SIMULATION OF SOIL-WATER DYNAMICS AND HERBICIDE PERSISTENCE IN A SILTLOAM 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, Ge rmany. 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 t o crop water uptake. Occasional discrepancies between model prediction s and measurements were attributed to temporal variation in the hydrau lic effectiveness of macropores at the soil surface and also to the us e of inappropriate soil water retention curves in subsoil horizons. So il temperatures were mostly predicted to within +/-3 degrees C, except for winter periods characterized by snow and soil freezing. Field-mea sured persistence of the herbicides in the topsoil was closely predict ed by the model using half-lives measured in the laboratory.