Methane emissions from a rice agroecosystem in South China: Effects of water regime, straw incorporation and nitrogen fertilizer

To quantitatively assess the effects of agricultural practices on methane (CH4) emissions from rice fields, a two-year (2005/2006) field experiment with 2(3) factorial designs was conducted to assess the effects of three driving factors on CH4 emissions in South China: continuously flooded (W0) and mid-season and final drainages (W2), straw (S1) and nitrogen fertilizer (N1) applications and their controls (S0, N0). Results showed that averaged across all the treatments about 75 % of the seasonal total CH4 occurred between the rice transplanting and booting stage, while constituted only 33 % of the seasonal total rice biomass during the same period. Averaged across the treatments in 2006, CH4 emissions were substantially decreased by mid-season drainage up to 60 % (15.6 vs. 39.0 g m(-2)). The decreased CH4 emissions represented almost all of the decrease in the total global warming potentials. Without straw incorporation CH4 emissions substantially decreased up to 59 % (15.9 vs. 38.7 g m(-2)). The stimulating effects of straw were significantly greater for W0 than W2 treatment, being also greater in the 2005 than in the 2006 season. A significant inter-annual difference in CH4 emissions was found when averaged across straw incorporation and N fertilizer applications for the W2 treatment (42.8 and 15.4 g m(-2) in 2005 and 2006, respectively). Moreover, N fertilization has no significant effect on CH4 emissions in this study. Our results demonstrate that although straw effects varied greatly with specific management, both straw managements and water regimes are equally important driving factors and thus being the most promising measures attenuating CH4 emissions while achieving sustainable rice production.