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 model of water and solute transport in macroporous soil (MACRO) to lysimeter leaching experiments using two herbicides (dichlorprop and bentazon) and five soils with textures ranging from sand to clay. The model, which accounts for nonequilibrium transport of pesticide in soil macropores, is briefly described. Parameter estimation for the model simulations is then discussed. The model simulations showed that MACRO was able to reproduce the pattern of leaching in the clay‐ and loam‐textured soils, providing macropore flow was accounted for. When run in one flow domain, the model failed to reproduce the observed pattern of leaching in all five soils. It was concluded that preferential flow influenced the pattern and amount of herbicide leached, not only in the structured clay and loam soils, but also in two sandy‐textured soils.