydrogen Peroxide. Country and sea air contains a small 
quantity of a powerful oxidizing agent, which, according to 
1 Miller, Jour. Agr. Sci., 1905, p. 280. 



THE PLANT AND THE ATMOSPHERE 49 

Schone, 1 is hydrogen peroxide, though it is often said to be ozone. 
This substance is destroyed by putrescible substances, and it 
destroys bacteria. The presence of hydrogen peroxide is thus 
evidence of the purity of the air as regards freedom from bacteria 
and putrescible bodies. Hydrogen peroxide does not occur in 
the air of towns or marshes, since any formed is instantly 
destroyed by the organic matter present. 

At Montsouris, near Paris, the amount of hydrogen peroxide 
in the air was estimated to be on, an average, about one part in 
100,000,000 for a period covering thirteen years. 

Hydrogen peroxide may be formed by electrical discharge 
(lightning) and in some processes of oxidation. It acts upon 
iodide of potassium, liberating iodine, which turns starch blue. 
Paper impregnated with potassium iodide and starch is a delicate 
test for ozone, or hydrogen peroxide, since very small quantities 
of these substances suffice to turn it blue. 

Other Constituents of the Air. Marsh gas (CH 4 ) is a colorless 
and odorless gas produced in the decay of vegetable matter under 
water, as in marshes, and in the digestion of hay and other food 
by herbivorous animals. Small quantities of it occur in the air. 

Sulphur dioxide may occur in the air in the neighborhood of 
smelters, factories, or in towns. If present in appreciable quan- 
tity, it is injurious to vegetation. It is evolved from the oxida- 
tion of sulphur during the combustion of coal. 

Dust particles, organic matter, and salts from the evaporation 
of the spray of the sea, are found in the air. 

Bacteria are also present, in much greater numbers in the city 
than in the country. Levy found 345 per cubic meter in the air 
of Montsouris, 4,790 in the air of Paris (average of 13 years). 

Composition of Rain Water. Rain water has been converted 
into vapor by the sun, and condensed again into a liquid. In 
its passage through the air, rain water takes up ammonia, nitrates 
dust, chlorides and other constituents of the air. Rain water, 
therefore, though it is the purest natural water, is not absolutely 
pure. 

1 Berichte, 1880, p. 1503. 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



In exceptional cases it has been known to contain so much dust 
as to assume a red or black color. It usually contains a small 
amount of chloride of sodium, and sulphates. The following is 
a summary of a large number of analyses of rain water made by 
Angus Smith. 1 

ANALYSES OF RAIN WATER PARTS PER MILLION. 





Chlorides 
(as sodium 
chloride) 


Sulphates 
(as sodium 
sulphates) 


Ammonia 


Nitric acid 


Scotland 
Five coast country places . 
Twelve inland country places 


20.3 

5-6 

9-7 
14.4 


6.4 
3-5 
19.2 
60.7 


0.48 

0-53 

3-82 

4-99 


0-37 
0.31 

i.z6 

0.85 







We find from the table that the coast rain water contains more 
salt (sodium chloride) than the rain of inland places. This is 
due to the salt spray from the sea, which is broken up into fine 
particles, and carried by air currents for long distances. The 
effect of the sea upon rain water is often noticeable for a hun- 
dred miles inland. 

Comparing rain water of the city and of the country, we find 
that the former is marked by the presence of considerably more 
sulphates and ammonia, and that it also contains free acid. The 
increased quantity of sulphates and the sulphuric acid in the 
rain water of cities can be traced to the combustion of coal con- 
taining sulphur. 

Arid and Humid Climates. In a humid climate, the rainfall is 
sufficient, or more than sufficient, for the production of culti- 
vated crops. In an arid climate the rainfall is insufficient in 
quantity, and crops can be grown only through irrigation, or 
by means of special methods of culture. The character of the 
rainfall also influences the relation of the climate towards crops. 
A comparatively small amount of rain distributed through the 
growing season may give a locality the characteristics of a humid 
region, while a heavier rainfall so distributed that very wet 
periods are followed by long intervals of little or no precipita- 
1 Jour. Chem. Soc., 1872, p. 33. 



THE PI.ANT AND THE ATMOSPHERE 51 

tion, may give an arid or semi-arid climate. When the average 
annual rainfall is 20 inches or below, it is generally assumed that 
crops cannot be grown without irrigation. 

Soil Atmosphere. The gases which occupy the pores of soils 
differ in composition from the atmosphere, chiefly in the fact that 
they contain much more carbon dioxide and less oxygen. 

The oxygen of the soil atmosphere performs the following 
functions : 

(1) It oxidizes the organic matter, producing carbon dioxide. 
Bacteria play an important role in this change. In the absence 
of air, putrefaction takes place, with production of acid or bad 
smelling bodies. 

(2) It is necessary for the oxidation of organic nitrogen or 
ammonia to nitrates. 

(3) It is necessary for the roots. 

(4) It oxidizes partly oxidized mineral compounds, such as 
ferrous or manganous salts. 

The nitrogen of the soil atmosphere is fixed by legumes, in 
co-operation with certain bacteria, producing organic nitrogenous 
compounds. 

The carbon dioxide of the soil atmosphere is formed by pro- 
cesses of oxidation, and it is also evolved by the roots of plants. 
If not removed with sufficient rapidity, it excludes oxygen, and 
thereby interferes with the normal processes of the soil. The 
carbon dioxide of the soil increases the solvent action of the soil 
water, thereby aiding in the disintegration of the minerals of 
which the soil is composed, and in the solution of plant food. 

Processes of Soil Ventilation. The exchange of gases between 
the atmosphere and the soil atmosphere depends to a consid- 
erable extent upon the character of the soil. A coarse-grained, 
open soil is much more easily ventilated than heavy, stiff soils. 
Indeed, it is possible that processes of oxidation take place too 
rapidly in some porous soils, resulting in the rapid loss of nitro- 
genous material and consequent poverty of the soil. 

The particles of air in the soil tend to move out into the atmos- 



52 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

phere, and those without move in. This process, known as 
diffusion, though a slow process, aids in soil ventilation. 

Air expands when its temperature is raised, and contracts 
when it cools. These changes also aid in soil ventilation. So 
do the expansion and contraction resulting from barometric 
changes. Gusts of wind exert a suctional effect. When water is 
removed from the soil, air enters in its place. 



CHAPTER IV. 



ORIGIN OF SOILS. 

The soil is the solid outer covering of the earth, which, by 
being disintegrated into particles, and provided with organic 
matter and nitrogen, has become capable of sustaining the growth 
of cultivated plants. 

The chemical composition and physical character of the soil 
are closely related to the material of its origin and its mode of 
formation. 

Geology teaches that ages ago the surface of the earth was a 
mass of rock, formed by the solidification of molten material. 
Since then mountain chains have been elevated and razed, and 
succeeded by new mountains which have been likewise eroded and 
succeeded by others. Lakes have been filled up or drained, 
rivers have eroded channels and deposited sediment. Land now 
dry has been deposited under water. Great changes of climate 
have occurred. During one period the vegetation was tropical in 
character. At another time, the climate was colder, and 
immense sheets of ice covered the northern part of 
North America. Races of plants and animals have appeared 
and disappeared. The agencies of the air, and water, 
have broken up rocks, carried the particles away, and laid 
them down, perhaps to be formed into rock, elevated into land, 
and to go through another series of decomposition and rock 
formation. This process has occurred over and over again. In 
this way a variety of rocks and a great many soils have been 
formed. 

Soils Formed from Rocks. Soils are formed by air, water, heat, 
cold, and plant life, which are termed weathering agencies, acting 
upon rocks. The term rock in the geological sense, means any 
layer of the earth's crust, whether hard or soft. Thus loose 
sand and clay are rocks to the geologist as truly as sandstone 
or granite. The soil chemist, however, does not consider un- 
consolidated surface deposits as rocks. A deposit formed by 
wave action, and afterwards elevated so as to become a soil, is 
not considered as a rock, but as a transported soil. 



54 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

Weathering agencies act upon consolidated and unconsolidated 
rocks exposed on the surface of the earth, reduce the size of 
the particles, and change the rocks chemically and physically. 
The rocks are changed into soil capable of supporting the growth 
of cultivated plants. 

Broken rocks, however finely pulverized, do not constitute 
soil. Besides the mere mechanical breaking of the rock, two 
other processes take part in the conversion of rock into soil. 
First, a greater or less quantity of organic matter and combined 
nitrogen are stored up. This process begins with the bare rock. 
Bacteria first appear. These take up carbon dioxide and nitrogen 
from the atmosphere and leave organic matter and nitrogen when 
they die. Then mosses and lichens begin to appear. They also 
have the power of taking nitrogen from the air. As the weather- 
ing agencies deepen the soil, the variety of plants increases, but 
almost always some of the species are present which have the 
power of causing atmospheric nitrogen to enter into combination. 
The residues left when the plants die, store the soil with organic 
matter and nitrogen. A small amount of organic matter and 
nitrogen are contained in rocks. 1 

The second change in the conversion of rock to soil is due to 
the fact that plant food becomes more easily taken up by plants 
than it was in the original rock. This is in part due to chemical 
changes, and in part to the action of the organic matter which 
has been added, but perhaps to the greatest extent to the work- 
ing over of the plant food by the past generation of plants. 

Weathering Agencies. Weathering is the term applied to the 
natural decomposition or breaking* up of rocks, and weathering 
agencies are the agencies which do this work. Weathering and 
weathering agencies are studied by observing the changes which 
are now going on, and by comparing altered rocks with the 
original masses from which they were derived. 

Weathering processes are both mechanical and chemical. They 
are mutually helpful. Mechanical processes reduce the size of 
the rock fragments, thereby affording more surface for chemical 
1 Hall and Miller, Jour. Agr. Sci., 2, p. 343. 



ORIGIN OF SOILS 



55 



action. Chemical processes often disintegrate the rock into very 
fine particles. 

Changes of temperature, moving water, and ice, act mechanic- 
ally. The chemical agencies are chiefly water and air. Plant 
and animal life act both mechanically and chemically. 

Changes of Temperature. Changes of temperature act in sev- 
eral ways. 

(i) Molten rock masses contract on cooling and become per- 
meated by fissures, cracks, and joints. 




Fig. 10. Rock split by heat and cold. 

(2) Water enters into the cracks between rock masses, and, to 
some extent, into the pores of the rock. When this water freezes, 
it expands one-fifteenth of its bulk and exerts a tremendous force. 
It thus splits up rock masses, and disintegrates rocks which are 
porous. 

(3) Rocks are usually composed of two or more minerals, 
which expand differently under the influence of heat. Heat 
causes the different minerals to expand and to press on one an- 
other, and cold makes them contract and move apart. In time 
these movements so impair the coherence of the particles as to 
cause gradual disintegration of the rock. 

(4) Large pieces have been observed to split off from bare 
rocks exposed to the sun. This is due to expansion under 
the influence of heat, and can take place to any extent 
only on mountain sides where the fragments fall away from the 
rock surface. 



5 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

Moving Water and Ice. Water, moving from higher to lower 
levels, uses the rock particles it carries as tools to scour channels 
even in the hardest rocks. The sides of the channel, being under- 
mined by the stream and loosened by frost, fall into the stream. 
The rocks grind each other to smaller fragments. All of this 
material is on its way to the sea or to a lower level and is ground 
finer as it is carried on. 

The rate of movement depends upon the size of the rock, and 
the size and velocity of the stream. A portion of the material 
is deposited by the stream, perhaps building up alluvial soils, but 
sooner or later the stream will begin moving it towards the sea 




Fig. n. A glacier in the Alps. 

again. Water-borne materials are sorted, that is, material of 
nearly the same size is deposited together. Layers of different 
material may alternate, varying with the velocity of the water 
current. 

Rivers of ice, or glaciers, are formed in very cold climates, or 
flow from the sheets of perpetual snow covering high moun- 
tains. They move slowly, grinding rocks together with enormous 
force, and form deposits different in character from those of 
rivers. The fragments are more angular and the deposit consists 



ORIGIN OF SOILS 57 

of all sizes of particles together. It is said that the Rhone, which 
is fed chiefly from the glaciers of the Alps, carries such a volume 
of rock dust that its muddy waters may be traced six or seven 
miles after they have entered the Mediterranean. The action of 
glaciers is mechanical ; the rock is ground up, but not decomposed. 

Chemical Action of Water and Air. Water acts chemically 
upon rock-minerals by solution and by hydration. Rain, in pass- 
ing through the air, dissolves oxygen, carbon dioxide, and other 
substances. In the soil the water absorbs acids formed by the 
decay of vegetable matter. These substances aid in its weather- 
ing action. 

Hydration is a chemical change in which the mineral combines 
with water. Some minerals take up water, increase in bulk, and 
fall to a powder. Hydrated silicates are formed from various 
silicates. 

Solution. There are very few minerals which do not give up a 
portion of their constituents to water, though the amount of 
material which goes into solution is usually very small. If 
pulverized felspar, amphibole, etc., are moistened with pure water, 
the latter at once dissolves a trace of alkali from the mineral, as 
shown by its turning red litmus blue. This solvent action is slight 
on a smooth mass of the material, being limited by the extent of 
surface. Pulverization, which increases the surface, increases 
the solvent effect considerably. 

This solution involves a chemical change, new bodies with new 
properties being formed. Carbon dioxide and oxygen aid the 
action greatly. For example, potash felspar is decomposed by 
water with the formation of potassium silicate and aluminium 
silicate. In the presence of carbon dioxide, potassium carbonate 
is produced and hydrated silica set free, the quantity depending 
upon the amount of carbon dioxide present. A lime felspar is 
decomposed in the same way, and the calcium carbonate dissolved 
by aid of the carbon dioxide the water contains. Silicates of iron 
are decomposed with the production of hydrated oxides of iron 
and silicic acid. If the silicate is a ferrous silicate, the iron is 
oxidized by the oxygen in the water. 
5 



58 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

Carbonic acid increases the solvent power of water. Rain water 
contains from 5 to 10 parts (by volume) of carbon dioxide. River 
and spring waters contain more, but most of it is in combination 
with lime. The capillary water of soils containing much organic 
matter, holds more carbonic acid in solution than river or spring 
water. 

Water containing carbon dioxide is especially active in dissolv- 
ing carbonate of lime or limestone, and removing it from the soil 




Fig. 12. Limestone cavern. 

or rock. Carbonate of lime is slightly soluble in water (20 parts 
per million), but much more soluble in water containing carbon 
dioxide, owing to the formation of calcium bicarbonate : 
CaCO, + H, 2 O = Ca(HCO 3 ) 2 . 

Water saturated with carbon dioxide dissolves about 880 parts 
per million. This solvent action has resulted in the formation 
of large caverns in limestone regions. 

Oxygen is also dissolved in most natural waters, and acts upon 
the ferrous or manganous compounds which occur in a great 
number of minerals. When oxidized, these occupy a larger space 
than before, and thus hasten the disintegration of the minerals 
containing them. Some ferrous silicates are oxidized rapidly on 
exposure to moist air, falling into a brown powder in a few weeks. 



ORIGIN OF SOILS 59 

As a rule, silicates containing much iron are easily changed by 
weathering agencies. 

Action of Animal and Vegetable Life. Animal and vegetable 
life act on rocks, both by their living activities and the decay of 
their remains. Vegetation acts both mechanically and chemically 
upon the soil and rocks. Roots of plants penetrate the crevices 
of rocks, and, as they grow, split even large rocks. The shelter 
of growing plants keeps the rock surface moist, thus enabling the 
water to act upon the rock, and the carbon dioxide excreted from 
roots, adds its effect to that derived from other sources. Plants 
take up material, which, under natural conditions, returns to the 
soil in a modified form. 

Earthworms in some cases bring to the surface large quantities 
of soil, most of which has passed through their intestines and 
undergone mechanical and chemical changes. 

Vegetable or animal residues aid weathering in several ways : 

(a) By maintaining more moisture in the surface of the soil. 

(b) By supplying copious quantities of carbonic acid. The 
following figures of Boussingault and Levy 1 exhibit the amount 
of carbonic acid in the air of the soil under different conditions : 

Carbonic acid in 
10,000 parts by weight 

Ordinary air 6 

Air in sandy subsoil of forest 38 

Air in loamy subsoil of forest 124 

Air in surface soil of forest 130 

Air from surface soil of pasture 270 

Air from surface soil rich in humus 543 

Newly manured sandy field in wet weather 1413 

(c) By direct action of organic acids such as acetic, propionic, 
"humic," etc., which are found in vegetable matter or produced 
in its decay. 

(d) By furnishing a medium for the activity of the lower 
soil organisms, such as bacteria and molds. 

Products of Weathering. The general tendency of weathering 
is towards the production of simpler compounds from more 
complex ones. The oldest rocks (which are igneous in origin) 
1 Jahresber. der Chem., 1852, p. 783. 



60 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

contain complex silicates of aluminium, iron, potassium, sodium, 
lime, etc. The tendency of weathering is to reduce these to 
simple compounds, such as silica, hydrated oxides of iron, 
hydrated silicates of aluminium, carbonates or sulphates of lime 
and magnesia, chlorides of sodium and potassium, and sili- 
cates of magnesia. The complex silicates are not changed directly 
to these simple bodies, but various intermediate products are 
formed. A long period is required for this process to become 
complete, so that in many soils all stages of the change may be 
present, from particles of the original minerals, through various 
hydrated silicates derived therefrom, down to the simpler com- 
pounds. The conditions under which the weathering occurs 
determine the degree of decomposition. If the weathering agen- 
cies are chiefly mechanical, the rock may be reduced to a powder 
with little chemical change. 

Loss of Material by Weathering. In every case of weathering, 
a greater or less portion of the constituents of the rock have been 
carried away. An estimate of the loss may be made where the 
soil rests directly upon the rock from which it is derived. 
Samples of the soil, and of the unchanged rock beneath it, are 
subjected to analysis. We assume one ingredient of the rock 
has lost nothing in weathering, and calculate the quantity of the 
original rock containing the amount of this ingredient found in 
100 parts of the soil. This gives us the quantity of original rock 
from which 100 parts of soil was secured. When the composition 
of both is known, it is a simple matter to calculate the loss of each 
ingredient. 

Suppose, for example, the original rock contained 30 per 
cent, alumina, and the weathered product contains 45 per cent, 
alumina. It being assumed that no loss of alumina took place, 
150 pounds of the original rock would contain 45 pounds of 
alumina; that is, 150 pounds has weathered to 100 pounds. If 
the original rock contained 2 per cent, magnesia, and the weath- 
ered product 0.5 per cent., then 150 pounds contained three 
pounds, and we have 0.5 pound left, giving a loss of five-sixths 
or 83^ per cent, of magnesia. Two assumptions are made in 
this procedure ; one being that some constituent has not been lost 



ORIGIN OF SOILS 



61 



at all, the other being that the rock from which the soil was 
derived was exactly the same as the underlying rock. As neither 
assumption is strictly true, the method gives merely approximate 
results. 

The following figures, secured by the method outlined above, 
are compiled from Merrill's "Rocks, Rock Weathering and 
Soils." 

CALCULATED PERCENTAGE Loss IN WEATHERING. 





Granite 
Virginia 


Syenite 
Arkansas 


Limestone 
? 


Basalt 
Bohemia 


Soapstone 
Maryland 


Silica (SiO ) 


52.5 
O 

14.4 

100.0 

74.7 

83.5 

95.0 


52.3 



86.2 

57-9 
82.1 
81.9 
97.1 


O 
II. 4 

89.4 
66. 3 

53-3 


33-i 



50.2 

84.5 
74.1 
6i.7 


43-6 



4i.5 
44.2. 
76.2 
47-1 


Alumina ( A 1 O ) 


Ferric oxide ( Fe. 2 O 8 ) 
L/ime ( CaO ) 




p f a cVi ( K O^ 


c or i a /Nfl Q\ 





The order in which these constituents are lost varies with the 
rock and the conditions ; the following is the mean order in seven 
cases : 

(i) Lime, (2) potash, (3) magnesia, (4) soda, (5) iron, 
(6) silica, (7) alumina. That is, the greatest loss is usually of 
lime, the next greatest is potash, and so on. The figures given 
in the table preceding are sufficient to show the profound change 
which may occur in the transformation of rock into soil and the 
large amount of material which is carried away during weather- 
ing, probably for the most part dissolved in water. 

Sedentary and Transported Soils. A sedentary soil is a soil 
derived from the weathering of a rock in the present location of 
the soil. On making an excavation, if the soil is sedentary, we 
find the following : First, the surface soil ; then the subsoil, 
lighter in color but of the same general character ; and at a lower 
depth, we find the subsoil mixed with fragments of partly weath- 
ered rock. The fragments increase in quantity until finally we 
come to the solid rock. We thus observe a gradual transition 
from soil to rock, and therefore infer that the overlying soil is 
derived from the decomposition of rock which formerly occu- 



62 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



r// 



7/y 



ORIGIN OF SOII^S 63 

pied its position. The soils derived from limestone deposits in 
Kentucky and in Texas are sedentary, and so are the soils 
derived from granite and other igneous rocks which are common 
in the Piedmont plateau of the Atlantic states. Old sedentary 
soils, from whatever kind of rock derived, are as a rule clays 
colored by iron. The various mineral constituents are often in 
an advanced stage of decay, the more soluble constituents having 
been largely washed out. 

A section of the soil may not show a gradual change to the 
underlying rock, but the change may be abrupt and sudden. 
Such a soil may be formed when the soil particles are brought 
from other localities, and deposited, in which case the soil is 
termed a transported soil. 

Colluvial and Cumulose Soil. A colluvial soil is one which 
has been removed, to some extent, from the original position, so 
as to mingle with other rocks and layers, as when a soil is 
washed or moved down hillsides or sloping land. Such soils 
commonly "creep" or have a slow annual movement. Colluvial 
soil particles have been partly moved by water, but have not 
been laid down under water as have alluvial soils. A cumulose 
soil has been formed by the accumulation of vegetable matter, 
such as occurs in swamps. Peat and muck are cumulose. 

Soils from Igneous Rocks. Igneous rocks are formed by the 
cooling of molten matter which has been spread out upon the 
surface of the earth or injected between layers of other rocks. 
Metamorphic rocks were laid down by water or other agencies, 
but were afterwards subjected to such intense heat and pressure 
as to crystallize minerals in them. 

The physical and chemical character of the rock and of the 
soil which may be derived from it, depends upon its chemical 
composition, and the rapidity with which the igneous rock solidi- 
fies. If the molten mass cools off rapidly, so that it solidifies in 
a comparatively short time, minerals do not have time to crys- 
tallize, and a hard, homogenous, glassy mass is produced (glassy 
rock). If the molten material remains liquid for a long time 
and cools slowly, the rock produced is a mixture of definite 
minerals which can be easily distinguished (crystalline rock). 



6 4 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



Other conditions of cooling may give rise to a compact, stony 
mass, composed of minute crystals (stony rock) or to a rock 
containing large crystals of one or more kinds of mineral em- 
bedded in a stone or glass matrix (prophyry). These differences 




Fig. 14. Microscopic appearance of porphyry. 




Fig. 15. Microscopic appearance of granite. 

in the structure of rocks of the same composition will give rise 
to different soils. Glassy rocks will produce more or less homo- 
genous particles, while crystalline rocks will weather into par- 
ticles of different kinds, perhaps composed of the different 
minerals. 



ORIGIN OF SOILS 65 

The chemical classification of igneous rocks depends on the 
relative quantities of silica and bases present. Since silica is the 
acid portion of minerals, rocks containing 65 to 75 per cent, of 
silica are termed acid rocks, those containing 55 to 65 per cent, 
are called intermediate, and those carrying 40 to 55 per cent, are 
called basic. Crystalline acid rocks contain quartz, while basic 
rocks do not contain enough silica for free quartz to crystallize 
out. 

The granite group comprises rocks rich in silica and alkalies, 
containing 65 to 75 per cent, silica and 5 to 8 per cent, of alkalies, 
of which y^ to 2 /z consists of potash. They are, as a rule, much 
richer in potash than other igneous rocks, and form correspond- 
ingly better soils. 

Granite, the crystalline rock of this group, is very abundant, 
and soils derived from it are quite common. Granite soils are 
usually clay containing particles of quartz and mica, and they are 
often fertile, being especially rich in potash. Rhyolite, which 
is a porphyritic rock of this group, is extensively distributed 
in the western part of the United States. 

The syenite group of rocks resembles the granite group, except 
that the rocks contain less silica (55 to 65 per cent.) and more 
bases to correspond. Like the granites, the syenites are rich in 
potash. 

The diorite group contains about the same amount of silica as 
the syenites, but less alkalies and more lime and magnesia. 

The basalt group contains the basic rocks (40 to 55 per cent, 
silica). These rocks contain small amounts of alkalies, and are 
rich in iron, lime, and magnesia. 

The soils of the Piedmont plateau, in the eastern part of the 
United States, are derived mostly from igneous or metamorphic 
rocks, and. consist of sands and clays containing quartz and mica. 
This area extends from New York City to near the middle of 
Alabama. The soils of the eastern Appalachian Mountain region 
are also of similar origin. An extensive area in Washington, 
Oregon, and Montana is covered with soils derived from the 
weathering of basalt and other igneous rocks. 



66 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



Alluvial Soils. The water falling on the ground and running 
off on its surface, carries soil particles with it. Streams or rivers 
take up particles of rocks or soil materials and carry them along. 
In time of flood, when both the volume and velocity of the stream 
are increased, this burden becomes much greater, since the carry- 




CULF or vex/ co 



Fig. 16. Sketch map showing the flood plain of the lower 
Mississippi. U. S. D. A. 

ing power of water increases with the sixth power of the 
velocity with which it moves. That is, a river moving at the rate 
of four miles an hour may carry particles sixty-four times as 



ORIGIN OF SOILS 67 

heavy as a river moving at the rate of two miles an hour. While 
being carried, the particles are ground together and reduced in 
size. 

Whenever the velocity of a stream is decreased, it deposits a 
portion of its burden, the heavier particles being deposited first. 
Thus, when a swollen mountain stream issues from a gorge and 
spreads out over a plain, it deposits a portion of the material on 
the surface of the plain. When a river in flood leaves its banks, 
the velocity of the water is checked on spreading over the plain, 
and it deposits the coarser particles which it carries near the 
channel of the river. The finer particles are carried farther, and 
are deposited in the swamps or low ground at some distance from 
the river. The tendency of a river bearing rock debris is to build 
its banks up above the level of the surrounding country. The 
area over which a river spreads when in flood, is termed its 
Hood plain, and the soil formed from the particles which it 
deposits is termed an alluvial soil. Some of the richest soils in 
the world are alluvial soils. The soils are deep, and as they 
receive the surface soil washed away from less fortunate regions 
from time to time, their fertility is maintained. The valleys of 
the Nile, of the Ganges, the Mississippi, the Red river, the Brazos, 
and others, contain some very rich soils, which are alluvial in 
origin. The soils near the river are lighter in texture than those 
in the low grounds back from the river. The latter are very 
heavy, and difficult to work, but are often very productive. 

River deposits are stratified; that is, the material is sorted and 
deposited in layers consisting of material of very nearly the same 
fineness. Layers of fine and coarse material may alternate accord- 
ing to river conditions. 

In arid regions, where the streams decrease as they flow from 
the mountains out upon the dry lowlands and are therefore com- 
pelled to lay aside a large portion of their burden, mountain 
streams may form wide-spread alluvial plains, which are called 
piedmont (meaning foot of the mountain) alluvial plains. The 
streams which flow eastward from the Rocky Mountains have 
formed a continuous alluvial plain which stretches hundreds of 



68 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



miles from the base of the mountains, the deposits being in places 
five hundred feet thick. These deposits are now being eroded 
and reworked by streams. 




Fig. 17. Profile showing how a river builds up its banks 
near the channel. U. S. D. A. 

Alluvial soils, especially if deposited by large rivers, are derived 
from a mixture of minerals from different sources. The soils 
are more or less generalized and are usually very productive. 
Alluvial soils are found near rivers in all sections of the country. 
The most extensive alluvial soils are those near the Mississippi 
River and its tributaries, especially the Red River, the Arkansas, 
and the Missouri. 




Fig. 18. Alluvial cones, Wyoming. 

Glacial Soils. A glacier is a river of ice. It carries upon its 
surface and within its mass, soil and rock fragments derived from 



ORIGIN OF SOILS 



6g 



the hills and cliffs which it passes. This material consists of all 
grades of particles, from fine fragments to large pieces of rock. 
The rock fragments are usually angular, and some of them may 
be marked with parallel scratches. These scratches are caused by 
a rock held in the moving ice and pressing against another rock 
in the earth's crust. 




Fig. 19. Unstratified glacial drift near Chicago. 

At the end of the glacier is deposited a mixture of earth and 
rocks of all sizes, which is known as a moraine.- When the 
coming of a higher yearly temperature causes the front of a 
glacier to retreat, it leaves the surface of the earth covered with 
the mixed deposit characteristic of glaciers. The deposit beneath 
the glacier, which is called till, is sometimes an extremely dense, 
stony clay, having been compacted under the pressure of the 
moving ice. 



7O PRINCIPLES OF AGRICULTURAL CHEMISTRY 

The northern part of the United States was once covered by a 
great glacier sheet, stretching down from Canada. Glacial soils 
are accordingly found in New York, Ohio, and other Northern 
States. Some of these deposits have been reworked by rivers 
until their glacial characteristics are no longer easily recognized. 
Glacial soils are especially important in New York and states 
north of it, and in the states north of the Ohio and Missouri 
rivers. They frequently contain considerable amounts of car- 
bonate of lime. 




Fig. 20. Hypothetical map of glacial sheets of North 
America. Salisbury. 

The waters from the melting of the glacial sheet also carried 
ground-up material. Though this was sorted by the water, it is 
different from ordinary alluvial soils. These soils are found in 
the area adjacent to the glacial regions. 

Loess, finely ground material derived from glacial drift and 
transported by winds or flowing water, consists of grains of 
quartz, feldspar, mica, hornblende, with some limestone and clay. 



ORIGIN OF 

Wind Blown Soils. In any region where the soil becomes very 
dry and is not covered with vegetation, as in deserts or arid 
sections, the soil particles may be taken up by wind, and perhaps 
carried considerable distances. The attrition of the wind-borne 
particles reduces the softer minerals rapidly to dust, and harder 
minerals, such as quartz, more slowly. The dust and sand are 
separated, as the dust is carried farther. Wind-borne desert 
sands thus consist largely of quartz. Dust carried by upward- 
whirling winds into the higher currents of the air, is. often trans- 
ported for hundreds of miles beyond the arid region from which 
it is taken. In 1901 dust carried from the Sahara northward by 
a storm, fell with rain over southern and central Europe and as 
far north as central Germany and Denmark, causing a "black 
rain." 




Fig. 2i. Dune sands, Lake Michigan. 

In northern China an area as large as France is deeply covered 
with a yellow pulverulent earth called loess, but which many 
consider a dust deposit blown from the great Mongolian desert 
to the west of it. The soils of some of our western States are 
wind-blown soils. 

Even in humid climates, in many places along the seashore, or 
lake beaches, as in New Jersey or Michigan, the beach sand is 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



heaped by the wind into wave-like hills called dunes. Dunes 
whose sands are not fixed by vegetation, travel slowly with the 
wind, and they may invade and destroy forests and fields, and 
bury villages beneath their slowly advancing waves. River 
deposits on flood plains are often worked over by the winds dur- 
ing summer droughts, and much of the silt is caught and held by 
the forests and grassy fields bordering on the area. 

Wind-blown materials may aid in the formation of soils even 
in humid regions. Thus, Hall 1 relates that a beach composed of 
coarse rocks (shingle) was found in years to have accumulated 
a few inches of a black powder, probably borne there by the 
wind. 

Soils from Oceanic Deposits. The more important oceanic 
deposits from which soils are derived are sands and sandstones, 




AfudandC/ays Limestone Sand 



Fig. 22. Present distribution of deposits in the Atlantic near 
the United States. 

muds, shales, and other consolidated sediments, and limestone 
deposits. The material of the oceanic deposits comes from the 
wear and tear of the waves on the shore, and from the waste 
1 The Soil, p. 10. 



ORIGIN OF SOILS 73 

brought down by rivers. It is estimated that the waste derived 
from cliffs, etc., along the seashore is about three per cent, of that 
brought down by rivers. 

Sands are deposited along the shores of the sea. Boulders, 
pebbles, and coarse sand, are deposited in order near in shore, and 
the finer sands farther out. Beach sand derived from rocks of 
neighboring cliffs or brought down by torrential rains from 
mountain regions is dark, and contains grains of many minerals 
other than quartz. These sands contain more plant food and 
make richer soils than sands from low-lying shores. The white 
sand of low shore beaches, such as those on the east coast of the 
United States from Virginia to Florida, consists almost entirely 
of quartz grains. The other and softer minerals have been 
entirely beaten to mud and deposited farther out during the long 
period that the material has been exposed to the waves. These 
sands are poor in plant food, but they are excellent soils for some 
purposes. 

Sandstone consists of sand grains cemented together by silica, 
carbonate of lime, or oxide of iron. Such deposits are widely 
distributed, and many soils are derived from them. The quality 
of the soil depends largely upon the origin of the sands. Quartz 
is sandstone, which, by the action of heat and pressure, has been 
metamorphosed in the crust of the earth. 

Muds are deposited beyond the sand deposits, and also in quiet 
water near shore, and in river deltas. Muds contain the finer 
particles from the wear of rocks. The soils derived from them 
contain more plant food than sands and produce longer, but are 
not adapted to the same kinds of plants. 

Muds may be consolidated into mudstone or shales or 
metamorphosed by heat and pressure into schists and slates. Soils 
are formed by the weathering of all these deposits. 

Limestone deposits are formed from the shells of molluscs, and 
deposits of coral, and other marine organisms which secrete car- 
bonate of lime from solution in the sea-water, some of which are 
minute in size. These deposits are usually formed in the shallow 
water beyond the area in which mud is deposited ; they also make 
6 



74 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

up a large part of the deep sea deposit. Phosphoric acid is fixed 
in small quantities in these deposits. 

Limestone deposits may be metamorphosed into limestone rock, 
marble, or other crystalline forms of lime. By the weathering of 
such deposits, many fertile soils have been farmed. Some old 
soils of limestone origin are practically free of carbonate of lime, 
and are very poor. 

Deposits in Lakes. Lakes are not permanent, geologically, but 
are gradually filled with deposits of waste brought into them by 
rivers, unless the lake is drained before such filling takes place. 
The lake is first converted into a swamp, and finally into dry land. 

In lakes without an outlet, various salts are deposited. Such 
lakes can exist only in dry climates, where the loss by evaporation 
is equal to or greater than the amount of water brought in by 
rivers. Rivers carry with them not only visible waste, consisting 
of particles of rock in suspension, but also invisible waste, or 
material in solution, which consists of carbonate of lime, sulphate 
of lime, chloride of soda or common salt, etc. This waste 
accumulates in lakes having no outlet. Deposits of gypsum 
(sulphate of lime), salt, carbonate of lime, and other salts, are left 
when such lakes dry up. The carbonate of lime is first deposited, 
then gypsum. As the liquid becomes more concentrated, com- 
mon salt is deposited, next sulphate of magnesia, then potash 
salts, and chloride of magnesia. The deposition may be checked 
by influx of water at any stage, the deposits already made being 
perhaps covered with mud, and a new series of deposits started on 
top of these. The German potash salts are supposed to be of 
such origin. 

Peat and Muck Soils. When a soil is saturated with water, 
vegetation does not decay as rapidly as in a drained soil, but 
accumulates, forming a peat or muck soil. Peat soils are also 
formed in cool and damp climates, by the growth of a moss, 
which is able to hold water tenaciously. 

Soil Provinces of the United States. The Bureau of Soils 1 of 
the U. S. Department of Agriculture divides the United States 
1 Bulletin No. 55. 



ORIGIN OF SOILS 



75 



into thirteen provinces, based chiefly on climate, origin and topo- 
graphy of the soils. These are better shown in the map than 
described. Two great divisions are based on climate ; first, humid, 
and second, arid and semi-arid. The soil provinces are as follows : 
Humid Division. i. Atlantic and Gulf Coastal Plains. These 
consist of a belt of land narrow in New Jersey but much wider 
towards the south. The surface is a plain cut into hills and 
valleys by rivers, about 200 to 300 feet above sea level along the 
inner margin, but nearer the coast it has many areas with deficient 
drainage. The soils are made up of gravels, sands, and sandy 
clays. The deposits on the Atlantic coast are derived from the 
Piedmont Plateau through oceanic agencies, while the deposits on 
the gulf coast are derived from material transported from glacial 
deposits and from the western plains. There are also some soils 
derived from limestone deposits. 




Fig. 23. Shell rock, Florida. 

2. Piedmont Plateau. This area lies between the coastal plain 
and the Appalachian Mountains, and is most extensive in Virginia, 
North Carolina, South Carolina, and Georgia. The altitude 
varies from 300 to over 1,000 feet above sea level. These soils 
are derived largely from the weathering of igneous and 
metamorphic rocks in place. The prevailing series of these soils 
are the Cecil series and the Chester series. Both these series 
usually contain mica and quartz. 



76 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

3. Appalachian Mountains and Allegheny Plateau. The soils 
of the eastern ranges of these mountains are of igneous or 
metamorphic origin, while the western ranges and the Allegheny 
plateau are of sedimentary origin. General farming is not 
practiced in a large part of this area on account of the unevenness 
of its topography. The land is, however, well suited to grazing 
and fruit growing. 

4. Limestone Valleys and Uplands. These occur in narrow 
valleys among the Appalachian mountains and plateaus near by, 
and in two large areas, one in central Kentucky and Tennessee, 
the other in Missouri and northern Arkansas. The limestone 
soils are derived from the weathering of limestone, and many of 
them contain but a small percentage of the original limestone 
rock. Each foot of the soil is the residue from the weathering 
of many feet of the rock. 

5. Glacial and Loessial Deposits. This area covers a large 
portion of the United States, especially in the north-central 
states. A large portion of this area was covered by a great con- 
tinental glacier, which in its southern movement filled up valleys, 
plowed off hills and mountains, and deposited the ground-up 
material varying from a few feet to over 30 feet in thickness. 
The soils are partly till, or heavy clay compacted under the 
glacier, but largely "loess," a fine silty deposit containing lime- 
stone and very fertile. Some of the material was brought long 
distances, but most of it is composed of ground-up underlying 
rock largely deposited from glacial streams. 

6. Glacial Lake and River Terraces. These are deposits 
formed by the Great Lakes, after the close of the glacial period, 
when they were much larger than they are now. Several terraces 
marked by the old shore line can be observed. The soils vary from 
beach gravels to off-shore deposits of heavy clays, and the 
material worked over by the water is partly of sedimentary and 
partly of igneous origin. 

7. River Flood Plains. These soils are most extensive along 
the Mississippi and its tributaries, and along rivers in Texas and 
Louisiana, though soils of this group are found in all areas. The 



ORIGIN OF SOILS 



77 



deposits derived from various kinds of materials has been laid 
down by the river when in flood. Such soils are usually fertile, 
though they may not always be profitably cropped. 

Arid and Semi-Arid Division. 8. Great Basin. The soils are 
derived from a great variety of rocks and consist of colluvial soils 
of the mountain slopes, lake and shore deposits, stream valley 
sediments, and river-delta deposits. 

9. Arid Southwest. These soils occupy slopes at the foot of 
mountains, alluvial plains, sloping or nearly level plains, and 





Fig. 24. Soil provinces of the United States. Bureau of Soils. 



stream valleys. The soils are colluvial, alluvial, and lake deposits. 
Without irrigation, these soils have little agricultural value. 

10. Residual Soils of the Western Prairie Regions. These 
soils occupy the unglaciated part of the prairie plains. The rocks 
from which the soils are derived are of the carboniferious age and 
consist of sandstones, shales, and limestones. 

11. Northwestern Inter-Mountain Region. The soils of this 
area consist mostly of residual material derived from basaltic 



78 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

lava and in some cases granitic rocks. Some are derived from 
ancient lake beds. 

12. Rocky Mountain Valleys, Plateaus and Plains. These 
soils are derived from a great variety of igneous, metamorphic, 
and sedimentary rocks. The soils of the mountain slopes are 
usually of little agricultural value, while those of the plateaus, 
valleys, and plains range from grazing land of low value to soils 
adapted to fruit, sugar beets, and other special crops. 

13. Pacific Coast. Soils found in this region range from 
residual and colluvial soils of the mountain sides, foot slopes and 
foot hills, to deep and extensive river flcod plains and delta sedi- 
ments, and ancient and modern shore and lake deposits. Their 
value depends largely upon possibilities of irrigation, and local 
conditions of rainfall and temperature. 



CHAPTER V. 

PHYSICAL COMPOSITION AND CLASSES OF SOILS. 

Soils are composed of particles of different sizes, ranging from 
over 2 mm. to o.oooi mm. or less, in diameter. Many of the 
physical properties of soils are closely related to the relative 
abundance of particles of different sizes. The surface area of a 
cubic foot of the particles increases with their fineness of division. 
The retentive power for moisture, the area exposed for chemical 
action and for the feeding of roots, the capillary action of the 
soil, etc., are closely related to the size of the soil particles. 

Soil particles may be found independent of one another, but 
they are usually more or less united into crumbs, compound 
particles, or lumps. 

Mechanical Analysis. By the mechanical analysis of a soil, we 
mean the estimation of the relative quantities of soil particles of 
different sizes. As the particles which make up the soil have 
almost an infinite variety of size, all that can be done is to group 
them, by placing all that are between certain dimensions in a certain 
group. The sizes selected for the groups, and the name given to 
each, are purely arbitrary. A number of systems of soil analysis 
is possible. The principal groupings of soil particles in mechan- 
ical analysis used in the United States are those of Hilgard, and, 
those of the Bureau of Soils. Other systems are used abroad. 
The Bureau of Soils makes seven separations. Dr. E. W. Hilgard 
has made a number of analyses based on the velocity of a current 
of water holding the particles in suspension, stated in millimeters 
per second (hydraulic value). For example, sand of 0.5 to 0.30 
mm. in diameter is held in suspension by a current of water 
moving at the rate of 64 millimeters per second. 

There has been little or no work to determine the classification 
of soil particles which would best correlate the properties of the 
soil with the physical analysis. So far as the writer has been able 
to find, the division into groups is arbitrary. 

The following table compares the systems of Hilgard and of the 
Bureau of Soils : 



So 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



Bureau of Soils 


Hilgard 


Name 


Sizes of particles 
MM. 


Sizes of particles 
MM. 


Hydraulic 
Value 


Name 


Stones, sticks, etc-- 


Over 2 

2-1 

1-0.5 
0.5-0.25 

0.25-0.1 

O.I-O.O5 
0.05-0.005 


3-i 
1-0.5 
0.5-0.3 
0.3-0.16 
O.J6-0. 1 2 
0.12-0.72 

O.O72-O.O47 
0.047-0.036 
0.036-0.025 
O.O25-O.OI6 
0.016-0.010 
0.010- ? 


64 
32 }> 
16 

8 J 
4 1 

2 
I } 

05 
0.25 J 


Grit 
Sand 

Silt 
Clay 






Fine suiid 




Silt 


Clav 





It is possible, by combining some of the groups of Hilgard, to 
compare the results with analyses of the Bureau of Soils. As 
Hilgard 1 remarks, a subdivision of six or seven classes, as is 
made by the Bureau of Soils, is sufficient for a great many cases. 
There is, however, considerable difference in the properties of the 
grades of silt which are separated by Hilgard but grouped 
together by the Bureau of Soils. 

Methods of Analysis. For the separation of the finer particles, 
all methods of mechanical analysis take advantage of the different 
rates of subsidence of particles of different diameters when sus- 
pended in water. Methods such as that of Osborne depend upon 
subsidence under the influence of gravity in stationary columns 
of water. Hilgard's method depends upon the difference between 
the action of gravity and the carrying power of a current of 
water. The Bureau of Soils throws down all except the clay 
particles by centrifugal force. Sieves are used for separation of 
the coarser particles ; compound particles are broken down by shak- 
ing with water, or boiling. Since clay is liable to form compound 
particles, and otherwise interfere with the separations, it is 
removed first. 
1 The Soil. 



PHYSICAL COMPOSITION AND CLASSES OF SOILS 



Si 



Method of the Bureau of Soils. 1 The following is an outline 
of the method of mechanical analysis of soils used by the Bureau 
of Soils. Five grams of soil are shaken for six hours or longer 




Fig. 25. Centrifugal machine used in mechanical analysis of soils. 

with water containing a little ammonia, in order to decompose the 
compound particles. The soil is then washed into a centrifugal 
tube, and the centrifugal machine run at full speed for about 
1 Bulletin 24, and Bulletin 84. 



82 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

three minutes, the time depending on the speed of the machine 
and the quantity of suspended material present. The material 
in suspension is then examined with a microscope carrying a 
micrometer eye-piece, to see if any particles larger than clay (.005 
mm. in diameter) remain in suspension. If larger particles are 
found, the centrifugal is run until they settle. When the water 
contains only clay particles, it is decanted. The residue is stirred 
up with water, the machine started, and the separation made as 
before. The operation is repeated until the clay has been all 
removed, as shown by a microscopic examination of the residue. 
The water is evaporated to dryness, and the clay weighed. 

The residue left in the tubes is brought in suspension with 
water, and allowed to settle, until microscopic examination shows 
only silt in suspension. This requires but a short time. The silt 
water is decanted, and the operation repeated until all the silt 
(less than .05 mm. in diameter) has been washed out. The silt, 
after being allowed to settle, is collected, dried and weighed. The 
sand is then collected, dried, and separated into five groups by 
means of a nest of four sieves, two of brass with circular 
perforations I mm. and 0.5 mm. in diameter, and two of silk 
bolting cloth with openings 0.25 and o.i mm. wide. The various 
separations are then weighed. 

Hilgard's Method. The following is an outline of Hilgard's 
method. (For full details see Wiley's "Agricultural Analysis.") 
The two grades of grit are removed by sieves. Ten or 15 grams 
of the sifted soil are boiled with water to break up the compound 
particles, transferred to a beaker, mixed with water, and allowed 
to stand a short time until only the finest silt and clay remain 
in suspension. The treatment with water is repeated until the 
water has removed all the finest silt and clay. The mixture 
of clay and silt-water is allowed to stand 24 to 60 hours, until all 
silt is deposited. The sediment is rubbed with a rubber pestle, 
mixed with water, and allowed to settle again until free from 
clay. It is then dried and weighed. An aliquot of the clay-water 
may be evaporated to dryness and the residue weighed, or the 
clay may be precipitated by coagulation with salt. 



PHYSICAL COMPOSITION AND CLASSES OF SOILS 83 

The mixed sediments, containing the sand and all the silt 
except the finest, is placed in an upright glass cylinder, containing 
a rotating fan or churn, run by a suitable motor. This breaks up 
the compound particles. A current of water is run in so that it 
moves through the cylinder at the rate of 0.25 mm. per second, 
until the water becomes clear. The particles carried over are 
allowed to settle, dried and weighed. The current of water is 
increased to 0.5 mm. per second, so as to remove another grade 




Fig. 26. Hilgard's apparatus for mechanical analysis by means 
of a current of water. 

of particles, and these operations are repeated until all the grades 
of particles are separated. 

Relation of Grain Size to Soil Texture. This relation is studied 
by ascertaining the mechanical analysis of soils of known prop- 
erties, and also by investigating the properties of the various 
groups of particles separated in the analysis. 

In sands the coarser particles of the soil predominate. Such 
soils are open or porous, easy to cultivate, not very retentive of 
moisture, and warm up early in the spring. Coarse sands are 
least retentive of moisture and most porous. Soils containing 
quantities of very fine sand are much more retentive of moisture. 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



In heavy clay soils, the fine clay particles are present in large 
quantity. Such soils are very retentive of moisture, require 
much labor in cultivation, are likely to be tough and sticky when 
not ploughed at exactly the right time, are not easily penetrated 



UNITED STATES DEPARTMENT OF AGRICULTURE, 



)l VISI..N >F AGRICULTURAL SO 



THE TEXTURE OF A TYPICAL TOBACCO LAND AT HATFIELD. MASSA 



Par Cent of Gravel. Sand. Silt, and Clav in 2O Cirams of Subsoil 




DIAMETER OF THE GRAINS IN MILLIMETERS. 



Fig. 27. Physical analysis of a soil sample. Bureau of Soils. 

by water, and do not warm up rapidly in the spring. Twenty per 
cent, clay particles usually make a soil difficult to work. 

Soils with much silt and little or no clay, are likely to adhere 



PHYSICAL, COMPOSITION AND CLASSES OF SOILS 85 

to the plow very tenaciously when too wet. They plough fairly 
well when in right condition, but turn up in clods if ploughed 
when dry. Loams are intermediate between sands and clays, in 
physical character and in properties, and in general are good soils. 

The coarse soil particles, therefore, tend to make the soil more 
open and porous and more easily tilled. The fine particles tend 
to make the soil more compact and less easily tilled. The final 
resultant depends upon the relative quantities of the different 
kinds of particles, as well as their chemical composition or their 
properties. The presence of a certain amount of clay in a sand 
is desirable. If no clay is present, the soil is liable to pack on 
wetting, but clay holds the particles into crumbs characteristic of 
a well tilled soil. Further, sands containing less than 4 per cent, 
clay have little power of retaining moisture and are particularly 
liable to suffer from drought Sand particles in a clay will not 
diminish its stickiness, while silt particles make the clay less 
adhesive, though perhaps more heavy to work. 

Mechanical analysis is also to be interpreted with consideration 
as to the amount and distribution of rainfall and the temperature 
and the effect of the underground water. A light soil under 
heavy rainfall may behave like a heavier soil under light rainfall. 
A soil with ground-water at such distance that it may be brought 
to the roots of plants by capillary action, is in better condition than 
when the ground-water is deeper. 

Classes of Soil Related to Mechanical Analysis. Soils are 
classed as sands, loams, clays, etc., according to their physical 
characteristics. There is room for difference of opinion as to 
exactly what characteristics should be signified by each term. The 
classification is made partly by field observations, and partly by 
mechanical analysis. 

As a result of the mechanical analysis of a great number of 
soils, the Bureau of Soils 1 of the U. S. Department of Agriculture 
finds different types to have the following average composition 
(see table). 

The predominance of various grades of material is well brought 
out in the table. For example, the coarse sands contain on an 

1 Bulletin No. 78. 



86 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



average 31 per cent, coarse sand particles, the sands 37 per cent, 
of fine sand particles, the fine sands 57 per cent, fine sand 
particles. The clays contain 42 per cent, clay particles. 

AVERAGE COMPOSITION OF SOIL TYPES AS ANALYZED IN CONNECTION 
WITH THE SOIL SURVEYS. 



Soil classes 


Num- 
ber of 
sam- 
ples 


Fine 
gravel 


Coarse 
sand 


Med- 
ium 
sand 


Fine 
sand 


Very 
fine 
sand 


Silt 


Clay 


Coarse sands 


flC 


Pet. 


Pet. 


Pet. 


Pet. 


Pet. 


Pet. 


Pet. 


Sands 


1 OJ 




3 1 


J V 






7 


5 


Fine sands 


C T T 




J o 


Z 6 


37 




7 




Sandy loams 


O 1 A 

I I A.\ 








01 


A/ 







Fine sandy loams 


934 


I 


J o 

3 


4 


32 


1 6 

24 


24 


12 
T 


Silt loams 


oy 

T 2fi<S 




5 






7 


4 






162 




Q 





5 




5 


!5 




7l8 








3 




T 3 

-Q 


2 7 
if* 




7 Ac- 






' 


M 


13 


3 
fir 




Clav . . 


/ U O 
I Q7O 








Q 


Q 


T.ft 


*0 




J >y/ u 












3 


4^ 



The classification of soils with regard to physical composition, 
as used by the Bureau of Soils, 1 is shown in the following table. 
The classification is controlled by field observations. 

CLASSIFICATION OF SOIL MATERIALS. 
Soils containing 20 silt and clay : 

Coarse sand . f 2 5-f fine gravel and coarse sand, 

\ and less than 50 any other grade. 

c an( j I 2 5+ fine gravel, coarse and medium 

\ sand, and less than 50 fine sand. 

!5o-f fine sand, or 25 fine gravel, 
coarse and medium sand, 50+ 
very fine sand. 

Very fine sand 50+ very fine sand. 

Soils containing 20-50 silt and clay : 

Sandy loam . / 25+ fine gravel, coarse and medium 

( sand. 

Fine sandy loam | 50+ fine sand, or -25 fine gravel, 

(. coarse and medium sand. 

Sandy clay 20 silt. 

Soils containing 50+ silt and clay : 

Loam 20 clay, 50 silt. 

Silt loam 20 clay, 50+ silt. 

Clay loam 20-30 clay, 50 silt. 

Silty clay loam 20-30 clay, 50+ silt. 

Clay 30-1- clay. 

1 Bulletin No. 78. 



PHYSICAL, COMPOSITION AND CLASSES OF SOILS S/ 

The figures given represent per cent. ; the minus sign ( ) repre- 
sents, less, and the plus sign (-(-) represents more; and the sign 
(-) when used between two figures, thus 20-50, gives limiting 
values, and should be read from 20 per cent, to 50 per cent. Thus, 
25 + means 25 per cent, or more; 25 means less than 25 per 
cent. 

For example, a soil containing less than 20 per cent, silt and 
clay and over 50 per cent fine sand, would be called a fine sand. 
A soil containing over 50 per cent, silt and clay particles and over 
30 per cent, clay would be called a clay soil. 

Relation of Chemical Composition to Soil Texture. The effect 
of the physical composition of a soil is modified by the chemical 
character of its constituents. The three important modifying 
constituents are organic matter, colloidal clay, and carbonate of 
lime. 

Organic matter binds a loose soil, and lightens a heavy soil, 
and thus reduces the difference between them. When there is a 
large quantity of organic matter, the mechanical analysis loses 
much of its significance. 

Carbonate of lime (i to 2 per cent.) also lightens a clay soil 
and otherwise modifies its properties. For example, 1 the follow- 
ing pairs of soils had similar physical composition but differed 
decidedly in properties : 





Per cent, carbonate lime 


Holsey green 


Rothamsted 


( Q\ foo sticky to be cultivated 


0.48 
1.02 


0.16 

3-0 


( \)\ Heavy soil but works well 





It is very well known that calcareous clay soils are more easily 
cultivated and break up better than similar soils deficient in lime. 

The clay particles, so called, may be composed of quartz dust, 

hydrated oxide of iron, gelatinous silica, carbonate of lime. 

hydrated silicates, and of true clay, or hydrated silicate of 

alumina. These substances have different properties, and the 

1 Hall, Jour. Agr. Sci., 1911, p. 187. 



88 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

composition of the clay particles undoubtedly influences the char- 
acter of the soil. The term "Klay" has been proposed to dis- 
tinguish the clay particles of a soil from the hydrated aluminium 
silicate termed clay by the chemist. 

True clay is present in the soil in two forms. First, as colloidal 
clay in a swelled condition; and second, as clay in non-colloid, 
or shrunken condition. In the colloid condition, clay remains 
suspended in water indefinitely. Small amounts of lime and other 
substances coagulate the clay and cause it to separate out in flakes. 
When the coagulating substance is removed, the clay again 
becomes colloidal. This may be easily shown by washing a clay 
soil with acid to remove lime, then with water, and shaking it 
with ammonia. Clay will enter into suspension and remain sus- 
pended a long time, but if ammonium sulphate, ammonium car- 
bonate, or other salts are added, the clay quickly separates in 
flakes. 

Colloidal clay was prepared by Schloesing. 1 He brought the 
clay into suspension in water, as iri the mechanical analysis of a 
soil, and precipitated the clay with a small quantity of acid, 
collected the colloidal clay on a filter, and washed with distilled 
water. The residue on the filter was treated with ammonia, and 
diffused in a considerable quantity of distilled water. This was 
then left until deposition ceased, which required several months. 
The microscope could then no longer detect particles of visible 
dimensions in the solution. The liquid was decanted off, and the 
colloidal clay precipitated by the addition of a small quantity of 
acid. It dried to a translucent, horn-like mass. According to 
Schloesing, even the stiffest natural clays seldom contain more 
than 1.5 per cent, of such true colloidal clay. 

Colloidal clay has much higher binding properties than shrunken 
or coagulated clay. The tenacity of a soil containing colloidal clay 
is greatly influenced by its condition. If the clay is in its fully 
swelled condition, the soil exhibits its maximum cohesion, and if 
a sufficient quantity of clay is present, it will be quite impervious 
to water. If the colloidal clay is in a shrunken coagulated state, 
1 Chimie Agricole, 1885. 



PHYSICAL COMPOSITION AND CLASSES OF SOILS 89 

the same soil may be pervious to water and susceptible of success- 
ful tillage. 

Boiling in water, freezing, working the wet soil, alcohol, ether, 
sodium or potassium hydroxides, ammonia, and sodium or 
potassium carbonates, cause the clay to swell and increase its 
colloidal properties. These agencies, therefore, tend to make 
clay soils more impervious, sticky, and difficult to work. Lime, 
magnesia, bicarbonate of lime, certain acids, such as hydrochloric 
or sulphuric, and certain salts such as sodium chloride, sodium 
sulphate, calcium sulphate, coagulate the clay particles. These 
substances, therefore, tend to make clay soils less sticky and more 
permeable to water. 

If clay is washed and kneaded when wet, it becomes plastic 
and sticky, and may be moulded into forms which retain their 
shape and become hard and stony when dried and baked. 
Advantage is taken of this property in the manufacture of brick, 
earthenware, and chinaware, but it is not a desirable property in 
a soil. 

Hydrated oxide of iron, and some of the other bodies which 
occur in the clay separation do not have the binding properties of 
true clay, and if present to any considerable extent, the soil may 
not have the characteristics which would be expected from the 
quantity of clay in it. Hilgard, 1 for example, finds that a certain 
clay soil containing 40 per cent, of clay was scarcely as adhesive 
as another soil containing 25 per cent, of clay, and not nearly as 
sticky when wet as a third soil containing 33 per cent. clay. The 
soil first named, however, was rich in ferric hydrate, a large por- 
tion of which is probably in the clay particles. This accounts for 
the behavior of the soil. Ferric oxide appears to diminish the 
tenacity of a clay. 

Rivers which contain little lime are turbid from presence of 
clay, but 70 to 80 mg. lime per liter precipitates the clay and leaves 
the water clear. 

Calcareous clays are very sticky when wet, but many of them 
disintegrate into a mass of crumbs on drying, thereby producing 
1 The Soil, p. 100. 
7 



9O PRINCIPLES OF AGRICULTURAL CHEMISTRY 

good tilth, even though worked when wet. Non-calcareous clays 
under such conditions are likely to contract into stony masses. The 
exact proportions of carbonate of lime necessary to produce this 
condition of the soil remains to be determined. 

The black prairie soil of Texas locally called "black waxy" and 
termed the "Houston black clay" by the Bureau of Soils, is an 
example of this kind of soil. When wet it is gummy and waxy, 
but when dry and well cultivated it is friable and easily worked. 
This soil contains one per cent or more of lime. Clay, unlike silt, 
chalk, and humus, increases greatly in coherence when it dries, 
and finally becomes a hard, solid substance. 

Nature of Tilth. 1 If the particles of a soil are each inde- 
pendent of the other, so that their relative positions are easily 
shifted by gravity or water, they are said to possess the single- 
grain structure. Such soils, if sandy, are loose, and become as 
compact as their particles allow. Clay soils of this character are 
very sticky when wet, and if worked while wet form clods on 
drying. 

A soil which, when plowed, breaks up into a mass of compound 
particles of various sizes, loosely piled upon one another and 
separated by comparatively large interspaces, is said to possess the 
crumb structure and to be in good tilth. The crumbs may be 
held together by moisture, clay, humates, carbonate of lime, and 
sometimes silica and oxide of iron. 

Crumbs of sand held together by water collapse on drying. 
Clay is frequently the substance which holds the crumbs together ; 
in such case, the crumb structure remains even after the land 
dries out. Beating rains and cultivation while too wet destroy 
these crumbs. 

Soil particles united by carbonate of lime, humates, silica, or 
oxide of iron are more or less permanently cemented into com- 
pound particles. In some calcareous soils we find sandy and silt 
concretions varying from several inches in size to microscopic 
proportions. Humus is a great aid in securing good tilth. 

Compound particles are also formed by natural processes, due 
1 Warington, Physical Properties of Soil, p. 36. 



PHYSICAL COMPOSITION AND CLASSES OF SOILS 9! 

to changes in temperature, or to changes in moisture content. If 
the soil is beaten or mixed when too wet, compound particles are 
destroyed and the soil dries into a hard compact mass. 

Tilth is a condition of the soil, and only indirectly due to pro- 
cesses of tillage. A heavy soil is not reduced to powder by the 
mechanical force exerted through implements. Tillage stirs the 
soil, and places it so that natural forces exert their greatest effect 
upon it. The soil in good tilth falls into a powder 
under the action of the various instruments. Such a con- 
dition of the soil is very desirable. It allows the preparation of a 
good seed bed ; it is most suitable for ensuring the best conditions 
of moisture, temperature, and chemical action in the soil during 
the growth of the plant. The maintenance of good tilth is 
especially important on clay soils. 

The production of a good tilth, and the permeability of a clay 
soil to water, depend largely upon the formation and maintenance 
of compound particles. The conditions favorable to the forma- 
tion of compound particles are also favorable to the coagulation 
of clay. Any change which converts the clay from a coagulated 
to a swelled condition is necessarily destructive to compound 
particles, but it is quite possible to destroy compound particles 
without affecting the coagulated condition of the clay. 

Relation of Physical Composition to Adaptation of Crops. The 

adaptation of different crops to particular kinds of soil is due to 
different needs of the crops for moisture, for soil atmosphere, for 
temperature, and their habits of root growth. The differences in 
physical composition cause soils to respond differently to these 
needs, and hence vary their adaptation. But climatic conditions of 
rainfall, temperature and situation, modify the way which 
the soil fulfills these conditions. Under similar conditions, and 
in a general way, there is a relation between the physical character 
of the soil and its adaptation to crops, and this is shown by the 
general agricultural practice and treatment of such soils. 

The relation of physical character to adaptation to crops is 
studied by ascertaining the kinds of crops actually grown upon 
the various classes of soils, and how well they thrive on them. 



92 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

The relation between physical character and adaptation in the 
soils of the Atlantic and Gulf Coastal Plains, as ascertained by 
field agents of the Bureau of Soils, 1 is as follows : 

Sands. These soils are characterized by open structure, thor- 
ough drainage and warm nature. They are the earliest truck 
soils, produce light yields, and are not well adapted for general 
farming. 

Fine Sands. These are more retentive of moisture than the 
sands, mature truck ten days to two weeks later, and give heavier 
yields. They are not well adapted for general farming. 

Sandy Loam Soils. These are the medium early truck and 
light general farming soils of the Atlantic and Gulf Coastal Plains. 
They are the lightest desirable soils for general farming, are 
more retentive of moisture than the fine sands, and mature crops 
about two weeks later. In general farming, crop returns are 
light. 

Fine Sandy Loams. These soils are adapted to medium truck 
crops, give moderately good yields of vegetables, and give average 
yields of general farm crops. Cotton matures somewhat later 
than on the sandy soil. 

Loams. These soils produce medium-late truck crops and are 
the best soils for general farming in this region. They are easily 
kept in good condition of tilth and are very retentive of moisture. 
Vegetables mature late but the yields are good. Small grains and 
grasses do well. 

Silt Loams. These are adapted to late truck, vegetables for 
canning purposes and for heavy farm crops or for special pur- 
poses. Hay does well on this type of soil. 

Clay Loams. These are too stiff and too late in maturing crops 
for vegetables. A small number of farm crops is adapted to this 
type. Wheat, oats, rice, forage crops, and grass do well. 

Clays. These are adapted to heavy farm crops, such as wheat, 
grass ; rice, and forage crops for ensilage. Cultivation is difficult. 
Early varieties of cotton do well outside of boll weevil districts. 

A specific example of the relation between the use made of 
1 Bulletin No. 78. 



PHYSICAL COMPOSITION AND CLASSES OF SOILS 



93 



a soil and its physical analysis, is shown by the analyses of typical 
Maryland subsoils published by Whitney. 1 

PHYSICAL ANALYSES OF MARYLAND SUBSOILS. 





Diameter 
of 
particles 


Early 
market 
garden 


Market 
garden 


Tobacco 
land 


Wheat 
soil 


Wheat 
and 
grass 


Grass 
and 
wheat 


Fine gravel 
Coarse sand 
Medium sand 
Fine sand 


2-1.0 
1.0-0.05 
0.5-0.25 
O 2^-O IO 


0.5 
5-0 
4O.2 

27 6 


0.4 
2.O 
28.6 
JQ 7 


1-5 

5-7 
13-3 

8 4. 


0.4 
0.6 

22 6 


O.2 

1-3 
4.0 


1-3 
0-3 
I.I 
I.o 


Very fine sand 
<^ilt 


O.IO-O.O5 


12. 1 

77 


11.4 
50 


15.0 

28 Q 


30.6 

14 o 


11.6 

JQ O 


6.9 

2Q I 


Fine silt 




2 2 


.- 

2 O 


7 8 


A I 


11 


II O 


Clav 




4 A 


8 8 


14 6 


22 O 


12 7 


47 A 



















The early market garden soil contains nearly 73 per cent. sand. 
It has little power of retaining water and is therefore warm and 
dry. It produces vegetables about ten days earlier than any other 
soil in Maryland. 

The market garden soil contains more fine sand and more clay. 
It is more productive but later in maturing spring crops than the 
soil named above. It is superior to the first soil for peaches, 
small fruit, and autumn crops. 

The tobacco soils contain 10 to 20 per cent, clay, the lighter 
soil yielding a smaller crop but a better quality of leaf. The 
wheat soils are somewhat heavier. The wheat soil (No. 4) is the 
lightest soil upon which wheat can profitably be grown in Mary- 
land. The soil is too light for permanent meadow or pasture 
and too heavy for the best quality of tobacco. The wheat and 
grass land is more productive than the wheat soil. The grass and 
wheat soil is still more productive. 

Similar relations can be traced for other soils, between the 
physical composition and crops adapted to them. Other factors 
come into play, however, such as the location of the soil, its 
depth, and its chemical composition. The physical properties of 
a soil depend upon other things in addition to its physical com- 
position, as we shall see. The relation between soil composition 
and crop adaptation probably depends to a large extent upon 
1 U. S. Weather Bureau, Bulletin No. 4. 



94 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



water conditions, which is largely influenced by the physical com- 
position of the soil. 

Similar relations between physical character and crop adaptation 
were traced in England by Hall. 1 He found very heavy soils 
generally used for pasture. Wheat soils are heavy. Barley soils 
are lighter than wheat soils, potato soils are still lighter. Hop 
soils are somewhat like barley soils. Fruit soils are lighter than 
hop soils. The different kinds of fruit have their own require- 
ments. Waste soils are characterized by large amounts of coarse 
sand, small amounts of clay and fine silt, an acid reaction and 
absence of calcium carbonate. 

Analyses of typical soils used for various crops in the area 
studied by Hall are shown in the table. The reader will notice 
that the groups of soil particles are different from those else- 
where mentioned in this chapter. 





Wheat 


Barley 


Potatoes 


Hops 


Fruits 


Fine gravel above i mm 


1.4 


1.2 


0.9 


1.2 


1.0 


Coarse sand 1-0.2 ' 


3-7 


18.3 


2O. I 


4.8 


6.8 


Fine sand 0.2-0.04 


24-5 


32.0 


43-5 


33-3 


42.0 


Silt 0.04-0.01 


23.0 


18.2 


II. 


28.3 


23-3 


Fine silt 0.01-0.002 


12.8 


8.0 


6.4 


8.7 


' 7-3 


Clay below 0.002 


20.8 


11.9 


9-7 


12. 1 


10.9 



The subsoil is generally heavier in texture, or contains more 
clay, than the surface soil. This is largely due to the action of 
water moving the finer particles of the soil into its lower portions. 

Soil Types and Soil Series. A soil type is a definite soil, with a 
definite physical composition and other definite properties. It 
may vary somewhat in different parts of the area, but in all 
essential respects, it is the same soil. 

Soil series are groups of soil types related to one another 
through source of material, method of formation, topographic 
position, coloration, and other characteristics. The soil types in 
the series vary chiefly in physical composition and other char- 
acteristics caused thereby. A soil series, to be complete, would 

1 Jour. Agr. Sci., 1911, p. 206. 



PHYSICAL COMPOSITION AND CLASSICS OF SOILS 95 

contain all the possible physical classes of soils already mentioned. 
Comparatively few soil series, however, are complete. 

In establishing soil types and soil series, the texture of the soil, 
its mechanical composition, its origin, the topography of the soil, 
native vegetation, color, depth, drainage, and all other factors 
which influence the relation of the soil to the crop, are considered, 
as far as possible. Both the surface soil, and the subsoil should 
be considered. All the types in a given locality have been formed 
by the same general processes, and will naturally grade into one 
another. In humid regions, the description of a type covers the 
material to an average depth of three feet; in arid regions to a 
depth of six feet. Minor variations of texture, structure, organic 
matter content, or succession of materials, which occur in sections 
representing 10 acres or less, are described as phases by the field 
agents of the Bureau of Soils. There is some local variation in 
types. Differences in agricultural value may be due to differences 
in treatment of the same soil. 

The soil name of a type does not mean that it belongs to that 
class necessarily. For example, Norfolk sandy loam may be a 
coarse to medium yellow or gray sand or light sandy loam. 

Pippin 1 suggests the following scheme of soil classification. 
The broadest division is based on temperature, into (I) tem- 
perate, (II) subtropical, (III) tropical regions. Each of these is 
sub-divided into (A) humid, (B) semi-arid, (C) arid sections 
based on rainfall. The next two sub-divisions are into divisions 
and provinces according to mode of formation; (a) sedentary, 
soils sub-divided into (a ) residual soils and (a 2 ) cumulose soils 
and (b) transported soils, sub-divided into (& x ) colluvial, (b. 2 ) 
wind borne, (A,) transported by water; namely, (b 3a } ocean, 
( 3 *) lakes, (b y ) rivers. The soils of different origin are next 
divided into groups based on the source of material (i) acid and 
basic igneous rock; (2) shale and slate; (3) sandstone and 
quartzite; (4) limestone and marble rock: (5) muck, peat, and 
swamps (cumulose soil). The next sub-division is into series, 
based on color, organic matter, drainage, lime content, and special 
1 Proc. Am. Soc. Agron., 1911, p. 88. 



96 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

chemical properties. Finally, the types, or individual soils, are 
based on texture and structure. This scheme offers good possi- 
bilities; the group, acid and basic igneous rocks, is, however, a 
broad one and should be sub-divided. 

Some Soil Series. Soil types numbering 715 have been 
established by the Bureau of Soils of the United States Department 
of Agriculture. These types have been divided into 86 series. 
A full list and description of these types and series is found in 
Bulletins 55 and 78 of the Bureau mentioned. The following are 
a few series, mentioned for the sake of illustration. 

Atlantic and Gulf Coastal Plains. Houston Series. Dark-gray 
or black calcareous prairies. One of the most productive series 
for upland cotton, and well adapted to alfalfa and other forage 
crops. 

Norfolk Series. Light-colored soils with yellow sand or sandy 
clay subsoils. This series contains some of the most valuable 
truck soils of the Atlantic and Gulf Coast States, and certain 
members of the series are adapted under certain climatic condi- 
tions to wheat, grass, tobacco, and fruit. 

Orangeburg Series. Light-colored soils with red sandy clay 
subsoils. This series constitutes some of the best cotton soils of 
the South, and certain members of the series are particularly 
adapted to tobacco. 

Portsmouth Series. Dark-colored soils with yellow or mottled 
gray sand or sandy clay subsoils. Where drainage is adequate, 
this series is adapted to some of the heavier crops, to small fruits, 
and to Indian corn. 

Susquehanna Series. Gray soils with heavy red clay subsoils 
which become mottled and variegated in color in the deep subsoil. 
Only one member of the series, the sandy loam, has been 
developed to any considerable extent. This one is used for fruit 
and general farm purposes, but the other members are particu- 
larly refractory and difficult to bring into a productive state. 

River Flood Plain. Miller Series. Brown to red alluvial soils 
formed from the reworking of materials derived from the 
Permian Red Beds. Very productive soils, suitable for cotton, 



PHYSICAL COMPOSITION AND CLASSES OF SOILS 97 

corn, sugar-cane, alfalfa, and vegetables; especially adapted to 
peaches. 

W abash Series. Dark-brown or black soils subject to over- 
flow. Very productive soils, used for cotton, sugar-cane, corn, 
wheat, oats, grass, alfalfa, sugar beets, potatoes, and other 
vegetables. 

Piedmont Plateau. Cecil Series. Gray to red soils with 
bright-red clay subsoils, derived from igneous and metamorphic 
rocks. Constituting by far the larger portion of the plateau, 
these soils are well adapted to and are used for cotton, export 
tobacco, and fruit, and the lighter members for truck crops. As 
a rule they are not highly developed, but where properly handled, 
the heavier members produce excellent crops of corn and grazing 
and hay grasses. 

Appalachian Mountains and Plateau. Dekalb Series. Brown 
to yellow soils with yellow subsoils, derived from sandstones and 
shales. Soils of this series are used, according to texture, eleva- 
tion, exposure, and character of surface, either for the production 
of hay, for pasture, or for orchard and small fruit. 

Porters Series. Gray to red soils with red clay subsoils, 
derived from igneous and metamorphic rocks. This is the 
most important series for mountain fruits of the eastern United 
States. It is also used for general farming. 

Limestone Valleys and Uplands. Clarksville Series. Light- 
gray to brown soils with yellow to red subsoils, derived mainly 
from the St. Louis limestone. Apples and peaches are com- 
mercially important. Tobacco is a leading product. 

Cumberland Series. Brown surface soils, derived from the 
deposit of sedimentary material overlying residual limestone sub- 
soils. Used for cotton and other general farm crops, truck, and 
fruit. 

Glacial and Loessial Regions. Marshall Series. Dark-colored 
upland prairie soils. The principal soils of the great corn belt 
belong to this series, while in the Northwest the finest wheat soils 
are found in this group. They are among the best general farm- 
ing soils of the entire country. 



98 PRINCIPLES OF AGRI CULTURAL CHEMISTRY 

Miami Series. Light-colored upland timbered soils. The 
different members of this series are considered good general farm- 
ing soils and have in addition special adaptations for truck, small 
fruit, and alfalfa. 

Glacial, Lake and River Terraces. Clyde Series. Dark-colored 
swamp soils formed from reworked glacial material deposited in 
glacial lakes. A special use for these soils is the production of 
sugar beets, while general farm crops, truck, and canning crops 
are grown extensively. 

Fargo Series. Black calcareous soils rich in organic matter 
formed by deposition of material in glacial lakes. This is the 
most important group of soils in the Red River Valley, and 
includes exceptional soils for the production of wheat, barley, and 
flax. 

Residual Soils of the Western Prairie Region. Crawford 
Series. Brown soils with reddish subsoils, derived from lime- 
stones. The soils of this series range from rough areas suited 
mainly for pastures to fertile general farming, fruit-growing, and 
trucking soils. 

Great Basin. Bingham Series. Porous dark or drab colluvial 
and alluvial soils underlaid by gravel or rock, occupying lower 
mountain slopes. The lighter types, when irrigable, are devoted 
to orchard fruits, and the heavier types, to alfalfa and sugar beets. 

Northwestern Intermountain Region. Bridger Series. Dark- 
colored soils with sticky yellow subsoils, of colluvial and alluvial 
origin. These soils generally occupy elevated foot slopes or 
sloping valley plains and have not been developed to a great 
extent. They are most extensively used for the production of 
grain, and when irrigated, are utilized in the production of alfalfa 
and other hay crops ; under favorable climatic conditions they are 
adapted to fruits. 

Rocky Mountain Valleys, Plateaus, and Plains. Billings Series. 
Compact adobe-like gray to dark or brown soils and subsoils, 
formed mainly by reworking of sandstones and shales and 
occupying old elevated stream terraces. This is an important 
series adapted to alfalfa and general farm crops and stock raising; 



PHYSICAL COMPOSITION AND CLASSES OF SOILS 



99 



also used to a considerable extent in the production of sugar beets. 

Arid Southwest. Gila Series. Light to dark brown soils of 
flood-plain alluvium underlaid at varying depths by coarse sands 
and gravels. Under favorable irrigation and drainage conditions, 
the members of the Gila series are adapted chiefly to the produc- 
tion of alfalfa, potatoes, truck, and root crops. 

Pacific Coast. Fresno Series. Light-colored soils with light- 
gray, ashy subsoils and alkali-carbonate hardpan, derived from 
old alluvial wash. Where protected from alkali accumulations, 
these soils have been very successfully used for vineyards and 
raisin grapes, and are particularly adapted to almonds, peaches, 
and apricots. 



I 

. 

V *-'%.; 

I 

x :;K l 







Fig. 28. Photograph of a soil map, Willis area, Texas. 



Soil Survey. The soil surveyor is provided with a map, com- 
pass, measuring instruments, and soil sampler. After a general 
inspection has been made, and the provisional types decided upon, 
the mapping is begun. Preliminary borings in the soil are made 
to outline the location of a body of soil of uniform character. 
This is then colored in on the map. The surveyor then works 
away from this area until a different type of soil is encountered. 



100 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

The line of separation between these two types (which may 
consist of a narrow strip of intermediate soil) is then outlined on 
the map. Other areas are outlined in the same manner. 

The identification of the types is aided by physical analysis. 
It is, of course, not possible to make a great number of types in a 
given area, and a certain latitude must be allowed, between which 
limits the soil may vary. As a rule the different types of soil and 
their properties are very well known to the farmers in the area 
surveyed. So far the types have been largely based upon physical 
differences as observed by the surveyor, with no great emphasis 
on the physical analysis. 

Value of Soil Survey. A soil survey outlines the various types 
of soil in the area surveyed, shows their extent and relative 
importance, and exhibits, to some extent, the soil problems of the 
locality. It also indicates the adaptation of the various types of 
soil to different crops. 

A soil survey should not be considered as an end in itself, but 
as a means of ascertaining the various types of soil in the area, 
as a basis for further study. Thorough chemical, physical, 
bacteriological, and other studies should then be made of the 
various types of soils. The results of these studies can then be 
applied to definite areas. 

Soil surveys also show what crops may possibly be grown upon 
the various types of soil in question. Information secured upon 
the same types in other districts, may be made available. Results 
of fertilizer experiments made upon definite types of soil can be 
applied to similar types of soils elsewhere, but not indis- 
criminately, as has been too often done. Other experimental 
work can also be definitely applied to the kind of soil on which it 
is carried out. Relations between the various types should be 
traced so that work on one type may be applied to other types. 



CHAPTER VI. 



PHYSICAL PROPERTIES OF SOILS. 

The soil affects the growth of the plant through both physical 
and chemical properties, which react upon, and modify one 
another. The chief physical conditions which affect the plant are 
the depth of the soil, its temperature, the amount of water it 
supplies, and the composition of the soil atmosphere. These are 
modified by a variety of factors. The chief chemical condition 
which affects plants is the supply of plant food, but this supply 
is to some extent dependent upon physical factors. The chemical 
composition of the soil has other effects upon plants. It affects 
the physical character of the soil. It is related to the condition 
of the soil as regards neutrality, and the absence or presence 
of injurious substances, which also modify the relation of soil to 
plants. 

The physical and chemical properties of the soil are closely 
related, and are more or less dependent upon one another. They 
cannot be entirely separated without presenting a very one-sided 
view of the functions of the soil. 

Soil and Subsoil. Going down into the soil from the surface, 
we generally find the following layers : First, the top, or surface 
soil, varying from 3 inches to a foot or more in depth, and usually 
darker in color than the layers below. Next is the subsoil, from 
a few inches to several feet in depth. If the soil is sedentary, 
below this is a mixture of rock fragments and soil, and then comes 
the rock of the locality, the upper layers of which are decom- 
posed and rotten. Sometimes the layer of soil rests directly upon 
the solid rock. Sometimes the surface soil has been washed 
away, leaving the unproductive subsoil. 

The surface soil is distinguished from the subsoil by its darker 
color, due to the decaying vegetable matter contained in it, 
derived from roots and plant residues. The depth of the surface 
soil is, in humid climates, often determined by the depth of 
plowing, and is generally from 4 to 12 inches. 

A different definition of soil and subsoil is used by the Bureau 



IO2 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

of Soils. The surface soil is the upper layer of the earth, and 
continues until there is a decided change in physical character. 
In other words, the distinction between soil and subsoil is based 
upon differences in mechanical composition. 

In humid sections, the subsoil is not well suited for the growth 
of plants. If it is exposed by removal of the surface soil, it is 
in most cases unproductive until it has been subjected to 
atmospheric influences for some time. Organic matter added to 
the soil, such as manure, is said to aid in converting the raw sub- 
soil into productive soil. If too much subsoil is mixed with the 
surface soil, by deep plowing, the productiveness of the soil may 
be decreased. In arid regions, according to Hilgard, 1 the soil is 
suitable for plants to the depth of three to ten feet, or more. 
Material from the depth of eight feet has been put on gardens 
and served well the first year. In preparing land for irrigation, 
the land is leveled without regard to the subsoil, and no bad 
effects are noticed. These practices would be injurious to humid 
soils. The difference is due to the greater depth of penetration 
of air and the roots of plants, under arid conditions. 

Penetration of Roots. The depth to which roots penetrate 
into the soil depends upon the condition of the soil and subsoil, 
the climate, and the kind of plant. The roots of plants grown in 
humid regions penetrate only a comparatively short distance. In 
arid climates it is necessary that the roots penetrate deeply, in 
order that they may endure drought. 

According to Hilgard, the roots of the hop have been found, in 
arid climates, to penetrate to the depth of 18 feet; roots of wheat 
and barley may reach to 4 to 7 feet in sandy soil ; roots of grape 
vines have been found at the depth of 22 feet below the surface. 
Thus in arid climates, where a drought of five or six months pre- 
vails during the growing season, the roots of plants, by penetrating 
to considerable distances, will secure water in the depths of the 
soil. The depth to which plants send their roots affects the 
quantity both of water and of plant food at their disposal. Differ- 
ences in the needs of plants for food may, in part, be due to 
1 The Soil, p. 163. 



PHYSICAL, PROPERTIES OF SOILS 



103 



differences in rooting habits. Further, the character of root 
growth is also related to the kind of tillage which should be given. 
Crops whose roots extend near the surface of the soil should 
not have these roots cut by deep cultivation. 




Fig. 29. Distribution of roots of corn, Kansas. 

Exhibition specimens of roots are secured in the following 
manner. 1 A block of soil is cut out, with the plant in the center, 
and a wooden frame covered with one-half inch mesh wire netting 
is slipped over it. Plaster of Paris paste is then poured on the 
top to hold the plant and large numbers of sharpened wires are 
pushed through the soil and fastened to the netting, to hold the 
1 Kansas Bulletins 75, 127; North Dakota Bulletin 43, 64. 



IO4 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

roots in place. When the plaster hardens the dirt is washed away 

by a stream of water. 

Sanborn 1 drove an iron frame into the soil, removed the soil in 

layers of one inch to the depth of a foot, and washed out the 

roots. The roots were dried and weighed in order to ascertain 

their distribution in the soil layers. 

At the Arkansas Experiment Station, 2 plants were grown in 

boxes 10 by 12 inches and 4 feet deep, and the quantity of roots 

in different layers of the soil was determined. These conditions 

are somewhat artificial, and the roots would probably penetrate 

deeper than in a natural soil. 

The results of the preceding experiments are summarized in 

the following table : 

Barley 96 per cent, of roots in first 7 inches (Utah) 

Corn 90 " " 7 

Corn 93 " " " 7 

Clover 4 years old -. 94 " "7 

Clover Evenly distributed between the first 2 feet 

(Arkansas). 

Millet 80 per cent, in the first 12 inches (Arkansas) 

Oats 96 " " 7 " (Utah) 

Orchard grass 90 " 20 (Arkansas) 

Peas Mostly in 12 to 18 inches of soil 

Potatoes 70 per cent, in 7th to i3th inch (Utah) 

Timothy 87 " in first 7 inches (Utah) 

Timothy 95 ' " 6 " (Arkansas) 

Wheat 92 " " 7 " (Utah) 

It appears that barley, corn, oats, timothy, and wheat developed 
over 86 per cent, of their roots in the first seven inches of soil. 
Most of the plant food and water which they take up must 
necessarily be drawn from this layer. Clover, millet, peas, 
orchard grass, and potatoes appear to send their roots deeper, but 
these results (with the exception of the potatoes) are from the 
Arkansas Station, where the plants were grown in boxes and not 
in the free soil. Plants grown in boxes, as in the Arkansas 
Experiment, would have a tendency to send their roots deeper 
than plants grown in the natural soil, on account of the pulveriza- 

1 Utah Experiment Station, Bulletin 32. 

2 Bulletin 29. 



PHYSICAL PROPERTIES OF SOILS IO5 

tion and exposure to the atmosphere that the soil received in fill- 
ing the boxes, and also because the boxes were probably under- 
drained. 

Other experiments made at the Kansas, New York, North 
Dakota, Iowa, and Minnesota Stations, show that the greatest 
proportion of the roots of plants develop in the surface foot of 
the soil, but appreciable quantities of roots may penetrate much 
deeper. These experiments were qualitative. Further quantita- 
tive experiments are needed, as it is very important for scientific 
soil studies, to know the quantitative distribution of the roots of 
various plants in various soil types and in various sections of the 
country. 

The depth to which roots of some plants may penetrate is 
shown in the following table, taken from experiments made in 
Kansas and North Dakota. The subsoil was in some cases a 
stiff, clay soil. 

DEPTH OF PENETRATION OF ROOTS OF PLANTS. 
Alfalfa 6 to 10 feet. Clover 2^ feet. 



Corn 2>^ to 6 

Grasses 2^ to 3 

Millet 2 to 3 

Oats 4 

Rye 3 

Sugar beet 3^ to 4 



Cowpeas 3 

Kaffir corn... 3^ to 5 

Milo maize 3^ to 4 

Potatoes 3 

Sorghum 3 % to 4 

Wheat 4 



Effect of Depth of Soil on Plants. The depth to which the 
roots of plants penetrate depends both upon the character of the 
soil and the habit of the plant. The roots of plants can penetrate 
easily in a sandy subsoil, but may have difficulty in entering heavy 
clay. 

In general, the deeper the roots can penetrate the soil, the 
better the growth of the crop. Roots which occupy 12 inches of 
soil will have twice as much soil to draw upon for moisture and 
for plant food, as those which occupy only 6 inches. They will 
also have twice as much space in which to expand their roots. 

The experiments of Lemmerman 1 may be cited as showing the 
effect of root space upon plant growth. He grew mustard in pots 
of the same surface area, but of different depths. One vessel of 
1 Jahresber. f. Agr. Chem., 1903, p. 42. 
8 



io6 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



each size received no fertilizer, and one of each size received I, 
2, and 3 grams fertilizer respectively. The results are as follows : 

WEIGHT OF CROP IN DIFFERENT SIZED VESSELS. 



Fertilizer 


Iarge vessel 


Small vessel 




Grams 

26 8 


Grains 
IQ 7 




do ^ 


26 2 




7 S 
61 i 


47 8 




62 i 


A8 T. 









The increase of fertilizer from 2 to 3 grams had little effect 
upon the crop in the pots of either size. That is, the limiting 
condition is the size of the pot. The crop in the large pot is con- 
siderably larger than in the small one ; this shows that the space 
occupied by the roots has considerable influence. However, this 
difference may be due to differences in moisture content. 

Limitations of Soil Depth. The depth of the surface soil, as 
stated, is largely dependent upon the depth of plowing. The sur- 
face and subsoil together may be so shallow as to interfere 
seriously with the productiveness of the soil. The limiting condi- 
tion may be hard pan, the water table, rock, or heavy subsoil. 

Hard pan is a layer of hard earth, sometimes rock-like, which 
cannot be penetrated by plant roots. Hard pan may be caused by 
constant plowing at the same depth. The sole of the plow con- 
solidates the layer of soil on which it slips. Such hard pan is 
most liable to occur in heavy clay soils. Hard pan may also be 
caused by deposition of matter from drainage or irrigation waters. 
The deposited matter cements the soil grains into rocky masses. 
The cement is usually carbonate of lime, but sometimes it is an 
iron cement, or a humate. 

Hard pan may be prevented by varying the depth of plowing, 
or by an occasional subsoiling. It is particularly liable to occur 
in arid climates. In some localities it should be destroyed with 
dynamite or other explosives before fruit trees are set out. 

Rock, when too near the surface, forbids the use of the soil for 



PHYSICAL PROPERTIES OF SOILS lO/ 

cultivated crops, though the land may possibly be used for timber 
or grazing. 

The water table, -when too near the surface, converts the soil 
into a swamp. When somewhat lower, the soil is suitable for 
some plants, but is too wet for agricultural purposes. If from 
4 to 6 feet below the surface, the soil is suitable for cultivation, 
but the water table is often considerably lower than this. 

In arid climates a proper substratum is much more important 
than in humid climates, since the roots must be able to penetrate 
deeply in order to endure drought. Hilgard 1 gives the following 
examples of faulty substrata found in California. 

A. The surface soil of about 12 inches is underlaid by horizon- 
tal layers of shale. This soil might possibly be rendered useful 
by blasting with explosive. 

B. The surface soil of 12 inches is underlaid by a heavy red 
clay, which can hardly be penetrated by roots. After blasting 
with dynamite this soil has been used successfully. Without 
blasting, orchards die in about three years. 

C. This soil has a calcareous hard pan at the depth of about 
four feet. On account of the arid climate, the roots of trees must 
be able to penetrate to a greater depth than this. 

D. The water level is about three feet. This prevents root 
penetration and restricts the use of the soil to shallow rooted 
crops. This condition may arise from the leakage of water from 
irrigation ditches. 

E. The soil is underlaid by a layer of coarse sand or gravel at 
the depth of about four feet, through which roots will not 
penetrate to the water below. A large number of orchards have 
died from this cause. 

Soil Temperature. Processes of plant and animal life can go 
on only between certain limits of temperature. The temperature 
to which the plant is subject depends upon both the soil and 
atmospheric conditions, the latter being perhaps the controlling 
factor. 

1 The Soil, p. 177. 



io8 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



The earlier the soil warms up in the spring, the earlier it can be 
planted. Some few seeds begin to germinate at the freezing 




Fig. 30. Fruit grown against a wall so that it will ripen. France, 
point, but most seeds require a higher temperature. Haberlandt 1 
1 Landw. Versuchs-stat., 17, p. 104. 



PHYSICAL PROPERTIES OF SOILS 



109 



tested various seeds at several temperatures and found the lowest 
temperature at which germination took place was as follows : 
Alfalfa, beets, barley, beans, red clover, oats, peas, turnips, wheat 32-40 F. 

Indian corn, carrots, sorghum, sunflower, timothy 40-51 F. 

Cucumbers, melons 60-65 F. 

The time required for germination decreases as the temperature 
rises, until the optimum temperature is reached. For example, 
corn required 11% days to germinate at 50, 3>4 days at 60, and 
3 days at 65 F. While the sunflower seeds required 25 days at 
51, at 60 they required only 3 days to germinate. 

