Fate of fertilizer nitrogen in a multiple cropping system

The fate of 15N-labelled fertilizer nitrogen, applied to the maize crop only, in a multiple cropping system for two crop rotations of maize-wheat-moong, has been studied. The pattern of fertilizer uptake by this crop, the utilization of fertilizer nitrogen residue by the succeeding crops of wheat and moong, residual nitrogen in the soil, and losses due to leaching and other processes were measured. The nitrate content of tube-well waters of an agricultural farm of the Indian Agricultural Research Institute, monitored for three years (June 1975 - March 1978), varied from 5 ppm to 35 ppm. Broad conclusions based on the experimental data, for increasing the efficiency of applied nitrogen and reducing the nitrate pollution of groundwater in relation to fertilizer practices and the change in cropping pattern are discussed. (author)