GIFT OF

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Issued January IT, WIS

U. S. DEPARTMENT OF AGRICULTURE,

BUREAU OF SOILS— CIRCULAR No. 74.

MILTON WHITNEY, Chief of Bureau.

THE ORGANIC CONSTITUENTS OF SOILS.

BY

OSWALD SCHRETNER,

Scientist in Charge, Soil Fertility Investigations.

WASHINGTON:

GOVERNMENT PRINTING OFFICE.
1913

BUREAU OF SOILS.

MILTON WHITNEY, Chief of Bureau.
ALBERT G. RICE, Chief Clerk.

SCIENTIFIC STAFF.

FRANK K. CAMERON, in charge of Physical and Chemical Investigations.
CURTIS F. MARBUT, in charge of Soil Survey.
OSWALD SCHREINER, in charge of Fertility Investigations.
R. 0. E. DAVIS, in charge of Soil Water Investigations.
2

LETTER OE TRANSMITTAL

U. S. DEPARTMENT OF AGRICULTURE,

BUREAU OF SOILS,
Washington, D. C., October 16, 1912.

SIR: I have the honor to transmit the manuscript of an article on
the Organic Constituents of Soils, by Dr. Oswald Schreiner, scientist
in charge of soil fertility investigations of this bureau, and to recom-
mend that it be published as Circular No. 74 in the series issued by
the Bureau of Soils.

Very respectfully,

MILTON WHITNEY,

Chief of Bureau.
Hon. JAMES WILSON,

Secretary of Agriculture.

THE ORGANIC CONSTITUENTS OF SOILS.1

The reports on the various phases of soil studies by the investi-
gators who have preceded me in this symposium must have impressed
you with the fact that the subject of soil fertility and infertility is
by no means a simple matter of arithmetic, which involves only a few
of the mineral constituents of the soil. It must also have become
clear to you that the problem of soil fertility or infertility has not
been solved by the application of these simple arithmetical means
based on soil analysis or by the crop statistics accumulated in the
years which have elapsed since Liebig first announced his views on
soil fertility, which gamed for him for all time the title of "Father of
Agricultural Chemistry." It is particularly gratifying to me, since
I am to talk to you to-day on the subject of the organic constituents
of soils, their chemical nature and other properties, that Liebig is
also known as the "Father of Organic Chemistry." To what tre-
mendous proportions and significance in the world's industries and
science this child of his (Organic Chemistry) has grown is familiar
to all of you, and I assure you that Liebig, were he to return to-day,
would be proud of its parentage. But I fear he would be displeased
with his other child, as having made so little progress in the inter-
vening years, although he started it in life strong and virile and full
of promise. Up to a few years ago agriculture had not shared in the
great impulses which modern science has given to other arts and
industries, and the domination of the mineral-requirement theory
proposed in the first half of the last century and accepted without
adequate proof of its validity is largely responsible for the lack of
development in agriculture, commensurate with the enormous strides
of other arts and industries under the guidance of modern scientific
thought and research. But a new era of scientific inquiry is at hand,
and all phases of scientific endeavor are being applied to the solution
of the problems connected with soil fertility and infertility — lines of
endeavor which were not even known in Liebig's time, but which
to-day are well-recognized factors in soil fertility. I refer to the
study of soil bacteria, soil fungi, soil protozoa, and other micro-
organisms, and all the biochemical functions of these, as well as of

i Address given at the Symposium on Soils at the Washington meeting of the American Association for
the Advancement of Science. The detailed results of the investigations mentioned in this address can be
found in Bureau of Soils bulletins Nos. 40, 47, 53, 56, 70, 73, 74, 80, 83,.86, 87, 88, 89 90.

5

6 ORGANIC CONSTITUENTS OF SOILS.

the higher plants, such as oxidation, reduction, enzymotic and
catalytic, producing and destroying in the soil the organic constitu-
ents of which I shall speak presently.

