Effects of water-saving irrigation,reduced nitrogen application and different cultivars on CH4 emissions in a double rice cropping system
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 de-sign 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 irri-gation(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 retur-ning.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.
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