Changes in CH4 emission from rice fields from 1960 to 1990s - 2. The declining use of organic inputs in rice farming

Previous studies have shown that organic amendments used in paddy rice cult ivation strongly enhance methane emission from rice fields. Because of the increased availability of mineral fertilizer and the labor-intensive nature of many organic amendments, it is likely that the use of organic amendment s in rice farming has decreased in recent years. If so, a significant decre ase in CHS emissions from rice fields could be the result, but quantificati on is difficult because data on organic amendments are scarce. In this pape r data on green manure application in China are used to quantify the impact of changes in an organic amendment on CH4 emission. The trend in CH4 emiss ions over time, taking green manure application explicitly into account. su ggests that CH4 emissions from Chinese rice fields from the 1970s to the ea rly 1980s may have been considerably higher than at present. The results pr esented here and in a previous study [Denier van der Gon, 1999] indicate ti at changes in agricultural management and technology need to be considered in assessments of the CH4 source strength of wetland rice fields and their role in the global CH4 budget of the past, present, and future.