Estimating molecular diffusion coefficients of urea in unsaturated soil

Abstract

The objective of this study was to modify the parameters in an empirical equation of R.J. Papendick and G.S. Campbell and, if necessary, develop a new relationship to estimate the value of the molecular diffusion coefficient of urea in soil (Ds) in soils. Laboratory studies were conducted on seven soils in which the clay content ranged from 10 to 51%. Urea concentrations with depth at 48 h following surface-application were measured and also computed using numerical techniques with an initial estimate for Ds instead of computing it using Papendick and Campbell's equation. The Ds was modified incrementally, until the difference between computed and measured concentrations was minimized. In all seven soils, good agreement was obtained between measured and computer urea concentrations with depth.