SIMULATION OF DICHLORPROP AND BENTAZON LEACHING IN SOILS OF CONTRASTING TEXTURE USING THE MACRO MODEL

This paper presents an application of a physically based two-domain mo del of water and solute transport in macroporous soil (MACRO) to lysim eter leaching experiments using two herbicides (dichlorprop and bentaz on) and five soils with textures ranging from sand to clay. The model, which accounts for nonequilibrium transport of pesticide in soil macr opores, is briefly described. Parameter estimation for the model simul ations is then discussed. The model simulations showed that MACRO was able to reproduce the pattern of leaching in the clay- and loam-textur ed soils, providing macropore flow was accounted for. When run in one flow domain, the model failed to reproduce the observed pattern of lea ching in all five soils. It was concluded that preferential flow influ enced the pattern and amount of herbicide leached, not only in the str uctured clay and loam soils, but also in two sandy-textured soils.