Thesis: The influence of low water content and dissolved organic carbon on soil water repellency
Soil water repellency (SWR) limits the soil to wet up. In severe cases, the water will pond on the surface and the underlying soil will remain dry. As a result, SWR can decrease the emergence and growth of agricultural crops. Maximum SWR is commonly thought to occur when the soil is at its driest (0% water content) and following drying at high temperatures, >40˚C. However, there are instances when maximum repellency has been observed at low, but not completely dry, soil water contents (~4% water content for sands). This phenomenon is not fully understood. In addition, my thesis will explore mechanisms to explain the maximum SWR at low water content. As soils contain dissolved organic carbon (DOC), which were found to induce SWR, my research will also investigate the interactive effect between DOC and low soil water content on SWR. Scientific research has demonstrated that soluble organic compounds may either increase or decrease SWR. Thus DOC could potentially control the severity of SWR, while implementation of appropriate farming practices may influence soil DOC concentrations and in turn SWR.
Why my research is important
Globally and nationally SWR is known to restrict soil water infiltration and limit agricultural production. Furthermore, according to CSIRO Marine and Atmospheric Research (http://www.cmar.csiro.au/e-prin/open/projections2001.pdf), by 2030, Australia is forecasted to experience warmer temperatures and declining annual rainfall. Thus the incidence and severity of SWR may further increase. In Western Australia, it has been estimated SWR decreases agricultural grain production by $250M to $330M per annum. Some mitigation and amelioration strategies have been developed to address the issue, however they have practical limitations or are expensive. Examples of some remedial strategies include soil inversion, claying and the use of surfactants. The fundamental understanding of low water content and dissolved organic carbon on SWR may provide an opportunity to develop alternative effective strategies to decrease the incidence and management of SWR.