NITROUS-OXIDE EMISSIONS FROM AGRICULTURAL SOILS

This paper addresses three topics related to N2O emissions from agricu ltural soils. First, an assessment of the current knowledge of N2O emi ssions from agricultural soils and the role of agricultural systems in the global N2O are discussed. Secondly, a critique on the methodology presented in the OECD/OCDE (1991) program on national inventories of N2O is presented. Finally, technical options for controlling N2O emiss ions from agricultural fields are discussed. The amount of N2O derived from nitrogen applied to agricultural soils from atmospheric depositi on, mineral N fertilizer, animal wastes or biologically fixed N, is no t accurately known. It is estimated that the world-wide N2O emitted di rectly from agricultural fields as a result of the deposition of all t he above nitrogen sources is 2-3 Tg N annually. This amounts to 20-30% of the total N2O emitted annually from the earth's surface. An unknow n, but probably significant, amount of N2O is generated indirectly in on and off farm activities associated with food production and consump tion. Management options to limit direct N2O emissions from N-fertiliz ed soils should emphasize improving N-use efficiency. Such management options include managing irrigation frequency, timing and quantity; ap plying N only to meet crop demand through multiple applications during the growing season or by using controlled release fertilizers; applyi ng sufficient N only to meet crop needs; or using nitrification inhibi tors. Most of these options have not been field tested. Agricultural m anagement practices may not appreciably affect indirect N2O emissions.