免耕一膜多用对土壤有机碳及农田碳平衡的影响

Plastic residues pollution is an important content of the agricultural non-point source pollution in China. Degradable plastic film, film residues recycling and ‘one film for multiple years’ are three pathways for the prevention and control of film residues pollution in China. Related research suggested that ‘one film for multiple years’ with no-tillage was effective on improving the economy benefits of agriculture production without reduction on crop yield, and represented a good prospect in the future. Soil organic carbon plays important roles in reducing CO2 emission and improving soil productivity. ‘one film for multiple years’ may influence the soil organic carbon pools through its effects on soil temperature and moisture conditions, crop residues biomass, and soil disturbance. However, those effects have still not been revealed systematically. Based on a establish experiment, this project will reveal the influences of ‘one film for multiple years’ on soil carbon storage, carbon component and stability in the 5-8 years of the experiment; with 13C pulse-labeling technique, this project will study its influences on root residues, carbon fluxes from plants to soil, soil respiration and root respiration; at last, with life cycle method, this project will calculate the farmland carbon balance and point out the carbon source/sink role of farmland under ‘one film for multiple years’. Expected results will provide a scientific basis for the carbon cycling mechanism in farmland under ‘one film for multiple years’ and the further improvement direction.

残膜污染防控是我国当前农业面源污染防控的重要内容之一。降解地膜替代、残膜回收和一膜多用是当前残膜污染防控的主要技术途径，相关研究表明通过免耕实行一膜多用可在不降低农作物产量情况下大幅减少地膜残留，在生产中具有良好的应用前景。土壤有机碳在减缓温室效应和提高土壤生产力中起重要作用，免耕一膜多用可通过影响土壤温湿度，作物残体生物量以及土壤扰动而影响土壤有机碳库，但这些影响尚未得到系统揭示。基于此，本项目拟依托免耕一膜多用定位试验第5-8年研究技术应用对土壤碳储量、碳组份和稳定性的影响机理；利用13C脉冲标记技术研究其对土壤根系残体、根系分泌物、土壤呼吸和根系呼吸等有机碳周转过程的影响；基于生命周期法研究免耕一膜多用的碳平衡机理，明确其碳源/碳汇作用及关键环节。预期研究结果将明确免耕一膜多用对农田碳循环的影响机理，为农田碳循环调控提供技术支撑。

地膜覆盖作为一项关键农业技术对保障我国农产品安全发挥了巨大作用，但地膜应用带来污染严重威胁土壤健康和农业环境，免耕一膜多用是一种新型地膜覆盖方式，能减少地膜投入。本项目依托国内首个免耕一膜多用田间长期定位试验，基于田间监测数据和生命周期核算方法，对免耕一膜多用下作物产量响应、土壤有机碳和农田碳平衡变化机制进行了研究，获得以下研究进展：（1）免耕一膜多用可在地膜减量情况下保障玉米产量。连续8年玉米单产监测结果显示，与不覆盖地膜相比，免耕一膜两用模式能使玉米单产提高24%，与常规覆膜无显著性差异；（2）免耕一膜多用模式下，土壤有机碳和活性组分与其他模式下基本一致。定位试验7年后，土壤碳测定数据显示，裸地栽培、常规地膜栽培和免耕一膜多用对有机碳、易氧化碳和水溶性碳的影响一致，相互无显著性差异，表明免耕一膜多用不会引发土壤总有机碳与活性组分的衰退；（3）免耕一膜多用能降低土壤温室气体排放和作物生产碳足迹。与传统覆膜种植的施肥方式相比，免耕一膜多用模式的施肥是在膜间进行，能有效避免地膜覆盖下土壤高温高湿对氮素硝化和反硝化的影响，降低玉米生育期N2O排放；由于地膜投入量减少和温室气体排放降低，与常规地膜栽培方式相比，免耕一膜两用技术使玉米单位面积和单位产量碳足迹分别降低11%和14%；（4）免耕一膜多用模式下玉米田具有碳源作用。碳平衡分析结果表明，裸地栽培、常规地膜栽培和免耕一膜多用栽培均具有碳源作用，由于旱地农田初级生产力低、外源有机碳投入量低和碳返还量低等因素导致的，同时碳足迹对净碳平衡敏感性最高，表明农田净碳平衡是限制旱地低碳减排的关键环节。在过去四年中，项目组开展大量的地膜应用与污染防控的科普工作，在国内外做学术报告和培训20多场次；已发表论文9篇；出版专著1部；取得发明专利1项，获得2项奖励，培养研究生5名；项目研发完善的技术在国家地膜科学应用与回收处理等方面发挥了支撑作用。