The soil is not simple, but complex. The soil properties and
functions are likewise complex, not simple. All of the investigators
preceding me in this symposium have emphasized to you by their
papers how complex the subject is and how much remains to be done
before a clear insight is obtained, buf they have also shown to you
clearly that a well-trained army of scientists is at work on the prob-
lems connected with soil fertility, applying thereto all the principles
of modern science. The old view was simplicity itself; the soil was
a mere trough in which the plant found its nourishment. But I can
do no better than to let Liebig speak for himself. I quote from
Letter XII of his "Familiar Letters on Chemistry":

A field in which we cultivate the same plant for several successive years becomes
barren for that plant in a period varying with the nature of the soil; in one field it
will be three, in another seven, in a third twenty, in a fourth a hundred years. One
field bears wheat and no peas; another beans and turnips but no tobacco; a third
gives a plentiful crop of turnips but will not bear clover. What is the reason that a
field loses its fertility for one plant, the same which at first flourished there? What
is the reason one kind of plant succeeds in a field where another fails?

Liebig answered these questions by saying:

Wheat, clover, turnips, for example, each require certain elements from the soil;
they will not flourish where the appropriate elements are absent. Science teaches
us what elements are essential to every species of plant by an analysis of their ashes.
If, therefore, a soil is found wanting in any of these elements, we discover at once the
cause of its barrenness, and its removal may now be readily accomplished.

But has science removed the causes of the barrenness of a soil
by the analysis of the soil or of the ashes of the plants ? In this
connection it might be well to quote a statement from an article by
Coleman, which was awarded the prize of the Royal Agricultural
Society of England in 1855. The author says:

The causes which operate in producing the fertility or barrenness of soils have
hitherto to a great extent been shrouded in mystery, not from any want of study, but
owing to the difficulties which meet the inquirer at every step and the fact that most
important results frequently depend upon causes which have eluded the search of
the experimenter. The science of chemistry it was hoped would afford the key
wherewith to unlock the mysteries of nature, but though its discoveries have con-
ferred much practical benefit on the agriculturist, it has up to a very recent period
effected comparatively little toward settling the cause of fertility or sterility. The
theories of scientific men led us to expect that fertility depended upon the presence
of certain mineral substances which were found invariably present in the ashes of
plants, and the analysis of the soil it was believed would confirm the practical experi-
ence of the farmer; these hopes have been falsified except in the few cases of almost
simple soils, such as pure clays and sands. In all other cases the analysis presented
the existence in varying proportions of those substances supposed to induce fertility
in the barren as well as in the fertile soil. The proportion of the various ingredients

OKGAXIC CONSTITUENTS OF SOILS. 7

was next proposed as a sign of quality, but researches into the amount of inorganic
matter abstracted by each crop have demonstrated that soils at a mixed character
contain abundant supplies of mineral food for numerous crops.

Tliis was over 50 years ago, and the statements made are practically
as true to-day as they were then. There has been a marked advance
in agricultural practice, but until quite recently comparatively little
light has been shed upon the scientific principles which underlie
those practices.

In all justice to Liebig, however, I must make another quotation
from his works to show that he himself recognized the insufficiency
of the views expressed by the above quotations. He says:

But it has been observed that the crops are not always abundant in proportion
to the quantity of manure employed, even though it may have been of the most
powerful kind; that the produce of many plants, for example, diminishes in spite of
the apparent replacement by manures of the substances removed from the soil when
they are cultivated on the same field for several years in succession.

From the above quotation it may be seen that Liebig recognized
that there are many cases which his theory of mineral requirement
failed to cover. Indeed, if he had followed the idea embodied in
the quotation to its final analysis he would have reached some
conclusions similar to those presented to you in the various papers
to-day.

Even before, and especially since, the time of Liebig much material
has been accumulated and handled in a statistical manner. I
should here say that much valuable information has been thus
obtained, but it should be needless for me to add that even with all
these years of crop statistics at hand the difficult problems of the
causes of fertility or infertility of our agricultural lands have not
been thereby determined nor eliminated. The problem is not
solved, though much progress has been made through the applica-
tion of modern sciences. If the problem of soil fertility had been
solved by the application of such statistics, this symposium would
not have been held. The pessimistic views expressed by some I can
not share. Science is ever optimistic; the scientific investigator
must above all things be optimistic and have an abiding faith that
science will solve the intricate questions connected with his prob-
lem. The problem of soil fertility and infertility is broad enough
and big enough for many workers and methods of attack. We can
not all begin to unravel the tangled threads at the same point; there
are different viewpoints, and it is not improbable that some may
have a clearer vision than others to see the particular thread that
will undo the snarl. The solution of the problem can be reached only
through diligent experimentation, not by the statistics of even a
hundred years.

