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<br />Savage, S.M., Martin, J.P.., and Lete}', John, 1969a., Contributio:l of some: soil fungi to
<br />natural and heat-induced water repellency in sand: Soil Science Society of
<br />America Proceedings, Y. 33, p. 405-409.
<br />One of the earlier studies attem~ting to understand water-repellent soils, this paper offers
<br />some alternate explanations on the mechanism of water-repell, ncy afte! heating. In
<br />particular, it suggests that heat-induced repellency is the result of a chemical reaction
<br />(pyrolosis), rather than physical v,porization and subsequent condensation on cooler soil
<br />particles, as proposed by DeBano (1966). It also indicates that concensed materials must be
<br />heated in situ to confer a high c,e~;ree of water repellency to a soil, and demonstrates the
<br />in:1portance of soil fungi (ra1her than litter alone) in producing water. repellency after heating.
<br />
<br />Savage, S.M., Martin, J.P., and Letey, John, 1969b., Contribution of humic acid and a
<br />polysaccharide to wate! repellency in sand and soil: Soi L Science Society of
<br />America Proceedings, v. 33, p. 149-151.
<br />Researchers evaluated the effects 0:' microbially-generated polysacd arides, humic acids, and
<br />their metal salts, on water repellency in sand and soil. Of all the substances tested, only one
<br />humic acid caused water repellency. Tbe repellency in this instan:e was found to be pH
<br />dependent. Results also indicated that a larger amount of the hyd rophobic substance was
<br />needed in the soil than in the sand, pre~umably because of the larger surface aIea of the soil.
<br />Researchers concluded that: the contribution of polysaccharides ar d humic acids to water
<br />repellency is minimal.
<br />
<br />Savage, S.M., Osborn, J., Lete)', Jlohn, and Heaton, c., 1972, Su~stances contributing
<br />to fire-induced water repellency in soils: Soil Science Sc ciety of America
<br />Proceedings, v. 36, p. 674-.678.
<br />This investigation attempted to identify the source and chemical na1 ure of materials moving
<br />from a heated soil, and to deterrrune if these materials were ca pable of causing water
<br />repellency. Water-repellent soil was taken from the Red Moc ntain area in southern
<br />Califomia, where chamis chaparral brctsh is the dominant vegeta tion type. Researchers
<br />concluded that the processes responsible for causing fire-induced water repellency began
<br />between 3000 and 4000C, in contrast to DeBano et al. (1967) who n ported that soils reach a
<br />ma.ximum repellency at around 3000c:. They also found the m )st effective substances
<br />causing fire-induced water repe:Je::lCY to be aliphatic hydrocarbo lS, and determined the
<br />source of these compounds to be sw:face soil litter. Results fu rther indicated that the
<br />mechanism involved in producirLg water repellency after heating" as probably a structural
<br />change in the substances, rather than simple condensation of volat lized material on cooler
<br />soil particles. The authors also concluded that in situ heating of these' materials was necessary
<br />to cause repellency.
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