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Effect of pH on the Sodium-Calcium Exchange Equilibria in Soils¹

ABSTRACT

The Na-Ca exchange equilibria in 10 acid soils were measured at pH values of 5, 6, 7 and 8 and the results related to a theoretical ion exchange equation based on the Poisson-Boltzmann differential equation of the electrical double-layer. The theoretical equation satisfactorily predicted the relative change in ratio of adsorbed Na to adsorbed Ca as the pH of the equilibrium solutions decreased. The actual values of ratios of adsorbed Na to adsorbed Ca agreed with the theory when the surface charge densities for each soil were multiplied by an appropriate factor. This factor varied from 1.0 to 2.1 but was the same for all pH values for a given soil.

¹ Paper No. 1355, University of California Agr. Exp. Sta., Riverside.

² Associate Chemist, Department of Soils and Plant Nutrition, Riverside; Assistant Chemist, Department of Soils and Plant Nutrition, Davis; Assistant Horticulturist; Department of Horticulture, Riverside, respectively.

Received for publication June 9, 1961. Accepted for publication October 9, 1961.