SIMULATION OF SOIL-WATER DYNAMICS AND HERBICIDE PERSISTENCE IN A SILT LOAM SOIL USING THE MACRO MODEL

This paper presents an application of the model MACRO to measurements of soil water dynamics and persistence of three herbicides (metamitron, methabenzthiazuron and simazin) in a silt loam soil at Krummbach, Germany. The model is briefly described and parameter estimation for the simulations discussed. Soil water dynamics were accurately predicted by the MACRO model following calibration of model parameters related to crop water uptake. Occasional discrepancies between model predictions and measurements were attributed to temporal variation in the hydraulic effectiveness of macropores at the soil surface and also to the use of inappropriate soil water retention curves in subsoil horizons. Soil temperatures were mostly predicted to within +/-3 degrees C, except for winter periods characterized by snow and soil freezing. Field-measured persistence of the herbicides in the topsoil was closely predicted by the model using half-lives measured in the laboratory.