Simulating the Transport and Fate of Trifluralin in Soil

Understanding herbicide dynamics in agricultural soils is crucial to evaluate herbicide application efficiency and its envi ronmental consequences. A model for herbicide trifluralin (α,α,α-reifluoro-2,6-dinitro-N,N-dipropyl- ρtoluidine) dynamics namely runoff, erosion, leaching, volatilization, and degradation losses in agricultural soils was developed using the software package Structural Thinking and Experiential Learning Laboratory with Animation (STELLA TM ). The model was calibrated using field data with a good agreement between model predictions and field measurements before its applica tions. A simulation scenario was then performed to predict trifluralin dynamics in a 1.26 ha soybean field. Simulation results showed that in general, the rate of water runoff decreased with the rate of rainfall; however, the rates of triflu ralin and sediment losses in runoff depended not only on the rate of rainfall but also on the content of trifluraline in the liquid and solid phases. The rates of trifluralin leaching and volatilization decreased sharply within the first couple of days following the surface spray of trifluralin due to its strong adsorption and soil incorporation. Simulation results further revealed that the rate of trifluralin degradation in the soil decreased exponentially with time. About 6% of the total applied trifluralin remained in the soil at the end of the simulation period (120 days). This study suggests that the model, developed with STELLA TM , is a useful tool for estimating herbicide dynamics in agricultural soils.