Second, soil-water may be lost by direct evaporation from the
surface soil. The conditions prevailing in arid districts favor
strongly this manner of loss of soil-moisture. It has been shown,
however, in the preceding chapter that the farmer, by proper and
persistent cultivation of the topsoil, has it in his power to reduce
this loss enough to be almost negligible in the farmer's
consideration. Third, soil-water may be lost by evaporation from the
plants themselves. While it is not generally understood, this source
of loss is, in districts where dry-farming is properly carried on,
very much larger than that resulting either from seepage or from
direct evaporation. While plants are growing, evaporation from
plants, ordinarily called transpiration, continues. Experiments
performed in various arid districts have shown that one and a half
to three times more water evaporates from the plant than directly
from well-tilled soil. To the present very little has been learned
concerning the most effective methods of checking or controlling
this continual loss of water. Transpiration, or the evaporation of
water from the plants themselves and the means of controlling this
loss, are subjects of the deepest importance to the dry-farmer.
Pages:
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166