Cattle (12,401 Mg in 1990) were the largest source of N2O emissions, pigs (6,608 Mg in 1990) the smallest, and the rest was poultry (10,372 Mg in 1990) (Fig. 40.4), a result related to the different amounts of livestock excreta produced by these classes of livestock. N2O emissions by cattle, pigs, and poultry during the period were relatively constant at 40%, 25%, and 35% of total, respectively. Crop production
In 1985, when crop N2O emissions were highest, paddy rice (4,714 Mg) was the largest source of N2O and forage crops (3,376 Mg) the second highest, because these crops occupied about 60% of farmland (Fig. 40.4). In 2005, when N2O emissions were lowest, 70% of N2O came from paddy rice (2,770 Mg), vegetables (2,810 Mg), and forage fields (2,850 Mg). Over the study period, the area of paddy rice declined from 27% to 23% and that of vegetables increased from 17% to 23%. N fertilizer input to paddy rice declined from 114 to 72 kg N ha-1 and N fertilizer input to vegetables increased from 180 to 201 kg N ha-1. Tea comprised 10% to 13% of total crop production of N2O emissions during the period. Although the area planted in vegetables and tea was small (12% and 1% of total planted area in 2005, respectively), vegetables and tea were significant sources of N2O. This result shows that vegetables and tea are hotspots of N2O emissions in the crop production sector, because of the higher chemical N fertilizer and manure input to vegetables than other crops and a high emission factor for tea. Tea received the highest rate of chemical N fertilizer among the crops during the period, but application levels declined from 613 kg N ha"1 in 1985 to 459 kg N ha"1 in 2005.
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