Observed and Predicted Rates of Phosphorus Diffusion in Soils of Varying Bulk Density and Water Content

Abstract

AbstractThe self‐diffusion coefficient of phosphorus (D) was measured at bulk densities of 1.25, 1.45, 1.60 and 1.75 g/cm3 and at three levels of soil water content in Choa sandy loam and Haibowal silty clay loam. The tortuosity factor was calculated from the self‐diffusion coefficient of 36Cl. Appropriate values of the adsorption isotherm and the tortuosity factor were used to predict P diffusion coefficient in both soils.The tortuosity factor increased with increase in soil bulk density and increase in water content from 7 to 18% in the Choa soil and 14 to 25% in the Haibowal soil. As bulk density increased from 1.25 to 1.60 g/cm3, the observed diffusion coefficient values averaged over all water contents, increased from 0.05 × 10−10 to 0.31 × 10−10 and 2.13 × 10−10 to 5.07 × 10−10 cm2/sec in Choa and Haibowal soils, respectively. Further increase in bulk density to 1.75 g/cm3 decreased the diffusion coefficient. At high bulk density changes in water content affected the self‐diffusion coefficient of P in both soils to a greater extent than at low bulk density. The phosphate ion‐soil particle interaction was minimum at a soil bulk density of 1.60 g/cm3.