Models for Predicting Volatilization of Soil‐Incorporated Pesticides

In the absence of appreciable mass transfer due to water movement, diffusion processes in the soil account for the movement of pesticides to the soil surface to replace that lost by volatilization. Published solutions for heat flow equations have been applied to the volatilization of lindane and dieldrin from Gila silt loam for a number of different initial and boundary conditions. Predicted fluxes agreed well with experimental values. Five models have been proposed to describe various environmental conditions found in the field. Models I, II, and III assume pesticide concentration at the soil surface is maintained at zero concentration by air movement. Model IV assumes surface pesticide concentrations greater than zero with air turbulence sufficient to maintain zero pesticide concentration gradient in the air above the soil. Model V assumes a nonmoving air layer of various depths above the soil surface so that the pesticide concentration gradient in the air controls the rate of volatilization.