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Effects of pH on the Contributions of Organic Matter and Clay to Soil Cation Exchange Capacities¹

ABSTRACT

The cation exchange capacities versus pH of 12 soils from 10 states were determined by measuring Ba adsorbed by the unlimed soils from buffered solutions adjusted from pH 2.5 to 8.0, and K adsorbed from 1.0N KCl by incrementally limed (and incubated) soils. The contributions of organic matter and clay to soil CEC at various pH's were computed by multiple regression analysis of the CEC(BaCl₂) and CEC(KCl) data for whole soils. The results indicated that the method can be used satisfactorily for either type of data, and comparison of the two sets of computed data revealed that organic exchange sites which were active for adsorbing Ba from the buffer at low pH were not active for adsorbing K from unbuffered KCl in soils of comparable pH. Evidently nonexchangeable Al was involved in the latter, since it generally correlated closely with organic matter content of the soils, and the average exchangeable Al doubled when OM was destroyed with H₂O₂.

¹ Published with the permission of the Director of the Ohio Agricultural Research and Development Center as Journal Article 22–69. Presented before Div. S-2 Soil Science Society of America, New Orleans, La., Nov. 12, 1968. The results are from an M.S. thesis by the junior author, The Ohio State University, 1968. Financial support from the Institute of International Education and the Organization of American States to the junior author is gratefully acknowledged.

² Professor and former graduate student now with Instituto Colombiano Agropecuario, Colombia, S.A.

Received for publication February 28, 1969. Accepted for publication July 14, 1969.