Modeling the Fate of Acetochlor and Terbuthylazine in the Field Using the Root Zone Water Quality Model

Abstract

0.91). The mean dissipation half‐life was 16 d for acetochlor and 25 d for terbuthylazine. Relatively small amounts of the pesticides leached below 5 cm and none leached below 10 cm. Predicted soil water contents in the soil profile were not significantly different from those measured in the field ( p > 0.84). Predicted acetochlor and terbuthylazine masses in the soil profile based on a linear instantaneous‐equilibrium (I‐E) partitioning model matched those measured in the field (adjusted r 2 > 0.93). However, predicted pesticide concentrations in the soil profile were less satisfactory, with 68 and 35% of the predicted concentrations being within a factor of 2 of the measured concentrations for 0‐ to 5‐ and 5‐ to 10‐cm depths, respectively. Calibration of each pesticide sensitive parameter individually did not significantly improve the overall predictions of pesticide mass and concentrations in the soil profile when the I‐E partitioning model was used. The predictions were improved when a two‐site, equilibrium‐kinetic (E‐K) sorption model was used.