SOIL MEASUREMENTS DURING HAPEX-SAHEL INTENSIVE OBSERVATION PERIOD

This article describes measurements made at each sits and for each veg etation cover as part of the soils program for the HAPEX-Sahel regiona l scale experiment. The measurements were based on an initial sampling scheme and included profile soil water content, surface soil water co ntent, soil water potential. infiltration rates. additional measuremen ts on core samples, and grain size analysis. The measurements were use d to categorize the state of the surface and profile soil water regime s during the experiment and to derive functional relationships for the soil water characteristic curve, unsaturated hydraulic conductivity f unction, and infiltration function. Sample results for different super sites and different vegetation covers are presented showing soil water profiles and total soil water storage on days corresponding to the ex perimental 'Golden Days'. Sample results are also presented for spatia l and temporal distribution of surface moisture content and infiltrati on tests. The results demonstrate that the major experimental objectiv e of monitoring the supersites during the most rapid vegetative growth stage with the largest change of the surface energy balance following the rainy season was very nearly achieved. Separation of the effects of probable root activity and drainage of the soil profile is possible . The potential for localized advection between the bare soil and vege tation strips of the tiger bush sites is demonstrated.