8 ORGANIC CONSTITUENTS OF SOILS.

The Bureau of Soils has undertaken its work from a new view-
point and has achieved some important results which throw much
light upon the dark subject of the cause of fertility and infertility
of our agricultural lands. I am very glad of this opportunity to
present to you the results of a phase of this investigation, namely,
the importance of the organic constituents of soils.

I have brought with me a tangible result of this work in the form
of specimens of the organic compounds which have been found in
soils. Their isolation and identification give definite information
about a portion, and a very important portion, of the soil, the value
of which has been recognized in practice, but about which no definite
information was at hand until this work was undertaken. By the
application of modern methods of research to the intricate problems
of the soil we have been able to throw such light upon the biochemical
changes in soils that the old views of soil organic matter, soil humus,
and the process of humification are entirely overthrown. The
compounds of which Mulder, the contemporary of Liebig, writes,
such as humic acid, geic acid, ulmic acid, etc., terms which have
appeared in textbooks ever since, have absolutely no existence, but
are shown to be mixtures of many different, and widely different,
compounds. Not only were the compounds contained in these
specimen tubes not known as soil constituents to Mulder or Liebig,
but they were compounds unknown to the science of the time. With
the advance of science, especially of biochemistry, since that time
results such as these have been made possible. Some of these com-
pounds contain only carbon and hydrogen; some carbon, hydrogen,
and oxygen; some carbon, hydrogen, oxygen, and nitrogen; and
some carbon, hydrogen, oxygen, nitrogen, and phosphorus. The
compounds represent a great variety of chemical classes; there are
paraffin hydrocarbons, hydroxy fatty acids, and other organic acids,
esters and alcohols, carbohydrates, hexone bases, pyrimidine de-
rivatives, purine bases, and pyridine derivatives. The individual
compounds isolated or found are as follows :

ORGANIC COMPOUNDS ISOLATED FROM SOILS AND IDENTIFIED.

Agroceric acid.

Agrosterol.

Arghi ine.

Creatinine.

Cytosine.

Dihydroxystearic acid.

Glycerides, liquid.

Hentriacontane.

Histidine.

Hypoxanthine.

Lignoceric acid.

Monohydroxystearie acid.

Paraffinic acid.

Pentosan.

Pentose.

Phytosterol.

Picoline carboxylic acid.

Resin.

Resin acids.

Resin esters.

Xanthine.

ORGANIC CONSTITUENTS OF SOILS. 9

In addition to those here mentioned a number of others are already
isolated and will soon be reported.1 It is obvious that definite
chemical information of this kind sheds much light upon the nature
of soil organic matter and the processes going on in the soils. The
compounds encountered are the same as those encountered in other
lines of biochemistry, and, therefore, the knowledge in regard to chem-
ical relationships, origin, and processes of change accumulated in
such other lines can be directly applied to the understanding of the
biochemical changes in soils and the constitution of soil organic mat-
ter. It is not my purpose to discuss the biochemical changes here,
other than to say, in passing, that the occurrence of these products
which have an obvious chemical relationship with the great classes of
tissue material contained in the plant and animal debris that gets into
the soil, the carbohydrates, the fats, the proteins, the nucleic acids,
the lecithins, etc., proves conclusively that the process of humification
is not a mysterious process which takes place in the soil and can not
be understood, but rather that the process of change in the soil is,
after all, very closely paralleled by the processes known to take place
in the laboratory when the complex organic substances are split by
hydrolysis, oxidation, reduction, or deamidization, into simpler deriv-
atives. It is my purpose, however, to bring strongly before you the
fact that these soil constituents affect plants directly.

As scientists personally interested in all that has to do with plant
life and development you will be glad to learn that we have studied
as many as possible of these compounds in such a way as to determine
what their possible functions in the soil may be. Indeed, the reason
why this investigation of the organic matter in soils was undertaken
is to be found in the fact that certain soils and soil extracts behaved
toward plants as if they contained something detrimental to crops.
This harmful effect on plant growth can be shown very readily by
anyone with such a soil under investigation. The soil is shaken with
distilled water for several minutes, allowed to settle, and the super-
natant liquid filtered off, which must usually be done with a Pasteur-
Chamberland filter in an apparatus specially designed for such work,
in order that all solid material may be removed. The clear filtrate
is then used as a medium for the growth of wheat seedlings in bottle

i These compounds have since been reported in Bulletin No. 88 of the Bureau of Soils, entitled: "Some
Organic Soil Constituents," by Edmund C. Shorey, and, in addition to the classes of compounds enumer-
ated above, contain aldehydes, sugars, and sulphur derivatives. The soil compounds described in this
bulletin are:

Acrylic acid. Oxalic acid. Sulphur.

