Diffusion of Zinc in Soil: II. The Influence of Soil Bulk Density and its Interaction with Soil Moisture

Abstract

Abstract Effective Zn diffusion coefficients were determined at four soil bulk densities and three moisture levels in five silt loam soils. The tortuosity of the diffusion path, f 1 , for each set of soil conditions was estimated from 36 Cl diffusion data. In each soil and for each soil moisture level the diffusion path was least tortuous near 1.3 g/cm 3 . The observed order for the influence of soil bulk density on tortuosity was 1.6 > 1.5 > 1.1 > 1.3 g/cm 3 . Soil bulk density interacted significantly with soil moisture in affecting the Zn diffusion coefficients. The maximum rate of Zn diffusion did not always occur at a soil bulk density of 1.3 g/cm 3 where the diffusion path was least tortuous. At 20 and 30% moisture the Zn diffusion rate reached a maximum near 1.5 g/cm 3 indicating that tortuosity was not the only factor influencing the rate of Zn diffusion. As the soil moisture was increased, a reduction in the effect of the interaction of Zn with the soil was greater than the effect of tortuosity in determining the effective rate of Zn diffusion in each soil. When the bulk density was increased from 1.5 to 1.6 g/cm 3 , an increase in both the degree of interaction and toruosity combined to cause a sharp decrease in the Zn diffusion coefficient.