Seasonal variation in potential water repellence has not been widely reported in the literature, and little is known of the processes that cause changes in potential water repellence. In this study, the severity and stability of potential water repellence varied seasonally from being weakly hydrophobic in July 2009 (water drop penetration time, 0.19 min; water entry potential, 0.0 cm) to severely hydrophobic (water drop penetration time, 54 min; water entry potential, 14.3 cm) in May 2009. Seasonal variation in the stability of potential water repellence was significantly correlated with cumulative rainfall, air temperature and soil water deficit, which indicated that the accumulation of water-repellent compounds, presumably polar waxes, resulted from microbial or plant inputs to the soil. Laboratory experiments demonstrated that saturating and mixing the soil resulted in a two to three order of magnitude reduction in the stability of potential water repellence, even after oven drying at 40
°C and 60 °
C. Repeated leaching resulted in sequential reduction in both the stability and severity of water repellence. The significant correlation between soil water repellence and dissolved organic carbon content of the leachate, together with pedological evidence of organic staining of ped faces in the clay subsoil indicate that seasonal rainfall leached soluble water-repellent compounds from the topsoil. The reestablishment of water repellence after saturation and leaching required the input of new water-repellent compounds. These findings suggest that the use of surfactants before sowing may assist to leach water-repellent compounds from the topsoil, allowing improved infiltration and reduced runoff through the remainder of the cropping season.

Item Type:	Refereed Article
Keywords:	hydrophobic, duplex soil, texture-contrast soil, water entry potential
Research Division:	Environmental Sciences
Research Group:	Soil Sciences
Research Field:	Soil Physics
Objective Division:	Environment
Objective Group:	Soils
Objective Field:	Farmland, Arable Cropland and Permanent Cropland Soils
Author:	Hardie, MA (Mr Marcus Hardie)
Author:	Cotching, WE (Dr Bill Cotching)
Author:	Doyle, RB (Dr Richard Doyle)
Author:	Lisson, S (Dr Shaun Lisson)
ID Code:	79586
Year Published:	2012 (online first 2011)
Web of Science® Times Cited:	12
Deposited By:	Agricultural Science
Deposited On:	2012-09-23
Last Modified:	2013-09-05
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