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

A functional model, the pesticide leaching model (PLM), designed to si mulate the transport of pesticides through macroporous soil is describ ed. The concept of mobile and immobile water is used, but the mobile p hase is partitioned to simulate how through smaller water-filled pores and rapid preferential flow through larger macropores and fissures. P esticide adsorption is described using a linear adsorption isotherm. P esticide degradation is calculated using a simple half-life adjusted f or moisture and temperature effects. The model is used to simulate lea ching of the herbicide dichlorprop and the results are compared with d ata from a leaching study on three soils of contrasting texture carrie d out at the Swedish University of Agricultural Sciences, Uppsala. Usi ng independently measured soil and pesticide data as input, the model simulates the hydrologic results quite well but not the amounts of pes ticide leached. However, by optimizing some of the model parameters wi th reference to the measured data, an acceptable simulation of the res ults is achieved.