Computer Simulation of Leaching of Aldicarb Residues from Arable Soils in Winter

Abstract A computer model was used to simulate the movement and conversion in soils of two biologically active oxidation products of aldicarb, its sulfoxide and its sulfone. Basic data on these compounds, as measured in the laboratory, were introduced into the computations. Starting points were the moisture profiles and concentration patterns in soil measured in a field experiment with columns of grassed soils 0.8 or 1.0 m long in the autumn, 165d after application of al dicarb in spring. Weather data and soil characteristics were introduced as measured or estimated in the same experiment. The amounts of percolation water simulated to flow from the soil systems during the winter period with 4 70 mm of precipitation were mostly somewhat lower than measured. The shape of the effluent curves for the sulfoxide and sulfone were fairly well described by the computations, as were the concentration patterns remaining in the lower part of loam soil columns. Cumulative leaching of sulfoxide plus sulfone from the two loam soil systems 1.0 m long was simulated to be 1.9 and 1.5% of the dosage, respectively, which was in the range of values measured in the experiment. Leaching from the humic sand soil 0.8 m long was simulated to be 17% of the dosage, whereas measured leaching ranged from 10 to 16% of the dosage.