Spatial Variability of Pesticide Sorption: Measurements and Integration to Pesticide Fate Models

Abstract

Pesticide fate models are useful in testing the impact of agricultural management practices on the quality of water resources. The sorption parameter is among the most sensitive of the input parameters used by pesticide fate models. Numerous pesticide sorption experiments have been conducted in the past 75 years, but mainly focussed on surface soils. The batch equilibrium procedure is a conventional technique to quantify sorption parameters. In this chapter, we summarize selected batch equilibrium studies to demonstrate that sorption parameters vary widely among sampling points within soil-landscapes. We recognize that probability density functions (PDFs) have been incorporated into stochastic simulations of pesticide fate to help account for sorption spatial variability, but also show that PDFs can vary widely for different pesticides and/or soil depth. We propose that near-infrared spectroscopy (NIRS) can be used in combination with batch equilibrium techniques to more rapidly quantify the sorption variability of herbicides. We demonstrate that NIRS can be integrated into the Pesticide Root Zone Model version 3.12.2 to improve spatial resolutions for calculating the mass of herbicide leached to depth at the field scale. Better quantification of herbicide sorption variability and hence leaching potential will provide greater confidence in using pesticide fate models in regulatory practices, as well as in management programs that promote both sustainable agriculture and adequate environmental protection of water resources.