Assessment of soil water repellency as a function of soil moisture with mixed modelling

An understanding of the relation between soil water repellency (SWR) and soil moisture is a prerequisite of water-flow modelling in water-repellent soil. Here, the relation between SWR and soil moisture was investigated with intact cores of soil taken from three types of soil with different particle-size distributions. The SWR was measured by a sessile drop contact angle (CA) during drying at soil pF values that ranged from - to 4.2. From the measured CA, the work of adhesion (W-a) was calculated and its relation with the pF-value was explored. Mixed modelling was applied to evaluate the effects of pF, soil type and soil depth on CA and W-a. For all soil types, a positive relation was observed between CA and the pF-value that could be represented by a linear model for the pF-range of 1-4.2. The variation in slope and intercept of the CA-pF relationship caused by heterogeneity of the samples taken from a single soil horizon was quantified. In addition, the relation between CA and water content (WC) showed hysteresis, with significantly larger CAs during drying than during wetting.