A category for estimate of CH4 emission from rice paddy fields in China

Based on key factors influencing CH4 fluxes from rice paddy fields in China, a category for estimation of total CH4 emission was suggested and the constraints for the estimation were discussed in the paper. Recently, CH4 fluxes measured in situ have been built up dramatically with the efforts of both Chinese scientists and those from abroad. After reviewing published data on CH4 fluxes from rice paddy fields, we found that although there are many other influencing factors, water regime and organic manure application are two key factors controlling CH4 emission; thus, rice paddy fields in China were classified by these two factors to estimate CH4 emission. In the suggested category, the water regime of rice paddy fields was classified into mid-season aeration at least once during the period of rice growth (MSA), continuous flooding during the period of rice growth but well-drained after rice harvest (CFD), and permanent flooding (PF) even in winter, and fertilization was classified into mineral fertilizers only (MIN), amendment with organic manures at the rate of less than or equal to 15 t ha-1 (MU < 15) and at the rate of higher than 15 t ha-1 (MU > 15), and with rice straw or other fresh plant materials (RS). Combining both water regime and fertilization together, we classified rice paddy fields in China into 12 types. The seasonal mean CH4 flux of each type of rice paddy field was calculated by the data available and showed that the lowest CH4 flux was found in the type MSA-MIN, and the highest in PF-MU > 15. The total emission estimated by this category was 8.05 Tg CH4 yr-1 with a standard deviation of 3.69 Tg CH4 yr-1.