Methane Emissions from Rice Paddies, Factors Affecting

Abstract

methane emission gradually increases during the vegetative phase correlating with increasing plant biomass, and peaks near panicle differentiation, a period of rapid root development. Emission remains relatively constant during the reproductive stage, but may decrease during late grain filling because of root degradation. Prior to the end of the season, a second emission peak may be observed. This late-season increase in emission can be attributed to an increase in soil C substrate due to accelerating leaf and root senescence. [1] The addition of readily degradable C, such as rice straw, before planting results in an increase in the early-season methane emission. The decomposition of the straw may also result in an enhanced or additional early-season emission maximum. [1] Photosynthetic Activity In irrigated tropical rice paddies with double cropping, both methane emission and rice grain yields are consistently higher in the dry season than in the wet season. [2] One interpretation of this finding is that higher photosynthetic rates during the sunnier days of the dry season lead to larger amounts of C available to methanogenic bacteria and, consequently, greater production and emission rates of methane. Seasonal rates of methane emission and rice grain yield have been positively correlated with accumulated solar radiation. [3] A1 % increase in accumulative solar radiation is accompanied by a 1.1% increase in methane emission and a 1% increase in rice grain yield. These findings are consistent with the hypothesis that solar radiation, and hence photosynthetic activity of the rice plant, correlates with methane production and grain yield through the partitioning of nonstructural carbohydrates to the root system and grain panicle.