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THE SOIL SOLUTION
Published by
The Chemical Publishing Co.
Easton, Penna.
Publishers of Scientific Books
Engineering Chemistry Portland Cement
Agricultural Chemistry Qualitative Analysis
Household Chemistry Chemists’ Pocket Manual
Metallurgy, Etc.
The Soil Solution
The Nutrient Medium for Plant Growth
By
FRANK K. CAMERON
In Charge, Physical and Chemical Investigations,
Bureau of Soils,
U. S. Department of Agriculture
EASTON, PA.:
THE CHEMICAL PUBLISHING CO.
1911
LONDON, ENGLAND:
WILLIAMS & NORGATE
14 HENRIETTA STREET, COVENT GARDEN, W. C.
COPYRIGHT, 1911, BY EDWARD HART
Preface.
It has long been the custom to regard soil chemistry from one of two
diametrically opposed points of view. Either, it has been considered
extremely simple, or complex and hopelessly difficult. In either case
the impression has generally prevailed that practical work in soil
chemistry consists in treating the soil with some solvent or other and
analyzing the resulting solution for “available” plant food elements;
in other words, that the chemist’s role in soil studies is merely that
of an analyst.
Soil chemistry is complex, but not by any means hopelessly so.
Unfortunately, the complexity of most of the problems presented has
deterred the student of pure chemistry from attacking them, and
because they do not offer any material pecuniary rewards, they have
not appealed strongly to the investigator in applied chemistry.
Investigations in soil chemistry, for their own sake, or for the sole
purpose of increasing the sum total of human knowledge concerning the
phenomena taking place in the soil, have been comparatively rare. The
subject has generally been regarded from the analytical point of view
and as incidental to agronomic studies.
One purpose of this little book is to show the investigator in
chemistry who is not limited by the condition that his work must bring
some personal financial return, that the soil and its problems offer
a field for his efforts quite worthy of ranking along-side the most
interesting branches of pure chemistry, as well as being of the very
highest importance to the development of the welfare of the human race.
Another purpose is to point out the line of attack upon the problems of
soil chemistry which at this time offers the largest opportunity for
results. In how far the details of the story in the following pages are
correct, time with its further investigations will tell. In a sense,
the correctness of the details is of secondary importance. It is of the
first importance, however, that there should be a general recognition
that soil phenomena are essentially dynamic in character, and that the
investigation of the properties of the soil solution and its relation
to crop production is a procedure certain to yield results of positive
value.
Again, it is a purpose of this book to make available for students
of agriculture, a systematic outline of the work so far accomplished
in this particular field. It is to the students of to-day from whom
are to come the investigations of the near future that the book is
particularly addressed. Some of the details presented in the following
pages are matters on which opposed opinions are now held strongly
by different authorities, and to the unbiased minds of the coming
investigators must be left the decision as to how closely the truth
has been approximated in what is written to-day. The field of effort
covered by this book is one in which there is an increasing activity,
and new facts and deductions will inevitably bring modifications to
present opinions. To encourage this further acquisition of knowledge is
the main purpose of the book.
The material brought together in this book has been presented to the
faculties and students of several of our Agricultural Colleges, in the
form of a short course of lectures. In large part, moreover, it has
been published in Volume XIV of the Journal of Physical Chemistry. To
make it accessible to and more easily read by one familiar with the
progress of technical soil investigations, it has been recast in its
present form.
It has been assumed that the reader will have a fair working knowledge
of the concepts of modern chemistry. Nevertheless, an effort has been
made to avoid technical terms so far as this can be done without undue
sacrifice of lucidity of expression. Free references have been made to
the bulletins of the Bureau of Soils, U. S. Department of Agriculture,
because they are generally accessible to the American student, and
because in them will be found detailed discussions and bibliographical
material pertinent to the subjects outlined here. To his coworkers,
the author is indebted for many criticisms and suggestions; and more
especially in the making of the book is he indebted to Mr. S. C. Stuntz.
Washington, D. C.
1911.
Table of Contents.
PAGE
Preface iii
I. The Soil 1
II. Soil Management or Control 4
III. Soil Analysis and the Historical Methods of Soil
Investigation 8
IV. The Plant-Food Theory of Fertilizers 16
V. The Dynamic Nature of Soil Phenomena 18
VI. The Film Water 24
VII. The Mineral Constituents of the Soil Solution 31
VIII. Absorption by Soils 59
IX. The Relation of Plant Growth to Concentration 70
X. The Balance Between Supply and Removal of Mineral
Plant Nutrients 75
XI. The Organic Constituents of the Soil Solution 79
XII. Fertilizers 105
XIII. Alkali 110
Index 127
AN INTRODUCTION TO THE STUDY OF THE SOIL SOLUTION.
Chapter I.
THE SOIL.
