COMPUTING THE MOVEMENT OF ETHOPROPHOS IN SOIL AFTER APPLICATION IN SPRING

Abstract

The movement of the insecticide-nematicide ethoprophos in soil under field conditions was simulated in a computation model. Daily rainfall patterns were taken from meteorological records and evaporation from the soil surface was estimated. Water flow in soil was simulated using hydraulic characteristics reported in the literature. The adsorption of ethoprophos by 4 soils was measured, and 2 representative values of the adsorption coefficient were introduced into the computations. In only 1 soil, a sandy loam that showed moderate to weak adsorption of the pesticide, was a significant penetration of the pesticide computed below the incorporation depth (0.10 m). In a humic sandy soil the computed redistribution was much smaller: the concentrations that penetrated about 0.05 m in the sandy loam moved less than 0.01 m in the humic sand. In comparatively dry spring periods with little redistribution, upward water flow resulted in a distinct accumulation of the pesticide near the soil surface. Simulation experiments showed that convective dispersion may be expected to be the predominant spreading process; diffusion through the liquid and gas phases contributes little to the macroscale spreading. Volatilization from soil was estimated to be limited to a small percentage of the dosage. The conclusion was that, under normal rainfall conditions in spring, ethoprophos should be deeply and homogeneously incorporated into the plow layer to protect the root systems of the crop adequately.