Changes in fertilizer-induced direct NO emissions from paddy fields during rice-growing season in China between 1950s and 1990s

摘要

Nitrogen fertilizer-induced direct nitrous oxide (NO) emissions depend on water regimes in paddy fields, such as seasonal continuous flooding (F), flooding-midseason drainage-reflooding (F-D-F), and flooding-midseason drainage-reflooding-moist intermittent irrigation but without water logging (F-D-F-M). In order to estimate the changes in direct NO emission from paddy fields during the rice-growing season in Mainland of China between the 1950s and the 1990s, the country-specific emission factors ofNO-N under different water regimes combined with rice production data were adopted in the present study. Census statistics on rice production showed that water management and nitrogen input regimes have changed in rice paddies since the 1950s. During the 1950s-1970s, about 20-25% of the rice paddy was continuously waterlogged, and 75-80% under the water regime of F-D-F. Since the 1980s, about 12-16%, 77%, and 7-12% of paddy fields were under the water regimes of F, F-D-F, and F-D-F-M, respectively. Total nitrogen input during the rice-growing season has increased from 87.5 kg N hap# in the 1950s to 224.6 kg N hap# in the 1990s. The emission factors of NO-N were estimated to be 0.02%, 0.42%, and 0.73% for rice paddies under the F, F-D-F, and F-D-F-M water regimes, respectively. Seasonal NO emissions have increased from 9.6 Gg NO-N each year in the 1950s to 32.3 Gg NO-N in the 1990s, which is accompanied by the increase in rice yield over the period 1950s-1990s. The uncertainties in NO estimate were estimated to be 59.8% in the 1950s and 37.5% in the 1990s. In the 1990s, NO emissions during the rice-growing season accounted for 8-11% of the reported annual total of NO emissions from croplands in China, suggesting that paddy rice development could havecontributed to mitigating agricultural NO emissions in the past decades. However, seasonal NO emissions would be increased, given that saving-water irrigation and nitrogen inputs are increasingly adopted in rice paddies in China.