The contradictory nature of soil water repellency: A mechanistic understanding of why soil water repellency initially increases with soil water content in sandy soil

Soil water repellency (SWR) occurrence is a key constraint to agriculture production globally. Mechanisms for why SWR increases with soil water content below the wilting point have remained elusive. Utilising dynamic vapour sorption and novel inverse gas chromatography, this thesis demonstrates SWR only increases when above a threshold soil water content in a sandy soil, to coinciding with the onset of capillary water condensation and likely due to the decrease in surface charge by counterions. Previously proposed mechanisms based upon thin layer of water molecules, blockage of soil pores and transition from Cassie-Baxter to Wenzel wetting regime are not supported.