Diffusion of Zinc in Soils: III. Relation to Zinc Adsorption Isotherms
1973
Warncke, D. D. | Barber, S. A.
The rate of cation diffusion in soil is influenced by the buffering effect of the adsorbed cation on the solution concentration, dCₗ/dC, i.e., the change in solution zinc concentration with respect to change in the total diffusible soil zinc concentration. This effect was studied with Zn using four silt loam soils having a wide range of initial exchangeable Zn contents and cation exchange capacities (CEC). Zinc adsorption isotherms for these soils had slopes that increased as CEC decreased. The effective zinc diffusion coefficient, Dₑ, was measured at five Zn levels on each soil. Measured Dₑ, correlated with dCₗ/dC (r² = 0.86). Values of Dₑ calculated from known values for volumetric moisture content, tortuosity, and dCₗ/dC were larger than observed Dₑ by factors of 5.5 to 18.2. Inclusion of CEC in a multiple regression of observed Dₑ with calculated Dₑ significantly increased r² from 0.87 to 0.90. An additional soil factor related to CEC needs to be included to accurately calculate Dₑ values for Zn.
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