The growth of the plant also depends upon the temperature to 
which it is subjected. Between the extremes of heat and cold 
fatal to plants, is an optimum temperature, varying for different 
plants, at which the maximum growth takes place. For example, 
Bialablocki 1 grew rye, barley, and wheat 20 days at different soil 
temperatures, and determined the dry matter produced, with the 
following results : 

WEIGHT OF PLANTS GROWN AT DIFFERENT TEMPERATURES. 



Temperature 


Rye 


Barley 


Wheat 


Degrees 



Mg. 
27,. Q 


MR. 
17 I 


Mg. 

IS 8 




20 8 


18.0 


*O'<-> 

20 8 




*2 4 


14 A 


20 : 


I 5 


4Q 5 


T>6.7 


JQ 8 




42 4 


42 o 


A*J Q 


25 


47 O 


-7C O 


4^-y 

d6 Q 


3 


-21 2 


26 1 


4O 1 


4 









In this experiment, 20 was the most favorable temperature for 
rye, 25 for barley, and 30 for wheat. The wheat plant grown 
at 30 is three times as large as that at 8 C. 

The temperature of the soil has a direct influence not only upon 
the plant, but upon processes in the soil, especially those relative 
to the preparation of soil nitrogen for plant food. 

Factors which Influence Soil Temperature. The temperature 
of the soil varies to a certain extent with that of the air, but the 
1 Jahresber f. Agr. Chem., 1870-72, p. 190. 



no 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



changes are slower and more restricted in depth. The tempera- 
ture of the soil is influenced by its color, water content, location, 
composition, etc. 

Location. The following figure illustrates the effect of location 
upon the light and heat received by the soil from the sun. Let E 
and F. represent two equal beams of sunlight, falling upon the 
south (A B) and the north (C D) side of a hill. It is evident 




Fig. 31. The south side of a hill receives more heat than the north. 

that the ray F is distributed over more surface than the ray E and 
that its heat has a greater area to warm. The soil on the north 
side thus receives less heat than that on the south side. The 
difference depends on the situation of the sun, and the inclination 
of the hill. It is for this reason that the south sides of hills in 
northern regions may be green with vegetation while the north 
side is covered with snow. A wall or hedge, by protecting the 
soil from wind, or by reflecting heat upon it, may cause the soil 
to be warmer. Maligoti arid Durocher found the average soil 



PHYSICAL PROPERTIES OF SOILS III 

temperature on the south of a garden wall 8 C., higher than on 
the north side. In cool climates, fruits which refuse to ripen 
under ordinary conditions may attain perfection when trained 
against the sunny side of a wall. 

Water Content. The quantity of heat required to raise the 
temperature of the soil depends upon the materials of which it is 
composed, but it increases with the quantity of water present. 
Approximately five times as much heat is required to raise the 
temperature of one pound of water one degree as for one pound 
of soil. Since wet soil does not warm up as rapidly as a dry soil, 
draining a wet soil makes it warmer, as a general rule. Clay 
soils, since they contain more water, do not warm up as quickly 
as sandy soils, which retain much less water. This is probably 
the reason sandy soils are so much better suited to early truck 
crops than are clay soils. They warm up quicker, and maintain a 
higher temperature during the early part of the year, thereby 
forcing the growth of the crop. 

The evaporation of water from wet soils also makes them 
colder than dry soils, as water in passing into the form of a vapor 
takes up considerable amounts of heat. King found that a clay 
soil was 4 to 7 F. lower in temperature than a sandy soil. 

Color. The color of the soil has an effect upon its tempera- 
ture. A dark soil warms up more rapidly than a light one, pro- 
vided they contain an equal quantity of water and other con- 
ditions are equal. Schubler exposed two layers of the same soil 
to the sun, under the same conditions, making one white by means 
of a thin layer of magnesia, and the other black with lampblack. 
The temperature of the blackened soil became 13 to 14 higher 
than that of the whitened one. Lampadius has given the soil a 
coating of coal dust an inch thick to aid in ripening melons, and 
in Belgium and Germany it is found that the grape matures best 
on certain soils covered with gray slate. These fragments, how- 
ever, retain the heat through the night. Black soils often contain 
more water than light soils, and the light soils therefore warm 
up first. 

Organic matter, in decaying, gives off heat. This heat is 



112 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

utilized in preparing hot beds with manure and earth. The decay 
of the manure raises the temperature of the hot bed. 

The quantity of organic matter in the soil is seldom sufficient 
to affect its temperature to a practical extent. An application of 
10 tons of partly decayed manure per acre may raise the tempera- 
ture of the soil 2 F. for the first five days, iF. for the second 
five days, and 0.6 F. the third. This is according to the experi- 
ments of -Georgeson. 1 This increase in temperature might aid in 
hastening the germination of seeds and in protecting a spring crop 
from frost. 

Wagner found an average increase of temperature 0.7 to 0.2 
F. during four to twelve weeks, due to heavy applications of 
manure under field conditions. 

Control of Temperature. Artificial regulation of temperature 
is practiced comparatively little in agriculture, though of con- 
siderable importance in horticulture, in which hot beds, cold 
frames, and green houses are used. The growth of tomato plants, 
sweet potato vines, and other plants under glass or in protected 
places, for transplanting when the soil becomes sufficiently warm 
or danger of frost is past, is a kind of regulation of temperature. 
In some regions, smoke fogs are produced to prevent frost and 
thereby protect tender plants, or plants at critical stages of 
growth. 

Color of Soils. Soils range in color from almost pure white, 
through yellow, red, or gray, to black. The yellow or red colors 
are due usually to hydrated oxides of iron. Organic matter gives 
a soil a black color when wet, or a gray or brown or black color 
when dry. The color thus affords some indication as to the char- 
acter of the soil. Black or red soils are generally preferred by 
practical farmers. The intensity of the color is not always an 
indication as to the quantity of organic matter or oxide of iron 
present. A coarse sand, by having a smaller surface to be colored, 
requires much less coloring material than a clay soil which has a 
large surface. 

1 Agr. Science i, p. 251. 



PHYSICAL PROPERTIES OF SOILS 113 

Specific Gravity of Soils. The specific gravity of a body is the 
weight of the body divided by the weight of an equal volume of 
water. Suppose we place 10 grams of soil in a bottle of known 
weight which holds exactly 25 cubic centimeters, and weigh. 
Then fill the bottle exactly full of water, so that it contains no 
air, and weigh again. The gain in weight subtracted from the 
weight of 25 cubic centimeters of water gives the weight of water 
displaced by 10 grams soil. Ten divided by this gives the specific 
gravity of the soil. 

In estimating the specific gravity of a body, we must allow for 
the space occupied by air. If the soil could be fused into a solid 
mass without chemical change, the weight of i cubic centimeter 
expressed in grams would be the specific gravity. 

The specific gravity of some soil materials is given in the 
following table: 

SPECIFIC GRAVITY OF SOIL MATERIALS. / 

/ 

Quartz 2.6 Water i.o 

Felspar 2.5-2.8 Humus 1.2-1.5 

Limestone 2.6-2.8 Mica 2.8-3.2 

Granite 2.6-2.7 Hornblende 2.9-3.4 

Clay 2.5 Talc 2.6-2.7 

SPECIFIC GRAVITY OF SOILS. 

Clay soil 2.65 

Sandy soil 2. 67 

Fine soil 2.71 

Humus soil 2.53 

Apparent Specific Gravity. The apparent specific gravity of 
a soil is the weight of a given volume of the soil, including air 
spaces, compared with the weight of an equal volume of water. 

Apparent specific gravity depends upon the true specific gravity 
of the soil particles, and the amount of air spaces in the soil. The 
former is constant, the latter is variable, as it depends upon the 
size and shape of the soil particles and the treatment to which the 
soil has been subjected. A cultivated soil contains more air 
spaces than the same soil in pasture. 

The apparent specific gravity will vary, then, with the treat- 
ment to which the soil has been subjected, if it is determined in 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



the field. In the laboratory the apparent specific gravity will vary 
with the method used for determining it. 

The apparent specific gravity of a soil is determined by weigh- 
ing the dry soil that occupies a given volume. In the field this is 
accomplished by driving a tube of definite size, not less than 2 
inches in diameter, into the soil, so as to remove a core of known 
volume. The core is removed, dried and weighed, and the weight 
divided by the volume is the apparent density. 

Apparent density is determined in the laboratory by packing 
200 to 1000 cc. of the soil into a glass cylinder, and weighing it. 
This method to a certain extent is applicable to incoherent soils, 
but is not well suited to clay soils, in which the action of water 
has a decided effect upon the apparent density. It represents the 
weight of the soil when in condition of good tilth. 

The apparent specific gravities of different kinds of soils are 
as follows, according to Schubler i 1 





Apparent 
specific gravity 


Weight of 
dry soil per 
cubic foot 


Weight per acre 
to the depth of 
i foot in pounds 


Sand 


T 7fi 








1. /D 

I 28 


80 QO " 








7( - 


o o<y u<j > uiju 


Peat 


o 480 80 


/o 

JO ^O " 








o u o u 





Sandy soils, usually termed "light," are the heaviest of all, 
while clayey land, termed "heavy" weighs less than ordinary soils. 
The terms "light" and "heavy" refer to the readiness with which 
the soils are worked by the plow, light soils requiring much less 
labor than heavy ones. 

The actual weight of the soil in the field varies with the quantity 
of water present. A peaty soil saturated with water is very 
heavy. 

Since soil analyses are made by weight, differences in the 
apparent specific gravity of soils must be taken into consideration 
in interpreting the results. 

1 Stockbridge, Rocks and Soils, p. 153. 



PHYSICAL PROPERTIES OF SOILS 



The apparent specific gravity of soils taken in the field appears 
to increase as we go downward. This is in part due to the 
pressure of the overlying stratum ; in part to the action of rain 
carrying the finest particles of the soil into the open spaces of the 
subsoil ; in part to the loosening action of tillage and plant and 
animal life on the surface soil and to the presence of their 
residues. 

The weights of the soil per acre were studied 1 at Rothamsted 
and Woburn, England, by driving down an iron frame 6 inches 
square and 9 inches deep. The core of soil was removed, dried, 
and weighed. 

WEIGHT OF SOIL PER ACRE. 





Pasture 
Rothamsted 


Arable land 
Rothamsted 


Arable land 
Woburn 






2 QOO OOO 


3 200 ooo 








-I A oo OOO 


Third. Q inches 


3 100 ooo 


-i 2OO OOO 


3 TOO OOO 




37OO OOO 


3-7OO 000 


3 TOO OOO 











The Rothamsted soil is a heavy loam or clay subsoil beneath 
which is the chalk. The Woburn soil is a light sand. 

Air Space in Soils. The quantity of air space in soils may be 
calculated from the apparent and the real specific gravity. To 
say that the soil has an apparent specific gravity of 1.20 means 
that i cc. of the loose soil weighs 1.20 grams. If the soil material 
has the real specific gravity of 2.5, then I cc. weighs 2.5 grams, 
and i. 20 grams of it occupies 1.20 divided by 2.50 equals 0.48 cc. 
Thus 0.52 cc. or 52 per cent., is air space in this particular 
instance. 

Adhesion and Cohesion. Cohesion is the force with which the 
soil particles adhere to one another. It varies with the amount 
of water present and the nature of the soil, from zero in some 
sands, to a high degree in some clays when dry. Soils with little 
cohesion when dry are liable to be blown by winds unless pro- 
tected by vegetation. The larger the particles of soil, the less is 

1 Warington, Physical Properties of Soil, p. 46. 



Il6 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

the cohesion between them. When the particles correspond in 
size to silt, the wet soil may be a sticky mud, like clay, and is often 
spoken of as a clay soil, but when dry it easily falls to powder. 

The behavior of soils upon drying is a matter of great practical 
importance. Some soils in drying crumble easily, while others 
form clods which are difficult to break down. This behavior 
depends to a certain extent upon the amount of water present. 
Some soils crumble easily when plowed in the right condition, but 
when too much water is present they form intractable clods. 

Cohesion may be determined in the dry state, or the wet state. 
For dry cohesion, the soil is mixed with water, molded into cakes 
of uniform size, and dried. The amount of force required to crush 
the cakes is then determined. This throws light on the liability 
to form clods. 

For moist cohesion, the soil is mixed with water to 50 per cent, 
of its water capacity, and the power required to separate a sec- 
tion of the soil of a given area determined. This is related to 
the plowing of the soil. 

The ease or difficulty of plowing or cultivating a given field 
depends largely on the cohesion of the soil. A measure of this is 
the draft of the plow. The draft of a plow on sandy soil may 
be as low as 27 pounds per inch in depth of furrow, as against 
100 pounds per inch for clay. This means that the former would 
be light work for one horse, the latter heavy work for three 
horses. 

Increasing the amount of organic matter in the soil has the 
effect of decreasing the cohesiveness of clays, and increasing it 
for sands. A dressing of lime also tends to decrease cohesiveness 
of a soil. 

The state of dryness has an influence. Sand, lime, and humus 
have little adhesion when dry, but considerable when wet. Clay, 
under certain conditions of moisture, is very hard to plow. The 
English practice of burning clays overcomes adhesion. When 
clay is burned and then crushed, the particles no longer adhere 
tenaciously when wet, and the mass is sandy-like rather than 
clayey. 



PHYSICAL PROPERTIES OF SOILS 117 

Shrinking on Drying. Some soils increase in bulk when they 
become wet, and shrink on drying. The shrinkage is very per- 
ceptible in some clay soils. They become full of cracks and rifts 
on drying, and, since they harden about the rootlets imbedded in 
them, the roots may become ruptured during dry weather. Heavy 
clays may thus lose one-tenth or more of their volume. 

Sand does not change in bulk on wetting or drying, and, when 
present to a considerable extent in the soil, its particles prevent 
the adhesion of the clay particles. Although a loam shrinks on 
drying, the lines of separation are more numerous and less wide 
than in a clay. 

Some soils crack into comparatively small masses on drying. 
These are often termed buckshot soils. Others crack into larger 
masses, several feet in size. In others irregular cracks are found, 
sometimes an inch in width. Schubler prepared cubes of various 
soil constituents and determined the contraction in volume on 
drying. Pure clay contracted 18.3 per cent, of its volume; humus 
from the center of a decayed tree 20 per cent. ; a sandy clay 6 per 
cent. ; an arable soil 12 per cent. ; a garden soil 14.9 per cent. The 
rifts allow an easier drying of the subsoil. The results of drying 
are afterwards favorable in a clay soil, the fissues affording 
drainage lines. The texture is improved, drying and moistening 
being favorable to formation of compound particles. Air is also 
admitted to the subsoil, and oxidation in the subsoil is promoted. 

Number of Particles in Different Types of Soil. These have 
been calculated by Whitney 1 as follows : 

Early truck 1,955,000,000 

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 

The basis of this calculation is the assumption of a certain 

average size for each grade of soil particle. Knowing the size 

and the specific gravity of the soil, the weight of each grade of 

particle can easily be calculated. Then the numbers of particles 

1 Bulletin 21, Maryland Station. 



Il8 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

of each size can be calculated from the weights of the various 
separations made in the physical analysis of the soil. 

Relation of Fineness to Fertility. The state of division of a 
soil has some effect upon its fertility. If two portions of a rock 
are prepared, one coarse, and the other finely ground, plants will 
grow better on the latter. With the same material, the rapidity of 
solution is in direct ratio to the extent of surface it exposes. The 
finer the particles, the more abundantly will the plant be supplied 
with the necessary nourishment. For example, a cube of rock I 
foot square has 6 sides each 12 inches square, or 6 times 144 
square inches of surface. Cut this cube into cubes of I inch 
square, or 12 times 144 cubes, each of which has six sides, one 
inch square, or the exposure is 6 times 144 square inches. It is 
easily seen that as the division increases, the surface exposed to 
the action of roots also increases. 

It must not be assumed, however, that finely pulverized sandy 
soils would yield the same amount of plant food as clay soils. 
While this might be true in exceptional cases, as a rule sandy 
soils contain less plant food, as may be shown by a complete 
chemical analysis of the soil. 



CHAPTER VII. 



THE SOIL AND WATER. 

The plant food is dissolved in water and enters the plant 
through its roots. Water also serves as the medium by which 
matter is transferred, and it supplies the hydrogen and a part of 
the oxygen used in the synthesis of organic matter. 

A large amount of water is required by plants, not only because 
plants contain considerable water, but also because the passage of 
water through plants is one of the most important means of plant 
nutrition. The evaporation of water from the surface of the 
leaves produces an upward current of water which carries into 
the plant needed mineral material. The greater the evaporation, 
the greater is the transference of plant food from the soil to the 
plant, other things being equal. 

Transpiration. The loss of water through the leaf of the 
plant is termed transpiration. The amount of loss by transpira- 
tion is easily determined with plants in pots. 1 We weigh the pot 
of soil containing the plants at the beginning of the experiment 
and at the end of certain periods weigh it again; the loss of 
weight plus any water added, is water evaporated by plant and 
soil. The water evaporated from a pot of similar soil but with 
no plants, under the same conditions, is taken to show the 
evaporation from the soil alone, although the shade of the plant 
make's a difference. The loss of water by soil and plants, less the 
loss from soil alone, gives the loss by the plant alone. Correction 
must be made for the increase in weight of the plant, if the 
experiment is conducted for some time. In another form of 
apparatus, the soil is covered with a galvanized iron cover, and 
the openings through which the plant extends is rendered water- 
tight by means of modelling clay. Plants may be grown in the 
free air by this apparatus, without danger of irregular results due 
to varying amounts of rain falling in different pots of the same 
series. 

If the plant is contained in pots or other vessels set in the 
1 Montgomery, Proc. Am. Soc. Agron., 1911, p. 257. 



I2O PRINCIPLES OF AGRICULTURAL CHEMISTRY 

ground, or if it is too large to be weighed, the evaporation of 
water may be estimated by determining the quantity of 
water in the vessel at the beginning and at the end of the experi- 
ment (by analysis of the soil), and measuring the quantity of 
water received by the vessel during the course of the experiment. 
In the transpiration experiments of the Bureau of Soils, the 
plants are grown in wire baskets covered with paraffin. Before 
the measurements of transpiration are begun, the pot is sealed 
with a sheet of paper coated with paraffin so as to exclude 
evaporation as much as possible, a suitable hole being left for the 
plants. The pots are weighed, and the loss of water is restored 
daily. 

Factors of Transpiration. The amount of water transpired 
by plants depends upon several factors : 

Humidity of Air. Transpiration decreases as the humidity 
of the air increases, for evaporation into dry air is much more 
rapid than into moist air. At the Nebraska Experiment Station, 1 
plants were grown in an open greenhouse, in which the air was 
dry, and in a closed greenhouse in which floors and benches were 
kept wet, and water atomized into the air. The weights of water 
transpired per gram of dry weight, were as follows : 

In dry greenhouse 340 

In moist greenhouse 191 

Available Water. Plants appear to transpire more as the 
available water increases. The following figures show the 
amounts of water transpired from the same soil containing differ- 
ent quantities of water : 

Grams water used 

Per cent, saturation per grams dry 

weight produced 

IOO 290 

80 262 

60 239 

45 229 

35 252 

The plants grown with 35 per cent, saturation of the soil, did 
not grow normally. 

1 Montgomery, Proc. Am. Soc. Agron., 1911, p. 276. 



THE SOIL AND WATER 



121 



Light. More water is transpired in the light than in darkness. 
For example, Deherain 1 determined the water evaporated per 
hour and 100 grams of leaf, to be as follows: 
WATER EVAPORATED. 





Wheat 


Barley 




Grains 

88.2 
17.8 
J.I 


Grams 

74-2 
18.2 

2.3 









On the other hand, excess of light may diminish transpiration. 

Composition of the Soil or Solution. The solution brought in 
contact with the roots or stem of a plant exerts a decided influence 
upon the amount of water transpired. According to Burger- 
stein, 2 small quantities of acid added to distilled water increase 
transpiration, alkalies retard it, and the effects of salts depend 
upon the nature and concentration of the solution. With single 
salts, transpiration increases with the concentration of the solu- 
tion, until a maximum is reached. The effect of mixtures of two 
or more salts depends upon the nature of the salts used. Of 
greater agricultural importance is the fact that a complete nutri- 
tive solution decreases transpiration. The following table gives 
some examples : 

The fertility and nature of the soil also appear to exert an 



Salts 


Period 
(hours) 


Grams water 
transpired per 100 
grams dry matter 


With 
distilled 
water 


With 0.170 
per cent, 
solution of 
the salts 
named 


Potassium 
Potassium 
Potassium 




94 
96 
120 


grams. 

1,838 
1,670 

2,794 


grams. 

1,142 
I,l6l 
i,939 




nitrate and magnesium sulphate 



1 Jahresber. f. Agr. Chem., 1868, p. 273 
* Jahresber. f. Agr. Chem., 1875, p. 388. 
9 



122 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



influence upon the quantity of water transpired. Widstoe 1 found 
that the transpiration of corn is from 552 per gram dry matter 
on a loam, to 1616 on a sand or clay. 




Fig. 32. Pot experiments, on moisture used by plants. Utah Station. 
Demoussy, at the Grignon Experiment Station, found that the 
poorer the soil, the more water was transpired. The following 
figures are quoted from him. 
GRAMS OF WATER TRANSPIRED PER i GRAM DRY MATTER PRODUCED. 





Rye grass 


Clovers 




630 
233 
435 
449 
630 


454 
398 
255 
272 
322 













1 Utah Bulletin, No. 105. 

2 Not manured the same as the rye grass. 



THE SOIL AND WATER 123 

In some pot experiments of Konig, similar results were secured. 
The relative quantity of crop he produced on three soils was 
100:122:134, while the relative transpiration of water was 
100 : 74 : 63, being in the opposite direction. Gardner 1 found in 
wire basket experiments, that as fertilizers increase plant growth, 
there is a marked diminution in water transpired per unit of 
growth. 

It would appear that a fertile soil conserves moisture, so far as 
transpiration is concerned, much better than a poor one. That 
is to say, the better supplied a soil is with plant food, the larger 
is the crop which it can produce with a limited supply of water. 
The presence of plant food results in an economy of water. The 
smaller the quantity of available plant food present, the greater 
seems to be the effort made by the plant to secure sufficient plant 
food, by increasing the current of water passing through it. 

Results of an experiment with corn on soil types at the 
Nebraska 2 Experiment Station, are as follows : 



Character of soil 


Water transpired per gram 


Unmanured 


Manured 


"Very poor (15 bu ) 


540 
478 
391 


350 
34J 
346 


Intermediate ( ^o bu ) 


Quite fertile (50 bu ) 





Variety of Plant. The difference in the transpiration of differ- 
ent kinds of plants is probably a factor in the adaptability of 
plants to climate and soils. Plants which live in dry regions, 
such as cactus, salt bush, etc., transpire less water than plants 
adapted to moist sections. There are other causes of endurance 
of drought, however, such as the deeper rooting already dis- 
cussed. 

According to Fittbogen there is no relation between transpira- 
tion and the production of organic substance, as measured by the 
carbon dioxide decomposed. 

1 Bureau of Soils, Bull. 48. 

2 Proc. Am. Soc. Agri., 1911, p. 277. 



124 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



Amount of Water Required by Plants. The amount of water 
transpired during the growth of a plant may be calculated as parts 
of water per one part of dry matter of the plant, and may be 
considered to represent the amount of water required by the 
plant. This quantity will vary considerably according to the con- 
ditions surrounding the plant, as we have seen in the preceding 
paragraphs. An estimate of the amount of water required to 
produce a given weight of dry matter is, therefore, only approxi- 
mate. Such an estimate may, however, aid in the consideration 
of problems relating to the water content of the soil. The figures 
given in the table were secured in experiments of four 
investigators. 1 

POUNDS OF WATER EVAPORATED BY THE PI,ANT PER POUND OF 
DRY MATTER PRODUCED. 





Lawes 
and Gilbert 


Hellriegel 


King 


Wollny 


Barley 


262 


y TO 


JQ7 








*, 
262 


obO 






214 






fi/lfi 






O/ 1 






Clover (red) 






*/ 


2 33 




*4y 


6o u 


4oo 




Millet 




o/o 




416 


Mustard 








SAI 


Oats 




4O2 


c C7 


66 c 


p pa c 








w*0 


Potatoes 


*oo 


292 


4// 


447 


Rape 






4-^0 




Rve 








912 


xv_yc 




oil 






Wheat 


22^ 






q.yu 




"0 


OOV 







In some of the arid states of the United States, fair crops of 
wheat are grown with an annual rainfall of 13 to 18 inches, most 
of which falls in the winter before the growing period of the crop 
begins. This small quantity of water is effective, partly because 
the soils are rich in soluble plant food, partly because the saline 
matter in solution decreases transpiration. 

1 Exp. Sta. Record 4, 532, Rep. Wis. Station, 1894; Jour. Hort. Soc. 
Eng. , 1850. See also Widstoe, Utah Bui. No. 105 ; Montgomery, Proc. Am. 
Soc. Agri., 1911, p. 261. 



THE) SOIL AND WATER 



125 



In regions of deficient rainfall, the crop produced is, as a rule, 
somewhat proportional to the water supply. S. Fortier 1 in 
Montana made experiments with wheat grown in tanks. The 
crop secured increased quite regularly with the amount of water 






I 



pig 33. Relation of rainfall for June, July and August to yield 
of corn per acre. U. S. D. A. 

supplied. In California, he found that the natural rainfall, 4^ 
inches during the growth of the wheat, produced straw, hut no 
grain ; four inches of irrigation water produced at the rate of 10 
bushels, and sixteen inches of water increased the yield to thirty- 
eight bushels per acre. Even in humid climates, irrigation may 
result in largely increased yields. 2 King 3 in Wisconsin grew 
crops in barrels sunk level with the ground surrounded by the 
same crop as was in the barrel. The soil was kept saturated with 
water six inches above the bottom of the barrel. The crops pro- 
duced far exceeded those produced in the surrounding field. 
The water used equaled 24 inches. The yield of oats and barley 

1 Rep. Montana Exp. Sta., 192-3. 

2 King, Farmers' Bulletin No. 46. 

3 Rep. Wis. Exp. Sta., 1893. 



126 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



was 10,000 pounds dry matter per acre. The abundant supply 
of water thus had a striking effect. 

Smith 1 has studied the relation of the rainfall to the yield of 
corn. Figure 33 shows the relation between the average yield of 
corn in bushels per acre, and the rainfall, in Ohio, Illinois, Indiana, 
Iowa, Nebraska, Kansas, Missouri, and Kentucky for the years 
1 883 to 1902 inclusive. 

Duty of Water. Duty of water is a term applied by irrigators as 
the measure of the quantity of water used per acre, but the term is 
also applied to the service which water may render in producing 
crops. McGee 2 estimates that it requires approximately 1,000 
pounds of water during the year to produce one pound of grains, 
etc. This estimate allows for losses by evaporation, and its basis 
is the aggregate yearly supply of water from all sources He 
presents the following table, based on personal observation, show- 
ing estimates of crop yields with varying amounts of water for 
the entire year : 



Depth per acre 


Corn 


Oats 


Wheat 


1 8 inches .... 


bushels 

IO 


bushels 

T r 


bushels 
5 


^6 inches 


7 C 


x o 
An 


12 


48 inches 


6j 

7O 


80 


2c 




/ w 
TOC 


1 2O 


*3 

A.O 




1W O 







These figures, are roughly approximate, as there are great 
variations in conditions. According to this table, 36 inches yearly 
rainfall will produce, on an average, 35 bushels of corn. 

Quantity of Water in Soil. The following figures of Hellriegel 3 
are the result of an experiment to ascertain the effect of the 
amount of water in the soil upon the crop production. The 
experiment was carried out in pots. 

1 Yearbook, U. S. Dept. Agr., 1903, p. 216. 

2 Yearbook, U. S. Dept. Agr., 1910, p. 174. 

3 Jahresber, f. Agr. Chem., 1870-2, p. 161. 



THE SOIL AND WATER 
EFFECT OF MOISTURE ON CROP. 



127 



Moisture in percentage water capacity of the sand 


Barley 


, Total 


Grain 


80 


19.69 
22.76 
21.76 
17.19 
14.62 
6.30 
0.12 


8.77 
9.96 
10.51 
8.70 

7-75 
0.72 


60 






6^ ' ' 


jO ... 







The most favorable quantity of water in this case was 40 per 
cent, of the water capacity of the sand. Necessarily in this 
respect there will be a difference for different kinds of plants. 

According to this experiment, there is an optimum condition 
of the soil at which the moisture content is most favorable to 
plant growth. Below or above this optimum, there is a decrease 
in yield, independent of the wilting of the plant. Wilting is a 
sign of distress, signifying that moisture is lacking to an extent 
that endangers the life of the plant. The growth may suffer 
from lack of water long before wilting takes place. The experi- 
ments of Hellriegel were carried on in pots, in which there was a 
limited amount of soil at the disposal of the plants. In the open 
field, in which a greater range of root development is permitted, a 
smaller percentage of available water may suffice. 

Forms of Water in the Soil. Water is present in the soil as 
water of hydration, hygroscopic water, capillary water, and flow- 
ing water. 

Water of hydration is water in chemical combination with cer- 
tain soil constituents, such as hydrated silicates (zeolites) and 
hydrated oxide of iron. Most of it is retained when the soil is 
dried at 100, and is driven off on heating the soil to a high tem- 
perature. As water of hydration cannot be taken up by plants, it 
cannot be considered to be of value to the plant. 

Hygroscopic Water is water which is absorbed by the soil from 
the atmosphere. Every body in a moist atmosphere has a layer of 
water upon it, the thickness of which depends upon the tempera- 



128 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

ture and the degree of saturation of the atmosphere. The 
capacity of the soil to hold hygroscopic water can be determined 
by placing a thin layer of soil in a vessel, the air of which is 
saturated with* water ; the soil will take up a certain amount of 
water, which can be determined by the gain in weight of the soil. 
The temperature of the containing vessel must be uniform, for 
variations in temperature in a saturated atmosphere will be liable 
to form dew on the soil. The layer of soil must be very thin, not 
over one millimeter thick. This method gives the maximum 
hygroscopic capacity ; if the air is not fully saturated, lower 
results will be obtained. 

The amount of hygroscopic water taken up depends very 
largely on the character of the soil. According to Hilgard and 
Loughridge, 1 soils absorb the following amounts of hygroscopic 
moisture : 

Hygroscopic moisture 
Per cent. 

Sandy soils (less than 5 per cent, clay) 3 

Sandy loams 3-5 

Loams 5 

Clay loams 5-7 

Clay 7-10 

The amount of hygroscopic water taken up by a given sub- 
stance depends partly upon its surface area. A mass of quartz 
will absorb much more moisture when in fine powder than when 
in large fragments. It is also greatly influenced by the amount 
and character of the colloid constituents in the soil, such as 
hydrated ferric oxide, alumina, gelatinous silica, hydrated silicates, 
and especially humus. Pure clay has a somewhat lower absorp- 
tive power than these. 

Value of Hygroscopic Moisture. Plants are not able to utilize 
the hygroscopic moisture of soils. At least, they wilt before the 
moisture in the soil is withdrawn to the amount held by 
hygroscopic power. 

Heinrich 2 grew plants in very small boxes until well developed 

1 Rep. Cal. Exp. Sta., 1897-8. 

2 Jahresber, f. Agr. Chem., 1875-6, p. 368. 



THE: soiiv AND WATER 



129 



and then placed them under conditions of very little evaporation 
until they began to wilt. The moisture in the soil was then 
determined. The hygroscopic moisture was also determined by 
the method already indicated. A variety of soils and plants were 
used. The following table shows the average results secured with 
Indian corn and oats : 





Water per 100 of dry soil 


When plants 
wilted 


Hygroscopic 
water 




1-5 

4.6 

6.2 

7.8 
9.8 
49-7 


1.2 

3- 
4.0 

5-7 
5-2 
42.3 








Calcareous soil 


pAOf 





It appears that hygroscopic water may be of advantage in 
regions of hot, dry winds ; the higher the hygroscopic water, the 
less rapidly the soil dries out and heats up. It also appears that 
heavy fogs, such as occur in parts of California, may add to the 
hygroscopic water of the soil, and keep the plant growing slowly 
when rainfall is lacking. 

Capillary Moisture. This is the thin film of water surround- 
ing the soil particles and so held between them that it cannot flow 
off. In a clean glass tube of i mm. internal diameter, capillary 
attraction will cause water to rise 15.3 cm; if the bore is o.i mm. 
the water will rise 153.6 cm; if it is o.oi mm. the water will 
rise 1536.6 cm. That is, the height to which the water is carried 
varies inversely as the diameter of the tube. It also varies with 
the temperature and the liquid used. 

If glass tubes be filled with various soils and the lower ends of 
these be set in water, a great difference will be observed, both in 
the speed and in the height to which the water rises in them. This 
is the method used for comparing the capillarity of dried soils. 

The following table 1 exhibits the differences in the height to 
which water rises in some soils : 

1 Meister, Jahresber. f. Agr. Chem., 1859-60, p. 42. 



130 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 





5J hours 


2\Yz hours 




inches 

44 
44 
38 
37 
26 

21 


inches 

80 
70 
64 
45 
36 
28 






Quartz sand 









Briggs and Lapham 1 found that water rose 37.5 cm. in a dry 
soil, while in a moist soil it rose over 165 cm. The method of 
work was as follows : 

Two tubes of glass were provided with perforated bases, filled 
with soil, and saturated with water by sucking it up through the 
earth. One tube was then sealed at the base, and the other 
inserted into a reservoir of water. At various intervals of time, 
both tubes were weighed. If 'water rises by capillary action, the 
tube with reservoir attached will lose water more rapidly than 
the other one. If not, a section of the tube was removed after a 
suitable interval, and the operation repeated. For example, with 
one soil, no loss occurred at 180 cm. ; loss occurred at 165 cm. 
The capillary water rose 165 cm., but did not rise 180 cm. 

The so-called capillary moisture of the soil is held as thin films 
of water surrounding the soil particles, due to what is called "sur- 
face tension." The surface of the film of water surrounding the 
soil particle is in the condition of an elastic membrane exerting 
considerable pressure and consequently holding the water firmly 
against the soil particle. In a fully drained soil there is a condition 
of equilibrium between the force of surface tension and the force 
of gravity. If the film of water becomes thicker and heavier, the 
force of gravity will gradually draw away the excess of water. 
If the films become thinner, a force is developed which may cause 
a flow of water from thicker neighboring films. 

Loughridge 2 studied the capillary action of soils placed in 
copper tubes one inch in diameter and in one foot lengths, fitting 

1 Bulletin 19, Bureau of Soils. 

2 Rep. Cal. Exp. Sta., 1892-4 



THE; SOIL AND WATER 131 

into each other. One side of the tube was made of glass so that 
the contents might be observed. The bottom tube was closed at 
its lower end with muslin and the tubes filled with air-dry soil, 
stirred in with a wire and made firm by a slight tapping on the 
table. In experiments with a sandy soil, an alluvial soil, a silty 
soil, and an adobe soil, water rose rapidly in the two coarser soils, 
reaching 8 to 9 inches in the first hour, while the water in the 
stiff soil rose only i to 2 inches. The water rose rapidly in the 
sand, but only reached a final height of i6*/2 inches. The other 
three soils, in 125 or 195 days, reached nearly the same height, 
but the alluvial soil, composed mostly of fine sand and silt, carried 
the water up most rapidly. This experiment is an instructive 
illustration of the difference in the capillary powers of soils. 

Water thus tends to distribute itself in the soil, through 
capillary passages or by the slower processes of surface distribu- 
tion. When these operations are assisted by gravitation, as when 
rain falls, the water moves rapidly. When the movement of 
water is opposed by gravitation, as when a soil dries at the sur- 
face and is wet below, the movement is retarded by the increasing 
height of the column of water lifted, until finally it entirely 
ceases. 

Capillary action has some effect in raising water from the 
water table in a few instances when the water table is less than 
about four feet from the surface. One great function of capillary 
action and surface tension is to distribute water to the roots. 
When water is withdrawn at one place by the roots, it disturbs the 
equilibrium and causes a flow of water from points of least 
resistance. 

Flowing Moisture. Water present in excess of the hygroscopic 
moisture held by capillary action, may be termed flowing water. 
It will pass downward through the soil at a rate depending upon 
the permeability of the soil. 

The quantity of water in a saturated soil depends entirely upon 
the air space in the soil. The soil is saturated when all the air 
space is filled with water. The air space can be calculated from 
the real and the apparent specific gravity of the soil. 



132 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



Sand and gravel separately have an air space corresponding to 
about 40 per cent, of their total volume. When mixed together, 
the small particles of sand enter the free space of the gravel, and 
diminish the volume of the free space. In ordinary soils, the vol- 
ume of the free space is somewhat greater than in sand or gravel, 
owing to the presence of porous or compound particles. 
A soil abounding in porous compound particles decreases in water 
capacity when reduced to a powder. Zenger found that the soil 
from a peaty meadow held 178 parts water to 100 parts soil, 
but it held only 103 parts water when finely powdered. Colloidal 
bodies take up water and make the soil swell when wet. 

A soil is seldom completely saturated under natural conditions. 
The soil cannot become fully saturated unless the air which fills 
the interstices of the soil is allowed to escape. Rain covers the 
surface of the soil and closes the path of the air so that it gets 
out with difficulty. Only after long continued rains do soils be- 
come nearly saturated. 

The following table shows the quantity of water in naturally 
saturated soils, the samples being collected after continued rains : 






Water in naturally saturated soils 


Parts per 
100 of wet soil 


Parts per 
100 of dry soil 




18.4 
22.4 

24.1 

25-7 
23.0 
24.7 

37-6 


22.5 
28.9 
31-8 
34-7 
29.9 
32-8 
60.2 


Clay loam 








L/oani artificial manure 26 years 







The first four analyses were made by King. 1 The last 
three samples, from the Rothamsted 2 Experimental fields, 
show the effect of humus upon the water capacity. The 
accumulation of humus in the soil manured with barnyard manure 
increases the water capacity of the soil decidedly. On account 

1 Wisconsin Report, 1890. 

' 2 Jour. Roy. Agr. Soc., 1871, p. no. 



THE; sou, AND WATER 



133 



of the larger amount of stubble left by the crop produced with a 
complete mineral fertilizer, this soil also holds more water than 
the one with no manure. 

Method of Expressing Water in Soils. The amount of water 
contained in a soil may be expressed in three ways 1 ; first, in 
terms of the volume of water which occupies a given volume of 
soil ; second, in percentage of water contained in the wet soil ; 
third, in percentage of the dry soil. The following table (after 
Warington) gives the water in some soils fully saturated: 





Water in saturated soils 


Volume of 
water per 100 
volume of soil 


Water by weight 


In 100 
of wet soil 


Per 100 
of dry soil 




39-4 

45-4 
49-5 
50.0 
60.1 
69.0 
84.0 


19.8 

23.3 
28.2 
2 7 .8 
31.2 

43-4 
78.2 


24.7 
30-4 
39- 2 
38.5 
45-4 
76.8 
259.0 




Chalk soil 


Olflv 


^ ia y 









It is better to compare volumes of water in given volumes of 
soil in considering the water content of different soils. The roots 
of the plant are distributed through a given space, which varies 
according to the kind of plant, depth of soil, etc., and it is the 
quantity of water and plant food in the space occupied by the 
roots which is important. This method of expression is, how- 
ever, cumbersome; for, in addition to the weight of soil and weight 
of water, there must enter into the calculation the real and appar- 
ent specific gravity of the soil. 

The expression of the water absorbed in terms of the weight of 
the dry soil has decided advantages, especially in laboratory work. 
Only two quantities are involved, the weight of the soil and the 
weight of the water. It is thus easy to calculate the amount of 
water which should be present in a given weight of soil to produce 
a definite degree of saturation. 

1 Warington, Physical Properties of Soils, p. 69. 



134 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

Expressing the water present by weight in 100 parts of dry soil 
exaggerates the differences between soils. This is most marked 
when peat is compared with a sand, for we really compare the 
water in seven volumes of wet peat with one volume of wet sand. 

Retention of Water by the Soil. A soil, though protected from 
evaporation, does not remain fully saturated, but loses water 
through capillary action and the action of gravity. If a wide 
tube of sufficient length, filled with coarse sand of uniform sized 
particles, is saturated with water and allowed to drain, we find 
two distinct layers; a short column of sand fully saturated, 
and a long column above it fully drained, and containing a nearly 
uniform quantity of water. 

If the particles of sand are not uniform in size, as in an 
ordinary soil, then we find three layers, but not sharply distinct as 
in the preceding case. The highest layer is fully drained, and 
the content of water of the soil increases, until the lowest layer 
is fully saturated. The water in the fully drained layer not only 
coats the particles but fills the finest of the interspaces. The pro- 
portion of interspaces occupied by water increases toward the 
bottom of the tube, until finally all the interspaces are filled and 
the soil is saturated. 

The following experiment of King 1 exhibits the differences 
between two classes of soil material. Tubes 10 feet long and 6 
inches in diameter were filled with sand prepared by sifting 
through sieves of different degrees of fineness. The sand was 
saturated with water, and allowed to drain, protected perfectly 
from evaporation, for in days. The water in each 6 inches of 
the columns was then determined. Two of the series are shown 
in the table . 

The particles in tube I are nearly uniform ; the water content 
is nearly constant until the ninth foot is reached, when it suddenly 
increases. The particles in tube II are of varying size; the water 
content increases constantly from the top to the bottom. 

The amount of water retained by a drained soil depends upon 
the smallness of the spaces between the particles, and also on 
1 Report Wisconsin Station, 1893. 



THE: SOIL AND WATER 



whether or not the particles are porous. The smaller the particles 
and the more porous they are, the greater the quantity of water 
held. Humus and other organic matter, being porous, increase 
the water retained considerably. 





i 
Particles 
1/60" to 1/80" 


ii 

Particles 
less than i/ioo" 




Per cent. 

2.40 
2. 7 2 
2.79 

2.93 
2.98 
3.12 
3-H 
3-54 
I3-50 
20.51 


Per cent. 

3-35 
3-53 
4-03 
5-i6 
6.99 

9.83 
10.98 
15.88 
18.90 
19.99 




Third foot 




Fifth font 


'viirtVi foot 


SpvfMit H foot 


Eighth, foot ' 


Ninth foot .... 


Tenth foot 





The water held by drained soils may be determined by placing 
the soil in tubes which can be divided into sections, as in the ex- 
periment of King cited, though the tubes need not be so large. 
After the soil has been saturated and is fully drained, the water is 
determined in the different sections. Unless the tube is sufficiently 
long, the upper sections will not be fully drained. The length of 
tube required depends upon the character of the soil. The follow- 
ing figures of Schloesing show the quantity of water held by fully 
drained soils : 

Weight of water in 
100 parts of drained soil 

Coarse sand 3.00 

Fine sand 7.30 

Calcareous sand 32.00 

Clay soil 35-oo 

Forest soil 42.00 

The state of consolidation of soil affects the water held by it. 
Closely packed particles will retain at least twice as much water 
per unit of volume as particles loosely packed. Sandy soil has its 
capacity increased by rolling, and that of clay soil is reduced by 
pulverization. 



136 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

Water Capacity. The water capacity of a soil is the amount 
of water held by the partly drained soil. Fifty grams of soil 
are placed in a tube i% inches in diameter, allowed to drain, and 
weighed. The gain in weight, expressed in per cent., is the water 
capacity. Other methods which vary in detail are used. The 
percentage of water held will vary with the height of the column 
of soil, and to some extent, with the time of draining, but the 
results are comparable if the same method is used on different 
soils. 

The following figures show the water capacity of some types 
of soils, determined by the method given above : 

Water capacity 

of some soils 1 

Per cent. 

Tarboro sand 25. i 

Norfolk sand 29 .6 

Cecil clay 45.0 

Cecil sandy loam 36.8 

Durham sandy loam 28.9 

Amount of Water at Disposal of Plant. The amount of water 
at the disposal of the plant varies from time to time, according to 
a number of factors. The principal groups of factors are as 
follows: (i) The available water in the soil; (2) the root area of 
the plant; (3) the losses and gains of water by the soil; (4) the 
depth of the water-table. 

Available Water in the Soil. The amount of available water 
in the soil depends upon the nature of the soil, and the nature of 
the plant. 

Nature of Soil. The forces which cause water to enter a plant 
are opposed by the osmotic pressure of the soil solutions and by the 
hygroscopic attraction of the soil particles for water. The soil 
attraction increases as its moisture content diminishes, con- 
sequently decreasing the rate of entrance into the plant, and 
diminishing the production of organic substance if the amount 
supplied is below the optimum. When the outgo of water 
becomes greater than the income, the plant wilts. The point at 
which wilting takes place varies with the nature of the plant, but 
1 Rep. N. C. Exp. Sta., 1902-3, p. 39. 



THE: SOIL AND WATKR 137 

depends also on the nature of the soil, the temperature, and the 
humidity of the air. 

Briggs 1 and associates have elaborated methods for the deter- 
mination of the wilting point of plants, and traced the relation 
between the moisture content of the soils at the time of wilting, 
and the moisture equivalents of the soils, their hygroscopic power 
and their capacity to hold moisture. The moisture equivalent is 
the percentage of moisture the soil will retain in opposition to a 
centrifugal force 1,000 times the force of gravity. The relations 
between these factors he expresses as follows : 

moisture equivalent 
Wilting coefficient - 

i .84 

hygroscopic co-efficient 

0.68 

moisture-holding capacity 21 
2.90 

The water which cannot be withdrawn from soils by a plant 
may be termed unavailable water, and that in excess of this, 
available water. The California Experiment Station holds the 
available water to be practically the hygroscopic water, that is, 
the moisture absorbed from the soil by a damp atmosphere. 

Nature of the Plant. Plants vary in their power of absorbing 
water from soils. That is to say, some plants will reduce the 
water in the same soil to a lower percentage than others, before 
wilting. This may be due in part to difference in the ratios be- 
tween root area and surface growth, enabling a lower rate of 
water to supply the requirements of the plant ; or to greater root 
attraction for water by some plants, causing a larger flow of water 
into the one plant than in the other, under the same conditions of 
soil moisture; or to differences in the amount of water transpired. 

During a severe drouth, the California Experiment Station 2 
determined the amount of water in a large number of soils, where 
plants were doing well, or were suffering. California soils, it 
must be recalled, are different from soils of humid climates, there 

1 Proc. Am. Soc. Agr., 1910, p. 138; 1911, p. 250; Bui. 230, Bureau 
of Plant Industry. 

- Report 1897, p. 95. 
10 



138 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

being no distinction between subsoil and surface soil, the roots 
thus being able to strike deep into the soil. For this reason 
smaller quantities of water may suffice for crops. The results are 
as follows : 



Available water per cent. 


Doing well 


Suffering 




Apricots 
Citrus 
Almonds 
Pears 
Wheat 
Sugar Beets 


Citrus 
Almonds 
Barley 
Wheat 


I- 1 ^ 


1 ' -0 
T ^-2 


*O * ' 

3 .A 


q. 
4_c 


<;-6 . 





Root Area of Plants. The greater the volume of soil occupied 
by the roots, the greater the quantity of water (and also of plant 
food) at the disposal of the plant. Hence operations which 
deepen the surface soil or loosen the subsoil, so as to allow the 
roots to penetrate more deeply, have a favorable effect upon the 
amount of water offered to the plant. The volume of soil 
occupied by plants depends upon the nature of the plant. 

Water-Table. The water-table is the depth at which the soil is 
saturated with water, and is indicated by the depth of the water 
surface in shallow wells, which is slightly below the water-table. 
The water in the water-table is termed ground water. All perman- 
ent lakes and ponds may be considered as extension of the water- 
table above the surface of the land. The surface of the water- 
table follows, in a general way, the contour of the land, standing 
highest where the ground is highest, and low where the land is 
low. Land at the foot of hilly ground may receive a continuous 
supply of underground water, even in time of drought. 

If a bed of impervious clay is present in the subsoil, the under- 
ground water accumulates on its surface. The water level may 
generally be lowered by drainage ditches or tile drains. 

The height of the water-table depends upon the character of 
the soil, the rainfall, and the climate. It usually fluctuates, 
rising during wet seasons and sinking during a drought. \Yhen 
the height of the saturated layer reaches a certain point, discharge 
takes place in the form of springs or as general drainage. 



THE SOIL AND WATER 139 

If the water-table is only a few inches beneath the surface, we 
have a swamp or bog; at one and a half to three feet in depth, 
we ha\e a wet soil in which some plants, especially grasses, may 
flourish. A depth of four to eight feet is favorable to agricultural 
conditions, though in many regions the water-table is much lower 
than this. 

In general, agricultural plants are injured if their roots are im- 
mersed for any length of time in the ground water, though many 
plants may send down roots to this water. 

Gains of Water by the Soil. The chief ways in which the soil 
may gain water are by rainfall and irrigation. In addition, ground 
water may be brought up to within reach of the plant roots 
by capillary action. 

Regions having more than 20 inches rainfall are said to have 
a humid climate. The character of the rainfall must be con- 
sidered as well as the total quantity. If it is heavy 
and infrequent, a large proportion of the water will 
run off on the surface and the region may possess more 
characteristics of an arid climate than a region with a moderate 
rainfall well distributed. 

The amount of water gained from rain depends upon the 
nature and the extent of the rainfall, the drainage, etc. A heavy, 
rapid rainfall may saturate the surface and flow off without any 
large quantity sinking into the soil. A slight rain may decrease 
the water content of the soil by establishing such capillary connec- 
tion between surface soil and lower layers, as to bring water to 
the surface which is lost by evaporation. 

If the surface of the soil is compact, the rain may flow off 
instead of penetrating the soil; but if the soil is loose, it will 
absorb considerable quantities of rain. ' One method of prevent- 
ing the washing of hilly land consists in deep plowing or subsoil 
plowing, so that the water will sink into the soil instead of run- 
ning off. In regions of slight rainfall, where it is desirable to 
save all the rain, the subsoil is stirred, and packed ; this increases 
the capillarity of the soil and its power of holding water. These 
are the methods of dry farming. 1 
1 See Dry Farming, by Widstoe. 



140 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

Capillary Action. If the water-table of the soil is so low that 
capillary action cannot raise water to the plant roots, it has no 
effect upon the plant. If it is within such distance that water 
can be raised to the soil's surface, the water raised by capillarity 
will tend to replace the water lost by evaporation and transpira- 
tion. The extent to which this replacement takes place depends 
upon the relative rates of evaporation and transpiration, and the 
rate of capillary action. 

King 1 studied the amount of water which can be brought up- 
ward by capillary action, using cylinders 4 feet high and one foot 
in diameter, which could be supplied with water from below. The 
cylinder was partly filled with water, soil dropped in and stirred, 
and the operation repeated until the cylinder was filled. The water 
level was then lowered to one foot below the surface, and main- 
tained at this point, while the surface of the cylinder was exposed 
for eight days to a strong current of air, and the quantity of water 
evaporated determined. The evaporation was determined for 
depths of i, 2, 3, and 4 feet of the water-table. At the depth of 
4 feet, the average evaporation from a fine sand and a clay loam 
was 0.9 pounds per day and square foot. In order for this 
experiment to be complete, it would be necessary to prove that 
this quantity of water passed upward from the water-table. The 
evaporation of the water may have been due, in part, to the 
natural drying of the soil, although it decreased as the water-table 
was lowered. In Wisconsin, crops in this soil suffer considerably 
from drought, though the water-table is only five feet from the 
surface, showing that in the natural condition the soil is able to 
raise but little water even a distance of five feet. 

The effect of capillary action in bringing up water is also shown 
by the Rothamsted drain gauges. The shallow one is 20 inches 
deep, the deeper one 40 inches. On an average of twenty-five 
years, the annual evaporation from the deeper gauge is only 0.6 
inches greater than from the shallow ; this probably represents the 
quantity of water brought to the surface from below the depth of 
20 inches. 

1 Report Wisconsin Station 1889-1890. 




34. Corn on heavy clay soil (a] undrained (b) tiles 70 feet 
apart (c) tiles 44 feet apart. Wisconsin Station. 



142 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

The roots of plants, however, may sometimes extend to con- 
siderable depths, and the presence of the water-table at a mod- 
erate distance from the surface, is thus an advantage. 

If moist air comes in contact with a cold surface it will deposit 
water. A soil may gain water from the air when the air is moist 
enough and the surface of the soil cool enough. It has been 
thought that water is sometimes distilled, as it were, from the 
lower layers of the soil into the upper. 

The monthly drainage from Mr. Greaves drain gauge 1 in Eng- 
land, filled with gravel and free of vegetation, has in fourteen 
years exceeded the monthly rainfall nineteen times; twice in 
December, seven times in January, seven times in February, and 
three times in March. The amount of water condensed from the 
air must, therefore, have been in each case more than that lost by 
evaporation from the soil, and may therefore increase the 
moisture of the soil. In Texas very heavy dews have been 
observed at various times. Drain gauges in England sometimes 
run more water than falls as rain, especially in January, 
February, and March. 

Losses of Water from the Soil. The water which comes to the 
soil is lost in several ways. Part flows away without penetrating 
the soil, as surface water. Part percolates through the soil to 
the water-table and reappears in drains, wells or springs, or 
passes through subterranean channels to the sea; this may be 
called percolation water. Another portion of the water is evapo- 
rated from the soil into the atmosphere. Finally, the water taken 
up by plants is passed off through their leaves into the air 
(transpiration). 

The proportion of the rainfall which passes off as surface water 
depends upon (a) the character and condition of the soil; (b) 
the slope of the land; (c) the amount and duration of the rain- 
fall. If the soil is loose and porous, either naturally, or rendered 
so by cultivation, a larger amount of water will penetrate it. The 
slope of the land determines the rate at which the water runs off ; 
the shorter the time of contact between soil and water, other 
1 Warington, Physical Properties of the Soil. 



THE SOIL AND WATER 



things being equal, the smaller will be the amount of water 
absorbed by the soil. The greater the quantity of water pre- 
cipitated in a given period of time, the larger the proportion of it 
will run off as surface water. The more rapidly the water runs 
off, the more soil it carries along with it, and the more likely it is 
to do damage by washing. 

Percolation. The rate at which water passes through the soil 
depends upon the character of the soil and the treatment to which 
it has been subjected. Sands allow water to percolate rapidly, 




3 Drain Gauges 

Each 7 feet 3- 12 in. x 6 feet = ^th acre area : 
Respectively 20, 40, and 60 inches depth of soil, 
collectors, each holding Drainage = 0*500 in. 
Gauge-tubes graduated to .. .. 0-002 in. 
Overflow tank to hold Drainaee. .=. 2- 000 ins. 

Fig- 35- Drain gauges, Rothamsted, England. 

and since they usually have a low capillary power, they often 
suffer from drought. Some clays allow water to pass through 
so slowly that they remain wet and heavy, do not warm up 
quickly, and are often hard to work. The amount of water 
which percolates may be decreased by increasing the water cap- 
acity of the soil or subsoil. 

Drain Gauges. Drain gauges are used to study the gains and 



144 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 




I 

vl 

L 



O ; 
3"7//e: '' ( ':'(<'. 



Bnass* 

ftpe Q 





. 




**3" 




^Graote 




' 




| 


J 


L 


,'-': 




AV 


Q 




v> 




;-- 


S 1 




^ 






N 


\; 


i^^^r^j^^ 


1 










: .-::. . O 



C/nofer 





Fig. 36. Concrete tubs for soil investigations, Neu York 
(Cornell) Station. 



THE: SOIL AND WATER 145 

losses of water by percolation and evaporation. The composition 
of the drainage water may also be studied. 

A drain gauge is a water-tight vessel rilled with soil and ex- 
posed to the rain under natural conditions. The water which 
passes through a given depth of soil is collected, measured, and 
otherwise examined, as desired. The soil may be kept bare, or 
cultivated or planted to various crops. The drain gauges at 
Rothamsted are filled with undisturbed soil of that place. Excava- 
tions were made along the side of the block of earth desired; it 
was bricked up and isolated. Each drain gauge consists of a 
rectangular mass of heavy loams with flints, of an area of i/iooo 
acre, 20, 40, and 60 inches deep, respectively. All the rainfall 
either passes through this mass of earth or evaporates. Drain 
gauges filled with loose earth represent unnatural conditions, and 
time should be allowed for the earth to consolidate before 
measurements are begun. 

Another method of studying drainage waters is to measure the 
water going off through tile drains, but this is not a good method, 
since only the excess of ground water passes off through the 
drain. A large portion of the percolating water passes into the 
country drainage. 

Evaporation. The rate at which water is lost by evaporation 
depends upon the nature and moistness of the soil, its capillary 
condition, the temperature, velocity of wind, humidity of air, etc. 

The wetter the soil, the less the humidity of the air, the greater 
the velocity of the wind, and the higher the temperature, the 
greater is the loss by evaporation. 

If the upper layer of the soil is loose and porous, it will dry out 
quickly, and the rate of loss will then be influenced by the rate at 
which water is brought to the surface by capillary action. 
Evaporation is greatly checked if the connection between the top 
soil and the under layer is broken by cultivation. Evaporation is. 
also influenced by the rapidity with which the water penetrates 
the soil. Much larger quantities of water will be lost by 
evaporation if the water is retained near the surface, than if it 
sinks into the soil. 



146 



PRINCIPLES OF AGRICULTURAL, CHEMISTRY 



The annual evaporation from the bare soil in the Rothamsted 
rain-gauges is apparently unaffected by the amount of rainfall. 
During nine years the rainfall varied from 22.9 to 42.7 inches ; 
the evaporation from the shallow gauge varied from 16.6 to 18.4 
inches, while the percolation varied from 5.6 to 25.5. inches. 

The losses of water from soil carrying vegetation is greater 
than from a bare soil. In the rotation of crops, it is necessary 
to consider this fact. For example, King 1 determined the per- 
centage of water in two portions of a field about to be planted to 
corn ; one portion had previously been a bare fallow, the other 
had carried clover. The clover land contained much less water 
than the bare fallow land, and the corn on the bare fallow would 
thus be far better able to stand a summer drought. One injurious 
effect of weeds is to remove water from the soil. 

Relation of Water Content to Evaporation. In the following 
table (by Schubler) the amount of water absorbed by soils is com- 
pared with the amount of evaporation during four hours : 





Percentage 
of water held 
by soil 


Percentage of 
water present 
evaporated 




25 
27 
2 9 

51 
6r 
70 

85 
89 
181 
256 


88.4 
71-7 
75-9 
45-7 
34-9 
31-9 
28.0 

24-3 
25-5 
10.8 




L/ime sand 


L/oam 






Fine carbonate of linie 











It is evident that the finer soils have not only a greater water 
capacity, but also allow less evaporation to take place. 

Control of Water. The control of water, so that plants may 
at all times receive the optimum amount, or as near it as possible, 
is one of the most important parts of agricultural practice and 
the chief object of many operations of tillage. 

Control of the water supply is exercised by storing water in the 
1 The Soil, I9r. 



THE: SOIL AND WATER 147 

soil, by irrigation, by improving capillary conditions, by preven- 
tion of loss, by decreasing transpiration, by drainage. In regions 
where rainfall is deficient, especially during the crop season, it 
may be necessary to store up the rain as much as possible. Sur- 
face water may be conserved by plowing the soil before the rainy 
season. Due regard should be paid to proper ditching, to prevent 
washing. The subsoil may also be plowed and in arid regions (dry 
land farming) it is packed after plowing so as to restore its capill- 
ary spaces. In some dry regions a crop is grown only every alter- 
nating year. The first year, the soil. is plowed, and the surface is 
kept loose and porous so as to reduce the loss by evaporation; 
the second year the crop is grown. 

The capillary condition of soils which are too loose and porous, 
and also those too heavy and compact, is improved by incorporat- 
ing vegetable matter with the soil. Capillary conditions may also 
be improved by plowing of soil or subsoil when in suitable condi- 
tion. 

Under-drainage, by aerating the soils, allows roots to go deeper, 
and so places at their disposal a larger volume of soil containing 
plant food and water. Since an excess of water keeps the soil 
cold, drainage causes the land to warm up sooner in the spring. 

Losses of water by evaporation may be prevented by tillage. 
Surface cultivation of the soil breaks up the capillary pores, and 
prevents water rising to the surface. The following table of 
King illustrates the effect : 

Water evaporated 

in 221 days. 

Inches 

Compact soil 7.98 

Stirred i inch 5.09 

Stirred 2 inches 4.20 

Stirred 3 inches 3.66 

Stirred 4 inches 3.60 

Compacting the soil by rolling increases evaporation, since it 
increases the efficiency of the capillary pores. Rolling after plant- 
ing grass seed is often advantageous, as it brings moisture to the 
surface to sprout the seed. 

The destruction of weeds prevents loss by evaporation. In 



148 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

orchards it is often advisable to keep the soil cultivated and free 
from weeds or crops in order to prevent injury to the trees from 
want of water. 

Wet and Dry Soils. Dry soils are composed of coarse par- 
ticles, with free percolation and little power of retaining water. 
Wet soils are composed of very fine particles having an enormous 
extent of intersurface and offering great resistance to the passage 
of water. 

The character of the subsoil is also of great influence. A sandy 
surface soil acts differently when it has a subsoil of loam or clay. 
A clay soil is no longer wet when it has an open porous subsoil. 
Whether the soil is level or on a hill side or receives the drainage 
of higher land, influences the water held in the soil. 

The most suitable physical composition of a soil depends on the 
climate and the situation in which it is placed ; soils of great value 
in one situation may be of little value in another. A clay land 
which can be used only for pasture with an available rainfall of 
forty inches, may be used to great advantage where the rainfall is 
only twenty-five. 

Effect of Cultivation and Manure. Shallow surface cultiva- 
tion conserves moisture. Rolling compacts the soil and causes 
water to rise to the surface. Fall plowing allows water to 
penetrate the soil, and if followed by surface cultivation, may 
allow a balance of water to be carried over to the next season. 
Spring plowing, if followed by dry weather, causes loss o"f moisture 
by evaporation ; it should therefore be followed by surface cultiva- 
tion. Manure or straw, spread as a mulch, prevents loss of water 
by evaporation. 



CHAPTER VIII. 



CHEMICAL CONSTITUENTS OF THE SOU. 

The soil is composed of disintegrated rocks, containing organic 
matter. Its constituents are, therefore, inorganic and organic. 

The inorganic constituents consist of the original rock minerals, 
products of their partial decomposition, and their final products 
of decomposition. The organic constituents consist of unchanged 
residues of plants and animals, intermediate substances formed by 
the action of bacteria, molds, and other agencies, and the final 
products of decomposition, namely, carbon dioxide and water. 

Primary and Secondary Minerals. By far the greater portion 
of the crust of the earth, and of the soils thereon, is composed 
of silica, and combinations of silica with bases, termed silicates. 
A large number of silicates are known, many of which are very 
complex in constitution. Igneous rocks, which are the oldest 
rocks, are composed entirely of silica or silicates. Primary sili- 
cates undergo chemical changes, under the action of the air, 
water, and other natural agencies, whereby other silicates and 
other minerals are formed. The unchanged minerals found in 
igneous rocks are for this reason termed primary minerals, and 
those produced from them by chemical agencies are called 
secondary minerals. 

Soils are composed of three classes of minerals : 
(a-) Primary minerals, the unchanged minerals of igneous 
rocks, not easily affected by chemical reagents. . 

(b) Hydrated silicates, which are intermediate products of the 
decomposition of the primary minerals, and more easily acted on 
by chemical reagents and the roots of plants. 

(c) Final products of weathering. 

The relative abundance of these three classes of minerals in the 
soil will depend on the age and nature of the rock material and 
the nature and activity of the weathering agencies. Old soils are 
naturally more highly decomposed than are soils of more recent 
origin. Transported soils consist of a greater variety of minerals 



I5O PRINCIPLES OF AGRICULTURAL CHEMISTRY 

than soils formed from rocks in place, and not mixed with the 
products of the decomposition of other rocks. 

Primary Minerals. Dr. F. W. Clarke, 1 Chemist to the U. S. 
Geological Survey, has calculated the relative abundance of the 
minerals of igneous rocks to be as follows : 

Per cent. 

Feldspars 59 5 

Hornblende and pyroxenes 16.8 

Quartz 1 2.0 

Biotite 3.8 

Titanium minerals 1.5 

Apatite o. 6 

Less frequent minerals 5.8 

Quartz is crystallized silicon dioxide (SiCX) and is widely dis- 
tributed in nature. It is insoluble in water or any acid except 
hydrofluoric. It is very hard and not easily broken. It cannot 
be dissolved or decomposed by natural agencies, although it may 
be reduced to a fine powder. It is often found as pebbles, sand, 
and sometimes a very fine powder,' in residues from rocks which 
have otherwise undergone serious changes. It is of common 
occurrence in soils. It has no value to plants as food. 

Felspars are double silicates of alumina with potash, soda, or 
lime. They are widely distributed, making up about sixty per 
cent, of the average igneous rock. The chief varieties of felspar 
are: 

Orthoclase, a potash felspar KAlSi 3 O 8 

Albite, a soda felspar NaAlSi 3 O 8 

Anorthite, a lime felspar CaAl 2 Si.jO 8 

A number of intermediate varieties occur, such as oligoclase, a 
soda-lime felspar. 

Felspars are not acted upon by strong acids (except hydro- 
fluoric) and can only be brought into solution after fusion with 
carbonate of soda, or by decomposition with hydrofluoric acid. 
They are slowly decomposed by weathering agencies. If finely 
ground felspar is brought in contact with water containing 
phenolphthalein, the liquid assumes a red color. This is due to 
the solution of a small amount of soda and potash, which, being 
1 Bulletin 419, p. 9. 



CHEMICAL CONSTITUENTS OF THE SOU, 151 

alkaline, turn the phenolphthalein red. A number of other 
minerals behave in the same way. The quantity of alkali which 
goes into solution is, however, very small. Only a small fraction 
of felspar is dissolved by the concentrated hydrochloric acid used 
in soil analysis and about i to 4 per cent, of the total potash. The 
potash held in felspar has only :i slight value to plants, as it is dis- 
solved very slowly. 

Micas are primary silicates, which are easily split into thin, 
flexible, and elastic leaves. They have a complex and varying 
composition, being silicates of alumina with potash, lithia, 
magnesia, iron or manganese. Muscovite is light colored potash 
mica, K 2 Al 6 Si 6 O l22 2H 2 O. Biotite, a dark colored mica, is a com- 
plex hydrated silicate of alumina, iron, potash, and magnesia. 

Micas are decomposed very slowly. They persist for a long 
time after the other rock minerals have been entirely changed by 
weathering. Almost any soil derived from granite contains flakes 
of mica, which are more easily seen if oxides of iron are removed 
with a little hydrochloric acid. Micas aid in the decomposition 
of rocks in which they are present, by allowing water to percolate 
into their fissures. Mica is, to a large extent, dissolved by strong 
acids, and it is probable that the plant food it contains is more 
easily used than that of felspar. 

Hornblendes and Pyroxenes include a number of silicates of 
varying composition, though with related properties. They are 
complex silicates of magnesia, alumina, lime, and iron. They are 
usually green, brown, or black in color. They are easily affected 
by natural agencies. Olivine is a silicate of iron and magnesia 
(MgFe) 2 Si 2 O 4 . 

Apatite Ca 3 PO 4 Ca(ClF) 2 is a crystallized phosphate of 
lime. It is considered to be the chief form in which phosphoric 
acid occurs in igneous rocks. 

Secondary Minerals. The minerals formed from the primary 
minerals by processes of combination with water, by solution, 
oxidation, or by partial or complete decomposition, are termed 
secondary minerals. They occur in rocks formed by decomposi- 
tion of the igneous rocks, and in soils. A few of them are 
described in the following paragraphs. 



152 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



Hydrated Silicas are formed by the deposition of silica from 
aqueous solutions. From many silicates water dissolves silica, 
which may be deposited as various forms of hydrated silica. 
Hydrated silicas are probably present in some soils. 

Hydrated Silicates are produced by combination of water with 
primary or secondary silicates, with or without loss of matter by 
solution. The complex hydrated silicates are more easily decom- 
posed, and otherwise enter into reactions much more readily than 
the primary silicates, from which they were formed. They are 
also more easily decomposed by acids. Hydrated silicates appear 
to be of considerable importance in the soil. A great number of 
hydrated silicates are known. 

Zeolites are hydrated silicates of alumina, with varying amounts 
of potash, soda, lime, etc., produced by hydration and decomposi- 
tion of many varieties of minerals. They are easily decomposed 
by acids. A large number of zeolites are known. They take 
part in some important reactions which occur in the soil, especially 
the fixation of potash. 

Chabazite (HK) 2 CaAl 2 Si 5 O 15 +6H 2 O, stilbite (CaNa) 2 Al 2 Si 6 - 
Q 16 +6H 2 O, analcite Na 2 Al 2 Si 4 O 12 +2H 2 O and prehnite H e Ca 2 - 
Al 4 Si 3 O 12 , are hydrated silicates belonging to the zeolite class. 
They are soluble in hydrochloric acid, the silica being separated. 
When brought in contact with salts of potash, they remove some 
of the potash from solution and replace it with equivalent 
quantities of lime or soda. For example, the minerals named 
below 1 were treated with a strong solution of sulphate of potash, 
washed and subjected to analysis : 





Original mineral 


After treatment 




Per cent, potash 

0.25 
0.17 

o.47 
0.90 

I.OO 


Per cent, potash 

3-95 
4.09 

1-54 
4.82 

5.96 


Stilbite anotVier sample 




Cliaba/ite 







1 Texas Station, Bulletin 106, p. u. 



CHEMICAL CONSTITUENTS OF THE SOU, 153 

The reaction may be represented as follows : 

Chabazite + K 2 SO 4 = K Chabazite + CaSO 4 . 

The reaction is reversible. When treated with sulphate of 
lime, or other lime salts, the absorbed potash is partly replaced by 
lime. 

K Chabazite + CaSO 4 K,SO 4 + chabazite. 

The extent of the change depends on the conditions of the 
experiment and will be discussed under the topic of fixation by 
the soil. It is possible that other hydrated silicates besides zeolites 
take part in the fixation of potash. 

Finite is a hydrated silicate of alumina and potash, resulting 
from the decomposition of felspar and some other minerals. 

Kaolinite is a hydrated silicate of alumina having the formula 
Al a Si 2 O 7 2H 2 O. Kaolin is largely composed of kaolinite. Clay 
contains kaolinite. Kaolin may be considered as a final product 
of weathering of felspar and other silicates containing alumina. 
The reaction which occurs in the formation of kaolin by the action 
of water containing carbon dioxide upon felspar, may be written 
as follows : 
K 2 Al 2 Si 6 O 16 + H 2 O + CO 2 == Al_Si 2 O- + K 2 CO 3 + H 2 Si 4 O 9 . 

If lime or soda is present, its carbonate is formed in this decom- 
position. The lime or soda may be converted into sulphate or 
chloride if sulphur or chlorine is present in the rock. 

Chlorites are hydrated silicates of alumina, magnesia, or 
iron. They are products of the decomposition of hornblende, 
augite, and magnesium micas. Further decomposition results in 
serpentine. 

Talc and Serpentine are hydrated silicates of magnesia. They 
are soft, with a greasy feeling. Serpentine results from the decay 
of olivine, and, though less often, from augite or hornblende. 

Glauconite is a hydrated silicate of alumina and iron, contain- 
ing a small quantity of lime, magnesia, potash, soda, and phos- 
phoric acid. It often occurs as grains of a green color, and is 
termed green sand. Green sand marl is a mixture of glauconite 
and calcium carbonate. 

Carbonates of Lime and Magnesia result from the action of 
1 1 



154 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

carbon dioxide and water upon many silicates containing lime 
and magnesia. Both compounds are slightly soluble in water, 
and more soluble in water containing carbon dioxide. All waters 
which have been in contact with the earth contain lime and 
magnesia. Large limestone deposits have been formed by shell 
fish and other organisms, which withdraw carbonate of lime from 
solution. Many of our most fertile soils are derived from lime- 
stone deposits, or contain two per cent, or more of carbonate of 
lime. Carbonate of lime is an important soil constituent. Its 
presence flocculates clay and makes clay soils less sticky and more 
easily worked. In calcareous soils, the phosphoric acid and 
potash is generally held in more available forms. Carbonate of 
lime unites more or less slowly with soluble phosphates which 
may be present or introduced into the soil, forming compounds 
which, while less soluble than before and of less value to plants, 
are more soluble and apparently of greater value to plants than 
the soil compounds of phosphoric acid with iron or aluminium. 
Other actions of lime will be referred to later. 

Sulphate of lime is found in small quantities in many soils, in 
large quantities in a few soils. 

Iron Minerals. By the decomposition of silicates containing 
iron, various compounds of iron are produced, mostly oxides and 
carbonates. These bodies ordinarily occur in the soil, often 
giving the soil a red, brown, or yellow color, depending on the 
stage of oxidation. Hematite is anhydrous ferric oxide Fe^CX, 
red when finely powdered. Magnetite Fe ; ,O 4 is black oxide of 
iron. Limonite is hydrated ferric oxide 2Fe 2 O,3H 2 O, and has a 
yellow or brown color. Siderite is carbonate of iron, and is gray 
or brown in color. It is affected with difficulty by cold acids, 
easily by hot acids. The bulk of the phosphoric acid of ordinary 
soils is probably in combination as basic phosphates of iron or 
aluminium, or in basic silicates of these elements. Such forms of 
combination are apparently not as valuable to the plant as the 
calcium phosphates. Limonite is deposited from water contain- 
ing iron. Oxides of iron are reduced by decaying vegetable 
matter and combine with carbonic acid to form ferrous car- 



CHEMICAL CONSTITUENTS OF THE SOIL 155 

bonate, which dissolves in water. On exposure to the air, the 
ferrous carbonate is oxidized and is precipitated as insoluble 
hydrated ferric oxide. This action does not take place in soils 
containing carbonate of lime. A layer of hard pan, consisting of 
rock grains cemented by limonite, is often formed below poorly 
drained soils. 

Pyrite FeS 2 has a light yellow color and is often called fool's 
gold. It is easily oxidized to sulphates by atmospheric agencies. 
It is sometimes formed in badly aerated soils. 

Phosphate Minerals. Phosphates do not, as a rule, occur in 
large quantities in the soil, but are important on account of their 
indispensability to plant life. The important phosphate minerals 
are: Apatite, or crystallized calcium phosphate Ca 3 (PO 4 ) 2 ; phos- 
phate rock, or amorphous calcium phosphate ; vivianite, which is 
hydrated phosphate of iron; wavellite, or hydrated phosphate of 
alumina. The three phosphates named last probably occur in 
soils. A large number of mineral phosphates are known. Dr. 
F. W. Clarke, of the U. S. Geological Survey, assumes that all 
the phosphoric acid of igneous rocks is present as apatite. As 
stated above, phosphates are also found in the soil as basic com- 
pounds of iron and aluminium. Organic phosphorus compounds 
are also present in the soil. 

Soluble Salts. Sulphate of soda, or glauber's salt, sulphate of 
magnesia, chloride of soda, carbonate of soda and nitrate of soda 
may be found as constituents of soils in arid sections, and, if 
present in excessive quantity, are detrimental to vegetation and 
give rise to alkali soils. 

Investigations of the Mineral Constituents of Soils. Studies of 
the mineral constituents of the soil 1 are made by means of micro- 
scopic examination with the aid of polarized light, stains, and other 
tests. Comparatively few mineralogical studies of the soil have 
been made. They are sufficient, however, to show that there are 
considerable differences in the mineral content of soils, particu- 
larly of those widely different origin. 

Chemical examination also throws some light upon the mineral 
1 Bull. 91, Bureau of Soils. 



156 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

composition of the soil. The quantity and character of the sub- 
stances brought into solution by means of various solvents, may 
be compared with the effect of the same solvents under the same 
conditions upon minerals in the proportions in which they may 
occur in soils. For example, 1 known phosphates of lime are com- 
pletely dissolved by fifth normal nitric acid under certain condi- 
tions ; some phosphates of iron and aluminium are also completely 
dissolved, while basic phosphates of iron and aluminium are dis- 
solved by the solvent only to a slight extent. Hence treatment of 
the soil with this solvent gives an idea as to the condition of the 
inorganic soil phosphates. This matter will be discussed later. 
Hilgard 2 determined the alumina dissolved and the silica which 
was liberated by strong acids, and by comparing the relative 
quantities, came to the conclusion that the quantity of silica was 
not sufficient to combine with the alumina to form known silicates, 
and that a portion of the alumina in certain soils is present as 
hydrated alumina, probably Gibbsite A1(OH) 3 . 

Organic Matter. The organic matter and nitrogen of the soil 
are closely related, for nitrogen is chiefly in organic combination. 
The organic matter of the soil consists of the residues of plants 
and animals, animal excremenls, and the products of their decay. 
All the compounds which are found in plants or animals, enter the 
soil, through the presence of some of them is very transitory. 3 
Sugars, urea, and similar substances, are rapidly changed into 
other bodies. Cellulose and lignin, which make up the woody 
matter of plants, decay much more slowly, and may remain in the 
soil for some time. Lactic, acetic, and butyric acids are pro- 
duced in the fermentation of sugars and starches. Vegetable 
acids, such as oxalic, citric, tartaric, and malic acid are introduced 
into the soil in plant residues, but are quickly destroyed by 
bacteria. Proteids and fats persist for a longer or shorter time, 
according to their nature. It is thus possible for all the organic 
compounds found in plant or animal residues to be present, in 

1 Texas Station Bulletin 126. 

2 The Soil, p. 389. 

8 Wollny, Die Zersetzung d Org. Stoffe. 



CHEMICAL CONSTITUENTS OF THK SOII, 157 

greater or less quantity, in the soil, and the student of soil 
chemistry must bear this possibility in mind. 

Organic Compounds Isolated. Chemical study of the organic 
matter of the soil has rendered probable the existance of a number 
of organic bodies in the soil. The organic compounds claimed to 
be isolated, so far, make up only a comparatively small percentage 
of the total organic matter. 

Schreiner and Shorey 1 claim to have isolated sixteen com- 
pounds. 

Hydrocarbons. Hentriacontane C 3 H 64 from a North Carolina 
soil. 

Acids. Dihydroxystearic acid C 1S H 36 O 4 and picoline carboxylic 
acid C 3 H 7 O, 2 H from several soils. Paraffinic acid C 24 H 48 O,, and 
monohydroxystearic acid C 18 H 36 O 3 , lignoceric acid C, 4 H 48 O.>, 
agroceric acid C 21 H 42 O 2 and resin acids from individual soils. 

Glycerides. Glycerides of fatty acids identified in one soil and 
probably present in several soils. 

Wax Alcohols. Phytosterol C 26 H 44 O.H 2 O and agrosterol 
C C H 44 O.H 2 O from individual soils. 

Nitrogenous Compounds. These are chiefly bases, and form 
salts with acids. Arginin, cytosine, xanthine, and hypoxanthine, 
were claimed to be isolated from several soils. 

Pentosans. The presence of pentosans in the soil was demon- 
strated by de Chalmot 2 and others and confirmed by Schreiner 
and Shorey. In ten soil samples, pentosan carbon made up 1.30 
to 28.5 per cent, of the total carbon. 

Ether Extract? The soil gives up about 0.02 per cent, material 
to ether, and about the same quantity to chloroform following the 
ether. The ether extract consists of fatty acids and wax alcohols, 
such as are found in plants. 

Significance of the Organic Compounds. As stated above, the 
organic compounds mentioned make up only a very small fraction 
of the total organic matter of the soil. The bulk of the organic mat- 

1 Bulletins 53 and 74, Bureau of Soils. 

2 Am. Cliem. Jour., 1894, p. 229. 
* Texas Bulletin, 157. 



158 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

ter is made up of so-called humus, which will be discussed later. 
There is still much room for investigation in distinguishing var- 
ious chemical compounds in the soil. Some of the organic com- 
pounds mentioned above have been found in only one or two soils, 
while others are perhaps of general occurrence. Most of them 
appear to be indifferent toward plants, and their significance to- 
wards plant growth or soil chemistry is not known. The import- 
ance of these substances is at present chiefly due to their relation 
to the toxic theory of soil fertility. 

The Toxic Theory. According to the toxic theory of the 
Bureau of Soils, "the production of toxic excretions by the 
roots of plants is undoubtedly a factor in soil fertility." 1 "So- 
called exhausted soils are poisoned soils." 2 "Practically all soils 
contain sufficient plant food for good crop yields and this sup- 
ply will be indefinitely maintained." 3 "The small yields of unpro- 
ductive soils can be greatly improved by treatments which destroy 
toxic substances in these soils." 4 "The soil is the one indestruct- 
ible immutable asset that the nation possesses. It is the one re- 
source that cannot be exhausted, that cannot be used up." 5 

The evidence offered in support of this theory is based 
chiefly upon experiments in water cultures and wire-basket tests 
of about three weeks duration. The aqueous extract from an 
unproductive soil grew larger wheat plants when ferric hydrate, 
calcium carbonate, or carbon black were added to it. 6 Pure water 
is better suited for growing wheat plants than is the soil extract 
of poor soils. 7 The extracts of the poor soils are benefited by 
nitrate of soda, carbon black, pyrogallic acid and tannic acid, 
and the same chemicals have similar effects when added to the 
soil. 8 Dihydroxystearic acid and picoline carboxylic acid isolated 

1 Bulletin 40, p. 40. 
'* Bulletin 28, p. 28. 

3 Bulletin 22, p. 63 4. 

4 Bulletin 47, p. 51. 

5 Bulletin 55, p. 66. 

6 Bulletin 28. 
' Bulletin 36. 
8 Bulletin 36. 



CHEMICAL CONSTITUENTS OF THE) SOIL 159 

from soils kill wheat seedlings at dilutions of 100 parts per 
million, and are injurious in lower amounts. 1 Fertilizers decrease 
the injurious effects of certain organic substances. 2 

Dauheney/' at Oxford, England, tested the old toxic theory of 
De Condalle by a rotation experiment, in which 18 different crops 
were grown continuously on the same plots in comparison with 
the same crops grown in various rotations ; the yields were not 
sufficient to justify the assumption of the existence of a toxin. 
Russell 4 grew six crops of rye in succession on sand containing 




1 ! t 



J 3 




Fig. 37. Wheat seedlings ten days old grown in water containing di- 

hydroxystearic acid (i) 200 parts per million ; (2) 100 parts; (3) 50 

parts ; (4) 20 parts ; (5) o parts. Bureau of Soils. 

nutrient salts. A seventh crop grown on this sand, and another 
crop on fresh sand, were practically equal in size. Other experi- 
ments with rye on soil, and with buckwheat and spinach on sand 
and on soil, give practically the same results. Hence there is no 
evidence that the previous crops left toxic residues. 

1 Bulletin 47. 

2 Bulletin 70. 

3 Phil, Trans., 1845, p. 179. 

4 Soil Conditions and Plant Growth, p. in. 



i6o 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



Russell 1 states that single salts of potassium, magnesium, 
sodium, etc., are toxic to plants, in water culture, while a mixture 
of salts is not. Breazeale and Le Clerc 2 show that wheat seed- 
lings grown in culture solutions containing 10 parts per million of 
potassium chloride or potassium sulphate, cause the solution to 
become acid. The acidity affects injuriously the development 



go on 



Fig. 38. Wheat seedlings (second crop) grown in, (i) distilled water, (2) 

distilled water and calcium carbonate, (4) potassium sulphate 

and calcium carbonate, compared with (3) those grown 

in potassium sulphate solution. 



of succeeding plants grown in the solution, and a similar effect is 
shown by solutions of sulphuric acid or hydrochloric acid. 
Sodium hydroxide, lime, ferric hydrate or carbon black, remove 
the acidity and render the solution less injurious. 

1 Soil Conditions and Plant Growth, p. 43. 

2 Bulletin No. 149, Bureau of Chemistry. 



CHEMICAL CONSTITUENTS OF THE SOIL l6l 

There is thus not sufficient experimental evidence to support 
the theory that low yields are ordinarily due to toxic substances in 
the soil, rather than to deficiency of plant food. The injurious 
effects observed in the water culture experiments may be due to 
acidity. It is, of course, possible that some soils may contain 
organic toxic substances other than acids, but this fact has not 
been established. 

Assimilation of Organic Compounds by Plants. Experiments 
have been made to ascertain whether organic compounds may be 
assimilated by plants. The organic compounds most important 
are those which may enter in the soil in animal excrements 
or plant or animal residues, or may be formed in the decay of 
these. Uric acid and urea are found in urine, hippuric acid 
occurs in the urine of cows, sheep, etc., leucin, tyrosin and 
asparagin, are found in plants or formed in their decay. Other 
organic bodies formed in the decay of plants or animals, are prob- 
ably of little importance. 

The question as to the assimilation of these substances as such 
is complicated by the fact that they are for the most part 'easily 
transformed into ammonium salts, which may be assimilated. 

Baeyer found oats to grow well in a solution of urea, and the 
plants contained considerable amounts of urea. But ammonia 
had formed in the solution. Hampe 1 grew corn with urea and 
found the leaves to contain 0.25 to 0.8 1 per cent. urea. The 
solution was changed every day to avoid error by decomposition, 
and, though the corn possibly assimilated some ammonia, the 
evidence is that it utilized urea also. A. Thomson 2 compared 
sodium urate, sodium hippurate, urea, and sodium nitrate, on oats 
and barley in water cultures, and found that uric acid and urea 
have the same value as nitric acid, but hippuric acid has not. This 
investigator did not correct for decomposition of the compounds. 
Other experiments 3 could be quoted tending to prove that leucin, 

1 Landw. Versuchs-stat. , 1867, p. 79. 

2 Exp. Station Record 13, p. 919. 

3 Hutchinson and Miller, Jour. Agr. Sci., 1912, p. 283, references being 
given. 



l62 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

tyrosin, asparagin, and hippuric acid can serve directly as sources 
of nitrogen for cultivated plants. Hippuric acid is decomposed 
into glycocoll and benzoic acid, the glycocoll taken up and the 
benzoric acid left behind. It is also claimed that humic acid 1 
can be absorbed. 

Humus. The term humus is applied by some chemists (prin- 
cipally in European countries) to the entire quantity of organic 
matter in the soil, in whatever form it may be present. In 
America, it usually refers to the organic matter dissolved by am- 
monia after the lime has been removed by acids. This ammonia- 
soluble organic matter is supposed to be more valuable than that 
not soluble in ammonia, though satisfactory evidence that such is 
the case has not been presented. 

Ammonia-Soluble Organic Matter. In the preparation of the 
ammonia-soluble organic matter, the lime is first extracted with 
acid and the soil washed free from acid. The soil is then treated 
with ammonia, but a quantity of clay is also suspended in the 
liquid. The clay is precipitated by addition of ammonium sul- 
phate, ammonium carbonate, or other salts, and the ammonia 
neutralized. The precipitate is collected and washed thoroughly. 
The precipitated substance is a black, amorphous body, slightly 
soluble in water. It has acid properties. It decomposes calcium 
carbonate, liberating carbon dioxide. A portion of it is soluble 
in alcohol. 2 It is soluble in ammonia, and when the excess of 
ammonia is evaporated, retains 4 to 6 per cent, nitrogen in the 
form of an ammonium salt. It is precipitated by salts of lime, 
barium, copper, zinc, lead, etc., forming salts of these metals. Its 
combining weight varies from 228 to 327. The magnesium salt 
is soluble in water, and also the sodium, potassium and ammonium 
salts. When dissolved in ammonia, a portion of the humate 
diffuses through parchment paper. 

Analysis of the substance prepared from several soils by 

1 Brial, Exp. Sta. Record 6, p. 484. 

2 Fraps and Hamner, Texas Bulletin 129. 



CHEMICAL CONSTITUENTS OF THE SOIL 163 

precipitation with acid from ammonia solution, gives the follow- 
ing results : l 

Per cent. 

Carbon 44.09-63.58 

(usually about 55 per cent. ) 

Hydrogen 3- 2 7~ 5-45 

Nitrogen 3-36- 6.22 

Ash 1.57-15.74 

The substance is probably a mixture and not a single definite 
compound. 

According to Hilgard and Jaffa, 2 the humus of humid soils 
(extracted with caustic potash) contains about 5 to 5.5 per cent, 
of nitrogen, while that of arid soils may contain as much as 18.5 
per cent, nitrogen. Hilgard believes that the nitrogen content of 
humus should not fall below 4 per cent., if the soil is to be pro- 
ductive. 

Attempts have been made to separate definite chemical com- 
pounds from humus, the success of which is doubtful. Detmer 3 
extracted humus from the soil with ammonia, and after repeated 
purifications obtained a compound said to be of the formula, 
C 20 H ]8 O 9 . It was a black acid substance which reddens litmus, 
expels carbonic acid from carbonates, and forms salts with lime, 
silver, iron, ammonia, potassium, etc. These salts are all in- 
soluble with the exception of salts of the alkalies. Other acids 
in addition to this one are claimed to have been separated from 
the soil. There is doubt, however, whether the bodies in question 
are really definite chemical compounds or more or less impure 
mixtures. 

There is no evidence that the ammonia-soluble humus of the 
soil consists entirely of acids, or that it is formed by decomposi- 
tion in the soil. Various bodies known to be non-acid are found in 

1 Fraps and Hamner, Texas Station Bulletin 129. 

'* Rep. Cal. Exp. Sta., 189, p. 2-4. 

3 Jahresber, f. Agr. Chem., 1870-2, p. 68. 



164 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

plants, such as proteids and lignin, and are soluble in ammonia. 1 
No doubt they also occur in the soil. In attempts to determine 
the formation of humus in the soil, these ammonia-soluble 
materials introduced with the ingredients have been neglected. 
In experiments 2 in which the ammonia-soluble organic matter 
originally in the soil and that added to it, were estimated before 
and after decomposition for several months, there was a loss, 
and not a gain, of ammonia-soluble material. The following is 
an example : 

Percentage of humus in original soil 1.36 

Dry soil with meat 2. 29 

Soil with meat moist for 14 weeks 1.68 

Estimation of Ammonia-Soluble Humus. In the estimation of 
ammonia-soluble humus, 3 the soil is first extracted with I per 
cent, hydrochloric acid, to remove lime and decompose the com- 
pounds of humic acid. It is then washed free from acid, and 
treated with 4 per cent, ammonia for some time. After remain- 
ing in contact for several days, the solution is allowed to settle, 
and an aliquot part evaporated to dryness, dried and weighed, 
ignited and weighed again. The loss in weight is ammonia- 
soluble humus. 

This method is highly inaccurate on account of the presence of 
clay. Clay will remain in suspension in ammonia-water for 
months, and, as it contains chemically combined water, will lose 
weight on ignition, after drying. It is also present in the humic acid 
precipitated with the solution, unless previously removed. The 
clay may be easily removed by precipitation with ammonium car- 
bonate. 4 The ammonium carbonate is volatilized along with the 
ammonia when the solution is subsequently evaporated to dryness. 

Humus of Peat and Swamps. As we have already stated, acid 
bodies are formed in peat and muck soils, which must be 
neutralized by lime before the soil can be cultivated profitably. It 

1 Hoffmeister, Landw. Versuchs-stat., 1898, p. 347. 

2 Fraps and Hamner, Texas Bulletin 129. 

3 Methods of the Association of Official Agricultural Chemists. 

4 Rather, Bulletin 139, Texas Station. 



CHEMICAL CONSTITUENTS OF THE SOIL 165 

is also possible that the lime, by combining with the peat resin, 
causes the peat and muck to oxidize more rapidly. 

Certain investigators claim to have separated ulmic acid, crenic 
acid, and other acids from peat. 