Adenine. Rhamnose. Trimethylamine.

Lysine. Saccharic acid. Trithiobenzaldehyde.

Mannite. Salicylic aldehyde.

Nucleic acid. Succinic acid.

The isolation of guanine from a heated soil is described in Bulletin 89 of the Bureau of Soils, entitled:
" The Chemistry of Steam Heated Soils," by Oswald Schreiner and Elbert C. Lathrop.

-Cir. 74—13 2

10 ORGANIC CONSTITUENTS OF SOILS.

cultures. A control in pure distilled water or in an extract from a
fertile soil should be run at the same time. In such cases the plants
grown in the extract from the poor soil will show many peculiarities
not shown by the plants either in the pure distilled water or in the
extract from the good soil. The plant will be smaller, with swollen
tips, which are sometimes bent into hooks, a phenomenon character-
istic of certain toxic action. The growth in this soil extract may
even be considerably less than the growth in the distilled water,
although the soil extract contains plant nutrients, whereas the dis-
tilled water contains none.

If a separate portion of the original extract be treated with carbon
black, made from natural gas by imperfect combustion, much as
lampblack is formed on lamp chimneys, agitated, and filtered, the
filtrate will be a good medium for the growth of the seedlings. This
simple treatment with carbon black has, therefore, removed by
absorption the harmful properties of the soil extract, and the growth
is now even better than in the distilled water.

Another experiment with soil and carbon black was made as follows :
A layer of moist carbon black was covered with a layer of moist unpro-
ductive soil, and this in turn by a layer of moist carbon black. In
this experiment the moisture could circulate from the soil to the car-
bon black and back again, and thus gradually the soil fluids would be
freed of any injurious compounds by absorption into the carbon black.
At the end of a day or two of this interaction the soil was freed from
the carbon layers, plants were grown in it, and when compared with
soil not so treated a very marked improvement was shown, again
indicating that a harmful body was originally present and had been
removed in whole or in part by this carbon-black treatment.

Observations of this kind on many soils, together with a study of
the properties of the material dissolved in the water, led to no definite
isolation of the compound or compounds showing the harmful effect,
owing to the fact that the quantities in the water extract were too
small for identification, but they did lead to a recognition of the
fact that the substances were not mineral in character, but were
constituents of the organic matter of the soils.

That organic substances could produce such effects in such small
quantities as must be present in soil solutions was not apparent from
the literature, and it became necessary to establish this point. With
this in view about 40 substances of organic origin which may get into
the soil or be formed therein were tested, and it was conclusively
shown that a number of these are decidedly harmful to plants, even in
very dilute solutions comparable with the organic content of soil
solutions.

It therefore became essential to make a study of the organic mat-
ter of the soil. This, however, was a subject about which the older

OEGANIC CONSTITUENTS OF SOILS. 11

chemistry of agriculture had much to say but in regard to which
modern science was discreetly silent. With no established facts and
no methods of attack worked out progress was necessarily slow at
first but gained speed with each compound isolated or identified,
until to-day there have been isolated in these laboratories more than
25 1 definite compounds from soil organic matter, and the work is
progressing at a rapid pace.

The search for this supposedly harmful constituent was rewarded
by the discovery, among others, of dihydroxystearic acid, a com-
pound which, on account of its frequent occurrence in soils, has been
rather thoroughly studied in regard to its effect on plant develop-
ment and growth.

The isolated and purified dihydroxystearic acid was tested by
dissolving it in pure distilled water, and it was found to have de-
cidedly deleterious action on the wheat seedlings used in the tests.
The acid prepared in the laboratory behaved in the same manner.

Its effect in the presence of nutrient salts was also extensively
studied in solutions containing calcium acid phosphate, sodium
nitrate, and potassium sulphate, alone and in combinations of two
and three of these salts, a total of 66 cultures being used in a single
test. The injurious effect of the dihydroxystearic acid was less where
all three of the nutrient elements were present than where only one
or two were present. The injurious effect was least in those cultures
of three nutrients where the nitrate was high. This indicates that
the action of the nitrate tends especially to overcome the harmful
effect of the compound, or else it enables the plant to resist or over-
come its effect.

