WATER INFILTRATION CONTROL AT THE SOIL SURFACE - THEORY AND PRACTICE

This paper traces the course of research conducted by the author and several coworkers beginning in 1960 and continuing to the present time. A review of water infiltration literature and some early infiltrometer trials led to the formulation of the Air-Earth Interface (AEI) concept for water infiltration into initially dry soils. This concept states that the micro-roughness and macroporosity of the AET regulate the exchange of surface water and displaced soil air across the AEI with the rough-open interface having very high exchange rates and with the smooth-closed interface having very low rates. This concept was supported and verified by a series of sprinkling infiltrometer studies, wherein manipulation of surface microroughness and macroporosity (roughness and openness) provided an order of magnitude control over water infiltration. The infiltration role of displaced soil air was elucidated by inventing and using devices referred to as border-irrigation and closed-top infiltrometers. Results obtained with these devices showed that very small soil air pressures can greatly affect infiltration by blocking downward water flow in macropores. The next step was to apply the AEI Infiltration Concept to reversing global land desertification (degradation) by restoring high infiltration rates to barren soils. What war needed was a device or machine that would economically restore stabile roughness and openness to the smooth-sealed desertified AEI which, in turn, would restore the high rates of rainwater infiltration required for successful revegetation. This led to the invention and development of a series of land imprinting devices. By efficiently controlling rainwater infiltration at the soil surface, these devices have already restored perennial grasses to 20,000 hectares of desertified rangeland in southern Arizona alone. With the successful development of land imprinting, the AEI concept evolved into the AEI model for reversing desertification through infiltration control. This diagrammatic/verbal model of four AEI processes helps guide revegetation projects to successful completion. However, progress toward reversing global desertification will require at least a three order-of-magnitude increase in finding from the developed countries.