The soil, or that part of the land surface of the earth adapted to
the growth and support of crops, is a heterogeneous mixture composed
of solids, gases and a liquid, and containing living organisms. There
are present: mineral debris from rock degradation and decomposition;
organic matter from the degradation and decomposition of former plant
and animal tissues; the soil atmosphere, always richer in carbon
dioxide and water vapor and possibly other gases than the atmosphere
above the soil; living organisms, such as various kinds of bacteria and
fungi, with the products of their activities, notably the “nitrogen
carriers” and the enzymes; and finally the soil moisture, a solution
of products yielded by the above components and in equilibrium or
approaching equilibrium with the solids and gases with which it is in
contact.
In its relation to crop plants,[1] that part of the soil of immediate
importance is the soil moisture. From this solution the plants, through
their roots, draw all the material involved in their growth, except
the carbon dioxide absorbed through their leaves. The soil solution is
the natural nutrient medium from which the plants absorb the mineral
constituents which have been shown to be absolutely essential to their
continued existence and development. And from this solution plants
sometimes absorb dissolved organic substances, but such absorptions
are probably adventitious and incidental to the growth of the plant in
a particular environment. While it appears certain that no organic
substance in the nutrient medium is necessary to the maintenance of
plant growth, nevertheless organic substances are probably always
present under natural conditions. They may or may not be absorbed by
the plant and may affect it beneficially or otherwise.
[1] By crop plants are meant the ordinary green plants employed in
agriculture. As is well-known, the fungi as well as certain parasitic
and saprophytic non-green seed plants obtain their nutriment in a very
different way from ordinary green crop plants.
The study of the soil solution is of the first importance in the
investigation of the relation of the soil to plant growth, and in the
following pages there is given an outline of our present knowledge of
the chemical principles involved, with such discussion of the physical
and biological factors as is essential to an orderly presentation of
the subject.
To understand clearly the relations of the soil solution to the soil
as a whole and to the plant which it nourishes, it is desirable to
consider some attributes of soils in general. Every soil, no matter
of what type it may be, is a complex system. In it various processes
are continually in operation, excepting possibly in the extreme case
when it remains frozen for a time at some definite temperature. The
resultant or summation of these processes, whether expressed in
plant production or otherwise, will vary from time to time, both
quantitatively and in direction; for instance, as to the amount and
kinds of plant growth it produces. That is to say, any particular
soil area is seemingly an organic entity, functioning according to
its own inherent properties, but subject to the modifying influences
of environment, as by exceptional climatic extremes, flood, fire, and
especially by artificially imposed agencies of control.
From the practical point of view the problem of the soil in its
relation to crop production is like the problem of the factory or of
any other industrial endeavor, in that it is a problem of management
or control. The soil possesses this distinction, however, that it
is both the raw material and the factory.[2] The processes involved
are physical, chemical and biological, are always numerous and
interdependent, and are never (speaking generally) exactly the same,
so that each soil possesses marked individuality. No matter how soils
may be classified, as for instance into provinces, series and types,[3]
the fact remains that the soil of the individual field has properties
which give it a crop-producing power, an adaptation to a specific
crop or crop rotation, or a responsiveness to cultural treatment,
which can not be anticipated in any other field. Consequently, there
is no possibility of reducing soil management or agriculture to the
state of an exact science. That is to say, scientific investigation of
the problems involved cannot be expected to yield absolute results,
although furnishing the best possible basis on which to form judgments.
Soil management, like other agricultural practices, is an art, more or
less well founded on scientific principles, perhaps, but susceptible of
much higher development as the scientific principles involved become
better understood.
[2] According to S. W. Johnson—Some points of agricultural science, Am.
Jour. Sci. (2), =28=, 71-85 (1859)—“The soil (speaking in the widest
sense) is then not only the ultimate exhaustless source of mineral
(fixed) food, to vegetation, but it is the storehouse and conservatory
of this food, protecting its own resources from waste and from too
rapid use, and converting the highly soluble matters of animal exuviæ
as well as of artificial refuse (manures) into permanent supplies.”
[3] For definitions, see Soil Survey Field Book, 1906, Bureau of
Soils, U. S. Dept. of Agriculture, pp. 15-24. On the ground that
experience has shown that genetic classifications are the ones which
have generally persisted and proved the most useful, objection might be
made to the classification just cited. But a careful inspection of the
results of the Soil Survey by the U. S. Department of Agriculture will
show that while not categorically stating the fact, to all intents and
purposes it has employed a genetic classification. This is exemplified
by the fact that its delineation of soil provinces corresponds quite
closely with the recognized physiographic provinces of the United
States. See map accompanying Soils of the United States, by Milton
Whitney, Bull. No. =55= Bureau of Soils, U. S. Dept. Agriculture, 1909.