Since 1986, the occurrence of water repellency has been observed in soil samples collected for soil surveys conducted by the Soil Department of Federal Rural University of Rio de Janeiro (UFRRJ) and by the National Center for Soil Research of EMBRAPA. With the objective of studying the causes of this phenomenon, seven soils were selected and their water repellence rating was determined by two methods: the molarity of ethanol droplets and water drops penetration time. Two methods of extraction were used to isolate and identify the organic compounds responsible for the water repellency. The first one was based in a partition with isopropanol:distilled water and the other one, developed by the authors, was based on single extractions with n-hexane, chloroform and ether and partitions with n-hexane:distilled water and chloroform:distilled water. Both methods made the water-repellent soils wettable after the extraction. The extracted substances were analyzed in the Institute of Biosciences of the University of São Paulo. The results indicate that the isolated substances had their origin in the vegetation cover and that the alcanes of high molecular weight were responsible for the repellency in these soils.
water repellency; hydrophobic soils; extraction