Burr,
working under Great Plains conditions in Nebraska, has shown that
the spring and summer rains penetrate the soil to the depth of 6
feet, the average depth of the borings, and that it undoubtedly
affects the soil-moisture to the depth of 10 feet. In general, the
dry-farmer may safely accept the doctrine that the water that falls
upon his land penetrates the soil far beyond the immediate reach of
the sun, though not so far away that plant roots cannot make use of
it.
Importance of a moist subsoil
In the consideration of the downward movement of soil-water it is to
be noted that it is only when the soil is tolerably moist that the
natural precipitation moves rapidly and freely to the deeper soil
layers. When the soil is dry, the downward movement of the water is
much slower and the bulk of the water is then stored near the
surface where the loss of moisture goes on most rapidly. It has been
observed repeatedly in the investigations at the Utah Station that
when desert land is broken for dry-farm purposes and then properly
cultivated, the precipitation penetrates farther and farther into
the soil with every year of cultivation.
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