NITRATE IN GROUNDWATER AND N-CIRCULATION IN EASTERN BOTSWANA

Nitrate pollution due to deep leaching from pit latrines has caused wa ter supply wells in eastern Botswana to exceed health limits concernin g nitrate. It was deduced from the estimated intake of salt and protei n by the population that, as an average, about 10 percent of the human nitrogen excretion is leached to the groundwater. This fraction was a lso found in southern India, where on-the-ground excretion is customar y. The nitrogen circulation in general in the savanna ecosystem is not appreciably affected in spite of a large livestock density. Overall n itrate leaching is in the order of 1.5 kg N/ha/y, similar to that in a nother semiarid area in southern India. However, in India, there seems to be a more diffuse areal leaching from agriculture as well as from villages. Measures to minimize the nitrate leaching could be to plant deep-rooted trees adjacent to pit latrines or to use latrines that sep arate the urine from the faces for a more near-surface infiltration fa cilitating plant uptake. Measures to minimize leaching will also lesse n the rick for bacterial pollution of the groundwater.