METHANE EMISSION FROM RICE PADDIES AND POSSIBLE MITIGATION STRATEGIES

Though data presently available from field measurements of methane emission from rice paddies allow only a rough estimate of the source strength on a global scale, rice cultivation has been identified to represent one of the most important individual sources of atmospheric methane. Extrapolation of data derived from measurements performed in one of the most extensive rice growing areas of the world, the People's Republic of China, resulted in an estimate for the global methane source strength of rice paddies of 100 +/- 50 Tg per year. This estimate has a high degree of uncertainty, since the impact of several parameters like e.g. soil type, soil temperature, field management, type and mode of application of fertilizers on methane emissions from rice paddies is far from beeing understood. The processes involved in methane emission from rice paddies to the atmosphere include: methane production in the soil by methanogens, methane oxidation in aerobic parts of the soil and the water column by methanotrophs, and plant mediated transport. A detailed understanding of these processes and their interconnections are required, to identify and to enforce strategies focussed on reduction of methane emissions from paddy fields. Possible mitigation options should be based on nutrient and water management of rice paddies, inhibition of methanogenesis, stimulation of methane oxidation, and selection of rice-cultivars with reduced methane-transport capacity.