Non-wetting soils or soil water repellence is caused by a waxy coating on soil particles and hydrophobic particulate organic matter (water repellent fine organic matter). It primarily occurs in the topsoil with low clay content. The coatings are made up of hydrophobic (water repelling) substances, primarily plant leaf waxes and their biodegradation products.
Soil water repellence restricts and diverts water infiltration into the soil, which impacts on seed germination, nutrition, crop pasture, weed establishment and grain and livestock production as well as inducing increased risk of wind and water erosion.
Water repellence is mostly associated with sandy-textured soils, but can affect some heavier textured soils (for example forest loamy gravels). Water repellence influences more than five million hectares of western and southern Australian soils.
See more at: http://www.grdc.com.au/Research-and-Development/Major-Initiatives/Non-wetting-soils#sthash.ggmRjhWz.dpuf