9 
character of the soil would not permit its absorption. Herein will be 
found one of the most helpful uses of groves in Western agriculture. 
The tree tops will protect the surface of the soil, which, after the few 
years’ cultivation given the trees immediately following planting, will 
become much more absorptive than when protected only by the slight 
covering of grasses which nature has placed there. The annual crop 
of leaves falling in the grove becomes an additional absorbent, so that 
the grove becomes in time a reservoir of moisture, increasing in utility 
with age. This moisture becomes available to the surrounding fields. 
In the sand hills of Nebraska and Kansas, where the soil has but a 
slight percentage of clay as compared with its large proportion of sand, 
even after long periods of drought only the few inches of surface soil 
become dry. Scratch away but a few inches and the sand is found 
moist to the touch, and this despite an even scantier cover than is 
found in the clay loams that form the typical soil of the plains. This 
would seem to establish the fact that soil moisture in any given locality 
is quite as dependent, if not more so, upon the physical structure of 
the soil itself as upon the amount of rain falling thereon. 
Again, the character of the subsoil plays a very important part in 
determining soil moisture. There is always somewhere below the sur- 
face a moisture-bearing layer. It may be deep in the earth, as are the 
strata which yield the water of artesian wells, or it may be on a level 
with the streams, as is the case in the great bottom lands of the 
Arkansas River. But even where the water-bearing stratum is but a 
few feet below the surface, if between it and the surface soil a compact 
clay intervene, the results are almost as deleterious to vegetable growth 
as though the ground were dry to an unknown depth. These stiff 
clays are of frequent occurrence throughout the West, and they form 
a practically impenetrable cover to the water-bearing stratum below, 
preventing the upward rise of water by capillarity, as would happen in 
a porous soil. As the dry air is constantly taking moisture from the 
surface soil by evaporation, unless the loss thus suffered can be replaced 
the supply becomes reduced to a point where only the lower forms of 
vegetation can be sustained. The loss of moisture can be supplied in 
only one of two ways: (1) by application of water to the surface, as by 
rain or irrigation, or (2) by a rise of water from the lower strata of the 
soil. These lower strata may secure their water supply from far dis- 
tant sources, the porous character of the subsoil permitting the transfer 
of water for hundreds of miles from the place where it first came to 
earth as rain or snow. 
From what has been said it will be readily understood that, while a 
stiff clay subsoil is unsuitable for trees and should be avoided if pos- 
sible, it yet remains true that the trees themselves by their growth 
eradually improve the soil conditions. By Shading the surface soil 
they render it much more absorbent, and their roots gradually pene- 
trate the stiff subsoils, thus permitting moisture to penetrate to a 
greater depth than would otherwise be possible. 
