Modeling methane emissions from rice agriculture in China during 1961-2007

We assessed decadal changes in CH4 fluxes from rice fields in China during 1961-2007 using an empirical model that was modified to include the effects of changing patterns of fertilizer use and water management. We reviewed studies of the effects of organic amendments and found that an application rate of 6 tons/ha increased emissions by 115 +/- 42% based on experimental manipulations from 10 studies. We also reviewed studies of mid-season drainage in rice fields and found that drainage reduced CH4 emissions by 35 +/- 12% based on experiments reported from nine studies. Our simulations showed that the CH4 flux was about 8 Tg/year in 1961, gradually increased to a maximum of approximately 17 Tg/year in 1982, and then gradually declined to 7.5 Tg/year in 2007. The reduction in the total rice emissions after 1982 was caused primarily by changing agricultural practices, including mid-season drainage, increases in inorganic fertilizer use, improved crop yields, and decreases in the area used for rice production.