The Storage and Use of Soil Moisture 
49 
face of the plat not mulched would permit a more rapid loss of 
water by evaporation. 
LOSS OF WATER FROM THE SOIL. 
There are three ways by which water may be lost after it has 
been gotten into the soil : First, by escape downward by percola- 
tion; second, by evaporation from the surface; third, by trans- 
piration, or by being used by plants. 
Of the first-named means of loss little need be said. It is sel- 
dom that we get enough water into the soil at this Station to 
allow percolation beyond the reach of the plant. Percolation does 
not take place until a soil is filled beyond its carrying capacity. 
This point is seldom reached, and, if reached, we cannot control 
percolation. 
The second means of escape, that is, by evaporation from the 
surface, is to a certain extent under the control of the farmer. 
There will always be some loss, but it can be reduced to a mini- 
mum. The water that evaporates from the surface reaches the 
surface much the same as oil from the bowl of the lamp reaches 
the flame. The water passes from one soil particle to another 
until it reaches the surface and is lost by evaporation. This up- 
ward movement is much more rapid when the soils are wet and 
is retarded as they dry out. If the surface of the soil is cultivated 
it becomes loose and dry. Either condition tends to retard the 
further movement of water to the surface. Water moves very 
slowly thru a loose or dry soil. In this section a rain is usually 
followed by a hot sun and wind. These cause a more rapid loss 
of water from the surface than can be supplied by capillarity 
from adjoining soil particles. The result is that the soil surface 
soon dries. This is in itself a check to surface evaporation. The 
water from below moves slowly thru the dry surface. If the rain 
was of sufficient amount to make the surface smooth and connect 
with the under moisture, it should be stirred as soon as practical. 
In order to reduce evaporation from the surface to a minimum, 
it is essential to have on the surface not only a dry soil, but a 
loose soil. Cultivation will stir the surface soil, cause it to dry 
out more quickly, and leave the soil grains not so closely in con- 
tact. The fewer the points of contact between the small particles 
of soil and the drier they become, the more effective is the mulch 
in reducing evaporation. Another reason for cultivation soon 
after a rain, especially where a field is bare, is that a smooth soil 
blows much more quickly than a rough soil. This, of course, 
applies to the soils that are light enough to blow and in regions 
of frequent high winds. 
