Soil water repellency in sandy soil depends on the soil drying method, incubation temperature and specific surface area

Abstract Soil water repellency (SWR) is problematic in rainfed cropping soils as it decreases plant water use efficiency. The occurrence of SWR is often dependent on the prevailing soil water content, but the response of SWR to soil water content varies among studies. We undertook three experiments to investigate how the (i) drying method prior to experimentation (oven-dried at 105 °C or vacuum-dried at 20 °C), (ii) incubation temperature (4 °C, 20 °C and 40 °C), and (iii) specific surface area (SSA) of four sieved soil fractions (0.49 m2 g−1, 0.59 m2 g−1, 0.65 m2 g−1 and 1.61 m2 g−1) influenced the response of SWR to soil water content. In all experiments, SWR (measured by molarity of ethanol droplet) remained constant up to a ‘threshold soil water content’, and then responded linearly with increasing soil water content. However, oven-dried soil at 105 °C had lower SWR than soil dried anoxically at 20 °C, which remained constant up to a threshold soil water content. The SWR response rate to soil water content above the threshold was also lower in the 105 °C oven-dried soil than the 20 °C anoxically vacuum-dried soil. Whereas, increasing the incubation temperature increased the SWR response rate to soil water content above the threshold. The four sieved soil fractions had increasing threshold soil water contents with increasing SSA, which could be related to the total carbon content of the soil. In conclusion, the same drying method and incubation temperature should be used throughout an experiment and between studies when investigating the response of SWR to soil water content to avoid methodological errors.