The effects of climatic and soil properties on soil water repellency

Soil water repellency (SWR) is a major agro-ecological soil management issue caused by hydrophobic organic compounds that hinder soil water absorption and affect soil function. Recent modelling studies indicate that climate change will increase the severity of SWR, compounding these effects. This study investigated the effects of climatic and soil factors on SWR in surface (0–10 cm) soils from 355 sites under uniform land-use across an area of 60,000 km² in south-western Australia, a region with a Mediterranean climate. There were marked gradients in temperature (mean minimum temperature (Meanmin, 7.7–12.2 °C), mean maximum temperature (Meanmax, 19.0–22.9 °C), rainfall (507–1443 mm/year) and pan evaporation (Evap, 1169–1772 mm/year) across the sites. SWR was measured in the laboratory on oven dried samples using the ethanol droplet test. Boosted regression tree analysis showed that 10 soil variables explained 78 % of the variance in SWR, with clay, silt and OC contents the main contributors. Incorporating the four climatic variables explained 84 % of the variance of SWR, with Meanmax the major contributing factor. Thus, while soil properties dominated the expression of SWR, climate had a secondary impact. Meanmax however, was inversely related to SWR, suggesting that rising temperatures due to climate change could result in a reduction in SWR. Furthermore, given the strong relationship between SWR and OC content, climate mitigation projects aimed at enhancing soil OC storage may inadvertently increase the expression and severity of SWR. Recognition of this should be included in soil carbon mitigation project protocols.