Importance of Humus. The functions of the organic matter 
in the soil may be summed up briefly as follows : 

1. It contains the store of nitrogen of the soil. 

2. It furnishes nutriment for bacteria and other forms of life, 
which aid in changing plant food so that the plant can take it up. 

3. It produces carbon dioxide and other acids in its decay, 
which increase the solvent action of the soil water on plant food. 

4. It increases the retentiveness of sandy soils for water, and 
binds the fine particles of clay into compound particles, so that 
the clay has better tilth. 

5. Like lime, an abundance of humus renders a soil productive 
even though only small quantities of plant food are present. 

Classification of Soils with Respect to Humus. Knop 1 makes 
the following divisions, using the term humus to mean the entire 
quantity of organic matter present : 

Per cent. 

Poor in humus o.o to 2.5 

Fair 2.5 to 5.0 

Good 5.0 to 10.0 

Rich 10.0 to 15.0 

Excess 15.0 and over 

The humus in the soil decreases from the surface. The follow- 
ing analyses by Kosticheff of the black soil of Russia illustrates 
this: 

Depth Percentage 

inches of humus 

i to 6 5.4 

6 to 12 4.8 

12 to 18 3.6 

18 to 24 2.6 

24 to 3c 2.6 

301036 1.9 

3 6 to42 1.3 

1 Quoted by Wollny, Zersetzung d Orgnanischen Stoffe, p. 192. 



1 66 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

Ammonia-Soluble Phosphoric Acid. The ammonia-soluble phos- 
phoric acid of the soil is assumed by some chemists to be in com- 
bination with the organic matter which accompanies it, and to be 
of considerable value. It comes in part, however, from inorganic 
phosphates which occur in the soil and are decomposed by am- 
monia, allowing a portion of their phosphoric acid to go into solu- 
tion. 1 The humic acids precipitated with acids contain a small 
portion of the ammonia-soluble phosphoric acid, and this is prob- 
ably in organic combination. The quantity of phosphoric acid held 
in this way is small, even in soils richly supplied with humus. It 
cannot be taken up until released by oxidation of the humus, and 
can only be regarded as a reserve store of phosphoric acid, not 
nearly so important as the nitrogen held in the humus in much 
larger proportion. 

1 Fraps, Am. Chem. Jour., 1898, p. 574; Bulletin 135, Texas Exp. Sta. 



CHAPTER IX. 



CHEMICAL COMPOSITION OF THE SOU. 

Chemical analysis shows that the greater bulk of the soil 
is composed of compounds of silica, oxides of iron, and oxides 
of alumina, in various compounds. These substances have no 
value as plant food, except iron, and only very small amounts of 
it is essential. They serve a useful purpose, however, in holding 
moisture, modifying the supply of plant food, supporting the 
plant, and, giving it a medium in which to develop its roots. 

The important plant foods nitrogen, phosphoric acid, and 
potash make up only a small percentage of the soil. The 
quantity of plant food may be large in pounds per acre, sufficient 
for several hundred crops, if it were all available for use of the 
plant. But the proportion of plant food to the total quantity of 
soil is small. Further, the amount which can be taken up by 
plants may be only a small proportion of the total amount pres- 
ent ; so that although several hundred pounds of phosphoric acid, 
for instance, may be present in the soil, the addition of a few 
pounds of highly available phosphoric acid may produce a large 
increase in the crop. 

Methods of Examination. Four chief methods of examining 
soils have been used. In addition, special methods are used for 
special analyses. 

(1) Complete decomposition of the silicates. This method 
gives the total quantity of the constituents of the soil. 

(2) Partial decomposition with strong acid. This method 
attempts to determine the quantity of plant food which may be- 
come available to the plant in a series of years. It distinguishes 
between the most resistant silicates, and those decomposed by 
acids. 

(3) Weak Solvents. This method attempts to determine the 
immediate needs of the soil for plant food. 

(4) Water-Soluble Constituents. This method considers the 
material extracted from the soil by water. 



i68 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



Complete Decomposition. The complete analysis of the soil 
ib made in two ways: 

First Method. The soil is fused with a mixture of sodium 
carbonate and potassium carbonate. The silica unites with the 
soda or potash, forming silicates ; oxides or carbonates are 
formed from the bases. On treatment with water and acids, the 
carbonates and oxides dissolve. The silica can easily be separated 
and the bases determined in the solution. If potash or soda is 
to be estimated, they must be brought into solution by some other 
method, such as that named below, or by fusing the silicate with 
lime. 

Second Method. The soil is treated with hydrofluoric acid, 
until the silicate is completely dcomposed and the silica driven 
off as gaseous silicon fluoride SiF 4 . The residue is then dis- 
solved in acids, and subjected to analysis. The estimation of the 
silica, if desired, is accomplished by the first method. 

Complete decomposition of a soil shows the constituents which 
are locked up in the most refractory silicates, as well as those 
which are easily affected by plants. So far as the writer has been 
able to find, there have been no investigations made as to the 
relation of the complete analysis of the soil to its wearing 
qualities, or needs for plant food. The utmost information such 
analysis provides at present, is the amount of plant food which 
may some day become available. 

The complete analysis of some groups of soils is shown in the 
following table, compiled from Bulletin No. 54 of the Bureau of 
Soils : 

COMPLETE COMPOSITION OF SOME SOIL GROUPS, PER CENT. 





No. 
averaged 


P 2 5 


CaO 


MgO 


KoO 








o 16 






"D pel filial 




o 18 


o 67 


o -6 


*// 

2 08 


Glacial 


jO 


O 22 


i ^ 


o 80 








O 27 




o 86 


2.Uy 
2 go 















Relation to Sizes of Particles. Chemical analysis of the differ- 
ent grades of particles have not always given the same result, but 



CHEMICAL COMPOSITION OF THE SOIL 



169 



as a rule, the percentages of alumina, potash, and lime increases 
as the size of the particles decrease. For example, Failyer 1 
determined phosphoric acid, lime, magnesia, and potash in 
separate grades of particles from a number of soils of the United 
States by the method of complete decomposition. In the follow- 
ing table is given the average percentage of three ingredients of 
the sand, silt, and clay of four groups of soils : 





Phosphoric acid 




Ivime 
Silt 


Clay 


Potash 


Sand 


Silt 


Clay 


Sand 


Sand 


Silt 


Clay 


7 Coastal plains so^s 


0.03 
0.07 

0.15 
0.04 


O.IO 
O.2I 
0.23 
O.O7 


0-34 
0.67 
o'.86 
o. 16 


0.07 
0.50 
1.24 
1. 80 


0.19 
0.82 
1.30 

1.88 


0-55 
0.94 
2.68 
2.8 5 


32 

1.72 

0.18 


1-33 
2-37 
2-35 
i. 02 


1.76 
2.86 
3-o8 
0.84 




jo Glacial soils 


5 Limestone and shale soils. . 



It is seen that the finer particles of the soil are, on an average, 
richer in phosphoric acid, lime, and potash than are the coarser 
particles. The percentage of each of the constituents named 
increases with the fineness of the particles, the only exception in 
the table being the potash in the clay of the limestone and shale 
soils. The relative abundance of the various grades of particles 
would determine the quantity which each contributes to the 1 soil. 
The coastal plains soils have been so weathered and leached, that 
they are lower in phosphoric acid, lime, and potash than the less 
extensively weathered residual soils, and these in turn are lower 
than the glacial soils, which consist largely of crushed rocks, many 
of which have not been weathered to a great extent. 

Analysis by Extraction with Strong Acids. This is the method 
usually employed in the analysis of the soil. It consists in treat- 
ing the soil with strong acid and estimating the constituents which 
go into solution. The extent of the solvent action depends upon 
the nature of the soil, the kind of acid, strength of acid, tempera- 
ture, time of contact, and ratio of soil and acid. The methods 
used by different chemists vary. In the methods of the Asso- 
ciation of Official Agricultural Chemists of North America 
1 Bulletin 54, Bureau of Soils. 
12 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



10 grams soil are digested with 100 cc. hydrochloric acid 
of 1.115 specific gravity for 8 hours at the boiling tem- 
perature. Dr. E. W. Hilgard digests the soil on the 
steam bath for five days, a method which appears to give 
nearly the same results as the official method, with the exception 
of potash, and oxides of iron and alumina. In the one comparison 
made by Dr. Loughridge, 1 0.35 per cent, potash was dissolved by 
the one method, and 0.63 per cent, by the other, or nearly twice 
as much. This difference must be considered in comparing the 
analyses made by Hilgard's method with the analyses made by the 
methods of the Association of Official Agricultural Chemists. 

The proportion of the constituents of the soil which are dis- 
solved by strong hydrochloric acid varies considerably with differ- 
ent soils. For example, Veitch 2 determined in 16 Maryland soils 
the total quantity of each constituent and the quantity dissolved 
by strong acid by the A. O. A. C. method. The results are pre- 
sented in the following table, expressed in percentage of the total 
quantity of each ingredient present : 

PERCENTAGE OF TOTAL PHOSPHORIC ACID, ETC., DISSOLVED BY 
STRONG ACIDS. 






Average 


Minimum 


Maximum 




6l 
I? 
35 
56 
54 
82 


32 
5 
10 
10 
24 
57 


100 
33 
77 

100 
IOO 
IOO 


Potash 













The average order in which the constituents of these soils were 
dissolved was as follows, beginning with the most soluble: oxide 
of iron, phosphoric acid, magnesia, alumina, lime, and potash. On 
an average, only 17 per cent, of the total potash of the soil was 
dissolved by the A. O. A. C. method. None of the soils in ques- 
tion were highly calcareous, otherwise a much greater proportion 
of lime and magnesia would have been dissolved. 

1 Hilgard, The Soil, p. 341. 

2 Maryland Bulletin No. 70. 



CHEMICAL COMPOSITION OF THE) SOIL 



Relation of Composition to Fertility. The relation of the com- 
position to the fertility of the soil is studied by comparing the 
chemical analysis with the productiveness of known soils. 

Soils containing comparatively high quantities of plant food 
are generally very productive and durable, under favorable 
physical conditions. The following table shows the composition 
of some very productive soils. 1 These soils are all well known 
for their fertility and wearing qualities. 

PERCENTAGE COMPOSITION OF FERTILE SOILS. 





California 
Arroyo Grande 
Valley 


Mississippi 
Yazoo Bottom 


Texas 
Rio Grande 
Bottom 


Russia 
Tchernozen 


Phosphoric acid 


O7I 


















Potash . 










L/itne 






3 1 


0.72 


Magnesia 


2 ofi 


167 


1 4-43 


I -5 I 


Carbon dioxide 


I 82 


l.O/ 


53 


-73 


Sulphur Trioxide .... 






9 1 




Alumina 










Oxide of iron 




JU -04 

c Q 2 


.11 


.22 


Insoluble and soluble 
Silica 


*O 

72 A1 


o-^ 

71 77 


4- u y 


.12 




6 61 


/*// 

717 




22 78 






01 




^./O 













The Arroyo Grande Valley soil is considered one of the richest 
soils in the world. The other soils mentioned in the table are all 
productive and durable. The analyses were made by Hilgard's 
method. Soils containing about I per cent, lime, 0.15 per cent, 
phosphoric acid, and I per cent, potash, by Hilgard's method, may 
be regarded as highly fertile. The same standards apply to the 
Association method, excepting it is possible that 0.50 per cent, 
potash is sufficient for a fertile soil. This, however, remains to be 
demonstrated. 

When soils contain only small quantities of plant food, they 
will usually be found deficient in plant food for crops, or become 
so in a comparatively short time after being placed in cultivation. 
It appears probable that the plant food which can be taken up by 

1 Hilgard, The Soil, p. 343. 



172 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



plants is, to a large extent, proportional to the total quantity 
present, though this depends on the changes going on in the soil. 

A comparatively small amount of plant food in the soil is 
sufficient to make it productive, if present in an available form. 
If we assume the weight of one acre of soil to the depth of one 
foot to be $y 2 million pounds, then o.oi per cent, corresponds to 
350 pounds per acre foot. A crop of 40 bushels of corn, including 
ears, stalk and leaves, requires about 25 pounds phosphoric acid, 
which would be about 0.0007 per cent., or 7 parts per million. Con- 
sequently as much as o.oi per cent, phosphoric acid could supply 
14 crops of corn of this size, if the plant could get it. But soils 
containing only this quantity of phosphoric acid usually respond 
to applications of phosphoric acid greatly. 

The analysis by strong acids does not differentiate between com- 
pounds which may have different values to crops. Hence two 
soils may have the same composition but react differently to 
fertilizers. The chemical composition as determined in this way, 
is more closely related to the wearing qualities of the soil than to 
the immediate needs of the soil for plant food. 

Number of Crops the Plant Food Will Supply. This depends 
on the size and kind of crop, as well as on the composition of the 
soil, Assuming the entire removal of a crop of 40 bushels corn 
per acre, the following is the number of crops which could be 
supplied by the acid-soluble phosphoric acid and potash, and the 
total nitrogen in some Texas soil types, 1 if they were in such 
forms that they could be used by the crops without any loss. 



Corn 


Number of crops the plant food will supply 


Phosphoric 
acid 


Nitrogen 


Potash 




28 
70 
28 
42 
8 4 
154 


29 

35 
29 

4i 
82 
56 


IOO 
308 
91 
I8 3 
290 

325 















Bulletin 126, Texas Station ; see also No. 99. 



CHEMICAL COMPOSITION OF THE SOIL 173 

Interpretation of Partial Soil Analyses. The chemical analysis 
of a soil must be considered in connection with a knowledge of its 
location, depth, drainage conditions, permeability to water and 
air, and, if possible, the amount of crops it produces. Without 
consideration of the other factors which influence the fertility of 
a soil, the chemical analysis may not lead to satisfactory con- 
clusions. We must also remember that the same general type of 
soil varies somewhat in composition, physical properties, and pro- 
ductiveness within a given area, and also that different methods 
of farming may cause considerable differences in soils originally 
the same. 

The interpretation of a chemical analysis unaccompanied by 
knowledge of the other soil conditions which affect its fertility, 
may be unsatisfactory in a large proportion of cases. A careful 
interpretation of results with the aid of the knowledge referred to 
may sometimes be disappointing, but it is more often correct. 
Analyses of miscellaneous samples of soils is also of less value 
than systematic studies of definite areas. Analyses of virgin 
soils, or soils which have not been long under cultivation, or not 
treated with fertilizers, are more likely to yield a satisfactory 
interpretation than analyses of soils whose properties have been 
modified by long continued cultivation, or by applications of 
fertilizers. It cannot be expected that chemical analysis of soils 
will always give a satisfactory interpretation ; there will be 
exceptions which may be difficult to understand until the scope of 
our information has been widened. 

Chemical analysis of a soil with strong acids, together with 
other information concerning the soil, should aid us in applying 
the results secured by field experiments in one locality on a given 
type of soil, to other localities and to other types of soil. It is 
well known that the results of field experiments with fertilizers 
are applicable only to the same types of soils under similar con- 
ditions and with similar chemical composition, and may, or may 
not, be applicable to other types of soils. Chemical analysis, and 
the other information referred to, should aid us in applying 
knowledge secured by field experiments and by experience, to the 



174 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

same type of soils located in different sections, and even to differ- 
ent types of soil from those under experiment. 

The analysis of a soil with strong hydrochloric acid does not 
show exactly what fertilizer to apply to it, but it does give indica- 
tions (a) as to the wearing qualities of the soil, (b) what elements 
are likely to become deficient first under a given system of 
cropping, (c) what deficiencies already exist in the soil, or will 
soon be brought out. 

Virgin soils containing high percentages of plant food are 
highly productive unless improper physical conditions interfere 
with the welfare of the plant. Low percentages of plant food do 
not necessarily indicate low production when first put in cultiva- 
tion. To use Hilgard's illustration, suppose a heavy alluvial soil 
of high plant food content is diluted with its own weight of sand. 
By improving the physical condition of the soil an increased crop 
will very likely result, though the percentage of plant food has 
been reduced by half. The root system of the plant in the diluted 
soil will probably be better developed and in more intimate contact 
with the soil particles, than in the undiluted soil. We may con- 
tinue the dilution, using say 4 parts of sand to one of soil, 6 parts 
of sand to one of soil, and so on. At some point, the size of the 
crop will begin to decrease on account of the difficulty of secur- 
ing plant food. How far the dilution may be carried depends 
upon the plant and on the soil, and is a subject worthy further 
study. 

Standards for Interpretation. Varying methods of analysis 
for soils, and varying standards of interpretation are used accord- 
ing to the method of analysis and the individual opinions of the 
analysts as to what constitutes a good soil. The standards of 
Hilgard 1 are based upon a large number of analyses and wide 
observation, and appear well adapted to American conditions. 
These standards give best results when applied to virgin soils. 

Phosphoric Acid. Hilgard states that phosphoric acid is 
seriously deficient in virgin soils when below 0.05 per cent., unless 
accompanied by a large amount of lime. In heavier virgin soils, 
1 Tenth Census of the U. S. 



CHEMICAL COMPOSITION OF THE SOU, 



175 



o.i per cent, phosphoric acid, when accompanied by a fair amount 
of lime, secures fair productiveness from eight to fifteen years; 
with a deficiency of lime, twice the percentage will only serve for 
a similar time. Soils containing between o.i and 0.05 per cent, 
of phosphoric acid are considered as likely to respond to fertiliza- 
tion with phosphates in a short time. A large supply of organic 
matter appears, like a large supply of lime, to offset a deficiency in 
phosphoric acid. Large quantities of hydrated ferric oxides may 
render even large quantities of phosphoric acid inert and unavail- 
able to plants. 

Lime. Lime is exceedingly important to the soil. Low 
percentages of potash, phosphoric acid, and potash are 
adequate when a large proportion of lime carbonate is present. 
Many of our richest soils are calcareous soils, such as the blue- 
grass soils of Kentucky, the black prairie soils of Mississippi and 
Texas, the calcareous prairie soils of Illinois, Indiana, and Iowa. 
These soils are productive and durable. 

Heavy clay soils with less than 0.5 per cent, of lime do not, 
according to Hilgard's observation, carry the plants characteristic 
of calcareous soils. The lightest sandy soil should not contain 
less than o.io per cent, of lime; clay loams should contain 0.25 
per cent. There is no advantage in more than 2.00 per cent. It 
appears that an excess of potash may offset deficiency of lime. 

The following examples 1 show the effect of lime in overcoming 
a deficiency in phosphoric acid : 





A 


B 


C 


D 




0.068 
1.254 
0.366 


0.033 

I-37I 
0.699 


0.030 
0.129 
0.259 


0.038 
0.034 

0.218 




Potash 





Soils A and B were highly productive, falling off suddenly at 
the end of 15 or 20 years. Soils C and D scarcely produced 500 
pounds seed cotton per acre when fresh, and then only for three 
or four years. The difference appears to be due to an abundance 
of lime in the first two, a deficiency in the second two. 
1 Tenth U. S. Census. 



176 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 





E 


F 


G 




0.411 
0.197 
0.422 


0.188 
0.047 
0.178 


o 042 

0.286 
0-334 




Potash * 





Soil E with a very high percentage of phosphoric acid and only 
a moderate supply of lime, is very productive. Soils F and G 
the one with fair lime and low phosphoric acid, the other with 
the proportions reversed, are both about equally productive. 

Potash. According to Hilgard, sandy soils of great depth may 
contain less than o.io per cent, potash without being deficient 
therein; sandy loams contain 0.3 to o.i per cent.; loams 0.45 to 
0.3 per cent., heavy clays and clay loams o.8c to 0.45 per cent. 
As a rule, soils containing less than 0.25 per cent, potash are 
likely to require fertilization with potash salts early, while as 
much as 0.45 per cent, seems to be sufficient for the same soils. 
Sometimes, however, a soil rich only in lime and phosphoric acid 
shows good productiveness despite a low potash percentage, and 
conversely a high percentage of potash may offset a low per- 
centage of lime. 

The availability of the potash depends upon the general char- 
acter of the soil. With a good supply of available lime and 
magnesia, the potash of the soil is usually in an available form. 

The above standards are for potash estimated according to 
Hilgard's method. The Association method dissolves less potash 
and calls for lower standards. Exactly what these standards 
should be, remains to be determined. 

Nitrogen. Nitrogen is present in the soil in organic compounds 
which cannot be taken up by plants, and which change slowly into 
compounds which can be assimilated. This change depends 
largely upon physical conditions, though the composition and 
nature of the soil also have an influence. The rapidity of the 
production of active plant food is more important than the 
quantity of nitrogen. It is thus evident that it is difficult to fix 
a standard for nitrogen. It has generally been assumed that o.io 
per cent, is adequate. With less than 0.07 per cent, the soil is 



CHEMICAL COMPOSITION OF THE SOIL 



177 



usually deficient. Lime, as with other plant foods, also has an 
influence. 

Examples of Interpretations of Soil Analyses. The following 
examples are taken from Hilgard 1 . See accompanying table. 

Soils No. i and No. 2 are highly productive, and No. 3 is a 
very good soil. There is a great difference in the chemical com- 
position. No. i, however, is a heavy clay soil, while Nos. 2 and 
3 are sands, and hence need to contain less plant food. Plant 
roots can also exercise their functions to the depth of three or 
four feet in them, while in soil No. i, the roots rarely reach below 
12 or 15 inches. Soils No. 4 and 5, almost worthless, are deficient 
in phosphoric acid, and No. 4 is also deficient in lime. In addi- 
tion, these soils are underlaid by an almost pure sand at the depth 
of 12 inches. These facts are sufficient explanation of their 
character. 

PERCENTAGE COMPOSITION OF SOILS. 





No. i 

stiff 
buckshot 
soil, highly 
productive 


No. 2 

Very sandy, 
highly 
productive 


No. 3 

Sandy soil, 
medium pro- 
ductiveness 


No. 4 

Gray sand, 
almost 
worthless 


No. 5 

Gray sand, 
almost 
worthless 


Phosphoric acid . . . 
Lime 


0.30 


O.o8 


0. 10 


0.02 


0.03 


Potash 


1 -oo 

I IO 








J 3 






<_>. 13 






2 5 




No. 6 

Stiff red 
soil, fairly 
productive 


No. 7 

Stiff black 
prairie, very 
productive 


No. 8 

Stiff soil, 
practically 
worthless 


No. 9 

Stiff black 
prairie, very 
productive 


No. 10 

Stiff 
flatwood 
inferior 
quality 


Phosphoric acid . 


0.19 


0.03 


O.o6 


O. IO 


0.05 
r T 


Potash . 


U -O4 


o/ 




I -73 

n iS 






u -4o 




53 


0.30 


-75 



Soils Nos. 6 to 10 exhibit the effect of lime on the character of 
the soil ; soils 7 an d 9 being rich in lime, the others being poor 
in this ingredient. Soils 7 and 9 are very productive. Soil 7 
shows the effect of a large amount of lime in overcoming a 
deficiency in phosphoric acid, soils 6, 8 and 10, with more phos- 
1 Tenth U. S. Census. 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



phoric acid, being much poorer soils. Soil 6 is fairly productive 
in good seasons, soil 8 is considered practically worthless, and 
soil 10 is of inferior quality . 

Iron and Alumina. The percentage of alumina is an imperfect 
indication of the amount of clay in the soil. Enough 
silica seldom dissolves to satisfy the requirement for combining 
with alumina to form kaolinite. The percentage of alumina 
extracted is always larger. In numerous cases so little silica 
is present as to raise a question as to the form of alumina in the 
soil, the hydrate (Gibbsite) being almost the only possible one, 
aside from zeolitic minerals. 

From 1.5 to 4 per cent, are ordinary percentages of ferric oxide, 
occurring even in soils but little tinted. Ordinary ferruginous 
loams vary from 3.5 to 7 per cent. ; highly colored red lands have 
7 to 12 per cent, ferric oxide and occassionally 20 per cent, or 
more. Since highly ferruginous soils rarely have a high per cent, 
of humus, it appears that the iron acts as a carrier of oxygen, and 
this probably favors oxidation. 

Relative Composition of Soils of Arid and Humid Regions. 
Hilgard 1 has compiled a great number of analyses of soils of arid 
and humid regions, made with strong acid, with the result that 
the soils of the arid region are found to be, on an average, 
richer in plant food and in lime, than soils of the humid region. 
Arid soils are prevailingly calcareous, while humid soils are 
siliceous. This may be in large part due to the fact that the con- 

PERCENTAGE COMPOSITION OF SOILS OF ARID AND HUMID REGIONS. 





Humid, 
average of 
696 analyses 


Arid, 
average of 
573 analyses 




0.12 
0.21 
O.I 3 
0.29 
005 

3.66 
3-88 
88.21 
4.40 


0.16 
0.67 

i-43 
1.27 
0.06 
7.21 
5-48 
75.87 
5-15 


PntfmVi 


T imp 














1 



1 Bulletin No. 3. U. S. Weather Bureau. 



CHEMICAL COMPOSITION OF THE SOIL 



179 



tinued leaching of the soils in humid regions washes out the plant 
food. It may also be partly due to the difference in origin, as 
many of the humid soils are coastal deposits worn by the water, 
while many soils in the arid region are comparatively new soils 
from igneous rocks. 

Soils and Subsoils. If we compare the composition of soils 
with the corresponding subsoil, we find, almost always, that the 
subsoil contains less nitrogen than the surface soil. It often con- 
tains more potash, more oxide of iron and alumina, and less in- 
soluble material, than the surface soil. This difference is largely 
due to the percolating water carrying the finer particles of the 
soil (clay) into the subsoil. There is, however, a good deal of 
difference in soils in this respect. 

Relation of Composition to Type. Soils of different type differ 
to some extent in chemical composition, though such is not in- 
variably the case. There is also some variation in individual 
members of the type. Differences in composition are usually 
accompanied by differences in properties, productiveness or value 
of the soil. 

AVERAGE PERCENTAGE COMPOSITION OF SOME TYPICAL TEXAS SOILS. l 





Phos- 
phoric 
acid 


Nitro- 
gen 


Potash 


Lime 


Mag- 
nesia 




O.O2 
O.O2 
O.O2 
0.04 
0.08 
0.08 
O.OI 

0.09 
0.04 
0.04 


O.o6 
O.O2 
O.O4 
O.o6 
O.O9 
O.O7 
O.O7 
0.13 
0.12 
O.I I 


0.09 
0.08 
O.I 2 
0.12 
O/62 
0.63 
O.T2 

0.88 
0.25 
0.40 


0.08 
0.06 

O.I I 

0.14 

O.20 
0.12 

0.51 


0.03 
O.o6 
0.92 
0.16 

0-35 
0.09 

0.40 




Susquehanna fine sandy loam (3 samples) . 




Orangeburg fine sandy loam (6 samples) . . 











Detailed analyses and discussion of the soils of the United 
States are to be found in Bulletin 57 of the Bureau of Soils, and 
in "Soil Fertility and Permanent Agriculture" by C. G. Hopkins. 
1 Bulletin 126, Texas Station. 



CHAPTER X. 



ACTIVE PLANT FOOD AND WATER-SOLUBLE CONSTITUENTS 
OF THE SOIL. 

The complete analysis of the soil, or its partial analysis by 
strong acids, does not show clearly the immediate needs of the soil 
for plant food. Various weak solvents have been used for this 
purpose, with some measure of success. 

Active plant food is a term used to designate the potash and 
phosphoric acid soluble in fifth-normal nitric acid. We are not 
yet able to ascribe different values to the organic nitrogen com- 
pounds of the soil. 

Dilute Citric Acid. Numerous attempts have been made to 
ascertain soil deficiencies by means of weak solvents, such as 
water, water containing carbon dioxide, weak solutions of citric, 
hydrochloric, nitric, or oxalic acids, etc. 

Dyer 1 found that the root acidity of 100 plants expressed as 
citric acid, varies from 0.34 per cent, with Solanaceae to 3.4 per 
cent, with Rosaceae, and averages 0.91 per cent. He based on 
this work a method of estimating the available plant food by 
extracting the soil with a i per cent, solution of citric acid. The 
method was applied to Rothamsted soils. 2 The following are 
some of the results : 

BROADBAI.K WHEAT PLOTS. 



Treatment of 50 years 


Dissolved by i per cent, citric acid 


Average 
yield, 
6 years, 
wheat 


Phos- 
phoric acid 


Pounds 
per acre 


Potash 


Pounds 
per acre 




Per cent. 
0.0078 

0.0543 
0.0560 


2O2 

1418 
1307 


Per cent. 
0.0032 

0.0232 
0.0384 


83 

602 
896 


bushels 
I2# 

33^ 
38^ 


7 Phosphoric acid, Potash, 







The amount of phosphoric acid and potash dissolved by i per 

1 Jour. Chem. Soc., 1894, 115. 

* Bulletin 106, Office Exp. Sta., U. S. Dept. Agr. 



ACTIVE PLANT FOOD, ETC. iSl 

cent, citric acid thus corresponds with the treatment of the plot 
and the yield of wheat. The phosphoric acid soluble in strong 
hydrochloric acid was 0.114 to 0.219 per cent., potash 0.197 to 
0.285 ; thus while there was some difference, it is not a clear 
indication as to the fertility of the soil. 

The application of the citric acid method to soils of varying 
character has not always given good results. This may be due to 
several reasons : ( i ) The plant may have greater difficulty in 
obtaining citric acid soluble plant food in some soils than in 
others. In other words, it may be necessary that the standard 
vary according to the character of the soil, as Hilgard's standards 
do. (2) The soil may not have been deficient in phosphoric acid 
or potash when it was supposed to be. (3) Different rates of 
change of potash and phosphoric acid into more soluble com- 
pounds in different soils may interfere. 

According to Dyer, less than o.oi per cent, phosphoric acid or 
potash soluble in phosphoric acid indicates a deficiency. 

Other Weak Solvents. 1 These include N/5 nitric or hydro- 
chloric acid, N/2OO hydrochloric acid, 2 and N/5 oxalic acid which 
have been suggested for the same purpose as I per cent, citric acid. 
Some of these solvents have the advantage of greater ease of 
manipulation than citric acid. The results vary according to the 
solvent employed. 

The most promising solvent is fifth-normal nitric acid. Fifth- 
normal nitric or hydrochloric acid gave the same results on cer- 
tain of the Rothamsted soils as citric acid, and upon some other 
soils tested by the Association of Official Agricultural Chemists 
the results were more nearly in accordance with the needs of the 
plant. 

Factors of Availability of Plant Food. 3 The amount of any 
given plant food which is withdrawn from the soil by the plant 
does not depend upon one condition only, but is dependent upon 

1 See Proceedings Association Official Agr. Chem., Bulletins 47, 49, 
51, 56, 67, 73, Division Chem., U. S. Dept. Agr. 

2 Moore, Jour. Am. Chem. Soc., 1912, p. 791. 

3 Fraps, Am. Chem. Jour., 1904, p. i. 



l82 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

a number of factors. These factors may be grouped as 
follows : 

(1) The quantity of the element present at the beginning of 
the growing season in forms of combination which can be partly 
or completely absorbed by the plant. This may be called chem- 
ically available plant food. 

(2) The condition of the soil particles. Compounds chem- 
ically available may be enclosed in the soil particles so as not to 
be exposed to the action of plant roots. Such compounds are 
physically unavailable. If the encrusting substance is removed, 
such bodies become chemically available. 

(3) The amount of the plant food transformed during the 
growing season into forms of combination which can be absorbed 
by plants. This factor is certainly of importance with respect 
to nitrogen; its importance in the case of phosphoric acid and 
potash is apparently not so great but the matter requires study. 
This factor may be called weathering availability. 

(4) The nature of the plant. Plants differ in both their 
capacity for absorbing food and their need of it. Whatever the 
cause of these differences, there is no doubt but that they exist. 
We will call this factor physiological availability. 

The character of the soil, its chemical composition, the condi- 
tions which prevail during the growth of the plant, and perhaps 
other factors influence the amount of plant food taken up. 

Factors Influencing the Composition of the Soil Extract. 1 The 
amount of phosphoric acid extracted from the soil by a given 
solvent is the difference between that dissolved from the phos- 
phatic or potash mineral and that absorbed by the fixing particles 
of the soil. That is to say, the soil extract does not necessarily 
represent the solubility of the mineral exposed to the action of the 
solvent, but is the resultant of the solvent and fixative 
forces. Furthermore, the quantity of phosphoric acid exposed 
to the action of the solvent depends upon its con- 
dition in the soil and the solubility of protecting material in the 
solvent used. If the phosphate mineral is enclosed within quartz, 
1 Texas Bulletins 126-145. 



ACTIVE; PLANT FOOD, ETC. 183 

it is quite effectually protected from any solvent. If it is con- 
tained within zeolites, it may be affected by some solvents and not 
by others. If it is contained in carbonate of lime, the latter will 
be dissolved by any acid solvents, with consequent exposure of the 
included phosphate to the action of the solvent. 

The quantity of phosphoric acid or potash contained in the soil 
extract thus depends upon three factors : 

(1) The quantity of phosphate or potash mineral exposed to 
the solvent, and its solubility under the conditions of the extrac- 
tion. 

(2) The solubility of the soil materials which protect or 
enclose phosphates or potash compounds. 

(3) The power of the soil to fix phosphoric acid or potash 
under the conditions of the extraction. 

The strength of the solvent, its nature, the period of digestion, 
the temperature, and the proportion of soil to solvent, all affect 
the quantity of phosphoric acid and potash contained in the soil 
extract, but they have their effect through action on the three 
factors mentioned above. 

Solubility of the Soil Minerals. This subject 1 is studied by 
bringing phosphate or potash minerals in contact with N/5 nitric 
acid, in the proportions in which these minerals may occur in the 
soil, and under the conditions of the soil extraction. 

Phosphoric Acid. The phosphates of lime are completely 
soluble, the precipitated phosphates of iron and aluminium are 
completely soluble, and vivianite and triplite are nearly so, in N/5 
nitric acid. The aluminium phosphates (variscite and wavellite) 
and the basic ferric phosphates are comparatively slightly dis- 
solved. 

It is hardly probable that ferrous phosphate (vivianite) is of 
common occurrence in ordinary cultivated soils, though it may 
exist in some soils which are not well aerated. Fifth-normal 
nitric acid dissolves calcium phosphates completely, but dissolves 
mineral aluminium phosphates or basic ferric phosphates only to 
a slight extent. It thus distinguishes between these two classes 

1 Texas Station Bulletins 126-1.15. 



184 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

of compounds in the soil. Apatite, phosphate rock, ferric phos- 
phate (precipitated), aluminium phosphate, vivianite, and triplite 
are practically equally soluble. We also feel justified in saying 
that acid phosphate would be completely dissolved. But no one 
can yet claim that these materials possess the same value to plants. 
Fifth-normal nitric acid may not distinguish between minerals 
which have unequal values to plants. We have no solvent which 
would dissolve phosphoric acid from the phosphates mentioned, in 
the same proportions as would be taken from them by plants. 
What we cannot do with known mineral phosphates of known 
character outside of the soil, we could not expect to do with the 
same phosphates after they are put into the soil, and with the un- 
known phosphates already within the soil. 

Soils may, therefore, contain equal quantities of phosphoric 
acid soluble in fifth-normal nitric acid, and yet give up unequal 
quantities of phosphoric acid to plants on account of differences 
in the phosphates present. This consideration must give rise to 
caution in comparing the results of all kinds of soils with one 
another. 

Only those soils should be compared which probably contain 
the same kinds of phosphates. Soils widely dissimilar in origin 
and character should not be compared, unless there is evidence 
that they contain similar phosphates. 

Study of potash dissolved from minerals in a similar way shows 
that very little is taken from the felspars, microcline and 
orthoclase, less than ten per cent, from glauconite and biotite, and 
from 16 to 60 per cent, from muscovite, nephelite, leucite, 
phillipsite, and apophyllite. Potash absorbed by chabazite and 
some other minerals is extracted to the extent of 70 per cent. 
The dissolved potash thus represents a large portion of some 
easily dissolved mineral, or a small portion of some difficultly 
attacked mineral. 

Fixation of the Dissolved Phosphoric Acid and Potash. The soil 
has the power to withdraw potash and phosphoric acid from 
solution, both in water and in acids. The method of studying 
this factor consists in extracting two portions of the soil of 



ACTIVE PLANT FOOD, ETC. 185 

known fixing power with the solvent, one part with the acid alone, 
and the other with a known quantity of phosphoric acid or potash. 
The quantities should be such as might be dissolved from the 
soil. The following is an example i 1 

Phosphoric acid 
Parts per million 

Extracted from soil alone 8.5 

Added to solvent 194.0 



Total present 202.5 

Actually recovered 48.0 

Absorbed by soil 154-5 

With 17 soils, the fixation of the added phosphoric acid ranged 
from 5 to 94 per cent, of the quantity added. Thus the phos- 
phoric acid extracted by the N/5 nitric acid does not necessarily 
represent that which has gone into solution, but represents the 
resultant of the solvent, and the fixing power of the soil. With 
some soils, the fixing power is so high that it must be considered 
very seriously in interpreting the results of the analysis. Fixation 
also takes place from acids stronger than fifth-normal. 

Fixation of potash takes place under the same conditions as the 
fixation of phosphoric acid, but to a much less extent, and the 
factor of fixation is much less important with potash. 

Soils containing easily-soluble phosphoric acid or potash com- 
pounds give decreasing amounts to successive extractions, but 
soils containing little or no compounds of high solubility give 
successive extracts of nearly constant composition. 

Solubility of Constituents of the Soil. The solubility of the 
constituents of the soil must be considered as a factor in the 
analysis of soils with weak solvents. If any quantity of the soil 
passes into solution, phosphates will thereby be exposed to the 
action of the solvent, which were protected from the action of 
soil moisture and roots, and which are really physically unavail- 
able. This factor must be given careful consideration. For 
example, N/5 nitric acid dissolves 320 parts per million of lime 
(CaO) from one soil, while from another soil it dissolves 53,250 
parts, which corresponds to nearly 10 per cent, carbonate of 
1 Texas Station Bulletin 126, p. 16. 
13 



l86 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

lime. The amount of phosphoric acid and potash brought into 
action through the solution of the lime in the soil first named, may 
not be large, but in the case of the second soil, 10 per cent, of the 
soil enters into solution, and all the phosphoric acid and potash 
protected within this 10 per cent, is exposed to the action of the 
solvent. This action is further emphasized, in the case of the soil 
just mentioned, by the fact that a second treatment with acid dis- 
solves 43,400 parts per million of lime, and a third treatment dis- 
solves 46,360 parts, making a total of about 14 per cent, of lime 
dissolved from the soil, corresponding to about 25 per cent, car- 
bonate of lime. 

This soil, of course, represents an extreme instance, but it 
emphasizes the difference between a calcareous and a non- 
calcareous soil. In a non-calcareous soil, the phosphoric acid and 
potash inclosed within the soil particles are protected from the 
solvent, while in a calcareous soil, that portion of the phosphates 
and potash minerals included in the calcareous matter dissolved 
by the acid is exposed, and may be dissolved. 

Since the plant food dissolved from a non-calcareous soil is 
present on the external surface of the soil grains, and accessible 
to the roots of the plants and the action of soil moisture, while 
that dissolved from calcareous soils is, without doubt, in part 
included within the soil grains, and not accessible to plant roots, 
it is obvious that calcareous soils may contain a larger quantity of 
seemingly active plant food than non-calcareous soils, and yet 
require fertilization on account of the phosphoric acid being pro- 
tected. 

Two calcareous soils may also contain the same amount of 
active plant food, and yet differ in the amount plants can take 
from them. In one the plant food may be on the extreme surface 
of the soil grains, in the other it may be disseminated through 
them. 

Calcareous soils are more durable than non-calcareous soils. 
This may be explained by the fact that the gradual weathering of 
such soils continually exposes fresh surfaces of plant food. 



ACTIVE PLANT FOOD, ETC. 187 

Significance of the Dissolved Plant Food. 1 In considering the 
significance of the dissolved plant food, it is necessary to regard 
the active phosphoric acid and potash, the "acid consumed," and 
the fixing power of the soil. The fixing power is of importance 
chiefly in connection with soils which fix more than 80 per cent, 
phosphoric acid. With such soils, the extracted phosphoric 
acid may, or may not, represent the soluble phosphates. 

The "acid consumed" is a measure of the bases dissolved by 
the solvent, and is estimated by titrating 10 cc. of the solution 
after the extraction is complete. 

When 10 parts per million of phosphoric acid, or less, is 
extracted, associated with a fixing power of less than 50 per cent., 
and with acid consumed less than 90 per cent., it indicates that 
practically none of the phosphoric acid of the soil is present as 
apatite, calcium phosphate, or similar compounds, but must be 
present as basic iron or aluminium phosphates or in organic com- 
bination. When 10 parts phosphoric acid, or less, are present and 
the soil has a high fixing power for phosphoric acid (75 per cent, 
or more), calcium phosphates may or may not be present. That 
is to say, the method can not in this case distinguish between 
phosphoric acid which goes into solution from calcium phosphate 
and is then removed by fixation, and that which comes from the 
basic phosphates of the soil. The origin of the soil will throw 
some light upon the matter. If the soil is geologically old, the 
phosphoric acid has probably all been converted into basic phos- 
phates. If the soil has been recently formed from rocks contain- 
ing apatite and other phosphatic minerals, it is possible that cal- 
cium phosphate may still be present and the same is true if the 
soil has been fertilized. In the majority of soils having a high 
fixing power and a low content of phosphoric acid, provided that 
.they have not been fertilized, the phosphoric acid is probably 
present as basic iron and aluminium phosphates. 

A soil of high fixing power such as above mentioned would 
yield up the same quantity of phosphoric acid to the solvent, 
whether fertilized or not fertilized, unless a very heavy applica- 
1 Texas Station Bulletins 126 and 145. 



1 88 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



tion of phosphoric acid has been made. One thousand pounds of 
16 per cent, acid phosphate would represent an application of 80 
parts per million of phosphoric acid, and this heavy application 
would not increase very much the phosphoric acid removed from 
soils of very high fixing power. 

A soil containing 100 parts per million of phosphoric acid, with 
a low acid consumed, and with a fixing power of less than 50, 
probably contains a corresponding amount of calcium phosphate 
accessible to the roots of plants. 



too 





30 



fiO 



40 



eo 



/ ? 3 4 5-6 7-3 3-10 1 1- IB 

GROUP. BASED ON ACTIVE. PHOSPHOR/C ACID 

Fig- 39 Relation of the active phosphoric acid of the soil to the phosphoric 

acid withdrawn by crops in pot experiments, expressed 

as bushels corn per acre. 

A soil containing 100 parts per million of phosphoric acid, with 
an acid consumed of 20 per cent., may or may not expose much 
phosphoric acid to the roots of plants. It is impossible to say 
how much of it is protected by the calcareous material. 

It is impossible to distinguish phosphoric acid in its several 
different forms. For example, suppose plots were fertilized 
with equal quantities of phosphoric acid, Thomas phos- 
phate, phosphate rock, acid phosphate, and apatite. We 
could not expect to find a relation between the phosphoric 



ACTIVE PLANT FOOD, ETC. 



189 



acid dissolved from these plots and the crop production. All 
these materials would give up their phosphoric acid equally well 
to the solvent used. 

A soil containing less than 50 parts per million of active potash 
probably contains all its potash in the form of highly insoluble 
silicates, such as the felspars. A soil containing over 50 parts per 
million of active potash contains some of more easily dissolved 
potash minerals or compounds. Since the solvent does not 




Fig. 40. Corn grown with and without phosphoric acid on four soils con- 
taining 60 to 100 parts per million of active phosphoric acid, Te^as Station. 

decompose such minerals fully, and some fixation also occurs, the 
quantity of potash extracted is less than the quantity present in 
easily soluble compounds. 

Relation of Active Phosphoric Acid to Growth in Pot Experi- 
ments. At the Texas Experiment Station, studies were made of 
the relation between the active phosphoric acid present in the soil 
and the crop produced in pot experiments. The comparison was 
made between the crops grown with phosphoric acid, nitrogen, and 
potash, and those grown with nitrogen and potash only. The 



190 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



behavior of the corn crop was closely related to the quantity of 
active phosphoric acid in the soil. Soils containing 20 parts per 
million, or less, of active phosphoric acid are clearly deficient in 
phosphoric acid. Soils containing 30 to 100 parts per million 




Fig. 41. Corn grown with and without phosphoric acid on four soils con- 
taining less than ten parts per million of active phosphoric acid, Texas Sta. 

were, as a rule, deficient. Soils containing 100 to 200 parts per 
million were deficient in about one-half of the experiments. 
AVERAGE CORN POSSIBILITY AND AVAILABILITY OF PHOSPHORIC ACID. 



Active phosphoric acid 



Corn equivalent 
(bushels per acre) 





Average 


Maximum 




4r 


Q O 










i*.0 

20 8 


31.0 

36 o 










i y-/ 

2/1 A 


o/- IJ 

A2 O 


60 to 80 


26 =; 


CQ Q 




22 o 


^Q O 




C2 C 


OV-^ 
IOI O 




60 7 


QI O 









The quantity of phosphoric acid withdrawn from the soil was 
also related to the quantity of active phosphoric acid. In the 



ACTIVE PLANT FOOD, ETC. 



191 



table 1 on page 190 the quantity of phosphoric acid withdrawn by 
the crop is expressed as bushels of corn per acre which could be 
produced with it. 

Potash? A similar series of experiments carried out with 
potash lead to similar results. The percentage of deficient crops 
decreases with the quantity of active potash in the soil. The 
average percentage of potash in the crop increases with the per- 
centage of active potash in the soil. The actual quantity of potash 




POTASH iu SOIL IN PARTS PER MILLION 

Fig. 42. Relation of the potash content of the crop to the 
active potash of the soil. 

removed by the crop increases with the active potash of the soil. 
After cropping, the soil, on analysis, was found to contain less 
active potash than it did before cropping, showing the dis- 
appearance of active potash due to the crop. 

RELATION OF ACTIVE POTASH TO POT EXPERIMENTS. 



Active potash in soil 


Percentag 


e of crops 


Average 
weight of 
crops without 


Average 
percentage 


(parts per million) 


Deficient 
in potash 


Injured 
by potash 


potash divided 
by crop with 
potash 


of potash in 
corn crop 




86 7 


6 7 


67 


T l8 




cr T 


16 7 


W 
7O 


I.JO 


IOO to I SO 


OO' A 
CA 7 


16 i 


79 
SA 


l./U 
2 2Q 










^ Z 9 




O7' 1 


1 i '* 


9 1 


55 
i &z 




O/'O 


6 1 '6 


08 


3-5 






^D-o 
A c 6 


9 


53 

i 81 




l^.U 

18 o 


4o- u 
4" 8 


116 


3-3 






4.5- 




3 1 



1 Texas Station Bulletin 126, p. 69. 

2 Texas Station Bulletin 145. 



192 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



The actual amount of potash removed, on an average, from the 
different soils, is given in the following table. In order to make 
the table more concrete, the amount of potash is also expressed 
in bushels of corn per acre which could be produced by this quan- 
tity, both stalk and grain included : 



Active potash in soil 
(parts per million) 


Active potash removed 
(parts per million) 


Corn in 
bushels 
equivalent to 
average potash 
removed 


Average 


Maximum 




29.7 
37-2 

80^9 
I2O.O 

150.9 
II9.4 
^06.9 


53-4 
143-2 
176.2 
249.6 
434-6 
354-8 
295.8 
380.8 


58.6 

74-4 
102.0 
l6l.8 

240.2 
313.8 
238.8 
413.8 


CQ to IOO 


ioo to I so 















Importance of the Active Plant Food. The active plant food 
is thus related, on an average, to the ability of the soil to supply 
plant food. Variations undoubtedly occur, due to variations in 
the nature of the active plant food. The relation of the active 
plant food to field results must be studied and worked out. 
Deficiency as shown in pot experiments must be considered as 
relative deficiency, and in applying the results to field conditions, 
the possibilities of the soil under the prevailing climatic condi- 
tions must be considered. For example, in our pot experiments, 
soils containing ioo to 150 parts per million of active potash were 
deficient in potash in 54.3 per cent, of the tests, and yet on an 
average, they gave up enough potash for 102 bushels of corn, 
the maximum being 352 bushels. In other words, the pot experi- 
ments demanded more potash than would suffice for the crop 
indicated above. Had the demands for potash been smaller, the 
soil would not have been deficient. 

The importance of the estimation of the active potash and 
phosphoric acid is to show the relative deficiency of the soil for 
these elements. The tables we have given are an aid in this con- 
sideration. For example, a soil containing 10 parts per million 
of active phosphoric acid and 50 parts of active potash, would 



ACTIVE PLANT FOOD, ETC. 



193 



have an average corn possibility of 4.5 bushels for phosphoric 
acid and 58.6 bushels for potash. Evidently there is greater need 
of phosphoric acid than of potash, and the two become equal by 
the addition of sufficient phosphoric acid for 54.1 bushels corn. 



















/ 


7 












$ 

V 


S\ 


\/ 


7 




too 








^ 


/ 










80 








f y 
















i 


f 












60 






J 














20 


**"* 


















SO /OO I5O 2OO 3OO 4OO 5OO 6OO S-T-* 



ACTIVE POTASH IN Son. //v PARTS PER MILLION 

Fig. 43. Relation of the potash removed by crops in pot experi- 
ments to the active potash contained in the soil. 

This, however, is only an illustration. Field experiments must 
show the exact relation of the two. 

Relation of Total Nitrogen to Results of Pot Experiments. 1 Pot 
experiments similar to these just described have been used to 
trace the relation between the total nitrogen of the soil and the 
effect of the fertilizers. They will be described here on account 
of their relation to the preceding work. The effect of the fertilizer 
is, in general, related to the content of nitrogen in the soil. The 
percentage of nitrogen in the crop increases as the percentage of 
total nitrogen of the soil increases. The average corn possibility, 
1 Texas Station Bulletin No. 151. 



194 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

in bushels per acre, based on the quantity of nitrogen removed 



/9 
If 






















/ 






















/ 




5a/2 
















/\ 




/ 




4'* 








A/^ 


^X 


X"- 


-S 




^V 












A 


















1 

fQ 




A 


/ 




















"T 
/ 


/ 






















j 















































JO+ Of .OB .10 .11 



.16 ./a .& 21 



Fig. 44. Relation of total nitrogen to the average weight of the crops 
grown without addition of nitrogen in pot experiments. 



500 




\ I 

os wif/touf- Ntfrogefi 



PERCENTA GE5 OF NITROGEN IN SOIL 

Fig. 45. Relation of total nitrogen of the soil to the average effect 
of fertilizer nitrogen in pot experiments. 



from the soils in pot experiments, is given in the following table 



ACTIVE PLANT FOOD, ETC. 



Average 
sibil 



Percentage of corn possibility 

nitrogen in soil (bushels per acre) 

O.OOO to O.O2 5-7 

O.O2I to 0.04 9.4 

0.041 to 0.06 13.6 

0.061 to o. 16 22.3 

o.i6itoo.i8 42.9 

Interpretation of Soil Analysis with Weak Solvents. The "corn 
possibility" figures may be used for the purpose of ascertaining 
the probable relative deficiency of a soil. Suppose, for example, 
a soil contains .086 per cent, nitrogen, 8 parts per million active 
phosphoric acid, and 105 parts per million active potash. 
Referring to the tables, we find : 

Corn possibility 
(bushels) 

For nitrogen 22.0 

For active phosphoric acid 4.5 

For active potash 102.0 

Thus this soil would probably be most deficient in phosphoric 
acid, next in nitrogen, and least in potash, if tested in pot experi- 
ments. 

The active phosphoric acid and potash and the total nitrogen 
are not, however, the only things to consider under field con- 
ditions. The form of the phosphoric acid, depth of soil, kind of 
cultivation, season, etc., all influence the size of the crop. It is 
thus not possible to say that the corn possibility represents what 
should actually be produced in the field. Field results must be 
worked out for different localities, as no doubt climate and tem- 
perature will cause soils of the same analysis to give different 
results in different sections. 

The fact that there is possibly a close relation between chemical 
analyses and field results is shown in certain results secured at 
the Texas Experiment Station. 1 Eight soils in which total 
nitrogen was probably the controlling condition, averaged n 
bushels per acre corn possibility, while the actual yield as claimed 
by the farmers was 18 bushels. Five soils controlled by active 
1 Proc. Int. Cong, of Applied Chem., 1912. 



196 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



phosphoric acid averaged 12 bushels corn possibility, and actual 
production averaged 14. Considering the fact that the, actual 
yields given were estimates, and that the corn possibility is prob- 
ably a little low, the agreement is good. This matter requires con- 
siderably further study. 

Water-Soluble Constituents. The water-soluble constituents of 
the soil are of significance from the fact that material can enter 
the plant only in solution. The root is composed of cells, 
through which there are no openings for the entrance of solids. 

\Yhen a liquid containing a substance in solution is 




Fig. 46. Enlarged plant cell, normal below, and with the protoplasm 
contracted by nitrate of soda above. 

brought in contact with another portion of the same 
liquid which does not contain that substance, the dissolved sub- 
stance passes into that portion until all parts of the liquid have a 
uniform composition. This is called diffusion. The same occurs 
when the liquid is separated by a membrane, which the dissolved 
substance is able to penetrate. Substances which cannot generally 
pass through membranes are termed colloids, examples being 
albumen, glue, etc. Salt, sugar, calcium sulphate, which can pass 
through, are called crystalloids. If, then, a plant cell is brought 



ACTIVE: PLANT FOOD, ETC. 197 

in contact with a solution of a substance which can penetrate the 
membrane, diffusion will take place until the number of ions 
of the same kind entering the cell walls is equal to the num- 
ber leaving it. If the cell life appropriates any of the ions, and 
holds them, so that they become incapable of diffusion, the ions 
continue to enter the cell until the cell life becomes satisfied, and 
the number entering and leaving become equal. The same 
phenomenon occurs with an aggregate of cells or the entire plant. 
It is then possible for plants to extract elements from very dilute 
solutions, and accumulate them in their tissues, and also for plants 
to live in comparatively strong solutions of a salt without taking 
up large quantities of the substance. 

Diffusion into Cells. According to Pfeffer, plant cells are 
composed of three parts ; an outer cell wall, of cellulose or some 
other membrane ; a layer of protoplasm or living material adherent 
to the cell wall ; and the cell sap. The cell wall is in general more 
permeable to dissolved substances than the protoplasm, and hence 
many substances pass through the cell walls but not through the 
living plasma within. "It is indeed possible that the water and 
salts absorbed by the roots pass mainly if not entirely through the 
walls of living cells or the walls and cavities of dead wood fibers, 
so that only on reaching the leaves of a tree do they penetrate the 
living protoplasts there." The character of the cell wall and of 
the protoplasm membranes determine whether a given substance 
will penetrate to the interior of a cell, and any such substance 
will continue to be absorbed until a condition of equilibrium is 
reached, when all further absorption ceases. If this condition of 
equilibrium is disturbed, absorption may continue, and relatively 
large quantities of a particular substance may be absorbed from 
a very dilute solution. 

Every substance which can pass through the different cellular 
membranes penetrates the protoplasm independently of whether it 
is useful, unnecessary, or even injurious. 

Cells may convert bodies which diffuse into them into non- 
diffusing compounds, and the substance will continue to enter as 
long as this takes place. The non-diffusing compound may be 



198 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

soluble or insoluble. Thus methyl blue is fixed in an insoluble 
form in the roots of Azalla, while in the roots of Lemna minor it 
accumulates in a dissolved form. In both cases the dye is 
accumulated from very dilute solution, and the cells become dis- 
tinctly colored. The dissolved substances in the cell sap (sugar, 
salts of organic acids, potassium nitrate, etc.,) must be present in 
a non-diffusing form. The presence of nitrates in dead cells 
does not indicate that they are so present in the living cell, for the 
non-diffusing substances may decompose immediately on the 
death of the cell. 

Transpiration Movements. Diffusion alone is a very slow 
movement. It requires 319 days to transport I mg. the distance 
of i mm. from a 10 per cent, solution into pure water. Most of 
the material which enters the roots of a plant, though it must 
diffuse through the root wall, enters in the current of water after- 
wards transpired, rather than by diffusion alone. 

Active transpiration must lead to the continuous introduction 
of new traces of salts by the water current, since backward 
diffusion is slow. This explains how relatively large amounts of 
saline materials are sometimes found in plants. Nobbe and 
Siegert actually found patches of saline incrustation on the leaves 
of buckwheat and barley when the plants were grown in a one 
per cent, solution of salts. Soluble incrustations are sometimes 
found on plants, and calcareous scales are often found on the 
leaves of many Saxifrage and other plants. Transpiration may 
also aid in the deposition of silica in the cells of plants. 

Absorption by the Root. Excepting carbon dioxide (and nitro- 
gen in some cases perhaps) the roots absorb all the compounds 
used to buld up the plant ; namely, water, hydrogen, and oxygen, 
and all the other elements in the form of salts. Salts of iron, cal- 
cium, magnesium, sodium, manganese, potassium, silicon, chlorine, 
nitrogen, sulphur, and phosphorus are thus taken up. 

Salts in solution are more or less decomposed into ions, which 
are atoms or groups of atoms charged with electricity. Thus, 
sodium chloride is broken down into the ions, Na and Cl, sodium 
sulphate into Na and SO 4 , potassium nitrate into K and NO 3 . 



ACTIVE: pivANT FOOD, ETC. 199 

Plants have the capacity of taking up one or the other of these 
ions alone. From a solution of potassium chloride, the plant may 
take up more potassium ions than chlorine ions, leaving hydrogen 
in place of the potassium. The liquid would then become acid 
from the presence of hydrochloric acid. The plant may remove 
the nitrate ions from a solution of calcium nitrate. The calcium 
ion would then unite with carbon dioxide and form insoluble cal- 
cium carbonate. 

The above considerations are essentially modified in the pres- 
ence of two or more salts ; as a rule, when two salts are present, 
which are required by the plant, their absorption is accelerated. 
For example, potassium salts are taken up in much larger quantity 
when a calcium salt is present. Potassium nitrate may be entirely 
removed from a solution containing calcium nitrate. In the 
presence of other ions, the potassium ion, nitrate ion, phosphate 
ion, and sulphate ion can be completely removed from solution, 
while calcium or magnesium ions become more concentrated in 
the solution, as a rule. 

A study of the effect of the amount of water evaporated upon 
the ash constituents taken up has shown that the stronger the 
evaporation, the more dilute is the solution taken up by the plant, 
but at the same time the more substance is taken up, since the 
decrease in concentration is in a less ratio than the increase in 
water evaporated. 

Soil Solution. The soil solutions are exceedingly dilute. From 
what has been said, however, it is seen that plants may withdraw 
nourishment from very dilute solutions. It is self-evident, that 
when the dilution goes below certain limits, diffusion will not 
take place with sufficient rapidity to satisfy the requirements of 
the plants, and limits are conceivable at which only a minimum 
growth w^ill take place. 

In other words, there is an optimum of concentration, above 
and below which a lesser production of plant substance takes 
place. Below, because transpiration and diffusion do not provide 
sufficient food. 



2OO 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



An example of the effect of dilution is presented below. 

Yields gm. dry matter 

i part per thousand 0-4934 

3 parts per thousand 0.7320 

5 parts per thousand i . 1540 

The plants were grown in water containing a mixture of the 
various necessary salts. 

Solvent Action of Roots. Although plants can take up sub- 
stances only in a state of solution, they have some power of 
bringing substances into solution. Etchings showing the shape 
of the root can be obtained by causing plants to grow upon 
polished marble, and such etchings are often found in nature. 

The solvent action of roots is aided by the intimate contact 
between root hairs, and soil particles, the latter often being 
literally imbedded in the roots. The solvent action observed may 
be brought about by the action of carbonic acid given off by the 
roots, and the etchings mentioned above may be formed in this 




Fig. 47. A root hair, highly enlarged, showing the intimate 
contact of root and soil. 

manner. According to Czapek, roots excrete potassium acid 
phosphate, which has an acid reaction. The vegetable acids in 
the root juices may also be effective, without actually passing 
through the membrane. The vegetable acids are dissociated to a 
certain extent into hydrogen and other ions ; for example, oxalic 
acid may dissociate into the ions H and HC 2 O 4 . The ion HC 2 O 4 
may be held in a non-diffusing condition, while the hydrogen is at 
liberty to pass through the membrane, and thus exert an action 
upon external substances. In this way there may be an exchange 
of H and Ca ions, for example. Whatever the cause of the 
solvent action of plant roots, it is well demonstrated that plants 
can take up material not dissolved in the solution which extends 
between the soil particles. 



ACTIVE PLANT FOOD, ETC. 



2O I 



Water Extract of Soils. In arid climates, water-soluble mate- 
rial may accumulate and give rise to alkali. The solvent action 
of water in a soil under natural conditions is increased by the 
carbon dioxide formed from decaying organic material. 

On shaking a soil with water, a small amount of soil ingredients 
enters into solution. The extract does not represent the solubility 
of the soil constituents in water, but is the resultant of the solvent 
and fixative forces, as in the case of the acid extract. The soil 
has a much greater power of withdrawing material from water 
than from acid solution, and hence the aqueous extract is a much 
poorer measure of the solubility of soil materials. For example, 1 
on shaking a certain soil with water, the resulting extract con- 
tained 2.3 parts per million of phosphoric acid, and the same 
results were secured on shaking it with a solution of potassium 
phosphate containing 10 parts per million of phosphoric acid. 

Composition of the Water Extract. The soil extract varies 
widely in composition, even from soils of the same type. The 
following results are compiled (and recalculated) from Bulletin 22 
of the Bureau of Soils : 

VARIATIONS IN COMPOSITION OF SOIL EXTRACT. 





Parts per million of soil 


Pounds per acre-foot 


Phosphoric 
acid 


Nitrogen 


Potash 


Phosphoric 
acid 


Nitrogen 


Potash 


Windsor sand . 
Norfolk sand . 
Sassafras loam . 
Leonard town 
loam 


1.6- 7.6 
1.0- 9.7 
1.3-12.7 

1.7- 9.7 
1.4-24.0 


N 

0.2- 7.2 
0.2- 6.4 
O.I-IO.4 

trace 16.5 

trace 7.7 
trace 9.2 


K. 2 O 

13-1- 55-3 
13.9- 54.0 
9-5- 56.2 

72.1- 62.0 

9.0- 87.2 
5.9-100.6 


5.6-26.6 
3.5-53.9 
4-5-44-5 

1.0-57.1 
14.9-88.0 


N 

0.7-25.2 
0.7-22.4 
0.3-36.4 

trace 57.8 

trace 26.9 
trace 32-2 


K 2 O 

45.8-193.6 
48.7-189.0 

42.3-217.0 

31.5-285.2 
20.7-352.1 


Cecil sandy 


Cecil clay 



The Bureau of Soils claims that the composition of the soil 
extract is practically constant in all soils, but it is difficult to see 
how the preceding analyses can be reconciled with such claim. 
1 Texas Station Bulletin 82, p. 16. 



2O2 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



If we assume that in the production of one gram of dry matter 
500 grams water are transpired, we can calculate the concentration 
of the absorbed water required to give the average composition of 
various plants. This has been done and the results are in the 
following table : 





Percentage in 
dry matter of plant 


Necessary concentration of 
soil solution per million 


Phosphoric 
acid 


Potash 


Phosphoric 
acid 


Potash 




o-59 
0.80 

o.'68 
0.67 
0.16 
0.66 
0.63 


1.86 
2.36 
1.94 
2.62 
1.6 5 
0.45 
2.22 

1-73 


IO 
16 
II 
14 
13 
3 
13 
13 


37 
47 
39 
52 
33 
9 
44 
15 




Winter wheat (bloom). 






Red. clover 


Alfalfa 





If we compare this table with the preceding, we find that the 
soil moisture does not contain enough phosphoric acid. In only 
three of the soil series is even the maximum content of phos- 
phoric acid sufficient for the requirements of any of the plants 
(except sugar cane). The minimum content of the soil moisture 
in potash falls below the concentration required, but the maximum 
of all series of soils is above the maximum requirements of the 
plants given above. 

Investigations were made by King 1 upon the water-soluble salts 
of the soil, and the yield of corn and potatoes on eight types of 
soil in North Carolina, Maryland, Pennsylvania, and Wisconsin. 
He concludes that "there is a well-marked tendency for larger 
amounts of water-soluble salts to be removed by the methods 
adopted from the soils upon which the crops have made the 
largest yields." The water-soluble material was estimated to the 
depth of four feet. The addition of fertilizers was also found to 
increase the water-soluble salts, and where determined under large 
and under small plants in the same field, differences were also 
1 Bulletin 26, Bureau of Soils. 



ACTIVE PLANT FOOD, ETC. 



203 



evident, as the soil under the larger plants contained more water- 
soluble materials. 

The following table shows the water-soluble material dissolved 
from several types, according to King's 1 investigations : 

SAI/TS DISSOLVED BY WATER FROM SURFACE FOUR FEET OF SOIL 
TYPES (POUNDS PER ACRE). 





K 


Ca 


Mg 


N0 3 


HPO 4 


Norfolk sandy soil 


210 

I 9 2 
246 

257 


404 
415 
387 

1,036 
910 
1,070 
1,049 


177 
306 

420 


162 

147 
128 
262 
429 

200 


120 
221 

196 


Selma silt loam 


Norfolk sand 


Sassafras sandy loam 


Hagerstown clay loam .... 








224 


705 


,6 3 


1 06 


66 





The average quantity of plant food dissolved from the soil was 
sufficient to produce the following amounts of clover hay: 2 

Tons 

Potash 7.2 

Lime 24.6 

Nitrogen 2.7 

Phosphoric acid 13.2 

1 Bulletin 26, p. 65, Bureau of Soils. 

2 Bulletin 20, p. 78, Bureau of Soils. 



CHAPTER XL 



CHEMICAL CHANGES. 

The soil is not inert, but a great number of changes take place 
in it. some purely chemical, and others brought about by the 
action of bacteria and other forms of life. The most important 
changes have to do with organic matter and nitrogen. The bulk 
of the nitrogen in organic forms in soils is useless to plants, and 
must be changed before it can be taken up by them. Phosphoric 
acid and potash are fixed by the soil, and their compounds under- 
go various changes. 

Changes of Nitrogen in the Soil. Many changes take place in 
the nitrogen of the soil, all brought about by bacteria. There is, 
first, the transformation of organic nitrogen into ammonia, 
termed ammonification. Next is the change of organic matter, 
ammonia, and nitrites, to nitrates, a change called nitrification. 
Another change is 'the destruction of nitrates, either nitrites, 
ammonia, protein, or free nitrogen being formed, a change called 
dentrification. A further change is the production of organic 
compounds from the elementary nitrogen of the air, a change 
caled nitrogen fixation. As these changes are brought about by 
the agency of bacteria, it is necessary to give a little space to the 
study of soil bacteria. 

Soil Bacteria. 1 Bacteria are organisms so small as to be seen 
only under the highest power of the microscope. They are 
grown either in liquids or on the surface of slices of potatoes, 
solidified plates of gelatin, agar, or similar material, the proper 
nourishment being supplied. The plate method is used for isolat- 
ing and studying bacteria, since many kinds of bacteria form 
characteristic colonies, and a pure culture can easily be secured 
therefrom. Unfortunately many important soil bacteria do not 
grow well on such plates. This is especially true of the nitrate 
bacteria. Since bacteria abound everywhere, it is necessary 
in the study of bacteria to destroy all those which are originally 

1 Review of Investigations of Soil Bacteriology, Voorhees and Lipman, 
Bulletin 94, Office of Kxp. Sta. 



CHEMICAL CHANGES 



205 



present in the vessels or materials which are to contain those to 
be studied, and to guard as much as possible against contamina- 
tion from outside sources, such as the air. Bacteria may be pres- 




Fig. 48. Colonies of bacteria growing in a gelatine plate. Kansas Station. 

ent as spores which are a resting, or "seed" stage of bacteria, and 
are much more difficult to destroy than the growing bacteria. 

Methods. Forceps, cover slides, etc., are sterilized by heating 
in a bunsen burner. Glassware, such as flasks, beakers, pipettes, 
etc., and other articles which can be subjected to it, may be 
sterilized by dry heat one hour in an air bath or oven at a tem- 
perature of 170 C. In order to prevent contamination after 
sterilization, they are placed in closed vessels until needed. Flasks 
and pipettes may be plugged with cotton wool, which allows the 
entrance of air, but excludes bacteria. 



2O6 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

Distilled or tap water is sterilized by boiling. Boiling for five 
minutes will kill ordinary germs if no spores are present. Media 
are often sterilized by heating in steam at 100 C. Steaming one 
and one-half hours will sterilize any medium, but this injures 
some media, especially gelatin. The method adopted in such 
cases is to steam for 15 minutes on three successive days. This 
rests on the principle that all bacteria in the non-spored condition 
are killed the first day, while the spores which are not killed, 
develop into bacteria and are killed the second or third day. A 
rapid and effective method of sterilization consists of steaming 
under pressure at 115 C. from 7 to 15 minutes. 

A variety of media are used for growing bacteria, such as meat 
extract, broth, blood serum, milk, slices of potatoes, etc. 

Number of Bacteria. One method of estimating the number 
of bacteria in the soil is as follows : About a gram of the soil is 
shaken from a weighed tube into a liter of sterilized water, and 
the tube reweighed. The soil and water are then mixed thor- 
oughly. Tubes of modified agar 1 are then melted, and one inocu- 
lated with o.i cc. of water, another with i.o cc. The agar is then 
poured into flat dishes provided with a cover (petri dish) which 
have previously been sterilized, and, after the gelatin has 
hardened, it is set aside for the colonies to develop. This pro- 
cedure is termed plating. Each kind of bacterium that will grow 
upon the material used, produces a characteristic group or colony. 

The colonies are then counted. For example, if i cc. of water 
is used and 100 bacteria developed, the soil contains 100,000 to the 
gram, since the quantity of water used was shaken with o.ooi 
gram soil. 

The number of bacteria counted in this way in the soil is some- 
what variable ; from 8,000 to 6,000,000 per cubic centimeter have 
been found in the surface soil. The number decreases with the 
depth, until at the 5th to 6th foot comparatively few are found. 
The following is an example of such a test : 

1 P. E. Brown, Iowa Research Bulletin No. 2. 



CHEMICAL CHANGES 2O/ 

Number of bacteria 
Inches in one gram soil 1 

2 1 ,330,000 

4 1,500,000 

6 1,900,000 

8 260,000 

10 265,000 

12 124,000 

The number of bacteria so counted appears to have no direct 
relation to the ammonifying, nitrifying, or denitrifying power of 
the soil. Important groups of soil bacteria, such as the nitrify- 
ing, do not develop colonies at all. The bacterial count appears 
to be more closely related to the organic matter content than to 
anything else. If it is desired to study the bacteria further, the 
desired medium is inoculated with a portion of a colony grown on 
the plate. 

Another method- of estimating the number of bacteria consists 
in inoculating a series of suitable media from different dilutions 
of the soil, say equal to i mg., o.i mg., .01 mg., and .001 mg. of 
soil. Suppose that with ten tubes inoculated from .01 mg. soil, 
7 nitrify and 3 do not. Then we estimate that 7 bacteria were 
present in 10 times .01 mg. soil, or 7,000 are present in a gram. 
The solution for inoculating is prepared by shaking the soil with 
sterilized water as described above. 

Kinds of Soil Bacteria. 3 The general tendency of bacterial 
action in the soil is along well denned lines, although reverse 
changes occur and complicate the process. Organic matter, by 
decay or putrefaction, is finally converted into carbon dioxide, 
water, ammonia or nitrates, and mineral salts. Some soil bacteria 
produce organic matter from hydrogen or marsh gas and carbon 
dioxide, or use other inorganic materials (sulphur, or sulphides) 
as a source of energy, but, in spite of this, the general movement 
is as indicated. The general movement of organic nitrogen is 
towards the form of nitrates, through ammonia, in spite of the 
presence of bacteria which act in the reverse direction and con- 

1 Chester, Delaware Bulletin No. 65. 

- Wiley, Principles and Practice, Agr. Chem. Anal., Vol. i. 

3 Kansas Bulletin 117 ; New Jersey Bulletin 40. 



2C>8 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

vert nitrates into ammonia or bacterial substances, or ammonia 
into bacterial substance. Under special conditions favorable to 
the growth of the bacteria concerned, these reverse tendencies 
may predominate, or develop to such an extent as to materially 
modify the final results. 

The bacteria which affect the soil nitrogen are very important. 
Stoklosa 1 divides the bacteria into seven groups with respect to 
their action towards nitrogen : 

1 i ) Bacteria which decompose nitrogenous organic bodies and 
produce ammonia. 

(2) Bacteria which oxidize ammonia to nitrites. 

(3) Bacteria which oxidize nitrites to nitrates. 

(4) Bacteria which reduce nitrates to nitritec and ammonia. 

(5) Bacteria which reduce nitrates to nitrites and the latter to 
elementary nitrogen. 

(6) Bacteria which change ammonia, nitrites or nitrates into 
protein or bacterial body substance. This includes members of 
all the other groups. 

(7) Bacteria which fix atmospheric nitrogen and use it to 
form compounds. 

Bacteria have been found in the soil which take oxygen from 
sulphates, thus reducing them. Other bacteria are found which 
oxidize hydrogen sulphide to sulphates. 

As regards organic carbon there are two great classes of 
bacteria : 

(1) Those which oxidize organic carbon and produce carbon 
dioxide. 

(2) Those which reduce organic carbon and form marsh gas 
and solid products. Bacteria are also found in the soil which can 
utilize carbon dioxide and hydrogen to form organic matter, and 
there are also some which can use marsh gas. Bacteria which 
require oxygen are called aerobic, those which do best without 
oxygen, anaerobic. 

Ammonification. A large number of different bacteria and 
molds are capable of converting organic nitrogen into ammonia. 
1 Bulletin 94, p. 193, Office Exp. Sta. 



CHEMICAL CHANGES 2OQ 

Molds probably do the larger portion of the work in manure 
heaps and very peaty soils, but in ordinary arable soils bacteria 
predominate. Most of the bacteria which grow upon gelatin or 
agar are ammonifying. 

Bacterium mycoides, which appears to be the most im- 
portant, decomposes albumen with the production of ammonium 
carbonate and small quantities of formic, acetic, and butyric 
acids, carbon dioxide, and other products. It requires the pres- 
ence of oxygen; otherwise it reduces nitrates, if present, to 
nitrites or ammonia. The optimum conditions for its activity 
are a temperature of about 30, complete aeration, slightly alkaline 
medium, and a slight concentration of the nitrogenous substance 
in solution. 

The moisture and temperature conditions of the soil play a 
prominent part in determining the character of the bacterial flora, 
and hence also the character of the chemical products formed. The 
mechanical and chemical constituents of the soil are also of de- 
cided influence. Heavy clay or loam soils contain a greater num- 
ber and variety of anaerobic organisms than light sandy or sandy 
loam soils under the same conditions. But aerobic and anaerobic 
bacteria are found in both kinds of soils. Aerobic organisms may 
produce conditions favorable to the growth of anaerobic 
organisms. Ammonification in the soil is due, at times, to processes 
partaking largely of the nature of decay, and at other times of 
putrefaction. By decay we mean the complete volatilization of 
the organic matter, while in putrefaction ill-smelling bodies are 
found. 

Study of Ammonification. Ammonification may be studied in 
culture solutions, or in soils. The former is better adapted to 
certain bacteriological studies, but methods which involve the use 
of the soil approach more closely to natural conditions. In either 
case, at the end of a definite period of time, the extent of the pro- 
cess is compared by an estimation of the quantity of ammonia 
formed. 

Brown, 1 for example, uses a culture solution composed of 10 
1 Iowa Station Research Bulletin No. 2. 



210 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

grams, peptone in 1,000 cc. distilled water. He shakes 100 grams, 
soil with 200 cc. water, niters, and inoculates 100 cc. of the 
sterilized culture solution with 20 cc. of the nitrate. Ammonia 
is determined in the culture after incubation for six or seven 
days. When soil is to be used as a culture medium, 100 grams. 
air-dried soil are mixed with 5 grams, dried blood or 5 grams, 
cottonseed meal and 5 grams, water and inoculated with 20 cc. 
soil infusion, and incubated as before. 

Various conditions which affect the process of ammonification 
can be studied in this way, such as the temperature, character of 
medium, time of incubation, kind of bacteria, etc. If pure cul- 
tures of different bacteria are compared, it is of course necessary 
to estimate the number of bacteria in the liquid used for inocula- 
tion, according to the method already outlined. Two important 
ammonifying bacteria are Bacillus mycoides, and Proteus vul- 
garis, but a large number of bacteria take part in this process. 

The ammonifying power of the soil has been defined by some 
workers as the quantity of ammonia produced on inoculating a 
definite quantity of a suitable culture medium with a definite 
quantity of soil, and incubating under definite conditions. Am- 
monifying power measured in this way depends upon the number 
and activity of the bacteria in the soil at the time of inoculation, 
and will be affected by anything which affects them, such as the 
soil temperature, its moisture, kind and quantity of food present, 
character of soil, etc. In carrying out such tests, it is exceedingly 
important that the soils studied be kept under comparable condi- 
tions as regards these varying factors, so that only one factor, the 
one being studied, is variable. Ammonification in soils is, how- 
ever, quite different from ammonification in solution. 

Nitrification. Nitrification takes place in two stages: nitrates 
are first formed from ammonia, and then changed to nitrites, 
Two kinds of bacteria have been isolated, namely, the nitrous and 
the nitric organisms. 

The bacteria which oxidize nitrites to nitrates may be isolated 
from the soil without any great difficulty. 1 A solution is pre- 
pared as follows: 

1 Wiley's Principles and Practice of Agricultural Analysis, Vol. i. 



CHEMICAL CHANGES 



211 



Distilled water 1,000 cc. 

Potassium phosphate i gram 

Magnesium sulphate 0.5 " 

Calcium chloride trace 

Potassium nitrite 0.2 gram 

After sterilization, 100 cc. of the solution is inoculated with 
about o.i gm. moist soil. This medium is unfavorable to all 
bacteria except the nitrate organism. After the nitrate organism 




Fig. 49.- Microscopic appearance of nitrous bacteria. Winogradski. 

has developed, as shown by the formation of nitrates and the 
weakening or disappearance of the nitrous acid, a few drops of 
the culture are diluted with sterilized water, and fresh portions of 
the medium seeded with single drops of the diluted culture. Some 
of these cultures will probably contain only the nitrate organism, 
but at any rate, the other bacteria can be eliminated by a few 
more cultures. The purity is tested by plating with a 
drop from each culture. The nitrate organism does not 



212 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



grow on gelatin or agar, so that if no colonies appear, 
the solution is probably free from contaminating bacteria. 
The growth of these organisms produces scarcely any change in 
the appearance of the solution. After staining with coloring 
matter, the organisms may be seen under the microscope as 
minute, peanut-shaped bacteria. They are termed Nitrobacter. 






: -^r *-..-.$ 



" 



,'.:'- 



- < : %^A . 

s*' s '*&*&.** 

5* ^'* if ^^ 

^S/^J 



Fig. 50. Microscopic appearance of nitric bacteria. Winogradski. 

The nitrous organism, which converts ammonia to nitrites, is 
much less easily isolated than the nitric organism, for the reason 
that other bacteria will grow along with it, and also because 
it does not grow well on agar or gelatin plates. Winogradsky 1 
was finally successful in isolating it. He first cultivated the 
bacteria in a medium of the same composition as that given above, 
except the potassium nitrite was replaced by about 2 parts per 
thousand of ammonium sulphate. A little magnesium carbonate 
1 Wiley's Principles and Practice, Vol. i. 



CHEMICAL CHANGES 213 

was also added. Silica medium was prepared by treating water 
glass (sodium silicate) with hydrochloric acid, and dialyzing in 
distilled water until free from salts. The solution of silica was 
then concentrated, nutrient salts added (in proportions referred 
to above), and the liquid seeded with one drop of the culture 
mentioned above. The mixture was poured into a sterilized 
petri dish, and a drop of a saturated solution of salt added to 
coagulate the silica. This mineral jelly was very unfavorable to 
the growth of any except the nitro-organisms. 

The bacteria grow as very small colonies, but on the surface 
they form a white crust. Stained with dye, and examined under 
the microscope, they appear as round or roundish organisms. 
Winogradsky separated three varieties of nitrous bacteria : Nitro- 
somonas europaea from Europe, Nitrosomonas javanesis from 
Java, and Nitrosococcus from America. 

Study of Nitrification. Nitrification may be studied in culture 
solutions, or in the soil, and each method has its advantages for 
certain kinds of work. 

A culture solution may be prepared as follows i 1 

Distilled water 1,000 cc. 

Ammonium sulphate 2.0 gram 

Potassium phosphate I .o " 

Magnesium sulphate 0.5 " 

Ferric sulphate 0.4 " 

Sodium chloride 2.0 4< 

To each 100 cc. portion, i.o gm. magnesium carbonate is added. 
The solution is inoculated with a small amount of soil, or with 
soil extract, and incubated for 25 to 50 days. The quantity of 
nitrous and nitric nitrogen is then estimated. This method may 
be used for studying the effect of temperature, light, etc., or for 
estimating the inoculating power of soils held under different 
conditions. The differences in the effect of soils inoculated into 
different solutions will, of course, be due to differences in the 
number and activity of the organisms in them. 
1 Lipman, Report New Jersey Exp. Sia., 1907, p. 176. 



214 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

If a soil is to be used, 1 it is mixed with a small amount of am- 
monium sulphate, cottonseed meal or some other nitrogenous 
material, and water. Fresh moist soil may be used, or air-dry 
soil, which is inoculated with other soil to furnish the bacteria. 
It is hardly practical to sterilize the soil by heat, as this changes 
its chemical character decidedly. After incubation for a period 
of 30 to 50 days, nitrates are estimated in the soil. Nitrification 
in the soil is different from nitrification in solution. Cottonseed 
meal added to a soil will nitrify, while if added to solution, it will 
putrify. 2 

Nitrification, ammonification, and similar soil activities, may be 
studied with respect to the soil, or with respect to the organisms. 3 
Nitrifying capacity 4 may be defined as the capacity of a soil to 
serve as a medium for the growth of nitrifying organisms, com- 
pared with a standard soil, both soils being provided with equal 
members of bacteria of the same activity, with equal amount of 
nitrogenous compounds, and kept under similar conditions. 
Nitrifying power may be defined as the ability of a soil to set up 
nitrification in a soil or culture medium inoculated with it, and is 
a measure of the number and activity of the organisms in the soil. 
Similar terms may be applied to other bacterial activities. 

Conditions Favorable for Nitrification. The conditions favor- 
able for the development of the nitrifying organisms, as 
established by experiments, are as follows : 

(1) Suitable Food. Potash, phosphoric acid, lime, sulphates, 
and carbon dioxide appear to be essential. 

(2) Presence of Base. The nitric acid must be neutralized, as 
the organisms will not thrive in an acid medium. Calcium car- 
bonate or sodium bicarbonate are effective. Too much base is 
injurious. 

(3) Suitable Temperature and Moisture. Nitrification is 
most active at 36. It almost ceases at low temperatures. 

1 Am. Chem. Jour., 1903, p. 225 

2 Report North Carolina Exp. Sta. 1902-3, p. 27. 

3 Stevens and Withers, Proc. Ass. Off. Agr. Chem., 1909, p. 34. 

4 Texas Bulletin, 106. 



CHEMICAL CHANGES 



21 



(4) Absence of Strong Light. Light suspends the action of 
the organisms and finally destroys them. 

(6) Freedom from Excess of Salts. Ammonia chloride, car- 
bonate, calcium chloride, or other salts in excessive amounts 
inhibit its action. 

Physical Conditions. The three most important physical con- 
dition which affect nitrification are, looseness of the soil, tempera- 
ture, and water content. 

A loose and porous condition of the soil is more favorable to 
nitrification than a compact condition. Thus, a soil under cul- 
tivation allows more nitrification than the same soil in pasture. 
Stirring a soil also favors nitrification. For example. King 
obtained the following results in 285 days : 





Nitric nitrogen per acre foot 


Cultivated 
weekly 


Cultivated 
every two 
weeks 




Pounds 

326 

218 

323 

441 

387 


Pounds 

326 
213 
I 99 
401 
245 













The temperature also has a decided effect upon nitrification, as 
is shown by the figures of King and Bertz obtained in 27 days, 
expressed as nitric nitrogen in parts per million of soil. 



Temperature 
degrees F. 



34 
50 
70 
9 



Parts 
per million 

... 6.5 
7-7 
." 14.3 
... 29.1 



Nitrifying organisms, like other living things, have a minimum, 
maximum, and optimum temperature of existance. The mini- 
mum seems to be about the freezing point of water, and the 
maximum about 45 C., the optimum about 35 C. 

Production of Ammonia and Nitrates in the Soil. The produc- 
tion of active nitrogen in the soil depends upon the nature of the 



2l6 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



soil, and the conditions surrounding it. Nitrification and am- 
monification, if too slow, will not provide the growing plant with 
sufficient food ; if nitrification is too rapid, the excess of nitrates 
may be washed out and lost, thereby diminishing the productive 
power of the soil. 

The following is an illustration of the effect of moisture : 
EFFECT OF WATER ON PRODUCTION OF ACTIVE NITROGEN. 1 





Soil A 
Relative production of 


Soil B 
Relative production of 


Nitric 
nitrogen 


Nitric 
and ammonia 
nitrogen 


Nitric 
nitrogen 


Nitric 
and ammonia 
nitrogen 




72 
100 
76 

o 
o 


101 
100 
106 
70 
35 


135 
IOO 

189 

16 

18 


104 
IOO 
III 

7 
60 


ila " " 


C/Q " " 


o/y 

7/0 " " 


//V 
o/o " " 


9/9 



The most favorable amount of water for the production of 
nitrates in the first soil was 3/9 of its capacity. Little or no 
nitrification took place when the soil was very wet, though a con- 
siderable amount of ammonia was produced. Plants which grow 
in swamps or saturated soils must secure their nitrogen from am- 
monia or organic bodies. 

Nature of the Soil. By the nature of the soil is meant the 
complex of physical and chemical properties which make up the 
soil properties. Which of these properties are of predominating 
influence in the production of active nitrogen, remains to be ascer- 
tained. 

The nature of the soil has a decided effect upon the course of 
nitrification within it. Different soils when placed under similar 
physical conditions, and provided with an equal number of 
nitrifying organisms and the same food for them, produce differ- 
ent quantities of nitrates. The quantity of ammonia and nitrates 
together which is formed is not, however, so different. The 
following table shows the differences in some soils in the produc- 
tion of nitrates and ammonia: 
1 Fraps, Texas Station Bulletin 106. 



CHEMICAL CHANGES 



EFFECT OF NATURE OF Son, ON PRODUCTION OF NITRATES 

AND AMMONIA. 1 





Rank t 


ased on 


Soil 


Nitric 
nitrogen 


Nitric 
and ammonia 
nitrogen 




IOO 






42 


O4 




14 


V4 

84 








/o ' 
76 




77 

7O 









We find that while these soils varied from 100 to 5 in nitrify- 
ing capacity, the production of active nitrogen (nitrates and am- 
monia) varied only from 100 to 70. When the production of 
nitrates alone is considered, the soils vary greatly, but if nitrates 
and ammonia together are taken, the differences are much smaller. 
If nitrates are much more valuable to plants than ammonia, these 
differences are very important, but if there is little difference in 
the value of the two, soils under favorable conditions do not 
vary greatly in their power to supply nitrogen from the same 
organic bodies. According to Russell 2 plants on cultivated soils 
probably absorb all their nitrogen as nitrates. There is no doubt, 
however, but that plants have the power of absorbing ammonia, 
and that ammonia is present in the soil, though ordinarily it is 
present only in a small quantity. 

Effect of Chemical Additions to Soil. While carbonate of lime 
as a rule accelerates nitrification, it has little effect upon the total 
production of ammonia and nitrates together. Its use may result 
in the production of nitrates in excess of the needs of the crops, 
and consequent loss of fertility to the soil. 

Additions of fertilizing materials to the soil (acid phosphate, 
sulphate of potash) may increase or decrease the production of 
nitrates, but they have little effect upon the total active nitrogen 
produced. 

1 Fraps, Texas Station Bulletin 106. 
' 2 Soil Conditions and Plant Growth, p. 108. 
15 



2l8 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

Nature of the Material. Some substances are more easily 
attacked than others by the organisms whose final products are 
nitrates. While the importance of this fact is chiefly to be con- 
sidered in reference to organic nitrogenous fertilizers, yet it is 
necessary to bear in mind that the organic nitrogenous compounds 
of the soil may vary decidedly in the resistance which they offer to 
the nitrifying organisms. Probably in any soil, the less resistant 
compounds are oxidized first, and the remainder at a decreasing 
rate from year to year, so that the effect is a continual diminish- 
ing of the nitrates produced for the use of plants, unless measures 
are taken to introduce fresh nitrogenous material susceptible to 
nitrification. 

Denitrification. The term denitrification is applied to the 
destruction of nitrates. If an extract of stable manure is added 
to a solution of potassium nitrate, and kept at a favorable tem- 
perature, the nitrates in time will disappear entirely. 

Under certain circumstances the nitrates in the soil are de- 
oxidized with the production of organic bodies, nitrites, ammonia, 
or even free nitrogen. In the latter case there is a loss of nitro- 
gen from the soil. We have already seen that the bacteria which 
change organic nitrogen into ammonia require oxygen, otherwise 
they will take oxygen from nitrates. The conditions favorable 
for denitrification are as follows : 

(1) Insufficient Oxygen. In water-clogged soils, or soils which 
are so compact that air cannot penetrate them, denitrification will 
take place. 

(2) Presence of an Excess of Vegetable Matter. Cases are 
known in which a heavy application of manure destroyed the 
nitrates in the soil, and produced a smaller crop than if no manure 
had been used. Some believe that the denitrifying organisms 
introduced with the manure are the cause of the denitrification, 
but as has been pointed out by Waririgton and others, farm manure 
introduces into the soil another factor of importance, namely, 
a large increase in oxidisable organic matter, and this may favor 
denitrification both by lessening the gaseous oxygen and by tend- 
ing to rob the nitrates of their oxygen. Undoubtedly the 



CHEMICAL CHANGES 2IQ 

organisms are essential to the process, but they cannot thrive un- 
less the conditions are favorable to their activity, whether they 
are already present in the soil, or introduced in the manure. Such 
conditions are, either a diminished supply of oxygen, as by con- 
solidation of the soil or by saturation with water, or a very large 
quantity of oxidizable organic matter. 

Lipman 1 determines the "denitrifying power" of a soil by seed- 
ing 10 grams, of it into 100 cc. of a neutral solution containing 
definite amounts of nitrates, dextrose, citric acid, and nutrient 
salts. When the nitrates have disappeared (in about 10 days); 
the total nitrogen is estimated in the solution. The percentage of 
nitrogen lost from the various cultures is taken as a measure of 
denitrifying power of the soil. The solution used is as follows : 

1,000.0 cc. water 

2.0 grams magnesium sulphate 

2.0 " potassium phosphate 

i.o " potassium nitrate 

0.2 " calcium chloride 

5.0 " citric acid 

2.0 drops 10 per cent, ferric chloride. 

Neutralize while boiling with sodium hydroxide and add 2 
grams dextrose. 

The soil may also be used as a medium in which to grow the 
bacteria for the study of denitrification. 

