SIMULATION OF DICHLORPROP LEACHING IN 3 TEXTURALLY DISTINCT SOILS USING THE PESTICIDE LEACHING MODEL

A functional model, the pesticide leaching model (PLM), designed to simulate the transport of pesticides through macroporous soil is described. The concept of mobile and immobile water is used, but the mobile phase is partitioned to simulate how through smaller water-filled pores and rapid preferential flow through larger macropores and fissures. Pesticide adsorption is described using a linear adsorption isotherm. Pesticide degradation is calculated using a simple half-life adjusted for moisture and temperature effects. The model is used to simulate leaching of the herbicide dichlorprop and the results are compared with data from a leaching study on three soils of contrasting texture carried out at the Swedish University of Agricultural Sciences, Uppsala. Using independently measured soil and pesticide data as input, the model simulates the hydrologic results quite well but not the amounts of pesticide leached. However, by optimizing some of the model parameters with reference to the measured data, an acceptable simulation of the results is achieved.