Application of Soil Water Flow Theory in Field Simulation

A numerical model based on a finite difference approximation of the basic differential equation for soil water flow is described. The equation includes a sink term representing moisture extraction by root systems, and allowance for evaporation from the soil surface is made too. Estimation of these terms is based on a potential transpiration calculated from Penman-Monteith's equation, on a potential evaporation calculated from Ritchie's equation and in both cases on relations to soil moisture status over various soil depths. The model simulations are compared with field observations of moisture content and soil moisture tension. Further, the model has been applied in evaluating how irrigation treatment effects the increases in evapotranspiration and deep percolation.