MICROORGANISMS AND SOIL AGGREGATION

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Abstract
Six bacterial polysaccharides, 3 fructosans and 3 dextrans, were prepd. in quantity and their influence on soil aggregation and slaking detd. Compared to 28% aggregation for the controls, as little as 0.1% conc. of the polysaccharides in the soil bound from 44 to 70% of the silt + clay particles into water-stable aggregates larger than 50 [mu] in diam. 1% concs. brought about 66-88% aggregation and increased slaking time from 15 sec. to 3 days over the control. The polysaccharides alone had a greater effect on soil structure than either casein or lignin. When used in combination with casein and lignin, the beneficial effect on soil aggregation was, in most instances, as great as when used alone. The bacterial polysaccharides, in general, were attacked to a limited extent by common soil microorganisms. However, at least one and usually several microbes were capable of utilizing each.