Assimilation of Nitrates and Ammonia. By growing plants in the 
solution of a nitrate, it is easily proved that they have the power to 
absorb it, and as the plant grows vigorously (when other necessary 
elements are present), the nitrogen must be in a form to be 
utilized. The nitrate ion may be completely removed from solu- 
tion when the other nutrients are present. Plants have also the 
power to take up an excess of nitrates. Small amounts of nitrates 
are often found in plants. An instance is on record in which corn 
took up so much that crystals of potassium nitrate would fall out 
when the stalk was rapped on a table. Nitrates appear to be a 
form of nourishment most eminently fitted to all cultivated 
plants. They are easily and rapidly taken up by plants. All 
1 Report New Jersey Exp. Sta., 1907, p. 179. 



22O PRINCIPLES OF AGRICULTURAL CHEMISTRY 

compounds of nitrogen placed in the soil tend to change to 
nitrates. 

The absorption of ammonium salts by the roots of plants 
can be shown in the same way, as for nitrates, namely, 
by growing plants in solutions containing the salts. There 
can be no doubt that plants absorb ammonia. To decide 
whether ammonium salts can serve satisfactorily to produce 
organic matter, is more difficult, since transformation of 
the ammonia to nitrates must be excluded. Hampe grew 
corn in solution containing ammonium salts and other 
nutrients, which were repeatedly changed to exclude nitri- 
fication. The corn was apparently not nourished well at 
first, but later grew well. Kuhn and Wagner obtained 
similar results. Muntz deprived a soil of nitrates by washing, 
fertilized with ammonium salts, and took proper precautions, to 
prevent nitrification. Corn, beans, barley, and hemp attained a 
normal development, and their growth could only be attributed 
to the influence of the ammonium salts used as a fertilizer. Other 
experiments in the same direction could be cited. We must con- 
clude that ammonium salts, as such, serve as nourishment for 
plants. 1 

Fixation by Bacteria. Besides the bacteria which fix nitrogen 
in connection with legumes, other nitrogen fixing bacteria occur 
in the soil. 

These bacteria are not easily isolated, but may be separated 
by the dilution method. They may also be separated by 
plating. 2 The chief nitrogen-fixing bacteria are Chlostridum 
Pasteurianum and species termed azotobacter. Under favorable 
conditions, they decompose from 100 to 200 grams sugar for 
each gram nitrogen fixed. 

Nitrogen fixing power is estimated by Lipman 3 by inoculating 
loo cc. of the culture solution given below with 10 grams of soil. 
After incubating 10 days at 28"" C. the total nitrogen is estimated, 
the nitrogen in a portion of the original culture solution having 

1 Jour. Agr. Science 3, p. 179. 

2 Bulletin 66, Delaware Exp. Sta. 

3 Report New Jersey Exp. Sta., 1907, p. 181. 



CHEMICAI, CHANGES 221 

previously been estimated; the gain in nitrogen is a measure of 
the nitrogen-fixing power. 

The culture solution is prepared as follows: Water 1,000 cc. 
mannite 15 grams; potassium phosphate 5 grams; magnesium 
sulphate 0.2 grams; calcium chloride 0.02 gram; and ferric 
chloride, 2 drops of a 10 per cent, solution. The solution is then 
made alkaline with sodium hydroxide, and sterilized. Brown re- 
ports that much more satisfactory results may be secured by the 
use of a'soil as the medium for the culture. 

We have as yet no evidence that the quantity of nitrogen 
assimilated by these bacteria, is of importance under ordinary 
agricultural conditions. 

Experiments at the New Jersey Experiment Station 1 indicate 
the possibility of the addition of nitrogen to the soil in this way. 
An analysis of the soil at the beginning and end of two years, 
together with the estimation of the nitrogen in the crops har- 
vested, showed an undoubted gain of nitrogen. 

Assimilation of Elementary Nitrogen by Legumes. The fact 
that certain kinds of plants can utilize atmospheric nitrogen was 
not discovered until about 1882. At that time, Hellriegel 2 
demonstrated this fact by experiments described briefly as 
follows : 

Lupine seed were planted in pots of soil which had been heated 
sufficiently to destroy all forms of life in it, and which had been 
subjected to analysis so that the exact amount of nitrogen present 
in the quantity of soil taken was known. All the pots were pro- 
tected from bacteria and watered with sterilized water. To one 
series of pots, there was added a small amount of an aqueous 
extract from a soil in which lupines had grown well. To the 
other series, no addition was made. When the plants were 
grown, they were dried, and weighed. The quantity of nitrogen 
in the plants, and in the soil remaining in the pots, was determined 
by chemical analysis. As the nitrogen originally present in soil 

1 Report for 1907, p. 168. 

2 Exp. Sta. Record 5, p. 835. 



222 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

and seed was known, the loss or gain of nitrogen could then be 
easily calculated. Some results are as follows : 





No addition 


Soil 
extract added 




Grams 
I OI 


Grams 
4.O ^ 


Gain -I- or loss of nitrogen 


O OO7 


I T QC 









The experiment showed not only that the lupine could utilize 
the nitrogen of the air, but proved that the soil extract contained 
something which brought it about. Observations showed that 
the lupines assimilate nitrogen only when nodules are present on 
their roots. Examination of the nodules showed that they con- 
tained bacteria, and further experiments, similar to the one 
described above, proved that plants grown in soil inoculated with 
these bacteria evolved nodules and attained the power of 
assimilating elementary nitrogen. By experiments similar to 
those we have described, it was proved that alfalfa, vetch, clover, 
cow peas, and other leguminous plants have the power of utilizing 
the free nitrogen of the air when the proper bacteria are present ; 
but corn, wheat, oats, and most plants other than legumes, can 
take up only nitrogen in combination. 

Formation of the Tubercles. When a lupine seed is planted in 
inoculated soil free from combined nitrogen, the plant grows 
until the nutrient in the seed is consumed, then ceases to grow, 
and shows all signs of nitrogen starvation. In the meantime, 
tubercles are forming on its roots. In a few days, it begins to 
grow vigorously, and appears to possess an abundance of nitro- 
gen. The tubercles themselves pass through three stages. There 
is first vigorous growth, producing the tubercle filled with large 
numbers of small, rod-like bacteria; then the bacteria change to 
bacteriods, assuming a T or Y form; and finally the bacteriods 
begin to disappear and after a little they are absorbed almost com- 
pletely by the substance of the plant and the tubercles are left as 
empty pouches. The plant begins to receive benefit from the 



CHEMICAL CHANGES 223 

nodules when the bacteria assume the bacteriodal form. That the 
plant receives nitrogen from the tubercles is shown by analyses 
by Stoklosa 1 at different stages of growth : 

Nitrogen in 
tubercles 
Lupines Per cent. 

Flowering stage 5.22 

Fruit forming 2.61 

Plant mature 1.73 




Fig. 51. Branched bacteria from a clover nodule. 

The percentage of nitrogen in the tubercles becomes less as 
they grow older. 

Effect of Conditions on Tubercle Formation. The conditions 
here discussed are: (i) nature of the bacteria; (2) effect of 
fertility of the soil; (3) effect of salts. 

Nature of Bacteria. The more active the bacteria, the less 
quickly do they assume the bacteroidal form; the stronger the 
plant, the more easily it causes this change. A strong plant may 
indeed prevent the entrance of the bacteria into its roots and con- 
sequently no nodules will be formed. The nature of the bacteria 
seems to be modified by the host plant. That is to say, the 
bacteria in the nodules of one plant may not inoculate other plants 
very well ; it may produce nodules upon them, but not of such size 
1 Exp. Sta. Record 7, p. 922. 



224 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

or ir such numbers as on its parent plant. For example, the 
alfalfa tubercle bacterium will not readily inoculate red clover at 
first, but in the course of two or three generations, the bacterium 
may become accustomed to another plant. It is quite possible, 
however, that there are several kinds of these bacteria. 

Effect of Salts. Marchal 1 found that, in water culture, the 
formation of tubercles on peas was checked by solutions of the 
following strengths : Alkaline nitrates 0.05 per cent. ; ammonium 
salts 0.05 per cent. ; potassium salts 0.05 per cent. ; sodium salts 
0.33 per cent. ; calcium and magnesium salts and phosphoric acid 
favored their production. 

Effect of Fertility of Soil. As a general rule, the more nitro- 
gen can be taken from the soil by the plants, the less is taken 
from the air. Hellriegel found that the best development and 
largest number of tubercles are attained in a soil quite free from 
nitrogen, while if the soil contains very much nitrogen, the forma- 
tion of tubercles may be entirely suppressed. This is probably 
due to the fact that the plants are too vigorous to allow the 
entrance of the bacteria. The following examples are from pot 
experiments with alfalfa by Hopkins. 2 The difference in the 
nitrogen in the crops grown in inoculated and in uninoculated pots 
is taken to represent the gain through the agency of the bacteria. 

Gain per acre 
Pounds 

No addition 46 

With lime 33 

With lime and nitrogen 8 

With lime and phosphoric acid 55 

With lime, phosphoric acid and nitrogen 9 

With lime and potash 38 

With lime, potash and nitrogen 9 

In every case the addition of nitrogen to the soil decreases the 
amount taken from the air. It must not be understood that the 
crop decreases also. In many cases the crop is larger, but most of 
the nitrogen in it comes from the soil instead of the air. 

1 Exp. Sta. Record 13, 1017. 

2 Bulletin 76, Illinois Sta. 



CHKMICAL CHANGES 



225 



How the Nitrogen is Assimilated. There are three possibili- 
ties : ( i ) The bacteria secrete an enzyme which causes the plant 
to assimilate nitrogen through its leaves; (2) the bacteria 
assimilate the nitrogen and are then consumed by the plant; (3) 
the bacteria assimulate nitrogen and give it off as soluble com- 
pounds, which are taken up by the plant. 




Fig. 52. Nodules on the roots of the soy bean. 

The following facts are related to these theories: (i) As 
observed by Hellriegel, in a medium free from nitrogen the plant 
ceases to grow while the nodules are developing, then suddenly 
begins to grow vigorously as if it had a new source of nitrogen. 
(2) Young nodules contain more nitrogen than old ones. 



226 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 








Fig. 53. Peas without nitrogen (KP) grow as well as with nitrogen 
(KPS) but oats do not. Wagner. 



CHEMICAL CHANGES 



227 



Further, the plant absorbs the bacteria, and they disappear. 
(3) Nobbe and Hiltner found that the stronger the plant, the 
greater the resistance it offers to inoculation, and the sooner the 
nodules are emptied. 

Exactly how the nitrogen is transferred from bacteria to plant 
is not known. 

Inoculation of Legumes. When a legume is planted in new 
localities, the bacteria suitable to it may not be present to aid it 




Fig. 54. Showing difference in the growth of alfalfa caused by 
inoculation with bacteria. Illinois Station. 

in the assimilation of nitrogen. The safest plan is to inoculate 
the soil with the proper bacteria. There are two methods of doing 
this. 

(i) The first method consists in inoculating with soil from a 
field where the plants have been growing well. This is the surest 
method, but open to some objections. Freight charges on the 
soil may be expensive ; the soil may be difficult to secure ; injurious 
insects or diseases or weeds are likely to be brought into the soil. 



228 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

(2) The second method 1 consists in inoculating the soil or seed 
with a pure culture of the necessary organisms. This method 
was patented in Germany in 1880, but did not prove a commercial 
success. The method has been modified, and cultures are 
now upon the market. Pure cultures of the symbiotic 
bacteria may easily be prepared by inoculating a suitable 
sterilized culture medium with the bacteria. The bacteria 
are sent in a sealed tube ; before inoculating the seed or soil their 
number is increased by allowing them to multiply in a large quan- 
tity of water provided with necessary salts and sugar. The seed 
are then soaked in this liquid, dried, and planted, or the liquid is 
mixed with soil and the soil distributed and plowed under. 

The necessary bacteria are so generally distributed that it is 
often unnecessary to inoculate the soil. They grow not only upon 
cultivated plants, but also on many varieties of wild plants. 

Changes of Organic Matter. The organic matter in the soil 
consists of the unchanged residues of plants and animals, and the 
products formed from them by bacteria and other forms of life. 
Decay takes place in two directions, according to the presence of 
an abundance or a deficiency of air. 

In the presence of an abundance of air, decay is oxidation; the 
final products are water, carbon dioxide, ammonia, and nitrates, 
while the mineral material is left in forms which can be assimi- 
lated by plants. 

In the presence of little or no air, decay is a reducing process, 
oxygen is taken away from nitrates, or the higher oxides of man- 
ganese or rron. Gaseous products, such as carbon dioxide, marsh 
gas, hydrogen, and free nitrogen, are produced in comparatively 
srmll quantities and slowly. The organic material is converted 
into highly resistant bodies which hold their mineral content in 
forms not assimilable by plants. The vegetable matter is con- 
verted into brown substances, partly soluble in water and impart- 
ing a brown color to it. The compounds produced are acid sub- 
stances, somewhat antiseptic in nature and retard the decay of the 
vegetable matter. The oxygen required for the production of 
1 Progress in Legume Inoculation, Farmers' Bulletin 315, U. S. D. A. 



CHEMICAL CHANGES 



229 



carbon dioxide comes partly from easily reducible substances 
containing it, partly from the substance itself. In consequence 
of this loss of oxygen, the substance becomes richer in carbon. 
The following analyses 1 of three samples of peat of different ages 
show this enrichment in carbon : 
PERCENTAGE COMPOSITION OF ASH-FREE PEAT OF DIFFERENT AGES. 





Brown peat 
from surface 


Black peat 
at 85 inches 


Black peat 
from 1 70 inches 




57-75 
5-43 
36.02 
0.80 
2.72 


62.02 
5-21 
30.67 
2.IO 
7.42 


64.07 
5-01 
26.87 

4-05 
9.16 








Ash 





The older the peat, the richer it is in carbon and also in 
nitrogen. 

Conditions of Decomposition of Organic Material. Various 
experiments have been made to study decomposition of the 
organic matter of the soil. Many experiments have been 
carried out by Wollny 2 with the following method: A 
mixture of sand or earth and the organic material was placed in 
U tubes, moistened with water, and kept in a constant tempera- 
ture bath. The carbon dioxide formed was drawn out every 24 
hours and collected in a solution of barium hydroxide of known 
strength. The unused barium hydrate was treated with standard 
acid, and the quantity of carbon dioxide evolved calculated. 

The following are some of the results of these experiments : 

1 i ) Effect of Ratio of Organic Matter to Soil. Varying quan- 
tities of powdered horse dung were added to the same quantity of 
sand, other conditions remaining the same. The oxidation was 
decreased when the carbon dioxide formed exceeded certain 
limits, and was less rapid, the greater the proportion of organic 
substance. 

(2) Effect of Fineness of Division. These experiments were 
made with peat and with pea straw of different degrees of fine- 

1 Detmer, Landw. Versuchs-stat., 1871. 

2 Die Zersetzung d. Organischen Stoffe. 



230 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

ness. The finer the more difficultly decomposed substance, 
the more rapidly it oxidized. Easily decomposed substances, pea 
straw for example, did not oxidize more rapidly when finely 
divided. 

(3) The Stage of Decomposition of the Material. The more 
decomposed the substance, the less rapidly it is oxidized. The 
following figures are some results of Wollny: 

Volume of 

carbon dioxide 

per 100 volume of 

soil atmosphere 

Cattle manure, fresh 13-43 

Cattle manure 8 weeks old 11.71 

Cattle manure 20 weeks old 8. 25 

Peat 0-8 inches deep 2.93 

Peat 9-19 inches deep 2.72 

Peat 19-31 inches deep 2.55 

Peat 31-43 inches deep 2.39 

Peat 43-55 inches deep 2.26 

It is natural to expect the more easily oxidized material to dis- 
appear rapidly, and the more resistant materials at a slower rate. 

(4) Chemical Composition. Leguminous straws, on account 
of the presence of more proteids, are oxidized more rapidly than 
cereal straws. Waxy material hinders the decomposition of turf ; 
when it is removed by extraction with ether or alcohol, the ex- 
tracted turf is much more rapidly oxidized than the unextracted. 
Tannic acid decreases oxidation; rye straw, corn fodder, and soja 
bean leaves soaked in tannic acid were oxidized less rapidly than 
the untreated substance. The addition of plant food may 
accelerate the oxidation. 

(5) Animal residues oxidize more rapidly than vegetable 
residues. Green materials oxidize more rapidly than the same 
material dried and moistened. 

(6) The oxidation decreases with the supply of oxygen, though 
not proportional to the supply ; when the supply decreases beyond 
certain limits, the oxidation drops rapidly. 

(7) Temperature. The relative effects of different tempera- 
tures is shown by the following experiment on a compost mix- 
ture: 



CHEMICAL CHANGES 23! 

Temperature. Relative amount 

Degrees C. of carbon dioxide 

10 2.8 

20 ; 15.5 

30 - 3 6 - 2 

40 42.6 

50 76.3 

(8) Moisture. The oxidation goes on most rapidly at a cer- 
tain moisture content, which depends on the material. Increase 
or decrease of moisture causes decreased oxidation. 

(9) Character of Soil. The character of the soil has a great 
effect upon the changes of organic matter. The various factors 
which affect the decomposition may support or counteract one 
another, and the effect is due to the predominating quantitative 
relations. The easy permeability and more rapid warming up of 
quartz sand are favorable to the decomposition of organic matter, 
while its low water capacity is a retarding factor. Hence the 
supply of moisture is the controlling factor in organic decomposi- 
tion in a sandy soil. In humid regions, the decomposition may 
proceed so rapidly in such a soil that organic matter does not 
accumulate to any extent. In a dry climate, decomposition pro- 
ceeds more slowly than where sufficient moisture is present, but 
more rapidly in a sand than in other kinds of soil. 

Clay soils retain plenty of water, but there is a deficiency of air, 
and these soils are essentially cold. The decomposition of organic 
matter in clays is thus determined by the temperature and per- 
meability to air, and proceeds slowly under ordinary conditions. 
In humid regions, compact clays may exclude the air to such an 
extent that putrefaction predominates. Heavy rains may discon- 
tinue oxidation in clay soils, and bring about deoxidation pro- 
cesses, among them denitrification. 

(10) Vegetation. Oxidation of organic matter appears to go 
on much more rapidly in a bare soil than in a soil covered with 
vegetation. A straw mulch decreases oxidation, but not as much 
as a covering of vegetation. The following results of Wollny 
illustrate this point : 



232 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



AVERAGE OF 19 SUMMER WEEKS. 

Volume of 

carbon dioxide 

in 1,000 volumes air 

Under grass 2.1 

Under straw mulch 7.2 

Bare soil 9.4 

The thicker the plants, the greater their effect in reducing 
oxidation. The following experiment of Wollny show this fact : 

Volume of 
carbon dioxide 
Number of plants in 1,000 volumes air 

3 oats to o.i meter 5.0 

6 oats to o. i meter 3.4 

12 oats to o.i meter 2.3 

24 oats to o.i meter. ' 1.9 

The difference appears to be largely due to the drying out of 
the soil by the plants. 

A covering of vegetation thus conserves the organic matter of 
the soil ; cultivation and bare fallow decrease it. 

Value of Humus. The chief chemical action of humus results 
from its solvent action, and the solvent action of the carbon 
dioxide which it produces in its decomposition. Water contain- 
ing carbon dioxide has a much greater solvent power on minerals 
than pure water. This is illustrated by the following experi- 
ments of Dietrich. 

MINERAL MATERIAL DISSOLVED BY SOLVENTS. 





Distilled 
water 


Water con- 
taining carbon 
dioxide 




Gram. 


Gram 


Basalt 


u.u^y 


o 298 




o 012 














0.340 



The addition of humus (turf) to the soil increases its water 
capacity. 



CHEMICAL, CHANGES 233 

Water capacity 
in volume per cent. 

Loam 34.4 

3^ loam and X peat 39-Q 

Sand 11.7 

Sand ^ and peat # 22.7 

Except with soils very rich in humus, the greatest production 
will be secured only by extensive use of manures rich in organic 
matter, or other measures suitable to enrich the soil in humus 
materials. 

Action of Carbon Bisulphide on Bacterial Change. 1 Carbon 
bisulphide applied to the soil during the growing season may 
destroy or injure the crop, but if it is applied some time before 
planting, it increases the fertility of the soil to a decided extent. 
Its action appears due to its effect on the soil bacteria. In an 
ordinary soil, the bacteria have reached a condition of equilibrium. 
Carbon bisulphide destroys or injures the bacteria, and diminishes 
the production of active nitrogen. In time, new bacteria develop, 
but along different lines, and there occurs both an enormous in- 
crease in number of bacteria, and an abnormal predominance of 
certain species. The bacteria which prepare active plant food 
are more energetic, and the fixation of nitrogen also takes place 
to a greater extent than usual. The nitrogen is at first locked up 
in the bacterial bodies, and so is useless to the plants, but it be- 
comes active when they decay. Hence the action of the carbon 
bisulphide is depressing if applied to a growing crop, but it acts 
like a nitrogenous fertilizer to a succeeding crop. After a longer 
or shorter time, the soil is more exhausted than it was at first. 
This is probably due not only to the rapid transformation of the 
more easily decomposed organic nitrogen of the soil into active 
nitrogen, but also to the abnormal mixture of soil bacteria due to 
the changed conditions. 

Treating the soil with toluene, and heating the soil, have similar 
effects to carbon bisulphide. The heat, however, itself changes the 
chemical composition of the soil, rendering both organic and in- 
organic material more soluble. According to Russell, 2 the action 

1 Russell, Soil Conditions and Plant growth, p. 114. 

2 Jour. Agr. Science 3, p. in. 

16 



234 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

of these agents is due to the destruction of larger forms of life 
which feed on the bacteria and so keep down their number. 

Effect of Additions on Bacterial Changes. Fertilizers, lime, 1 
stable manure, and other additions to the soil affect the bacteria 
of the soil. In some soils, on fertilization with sodium nitrate, 
bacteria develop, which change nitrates into ammonia and pro- 
tein, and which may affect decidedly the utilization of the nitro- 
gen by plants. 

Azotobacteria appear to be dependent on the presence of lime 
and magnesium carbonates ; so much so that it has been suggested 
that this dependence may be utilized for the detection of the need 
of soils for lime. Liming the soil may thus increase the growth 
of nitrogen-fixing bacteria. 

Active plant food may also affect the bacterial relations. Some 
bacteria have greater power for securing their mineral nutrients 
than others. Additions of plant food to the soil may increase 
the number and activity of certain kinds of bacteria. The bacterial 
life of soils deficient in active plant food may also be low. 

Weeds may have an effect upon the bacterial relations of the 
soil. Cuizeit, by estimating the nitrifying power of soils seeded 
to oats alone, and to wild mustard, found that the mustard de- 
creased the nitrifying power of the soil, and the differences per- 
sisted the following year. He concluded that the unfavorable 
effect of weeds such as wild mustard was due not only to unfavor- 
able effects on general conditions of growth, but also to their 
unfavorable effects on the bacterial content of the soil. 

Fixation of Phosphoric Acid and Potash by the Soil. When a 
solution of potassium chloride is brought in contact with a soil, 
and afterwards subjected to analysis, it is found that a portion 
of the potash has disappeared from solution. This phenomenon 
is called absorption, or fixation. Phosphoric acid, organic matter 
and other bodies, likewise disappear from solution. 

Fixation may be studied by bringing a weighed quantity of soil 
in contact with a definite quantity of a solution of known com- 
position, for a definite time, shaking from time to time and then 
1 Brown, Iowa Research Bulletin No. 2. 



CHEMICAL CHANGES 235 

withdrawing a portion of the solution for analysis. By keeping 
all conditions constant except the one to be studied, we may 
determine the effect of (a) the nature of the soil, (b) the ratio of 
soil to solution, (c) the concentration of the solution, (d) the 
time, (e) the temperature, and (/) the nature of the salt used. 
These are the principal factors which affect fixation. 

Another way 1 of studying fixation is to allow a solution of de- 
finite composition to percolate through a column of soil, but this 
method is open to the objection that the solution afforded to dif- 
ferent layers of the soil is of different composition, since it be- 
comes progressively weaker as it percolates into the soil. This 
method is in principle the same as mechanical washing devices, 
in which fresh water flows where the clean material comes out, 
and the dirty material enters where the dirty water flows out.- 

Factors of Fixation. The important factors governing fixation 
are as follows : 

(i) The Character of the Salt. Potash, phosphoric acid, am- 
monia, lime, magnesia, and soda are fixed by the soil. Chlorine, 
nitric acid, and sulphates are not fixed from strong solutions ; but 
from very weak solutions it appears that some fixation may take 
place. 

That is to say, if potassium chloride, nitrate, or sulphate in 
solution are brought in contact with a soil, a portion of the potash 
disappears, but the amount of chlorine, nitrate, or sulphate in the 
solution remains nearly as it was before. The potash is replaced 
by an equivalent amount of lime, soda, and magnesia. 

Different percentages are absorbed when potash, phosphoric 
acid, etc., are brought in contact with the same soil in equivalent 
proportions, that is, in the proportion of their combining weights, 
such as ninety-five parts of potash to 62 parts soda and so on : 

K 2 : Na 2 : CaO : MgO : 2 NH 3 : i/3P 2 O 5 

95 62 56 39 34 47+ 

The percentages absorbed are not always in the same order for 

1 Schreiner and Failyer, Bulletin No. 32, Bureau of Soils. 



236 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

different soils. We give, in the following table, some results 
secured with 100 grams soil in contact with 250 cc. solution con- 
taining 0.07 gram calcium sulphate three days, and equivalent 
quantities of the other salts: 

Percentage absorbed 1 

N H 3 from ammonium sulphate 60 

K. 2 O from potassium sulphate 55 

Na 2 O from sodium sulphate 19 

MgO from magnesium sulphate 46 

CaO from calcium sulphate 26 

P 2 O 5 from sodium phosphate 17 

SO 3 from sodium sulphate o 

Cl from sodium chloride o 

All soils appear to absorb phosphoric acid, potash, and am- 
monia; but lime, magnesia, etc., are not always absorbed. For 
instance, Biedermann 2 found that two out of nine soils absorbed 
lime, six absorbed magnesia, one absorbed sulphuric acid, and all 
absorbed phosphoric acid and potash. 

The form of combination has also some effect upon the amount 
of absorption. For example, if we compare ^different salts of 
potash, such as the chloride, nitrate, and sulphate, we find differ- 
ent amounts of potash absorbed. 

Percentage 
K 2 O absorbed 

Potassium phosphate 57 

Potassium carbonate 65 

Potassium chloride 57 

Potassium sulphate 55 

Potassium nitrate 51 

(2) The Nature of the Soil. Sands, as a rule, have low 
absorptive powers; loams and clays, much higher. The absorp- 
tive power of the same soil depends upon the substance used to 
measure it. For example, it is different for potash and for phos- 
phoric acid. 

In the following table, the absorptive power is measured by the 
percentage of ammonia absorbed by 50 grams soil from a solu- 
tion of one gram ammonium chloride in 208 cc. water. 

1 Bretschneider, Jahresber, f. Agr. Chem., 1868, p. 17. 

2 Jahresber, f. Agr. Chem., 1867, p. 77. 



CHEMICAL CHANGES 237 

Soil Absorptive power 1 

Norfolk sand 4.0 

Tarboro sand 9.8 

Norfolk fine sandy loam 10.7 

Durham sandy loam 17.5 

Porters red clay 17.8 

Cecil clay 18. 7 

Porters black loam 27.5 

The black loam in question appeared to be rich in organic mat- 
ter. With 100 grams soil to 100 cc. solution containing 0.4283 
gram potash or 0.3032 gram phosphoric acid, respectively, Bieder- 
mann observed a variation in absorptive power from 6.0 to 58.7 
per cent, for potash, and 3.1 to 82.2 for phosphoric acid in 22 soils. 

(3) The Concentration of the Solution. If the ratio of soil to 
solution is kept constant, the stronger the solution of salt used, 
the greater the total amount absorbed, but at the same time the 
percentage is less. That is, the amount absorbed does not increase 
to the same extent as the concentration of the solution. The fol- 
lowing table illustrates this point : 

ABSORPTION 2 OF POTASH FROM POTASSIUM SULPHATE. 



Strength of solution 
(Grams per liter) 


Grams absorbed 

(250CC.) 


Per cent. 

absorbed 


o 4708 






o 0420 . ... 




54-5 


I 8840 


' u y// 


43-5 


47IOO 




33-5 


9 42OO 








^oo^o 


I 5'7 



(4) Effect of Temperature. Increase of temperature some- 
times increases absorption of potash but it always increases that 
of phosphoric acid, according to Biedermann. In the experiment 
50 grams soil was used and 100 cc. solution containing 0.3032 gram 

P.O.- 

1 Withers and Fraps, North Carolina Report, 1902-3. 

2 Bretschneider, Jahresber, f. Agr. Chem., 1865, p. 19. 



238 PRINCIPLES OF AGRICULTURAL CHEMISTRY 





Amount phosphoric acid absorbed 


Soil No. i 


Soil No. 2 




0.0065 
0.0941 
0.1768 
0.1389 


O.I07I 
O.II3I 
0.2694 

o. 2405 






-is C 


oo v - 



Seven additional soils gave similar results. 

(5) Ratio of Soil to Solution. Keeping the strength of solu- 
tion constant, and increasing the weight of soil brought in con- 
tact with it increases the total absorption, while the absorption 
per : gram soil decreases. 

(6) Time of Contact. Peters 1 studied the time of contact, 
using 100 grams soil to 250 cc. of solution containing 0.5889 
gram potash : 

Time Amount absorbed gram 

% hour 0.1417 

2 hours o. 1571 

4 hours 0.1690 

8 hours 0.1860 

24 hours 0.1990 

14 days 0.2037 

Absorption of potash takes place rapidly, and is practically 
complete in 24 hours. Similar experiments have shown that 
phosphoric acid is absorbed more slowly. 

Solubility of Absorbed Material. Absorbed material has a low 
solubility in water. Peters- estimated it as follows: 100 grams 
earth was brought in contact with 250 cc. water containing 0.5888 
gram K 2 O and after 24 hours 125 cc. was drawn off and replaced 
with water. This process was repeated every 24 hours for 9 
days, and each extract was subjected to analysis. The absorbed 
potash is more soluble in water than the soil potash, but not very 
soluble about i part in 28,000 parts water under the conditions 
of the experiment. 



1 Jahresber, f. Agr. Chern., 1860-1, p. 7. 
' 2 Jahresber, f. Agr. Chem., 1860-1, p. n. 



CHEMICAL CHANGES 239 

Water containing carbon dioxide dissolved in 8 days about one- 
third of the absorbed potash; acetic acid, (i 13), dissolved about 
two-fifths; and hot hydrochloric acid (1:3 parts water) dis- 
solved all the absorbed potash. 

.Replacement of Absorbed Material. If a soil is allowed to 
absorb one base, and is then subjected to the action of a second 
solution, a portion of the absorbed base will be replaced by the 
second base. Other bases in the soil will also enter into solution. 

For example, suppose a soil has absorbed potash from pot- 
assium chloride. If it be treated with a solution of sodium 
chloride, some of the soda w r ill be absorbed, and a portion of the 
absorbed potash, and also some lime and magnesia will enter into 
solution. Sodium nitrate, ammonium chloride, calcium chloride, 
calcium sulphate, magnesium chloride, and other salts have a 
similar action. 

The amount of potash displaced would depend upon the quan- 
tity present, and the nature and concentration of the salt solu- 
tion. 

Importance of Absorption. Absorption tends to preserve the 
potash, phosphoric acid, and ammonia of the soil from being 
washed out. Soda, lime, and magnesia, for which the soil has 
less attraction, are more easily washed out. The relative propor- 
tion of loss, will, however, depend upon the amounts of these 
bases present in the soil or rendered soluble. As we have seen 
in the preceding section, soluble salts of lime, magnesia, or soda 
decrease the absorption of potash or replace absorbed potash. 

Absorption tends also to prevent loss of the soluble plant food 
placed in the soil in the form of fertilizers ; for nitrates, however, 
the soil appears to possess little absorptive power. 

The practical importance of absorption lies chiefly in con- 
nection with the application of soluble plant food. It is im- 
portant to know whether soluble plant food applied to the soil will 
be washed out and lost. Nitrates are not absorbed. Potash, 
phosphoric acid, and ammonia, as we have seen, are fixed by the 
soil, and as the solution percolates through the soil, coming in 
contact with fresh masses, the larger part of the soluble material 



240 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

is removed. Thus, even with a soil of low absorptive power, on 
account of the great mass of soil which enters into consideration, 
almost all the material is absorbed. 

With a soil of good absorptive power, phosphoric acid is mainly 
retained by the uppermost layers, the first 9 inches ; with potash, 
although the uppermost 9 inches contains chiefly the greater por- 
tion of the unused fertilizer, a considerable amount penetrates to 
and is retained by the second and third 9 inches. 

The absorptive power of soils also enters into consideration 
when the land is to be irrigated, in which case it is desirable to 
know whether any of the fertilizer may be washed out or carried 
to too great depth by application of the water, and how long a 
time should elapse before irrigation will cause a loss of plant food. 

Some sandy soils have little absorptive power, and no doubt 
losses of plant food occur where heavy rains fall shortly after 
applications of potash and soluble phosphates. 

Cause of Absorption. The causes of absorption are different 
for the basic radicles, potash, soda, lime, magnesia, etc., and for 
the acid radicle, phosphoric acid. It is accordingly necessary to 
consider these two separately. 

In offering an explanation for the absorption of bases, we must 
consider the following facts : 

(1) The amount of absorption is often related to the quantity 
of silicates in the soil decomposed by hydrochloric acid. 

(2) When a base is absorbed, it is replaced by equivalent 
quantities of other bases. Treat a soil with sodium chloride, for 
example, and the absorbed sodium will be replaced largely by 
lime, magnesia, soda, and potash. 

(3) When a soil is treated with an acid, it loses its absorptive 
power almost entirely, but the addition of calcium carbonate 
restores it in great part. 

(4) Hydrated oxides of iron, and aluminum, hydrated alum- 
inum silicate, and sand have slight absorptive powers, but not 
sufficient to account for the absorptive power of soils containing 
them. Humus has a comparatively high absorptive power, but 
the small quantity in most soils will not account for the results. 



CHEMICAL CHANGES 24! 

The conclusion is reached that the absorptive power of soils 
for bases is due to the presence of silicates which react with the 
substance which it will absorb. The reaction is reversible. The 
lime, soda, magnesia, and potash of simple or complex silicates 
enters into reaction with the substance absorbed by the soil, until 
equilibrium is reached between the solution and the reactive soil 
particles. We can hardly expect the law of mass action to be 
followed, for the reason that the absorbing silicates are probably 
mixtures with different reactivity. 

Attempts have been made to explain absorption as physical ad- 
hesion to the soil particles. While a portion of the absorbed sub- 
stance may be held in this way in soils composed of fine particles, 
this theory does not account for the replacement of the absorbed 
base by other bases, or for the varying absorptive power of differ- 
ent soils of the same physical composition, or for the loss of the 
absorptive power of a soil by treatment with an acid, and partial 
restoration of it by addition of calcium carbonate. 

Absorption of Phosphoric Acid. When a phosphate is brought 
in contact with a soil, both base and acid will disappear partly 
from solution. The base follows the laws of absorption as out- 
lined above. The phosphoric acid follows about the same laws, 
but the cause of the absorption is different, and is due to reaction 
with basic substances, such as hydrated oxides of iron and alum- 
inium, and carbonate of lime, with production of the much less 
soluble phosphates of calcium, aluminium, and iron. It is also 
possible that the phosphates have power to decompose some of 
the weak silicates. Phosphates are absorbed more slowly than 
bases. 

Changes of Phosphoric Acid in the Soil. Calcium phosphate, 
in the presence of aluminium and iron hydroxides, has a tendency 
to change into phosphates of these bases, which are much 
less available to plants. The calcium phosphate dissolves, 
and the solution reacts with the hydroxides in question, forming 
phosphates which are much less soluble. The presence of calcium 
carbonate will hinder the reaction, since it also will react with the 
phosphoric acid in solution. 



242 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

PHOSPHORIC ACID DISSOLVED. l 

( i gram substance to 400 cc. water. ) 

Parts per million 

From calcium phosphate 43 

From ferric phosphate 42 

From basic ferric phosphate 33 

From aluminium phosphate 58 

From basic aluminium phosphate 4 

Decaying organic matter, by reducing ferric to ferrous phos- 
phate, and perhaps by combination with the phosphoric acid, tends 
to render phosphoric acid available. 

The slow process of weathering breaks up the complex silicates 
of the soil grains and releases the compounds of phosphoric acid 
therein. At the Rothamsted Experiment Station, where wheat 
has been grown with various fertilizers since 1852, the amount of 
phosphoric acid soluble in citric acid was as follows, on plots 
that did, and did not, receive phosphoric acid. 



Pounds per acre 





1865 


1881 


1893 


No fertilizer ... 


24/1 


TO2 


2O2 


Phosphates 


672 


ly* 

Sri 


I O^O 






OO 





The first plot produced on an average 12^4 bushels wheat con- 
tinuously, but the weathering was sufficient to maintain nearly 
constant the quantity of phosphoric acid soluble in citric acid. In 
the other case (producing 24 bushels wheat) the addition of 
fertilizers made a considerable increase in the soluble phosphates 
present. The weathering of the minerals constantly releases the 
phosphoric acid inclosed therein. In the presence of decomposable 
compounds of iron, and aluminium, there is a constant tendency 
for the phosphoric acid to change to less soluble forms. Calcium 
phosphate is dissolved by the soil water, brought in contact with 
iron and aluminium oxides and unites with these to form phos- 
1 Bureau of Soils, Bulletin, 41. 



CHEMICAL CHANGES 243 

phates. If calcium carbonate is also present, the distribution of 
the phosphoric acid will be modified by the quantitative relation 
between the fixing materials, and the change to iron and aluminium 
phosphates may be reduced or even reversed. 

On the other hand, decaying vegetable matter may reduce 
ferric to ferrous phosphates, with the production of more soluble 
bodies. 



CHAPTER XII. 



SOIL DEFICIENCIES. 

Any condition or defect of the soil which tends to prevent the 
maximum production of crops, or to render it unsuitable for cul- 
tivation, may be termed a soil deficiency. Soil deficiencies may 
be physical or chemical. 

Physical Deficiencies. These are mentioned here merely for 
the sake of completeness. As regards physical deficiencies, a soil 
may be too porous or too stiff, too wet or too dry, too cold or too 
shallow. 




Fig. 55. Experimental plots, Gottingen, Germany, 
Agricultural Institute. 

Cold soils, which are usually wet, when drained become warmer. 
The depth of shallow soils may be increased by plowing a little 



SOII, DEFICIENCIES 245 

deeper every year or by subsoiling. Both porous and stiff soils 
are benefited by organic matter, which makes the former less 
porous and the latter less stiff. Lime may improve stiff soils by 
making them more pulverulent. Wet soils are improved by under- 
drainage. Dry soils may be aided by frequent stirring to prevent 
evaporation of water from them, or by irrigation. Hard pan may 
sometimes be removed or prevented from forming, by proper 
plowing, or subsoiling. In some cases it is profitable to use ex- 
plosives to remove it. 

Chemical Deficiencies. The chief chemical deficiencies of soils 
are acidity, alkali (excess of soluble salts), deficiency in organic 
matter, deficiency in lime, and in available plant foods, phosphoric 
acid, potash, or nitrogen. These deficiencies have been dis- 
covered by means of field experiments, aided by other methods of 
experiment. 

Recognition of Chemical Deficiencies. There are three general 
methods of ascertaining the probable chemical deficiencies of 
soils : 

1 i ) Field experiments. 

(2) Pot experiments. 

(3) Chemical analysis. 

Field Experiments. All soil theories must eventually be tested 
in the field. Field experiments are, therefore, fundamental, and 
information secured by other methods must eventually be brought 
back to the field, and stand the test of actual crop production 
upon the soil. The more removed from field conditions the work 
of the investigator, the more careful he should be to bring his 
results into relation with actual crop production. Unless tested in 
this manner, theories may be developed which are entirely too far 
removed from agricultural conditions. 

Methods of making field experiments with fertilizers are out- 
lined in Chapter XVI. Similar methods are used in other experi- 
ments, arranged according to the information desired. 

Field experiments are subject to vicissitudes of weather, insect 
pests, variations in soil, etc., and hence must usually be carried on 
for several years, or else en an extensive scale. Unexpected 



2 4 6 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



variations are liable to occur, and this fact must be allowed for in 
all consideration of the data. 

Pot Experiments. In pot experiments, 1 plants are grown in 
the soil to be tested, various additions being made to the soil 
according to the information desired. The soil can be mixed until 




Fig. 56. Pot experiments. New Jersey Station. 




Fig. 57. Protection of pot experiments from inclement weather. 
New Jersey Station. 

uniform, and the pot supplied with a favorable amount of water, 
kept at a favorable temperature, and the crops protected from 
damage by insects, birds, or storms. The conditions can be more 
1 Exp. Sta. Record 7, p. 77; 5, p. 849. 



SOIL DEFICIENCIES 



247 



easily controlled than field conditions, and certain problems can 
be much more easily studied. Conditions are relatively more 
favorable than in the field, and the relation between the pot ex- 
periments and field results, must be traced out. 

The pots used vary much in size, shape, and material. 
They may be made of glass, galvanized iron, enameled 
iron, or earthenware, and may vary in size from a few 
inches in diameter to those which cannot well be handled 








Fig. 58. Pot experiments. New Jersey Station. 



and are imbedded in the ground. Galvanized iron is open 
to the objection that the zinc may corrode and form 
poisonous compounds. An ordinary form of pot consists of a 
cylindrical vessel about 8 inches in diameter and 8 inches deep. 
It first receives a layer of gravel, covering a metal or glass 
ventilating tube which reaches above the top of the pot. The soil 
is placed on this, and receives the desired additions. The seed 



248 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

planted should be of uniform size and vary in moderate limits in 
weight, such as 41 to 47 mg. each for wheat grains. The seed 
are often germinated, and the seedlings planted. During the 
period of growth, the pots are usually weighed at suitable inter- 
vals, and sufficient water added to keep the moisture content uni- 
form. The pots are kept in glass houses, in canvas houses, in 
wire houses, or in the open air on trucks which can be run into 
a glass house for protection against storms. The pots are also 
buried in the ground sometimes, but the water content of the soil 
is much less easily regulated under such conditions. Examples 
of pot experiments have been given in the text. 

The following is the method of procedure used at the Texas 
Experiment Station : l 

Washed gravel is added in sufficient amounts to an 8-inch 
Wagner pot to make the total weight 2 kilograms. Five kilograms 
of soil are then added. The soil is previously pulverized in a 
wooden box with a wooden mallet until it will pass a 3 mm. sieve, 
the gravel being removed. 

The addition of fertilizer consists of 2^ grams of acid phos- 
phate, and 10 cc. of solution containing I gram nitrate of soda, 
and T gram sulphate of potash. In later experiments I gram of 
ammonium nitrate was used in place of nitrate of soda. If the 
size of the crop appears to render it necessary, more nitrate of 
soda or sulphate of potash is added to the pot, the solution being 
diluted with about 200 cc. of water. 

The seed are weighed out so that each pot receives the same 
amount of seed within o.i of a gram. Water is added to one- 
half the saturation capacity of the soil. If this quantity is found 
to be too great, it is afterwards reduced, but this is the case in 
only a few instances. The pots are weighed, placed on scales 
three times a week, and water added to restore the loss in weight. 
If the plants need water between weighings, such quantity is 
added as appears necessary. The object of the weighing is to 
maintain as closely as possible a constant amount of water in the 
soil. These pots are kept in a house with glass roof, and canvas 
1 Bulletin 126. 



SOIL DEFICIENCIES 249 

sides and top, for protection against heat, storm, and insect pests. 
Wire basket experiments 1 are made in baskets of wire netting, 
about 3 inches in diameter and 3 inches high, filled with about 200 
grams soil, and dipped into melted paraffin. The surface of the 
soil is covered with paraffined paper, excepting for an opening to 
admit the seedlings. The pots are weighed daily, and the loss 
of water restored. The plants are grown for about three weeks. 




Fig- 59- Construction of wire baskets. Bureau of Soils, U. S. D. A. 

Since air is excluded from the soil and since the seedlings develop 
for the most part from the material in the seed, these experiments 
are more remote from field experiments than ordinary pot experi- 
ments ; still greater caution, therefore, should be exercised in 
interpreting the results. According to the work of the Rhode 
Island Station, 2 this method does not give the same results at 
different times, and the results do not agree with those obtained in 
field practice. 

1 Whitney, Farmers Bulletin No. 257. 
- Bulletin 131. 
17 



250 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

Water culture experiments have been previously described 
(Chapter II), and are well suited to certain purposes of experi- 
ment. They have been used to a certain extent for studying soil 
deficiencies, by growing the plants in an aqueous extract of the 
soil. Conditions in water culture are radically different from 
those in the soil, and still greater caution must be exercised in 
applying conclusions secured by this method of experiment to the 
soil. It is quite possible that materials will be injurious in water 
culture which are innocuous in the soil. Hence it is necessary 
to confirm conclusions drawn from experiments made in this 
way by pot and field tests. 

Chemical Analysis. Chemical analysis can be used for the 
detection of certain soil deficiencies, such as acidity, and the 
quantity of alkali present. Chemical methods can also be used 
to form an opinion as to the needs of the soil for phosphoric acid, 
potash, and nitrogen, as shown in Chapter IX. Chemical analysis 
is also useful in extending the conclusions from field experiments 
and pot experiments to other soils under similar conditions. 

Acid Soils. Acid soils contain free inorganic or organic acids 
or acid salts, which therefore give it an acid reaction. In some 
cases acidity is due to the decomposition of the remains of plants 
in the soil, forming organic acids, but it may also be due to in- 
organic acids. 

The acidity of soils is usually neutralized by lime. A soil which 
receives benefit from lime is not necessarily an acid soil, as lime 
has other effects than that of correcting acidity; it makes the 
phosphoric acid more available, liberates potash, increases nitri- 
fication, and changes the physical properties of the soil. 

Plants behave differently towards acid soils ; some receive bene- 
fit from liming, while others do not. The Rhode Island Experi- 
ment Station 1 has conducted a large number of experiments on 
an acid soil, limed and unlimed, with the addition of acid phos- 
phate, muriate of potash and sulphate of magnesia, and nitrate of 
soda or sulphate of ammonia. These experiments, begun in 1893, 

1 See their reports and bulletins; also Veitch, Bulletin 90, p. 183, Bureau 
Chemistry, U. S. Dept. Agr.; Bulletin No. 66, Maryland Exp. Sta. 



SOIL DEFICIENCIES 



251 



were conducted upon permanent experiment plots of the Rhode 
Island Station. Air slaked lime was applied in 1893 to two of the 
plots at the rate of 5,400 pounds per acre, and 1,000 pounds in 1894, 
and none since. Equal quantities of potash, phosphoric acid, and 
nitrogen have been applied annually to each plot, and, since 1899. 
sulphate of magnesia. Two of the plots receive nitrogen as sul- 
phate of ammonia, and two as nitrate of soda. The tendency of 
the two plots which receive sulphate of ammonia is to become 




Fig. 60. Bare spot in barley caused by acid soil. Woburn, England. 

acid, since removal of the nitrogen leaves sulphuric acid; while 
the latter two plots tend to become basic, since the residue left 
is soda. 

Equal numbers of plants were set out on each plot. A great 
number of different crops have been grown at various times. A 
few results are as follows : 



Plot 
number 


Treatment 


Asparagus 
(pounds) 


Barley 
(pounds) 


Onion 
(pounds) 


Turnip 
(pounds) 


23 
25 
27 
2 9 




O.O 

3-4 
i.i 

4-7 


0.7 
6.5 

2.6 

7-5 


0.2 

41-5 
24.0 

44-3 


2-5 
35-5 
38.0 
44-0 


Sulphate of ammonia limed 
Nitrate of soda 


Nitrate of soda limed 





252 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



The acid soils (Nos. 23 and 27) give smaller yields with these 
crops than the limed soils. The nitrate of soda plot, which, as 
stated, has a tendency to become basic on account of the basic 
residue left when the nitrogen is taken up, gives better yields than 
the ammonium sulphate plot, which has a tendency to become 
acid. 

Effect of Lime on Crops an Acid Soil. 1 Benefited by Lime. 
The following gives the ascertained effect of lime on various 
crops as found by experiments such as described above : 




Fig. 61. Sorghum on acid soil, (A) limed and nitrate of soda, (B) unlimed 
and nitrate of soda, (C) limed and sulphate of ammonia, (D) un- 
limed and sulphate of ammonia. Rhode Island Station. 

Alfalfa, asparagus, barley, beets, clover, celery, cauliflower, cur- 
rants, cabbage, cucumbers, corn, lettuce, mangelwurzel, onions, 
okra, oats, peas, peanuts, pepper, parsnip, pumpkin, sorghum, 
salsify, seed fruits, stone fruits, squash, spinach, sugar beets, salt 
bush, timothy, and tobacco. 

1 Wheeler, Farmers Bulletin No. 77, U. S. D. A. 



SOII, DEFICIENCIES 253 

Indifferent to Lime. Blackberries, millet, potatoes, rasp- 
berries, rye, and red top grass. 

Injured by Lime. Cranberries, cowpeas, sheep sorrell, lupine, 
serradilla, and watermelon. 

In these experiments, it will be noted that the plants were sup- 
plied with an abundance of phosphoric acid, potash, and nitrogen. 
Such being the case, the beneficial effect of the lime could not be 
to render potash or phosphoric acid available. Other experi- 
ments showed that caustic magnesia, or sodium carbonate also 
had a good effect. These substances would also neutralize acidity. 

Detection of Soil Acidity. The most satisfactory method of 
ascertaining whether a soil needs lime is to determine the gain in 
crop by its application. It does not necessarily follow that a soil 
which responds to lime is acid. 

The tests for acidity used at present are as follows: 

1. The Litmus Test. 1 The soil is moistened with water and 
brought in contact with blue litmus paper. If acid, the litmus 
turns red. Carbonic acid also reddens litmus, but to a less degree 
that, an acid soil. 

2. Ammonia Test. 2 The soil is treated with ammonia water, 
and if the liquid assumes a dark brown or black appearance, the 
soil may be acid. This test applies only where the acidity is due 
in a considerable measure to acid organic substances, and may 
not apply to all sections of the country. 

3. Salt Method?. The soil is shaken with a solution of potas- 
sium nitrate and the solution, after being boiled to remove car- 
bonic acid, titrated with caustic soda and phenolphthalein. Part 
of the acidity is due to formation of aluminium and iron chlorides, 
which are decomposed in the titration. 

4. Lime Water Method. 4 The soil is treated with standard 
lime water, evaporated, taken up with water, and the nitrate tested 
by evaporating it nearly to dryness with a few drops of 
phenolphthalein. If the phenolphthalein indicator becomes pink, 

1 See Circular No. 71, Bureau of Plant Industry. 

2 Bulletin 62, Rhode Island Exp. Sta. 

3 Proceedings Association Off. Agr. Chem., 1902. 

4 Jour. Am. Chem. Soc., 1902, p. 120. 



254 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

an excess of lime water has been used. If it does not become 
pink, the soil is still acid. A number of tests are made, so as to 
ascertain two quantities of lime water, with one of which the soil 
is acid, by the other, made alkaline. This appears to be a good 
method. 

Other Effects of Lime. We have already seen that lime is 
necessary to plant life. Cereal grasses require from about Y\ to 
YZ as much lime as potash, while leguminous plants take up as 
much lime as potash, if not more. Lime is usually considered as 
present in abundance in the soil, but it is quite possible that some 
soils, especially sandy soils do not supply a sufficient quantity of 
active lime for the use of certain leguminous plants. 

The following is a brief summary of the part which lime 
(chiefly in the form of carbonate) plays in the soil 1 : 

1. It flocculates clay particles, making the soil more crumbly 
and, with better tilth, more retentive of water and more easily 
penetrated by rain. 

2. It aids growth of bacteria which convert organic nitrogen 
to nitrates, those which assimilate nitrogen and other bacteria. 

3. It neutralizes acids and maintains the soil in an alkaline 
condition, which is the condition most favorable to the majority 
of cultivated plants. 

4. It makes a soil productive which contains relatively small 
quantities of plant food. 

5. It counteracts the deleterious effect of an excess of magnesia 
in the. soil. 

6. It liberates potash in the soil. 

7. It unites with phosphoric acid, preventing it from forming 
less valuable phosphates of iron and alumina. 

An excess of carbonate of lime may prove injurious to some 
plants, notably grape vines and citrus plants. From eight to 
twenty per cent, of lime may have this effect. 

Carbonates of magnesia may, to a certain extent, act in the 
same way as lime. We have already seen that it is well for lime 
1 See Kellner, Landw. Versuchs-stat., 1896, p. 210. 



SOIIy DEFICIENCIES 



255 



to have a certain ratio to magnesia. An excess of either lime or 
magnesia is not desirable. 

Lime Compounds in the Soil. Lime is found in the soil as the 
carbonate, sulphate, humate, and various more or less complex 
silicates. Calcareous soils contain considerable amounts of car- 
bonate of lime. It is quite probable that some soils rich in humus 
contain fair amounts of calcium humates. As a rule, the lime 
is present in the form of silicates, which are more or less resist- 
ant to the action of acid and weathering agencies. 




Fig. 62. Distributing lime. Ohio Station. 

Application of Lime. 1 Lime is applied to the soil as (a) Land 
plaster or gypsum, CaSO 4 2H 2 O which has no power to counter- 
act acidity; (b) Quicklime CaO, which is the most active form of 
lime. It is usually slacked before it is worked into the soil. It 
soon takes up carbon dioxide, and changes into the carbonate. 
It is made by heating the carbonate, and so is often called burned 
1 Bulletin 159, Ohio Station ; Wheeler, Farmers Bulletin No. 77. 



256 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



lime, (c) Ground Limestone: Ground limestone is more mild 
in its action than quicklime and can be used in larger amounts. 
The finer it is ground, the more effective it is. 
CaO : 56 : CaCO 3 : 100 
Lime Limestone 

One hundred parts of pure limestone contain 56 parts lime, 
equivalent to 56 parts of pure burned lime, (d) Oyster Shells: 
Oyster shells contain some plant food. They may be applied 
unburnt and burnt, (e) Marl contains less lime than shells. All 
forms of lime should be applied some weeks before planting. 

Quick lime is applied as a top dressing on land at the rate of 
200 to 500 pounds per acre. Excessive applications of lime are 
injurious. Ground limestone is used in larger quantity, particu- 
larly when alfalfa is to be planted. One or two tons per acre of 
ground limestone may be used every four to six years; even as 
much as ten tons may be applied. 

Lime Liberates Potash. Lime releases absorbed potash, mak- 
ing it more readily available to plants. Hence the lime would act 
as an indirect potassic fertilizer. Boussingault 1 found the follow- 
ing amounts of potash and lime removed by clover from a limed 
and an unlimed soil, in Kg. per hectare. 





Potash 


lyiine 


Phosphoric 
acid 


Unlimed. first year 


26 7 


12 2 


1 1 O 


L/imed first year 


Q> 6 


&+* 

7Q A. 


24 2 


Unlimed second year 


Vo- u 

28 6 


79 2 


7O 






O*'* 

TO? 8 






97.2 




22.9 



It does not follow from the above experiment that the lime 
"released" potash. The liming made conditions more favorable 
for the clover, and a larger crop was produced, with a heavier 
draft on the soil. The availability of the plant food was not 
necessarily changed because more of it was withdrawn from the 
soil. 

It appears to be generally conceded that lime releases potash, 
1 Storer, Agriculture. 



SOIL DEFICIENCIES 



257 



though the writer has been able to find little experimental evidence 
that such is the case under actual field conditions. In the section 
on absorption, evidence is given that in the laboratory, lime and 
other salts replace absorbed potash. 

Experiments with Burned Lime or Ground Limestone. In 

experiments at the Pennsylvania and at the Maryland Experi- 
ment Station, 1 ground limestone has given better results than 
burned lime. At the Pennsylvania Station, lime was used in a 
four year rotation of corn, oats, wheat, and hay, at the rate of two 
tons per acre of burned lime every four years or two tons of 
ground limestone per acre every two years. The average yield 
for 20 years is as follows : 





No lime 


Burned lime 


Ground 
limestone 


Corn bushels per acre .-.. 


AO Q 


7J. Q 


1Q Q 








16 7 




33-9 


o u< 9 


o u - / 
16 5 




13-9 


1 o-y 
II 8 


.LVJ-O 




**0 







The burned lime injured the corn, oats, and hay, while the 
ground limestone was of benefit to the oats, wheat, and hay. 
Analysis of the soil showed that the soil receiving burned lime 
had lost more nitrogen than the other. 

At the Maryland Experiment Station, different kinds and 
amounts of lime were applied to various plots at the beginning of 
the experiment. The results of 11 years test with 1,400 pounds of 
burnt lime, or an equivalent amount of carbonate of lime from 
shell or marl, with the rotation of corn, wheat, and hay, are as 
follows : 





No lime 


Burned lime 


Carbonate 
of lime 




24-5 
10.7 
0.65 


32.0 
II. 

0.85 


37-0 
14.1 
1.07 









1 Report for 1902. 



258 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

Here also the carbonate of lime gave better results than the 
quicklime. 

Salt. Salt is used to some extent as an application to the soil. 
It acts as an indirect fertilizer. 

Gypsum or sulphate of lime CaSO 4 2HX), is used to a small 
extent at present. Formerly it was held in high esteem, but at 
present, preference is given to lime, limestone, or direct fertilizers. 

Toxic Substances. It is possible that some soils may contain 
injurious substances besides alkali or acids. The theory of 
Whitney and Cameron, that plants excrete toxic substances, has 
already been discussed. 

Sulphur. The amount of sulphur 1 in plants has been for a 
long time under-estimated. Recent work 2 has shown that many 
plant products (especially seeds) contain much more sulphur than 
was once thought. Most soils contain only small quantities of 
sulphur. It is therefore quite possible that some soils are deficient 
in sulphur. It is possible that the sulphates contained in acid 
phosphate are often directly beneficial to plants. Direct experi- 
mental evidence that such is the case has not yet been furnished. 

Alkali Soils. 3 Alkali consists of soluble salts. When present 
in the soil in excessive quantities, these salts interfere with the 
growth of plants, or prevent their growth entirely. 

The ordinary "alkali" salts are sulphate of soda, chloride of 
soda, and carbonate of soda. The salts first named, when crys- 
tallized in the surface of the soil, appear as white substances, 
and generally form what is known as white alkali. Carbonate of 
soda has a corrosive action upon vegetable matter (usually found 
in the soil) producing a black solution or substance, and for this 
reason is called black alkali. 4 Carbonate of soda is especially in- 
jurious, for it causes the soil to become hard so that water will 
not easily penetrate it. It is also more injurious to plants than 
the less corrosive alkali salts. 

1 See, however, Arendt, Jahresber, Agr. Chem., 1858, p. 125. 

2 Withers and Fraps, Report North Carolina Exp. Sta., 1902-3, p. 53. 

3 Alkali Soils of the United States, Bulletin 35, Bureau of Soils. 

4 California Bulletin 128. 



SOIIv DEFICIENCIES 



259 



Other salts than those mentioned above may be present in 
alkali. Calcium chloride, for example, may give the soil a black 
color, and have the appearance of black alkali, but it is not as 
injurious as carbonate of soda. Nitrate of soda has been found 
in Colorado soils. 1 

Origin of Alkali. Alkali conies originally from the decompo- 




Fig. 63. Alkali spot remaining in reclaimed field, Utah. Bureau of Soils. 

sition of rocks. In climates where there is an abundance of rain, 
and much water passes through the soil, the alkali salts are 
1 Headden, Bulletin 178, Colorado Station. 



260 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



washed out about as fast as they are formed and carried into 
streams, and thence to the sea. 

In arid climates, since the rainfall is not sufficient to wash out 
the soluble salts, they accumulate. As long as these salts are dis- 
tributed uniformly through the mass of the soil, they cause no 



50000 



POUNDS OF SALT PER ACRE. 

10,000 15,000 0,000 25,000 



30,000 35,000 




Fig. 64. Salt content of sandy land and of gumbo soil, before and after 

irrigation. Irrigation causes the alkali to rise to near the 

surface of the gumbo soil. Bureau of Soils. 

injury, but the alkali may accumulate in the surface-foot of the 
soil, or it may be carried away to accumulate in another field. 

When water comes in contact with the soil, it dissolves the 
soluble constituents as far as it penetrates. If afterwards it 



SOIL DEFICIENCIES 26l 

rises and evaporates, it leaves there all the alkali which it held in 
solution. Thus the alkali originally distributed through the soil 
may be concentrated near the surface, thereby causing injury to 
plants. Checking evaporation by cultivation, mulching or shad- 
ing the land by crops, will check the rise of alkali. It sometimes 
happens that the alkali is concentrated in the eleventh or twelfth 
foot of the soil. Under moderate irrigation, the water will not 
penetrate to this depth, but excessive irrigation will carry water 
to such depths as to dissolve the alkali in the depths of the soil, 
and evaporation may then bring it near the surface, so as to cause 
injury. Soils have the power of elevating water to some dis- 
tance, through the small spaces between the particles. 

Irrigation waters, so necessary in arid regions, always contain 
dissolved salts. These are left behind when the water evaporates. 
If the water is of poor quality, only a few applications may be 
sufficient to charge the soil with alkali. Even a good irrigation 
water may give rise to alkali if all the salts it contains are allowed 
to accumulate in the soil. 

Excessive irrigation, without under-drainage, gives rise to 
alkali. 1 This is evident first in the low-lying lands. The excess 
of water flows off into them, and raises the level at which the 
water saturates the soil (known as the water table), until in some 
cases, the water comes to the surface. The alkali is washed from 
the higher ground, and the water evaporates in these low places, 
leaving the alkali near the surface. The land is thus converted 
into alkali flats. ' Even where the water does not come to the sur- 
face, whenever it comes within such a distance of the surface that 
the capillary action of the soil grains has the power to bring it 
to the evaporating point, alkali will accumulate. The constant 
rise of the water containing salts and the evaporation of the 
water, leaving the salts behind, will accumulate alkali even if the 
water in the soil does not contain much alkali. Usually, how- 
ever, such water contains some alkali. 

Alkali will accumulate at any point where the water constantly 
evaporates, as on the sides of irrigation canals. 
1 Dorsey, Bulletin 34, Bureau of Soils. 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 




Fig. 65. Distribution of alkali in soils near Tempe, Arizona less than 
25 per cent., 25 to 50 per cent, and over 50 per cent. 




Fig. 66. Distance to standing water in soils near Tempe, Arizona less 
than 10 feet, 10 to 20, 20 to 50 feet. Compare Fig. 65. Bureau of Soils. 



SOIL DEFICIENCIES 263 

Whenever the water table rises, in land under irrigation in arid 
sections, to within four or five feet of the surface, it is a sign of 
danger. Such a rise means that the water in the soil is in such a 
distance of the surface that the salts will be constantly moving 
from the reservoir in the soil water, and accumulating in the soil. 
Injury will result if such an action continues. The remedy is 
drainage. 

The bulk of the alkali salts in an arid region will be usually 
found some distance from the surface of the soil, when the water 
table is many feet below the surface. The depth at which this 
accumulation occurs depends to some extent upon the depth to 
which the rainfall penetrates. For example, Thomas H. Means 
found that the alkali salts in coarse sands of a certain district 
were largely four to eight feet from the surface, while in sandy 
loam, in which the rain can not penetrate so deeply, the alkali 
occurs at a depth of three or four feet. The rain dissolves the 
alkali and carries it down into the soil. On evaporation, some 
of the alkali returns to the surface, but the bulk of the evapora- 
tion must take place below the surface, for otherwise the alkali 
which is washed down would be brought up again. 

Surface accumulations of alkali salts take place where the 
ground-water is sufficiently near the surface to cause the bulk of 
the evaporation of water to take place at or near the surface. 
Dissolved material from the soil, and that brought in by the 
ground-water, will be brought to the surface. Hence basin-like 
depressions surrounded by sloping land usually contain alkali. 

Effect of Alkali on Plants. Alkali 1 usually causes injury at 
the base of the trunk, or the root crown of the plant. The bark 
of green herbaceous stems is usually turned to a brownish color 
for half an inch or more, and is soft and easily peeled off. The 
rough bark of trees is turned nearly black, and the green layer 
turns brown. The plant either dies, or becomes unprofitable to 
the grower. 

The amount of alkali which various plants will stand depends 
upon a number of conditions, among which are the age of the 
1 California Bulletin 128, p. 5. 



264 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



plant, the character of the soil, the composition of the alkali, the 
distribution of the alkali, and other conditions which influence the 
growth of the plants themselves. The most injurious salts are 
the carbonates; the least injurious are the sulphates. 

The California Experiment Station 1 has endeavored to deter- 
mine the tolerance of various plants for alkali by estimating the 
amount of alkali in soils in which the respective plants did well 
or ill. The depth of four feet was chosen, because the strata be- 
low that depth contain little alkali, and because rainfall or irriga- 
tion water ordinarily does not penetrate below that depth. The 
total amount in this depth must be considered. 

The results of these California investigations are as follows. 
These figures, as stated, are tentative and subject to change: 

HIGHEST AMOUNT OF ALKALI IN WHICH PLANTS WERE FOUND 

UNAFFECTED, IN POUNDS PER ACRE TO THE 

DEPTH OF FOUR FEET. 





Sulphate 
(sodium 
sulphate) 


Carbonate 
(sodium 
carbonate) 


Chloride 
(sodium 
chloride) 


Total salts 




40,800 
30,640 
24,480 
22,720 
18.600 
17,800 
14,240 
9,600 
9,240 
8,640 
4,480 
3.360 
125,640 
102,480 
11,120 
61,840 
52,640 
52,640 
51,880 
15,120 
5.700 
63.720 


7,550 
2,88o 
1, 1 2O 
1,440 
3, 8 4o 
1,760 
640 
680 
1,360 
470 
480 
160 
18,560 
2,760 
2,360 
9,840 
4,000 
1,760 
8,720 
1,480 
11.300 
2,160 


9,600 
6,640 
800 
2,400 
3.360 
1,360 
1,240 
I.OOO 
1,200 
9 60 
800 
800 
12,520 
5,760 
7 60 
9,680 
5,440 
5,440 
2,240 

1,160 
3,160 


45,800 
40,160 
26,400 
26,560 
21,840 
20,920 
16,120 
11,280 
1 1, 800 
10,080 

5,760 
5.760 
156,720 
110,320 
13,120 
81,360 
59,840 
59,840 

62,840 

17,280 

17,000 

63,360 


Olives 


Ficrc 


ri lS a 




Pears 




ppopVipc 










Salt bush 


Alfalfa (old) 




Sorghum 




Radish 


Wheat 









L,oughridge, Bulletin 133. 



SOIIv DEFICIENCIES 



The Bureau of Soils 1 of the United States Department of 
Agriculture divides soils into six grades, according to their 
average content of soluble salts to a depth of six feet. 





Percentage of 
total salts in soil 


Black alkali 
per cent. 


Crop behavior 


Grade i 


0.0-0.20 


Less than 0.05 


Common crops not injured un- 
less salt is concentrated in 
first foot. 


Grade 2 


0.20-0.40 


0.05-0. 10 


All crops will grow except those 
most sensitive, but at the 
higher limit all except those 
that are truly resistant are 
distressed. Alfalfa grows but 
hard to get a good stand. 
Sugar cane, sorghum and 
barley do well. 


Grade 3 


0.40-0-60 


o. 10-0. 20 


Not suitable for common crops. 
Usually devoted to pasture. 


Grade 4 


0.60.1.0 


0.20-0.30 


Almost worthless for farming 
or fruit growing. 


Grade 5 


1.0-3.0 


Over 0.30 


Worthless. 


Grade 6 


Over 3.0 




Worthless. 



The quantities of alkali mentioned above refer to the total 
quantity of soluble salts. 

Utilization of Alkali Soils. 2 (i) Growth of Resistant Crops. 
One method of utilizing alkali soils is to grow crops which will 
resist the action of the alkali present. One of the most resistant 
crops is salt bush, which endures drouth as well as alkali, and is 
used for pasturage, or as a hay crop. Sorghum, oats, and sugar 
beets have a high resistance for alkali, also some varieties of 
barley, but it is difficult to secure a stand of these crops when 
more than 0.6 per cent, of the total salts is present. 

(2) Treatment of Black Alkali. Black alkali, due to sodium 
carbonate, may be converted into sodium sulphate by means of 
gypsum. The sulphate is much less harmful to plants and the 

1 Dorsey, Bulletin 35, p. 24. 

2 Hilgard, Bulletin 128, California Exp. Sta. 

18 



266 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 




Fig. 67. Orange grove, (A) suffering from alkali, (B) after the alkali has 
been driven down by irrigation. California Station. 



SOIL DEFICIENCIES 267 

tilth of the land is decidedly improved. If much alkali is present, 
gypsum alone will not be sufficient because it does not remove the 
alkali, but merely changes it to another form. No chemical treat- 
ment is known which will counteract the effects of white alkali. 

(3) Scraping the Surface. At the end of a dry season, when 
the alkali has risen to the surface, it may be scraped off and 
carted away. This method might be used for small spots. 

(4) Flushing the Surface. This method consists in flooding 
the land with water and drawing it off after a short time. This 
method can not be used for any soil in which the water sinks in 
rapidly, because the water will carry the alkali with it into the 

soil. With rather heavy, impervious soils, with the alkali largely 
at the surface, the method may prove successful. 

(5) Flooding Without Drainage. For this method, the soil 
must be naturally well under-drained, with the water table several 
feet below the surface. The water used in flooding must go 
through the soil, and into the drainage. The method employed is 
to level the field, and cover the soil with water to the depth of 
several inches, the water being held on the soil by means of dikes 
or levees so that it soaks into the soil. Repeated flooding will 
carry the alkali out in the drainage waters. As already 
pointed out, this method can only be applied to soils which are 
naturally well under-drained, and on which the flooding will not 
raise the level of the water-table to a dangerous extent. 

(6) Flooding and Drainage.^ Flooding together with artificial 
drainage will reclaim any alkali land; provided, of course, that 
the flooding is carried out often enough, and with sufficient water, 
and provided that the drainage is sufficient. Drainage is largely 
a matter of engineering. The drains should be at least three feet 
deep; on some soils four or five feet is better. In heavy soils 
they should be from 25 to 100 to 150 feet apart; in sandy soils 
intervals of 250 to 300 feet may answer the purpose. 

Prevention of Alkali. Accumulation of an excess near the 
surface is most to be feared. If the alkali is below the root zone 
of the plants it can do no damage. Plants may grow and do well 
1 Bulletin 34, Bureau of Soils, also Bulletin 44. 



268 PRINCIPLES OF AGRICULTURAL, CHEMISTRY 

with their roots just above an accumulation of alkali, but if the 
alkali rises to the roots, or if deeper rooting crops are grown, 
injury will result. 

In order to prevent the rise and accumulation of alkali, the 
irrigator must keep the main movement of the water downward 
through the soil and out in the ground-water. If the water 
movement is maintained in this direction, the alkali will not 
accumulate in the soil. The movement need not be at all times 
in this direction, but the main movement must be this way, or 
alkali will accumulate. 

If the main movement of the water is up through the soil, 
alkali will accumulate. In a sub-irrigated soil, the movement of 
water is up, due to evaporation of water, and to transpiration 
from the leaves of plants. Hence, sub-irrigation means an 
accumulation of alkali. 

Furrow-irrigation is a kind of sub-irrigation. The soil at the 
top of the furrow is irrigated from below, and, in this particular 
part of the soil, the movement of the water and dissolved salts 
is up ; so that it will accumulate alkali. If furrow-irrigation is 
used in places liable to alkali, the soil should occasionally bq 
leveled and flooded sufficiently often to keep the main move- 
ment of the water down through the soil. 

If flooding is practiced, and hillocks occur which are not 
covered by the water, such spots are sub-irrigated, and alkali 
will accumulate in them. Within these hillocks, the movement of 
water is upwards, due to evaporation from the surface. Such 
hillocks should be leveled before flooding begins. 

Anything which will counteract surface evaporation will aid in 
keeping the main movement of the water down and through the 
soil. The greater the extent that evaporation is prevented, the 
less water is needed for the irrigation. Evaporation from the 
surface, therefore, should be prevented as much as possible. 
Careful and frequent cultivation will produce a mulch which will 
do much towards checking evaporation. Trees or crops on the 
land will also shade the surface and check evaporation. 

If the water-table is too near the surface, flooding must be 



SOIIy DEFICIENCIES 269 

more frequent or the land must be under-drained. Too frequent 
flooding may keep the ground too wet, so that under-drainage is 
really the practical remedy. Whenever the water-table is at such 
a distance that the capillary action of the soil can bring water 
from it to the surface, there is great danger of alkali. In such a 
soil, the rise of water from the ground water is continuous, so 
that more must be used in irrigation to cause the main movement 
of the water to be downwards. By lowering the water-table by 
means of drainage, the water-table may be brought below the 
power of the soil to elevate it, thus checking the movement of 
water, and the alkali with it, towards the surface. The right 
depth for the water table depends upon the character of the soil. 
In coarse sand, water may be raised over five feet. It appears 
possible that in fine sand, so often found in alkali districts, water 
may be raised as much as twelve to fifteen feet. 

How much flooding will keep the main movement of the water 
downward and through the soil will depend, therefore, upon the 
water-table and the character of the soil, and the thoroughness of 
the cultivation. The composition of the ground-water, and the 
composition of the irrigation-water are important factors to 
consider. 

The alkali question is, in many localities, largely a question of 
proper drainage. 

Quantity of Irrigation Water. The quality of the irrigation 
water which can be used upon soils without injury depends upon 
the kind of soil, the character of the under-drainage, the rainfall 
of the area, and the manner in which the water is used. If the 
soil is easily penetrated by water, and well drained, water of 
comparatively high mineral content may be used, provided that 
it is used in such a manner as to keep the main movement of the 
water through the soil and into the drainage. In humid regions, 
a water containing more salts may be used than in arid regions, 
since less water is used and the natural rainfall will aid in wash- 
ing the alkali out of the soils. With a heavy clay soil, however, 
and especially if alkali carbonates are contained in the water, 
there is always danger. 



270 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

The limit of concentration of irrigation water has been placed 
by some authorities at 2,000 or 3,000 parts per million. With these 
concentrations, however, injury will result if the alkali is allowed 
to accumulate, and is not washed from the soil. Even compara- 
tively small amounts of mineral matter may give rise to alkali in 
time, if the soluble salts are allowed to accumulate. 

Thomas H. Means 1 found water containing as much as 8,000 
parts per million of soluble salts used in the Desert of Sahara, 
many of the crops grown being quite sensitive to alkali. The 
Arab gardens are divided into plots about twenty-feet square, 
with drainage ditches about three feet deep between them. A 
large quantity of water is applied at least once a week ; more 
often, water is applied twice, the check method of irrigation 
being used. Thus a continuous downward movement of water is 
maintained, and, since the soils are light and sandy, they are well 
drained, and there is little opportunity for the soil water to be- 
come more concentrated than the water applied. 

It is evident that the more salts contained in the water, the 
better should be the under-drainage, and the more freely the 
water should be used. On clay soils, the matter is more difficult. 
Alkali is so hard to remove from some of these soils, even if 
under-drained, that it is doubtful if any except water of high 
purity should be used on such soils. 
1 Circular No. 10, Bureau of Soils. 



CHAPTER XIII. 



LOSSES AND GAINS BY THE SOIL. 

Under natural conditions, a large portion of the material taken 
from the soil by plants returns to it again. The plant dies and 
decays. Droppings from animals which have eaten plants are 
distributed on the soil. Nevertheless there is some loss of 
material due to leaching. We have seen that in the weathering 
of rocks into soils, large percentages of material are removed, but 
this process has taken long periods of time. Soils which are 
highly weathered contain much less plant food than those less 
weathered ; this shows that losses by percolation occur under 
natural conditions. Under cultivation, there may be much greater 
losses, due to the smaller amount of vegetation on the soil at cer- 
tain seasons, and to the removal of the crops. 

Gain by Rainfall. In Chapter III we saw that the rain dis- 
solves and brings down small amounts of ammonia, nitrates, dust, 
and other substances. The quantity of the most important con- 
stituent, nitrogen, brought down by the rain, has been shown to 
average about 8.0 pounds per acre. (Chapter III.) 

Loss in Percolation. Of the water which falls on the soil, a 
portion runs off, a portion evaporates or is transpired by plants, 
and a portion penetrates through the soil, and either reappears in 
springs, drains, wells, or seepage water, or else sinks deep into 
the earth. This is the percolating water. The water which per- 
colates dissolves some of the material that comes in contact with 
it, thereby causing a loss of material. The water contains silica, 
organic matter, potash, soda, lime, and magnesia, in the form of 
carbonates, sulphates, phosphates, chlorides, and nitrates. The 
more important of these constituents, from an agricultural point 
of view, are the potash, phosphoric acid, nitrogen, and lime. 

The amount of loss by percolation depends upon a number of 
factors : 

(i) The Quantity of Percolating Water. This depends upon 
the amount of rainfall, whether the land is bare or covered with 
vegetation, the character of the soil, etc. Unless the rainfall is 



272 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

sufficient to saturate the soil, and pass into the ground water, 
there is no percolation. Plants, by withdrawing water from the 
soil and causing it to evaporate, diminish the quantity which 
percolates. As more of the rainfall will penetrate an open, 
porous soil than a compact soil, there would be a greater surface 
off-flow from the latter. Soils which retain water near the sur- 
face suffer greater losses by evaporation. See Chapter VII. 

(2) The Composition of the Soil Extract. This depends upon 
the fixing power of the soil and the solubility of its constituents. 
It also depends on the kind and quantity of the various additions 
made to the soil. The application of fertilizers almost always in- 
creases the quantity of potash and nitrogen in the soil extract and 
consequently increases the loss of plant food. Ammonium sul- 
phate and potash salts also increase the quantity of lime in the 
soil extract. 

(3) The Presence or Absence of Vegetation. Besides affect- 
ing the amount of percolation, vegetation withdraws plant food 
from solution and thereby diminishes the loss in percolating water. 

Study of the Loss. The loss by percolation may be studied in 
two ways, both of which have their limitations : 

(i) By determination of the amount and composition of the 
percolating water. For the purposes of this experiment, a sec- 
tion of the soil must be enclosed in a water-tight receptable, so 
arranged that all the water which percolates may be collected, 
measured, and subjected to analysis. 

A section of soil in its natural condition, may be isolated by 
trenches, enclosed by brick walls, and then separated from the sub- 
soil, so that the percolating water may be collected in a suitable 
vessel. This was the method used in preparing the drain-gauges 
(as they are called) at Rothamsted. See Chapter VII. 

Soil may also be placed in boxes of cement 1 or cans of gal- 
vanized iron, or other material, arranged with suitable tubes and 
collecting vessels. In such case, the soil is stirred and aerated 
and is otherwise under unnatural conditions. The apparatus 
1 New York, Cornell Station Report, 1909. 



LOSSES AND GAINS BY THE SOIL, 



273 



should be left for sufficient time to allow readjustment to take 
place. 

All the water which falls on the soil in such an apparatus must 
either percolate or evaporate. The percolation will therefore be 
in excess of that in a free area, where a portion of the water runs 
off. 

(2) The second method 1 consists in determining the quantity 
and composition of the water from tile drains in the field. Tile 
drains run when the water does not pass into the subsoil rapidly 
enough to keep the soil from becoming saturated in the vicinity 
of the drains. The quantity of drain water does not, therefore, 
represent the quantity of water which percolates, but its com- 
position should represent to a certain extent the composition of 
the percolating waters. 

Quantity of Loss by Percolation. The composition of the 
drainage water from some of the plots at Rothamsted 2 is given 
in the following table : 

ANALYSIS OF DRAINAGE WATERS IN PARTS PER MILLION. 



Rothamsted 


Phosphoric 
acid 


Potash 


Nitric 
nitrogen 


Lime 










Q Q T 


Ammonium salts only 
Ammonium salts and super-phos- 


1.44 

i 66 


-/ 

i-9 


9 

13-9 


90.1 
I54-I 

T^C fi 


Full mineral dressing and ammonia 


o 91 


2.9 


1 o-o 
14.0 
16 i 


l8l.4 






4 




14/.4 



[f we assume a downward percolation of 10 inches of drain- 
age water, i part per million of water corresponds, in round num- 
bers, to 2 l /4 pounds per acre per annum. According to this 
estimate, from i l / 2 to 334 pounds phosphoric acid, 2 l / 2 to i2 l / 2 
pounds potash, and 9 to 36 pounds nitrogen are lost in the drain- 
age waters a year, according to the condition of the soil. 

At Rothamsted, the average amount of nitrogen contained in the 
crops (wheat) in 30 years on the unmanured plots was 18.6 and 
20.3 pounds ; the estimated loss by drainage from tiles, 10.3 and 

1 Jour. Agr. Sci., 1906, p. 377. 

2 Hall, An Account of the Rothamsted Experiments, p. 237. 



274 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

12.0 pounds respectively, with an estimated gain of 5.0 pounds 
nitrogen derived from rain and dew. From 2/9 to *4 of the 
total loss of nitrogen passes into the drainage waters. 

Gains by Material Dissolved in Capillary Water. A certain 
portion of the water which sinks into the subsoil, rises again to 
be evaporated near the surface or transpired by plants. It has 
been claimed that this water may bring dissolved material to the 
surface soil. Such is indeed the case in arid regions where 
soluble salts are within reach of the water. The alkali zone may 
rise or sink to some extent with the dry or wet character of the 
season. In humid sections, however, material is dissolved by the 
water as it passes through the surface soil, and the gain can be 
due only to a longer contact with the subsoil. There may be some 
gain of this kind, but it would have to be considerable to counter- 
balance the material dissolved in soil water which enters the 
ground water and does not return to the surface. The writer has 
been able to find no experimental data showing the relative 
solubility of the material of soils and subsoils, and the relative 
quantity of water which reaches the subsoil and which returns to 
the surface. 

Losses by Washing. Water running off on the surface carries 
soil particles with it, so that as a general rule the surface soil is 
deeper in valleys and thinner on hill-sides. The particles are car- 
ried to some extent in the water of streams, and may be deposited 
elsewhere along the course of the stream, or carried to the sea. In 
regions of heavy rapid rains, the running water may cut ravines 
and gullies, and practically destroy unprotected hillside land. 
Vegetation is a protection against such loss, and so is anything 
which checks the rapidity of the flow of the water. Proper hill- 
side terracing is the best treatment for cultivated land. 

Loss by Bacterial Action. The losses by bacterial action fall 
on the organic matter and the nitrogen of the soil, none of the 
other materials being directly lost in this way. Excessive nitri- 
fication is followed by losses of nitrogen as nitrates in the drain- 
age water, usually as calcium nitrate, which involves a loss of 
lime, also. Nitrogen is also lost to the soil by denitrification, par- 



BOSSES AND GAINS BY THE SOIL 275 

ticularly when the soil is water-logged or receives excessive 
quantities of manure. Considerable losses of nitrogen take place 
in cultivated soils. 

Organic matter is lost from all cultivated soils by oxidation. 
The factors which influence the oxidation of organic matter have 
been discussed in a previous chapter. 

Gains of Nitrogen by Bacterial Action. Considerable amounts 
of nitrogen may be assimilated by legumes in connection with 
bacteria. Crimson clover, according to the New Jersey Station, 
may take up 200 pounds nitrogen per acre per year. Similar 
studies at the Delaware Station 1 with various legumes showed 
the yields to range from 31 to 140 pounds nitrogen per acre. 
Velvet beans gained 213 pounds per acre in Alabama experiments, 
172 pounds in Louisiana, and 141 pounds nitrogen in Florida. 
Cowpeas gained 70 pounds in Alabama, 2 and 35 per cent, was 
left in leaves and stubble if the vines were mowed. Like results 
with other legumes showed an average gain of 122 pounds 
nitrogen per acre for sixteen States. 

It is believed by some that appreciable quantities of free nitro- 
gen may be fixed by soil bacteria, which have no connection with 
legumes, especially when the soil receives manure or other 
vegetable matter for the bacteria to feed upon. This subject 
requires further investigation. Bacteria which have this power 
are certainly present in the soil, but to what extent they aid in 
maintaining the supply of combined nitrogen in the soil, is not 
known. 

Losses in Cropping. This is due to the removal of plant food 
in that portion of the crop which is taken from the land. The 
amount lost in this way varies largely, depending on (a) the size 
of the crop, (b) the kind of crop, (c) the portion of the crop 
removed, and (d) the treatment of the residual portion, besides 
the various factors which influence the amount of plant food 
taken from the soil by the crop. 

The fact that the amount of plant food removed depends 

1 Bulletin No. 60. 

2 Bulletin No. 120. 



276 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



largely on the size of the crop, requires little discussion. The 
plant food removed varies largely with the kind of crop. The 
following figures show the relative amounts of plant food re- 
moved by a portion of different crops. These figures are from 
average values ; indivdual analyses may vary somewhat. 

The quantity of plant food removed by the marketed portion of 
various crops of the size named, 1 is as follows : 
POUNDS OF PLANT FOOD. 





Phosphoric 
acid 


Nitrogen 


Potash 


Corn 40 bushels (corn and cob) 




78 o 




\VheEt 2*5 bushels 


T 1 O 




1 v5- u 




i^.u 




y.u 


Cotton lint (250 pounds) 


O I 


^5.0 
o 8 


.u 














98 o 








181 o 2 


/^.u 




T r Q 




14^5. u 




1^. u 

17 O 


1 oo- u 

72 O 




Rice i ooo pounds 


O/-^ 
12 O 


/^.<J 


/^ u 






3w 


.u 



Loss in By-Products. The by-products consist of the straw, 
chaff, cottonseed, etc., and the loss of plant food depends upon 
how they are disposed of. If they are removed, and sold, or 
otherwise taken away, all the plant food in them is lost. If 
burned and the ashes returned to the soil, the nitrogen is lost. If 
turned under, the loss is much less. If made into manure, which 
is afterwards placed in the soil, there is still some loss. 

PLANT FOOD IN BY-PRODUCTS OF THE CROPS IN PRECEDING TABLE. 





Phosphoric 
acid 


Nitrogen 


Potash 


Cotton seed ( 500 pounds) 




16 


Q 












5 


3 2 


2 3 








29 


Oat straw 




: 3 


1 4 


Rice straw 












X 4 


37 



1 Bulletin No. 125, Texas Station. 

2 A portion of this nitrogen comes from the air. 



LOSSES AND GAINS BY THE) 



277 



Loss of Various Cropping Systems. When a soil is continu- 
ously cultivated to the same crop, such as wheat, and all the 
material removed, it decreases in productiveness, until it reaches 
a low crop level, at which production may be maintained for a 
number of years. 

If the soil receives fertilizers or manure continuously, the losses 
of plant food will be greater, and the soil will adjust itself to a 
higher level of productiveness as long as conditions are so main- 
tained. 

Distribution of the Losses of Nitrogen. At Rothamsted, study 
was made of the disposition of the nitrogen added to the soil dur- 
ing a period of 50 years. Analyses were made of soil from 
different plots treated differently, at the beginning and end of 
the period, of the crops, and of the water from tile drains. 
Of 86 pounds nitrogen added per acre per year in 50 years, the 
disposition seemed to be as follows : 

DISPOSITION OF NITROGEN, PER YEAR. 1 





Average 


Maximum 


Minimum 




r6 7 


2C o 


8 O 




7 6 


z^.u 

TO C 


30 




/.u 

26 7 


A -*'0 

-7T O 


.u 
IQ O 




jc O 


Jl.O 
A A Q 


26 o 




oo- u 







The maximum loss took place with ammonium salts alone. The 
amount of the total loss was estimated by adding the amount of 
nitrogen in the soil at the beginning to the total amount added as 
a fertilizer and subtracting from this the amount present in the 
soil at the end of the fifty years. The nitrogen lost may have 
passed into the ground water below the drains. In this work, 
only 17 per cent, of the nitrogen was used by the crop. It is 
quite possible that with smaller applications of nitrogen, much 
smaller losses and much better utilization of the nitrogen, would 
have taken place. The excessive amounts of nitrogen used 
caused heavy losses. 

1 Bulletin 106, Office Exp. Sta., U. S. Dept. Agr. 



278 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

Gains of Organic Matter. The soil gains organic matter 
through residues of crops, weeds, green crops, and manure. Crops 
are divided into two classes with reference to their effect upon 
the organic matter of the soil namely humus-decreasing and 
humus-increasing. Those crops which leave enough, or more 
than enough vegetable matter in their roots and stubble to restore 
the loss which takes place during their growth, are called humus- 
increasing crops. They are generally crops which receive little or 
no cultivation, and which leave large amounts of roots and 
stubble. Crops such as clover and grasses are humus-increasing. 

Those crops which do not leave enough organic matter to re- 
place the loss by oxidation during their growth are called humus- 
decreasing. On account of the cultivation which these crops 
receive, there is a greater loss of organic matter than with the 
first group mentioned, and less organic matter is contained in the 
stubble. Cotton, corn, potatoes, and beets belong to this group. 

There are some crops which belong to the one or the other of 
these groups according to the disposition made of the residues 
therefrom. For example, if rice straw is removed or burned, it 
is a humus-consuming crop, while if the straw is plowed under 
there may be little or no loss of humus. 

The quantity of organic matter lost when humus-consuming 
crops are grown also depends upon the disposition of the residues. 
Any treatment which results in loss of organic matter that might 
be plowed under, such as burning off of corn stalks or grass, etc., 
increases the loss of organic matter from the soil, and vice versa. 

Green crops, when plowed under, increase the organic matter 
of the soil. Their chief use is to secure nitrogen from the air. 
Plowed under very green, they decompose rapidly and may sour 
the soil. If allowed to mature, decomposition takes place much 
more slowly. Manure is one of the best means of maintaining 
the organic matter of the soil, but many farms do not make 
enough manure to suffice for this purpose. 

Formation of Humus. The accumulation of humus takes place 
more largely under conditions of reduction than conditions of 
oxidation. Climate, weather, nature of soil, etc., are all of in- 



LOSSES AND GAINS BY THE SOIL 



279 



fluence. A high temperature is favorable to decay only when 
accompanied by sufficient moisture, but, as a general rule, a low 
temperature is favorable to accumulation of humus. The less 
the permeability of the soil, the slower is the oxidation and the 
greater is the accumulation of humus. The greater the quantity of 
plant substance produced, the larger the accumulation of organic 
matter in the soil. Dry plant residues decay more slowly than 
green, the straws of cereals more rapidly than the leaves of trees. 
Wood decays more slowly than any of the other materials named. 
In cultivated soil, in spite of the addition of manure, the 
accumulation of humus is less than in similar uncultivated soils 
covered with perennial crops, such as pastures, forests, etc. Both 
lose organic matter, but the protective covering of the latter de- 
creases the loss or even causes an increase. The following table 
shows the carbon content of the soil under three forms of treat- 
ment : 

GRAMS. OF CARBON PER 1,000 GRAMS. SOIL. 





Corn 


Potatoes 
and barley 


Sanfoin 


At the beginning 


J5-2 
7.6 

7-6 


16.2 

7-i 

9-i 


I2. 9 
13-3 

0.4 






Gain ... 





A loss of over half the organic carbon in the soil occurred with 
the cultivated crops, while with the uncultivated crop (sanfoin) 
there was a slight gain. Manure was added to the cultivated plots. 

It appears that cultivated soils become poorer in carbon, no 
matter how much manure is applied, and this impoverishment 
ceases and the soil begins to get richer when the land is filled 
with perennial plants. 



CHAPTER XIV. 



MANURE. 

