This, of course, is seldom
the case in dry-farm districts. In any soil, excepting one already
saturated, the addition of water will produce a thickening of the
soil-water film to the full descent of the water. This immediately
destroys the conditions of equilibrium formerly existing, for the
moisture is not now uniformly distributed. Consequently a process of
redistribution begins which continues until the nearest approach to
equilibrium is restored. In this process water will pass in every
direction from the wet portion of the soil to the drier; it does not
necessarily mean that water will actually pass from the wet portion
to the drier portion; usually, at the driest point a little water is
drawn from the adjoining point, which in turn draws from the next,
and that from the next, until the redistribution is complete. The
process is very much like stuffing wool into a sack which already is
loosely filled. The new wool does not reach the bottom of the sack,
yet there is more wool in the bottom than there was before.
If a plant-root is actively feeding some distance under the soil
surface, the reverse process occurs.
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