Nitrate in the unsaturated zone under agricultural lands

Because of a tremendous increase in the concern for nitrate (NO₃̄) in surface and ground waters, the study of NO₃̄ leaching has become very important. The present investigation was undertaken to determine the potential contribution of fertilizer N use on citrus and row crops to the NO₃̄ in ground waters in the Santa Ana River Basin of Southern California where a deep unsaturated zone exists between the soil profile or crop-root zone and the water table or saturated zone. The objectives were to relate NO₃̄ concentrations in the unsaturated zone to N inputs, N removal by harvested crops and the volume of drainage water, to obtain some estimates of transit times for drainage water through the unsaturated zone, to estimate denitrification losses on a field basis, and to assess the probable effects of present fertilizer N recommendations on NO₃̄ in ground waters.