SWBACROS: A model for the estimation of the water balance of a cropped soil

The mathematical model SWBACROS (Simulation of the Water BAlance of a CROpped Soil) is presented. The model is based on the numerical solution of the partial differential equation which describes the unsaturated transient water flow in a heterogeneous soil in the presence of a crop. The equation is solved by the Douglas - Jones predictor-corrector method or by the implicit method. Output of the model includes water content and pressure head profiles with respect to time and also fluxes through top and bottom boundary, actual evaporation and actual transpiration. Input data include climatological data necessary for the computation of the potential evapotranspiration by the modified Penman method, rainfall and/or irrigation data and the definition of the different horizons of the soil profile. The model uses the Rosenbrock method to solve the soil parameters estimation problem. Depending on the available information the sum of the squares of the errors of moisture content and pressure head can be chosen as objective function. Estimation of parameters in any horizon(s) is allowed.The model is applied in a soil cultivated with cotton in Central Greece with data collected from 15 April, 1990 to 10 September, 1990. It is also compared with the well known model SWATRE (Belmans et al., 1983). The results are very satisfactory.