Revised water drop method for assessing soil water repellency in sandy soils

Water repellency or hydrophobicity in soil is a widespread condition found in soils around the world. Some effects of water repellency in soil are decreases in wetting front movement and water infiltration and preferential flow of water and solutes. The water drop penetration time (WDPT) method is a widely used technique to determine soil water repellency. This method, although effective, does not include post-drop penetration observations and analyses. The objective of this study was to modify the WDPT method to include evaluation of the size of soil wetted area (SWA) over time after drop infiltration. Soil samples evaluated came from three different vegetation types, prairie, pine plantation, and mixed prairie and forest encroachment, growing on a sandy soil. Methods performed were WDPT and SWA, which consists of measuring the SWA after drop infiltration. The SWA was better at establishing a range of wettability differences for slightly hydrophobic soils, whereas WDPT was superior at displaying differences in extreme degrees of soil water repellency. It is recommended that both WDPT and SWA be measured to obtain a more comprehensive understanding of different degrees of soil water repellency.