Loss by evaporation chiefly at the surface
Evaporation goes on from every wet substance. Water evaporates
therefore from the wet soil grains under the surface as well as from
those at the surface. In developing a system of practice which will
reduce evaporation to a minimum it must be learned whether the water
which evaporates from the soil particles far below the surface is
carried in large quantities into the atmosphere and thus lost to
plant use. Over forty years ago, Nessler subjected this question to
experiment and found that the loss by evaporation occurs almost
wholly at the soil surface, and that very little if any is lost
directly by evaporation from the lower soil layers. Other
experimenters have confirmed this conclusion, and very recently
Buckingham, examining the same subject, found that while there is a
very slow upward movement of the soil gases into the atmosphere, the
total quantity of the water thus lost by direct evaporation from
soil, a foot below the surface, amounted at most to one inch of
rainfall in six years. This is insignificant even under semiarid and
arid conditions.
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