Distribution of Soil Water Repellency along Different Particle Sizes of Coastal Sand Dunes in Sri Lanka

Abstract

Water repellent soils do not wet spontaneously when a drop of water placed on the soil surfaces. Although water repellency has been reported for all major soil types in the world, occurrence of water repellency in Sri Lankan soils has not been reported so far. The objective of this study is to examine the presence of water repellent condition of a sand dune in Dry zone of Sri Lanka under Casuarina equisetifolia land cover and the distribution of water repellent conditions along the difference particle sizes. Water repellency was determined using water drop penetration time (WDPT) and contact angle. The uppermost or the surface soil layer [0-5 cm depth) showed the highest water repellency as measured by WDPT and the contact angle in all the particle sizes. Water repellency decreased with increasing depth of the soil. Both WDPT and the contact angle increased as the particle size decreased. The WDPT for soils in the 0-5 cm layer increased only from 22 to 1705 s with decreasing particle size from 0.15 mm < 0.04 mm. Samples were non-repellent [ WDPT< 1 s) for particle sizes >0.09 mm in the 5-10 layer and particle sizes >0.04 mm in the 10-15 cm layer. Soils changed from non-repellentto severely repellent with decreasing particle size from 0.09 to < 0.04 mm in the 5-10 cm layer, and from non-repellent to slightly repellent with decreasing particle size from 0.04 to < 0.04 mm in the 10-15 cm layer. Smaller particle sizes seemed to contribute more to the occurrence of soil water repellency.