ENVIRONMENTAL-EFFECTS OF N FERTILIZER USE - AN OVERVIEW

In recent years concern has grown over the contribution of nitrogen (N) fertilizers to the environmental problems of nitrate pollution of waters and the pollution of the atmosphere with nitrous oxide, other oxides of nitrogen, and ammonia. These gases potentially contribute to the 'greenhouse effect' or global heating because of their increasing concentrations in the atmosphere and to the destruction of the stratospheric ozone layer, which protects the earth from ultraviolet radiation. In light of these concerns, proposals to mitigate these problems have been considered, and others will be forthcoming. When they have been used in high amounts, fertilizers and animal manures have created problems of nitrate pollution. Nitrous oxide (N2O) is a greenhouse gas and may also contribute to the destruction of the stratospheric ozone when it is converted to nitric oxide. N2O is primarily produced in the biological processes of nitrification and denitrification. Nitric oxide and nitrogen dioxide are also produced in biological processes and are important in atmospheric reactions in the troposphere and stratosphere. There is little indication that N fertilizers contribute very much to the production of nitrous oxide. More research is needed to characterize and measure the emissions of the oxides of nitrogen and ammonia and to make better estimates of global emissions based on process-related models. More efforts to increase the efficiency of nitrogen fertilizer use through modifications or use of inhibitors of biological processes as well as better management of rates, timing, and incorporation are needed to ensure increased food production while conserving natural resources.