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A Chemical-Microbiological Study of Effects of Exchangeable Cations on Soil Aggregation¹

ABSTRACT

This paper presents data obtained in a study of the effect of various exchangeable cations on soil aggregation and microorganisms. Twenty-one treatments involving various combinations and ratios of exchangeable Ca, Mg, Na, K, and H were compounded by appropriate treatment of a Hanford sandy loam and a Yolo sandy loam. The soil samples of varying cation composition were incubated alone and in combination with organic matter sources of high and low carbon-nitrogen ratio for a period of 200 days. Soil aggregation measurements and counts of kind and number of soil microorganism were made at various intervals during the incubation period. In comparison with a calcium system, the following results were noted: (1) A high percentage of Mg has no effect on aggregation. (2) Depending on the soil, a high percentage of exchangeable K may or may not reduce aggregation. (3) Increasing Na reduces aggregation. (4) An excess of free lime reduces aggregation. (5) Kinds and numbers of microorganisms are affected more by organic matter additions than by cation composition of soil. (6) Organic matter additions increase aggregation regardless of cation composition.

¹ Paper No. 795, University of California Citrus Exp. Sta., Riverside, Calif. Presented before Div. I, Soil Science Society of America, Dallas, Tex., Nov. 19, 1953.

² Associate Chemists.

Received for publication November 19, 1953.