NITROGEN APPLICATION AND UNDERGROUND WATER CONTAMINATION IN SOME AGRICULTURAL SOILS OF SOUTH WESTERN NIGERIA

The effect of nitrogen fertilizer application on nitrate leaching and contamination of underground and surface waters in a continuously cropped lowland area of South Western Nigeria has indicated a high potential for nitrate leaching. It was estimated that with 100 kg N ha-1 applied, as much as 29.5 kg N ha-1 could be lost through leaching below the root zone of a maize crop, Over a 3 year period the applied nitrogen contributed to nitrate pollution of underground water significantly in excess of the maximum level accepted for potable water. This was particularly high in valley bottoms. where the nitrate nitrogen content ranged from 12.8 to 24.6 mg L-1. Contribution to adjacent stream was, however, not significant.