Y. Mualem - Faculty of Agriculture,The Hebrew University of Jerusalem, Rehovot, Israel

Arid zones are characterized by vast areas of bare soils, low annual precipitation, but high rainfall intensities with high kinetic energy. Desertification of less arid regions may also be a result of overgrazing and exploitation of vegetation beyond the land’s productive potential. Bare soils exposed to rainfall are subjected to physical and chemical processes which change the properties at the vicinity of the soil surface. When dried, a hard layer is formed in the soil surface which is viewed as a “crust”. This phenomenon, when disregarded, may be harmful to agriculture. It decreases the infiltration rate, reduces the available water at the root zone, increases runoff and soil erosion and affects seedlings and plant growth. Duley (1939) reported that raindrop impacts on the bare soil surface are the cause of such a low permeability crust. Hoogmoed and Stroosnijder (1984) studied the semi-arid region of the Sahel in Central Africa and concluded that it was very sensitive to crust formation and that, on average, 25% of the rain is lost by runoff. They also noted that on untilled soils, the presence of a crust is a permanent feature. The crust formation, which limits the cumulative infiltration of valuable water to the root zone, induces in fact a vicious cycle since it affects vegetation cover, thus leaving the soil surface bare and exposed to rainfall.

Part of the Water Science and Technology Library book series (WSTL, volume 21)