Dihydroxystearic acid has another quality which should be men-
tioned here as having a considerable bearing on its effect on crops,
even in such soils as contain much plant nutrient material in the
most readily available form. This is its influence on the absorptive
power of the roots of the plants growing in the soil, the soil solution,
or solutions of nutrient salts when dihydroxystearic acid is present
in them. The absorption of potassium and phosphate was greatly
interfered with, although both were present in soluble form in the
culture solutions; only the nitrate was consumed in any quantity.
This is in harmony with the fact stated above that when nitrates
were plentiful in the solutions the best growth was obtained and the
effect of the harmful compound was minimized or entirely overcome.

The occurrence of dihydroxystearic acid was specifically studied.
For this purpose soil samples of good and poor fields were collected
and examined for this constituent. Soils from 18 different States,
extending from Maine to Oregon and southward to Texas, of widely

i The total number is now 36; see Bulletins 88 and 89, Bureau of Soils.

12 OBGANIC CONSTITUENTS OF SOILS.

different origin, topography, texture, climate, drainage, and crop-
ping, varying from soils of the highest productivity to soils incapable
of producing profitable crops, were examined for dihydroxystearic
acid.

One-third of all the soils examined showed the presence of this
compound. It was found in virgin soils as well as in soils under
long cultivation; in soils continually cropped as well as in soils under
permanent sod; in soils from the Atlantic coast; in soils from the
Pacific coast; and in soils from the Gulf States. This compound is
therefore a common soil constituent and is likely to be encountered
in soils anywhere. Its formation or its accumulation is doubtless
due to local conditions in any one section, but these local soil con-
ditions are not confined to any region of the United States and prob-
ably not to any country or continent.

When the soils examined are separated into good and poor soils, as
based on field observations, their relationship with dihydroxystearic
acid is rather striking. Among the good soils only two contained
dihydroxystearic acid, and they were of only moderate productivity.
Among the poor soils the number of those containing this compound
was approximately one-half. Of the soils which had a definite
record for infertility, dihydroxystearic acid was found in each and
every case.

Judging from the foregoing relationships established by this inves-
tigation, it would seem that diliydroxystearic acid is either a direct
or indirect factor in the low productivity of soils; direct by virtue
of its harmful effects on growing crops, indirect as an indicator of
other compounds or conditions which cause soil to become less pro-
ductive and even infertile. It is not possible to state from the data
at hand that dihydroxystearic acid is the only factor which con-
tributes to the infertility or unproductivity of those soils in which
it was found, for it must be remembered that this is only one of many
compounds, both organic and inorganic, harmful and beneficial, as
I shall show presently, which exist in the soil, any and all of which
play a part in its relative fertility and infertility. It is certain,
however, that the determination of even this one constituent leads
to a recognition of the kind of infertility in the soils examined, and
is therefore a readily recognized symptomatic factor of poor soil
conditions.

The isolation of harmful constituents is, however, only a part
of the entire field covered by these investigations into the nature
and properties of soil organic matter, and I am very glad to be able
to announce to you the existence in the soil of organic compounds
decidedly beneficial to plant growth. Here, for example, is a speci-
men of creatinine, a nitrogenous compound, which we have isolated
from soils. The occurrence of this compound has always been asso-

