Only the water,
safely stored in the soil within reach of the roots, can be used in
crop production. Of nearly equal importance is the problem of
keeping the water in the soil until it is needed by plants. During
the growing season, water may be lost from the soil by downward
drainage or by evaporation from the surface. It becomes necessary,
therefore, to determine under what conditions the natural
precipitation stored in the soil moves downward and by what means
surface evaporation may be prevented or regulated. The soil-water,
of real use to plants, is that taken up by the roots and finally
evaporated from the leaves. A large part of the water stored in the
soil is thus used. The methods whereby this direct draft of plants
on the soil-moisture may be regulated are, naturally, of the utmost
importance to the dry-farmer, and they constitute another vital
problem of the science of dry-farming.
The relation of crops to the prevailing conditions of arid lands
offers another group of important dry-farm problems. Some plants use
much less water than others. Some attain maturity quickly, and in
that way become desirable for dry-farming.
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