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<br />Letey, John, Osborn, J., and Pelishek, R.E., 1962b., The influence of the water-solid <br />contact angle on water movement in soil: Bulletin of the International <br />Association of Scientific Hydrology, v. 7, p. 75-81. <br />Researchers investigated the effect of contact angle on capillary rise, moisture retention, <br />saturated hydraulic conductivity, and evaporation. The paper includes water inf1ltration <br />curves that sharply contrast those normally observed for a wettable soil. Water inf1ltration <br />was slower and evaporation rates were lower in the water-repellent samples than in the <br />wettable soils. Water-repellent soils also drained at a lower suction than wettable ones. <br /> <br />Mansell, R.S., 1970, Infiltration of water into soil columns which have a water- <br />repellent layer: Proceedings, Soil and Crop Science Society of Florida, <br />Proceedings, vol. 29, p. 92-102. <br />The object of this paper was to provide a physical analysis for the influence of a layer of <br />water-repellent soil upon inf1ltration into an otherwise wettable prof1le. Green and Ampt's <br />equation for inf1ltration velocity was used to analyze inf1ltration of water into a soil proftle <br />that has a subsurface layer of water-repellent soil. A comparison of inf1ltration for vertically <br />downward, horizontal, and vertically upwards cases revealed that the relative decrease in <br />velocity due to the presence of a water-repellent layer was the greatest for the upward case, <br />the least for the downward case, and intermediate for the horizontal case. This a water- <br />repellent soil layer should be most effective in reducing surface evaporation by decreasing <br />upward capillary flow, less effective in reducing lateral water flow to plant roots, and least <br />effective in reducing downward flow during rainfall or irrigation. However, on sloping <br />surfaces a layer of soil that is even marginally water-repellent effectively reduces downward <br />inf1ltration, and, consequently, increases surface runoff. Experimental results from <br />inf1ltration into a horizontally positioned soil column showed that a water-repellent layer <br />located behind wettable soils does signifIcantly reduces the inf1ltration velocity. <br /> <br />Ma'shum, Mansur, and Farmer, V.C., 1985, Origin and assessment of water <br />repellency of a sandy South Australian Soil: Australian Journal of Soil <br />Research, v. 23, p. 623-626. <br />This paper addresses the variations in water repellency resulting from different extraction <br />and drying procedures. The study tested samples of a sandy lucerne pasture soil from South <br />Australia, and found that water repellency can be falsely removed with one treatment (i.e. <br />hot water extraction), but reestablished with subsequent chloroform treatment, indicating <br />that the water repellent substances were not removed. It also shows that different drying <br />procedures result in different degrees of water repellency (i.e. air-dried soil was less repellent <br />than oven-dried soil). This variability was attributed to changes in the molecular <br />conformation of organic matter. Further tests on the effects of agitation on water repellency <br />led to the conclusion that the water repellency of the original soil was due to both coatings <br />on sand particles and inter-mixed, partially decomposed plant remains. <br /> <br />25 <br />