ORGANIC CONSTITUENTS OF SOILS. 13

elated with animal material, but in addition to finding it in soils we
have also found it in many plant materials, such as wheat seeds,
wheat seedlings, wheat bran, rye, clover, alfalfa, cowpeas, and pota-
toes; and if, as is suggested by several investigators, creatinine
in the animal occurs as the result of the breaking up of albumin,
then it seems reasonable to expect that creatinine will be found in
practically all plants. From the standpoint of root excretion, I
should also mention the fact that of samples of the same soil, planted
and unplanted, the planted soils give larger amounts of creatinine,
thus showing that the increase in creatinine is connected in some
way with plant growth. When the roots of wheat were bathed
in water the creatinine could also be found in the culture water.
One of the sources of creatinine in soils would seem, therefore,
to be found in plants, since by their decay and by direct sloughing,
or even by excretion, the creatinine is left in water and soil. Its
occurrence in stable manure and also in green manures suggests
another source of supply, and its formation by soil organisms may
be another. Whatever its origin, it occurs in soils, appearing to be
a normal and frequently occurring constituent, and is present in
amounts comparable with the amounts of soil nitrates found in
ordinary agricultural soils. Its effect on plants, as I have implied
earlier, is decidedly beneficial. When a series of cultures containing
only potash and phosphates in varying proportions is set up together
with another set containing in addition some 50 parts per million
of creatinine the increased growth hi the latter set is rather striking,
being fully comparable with the increased growth produced by
nitrates under the same circumstances. When nitrates are present
at the same time the additional effect of the creatinine is not so
marked, but an analysis of the culture solution reveals the fact that
far less nitrate is used by the plants in the presence of the creatinine,
although a larger plant growth takes place. In other words, the plants
absorb the creatinine, make use of it in building up tissue, and in so
doing a lighter draft is made on the supply of nitrates. It appears,
therefore, that this soil constituent is fully as valuable as soil nitrates,
can be present in amounts comparable to the amounts of nitrates in
soils, and is able to replace the latter in its effect on plant growth.
The significance of this in agricultural investigations is apparent.

Nor is creatinine the only constituent that behaves in this manner.
The same beneficial characters are shown by other soil constituents —
by hypoxanthine and xanthine, by argininc and histidine, and
by nucleic acid. All these show the same influence on plant growth
and the same effect on the consumption of nitrate. Based on the
results of these rather extensive investigations, I am ready to for-
mulate the theory that these degradation products of protein are
absorbed by the plant directly from the soil and that the plant uses

14 OKGANIC CONSTITUENTS OF SOILS.

these units for building up the complex proteins as far as it is possible
to do so. Nitrate is usually considered as the best form of nitrogen
for plant food. In order to use nitrate, a highly oxidized form of
nitrogen, to form the amido and imido groups of the protein molecules,
a reduction must take place. .

It is obvious that the plant must expend considerable energy in
making this transformation. What is more reasonable than to
suppose that the unit parts of the complex protein molecules, when
presented to the plant, will be used by it in preference to preparing
these units from the nitrate ? If a soil be liberally supplied with all
of these units it is conceivable that good plant growth will result,
even without nitrate. If only a limited amount or kind of the units
be present the plant must have nitrates from which to supply the
missing units. The knowledge, therefore, that such compounds
exist in soils and play such a prominent part in the metabolism of
the growing plant is of fundamental significance in the study of soil
fertility and gives a breadth of view to the subject which in its horizon
can not be compared with the restricted vision imposed by the
purely mineral-requirement theory of Liebig as this is used by his
followers.

Nitrates are not produced in these cultures. Ammonia, if formed,
is insignificant in amount, nor does ammonia produce the striking
results shown by these organic compounds. There is a limit to the
amount of any one of these soil constituents which the plant can
profitably use and show increased growth. When a mixture of sev-
eral of these units is presented at once the growth is better than if
an equivalent or even larger amount of any single one is presented.

These compounds are all nitrogenous, but it must not be inferred
that all nitrogenous compounds are beneficial to plant growth.
Tyrosine, also a degradation product of protein, is distinctly harm-
ful, and picoline carboxylic acid, isolated from soils, is moderately
toxic. Guanidine, a compound not yet isolated from soils, but
whose presence is indicated, has also been rather thoroughly studied
and is decidedly harmful to plants, producing an effect on the cul-
tures similar to that shown by certain plant diseases. The leaves
become spotted with bleached dots, which spread and ultimately
coalesce, producing a wilting of the plant and finally death. Not
only is the guanidine harmful in contradistinction to the beneficial
nitrogenous substances just discussed, but it differs from these com-
pounds in its behavior when nitrates are present. The latter
fertilizer ingredient very greatly increases the toxic action of this
compound. This is especially striking when a large series of cultures
with and without guanidine in the presence of many ratios of phos-
phate, potash, and nitrate is set up and the cultures arranged accord-
ing to the nitrate content. Both groups of cultures with and without

