Estimates of N2O, NO and NH3 Emissions From Croplands in East, Southeast and South Asia

Agricultural activities have greatly altered the global nitrogen cycle and produced nitrogenous gases of environmentally significance. More than half of the global chemical nitrogen fertilizer is used for crop production in East, Southeast and South Asia where rice the center of nutrition. Emissions of nitrous oxide (N₂O), nitric oxide (NO) and ammonia (NH₃) from croplands in this region were estimated by considering both background emission and emissions resulted from nitrogen added to croplands, including chemical nitrogen, animal manure used as fertilizer, biological fixed nitrogen and nitrogen in crop residue returned to field. Background emission fluxes of N₂O and NO from croplands were estimated at 1.16 and 0.52 kg N ha^-1yr^-1, respectively. A fertilizer-induced N₂O emission factor of 1.25% for upland was adopted from IPCC guidelines, and a factor of 0.25% was derived for paddy field from measurements. Total N₂O emission from croplands in the region was estimated at 1.16 Tg N yr^-1, with 41% contributed by background emission which was not considered in previous global estimates. However, the average fertilizer-induced N₂O emission is only 0.93%, lower than the default IPCC value of 1.25% due to the low emission factor from paddy field. A fertilizer-induced NO emission factor of 0.66% for upland was derived from field measurements, and a factor of 0.13% was assumed for paddy field. Total NO emission was 572 Gg N yr^-1 in the region, with 38% due to background emission. Average fertilizer-induce NO emission factor was 0.48%. Extrapolating this estimate to global scale will result in a global NO emission from cropland of 1.6 Tg N yr^-1, smaller than other global estimates. Total NH₃ emission was estimated at 11.8 Tg N yr^-1. The use of urea and ammonium bicarbonate and the cultivation of rice lead to a high average NH₃ loss rate of chemical fertilizer in the region. Emissions were distributed at 0.5° grid by using a global landuse database.