A sandplain paddock growing blue lupins continuously for about five years will develop moderate to severe repellence. Sheep camps tend to be more water repellent because of the accumulation of organic matter. The waxy substances in plants are not effectively broken down by their passage through the sheep. The soil property which is closely linked to susceptibility to water repellence is the surface area. For instance, coarse sands can be more repellent than fine sands when the same amount of organic matter is added.
Coarse sand has a lower surface area than the same weight of fine sand.
Clay has a very much larger surface area than sand, because it consists of much finer particles. Thus soils with greater than about 5 per cent clay content rarely exhibit repellency. Coarsely aggregated clays and soils with an abundant supply of hydrophobic material, such as beneath brown mallet hilltops, can be exceptions to this general rule. Microbial activity breaks down dead plant material in a way that contributes to the development of water repellence in susceptible soils. It seems there is selective degradation of less hydrophobic waxes resulting in concentration of the more repellent polar waxes.