Effects of organic compounds, water content and clay on the water repellency of a model sandy soil
Leelamanie, D.A.L.(Tokyo Univ. of Agriculture and Technology, Fuchu (Japan)) | Karube, J.
Soil water repellency is related to organic matter and clay, and varies non-linearly with soil water content. The purpose of this study is to assess the combined effects of organic compounds, water content and clays on water repellency of a model sandy soil under wetting and drying processes. Hydrophobic stearic acid and hydrophilic glucomannan were used as the organic compounds, and kaolinite or montmorillonite was used as the clay conditioner. Water repellency was estimated using the water drop penetration time test. Repellency did not appear in samples free of stearic acid. Samples containing both stearic acid and glucomannan showed higher repellency compared with samples containing stearic acid alone during the wetting process. Glucomannan with stearic acid increased the critical water content and widened the range of water content at which soils showed slight repellency. During the wetting process, the repellency of most samples increased with increasing water content under relative humidity conditions ranging from 33 to 94%. During the drying process, repellency appeared, reached a maximum and then decreased in samples containing stearic acid. Maximum repellency was observed not at oven-dried but at air-dried water content. Repellency was highly sensitive to water content at around air-dried condition. The effects of organic compounds and clay on the water repellency of sandy soils were negligible in oven-dried condition. Repellency tended to increase with the addition of a small amount of clay (1-2%) as a dry mix during the wetting process. Once wetted, repellency disappeared with the addition of montmorillonite, but not with kaolinite. The higher the kaolinite content, the higher the critical water content.
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