FERTILIZERS.
It is generally recognized that the great practical problem confronting
the soil chemist is the proper use of soil amendments or fertilizers.
The farmers of the United States now spend annually for fertilizers
upwards of $100,000,000. It is estimated by various authorities that
a large fraction, perhaps as much as three-fourths, of the material
represented by this expenditure is misapplied for lack of intelligent
direction. Yet all of this enormous mass of fertilizers can be used
to advantage. Great as it is, it is relatively small beside the total
which will, and must, be used in a not distant future, with the growth
and development of intensive methods of cultivation consequent upon
the rapid settling of the country, the practical disappearance of new
lands and the increase in money value of the old lands. The commercial
importance of the problem, therefore, makes it desirable that special
emphasis should be given to fertilizers from the point of view
developed in the preceding chapters. It should be recalled that the use
of fertilizers constitutes one of the three great general methods of
soil control, and further that while tillage methods, crop rotations,
and fertilizer applications can be used to supplement one another, no
one of these methods can be expected to take satisfactorily the place
of another.
Crop production is dependent upon a large number of factors. Upon the
rainfall, both as to the amount and distribution; upon the sunlight, as
to amount and distribution; upon the chemical and physical properties
of the soil; soil bacteria and other biologic agents; enzymes in the
soil; biological factors in the plant, and probably many other things.
Opinions do and will continue to differ as to what these factors are,
but at least every one agrees that they are many.
Attempting to formulate these factors develops fundamental
difficulties, since it is not positively known how far the variables
are dependent or independent, and we have no idea as to the nature of
the function or functions. The weight of existing evidence favors the
view that all the factors are dependent variables, although numerous
attempts have been made from time to time to show that some one factor,
such as the rainfall for instance, or the mean annual temperature, or
available plant-food, is _practically_ an independent factor. Although
it should be rather easy to determine experimentally the nature of the
function, if any of these various factors were independent, this has
never been done, and this fact is itself a strong argument that all the
factors in crop production are dependent on one another.
When there is introduced into the equation a factor for any one of
the methods of soil control, _i. e._, tillage, crop rotation, or
fertilizers, it becomes even more apparent that the function is
determined by dependent variables, for the new factor always more or
less affects several if not all of those already cited. For instance,
fertilizers certainly affect the chemical properties of the soil, its
physical properties, the soil bacteria, perhaps the plant-food supply,
the oxidation of plant effluvia and other factors. It is obvious,
therefore, that a satisfactory theory of fertilizer action can not be a
simple one but must of necessity be complex; and the same statement is
no less true as regards tillage and crop rotation.
The recognition of the fact that the action of fertilizers is a complex
function depending upon many factors and groups of factors which vary
among themselves and with each individual soil, carries with it the
conviction that an exact or quantitative fertilizer practice, while
theoretically possible, is probably unattainable since methods for the
solution of such complex functions are generally wanting. It is not
surprising, therefore, that the empirical experience of the past has
failed to develop a quantitative practice. However disappointing this
may seem at first sight, the prospect is not altogether hopeless, for
this point of view indicates a systematic scheme for experimentally
determining a qualitative, but nevertheless rational, fertilizer
practice. The dominance of the plant-food theory of fertilizers in
the past, shutting off, as it has, a rational attack of the problem,
is causing the annual waste of millions of dollars in misapplied
fertilizers, and it is of scarcely less economic than scientific
importance to investigate and extend our knowledge of the effect
of soil amendments upon the many factors in crop production. With a
knowledge of the effect of fertilizers upon the physical, chemical
and biological factors in crop production, and of the nature of the
interdependence of these factors, will come the ability to manage
intelligently the individual field for the particular crop. This
knowledge can only come by attacking the problem from the dynamic
viewpoint, and so far as the soil factors are concerned, they can
apparently be studied best as they affect the properties of the soil
solution.
While it seems certain that some fertilizer effects are directly upon
the soil and secondarily upon the plants, it cannot be doubted that in
others, the phenomena are more directly concerned with the absorption
by and the metabolism within the plant and until these plant processes
are better understood, nothing approaching a satisfactory practice can
be anticipated. Why and how plants exercise the selective powers they
appear to possess are fundamental questions yet to be answered. The
important effects sometimes produced by adding to the nutrient medium
such substances as manganese salts which are not necessary to the
growth of the plant, can no more be neglected than the study of the
phosphorus needs. The presence in the soil universally of substances
other than the recognized mineral nutrients,[122] may very well have a
significance for plant production hitherto unsuspected, for the fact
that an organism can continue to function in the absence of a substance
is no argument, much less proof, that it would not function better with
that substance present. Recent investigations, showing that animal
organisms are sometimes more resistant to certain toxins and diseases
under starvation conditions or when ingesting substances unnecessary
to normal development, suggest the possibility at least of similar
phenomena with plants. It is at any rate clear that the practical
problem of the best production of plants from soils is not merely one
of providing a relatively large supply of potassium, phosphorus and
nitrogen.
[122] See, for instance, Barium in soils, by G. H. Failyer, Bull. No.
=71=, Bureau of Soils, U. S. Dept. of Agriculture, 1910.
In this connection it is well to consider what constitutes a commercial
fertilizer. It must be a substance the addition of which either
directly or indirectly affects the properties of the soil or the
growing plant; it must be obtainable in large quantities and from a
source or sources of supply not readily exhausted; and it must be
cheap. Of the many substances filling the first condition, all those
which fulfill also the other conditions are used as fertilizers, with
the exception of common salt and human excrement. In spite of the fact
that it does not contain a conventional plant-food, sodium chloride
appears to produce results quite similar to those produced by the usual
fertilizer salts. Its use has been followed generally by an increased
yield of crop, but occasionally by a decreased one, and it appears not
improbable that further investigation would show sodium chloride to
have a considerable value as a fertilizer. Human excrement or night
soil, and the sewage and garbage refuse of our large cities are not
commercial fertilizers, although having undoubtedly a high agricultural
value. Objection has been urged to them that they are “filthy” and
liable to contain dangerous pathogenic organisms. Both objections could
be met. It seems a more rational explanation that the agricultural
methods of this country have not yet become sufficiently intensive to
necessitate the conservation of such materials or to justify their
commercial exploitation.
New products will come into use from time to time, as in the case of
calcium cyanamid and basic calcium nitrate. But it is worthy of note
that these substances have become available not so much because of
their agricultural value, but incidentally to the efforts of inventors
and manufacturers to produce cheap nitric acid for the preparation of
high explosives.[123] There seems no reason to doubt that an ample
supply of desirable substances will always be available for fertilizer
purposes. The immediate practical problem for the future is not the
seeking of new fertilizers but the rational use of those at hand.
[123] In this connection it may be of interest to call attention to
the fact that the Twelfth Census shows less than a fifth of the sodium
nitrate brought into the United States goes into the fertilizer trade.
Moreover, the production of ammonium salts by the extensive coke and
gas plants of the country has been practically _nil_ not because of any
inherent difficulties in making them or because the cost of production
has been high, but because the market demands in this country have been
too small.