Application of pesticide leaching models to the Vredepeel dataset: II Pesticide fate

The performance of nine deterministic, one-dimensional, dynamic pesticide leaching models with different complexity was evaluated using a field experiment with bentazone and ethoprophos on a humic sandy soil with a shallow groundwater table. All modelers received an extensive description of the experimental data. Despite this fact, the interpretation of the experimental data was ambiguous, leading to tremendous user-dependent variability of selected model inputs. Together with the fact that most modelers calibrated at least part of their model, the possibility for evaluating model concepts was limited. In the case of bentazone, most model predictions were within the 95% confidence intervals of the observations. In the case of ethoprophos, model performance was often poor due to the ignorance of volatilization, kinetic sorption and adaptation of the microbial population. Most models were calibrated using on-site measured data, limiting the possibility for extrapolation for policy-oriented applications.