5S 
THIRTEENTH REPORT. 
contact with them, so that there is continually being brought to the 
surface of our soils a solution containing the mineral elements, includ- 
ing those necessary to plant growth. So far as investigation can de- 
termine the matter at present, it appears that the concentration of this 
solution does not vary very much in composition with respect to those 
mineral constituents which are recognized as of importance to plant 
growth, at least within a given area or in areas under similar climatic 
conditions, and the concentration of the solution, except in special cases, 
is much higher than that of the seepage water, being on the average in 
the United States probably ten times as high. 
Calculations based on observations of the rainfall and runoff of our 
principal areas, as well as some direct experimentation, show that under 
normal conditions such as those obtaining in the humid areas of the 
United States, upwards of two-thirds of the rainfall enters the soil, 
penetrates to the subsoil, and returns to the surface, carrying with it dis- 
solved material which is available for plants. A consideration of this 
line of inquiry leads to the conviction that practically all the mineral 
plant food utilized by growing crops is being brought to them from the 
subsoil where the roots do not actually penetrate. There is much evi- 
dence in favor of this view, though time will not permit me to lay it be- 
fore you today. But it is clear that we must recognize not only the inter- 
dependence of soil factors as well as other factors in crop production, 
but we must recognize furthermore that every factor in the soil affecting 
crop production is continually changing, and that the problem is essen- 
tially a dynamic one, not susceptible to the application of static con- 
siderations, which have so long been popular and in some quarters are 
still so. The analogy of the soil to a bank from which deposits of plant 
food are being drawn is essentially false. Rather is the soil like to a 
complicated machine with many parts, each running according to its 
own specific purpose, but the whole to the general purpose of turning 
out a definite finished product; and this product in quality and in 
quantity is determined by the way each separate operation is performed, 
as well as bv the character of raw material furnished. Like such a 
c- 
, machine the soil if not used or if misused, “rusts,” but properly used it 
increases in efficiency. Analogies are. however, very dangerous as argu- 
ments, and I would not have you fail to recognize that in some essential 
features the soil no more resembles such a mechanical device than it 
does a bank. 
With these soil factors admitted, another conviction comes to mind. A 
simple substance has but relatively few characteristics. One amoeba is 
like another, one drop of water is not essentially different from another. 
As complexity increases, so does differentiation, and as we pass to the 
highest complex of which we have any knowledge, the civilized human 
being, the differences between one man and another are quite as promi- 
nent as the similarities. Two engines built from the same shops, from 
the same patterns and in (he hands of the same engineer differ in per 
formance as a rule. The soil is extremely complex, consequently no two 
soils are alike, and the more they are studied the more it becomes ap- 
parent that Hie differences not only between soil types but between dif- 
ferent fields of the same soil are fully as important as are the similarities. 
No two fields can be exjieeted to have the same crop producing power 
or the same adaptability to crops or rotations of crops, or the same 
