Techniques were developed to simulate the soil-plant environment as a semi-dynamic hydrologic system. Exponential expressions give reasonable estimates of soil evaporation prior to corn plant emergence. A family of nonlinear curves were used to estimate evapotranspiration after emergence. These curves assumed that pan evaporation was the integrated result of atmospheric demands. Precipitation excess was estimated from an exponential expression using total water storage capacity in the Ap or A soil horizon. Corn plant heights were simulated with a 2-part nondimensional exponential relationship. Rainfall interception was assumed to be a function of rainfall, plant height, and density of cover. Vertical water movement through the soil was assumed to be related to its saturated hydraulic conductivity. All aspects of the model were programmed in the Fortran language for an IBM 360 Computer. A comparision of simulated with observed data indicates very good agreement. With few exceptions, the simulated results were well within sampling variation. (WRSIC abstract)