Effect of Environmental Factors on Evaporation Rates from Soils in the Presence of a Water Table

Laboratory studies were conducted to assess the effect of external environmental factors on evaporation rates from soils in the presence of a water table. Columns of fine quartz sand and Miami silt loam were used, and water table was maintained at desired depths. Radiant energy was supplied by an incandescent lamp suspended above the surface of soil column, and air turbulence was created by an electric fan. Humidity and temperature were not controlled. An integrated effect of all ambient factors was measured in terms of evaporation rate from a free water surface, which was referred to as potential evaporation rate. It was observed that evaporation rate was mainly governed by external conditions when the water table was within 60 to 90 cm of the surface. The nature of the soil played no significant role. For deeper water tables, tne capillary coniuctivity of the soil became the main controlling factor. Lowering the water table appreciably reduced the evaporation rates, but even from very deep water tables, the evaporative losses continued at the rate of about 0.05 cm/day. This can lead to salinization of soils in a period of time, depending upon the concentration of salts in the ground water. Additional studies were made on measurement of capillary conductivity. Gamma-ray attenuation technique was employed for non-destructive and frequent sampling of moisture content in soil profile above the water table.