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Dispersion and Aggregation of Soils as Influenced by Organic and Inorganic Polymers and Inorganic Polymers

Department of Soil Science, 108 Hilgard Hall, Univ. of California, Berkeley, CA 94720

*Corresponding author.

ABSTRACT

In this study, the influences of three organic polyanions (a soil humic acid, a soil polysaccharide, and a commercial anionic polysaccharide) and hydroxy-Al polycations (Al-p) on soil clay dispersion, aggregation, and subsequently hydraulic conductivity were investigated. It was found that the organic polyanions, especially humic acid, were not flocculating agents, but were effective dispersing agents for the Na-clays and Na-soils. Removal of soil organic matter reduced soil clay dispersibility, whereas addition of small amounts of the polyanions increased soil clay dispersion. The Al-p effectively screened the surface negative charge on clay colloids and, in addition, acted as bridges between negatively charged colloids and the anionic polysaccharide, and thus prevented soil clay dispersion. Hydraulic conductivities of soil columns treated with Al-p or its combinations with the anionic polysaccharide or humic acid were about two orders of magnitude higher than those without addition of Al-p throughout the 5-d leaching period. Although treatment of the Na-soils with the anionic polysaccharide increased soil aggregate stability as measured by the wet-sieving method, it did not result in an increased soil hydraulic conductivity, due to redispersion of clay colloids after leaching with distilled water. This study indicates that soil colloidal stability is strongly influenced by soil organic components in addition to factors such as pH, ionic strength, and composition. In the absence of polyvalent cations, negatively charged humic substances, especially humic acid, may not contribute to stable soil aggregation, whereas the presence of both polyvalent cations and polyanions may be additive in preventing soil clay dispersion.

Received for publication February 14, 1992.

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