Modeling the Transport of Spray-Applied Pesticides from Fields with Vegetative Cover

摘要

This study presents the development and qualitative evaluation of numerical and analytical solutions for the transport of spray-applied pesticides in runoff. The model development focuses on the enhancement of the solution algorithms of earlier researchers by adding chemical reactions that represent more completely the pesticide exchange processes between vegetation, soil, and overland flow and including reactions that are consistent with the short time spans encountered during experimental rainfall/runoff events. The influence of these revised assumptions was evaluated by comparing model outputs from the different models. These tests revealed that for bare soil cases model simulations diverge only where rates of desorption from soils become limiting. Differences in simulation results were more dramatic where a vegetative cover was present, due to divergence in assumptions on the movement of water between plant surfaces and overland flow. Parameter testing revealed several key model parameters that influence simulation results: depth of mixing zone, soil-water partition coefficient, and kinetic rate of desorption from soil solids. A comparison of numerical and analytical model formulations demonstrated that a closed-form solution was adequate to capture the general response of pesticides in runoff that was estimated with a more detailed numerical solution.