Manure consists of the excrements of domestic animals, mixed 
with more or less bedding or litter. Barn-yard manure is the 
ordinary mixture of animal excrements, litter, etc., which are 
accumulated on the farm. 

Composition of Manure. Manure is very variable in composi- 
tion, depending on the kind and age of the animal, the kind and 
amount of food, the litter or absorbents used, and the method of 
keeping or preserving it. Ordinary barn-yard manure which has 
received reasonable care, may be safely assumed to vary in 
composition between the following limits: 





Per cent. 


Average 
per cent. 




o 4-0 8 


O47 


Phosphoric Ecid. 


O 2-O ^ 




T>ntactl 




^66 


"\X7otpr 




0.49 
67 f> 









The average composition of carefully preserved manure from 
different animals is about as follows : x 

PERCENTAGE COMPOSITION OF MANURE. 





Water 


Nitrogen 


Phosphoric 
acid 


Potash 


Sheep 


CQ C 


O 77 






Calves 


oyo 

77 7 


u.// 

Or/-) 


u -oV 
o 1 7 


u -oV 


TT op -c 




OS/i 


*** / 


u Ov3 


Oow<; 


Jtl-L 




39 


3 3 




/O'O 
/l8 7 


u -4o 




n /i8 


Hens 


4'/ 


U '4V 

















Comparative Value of Solid and Liquid Manure. The solid 

manure of animals consists of the undigested residues of the food. 

The urine contains the fertility ingredients which have been 

digested. The composition of the solid and liquid excrement 

1 Beal, Farmers Bulletin No. 77. 



MANURE 



281 



from farm animals is approximately as follows, though con- 
siderable variations occur : 

PERCENTAGE COMPOSITION OF EXCREMENTS. 





Water 


Nitrogen 


Phosphoric 
acid 


Potash 


Solid 


Liquid 


Solid 


Liquid 


Solid 


Liquid 


Solid 


Liquid 




7 6 

8 4 
80 
58 


89.0 
92.O 
97-5 

86.5 


0-5 
0-3 
0.6 
0.8 


1.2 

0.8 

0.3 

1.4 


0.4 
0-3 
0-5 
0.6 


trace 
trace 

0.13 
o 05 


0.4 
O.I 

0.4 
0.45 


1-3 

1-3 
0-45 

2.O 






Sheep 





Poultry excrement, when fresh, contains about I per cent, 
nitrogen, 0.8 per cent, phosphoric acid, and 0.4 per cent, potash. 
The results of an experiment made at the Pennsylvania Experi- 
ment Station, to ascertain the distribution of the fertilizing in- 
gredients among the solid manure, the liquid manure, and the 
milk or increase in weight, are as follows : 





Liquid 
manure 


Solid 
manure 


Milk 
or increase 




Per cent. 

CQ 


Per cent. 


Per cent. 

1 7 


Phosphoric acid. 


U 


oo 

7c 


1 / 
or 


Potash 


IJC 


/O 

16 


O 




/O 







Loss of urine therefore involves the loss of 50 per cent, of the 
nitrogen fed, and about 75 per cent, of the potash. 

Influence of Age and Kind of Animal. An animal which is 
not gaining flesh, producing milk, or laying eggs, etc., will excrete 
practically all the potash, phosphoric acid, and nitrogen eaten. 
These ingredients are taken in with the food, used, and are ex- 
creted in the waste products. If no flesh, etc., is produced, the 
outgo and income must be equal. A young growing animal retains 
in the bones, flesh, etc., a portion of the fertilizing materials fed to 
it. Animals producing milk, laying eggs, etc., utilize some of the 
phosphoric acid, and nitrogen in these products. 
19 



282 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

The Mississippi Experiment Station determined income and 
outgo of plant food, and found that young fattening steers excrete 
on an average 84 per cent, of the nitrogen, 92 per cent, of the 
potash, and 86 per cent, of the phosphoric acid of the food con- 
sumed. 

Differences in the composition of manure from differ- 
ent animals are due in part to difference in the food eaten by the 
animal, and in part to the water-content of the manure. Animals, 
such as hogs, which feed on concentrated foods, produce a 
stronger manure than those which require more bulky food, such 
as horses and cows. 

Sheep manure is a rich manure containing only a small amount 
of water. It ferments more rapidly than cow manure, but not 
as readily as horse manure. It is concentrated and valuable for 
gardening purposes. 

Horse manure is dry, undergoes fermentation rapidly, and gen- 
erates a high heat on account of its loose texture. In the pro- 
cess of fermentation the nitrogen is converted into ammonium 
carbonate, which, being volatile, is liable to be lost. A well fed 
horse at ordinary hard work will produce about 50 pounds of 
solid and liquid excrement per day. 

Hog manure is very variable in composition. It contains much 
water, ferments slowly, and generates little heat in fermentation. 

Coiv manure is poorer than hog manure, decomposes slowly 
and generates little heat. A milch cow will excrete daily about 20 
to 30 pounds liquid and 40 to 50 pounds solid excrement per day. 

Poultry manure is rich in nitrogen. It ferments rapidly and 
easily loses nitrogen. In order to prevent loss from volatilization 
as ammonia, some preservative should be added to it. 

Quality and Quantity of Feed. Since manure can contain only 
the fertilizing constituents of the food, the composition of 
manure depends largely on the composition and amount of the 
food. If the food is poor in nitrogen, phosphoric acid, and 
potash, the manure will also be poor. The richest manure will 
be obtained when concentrated materials rich in nitrogen are fed, 
such as cottonseed meal, gluten meal, bran, clover hay, etc. Since 



MANURE: 



animals fed on heavy rations for fattening or for the production 
of milk must be fed concentrated food, it follows that manure is 
more valuable from these animals than from animals fed for 
maintenance. In many instances the value of the fertilizing 
materials contained in purchased feed is nearly as great as the 
food value. This is very often the case with cotton seed meal 
purchased in the Southern States. The farmer who saves both 
solid and liquid excrement in the manure, is getting two values for 
the money expended. If the liquid excrement is lost, something 
over 50 per cent, of the fertilizing value of the feed goes with it. 
The fertilizer constituents of the liquid manure are also more 
valuable, pound for pound, than those in the solid manure. The 
liquid manure contains in solution and readily available those 
substances which have been digested by the animal. The pur- 
chase of feeding stuffs accompanied by the careful saving of 
manure, is one way to secure plant food for the farm. This 
method is extensively applied in European countries. 

Different feeding stuffs vary considerably in their content of 
plant food. The following table gives the manurial value of 
some farm products. 

MANURIAL VALUE OF FARM PRODUCTS, POUNDS PER TON. 





Nitrogen 


Phosphoric 
acid 


Potash 






8, 


l{\ A 








if> f\ 








30.0 




.u 

Ar\ 2 


* 


II.4 
08 f\ 




TQC 7 




tA Q 




1U O- / 
T 7 c 7 


o*--* 

eft 2 




\yheat 


M> / 

1*] r 


O u -^ 
jr ft 


29.2 


Oats 


6/-5 
?5 A. 


1^.0 
T 2 A 


Q Q 


Porn 




T T 8 




Rarlpv 


66' l 




7-4 


Milk 


oV- / 


i o-4 


9.0 


Cheese 


QO 6 


4 


3- 




yu.u 
C7 2 


23.0 


5- 




JJ-* 


Ol" i 


3- 



Kind and Amount of Litter. Litter is used to furnish a clean 
bed for the animal and to absorb the liquid excrement. It makes 
the manure easier to handle, increases its physical (and in some 



284 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



cases, its chemical) action on the soil, and checks and controls 
decomposition. The materials used for litter are not, as a rule, 
rich in fertilizing ingredients. It is more important that all the 
fertilizing ingredients of the manure should be preserved than 
that its percentage composition should be increased or diminished. 

Straw is usually used for litter because it is one of the by- 
products of the farm. It is a good absorbent, though rather poor 
in fertilizing constituents. 

Leaves are good absorbents. 

Dry peat is an excellent material, as it has a high absorbing 
power and contains fair amounts of nitrogen. 

Sawdust is a good absorbing material, but poor in fertilizing 
constituents. 

The composition of some materials used as litter is as follows : x 
POUNDS PER TON OF LITTER. 





Nitrogen 


Phosphoric 
acid 


Potash 




l6 


6 


6 


Straw 


8-12 


A 6 


1 2 12 




16 




* d* 


Sa wflimt 




5 












Peat 

















Losses of Manure. All the plant food in the excreta of animals 
cannot be saved. There are some unavoidable losses in nearly all 
methods of collecting manure. The least loss of fertility occurs 
when the animals are fed in the field to be manured, as the 
excreta, solid and liquid particularly the liquids are then 
absorbed by the soil. When manure is stored or preserved, there 
is always a loss of plant food. The Rothamsted Experiment 
Station estimates that, as a rule, under English conditions, one- 
half of the nitrogen of the feed is lost, one-fourth of the phos- 
phoric acid, and none of the potash. The chief causes of loss are 

(1) seepage, or penetration of the liquid manure into the soil; 

(2) weathering, or exposure to rain; (3) fermentation. 
1 Beal, Farmers Bulletin No. 77. 



MANURE: 285 

When the animals are stabled on a wood or dirt floor with in- 
sufficient bedding, a portion of the liquid excrement soaks into 
the ground. The quantity depends upon the tightness of the floor 
and the absorptive power of the manure or the litter. A similar 
loss occurs when the manure is stored in piles on the earth. A 
portion of the liquids sink in the earth. Cement floors prevent 
such losses, and are used to a considerable extent in certain 
localities. Clay when worked until puddled, and then tamped, 
makes a fairly good floor. 

Loss by seepage may be decreased by using the proper quantity 
of litter, and by collecting and preserving the manure on an im- 
pervious floor. An excess of litter makes the manure too coarse. 
The following table 1 shows the absorptive power of various 
litters : 

Water retained by 

100 pounds material 

after 24 hours 

Wheat straw 220 

Oak leaves (partly decomposed) 162 

Sawdust 435 

Peat 600 

Peat moss 1,300 

Soil rich in humus . 50 

The amount of litter should depend on the character of the 
food. Watery foods and those containing much nitrogen increase 
the secretion of urine and so increase the amount of litter neces- 
sary to absorb the urine and keep the animal clean. Manure pro- 
tected from rain by a shed, according to Kinnard, produced 4 
tons more per acre of potatoes, and n bushels more wheat, than 
the same quantity of manure not protected by a shed during the 
same period of time. 

When manure is exposed to rain, a part of the fertilizing con- 
stituents is washed away, somewhat in proportion to the length 
of the exposure and the amount of rain. The soluble ingredients 
so lost are the more available and more valuable part of the 
manure. Experiments have been made in which a quantity of 
manure was weighed and subjected to analysis and after a certain 
1 Herbert, Exp. Sta. Record No. 5, p. 144. 



286 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



period, again weighed and analyzed. The following are some of 
the results : 





Where made 


New York 


New 

Jersey* 


New 

Jersey 1 


Canada 


Ohio? 


Material 


Hon-e 
manure 


Cow dung 


Dung 
and urine 


Horse 
manure 


Steer 
manure 




1 80 
5<># 

50 fo 
50 % 


109.0 
37-6 

51-9 

47.1 


109 
51 
51 
61 


365 
33 
16 

34 


90 
28 
H 
58 


L/oss of nitrogen per cent . . 







Exposure to rain certainly involves a considerable loss of 
fertility. 

Fermentation. 3 Two classes of bacteria take part in the fer- 
mentation of manure ( I ) Aerobic, which live only in the presence 
of oxygen, (2) Anaerobic, which live only when oxygen is ex- 
cluded. On the outer surface of the heap, the aerobic bacteria 
are active, while the anaerobic ferments act in the interior of the 
heap where the supply of air is limited. The anaerobic bacteria 
are less vigorous in their action than the aerobic. They often 
produce foul smelling gases. The fermentation also varies ac- 
cording to circumstances. It depends on the temperature, the 
supply of air, the moisture, the composition of the material, and 
the preservatives used. 

The optimum temperature for manure fermentation is about 
131 F. The temperature may rise high enough to set the mass 
on fire, if it is dry enough. The temperature of the interior of 
the heap, where anaerobic fermentation is in progress, rarely 
rises over 95 F. 

The supply of air is determined by* the compactness of the heap. 

1 Bulletin 150. 

2 Bulletin 183. 

3 Herbert, Exp. Sta. Record 5, p. 146. 



MANURE 287 

If the heap is too loosely built, the fermentation is too rapid, and 
large losses of nitrogen will occur. 

Moisture, by lowering the temperature and excluding air, re- 
tards fermentation ; loss of manure is decreased by keeping the 
manure properly moistened. Alternate wetting and drying is 
also bad. 

Manure decreases rapidly in bulk during fermentation, the 
substances of which it is composed being decomposed partly into 
carbon dioxide and water. When the fermentation is not 
properly controlled, nitrogen may escape as free gas or as am- 
monia. The coarse materials are gradually decomposed and are 
to a considerable extent dissolved in the black liquid which oozes 
out of the manure heap. The mineral matter is also rendered 
more soluble. 

The nitrogen in the liquid excrement is mostly present as urea 
or hippuric acid. These undergo fermentation rapidly, especially 
in a warm climate, producing ammonium carbonate, and con- 
siderable amounts of ammonia may escape into the air. Ammonia 
is produced in fermenting manure, and if the manure is 
allowed to dry out, or is too freely exposed to the air, consider- 
able losses of ammonia take place. 

Fermentation is controlled by keeping the manure heap com- 
pact and moist, and by the use of preservatives. Sprinkling the 
mass with water or liquid manure excludes air and prevents loss 
of ammonia. If the mass dries out, nitrogen is lost. Gypsum 
(land plaster), kainit, and acid phosphate are preservatives re- 
commended to prevent loss of manure during fermentation, but 
it is doubtful whether they have any appreciable effect. 

Methods of Saving Manure. The following are some methods 
of saving manure: 

(i) Grlgnon Method. This method is used extensively in 
France. The manure is piled upon a stone or cement pavement 
in the farm courtyard, in flat, well packed layers. The liquid 
manure, and the drainage from the manure pile runs into a stone 
cistern. From time to time the liquid manure is pumped over the 
pile of solids. The object of this is to keep the manure moist 



288 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



and to prevent loss by excessive fermentation, and also to cause 
the manure to decompose evenly. When thoroughly rotted, the 




Fig. 68. The Grignon system of keeping manure. 




Fig. 69. Liquid manure spreader. Switzerland. 

manure is very dark, brittle mass, and is said to be very effective 
in its action. 



MANURE 289 

(2) Liquid Manure Method. This method is used in Ger- 
many, Belgium, and Holland. The liquid manure is carried to an 
underground tank by means of stone troughs. The solids are 
kept separate. The liquid manure is pumped out and applied to 
the soil about six times a year, or oftener. 

(3) Deep-Stall Method. The animals are kept in deep stalls 
with paved floors. Sufficient bedding is used to keep the animal 
dry and the manure is allowed to accumulate in the stall. The 
feeding rack and water vessels are hung on chains, so that they 
can be raised as the manure accumulates. The manure is taken 
out once or twice a year. When the climate is cool, this method 
has given good results. At the Pennsylvania Station, 1 there was 
a loss of only 5.7 per cent, of the nitrogen, 5.6 per cent, potash, 
and 8.5 per cent, potash, compared with 34.1 per cent, nitrogen, 
19.9 per cent, potash, and 14.2 potash lost from similar manure 
in a covered shed. 

(4) Absorption Method. The liquids are absorbed with straw, 
peat, sawdust, or dirt, etc., and taken out with the solids. The 
manure is allowed to accumulate, or hauled out to the fields daily. 

( 5 ) Feeding Off and Pasturing. When the crops are pastured 
or fed off, the manure is dropped directly in the field. 

Application of Manure. The kind and amount of manure to 
be applied depends on conditions. The least loss takes place when 
the manure is applied as fresh as possible. Manure decays more 
rapidly in an open soil than in a close soil (clay). If it is desired 
to improve the mechanical condition of a clay, fresh manure should 
be applied, but the fertilizing constituents act more rapidly in a 
clay soil when manure is well rotted. Fermenting manure seri- 
ously injures the quality of tobacco, sugar beets, and potatoes. 

The manure may be (a) placed in heaps, and then spread, (b) 
spread broadcast and ploughed in, (c) applied in hill or drill with 
seed. The first method is objectionable, as the small heaps may 
lose fertility rapidly, and the spots made much richer than the 
remainder of the field. The second method is good if the manure 
1 Bulletin 63. 



2QO PRINCIPLES OF AGRICULTURAL CHEMISTRY 

is soon ploughed in. The third method is applicable to some 
truck crops. 

The amount of manure applied varies from 3 to 40 tons per 
acre. In arid JOT dry climates, the manure should be composted, 
and well rotted. Coarse manure should not be plowed under in 
the spring in dry sections, as the layer of manure will break the 
connection between plowed and unplowed soil, and cause the 
plowed soil to dry out more rapidly, thereby losing water needed 
for the crops. Coarse manure may be applied best as a top dress- 
ing on pasture land. 

Well rotted manure may cause wheat to lodge. It can be 
applied to corn. 

Practice in applying manure varies. In some places, heavy 
applications are made every four years or more. In other places, 
it is applied annually in smaller quantities. It is probably better 
to apply the manure once in a rotation of crops to the crop which 
does best with it. Manure is valuable not only for the plant food 
which it contains, but also for its physical and chemical effects on 
the soil. The lasting effects of manure are shown by experi- 
ments at Rothamsted and Woburn, England. At Rothamsted, 
one plot had received manure for 20 years, and none after that. 
Barley has been grown on this plot for 58 years, and still shows 
the effect of the manure applied 38 years ago. Thirty years 
after the last application of the manure, the crop of barley on the 
manured plot was twice as large as that which had never received 
any fertilizer or manure. At Woburn a plot which had received 
manure a few years continued for 25 years to give better yields 
than one which had received no manure. 

Green Manures and Cover Crops. 1 Green manures and cover 
crops are planted to be plowed under. It is of course more de- 
sirable to feed the crop and save the manure, thereby utilizing its 
feeding value and most of its fertilizing value, but this procedure 
is not always practicable. 

The objects of green manure and cover crops are as follows : 

(i) To supply organic matter to the soil. 
1 Farmers Bulletin 278. 



MANURE: 



291 



(2) To prevent loss of plant food by leaching. The soil is 
covered with a crop instead of being left bare. The crop takes 
up most of the plant food in solution and prevents it being washed 
out of the soil. 

(3) To secure nitrogen from the air for the use of succeeding 
crops. For this purpose, leguminous crops should be grown, and 
they must be infected with the proper organism. 

Green manures should, if possible, be allowed to mature before 
being plowed under. A large mass of easily decaying matter 
may sour the soil and injure it for some years. Lands which are 
decidedly wet are also not benefited by green manures, as they 
may denitrify. An acid condition of the soil may be corrected by 
lime. 

As a rule, it is best to follow green manures with cultivated 
crops. The tillage of such crops hastens the decay of the 
vegetable matter, and by aerating the soil, favors additional nitro- 
gen fixation by the soil bacteria. Corn, cotton, potatoes, and 
heavy tobacco derive great benefit from green manures. 

The following table shows the effects of green manures on 
crops compared with crops on the same soil which had no green 
manure. 



Locality 


Manure crop 


No manure 


Green manure 


Illinois 
Ottawa . 


red clover 


35.7 (grown continuously) 
^8 8 ( T vear^i 


55.1 bu. corn 


Ottawa . 




2Q o . .... 




Arkansas 
Alabama 


cowpeas 
cowpea vines 


10.1 (continuous 4 years) 

877 o . 


14.1 bu. wheat 


Alabama 


cowpea vines 


12 A. bushels 


22 8 bu oats 


Maryland 


crimson clover 


C2 8 bushels 




Maryland. 


crimson clover 


67 8 bushels 













Fallen leaves and stubble have some fertilizing value, even 
when the crop is cut for hay. For example, at the Alabama Ex- 
periment Station, 36.6 of the entire weight of the cowpea plant 
was found to be in the fallen leaves and stubble. The hay in one 
experiment contained 55.8 pounds nitrogen per acre, the fallen 
leaves and stubble 31.4 pounds. 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 

Effects of Manure. Some effects of manures are as follows: 
(i) They make clay soils more porous, in better tilth and more 
easily worked. (2) They make sandy soils more retentive of 
moisture. (3) They improve the physical character of the soil 
and make it better suited for plant growth. (4) They supply 
nitrogen and other plant food. (5) They supply organic matter 
which may aid soil bacteria to fix free nitrogen. (6) They are 
lasting in their effects. 



CHAPTER XV. 



SOURCES AND COMPOSITION OF FERTILIZERS. 

When knowledge that certain elements are essential to plant 
life was first secured, the action of various elements were tested 
in practice upon soils in order to see which of these are not pres- 
ent in sufficient quantity. For example, at Rothamsted, plots are 
still fertilized with sulphate of magnesia. In the process of time, 
it was found that phosphoric acid, potash, and nitrogen were the 
substances needed for plant food, and a fertilizer is now generally 
defined as a substance which contains phosphoric acid, potash, or 
nitrogen, or a mixture of them, and is used as an application to 
the soil to promote the growth of plants. A further requirement 
is that the potash, phosphoric acid, or nitrogen be in such forms 
as to be readily taken up by plants. The value of the fertilizer 
is based upon the amount of these three substances it contains. 

Fertilizers have other effects on the soil in addition to their 
supply of plant food. They may affect its acidity or alkalinity, 
its physical structure, etc. Substances which contain little or 
no phosphoric acid, potash, or nitrogen, and are used upon the 
soil for other reasons, are termed amendments. Lime, for 
example, is an amendment. 

Nitrogenous Fertilizers. Nitrogenous fertilizers are divided 
into two groups, inorganic and organic. The two inorganic 
materials, nitrate of soda and ammonium sulphate, may be directly 
assimilated by plants, though the ammonium sulphate usually 
undergoes some nitrification and is converted partly into nitrates. 
Organic substances, such as dried blood, cottonseed meal, tank- 
age, etc., must first undergo changes in the soil, by which the 
nitrogen is converted into ammonia or into nitrates, or into 
organic compounds which can be assimilated by plants. The dif- 
ferent nitrogenous fertilizers have different agricultural values, 
depending on the readiness with which they can be assimilated. 

Inorganic Nitrogenous Materials. Nitrate of soda is found in 
the rainless districts of South America mixed with dirt and com- 
mon salt, as deposits termed caliche. It contains on an average 



294 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



about 25 per cent, nitrate of soda. The best quality of caliche con- 
tains approximately 50 per cent, nitrate of soda, NaNO 3 , 26 per 
cent, common salt, 6 per cent, sulphate of soda, 14 per cent, dirt, 
etc., insoluble in water, and about 4 per cent, magnesium sulphate 
and chloride, with small amounts of sodium iodide. The caliche 
is treated with hot water and the solution run into crystallizing 
vats. The crude nitrate of soda crystallizes out on cooling. 
Nitrate of soda is readily soluble in water, easily taken up by 




Fig. 70. Nitrate of soda, partly blasted up. 

plants, and, unless taken up by plants, will be washed from the 
soil. It contains about 15 per cent, of nitrogen. It is often 
called chile saltpeter. 

Sulphate of ammonia is a by-product obtained in the manu- 
facture from coal, of illuminating gas, and of coke. A part of the 
nitrogen of the coal passes off as ammonia, and is removed by 
passing the gas through sulphuric acid, forming sulphate of am- 
monia (NH 4 ) 2 SO 4 . It contains about 20 per cent, of nitrogen. 
Ammonia is fixed by the soil, and is not as available to plants a$ 



SOURCES AND COMPOSITION OF FERTILIZERS 



295 



nitrates, or as easily washed out. It changes to nitric acid in the 
soil, and nitric acid and sulphuric acid unite with lime to form 
nitrates and sulphates. The use of ammonium sulphate tends to 
decrease the carbonate of lime in the soil, or to render the soil 
acid. 

Calcium Cyanamide. This substance is prepared by passing 
atmospheric nitrogen over calcium carbide. It decomposes slowly 




Fig. 71. Crystallizing pans with nitrate of soda. 

in the soil, with the production of nitrates. Under the most 
favorable conditions, it appears to have a value equal to sodium 
nitrate, but if applied too soon before planting, or to acid humus 
soils, it may have injurious effects. 

Organic Materials. The organic nitrogenous fertilizers cannot 
be taken up directly by plants but must first be converted into am- 
monia or nitrates. Their value depends upon their content of 
nitrogen, and the readiness with which they undergo decomposi- 
tion in the soil. 



296 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

Dried blood comes from the large slaughtering establishments, 
and is of two kinds, red and black. The red dried blood results 
from drying at the temperature of boiling water, at which tem- 
perature it does not char. The black dried blood is dried at a 
higher temperature, and decays more slowly. Dried blood is one 
of the most concentrated organic nitrogenous fertilizers. It con- 
tains about ii per cent, nitrogen. It decays quickly in the soil. 

Dried meat or meat meal is obtained from rendering establish- 
ments, where the different portions of dead animals are variously 
utilized. It is rich in nitrogen, and, like blood, decays rapidly. It 
also comes from slaughter houses where the waste meat is kept 
separate from the tankage. 

Dried fish or fish scraps come from two sources : first, the offal 
of fish canneries, and second, the fish pomace resulting from the 
extraction of oil from Menhaden or other fish. The latter pro- 
duct is more uniform than the former, containing 7 to 9 per cent, 
of nitrogen and 6 to 8 per cent, phosphoric acid. Fish unfit for 
eating may be caught, the oil extracted, and the residue prepared 
into fish guano. 

Tankage consists chiefly of the dried animal wastes from the 
large slaughtering establishments; to some extent it comes from 
the garbage plants of large cities. It is very variable in com- 
position, since it contains all parts of the carcass which cannot be 
used for other purposes the bones, tendons, flesh, etc. Tankage 
varies so much that it is always sold in the trade on the basis of 
its composition, and each shipment is subjected to analysis. It 
contains 5 to 10 per cent, nitrogen and 6 to 15 per cent, phosphoric 
acid. As a rule the fat and gelatine are removed by treatment 
with super-heated steam. Garbage tankage is less valuable than 
slaughter house tankage. It contains approximately 3 per cent, 
nitrogen and 1.2 per cent, each of phosphoric acid and potash. 

Cottonseed meal is prepared by grinding the cake left from 
pressing the oil from cottonseed kernels. It is one of the best 
vegetable fertilizers. It is an excellent cattle feed, and its most 
economical use takes advantage of both its feeding and its 
fertilizing values, by feeding the meal and saving the manure. It 



SOURCES AND COMPOSITION OF FERTILIZERS 297 

contains 6 to 8 per cent, nitrogen, about 1.5 per cent, potash, and 
2.5 per cent, phosphoric acid. 

Cotton seed have approximately one-half the fertilizing value of 
the meal. They contain approximately 3 per cent, nitrogen and 
1.2 per cent, each of phosphoric acid and potash. 

Linseed meal contains less nitrogen than cottonseed meal. The 
demand for this product for feeding purposes makes it an 
expensive source of nitrogen in fertilizers. 

Castor pomace is not useful as a cattle food. It is about as 
rich as linseed meal, and is a good fertilizer. It contains 5 to 6 
per cent, nitrogen and i.o to 1.5 per cent, each of phosphoric acid 
and potash. 

Bat guano is the excrement of bats, found to a limited extent 
in caves in Texas, Mexico, and Porto Rico. It is liable to 
spontaneous combustion, the residue being known as bat guano 
ash, which is not easily distinguished from bat guano. Bat guano 
is variable in composition, ranging from a compound rich in nitro- 
gen to one rich in phosphoric acid. It contains from 2 to 12 per 
cent, nitrogen and from i to 8 per cent, phosphoric acid. 

Hoof and horn meal is a by-product from the making of var- 
ious articles from hoofs and horns. It contains about 14 per 
cent, nitrogen. 

Slowly Available Nitrogenous Fertilizers. These materials give 
up their nitrogen very slowly, so that they often have little or no 
effect upon the crop to which they are applied. In many States 
the use of these materials in mixed fertilizers is prohibited. 

Leather scraps is a waste product from various factories, and 
is sold as raw leather, steamed leather, and roasted leather. It 
contains about 7 to 8 per cent, nitrogen. 

Hair is a product from slaughter houses, containing 9 to 14 per 
cent, nitrogen. 

Peat and muck may contain as much as 2 per cent, nitrogen. 

Wool waste is a by-product from woolen factories. 

Availability of Nitrogenous Fertilizers. The nitrogen of nitrate 
of soda and ammonium sulphate may be taken up directly by 
plants, but the value of the other nitrogenous materials depends 
20 



298 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

upon the rapidity and extent with which they become changed to 
nitrates and ammonia in the soil. It is important to know the 
relative values of these materials. The measure of their value is 
the quantity of nitrogen which may be secured from them by 
plants under favorable conditions. This is termed availability. 

Availability is based upon value to plants in pot experiments. 
For the purpose of comparing nitrogenous materials, a soil 
decidedly deficient in nitrogen is selected, mixed thoroughly, and 
an equal quantity placed in a number of pots. Each pot then 
receives an equal and abundant amount of phosphoric acid, 
potash, and lime if necessary. One set of pots (two or more) re- 
ceives no nitrogen. The others receive an equal quantity of nitro- 
gen, say 0.3 gram for example, in the form of nitrate of soda, sul- 
phate of ammonia, cottonseed meal, or other substances to be 
tested. An equal number of seeds of equal weight are planted in 
eacn pot, and the crops are grown under the same conditions as 
regards moisture, air, light, etc. They are then harvested, and 
the quantity of nitrogen secured from each pot determined. This 
nitrogen comes from both soil and fertilizer. The quantity of 
nitrogen secured from the pots to which no fertilizer nitrogen 
has been added is subtracted from the others to ascertain how 
much nitrogen was secured from the fertilizer. The amount of 
nitrogen taken from one of the materials (usually sodium nitrate) 
is adopted as a standard, (equal to 100) and the results expressed 
in terms of this. For example, if 0.250 gram nitrogen was secured 
from sodium nitrate by the plants and 0.180 gram from cottonseed 
meal, the availability of the nitrogen of cottonseed meal would 
be 0.250 : 180 : : 100 : x, or equal to 72. 

Considerable care is required in the conduct and planning of 
experiments of this kind. Two or more pots must be used for 
each material. Nitrogen must be the controlling factor in the 
growth of the crop, and, in order to be certain such is the case, it 
is best to have several sets of pots with different amounts of nitro- 
gen, such as 0.3, 0.6, 1.2 grams per pot for example. If nitrogen is 
the limiting condition, as it should be, the amount of nitrogen 
taken up by the plants will be in proportion to the quantity 



SOURCES AND COMPOSITION OF FERTILIZERS 



299 



applied. If there are other limiting conditions, the series to 
which they apply should be rejected. 

Some workers have taken the weight of the crop as a measure 
of the availability of nitrogen, but since the object of the work is 
to ascertain what proportion of the nitrogen of the fertilizer can 
be taken up under the most favorable conditions, it is obvious that 
the amounts of nitrogen recovered is the only correct measure. 
The nitrogen taken up by the crops is not necessarily in propor- 
tion to their weights. For example, Johnson, Britton, and Jenkins 1 
secured the following results, with oats : 



Amount of nitrogen applied grams . . 
Ratio of nitrogen 


0.8 

IO.O 

31.7 

IO.O 

0.384 

IO.O 


1.6 

2O.O 

57-8 
18.0 
0.778 

20.0 


2.4 
30.0 
27.7 
9.0 
1.064 
28.0 


3-2 
40.0 

40.7 ' 
13.0 
1.404 

36.5 


^^eight of crop granjt> 











In this experiment, the quantities of nitrogen taken up are 
nearly in proportion to the amounts of nitrogen applied, but the 
weights of the crops are not. 

Conditions which Affect Availability. The conditions which 
affect nitrification also affect availability, since nitrification is 
a necessary process for the preparation of active nitrogen. The 
length of the growing season is an important factor ; a long grow- 
ing season being relatively more favorable to the slowly nitrified 
materials. If a crop is grown and harvested and then a second crop 
grown without any addition of fertilizer nitrogen, the slowly act- 
ing nitrogen will appear relatively more effective than if one crop 
only is considered. For example, Voorhees found the availability 
of fresh solid manure (compared with nitrate of soda equal to 
100) to be 12 when one crop (oats) alone was considered, but 43 
when the nitrogen in two crops, oats and millet, was taken. 

On account of the effect of the conditions of the experiment, 

and also on account of the error inherent in the method of work, 

considerable differences in the availability of the nitrogen of 

fertilizers are observed by different workers. The following 

1 Report Connecticut Exp. Sta., 1893. 



300 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



table gives some determinations made on some ordinary nitro- 
genous materials : 

COMPARATIVE AVAILABILITY OF NITROGEN FERTILIZERS. 





Connecticut Station 
4 seasons. 1894-7 


Wagner 
3 years 

Average 


Pfeiffer 
et. al., 1895-7 

Average 


Maximum 
and 
minimum 


Average 


Nitrate of soda 


100 

60-78 
72-87 
64-70 

57-77 

49-73 
65-81 
69-74 
0.0-1.9 
55-76 
8.1-18.5 
7.1-10.2 


ICO 
69 

68 
17 
67 

66 

70 
i 
65 
13 
9 


100 
6 9 

64 
61 

63 
67 

20 

54 
33 
68 

32 


100 
87 
85 

8 5 

66 

46 
56 








Fish 






























Barnyard manure preserved 





Comparative Availability. The availability of nitrogenous fer- 
tilizers for different series of experiments made by the same in- 
vestigator exhibit considerable differences. Some workers have 
studied only the effect upon the first one or two crops, while 
others take into consideration the effect on several succeeding 
crops. The results of the Connecticut Station 1 given in the table, 
were secured in three series of experiments with (i) corn, (2) 
oats and corn, and (3) corn, in 10 pounds artificial soil composed 
of coal ashes and 3 per cent, moss, the root and fertilizer residues 
remaining in the soil from year to year. A fourth series, with 



1 Connecticut State Station Report, 1897, p. 257. 



SOURCES AND COMPOSITION OF FERTILIZERS 



301 



oats and Hungarian grass was made on 25 pounds sandy loam. 
The results of Wagner were on small plots with summer rye, flax, 
summer wheat, and carrots, and are the average of 3 seasons. 
Pfeiffer and associates used 27 kgs. poor sandy soil, and the 
effect of the residues for two years was considered, which in- 
creased the value of stable manure decidedly. 

Voorhees at the New Jersey Experiment Station 1 made experi- 
ments with out-of-door cylinders, 3 square feet surface area and 
4 feet deep, with corn, oats, and millet, oats and corn. Considera- 
tion of the second crop in each case increased the availability of 
manure decidedly. Root residues and fertilizer residues probably 
remained for succeeding crops, unless washed out during the 
winter. Some of his results are as follows : 





Oats 


Oats and 
millet 


Oats 


Average 2 

1898-1907 


Ammonium sulphate 








flC\ 1 


Dried blood. 


/**y 

c c 


77-9 
fii i 


yo. 2 

f.Q A 


09-7 


Fresh manure solid 


o-o 


01 .<, 




O4.4 


Solid manure leached 


12 O 


4o- u 




35-9 

3Q Q 


Solid and liquid fresh 


tr o 


88 o 




o.y 


Solid liquid leached 




27 Q 




OO' U 






OO' U 




4o >x 



Biological Methods of Availability. Since organic materials 
must be transformed into ammonia and nitrates before being 
taken up by plants, the quantity of ammonia and nitrates pro- 
duced from a given amount of nitrogen in the soil, with not too 
short a period, may be used for comparing nitrogenous materials. 
The quantity of nitrates produced from 0.3 gram nitrogen in 500 
gram soil in four weeks varied with different soils, and was not in 
proportion to the value of the materials, but the quantity of nitro- 
gen converted into nitrates and ammonia was in proportion to the 
availability of the material. The following table gives some of 
the results. 

1 Report, 1901, p. 144. 

- Voorhees and Lipman, Bulletin 221, New Jersey Station. 



3 02 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



Fertilizer 1 


Percentage of added nitrogen converted into 


Nitrates 


Nitrate 
and ammonium 




Soil No. 75 
8.2 

6.6 
18.6 
17.5 


Soil No. 77 

20.3 

23-1 
17.6 
17-8 
9 .6 


Soil No. 75 

SI'S 

56.4 
20.7 
29.1 


Soil No. 77 

394 
43-9 

23.9 
24.8 

9.9 


Rlood 











Chemical Methods. Chemical methods do not determine the 
relative availability of the material, but distinguish between sub- 
stances of high and of low availability. Three methods have been 
proposed : 

(1) Digest with pepsin hydrochloric acid, filter, wash, and 
determine nitrogen in the residue. 

(2) Digest 2 with neutral permanganate of potash in a boiling 
water bath, filter, wash, and determine nitrogen in the residue. 

(3) Distil with caustic soda and permanganate, and determine 
the ammonia which passes over. 

Each of these methods has its advantages and disadvantages. 
Method (3) is not applicable to cottonseed meal. All the 
methods depend on differences in the resistance of the various 
materials to the reagents employed. 

Influence of Conditions on Availability. Various conditions 
affect the availability of nitrogen in fertilizers, such as acidity of 
soils, fineness of division of bone, etc. 

Wheeler, 3 in an unlimed acid soil, found the availability of 
blood to be 45.5, and ammonium sulphate injurious, while on the 
same soil limed, their values were 90.3 and 45.5 respectively. 
Johnson, Jenkins, and Britton 4 tested the availability of nitrogen 
in bone of different degrees of fineness; for meal less than 1/150 

1 Fraps, Bulletin 106, Texas Station. 

2 See Street, Report Connecticut Exp. Sta., 1911, Fertilizers, p. 9. 

3 Bulletin 53, Rh6de Island Station. 

4 Connecticut State Station Report, 1897, p. 257. 



SOURCES AND COMPOSITION OF FERTILIZERS 303 

inch, compared with nitrate of soda as 100, it was 11.3; 1/150 to 
1/50 inch, 8.5; and 1/25 to 1/50, 5.6. 

Any agency which accelerates the transformation of organic 
bodies into assimilable compounds would increase the availability 
of the nitrogen. The temperature, nature of soil, and activity of 
the organisms in the soil would thus be of effect. 

Agricultural Value. The availability of a nitrogenous fer- 
tilizer is measured by the amount of nitrogen which plants can 
secure from it under the most favorable conditions. Availability 
does not necessarily represent agricultural value, or crop produc- 
ing power in the open field, since other factors enter in the ques- 
tion, some of which are as follows : 

1 i ) Kind of Season. In a very wet season, nitrate of soda is 
less useful than other forms because it is liable to be washed below 
the reach of the roots and lost altogether unless applied just when 
needed, or on a heavy soil. 

(2) Kind of Crop. Some crops grow and develop quickly, 
while others grow for a comparatively long period. Quick-acting 
fertilizers like nitrate of soda or ammonium sulphate, would be 
more effective on the former than organic fertilizers, which must 
undergo change before their nitrogen is available. The slower- 
acting organic materials would be better for plants with a long 
growing period, unless a number of applications of the quick- 
acting fertilizers are made. 

(3) Season of the Year. The change from organic nitrogen 
to ammonia or nitrate takes place more readily as the temperature 
approaches 98 F. Hence the organic materials would be re- 
latively less effective for winter crops than for summer ones. A 
material which gives excellent results when applied to a crop dur- 
a warm and moist season, might be very unsatisfactory when the 
season is short, cold, and dry. 

Phosphatic Fertilizers. Phosphatic fertilizers are of two kinds, 
crude phosphates, and treated phosphates. 

Phosphates. The more important crude phosphates are bone, 
bone tankage, bone black, rock phosphate, apatite, and Thomas 



304 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

phosphate. Bat guano and guano ash also contain phosphoric 
acid. 

Raw bones consist of mineral matter, which is chiefly phos- 
phate of lime, and organic matter, which is partly fat and partly 
ossein, a nitrogenous body. The ossein decomposes in the soil, 
and increases the availability of the phosphoric acid of the bone. 
Bone contains 18 to 25 per cent, phosphoric acid and 3 to 5 per 
cent, nitrogen. 

Raw bone meal is crushed or ground bone and its value depends 
largely upon its fineness of division. The more finely it is 
ground, the more rapid its action. Bone meal is a good fer- 
tilizer, but acts slowly. 

Steamed bone meal is made from bone which has been steamed 
to remove the fat and the nitrogenous matter, the latter being 
made into glue or gelatine. The steaming makes the bone soft 
and crumbly, and the phosphoric acid is more quickly available 
than in raw bone. ' Steamed bone meal contains 22 to 29 per cent, 
phosphoric acid and 1.5 to 2.5 per cent, nitrogen. 

Bone black is made by distilling or charring bones out of con- 
tact with air. It consists chiefly of phosphate of lime and char- 
coal, and is used for removing the coloring matter in the refining 
of sugar. It contains 32 to 36 per cent, phosphoric acid. Spent 
bone black is treated with sulphuric acid like phosphate rock. 

Rock Phosphates. Rock phosphates such as are used for 
manufacture of acid phosphate consist chiefly of calcium phos- 
phate, though they contain a small amount of iron and alumina. 
They are found in South Carolina and Florida as nodules, 
pebbles, or boulders, and in Tennessee in veins and pockets. 
These rock phosphates range from 25 to 40 per cent, in phos- 
phoric acid. 

Rock phosphates containing excessive amounts of carbonate of 
lime or of oxides of iron or alumina, are not suitable for the 
manufacture of acid phosphates, though they may be used for 
direct application to the soil. The carbonate of lime consumes 
sulphuric acid, while the oxide of iron and alumina react with 
soluble phosphates, causing them to revert. 



SOURCES AND COMPOSITION OF 



305 



Rock phosphate is used to a certain extent as a fertilizer. 
When ground very fine, so the particles may float in the air, it is 
known as floats. It does not act as quickly as acid phosphate, 
and may give little results the first year. Some soil chemists 1 
advocate the use of heavy applications of ground rock phosphate, 
together with liberal applications of manure or green crops plow- 




Fig. 72. Mining pebble phosphate. 

ed under, for staple crops like corn. According to the Ohio field 
experiments, acid phosphate used with manure gives larger net 
returns than rock phosphate. 2 

Apatite. This is a crystallized calcium phosphate which occurs 
in quantity in Canada. The highest grade contains 40 per cent. 
phosphoric acid. 

1 Hopkins, Soil Fertility and Permanent Agriculture, p. 226. 

2 Circular 120, Ohio Station. 



306 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

Thomas phosphate is a by-product from the manufacture of 
steel from phosphatic pig iron. It contains 15 to 20 per cent, 
phosphoric acid in connection with large amounts of lime and 
oxide of iron. The phosphoric acid was believed to be present 
as tetra-calcium phosphate, but according to Morison, 1 it is a silica 
phosphate of lime and ferrous iron. Thomas slag has its greatest 
effect upon soils rich in organic matter and poor in lime. It con- 
tains free lime, which may neutralize soil acids. It is a slow 
acting fertilizer. 

Acid Phosphate. It has been found by experiment that treat- 
ment, of phosphates with sulphuric acid exerts a powerful in- 
fluence upon their crop-producing power, and immense quantities 
are so treated for this reason. The rock is first ground to a 
powder, and treated with approximately an equal weight of sul- 
phuric acid. The following reaction takes place : 

(1) Ca 3 P 2 O 8 + H 2 SO 4 = H 3 PO 4 + CaSO 4 . 

(2) Ca 3 P 2 8 + 4H 3 P0 4 == 3CaH 4 P 2 O 8 . 

Mono-calcium phosphate soluble in water is produced from cal- 
cium phosphate. The calcium sulphate, or gypsum, unites with 
water and causes the mass to harden. On standing the following 
reaction may take place, di-calcium phosphate being formed : 

(3) CaH 4 P 2 O a + Ca,P 2 0, = 2Ca 2 H 2 P 2 O 8 . 

This process is called reversion, and the di-calcium phosphate 
is termed reverted phosphoric acid. Reversion is also caused by 
the presence of iron and aluminium. The reaction is not clearly 
understood but may possibly be as follows : 

(4) 2CaH 4 P 2 8 + Fe 2 3 = Fe, 2 P 2 O 8 + Ca,H 2 P 2 O 8 + 3H 2 O. 
The reverted phosphoric acid is assumed to have a value equal 

to water-soluble phosphoric acid. It is also termed citrate-soluble 
phosphoric acid, since it is dissolved by ammonium citrate in the 
chemical analysis of the fertilizer. Reversion by iron oxide and 
alumina produces ferric or alumina phosphate, both of which 
contain the phosphoric acid in an insoluble form. Some alumina 
phosphates are, however, citrate-soluble. 

Phosphoric acid is thus present in an acid phosphate in three 
1 Jour. Agr. Sci., 1909, p. 161. 



SOURCES AND COMPOSITION OF FERTILIZERS 307 

forms water-soluble, reverted, and insoluble. Free phosphoric 
acid may also be present. The insoluble is the phosphoric acid 
insoluble in water and in neutral ammonium citrate. It is either 
the original tri-calcium phosphate of the untreated rock, or phos- 
phoric acid which as reverted to the insoluble condition. 

When the rock is treated with an excess of acid, some free 
phosphoric acid or sulphuric acid is present, which rots the bags 
and also causes the acid phosphate to be very sticky, especially in 
moist climates, so that it cannot be easily drilled in. 

Available phosphoric acid is the sum of the reverted and water- 
soluble. In speaking of an acid phosphate, the phosphoric acid 
referred to is the available. Thus, if we speak of a 16 per cent, 
acid phosphate, we mean that it is guaranteed to contain 16 per 
cent, of available phosphoric acid, regardless of the total quantity 
present. Acid phosphate contains 12, 14, or 16 per cent, available 
phosphoric acid. The 12 and 14 per cent, grades are often made 
by mixing dirt or sand with the 16 per cent, phosphate. Such a 
mixture is not an acid phosphate, but is a mixture of acid phos- 
phate and dirt or sand. 

Treated phosphates may be made from phosphate rock, apatite, 
bones, bone ash, or bone black. Whatever the original material 
used, equal quantities of water-soluble or reverted phosphoric 
acid have equal values. That is to say, the water-soluble acid 
produced from apatite is equal in value, pound for pound, to that 
from bones. 

Dissolved bone should be a treated phosphate prepared from 
bone. It should contain 2 to 3 per cent, nitrogen. Dissolved 
bone black is prepared from bone black. 

Superphosphates. Concentrated phosphates are prepared for 
long distance shipments, when the saving of transportation will 
more than pay the extra expense of manufacture. High grade 
phosphate rock is treated with dilute sulphuric acid, with the pro- 
duction of calcium sulphate and phosphoric acid : 

Ca 3 (P0 4 ) 2 + 3H 2 S0 4 = 3CaS0 4 + 2 H 3 PO 4 . 



308 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

The calcium sulphate is filtered off, the solution of phosphoric 
acid concentrated and then mixed with phosphate rock. 

Ca 3 (P0 4 ) 2 + 4 H 3 P0 4 = 3 CaH 4 (P0 4 ) 2 . 

2Ca 3 (P0 4 ) 2 + 2H 3 P0 4 = 3 Ca a H 2 (P0 4 ) 2 . 

The product contains 30 to 45 per cent, available phosphoric 
acid, depending on the degree of concentration of the acid and 
the kind of rock used. 

Availability of Phosphatic Fertilizers. The values of different 
forms of phosphoric acid are compared in the same way as nitro- 
gen, namely, plants are grown under such conditions that phos- 
phates are the limiting factor and a comparison made of the 
amounts of phosphoric acid taken up by the crops. 

The availability of phosphoric materials depends upon other 
conditions in addition to the form of combination of the material, 
such as the presence of carbonate of lime or some other sub- 
stances in the soil, the fineness of the material, the nature of the 
plant, etc. The effect of these conditions has not been studied to 
a great extent. 

Potash Materials. Potash is of relatively less importance than 
nitrogen or phosphoric acid, because potash is more abundant in 
the soil than either nitrogen or phosphoric acid, and, though 
larger quantities are removed, the potash is more likely to be re- 
turned. The potash taken up is most largely in the stems and 
leaves of plants, that is, the portion of the plant which is gen- 
erally returned to the soil either directly, or indirectly in manure. 
When the entire crop is removed, the loss of potash is large. 
Potash is a very necessary constituent of fertilizers for some soils 
and some crops. 

The chief commercial potash materials are tobacco stems, wood 
ashes, and the German potash salts, kainit, muriate of potash, and 
sulphate of potash. 

Tobacco stems are a by-product from tobacco factories. They 
contain 6 to 8 per cent, potash, 2 to 2.5 per cent, nitrogen, and 3 
to 5 per cent, phosphoric acid. They are used largely as an 
insecticide, but may sometimes be secured for a sufficiently low 
price to allow their use as a fertilizer. 



SOURCES AND COMPOSITION OF FERTILIZERS 



309 



Wood ashes are variable in composition, and their value 
depends upon the kind of wood from which they are made, and 
whether they are leached or unleached. Hard wood yields the 
most valuable ash. Ashes exposed to the weather lose most of 
their potash by leaching. Unleached ashes contain 4 to 8 per 
cent, potash and about 2 per cent, phosphoric acid. 

Goessmann gives the following analyses of ashes : 







Average per cent. 


Unleached 
Potash 


2.5 to 10.2 
0.3 to 4.0 
18.0 to 50.0 

about 0.5 
about 40.0 
about 1.5 


5-5 
1-9 

34-0 


Phosphoric acid 


L/ime 


Leached 
Potash 









Coal ashes contain little plant food. Since ashes contain car- 
bonate of lime and carbonate of potash, they are especially bene- 
ficial to acid soils, or those needing lime. 

German Potash Salts. The German potash salts are mined and 
concentrated in the region around Strassfurt, Germany, where 
they occur in immense beds at depths of from 1500 to 2500 feet 
below the surface. The important minerals found are as 
follows : 

Carnallite, KC1, MgCl 2 , 6ELO. 

Kainit, K 2 SO 4 , MgSO 4 , MgCL,, 2H 2 O. 

Sylvinite, KC1, NaCl, K 2 SO 4 , MgCl 2 , 6H 2 O, MgSO 4 . 

Hartsalz, KC1, NaCl, MgSO 4 , H 2 O." 

Carnallite, the chief source of potash, usually occurs mixed with 
rock salt and other minerals, and contains, as mined, about 9 per 
cent, potash. Kainit, as mined, contains about 30 per cent, rock 
salt and about 12 per cent, potash. Sylvinite is a mixture of 
sodium and potassium chlorides, containing 14 to 18 per cent, 
potash. The potash salts chiefly used in this country are kainit, 
muriate of potash, and sulphate of potash. 



3IO PRINCIPLES OF AGRICULTURAL CHEMISTRY 

Kainit, correctly speaking, is a mineral composed of sulphate 
of potash and magnesia, K 2 SO 4 , MgSO 4 , MgCl 2 , 6H 2 O. The 
term is also used for crude potash salts containing not less than 
12.4 per cent, potash, which may be crude kainit or mixtures of 
other crude salts. Since kainit is prepared from crude salts, no 
expense of manufacturing is attached to it. On the other hand, 
freight per unit of potash is higher than for the more 
concentrated potash salts. At a distance from the mines, 
the freight cost is greater than the manufacturing cost, 
so that the concentrated salts are cheaper. Since kainit contains 
chlorides, it is not suitable for use on tobacco or potatoes. Kainit 
is used as a preservative in saving stable manure, to check attacks 
of injurious insects, and as a remedy against cotton rust. 

Muriate of potash is a concentrated potash salt prepared from 
the crude potash minerals by solution and crystallization. Various 
grades are prepared, ranging from 70 to 98 per cent, muriate of 
potash equivalent to 46.7 to 62 per cent, potash (K 2 O). 

Sulphate of potash is prepared by reaction between the muriate 
of potash and. sulphate of magnesia, also found in the potash 
mines. The two are mixed in solution, and the sulphate of 
potash, being less soluble, separates out. Various grades are 
prepared, containing 45 to 53 per cent, potash (K 2 O). 
2KC1 + MgSO 4 = K 2 SO 4 + MgCL, 

Double Manure Salts. This is an impure sulphate of potash 
containing about 30 per cent, potash. It contains considerable 
amounts of sulphate of magnesia. 

Forms of Potash. The compounds of potash used in fer- 
tilizers are all soluble in water, and there is practically little differ- 
ence in their availability. Some forms are, however, better 
adapted to some crops than others. Fertilizers free from 
chlorides are desirable for potatoes and tobacco, since chlorides 
make the potato less mealy and injure the burning quality of the 
tobacco. 

Miscellaneous Fertilizing Materials. The analyses of some mis- 
cellaneous fertilizing materials are given in the table. Most of 



SOURCES AND COMPOSITION OF FERTILIZERS 



them are very variable in composition, but may furnish cheap 
sources of plant food. 





Phosphoric 
acid 


% Nitrogen 


Potash 




Per cent. 


Per cent. 


Per cent. 






2 O-2 *\ 






.u 4-u 

2 C- 8 O 




.u- ^.u 












1 O- I *\ 


o ^-O 8 


Q c_ o 8 




20- -1 Q 


I o-l 6 


i o- i 6 




O 2 


o o^ 


OC 


Mussels fresh 


O Q 


O 12 


i "* 






2 Q 




WooH a;he; 










u.j 4.^ 








O 




u -o 



CHAPTER XVI. 



PURCHASE AND USE OF FERTILIZERS. 

Commercial fertilizers consist; first, of acid phosphate, cotton- 
seed meal, potash salts, and other commercial substances contain- 
ing plant food; and secondly, of mixtures of these substances, 
made to secure a product of a desired composition. The mixture 
usually contains all three kinds of plant food, though a number of 
mixtures are on the market which contain only two, phosphoric 
acid and potash, or phosphoric acid and nitrogen. 

Mixed Fertilizers. Mixed fertilizers are of two classes dry 
mixed and wet mixed. In dry mixing, the materials are weighed 
out, ground when necessary, mixed thoroughly, then passed 
through a screen so as to make them of uniform size. The nitro- 
gen is generally in two or more forms, one highly available, the 
others less so. A filler is added when the sum total of the in- 
gredients containing plant food do not make up the required 
weight to give the desired composition. Any substance which 
contains no plant food, or quantities much lower than the content 
of standard fertilizer ingredients, should be considered as a filler. 
The filler is usually sand or dirt, but sometimes objectional fillers 
are used, such as limestone, lime, or pyrite cinder, which con- 
tains oxide of iron. Small quantities of lime are sometimes used 
to dry the fertilizer. 

In wet mixing, the organic nitrogenous material is first mixed 
with the sulphuric acid, then the phosphate rock is added, and the 
mixture is dumped out and allowed to harden as in the manu- 
facture of acid phosphate. Potash salts or nitrate of soda, if 
either is used, is added while the product is being ground or 
otherwise prepared. In wet mixing, the nitrogenous material is 
to a certain extent acted on by the acid. There is no doubt that 
this treatment increases the availability of low-grade nitrogenous 
materials, but little experimental work has been done to show the 
availability of the product. Street 1 found the following changes 
in the nitrogen of one sample commercially treated in this way : 
1 Report Connecticut Exp. Sta., 1911, p. 14. 



PURCHASE AND USE OF FERTILIZERS 



313 






Before 
treating 


After 
treating 
(two days) 


Ammonia nitrogen 


6 r 




\Va.ter-soluble organic nitrogen 


o 

7 8 


J4-3 


\Vater insoluble organic nitrogen 


gc 7 


O/'/ 

28 o 




O-/ 





In a pot experiment on oats and millet the treated nitrogenous 
material had an availability of 66 compared with that of nitrate 
of soda as 100, cottonseed meal 47, hair waste 29, garbage tank- 
age 28, and peat 4. 

Guarantee of Fertilizer. A fertilizer is valuable on account 
of the quantity and kind of plant food it contains. The manu- 
facturer buys on analysis, that is, he pays on the basis of the 
chemist's analysis of a fair sample of the shipment. The in- 
dividual farmer, or one who purchases on a small scale, cannot 
afford to pay for a chemical analysis and can tell little or nothing 
about the substance by inspection. Hence the laws of most States 
in which fertilizers are used, provide for a guarantee of com- 
position, penalties for failure to deliver guaranteed ingredients, 
and officials who are charged with the inspection and analysis of 
fertilizers. The simplest guarantee consists of a statement of the 
guaranteed minimum percentages of the available or total phos- 
phoric acid, the nitrogen, and the potash. The total phosphoric 
acid is guaranteed only with respect to bone meal or rock phos- 
phate, which contain little "available" according to chemical 
methods. 

In some States, the term ammonia is used instead of nitrogen, 
and in one or two States, phosphorus and potassium instead of 
phosphoric acid and potash. Otherwise the latter terms are used 
the world over. A a varying guarantee, such as "2 to 3 per cent, 
potash," is allowed in some States, but is not desirable. Other 
States require a guarantee of water-soluble and reverted phos- 
phoric acid. The use of the terms "potash as sulphate" etc., 
allowed in some States, is confusing to the average purchaser. 
21 



314 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

Commercial Valuation. The commercial value of a fertilizer is 
the selling price of the plant food ingredients as determined by 
market and trade conditions. The agricultural value, or crop- 
producing power, often has no relation to the commercial or mar- 
ket value of the material. Thus it frequently happens that an 
element costs less in a highly available form than in a less avail- 
able form. Organic nitrogen may cost more than nitric nitrogen, 
while the nitric nitrogen is more available and would have a 
greater crop-producing power if properly applied. 

The commercial value is usually fixed by the cost of the plant 
food in the raw materials in ton lots at retail, and frequently at 
the seaboard. Cost of transportation must be added. Fluctua- 
tions in the values take place according to trade conditions. 

An illustration of the commercial value is as follows : Suppose 
that 14 per cent, phosphoric acid costs $16.80 a ton. A ton con- 
tains 14x20 = 280 pounds available phosphoric acid, so that one 
pound costs 6.0 cents. This is the commercial or trade value. 

If the commercial valuation of phosphoric acid is 6 cents, 
potash 6 cents and nitrogen 20 cents, it does not follow that a 
pound of nitrogen will give an increase of crop worth 20 cents, 
or that a pound of phosphoric acid will give a 6 cent increase, or 
that the effect will be in that ratio. 

1911 

Cents per pound 

Nitrogen in nitrates 16.0 

Nitrogen in ammonia salts 16.0 

Organic nitrogen in dry and fine ground fish and blood- 23.0 

Organic nitrogen in cottonseed meal and castor pomace- 21.0 
Organic nitrogen in fine ground bone and tankage and 

mixed fertilizers 20.0 

Organic nitrogen in coarse bone and tankage 15.0 

Phosphoric acid soluble in water 4.5 

Phosphoric acid soluble in ammonium citrate 4.0 

Phosphoric acid in fine ground bone and tankage 4.0 

Phosphoric acid in coarse bone and tankage 3.5 

Phosphoric acid insoluble (in water and in ammonium 

citrate ) in mixed fertilizers 2.0 

Potash in high grade sulphate and in mixtures free from 

muriate (chloride) 5.0 

Potash as muriate 4.5 

Potash in cottonseed meal and castor pomace 5.0 



PURCHASE AND USE OF FERTILIZERS 315 

The preceding schedule of trade values is the one agreed upon 
by the Experiment Stations of Massachusetts, Rhode Island, 
Connecticut, New Jersey, and Vermont, after a careful study of 
prices ruling in the larger markets of the southern New England 
and middle States. 1 

These trade values are, as nearly as can be estimated, the 
average figures at which, in the six months preceding March i, 
1911, the respective unmixed ingredients could be bought at retail 
for cash in the larger markets (Boston, New York, etc.) They 
also correspond to the average wholesale prices for six months 
ending March ist, plus about 20 per cent, in the case of goods for 
which there are wholesale quotations. The valuations obtained by 
the use of the above figures, it is claimed, will be found to agree 
fairly with the reasonable average retail price in the large mar- 
kets of standard raw materials, such as nitrate of soda, sulphate 
of ammonia, dried blood, cottonseed meal, acid phosphate, 
muriate of potash, and sulphate of potash, etc. 

The valuations used in Texas 2 for the season of 1911-12 are 
as follows : 

Cents per pound 

Available phosphoric acid 6 

Total phosphoric acid in bone and tankage 4 

Nitrogen in mixed fertilizers, bat guano and cottonseed meal 20 

Nitrogen in tankage 18 

Potash 6 

The valuation of nitrogen in Texas depends largely on the 
cost of cottonseed meal. 

Calculation of Commercial Valuation. Two methods are used, 
namely, the pound method and the unit method. 

(o>) The Pound Method. Calculate the number of pounds of 
each ingredient per ton and multiply by the cost per pound. For 
example, in an 8.00 - 1.65 - 2.00 fertilizer: 

0.08 X 2,000 = 160 pounds X 6 cents-. = $9-6o 

0.0165 X 2,000 = : 33 pounds X 20 cents = 6.60 

0.02 X 2,000 = 40 pounds X 6 cents = 2.40 

Valuation per ton $21.60 

1 Report Connecticut Exp. Sta., 1911, p. 7. 

2 Texas Station Bulletin No. 149. 



316 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

(b) The Unit Method. A unit is i per cent., and i per cent, 
of a ton is 20 pounds. Hence 20 times the value of a pound gives 
the value of a unit. To calculate the valuation, multiply per- 
centage by value per unit. With nitrogen at 20 cents a pound, a 
unit costs $4.00. With potash at 6 cents, the unit costs $1.20. 
Using the example given above: 

8.0 X $1.20 = $9.60 

1.65 X 4-0 - 2.60 

2.0 X 1-20 = 2.40 

Valuation per ton $21.60 

The Meaning of Commercial Valuation. The valuation of a 
brand of fertilizer by the State Fertilizer Control does not repre- 
sent its proper selling price at the point of consumption. Neither 
should it be inferred that the ingredients in the brand in question 
have of necessity the commercial value indicated. It may be greater 
or less than is shown. The valuation system is based on the as- 
sumption that all brands compared are solely of high grade in- 
gredients, an assumption which may be erroneous. "Valuations" 
should not be construed as showing the commercial worth of a 
given fertilizer, but the retail trade value at the seaboard, of 
amounts of nitrogen, phosphoric acid, and potash, equal to those 
contained in a ton of the brand in question, in unmixed, standard 
raw materials of good quality. 

Valuations thus construed, while not infallible, are helpful : 

(a) To show whether a given fertilizer is worth its cost from 
the commercial standpoint. 

(b) As a common basis on which to compare the commercial 
value of different brands, enabling buyers to note whether prices 
asked are warranted by values contained, and aiding buyers to 
secure the most value for the least money. 

Agricultural Value. The agricultural value of a fertilizer is 
measured by the value of the increased crop produced by its use. 
It is variable, depending upon the availability of the constituent, 
the value of the crop, the needs of the soil, weather conditions, 
etc. For example, the agricultural value of a pound of water- 
soluble phosphoric acid is likely to be greater than that of 



PURCHASE AND USE OF FERTILIZERS 



317 



an equal amount of insoluble phosphoric acid, when used under 
the same conditions, because it is much more easily used by plants. 
But the water-soluble phosphoric acid may produce an increased 
yield of a crop on some soils and still not cause an increase in 
value sufficient to pay the cost of the application, while on an- 
other crop the application may result in a very great increase in 
value. On a soil which needs phosphoric acid its use may be 
profitable, while on one which does not need this form of plant 
food, it will have no effect. A fertilizer may produce a com- 
paratively small effect upon a crop of high selling price, and yet 
be profitable ; while on a crop of low selling price the increase may 
not offset the cost of the fertilizer. 

Basis of Purchase. Large sales of fertilizing material are 
usually at a certain price per unit. A unit means one per cent, on 
the basis of a ton. That is 20 pounds. For example, $1.00 per 
unit for phosphoric acid would be $1.00 for 20 pounds, or 5 cents 
per pound. 

The ton basis of purchase is used for the sale of manufactured 
fertilizers. The purchaser must consider the guarantee, and 
valuation of the fertilizer before purchasing. For example, sup- 
pose fertilizer A is offered for $21.00 a ton, and fertilizer B for 
$24.00 a ton : 





A 


B 




Per cent. 

1-5 
6.00 

I.OO 


Per cent. 
2.00 

8.00 

2.00 




Potash 





Taking the valuations given elsewhere, we have the following : 





A 


B 




$6 oo 


$8 oo 


Available phosphoric acid. (6 cents) 


















Total 








#14.40 





PRINCIPLES OF AGRICULTURAL CHEMISTRY 



There is thus a difference of $3.00 in the price and $5.60 in the 
valuation. Fertilizer B contains more value for the money. But 
the purchaser must consider the needs of his crop and his soil 
also, and not seek to secure merely the most value for the least 
money. 

Home Mixing of Fertilizers. By home mixing of fertilizers, 
we mean the purchase of the ingredients, and mixing them in the 
proportions to form the fertilizer desired. The preparation of 
acid phosphate from phosphate rock, or the grinding of bones or 




Fig- 73- Instructing negro students in the home mixing of fertilizers. 

other hard material, is most economically conducted on a large 
scale. In home mixing, then, we simply mix the ingredients 
which have already been prepared by grinding or otherwise. 

The operation is very simple, the apparatus required being a 
clean floor, one or two shovels, and a sand screen, with meshes 
of about 4 to an inch. The materials are first weighed out, one 
by one, and piled on the floor, any large lumps being broken down 



PURCHASE AND USE OF FERTILIZERS 319 

with a shovel. The pile is then shoveled over several times, and 
the mixture passed through the screen. Any lumps which fail 
to pass the screen are beaten up, and added to the mixture. The 
mixture is then shoveled over several times more. It is possible 
to prepare the mixture without any screen, but better results are 
secured with it. 

The question whether home mixtures equal factory mixtures 
has been studied bv a number of Experiment Stations in the fol- 
lowing way : Samples of mixed fertilizer prepared at home were 
secured, and examined as to mechanical character, and the chem- 
ical composition was compared with that calculated from the 
amount and composition of the ingredients used. The mechanical 
condition was, as a rule, good and the chemical composition did 
not vary to any greater extent than samples of factory mixed 
goods as sold on the market. The New Jersey Experiment 
Station 1 says that it amply demonstrated in 1893, and corrobor- 
ated in 1894, that farmers, with their ordinary farm appliances, 
can prepare mixtures that compare very favorably with pur- 
chased mixtures, both in mechanical condition and chemical com- 
position. The Vermont and Maine Experiment Stations make 
similar statements. The Ohio Experiment Station 2 compared 
factory mixed goods with ready mixed goods in field experi- 
ments, on corn and wheat and found that the home mixed goods 
gave as good results as the factory mixed, or better. The New 
Hampshire Experiment Station 3 secured a similar result on 
potatoes. These experiments show that complete fertilizers can 
be prepared by home mixing, which are equal in every respect 
to the purchased article. It might sometimes happen that a mix- 
ture is difficult to prepare, owing to the fact that the materials 
have become lumpy and hard to beat up, but this is the exception 
and not the rule. 

Whether or not it is profitable to make home mixtures depends 
upon the conditions. It is certainly more economical to buy the 

1 Bulletin No. 113. 

2 Bulletin No. 100. 

3 Bulletin No. in. 



32O PRINCIPLES OF AGRICULTURAL CHEMISTRY 

unmixed materials in large lots for cash, and make mixtures, than 
to purchase mixed goods at retail, especially at credit prices. In 
this way one can secure somewhat more plant food for $20.00, 
than can be secured for $30.00, in a mixed fertilizer. The Ex- 
periment Stations of New York, Connecticut, New Jersey, North 
Carolina, and other States have demonstrated this to be a fact. 
When the unmixed materials are purchased in small quantity, at 
retail, it may or may not be profitable to make home mixtures. 
One can easily decide this question for himself by securing prices 
on mixed goods, and calculating the amount he would have to 
pay for the unmixed materials to make the same mixture. 

Mixed fertilizers purchased direct from the manufacturer in 
carload lots may often be secured more cheaply than the home 
mixture can be made, since the cost of mixing is less to the manu- 
facturer, who has appliances for economically handling large 
quantities. 

It may be said further in favor of home mixtures, that one can 
know exactly what ingredients are used, whether they are of high, 
medium, or low grade. It is also easy to vary the mixture as de- 
sired, and to test the effect of different combinations upon the 
soil. 

It has been objected to home mixing that the materials may not 
always be easily secured and that the mechanical condition is 
not as perfect as in the commercial mixed fertilizer. Mixed fer- 
tilizers are widely distributed and easily secured. 

Calculating the Ingredients of a Mixture. The calculation of 
the ingredients to make a fertilizer of a desired composition, is a 
simple mathematical matter. It is necessary, of course, to know 
the composition of the ingredients to be used. Suppose it is 
desired to make a fertilizer containing 8 per cent, available phos- 
phoric acid, 2 per cent, nitrogen and 2 per cent, potash, using acid 
phosphate containing 14 per cent, available phosphoric acid, 
kainit containing 12 per cent, potash, and cottonseed meal con- 
taining / per cent, nitrogen, 2 per cent, available phosphoric acid, 
and 1.5 per cent, potash. 



PURCHASE: AND USE OF FERTILIZERS 321 

The desired fertilizer would contain, in 1,000 pounds, 80 
pounds available phosphoric acid, 20 pounds nitrogen, and 20 
pounds potash. 

Since i pound cottonseed meal contains 0.07 pounds nitrogen, 
it would take 20 -- 0.07 = 286 pounds cottonseed meal to furnish 
20 pounds nitrogen. This 286 pounds would contain also 
286 X 0.02 = 5.7 pounds phosphoric acid and 286 X i-5 = 4-3 
pounds potash. 

The 80 pounds available phosphoric acid required, less 5.7 
pounds, in the cottonseed meal, leaves 74.3 pounds to be secured 
from the acid phosphate. 74.3 -f- 0.14 = 531 pounds acid phos- 
phate. 

The 20 pounds potash required, less 4.3 pounds in the cotton- 
seed meal, leaves 15.7 pounds to be secured from the kainit. 
15.7 -r- 0.12 = 131 pounds kainit. 

Then the desired ingredients to make 1,000 pounds of the 
fertilizer, would consist of : 

Pounds 

Cottonseed meal 286 

Acid phosphate 531 

Kainit 131 

Total 948 

Filler 52 



I ,OOO 

It would thus be necessary to add 52 pounds filler to make the 
desired composition. 

The ingredients for other fertilizer mixtures may be calculated 
in a similar way. In factory work, it is necessary to allow for 
variations in the composition of the ingredients by providing for 
a slight over-run. Otherwise, some of the mixtures may fall be- 
low guarantee. 

Incompatibles in Fertilizer Mixtures. Certain materials should 
not be mixed in making fertilizers, for the following reasons : 

( i ) Chemical reactions take place which result in the loss of 
nitrogen in the form of ammonia. For this reason, ammonium 
sulphate, guano, or barnyard manure should not be mixed with 
lime, ashes, or Thomas slag. 



322 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

(NHJ 2 S0 4 + Ca(OH) 2 =: 2NH 8 + CaSO 4 + 2H 2 O. 

(2) Chemical changes convert the phosphoric acid into less 
soluble forms. Acid phosphate should not be mixed with Thomas 
slag, lime or ashes. 

CaH 4 (PO 4 ) 2 -f 2CaO == Ca 3 PO 4 + 2H 2 O. 
Lime is, however, sometimes mixed with moist acid phosphate 
to improve its physical condition, so that the resulting mixture 
may be applied with a fertilizer drill. 

(3) Certain mixtures will harden or cake and thus become 
difficult to distribute if kept for some time after mixing. Hence 
they should be applied soon after mixing. This applies to mix- 
tures of lime or Thomas slag with potash salts, nitrate of soda, 
and kainit. 

Conditions which Modify Use of Fertilizers. These are : ( i ) 
Deficiency of soil; (2) Value of crop; (3) Character of crop; 
(4) Kind of rotation. 

Deficiency of Soil. A knowledge of the nature of soils with 
respect to the deficient elements is important, in order that those 
elements which are present in abundance may not be added to, but 
that they may be supplemented by such quantities of the deficient 
elements as to permit maximum profitable crops. This matter 
of soil deficiencies has been treated elsewhere. 

An opinion as to the deficiency of the soil may be based on : 

(a) The chemical composition of the soil. 
(&) The behavior of the crop. 

(c) Previous experience in the use of fertilizers. 

(d) Field tests to ascertain needs of the soil. 

The value of the crop is of importance in deciding the profit- 
able application of fertilizers. Crops may roughly be divided into 
two classes : the first class have a relatively low commercial value 
per acre, the second have a high commercial value per acre. 

Wheat, corn, oats, cotton, etc.,, belong to the first class. These 
crops remove large amounts of plant food in proportion to their 
value. For example, a ton of wheat removes 38 pounds of nitro- 
gen, 19 pounds phosphoric acid, and 13 pounds of potash. With 
nitrogen at 20 cents and phosphoric acid and potash at 6 cents, the 



PURCHASE: AND USE OF FERTILIZERS 



3^3 




Fig- 74- Corn grown (A) continuously, (B) in five year rotation. 
Minnesota Station. 



324 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

value of this plant food would be $9.50. Wheat at $1.00 per 
bushel would bring $33.33 per ton. The value of plant food in 
the grain is thus nearly y$ the selling price of the crop. Economy 
in the application of fertilizers is essential to profit with such crops. 
Nitrogen should be secured as much as possible from the air by 
legumes. Application of fertilizers should be based largely upon 
the needs of the soil. 

Onions, asparagus, melons, cabbage, and tomatoes, are ex- 
amples of crops which have a high value per acre. Such plants 
may be fertilized liberally, since the cost of even large applications 
of fertilizer is in small proportion to the value of the crop. 
Manure or legumes turned under should also be used on account 
of their beneficial effect on the soil. 

Character of the Crop. Plants vary in the quantity of plant 
food needed and in their ability to secure it. The season of 
growth is also of significance, since plants growing during the 
cooler period of the year are supplied with less nitrogen by the 
soil than those growing during the warm season. 

While each plant possesses individual characteristics which 
distinguish it from others, they may be divided into groups which 
have somewhat similar characteristics, particularly as regards 
method and time of growth and their capacity for acquiring food 
from soil sources. 

The cereals have a wide root growth and are able to acquire 
food from insoluble phosphates and potash readily. As, with the 
exception of Indian corn, their development takes place 
early in the summer before conditions are favorable for rapid 
nitrification, they are particularly benefited by nitrates. Corn 
does not usually require as large proportions of nitrogen as of 
mineral constituents, as its growth is made in the summer while 
the conditions are very favorable for nitrates. 

The grasses resemble the cereals in their power of acquiring 
mineral food and are also benefited by application of nitrogen. 

The clovers readily acquire mineral food, and also take nitro- 
gen from the air. 



PURCHASE: AND USE OF FERTILIZERS 325 

Root crops (beets, mangels, turnips, carrots, Irish and sweet 
potatoes) cannot make ready use of the mineral constituents of 
the soil. Phosphates are especially useful for turnips, while beets 
and carrots require more nitrogen. Potash is particularly useful 
to potatoes. 

Market garden crops have a high commercial value with a low 
fertility content. Hence they can be profitably supplied with an 
abundance of plant food. This supply also increases rapidity of 
growth, which is desirable, as the price is often in proportion to 
their earliness. 

Fruit crops have a longer season of preparation and growth, 
and require a constant transfer of food from the tree to the fruit 
during the growing season. Food that will encourage a slow and 
continuous growth, rather than a quick one, is required. 

The Kind of Rotation. The order in which the crops 
follow one another in rotation, the kind of crop previously grown, 
and the treatment given it, are factors in intelligent fertilization. 
If the previous crop is a legume, and has left considerable 
residues, the succeeding crop stands less in need of nitrogenous 
fertilizers. A crop succeeding an exhaustive crop not liberally 
fertilized, may require liberal applications of plant food. The 
further removed the crop is from the legume crop, the greater 
its probable needs of nitrogenous fertilization. 

Effect of Phosphoric Agid, Potash and Nitrogen on Plant 
Growth. While the entire plant requires all forms of plant food, 
it may be said that nitrogen and potash stimulate the growth of 
leaves and stem, and phosphoric acid stimulates ripening of the 
fruit. An excess of nitrogen tends towards a large development 
of leaf and late maturity. Thus at Rothamsted, on the wheat 
plots which receive nitrogen and potash but no phosphoric acid, 
the grain hardly ripens at all. The use of phosphoric acid, how- 
ever, hastens the maturity of the plant. 

Fertilizer Experiments. A great number of fertilizer experi- 
ments have been carried out by Experiment Stations, and other 
investigating agencies. The plans of the experiments vary a great 
deal, according to the crop to be tested, the information desired, 



326 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

etc. The fertilizer is applied to plots varying from 1/50 to 1/2 
an acre, but generally of T/IO to 1/20 acre. The effect of the 
different applications is measured by the weight of the product 
on the different plots. The only variable should, of course, be 
the fertilizer. All other conditions should be the same for all 
the plots. The crop, however, is subject to other variables, such 
as differences in soil or subsoil, in stand, damage by insect pests, 
nearby trees or fences, etc. The best results are secured when 
the experiment is carried out on the same land for a number of 




A B 

Fi g- 75- Tobacco, fertilized (A), and unfertilized (B). Ohio Station. 

years to eliminate seasonal differences. It is also well for plots 
to be repeated a number of times in order to eliminate error due 
to inequalities of the soil. 

In order to study the effect of variable soil on the crop, several 
experiments have been made in which a field of apparently uni- 
form soil, bearing a crop under similar conditions in all parts, has 
been subdivided and harvested in separate small areas. Com- 



PURCHASE: AND USE OF FERTILIZERS 



327 



parison shows the differences between these, and combination and 
comparison shows the differences of larger areas. For example, 
Morgan 1 selected a strip of land 112^2 feet wide apparently uni- 
form in texture, etc., which was planted in wheat first and then 
corn. It was measured off in strips 15x112^ feet, (about 1/25 
acre) and the wheat or corn harvested separately from 63 plots 
which should thus be all alike. With the average yield at 100, 
the wheat crop varied from 65.0 to 130, and the corn crop from 

169.3 to 42.3. 

The plot yielding the lowest with wheat gave an average yield 
with corn, the highest with wheat 88.5 with corn. The plot lowest 
with corn was 1 13.7 with wheat, and the plot highest with corn was 

100.4 with wheat. Thus the differences were not in the same 
direction with the two successive crops. Assuming that the 
theoretical yield depended upon the distance from the check plot, 
the following average errors were found : 





Average 
error 

Wheat 


Average 
error 

Corn 




Per cent. 

8.3 

8-4 
6.4 
5-6 


Per cent. 

23.1 
15.7 
15-7 
ii. 3 











Assuming different treatments for the plots, the average and 
maximum error was found to be as follows : 





Average error 


Maximum error 


Wheat 


Corn 


Wheat 


Corn 


Every plot different treatment . . '. . . 


Per cent. 

12.4 
5-9 
5-8 
5-o 


Per cent. 

31.7 
4-7 

3-2 

2-3 


Per cent. 

64.0 
ii. 5 
7-6 
3-8 


Per cent. 

I58.I 
15-7 

II. 

4-7 









Proc. Am. Soc. Agri., 1909. See also Lyon, ibid., 1910, p. 35-38. 



328 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

This experiment shows the great variation in the produce of 
two crops grown under apparently the same conditions in a field 
apparently uniform. It also shows that the error resulting from 
variations may be reduced by using a sufficient number of check 
plots, and by repeating the treatment on different plots. Great 
care must, therefore, be exercised in planning and conducting field 
experiments. 

A similar experiment is reported by Smith from the Illinois 
Experiment Station, on 120 one-tenth acre plots of corn all treated 
alike for three years. In 1895 the yield varied from 11.4 to 50.2 
bushels per acre, in 1896 from 48.5 to 103.9, an d in 1897 from 
44.2 to 80.2 bushels. The lowest yield in 1897 was on the plot 
which gave the highest yield in 1896. The maximum variation in 
adjoining plots was 18 bushels in 1895, n bushels in 1896, and 8 
bushels in 1897. 

Precautions in Making Fertilizer Experiments. The following 
are some of the precautions 1 to be used : 

(1) The greatest care should be taken to select land which is 
as uniform as possible in fertility. Lack of uniformity will give 
misleading results, and often render the experiments of little 
value. 

(2) Level land should be selected if possible. If such cannot 
be had, the plots should run up and down the slopes, so that the 
washing by rain will not carry fertilizing materials from one plot 
to another. 

(3) The experimental plots should be measured off carefully, 
and each plot indicated by stakes or stones. 

(4) It is best to have the experimental plots long and narrow, 
because thus they will average up for uneveness of soil. 

(5) It is best to separate plots by paths, to prevent roots of 
plants in one plot from feeding on the fertilizer supplied to ad- 
joining plots. 

(6) Avoid windy days in applying fertilizers, so that they may 
not be blown and scattered unevenly over the plots. 

1 Thome, Circular 96, Ohio Exp. Sta. 



PURCHASE AND USE OF FERTILIZERS 



329 



(/) All the plots must be treated alike in every respect, except 
as to the amount and kind of fertilizer applied. The same kind 











Sect 


ion A 


K X X * XXX 


XXX X X x X 






Sec 


ionB 


>: x x x xxx 


xxx x y x x 










Sec 


ionC 


X X X X XXX 








Sec 


ion D 




x x x x x x X 







Fig. 76. Plots for a fertilizer and rotation experiment, four sections of 40 
plots each. The plots marked (X) are check plots. Ohio Station. 

and quality of seed must be used over the entire area. The 
plowing or sowing on all the plots must be done the same day. 

22 



330 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



If part of the crop be planted before and part after a rain, the 
experiment may become valueless. Every precaution should be 
used to secure a full stand of plants, and if a uniform stand is 
not secured at the first planting, the whole field should be re- 
planted. The same number of rows should be arranged on each 
plot, and the same number of hills and plants in each row, as 
nearly as possible. The plots should be plowed and cultivated 
alike, and whatever operation is needed on one experimental plot 
should be carried out uniformly on all the plots. 

(8) The harvesting of the crop and weighing of yields must be 
accurate. A small mistake is multiplied many times when cal- 
culated to an acre. 

(9) Provide liberally for check plots, and for plots on which 
repetition is made, so as to allow for inequalities of the soil. 

At the Rhode Island Station, 1 the plots are 193.6 feet long by 
30 feet wide, with 3 foot paths between, and roads at the end. 
Before the final harvest, the crop from a strip of land three feet 
wide on the sides and six feet wide at the ends, is cut and re- 
moved, this leaving exactly one-tenth acre to be harvested. This 
arrangement eliminates the error due to greater growth on the 
edges of the plot. 

The importance of continuing field tests several years is shown 
by Thome.- The results from the first year test on wheat is 
quite different from the ten year average : 



Addition 


Increase + and decrease 
in yield of wheat in bushels 
per acre. 


First year 
1894 


Average 

for 10 years 




bushels 
2.8 

+5-6 

1. 21 

4-7 

0. 4 


bushels 

+ 6.5 
h 1-3 

h 1.8 
+ u .4 
+ 14.8 






Acid, phosphate and. nitrate soda. 


Acid phosphate potash and nitrate 





1 Report for 1904. 

' 2 Ohio Circular No. 96. 



PURCHASE AND USE OF FERTILIZERS 



33* 



He also shows the effect of the fertilizer to increase from year 
to year, as per the following results on a plot receiving a complete 
fertilizer. 





Bushels per acre 


Corn 


Oats 




8-5 
II. 2 

15-2 


12. 1 

14-5 
18.0 









Thorne 1 corrects for variations in the soil by assuming that 
variations in fertility are regular from one check to the next. 
The difference between this method and the method of deducting 



If 



309* 



Pig, 77. The same fertilizers give the same increase if the land decreases 

regularly (CD) from the checks, but not if the average of 

the checks (A B) is deducted. Ohio Station. 

the average of all plots, is well brought out in Thome's diagram. 
This represents four plots fertilized alike and three check plots. 
The increase in the average crop is regular if the soil varies uni- 
formly, but the results are unconsistent if the average yield of 
the plots are deducted. 

1 Circular 96, Ohio Station. 



332 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



Examples of Fertilizer Experiments. The oldest and most 
famous fertilizer experiments are those at Rothamsted, England. 
Other important, long continued field experiments are those of 
the Ohio Experiment Station at Wooster, the Rhode Island Ex- 
periment Station, at Kingston, the Pennsylvania Experiment 
Station at State College, and the North Carolina State Board of 
Agriculture at Statesville, Red Springs, and Edgecombe, North 
Carolina. 




Fig. 78. Experimental plot at the University of Nebraska. 

The Rothamsted experiments were begun in 1848, and are im- 
portant not only for having been long continued under the same 
plan, but also for the other valuable scientific studies made there. 
The Rhode Island Experiments are most important for their bear- 
ing upon soil acidity. The Ohio 1 experiments are very significant 
as regards rotation and manure. 

The Rothamsted experiments comprise seven experimental 
fields: (i) crops grown in rotation, (2) wheat continuously 
1 Bulletins uo, 182, 183 and 184. Circular 120. 



PURCHASE AND USE OF FLvRTFUZKRS 



333 



grown, (3) wheat alternating with fallow, (4) barley continu- 
ously, (5) potatoes continuously, (6) hay continuously, (7) ex- 
periments on root crops. Most of the plots are about ^2 acre 
each. The plots are very long and narrow and separated by 
paths. 

The following is part of the plan of the wheat experiments on 
Broadbalk field 1 with some of the results. 



Plot 



Application 



Average bushels 

wheat, 51 years, 

1851-1962. 



9 

10 

ir 

12 
13 
H 
15 

16 

I? 
18 

19 



nitrogen as ammonium 

nitrogen as ammonium 

nitrogen as ammonim 



Manure, 14 tons 

Nothing 

Minerals 2 

Minerals and 43 pounds 

sulphate 

Minerals and 86 pounds 

sulphate 

Minerals and 129 pounds 

sulphate 

Minerals and 43 pounds nitrogen as nitrate of soda - . 

86 pounds nitrogen as ammonium sulphate 

86 pounds nitrogen as ammonium sulphate. and acid 

phosphate 

Same as n, plus sulphate of soda 

Same as n, plus sulphate of potash 

Same as 1 1, plus sulphate of magnesia 

Mineral plus 86 pounds nitrogen as ammonium 

sulphate ( applied in autumn ) 

Minerals plus 86 pounds nitrogen in nitrate of soda- . 
J Minerals alone or 86 pounds nitrogen as ammonium 

( sulphate alone in alternate years 

92.6 pounds nitrogen in rape cake 



35-7 
13-1 
14-9 

24.0 
32.9 

37-i 

(27-3) 3 

20.7 

24.0 
30.0 

3i-5 
30.1 

30.6 



40. 4 
(28.0)* 



Pennsylvania Experiments 6 at State College, were begun in 
1882, on four fields of 144 plots of Y% acre, about i 1 /^ rods wide 
by 1 6 rods long. A four-year rotation of corn, oats, wheat, and 
hay of mixed clover and timothy is followed, each of the crops 

1 An Account of the Rothamsted Experiments, Hall. 

2 Minerals consist of superphosphate, with sulphates of potash, soda, 
and magnesia. 

3 Average for 10 years only. 

4 Average for minerals. 

5 Average for nitrogen. 

6 Report 1910-11. 



334 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



being grown on one of the four fields every year. There are at 
least four plots of the same treatment, one in each field. The 
fertilizer is applied to the corn and wheat only. 

Son, TREATMENT (PENNSYLVANIA). 



i-O 


i3-Plasler 


25-PK 


2-N 


14-0 


26-PNK(Na) 


3-P 


I5-PK 


27-PK2N(Na) 


4-K 


i6-Manure 12 


28-PK3N(Na) 


5-PN 


I7-PNK 


29-PK 


6-NK 


i8-Manure 16 


3 o-PNK(S0 3 ) 


7-PK 


I9-PK2N 


3i-PK2N(SO 3 ) 


8-Manure (prior to 1882) 


20-Manure 20 


3 2-PK 3 N(S0 3 ) 


9-PKN 


2I-PK3N 


33-Plaster 


10-PK2N 


22-CaO Manure 12 


34-Limestone 


n-PNK(Bn) 


23-CaO 


35-PNK(Bn) 


I2-PNK 


24-0 


3 6-0 



N stands for 48 pounds nitrogen, 2N for 96 pounds, 3N for 144 
pounds per acre. Blood was used in the first 24 plots, except No. 
n, Nitrate of soda in plots 26-7-8 (marked Na) and sulphate of 
ammonia in plots 30-1-2 (marked SO 8 ). K signifies 160 pounds 
muriate of potash, P for phosphoric acid in dissolved bone black. 
Manure was used at the rate of 12, 16, and 20 tons per acre. 
Plaster is 640 pounds land plaster (gypsum). CaO is 2 tons 
caustic lime. Limestone is 4 tons ground limestone. Blood and 
bone were used on plots 1 1 and 35 for nitrogen and phosphoric 
acid, respectively. 

Comparative Effects of Different Plant Foods. In comparing 
the results of plot experiments, it is important to determine the 
effect of the individual fertilizing constituents, namely, of phos- 
phoric acid, nitrogen, potash, or lime. The fertilizing constituents 
exert some influence upon the relative action of each other, but 
nevertheless it is often advisable to estimate the value of each in- 
dependently. This can be done by subtracting the yield without 
the constituent in question from that with it. Thus the yield with 
phosphoric acid, potash, and nitrogen less that with phosphoric 
acid and potash gives the effect of nitrogen; by subtracting the 
yield with phosphoric acid and nitrogen we get the effect of 



PURCHASE AND USE OF FERTILIZERS 



335 



potash, and so on. Calculated in this way, the following table 
gives the increase in yield of ear corn produced by phosphoric 
acid, potash, and nitrogen respectively, from the Wooster Experi- 
ment Field of the Ohio Experiment Station. 





Bushels of ear corn produced by 


Phosphoric 
acid 


Potash 


Nitrogen 




6.6 

6.7 
9- 2 

II. O 

&4 


4.0 
4.2 

0.2 
2.1 

' 2.6 


3-9 

6.5 

o.o 

4-7 
3-8 




With potash 











These figures show the effect of phosphoric acid or potash or 
nitrogen, alone, or added to the other forms of plant food. On 
this particular soil phosphoric acid had the greatest effect, nitro- 
gen next, and potash least. 

Other studies and applications of the experiments are made, 
according to their character. 

Value of Increase. The profit in the use of different fertilizing 
ingredients depends chiefly on the cost of the fertilizer and the 
market value of the product. These two factors vary from year to 
}ear, so that the prices used must always be given, and must be 
carefully compared with present prices in studying the figures at 
later periods of time. The profit can be calculated by subtract- 
ing the cost of the fertilizer from the value of the increase in 
crop. We can also calculate the profit or loss due to the use of 
specific ingredients of the fertilizer as explained in the preceding 
section. For example, the following results were secured from 
seven years experiments with a rotation of corn, oats, wheat, and 
hay on the Strongsville Farm of the Ohio Experiment Station. 1 
1 Bulletin 184. 



336 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 





Total profit ( + ), or loss ( ) 
per acre from the use of 


Phosphoric 
acid 


Potash 


Nitrogen 




+ I2.I6 

+ 11.42 

+ 13-79 
+ 15.08 


5-97 
-6. 7 I 

4-57 
-3-28 


11-43 
9.80 
10.03 

- 6.37 




With potash 


^^ith nitrogen 






+ I3- 11 


5 14 


- 9-41 





On this particular soil, with the amounts of fertilizers used and 
crops grown and at the prices given, phosphoric acid alone was 
profitable, potash and nitrogen being applied at a loss in both 
cases. On other soils and with other crops, different results 
would be secured. These figures are merely given to show the 
method of calculating. Additional expense due to handling the 
increased crop, and the fertilizer, should also be considered. 

