It is further to be remembered that roots are in constant search of
food and water and are likely to develop in the directions where
there is the greatest abundance of these materials. Under systems of
dry-farming the soil water is stored more or less uniformly to
considerable depths--ten feet or more--and in most cases the
percentage of moisture in the spring and summer is as large or
larger some feet below the surface than in the upper two feet. The
tendency of the root is, then, to move downward to depths where
there is a larger supply of water. Especially is this tendency
increased by the available soil fertility found throughout the whole
depth of the soil mass.
It has been argued that in many of the irrigated sections the roots
do not penetrate the soil to great depths. This is true, because by
the present wasteful methods of irrigation the plant receives so
much water at such untimely seasons that the roots acquire the habit
of feeding very near the surface where the water is so lavishly
applied. This means not only that the plant suffers more greatly in
times of drouth, but that, since the feeding ground of the roots is
smaller, the crop is likely to be small.
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