Water repellent Soils: Origin, Characteristics, and Significance in Sri Lankan context.

Abstract

In general, dry soils readily absorb water. Usually a strong attraction exists between mineral soil particles and water. However, all sorls do not exhibit these wettable characteristics, as some soils may repel water. A wat,,r repellent soil can be defined as a soil that does not wet spontaneously when water is applied on the surface. When placed on a water repellent soil, water just , emain on the surface or runs off instead of soaking into the soil. Reduced waier entry, or the infiltration, into water repellent soils will consequently lead to increased surface runoff and topsoil erosion, contributing to the land degradation. In additio11, water repellency induces the development of fingered ,,r preferential flow paths, md creation of unstable, irregular wetting fronts. As a result of reduced infiltration, gett, ng the required water into the root zone becomes a major problem. Less availability of ,,ater in the root zone retards plant growth, reducing the quantity and the quality of crop production. In contrast to its negative impacts, water repellency (hydrophobicity) of soil aggregates reduces their affinity for water. Reduction of the rate of water entrv into the aggregates may help in hampering the pressure buildup within aggregates, improving their stability against slaking.