Systems of Fertilization. There is a great diversity in soils, 
crops, climatic conditions, and other factors which modify the 
effect of fertilizers. Individuals must study their own condi- 
tions, try various combinations, and use such mixtures as give 
most profitable results under their conditions. Fertilizers which 
give good results are recommended in the various publications on 
the subject, but the application which will be the best and the 
most profitable will depend upon individual conditions. 

Systematic use of fertilizers is more profitable than haphazard. 
The following are some of the systems 1 which are used. Every 
system should include a rotation of crops, with liberal use of 
manure or green crops plowed under. 

i. System Based on Influence of a Single Element. This 
system assumes that plants can be divided into three groups ; one 
group most benefited by nitrogenous fertilizers, another by phos- 
phatic, and the third by potassic. Nitrogen is said to be the 
dominant element for wheat, rye, oats, barley, meadow grass, and 
beet crops. Phosphoric acid is dominant for Indian corn, sorg- 
1 Voorhees' Fertilizers. 



PURCHASE AND USE OF FERTILIZERS 337 

hum, sugar cane, turnips, and Swedes. Potash is the ruling 
ingredient for peas, beans, clover, vetch, flax, and potatoes. If 
the soil is fertile, the dominant element would be supplied to 
force a maximum growth of the crop, in such quantity as might 
be found necessary. If the soil is not fertile, moderate applica- 
tions of the other plant foods are made, supplemented with more 
liberal additions of the dominant element. 

2. System Based on Necessity of an Abundant Supply of the 
Minerals. This system is based upon the fact that potash and 
phosphoric acid are cheap and not easily washed from the soil, 
while nitrogen is expensive and easily lost. According to the 
needs of the soil, a reasonable excess of phosphoric acid and 
potash is applied, sufficient to satisfy more than the maximum 
needs of any crop, and then the nitrogen is applied in active 
forms, such as nitrate of soda or sulphate of ammonia, and at 
such times as will insure the minimum loss of nitrogen and 
the maximum development of the plant. The phosphoric acid 
may be drawn from the cheaper mineral substances, such as 
ground bone, tankage, and ground phosphate rock. 

This system is useful in building up a very poor soil when ac- 
companied by a rotation which involves the use of legumes and 
manure. 

3. A System Based on the Amount of Plant Food Taken up by 
the Crop. According to this system, different plants are fertilized 
with phosphoric acid, nitrogen, and potash in the proportions in 
which chemical analysis shows them to exist in the plants. If 
care is taken to supply an abundance of plant food, this method 
may result in complete, though not economical, feeding of the 
plant, and may be profitable for crops of high value per acre, but 
for ordinary farm crops, it is likely to be unprofitable. 

This system does not take into consideration the fact that one 
plant may have much greater power of taking up an element than 
another. Neither does it consider that the period or season of 
growth exercises some effect on the capability of a plant to ac- 
quire plant food from the soil. It may, however, be taken as a 
general rule that an application of easily available plant food 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 

largely in excess of the requirements of the crop, is not advisable. 
Such an application is likely to lead to loss of plant food, either 
by percolation or by fixation. 

4. The Fertilizer is Applied to the Money Crop in a Rotation. 
In this system, the money crop is supplied with an abundance of 
plant food, so as to insure continuous feeding and maximum pro- 
duction. The remaining crops, or those immediately succeeding 
in the rotation, are nourished by the residues, with small applica- 
tions of fertilizer, if necessary. If, for example, the rotation is 
cotton, corn, and cowpeas, the cotton would be liberally fertilized, 
the corn and cowpeas being allowed to feed on the residues. 

Use of Nitrate of Soda. Nitrate of soda is easily soluble in 
water, and distributes itself through the soil, and as the nitrogen 
can be easily taken up by plants, it is quickly effective. On the 
other hand, it is so soluble in water that it is easily washed from 
the soil by rains, and there may be loss from leaching when 
applied previous to the growth of the plant, or in too large 
quantities at the wrong time, or when heavy rains occur im- 
mediately after its application. 

The best use of nitrate of soda 1 is secured when an abundant 
supply of potash and phosphoric acid is present. We have al- 
ready seen that the size of a crop is controlled by the most un- 
favorable condition, and if potash or phosphoric acid are deficient, 
this deficiency cannot be overcome by the use of nitrate of soda. 

The best use of nitrate of soda is also secured when it is applied 
to soils in good condition rather than to poor or worn out soils. 
Larger quantities may profitably be applied to good soils than to 
poor soils. Clods and lumps prevent a proper distribution of the 
material as well as a ready absorption of plant food, which are 
also necessary for good results. The application of nitrate of 
soda is especially advantageous for quick growing vegetable crops, 
where market quality is measured by rapid and continuous 
growth, and for those field crops which make their greatest 
development in spring, before the conditions are favorable for the 
change of the nitrogen in the soil into forms usable by plants. 
1 Bulletin 172, New Jersey Station. 



PURCHASE AND USE OF FERTILIZERS 339 

Apply 100 pounds per acre on poor soils, 150 pounds on good 
soils, as a top dressing in the spring after the grass or crop is well 
started. For ordinary field crops, since nitrogen is so expensive, 
the increase in yield may not pay for nitrogen used in fertilizer. 

Crops grown in the early spring, such as early spring forage, 
or spring wheat, oats, etc., may be unable to secure sufficient nitro- 
gen from the soil to permit of rapid and maximum development. 

The agencies which change organic into active nitrogen may 
not be sufficiently active to produce a sufficient supply of active 
nitrogen. Hence an application of active nitrogen in the form of 
nitrate of soda may cause great gains to take place. Some crops, 
as tomatoes, cabbage, potatoes, etc., must be grown and harvested 
early, in order to be highly profitable. Hence their growth must 
be forced at a time when the natural agencies are not very active. 

According to bulletins of the New Jersey Experiment Station, 
the use of 150 pounds per acre of nitrate of soda has increased the 
wheat crop 9 bushels per acre. Early tomatoes were increased in 
value 50 per cent, by 150 to 250 pounds, early cabbage 40 to 80 
per cent, by 400 pounds, musk melons doubled in value by 200 
pounds. 

Quantity of Fertilizer. The applications of different quanti- 
ties of the same fertilizer follows the law of diminishing returns. 
That is, the increase produced by each successive increment of fer- 
tilizer diminishes as the quantity of fertilizer increases. Thus the 
cost of the increment increases with the quantity of fertilizer. 
The fertilizer is profitable up to a certain point, after which the 
value of the increase is not equal to the cost of the additional 
amount of fertilizer. The most profitable quantity depends upon 
the character of the soil, the kind of crop and its value, and 
climatic conditions. The more valuable the crop, the larger the 
quantity of fertilizer which may be profitable. 

As an illustration, we will cite the experiments conducted for 

four years by the New York (Geneva) Experiment Station 1 to 

ascertain the most profitable quantity of fertilizer for potatoes. 

The fertilizer used contained 8 per cent, available phosphoric acid, 

1 Bulletin 187. 



340 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



4 per cent, nitrogen, and 10 per cent, potash, costing $25.00 per 
ton. The average of the four crops is as follows : 



Pounds fertilizer per acre 


Increase 
in fertilizer 


Increase in yield 
due to increase in 
fertilizer 


Cost of fertilizer 
for each additional 
bushel potatoes 






Bushels 






CQO 


2"? -I 


$0 27 


3W" 


^uu 
cr)O 


^6-6 
2O Q 






CQO 


^vj.y 
112 


o ^6 




CQO 


6 


I Od. 











The first 500 pounds fertilizer produced an increase of 23.3 
bushels potatoes, a cost of 27 cents per bushel for fertilizer. The 
last 500 pounds produced 6.0 bushels at a cost of $1.04 per bushel 
for. the fertilizer. 

Secondary Actions of Fertilizers. The supplying of available 
plant food is the primary action of fertilizers. They have other 
secondary actions upon the soil, which may not be unimportant at 
times. 

Reaction. Sulphate of ammonia leaves an acid residue in the 
soil, which unites with lime, increases the loss of lime, and may 
cause a soil not rich in lime to become acid. This has taken 
place at the Woburn (England) Experiment- Farm, where the 
plot which receives sulphate of ammonia has become acid and will 
not grow barley. Addition of lime corrects the acidity. 

Acid phosphate may also have a slight tendency towards caus- 
ing soil acidity. Nitrate of soda leaves a basic residue in the soil, 
and hence has a tendency to correct acidity. Organic nitrogenous 
fertilizers do not affect the reaction of the soil. 

Physical Structure. Acid phosphate tends to flocculate a clay 
soil. Nitrate of soda tends to cause it to puddle or run together. 
Potash salts vary somewhat in their action, according to the 
nature of the soil. 

Fertilisers Conserve Moisture. Fertilizers may decrease trans- 
piration and reduce the quantity of water required to produce 
growth. For example, Widstoe reports the quantity of water 



PURCHASE: AND USE OF FERTILIZERS 341 

transpired per i gram dry matter produced in one experiment on 
corn in pots as follows : 

Grams 

No fertilizer 1,012 

Phosphates 735 

Nitrates 555 

Phosphate and nitrate 1 78 

Bacterial action is undoubtedly affected by fertilizers, but to 
what extent or of what importance is not known. 

It is claimed that the sulphate of lime which is present in acid 
phosphate may liberate soil potash and so render it available to 
plants. It is also possible that this sulphate of lime may supply 
plants directly with sulphur, but this is a matter which requires 
further study. 

Whitney claims that fertilizers destroy toxic substances in the 
soil, but no direct evidence has been brought forward to show 
that such is the case. 

Relation of Fertilizers to Losses and Changes of Plant Food. 
When nitrogen, and, to a less extent, potash, is added to the soil, 
the loss due to percolation increases. This is shown by analyses 
of percolation waters from drain gauges or tile drains. See 
Chapter XIII. There is also an increased los; due to denitri- 
fication, which can be ascertained by analysis of the soil after a 
number of years, provided loss by percolation and cropping is 
also known. Little loss of phosphoric acid takes place, except 
possibly on very light sandy soils. 

Fertilizers improperly used may diminish the fertility of the 
soil. Thus acid phosphate alone will give good results on some 
soils for a few years, but the increased crop increases the draft 
upon the nitrogen and potash of the soil. Unless provision is 
made to restore the loss of nitrogen and potash, the acid phos- 
phate will become less and less effective. The same is true, 
though to a less extent, of fertilizers containing large percentages 
of phosphoric acid and small percentages of nitrogen and potash, 
such as a fertilizer containing 8 or 10 per cent, available phos- 
phoric acid, 2 per cent, nitrogen, and 2 per cent, potash, such as 
are commonly used in the South for fertilizing cotton and corn. 



342 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

Used in small quantities, these fertilizers tend to deplete the soil 
of nitrogen, unless provision is made to restore it otherwise. The 
use of such fertilizers in large quantity is not to be recommended, 
since a great deal more phosphoric acid is supplied than can 
possibly be utilized by the crop. If more fertilizer is used, it 
should be richer in nitrogen. 

Effect of Fertilizer on Succeeding Crops. The effect of fer- 
tilizer carried over to a subsequent year is shown in the experi- 
ments at Rothamsted. Plot 17 and 18 receive "mineral manure" 
consisting of superphosphate and sulphates of potash, soda, and 
magnesia one year, and 86 pounds nitrogen in sulphate of am- 
monia the second year. These applications have alternated for 
51 years. The average results are as follows: 

Bushels of wheat 
per acre 

Plot 5 mineral manure " 14.9 

(A) Plots 17-18 when mineral manure etc., is applied 15.3 

(B) Plots 17-18 when sulphate of ammonia is applied 30.4 

Plot 7 complete fertilizer 32.9 

Thus plots 17-18 produce little more crops the year after the 
application of sulphate of ammonia (A) than plot 5 which re- 
ceives no ammonia. Plots 17-18 produce nearly as much the 
year after the application of the phosphoric acid and potash, as 
they do in plot 7 which receives them every year. That is to say, 
the phosphoric acid and potash remain in the soil in an available 
form, so as to be useful to the next crop, while the nitrogen was 
leached out or otherwise rendered of little value to the plant. 

Fixation. It is commonly supposed that phosphoric acid and 
potash of fertilizers are fixed and rendered less soluble almost as 
soon as they are placed in the soil. This is not, however, the 
case. Some of the lumps of fertilizer are '% inch in diameter, 
and do not dissolve at once. When they do dissolve, 
diffusion is not a rapid process, and the soil particles 
nearest the fertilizer are brought in contact with the more con- 
centrated solution, and fix larger proportions of it, than those 
farther away. Hence the fertilizer becomes the center of a zone 
of concentrated plant food, more dilute towards the outside. This 



PURCHASE AND USE OF FERTILIZERS 343 

is even to some extent true of the easily soluble fertilizers, like 
nitrate of soda, for which the soil has little power of fixation, but 
still more so for the less soluble acid phosphates. In the case of 
organic nitrogenous materials, the particles become centers for 
the production of ammonia and nitrates, which may eventually be 
taken up by the rootlets as fast as they are formed. The well 
known fact that moderate applications of fertilizer are more 
effective when applied in the vicinity of the plant or seed than 
when applied broadcast, is evidence that the plant food does not 
become rapidly and uniformly distributed through the soil mass. 

The Practice of Fertilization. 1 There is such a variation in the 
needs of crops and soils for fertilizers, in the effect of climatic 
conditions, and previous treatment, upon their behavior towards 
fertilizers, that it is impossible to lay down specific rules for fer- 
tilization. The fertilizer which produces heavy yields of potatoes 
in the North, would not necessarily be suitable for the warmer 
climate, lighter yields, and earliness, associated with the same 
crop in the South. Onions grown on the sandy soils of Long 
Island, New York, require different treatment from those grown 
in the warmer climate and much richer soils under irrigation at 
Laredo, Texas. Applications suited to crops grown under favor- 
able conditions of moisture may be unsuited to crops which may 
have to endure a period of drouth or mature on a moderate 
amount of moisture. The best that can be done is to lay down 
general principles, and to give the applications which have proved 
successful under certain stated conditions. The individual farmer 
must study his own conditions, with the help of his State Experi- 
ment Station, and learn by his own experience the most profitable 
applications for him to make. A few brief notes are made below 
on fertilizers for various crops. 

Field Crops. Rotation of crops, including legumes, to be 
turned under or fed and the manure saved, is essential to mainten- 
ance of fertility for ordinary field crops. Only in this way can 
nitrogen be secured cheap enough. Phosphates and potash may 
1 See Voorhees, Fertilizers ; Van Slyke, Soils and Fertilizers ; Bulletins 
of Bureau of Soils and of State Experiment Stations. 



344 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

be purchased as necessary, together with supplementary small 
amounts of nitrogen. Field crops, especially grasses and clovers, 
utilize insoluble phosphates fairly well. 

Corn. A suitable rotation, including careful saving of all 
manure, together with the use of phosphoric acid, will maintain 
corn lands at a good level of productiveness, or increase the yields. 
The phosphoric acid may be supplied in 200 pounds per acre of 
acid phosphate applied annually, or 2,000 pounds of rock phos- 
phate applied every five or six years. An application of nitrogen, 
such as contained in 200 pounds cottonseed meal, may also be 
effective. Potash is needed on some soils. The ordinary corn 
and cotton fertilizer used in the South contains 8 to 10 per cent, 
available phosphoric acid, 1.65 to 2.5 per cent, nitrogen, and I to 
3 per cent, potash. It is used at the rate of 100 to 400 pounds 
per acre. 

Oats. Oats in a rotation often receive benefit from 100 pounds 
acid phosphate applied at the time of planting, and a top dressing 
of 100 pounds nitrate of soda when the plants begin their vigorous 
spring growth. 

Wheat. Same as oats. Clover uses much potash and is often 
benefited by 100 pounds acid phosphate and 50 pounds muriate of 
potash per acre. Timothy may receive the same application as 
clover and in addition a top dressing of 100 pounds nitrate of 
soda in the spring. Alfalfa requires lime and draws heavily on 
the potash of the soil. A good application is 200 pounds acid 
phosphate, 20 pounds nitrate of soda, and 100 pounds muriate of 
potash applied just before planting. This may be supplemented 
by 300 pounds acid phosphate and 200 pounds muriate of potash 
per acre per year. Peanuts are similar to alfalfa. A great deal 
depends on the soil. 

Cotton. Acid phosphate is used at the rate of 100 to 200 
pounds per acre on land which produces a good stalk but does 
not fruit well. An application of 200 to 400 pounds cottonseed 
meal gives good results on many soils. The Georgia Experiment 
Station recommends for old worn uplands, a mixture of 1,000 
pounds acid phosphate, 671 pounds cottonseed meal, and 296 



PURCHASE AND USD; OF FERTILIZERS 345 

pounds kainit applied at the rate of 400 to 800 pounds per acre. 
This fertilizer would contain 8 per cent, phosphoric acid, 2.4 per 
cent, nitrogen, and 2.4 per cent, potash. A rotation of crops in- 
cluding legumes should be adopted. 

Truck Crops. Rotation, manure, and heavy applications of 
fertilizers are used for truck crops. 

Potatoes in New York receive 1,000 to 2,000 pounds of a fer- 
tilizer containing about 8 per cent, available phosphoric acid, 4 per 
cent, nitrogen, and 10 per cent, potash. In Texas good results 
are secured with a mixture of 800 pounds acid phosphate and 
1,200 pounds cottonseed meal at the rate of 300 to 600 pounds 
per acre. Sweet potatoes in New Jersey receive 500 to 700 
pounds of a fertilizer containing 3 per cent, nitrogen, 7 per cent, 
available phosphoric acid, 12 per cent, potash. In Georgia, 200 
to 400 bushels per acre, according to soil and season, are secured 
with a mixture of 320 pounds acid phosphate, 360 pounds cotton- 
seed meal, and 640 pounds kainit. Early tomatoes in New Jersey 
receive about 350 pounds acid phosphate and 200 pounds muriate 
of potash just before planting, a top dressing of' 100 pounds 
nitrate of soda at time of setting out, and 100 pounds again three 
or four weeks later. Onions in New Jersey, do well on 1,000 
pounds of a fertilizer containing 5 per cent, nitrogen, 6 per cent, 
available phosphoric acid, and 10 per cent, potash. In Texas, 
they do well on 1,500 pounds cottonseed meal, or 1,000 pounds of 
a fertilizer containing 5 per cent, available phosphoric acid, 5 per 
cent, nitrogen, and 5 per cent, potash. Cabbage may receive an 
application of 1,000 pounds of a fertilizer containing 4 per cent, 
nitrogen, 8 per cent, phosphoric acid, and 5 per cent, potash, 
supplemented by a top dressing of 100 pounds nitrate of soda and 
100 pounds acid phosphate after the plants begin to grow when set 
out, and 100 pounds when the heads begin to form. 



CHAPTER XVII. 



CONSTITUENTS OF PLANTS. 

For the purpose of ordinary agricultural analysis, the various 
compounds in plants and feeds are divided into six groups, each of 
which, with the exception of the first (water), is composed of a 
number of chemical compounds, varying in their nature and rela- 
tive proportion according to the plant, or portion of plant, under 
examination. 

These groups are as follows : 

1 i ) Water, which is present in all feeds. 

(2) Ether Extract. This is the material extracted by ether 
and, in the case of seeds, is composed mostly of fats and oils, but 
it contains large quantities of substances other than fats in the 
case of hays, straw, and grass. 

(3) Protein. This includes all the nitrogenous constituents of 
the plant or feed. 

(4) Crude Fiber. This is the residue left on boiling the 
material with sulphuric acid and with caustic soda, a purely 
arbitrary method. It consists of cellulose, lignin, cutin, and 
other substances. 

(5) Ash. This is the residue left after the material has been 
burned, and consists of the substances not volatile at the tem- 
perature of the combustion. It consists chiefly of lime, magnesia, 
soda, and potash united with phosphoric acid, chlorine, carbon 
dioxide, sulphur trioxide, silica, and some unburned carbon. 

(6) Nitrogen-Free Extract comprises all the other ingredients 
of the plants not included in the above groups. In estimating 
its quantity, the water, protein, ether-extract, crude fiber, and 
ash, are added together, and the sum subtracted from 100. The 
difference is the nitrogen-free extract. 

Water. Water is abundantly found in the green and growing 
portions of the plant, as in leaves, tender shoots, and immature 
seeds, but chiefly in the sap, in which it transports the materials 
used in the growth of the plants. The older portions of plants, 
such as the stems, and old wood, and the mature seeds, contain 



CONSTITUENTS OF PLANTS 



347 



smaller percentages of water. Substances such as hays, meals, 
etc., which are apparently dry, contain appreciable quantities of 
water. 

The following table shows the percentages of water in some of 
the different classes of substances : 

WATER IN PLANTS. 



Green plants 


Per cent. 


Mature seeds and hays 


Per cent. 


Corn leaves 


7Q 1 


Corn fodder ... 


42 2 


Timothv 


/V'O 

61 6 


Ximothv hay 


4* * 


Red clover 


70 8 


Red clover hay 


1 o-^ 

T r i 




81 6 


Cowpea hay 


*5-3 
60 7 




78 Q 




T/1 8 




/ o -v 
86 e; 








OU O 
QO ^ 


Wheat (seed) - 


1U.^ 




yj-o 

7c A 




1U.^ 




/J-Q 







Determination of Water. The usual method is to dry the sub- 
stance at the temperature of boiling water until it no longer loses 
weight (about five hours). The operation is conducted in a 
water-oven. This consists of a double walled box. The space 
between inner and outer walls is partly filled with water, and the 
inner chamber is heated by the steam. There are certain sources 
of error in the estimation of moisture which must be guarded 
against, some of which are as follows : 

(1) Absorption of Oxygen. Certain fats and oils absorb 
oxygen when heated in the air, thus gaining in weight ; they may 
also become insoluble in ether. For instance, linseed oil, which 
occurs in linseed meal, absorbs oxygen with avidity. If materials 
containing such oils are dried in the air, the results on moisture 
are too low, and the ether extract is liable to be too low also. The 
remedy is to dry in a current of hydrogen, or of illuminating gas 
which contains no oxygen. Gasolene gas is not suitable. 

(2) Chemical Changes. At the temperature of boiling water, 
some compounds found in plants may undergo chemical change. 
The sugar in ripe fruits may be decomposed, or caramelized. For 
example, Snyder 1 found fresh tomatoes to contain 3.88 per cent. 

1 Bulletin 13, Minnesota Station. 



348 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

sugar, while after drying at 100 C. only 2.04 per cent, was pres- 
ent, a loss of nearly 50 per cent., due to decomposition. The de- 
composition may produce volatile bodies, and thus give too high 
results for water. 

Such materials should be dried in a vacuum, either at the 
ordinary temperature, or at a slightly elevated temperature. The 
drying may take place in a desiccator which contains sulphuric 
acid and has been exhausted with a vacuum pump. 

(3) Volatile Materials. Some substances lose volatile organic 
matter when dried at 100 in a current of air, or hydrogen. 

Silage loses acetic acid and ammonium acetate. Tobacco loses 
moisture. Atwater found that meats and fish in drying lost I 
to 4 per cent, of their total nitrogenous material. Animal excre- 
ments, both liquid and solid, may lose nitrogen. 

These losses may in some instances be avoided by drying in a 
vacuum. In others (as with urine and manure) analyses* should 
be made on the fresh materials, and correction made for the loss. 

Ether Extract. The mixture of substances which is removed 
from a plant by extraction with ether is termed ether extract. It 
is often termed "fats and oils" and this expression is correct when 
reference to concentrated feeding stuffs is intended, as in such 
cases the ether extract is composed mostly of fats and oils. But 
when applied to hays or fodders, the term "fats and oils" is not 
correct, since the ether extract may contain 30 to 70 per cent, of 
substances which are not fats or oils, such as chlorophyll, hydro- 
carbons, and wax alcohols. 

Ether extract is obtained from all plants, and nearly all parts of 
all plants. It is found in small quantities only, in roots and tubers, 
in somewhat larger quantities in hays, and straws, and in com- 
paratively large quantities in certain seeds, such as the -seeds of 
cotton, flax, peanut, soja bean, almond, and sunflower. These are 
called oil-bearing seeds. Certain fruits, such as the olive, are also 
rich in oil. 

The ether extract of seeds may not be distributed uniformly, 
but may be concentrated in certain parts of the seed. Thus, 
while the entire grain of corn contains 5.5 per cent, of oil, the 



CONSTITUENTS OF PLANTS 



349 



germ contains about 27 per cent, oil, which may be expressed 
from it for commercial purposes. The ether extract of rye and 
wheat passes mostly into the bran along with the germ. 

The percentage of ether extract in some of the different classes 
of materials is shown in the following table : 
ETHER EXTRACT IN PLANTS. 





Per cent. 




Per cent. 


Beets 


o I 




5c 


Potatoes 


O I 




O 
I A. 




i 6 


Sola bean 


16 Q 


Xitnottiy hav 


J 7 


Peanuts 


10.9 

-j 6 




O 








o 




1 9o 

rn A 








0/'4 



Composition of Ether Extract. The composition of the ether 
extract of some plants is contained in the following table : l 
PERCENTAGE COMPOSITION OF ETHER EXTRACT. 





Neutral fat 


Free 
fatty acid 


lecithin 


Unsaponi- 
fiable matter 


Hay 


23-7 
78.3 
59-2 
53.6 

95-5 
24.7 
92.9 

16.3 
23.0 


37-3 
16.4 

35-4 

II. 2 

1.2 
3 O.I 

56.9 

35-3 


trace 

3-3 
0.8 
27.4 

It 

4-4 

3-i 


30.8 

7-6 

2.7 
7-4 
1.5 
34-5 
i.i 
10.9 
10.7 




Q a ts 


p e as 








Potatoes .... 


Beets 





Stellwaag found, according to the above table, that nearly one- 
third of the ether extract of hay and malt sprouts is unsaponifiable 
matter. The ether extract of rye bran, peas, potatoes, and beets 
contain about 10 per cent, unsaponifiable matter. Over one- 
fourth of the ether extract of peas consists of lecithin. 

According to Fraps and Rather, 2 who examined 18 hays and 
fodders, from 39 to 71 per cent, of the ether extract consists of 
non-fats, chiefly wax alcohols. The average percentage of non- 
fats was 58 per cent, of the ether extract. 

1 Stellwaag, Landw. Versuchs-stat. 

2 Bulletin 150, Texas Station. 



350 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



PERCENTAGE COMPOSITION OF ETHER EXTRACT 





Unsaponi- 
fiable matter 


Saponifiable 
matter 


Alfalfa ha}* * 


67 






6c 


JO 

27 




? b 
60 


7Q 






oy 




7 1 
60 


3 




71 


o 
26 


Millet hay 


16 
1Q 


ro 




6y 
;8 


D^ 
16 






o w 



Determination of Ether Extract. The substance is dried and 
extracted with water-free ether for sixteen hours. The ether is 




C 



A 



Fig. 79. Fat extraction apparatus. 

then distilled off, and the fat, after having been dried in a water 
oven, is weighed. A form of apparatus is represented in the 



CONSTITUENTS OF PLANTS 351 

figure. The ether vaporized from the flask A is condensed by 
the cool water running through the condenser B and drops on the 
substance in C. It dissolves the ether extract and returns to the 
flask A, carrying the fat with it. It is then ready to be vaporized 
again and extract a fresh quantity of fat. When the exhaustion is 
complete, the ether is evaporated off and the fat is dried and 
weighed. This method is liable to several sources of errors, as 
follows : 

(1) Loss of volatile fatty acids during the drying of the sub- 
stance or of the extract. 

(2) Oxidation of fats if the preliminary drying of the material 
is carried out in the air. 

Fats and Oils. 1 The largest and the most important portion of 
the ether extract of concentrated feeds is composed of fats and 
oils. Fats are solid at the ordinary temperature, while oils are 
liquid. They consist of ethereal salts, termed glycerides, which 
are compounds of certain fatty acids with the tribasic alcohol, 
glycerol, C 3 H-,(OH) 3 ; thus, the fat palmitin C 3 H 5 (C 15 H 31 COo) 3 , 
is the glyceride of palmitic acid C 15 H 31 CO 2 H. When heated with 
alkalies, fats form glycerol and salts of the fatty acids, which are 
soaps. The process is called saponification. For example : 
QH 5 (C ]5 H 31 C0 2 ) 3 + 3NaOH = C 3 H 5 (OH) 3 + 3 C 15 H 31 CO 2 Na. 
Palmitin -|- Sodium hydroxide = Glycerol + Sodium palmitate. 

All fats are lighter than water and insoluble in it. When pure, 
they are colorless, odorless, and neutral in reaction; under con- 
tinued exposure to air, they begin to turn yellow, acquire a dis- 
agreeable odor and taste, and become acid that is, the fat be- 
comes rancid. The rancidity is due to partial decomposition of 
the glycerides, fatty acids being formed which are partly oxidized 
by the air to volatile substances having a disagreeable odor. 

Oils are divided into the non-drying oils, and the drying oils. 
The drying oils, of which linseed oil may serve as an example, 
are oxidized by the air to solid, varnish-like masses. They con- 
tain linolin and linolenin, which are the glycerides of unsaturated 
acids. The non-drying oils do not undergo this change. 
1 See Lewkowitsch, Oils, Fats and Waxes. 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



Fats and oils are concentrated forms of nutrition, containing 
more nourishment and energy than any other nutrient in feeding 
stuffs (2 J4 times as much as carbohydrates). 

The following table shows the formula and composition of the 
principal glycerides which occur in fats. 

COMPOSITION OF FATS. 



Name 


Glyceride of 


Formula 




Butyric acid 
Caproic acid 
Laurie acid 
Caprylic acid 
Palmitic acid 
Stearic acid 
Oleic acid 
Linolinic acid 
Linolinic acid 


C 3 H 5 (C 3 H 7 C0 2 ) 3 
C 3 H 5 (C 5 H n C0 2 ) 3 
C 3 H 5 (C n H 23 C0 2 ) 3 
C 3 H 5 (C 7 H 15 C0 2 ) 3 
C 3 H 5 (C 15 H 31 C0 2 ) 3 
C 3 H 5 (C 17 H 35 C0 2 ) 3 
C 3 H 5 (C 17 H 33 C0 2 ) 3 
C S H 5 (C 17 H 81 C0 2 ) 8 
C 3 H 5 (C 18 H 29 C0 2 ) 3 






Caprylin 


Palmitin 


Stearin 


Olein 









Palmitin, stearin, olein, linolin, and laurin are the principal 
glycerides which occur in fats and oils. Laurin, palmitin, and 
stearin are solid at the ordinary temperature, while olein is 
liquid. The consistency of a fat depends upon the predominating 
glycerides; the fats rich in palmitin and stearin are solid, while 
those rich in olein or linolin are liquid. Animal fats and oils con- 
tain the same glycerides as vegetable fats and oils. 

The glycerides which occur in some fats and oils are named 
below : 

Corn oil, chiefly olein and linolin, some stearin. 

Cottonseed oil, chiefly linolin, also stearin, palmitin, and olein. 

Sunflower oil, chiefly linolin. 

Linseed oil, linolin, linolenin, isolenin, olein, stearin, palmitin. 

Peanut oil, stearin, olein, linolin, arachiden. 

Olive oil, chiefly olein, some palmitin and stearin. 

Cocoanut oil, myrestin, laurin, palmitin, olein, caproin, caprylin. 

Examination of Fats and Oils. Different proportions of the 
same glycerides often occur in fats and oils of different origin. 
The following general methods are applied in the testing of fats 



CONSTITUENTS OF PLANTS 353 

and oils. Specific tests may be made to detect certain oils, such 
as cottonseed oil. 

The specific gravity is of importance. 

The index of refraction is the measure of the extent to which 
the fat bends a ray of light passing through it. It affords a 
rapid method for testing the purity of some oils. 

The saponification value is estimated by saponifying a weighed 
quantity of fat with a solution containing a known amount of 
alkali, and estimating the unused alkali by titration with an in- 
dicator and an acid of known strength. It is usually expressed 
in terms of milligrams of alkali neutralized by one gram fat. 

The volatile acids are estimated by saponifying a weighed quan- 
tity of fat, liberating the fatty acids with a non-volatile acid, and 
distilling off the volatile acids with water. The distillate is 
titrated with alkali of known strength. This method is especially 
valuable for butter, since it is the only ordinary fat which contains 
glycerides of volatile fatty acids. 

The iodine value is estimated by treating a weighed amount of 
fat with a solution containing a known amount of iodine. After 
sufficient time, the uncombined iodine is titrated and so estimated. 
The iodine combines with the unsaturated fats, and not with the 
saturated, so that the quantity of iodine absorbed depends on the 
quantity, and the condition of unsaturation of the fats present. 
The iodine number is the milligrams of iodine which combine with 
one gram of oil. The iodine number is a valuable index to the 
nature and purity of many oils. 

Free fatty acids are often present in the ether extract. If the 
substance is old, and the fat in it has become rancid, a large part 
of the ether extract may consist of free fatty acids. They come 
from the hydrolysis or decomposition of the fats into fatty acids 
and glycerol. If acids of low boiling point are present, the free 
acids are partly volatilized when the substance is dried before 
being extracted with ether, or when the ether extract is dried. 
They are best determined by extracting the substance without 
drying, and titrating the etheral solution with a standard solution 
of caustic potash, with the addition of alcohol. 



354 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

Lecithins. These are wax-like bodies which resemble fats in 
some respects. They contain nitrogen and phosphorus. Like 
fats, they are saponified by alkalies. When saponified they yield 
a soap, cholin, phosphoric acid, and glycerol. The quantity of 
lecithin in the ether extract is calculated from the amount of 
phosphoric acid found in it. The magnesium pyrophosphate 
multiplied by 7.25 is assumed to represent the lecithin. Calcium 
and magnesium phosphates have, however, been found in the ether 
extract of plants, their presence being attributed to the presence of 
metallic glycero-phosphates soluble in ether. When these sub- 
stances are present, the amount of lecithin in the fat is less than 
the amount calculated from the phosphoric acid present. 

Lecithin is not entirely extracted by ether from plant substance, 
but is completely extracted when the ether extraction is followed 
by extraction with absolute alcohol. If the alcoholic solution is 
evaporated at 40-50 C. and the residue taken up with ether and 
purified by shaking with water, the lecithin can be obtained fairly 
pure. 

Leguminous seeds are relatively rich in lecithin; the cereals 
(wheat, rye, and corn) contain much less. The table below shows 
the lecithin content of some substances: 

LECITHIN IN PLANTS. 

Per cent, 
in dry matter 

Young grass 0.45 

Young vetch plants 0.86 

Yellow lupine seeds 1.55 

Soja bean i .64 

Peas 1.23 

Wheat 0.65 

Rye 0.57 

Corn 0.74 

Sunflowers 0.44 

Vetch 0.98 

The alcoholic extract contains not only lecithin, but other 
organic compounds containing phosphorus, some of which con- 
tain sugar. Lecithin is of considerable value to the animal and 



CONSTITUENTS OF PLANTS 355 

also to the plant. It aids in the assimilation and transportation of 
the fat. 

Hydrocarbons are compounds of hydrogen and carbon. They 
have been detected in the unsaponifiable portion of the ether 
extract of plants. The ether extract of meadow hay contains a 
hydrocarbon, probably C 27 H I56 . Tobacco contains I per cent, of 
the hydrocarbons C 31 H 64 and C 27 H 56 . 

Wax Alcohols. The unsaponifiable matter consists of phytos- 
terol and other alcohols. Phytosterol C 28 H 34 (OH) is a solid 
alcohol which crystallizes from alcohol in glistening plates. It 
gives characteristic color reactions with certain reagents. 

The separation of phytosterol and Hydrocarbons from the fats 
is based upon the fact that while alkalies act upon fats to form 
compounds soluble in water (soaps), the phytosterol or hydro- 
carbons are not affected. The ether extract is saponified, and 
the soap extracted with ether, which dissolves the phytosterol and 
hydrocarbons. The etheral solution is evaporated, and the 
phytosterol purified by crystallization from alcohol. 

Wax alcohols are found in considerable proportions in the 
ether extract of hays and straws. They are digested to a certain 
extent by animals, though not so well as fats. The alcohols pres- 
ent are probably myricyl alcohol C 30 H 61 OH, and other similar 
alcohols of lower molecular weight. 

Chlorophyll. This is the green coloring matter of leaves. It 
contains nitrogen. It is soluble in ether, and gives a green color 
to the ether extract from hays and green plants. Its exact com- 
position is unknown. When the ether extract containing 
chlorophyll is saponified, and the unsaponified material is ex- 
tracted by means of ether, the chlorophyll remains with the fatty 
acids and colors them green. 

Protein. Protein is the nitrogen of the plant multiplied by 
6.25 and includes all the nitrogenous compounds of feeding stuffs. 
Protein includes amides, alkaloids, and inorganic nitrogen com- 
pounds (if present). Protein is found in all parts of all plants, 
as it is necessary to the life and growth of the plant. It is trans- 
ferred from the stem and leaves of plants to the seed when the 



356 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

plant matures. Protein is especially abundant in leguminous 
plants, and in seeds, particularly the seeds of legumes. The fol- 
lowing table shows the amounts of protein in some vegetable sub- 
stances : 

PROTEIN IN VEGETABLE MATERIALS. 

Per cent. 

Corn fodder, green 1.8 

Potatoes 2.1 

Onions 1.4 

Timothy, green 3.1 

Red clover, green 4.4 

Corn, grain 10.5 

Wheat, grain 11.9 

Cowpeas, grain 20.8 

Corn fodder 4.5 

Timothy hay 5.9 

Red clover hay 12.3 

Cowpea hay 16 6 

Soja beans 34.0 

The nitrogenous constituents of agricultural plants may be 
divided into the four following groups: (i) proteids; (2) amides 
and amido acids; (3) inorganic compounds; (4) miscellaneous 
bodies ; which include alkaloids, lecithin, chlorophyll, etc. Pro- 
teids and amides are of common occurrence in agricultural prod- 
ucts ; the other bodies, while of some importance, are of less 
general occurrence. 

Proteids. Proteids are complex bodies of unknown high mole- 
cular weight and unknown .constitution. They contain carbon, 
hydrogen, oxygen, nitrogen, sulphur, and sometimes phos- 
phorus. Proteids are exceedingly important, being necessary 
to the life of both plants and animals. The flesh of animals is 
composed largely of proteids, which are derived from vegetable 
proteids. When split up, proteids yield various amides, amido 
compounds, and other bodies. This splitting up takes place dur- 
ing digestion, and the digested constituents are reunited in the 
animal body to form animal proteids, which are different from 
the original vegetable proteids. The splitting up also takes place 
in the germination of seeds, when the reserve proteids are broken 
up into asparagin and other bodies, and used in the production 
of new tissue in the growing portions of the plant. 



CONSTITUENTS OF PLANTS 357 

Classes of Proteids. 1 The proteids are divided into three 
groups; simple proteids, conjugated proteids, and derived 
proteids. 

I. SIMPLE PROTEIDS. (a) Albumins. Albumins are soluble 
in water and are not precipitated by sodium chloride, or mag- 
nesium sulphate. They are coagulated and made insoluble by 
heat. The best example of an albumin is the white of an egg. 

(b) Globulins. Globulins are not soluble in water, but are 
soluble in solutions of sodium chloride, and other neutral salts. 
They are precipitated by removing the salts, or by saturating the 
solution with salts. 

(c) Protamins are proteids soluble in alcohol. Several have 
been isolated. Gliadin is found in wheat ; zein, in Indian corn, 
etc. 

(d) Glutelins. These are not soluble in water, salt solutions, 
or alcohol. The glutenin of wheat is the only well characterized 
representative of this group yet obtained, though there are indica- 
tions that they may be present in other cereals. 

(e) Albuminiods, (/) Histones, and (g) Protamines have not 
been found in plants. They are animal proteids. 

II. CONJUGATED PROTEIDS. Coagulated proteids are complex 
proteids which can be split up into proteids and other bodies. 
Nueclo-proteids, formed from nucleic acid and protein, have been 
isolated from some plants. Glycoproteids may be split up into 
proteids and carbohydrates. Phosphoproteids contain phosphorus. 

III. DERIVED PROTEIDS. Derived proteids are produced from 
proteids by the action of acids, alkalies, alcohol, or digestive 
juices. The three important groups are proteoses, peptones, and 
peptides. 

Proteoses. Proteoses are soluble in water, and are not 
coagulated by heat, differing in this respect from albumins. They 
are diff usable. 

Peptones. Peptones are very easily soluble in water, and are 
not precipitated by heat, by neutral salts, or by nitric acid. They 
are precipitated by tannic acid, by absolute alcohol, and by picric 
1 Osborne, The Vegetable Proteins. 



358 



PRINCIPLES OF AGRICULTURAL CHMISTPY 



acid. Proteoses and peptones are formed in the digestion of 
proteids within the animal body, by the action of the juices of the 
stomach (the gastric juice), which contain pepsin, upon them. 

Proteids in Plants. The names and occurrence of some plant 
proteids are as follows : 

Legumin, which is found in considerable quantity in seeds of 
pea, horse bean, vetch, and lentil. 

Vignin, the chief protein of the cowpea. 

Glycenin, a globulin, chief protein compound of soy bean. 

Gliaden, soluble in alcohol of 70-80 per cent., the most abundant 
protein of wheat kernels. 

Hordein, soluble in alcohol, found in barley. 

Zein, most abundant in corn, easily soluble in alcohol. 

Vicilin, a globulin found in pea, lentil and horse bean. 

Composition of Proteids. The proteids vary in composition 
and properties. The percentage composition of some important 
vegetable proteids is given in the following table i 1 





c 


H 


N 


S 


o 




51.71 

51.72 
54-29 

5 '-03 
52.72 

52.34 


6.86 

6-95 
6.80 
6.85 
6.86 
6.83 


18.30 
18.04 
17.20 
18.30 
I7.I6 
17-49 


0.62 

"39 
0.85 
0.69 
I 03 
1. 08 


22.51 

22.90 
20.86 

23-13 
21.73 
22.26 






Globulin wheat 









The factor 6.25 used for proteids requires 16.00 per cent, nitro- 
gen. The above proteids contain from 17.20 to 18.30 per cent, 
nitrogen. 

Amides and Amido Compounds. Amides, as distinguished from 
proteids, are nitrogenous compounds of known molecular weights 
and known constitution. They have little value in animal nutri- 
tion. 

In seeds they occur only in small quantity. They are more 
abundant in leaves and the growing parts of plants, and are parti- 
cularly abundant in germinating seeds. Nitrogenous material is 
converted into amides for the purpose of transportation through 
1 Osborne, The Vegetable Proteins, p. 49. 



CONSTITUENTS OF PLANTS 



359 



the plant. Amides are also formed from proteids by the action 
of acids, or the digestive juices of animals, or by other agencies. 

The most important amido compounds are leucin, tyrosin, 
phenyl-amido-proponic acid, asparagin, and glutamin. Of these 
asparagin is relatively the most common and most abundant. It 
has the formula C 2 H )5 (NH 2 ) (CONH 2 ) (COOH). Leucin, 
tyrosin, and phenyl-amido-propionic acid are amido-acids ; that is 
to say, they are acids in which the amido group NH 2 has 'replaced 
an atom of non-acid hydrogen. Thus leucin, C 5 H 10 (NH 2 )CO 2 H, 
is derived from capronic acid, C^H^COaH, by replacing an atom 
of hydrogen by NH 2 . 

Determination of Proteids and Amides. An accurate method 
for this determination is much to be desired. The usual method 
consists in boiling the substance with water and precipitating the 
proteids with copper hydroxide. The nitrogen in the precipitate 
multiplied by 6.25 is supposed to give the proteids. The differ- 
ence between the precipitated nitrogen and the total nitrogen, is 
the amide nitrogen. 

PROTEIDS AND AMIDES IN PLANTS. 1 (IN DRY MATTER.) 





Proteids 


Amides 




1 1.8 

8.3 
7-9 
9-i 
41.7 
13-9 

10. 1 

16.2 

4.4 
47.2 

5.3 


7.0 
4-7 
3-i 
2.4 
0.6 
3-1 

0.8 

1.2 

0.6 

0.7 

























The preceding table shows that the protein of seeds consists' 
mostly of proteids, but a considerable part of the protein of hays 
and fodders may consist of non-proteid materials. The per- 
centage of nitrogen in the amido compounds we have mentioned, 
is given in the following table : 

1 Bulletin 172, North Carolina Exp. Sta. 



360 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

NITROGEN IN AMIDO COMPOUNDS 

Per cent. 

Asparagin 21.37 

Glutamin 19.31 

Leucin 16.87 

Phenyl-amido-propronic acid 8.48 

Tyrosin 7-73 

Considering that asparagin is the most common amide in plants, 
it is evident that the factor 6.25 (which requires 16 per cent, 
nitrogen) is too high. A percentage of 21.37 nitrogen requires 
the factor 4.68. 

Inorganic Nitrogenous Bodies. Growing plants sometimes con- 
tain appreciable amounts of nitrates or ammonia. Very little is 
found in ripe seeds or plants. The nitrates or ammonia are 
taken up by the roots of the plants, and used for the production of 
organic nitrogenous bodies. 

Miscellaneous Nitrogenous Substances. Other nitrogenous sub- 
stances found in plants are alkaloids, lecithin, chlorophyll, etc. 

Alkaloids are substances of poisonous or medicinal character. 
Since they are bases, they unite with acids to form salts. 
Alkaloids are not found to any extent in ordinary agricultural 
products. 

Lupine seeds contain from 0.02 to 0.65 per cent, alkaloids, 
according to the variety. The principal alkaloid is called lupinin. 
The seeds are so bitter that, without special preparation, they are 
not eaten by animals. 

Tobacco contains 0.61 to 6.44 per cent, alkaloids, the chief be- 
ing nicotine. In the pure condition it is very poisonous. 

Caffeine is an alkaloid found in coffee and tea, to which they 
owe a portion of their properties. 

Chlorophyll contains nitrogen, and so is included in protein. 

Nitrogen-Free Extract. 1 This term is used for the reason that 
the material is soluble in acids and alcohols, and is free from 
nitrogen. The nitrogen-free extract of seeds, and of many con- 
centrated feeds consists largely of sugars, starches, and similar 
substances, which are easily digested and of high value to animals. 
But the nitrogen-free extract of hays, straws, and fodders con- 
1 See Tollens, Exp. Sta. Record 8, p. 641. 



CONSTITUENTS OF PLANTS 361 

tains only relatively small quantities 1 of sugars and starches, and 
large amounts of less easily digested material. 

The nitrogen-free extract makes up the largest part of most 
agricultural plants. In many instances it is as much as the sum 
of all the other constituents. The percentages in the dry matter 
of certain plants are given in the following table : 

NITROGEN-FREE EXTRACT. (!N DRY MATTER.) 

Per cent. 

Corn fodder 60.6 

Timothy hay 52.8 

Red clover 45.8 

Cowpea vines 43.6 

Potatoes 82. 2 

Corn 77.4 

Wheat 80.4 

Co wpeas 65. 5 

Soja bean 32.2 

The nitrogen- free extract may contain sugars, starches, pen- 
tosans, hemi-celluloses, gums, vegetable acids, and miscellaneous 
bodies. It is composed to a large extent of carbohydrates. 

Carbohydrates are compounds containing carbon, united with 
hydrogen and oxygen in the proportion to form water. 
Chemically, they are related to alcohols and aldehydes or ketones. 
The general formula of carbohydrates is Cm(H 2 O)n. Glucose, 
CgH^Oe, starch C 6 H 10 O 5 , and cane sugar (sucrose) C^H^On, 
are examples. Some carbohydrates are soluble in water 
and have a sweet taste, others are insoluble and taste- 
less. Some are easily acted upon by chemical reagents, 
while others, (particularly cellulose) are very resistant. All 
carbohydrates, however, may, by appropriate means, be converted 
into simple sugars. 

It is not correct to use the term "carbohydrates" to signify the 
nitrogen-free extract. The nitrogen-free extract consists partly 
of substances other than carbohydrates. Crude fiber also con- 
tains cellulose, which is a carbohydrate. 

Sugars. The sugars are carbohydrates which are soluble in 
water, and, as a general rule, have a sweet taste. Cane sugar, 
1 Frear, Report Pennsylvania Station, 1903-4. 
24 



362 



PRINCIPLES OF AGRICULTURAL, CHEMISTRY 



which is prepared from sugar cane or sugar beets, is the most 
common sugar. Sugars are divided into two groups : the simple 
sugars, or monosaccharides, represented by glucose, and the com- 
plex sugars, or polysaccharides, represented by cane sugar or suc- 
rose. The complex sugars can be split up into one or more kinds 
of simple sugars. The sugars can all be crystallized, but in some 
cases crystallization is difficult. 




Fig. 80. A polariscope. 

Sugars are acted upon by acids and alkalies, forming various 
products, some of which are brown in color. Boiled with con- 
centrated hydrochloric acid, cane sugar gives a black precipitate 
called humic acid, the name being given chiefly on account of its 
black color. 

Optical Properties of Sugars. If a ray of light is passed 
through a crystal of Iceland spar, it is split up into two rays, 
having peculiar properties, and called polarized light. If a ray 
of this polarized light falls upon another parallel crystal, in one 
position no light will pass through ; if the crystal is rotated at an 
angle of 45, all the light goes through, while in intermediate posi- 
tions only a part is transmitted. 

If the two crystals referred to above are placed so that all the 
light passes through, and a solution of sugar then placed between 
them, the polarized light will no longer all go through the second 
prism, but the prism must be rotated to a certain angle before the 
light will all pass through. The sugar has twisted the ray of 



CONSTITUENTS OF PLANTS 363 

polarized light, or as it is termed, it has rotated the plane of 
polarization. The degree of rotation depends on the kind of 
sugar, the strength of the solution, the length of the column, and 
the temperature. 

A polariscope 1 consists essentially of two Nicol prisms of Ice- 
land spar properly mounted, between which the substance is 
placed, having lenses for suitable management of the light and 
the image. In order to measure the rotation, either the second 
crystal (called the analyzer) may be rotated, and the angle of 
rotation read, or the rotation may be compensated by a quartz 
wedge, which is likewise read on a graduated scale. Several 
arrangements are made in order that the reading may be accurate. 
In one type of instrument, the circular ray of polarized light is 
split into two half-discs, so that if the crystal or quartz wedge is 
moved slightly to the right, one-half of the image becomes dark, 
and if it is moved slightly to the left, the other half becomes 
dark. The intermediate position, at which both sides are of 
equal brightness, is the one at which the reading is taken. The 
instrument can be adjusted so that only a very slight change 
throws the shadow on the one side or the other. 

The polariscope affords a very rapid and accurate method for 
estimating sugar, especially cane sugar, and it is used extensively 
in the analysis of sugar, sugar cane, sugar beets, and in the con- 
trol of the processes of manufacture of sugar from cane or beets. 

Reducing Power. When simple sugars and certain compound 
sugars are boiled with copper salts in alkaline solution, the copper 
is reduced to cuprous oxide (Cu, 2 O), and may be collected and 
weighed as such, or as metallic copper. This property is used 
for the detection of sugars, and also for their quantitative estima- 
tion. The amount of sugar solution required to reduce a given 
amount of copper may be used to measure the amount of sugar. 
The amount of copper reduced depends upon the nature of the 
sugar, the volume of the solution, the time of heating, the com- 
position of the copper solution, and other details of the analytical 
process. 

1 See Wileys Principles and Practice of Agr. Chem Anal., Vol. III. 



364 PRINCIPLES OF AGRICUI/TURAI, CHEMISTRY 

Tables have been prepared showing the amounts of copper 
which were found by experiments to be reduced by given sugars 
under fixed conditions ; these tables can be used in the estimation 
of sugars under the same conditions, but the details of the method 
used in preparing the tables must be followed carefully. 

The copper solutions used ordinarily are Fehling's solution, 
containing fixed quantities of copper sulphate, sodium potassium 
tartrate, and sodium hydroxide; and Allihn's solution, containing 
certain amounts of copper sulphate, sodium potassium tartrate 
and potassium hydroxide. Other solutions are used. Different 
sugars require different quantities of copper under the same con- 
ditions. For example, the same amount of copper will be reduced 
from Sachsse's solution by the following amounts of sugars : 
Fructose 213 mg. 
Maltose 491 mg. 
Lactose 387 mg. 

Fermentation. Under suitable conditions, yeast converts cer- 
tain sugars into alcohol and carbon dioxide according to the 
following reaction : 

C 6 H 12 6 = 2C 2 H 6 + 2C0 2 . 

Yeast is a plant which grows in the solution, and develops an 
enzyme which changes the sugar as described. Like all plants, 
yeast must have nitrogenous food, also phosphoric acid, potash, 
and lime. Yeast will not grow well in pure sugar. An enzyme 
is a substance which causes a chemical change, without itself be- 
ing changed in the reaction. 

The simple hexoses are easily fermented. Some of the com- 
pound hexose sugars ferment readily, while others must first be 
split up into the simple hexoses. Pentosans do not undergo the 
alcoholic fermentation. 

There are other kinds of fermentation, probably the most im- 
portant being the acetic fermentation, in which alcohol is con- 
verted into acetic acid (vinegar), and the lactic acid fermentation, 
in which sugar is converted into lactic acid. This takes place in 
the souring of milk. 



CONSTITUENTS OF PLANTS 365 

Fermentation is important in the manufacture of cider from 
apple juice; wine from grape juices; and alcoholic beverages and 
alcohol from materials containing starch or sugar, such as 
potatoes, corn, rye, barley, etc. 

Classes of Simple Sugars. Four groups of simple sugars are 
known to chemists, though only two of these are of agricultural 
importance. The groups are : ( i ) the trioses, containing three car- 
bon atoms in the molecule C 3 H 6 O 3 ; (2) the tetroses, containing 
four carbon atoms, C 4 H 8 O 4 ; (3) the pentoses, containing five 
carbon atoms; and (4) the hexoses, containing six. All the 
natural carbohydrates are related to either the pentoses or the 
hexoses. The principal simple sugars are xylose and arabinose, 
which are pentoses ; and glucose, fructose, mannose, and galactose, 
which are hexose sugars. 

Each of these sugars exists in three modifications, namely, one 
which rotates polarized light to the right, one which rotates 
polarized light to the left, and one which does not rotate it, and 
is inactive. Thus we have d-glucose, 1-glucose and i-glucose, 
dextro-, laevo-, and inactive glucose. Although many of these 
sugars are known, as a rule only one modification of each sugar 
is of natural occurrence. Thus natural glucose is dextro-rotatory, 
and was formerly called dextrose for this reason, and ordinary 
fructose is laevo-rotatory, and was called levulose. 

Pentose Sugars, C 5 H 10 O 5 . The pentose sugars occur to a very 
limited extent, if at all, in nature. They are of agricultural im- 
portance on account of their relation to the pentosans, which are 
found in large quantities in agricultural products. 

When distilled with strong hydrochloric acid, the pentoses and 
pentosans are converted into furfural, 1 which distils over with the 
acid: 

C 3 H 10 8 = C 5 H 4 2 + 3 H 2 
Pentose Furfural 

The furfural can be precipitated with a solution of phloro- 
glucinol, the product being furfural phloroglucid. The precipitate 
is filtered off, dried, and weighed. The quantity of furfural 
1 Landw. Versuchs-stat. , 42, p. 381. 



366 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

yielded by the different pentose sugars and pentosans under the 
conditions of the work have been determined by experiments. 

Stoklosa found considerable quantities of water-soluble pen- 
tosans in sugar beet seed, and DeChalmot found small quantities 
in the leaves and bark of a number of plants. But pentose sugars 
have not been separated as such from plants, but are prepared by 
the hydrolysis of certain pentosans. The pentoses do not fer- 
ment with yeast. 

Arabinose, C 5 H 10 O 5 = CH 2 OH(CHO) 3 CHO, has been pre- 
pared from the pentosans found in lupines, soja beans, rye bran, 
wheat bran, plums, and cherry gum. It is easily prepared by boil- 
ing cherry gum with 2 per cent, sulphuric acid. It crystallizes 
beautifully, and has a sweet taste, but not as sweet as sucrose. 

Xylose, C 5 H 10 O I5 , has been prepared from beech wood, jute, fir 
wood, cherry wood, laurel wood, wheat straw, corn cobs, oat 
straw, rye straw, corn bran, apples, etc. It crystallizes in prisms. 

Rhamnose, C 6 H, B O 3 = CH 3 (CHOH) 4 CHO, is methyl pen- 
tose, which yields methyl furfural by distillation with hydro- 
chloric acid. It is obtained from certain glucosides, and 
crystallizes in beautiful, sweet crystals. 

Hexose Sugars, C 6 H 12 O 6 . The two hexose sugars of common 
occurrence are fructose and glucose. They occur, in equal 
quantity, in sweet fruits, flowers, certain vegetables. The other 
hexoses are formed by the hydrolysis of certain carbohydrates. 
All the hexoses are fermented by yeast. 

d-Glucose, C 6 H 10 O 5 , or grape sugar, occurs in grapes, sweet 
fruits, tomatoes, seeds, roots, leaves, flowers, honey, etc. To- 
gether with fructose, it is formed by the hydrolysis of cane sugar. 
It is also formed by the hydrolysis of starch, and is the chief 
ingredient of many syrups. Nitric acid oxidizes it to saccharic 
acid, and glucose may be detected by means of this reaction. It 
is also detected through its optical properties. Glucose is a white 
crystalline substance, which is not so sweet as cane sugar. It is 
easily soluble in water and alcohol. It undergoes fermentation of 
various kinds readily. Glucose is produced commercially by the 



CONSTITUENTS OF PLANTS 



367 



action of dilute acids upon starch. The acid splits up the 
starch, and causes it to unite with water 

(C 6 H 10 5 ) + X H 2 = C 6 H 12 6 - 
Starch. Glucose. 

The thick syrup formed after the acid is neutralized and the solu- 
tion evaporated is called glucose syrup or corn syrup. It does 
not consist of pure glucose. If a solid mass is produced, it is 
called grape sugar. 

Fructose, C 6 H 10 O 5 , accompanies glucose in most fruits and 
vegetables. It is difficult to crystallize. It is obtained by hydrolysis 
of inulin. So-called invert sugar is a mixture of equal quantities 
glucose and fructose, and is formed by the hydrolysis of sucrose. 
Honey is a natural invert sugar, dissolved in water, with small 
quantities of impurities. While glucose may be separated from 
invert sugar comparatively easily, it is not easy to separate 
fructose on account of its difficult crystallizability. 

Mannose, C 6 H 10 O D , has not been found in nature. It has been 
prepared by the hydrolysis of vegetable ivory, the seeds of palms 
and lilies, coffee beans, and gum arabic, etc. 

Galactose, C 6 H 10 O 5 , has not been found as such in nature. It 
is a product of the hydrolysis of milk sugar, and of carbohydrates 
found in seeds of lupines, beans, soja beans, peas, vetch, cress, 
young clover, lupine, and lucerne plants, in gum arabic, fruits of 
pears, etc. Nitric acid oxidizes it to mucic acid, which is almost 
insoluble in water. A method for its estimation is based upon 
this fact. 

Compound Sugars. The most important compound sugars are 
cane sugar, milk sugar, raffinose, maltose, and stachyose. They 
are derived exclusively from hexoses. 



Name and Formula 


Hydrolized to 


Action towards 
Fehling solution 




Glucose and fructose 


No action 


\^anc sugar, Ma^n^i] 

TVTillr one/sir O "FT O 


Glucose sralactose 


Reduces 




Glucose 


Reduces 


T? oflfJtinQf* OHO 


Glucose fructose galactose 


No action 




Glucose fructose glucose 


No action 









368 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

Like the monosacchosides, the polysaccharides are neutral, 
sweet, colorless compounds, easily soluble in water, and they are 
readily crystallizable. They are easily converted into mono- 
saccharides by the action of warm dilute acids, or certain un- 
organized ferments. The ease with which this action takes place 
depends upon the nature of the sugar; simply warming for a 
short time with a dilute acid is sufficient to split cane sugar 
(sucrose) into glucose and fructose, while maltose requires to be 
boiled for some hours with the acid for complete inversion. 

Sucrose, CnH^On, is prepared from sugar cane, sugar beets, 
and maple sap. The impurities which accompany the sugar 
are different when prepared from these three sources, but no 
differences can be detected in the sugar when it has been thor- 
oughly purified. 

Sucrose is widely distributed. The juice of sugar cane, sweet 
sorghums, and sugar beets contains 10 to 20 per cent. 
Peanuts contain 4-6 per cent., sweet potatoes 1-3 per cent., the 
seeds of beans, peas, vetch, soja beans, hemp, and sunflower seeds 
contain 4-6 per cent. Some fruits contain 5 per cent, or more. 
Green corn, before the ears are formed, is quite rich in sucrose. 

Sucrose crystallizes in regular crystals belonging to the 
monocline system. It is easily soluble in water and has a high 
dextro-rotatory power. It melts at 160 C. and solidifies on cool- 
ing to an amorphorous glassy mass. A high temperature con- 
verts it into a substance known as caramel, which is used for 
coloring some food materials. A still higher temperature car- 
bonizes it with evolution of gases and vapors. 

Sucrose does not reduce Fehling's solution, but can easily be 
converted into invert sugar, which has reducing power. This is 
a method for its estimation. The polariscope is also used for the 
estimation of sugar. The inversion of sugar takes places in the 
ripening of some fruits, the curing of fodders, and in the cooking 
and preparation of human foods. 

Manufacture of Sugar. The processes of manufacture from 
sugar cane and sugar beets vary somewhat in details. The beets 
are first sliced, and the sugar extracted with warm water or sugar 



CONSTITUENTS OF PLANTS 369 

solution, in a series of vessels. The water comes in contact first 
with beet slices nearly exhausted of sugar, then it is brought in 
contact with slices richer in sugar, and finally passes through the 
vessel containing fresh beet slices. This system exhausts the 
beet, and at the same time secures a comparatively strong solu- 
tion of sugar. 

The sugar juice is acid. It is treated with lime to neutralize 
the acid, which would otherwise invert the cane sugar when the 
juice is heated and decrease the yield. The lime also precipitates 
a quantity of impurities. The lime which goes into solution is 
next precipitated with carbon doxide and the solution is finally 
neutralized and bleached with sulphur dioxide. 

The sugar solution is next evaporated until the sugar is ready 
to crystallize. Since inversion would take place at the tempera- 
ture required for rapid evaporation in the open air, and since 
there would also be danger of burning, the evaporation is carried 
on in a vacuum, in which the solution boils at a comparatively 
low temperature. The solution is drawn off when the sugar is 
ready to crystallize, allowed to cool, and the mother liquor ex- 
tracted from the crystals in a centrifuge by centrifugal force. 

Sugar is prepared from sugar cane in essentially the same way. 
The juice is squeezed out by passing the cane between heavy 
rollers, instead of being extracted by diffusion. The pressed cane 
is termed bagasse. The sugar is sent to a refinery for further 
purification. 

Syrup is prepared from sorghum, sugar cane, or maple sap by 
evaporating the juice, usually in open kettles, with or without 
previous purification with lime and sulphur. 

Milk Sugar, C 12 H 2! ,O n , (lactose) is not found in plants, but 
occurs in the milk of animals to the extent of 3 to 6 per cent. It 
remains in solution when the casein and fat of milk have been 
separated (as occurs in the manufacture of cheese), and may be 
prepared by evaporating the liquid and recrystallization of the 
product. It appears as hard white crystals with a slightly sweetish 
taste. It is not as easily soluble in water as cane sugar. It is 
hydrolyzed to d-galactose and d-glucose. 



3/o 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



Milk sugar reduces Fehling's solution and does not ferment 
until inverted. 

Maltose, C 12 H 22 O 1:L , is formed from starch by the action of 
diastase, a ferment found in sprouting barley and other seeds, and 
is important in the manufacture of beer, alcohol, and alcoholic 
beverages from starchy materials. It forms fine, white needles, 
is easily soluble in water, and is hydrolyzed to glucose. 

Raffinose occurs in small quantities in sugar beets, and in barley, 
and in considerable quantities in cotton seed. It crystallizes as 
needles or prisms, is easily soluble in water and methyl alcohol, 
but is scarcely soluble in ordinary alcohol. It does not act upon 
Fehling's solution. It is first broken down by hydrolysis into 
two reducing sugars, fructose and melibiose; the latter is then 
split up into glucose and galactose. 

Stachyose occurs in the tubers of stachys tuberifera. It is 
hydrolyzed to galactose, fructose, and glucose. 

Starch, C, 6 H 10 O 5 . This is found in the most different organs 
of plants in the form of granules having an organized structure. 




Fig. 81. Starch granules, (A) corn, (B) potato, (C) wheat, 
(D) bean. After Wiley. 

It is one of the first products of the assimilation of carbon 
dioxide, and can be easily detected in the chlorophyll granules of 
the leaf. It is transferred from the leaf in a soluble form, and 



CONSTITUENTS OF PLANTS 3/1 

used for the construction of other plant substance, or stored up as 
reserve material as such. Starch is thus found abundantly in 
many seeds, roots, and tubers, the parts of the plant concerned 
with new growth. 

The starch granules vary in size and structure according to 
their origin. Potato starch appears mostly as oval granules with 
an average diameter of 0.07 mm., but it contains large granules. 
Wheat starch contains circular granules of two sizes, smaller than 
0.007 mm - diameter and larger than 0.2 mm. with few granules 
of intermediate size. The structure of the granules, and their be- 
havior towards polarized light is also different, so that one 
familiar with their appearance can easily identify starches of 
different origin by means of a microscopic examination. 

The elementary composition of starch is represented by the 
formula C 6 H 10 O 5 , but its molecular formula is not yet known. 
Many chemists hold that the starch molecule may contain more 
than loo carbon atoms. 

Properties of Starch. Air-dry starch contains 10 to 20 per cent 
water. By carefully drying at 102-110 C., it may be obtained 
water-free. In cold water it is insoluble. With hot water the 
granules swell, break, and form starch paste, a pasty solution, 
from which a clear filtrate can be secured. By treating starch 
for several days with cold dilute mineral acids, it may be changed 
into "soluble starch," which dissolves in hot water without forma- 
tion of a paste. Starch is tasteless and colorless. 

Starch is especially characterized by the blue color it gives with 
iodine. This is a very delicate test for both starch and iodine. 
Starch is used as an indicator with volumetric solutions contain- 
ing iodine. 

When heated with dilute mineral acids under proper conditions, 
starch is converted almost quantitatively into glucose. As we 
have already seen, this property is utilized in the manufacture of 
glucose and glucose syrup from starch. 

Under other conditions, dilute acids change starch into a 
gummy substance termed "dextrin." This occurs in some 
mucilages made from starch. 



372 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

When heated to a temperature above 120 C., starch is changed 
to dextrin. This takes place in the browning of flour, prepara- 
tion of toast, and some other processes of cooking. 

When starch paste is treated with malt (this is best done at a 
temperature of about 65 ), it is converted into maltose and dextrin, 
and goes into a solution, which may be fermented. Advantage is 
taken of this property in the manufacture of alcohol or alcoholic 
beverages from materials containing starch, such as corn, rye, 
barley, etc. The grain is ground, heated with water, treated with 
malt, and to the aqueous solution yeast is added to cause fer- 
mentation. If alcohol or whiskey is desired, the fermented 
material is distilled. The residue from the treatment with 
malt is dried and used for cattle food (brewers' grains), or 
it may be fed without drying. 

Malt is partly sprouted barley, the sprouts being rubbed off. It 
contains an enzyme known as diastase, which acts upon starch as 
stated above. 

Manufacture of Starch. Starch is made from potatoes, corn, 
arrow-root, cassava, and other materials rich in it. The prepara- 
tion of starch from potatoes is a simple mechanical operation. 
The potatoes are washed and grated to a pulp to break the cell 
walls. The starch is washed out of the pulped mass on sieves. It 
is allowed to settle and dry. With some other materials such 
as wheat and rice, the proteids which accompany the starch must 
be brought into solution by fermentation or by means of caustic 
soda. 

Inulin, C 6 H 10 O 5 , is found dissolved, in a pasty condition in 
many plants of the Compositae family, and in these plants plays 
the part that starch does in most others. It is obtained from the 
dahlia tubers. It is a white powder, composed of small crystals, 
easily soluble in warm water, being slowly precipitated on cool- 
ing, but readily by alcohol. It is not colored by iodine, hardly 
affected by diastase, and is much more easily hydrolized by dilute 
acids than starch. Since it yields only fructose, it is used for the 
preparation of pure fructose. 

Glycogen, C G H 10 O r> . is a starch-like carbohydrate found in 



CONSTITUENTS OF PLANTS 373 

animals. From 0.6 to 07 per cent, is found in the muscles, but 
it disappears while the animal is at hard work or starving. It is 
contained in quantity in the liver, and is the reserve material 
formed from the excess of carbohydrates for the furnishing of 
sugar to the blood. 

Gums. Gums are found in many vegetable materials. They 
often exude from cut places. Both hexoses and pentoses are 
formed by fHe hydrolysis of gums. Some of the gums are the 
best materials for the preparation of the pentose sugars. 

The following are some gums and the sugars they yield on 
hydrolysis : 

Gum arable yields galactose and arabinose. 

Wood gum, extracted from wood by alkalies. 

Cherry gum yields arabinose. 

Peach gum yields galactose and arabinose. 

Barley gum yields galactose and xylose. 

Galactan yields galactose and other sugars, and is found in 
leguminous plants. 

Pectins. These are substances found in fruits and some fleshy 
roots. They are soluble in water, and precipitated as a jelly-like 
mass by alcohol. When boiled sufficiently, they jelly on cooling. 
If boiled too long, they will not jell. Pectins appear to be closely 
related to the carbohydrates, or belong to them. They are found 
in apples, pears, quince, cranberries, beets, turnips, etc. 

Cellulose, C 6 H 10 O 5 . Cellulose is the chief constituent of the 
cell walls of plants. It is insoluble in warm dilute acids or 
alkalies. In young parts of plants, the cell walls are composed 
of almost pure cellulose. In older organs the cellulose is inter- 
penetrated with "incrusting material." Cellulose is found 
abundantly in wood tissue and woody tissue of all kinds. Cotton 
is almost pure cellulose. Flax and hemp are composed largely of 
cellulose. It may be prepared by treating the material successively 
with ether, boiling dilute acid, boiling dilute alkali, and then with 
cold dilute nitric acid and potassium chlorate to remove the in- 
crusting material. The residue consists of cellulose. Cellulose is 
a colorless insoluble material. Its molecular weight is unknown 



3/4 PRINCIPLES OF AGRICULTURAL, CHEMISTRY 

Cellulose may be dissolved in a solution of copper oxide in am- 
monia. It also dissolves in concentrated sulphuric acid. If the 
solution is immediately diluted with water, a jelly-like mass is 
precipitated. If digested for some time with the acid, and the 
solution then diluted and boiled for some time, sugar is produced. 
The product is glucose from cotton and many other celluloses, 
but d-mannose is secured from some other celluloses, such as 
those from the coffee bean and sesame seed. The function of 
cellulose in plants is to form the structure of plant cells. In seeds 
it acts as a reserve material. Digested cellulose appears to be 
equal in value to other carbohydrates. Cellulose contains 44.4 
per cent, carbon. 

Lignin. This is the term applied to the incrusting substances 
which accompanies the cellulose in wood and woody cells. Crude 
fiber is largely composed of this mixture or, perhaps compounded 
of cellulose and lignins. The chemical nature of the lignins is 
not clearly known. They do not appear to belong to the group 
of carbohydrates, but contain 55-60 per cent, carbon. Cutin con- 
tains 68-70 per cent, carbon. 

The quantity of lignins in the plant increases with the age of 
the plant tissue. Young woody tissue may contain little lignin, 
while old woody tissue may be composed largely of it. The 
greater the quantity of lignin in the material, the lower its value 
for feeding purposes. 

Hemicelluloses. This term has been proposed for the carbo- 
hydrates of the cell walls which are insoluble in water, but, un- 
like cellulose, are brought in solution by dilute acids or alkalies. 
Such carbohydrates are of extensive occurrence. The sugars pro- 
duced by their hydrolysis are both pentoses and hexoses. 
Hydrated celluloses, formed by the union of cellulose with water, 
are largely dissolved by acids or alkalies, and hence would be 
classed with the hemicelluloses. 

Pentosans. Pentosans may be defined as carbohydrates insol- 
uble in water, which yield pentose sugars on hydrolysis. The 
reaction resulting in the formation of furfural when pentosans 
are boiled with strong acids, is used for their estimation. The 



CONSTITUENTS OF PLAX'i- 



375 



pentosans are accompanied with a substance 1 which yields a fur- 
fural-like product, but which product decomposes on standing 
and does not distil with the furfural a second time. Pentosans 
occur in most plant materials, and are particularly abundant in 
hays and straws. The pentosans are chiefly gums, pectins, and 
hemicelluloses, though a certain quantity is always found in the 
crude fiber. 

Digested pentosans appear to be of considerable value to the 
animal. Although it is possible that they have the same value 
as starch, when once digested, yet the digested portion of feed- 
ing stuffs rich in pentosans has a decidedly lower value for pro- 
ductive purposes than that of starchy materials. This appears 
to be due in part to the labor of chewing the crude fiber of such 
materials, but the labor of chewing does not account for the 
entire deficit. 

The following table shows the relative occurrence of these 
classes of substances in different materials. 2 

NITROGEN-FREE EXTRACT OF SOME FEEDING STUFFS. 





i 


*er cent, on 


dry matte 


r 




Simple 
sugars 


Compound 
sugars 


Pentosans 


Residues 




4O7 




TO 71 


16 88 




y/ 

I A2 


66 

O A 7 


ly. /i 

4'JC 


21 4O 




l.q* 


=; 66 


60 

6 81 


CO 2O 


Porn 


I 76 


oil 








522 


i 81 


95:7 


29 81 




O 22 


IO 7^ 


6 76 


54.6 













Crude Fiber. 3 The organic residue left after extraction of 
plant substance with ether and boiling it successively with i% 
per cent, acid and alkali, is termed crude fiber. The process is 
arbitrary, and the object in view when it was devised was to se- 
cure a product as free as possible from nitrogen. 

1 N. C. Bulletin, No. 178. 

2 Fraps, Jour. Am. Chem. Soc., 1900, p. 543. 

3 See Tollens, Exp. Sta. Record 8, p. 649. 



3/6 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

Crude fiber consists of cellulose, lignin, cutin, pentosans, and 
other substances. Digested crude fiber appears to be equally 
as good as starch, but the labor of chewing materials containing 
much crude fiber, largely counteracts the value of the food. 

Seeds and tubers contain little crude fiber. Hay, straw, chaff, 
and woody materials in general may contain considerable quan- 
tities. For the crude fiber content of some materials, see the 
tables of analyses. 

About 20 per cent, of the pentosans of hays and straws is in 
the crude fiber, making up 10 to 15 per cent, of the crude fiber. 



1 


Total 
pentosan 


Pentosan in 
crude fiber 




24.86 
26.25 
2O.OO 


5-15 
4-35 
5o6 









Organic Acids. Organic acids are found in plants and plant 
products, though often in very small quantities. They may be 
present in the free state, but are usually present as salts of lime 
or potash. In green plants the acids are found mainly in solu- 
tion in the sap ; later on they are deposited into the cell tissues. 

The quantity of organic acids in ordinary agricultural plants 
is very small. Appreciable amounts are found in fruits and some 
vegetables. Tartaric acid occurs in appreciable amounts in 
grapes, and is deposited as potassium acid tartrate in wine. 
Small amounts are found in pineapples, cucumbers, and tomatoes. 
Malic acid occurs in apples, from which it gets its name, but is 
widely distributed, occurring in a number of fruits and vegetables. 
Oxalic acid and succinic acid are found in many plants. 

Citric acid is present in lemons and limes, and in small amounts 
in pears, beans, cherries, and other fruits. Tannic acid is not 
present in food plants to appreciable extent, though it is found 
in tea and coffee. It is used for tanning leather. Some plants 
are grown for the tannic acid they contain. 

Lactic acid occurs in silage and sour milk. 

The organic acids have little food value, but affect the palat- 



CONSTITUENTS OF PLANTS 377 

ability of the food, and perhaps exert a favorable influence upon 
digestion by stimulating the secretion and flow of the digestive 
juices. 

Essential Oils. The characteristic flavor and odor of many 
plant products are due to volatile compounds known as essential 
oils. Turpentine, peppermint oil, oil of roses, and oil of lemon 
are examples of essential oils. Spices, flavoring extracts, condi- 
ments and appetizers in general, flowers, and certain fruits are 
characterized for the most part by the presence of essential oils. 
Hays owe a portion of their odor and flavor to essential oils. 
Rape, turnips, cabbage, and parsley contain essential oils. Some 
of the essential oils impart palatability to the food, and stimulate 
the secretion and flow of the digestive juices. While 
of little or no value for the production of muscle or energy, they 
aid the appetite of the animal. 

Certain feeds containing essential oils are undesirable for milch 
cows, as they impart a disagreeable flavor to the milk. Garlic, 
wild onions, and rape are examples of these. 

Organic Phosphorus Compounds. Plants also contain organic 
phosphorus compounds, chief among which is phytin, 1 which may 
be decomposed into inosite and phosphoric acid. This substance 
is found especially in wheat bran, rice bran, and cottonseed meal. 
Other organic phosphorus compounds are present. 

Heat Value. The energy of a feed or nutrient is measured by 
the heat which it produces when burned. The unit of heat is the 
calorie, written c., which is the amount of heat required to raise 
the temperature of I gram water i Centigrade. The large 
calorie (C) is 1,000 c, and the therm (T) is 1,000 C. Several 
kinds of calorimeters are used. In the bomb calorimeter, the 
material is placed in a platinum capsule in an iron vessel, lined 
with platinum or enamel. The bomb is filled with oxygen under 
high pressure, and placed in a vessel of water with a stirrer, and 
thermometer, and properly insulated to decrease heat changes. 
The material is ignited by means of an electric current which 
heats a small piece of iron wire, and the rise in temperature of 
the water is ascertained. Knowing the amount of heat required to 
1 N. Y. (Geneva) Bull. 250; Texas Bull. 156. 
25 



378 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



heat the apparatus, the quantity of water, the rise in temperature, 
and the loss of heat by radiation, the amount of heat produced 
by the known weight of substance may be ascertained. Urine is 




Fig. 82. Calorimeter (Atwater and Hempel) in which the substance 
is burned in compressed oxygen. 

either evaporated in a vacuum directly, or absorbed in paper of 
known heat value, and then dried. Heat measurements are made 
very often in investigations of animal nutrition. 1 

1 For discussion of heat values of nutrients, see Stohinann, Exp. Sta. 
Record No. 6, p. 590. 



CHAPTER XVIII. 



COMPOSITION OF PLANTS AND FEEDS. 

Feeding stuffs are divided into two great groups concentrates 
and roughages. A concentrate, or concentrated feeding stuff, 
consists of seeds, and various milling by-products. A concen- 
trate is rich in protein or in nitrogen-free extract and contains 
comparatively small amounts of crude fiber. As a general rule, 
the crude fiber of a concentrated feed does not exceed 10 per 
cent., though there are exceptions; crushed cottonseed cake, for 
example, contains about 27 per cent. Examples of con- 
centrates are corn, wheat, rice bran, cottonseed meal, gluten 
meal, wheat bran, etc. 

A roughage is a feed containing relatively high percentages of 
crude fiber and much smaller amounts of nitrogen-free extract 
and protein. Further, the constituents of the nitrogen-free ex- 
tract are less digestible and less valuable to the animal than those 
of concentrates. 

Seeds. The seed contains an embryo plant with sufficient plant 
food and organic matter to give the young plant a good start in 
life. Seeds of agricultural importance may be divided into three 
classes : 

(a) Starchy Seeds. Seeds of the cereals belong to this group. 

(b) Oily Seeds. Seeds of cotton, flax, hemp, sunflower, 
mustard, etc., belong in this group. OH is manufactured from 
them. 

(c) Seeds Rich in Protein. Seeds of peas, beans, and other 
leguminous crops belong in this group. 

Other classes of seeds are known, but they are not of great 
agricultural importance. 

Germination. In germination, the reserve material in the seed 
is converted into soluble forms, conveyed into the growing plant, 
and formed into new material. The chemistry of this change 
depends to some extent upon conditions. The proteids are con- 
verted into asparagin and other amido bodies, and the fat is 
oxidized and changed to soluble materials, which are used by the 



380 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

plant. The reserve carbohydrates undergo changes similar to 
the fat. In some seeds, as in barley, ferments are formed which 
change starch into sugar. 

The change in composition of seeds on sprouting may be 
studied by allowing a weighed quantity of seed to sprout in the 
dark, and determining the constituents of the original seed, and 
of the sprouted seed. The sprouting must take place in the 
dark, since when light is present carbon dioxide is assimilated 
and masks the change. 

Composition of Plants at Different States of Growth . Plants do 
not have the same composition at different stages of growth. The 
plant increases in weight up to maturity. In the earlier part of 
the life of the plant, nitrogenous material is taken up more 
rapidly. Before the formation of fruit, the reserve material pro- 
duced is stored up in leaves, stem, roots, or tubers. At the time 
of fruiting, this reserve passes into the seed. During the later 
stages of plant growth, lignification of the tissues takes place. 
That is to say, the cellular material becomes penetrated with 
lignin and the stems, etc., become more woody and difficult to 
digest. 

The composition of plants at different stages of growth mav 
be studied in two ways. 

The first method consists in selecting and analyzing averagt 
specimens of the plant at the desired periods of growth. This 
method of experiment shows the change in the individual plant. 

The second method consists in harvesting definite areas of the 
same field when the field has reached the average condition de- 
sired and subjecting samples to analysis. This method represents 
the production of the field at different stages of growth. The 
plants harvested are not all in the same condition of growth. 
This method is better suited for small plants and grasses than the 
first method. Both methods are open to error, as there may be 
differences in the soil or in the individual development of differ- 
ent plants. 

The general results of these experiments are as follows : 

The water in the green plant decreases with the age of the 



COMPOSITION OF PLANTS AND FEEDS 



plant. In order to eliminate the effect of this variation, the per- 
centages of other constituents of the plant should be calculated 
to percentages of the water-free substance, or dry matter of the 
plant. The statements below refer to the composition of the dry 
matter. 

The percentage of ash usually decreases with the age of the 
plant. That is, the production of organic matter takes place 
more rapidly than the withdrawal of ash material from the soil. 

The percentage of protein decreases decidedly. In some cases 
the percentages when the seed are nearly ripe are only about half 
those at the beginning of growth. The protein, however, consists 
largely of amides or amido compounds in the early stages of the 
plant's life, and these amides have little or no value for the pro- 

COMPOSITION OF SOME PLANTS AT DIFFERENT STAGES OF GROWTH. 







Water-free 




Water 








Nitro- 








Ash 


Protein 


Fiber 


gen-free 


Fat 












extract 




Corn 
















88 6l 


8.5 


17.2 


26.0 


45-1 


3-2 


uiy 2-2 


85.76 


8.0 


14.4 


27.3 


47-6 


2-7 


August 5, tasseled 


84.64 
82.08 
8l.I5 


5-9 

5.7 
4-7 


II.8 
II. 2 
8.9 


26.4 
24.1 
24.3 


53-6 
56.9 
60.3 


2.3 

2.1 

1.8 




K - 


76.81 


4.2 


9.2 


20.9 


63- 1 


2.6 




Timothy 














June 23, nearly headed- 


78.70 


7-5 


II. O 


28.7 


49.0 


3-8 


Julv 3, full bloom ' 7J-9 2 


6.1 


8-3 


33.3 


49-3 


3 >o 


July 14, out of bloom ..| 65.70 


5-2 


5-7 


34-7 


51-7 


2-7 


Julv 30, nearly ripe 


63.27 


5- 


5-5 


37-1 


50.2 


2.2 


Kentucky Blue Grass 
April 28, 3 to 6 inches... 


68.05 
66 71 


ii. 5 

TO. 7 


18.0 
M-5 


22.2 

22.7 


42.7 
48.9 


5.6 
4.2 


MayiS, panicles spread- 


63.3 


8.7 


II. I 


24-4 


51-9 


3-9 


May 28, early bloom 
June 7, after bloom 


j o 
62.91 
' 61.24 
1 51-67 


8.5 

8.7 

IO.O 


9-7 
7-9 
7-9 


29.1 
29.9 

3-5 


50.5 
51-8 
48. 5 


2.2 
2-7 
3' 1 




Red Clover 


61.21 
47-13 


8-3 

7-7 


14-3 
13-5 


27.8 
27.8 


47-9 
48.6 


1-7 

2.4 







382 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

duction of flesh. As the plants approach maturity, the per- 
centages of non-proteid nitrogen decreases. 

The fat is irregular, though it shows a tendency to decrease. 
The crude fiber increases with most plants. Indian corn is an 
exception, since the production of a large quantity of starchy 
seed decreases the percentage of fiber. The nitrogen- free extract 
usually increases, though the changes are somewhat irregular. 
The digestibility decreases. 

The total quantity of dry matter per acre appears to increase 
during the entire period of growth. In the latter stages of 
maturity of the plant, the increase is largely made up of crude 
fiber. 

Some analyses of plants at different stages of growth are shown 
in the table .- 1 

Time of Harvest. The best time to harvest depends on the 
kind of plant and the purpose for which it is grown, as well as on 
the weather of the harvesting period. 

Suppose hay is grown for market. The object then is to secure 
the largest possible quantity of hay of the highest market value. 
A large quantity of low grade hay may, or may not, be more 
profitable than a smaller quantity of high grade hay. 

Suppose hay is grown for feed. The object is then to get the 
largest possible amount of digestible nutrients per acre. The best 
period of harvest for this purpose is when the plant is in full 
bloom. 

Suppose the clover or grass is grown for seed. Then the object 
is to produce the most seed of the best quality. The seed must 
be well matured, but at the same time the harvest must not be so 
late that any considerable quantity is lost by shattering. 

Other Factors which Influence Composition. Other factors 
which influence the composition of crops are the seed, the soil, 
climate, and method of preparation or preservation. 

The composition and individuality of the seed influence the 
composition and size of the plant. In many cases, the heavier 
1 Compiled from Bulletin n, Office Exp. Station, U. S. Dept. Agr. 



COMPOSITION OF PLANTS AND FEEDS 383 

the seed, the more vigorous the young plant. The larger seed, of 
course, contain more reserve material and plant food. 

Selection of seed from individuals of a desired type may affect 
the composition of the plant. Thus, at the Illinois Station, corn 
of high and low protein and high and low fat have been produced. 
By selecting seeds from beets containing high quantities of sugar, 
the sugar content of the sugar beet has been increased 8 to 10 
per cent. It is not possible to improve all crops in this way. 

The soil affects the composition of the crops to some extent. 
Foliage crops grown upon rich soils contain a larger percentage 
of nitrogen than those grown on soils poor in nitrogen. Leaves 
and stems are influenced to a greater extent than seed by the soil, 
because the seed are more constant in composition. Wheat and 
other grains show material differences in composition when grown 
upon different soils. Not all plants are affected by the composi- 
tion of the soil. Lawes and Gilbert found that the use of nitro- 
genous and mineral manures for twenty years did not affect the 
nitrogenous content of wheat. 

As the plant contains more nitrogen during early stages of 
growth, anything which cuts short the growing season will cause 
the crop to contain slightly more nitrogenous material. If the 
growth of the plant is checked at the time of seed formation, 
shrunken or immature seed may result. Such grain contains less 
starch and more nitrogenous compounds than those fully matured. 
Plants grown in arid or semi-arid regions may contain a higher 
percentage of nitrogen than in regions of more abundant rainfall. 
For instance, the nitrogen content of Texas cottonseed meal 1 is 
considerably greater in the western or semi-arid part of the state 
than in the eastern part. 

Hay and Hay Making. Hay is the dried and partly fermented 
leaves and stems of certain grasses and clovers. Some fermenta- 
tion is requisite to develop the characteristic flavor and aroma. 
The method used for hay making depends on the character of the 
plant and the climate. A succulent plant and a moist climate 
demands more care than dryer plants and a dry climate. Some 
1 Texas Bulletin, 70. 



384 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

plants, such as cowpeas, are difficult to cure on account of the 
large succulent vines, which remain moist after the leaves have 
become dry and so brittle that they break off. For a similar rea- 
son alfalfa also is difficult to cure . Often alfalfa hay consists 
entirely of stems. 

The Arkansas Experiment Station found that young or vigor- 
ously growing vines of cowpeas very difficult to cure even 
under favorable weather conditions, while mature vines cured 
with little difficulty in favorable weather, and usually made good 
hay even after an exposure to rain and cloudiness from two to 
four* days. 

In hay making the plants are usually cut and allowed to lie ex- 
posed to the sun all day; then raked or piled into heaps more or 
less loose, for further curing, and finally piled into larger heaps, 
or taken to the barn. If the large heaps are formed while the 
material is too moist, excessive fermentation will take place, 
which in some cases has gone so far as set fire to the stack. In 
Wisconsin, Short found that by leaving hay out four days after 
cutting, during which time there was a rain, there was a loss of 
over 4^2 per cent, dry matter and 3^2 per cent, protein. Six 
weeks later nearly one-fourth of the dry matter and protein dis- 
appeared. 

Emmerling left grass exposed for 18 days, during nine of which 
rain fell, with the results given in the following table : 

PERCENTAGE Loss OF INGREDIENTS OF HAY IN EXPOSURE TO RAIN. 





In cocks 


In swaths 


Dry matter 


I8. 3 
31.0 
29.0 
19.8 


29.4 
41.0 
24.8 
38.8 


Fat 









Even without rain, when the process of drying is slow, a loss 
takes place due to the respiration of the living tissues, by which 
protein is decomposed or non-proteins oxidized. The loss has 
been as much as 12 per cent, dry matter in 10 days with young 



COMPOSITION OF PLANTS AND FEEDS 385 

Silage. Silage is a feeding-stuff preserved in a moist condi- 
tion. It is made by placing the finely chopped material in an air 
tight receptable. More or less fermentation takes place, 1 which 
destroys sugar, produces acids, and causes the loss of ten or twelve, 
per cent, substance. The acidity of the silage depends upon the 
conditions of preparation. If a silo is filled rapidly, the mass 
weighted down and the air excluded as much as possible, a slow 
fermentation takes place caused by bacteria, which results in a 
very acid product, termed sour silage. It may contain 0.6 to 1.6 
per cent. acid. If the material is put in slowly and loosely, a 
preliminary rapid fermentation takes place which heats the mass, 
destroys the acid-forming bacteria, and excludes air. Fermenta- 
tion then goes on more slowly, producing a sweet silage. Too 
high a temperature would produce bad results. Sweet silage is 
said to become moldy on exposure to the air, while acid silage is 
relatively resistant to decay. The changes are due to the living 
cell, and enzymes of the plant, as well as to bacteria. 

The following experiment shows the effect of temperature on 
the silage. The volatile acid is chiefly acetic acid, the non- 
volatile is lactic. 



Temperature of formation 


Volatile acid 
Per cent. 


Non-volatile 
acid. Percent. 


Below 32 C 


o 62 to i s6 




->2 to 49 C 






56 to 70 C- 













The fermentation also converts some of the proteid nitrogen 
into non-proteids, the action going so far as even to form a small 
quantity of ammonia. 

A silo must be perfectly air-tight, or the loss resulting will be 
great ; the walls must be rigid, the inner surface must be smooth 
and uniform, and it should dry out quickly and completely. 

