Water-dependent repellency of model soils as affected by clay

Clay is an important factor that affects soil water repellency. The purpose of this study was to examine the effects of clay content on water-dependent repellency curve using model soils with the clay content ranging from 0 to 20%. Water-dependent repellency was measured using the water drop penetration time (WDPT) test in a drying process. Water repellency appeared (WDPT 1 s), increased to be extremely repellent (WDPT 3600 s), and decreased to be wettable again during drying of the model soils. Both the marginal water content at which water repellency appeared with drying (WCWR) and the highest water content at which soils become extremely repellent (HWCE) increased with increasing clay content. In contrast, the lowest water content at which soils remain extremely repellent (LWCE) was found to be independent of the clay content. The water-dependent repellency curve was not entirely shifted, but expanded towards the higher water content by the increase in clay content.