However, the rate of loss of water by direct
evaporation from the lower soil layers increases with the porosity
of the soil, that is, with the space not filled with soil particles
or water. Fine-grained soils, therefore, lose the least water in
this manner. Nevertheless, if coarse-grained soils are well filled
with water, by deep fall plowing and by proper summer fallowing for
the conservation of moisture, the loss of moisture by direct
evaporation from the lower soil layers need not be larger than from
finer grained soils
Thus again are emphasized the principles previously laid down that,
for the most successful dry-farming, the soil should always be kept
well filled with moisture, even if it means that the land, after
being broken, must lie fallow for one or two seasons, until a
sufficient amount of moisture has accumulated. Further, the
correlative principle is emphasized that the moisture in dry-farm
lands should be stored deeply, away from the immediate action of the
sun's rays upon the land surface. The necessity for deep soils is
thus again brought out.
The great loss of soil moisture due to an accumulation of water in
the upper twelve inches is well brought out in the experiments
conducted by the Utah Station.
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