Soil water repellency is often recognized in surface layers of soils that dry out frequently. The degree of water repellency of a soil can be measured by using the water drop penetration time (WDPT) test on field-moist or dried samples, referred to as actual and potential water repellency, respectively. A soil layer is actually water repellent below and actually wettable above its critical soil water content. Findings of the present study indicated that the degree of potential water repellency might change with different drying temperatures. For four of the seven sandy soil sites studied in the Netherlands, potential water repellency was greater after drying at 65° C relative to drying at 25°C, whereas it decreased at two sites and remained unchanged at one. The most reliable estimate of water repellency was obtained from undried samples collected during dry periods.
Wetting rate measurements illustrated that water repellency increasing as a result of high drying temperatures led to decreasing water absorption by samples.
Micromorphological investigations indicated that high drying temperatures resulted in an increase in the formation of organic carbon coatings responsible for soil water repellency.