In general, the same action occurs in virgin
lands, but the methods of dry-farm cultivation and cropping which
permit a deeper penetration of the natural precipitation and a freer
movement of the soil-water result in a larger quantity of plant-food
reaching the upper two or three feet from the lower soil depths.
Such concentration near the surface, when it is not excessive,
favors the production of increased yields of crops.
The characteristic high fertility and great depth of arid soils are
probably the two main factors explaining the apparent increase of
the fertility of dry-farms under a system of agriculture which does
not include the practice of manuring. Yet, there are other
conditions that contribute largely to the result. For instance,
every cultural method accepted in dry-farming, such as deep plowing,
fallowing, and frequent cultivation, enables the weathering forces
to act upon the soil particles. Especially is it made easy for the
air to enter the soil. Under such conditions, the plant-food
unavailable to plants because of its insoluble condition is
liberated and made available.
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