Predicting rice pesticide fate and transport following foliage application by an updated PCPF-1 model

The Pesticide Concentration in Paddy Field (PCPF-1) model has been successfully used to predict the fate and transport of granular pesticides applied to the paddy fields. However, it is not applicable for pesticides in foliar formulation while previous studies have reported that foliar application may increase the risks of rice pesticide contamination to the aquatic environment due to pesticide wash-off from rice foliage. In this study, we developed and added a foliar application module into the PCPF-1 model to improve its versatility regarding pesticide application methods. In addition, some processes of the original model such as photodegradation were simplified. The updated model was then validated with data from previous studies. Critical parameters of the model were calibrated using the Sequential Uncertainty Fitting version 2 (SUFI-2) algorithm. The calibrated model simulated pesticide dissipation trend and concentrations with moderate accuracy in the two paddy compartments including rice foliage and paddy water. The accuracy of the predicted soil concentrations could not be evaluated since no observed data were available. Although the p-factor and r-factor obtained using the SUFI2 algorithm indicated that the uncertainty encompassed in the predicted concentrations was rather high, the daily predicted pesticide concentrations in rice foliage and paddy water were satisfactory based on the NSE values (0.36-0.89). The updated PCPF-1 model is a flexible tool for the environmental risk assessment of pesticide losses and the evaluation of agricultural management practices for mitigating pesticide pollution associated with rice production.