Estimation of nitrous oxide, nitric oxide and ammonia emissions from croplands in East, Southeast and South Asia

Agricultural activities have greatly altered the global nitrogen (N) cycle and produced nitrogenous gases of environmental significance. More than half of all chemical N fertilizer produced globally is used in crop production in East, Southeast and South Asia, where rice is central to nutrition. Emissions of nitrous oxide (N2O), nitric oxide (NO) and ammonia (NH3) from croplands in this region were estimated by considering background emission and emissions resulting from N added to croplands, including chemical N, animal manure, biologically fixed N and N in crop residues returned to fields. Background emission fluxes of N2O and NO from croplands were estimated to be 1.22 and 0.57 kg N ha(-1)yr(-1), respectively. Separate fertilizer-induced emission factors were estimated for upland fields and rice fields. Total N2O emission from croplands in the study region was estimated to be 1.19 Tg N yr(-1), with 43% contributed by background emissions. The average fertilizer-induced N2O emission, however, accounts for only 0.93% of the applied N, which is less than the default IPCC value of 1.25%, because of the low emission factor from paddy fields. Total NO emission was 591 Gg N yr(-1) in the study region, with 40% from background emissions. The average fertilizer-induced NO emission factor was 0.48%. Total NH3 emission was estimated to be 11.8 Tg N yr(-1). The use of urea and ammonium bicarbonate and the cultivation of rice led to a high average NH3 loss rate from chemical N fertilizer in the study region. Emissions were displayed at a 0.5degrees x 0.5degrees resolution with the use of a global landuse database.