APPLICATION OF THE PESTICIDE TRANSPORT ASSESSMENT MODEL TO A FIELD-STUDY IN A HUMIC SANDY SOIL IN VREDEPEEL, THE NETHERLANDS

The Pesticide Transport Assessment model (PESTRAS) is a process-orient ed model to simulate the fate and movement of water and pesticides in a cropped held soil. The model was evaluated using field data for brom ide, ethoprophos and bentazone, collected from a held experiment in a humic sandy soil near Vredepeel, the Netherlands. Model predictions we re generally within the 95% confidence intervals of the observations w hen site-specific model inputs were used. If generic parameter values were used, the model predictions sometimes deviated strongly from the observed data. This was especially true for pesticide degradation prop erties. The bromide simulations showed that preferential dow was not a n important process for this field soil. A significant fraction of the applied ethoprophos disappeared by surface volatilization. The downwa rd movement of this pesticide was slightly overestimated, due to not c onsidering sorption kinetics. The depth-dependence of pesticide transf ormation was atypical: an important fraction of the applied bentazone was transformed under micro-aerobic to anaerobic conditions in the sub soil. (C) 1998 SCI.