The Potentialities for Decreasing Soil Moisture Evaporation Loss

Abstract

AbstractThis paper has two objectives: (1) to make available to American workers the results of Russian work on soil moisture evaporation suppression; and (2) to lay a background for our present work along these lines; some of which is included.In the evaporation process, the loss of soil moisture can be divided into three stages. The first stage is that of rapid loss of water where capillary flow to the soil surface is sufficient to meet the evaporative demand of the above ground environment. The second stage in the evaporation process is one of rapid decline in rate of loss as the soil reservoir is depleted. In this case above‐ground conditions are no longer as important but intrinsic soil factors govern the rate of moisture flow to the soil surface. Capillary flow, vapor transfer, and the combination of the two in the capillary condensation evaporation process dominate the picture. The third stage of moisture loss is that of extremely slow rates and is governed by adsorptive forces of molecular distances at the soil liquid‐solid interface.Potentialities for suppressing this rate process lie in the first two stages of moisture loss.These potentialities group themselves into three categories: (a) Decreasing turbulent transfer of water vapor to the atmosphere by such procedures as, allowing stubble to stand, adding mulching material, increasing soil surface roughness. (b) Decreasing capillary continuity by tillage methods or chemical additives of the soil stabilizer type; and (c) Decreasing capillary flow and moisture holding capacity of the surface soil layers by chemical additives of the surfactant type.Each of these three catgories is discussed in turn. Recent work from this laboratory is cited, particularly that dealing with surfactants and mulches. Data presented in this regard demonstrate the influence of surfactants on capillary flow in clay‐water systems of the montmorillonitic and kaolinitic types. Net radiation data and temperature data obtained with mulched and bare field soils are presented, suggesting that the increased heat storage under a plant residue mulch may account for the surprising lack of evaporation suppression where mulching of this type has been practiced.