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Contribution of Organic Matter and Clay to Soil Cation-Exchange Capacity as Affected by the pH of the Saturating Solution¹

ABSTRACT

The effect of pH of the buffered saturating solution on the cation-exchange capacity (CEC) of 60 Wisconsin soils was determined within the pH range 2.5 to 8.0. The relative contributions of clay and organic matter to total CEC were measured using multiple regression analyses; the independent variables were clay and organic matter contents and the dependent variables, CEC at pH 2.5, 3.5, 5.0, 6.0, 7.0, and 8.0. The average CEC of the organic matter at each pH value was 36, 73, 127, 131, 163, and 213 me. per 100 g., respectively; while that of the clay was 38, 46, 54, 56, 60, and 64 me. per 100 g. Within the limits of the standard errors of the regression coefficients, CEC of both clay and organic matter increased linearly with pH. The regression equations indicated that the mean relative contribution of organic matter to total soil CEC in this group of soils varied from 19% at pH 2.5 to 45% at pH 8.0; the mean organic matter and clay contents of the soils studied were 3.28% and 13.3% respectively. Coefficients of multiple correlation varied from 0.927 at pH 3.5 to 0.959 at pH 8.0.

¹ Contribution from the Soils Dept., Univ. of Wisconsin, Madison. Published with the approval of the Director, Wis. Agr. Exp. Sta. Supported in part by a grant under Title IV of the National Defense Education Act of 1958. Presented before Div. S-2 Soil Sci. Soc. Am., Nov. 20, 1963, at Denver, Colo.

² Research Fellow, Assistant Professor, and Associate Professor of Soils, respectively.

Received for publication November 29, 1963. Accepted for publication January 14, 1964.