Losses in Silage Making. The loss in a silo depends upon its 
construction, on the crop siloed, and on the amount of moisture 
present. The loss is much lessened by proper construction of the 
1 Bulletin 70, Connecticut Station. 



386 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

silo. The amount of moisture present in the crop had the follow- 
ing effect in one experiment : 

Moisture, per cent. Loss, per cent. 

71.67 8.63 

74.61 10.01 

80.66 16.66 

An excess of moisture thus causes a greater loss. Water is 
sometimes added to crops siloed when they do not contain enough 
water to make good silage. 

As regards the nature of the crop, King found the necessary 
loss for corn to be 5 to 10 per cent., and for clover 10 to 18 per 
cent. Corn well matured and in good condition for shocking, but 
with leaves still green, is in the proper stage for silage. Silage 
from immature fodder is more acid than that from more mature 
plants. 

Feed Laws. Many of the States have laws regulating the sale 
of concentrated commercial feeding stuffs. The laws usually re- 
quire the feed to be true to name, and prohibit the sale of un- 
wholesome feed. A guaranteed analysis is usually required, but 
some states require a guarantee of protein and fat only, others 
require crude fiber in addition to protein and fat, and still others 
require a guarantee of nitrogen-free extract in addition to the 
others. A guarantee of protein and fat is not sufficient to show 
the quality of the feed, and laws which require only such guar- 
antee cannot be considered to provide sufficient protection. 

It is not sufficient that the feed should come up to the guar- 
anteed analysis, but it should be composed of the ingredients 
claimed, and no one should purchase a feed without knowing the 
feeding stuffs present. It is possible to make up the guaranteed 
analysis by means of substances of high composition but of low 
digestibility and low feeding value. Mixed feeds are often put 
on the market which contain ingredients that could not be readily 
sold separately, and are often sold at prices far in excess of their 
real feeding value. 

The guaranteed analysis of a feeding stuff must, therefore, be 
regarded as a guarantee of the quality of the particular feed 
claimed to be sold. The fact that the feed comes up to the 



COMPOSITION OF PLANTS AND FEEDS 387 

guaranteed analysis is not necessarily proof that the feed is com- 
posed of the ingredients named, but the feed should be examined 
microscopically or otherwise when necessary. Two feeds of the 
same guaranteed analysis do not necessarily have the same feed- 
ing value, unless they are the same feed. A feed should be 
true to name, regardless of the guarantee. If foreign matter has 
been mixed with it, the feed is adulterated, regardless of the 
chemical analysis. Feeds are sometimes adulterated with other 
by-products of the same process of manufacture. Wheat bran 
may be adulterated with screenings; cottonseed meal may have 
such a quantity of hulls left in it that it is no longer entitled to be 
called cottonseed meal; an excess of hulls may be run into rice 
bran. 

The term feeding stuff does not include indigestible materials, 
such as peat, earth, ground leather, sand, etc., or poisonous 
materials, such as poisonous plants, poppy seeds, castor-oil seed 
meal, etc. The value of a feed depends upon its nature and its 
chemical analysis. Chemical analysis alone is not sufficient, since 
materials vary considerably in digestibility and nutritive value, 
even with the same chemical composition. A microscopic ex- 
amination is also necessary. 

Injurious Feeds. Rust and smut fungi sometimes cause disease 
or injury to animals eating the diseased feed. Moldy feed is 
liable to be dangerous to animals, as poisonous substances may 
be present. Yeasts found in by-products from beverages, etc., 
cause fermentation in the stomach. Boiling or steaming will 
obviate such danger. Frozen fodder feed in quantity is liable to 
cause digestive disturbances. When it thaws, it readily decom- 
poses. Many kinds of weed seeds, such as field poppy, and corn 
cockles, have injurious effects. Sand, dirt, and ashes may cause 
no injury, but sometimes they give rise to serious digestive dis- 
turbances, constipation, or even death. 

Percentage of Water. The quantity of water in feeds, etc., 
may be seen on reference to the tables. Hay and straw contain 
12-17 P er cent -> cereal grains 11 to 15 per cent, and oil cake and 
meal contains 6 to 13 per cent. Meals, cakes, and grain easily 



3 88 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



undergo decomposition if they contain more than 14 per cent, 
water. 

Preparation of Feeds. Crushing or grinding the grain is often 
of advantage, especially for certain kinds of animals, or for those 
with defective teeth, when the grain is small or hard. The fol- 
lowing shows the effect of feeding oats to horses, with chopped 
hay: 

Per cent, 
dry matter digested 

Whole oats 64.6 

Crushed oats 68.6 

Coarse ground oats 72.7 

Corn, rye, buckwheat, Kafir corn, milo maize, and leguminous 

seed, should best be ground for all animals. The following are 

some differences: 





Dry matter digested 


Horses 


Pigs 




per cent. 

82.5 
89-5 


per cent. 

74-4 
88.4 







In a number of experiments with pigs, the effect of grinding 
the corn was to reduce by six per cent, the quantity needed for 
the same gain in weight. Moistening the feed prevents its being 
blown away and prevents the fine particles of meal from getting 
in the eyes or lungs. Cooking, scalding, or steaming kills weed 
seeds, injurious molds or bacteria, and animal parasites, but as a 
rule, decreases the digestibility of the feed. Cooked or steamed 
food, however, is valuable for pigs. The following shows the 
effect of cooking: 

Digestibility of protein 





Bran 


Hay 




per rent. 

77 O 


per cent. 
46 o 


Steamed 


70 o 


^O o 









COMPOSITION OF PLANTS AND FEEDS 389 

Conditions of Growth. The stage of growth, as we have 
already seen, affects the composition of the plant. Plants grown 
wide apart give coarser fodder than those sown thickly. Soil and 
manures also affect the nutritive values of plants, especially in 
meadows, where acidity or unfavorable soil conditions may 
promote the growth of plants not well suited for pasturage. 
Liming and drainage may encourage growth of clovers, vetches, 
and sweet grasses. Addition of nitrogenous manure may cause 
increased percentages of protein. Weather conditions also 
affect the quality of the plants. In wet years, the plant grows 
larger and is more woody. In dry season, the plant is short and 
compact. 

Composition of Feeding-Stuffs. The composition of feeding- 
stuffs shown in the various publications represents the average of 
variable analyses. 1 The average composition varies with differ- 
ent sections of the country, and for information in regard to the 
composition of local feeds, the student should consult the re- 
ports and Bulletins of his State Experiment Station. Reports of 
Feed Control officials also show the composition of concentrated 
feeding stuffs, while the guaranteed analyses are printed on the 
package, or a tag attached to it. 

Concentrates. The concentrates used in feeding are largely 
by-products from the manufacture of various articles. These 
feeding stuffs may be grouped according to their chemical com- 
position or according to their origin. They are distinguished from 
roughages by being rich in protein or nitrogen-free extract, and 
low in crude fiber. 

Classes of Concentrates. Concentrated feeds may be arranged 
in six groups, according to their content of protein: 

I. Protein 30 to 50 per cent. Cottonseed meal, gluten meal, 
linseed meal, dried distiller's grains, peanut meal. 

II. Protein 20 to 30 per cent. Malt sprouts, gluten feed, cot- 
tonseed feed, dried brewers' grain, germ oil meal, whole pressed 
cottonseed. 

1 Bulletin 11, Office Exp. Sta. 



390 PRINCIPLES OE AGRICULTURAL CHEMISTRY 

III. Protein 14 to 20 per cent. Wheat middlings, wheat bran, 
wheat shorts, oat middlings, flax feed, rye feed, cotton seed, sun- 
flower seed. 

IV. Protein 10 to 14 per cent. Rice bran, rice polish, ground 
oats, ground wheat, barley meal, rye meal, hominy feed, oats 
mixed with barley. 

V. Protein 8 to 10 per cent. Corn bran, corn meal, corn chops, 
corn and oat feed, oat feed, dried beet pulp, beet molasses, kaffir 
corn, milo maize, corn and cob meal, sorghum seed. 

VI. Protein less than 8 per cent. Cane molasses. 

Classes of Roughages. Roughages may be divided into the 
following groups : 

I. Fodders. Corn fodder, corn husks, katfir stover, sorghum. 
These contain from 3 to 12 per cent, protein and from 23 to 35 
per cent, crude fiber. 

II. Cereal Straws. Oat, barley, rice, rye, and wheat straws, 
containing 3 to 6 per cent, protein and 35 to 40 per cent, crude 
fiber. 

III. Grass Hays. Bermuda, Johnson grass, timothy, millet, 
etc., containing 5 to 15 per cent, protein, and 22 to 35 per cent, 
crude fiber. 

IV. Legume Hays. Alfalfa, clover, cowpeas, peanuts, vetch, 
etc., containing 12 to 20 per cent, protein and 20 to 28 per cent, 
crude fiber. 

V. Waste Milling Products. Peanut hulls, corn cobs, cotton- 
seed hulls, oat chaff, oat hulls, rice hulls, wheat chaff, etc., some- 
times mixed with concentrated feeds, but properly classed with 
roughage. They contain 2.5 to 5 per cent, protein and 30 to 48 
per cent, crude fiber. 

VI. Fresh Grass or Fodder. Millet, oats, barley, sorghum, 
timothy, etc., contain about 80 per cent, water and I to 4 per cent, 
protein. 

VII. Fresh Legumes. Alfalfa, clover, cowpea, vetch, etc., 
containing 70 to 85 per cent, water and 2.5 to 5 per cent protein. 

VIII. Silage. Corn, sorghum, clover, usually corn containing 
70 to 85 per cent, water and I to 4 per cent, protein. 



COMPOSITION OF PLANTS AND FEEDS 391 

IX. Roots and Tubers. Carrots, potatoes, turnips, beets, etc., 
containing 70 to 90 per cent, water and i to 3 per cent, protein. 

Description of Concentrates. A few of these feeding-stuffs 
will be discussed briefly. 

Cottonseed Meal is prepared by cooking and pressing the ker- 
nels of cotton seed. It contains 36 to 52 per cent, protein, accord- 
ing to its origin and freedom from hulls. The meal increases in 
protein from the eastern part of the country to the west, being 
richest in west Texas. The meal is often adulterated with hulls. 
The quantity of hulls may be roughly estimated by deducting 5 
per cent, from the crude fiber and multiplying the remainder by 
2 l /4. Thus a meal containing 10 per cent, crude fiber contains 
10-5 x 2^4 = 11.3 per cent, hulls, approximately. 

Brewers' grains are the dried residue from the treatment of 
cereals with malt, for the preparation of beer. 

Pressed zvhole cottonseed is made by pressing the whole 
cotton seed between rollers. It thus contains all the hulls. 

Wheat bran is the outer covering of the wheat grain. Some- 
times the screenings, containing oats, weed seeds, wheat, etc., are 
mixed with the bran, with or without grinding. This is not 
allowable under most feed laws. 

Alfalfa meal is ground alfalfa. It is properly a roughage and 
not a concentrate. 

Rice bran is the outer coating of the rice grain, including some 
of the germ. It contains about ten per cent, each of protein and 
fat, but is liable to become rancid. 

Rice polish is obtained in polishing rice. It contains some of 
the germ. 

Corn bran is the outer covering of the corn grain. 

Kafir corn and milo maize are similar to corn, but contain more 
protein. They have about 10 per cent, less feeding value than 
corn. 



CHAPTER XIX. 



DIGESTION. 

Digestion converts food into forms which can be dissolved in 
water, or absorbed and utilized by the body. The digestive 
organs vary in size, shape, and capacity with different kinds of 
animals. Some animals, such as dogs, fowl, pigs, and men, have 
short digestive organs, adapted only to concentrated foods, such 
as meat, cereal grains, etc. The digestive organs of other 
animals, such as sheep, goats, cows, etc., are large and adapted to 
bulky food containing small amounts of nourishment. Horses 
and hogs have smaller digestive organs. 

Outline of Digestive Process. The first step in digestion is 
preparation of the food by chewing or grinding. This usually 
takes place in the mouth. The food is there moistened with 
saliva, a slightly alkaline liquid, which not only softens the food 
and lightens the labor of chewing, but contains an enzyme termed 
ptyalin which converts starch into sugar. Most of the work of 
digestion is performed by enzymes, substances which have the 
power of transforming other substances into simpler substances 
without themselves being changed. Ptyalin acts only in an 
alkaline medium, and as soon as the food becomes acid by fermen- 
tation or by means of the gastric juice, its action stops. Grinding 
or other preparation of the food before feeding will partly de- 
crease the labor of chewing. Grinding is especially necessary 
for pigs, or for other animals when small hard seed are fed. 
When whole grain is fed to cattle, it is sometimes imperfectly 
masticated, and a considerable number of grains passes through 
undigested. 

The sheep and the ox have four stomachs. The first and sec- 
ond stomachs are used to store the food until it is returned to 
the mouth for a second mastication. The food then passes to the 
third stomach, which has a sieve-like structure, where the food is 
kneaded and ground up. The digestion takes place in the fourth 
stomach. 

These animals are called ruminants, and are able to utilize 



DIGESTION 393 

coarser feed than animals which have only simple stomachs. 
Fermentation takes place in the first stomach of ruminants, since 
temperature and other conditions are very favorable to the action 
of bacteria. Lactic acid is produced from soluble carbohydrates, 
proteids are split up, amides are affected, and even crude fiber 
may undergo some slight change. Carbon dioxide, hydrogen, 
marsh gas, acetic acid, butyric acid, and lactic acid are some of 
the products of the fermentation. This process dissolves some 
of the nutrients, and breaks up the cell walls, thereby allowing 
the entrance of digestive juices. It also softens the materials and 
so favors the disintegration of hard vegetable structures when 
chewed again in the mouth. The acids which are formed grad- 
ually decrease the fermentation, until they finally stop entirely 
the action of the bacteria, since an acid medium is unfavorable 
to their activity. 

Stomach Digestion. When food enters the true stomach, the 
gastric juice is slowly poured upon it. The gastric juice contains 
hydrochloric acid, lactic acid, and three enzymes, which can act 
only in an acid medium. Pepsin splits up the proteids into 
albumoses and peptones. Rennin which is found largely in the 
stomach of young animals, coagulates the casein of milk and 
other proteids. Lipase splits fats and oils into glycerol and fatty 
acids. Proteids are digested chiefly in the stomach, though the 
fats are also split up and digested to some extent. The proteids 
are converted into peptones and albumoses, which are soluble 
and can pass through the membranes of the stomach. Even 
water-soluble proteids are split up during digestion. 

Intestinal Digestion. When the food enters the intestines, it is 
gradually mixed with bile, the pancreatic juice, and intestinal 
juices, and, being alkaline, they put an end to the action of 
the gastric juice. 

Bile acts chiefly to form soaps with the fatty acids and to 
emulsify the fats and oils. The emulsion consists of minute 
drops of fat, suspended in the liquid, and both the emulsified fat 
and the soaps can be absorbed. Bile is also able to convert starch 
into sugar. 
26 



394 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

The pancreatic juice exerts a vigorous digestive action upon 
proteids, fat, and starch. It contains trypsin, which acts on pro- 
teids; amylopsin, which rapidly changes starch into sugar; and 
steapsin, which emulsifies and splits fat. The proteids are con- 
verted into crystallizable substances, such as leucin, tyrosin, 
aspartic acid, etc., as well as albumoses and peptones. 

Intestinal juices also exert a digestive action, especially on 
protein and starch. 

Bacteria increase in numbers as the food passes along the intes- 
tines; fermentation and putrefaction gradually supersede the 
action of the digestive juices. In herbivorous animals, digestion 
is aided by the enormous number of bacteria present in the lower 
portions of the intestines. These bacteria act upon the undigested 
food, split up fats, change starch, and other carbohydrates into 
lactic, butyric, and acetic acids, and exert considerable digestive 
action on crude fiber. Three gases, carbon dioxide, marsh gas, 
and hydrogen, are formed in the process. The crude fiber is 
digested only by such fermentation. A quantity of substances 
which would not be acted upon by the digestive juices are dis- 
solved and made useful to the animal. 

Absorption. The dissolved nutrients are absorbed to some 
extent by the walls of the stomach, but most largely by the intes- 
tinal walls, and pass either directly into the blood, or first into the 
chyle and then into the blood. 

The Proteids are taken up as albumoses, peptones, and, to some 
extent, as leucin, tyrosin, and other crystallizable nitrogenous 
bodies. But since these substances do not occur in the chyle or 
in the blood, they must have been synthesized into animal pro- 
teids in the membranes of the digestive organs. That is to say, 
the proteids of the food are first split up, then converted into 
necessary animal proteids. It is quite possible that some of the 
products of the digestion of the various proteids, are much better 
suited to the formation of animal proteids than others ; and some 
products may be entirely unsuitable for the purpose of the 



DIGESTION 395 

systhesis and must be oxidized. 1 It is also possible that the pro- 
ducts of digestion of certain proteids may be injurious. 

Fats are absorbed as fatty acids, as glycerol, as soaps, 
and in a finely divided form suspended in the digested 
solution, as an emulsion. There is a union of fatty acids and 
glycerol in the absorbing membrane, so that only fats enter the 
chyle or blood. 

Carbohydrates are converted into simple sugars (grape sugar, 
fructose, etc.,) or by fermentation, into acids, such as lactic acid, 
butyric acid, etc. These appear to some extent in the chyle, but 
more largely in the blood. 

Various methods are used in studying the processes of 
digestion. The digestive juices have been secured from animals, 
and their action tested upon various constituents of the food. 
The process of digestion has also been to some extent observed 
through openings made into the digestive organs by accident or 
intention. The contents of digestive organs have been removed 
and examined. 

Rennet, prepared from the stomachs of calves ; and pepsin, pre- 
pared from animals killed in the slaughter house, are commercial 
products, the former being used in coagulating milk in the manu- 
facture of cheese, and the latter for medicinal purposes. None 
of the digestive ferments so far isolated have the power of 
causing crude fiber to go into solution. The intestinal bacteria, 
however, when inoculated into a medium containing crude fiber, 
cause it to be partly dissolved, producing marsh gas, carbon 
dioxide, organic acids, and soluble products which can be absorbed 
and utilized. 

Excretion. The undigested residues, mixed with gallic acid, 
mucus, with other animal products (metabolic products), and with 
digested but unabsorbed material, are finally ejected. 

The excrement is by no means free of digestible materials. The 
quantity of digestible matter is small, however, unless the food 
is imperfectly masticated, or unless its premature evacuation is 
caused by digestive disturbances. 

1 See Wisconsin Research Bulletin No. 21. 



396 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

The time required for the passage of food through the body 
varies with different kinds of animals. Residues of the food 
begin to appear in 12 hours with the dog, 36 hours with the pig, 
and three or four days in the excrement of the cow, sheep, goat, 
or horse. The residues are usually completely excreted in 7 to 
8 days by cows, sheep, and similar animals, though bulky food 
may continue to appear for 14 days if followed by easily digested 
food, such as young grass, etc. 

Metabolic Products. The transformation which food under- 
goes within the animal is termed metabolism, and the products of 
the life action are termed metabolic products. The metabolic 
products in the excrement are residues of digestive juices and 
other animal products. A portion of the intestine, isolated but 
left within the body, has been found to collect a certain amount 
of waste material, which, under normal conditions, passes into 
the excrement. In ordinary digestion experiments, the metabolic 
products in the excrement may, for all practical purposes, be 
regarded as a portion of the undigested food, since they represent 
so much material lost from the body in the excrement. In 
other experiments, however, the metabolic products must be 
taken into account. The metabolic products contain protein, or 
fat and ash, but no carbohydrates or crude fiber. In some 
digestion experiments with food poor in fat, or with materials very 
poor in protein, more fat or protein has been found in the excre- 
ment than was present in the food eaten. The quantity of 
metabolic fat is, however, small, and of little importance. 

The metabolic nitrogenous substances are of more importance. 
There are two ways of estimating the quantity of metabolic 
nitrogen. One method consists in feeding the animal on 
materials nearly free of nitrogen, and estimating the nitrogen in 
the excrement. For example, Pfeiffer fed hogs on potato starch, 
cane sugar, olive oil, and salts, a ration almost free of nitrogen, 
and found the excrement to contain 4.4 per cent protein. Kell- 
ner obtained similar results with sheep which were fed sawdust, 
sugar, and starch. 

The other method does not give us the exact quantity of 



DIGESTION 397 

metabolic protein, but gives the maximum quantity that may be 
present. Kuhn 1 has devised a method for estimating digestible 
protein, by means of pepsin and hydrochloric acid. By experi- 
ments on animals he has proved that the indigestible protein fed 
(estimated according to this method) is exactly equal to the in- 
digestible protein excreted. That is to say, the animal cannot 
digest the protein found to be indigestible according to Kuhn's 




Fig. 83. Goats ready for digestion experiment. 
North Carolina Station. 

method. The metabolic products in an excrement, then, cannot 
be greater than the protein digested from it with pepsin-hydro- 
chloric acid, though they may be less. 

As a result of 20 experiments, Kuhn found from 0.36 to 0.58 
gm. of pepsin-soluble nitrogen in excrement from oxen, with an 
average of 0.48 gm. for each 100 gm. of digested dry matter. 
1 Landw. Versuchs-stat., 1894, p. 204. 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 

The averages of other workers are as follows: Pfeiffer 0.52 
gm., Jordan 0.44 gm., Wolfe 0.47 gm. It appears that, on an 
average, not more than 0.45 gm. of metabolic nitrogen (equal to 
2.8 gm. protein) is excreted per 100 grams of digested dry mat- 
ter. Some metabolic mineral matter is also present in the excre- 
ment. 




Fig. 84. Stall used for digestion experiments with sheep. 
Wyoming Station. 



Digestion Experiments. The nutrients which disappear during 
the passage of food through the animal body are said to be 
digested. All that disappear do not pass through the membranes 
of the digestive organs, however, as some of them are converted 
into marsh gas and carbon dioxide by fermentation and escape as 
gases. The object of a digestion experiment is to determine, by 
trials on animals, the actual amounts of the different nutrients 
which are digested. In a digestion experiment, a known quantity 
of food is fed, the excrement from it collected, and both food 
and excrement are subjected to analysis. The quantity of each 
nutrient fed and digested is calculated, and the quantity of 
nutrient digested is divided by the quantity fed. The dividend, 
expressed as percentages, is the coefficient of digestibility. 



DIGESTION 



399 



With men, the faeces from different meals are not mixed in 
the body, and can easily be separated by appropriate means. 
Thus, at the meal before beginning the experiment, the man 
swallows a capsule of charcoal. Then for two or three days he 
eats the ration to be tested. At the end of the period he takes 
another capsule of charcoal. The dividing line between excre- 
ments from the meal without charcoal and the one with charcoal, 
is easily distinguished, and the excrement from the ration tested 
can be separated easily. 




Fig. 85. Sheep arranged for digestion experiment. Wyoming Station. 

With domestic animals, the food from different meals is mixed 
so thoroughly in the stomach and intestines that not only is it im- 
possible to distinguish one meal from another, but the residues 
from a given meal may appear in the excrement for three or 
four days. Such animals are fed a uniform quantity of food 
long enough to ensure the elimination of previous food residues, 
and the excrement is collected for a definite number of days. It 



4OO PRINCIPLES OF AGRICULTURAL CHEMISTRY 

is assumed that the excrement corresponds to the food fed on 
corresponding days. This assumption is justified if the period 
of collection is long enough to compensate for the irregularities 
in elimination of the excrement. A period of only three or four 
days is likely to give incorrect results. The collection period 
should not be shorter than six days for pigs, eight days for sheep, 
and ten days for cattle. 1 

In digestion experiments with dry feeding-stuffs, a sufficient 
quantity of the feeding-stuffs should be secured before the ex- 
periment is begun. After ascertaining, by trial, how much the 
animal will eat, the feeding stuff should be mixed thoroughly, 
and the quantities to be fed each day should be weighed out care- 
fully before beginning the experiment ; at the same time, samples 
should be taken for analysis. 

The animal is fed exactly the same ration for a period of from 
16 to 1 8 days. The first 6 to 8 days feeding is for the purpose 
of eliminating residues from the previous ration, and is called the 
preliminary, or preparatory period. At the end of this period 
the digestion period begins, in which the excrement is collected 
for analysis. This lasts about 10 days. The excrement may be 
secured in rubber bags attached to the animal, or by special stall 
arrangements which prevent the solid excrement from being 
scattered or mixed with urine or bedding. With small animals, 
the excrement is collected every 24 hours, mixed thoroughly, and 
an aliquot part dried at a low temperature (60-70 C.). With 
horses and cattle, the aliquot should be taken every 12 hours, as 
the large masses remain warm and ferment rapidly. After dry- 
ing, the samples are mixed and analyzed. If green feeds, silage, 
or similar materials are to be tested, equal quantities should be 
weighed for feeding each day, and a sample for analysis should 
also be taken every day and dried at once. The quantity of 
feed should be adjusted to the appetite of the animal before the 
preliminary feeding period begins. Residues, even when weighed 
and analyzed, introduce disturbances and diminish the value of 
the work. 

1 See Kellner, Exp. Sta. Record 9, p. 504. 



DIGESTION 



401 



If a concentrated feeding-stuff is to be tested, the digestibility 
of hay is first determined, then the concentrate added, and the 
digestibility of the mixture ascertained. The nutrients digested 
from the hay are subtracted from those digested from the mix- 
ture, and the difference is assumed to represent the material 
digested from the concentrate. It is assumed that ingredients of 
the mixture are digested to the same extent as the feeds would 
be separately, but this is not always the case, as we shall see. To 
guard against abnormal conditions of the digestive organs, and 
also to secure a more accurate average, at least two animals 
should be used. 

The following is an example of an experiment 1 on one sheep. 
The preliminary feeding was eight days, and the digestion period, 
ten days. Three sheep were used, but the figures are given for 
for only one. 

DIGESTION EXPERIMENT WITH ONE SHEEP. 





Protein 


Fat 


Crude 
fiber 


Nitro- 
gen-free 
extract 


Water 


Ash 


Alfalfa hay fed, composi- 


1 6 17 


I AI 


28 1A 


Mo6 




ft T/t 


Excrement, sheep No. 2, 
composition per cent . 
Fed 4,400 gms. alfalfa, con- 
taining' gms 


II. 12 
71 1 O 


3-62 

62 o 


40.82 
I 246 I 


.yu 

27.78 
I ^"*7 2 


lu.yy 

7.26 


940 

-jcft O 


Excrement, 1,667 gins, 
containing gms 


185.4 


60.3 


680.5 


463.1 





X)- U 
156.7 


Digested 




T 7 


rfiir A 










O^O- U 
71 Q 


* / 


U O' U 

AC A 


1,0/4. l 




o oz ^ 




/o-y 


* 




uy.y 







Artificial Digestion. By artificial digestion we mean labora- 
tory tests to ascertain the digestibility of constituents of feeding- 
stuffs. Only with proteids has any measure of success been at- 
tained in this way. As before stated, the proteids not digested 
by Kuhn's method are not digested in the animal. Kuhn's 
method, then, offers us a means for ascertaining the maximum 
digestibility of the protein of feeding-stuff. The animal cannot 
digest any more proteids than is indicated by the method, though 
1 Bulletin 147, Texas Exp. Sta. 



4O2 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

it may digest less. In Kuhn's method, 2 grams of feeding-stuff 
are treated with I gram of pepsin dissolved in 500 cc. of 0.2 per 
cent, hydrochloric acid, maintained at the blood heat 48 hours, 
and the hydrochloric acid increased from 0.2 to i.oo per cent, by 
additions of acid at intervals of 12 hours. The residue is then 
filtered oft", washed, nitrogen determined in it and calculated to 
protein. 

Influence of Different Conditions on Digestion. The digestion 
of food depends upon a number of conditions. The kind, variety, 
and age of the animal, composition of the rations, the prepara- 
tion of the food, and other circumstances, have been studied by 
proper arrangement of the experiments. 

Kind of Animal. Differences in the digestive organs, digestive 
secretions, and habits of animals make considerable differences 
in their digestive power. The digestive organs of sheep and 
goats are twenty-seven times as long as their bodies ; of the ox, 
twenty times; of pigs, fourteen times; and of the horse, eleven 
times. Ruminants have greater ability to digest coarse fodders 
than other animals. Sheep digest less than cattle, particularly of 
coarse fodders which are hard to digest, apparently because the 
contents of the last intestinal tract of cattle is more moist and the 
process of fermentation continues longer. The more digestible 
the material, the less the difference. 

On account of shorter intestines and simpler organization of 
the stomach, the horse has a less digestive power than ruminants, 
especially for coarse fodders. The horse digests only about half 
as much from straw as does the ox. The difference is most 
marked with crude fiber and ether extract; there is little differ- 
ence in protein, especially in concentrated feeds. 

Pigs have less digestive power than horses or cattle for green 
feeds, and by-products containing much crude fiber. With grain 
and oil cakes the difference is less ; but there are many by- 
products, such as brewers grains, which the pig digests poorly. 

The following experiments were made to compare animals of 
different kinds, fed on the same fodder: 



DIGESTION 



403 



PERCENTAGES DIGESTED. 





Organic 
substance 


Crude 
protein 


Nitrogen- 
free ex- 
tract 


Crude 
fat 


Crude 
fiber 


Oat straw Cattle 


^8 


3 2 


58 
49 


43 
50 


49 


Sheep 


Difference 


IO 


13 


9 


7 


14 




Meadow hay Cattle 


67 
65 


6l 

57 


70 
69 


61 

57 


6 4 
61 


Sheep 


2 


4 


i 


4 


3 




Meadow hay, poor quality- 
Sheep 


47 


57 


62 
56 


24 


39 






ii 


3 


6 


22 


19 






5i 


56 


61 


2 9 


50 
37 




Difference 


5 





-3 


27 


13 






89 


79 

77 


9i 
94 


8 5 

61 


62 

70 


Horse 





2 


-3 


24 


8 




Clover, young Ruminant 
Hogs 


74 
54 


74 
49 


83 
7i 


65 
24 


60 
24 


20 


25 


12 


41 


36 




Corn (grain) Ruminant . . 
HOETS 


91 


72 


94 


85 


77 
44 


Difference 


I 


~ 7 





ii 


33 





Other conditions regarding digestion by the animal which have 
been studied are as follows : x 

1. Different breeds of the same animal have the same average 
digestive power. 

2. Different individuals of the same variety may have different 
digestive power, due to faulty teeth, too rapid consumption of 
food, defective chewing, great nervousness, abnormal conditions 
of the digestive organs, chronic sickness, or defects of the 
digestive organs. 

1 Kellner, Ernahrung d. Landw. Nutztiere, p. 45. 



404 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



3. The age of the animal has no influence, unless the animal is 
too young for the food given, or too old to masticate it properly 
on account of defective teeth. 

4. Animals resting or at moderate work have the same diges- 
tive power. Vigorous work appears to cause a slight decrease. 

5. Variations in light, temperature, and other external con- 
ditions, if great excitement is not caused thereby, have no effect. 

Composition of Feed. Different quantities of roughage fed 
alone are digested to the same extent. This is evident from the 
experiments of Henneberg and Stohmann with oxen, and E. 
Wolff with horses and sheep. 



Daily ration 
weight of roughage 


Dry 

substance 


Percentages digested by sheep 1 


Protein 


Fat 


Nitrogen- 
free ex- 
tract 


Crude 
fiber 


08 


61 
62 
62 


72 

75 
74 


26 
31 
32 


71 
68 

7i 


44 
48 

47 


JO 


j 2 





Different quantities of roughage and concentrates, mixed in 
the same proportions, appear to be digested slightly less with a 
heavy ration than with a moderate ration. 

The addition of fat and oil does not affect the digestibility of 
the other nutrients, provided not over I pound per 1,000 pounds 
live weight is fed. 2 The oil must also be emulsified or finely 
divided, for liquid oil may occasion depression in digestibility, 
probably because it hinders the wetting of the food, and thereby 
the entrance of the digestive juices. 

According to many experiments, the addition of digestible 
carbohydrates or non-protein will cause a depression of digesti- 
bility if the proportion of protein to carbohydrates is thereby 
made too wide. The following example is from Kuhn, in which 
starch was added to a ration of meadow hay fed to oxen. 

1 Landw. Versuchs-stat., 1878, p. 19. 

2 Kellner, Landw. Versuchs-stat., 1900, p. 114 and 199. 



DIGESTION 



405 



Assuming the starch to be completely digested, the results are as 
follows i 1 

PERCENTAGE DIGESTIBILITY. 





Organic 

substance 


Protein 


Fat 


Nitrogen- 
free ex- 
tract 


Crude 
fiber 




62 r 




2Q 2 


61 8 


67 *\ 


Meadow hay with 1,662 kg. 


U^O 

eft o 


D/- u 


zy.^ 

27 O 


CQ Q 


62 o 


Meadow hay with 2,866 kg. 




4y.u 
41 O 


27 o 


Cf) O 


61 o 















The depression in digestibility of protein may be in part due to 
increased excretion of metabolic products. As we have seen, 
2.5-3.1 grams of protein are excreted from every 100 grams of 
digested dry substance, and the additional quantity of protein 
excreted corresponds very nearly to the increase which would be 
caused by the addition of starch. However, we do not yet know 
the cause of the decreased digestion. Other carbohydrates, as, 
cane sugar, pectin, and purified cellulose, have the same effect as 
starch in decreasing digestibility. 

An increase of protein can partly or completely eliminate the 
depression caused by addition of carbohydrates. For example, 
Haubner found that the starch appeared in the excrement of 
sheep fed on potatoes, but when rape cake was added to the ration, 
starch was no longer excreted. Many exact digestion experi- 
ments have proved that the addition of protein can increase the 
digestibility of a ration poor in protein. 

Non-albuminoid nitrogenous compounds, such as asparagin, 
exert a similar effect. For example, Weiske found a ration 
nearly free of nitrogen digested 86 per cent., with addition of 
asparagin or fibrin it was digested 92 per cent. Kellner observed 
a similar action when asparagin or ammonium acetate was used. 

Concentrated feeding-stuffs exert an influence on digestion 
according to their content of digestible protein or carbohydrates. 
Foods poor in protein, as beets and potatoes, exert a depressing 
1 Landw. Versuchs-stat., 1894, p. 470. 



406 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

effect on digestibility, unless fed in connection with concentrates 
rich in protein. Concentrates of intermediate composition exert 
an appreciable effect upon digestion only when the ration con- 
tains more than 8 parts non-protein to I part protein. In gen- 
eral, it may be stated, that the digestion of a food is most com- 
plete when, for 7 to 8 parts digestible nitrogen-free nutriment 
(including fat X 2 - 2 5)> n ot less than I part digestible crude pro- 
tein is present. With pigs, which have a high digestive power for 
carbohydrates, the ratio may be as wide as i : 12. 

Free acid, in moderate limits, has no influence upon digestibility. 
Experiments were made with sulphuric acid and lactic acid 
added to the ration of sheep and oxen, as much as 2.67 per cent, 
lactic acid being fed. Free acids are found in silage. Horses 
and young animals are often very sensitive to acid. The effect 
on the teeth must also be considered. 

Carbonate of lime, even in high amounts, had no effect upon 
digestibility by sheep. Since the acid gastric juice could not have 
acted, being neutralized by the carbonate of lime, the work of 
digestion must have been performed by the alkaline pancreatic 
juice. 

Character of Feed. Dry fodder has the same digestibility as 
green fodder, when there is no loss in drying, but usually fer- 
mentation takes place, or leaves, etc., are broken off, leaving 
material of less digestible character. Young plants are, in gen- 
eral, more digestible than older ones, and also have a higher pro- 
ductive value. Corn, however, contains more digestible matter 
when fully ripe than if cut before the ears are grown. This is 
due to the production of a large quantity of highly digestible 
grain. 

Stage of Growth. The digestibility decreases with the stage of 
growth of the plant, more rapidly as the plant approaches 
maturity. An exception is Indian corn, which forms a large 
amount of easily digested grain as it approaches maturity. 

B. E. Wolff obtained the following results with clover cut at 
different stages of growth: 



DIGESTION 



407 



PERCENTAGES DIGESTED. 





Nitrogen-free 
extract 


Digested 
nitrogen-free 
extract and 
fiber 


Green clover 


A1 ^ 






4o-o 
A-t 7 


D* 7 




A7 Q 


4o-y 

A7 ^ 




A1 8 


4/ O 




4o- 





Preparation of Food. Cooking, steaming, roasting, etc., de- 
crease the digestibility of the protein of the food. Grinding is 
better for hard seeds, or for those which are so small as to be 
liable to escape mastication, such as flax, barley, sorghum, millet, 
etc. Horses and hogs masticate food less thoroughly than 
ruminants, and hence derive more benefit from grinding. 

The following are some American experiments 1 relating to 
these conditions : 

COEFFICIENTS OF DIGESTIBILITY. 





Protein 


Crude 
fiber 


Nitrogen- 
free ex- 
tract 


Ether 
extract 




67.8 
46.9 


75-5 
65.9 


49-6 

51.4 


8 7 .I 
71.7 






Decrease due to roasting 


20.9 


9 .6 


-1.8 


5-4 




Oat fodder early cut (sheep) ..... 


72.3 
67.8 


54-6 

43-5 


6>5 
61.1 


70.2 
67.5 


Oat fodder late cut (sheep) 






4-5 


u. i 


2.4 


2.7 




Timothy full bloom (sheep) 


60.4 
44-5 


62.1 

51-7 


71.8 
61.0 


51-5 
34-6 








15-9 


10.4 


10.8 


16.9 






86.1 
68.7 


29.4 
38.3 


94-2 
88.8 


81.7 
45-6 








174 


-8.9 


5-4 


36.1 





1 Bulletin No. 77, Office Exp. Sta. 



408 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



Coefficients of Digestibility. The following are coefficients of 
digestibility of a few feeding-stuffs. 1 

COEFFICIENTS OF DIGESTIBILITY OF SOME FEEDING STUFFS. 





Protein 


Ether 
extract 


Crude 
fiber 


Nitrogen- 
free ex- 
tract 




QQ A 






6n 6 


Cottonseed nulls 




93-3 

( c n 


55-5 




\Vheat bran 


J^.U 

77 8 


vV/ 

68 o 


96 6 


41. 1 
60 A 


Wheat shorts 


//.o 
7Q 8 


86 i 




9-4 

8 1 7 


Corn tneal 


67 Q 


00.3 


33- J 




Corn cobs 


w-y 

IQ 7 


yz.i 

CQ T 




y4- 

Xl8 7 




1 7-O 
60 I 


0^. A 
QT T 


o/O 






09.1 


yi.i 




V^'O 








AI A 


68 /i 




/O-6 


4 U *O 


40.4 






O/'O 


3-3 
78 6 


9 
60 i 


5 r -5 
6n 6 




i*O 


5' 
/i/t 6 


9-o 
66 9 


cA Q 


Rice straw 


4O-V 

26 6 




c8 o 








o u< 4 




4/- J 



Digestibility of Constituents of Nitrogen-Free Extract.-' Inves- 
tigations as to the digestibility of the constituents of nitrogen- 
free extract, show that the sugars and the true starch are prac- 
tically completely digested when the food is properly masticated. 
The pentosans are digested to about the same extent as the nitro- 
gen-free extract, while the remaining and unknown constituents 
of the nitrogen-free extract have a much lower digestibility. 3 It 

COEFFICIENTS OF DIGESTION OF CRUDE FIBER AND OF CONSTITUENTS 
OF THE NITROGEN-FREE EXTRACT. 



Feed 


Crude 
fiber 


Nitrogen-free extract 


Sugars 


Starch 


Pentosans 


Residue 




54-6 
52.3 
67-3 


86.2 

IOO.O 

95.0 

IOO.O 
IOO.O 


97-4 

99.6 
25.0 


86. 5 
58.0 
6r.o 


6 5 .2 
50.0* 
32-7 4 




Cottonseed meal and hulls. 
Timothy hay .... 


Qi-aJ3orra.ss hay 





1 Bulletins 147, 104, Texas Exp. Sta.; Bulletin 77, Office Exp. Sta. 
- Headden, Bulletin 124, Colorado Station. 

3 Fraps, Bulletin 104, Texas Exp. Sta. 

4 Starch included. 



DIGESTION 



409 



is possible that the fermentation and other changes which food 
undergoes within the animal, modify the crude fiber so that a 
portion of it becomes soluble in acids or alkali, and thus appears 
as a portion of the nitrogen-free extract. 

Digestibility of Ether Extract Constituents. The ether extract 
of concentrates consists chiefly of fats and oils, but that of rough- 
ages contain on an average nearly 60 per cent, unsaponifiable mat- 
ter, chiefly wax alcohols, as previously pointed out. It has been 
long observed that the ether extracts of hays and fodders have 
a low digestibility. Indeed, in a number of experiments, more 
ether extract was found in the excrement than was present in the 
hay. 

A study of the digestibility of the constituents of the ether 
extract shows that while the unsaponifiable materials or wax 
alcohols have a low coefficient of digestibility, the saponifiable 
material, containing the fatty acids and chlorophyll, have a much 
higher digestibility. Thus the observed low digestibility of the 
ether extract of hays and fodders is due to the small content of 
fats and oils and the high content of waxes and alcohols less 
easily digested. 

PERCENTAGE DIGESTIBILITY OF CONSTITUENTS OF ETHER EXTRACT^ 





Total 
extract 


Unsaponi- 
fiable 


Saponi- 
fiable 


Alfalfa hay 








Bermuda hay .... 


y 




59-1 


Burr clover .... 




6 L * 


Q f. 




"8 6 


28 O 


6/1 A 


Johnson grass hay 


cj 2 




04.4 
60 I 




;>** 

AC O 


12 8 




Millet 


rf. A 


,> * 


//4 
o, A 




O D> 4 


T 5-9 


01.4 



Composition and Heat Value of Digested Nutrients. We may 
determine the composition of digested crude fiber by the follow- 
ing method : The crude fiber fed in the feed and the crude fiber 
excreted in the digestion experiment are subjected to analysis. 
The quantity of carbon, hydrogen, and oxygen fed in the crude 
1 Fraps and Rather, Bulletin 150, Texas Station. 
27 



4io 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



fiber and the quantity excreted, is calculated from the known 
amounts of crude fiber fed and excreted. The quantity of crude 
fiber digested, and the quantity of carbon, hydrogen, and oxygen 
digested, are calculated from the data. From these figures we 
can calculate the composition of the digested crude fiber. 

The crude fiber and the nitrogen-free extract in the excrement 
contain more carbon and hydrogen than that digested, and have 
a higher heat value. Digested crude fiber and digested nitrogen- 
free extract have been found to have the composition and heat 
value of a carbohydrate. For this reason, the digested crude 
fiber and nitrogen-free extract are often referred to as carbo- 
hydrates. The lignin is not digested. 

The composition of digested ether extract, protein, etc., can 
be determined in the same way. The heat value of the digested 
nutrients is estimated by a procedure somewhat similar. 

Ether extract of hays, grasses, and other coarse feeding-stuffs 
contain waxes, etc., as we have seen, which are not digested so 
well as fats. They accumulate in the excrement and change its 
composition. The composition and heat value of the digested 
ether extract is about the same as pure fat, while the ether ex- 
tract in the excrement has a much higher heat value. 

Proteids have a heat value of 5,479 to 5,990 cal. per gram. The 
digested proteids have practically the same value. The average 
is 5,711 calories. 

HEAT VALUE OF CONSTITUENTS OF MEADOW HAY. 





Crude 
fiber 


Nitrogen- 
free ex- 
tract 


Ether 
extract 


Heat value of I 




4,426 
4,782 
4,220 


4,584 
5,265 
4,232 


9,194 
9,821 
8,322 


in Excrement 

F)i crperprl 





CHAPTER XX. 



UTILIZATION OF FOOD. 

Food is used by animals to maintain the body activities and 
restore waste of material. It is also used for the production of 
new material in growth and fattening, for milk production, and 
for energy to produce work. Whenever energy or heat are to be 
generated, oxygen unites with the substances, forming carbon 
dioxide and water from fats, organic acids, sugars, etc., and 
carbon dioxide, water, and urea or other nitrogenous waste pro- 
ducts, from proteids. The carbon dioxide is eliminated by the 
lungs, and the nitrogenous waste passes off in the urine. The 
oxidation does not take place at one time, but a number of inter- 
mediate products are formed. 

The following is the average composition of ten kinds of 
animals, according to analyses made by Lawes and Gilbert, at 
Rothamsted : 

Per cent. 

Protein 13.5 

Fat 28.2 

Water 49.0 

Ash 3.2 

Contents of stomach and intestines 6. i 

Total IGO.O 

The ash consists of approximately 86 per cent, calcium phos- 
phate, and 12 per cent, calcium carbonate, with small quantities 
of fluorides, chlorides, iron, potash, and magnesia. These 
materials must all be supplied by the food. 

Different nutrients of food have different values for the pur- 
poses above stated. The first bodily activity with respect to food 
is its mastication and digestion. This consumes food material, 
which although derived from food previously eaten, must be re- 
placed by the food being eaten. Different kinds of food require 
different amounts of energy in mastication and digestion. 1 

The food material remaining after deducting the losses due to 
mastication, digestion, and undigested residues, may be used for 
1 Hagemann, Exp. Sta. Record 10, p. 906. 



412 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

the purposes of the body. The necessary vital functions must 
first be subserved, such as the body heat, beating of the heart, 
movements of the lungs, etc., and all other functions necessary 
for the maintenance of the life of the animal. 

Any food values remaining after maintaining the animal, may 
be used for productive purposes, such as work, building of fat or 
flesh, production of milk, etc. 

The utilization of the various foods and nutrients by the body 
is studied by means of exact experiments on animals. The 
experiment must, of course, be adapted to the end in 
view. A study of the income and outgo of nitrogen is 
called the nitrogen balance. A loss of nitrogen means a 
loss of flesh ; a gain of nitrogen, a gain of flesh. The 
income and outgo of carbon, taken in connection with the nitro- 
gen balance, gives the loss or gain of fat. This is called the car- 
bon balance. The determination of the income and outgo of 
energy is called the energy balance. 

The Nitrogen Balance. In order to determine the exact amount 
of nitrogen the animal is gaining or losing, we proceed as in a 
digestion experiment, but collect and analyze the urine in addition 
to the solid excrement. 

The total quantity of nitrogen in the food fed is the income of 
nitrogen. The nitrogen in the solid excrement is undigested 
material; that in the urine, is the digested nitrogen which has 
undergone complete metabolism in the body. The nitrogen in 
the perspiration is so small that it is usually not considered. 

Income in food less outgo in solid and liquid excrement is the 
loss or gain of nitrogen. If income is greater than the outgo 
there is a gain ; if less, a loss of nitrogen. Since over ninety per 
cent, of the nitrogen in the animal body is in the form of flesh, a 
loss or gain of nitrogen represents a loss or gain of flesh. 

Water and fat-free flesh has been found to contain, on an 
average, 16.67 P er cent - of nitrogen and 52.54 per cent, of carbon. 
That is, i gram of nitrogen is contained in 6 grams of dry flesh, 
which also contains 3.15 grams carbon. Flesh contains on an 
average 77 per cent, water. Hence a gain of i gram of nitrogen 



UTILIZATION OF FOOD 



413 



means a gain of 3.17 grams of carbon in dry flesh, and a gain of 
26 grams of moist flesh or muscular tissue. 

The Carbon Balance. Carbon enters the animal in food and 
water, and leaves it in urine, solid excrement, perspiration, and 
as the gaseous bodies-carbon dioxide and marsh gas. The marsh 
gas and part of the carbon dioxide comes from the fermentation 
in the intestines, but most of the carbon dioxide comes from 
oxidation of carbonaceous bodies in the animal. For example, 
the air inhaled and expired by a horse was found to have 
approximately the following percentage composition : 





Inhaled 


Exhaled 


Ox 


20 96 


16 oo 




o o^ 


A AO 









The following table gives an example of the determination of 
the carbon and the nitrogen balance : 

CARBON AND NITROGEN BALANCE. 1 





Nitrogen 


Carbon 


Income per day : 


grams 

69.96 

50.9 
27.50 

37-05 
2.OI 


grams 

2,010.8 
1,572.0 
408.8 
138.4 
1,443.0 
2-7 














177.47 


5,575.5 




Outgo per day : 


106.55 
73.69 


1,609.6 

170.9 
3,112.5 








180.24 
7.23 


4,892.0 

672.5 







The gain of 7.23 grams of nitrogen means a gain of 7.23 times 
6 equals 43.4 grams of dry flesh, containing 22.8 grams of carbon. 
1 Kellner, Landw. Versuchs-stat., 1900, p. 4. 



414 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

This quantity of carbon, subtracted from 672.5 grams, leaves 
649.7 grams carbon, which is contained in 849.3 grams of fat, 
since beef fat contains 76.5 per cent, carbon. Hence this animal 
gained 43.4 grams of flesh and 849.3 grams of fat per day : 

Apparatus to Determine the Carbon Balance. The respiration 
apparatus 1 consists essentially of an air-tight chamber to hold the 
animal, provided with a window and door and suitable openings 
for the introduction of food and water. A current of air is 
sucked through the apparatus by a ventilating fan connected with 
a gas meter for measuring the volume of the air drawn through. 
A portion of the air entering the chamber is sucked out by a 
mercury pump and measured by a sma 1 ! gas meter. It then 
passes through a series of tubes containing a solution of barium 
hydroxide, of known strength, to absorb the carbon dioxide. 
Barium carbonate is precipitated, and the excess of barium 
hydroxide can be determined by titration with an acid of known 
strength. The carbon dioxide may also be absorbed by soda lime 
and weighed. This gives the amount of carbon dioxide in the 
air subjected to analysis, and the total quantity contained in the 
known quantity of air which passes through the respiration 
chamber can be easily calculated. Another measured portion of 
the air passes through a tube containing copper oxide, heated red 
hot by means of a combustion furnace, and then through a sec- 
ond series of barium hydroxide tubes. The marsh gas or other 
organic carbon compounds are oxidized in the tube to carbon 
dioxide, which is absorbed by the barium hydroxide as before. 
We thus know the total quantity of carbon as carbon dioxide and 
as organic carbon, which goes into the respiration chamber with 
the air taken in. 

Measured portions of the air which goes out of the chamber 
are withdrawn, and passed through an apparatus exactly similar 
to that described above. The exact quantity of carbon in carbon 
dioxide and in organic forms given off by the animal, is the 
difference between that in the air which leaves and that which 
enters the respiration chamber. 
1 Exp. Station Record 10, p. 813. 



UTILIZATION OF FOOD 415 

Energy Balance. The energy balance may be determined in 
two ways: 

First, the energy in the food fed, and in the solid and the liquid 
excrement may be determined by direct measurements, and that 
lost as marsh gas calculated. The heat value of the fat or flesh 
gained or lost may be calculated from the loss or gain of fat and 
flesh found by the nitrogen and the carbon balance. From these 
figures we estimate indirectly the energy used by the animal body. 

Second, the determination of energy in the food and in solid, 
liquid, and gaseous excrements is made as stated above, but the 
energy given off by the animal is measured directly. This form 
of experiment requires the use of a respiration calorimeter. 1 The 
results of the two methods should, of course, agree, but the sec- 
ond method is adapted to studying problems which cannot be 
solved by the first. For example, the energy given off during the 
time digestion is going on may be compared with that given off 
when no digestion is going on. In experiments with human be- 
ings, the extra energy given off during reading, work, etc., may 
be determined. 2 

Respiration Calorimeter. A respiration calorimeter consists of 
a respiration chamber arranged so that the heat given off by the 
animal can be measured. The chamber is insulated so that as 
little heat as possible may be lost or gained by it. The incoming 
air is cooled to a uniform temperature, and the outgoing air is 
cooled to the same extent. The heat given off by the animal is 
taken up by water circulating through tubes inside the chamber. 
The temperature of the water is taken before it enters the cham- 
ber, and when it leaves. The volume of water and the difference 
in temperature of the incoming and outgoing water being known, 
the heat eliminated is easily calculated to calories.. Allowance 
is also made for the heat changes involved in the condensation 
of water on the sides of the chamber, and for evaporation during 
the experiment. 

1 Armsby, Bulletin 104, Pennsylvania Station. Exp. Sta. Record 15, 
P- 1033- 

2 For description of human calorimeter see Bulletin 63, Off. Exp. Station. 



416 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



A respiration calorimeter is a complicated and expensive ap- 
paratus, but it secures information regarding the use of nutrients 
and the nutrition of the animal which is of the highest value, and 
which can be secured in no other way. 




Fig. 86. Model of respiration calorimeter at the Pennsylvania 
Station. U. S. D. A. 



Disposition of Food Materials. The carbon which enters an 
animal in food, is disposed of as follows : 

1 i ) A portion appears as undigested material in the solid 
excrement. 

(2) A portion escapes as marsh gas and carbon dioxide, pro- 
duced by fermentation. 

(3) A portion is eliminated as partly oxidized compounds in 
the urine. 

(4) A portion is eliminated as carbon dioxide in the gases 
expired from the lungs, being fully oxidized in the body. 

(5) A portion is used in the production of hair, flesh, fat, 
milk, etc. 



UTILIZATION OF FOOD 



417 



The nitrogen appears as follows : 

(1) In the undigested residues. 

(2) In the urine. 

(3) In perspiration (very small quantity). 

(4) Used in the production of hair, flesh, milk, etc. 
The energy is used as follows : 

1 i ) A part appears in the undigested solid excrement. 

(2) A part is used in fermentation and escapes as heat. 

(3) A part is lost in incompletely oxidized organic matter in 
the urine. 

(4) A part escapes in marsh gas produced by fermentation in 
the intestines. 



Fig. 87. Curve showing heat production of steers in respiration calorimeter, 

the arrows being pointed up if the animal is standing. 

Pennsylvania Station. 

(5) A portion is used to masticate and digest the food, and is 
eliminated as heat. 

(6) A portion used for bodily activities, such as beating of 
the heart, breathing, movements, warming the body, etc., and 
is eliminated as heat. 

(7) Any portion remaining after the above requirements are 
satisfied, may be used for external work, stored up in fat or 
flesh, or used in the production of milk, etc. 

Production of Marsh Gas. The effect of different nutrients or 
foods upon the production of marsh gas has been studied by the 
following method. First, the quantity of marsh gas evolved with 



4 i8 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



a given ration is exactly determined in the respiration chamber. 
Then the marsh gas evolved with the same ration plus fat, pro- 
tein, starch, crude fiber, or any other nutrient or feed, is 
determined. The increase or decrease in the quantity of marsh 
gas evolved, shows the effect of the addition. 

In this way it was found that fat and proteids do not affect 
the quantity of marsh gas. The methane appears to come en- 
tirely from the constituents of the nitrogen-free extract and 
crude fiber. The ratio of protein to non-protein, and other 
factors, also appears to affect its production. All additions which 
decrease the digestibility of the nitrogen-free extract decrease 
the production of methane, but in greater proportion; and addi- 
tions which increase the digestibility of the nitrogen-free extract 
increase the production of methane. The various factors which 
affect the production of methane require further study. 

A considerable portion of the value of the digested nitrogen- 
free extract and crude fiber is lost as marsh gas, as is seen from 
the following table : 





Sugar 


Starch 


Crude fiber 
(paper starch) 


Nitrogen-free 
extract and 
crude fiber 
(average of 100 
experiments) 


Grams methane for 100 


2 8/1 


317 


4A6 


420 


Heat value of methane- 
Heat value of substance 


37-9 Cal. 
395-5 Cal. 
o 6 


42.3 Cal. 
418.3 Cal. 


58.6 Cal. 
418.5 Cal. 


*y 

57-2 Cal. 
418.4 Cal. 




y.o 






I 3-7 



A considerable percentage of the material which does not 
appear in the solid excrement during a digestion experiment is 
not really digested, i. e., converted into soluble products and 
absorbed by the body, but is fermented and a portion of its 
value is lost as marsh gas. 

Organic Matter of the Urine. The digested nitrogenous bodies 
which have been oxidized by the animal body are excreted in the 
urine, in the form of urea CO(NH 2 ) 2 , uric acid C 5 H 4 N 4 O 3 , 
creatin C 4 H 9 N 3 O 2 , or hippuric acid, C 6 H 5 CO.NHCH 2 COOH, 



UTILIZATION OF FOOD 419 

and possibly other compounds. All these substances are incom- 
pletely oxidized, and represent a loss of energy from the food. 
Non-nitrogenous organic substances are also present in the urine. 
For example, the following is an analysis of the urine of a 
sheep : 

Water 86.48 

Urea 2.21 

Hippuric acid 3.24 

Ammonia 0.02 

Carbonic acid 0.42 

Other organic substances 2.07 

Ash 5.56 



The effect of various substances upon the urine may be studied 
by determining the amount and composition of the urine with a 
given ration, adding the substance to be studied to the ration, and 
determining the change in the urine caused by the addition. This 
effect is usually expressed in terms of energy (calories). Kell- 
ner, 1 assuming that only the proteids fed affected the loss of 
energy in the urine, obtained the following results with certain 
concentrates : 

Average energy in i gram digested proteids, Calories 5.71 

Average loss of energy in urine from i gram, Calories 1.29 

Average percentage loss of energy in urine 22.6 

Maximum percentage loss (with linseed meal) 26.6 

Minimum percentage loss (with gluten meal) 18.9 

The assumption of Kellner, however, is not correct, since the 
other constituents of the food have some effect upon the loss of 
energy in the urine. Only traces of sugar or pentosans are found 
in normal urine, but an addition of roughage to a ration increases 
the loss of energy in the urine to a considerably greater extent 
than the addition of an equal quantity of protein in the con- 
centrated feeding-stuffs mentioned above. Sometimes the in- 
creased loss is greater than the quantity of energy in the proteids 
fed in the roughage. Non-nitrogenous substances, therefore, 
1 Die Ernahrung d. Landw. Niitzture, p. 83. 



420 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

suffer a loss of energy in the urine, but at present little is known 
as to the nature of this loss and what factors modify it. 

Available Energy. A portion of the energy in the food fed to 
the animal remains in the undigested matter of the solid excre- 
ment, a portion appears in the urine, and a portion is lost in the 
form of marsh gas. None of the energy so lost is of any value 
to the animal, and may be termed unavailable energy. The 
available energy is the total energy in the nutrients less the losses 
in the solid, liquid, and gaseous excrements. A portion of the 
available energy is expended in the processes of mastication, 
moving the food, preparation of digestive juices, digestion, and 
other operations necessary to bring the digested nutrients into 
the body, and convert them into forms suitable for its use. This 
energy does not, of course, come from the food actually in pro- 
cess of digestion, but the digested food must replace the energy 
so used. The energy used in digestion, etc., appears as heat, and 
may aid to keep the animal warm, but any excess over the amount 
so required, serving no useful purpose, is evolved as heat. We 
will term the energy consumed in digestion of the food thermal 
energy. 

The available energy remaining after the thermal energy has 
been subtracted, may be used for processes requisite to the life 
of the animal, such as to keep the animal warm, to furnish energy 
for beating of the heart, breathing, and necessary movements of 
the body. Any excess over that needed by the animal body may 
be used for productive purposes for fat, flesh, milk, etc. We 
will term this portion of the energy of the food its kinetic energy. 

Estimation of the Energy Expended in Digestion. Two meth- 
ods may be used to estimate the energy expended in digestion of 
food. The first method can be applied only to animals, such as 
the dog, having small digestive organs, which can be completely 
emptied by starving for a few days. The heat evolved from a 
starving dog at a temperature of 33 is measured by placing the 
animal in a calorimeter. Sufficient food is then given to supply 
an amount of available energy equal to that lost daily while 
starving, and the heat liberated is again measured. Any increase 



UTILIZATION OF FOOD 421 

in the amount of heat evolved is due to processes essential to the 
digestion of the food, since at 33 no heat is required to maintain 
the body temperature of the animal. The heat evolved during 
starvation being put at 100, the heat evolved during the same 
length of time when food containing an equal amount of available 
energy (100) was fed was found by experiments of Rubner 1 to 
be as follows : 

Heat evolved 
in starvation 100 

Heat when 100 calories flesh was fed 130.9 

Heat when 100 calories fat was fed 112.7 

Heat when 100 calories gluten was fed 1 28.0 

Heat when 100 calories cane sugar was fed 105.8 

That is to say, the consumption of the food caused an in- 
creased production of heat, which was probably due to digestion 
of the food. Since 100 calories of available energy was fed, the 
increased quantity of heat evolved represents heat evolved by the 
digestion; that is, the percentage of thermal energy contained in 
the available energy. This ranged from 5.8 per cent, with the 
sugar to 30.9 per cent, with the flesh. 

The second method is applicable to herbivorous animals, but 
gives only indications. The animal is fed on a ration, and the 
heat evolved from the body is measured. The feed to be 
studied is added to the ration and the heat is again determined. 
The increase in heat is due to the digestion of the added feed. 

The following figures of Armsby 2 afford an illustration : 





Heat in 
feed digested 


Heat produced 
by animal 


Period I 


6 618 


9067 


Period II 


Q 482 


IO 206 




+ 2,864 


4-1,139 



An increase of 2,264 calories in the digested food caused an 
increase of 1,139 calories in the heat given off by the animal. 
That is, about 34 per cent, of the energy of the food was con- 
sumed in digestive processes. 

1 Quoted by Kellner, Die Ernahrung d. Niitztiere, p. 105. 

2 Proc. Soc. Prom. Agr. Sci., 1902, p. 100. 



422 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

The Productive Value of a Nutrient. As we have previously 
stated, the quantity of a ration in excess of the maintenance re- 
quirements of an animal, may be used for productive purposes. 
If the animal is a fattening animal, this excess may be used for 
putting on fat. 

Kellner 1 has estimated the fat produced by various nutrients 
and feeds by the following method. With the aid of the respira- 
tion apparatus, he determined the income of carbon and nitrogen 
in the food fed and in the water, and the outgo in the urine, the 
solid and the gaseous excrements, and so ascertained the quantity 
of the fat and flesh produced by a basal ration (Period I). This 
ration was sufficient to maintain the animal and produce a little 
fat. In Period II, the nutrient or food to be tested, was added 
to this basal ration and the amount of flesh and fat produced was 
again determined. The small quantity of flesh gained or lost 
was in each case calculated to the quantity of fat which would 
contain an equal amount of energy. The amount of fat gained 
in Period II less the amount of fat gained in Period I, gives the 
gain of fat due to the additional food or nutrient fed. The 
quantity of fat produced by 100 grams of the food or nutrient 
digested was then calculated from this data. The quantity of 
fat produced should be in proportion to the kinetic energy of the 
feed. 

'Experiments were first made with pure nutrients, with the 
following results : 

Fat produced by 
100 grams digested 

Cocoanut oil 59.8 

Ether extract of coarse feeding stuffs 47.4 

Ether extract of grasses 52.6 

Starch 24.8 

Cane sugar 18.8 

Lactic acid o.o 

Crude fiber (paper pulp) 25.3 

Proteids (albumen) 24.8 

Pentosans not determined 

1 Landw. Versuchs-stat., 1900, p. 450. See also Arnisby, Bulletin 71, 
Pennsylvania Station. 



UTILIZATION OF FOOD 



423 



Productive Value of Feeds. The substances thus mentioned 
represent the various groups of constituents of a feeding- 
stuff. 1 Kellner determined the composition and digestibility of 
a number of feeding-stuffs, and calculated the quantity of fat 
which each could produce, based upon the values given in the 
preceding table for the digestible nutrients. The following is an 
example of the method of calculation used : 

COTTONSEED MEAI,. 





Digested 


Fat pro- 
duced by 
i gram 


Total fat 




grams 

39-6 
13.0 

12. 1 


0.235 
0.598 
0.248 


grams 
9-30 

7-77 
3-00 


Fat in 100 grams 


Carbohydrates (including crude fiber) 


Calculated total for 100 grams 


20.07 
19.62 


Found by experiment 





Thus 100 grams of cottonseed meal should produce 20.07 
grams fat under the conditions given. We will term this the 
productive value. 

If the value of a feeding-stuff for producing fat is in propor- 
tion to the quantity of digested nutrients present, i. e., if the 
digested nitrogen-free extract etc., of one feed has the same 
value as that of any other (as has heretofore been assumed), then 
the above method of calculation should be correct. 

The results of a number of experiments and calculations are 
given in table on following page: 2 

The calculated quantity of fat is, in many cases, much greater 
than that actually found by experiment. That is to say, the pro- 
ductive value of different kinds of feeds is not necessarily in pro- 
portion to their content of digestible nutrients. 

1 See also Hagemann, Exp. Sta. Record 10, p. 907. 

1 After Kellner, Die Ernahrung d. Landw. Niitztiere, p. 163. 



424 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



FAT PRODUCED BY 100 GRAMS OF THE FEEDS NAMFD. 



Calculated 

from digested 

nutrients 



Found by 
experiment 



Percentage 
of calculated 



Peanut meal 18.9 

Palm nut meal 17.9 

Linseed cake meal 19.7 

Rice meal 16.8 

Rye meal 18.1 

Bean meal 17.3 

Rye bran 15.8 

Wheat bran 15.4 

Brewers grain (dry ^ 15.4 

Potatoes 18.5 

Sugar beets 15.0 

Beet residue ( wet ) 18. i 

Beet residue ( dried ) 18. i 

Wheat straw, I 10.4 

Wheat straw, II 8.4 

Oat straw 10.9 

Barley straw 11.7 

Meadow hay, I 12.9 

Meadow hay, II 15.6 

Clover hay 12.4 

Grass hay 13.3 



18.9 
18.3 
19.2 

18.3 
16.9 

16.3 
12.5 
ii. 9 
13.0 
18.1 

13-1 
17.4 

14.2 

2.1 
2.4 

6.6 

7-8 
8.1 
10.9 
8-5 
8-5 



100 

102 

9 8 

1 08 

93 
94 
79 
77 
84 
98 
87 
94 
78 

20 
29 

59 
64 

54 
55 
63 
64 



Relation to Character of Feed. The production of fat from 
the oil meals, potatoes, and rice meal was equal to that calculated. 
With rye meal and bean meal it was about 94 per cent. The 
beans and dried beet residues were deficient to the extent of 21 
to 23 per cent. The values of none of the concentrated feed-stuffs 
fell below 77 per cent, of the calculated. 

The fat production found to take place with the hays and 
straws was 20 to 64 per cent, of the calculated quantity. The de- 
ficiency was found to be related to the total quantity of crude 
fiber in the feed. For example, 100 grams of wheat straw No. I 
produced 8.3 grams less of fat than the calculated quantity, and 
contained 46.6 grams of crude fiber ; that is, there was a deficit of 
0.18 gram of fat for each gram of crude fiber present. For 
eight straws and hays, the maximum deficiency of fat per i gram 
of crude fiber present was o.iS gram, the minimum being o.n, 
and the average 0.14 grams. 

This deficiency is in part due to the work of chewing the feed. 
A number of experiments were repeated after grinding the feed, 



UTILIZATION OF FOOD 425 

with the result that the average deficit was found to be only 0.073 
gram of fat per i gram of crude fiber fed. The deficiency was 
no doubt due in part to the character of the nitrogen-free extract 
of hays and straws, which, as is well known, is not composed of 
sugars and starch, but largely of substances hard to dissolve and 
in part of unknown nature. They are not the same as the starch 
used by Kellner to represent the pure nutrient. 

Calculating Productive Value. Knowing the composition and 
coefficient of digestibility, the productive value in terms of fat 
of a given feeding-stuff may be calculated so as to be in accord 
with the experimental work cited. The results are expressed in 
pounds fat which may be produced by 100 pounds of feed. 

Concentrated Feeding-Stuffs. Multiply digestible proteids in 
100 pounds fed by 0.235. Multiply digestible fat by 0.598. 
Multiply digestible nitrogen-free extract and crude fiber, taken 
together, by 0.25. Add the products, and multiply by the per- 
centage of fat produced by the feeding-stuff in question as per 
preceding table. If the feeding-stuff is not named in the table, it 
will be necessary to use the factor for the feed most closely 
resembling it. The result is approximately the productive 
value in terms of fat. Chaff, rice hulls, and other by-products 
high in crude fiber are not considered as being concentrated feed- 
ing-stuffs. 

Roughage. Proceed as directed above, using the factor 0.526 
for digestible ether extract in grasses, and 0.474 for all other 
roughages, and sum up the fat values of the nutrients. Then, if 
the roughage is not ground, multiply the total quantity of 
crude fiber present in 100 pounds by 0.14 and subtract this quan- 
tity from the sum. If the roughage is ground, multiply the crude 
fiber by 0.07 and proceed as before. With green feeds contain- 
ing 8 per cent, or less crude fiber, deduct 0.085 gram fat for each 
gram of crude fiber; with those containing 8 to 10 per cent., 
deduct 0.095 ; with those containing 10 to 12 per cent., deduct 
0.108; with those containing 12 to 14 per cent, deduct 0.12; 14 
to 16 per cent., deduct 0.135; over J 6 per cent., deduct 0.14. 
28 



426 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

The following is an example of the method of calculating the 
fat value of a roughage : 

JOHNSON GRASS HAY 100 POUNDS. 

Digestible protein 3-3 X 0.235 = 0.78 

Digestible fat 0.7 X 0.474 = 0.33 

Digestible crude fiber 22.6 

Digestible nitrogen-free extract ... 28. i 

~50.7 X 0.25 = 12.42 

Total 13.53 

Total crude fiber 38.0X0.14= 5.32 

Productive value 8.21 pounds fat 

This means that 100 pounds of the Johnson grass hay added to 
a ration already sufficient to maintain the animal, should produce 
8.21 pounds fat. The fat value is the productive value for fatten- 
ing, when the feed is used for fat and for no other purpose. 

Kellner expresses the productive value of feeds and rations in 
terms of starch; that is, the quantity of starch which is capable 
of producing the same quantity of fat as 100 pounds of the feed 
is capable of producing. Armsby 1 expresses the productive value 
in terms of heat units (therms). There are two objections to 
this manner of statement. The first is, that the heat units are 
used for the total heat value of the feed, for the available heat 
value, and for the productive value, introducing some confusion in 
distinguishing between them. The second objection is, that the 
energy equivalent to the quantity of fat produced is not the pro- 
ductive energy of the feed, since no doubt some of the energy 
must be consumed in the process of transforming the nutrients 
into fat. The productive energy may be proportional to the fat 
produced, but is not identical with it. 

We therefore prefer to express the productive value of feed 
in terms of the actual experimental basis, namely, of the fat 
which they were found to produce. 

The productive value of a feed may be defined as the quantity 
of fat which the feed will produce, when it is fed in addition to a 
ration already sufficient to supply the needs of the animal for 
maintenance. 

1 Farmers Bulletin No. 346. 



UTILIZATION OF FOOD 427 

Significance of the Pjoductive Value. We have seen that a 
portion of the value of a food is lost in undigested material, a 
part as marsh gas, or oxidized in fermentation, a part in the in- 
completely oxidized material of the urine, and a portion is used 
for digestion and other processes fitting it for the use of animal. 
What remains of the food after these losses are deducted, may be 
used for maintenance, work, fat, flesh, milk, etc. It represents 
the net value of the food to the animal. It also corresponds to 
what we elsewhere termed the kinetic energy of the food. 

The productive value of a food is the best measure so far 
devised for the net value of a food. Rations have heretofore 
been calculated on the assumption that all digestible nutrients of 
the same group have the same value to the animal, regardless of 
the origin of the material. We now know, however, that the net 
value of a food may vary widely from its value based entirely on 
digestible nutrients, so that the value of a food for the purpose 
of producing energy is best measured by its productive value. 

It is quite possible that the kinetic energy of different feeds 
undergo somewhat different losses when transformed into fat, 
so that the quantity of fat produced may not be the most exact 
possible measure of the net values of feeds. The energy used 
in digestion and given off as heat may also prove useful under 
certain circumstances, such as with an animal on a maintenance 
ration in cold weather. 

While the fat values of feeding-stuffs probably represent their 
comparative values for fattening purposes, and perhaps for milk, 
it does not follow that they represent the values of the feeds for 
productive work and for maintenance of the animal. The con- 
version of proteids, etc., into fat undoubtedly consumes energy, 
and a greater quantity of energy may be required to convert the 
proteids of one feeding-stuff into fat, than those of another; 
whereas if the kinetic energy is used directly for work or main- 
tenance, these proteids might be equal in value for these pur- 
poses. We have seen that a feeding-stuff possesses both kinetic 
and thermal energy, and that the thermal energy may be used to 
keep the animal warm. While the thermal energy fed to an 



428 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

animal on a heavy ration may be so excessive that differences in 
the thermal energy of feeds may have no significance, an animal 
on a small or maintenance ration, may be able to utilize the 
thermal energy. 

The use of the productive value of a feed is no doubt a decided 
advance in the science of animal nutrition, as it emphasizes the 
differences in the productive values of the digested nutrients of 
different classes of feeds. It is clear that the digested nitrogen- 
free extract, for example, of hays and fodders, does not have the 
same value to the animal as that of grains and other concentrates. 

The value of a feed for nutrition is thus indicated by : 

1 i ) Its content of digestible protein, or power to produce flesh. 

(2) Its productive value in terms of fat, or its power to pro- 
duce fat. 

Mineral Materials. Animals require inorganic as well as 
organic materials. 1 The term "inorganic" is not strictly accurate 
when used in connection with phosphates, as the phosphorus is 
partly in organic combination. However, any addition of phos- 
phates to the ration is made as inorganic substances. Ash is left 
by all organs of the body when burned, and mineral matter ap- 
pears essential to their proper growth and development. Mineral 
substances are required in processes of digestion and metabolism. 
Animals fed on food from which the ash has beeen extracted be- 
come irritable, nervous, show weakness of the extremities, and 
die sooner than if not fed at all. 

The most important inorganic substances are salt, phosphoric 
acid, and lime. Salt is found in the digestive juices. In moderate 
amounts, it appears to favor the retention of proteids by the 
body. Cattle of average weight should receive 20 to 25 grams; 
sheep and pigs, 4 to 8 grams; and horses, 15 to 25 grams per day. 
With heavy rations of difficulty digestible foods, cattle may re- 
ceive as much as 80 grams; sheep, 12 grams; and pigs, 15 grams 
per day. An excess of salt increases the consumption of water, 
and is undesirable. It is best to mix the salt with the food. 
1 See Ohio Bulletin No. 207. 



UTILIZATION OF FOOD 



429 





B 

Fig. 88. Maud in her normal condition (A) and after nine months 
without salt (B). Wisconsin Station. 



43 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

Phosphoric acid is found in the flesh. The animal takes up 
phosphoric acid when it adds flesh, and it gives off phosphoric 
acid when it loses flesh. Phosphoric acid is also found in the 
bones, as phosphates of lime and magnesia. Phosphates are also 
present in milk. 

An animal which does not receive enough phosphoric acid, 
lime, and magnesia in its food, loses continually small quantities 
of phosphates of lime and magnesia. This is removed from its 




Fig. 89. Pens used in feeding experiments. Illinois Station. 

bones, making the bones porous, weak, and liable to break. This 
diseased condition occurs in some districts where the ' feeding- 
stuffs do not contain enough lime or phosphoric acid, and may 
be produced artificially by withholding phosphates from the 
animal. It may also be caused by an excess of acid in the food. 
Growing animals which do not receive sufficient lime and phos- 
phoric acid quickly suffer. Movement becomes painful to them, 



UTILIZATION OF FOOD 431 

the limbs and spinal column bend, the teeth remain small and 
loose, and the bones weak. Pigs especially are liable to suffer in 
this way because the potatoes and cereals fed to them do not con- 
tain enough lime. 1 Straw and chaff of cereals, the cereal grains, 
and their by-products, as bran, gluten meal, etc., malt sprouts, 
molasses, and whey, are poor in lime. The straw and chaff of 
grains, beet pulp, potato pulp, and molasses are poor in phos- 
phoric acid. Clovers, meadow hay, and leguminous seeds are 
rich in lime. Cereal grains, bran, oil cake, flesh, and fish by- 
products are rich in phosphoric acid. 

When lime is deficient in the feed, it may be supplied as pre- 
cipitated chalk. Lime and phosphoric acid together may be given 
in the form of precipitated phosphate of lime or finely ground 
bone. 

Lecithin 2 appears to stimulate the growth of the bones and 
body. For example, one guinea pig fed o.io gram lecithin per 
day, in addition to other food, increased 1,380 grams in 10 weeks; 
but another pig fed no lecithin, under the same conditions, gained 
300 grams. 3 

Water. Water lightens the work of chewing, and makes swal- 
lowing possible. It is indispensable to digestion and absorption 
of food. The digestive ferments can act only in solution, and 
the products of digestion can enter the body in dilute solution 
only. Concentrated solutions cause strong peristaltic move- 
ments, which end with the ejection of the material. Water also 
circulates in the blood and secretions, and carries out the ex- 
creted metabolic products in the urine. It aids to remove an 
excess of heat from the body by evaporation. One gram of 
water on being converted from the liquid to the gaseous state 
takes up 535.9 calories. 

Too little water delays digestion and absorption, and causes 
the nitrogenous metabolic products to remain in the body longer 
than usual. The blood gradually thickens, the body temperature 
is elevated, and the decomposition of fat and albumen con- 

1 See Missouri Bulletin No. 6. 

2 Missouri Bulletin No. 61. 

3 Compt. rendu., 1902, p. 1166. 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 





Fig. 90. Calf (A) from cowfedon corn products, activeat birth; calf (B) from 
cow fed on wheat products, unable to stand at birth. Wisconsin Station. 





Fig. 91. Cow (A) fed on corn products, vigorous; compare with cow (B) 
fed on wheat products, unthrifty. Wisconsin Station. 



434 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

sequently increases. Growing animals are injured by too little 
water, or by receiving it at irregular intervals. When water is 
placed freely at the disposal of the animal, an excessive 
consumption is not to be feared, unless caused by very watery 
food or too much salt. The amount of water taken up on an 
average for one pound dry matter is as follows : 

Pounds 

Swine 7 to 8 

Cows 4 to 6 

Oxen 2 to 3 

Horses 2 to 3 

Sheep 2 to 3 

The quantity of water consumed varies with the temperature, as in 
warm weather more is required to replace that lost in perspiration. 

Aromatic Bodies. These are the bodies which give an agree- 
able taste and odor to feeding-stuffs. They have no effect upon 
digestion, and, on account of their small quantity, little on pro- 
duction. Their chief effect is upon the nervous system. They 
awaken the appetite, and increase the activity of the secreting 
organs of the mouth and stomach. Special additions of aromatics 
are not necessary when good hay, sound grain, by-products of 
milling, oil cakes, or even good stray or chaff is fed, for these 
contain in themselves sufficient appetizers. 

Rations from Eestricted Sources. Experiments at the Wiscon- 
sin Experiment Station, 1 covering a period of four years, show 
that animals fed rations properly balanced, from different plant 
sources, were not alike in general vigor, size, and strength of off- 
spring, and capacity for milk secretion. Animals fed from the 
products of the wheat plant exclusively were deficient in vigor ; 
those fed from the corn plant were strong and vigorous ; those fed 
from the oat plant were not as vigorous as those fed the corn 
plant ; while those fed a mixed ration were intermediate between 
the wheat and oat rations in vigor. The significance of these in- 
vestigations is not yet apparent. 
1 Research Bulletin No. 17. 



CHAPTER XXI. 



MAINTENANCE RATION AND FATTENING. 

Maintenance Ration. The amount of food required to main- 
tain an animal is called the maintenance ration* A maintenance 
ration must provide enough energy to keep up the body heat, and 
to supply the digestive and vital processes, and enough proteids 
to replace the body waste, and provide for natural growth of 
hair, horn, etc. The amount of body heat required will depend 
upon the surrounding temperature. At about 33 C. none will 
be required; the amount necessary at lower temperatures will 
depend upon the size and shape of the animal, its protective 
coverings, the quantity and temperature of the drinking water, 
etc. 

Value of Food for Maintenance. The quantity of body sub- 
stance protected by given amount of food may be estimated as 
follows : 

Determine the income and outgo of carbon and nitrogen of the 
starving animal. Feed the nutrient to be tested, and again deter- 
mine income and outgo of the carbon and nitrogen. The 
amount of body fat and flesh protected by the known amount of 
nutrients fed is thus ascertained. 

For example, the following is an experiment of Rubner: 2 





Nitrogen 
eliminated 
per day 


Fat 
decomposed 
per day 




grams 

3-16 
20.63 


grams 

75-92 

30,72 






+1747 


45-20 





The meat fed increased the elimination of nitrogen and de- 
creased the destruction of fat. 

The meat equivalent to 17.47 grams of nitrogen ( = 113.4 

1 Armsby, Bulletin No. 42, Pennsylvania Station. 

2 Zeitsch f. Biol., 1886, p. 04. 



43^ PRINCIPLES OF AGRICULTURAL CHEMISTRY 

grams dry meat) protected 45.2 grams body fat from oxidation, 
so that 250 grams dry meat would protect 100 grams of fat. But 
the available energy of water-free meat is 404 calories ; and that 
of dog fat is 940 calories, so that 100 grams fat has the same 
heat value as 232 grams of meat, and the meat protected body fat 
approximately in proportion to its available energy. 

Similar experiments with sugar, starch, and other nutrients 
have shown that the value of different nutrients to an animal 
that is fed insufficient food are in proportion to their content of 
available energy. This is known as the law of isodynamic 
replacement of nutrients. This law holds only when the thermal 
energy of the food can be entirely utilized in maintaining the 
temperature of the body. When the thermal energy is of no 
value, as when the surrounding temperature is the same as that 
of the body, nutrients should replace one another only in propor- 
tion to their content of kinetic energy. (See Chapter XX). 
When the thermal energy is only partially utilized, the law is 
only partly true. 

Carnivorous animals may be maintained on a ration consisting 
of flesh alone. The quantity necessary is between three and four 
times as much as that oxidized by a starving animal. An addi- 
tion of fat, sugar, starch, or crude fiber decreases the amount of 
proteids required. 

Ascertaining the Maintenance Ration. The ration which will 
keep an animal without loss or gain of fat or flesh is termed the 
maintenance ration. The maintenance ration is ascertained 
exactly by feeding an animal on a given ration, and determining 
the loss or gain of flesh and fat by means of the carbon and 
nitrogen balance. The protein and non-protein in the ration are 
decreased, or increased, as appears necessary from the previous 
experiment, and the carbon and nitrogen balance again 
determined. That ration which produces only a very slight gain 
of flesh and fat is considered to be the maintenance ration. It is 
practically impossible to feed a ration which does not produce 
either a slight gain or loss. 



MAINTENANCE RATION AND FATTENINGS 437 

Factors which Affect the Maintenance Ration. The size of the 
maintenance ration is affected by several factors in addition to 
the vital needs of the animal. 

External Temperature. When the atmosphere has the same 
temperature 'as the animal body, no heat is required to keep the 
animal warm. The thermal energy of the food, produced in 
digestion, will maintain the animal heat for a few degrees below 
33, which will vary according to the character of the food. At 
lower temperatures, food must be oxidized to keep the animal 
warm. The amount of food so required will depend upon the 
temperature, and other factors. For example, Rubner 1 found 
the heat given off by a starving dog, is measured directly in a 
calorimeter, to be as follows : 

Temperature Heat evolved 

Degrees C. Calories 

7.6 86.4 

15-0 63.0 

20.O 56.0 

25-0 54-0 

30.0 56.0 

35-0 68.5 

About 65 per cent, more energy was used at 7.6 C. than at 
25. At 35 the elimination of heat is increased, probably owing 
to disturbances due to the high temperature. 

Feeding standards are based on a temperature of 15 to 20 C. 
At higher temperatures, less feed will be required, at lower tem- 
peratures, more. Since small individuals have a proportionally 
larger body surface than the large animals, they give off more 
heat, and so require more food. For example, it is estimated 
that a grown steer weighing 300 pounds would require per 100 
pounds weight, food of 0.19 pounds fat value, while a steer of 
800 pounds, requires per 100 pounds weight, food of 0.14 pounds 
fat value, or one-fourth less, weight for weight. 

The Condition of the Animal. The fatter the animal, the 
more food it requires for maintenance. The increased food 
required is not in proportion to the gain in weight, but the pro- 
1 Gesetz d. Energieverbrauch, 1902, p. 105. 



438 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

portion is greater than the gain, and increases as the animal be- 
comes fatter. 

Temperature of Drinking Water. Water consumed must 
have its temperature raised to the temperature of the animal 
body. That, of course, requires heat, the amount required being 
considerable if the water is cold. For an example, an ox weigh- 
ing 1,000 pounds requires for maintenance, food having the pro- 
ductive value of 750 grams fat per day. Such an animal may 
consume 50 kg. water per day. If this water has the temperature 
of 5 C. the temperature must be raised to 39, that is, 34, and 
the heat required is 34 x 50 = 1,700 calories, which is equal to 
about 190 grams fat. This is about 25 per cent, of the main- 
tenance ration. Cold drinking water must thus be compensated 
for by more feed. 

Value of Protein for Maintenance. Proteids alone will main- 
tain the animal body. The quantity of proteids required is con- 
siderably in excess of the amount of body proteids oxidized by a 
starving animal. By experiments on dogs, starved, and then fed 
on lean meat, it has been found that for 100 parts body proteids 
oxidized, 369 parts proteids in lean meat must be consumed to 
maintain equilibrium. 

The proteids in the body are in two forms, circulatory and 
body proteids. The circulatory proteids are rapidly oxidized, 
while the body proteids are much more resistant. Thus, the 
amount of proteids oxidized by a starving animal will depend at 
first upon the quantity of circulatory proteids in the animal, 
which in turn depends upon the quantity of proteids previously 
fed. The quantity of proteids oxidized while an animal is 
starving, rapidly decreases until it becomes nearly constant. 

The amount of proteids destroyed the first day depends upon 
the previous ration, but after the fifth day it becomes nearly 
constant. 

Ammonium acetate, asparagin, and other nitrogenous, non- 
proteid bodies, have little or no value for maintenance. An 
animal fed upon them, together with starch, fat, etc., will starve 
to death for want of proteids. 



MAINTENANCE: RATION AND BATTENINGS 



439 



Value of Non-Protein for Maintenance. Non-protein nutrients, 
such as sugar, starch, fat, etc., fed alone, will decrease the destruc- 
tion of body proteids by a starving animal to a certain extent, but 
not entirely, and the animal will starve if so fed. A certain 
quantity of proteids is essential. The most practical maintenance 
ration is one which contains both protein and non-protein. 

Feeding for Maintenance. Work animals may be placed on 
maintenance rations during periods of idleness; fat cattle, be- 
tween end of fattening period and time of sale; grown animals, 
until the time of fattening begins; and sheep kept for wool. 
Young animals, cannot be placed upon a maintenance ration, as 
a gain of flesh is the normal condition with them. 

The maintenance ration must provide sufficient energy and 
sufficient proteids for replacement of flesh and fat, and the 
growth of hair, horn, skin, and hoofs. It must be adjusted to 
the size and condition of the animal, and other external condi- 
tions, such as we have discussed. 

On account of the small quantity of kinetic energy and the 
relatively high amount of heat required for maintenance, and also 
because the feed should be bulky in order to satisfy the appetite 
of the animal without carrying large amounts of nutriment, hays 
and straws may be largely used. 

Standards for Maintenance. The following are the amounts of 
food found necessary for maintenance per day and per 1,000 
pounds live weight : 





Total weight 
dry matter 


Proteids 


Productive 
value 


Nutritive 
ratio 


Steers . 


pounds 


pounds 
o f\ o 8 






Sheep, coarse breeds. . . 
Sheep, fine breeds 
Fat steers 


18-23 
20-26 


I.O 

1.2 


1.50 
2.08 
2.2 5 


1 9 
i 9 
i 8 

T 8 








1.75 ^.-^o 





These standards are based upon experiments such as those just 
cited. Sheep must receive enough protein to provide for growth 
of wool. Methods for calculating rations will be given in an- 



44O PRINCIPLES OF AGRICULTURAL CHEMISTRY 

other chapter. The nutritive ratio given in the table is the ratio 
of protein to non-protein, and not of proteids. 

Coarse feeds are largely used for maintenance purposes. As 
they almost invariably contain enough phosphoric acid and lime 
to supply the needs of the animal, the ash needs little attention. 
Such an animal requires per 1,000 pounds live weight about 45 
grams of lime and 22 grams of phosphoric acid in the food. 

Utilization of Nutrients for Production of Fat. The object of 
fattening the animal is to finish it for market. Some of the facts 
and principles upon which the fattening rations are based will be 
discussed. Only the food fed in excess of maintenance require- 
ments may be used in fattening. In the preceding chapter, we 
not only had the evidence that proteids, crude fiber, fat, and 
nitrogen-free extract could furnish fat, 1 but also the quantity of 
fat which each could produce. Other methods of experiment 
have been used to ascertain whether the nutrients of the food 
may be used for the production of fat. 

Hoffman 2 fed a dog (previously starved for some days) on 
370.8 grams of fat, and 49 grams of proteids (lean meat) per 
day. In five days the animal gained 4.2 kilograms and then con- 
tained 1352.7 grams of fat. The amount of fat present at the be- 
ginning of feeding was estimated at 150 grams as ascertained by 
examination of the dog. The maximum quantity that could have 
been formed from the proteids fed was 130.5 grams. The re- 
mainder of the fat, at least 1,072 grams, must have come from 
the fat eaten. 

The following experiments of Soxhlet 3 show that carbo- 
hydrates may form fat. Three pigs 5 to 6 months old were first 
fed alike for 321 days. One was killed then and the body sub- 
jected to analysis to ascertain its fat content. The remaining 
two were fed on steamed rice for 75 days and 82 days, 
respectively, the nutrients digested being determined by analysis 
of food and excrement as in digestion experiments. The animals 

1 Soskin, Exp. Sta. Record 8, p. 179. 
- Landw. Versuchs-stat., 1894. p. 475. 
:i Centralblatt f. Agr. Chem., 1 88 r, p. 57.1. 



MAINTENANCE: RATION AND FATTENINGS 



441 



were then killed and subjected to analysis. A quantity of fat 
equal to that in the pig first killed was subtracted, and the differ- 
ence assumed to represent the gain in fat. The results of the 
experiment are as follows : 





Pig No. i 


Pig No. 2 




kg. 

T AA 


kg- 
I 60 




1.44 

o 89 


OA r 










O ^ 


TIC 


Fat possible from proteids decomposed (assuming pro- 


^JJ 

I 78 


\ 68 


Fat in food fed 


O-7O 


^.VJ<-> 

O ~\A. 


Total fat possible from proteids and fat of food 


2 08 


A Q2 


Gain of fat by animal 


10 08 


22 l8 










8 oo 


18 16 









Thus, after allowing for the greatest possible gain of fat from 
the proteids and the fat fed, there remains a large quantity of fat 
which could come only from the carbohydrates. 1 

The fat of the animal has been found to be modified by the fat 
of the food to a certain degree. In one experiment, a fat con- 
taining iodine was fed, and was found in the body fat, and also 
passed into the milk. A portion of the fat of the food may be 
stored in the animal. The body fat of each kind of animal 
possesses characteristic properties ; the cow produces only cow 
fat; the dog, dog fat, etc. Under ordinary conditions, only a 
small part of the animal fat comes directly from the food ; the 
major portion is a product of the transformation of matter in 
the cells of the animal. Only when foods rich in fat, such as oil 
cake, corn, rice bran, etc., are fed, can the characteristics of the 
food fat be observed in the fat of the body or of the milk. It is 
usually the custom to finish the animal on feed which will give 
the desired characteristics. The fat of animals fed on cereals 
and grains rich in carbohydrates and poor in oils, is hard. A 
softer fat is obtained when linseed cake, peas, wheat bran, oats, 
etc., are fed. Animals exposed to cold have a softer fat than 
1 See also Bulletin 22, p. 271, Office Exp. Sta., U. S. Dept. Agr. 
29 



442 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



those kept in warmer surroundings. A pig kept in a pen at 
freezing temperature had a softer fat than similar pig kept in a 
pen at 30-35 C. 