ORGANIC CONSTITUENTS OF SOILS. 15

guanidine will grow nicely for three or four days without any pecu-
liarity being noticeable in either group. The cultures higli in nitrates
will be the first to show the symptoms of guanidine poisoning, and
this effect will spread through the guanidine group of cultures, be-
coming more and more marked in those high in nitrates. At the
conclusion of two weeks the group of cultures containing no guanidine
will appear green and fresh, whereas the guanidine group appears
bleached and wilted in all of the cultures containing nitrates. The
cultures which contain no nitrate — that is, only potash and phosphate —
are the only cultures which have been able to withstand the ravages
of this poisonous compound. We have here not only a striking
illustration of the harmful effect of an organic nitrogenous com-
pound, but also an example of the increased harmful effect brought
about by the addition of the otherwise beneficial nitrate. This is in
striking contrast to the ameliorating effect of nitrates over all other
fertilizers in the case of the harmful soil constituent, dihydroxy-
stearic acid. Guanidine is harmful, and dihydroxystearic acid is
harmful, although this manifests itself in a different way. Nitrate
increases the harmfulness of guanidine, but decreases the harmful-
ness of dihydroxystearic acid. Here is an effect of a fertilizer which
is entirely unexplainable from the viewpoint of mineral require-
ment or plant-food addition.

This is not the only illustration of a differential action of a. fer-
tilizer salt. Nor is this behavior of nitrate in influencing the effect
of these organic substances on plant growth and development the
only illustration of the influence that different fertilizer salts exert
on this action of the organic compounds. Cumarin is another
substance which we have studied quite thoroughly in its effect on
wheat seedlings. Besides decreasing growth, it also has a very
peculiar and characteristic action on plants which enables the ex-
perimenter to pick out cumarin-affected plants at a glance from
those affected by any other toxic body studied by us. The leaves
arc shorter and broader than is normal for wheat, and only the first
leaves are usually unfolded, the other leaves remaining wholly or
partially within the swollen sheath. Such leaves as do break forth
are usually distorted and curled or twisted. Now, when cumarin is
contained in the cultures containing the various fertilizer salts it is
quite apparent that neither nitrate nor potash affect these charac-
teristic symptoms of cumarin poisoning, but the slightest addition
of phosphate causes a very decided change in the appearance of the
plants. This increases with increasing phosphate until nearly normal
development is obtained, as shown by comparison with the corre-
sponding cultures without cumarin.

I must also cite to you the influence of quinone when similarly
studied. The effect of quinone is decidedly different from the effect

16 ORGANIC CONSTITUENTS OF SOILS.

of cumarin, which produces short, broad, irregularly developed
leaves and stunted tops; the effect of quinone is to produce long,
thin leaves and tall, slender plants. The interesting part in this
connection, however, lies in the fact that the growth in the cultures
high in potash was nearer to the normal than the growth in either
the mainly phosphatic or mainly nitrogenous cultures and was, in fact,
poorest in the latter. Vanillin similarly studied behaved like the
dihydroxystearic acid, in that nitrates were the most efficient aid to
counteract its harmful effect on plants. These experimental facts
present much interesting material for discussion from various points
of view, but I wish here only to call your attention to the relations
between organic compounds, their effect on plants, and the action
of fertilizers in this connection, which action is apparently apart and
in addition to any food value of the fertilizer salts for plants in the
usually accepted sense. In the illustrations which I have given you
it is clear, then, that the various fertilizer salts acted differently in
overcoming the respective harmful effects of these toxic organic com-
pounds. The mainly phosphatic fertilizers were the most efficient
in overcoming cumarin effects; the mainly nitrogenous fertilizers, in
overcoming the vanillin and dihydroxystearic acid effects ; the mainly
potassic, in overcoming the quinone effects; and, in the case of
guanidine, the mainly nitrogenous fertilizers even had the effect of
increasing the harmfulness of this compound. It is clear that the
organic compounds in soils, whether already isolated and studied or
yet to be found, are potent factors in soil fertility, as they have a
direct effect on plant growth and plant metabolism and on the
action of fertilizers. These actions of the different fertilizer combi-
nations, or different fertilizer requirements, as they may be styled,
show a certain parallelism with field observations on soils and their
fertilizer requirements, and one is tempted to ask to what extent
the different fertilizer requirements of different soils, or of the same
soil under different conditions, may be influenced by the same cause.
That harmful bodies occur in soils has been amply shown, and that
these are influenced directly or indirectly by fertilizer salts is also
clear from this and other researches. That the constitution of the
organic matter varies from soil to soil and in the same soil under
different conditions of aeration, drainage, and cropping is likewise
clear. The presence of compounds inimical to plant growth by virtue
of a property resembling that of any of the above mentioned sub-
stances might, therefore, cause a different fertilizer requirement, a
requirement which might even change from time to time, according
to the nature of the biochemical relations producing the compound
or according to the nature of the plant remains in the soil; in other
words, according to the rotation with its necessary altered soil man-

ORGANIC CONSTITUENTS OF SOILS. 17

agement, and the altered biochemical changes produced in the dif-
ferent plant remains.

