The Relationship between Soil Moisture and Soil Water Repellency Persistence in Hydrophobic Soils

In this work, we modelled the response of soil water repellency (SWR) persistence to the decrease in moisture in drying soils, and we explored the implication of soil particle size distribution and specific surface area on the SWR severity and persistence. A new equation for the relationship between SWR persistence and soil moisture (theta) is described in this paper. The persistence of SWR was measured on ten different hydrophobic soils using water drop penetration time (WDPT) at decreasing levels of gravimetric water content. The actual repellency persistence showed a sigmoidal response to soil moisture decrease, where R-a(theta)=Rp/1+e(delta(theta-theta c)). The suggested equation enables one to model the actual SWR persistence (R-a) using theta, the potential repellency (R-p) and two characteristic parameters related to the shape of the response curve. The two parameters are the critical soil moisture theta(c), where the R-a increase rate reaches its maximum, and the parameter delta affecting the steepness of the curve at the inflexion point of the sigmoidal curve. Data shows that both soil carbon and texture are controlling the potential SWR in New Zealand pastures.