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Influence of Soil Exchangeable Cation Ratios on the Aggregating Effects of Natural and Synthetic Soil Conditioners¹

ABSTRACT

The aggregating effects of various natural and synthetic soil conditioners in normal soils and in soils varying widely in exchangeable cation percentages have been investigated. In the normal soils VAMA (a copolymer of vinyl acetate and the partial methyl ester of maleic acid), two dextrans from soil bacteria, IBMA (a copolymer of isobutylene and the half ammonium-half amide salt of maleic acid), fructosan from Bacillus subtilis, and mesquite gum exerted the greatest initial aggregating effect; carboxymethylcellulose and pectin exerted an intermediate effect; and ammonium alginate and arabogalactan (larchwood gum) exerted little or no binding action. Ammonium lignin sulfonate had a small initial effect which increased with time; it thus indicated dependence upon microbial activity.

The various soil exchangeable cation ratios greatly affected the aggregating action of some of the soil conditioners but had little influence on others. The binding action of VAMA was slightly reduced by 60% Na only, while that of IBMA (tested in Yolo loam soil only) was reduced by 10 to 60% Na and 30 to 60% K. The aggregating effect of polysaccharide type conditioners appeared to be directly related to the concentration of carboxylic acid groups in these materials. As the concentration of uronic acid groups increased, the binding action of the materials increased with increasing exchangeable H and decreased with increasing exchangeable Na or K. Possible explanations for this behavior are discussed.

The effectiveness of VAMA did not decrease with time up to 200 days. In the high Na, K, and Mg soils the effectiveness of IBMA decreased with time. The binding action of all the other materials used gradually decreased, but they were more stable in the acid soils than in the neutral to alkaline soils.

¹ Paper No. 826, University of California Citrus Exp. Sta., Riverside, Calif. Presented before Division III, Soil Science Society of America, St. Paul, Minnesota, Nov. 9, 1954.

² Associate Chemist and Chemist, respectively. The authors express appreciation to J. O. Ervin for laboratory assistance and to George Helmkamp and William Moje for suggestions concerned with possible mechanisms involved in the binding action of soil conditioner substances.

Received for publication September 11, 1954.