Hilgard believes that the hygroscopic
moisture can be of considerable help in carrying plants through
rainless summers, and further, that its presence prevents the
heating of the soil particles to a point dangerous to plant roots.
Other authorities maintain earnestly that the hygroscopic soil-water
is practically useless to plants. Considering the fact that wilting
occurs long before the hygroscopic water contained in the soil is
reached, it is very unlikely that water so held is of any real
benefit to plant growth.
Gravitational water
It often happens that a portion of the water in the soil is under
the immediate influence of gravitation. For instance, a stone which,
normally, is covered with hygroscopic water is dipped into water The
hydroscopic water is not thereby affected, but as the stone is drawn
out of the water a good part of the water runs off. This is
gravitational water That is, the gravitational water of soils is
that portion of the soil-water which filling the soil pores, flows
downward through the soil under the influence of gravity. When the
soil pores are completely filled, the maximum amount of
gravitational water is found there.
Pages:
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103