长期不同秸秆还田量对玉米-小麦轮作农田增产、固碳及减排温室气体的效应与机理

As population growth and the associated pressure on climate change continue to increase, global agriculture is faced with double challenges of safeguarding food security and mitigating greenhouse gas emission. China, as a major agricultural producer, plays an important role in providing food and reducing greenhouse gas emission as well as increasing soil organic carbon. As reported, the incorporation of crop straw was generally regarded as favorable management practice, since it helps maintain a sustainable level of soil organic carbon content and stimulate crop growth. So far, however, it is still unclear whether a win-win scenario can be achieved for soil carbon sequestration, greenhouse gas mitigation and crop productivity improvement after straw incorporation, especially for long-term scale, and how these variables response to different amount of straw incorporation. Thus, it is crucial to investigate straw effects on crop productivity, soil organic carbon and greenhouse gas emission simultaneously when assessing its economic benefit and environmental impact. Based on these aspects, this project intends to perform the study on changes in crop yield, soil organic carbon and greenhouse gas emission in a maize-wheat rotation cropping system after long-term different amount of straw incorporation, using in situ field measurements combined with laboratory incubation methods. The objectives of this project are to (1) determine crop yield, annual N2O/CH4 fluxes and the emission factors for treatments with different amounts of straw incorporation; (2) assess the long-term effects of straw incorporation on N2O/CH4 fluxes and the net greenhouse gas fluxes including soil organic carbon stock changes as well as greenhouse gas intensity; (3) improve understanding of the underlying mechanisms on regulating N2O/CH4 fluxes; and (4) identify a management scenario to minimize net greenhouse gas fluxes while sustaining or increasing crop yield. Such findings will provide the reliable parameter for accurate estimation of N2O emission inventory in the agricultural sector. Also, the results of this project will be helpful for providing the optimum management practice of straw incorporation for reducing greenhouse gas emissions while safeguarding food security.

随着气候变化加剧，全球农业面临着粮食安全和固碳减排的双重任务。中国是一个农业大国，在全球粮食供应和农田温室气体减排、土壤固碳方面发挥重要作用。以往研究表明，秸秆还田有利于农田固碳并促进作物生产力，但秸秆还田尤其是在长期施用条件下对土壤固碳、温室气体减排与作物生产力能否达到共赢，以及其与秸秆还田量的关系如何尚少见报道；而关于这些问题的答案，又是全面评估秸秆还田的经济效益与气候环境效应的迫切需要。因此，本项目拟以长期不同秸秆还田量模式下的玉米-小麦轮作农田生态系统作为实验平台，通过田间原位综合观测和室内控制试验相结合的研究，旨在阐明不同秸秆还田量对玉麦轮作农田作物产量、土壤有机碳和温室气体排放变化的影响规律与机理；获取作物秸秆的N2O排放因子及其与还田量的关系，为准确编制农业温室气体排放清单提供理论基础；明确不同秸秆还田量处理的温室气体净排放量和排放强度，为保障粮食安全和固碳减排提供技术支撑。

秸秆还田可提高土壤肥力，增进作物对养分的吸收；但秸秆还田也会改变土壤自身的C、N循环，从而影响有机碳（SOC）储量和CH4、N2O的产生和排放。本项目以长期不同秸秆还田模式下（不施肥且无秸秆还田（CK）、常规施化肥（NPK）、化肥配施一半作物秸秆产量还田（NPK+50%RMW）和化肥配施全部作物秸秆产量还田（NPK+100%RMW））的冬小麦-夏玉米轮作系统为实验平台，对土壤CH4、N2O排放通量和SOC以及作物产量开展了2016～2020连续4周年的原位测定。结果显示：.（1）各施肥处理的小麦和玉米产量分别为2.85～4.78和4.96～7.75 t ha-1。与NPK相比，NPK+50%RMW和NPK+100%RMW分别使作物籽粒产量增加了13.4%和17.3%。.（2）NPK小麦季、玉米季和轮作周年N2O平均排放值分别为0.76、1.43和2.19 kg N ha-1。与NPK相比，在整个轮作周年NPK+50%RMW和NPK+100%RMW分别使N2O平均排放量增加了45.3%和34.7%。各施肥处理小麦季、玉米季和轮作周年的N2O平均排放系数分别为0.46～0.89%、0.78～1.09%和0.63～0.98%。对于CH4而言，各处理均表现为大气CH4的吸收汇，其轮作周年的平均值为-2.11～-2.28 kg C ha-1，秸秆还田对CH4通量无显著影响。.（3）在2005年各处理SOC浓度为4.32～4.44 g C kg-1，处理之间无差异。在2016～2020观测期，各处理SOC平均浓度增加为5.01～8.76 g C kg-1；与NPK相比，NPK+50%RMW和NPK+100%RMW分别使SOC浓度增加了25.4%和32.5%。通过对比2016～2020观测期与2005年表层SOC储量的差异，计算得出各处理的SOC储量年变化率为0.12～0.98 t C ha-1 yr-1。.（4）基于CH4和N2O年平均排放总量以及表层SOC储量的年变化率，计算出各处理温室气体净排放量为-356～-2321 kg CO2-eq ha-1 yr-1，相应的排放强度为-158～-210 kg CO2-eq t-1。与NPK相比，NPK+50%RMW和NPK+100%RM均降低了该小麦-玉米轮作系统的综合温室效应。.可见，长期秸秆还田具有增产和降低温室气体净排放的效果