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Diffusion of Zinc in Soils: III. Relation to Zinc Adsorption Isotherms¹

ABSTRACT

The rate of cation diffusion in soil is influenced by the buffering effect of the adsorbed cation on the solution concentration, dC_l/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, D_e, was measured at five Zn levels on each soil. Measured D_e, correlated with dC_l/dC (r² = 0.86). Values of D_e calculated from known values for volumetric moisture content, tortuosity, and dC_l/dC were larger than observed D_e by factors of 5.5 to 18.2. Inclusion of CEC in a multiple regression of observed D_e with calculated D_e significantly increased r² from 0.87 to 0.90. An additional soil factor related to CEC needs to be included to accurately calculate D_e values for Zn.

¹ Journal Paper no. 4853. Purdue Univ. Agr. Exp. Sta., West Lafayette, Indiana 47907. Contribution from the Dep. of Agronomy.

² Former graduate assistant, now Research Associate, and Professor of Agronomy, Purdue Univ., respectively.

Received for publication August 23, 1972. Accepted for publication February 2, 1973.