NITRIC-OXIDE EMISSIONS FROM AGRICULTURAL SOILS IN TEMPERATE AND TROPICAL CLIMATES - SOURCES, CONTROLS AND MITIGATION OPTIONS

Global annual NO emissions from soil are of the order of 10 Tg NO-N. T his is about half the amount fossil fuel combustion processes contribu te to the annual global NOx budget. Reducing the emissions of soil der ived NOx requires an understanding of the source of the flux and the p rocesses that determine its magnitude. A thorough investigation of pos sible mitigation strategies and the consequences of their implementati on is also necessary. The ratio of NO and N2O emissions from soils can be used as an indicator of the dominant NO production pathway operati ng. Fertilizer application (rate, type and time of application), soil temperature, soil water content and soil management practices all affe ct the emission rate and are reviewed. Mitigation options include redu ction in N fertilizer use through an increase in fertilizer use effici ency, preferential use of NH4NO3 instead of urea, improved timing of f ertilizer application, the use of nitrification and urease inhibitors, improving the fertilizer uptake efficiency of crops in tropical agric ulture and changes in land management. Several of the viable mitigatio n strategies, mainly those increasing fertilizer use efficiency, have the capacity to reduce global annual NO emissions by 4% (0.4 Tg NO-N y (-1)). For other strategies including use of inhibitors, changing cult ivation or land use, the possible reductions are too uncertain to just ify quantification on the basis of present knowledge.