Composition of Gain of Weight in Fattening. The composition 
of the increased weight in fattening has been studied in two ways : 

First, animals of different degrees of fatness, but otherwise 
comparable, were killed and subjected to analysis. 

Second, animals raised alike were selected, and some killed at 
the beginning, others at intermediate stages, others at the end of 
the fattening experiment. The bodies were subjected to analysis. 

The animals killed at the end of the experiment or during the 
process, were supposed to have originally had the same composi- 
tion as those killed at the beginning of the experiment. When 
the live weight of the animals and their percentage composition is 
known, it is a simple matter to calculate the composition of gain 
in material during fattening. 

The composition of sheep at different degrees of fatness was 
found at Rothamsted 1 to be as follows : 

PERCENTAGE COMPOSITION OF SHEEP. 





Lean 


Half fat 


Fat 


Very fat 


Offal 


6 n 




5 o 




Carcass 


14 8 


l 
14 o 


122 


* 

jo Q 


f?of 


T 7 




7C 6 


iv.y 

AS 8 


AcV| 


10. / 


^o-o 

32 


5O- U 

2 8 


4o' 
2 Q 


Water 




C7 7 


* 

CQ 2 


A1 A 


**y 

TC 2 




O/-O 




4o-4 


6o"* 


Total 


IOO O 


IOO O 


IOO O 


IOO O 













It is noted that there is a decided decrease in the percentage of 
water, a slight decrease in the percentage of proteids, and a large 
increase in the percentage of fat, during the process of the fatten- 
ing. With other animals than sheep, the results were similar. 

The following table shows one calculation of the composition 
of the gain in fattening, and illustrates the method of procedure. 
The part of the offal in the gain is calculated also. 
1 Bulletin 22, p. 249, Office Exp. Sta., U. S. Dept. Agr. 



MAINTENANCE RATION AND BATTENINGS 



443 



COMPONENTS OF A FAT AND A LEAN SHEEP, SHOWING THE 
COMPOSITION OF THE GAIN IN FATTENING. 





Very fat 
kg. 


I,ean 
kg. 


Gain 
kg. 


Percentage 
composition 
of gain 


Total weight 


108.6 

11.83 
49-74 
3-15 
38.23 
5-6o 


44-3 
6.56 
8.2 7 
I.4I 

25.38 
2.6 7 


64.3 
5.27 
41.47 

1.74 
12.85 

2-93 


100.0 
8.2 

64-5 
2.7 
2O.O 
A.6 




Kat 


Ash 


Water 


Off a l . 





The average increase in body substance on fattening, exclusive 
of offal, from the experiments on oxen, sheep, and swine at the 
Rothamsted Experiment Station is as follows: 

Proteids 7.5 

Fat 66.6 

Mineral matter 1.5 

Water 24.4 

IOO.O 

It is seen that the increase is mostly fat, only a small part being 
proteids. The nutritive ratio of this gain is 1 : 20. These 
animals were not entirely grown. Grown animals, if in fair con- 
dition, gain very little flesh (proteids) when fattened. 

Factors which Influence the Fattening Ration. A number of 
factors influence the fattening ration: 

Requirements for Maintenance. Since only the excess of the 
productive value of the food over the maintenance requirements 
may be used for fattening, anything which affects the mainten- 
ance requirements will affect the fattening ration. An increase 
in the maintenance requirements will decrease the gain in fat. 

Stall Temperature. On account of the heavy ration fed, the 
animal has a large excess of thermal energy, and the temperature 
of the stall may fall lower than when fed on a maintenance ration 
without affecting the amount of fat gained. But if the stall be- 
comes too cold, maintenance requirements are increased and the 
animal gains less fat. If the animal has to warm the water con- 
sumed in cold weather to the body temperature, the maintenance 
requirements may be considerably raised. A large proportion of 
the material otherwise available for fat might be so used. It has 



444 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

often been found profitable to warm the drinking water, especially 
for hogs. 

If the external temperature is too high, the animal may have 
trouble in disposing of the heat from the excess of thermal 
energy, and will then eat less of the ration. For this reason 
fattening in summer may be difficult ; in some parts of the South, 
animals fatten better when fed out of doors where the perspira- 
tion may evaporate freely, than when confined. It is also often 
advisable to feed light, rather than heavy fattening rations during 
warm weather. 

Condition of Animal. The fatter the animal, the more food 
required for maintenance, and the less the proportion of it avail- 
able for fattening. Thus the cost of the production of fat in- 
creases with the duration of the fattening process. 

Age of Animal. South Dakota 1 experiments show the follow- 
ing relation between feed consumed and gain in weight, for cattle 
of different ages. 





Pounds eaten for each pound 
of gain in live weight 


Concentrates 


Hay 


Yearling steers 


6. 7 

7-9 

8.5 


4-3 
4.6 


Two-year-old steers 







Excess Over Maintenance Requirements. Only the excess of 
food over the maintenance requirement can be used for produc- 
tion. The larger the excess, within the limit of the ability of the 
animal to use it, the more economically the food is used. For 
example, if a steer weighing 1,000 pounds that requires 1.5 pounds 
productive value for maintenance, is fed 2.0 pounds, then only 
0.5 pounds, or one-fourth of the ration is used for production of 
fat. But this animal should be able to use 3.0 pounds productive 
value, and in such case 1.5 pounds, or one-half of the value of the 
food is used for fat. The fat produced by the first ration will 
require twice as much productive value as that formed by the 
1 Bulletin No. 125. 



MAINTENANCE RATION AND FATTENINGS 



445 



I 

5 

fe 



& 



I 



^ 
< 



IK 

I 



s 



:? 



446 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



second. The second ration should produce the same results in 
two months that the first would give in five. In the latter case 
there is not only a greater expenditure for food, but also twice as 
long to feed and care for the animal. 

This may be put in another way. Suppose a steer 
weighing 800 pounds is fed on 5 pounds cottonseed meal and 20 
pounds cottonseed hulls per day. This ration would have a 
productive value of 1.55. The animal would have a maintenance 
requirement of 1.2, leaving 0.35 pound for fattening, which 
would produce about 0.5 pound gain in live weight per day. Sup- 
pose one pound corn meal is substituted for one pound cotton- 
seed hulls. The ration would gain 0.17 pound in productive 
value, which should cause a gain of about 0.25 pound in live 
weight per day. An addition of 2 pounds corn meal would thus 
double the gain in weight per day. 

Too heavy a fattening ration taxes the capacity of the animal, 
and decreases the production of fat. The excess interferes with 
the digestive processes and makes the fattening less successful. 
Experiments have shown that an excessive ration does not pro- 
duce as large gains as a ration adapted to the capacity of the 
animal. The following are results of two series of experiments 
by Morgan 1 on sheep, in which the quantity of protein was kept 
constant, but the carbohydrates were increased. The effect of 
the increase in the ration is to decrease the gain in weight. 

DIGESTIBLE NUTRIENTS FED PER 1,000 POUNDS LIVE WEIGHT. 





Protein 


Carbohydrates 


Daily increase 
in weight 


Experiment i 


pounds 


pounds 
ifi c 


pounds 
i cfi 




54 


1D O 
T Q Q 


3-5 
i 76 


Group C ' 


oO4 




3-7 


Experiment 2 
Group A 


04 

; 18 


21.3 

18 i 


79 

A 06 




^ 18 


2O 7 


* 8? 


OTOUD O 


c T S 




o-/ 




J. 10 


*J-J 


./u 



Quoted by Kellner, Die Ernahrung d. Landw. Niitzture, p. 414. 



MAINTENANCE: RATION AND BATTENINGS 447 

Feeding Experiments, The values of feeding-stuffs for fat 
production are often compared by means of feeding experiments. 
Feeding experiments have also been of great value in establishing 
standards of feeding for various purposes. Feeding experi- 
ments do not give such exact values as experiments in which the 
carbon and the nitrogen balance are determined, but they are very 
useful in their proper field. 

Two systems of feeding experiments are used. In the first 
system, the same groups of animals are fed upon the different 
rations in succession. The method is open to the objection that 
the effect of any ration will depend to a considerable extent upon 
the preceding rations, and the same feed may give entirely differ- 
ent results according^to the character of the feeding which precedes 
it. The feed, of course, affects the condition of the animal, so that 
the maintenance requirements vary, and the excess of the ration 
over the maintenance requirements, which is the portion used for 
the gain in weight, will depend upon the previous feeding. The 
results of the feeding will thus depend upon the previous feed, 
as well as on the ration being studied. 

The second system consists in dividing the animals into groups, 
and feeding to the different groups the rations to be compared. 
This method gives good results when properly used. Care 
should be exercised to have the groups exactly equivalent at the 
beginning of the test. The groups should consist of 10 or more 
animals. Each animal should be matched in age, form, live 
weight, etc., with another animal in the other group. The groups 
should be compared by means of a preliminary feeding period, in 
which the animals receive the same ration for thirty days or 
more. If each group makes the same gain on the same feed, 
the experiment proper may be begun; but if there is only a 
slight difference in gain, the groups should be rearranged, and 
another test made. 

The best results are secured when the ration is about three 
quarters of the standards. If the production is forced to its 
upper limit, or if more feed is given than the animal can utilize, 
the differences, due to the different feeds, may be insignificant. 



448 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

When different feeds are added to a basal ration, the productive 
value should not be altered by other compensatory additions. For 
example, if cottonseed meal is compared with gluten meal, and 
straw is added to increase the nitrogen-free extract for cotton- 
seed meal, the experiment would be unfavorable to cottonseed 
meal, because the nitrogen-free extract of straw is not equal to 
that of gluten meal. The rations should be weighed out for each 
animal, and fed in such order or with such preparation that they 
will be completely consumed. 

The live weight varies very much on account of irregular ex- 
cretion of dung, irregular elimination of urine, unequal con- 
sumption of water from day to day, etc. The animals should be 
weighed three days in succession, just before the midday meal, 
every ten days. Since the first weighings are usually of little 
value, on account of the animals being excited, the animals should 
be accustomed to the weighing as early as possible. 

The feeding period should not be too short. Two months is 
the minimum for fattening and work animals, but it is better 
to continue the experiment with fattening animals, until they are 
fully fat and then to make a slaughter test on them. Important 
observations are sometimes made only when the experiment 
is continued a long time. 

When comparing two feeds, equal quantities should be fed. If 
one feed is more palatable than the other, and the animals allowed 
to eat more, they will have a larger excess over their maintenance 
requirements, and the results will be more favorable to the more 
palatable food. 

Standards for Fattening Rations. Since fattening animals put 
on little flesh, it would appear that they require little more pro- 
teids than animals on a maintenance ration. The heavy ration 
fed, however, demands a quantity of digestive fluids composed 
largely of proteids. Since the digestibility of the food is de- 
creased if the nutritive ratio is too wide, the nutritive ratio 
should not be wider than 1 : 10. A ratio narrower than i : 4 in- 
creases the oxidation of matter in the body, and so decreases the 
production of fat. Numbers of experiments have been made 



MAINTENANCE: RATION AND BATTENINGS 



449 



comparing wide and narrow rations. Wolff, 1 for example, taking 
the average of 18 experiments, found sheep to make equal gains 
whether the nutritive ratio was i : 7 to 8, or 1 : 4 to 5. Lehmann 2 
compared i : 12 to 1:5, with equal results. There is thus a 
wider margin in the quantity of digestible protein which may be 
fed, and if protein is sufficiently cheap, it may be used for the 
purpose of producing fat. 

If the animal is not in good condition, the ration should be 
moderate at first and gradually increased, beginning with a nutri- 
tive ratio not wider than i : 6. 

The quantity of fat fed is not important, but if fed to 
ruminants in greater quantity than one pound per 1,000 pounds 
live weight, it is liable to decrease the appetite or cause digestive 
disturbances and interfere with the fattening. Pigs can use more 
than this amount. 

The fattening ration for steers should not exceed 3.6 pounds 
productive value per day and per 1,000 pounds, but may be lower 
than this, according to the time it is desired to take for the fatten- 
ing. Rapid fattening is less expensive than slow fattening. The 
increase in live weight in fattening diminishes in the course of 
the process, since the maintenance requirements increase with 
the increase in weight of the animals. The cost of production 
of gain in weight increases considerably towards the end of the 
fattening period. 

The following are the amounts of nutrients desirable for fat- 
tening, per day and 1,000 pounds live weight: 





Total 
weight dry 
matter 


Proteids 


Productive 
value 


Nutritive 
ratio 


Pigs 


33-37 
28-33 
24-28 

24-3 2 

22-30 
24-32 
22-30 


3-0 

2.8 
2.0 

1.6 

1.8 
1.6 

1.4 


6.8 
6-5 
5-o 
3-6 

3-0 
3-0-3-6 
2.8-3.4 


i : 5-5 
i : 6.0 
1:6.5 

i :4-5 

i : 6.4 

i : 5-5 
i : 6.0 




Final period 


Fattening sheep 


Fattening oxen 









1 Landw. Jahrbuch, 1896, p. 193. 

2 Landw. Jahrbuch, 1902, p. 162. 



45O PRINCIPLES OF AGRICULTURAL CHEMISTRY 

The fattening standard calls for that quantity of feed which 
gives the most rapid fattening. Any excess of feed over the 
maintenance requirements produces fat; the fattening standard 
gives the largest quantity which should be used. 

Practice of Fattening. Straw has little value for fattening 
purposes. It is so bulky that the animal cannot eat sufficient 
feed for best results, when the straw is used in quantity in the 
ration. Even good meadow or clover hay has too great bulk in 
proportion to its nutritive content to be used in quantity in 
intensive fattening. Good pasturage is excellent for fattening, 
and in exceptionally favored localities may be the only fattening 
feed. But usually the animal is finished on more concentrated 
feed. 




Fig. 93. Carcass of hogs fed on, (A) corn and, (B) barley. 
North Dakota Station. 

In feeding large rations, care must be taken to render the food 
palatable, so that the animal will be induced to eat as much as 
possible. The use of well-flavored feeds, salt, molasses, or 
special preparation of the feed, may be of advantage in causing 
the animal to consume the desired amount. 



MAINTENANCE RATION AND BATTENINGS 451 

Anything that disquiets the animal, as irregular meals, rough 
treatment, insufficient bedding, etc., increases the oxidation of 
matter and decreases the production of fat. Armsby has found, 
by direct measurements, that an animal standing consumes about 
one-fourth more energy than when lying down. The temperature 
of the stall should be kept low rather than high, as the digestive 
processes of the fattening animal evolve a considerable amount of 
heat, which is partly radiated and partly carried off by evapora- 
tion of water from the body. If insufficient ventilation, heavy 
hair, or fat layers under the skin decrease evaporation, the animal 
instinctively consumes less food. 

The effect of fattening is chiefly perceptible in increase of live 
weight. At the beginning, the weight increases rapidly for a 
few days, due to filling the body with food and water. After the 
fattening proper has been begun, regular weighings, which are 
best made before the morning meal, shows the progress of the 
fattening. According to the quantity of the feed, a tolerably 
constant increase in weight occurs for a longer or shorter period. 
The weekly increase then gradually becomes less and less, until 
finally it disappears. When the increase of weight ceases, it 
does not prove that fattening has ceased. Fat continues to be 
deposited for a time, taking the place of water, until the capacity 
of the tissues is satisfied. The cost of production of the increase 
of fat and flesh increases considerable towards the end of the 
fattening period. 

Another cause of the decreased production with length of fat- 
tening period is the increase in the maintenance requirement of 
the animal, which takes place more rapidly than the increase in, 
weight. 

For the maintenance of fattening animals, rations much smaller 
than the fattening ration suffice, and should depend on the degree 
of fatness. The transition to a maintenance ration should be 
gradual. 

' Hogs i- l /2 years old require no specially high amounts 
of protein. As they have a high digestive power for 
carbohydrates the nutritive ratio may be as wide as i : 10. 



45 2 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

Excessive quantities of fat in the feed may injure the quality of 
the bacon. At the beginning of the fattening period, hogs may 
consume as much as 30 pounds food per 1,000 pounds weight, but 
as the fattening progresses, which ends in 3^ to 4 months, the 
consumption of food sinks considerably, until towards the end, 19 
to 20 pounds are used. The ration for the different periods of 
fattening are shown in the table previously given. 

If the hogs are in poor condition, a preliminary period of 2 to 
4 weeks with 4 pounds proteids is advisable. The proteids should 
also be increased if the animals are not fully grown. 



CHAPTER XXII. 



FEEDING WORK ANIMALS AND GROWING ANIMALS. 

Work requires energy, which is produced by the oxidation of 
organic matter within the tissues. It has been known for a long 
time that animals use up more oxygen and give off more carbon 
dioxide while they are doing work than when they are at rest. 
A considerable amount of investigation has been required to 
ascertain the value of different nutrients for producing work. 

Nutrients Oxidized During Work. The effect of work upon 
the proteids of the body can be studied by determining the quan- 
tity of nitrogen in the urine during periods of rest and periods 
of work. If the work necessarily involves a destruction of pro- 
teids, an increased elimination of nitrogen will result. Experi- 
ments have given contradictory results. For example, a dog fed 
on meat eliminated the following quantities of nitrogen, during 
three consecutive periods : 

Nitrogen in urine 
grams per day 

No work 54.9 

Working 48.6 

No work 55.0 

In other experiments, the proteid metabolism was considerably 
increased. The results depend on the ration being fed. If the 
ration supplies sufficient carbohydrates and fat to furnish energy 
for the work, proteids will not be oxidized, but if the ration is 
deficient in this respect, proteids will be oxidized to furnish the 
necessary energy. 

Animals at work exhale increased amounts of carbon dioxide, 
even though there be no increase in the quantity of nitrogen 
eliminated. This is evidence that fats or carbohydrates are be- 
ing used for the production of work. Further evidence that 
starch and other non-proteids can be used for the production of 
work, is afforded by experiments, such as the following: 

A working animal was fed on a ration poor in protein. In 
a second period the same ration was fed with the addition of 
starch and the amount of work was then increased until the 



K was 



454 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

same amount of nitrogen was eliminated as in the first period. 
When the same amount of protein was being decomposed, it was 
found that the animal was doing more work. That is, the starch 
was used for production of work. A similar experiment showed 
that oil enabled the animal to do more work. An experiment 
showing that proteids may be used in work was as follows : 
A horse was fed a ration rich in protein, and put on light work 
for about ten days. The work was then trebled, being a hard 
day's work. The excretion of nitrogen immediately increased 45 
grams per day, and the live weight of the animal gradually 
decreased. 

Exercise may cause muscular growth. For example, Atwater 
and Benedict found that a man at rest lost 0.7 gram nitro- 
gen per day and 7.8 grams fat; but when working, he gained i.i 
gram nitrogen and lost 48.4 grams fat on the same ration. 

Respiratory Methods. The following is a method 1 for deter- 
mining the consumption of energy during various kinds of work, 
which has also been of service in other studies, such as ascertain- 
ing the amount of energy involved in chewing. The animal to 
be studied is subjected to a surgical operation, and a tube inserted 
into its windpipe, so that while air may be inspired freely, the 
expired air passes through a rubber tube into a suitable vessel for 
collection. The expired air is measured, and the quantity of car- 
bon dioxide and oxygen in it determined. The quantity of nitro- 
gen eliminated in the urine is also determined, and shows how 
much proteids have been oxidized. When fats are burned, for 
every i cc. of oxygen which disappears, 0.707 cc. carbon dioxide 
is formed. With carbohydrates, I cc. oxygen is replaced by i 
cc. carbon dioxide. Hence the ratio of carbon dioxide to oxygen 
(corrected for proteids consumed) allows us to calculate the 
relative proportions of fats and carbohydrates oxidized. This 
method cannot be considered as highly accurate. By means of 
it, the expenditure of energy caused by walking or running on a 
smooth slope, going up-hill, drawing a load, etc., have been 
studied. 

1 Hagemann, Exp. Sta. Record 10, p. 813. 



FEEDING WORK ANIMALS AND GROWING ANIMALS 455 

Energy for Work. Work is measured in meter-kilograms, or 
foot-pounds. A meter-kilogram is one kilogram raised to the 
height of one meter. Exact experiments have shown that one 
large calorie, if completely transformed into kinetic energy, can 
perform 425 meter-kilograms work. Experiments have shown 
that an animal can utilize for work about one-third of 
the available energy in the food. In ten experiments on 
a man climbing stairs, the percentage was 33.1 per cent., 
and in eighteen experiments on a horse, it was 29 to 
38 per cent. It is estimated by Kellner that, after allowing for 
all losses, I gram of pure protein digested will yield 656 meter- 
kilograms work, i gram of fat 1,214, and I gram of carbohydrate, 
533. The rate of work, and the kind, both affect the consump- 
tion of nutrients, also the shape of the animal as related to the 
kind of work done. Being accustomed to a particular kind of 
work also decreases the oxidation of nutrients. It is said that a 
man working a treadmill oxidized 25 per cent, less nutrients after 
56 days work, though doing the same quantity of work per day. 
According to the structure of the working animal, the develop- 
ment of its muscles, and the position of the extremeties doing 
the work, the portion of the energy which appears in the work 
varies. For moving their own bodies, Zuntz found a variation 
of 0.284 to 0.441 calories per i kilogram weight and I meter dis- 
tance with different animals. Fatigue increases consumption of 
energy. 

Rations for Working Animals. Animals when at work require 
little more proteids than when not at work; a nutritive ratio of 
i : 7 is sufficient. 

Horses will work off nutrients fed in excess of the maintenance 
ration by increased movements in the stall, so that it is not 
possible to assume that the maintenance ration is secured when 
an equilibrium between income and outgo is secured. 

Standards for Work Animals. Two methods are used for 
studying the needs of working animals. One is to determine the 
maximum amount of work which can be secured with a given 
ration without loss of condition. The other method consists in 



456 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



starting with an insufficient ration, and gradually increasing it 
until it is sufficient to maintain the animal under the required 
conditions. Both these methods have been used to a consider- 
able extent for studying the rations for working horses. 

The following are standards for working animals, per day 
and 1,000 pounds live weight: 





Total 
weight dry 
matter 


Proteids 


Productive 
value 


Nutritive 
ratio 




T Q y-j 


Pounds 


Pounds 


ft 




10 ^3 

2T ift 




3 


6.9 

ft a 




2\ 28 


4 


3Q 


b.9 

A ^ 








.5 






22 28 




9 








1.4 
I 8 


** 




6 o 




*o 6^ 




* 





A working animal can utilize somewhat more fat than a fatten- 
ing animal. 

Feeding Horses. 1 In some large horse establishments only 
oat or wheat straw are used, as fewer cases of colic occur than 
when hay is used. Oats, barley, and corn are used for con- 
centrates, oats being preferred in northern climates and corn in 
southern. Corn appears to be equally as good as oats. Care 
should be taken that the food is not musty or damaged, and horses 
should be allowed 2 to 2^/2 hours for eating and rest. 

Growing Animals. Growth is the normal condition of a young 
animal. Equilibrium between income and outgo would be an 
abnormal condition, if it could be secured. 

With proper food, young animals gain in weight much more 
rapidly than mature animals with the heaviest fattening ration. 
The animals do not have smaller maintenance requirements, but 
they eat more in proportion to weight, and are able to store a 
greater excess over their maintenance requirements, than grown 
1 See Bulletin 125, Office Exp. Sta., U. S. Dept. Agr. 



FKKDING WORK ANIMALS AND GROWING ANIMALS 



457 



animals. A calf two to three weeks old has been known to re- 
tain 73 per cent, of the proteids consumed. As the animal grows 
older, the percentage of the food retained in the body decreases. 
The proportion of food eaten to live weight also decreases; thus, 
a larger proportion of the food must be used for maintenance. 

The following experiments of Weiske 1 were begun with lambs 
four months old, and carried out in 7 periods of i^ months each. 
The nutritive ratio was 1 : 4.6 at first and later, when about 15 
months old, was i : 6.3. 

PER 50 KILOGRAMS LIVE WEIGHT. 





F 


?d 




Daily gain 




Period 


Dry 
matter 


Protein 


Live 
weight 


Nitrogen 


Lime 


I 


Grams 
I IOI 


Grams 
1 88 


Grams 
-161 


6 75 


.20 


H 


I O71 


161 


o u o 

27T 


u - /o 

c T A 


37<S 


HI 


QI 7 


lu o 

1 1Q 


2O6 


0- 1<J 

1 71 


./u 
i 6^ 


iv 


V 1 / 

QOI 


J 07 

T-J 


1 r 7 


6" I * 
417 


5-D 


v 


SOQ 


1 O 


X6 




- 1 / 


VI 


ouy 
762 


i ly 

T08 


ftl 


.00 


2.50 
-> fi-j 


VIII 


/^ 


0,S 


3 

Qr 


94 


2.03 


IX 


/5o 


y 
61 


O 


77 

T 8/1 






o/* 








57 



The quantity of food per 50 kg. weight consumed, decreases 
with the age of the animal, and the gain in weight decreases much 
more rapidly. Thus, the food eaten in the 8th period is 7/11 of 
that in the first, while the gain is only ^. 

The increase in weight of young animals is largely flesh, body 
organs, and bones. They thus require considerable protein. 
Young animals also require more mineral matter than older ones, 
to build up the bones. Lime and phosphoric acid especially are 
required. The preceding table shows the decreased retention of 
lime with age of the animal. 

The following data compiled by Henry from the results of a 
number of feeding experiments with pigs at various Experiment 
Stations, shows the increase in the quantity of food required for 
a pound of gain as the animal grows older : 
1 Landw. Jahrbucher, 1880, p. 205. 
30 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 

Feed eaten per 

Weight 100 pounds gain 

pounds pounds 

15-50 293 

50-100 400 

100-150 437 

150-200 482 

200-250 498 

250-300 511 

300-350 535 

Mineral Matter. Growing animals retain from 40 to 60 per 
cent, of the lime and phosphoric acid in the food. As the skeleton 
of a calf a year old contains on an average 17 pounds lime and 15 
pounds phosphoric acid, the animal must take up 21 grams lime 
and 19 grams phosphoric acid per day, and the food should con- 
tain 40 to 60 grams each of these to meet the requirements. The 
body of a pig contains about 1.15 per cent, lime and i.io per cent, 
phosphoric acid, which would be equivalent to a daily increase of 
3.8 grams lime and 3.7 grams phosphoric acid for a pig a year old 
weighing 250 pounds. As about 3 grams must be present in the 
food for i gram stored up, the animal will need 12 grams per 
day each of lime and of phosphoric acid. It is important to pay 
attention to the mineral matter in the food of growing animals. 

Feeding Young Animals. Animals intended for fattening 
should be fed more liberally than those that are to be used for 
milk or work. But with all animals the natural development 
should proceed normally. It is a serious mistake to assume that 
improper feeding when young can be counteracted by liberal 
feeding afterwards. Young animals fed with a deficiency of 
proteids yield a carcass of poor quality overcharged with fat. 

The extreme sensitiveness of young animals requires care in 
avoiding all injurious influences, in food, as well as in care and 
protection. Food should be supplied often on account of the 
limited capacity of the animal. Regular feeding, clean vessels 
for eating and drinking, good care of the skin, a well ventilated 
stall, and clean, dry bedding are requisites to satisfactory growth. 
Drafts, cold, and wet, which affect young animals much more than 
old ones, are often very injurious. Sufficient exercise is neces- 



FEEDING WORK ANIMALS AND GROWING ANIMALS 459 

sary for the full development of bones and muscles, and increases 
the resistance to adverse influences of weather and disease. 

Calves. Calves should be allowed mother's milk for the first 
few days. Calves intended to be used as milch cows should receive 
daily 1/7 to 1/8 of their live weight of full milk, for at least 
three weeks. Animals to be used for fattening should receive 
daily 1/5 to 1/6 of their weight of milk for about six weeks. 
Fresh milk, while still warm, is best. Ten liters milk or 1.2 kilo- 
grams solids produce about I kilogram live weight increase. The 
increase is, of course, proportional to the excess over the main- 
tenance requirements and not to the live weight. 

Other food should be introduced gradually. Skim milk may 
replace the full milk gradually, replacing the fat lost in skimming 
by a paste made of linseed or oat meal, 25 to 30 grams, to y 2 liter 
of milk. Later linseed cake, bran, etc., may be used. Sour milk 
should be introduced gradually. 

Calves have only one stomach and can utilize only easily diges- 
tible food. As they grow older, other stomachs develop and they 
can then use hay, etc. The animal gradually becomes accustomed 
to hay. At the end of the third month, beets, straw, softened 
oats, barley or pea meal, oil meal, malt germs, etc., may be fed. 

When milk alone is fed, an addition of about 15 grams of pre- 
cipitated chalk per day has been found beneficial. There is sel- 
dom a deficiency of phosphoric acid, but if straw and much grain 
is fed, there may not be enough lime in the food. 

Lambs. Lambs are usually weaned from 3 to 4 weeks after 
birth. Good meadow hay, and soaked oats, are fed and not too 
cold water. They should be allowed to suck often, at first. 
Sudden changes from stall to pasture are injurious. Lambs thrive 
on pasture. They require stronger food than calves. 

Swine. Pigs suck 6 to 8 weeks, but when 2 to 3 weeks old 
they begin to eat. They may be given unground barley or wheat 
grains or soaked oats, also some wood charcoal, hard coal, earth 
or sand. After three weeks, whole cow's milk heated and diluted 
y 2 with water, may be fed. Milk and grain contain enough phos- 
phoric acid, but not enough lime. It is well to add some pre- 



460 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



cipitated chalk to the ration, which should be increased gradually 
from 8 to 10 grams per day. 

Experiments have shown that a nutritive ratio of 1 : 4 is best 
until the pigs are 5 months old, as it gives the greatest increase of 
live weight for the food consumed. After this age, the ratio 
i : 6 is better. 

Standards for Growing Animals. The following are standards 
for feeding growing animals : 

PER DAY AND 1,000 POUNDS LIVE WEIGHT. 



Pounds 
Total 



Proteids 
pounds 



Productive 

value 
pounds 



Nutritive 
ratio 



(I) Growing cattle, for milk cows 
or work: 



Age 2- 3 months 23 

" 3-6 " 24 

" 6-12 " 26 

" 12-18 " 26 

" 18-24 " 26 

(II) To be fattened: 

Age 2- 3 months 23 

" 3- 6 " 

" 6-12 " 26 

" 12-18 " 26 

" 18-24 " 26 

(III) Growing hogs, to be fattened: 

Age 2- 3 months 44 

" 3-5 " 36 

" 5-6 " 32 

" 6-8 " 28 

" 9-12 " 2 5 

Growing hogs, for breeding: 

Age 2- 3 months 44 

3-5 " 36 

11 5- 6 " 32 

" 6-8 " 28 

" 9-12* " 25 



3-4 
2.8 

2-3 
1.8 



4-5 
3-5 
2.8 

2.2 
1-5 



6.2 

4-5 
3-5 
3- 
2.4 

6.2 

4.o 



4-6 
3-7 
3-i 
2.6 

2-3 



4-9 
4-3 
3-6 
2.8 

2.5 



8-5 
8.0 
6.6 
6.1 
5-0 



8-5 
6.8 
5-8 
5-0 
3-9 



4-6 

4-9 
6.0 
7.0 
8.0 



4.4 
4-6 
5-5 
6-5 
7-5 



4.0 
5-0 
5-5 
6.0 

6.5 



4.0 
5-0 
5-5 
6.0 

6.5 



CHAPTER XXIII. 



FEEDING MILK COWS. 

Milk cows are fed for the purpose of producing milk or butter 
fat. It was formerly believed that milk is extracted directly 
from the blood of the cow. But casein and milk sugar, which are 
constituents of the milk, cannot be extracted from blood, because 
they are not present in blood. Apparently, milk is elaborated 
from the blood and lymph by chemical changes within the cells of 
the udder. 

Factors which Influence Milk Production. A number of fac- 
tors influence the quantity and composition of the milk. 

Breeds of Animals. Milk cows are divided into two groups of 
breeds, those giving relatively large quantities of milk with 
moderate fat content, and those giving less milk with a higher 
percentage of fat. To the first group belong the Holsteins, 
Ayrshires, Durhams, etc., and to the second, the Jersey and 
Guernsey. The average by Konig of about five hundred analyses 
of milk from animals belonging to these two groups, is as follows : 





Holstein group 


Jersey group 


Water 


per cent. 
87 AQ 


per cent. 
86 87 


ProteiHs 


/'4y 




Fat 


4/ 


3 




4 86 


4- u / 


Ash 


O 72 


O 7fS 




u. / ^ 





Individuality. Individuals of the same breed vary decidedly in 
the quantity and composition of the milk they give. For example, 
a study of each individual in a herd of 16 cows by Hitscher, 
showed the following differences : 





Minimum 


Maximum 




270 days 
2,330.0 kg. 
74.4 kg. 
2.63 


390 days 
4,702.0 kg. 
149-3 kg. 
3.81 











462 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



The best cow gave twice as much fat and milk as the poorest. 
Some cows are very profitable, while others are fed at a loss. It 
is important to test the individuals of a herd; the unprofitable 
animals should be sold, and the feed of the others adjusted to the 
quantity of milk produced. 

Fluctuations. The amount and composition of the milk from 
the same cow may vary considerably from day to day. Thus, 
Fleischmann 1 found by daily measurement and analysis, that the 
amount and composition of the milk from the same cow, varied 
as follows : 





Total quantity 
of milk 


Percentage 
of fat in milk 


April 
Minimum 


Kilograms 
IO 4 


2 76 






/ 

-, ,f. 




112 


o-4 

3O7 


May 


8 7 


U J 

2 62 


Maximum 


o./ 




Average 


L 6' / 


y*5 




1 1 .y 


.^u 



The table shows a variation of nearly 25 per cent, between the 
maximum and minimum for April, and 50 per cent, for 
May. The milk from the other cows in the herd varied also, but 
not on the same days, showing that the variations were not due 
to factors which influenced the entire herd alike, but to individual 
differences. 

Period of Lactation. The amount of milk given decreases with 
the time the animal has been giving milk, but the decrease 
varies with the animal. With some cows the decrease is 
regular and gradual, others give the same quantity for a long 
time and then suddenly fall oft". The following table from 
Fleischmann's experiments, shows how the milk may decrease 
with period of lactation, and it also shows that the percentage of 
fat increases. Cow No. I behaves somewhat differently from 
1 Lanclw. Jahrbuch, 1891. 



FEEDING MILK COWS 



4<'>3 



<0 

5i 



I 






1 

p- 






i 






464 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



cow No. 2, the decrease with the period of lactation taking place 
more regularly. 

EFFECT OF PERIOD OF LACTATION ON QUANTITY AND 
COMPOSITION OF MILK. 





Average quantity 
of milk per day 


Average percentage 
of fat in milk 


Cow No. i 


Cow No. 2 


Cow No, i 


Cow No. 2 


Anril 


II. 6 
12,0 
I0. 5 

8.8 
9-7 

9-i 

7-7 

6.6 
5-i 

2.2 


14.4 

J 5-9 
16.6 

12.8 

12.9 

10.5 
8.5 

6.7 
5-6 

2.8 


3-0 
3-3 
3-4 

3-5 

3-6 

3-7 
3-4 

3-8 
4-3 

5-8 


3-5 

3.1 

3.0 

3-2 

3-3 

3-6 
3-4 

3-5 
3-8 

4.7 


May 




Tulv . 




September 


October 











Age. The quantity of milk appears to increase slightly up to 
the fifth calf, and then decreases slightly. The fat content ap- 
pears to remain constant for a long time. 

Frequency of Milking. The more frequently the cow is 
milked, the greater the quantity of milk, provided the milking is 
not done so often as to irritate the udder. This is shown by the 
following experiment of Kaull i 1 



Period of milking 


per milking 


Milk per day 




kilograms 

3-81 
2.46 
2.06 

.66 

.07 


kilograms 

76 
9 .8 
12.4 
14.6 
I4.I 













As the udder fills, the formation of milk decreases. There is, 
1 Ber. d. Landw. Inst., Halle, 1891. 



FEEDING MILK COWS 



465 



however, a tendency for the capacity of the udder to adjust itself 
to the quantity of milk produced by the cow. According to 
Fleischmann, from 6 to 7 per cent, more fat and milk are secured 
by three milkings instead of two. The number of milkings should 
depend upon the cost of the milking and the value of the milk. 
Four milkings may sometimes be justified with fresh cows of 
high productiveness, but under ordinary conditions not more than 
three, and often only two should be made. 

The shorter the periods between milking, the richer the milk 
in fat and solids. Thus, when three milkings were made, the 
composition of the milk was found to be as follows in an experi- 
ment by Fleischmann : 

COMPOSITION OF MILK. 







Dry matter 


Fat 


4. oo A M 




per cent. 
II SI 


per cent. 
2 7Q 






1 1 7Q 


3QC 


7 oo P M 




12 AA 


1 76 











Portion of the Milking. If milk is gathered in fractions, and 
subjected to analysis, the first portions are found to be poorer in 
fat and solids than the succeeding portions. The following re- 
sults were secured by Boussingault i 1 

COMPOSITION OF SUCCESSIVE FRACTIONS OF MILK. 







Weight 
of fraction 
grams 


Peicentage 
of dry 
matter 


Percentage 
of fat 
















628 


7 


L. /U 








10 8s 









' " D 










6c 


1 1 61 







6 . . . . 


1 T C 


I 2 67 


14 

4 08 






0*0 







Not only are the strippings very rich in fat, but any milk left in 
the udder decreases the amount secreted. Hence all the milk 
possible should be removed at each milking. 
1 Ann. Chim., et Phv., 1866 



466 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

Work. Working the cow decreases the quantity of milk and 
fat produced, while the percentages of protein, fat, and ash in- 
crease. The effect depends upon the amount of work and the 
feed of the animal. Light work does not appear to decrease the 
total production of dry matter. 

Palatability of Food. It has been found that palatable food 
increases the yield of milk. In experiments in which two rations 
equal in feeding value were fed, the one tasteless, the other of 
well flavored hay, etc., the second ration always gave better re- 
sults than the first. 

Other Conditions. The milk secreting organs are closely re- 
lated to the nervous system. Rough treatment, disturbances, in- 
sufficient bedding, a cold stall, and other similar conditions de- 
crease the quantity of milk and fat produced. 

Methods of Investigation. In studying the effect of various 
conditions upon the production and composition of milk, it is 
necessary to eliminate the influence of all factors except the one 
to be studied. Some of these factors, such as the kind and fre- 
quency of milking, may be eliminated by treating the animals 
alike. Others, such as individuality, may be compensated for 
by taking a sufficient number of animals. Two systems of experi- 
ment 1 are in use the period system, and the group system, which 
correspond to the methods used for feeding experiments on 
fattening animals. 

The Period System. Ten or more cows are fed upon a standard 
ration for a period of two or three weeks. Next the cows are 
fed on the rations to be tested during three periods or more of 
the same length. The standard ration is then fed for another 
period. In each period, the production of milk and fat is deter- 
mined. From the production of fat and milk during the first and 
the last periods, we calculate the quantity which should be pro- 
duced during the intermediate periods, assuming that a regular 
decrease in production takes place. We compare the calculated 
production with that actually found to occur, and the difference 
gives the effect of the ration we are testing. 

1 See Kellner, Ernahriing d. Landw. Nutztiere, p. 500. 



FEEDING MII^K cows 467 

For example, suppose the .results with the standard ration 
during the first and fifth period of 20 days each, are as follows : 

First period, average 14.27 kg. milk and 4.38 grams fat per day 
Fifth period, average 13 63 kg. milk and 4.22 grams fat per day 

Decrease 0.64 kg. 0.16 kg. 

From the middle of the first to the middle of the fifth period is 
So days, or four periods. The decrease is thus 0.16 kg. milk 
and .04 grams fat for each period, and if the same ration were 
continued, the daily production for each period should be : 

Period i (found) 14.27 kg. milk and 4.38 grams fat per day 

Period 2 (calculated) 14.11 " " 4.34 " " 

Period 3 13.95 " " 4.30 " 

Period 4 13-79 " " 4.26 " 

Period 5 (found) 13.63 " " 4.22 " " 

The actual production with the ration being tested during the 
intermediate periods is compared with the calculated production. 
For example, if the production is 13.00 kg. milk and 4.10 grams 
fat in period 2, the ration fed has decreased the production i.n 
kg. milk and 0.24 grams fat. 

This method assumes a regular decrease in the production dur- 
ing the period of lactation. This assumption may or may not be 
true with one or two animals, but with eight or ten cows, it is 
practically true. 

The difference in the condition of the animal due to the 
previous feeding also has some effect upon the quantity and 
quality of the milk. 

Group System. This corresponds to the group system for fat- 
tening experiments. Each cow should be matched in race, age, 
weight, period of lactation, quantity and composition of milk 
against similar animals in the other groups. The groups are fed 
alike for a preliminary test period of 30 to 60 days, during which 
the yield and composition of the milk is estimated. If any 
differences in the groups appear, the cows should be rearranged, 
or new animals brought in, and another test made. When each 
group makes the same production with the same ration, the ex- 



468 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

periment is begun. The composition and quantity of the milk is 
then determined for a period of ten days. A test period follows in 
which the feeds to be tested are compared. One method of pro- 
cedure is as follows : Suppose Indian corn and Kaffir corn are 
to be compared. All groups are fed roughage, concentrates, and 
equal quantities of Indian corn and Kaffir corn during the pre- 
liminary period. At the beginning of the test period, Group A 
receives Kaffir corn in place of Indian corn and Group B Indian 
corn in place of Kaffir corn. Group C receives the same ration 
as before, containing equal parts Kaffir corn and Indian corn. 
Including the transition period, the feeding test lasts I to 2 
months, and every 8 to 10 days, as before, the average milk pro- 
duction is determined. In the last 10 days of the period the 
composition of the milk is also determined. An after period of 
i to 2 months follows, in which the food is the same as in the 
preliminary feeding period. The live weight is also to be de- 
termined on three successive days at the end of each period and 
in each sub-period. All factors except the feed tested should 
remain constant. 

Effect of Nutrition on Milk Production. The composition and 
quantity of milk depends ; first, upon the capability of the animal 
and the state of lactation ; and secondly, upon the food. The 
animal cannot increase the milk flow above the limits of the 
capacity of the animal. An excess of feed will go into body fat. 
A deficiency of food will decrease the milk flow, shorten the 
period of lactation, and may permanently injure the productive- 
ness of the animal. The food should be adjusted to the greatest 
quantity of milk possible to be produced and should be decreased 
gradually during the period of lactation. When the ration is 
reduced from a sufficient to an insufficient one, the milk glands 
do not respond immediately to the change, but they consume more 
or less body substance for the production of milk, and the condi- 
tion of the animal becomes visibly worse. This fact is observed 
so often with cows fresh in milk, that many believe that cows 
must always become thinner after calving. But the effect of in- 
sufficient food soon shows in a decrease in the quantity of milk 



FEEDING MILK COWS 



and the percentage of fat and dry matter, 
secured the following results : 



469 
For example, Fleischer 1 





Total 
milk produced 
per day 


Calculated-' 
production 


Decrease 




kilograms 


kilograms 


kilograms 




M-oO 


12 7O 


* 6c 


Period 3, insufficient food plus oil . 
Period 4, insufficient food plus bean 


V- u o 
8.8 5 

9T C 


12.05 
1 1 ^O 


o- u o 
3.20 

2 1^ 




A O 
IO IO 


IO I 5 * 


*'OO 











There was also a falling off in condition of the animal. The 
insufficient food decreased the milk nearly 30 per cent. 

Insufficient food also decreases the ability of the udder to 
secrete milk, which decrease may become permanent if an in- 
sufficient ration is fed for a long time. The decrease in produc- 
tion naturally occurring in the course of lactation, is accelerated 
by insufficient food, and diminished by abundant food. 

If we start with a very insufficient ration, and increase it, the 
production of milk will increase at first in proportion to the addi- 
tions, and then the increase in milk will be less for each equal 
increment of food, until no effect at all is secured. After a cer- 
tain amount of milk is produced, every increase of production re- 
quires a much larger amount of food, increasing quantities of 
which are stored as body fat. The highest milk production is 
associated with an improvement in condition. 

The greater the productiveness of the animal, the greater is 
the response to liberal feeding. For example, Kuhn 3 determined 
the effect of equal additions to the ration of cows having different 
productiveness, to be as follows : 

1 Jour. f. Landw., 1871, p. 371 ; 1872, p. 395. 
- Periods of different length. 
3 Jour. f. Landw., 1876, p. 190. 



470 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 





Cow No. i 


Cow No. 2 




kilograms 


kilograms 


Increase caused by addition of 1.5 kg. bean meal. . 
Increase caused by addition of 3.0 kg. bean meal . . 


11.77 
0.92 
2.40 


4O 

0-53 

I.OI 



The same quantity of bean meal produced twice as much in- 
crease in milk with cow No. i as with cow No. 2. 

Effect of Proteids. The effect of protein upon milk flow is 
studied by replacing feeds poor in proteids by those richer in 
proteids. For example, Fjard and Friis 1 replaced barely meal, 
which is poor in proteids, by oil cake rich in proteids, in a number 
of experiments on 8 farms and 1,152 cows, with the following 
average results: 





Group A 


Group B 


Group C 




I 08 




i 18 






J '*3 


1.38 






11 4o K s- 


1 I ./U K.g. 



Increase of proteids thus increased the quantity of milk. It 
had, however, no effect upon the composition of the milk. From 
these and other experiments, it is concluded that proteids exert 
a great influence upon the quantity of milk secreted. The water 
content of the milk, and the percentage composition of the dry 
matter are affected only when proteids are fed for a long time in 
quantities considerably exceeding the needs of the animal. In 
such event, the water content increases and the fat decreases. 
Ammonia salts can apparently be used for production of milk 
when fed in a ration poor in nitrogen but rich in carbohydrates. 

Nitrogen-Free Nutrients. Since fat and carbohydrates may 
promote flesh production indirectly or pass into body fat, it is 
evident that they may influence the milk glands and milk pro- 
duction. If the ration contains enough proteid but not enough 
carbohydrates or fat to induce the highest production, the milk 
production would not reach its highest limits, but a part of the 
1 Jahresber, f. Agr. Chem., 1893, p. 394. 



FEEDING MILK COWS 



471 



protein must replace fat or carbohydrates. The addition of 
carbohydrates or fat should, in such case, increase pro- 
duction. If there is sufficient proteids and the nitrogen- 
free nutrients are increased, the result depends upon the 
nutrition of the animal and the capacity of the milk 
glands, and also upon the depression in digestion of proteids 
caused by the additions. If the latter occurs to a great extent, a 
decided depression in milk yield will take place, while with more 
proteids in the ration, a less decided effect will be produced. With 
poorly nourished but productive animals, the additions would 
cause an increase in milk due to better nutrition, which would 
not appear in the case of a better nourished or a less productive 
animal. The result of the addition would therefore be different 
according to conditions, and experiments may give contradictory 
results. 

Both carbohydrates and fat of the feed take part in the pro- 
duction of milk fat. For example, from an experiment of W. H. 
Jordon, 1 we can calculate the maximum quantity of fat possible 
to be formed from the fat fed and the proteids fed, and we know 
from analyses the quantity of fat in the milk : 





Experiment i 


Experiment 2 


Fat fed in feed 


kilograms 


kilograms 


Pat possible from proteids 


'5 

7 X 


T7 8 


Total 


/ 


17.0 


Fat found in milk 


6 

17 6 




Excess, which must have been made from carbo- 
hydrates etc 


1 /.U 

Q i 


37-7 




-3 


17.7 



The increase of live weight showed that the animal did not lose 
weight. After allowing for all the fat possible from protein and 
fat in the food, there still remains a considerable amount of fat 
which could only come from carbohydrates. 

Increase of carbohydrates does not affect the fat in milk. Ex- 
1 Bulletin 197, New York Geneva Station. 



4/2 PRINCIPLES OF AGRICULTURAL CHEMISTRY 

periments to ascertain the effect of an increase in fat in the food 
on the quantity of fat in the milk, have given contradictory results ; 
but the weight of the evidence is to the effect that the percentage 
of fat in the milk is not modified by the quantity of fat in the 
food. 

Jt was observed in Holland that butter from cows on pasture 
in the fall decreased in volatile acids. Sjollema found that beet 
heads would prevent this, and later found cane sugar to have the 
same effect. The pasturage was found to contain less carbohy- 
drates in the fall. It is possible that a part of the volatile acids 
in butter originate from the fermentation in the animal, and for 
this reason, a smaller amount was present as the easily ferment- 
able carbohydrates in the food decreased. The character of the 
fat fed also has an effect upon the composition of the butter. 
Various experiments in adding oils to rations have produced but- 
ter that was somewhat affected by the character of the oil fed. 

Harrington 1 found that feeding cottonseed meal made the 
butter much harder, and decreased the quantity of volatile acids 
in it. For example, while normal butter contains approximately 
7.0 per cent, fatty acids volatile with steam, butter made from 
the milk of cows fed cottonseed contained in one case only 3.5 
per cent, volatile acids. 

Standards for Milk Cows. The amount of feed to be fed must 
depend upon the quantity of milk given as well as on the weight 
of the cow. The feeds should be adjusted to the individual 
animals, and not to the average of the herd. The adjustment 
may easily be made by arranging the cows in groups according 
to yield of milk, and adjusting the ration by measuring different 
quantities of the concentrates for each group. The value of the 
milk as related to the cost of the feed must determine whether the 
milk production should be forced to a maximum by giving a 
heavy ration, or whether a somewhat lower ration should be fed 
for more economical production. As stated before, the produc- 
tion of the largest possible amount of milk requires much more 
food than the production of a somewhat smaller amount, as the 
effect of each addition of food on production diminishes as the 
1 Texas Bulletin, u. 



FEEDING MILK COWS 



473 



quantity of feed is increased, and becomes very small near the 
upper limits of the capacity of the animal. 

For the production of one pound of milk, an animal requires 
about 0.05-0.065 pounds proteids, and 0.05-0.07 pounds produc- 
tive value, in addition to maintenance requirements. Milk contains 
o.i 8 per cent, lime and 0.15 per cent, phosphoric acid. Only about 
one-third of the lime and phosphoric acid is digested, so that id 
pounds of milk would require about 25 grams each of lime and 
phosphoric acid. To this must be added the maintenance re- 
quirements of 45 grams of lime and 22 grams of phosphoric acid 
per 1,000 pounds. The requirements for phosphoric acid are 
generally met by the food, especially when meadow hay, clovers, 
or good green fodders are used, but the requirements for mineral 
matter must not be entirely left out of consideration. Precipitated 
phosphate of lime may be used if the ration is deficient in lime 
and phosphoric acid. If deficient in lime alone, precipitated 
chalk will supply the deficiency. 

The following are the amounts of nutrients desirable per day 
and 1,000 pounds live weight for milk cows: 















Phos- 


Yield 


Total 
weight 


Proteids 


Produc- 
tive value 


Nutritive 
ratio 


Ume 
grams 


phoric 
acid 














grams 




22-27 






6 8 








** "t 


O 






7 U 


4/ 


Twenty pounds milk - 


25-29 


2.O 


2.7 


:6.8 


95 


72 


Thirty pounds milk 


27-33 


2.8 


3-5 


:6. 5 


120 


97 


Forty pounds milk . . 


27-34 


3-7 


4.2 


:6. 5 


145 


122 


For maintenance only 


15-21 


0.7 


i-5 


: 10 







For each 10 Ibs. milk . 




0-55 


0.6 












The figures given above for the productive value are for pro- 
duction at the maximum capacity of the animal. For a slightly 
smaller production, the productive value may be reduced 5 to 10 
per cent. The Wisconsin Experiment Station 1 recommends as 
a good working rule, to feed as many pounds of concentrates 
(grain feeds) each day, as the cow produces pounds of butter fat 
per week, in addition to as much roughage as she will eat up 
clean. 

1 Bulletin No. 200 ; Research Bulletin No. 13. 
3* 



CHAPTER XXIV. 



FEEDING STANDARDS AND FEEDING. 

Feeding standards, as have previously been given, are placed in 
the form of tables showing the quantity of the different nutrients 
which should be fed to animals of the .various kinds. 

Basis of the Standards. The standards are based, first, upon 
exact experiments to ascertain the needs of animals, such as de- 
scribed in the preceding pages ; secondly, on feeding experiments 
with various rations, carried on in large number and in various 
parts of the world, in which the effects of the rations were deter- 
mined; thirdly, on the experience of practical feeders of large 
numbers of animals. 

What the Standards Represent. The standards represent the 
rations which should, as a rule, give the best results. The in- 
dividuality of the animal will be considered by the wise feeder, 
and the ration adapted as may be necessary. The standards must 
in no case be regarded as iron-clad rules, but are merely intended 
to enable a feeder to start with a well-based, average ration. He 
should then modify or adapt the ration to suit the requirements 
of his animals. 

Suitability of Feed. Suitability of the feed must be consid- 
ered. Some animals are able to take only small quantities of a 
particular feeding-stuff, or none at all. The palatibility of the 
food is also to be considered. A mixture of a number of foods 
diminishes danger from any suspicious food, and distributes the 
work of digestion over the different digestive organs. Every 
change in food should be gradual, covering a period of 4 to 7 
days, even when the change consists only in a change in quantity. 

The Nutritive Ratio. The nutritive ratio is the ratio of digest- 
ible protein to digestible non-protein. We add together the 
digestible crude fiber, the digestible nitrogen-free extract, and the 
digestible ether extract multiplied by 2.25, and divide the sum by 
the digestible protein. The following is an example : 



FEEDING STANDARDS AND FEEDING 475 

Digestible Nitrogen-free extract 9.6 

Digestible crude fiber 14.7 

Digestible ether extract 22.4 X 2.25 50.4 

Total 74. 7 

Digestible protein 14.4 

Nutritive ratio I : 5.2 

The nutritive ratio is to be taken chiefly as an aid in calculating 
the ration. The productive value of the ration, and its content 
of proteids, are the important factors to be considered. The 
nutritive ratio should not exceed 1 : 10 for ruminants or 1 : 12 for 
hogs, but rations containing more protein can be used, if desired. 
Protein is usually the expensive portion of a ration, but there are 
localities in which feeds rich in protein are as cheap as other 
concentrates, or cheaper. Such feeds may then be used in 
moderate quantity for fattening or other productive purposes. 
The nutritive ratio is given in the table mainly to aid in calculat- 
ing the ration which contains a desired productive value 
associated with a certain quantity of protein. With some feeds 
it may be that the quantity of protein so calculated may exceed 
the requirements of the standards, but if so, adjustment may be 
made by the methods to be pointed out. 

Proteids. The amides and amido compounds have little value 
for the production or repair of flesh. They may aid in the diges- 
tion of food when there is a large quantity of non-protein com- 
pared with the quantity of protein present, but otherwise they 
apparently have little value. Hence it is better to base the ration 
on its proteid content, and not on the protein. The standards 
which we have given are based upon digestible proteids and not 
on protein. 

Pat. The quantity of fat is not material, provided that it does 
not exceed one pound per thousand live weight of the animal. 
If it exceeds this limit, it may derange the digestion of the 
animal. 

Ash. As a rule the food contains a sufficient quantity of ash 
for the body, but the ash requires consideration in the case of 
young animals. Young animals require lime and phosphoric 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 

acid for the purpose of forming bones. A deficiency of either 
of these is liable to cause injury, or disease. In certain localities, 
the food is deficient in ash. Deficiency in lime alone is corrected 
by the use of precipitated chalk; in phosphoric acid, by the use 
of precipitated or ground phosphate of lime. 

Exact Calculation of a Ration. Before beginning to calculate 
a ration, it is necessary to decide on the ration desired, the feeds 
available, and their probable composition. In calculating the 
ration we must consider: 

(1) The desired productive value. 

(2) The desired bulk. 

(3) The desired proteid content. 

All these may vary somewhat, especially the bulk and the 
proteids. 

We will term the method of calculation given below, the method 
of substitution. It is best illustrated by an example. Suppose 
we desire a ration with a bulk of about 28 pounds, proteids 2.0 
pounds, and productive value of 2.8 pounds, and wish to use 
corn chops, cottonseed meal, and cottonseed hulls, having the 
composition given in the table at the end of this chapter. As 
these feeds all contain about ten per cent, water, for which allow- 
ance has been made in considering the total bulk to be fed, it is 
not necessary to calculate to dry matter. 

First, let us assume that the 28 pounds fed is entirely cotton- 
seed hulls. This quantity of cottonseed hulls has a productive 
value of 0.84 pounds, and the value desired is 2.80 pounds, leaving 
a deficiency of 1.96 pounds. If now we replace cottonseed hulls 
having a productive value of 0.03 a pound by corn chops, having a 
productive value of 0.206, for every pound of cottonseed hulls re- 
placed, we gain 0.206-0.03 - 0.176 pounds productive value. 
Dividing 1.96 by 0.176 we have n.i pounds corn chops, which 
should replace an equal amount of cottonseed hulls. 

Cottonseed hulls 17.9 pounds and corn chops n.i pounds con- 
tain 0.86 pounds proteids, while 2.0 pounds is desired, a de- 
ficiency of 1.14 pounds proteids. Since cottonseed meal has 



FEEDING STANDARDS AND FEEDING 477 

nearly the same productive value as corn chops, it can replace 
corn chops without materially altering the productive value of 
the ration. If one pound average cottonseed meal containing 0.352 
pounds digestible protein replace one pound corn chops contain- 
ing 0.065 pounds digestible protein, the digestible protein increases 
0.352-0.065 = 0.287 pounds, so that to increase the ration 1.14 
pounds, we require 1.14 divided by 0.287 4.0 pounds cottonseed 
meal in place of an equal quantity of corn chops. The ration 
would then consist of 17.9 pounds cottonseed hulls, 7.1 pounds 
corn chops, and 4 pounds cottonseed meal. The substitution of 
i pound cottonseed meal for I pound corn chops decreases the 
productive value 0.206-0.195 = o.oi, or 0.04 pounds for the 4 
pounds substituted; and this can be adjusted by adding 0.25 
pounds corn chops, making a total of 7.35 pounds corn chops in 
the ration. This finally gives the ration desired. 

The method of calculation here given is as follows : 

(1) Assume the bulk desired is composed of the roughage to 
be used and calculate its productive value. 

(2) Calculate the quantity of concentrate which would give 
the desired productive value if it replaced a portion of the rough- 
age. 

(3) Calculate the proteids in the mixture having the composi- 
tion ascertained above, and then calculate the quantity of a con- 
centrate, rich in proteids, which must replace a portion of the 
other concentrate in order to give the desired quantity of pro- 
teids. The calculation is easier if the two concentrates have 
nearly the same productive value. 

(4) Adjust the ration by increasing or decreasing the quantity 
of one of the concentrates slightly, so that the change in the 
productive value caused by the second concentrate may be 
allowed for. 

Improving a Ration. Suppose a horse weighing 1,000 pounds 
at hard work, plowing for example, is receiving 7 pounds corn, 6 
pounds wheat bran, and 12 pounds timothy hay. How does this 
ration compare with the standard and how can it be improved? 



478 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



First, calculate the digestible proteids and productive value of 
the ration. 





Digestible proteids 


Productive value 


Corn 


7 X 68 o 48 


7\S Q 206 I AA 


Wheat bran . . 


6 X O 12 O 72 


6 X O 12 O 72 


Timothy hay 


12 X O O2I O 2^ 


12 X o 078 o 94 








Total 




7 TO 


Standard .... 


O 1 -4o 


J.J.V 

7 8 






O' 



The ration is too low in proteids and in productive value. Pro- 
ductive value may be increased by substituting corn for timothy 
hay. One pound corn substituted increases the productive value 
0.206-0.078 = 0.128; so to gain the 0.7 pound desired would take 
5.5 pounds corn chops. Each pound of corn chops substituted 
would increase the proteids in the ration 0.068-0.021 : - 0.047 
pounds, or 5.5 pounds would increase it 0.26 pound. This would 
increase the total proteids to 1.71, but would still leave a de- 
ficiency of 0.29 pounds proteids. If we replace corn by cotton- 
seed meal to supply this protein, we require 0.29 -4- (0.352-0.068) 
= i.o pound cottonseed meal. 

The calculated ration would then be as follows: 

Pounds 

Corn 7 -f 5.5 i.o = 11.5 

Wheat bran = 6.0 

Timothy hay 12 5.5= 6 -5 

Cottonseed meal = i.o 



Total 



25.0 



Reducing the Cost of a Ration. The commercial prices of 
feeding-stuffs are often not in proportion to their feeding values, 
and rations may often be modified so as to reduce the cost of the 
ration. There are four things to be considered in reducing the 
cost of a ration: (i) the suitability of the feed to the animal; (2) 
the cost of the productive value; (3) the cost of the digestible 
proteids per pound; (4) the cost of the bulk or volume of the 
feed. 



FEEDING STANDARDS AND FEEDING 



479 



The three last factors can be calculated from the known selling 
price, and the proteid content and productive value of the feeds. 
The bulk of the feed is of course measured by the total amount 
of dry matter. It often happens that hays cost more per unit of 
feeding value than concentrated feeds. In such cases, the cheaper 
bulky feeds should be used, and the difference in nutritive value 
compensated for by increasing the concentrates. The following 
table shows the relative cost of nutrients on the Texas market 
in 1910-11 : 

RELATIVE COST OF NUTRIENTS. 





Selling: price 
per ton 


Cost of one 
pound digesti- 
ble protein 


Cost 
of one pound 
productive 
value 




$28 oo 


Cents 
r < 6 


Cents 

7 "^ 


Wheat shorts 


28 oo 


5-v 

jo 7 


7 Q 




27 OO 


10 8 


112 




27 OO 


2O 7 


6 q 




oc OO 


17 8 


6 8 


Milo maize chops 


25 oo 


17 8 


68 


Rice polish 


24 oo 


I A A. 


c 7 




1 8 OO 




4C 






8 i 


o 

5C 




^O-O 
8 e;o 


70 8 


IA I 


Alfalfa hay 


18 ;o 


TO T. 


II 7 






***o 





Suppose a feeder who is using 6 pounds wheat bran at a cost of 
$30.00 a ton, can secure corn at $30.00 and cottonseed meal at 
$40.00. Would it pay to substitute? Six pounds wheat bran 
contains 0.72 pounds proteids and 0.72 pounds productive value. 
Three and one-half pounds corn would contain 0.72 pounds pro- 
ductive value and 0.241 pounds proteids, or a deficiency of 0.48 
pounds proteids. Replacing corn by cottonseed meal, 0.48 -r- 
0.352 -- 0.068 =1.4 pounds. That is, 1.4 pounds cottonseed 
meal and 3.5 pounds corn are equivalent to 6 pounds wheat bran. 
The cost would be 6 x 1.5 9 cents for wheat bran; and for 
the mixture, 1.4 x 2.0 = 2.8 cents for the cottonseed meal, and for 
the corn 3.5 x 1.5 = 5.25 cents, a total of 8.05 cents for the mix- 
ture or a difference of 0.95 cents, nearly one-ninth in favor of 



480 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



the mixture. The difference in bulk of the ration should be ad- 



justed when such substitutions are made, unless it comes within 
the range of the variations allowed. 

The preceding illustration shows the method which may be 
followed in reducing the cost of a ration. In substituting for pro- 
teids, a suitable feed providing the proteids at the lowest cost 
per unit should be used. In substituting for productive value 
a suitable feed providing the most productive value for 
the money should be used, and the same remark applies to sub- 
stituting for bulk. 

Tables of Feeding Value. The following tables show the feed- 
ing values of a number of feeds. 

AVERAGE FEEDING VALUE OF FEEDS. 



Total dry mat- 



Digestible pro- 



ter in 100 Ibs. teids in 100 Ibs 



Productive 
value in icolbs. 



GRAIN AND SEED 

Barley 89.1 

Corn 89. i 

Corn and cob meal 84.9 

Kaffir corn 89.9 

Oats 89.0 

Pea meal 89.5 

Milo maize 89.5 

Rye 88.4 

Wheat 89.5 

Cotton seed 89. 7 

BY-PRODUCTS 

Brewers grains, dry 92.0 

Cottonseed meal, average 91.8 

Cottonseed meal, Texas 92.0 

Gluten feed, dry 91.9 

Linseed meal, old process 90.8 

Linseed meal, new process 90 i 

Rye bran 88.2 

Wheat bran 88. i 

Wheat shorts 87.9 

Rice bran 90. i 

Rice polish 88.5 

Corn bran 90.9 

Peanut meal 89.3 

Cold pressed cottonseed cake 90.2 

Molasses (cane) 77.6 

Corn cobs 89.3 

Oat hulls 92.7 

Rice hulls 91.0 

Wheat chaff 85.7 

Cottonseed hulls 88.9 



8-4 
6.8 

4-5 

7.0 

8.0 

16.8 

7i 
8.1 

8-9 
H-5 

19.0 
35-2 
39-0 

20.0 
27-5 
29-3 

ii. 4 

12.0 
13.0 
9-0 
8-3 

6-5 
42.9 
17.1 

0.7 

0-3 
0.4 
0.9 
0.6 



18.8 

20.6 

16.5 
18.3 

150 

16.6 

18.4 
18.9 
17-3 

21.2 

14.0 

19-5 
I 9 .I 
18.4 
18.4 

17.4 
13.2 
12. 
I 7 .6 
19.8 
20.9 

18.6 

20.2 
10.0 
13.2 

5-3 

4.5 
0.7 

6.1 
3- 



FEEDING STANDARDS AND FEEDING 



481 



AVERAGE FEEDING VALUE OF FEEDS. (Continued.} 



Total 

dry matter 
in 100 Ibs. 



Digestible 
proteids 
in 100 Ibs. 



Productive 
value in 
100 Ibs. 



GREEN FODDER AND SILAGE 

Alfalfa 28.2 

Red clover 29.2 

Crimson clover 19.1 

Corn fodder 20.7 

Corn silage 25.6 

Rape 14.3 

HAY AND COARSE FODDER 

Alfalfa 91.6 

Clover hay I 84.7 

Corn forage 57.8 

Cowpea hay 89.3 

Oat hay 84.0 

Timothy hay 86.8 

Oat straw 90.8 

Rye straw 92.9 

Wheat straw 90 4 

Rice straw 88.0 

Corn shucks 87.2 

ROOTS AND TUBERS 

Carrots 11.4 

Mangel wurzels 9.1 

Potatoes 2 1 . i 

Rutabagas 1.4 

Turnips 9.4 



2.5 

2.2 

2.2 
0.4 
1.2 
2.2 

6 9 

5-4 

2.1 

8.6 
2.6 

2.1 
I.I 

0.6 
0.4 
i.o 
i.o 

0.4 

O.I 

0.5 
0.9 

O.2 



2.9 

3-8 

2.6 

2.9 

3-9 
2.6 



7-9 
8.1 



JO.O 

8.6 
7.8 
4-9 
4-9 
3-9 
3-4 
8.2 

1.8 
i.i 
4.2 
1.8 



INDEX 



Absorption, 152, 240. 
Acid consumed, 187. 
Acid, effect on digestion, 406. 
Acid phosphate, 306. 
Acid soils, 160, 162, 250. 
Acidity, detection, 253. 
Acids, fatty in feeds, 353. 
Acids in feeds, 376. 
Active plant food, 180. 

significance, 187. 
Ahesion of soils, 115. 
Aerobic bacteria 286. 
Agricultural chemistry, 2. 
Agriculture, object, i. 
Air, carbon dioxide in, 37. 

composition, 36. 

relation to plant, 6. 
Amendments, 293. 
Amides, 358. 

value in feeding, 475. 
Ammonia absorbed by leaves, 47. 

assimilation, 219. 

of air, 46. 

production in soil, 215. 
Ammonification, 204, 208. 
Ammonifying power, 210. 
Amylopsin, 394. 
Albite, 150. 
Albumins, 357. 
Alcohols, wax, 157, 349. 
Alfalfa, fertilizer for, 344. 

meal, 391. 
Alkali, black, 258, 265. 

effect on plants, 263. 

origin, 259. 

prevention, 267. 
Alkali, white, 258. 
Alkali soils, 258. 

classes, 265. 

utilization, 265. 



Alkaloids, 360. 
Alluvial soil, 66, 96. 
Animals, composition, 411. 

composition of gain, 442. 

feeding young, 458. 

growing, 456. 
Animal production, 3. 
Apatite, 15, 155, 184, 305. 
Appalachian mountain soils, 76. 
Appetizers, 434. 
Arabinose, 366. 
Argon, 46. 

Arid climate, 50, 139. 
Arid soils 77, 178... 
Ash, 346. 

constituents, n. 

effect of soil and season on, 22. 

essential, 10. 

excess taken up by plants, 24, 191. 

importance, 9. 

indifferent, 19. 

minimum needed, 20. 

needed by animals, 458. 

not created, 10. 

of leaves, 22. 

of plants (table), 23. 

of roots, 21. 

of seeds, 21. 

of straw, 22. 

of tubers, 21. 

stage of growth affecting, 26. 

strong and weak plants, 25. 

variations, 22. 

value in feeding, 458, 475. 

washed from plants, 20. 
Asparagin, 359. 

value for maintenance, 438. 
Atlantic and Gulf Coastal Plain 

soils, 75. 
Atmosphere, 36. 



4 8 4 



INDEX 



Atmosphere, soil, 51. 
Available energy, 420. 
Availability of plant food, 181. 

Bacteria, 205. 

classes, 208. 

destroyed by ozone, 49. 

in air, 49. 

in animals, 394. 

in manure, 286. 

soil, 205. 
Bacteriods, 222. 
Bagasse, 369. 
Barium in plants, n. 
Barley, depth of rooting, 104. 
Basalt, 65. 
Bat guano, 297. 
Bile, 303. 
Biotite, 151. 
Blood, 296. 
Bone black, 304. 
Bone meal, 304. 
Boron in plants, n. 
Buckwheat, water culture, 12. 
Butter, volatile acids of, 472. 

Cabbage, fertilizer for, 345. 
Calcareous soils (see lime), 186. 
Calcium cyanamid, 45, 295. 
Calcium, essential to plants 13. 
Caliche, 294. 
Calorimeter, 377. 

respiration, 415. 
Calorie, 377. 
Calves, feeding, 459. 
Cane sugar, 368. 
Capillary action, 140. 

moisture, 129. 
Carbohydrates, 361, 410. 

digestion of, 395. 

effect on digestion, 404. 

effect on milk production, 470. 

form fat, 440. 

Carbohydrates, used in work, 455. 
Carbon balance, 413. 



Carbon bisulphide, effect on soil, 

233. 

Carbon circulation, 39. 
Carbon dioxide in air, 36. 

in soil, 51, 59. 

solvent action, 39. 

sources, 37. 

test for, 36. 

weathering by, 57, 58. 
Carbon of food, use, 416. 
Carbonate of lime, effect on soil 
texture, 87. 

solubility, 58. 

effect on tilth (see lime), 90. 
Carnallite, 309. 
Cattle, feeding young, 460. 
Cells, 197. 
Cellulose, 373. 
Cereals, fertilizing, 324. 
Chabazite, 152. 
Chlorine for plants, 14. 
Chlorite, 153. 
Chlorophyll, 39, 360. 
Citric acid, 376. 

in soil, analysis ,180. 
Clay, 80. 

colloidal, 88. 

effect on soil texture, 87. 
Clays, 86. 
Clays, crops for, 92. 

physical composition of, 83. 
Clover, depth of rooting, 104. 

fertilizer for 344. 

Coefficient of digestibility, 398, 408. 
Cottonseed meal, 297, 391. 
Colloidal clay, 88. 
Colluvial soil, 63. 
Concentrates, 389. 

digestion experiments on, 401. 

effect on digestion, 405. 

productive value, 425, 480. 
Cooking, effect on digestion, 407. 
Copper in plants, n. 



INDEX 



485 



Corn, depth of rooting, 104. 

fertilizer for, 344. 
Cotton, fertilizer for, 344. 
Cottonseed, 297, 370. 
Cottonseed hulls, digestibility, 408. 
Cottonseed meal, 297, 391. 
Cover crops, 291. 
Cows, feeding, 461. 
Crude fiber, 346. 

digestion, 394. 

heat value, 409. . . 

loss of energy of, 418. 

productive value, 422. 
Crystalline rock, 63. 
Cultivation, 147. 
Cumulose soil, 63. 
Cutin, 374. 
Cyanamide, 45. 

Dextrose, 370. 
Denitrification, 204, 218. 
Diffusion, 197. 
Digestion, 392. 

artificial, 399- 

energy expended in, 417, 420. 

experiments, 398. 

influence of conditions on, 402. 

losses of energy in, 418. 

marsh gas produced in, 417. 

measure of losses of energy in, 
420. 

study of, 395- 

time of, 398. 
Diorite, 65. 
Drainage, 141. 
Drain gauge, 143. 
Dry farming, 139. 
Duty of water, 126. 
Dynamiting soils, 107. 

Elements, essential to plants, n. 
Energy, available, 420. 
Energy balance, 415. 
Energy in work, 455. 



Energy, kinetic, 420. 

loss of, 419- 

of food, disposition of, 417. 

productive, 426. 

thermal, 420. 
Enzyme, 364, 392. 
Essential oils, 377. 
Essential elements, 13, 27. 
.Ether extract, 346, 348. 

composition, 349. 

digestibility of constituents, 409. 

heat value, 410. 

of soils, 157. 

productive value, 422. 
Experiment, methods, 6. 
Experiment stations, I 

Fat, composition, 414. 

effect on digestion, 404. 

effect on milk production, 470. 

food required to produce, 444. 

modified by food, 441. 

productive value, 422. 

value in feeding, 475. 

value for maintenance, 435. 

value for work, 455. 
Fat value, 427. 
Fats, digestion, 39. 
Fats, used in work, 453. 
Fattening, practice of, 450. 
Fattening rations, factors which 

modify, 443. 
Feed laws, 386. 
Feeds, injurious, 387. 

mineral constituents of, 428. 
Feeds, preparation, 388. 
Feeds, productive value, 423. 
Feed, productive values (table), 
480. 

value for maintenance, 435. 
Feeding experiments, 447. 

on cows, 466. 
Feeding for maintenance, 439. 



486 



INDEX 



Feeding standards, 437, 474. 

calculation of ration, 476. 

fattening, 448. 

Feeding standards, growing animals, 
460. 

maintenance, 439. 

milk cows, 472. 

work animals, 455. 
Feeding stuff, 387. 
Fehling's solution, 364. 
Felspar, 150. 

Felspar, decomposition, 59. 
Fermentation, 37, 364. 

in stomach, 392. 
Fertilization, practice, 343. 

systems, 336. 
Fertilizer control, 313. 
Fertilizers, 293. 

agricultural value, 303, 316. 

availability, 297. 

calculating formulas, 320. 

effect on transpiration, 121. 

experiments, 325. 

fixation of, 342. 

guarantee, 313. 

home mixing, 318. 

mixed, 312. 

phosphates, 303. 

purchase, 317. 

quantity used, 339. 

use, 322. 

valuation, 314. 

wet mixed, 312. 
Field experiments, 245, 332. 
Filler, 312. 
Fish, dried, 297. 
Fixation, 240. 

by zeolites, 152. 
Flesh, composition, 412. 
Flood plain, 67. 
Fluorine, plant stimulant, 29. 
Fructose, 367. 
Furfural, 365. 



Galactose, 367. 

Gastric juice, 392. 

Germination', 109, 379. 

Gibbsite, 156. 

Glaciers, 56. 

Glacial soils, 68, 76, 97. 

Glassy rock, 83. 

Glauconite, 153. 

Globulins, 357. 

Glucose, 366. 

Glutelins, 357. 

Glycerides, 352. 

Glycogen, 372. 

Granite, 65. 

Green sand marl, 153. 

Grinding, effect on digestion, 407. 

Gums, 373. 

Gypsum, 255. 

Hair, fertilizer, 297. 
Hard pan, 106. 
Hay, 383. 

curing, 384. 
Hemicellulose, 374. 
Hentrioontane, 157. 
Hexose, 365, 366. 
Hippuric acid, 418. 
Hogs, fattening, 452. 
Hogs, feeding growing, 460. 
Hornblende, 151. 
Horse, digestive power, 402. 

feeding standard, 456. 
Humic acid, 362. 
Humid climate, 50. 
Humus, 162. 

estimation, 164. 

formation, 278. 

importance, 165. 

of peat and swamps, 164. 

theory of plant nutrition, 9. 

value, 232. 
Hydration, 57. 
Hydrocarbons, 355. 



INDEX 



487 



Hydrogen peroxide, 48. 
Hygroscopic water, 127. 

Igneous rocks, 63. 

Iodine in plants, 63. 

Inulin, 372. 

Ions, 198. 

Irrigation, 261. 

Irrigation water, quality, 269. 

Iron, essential to plants, 13. 

in soils, 178. 

minerals, 154. 

plant stimulant, 29. 

Kainit, 310. 
Kaolin, 153. 
Kaolinite, 153. 
Kinetic energy, 420, 427. 

Lactation, 462. 
Lactic acid, 376, 393. 

productive value 422. 
Lactose, 369. 
Lake deposits, 74. 
Lambs, feeding, 459. 
Law of minimum, 30, 32. 
Lead in plants, n. 
Leather, 297. 
Leaves, ash of, 21. 
Lecithin, 354,, 431. 
Legumes assimilate nitrogen, 221. 

inoculation, 227. 
Leucin, 359. 
Light, effect on plants, 5, 39, 40. 

control of, 42. 
Lignin, 374. 
Lime, 1 1 6. 

application, 255. 

and acidity, 250. 

burning, 37. 

carbonate, 154. 

effect on crops, 252. 

effect on digestion 406. 

effect on nitrogen assimilation, 224. 

experiments with, 237. 



Lime, effects, 254. 

in feeds, 428. 

liberates potash, 256. 

loss by weathering, 61, 273. 

need of animals for, 452. 

per cent, in soils, 175. 

ratio to magnesia, 28. 
Limestone, 73, 256. 

solubility 58. 

Limestone valley soils, 76. 
Linseed meal, 297. 
Lipase, 393. 
Litter, 283. 
Loams, 86. 

crops for, 92. 
Loess, 70, 71. 
Loess soils, 76. 

Magnesium, essential to plants, 13. 

Maintenance ration, 435. 

Malic acid, 376. 

Malt, 372. 

Maltose, 370. 

Maganese, plant stimulant, 29. 

Mannose, 367. 

Manure, 218, 280. 

application, 289. 

fermentation, 286. 

green, 290. 

horse, 282. 

losses of, 284. 

poultry, 282. 

saving, 287. 

sheep, 282. 
Marsh gas, 394. 
Marsh gas in air, 49. 

estimation, 414, 

from animals, 417. 
Men, digestion experiment on, 399. 
Metabolic nitrogen, 36. 
Metabolic products, 395: 
Metamorphic rock, 63. 
Mica, 151. 



488 



INDEX 



Milk, composition, 461. 

effect of conditions on, 462. 

effect of feed on production^ 

methods, 466. 
Milk fat, production, 471. 
Milk production, effect of nutrition 

on, 468. 

Milk sugar, 369. 
Milking, frequency, 464. 
Minerals, 149. 
Mineral matter, needed by animals, 

458. 
Mineral theory of plant nutrition, 

9- 

Moraine, 69. 
Mucic acid, 367. 
Muck soils, 74. 
Muds, 73. 

Muriate of potash, 310. 
Muscovite, 151. 

Nitrate of soda, 293. 

use, 338. 
Nitrates, accumulation, 218. 

electrical production 45. 

production in soil, 215. 
Nitric acid of air, 47. 
Nitrifying power, 214. 
Nitrifying capacity, 214. 
Nitrogen, accumulation in soils, 

54- 
Nitrogen, assimilation by bacteria, 

45- 

assimilation by legumes, 211. 
Nitrogen, availability, 300. 
Nitrogen balance, 412. 
Nitrogen, circulation, 45. 

combination of free, 45. 

essential to plants, 13. 

gains by soil, 275. 

in rain, 48. 

in rocks, 54. 

loss from soils, 273, 277. 

of air, 44. 



Nitrogen of food, use, 417. 

of soil atmosphere, 51. 

relation to pot experiments, 193. 

fixation, 204, 220. 

fixing power, 220. 
Nitrobacter, 212. 
Nitrification, 204, 210. 
Nitrification, conditions, 214. 

study of, 213. 
Nitrogen-free extract, 346, 360. 

composition, 375. 

digestibility of constituents, 408. 

heat value, 410. 

loss of energy of, 418. 

productive value, 426. 
Nitrogenous fertilizers, 293. 
Nutrients, productive value, 422. 
Nutrients used in work, 453. 
Nutritive ratio, 440, 474. 

effect on digestion, 406. 

Oats, fertilizer for, 344. 

Observation and experience, 7. 

Oils, 351. 

Onion fertilizer, 345. 

Organic matter (see humus), 4. 

decomposition, 229. 

decreases cohesion, 116. 

gains, 278. 

of soil, 228. 

and soil temperature, 112. 
Organic theory of plant nutrition, 

9- 

Orthoclase, 150. 
Oxalic acid, 376. 
Ox, feeding standard, 456. 
Oxen, compositon of gain, 443. 

fattening ration, 449. 
Oxygen, 42. 

for germination, 42. 

weathering action, 58. 
Oyster shells, 256. 
Ozone, 49. 



INDEX 



489 



Pacific coast soils, 78. 

Palmitin, 351. 

Pancreatic juice, 394. 

Peat soils, 74. 

Pectins, 373. 

Pentosans, digestibility, 408. 

in soils, 157. 
Pentoses, 365, 374. 
Pepsin 393- 
Peptones, 357. 
Percolation, 142, 271. 
Phytin, 377. 
Piedmont plains, 67. 

soils, 75. 
Pigs, digestive power, 402. 

fattening ration, 449. 

feeding young, 459. 
Finite, 153. 
Plants, absorption of carbon 

dioxide, 36. 

Plants and atmosphere, 6, 30. 
Plant constituents, n. 
Plant food, active, 180. 

definition, 17. 

factors of availability, 181. 

and crops, 276. 

and soils, 172. 

minimum requirements, 18. 

quantity needed, 20. 

washed out, 20. 
Plant life, conditions, 5. 

essentials, 9. 

products, 4. 
Plants, light on, 39. 
Plant production, 3. 
Plant stimulants 29. 
Polariscope, 363. 
Porphyry, 64. 
Plant, ash essential to, 10. 

ash of (table), 23. 

assimilation of organic matter, 
161. 
32 



Plants, color of light on, 40. 

composition at stages of growth, 
38o. 

conditions for life of, 5. 

constituents, 346. 

effect of temperature, ICQ. 

effect of space on development, 
105. 

essentials for life, 9, 30. 
Plants, harvesting, 382. 

law of minimum, 30. 

ratio essential elements, 27. 

selection, 383. 

variable conditions, 32. 

water required, 119, 124. 
Plowing, labor of, 116. 
Phosphates, soil, 155, 303. 
Phosphates, availability, 308. 
Phosphoric acid, 18. 

active, 183. 

ammonia, soluble 166. 

available, 307. 

changes in soil, 241. 

fixation, 184, 234. 

in rations, 428. 

percentages in soils, 174. 

needs of animals for, 458. 

relation of active to pot experi- 
ments, 189. 

reverted, 306. 

water-soluble, 306. 
Phosphoric acid essential to plants, 

13- 
Pot expe-riments, 184, 193. 

conduct, 246. 
Potash, active, 183. 

excess taken -up, 192. 

fixation, 185. 

loss from soils, 273. 

loss by weathering, 61. 

relation of active to pot experi- 
ments, 191. 
Potash salts, definition, 74. 



490 



INDEX 



Potash, sources, 308. 
Potash of soils, 176. 
Potassium essential to plants, 13. 
Potatoes, depth of rooting, 104. 
Potato fertilizer, 345. 
Prairie soils, 77. 
Primary minerals, 149, 150. 
Productive value, 427. 

calculation of, 423. 

of feeds, 422. 
Protamins, 357. 
Proteids, 356. 

classes, 357. 

digestion, 394. 

effect on milk production, 470. 

form fat, 440. 

value for maintenance, 438. 

productive value, 422. 

value in feeding, 475. 
Protein, 346, 355. 

digestion of, 405. 

used in work, 453. 

value for maintenance, 438. 

value for work, 455. 
Proteoses, 357. 
Ptyalin, 392. 
Putrefaction, 207. 
Pyrite, 155. 
Pyroxene, 151. 

Quartz, 150. 
Quicklime, 255. 

Raffinose, 367, 370. 

Rain, nitrogen in, 48.' 

Rainfall relation to yield of crops, 

125- 
Ration, calculation of, 476. 

improving, 477. 

reducing cost of, 4/8. 

restricted, 435. 
Rennin, 393. 
Respiration calorimeter, 415. 

chamber, 414. 



Respiratory methods, 454. 
Rhamnose, 366. 
Rice bran, 391. 
Rivers, carrying power, 66. 
River deposits, 67. 
Rock, crystalline, 63. 
Rocks, final weathering products 
of, 60. 

glassy, 63. 

granite, 65. 

igneous, 63. 

metamorphic, 63. 
Rocks, solution of, 57. 

weathering of, 54. 

stony, 64. 

Rocky Mountain soils, 78. 
Rothamsted, foundation of, 10. 
Root absorption, 198. 
Roots, ash of, 21. 

acidity, 180. 

depth of penetration, 102. 

need for oxygen, 43. 

solvent action, 200. 

root tubercles, 212. 
Roughage, 390. 

productive value, 425, 480. 
Ruminants, 392. 

Saccharic acid, 366. 
Saliva, 393. 
Salt, 428. 
Sand, 80. 
Sands, 73, 86. 

crops for, 92. 

particles of, 83. 
Sandstone, 73. 
Saponification, 351. 

value, 353. 

Secondary minerals, 149, 151. 
Sedentary soils, 61. 
Seeds, ash of, 21. 

classes, 379. 

need oxygen, 43. 
Serpentine, 153. 



INDEX 



491 



Siderite, 154. 
Silage, 348, 385- 
Silica, 152. 

function in plants, 16. 
Silicates, hydrated, 149, 152. 
Silt, 80. 

Soda, not essential, 16. 
Soil, adhesion in, 115. 
Soil acidity, 160, 250, 253. 

air space, 115. 
Soils, alluvial 56, 66, 76. 
Soil analysis, 167. 

apparent specific, gravity, 113. 

by strong acids, 161. 

interpretation, 173, 195. 
Soil atmosphere, 51. 

arid, 178. 

Soil bacteria, 204, 206. 
Soil carbon dioxide of, 5 1 - 

carbonate of lime in 154, 186. 

chloroform extract of, 157. 

chemical composition, 167. 

relation to adaptation to crops, 
II. 

classification, 85, 95, 117. 

cohesion, 115. 

color, 112. 

complete analysis, 168. 

colluvial, 63. 

constituents, 149. 

crumbs, 90. 

cumulose, 63. 

deficiencies, 174, 244, 245. 

depth, 102. 

depth limitations of, ic6. 

effects of manure on, 290. 

ether extract of, 157. 

extract, composition, 182. 

fertility of, relation to composi- 
tion, 171. 

relation to water, 123. 
Soil, fixation in, 234, 239. 

from igneous rocks, 63. 



Soil, from rocks, 54. 
glacial, 57, 68, 76, 97. 
investigation of minerals of, 155. 
limestone, 73, 76, 90, 97. 
maps, 99. 
losses and gains of, 61, 76, 271, 

341. 

mechanical composition, 86. 
mechanical analysis, 79. 
minerals, 147. 
minerals, solubility, 183. 
muck, 74. 
organic matter, 156, 228. 

ammonia-soluble, 162. 
particles, relation to texture, 83. 
particles, 79. 
peat, 74. 

pentosans in, 157. 
physical properties, 101. 
provinces of the U. S., 74- 
quantity of water in, 127. 
retention of water by, 134. 
sedentary, 61. 
series, 94. 
shrinking of, 117. 
specific gravity, 113. 
survey, 99. 
solutions, 199. 
temperature, 107, no, in. 
texture and composition 87. 
toxic theory of, 158. 
transported, 61. 
types, 94- 

types, composition, 179. 
ventilation, 51. 
water, 132, 136, 138. 
water control, 147. 
water losses, 142. 
water gains, 139. 
water and transpiration, 121. 
weathering, 61. 
water in, 132. 
water-soluble part, 196. 



492 



INDEX 



Soil, water extract, 201. 

water, effect on temperature, in. 

weight per foot, 114. 

wet soils, 148. 

wind blown, 71. 
Specific gravity of soils, 113. 

Stachyose, 370. 

Stage of growth, effect on diges- 
tion, 417. 
Starch, 367, 370. 

digestibility, 408. 

forms fat, 441. 

loss of energy of, 418. 

manufacture, 372. 

maintenance value, 439. 

productive value, 423. 
Steapsin, 394. 
Stilbite, 152. 
Stony rock, 64. 
Straw, 22. 

Steers, maintenance ration, 439. 
Sheep, composition of gain, 442. 

digestive power, 402. 

fattening ration, 449. 

maintenance ration, 439. 
Subsoil, 101. 
Sucrose, 368. 
Sugar, loss in drying, 347. 

productive value, 422. 
Sugars, 361. 

digestibility, 408. 

fermentation, 364. 

manufacture, 368. 

value for maintenance, 436. 
Sulphate of ammonia, 294. 
Sulphate of potash, 370. 
Sulphur dioxide in air, 49. 
Sulphur, essential to plants, 18. 

in soils, 258. 
Superphosphates, 307. 
Swamp, 139. 
Syenite, 65. 
Syrup, 369. 



Talc, 153. 

Tankage, 297. 

Tannic acid, 376. 

Tartaric acid, 376. 

Temperature, weathering by, 55. 

Therm, 377. 

Thermal energy, 420, 427. 

'Thomas phosphate, 306. 

Till, 69. 

Tilth, 90. 

Tobacco grown under shade, 41. 

stems, 308. 

soils, 93- 

Tomatoes, fertilizer for, 345. 
Toxic theory, 158. 
Transpiration, 119, 198. 
Transported soils, 161. 
Tripsin, 394. 

Truck crops, fertilizer for, 345. 
Tubercles, 12. 
Tyrosin, 359. 

Urea, 418. 
Uric acid, 418. 
Urine, 418. 

Vivianite, 155. 

Valuation of fertilizers, 314. 

Water, available, 136. 
Water, control of, 146. 

composition of rain, 49. 

evaporation, 145. 

estimation in plants, 347. 

effect of water temperature on 
food required, 438. 

flowing in soils, 131. 

irrigation, 261. 
Water, in feeding, 431. 

in plants, 346. 

losses from soil, 142. 

nitrogen in rain, 48. 

quality, 269. 

quantity required by plants, 123. 
Water culture, 10. 



INDEX 



493 



Water capacity of soils, 201. 
Water-soluble, soil constituents, 196. 
Water table, 107, 138. 
Wavellite, 155. 
Wax alcohols, 355. 

digestion of, 409. 
Weathering agencies, 53. 

loss by, 60. 

products of, 59. 



Wheat bran, digestibility, 408. 
Wilting coefficient, 137. 
Wire basket experiments, 249. 
Wood ashes, 309. 
Work animals, feeding, 453. 

Xylose, 366. 
Yeast, 364. 
Zeolites, 152. 



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