Prediction of Water Loss from a Fallow Field Soil Based on Soil Water Flow Theory

A simple technique based on soil water flow theory to predict evaporation from nonhomogeneous field soils is presented. From cumulative evaporation measurements on undisturbed cores of soil, a dimensionless curve is drawn relating fractional water loss to the square root of time divided by the amount of water available for evaporation. A procedure is described to account for the residual water left in the soil from one rainfall event to the next. Predictions of cumulative evaporation made by the use of the dimensionless curve were compared with 4 years' of lysimeter data on Rago silt loam. The system would work best in an area with high average potential evaporation and low rainfall such as the Great Plains.