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Contribution of Some Soil Fungi to Natural and Heat-Induced Water Repellency in Sand¹

ABSTRACT

Eight species of fungi isolated from a water repellent soil were incubated for varying periods of time in silica sand. In their latter stages of growth, two of the fungi, Aspergillus sydowi and Penicillium nigricans, caused limited water repellency in the sand. All the fungal sand cultures exhibited water repellency when heated briefly at temperatures between 200C and 400C. The times required to produce and destroy water repellency in the sand cultures at the various temperatures were similar to those required by the natural soil from which the fungi were isolated.

The fungal sand cultures and natural water repellent soils were extracted with either water, methanol, acetone, or ethyl ether. The methanol and water extractions destroyed the natural water repellency of the A. sydowi and P. nigricans cultures. Methanol and water extractions also destroyed the water repellency of the heated sand cultures if the extractions were made before the heat treatments; however, if the extractions were made after the sand cultures had been heated, the water repellency of the samples was not affected. Wettable silica sand treated with the methanol extracts of the sand cultures exhibited water repellency when heated. Both the heat-induced and natural water repellency of the soil was not affected by any of the solvent extractions, but wettable sand treated with each of the extracts was made water repellent by heat.

A variety of known organic substances was applied to wettable silica sand and the water repellency of the treated sand determined before and after heating. Amines were the only class of substances tested that caused water repellency in sand before heating. A variety of substances, however, caused heat-induced water repellency in the sand. The heating conditions required to cause water repellency were similar to those required by fungal sand cultures and natural water repellent soil.

The primary conclusion of the study was that heat-induced water repellency may be a universal property of soils rather than property specific to a limited number of soils.

Contribution from the Department of Soils and Plant Nutrition, University of California, Riverside. The study was supported by Forest Service, US Department of Agriculture, Washington, D.C., Grant no. 4000.

² Visiting Assistant Chemist, Professor of Soil Microbiology, and Professor of Soil Physics, respectively. Present address of the senior author is Department of Chemistry, Northern Arizona University, Flagstaff, Ariz.

Received for publication July 24, 1968. Accepted for publication January 3, 1969.