The soil has vital functions. The soil can not be considered as
the dead, inert remains of rocks and previous vegetation, but must
be considered as an accumulation of such material in which the proc-
esses of formation, alteration, and transposition are still at work.
In other words, the soil in its entirety is not dead or inert, but endowed
with functions analogous to those of life itself. In it take place the
same processes of solution and deposition that have taken place in
past ages and are taking place to-day in the geologic processes con-
nected with the action of water on the rocks and minerals of the
earth's crust. In it take place the same physical and chemical inter-
actions as take place in the movement of subsurface waters generally,
resulting in ore formations or depositions. In it take place the same
processes of fermentation, digestion, or decay of organic materials
that take place in animals and plants or in the production of industrial
products, such as cheeses, wines, and beers, brought about in the
soil as in these other processes by means of ferments, enzymes,
bacteria, and fungi or molds. In it take place the same processes of
oxidation and reduction which play so enormous a part in all life
processes, and recent researches have shown the nature of compounds
in the soil organic matter to be the same as those derived from such
life processes or from similar laboratory processes of digestion, oxida-
tion, or reduction. Organic matter is very changeable; it is the
material which forms the food, as it were, of all the micro-organisms
of the soil — of the bacteria, of the molds, of the protozoa — and
influences them favorably or unfavorably, just as the higher plants
are affected. In turn, these agents are great promoters of changes
in the organic debris of soil. All of these processes and the life forms
in the soil are affected by fertilizer salts when added to the soil, and
changes are produced in the soil, physical, chemical, and biochemical,
which influence it and affect its potential fertility entirely irrespective
of the added plant food. In other words, the soil has been changed
in many prominent characteristics, even before any crop is planted
therein.

I must not leave this subject of fertilizer action without saying
that the Bureau of Soils takes a very advanced view, not only on the
present use of fertilizers, but on their extension in agriculture, in
spite of reiterated statements to the contrary. The point of differ-
ence between certain other investigators and the Bureau of Soils lies
in the explanation of the action of fertilizers, one view being that
they are merely so much plant food which must replace that removed
by crops, the other being that in addition to any plant food value
which they possess they affect the soil and produce changes and

18 ORGANIC CONSTITUENTS OF SOILS.

influences such as are at least partially illustrated by the experimental
results cited here. Yi'e believe that these additional — note particu-
larly that I say additional — actions explain more fully the function
of fertilizers in agriculture. From the former view the application
of fertilizers would be restricted to poor and so-called exhausted
soils and poor systems of agriculture; from the latter viewpoint fer-
tilizers are indicated as well for fertile as for infertile soils, as an
adjunct to successful farming, and for bringing the soil to its highest
capacity of crop production.

The action of fertilizers on soils is a much contested question, but
the weight of evidence is against the assumption that their effect
is due altogether to the increase of plant food as such. If so simple
an explanation were the true one, nearly a century of investigation
of this problem by scientists of all civilized nations would surely have
produced greater unanimity of opinion than now exists in regard to
fertilizer practice. Thoughtful investigators everywhere are finding
that fertilizer salts influence many factors which contribute toward
plant production besides the direct nutrient factor for the plant. It
is this additional influence of fertilizers which makes them doubly
effective when rightly used and inefficient when improperly used.
To this influence of fertilizers on soil and biological conditions is due
their capriciousness when applied on the theory of lacking plant food.
Any study which throws further light upon the mooted question is
of direct help toward reaching that view of soil fertility and soil
fertilization which will eventually result in a more definite, more
rational, and more remunerative fertilizer practice than in the past,
and thus bring about the more extensive use of f ertilizers in agriculture.

Approved :

JAMES WILSON,

Secretary of Agriculture.
Washington, D. C., October 23, 1912.

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