In humid countries, the rain that falls during the growing season is
looked upon, and very properly, as the really effective factor in
the production of large crops. The root systems of plants grown
under such humid conditions are near the surface, ready to absorb
immediately the rains that fall, even if they do not soak deeply
into the soil. As has been shown in Chapter IV, it is only over a
small portion of the dry-farm territory that the bulk of the scanty
precipitation occurs during the growing season. Over a large portion
of the arid and semiarid region the summers are almost rainless and
the bulk of the precipitation comes in the winter, late fall, or
early spring when plants are not growing. If the rains that fall
during the growing season are indispensable in crop production, the
possible area to be reclaimed by dry-farming will be greatly
limited. Even when much of the total precipitation comes in summer,
the amount in dry-farm districts is seldom sufficient for the proper
maturing of crops. In fact, successful dry-farming depends chiefly
upon the success with which the rains that fall during any season of
the year may be stored and kept in the soil until needed by plants
in their growth.
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