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Abstract 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 (N 2 O), nitric oxide (NO) and ammonia (NH 3 ) 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 N 2 O 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 N 2 O 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 N 2 O 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 NH 3 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 NH 3 loss rate from chemical N fertilizer in the study region. Emissions were displayed at a 0.5° × 0.5° resolution with the use of a global landuse database.
Yan et al. (Wed,) studied this question.