Effect of rice cultivars and fertilizer management on methane emission in a rice paddy in Beijing

Experiments were conducted during April-Oct. 1994 in a Beijing rice field. Four types of rice varieties have been tested. Large cultivar differences in methane emission flux have been found. Variety 93812 emitted about fivefold more CH4 than did the Qiuguang variety. An organic amendment plus (NH4)2SO4 as the base fertilizer and (NH4)2SO4 as the topdressing applied in different amounts and growth stages, compared with no topdressing, reduced methane emission about 58% and increased rice yield about 31.7%. Emission peaks of CH4 in the tillering stage and reproductive stage were suppressed. A comprehensive strategy could meet both the goal for sustainable rice productivity and methane reduction. Such a strategy includes: 1. Selection of cultivars which have reduced root exudate and litter but increased root mass most of which growing in the oxidized soil layer, cultivars also need an effective number of tillers for optimum yield but with less CH4 transportation ability; 2. Application of organic manure combined with chemical fertilizers, that reduce CH4 emissions. Fertilizers such as SO4(2-) or other inhibitors can be maintained for a long period in soil; 3. Adoption of scientific irrigation mode such as flooding-drainage-intermittent irrigation, that can both increase the rice yield and decrease the CH4 emission, etc..