ECOSYSTEM CATALYSIS - SOIL UREASE ACTIVITY AND GRAZING IN THE SERENGETI ECOSYSTEM

The activity of soil ureases was evaluated in the laboratory in soils from three locations in the Serengeti National Park, Tanzania, differi ng in the grazing intensities that the grasslands there support. Ureas e activity was assayed by the instantaneous release of NH4 as soon as soils drained to held capacity after application of an aqueous urea so lution approximating N concentrations in ungulate urine. The appearanc e of NO3 and SO4 in extracts was used as an index of biological activi ty and pH changes; neither responded to urea addition. Ammonium appear ance in extracts of soils to which water but not urea was applied was low and identical; appearance in extracts where urea had been added wa s high and differed between sites, increasing with the level of grazer activity at a site. The data document ecologically meaningful levels of soil urease in Serengeti soils and a positive association of those levels with grazing intensity.