Wet and dry sand was tested for water repellency, after burning pine litter (Pinus coulteri D. Don). Four conditions were studied: a burn of 25 min over dry or wet sand and a burn at 5 min over dry or wet sand. The thickest and most intense water‐repellent layer was produced by a 5‐min burn over dry sand. Although organic materials were translocated deeper in the dry sand during the 25‐min burn (down to 4 cm), some of the water repellency was destroyed in the upper 1‐cm layer. In wet sand, water repellency was concentrated in the upper 0‐ to 1.5‐cm layer. The translocation of hydrophobic substances and resulting water repellency depends on changes in their polarity and oxidation state. Relationships developed for fire over a dry soil may not adequately account for movement of organic substances in a moist soil. These results suggest prescribed burning should be done when the soil is moist on areas where water repellency is a problem.

A soil susceptible to heat‐induced water repellency was heated at several temperatures and oxygen concentrations. The materials emanating from the heated soil were captured and their mass determined. The greatest quantity of products was captured at temperatures above 300C. Increasing amounts of material were produced with increasing oxygen concentrations up to 20%. From 0.3% to 1.75% of the total soil was captured as products.Fractionation of these captured products by adsorption chromatography resulted in the isolation of several different components. Three of these components were capable of causing extreme water repellency in sand if the treated sand were heated. Some evidence suggested that the heating of these substances on the sand surfaces altered their structure. These three effective components represented from 25–50% of the total materials collected from the soil.Elemental and spectroscopic analyses of the effective components indicated them to be basically aliphatic hydrocarbons.The undecomposed and partially decomposed plant materials present in the soil were determined to be the primary source of the products coming from the heated soils.

No abstract

A silica sand and Pachappa sandy loam were treated at various pH's with aqueous suspensions of three microbial humic acids, a soil and peat humic acid, a microbial polysaccharide, and metallic salts of the tested organic substances. Of all the substances tested, only one, a humic acid isolated from a Stachybotrys atra culture, caused water repellency in the sand and soil. The Fe3+ and Al3+ salts of this humic acid rendered the sand and soil practically impermeable to water. The organic matter content of the extremely water repellent sands was less than .05%. The final conclusion of the paper is that humic acid‐like substances and polysaccharides probably do not contribute much to water repellency in soils.

Humic acids from two Brunizem soils were oxidized with a view to obtaining and detecting intermediate products which would provide clues to their structures. A comparison of optimum conditions for the production of intermediate products showed that humic acid extracted from soil with 0.1M sodium pyrophosphate (pH 9.0) was more susceptible to oxidation than humic acid extracted with Q.5N NaOH. Intermediate products obtained from pyrophosphate humic acid by oxidation were different chemically from those derived from alkali humic acid.