Soil water repellency is a feature under many land uses, resulting, for example, in enhanced runoff, erosion and preferential flow. Water repellency is also a major management problem in turfgrass systems, where it can seriously compromise turf quality and growth. It is widely accepted that water repellency results from the presence of certain organic compounds with hydrophobic properties.
Despite considerable research effort into identifying the organic compounds responsible for soil water repellency, progress to date, however, has been less than might be expected. Reasons for this include (i) the vast number of potentially responsible natural organic compounds with hydrophobic properties occurring in the biosphere, (ii) the difficulty in fully isolating compound groups and individual compounds from soils and (iii) demonstrating that the compounds isolated are indeed responsible for water repellency of a given soil sample. Furthermore, the observed ‘strength’ of water repellency (as determined by contact angle measurements) is not solely determined by surface chemistry, but to a remarkable degree also by surface roughness. This, and the high temporal and spatial variability of water repellency expression observed at various scales, pose additional problems when comparing chemistries and ‘associated’ wettabilities of different samples.
A key outcome has been that only a very small fraction of soil organic matter is responsible for water repellency. Furthermore, hydrophobic compounds extracted from wettable soils have also shown to induce water repellency when applied to wettable sands. This raises the question, what factors in addition to the presence of these hydrophobic compounds control soil water repellency occurrence. Expanding on the issues raised above, this contribution provides a brief review of the current understanding of the chemical causes of water repellency in soils and in particular in turfgrass systems.