High Humidity‐induced Increase in Water Repellency in Some Sandy Soils

Abstract

Abstract The degree of resistance to water penetration of diverse water repellent soils was found to be controlled by their moisture states. Repellency was found to increase sharply when samples were incubated at 100% relative humidity and to decline when wetted or when incubated at humidities < 90%. A soil which was nonwater‐repellent in the field did not become repellent at 100% relative humidity. A Florida soil (St. Lucie series, hyperthermic, uncoated Typic Quartzipsamments) was used for detailed study. Repellency increase in this sand was temperature dependent and could be eliminated by gamma irradiation, indicating the biological nature of the process. Application of antibiotics prior to incubation suggested that prokaryotic organisms were essential to repellency increase. A dilution study of the St. Lucie soil incubated at 100% relative humidity for various periods revealed that the actinomycete population correlated best with the repellency increase. When incubated St. Lucie sand was investigated by electron microscopy, actinomycetes were found to dominate the visual field. A model for repellency increase and decline, based on soil humidity, is offered.