江汉平原不同稻作模式下温室气体排放特征

采用静态箱-气相色谱法在江汉平原开展早稻、晚稻、中稻、虾稻和再生稻5种稻作类型温室气体排放监测试验，研究不同稻作模式下稻田CH4和N2O排放特征、总增温潜势及温室气体排放强度，为准确评估稻田生态系统温室气体排放提供参考依据。结果表明：CH4排放集中在水稻前期淹水阶段，排放峰值最高为虾稻（85.7 mg·m-2·h-1），较其他稻作模式高71.7%~191.5%。N2O排放峰值主要出现于中期晒田和施肥阶段，排放峰值最高为再生稻（1100.7 μg·m-2·h-1），较其他稻作模式高16.8%~654.9%。CH4累积排放量从大到小依次为虾稻、再生稻、早稻、晚稻、中稻；N2O累积排放量从大到小依次为再生稻、早稻、晚稻、中稻、虾稻；总增温潜势从大到小依次为虾稻、再生稻、早稻、晚稻、中稻；温室气体排放强度从大到小依次为虾稻、早稻、再生稻、晚稻、中稻。CH4排放占比为82.9%~99.0%，稻虾田高排放主要原因为持续淹水时间长、秸秆还田和饲料投入，探究该模式CH4减排举措最为关键；中稻由于水旱轮作，稻田温室气体排放最低，可作为低碳减排的主要稻作类型。

Greenhouse Gas Emission Characteristics of Different Rice Cropping Patterns in Jianghan Plain

A field experiment is conducted in Jianghan Plain using static chamber-gas chromatography method to monitor greenhouse gas emissions from 5 different rice cropping systems:Early rice, late rice, middle rice, rice-crayfish coculture and ratooning rice systems. The emission characteristics of methane and nitrous oxide fluxes, global warming potential and greenhouse gas emission intensity in different rice patterns are analyzed, aiming to provide scientific references for accurate estimates of greenhouse gas emissions from rice paddy. The results show that methane emissions are concentrated in the early flooding stage of rice paddy, with a flux peak of (85.7 mg·m-2·h-1) for rice-crayfish system, which is higher than those of other patterns by 71.7%-191.5%. Nitrous oxide emissions are mainly observed during mid-season drainage or after nitrogen fertilization, and the highest flux peak is found for ratooning rice (1100.7 μg·m-2·h-1), which is 16.8%-654.9% higher than other patterns. The sequence of accumulated methane emission from largest to smallest is rice-crayfish (541.1 kg·hm-2), ratooning rice (293.7 kg·hm-2), early rice (177.2 kg·hm-2), late rice (133.7 kg·hm-2), and middle rice (115.3 kg·hm-2). For nitrous oxide emission, the sequence is ratooning rice (5.1 kg·hm-2), early rice (2.1 kg·hm-2), late rice (1.0 kg·hm-2), middle rice (0.6 kg·hm-2), and rice-crayfish (0.4 kg·hm-2). As for total emission calculated by global warming potential, the value of rice-crayfish is 13657.7 kg·hm-2, followed by ratooning rice (8857.0 kg·hm-2), early rice (5067.3 kg·hm-2), late rice (3647.0 kg·hm-2), and middle rice (3053.8 kg·hm-2). Rice-crayfish is also accompanied by high greenhouse gas emission intensity reaching up to 1.4 kg·kg-1, followed by early rice (0.79 kg·kg-1), ratooning rice (0.57 kg·kg-1), late rice (0.53 kg·kg-1), and middle rice (0.34 kg·kg-1). The total emission and intensity of middle rice is significantly smaller than those of rice-crayfish system by 77.6% and 75.7%. It is notable that methane emission accounts for 82.9%-99.0% of total emission among different rice cropping patterns, indicating that controlling methane is key for low-carbon production. Due to water flooding in rice paddy, nitrous oxide emission is small. The high emissions from rice-crayfish paddy are mainly attributed to the long duration of flooding, straw returning and large amount of fodder input, which has led to a long period of soil anaerobic condition, and plenty of carbon substrate for methane production. Thus, it is important to explore methane reduction practices and strategies in rice-crayfish paddy. The emission intensity of middle rice is the lowest due to paddy-upland rotation and can be considered as a low-carbon rice cultivation pattern.