Abstract: Straw return, high-efficiency fertilizer, water-saving irrigation, and reducing nitrogen application are the main technologies for agricultural green development in China. High-yield but low-emission cultivar is an important direction for reducing CH₄ emission in paddy fields. In this study, a field experiment was conducted to investigate the effects of straw return combined with nitrogen reduction application and water-saving irrigation on CH₄ emission of different double-cropping rice cultivars, using static chamber-gas chromatography. A split-plot experimental design was adopted, with four main plot factors: urea + intermittent irrigation (U), reduction of urea 20% + straw return + intermittent irrigation (US+S), reduction of controlled release urea 20% + straw return + intermittent irrigation (CRUS+S), reduction of urea 20% + straw return + water-saving irrigation (US+S+SWD), crossed with two sub-plot factors: conventional rice and hybrid rice. The results showed carbon input, nitrogen input, irrigation amount, and tillering number were main factors affecting CH₄ emission of double cropping rice field. Nutrients from straw return could replenish 20% reduction of nitrogen fertilizer, and significantly promoted CH₄ emission for both cultivars, among which the emissions of conventional rice increased by 60.0%-107.8%, and the emissions of hybrid rice increased by 99.8%-107.8%. This was mainly attributed to the large amount of organic carbon input by straw. Compared with US+S, straw return with controlled-release urea increased CH₄ emissions by 1.8%-9.7%, except for conventional late rice. Water-saving irrigation significantly reduced CH₄ emissions by 15.9%-23.1% with straw return. There were no significant differences in yield among treatments, indicating that straw return combined with nitrogen fertilizer reduction and water-saving irrigation could achieve stable yield. CH₄ emission and yield of hybrid rice were slightly higher than those of conventional rice, but without significant differences. In general, straw return significantly increased CH₄ emission, controlled-release urea and reduced nitrogen application did not affect CH₄ reduction, while water-saving irrigation could effectively reduce yield-scaled CH₄ emission under straw returning. Therefore, with the increases of straw return rates in paddy fields, optimizing water management to promote straw aerobic decomposition is the key to control CH₄ emission.

Key words: CH₄, straw return, nitrogen fertilizer reduction, controlled release urea, water-saving irrigation, rice