间歇灌溉稻田农田尺度CH4排放规律及其响应机制

Alternate wetting and drying of the intermittent irrigation paddy fields regulate and control methane emission, and research at home and abroad has not yet been elucidated the regulative process. The main reason is that traditional static box method has many weaknesses, such as limited spatial representativeness, low observing frequency, so that we could not clear the rule and influence mechanism of the intermittent irrigation mode on methane emission at field scale. Eddy covariance method (EC) could effectively minimize these weaknesses of the static box method, while in China, the study on methane emission from paddy fields by EC method is rarely reported. This project choose typical paddy fields in Poyang lake basin under intermittent irrigation as the research area, use EC system and other auxiliary observation systems to make long-term, continuous observation data in high temporal resolution of methane fluxes and environmental, soil elements, crop growth, etc. This project try to analyze the influence of alternate wetting and drying, draining and sunning at later tillering stage and steeping at crop alternative period on methane emission under the intermittent irrigation mode, estimate gross amount of methane emission from the rice paddy fields over Ganfu plain irrigation area, and then put forward methane emission reduction measures from the angle of the field scale. This project aims to clarify the dynamic variation rule of methane emission and the response mechanism of environmental factors change and crop growth on methane emission at field scale under the intermittent irrigation mode. The research could contribute to enhance the understanding of methane emission rules and it’s influence mechanism from larger spatial scale, and promote the transformation of methane emission observational studies from microcosmic scale to macroscopic scale.

间歇灌溉模式下稻田干湿交替调控着CH4排放，国内外对该调控过程还缺乏认识，一个重要原因是传统的静态箱法空间代表性差、观测频率低，以至于在农田尺度难以明确其动态变化规律和影响机制。涡度相关法能克服以上缺陷，但国内基于此法的稻田CH4排放研究还未见报道。本项目以鄱阳湖流域间歇灌溉稻田为研究对象，利用涡度相关系统和其它辅助仪器长期、连续观测稻田CH4排放通量以及环境、土壤、作物生长等要素，分析间歇灌溉模式下稻田干湿交替、分蘖后期晒田和作物交替期泡田对CH4排放的影响，估算赣抚平原灌区稻田CH4年排放总量，并提出稻田CH4减排方案。本项目期望从农田尺度阐明间歇灌溉稻田CH4排放的动态变化规律，揭示间歇灌溉稻田CH4排放对环境因子变化与作物生长发育的响应机制。研究成果将有助于从较大空间尺度上增进对我国稻田CH4排放规律和影响机理的认识，推动我国稻田CH4排放观测从微观尺度向宏观尺度的方向发展。

甲烷（CH4）是一种重要的温室气体，水稻田是CH4排放的主要人为源之一。我国水稻种植面积高达3000万hm2以上，因此研究我国稻田CH4排放状况对缓解全球气候变暖具有重要作用。本项目利用涡度相关法得到鄱阳湖平原稻田CH4和CO2通量数据，旨在探明间歇灌溉稻田CH4的排放规律和排放总量，评价CH4与CO2的增温潜势，揭示CH4排放对环境因子的响应机制，阐明干湿交替过程对CH4排放的影响，提出节水减排的田间管理技术。结果表明：稻田CH4通量以排放为主，即鄱阳湖流域稻田为CH4排放源。季节尺度上，稻田CH4通量有明显的强、弱排放期，早稻87.0%和晚稻85.3%~92.3%的CH4在强排放期被释放。早稻日CH4通量最大值为0.638g/(m2·d)，晚稻则为1.365~1.482g/(m2·d)。日尺度上，CH4排放存在3种模式，分别为显著单峰型、不显著单峰型和无规则型。早稻5月和晚稻7月的CH4日内排放通量最高、波幅最大。鄱阳湖平原双季稻CH4排放总量为46.64~52.63g/m2，其中早稻为20.70g/m2，晚稻为25.94~31.93g/m2。受益于水稻光合作用，早、晚稻最终均表现为碳汇，早稻碳吸收量为-4.73tCO2-eq/hm2，晚稻为-10.31~-3.58tCO2-eq/hm2。在评价稻田碳蓄积时若不考虑CH4排放，早、晚稻将分别低估5.17、6.48~7.98tCO2-eq/hm2的碳排放。稻田CH4排放通量与气温、土温、土壤含水率均呈指数关系，早、晚稻CH4排放启动温度分别为18℃和25℃，最低土壤含水率为80%饱和含水率。在间歇灌溉干湿交替过程中，干过程的CH4通量较湿过程的平均降幅达到48%~69%。直播稻出苗期自然落干能降低CH4排放，土壤水分落干至80%饱和含水率可使CH4排放在复水后也无法反弹到高速率。分蘖后期通过烤田可大幅降低CH4排放并使其持续保持低排放速率。施肥能提高稻田CH4排放，但当CH4通量处于较高排放速率时，施肥的促进作用不显著。间歇灌溉模式、延长苗期排水落干和分蘖后期烤田时间、减量施肥、气温较低时施肥等田间管理措施是稻田经济可行的CH4减排技术。研究成果可为可为准确评价中国长江中下游稻区碳排放与温室效应，优化我国稻田CH4通量数据库和排放模型，实现区域稻田CH4减排目标等提供技术支撑。