Nitrogen circulation and nitrate in groundwater in an agricultural catchment in Southern India

High contents of nitrate in groundwater, ranging up to 1,500 mg/l, have been found. High concentrations are more common in village wells than in irrigation wells situated in the fields. The losses of nitrogen from the soil zone through deep leaching into the groundwater are small (260 kg N/km²); however, due to a small net infiltration (29 mm/year), the median content in groundwater still approaches the permissible limit of 50 mg/l NO ₃ ^? . In villages about 10–20% of the nitrogen from excreta are leached into the groundwater. Mineralization of soil nitrogen during a dry period, followed by heavy rains, caused extremely high contents of nitrate in groundwater.