Abstract
Soil water repellency (SWR) is a widespread phenomenon that impacts plant growth, groundwater contamination, surface erosion and runoff in many regions of the world. It is a major constraint to agricultural production in southern Australia, affecting over ten million hectares of arable land and is a feature of natural ecosystems, and is particularly exacerbated by wildfire. Water repellency is caused by hydrophobic organic substances coating soil particle surfaces or within interstitial matter, derived from decomposing organic matter, root exudates and microbial by-products. The incidence of SWR predominantly depends on the interaction of soil organic matter (SOM) and the soil surface area.
Given the strong interest in increasing SOM contents to mitigate climate change, SWR will likely also increase. It is thus important to map soils in terms of both the current degree of SWR and its potential to develop in the future, based on intrinsic soil properties such as soil surface area. This will identify where amelioration techniques such as wetting agents and clay-rich amendments can be better targeted. Conventional SWR measurements are costly, time-consuming and labour-intensive and contain a high uncertainty in their representativeness and applicability in the field. This review will consider how different proximal sensing techniques can be used to assess the current incidence and severity of SWR and the risk of it developing, to provide integrated site-specific management.