Studies on non-wetting sands. I. the role of intrinsic particulate organic matter in the development of water-repellency in non-wetting sands

The bulk of the organic matter in sands from the south-east of South Australia is present as discrete particles which constitute 4-6% of the mass of the sand. Hydrophobic particulate organic matter was separated from non-wetting sand obtained from two sites in the south-east of South Australia and characterized with respect to size and ability to induce water-repellency. When heated with both a wettable acid washed sand and a natural sand (non-wetting sand washed free of particulate organic matter), the intrinsic particulate organic matter induced strong water-repellence. The degree of hydrophobicity created was higher with the natural-washed sand than the acid-washed sand which indicated that a precoated surface, even one with a low initial hydrophobicity, has a strong enhancing effect. Particulate organic matter, especially the larger size fractions, acted as a reservoir of waxes or hydrophobic materials which diffused onto the surfaces of sand grains during heating, and particularly during wetting/heating/drying cycles. Thus, intrinsic particulate organic matter plays a substantial role in the development of water-repellency in sandy soils. In addition to hydrophobic waxes which diffuse out under environmental conditions prevalent in the field, water-repellency increases significantly when these hydrophobic particles interact with the natural precoated hydrophobic surface of the sand.