HOW WATER MOVES IN A WATER REPELLENT SANDY SOIL .1. POTENTIAL AND ACTUAL WATER REPELLENCY

Water repellency is an important property of many soils. It causes rainwater to penetrate into the soil as preferential flow paths, and solutes can reach the groundwater more rapidly than in the case of a homogeneous wetting. Water repellency depends on several factors which are principally related to the characteristics of the organic matter of the soil. A distinction between ''potential'' and ''actual'' water repellency and the assessment of the ''critical soil water content'' are introduced and highlighted in this paper. Persistence and degree of potential water repellency of dried samples were examined from 10 trenches in a dune sand with grass cover using the water drop penetration time and the alcohol percentage tests. The spatial variability of water repellency and, therefore, soil wetting was extremely high. The actual water repellency was measured on field-moist samples to obtain critical soil water contents. The soil is wettable above and water repellent below these values. The critical soil water content varies between 4.75 vol % at 5-10 cm and 1.75 vol % at 45-50 cm depth in this sandy soil.