保护性耕作对华北平原土壤碳-氮关系的调控及其环境效应研究

The changes of soil carbon-nitrogen relationships can affect agro-ecosystem productivity and cause environmental issues, such as greenhouse gases emissions. Soil tillage plays an important role in soil carbon (C) and nitrogen (N) cycling, however, there is a knowledge gap in the understanding of the response of soil C-N relationships to tillage practices. North China Plain is one of the most important bases of Chinese grain production, and conservational tillage practices are widely ongoing in this region. Based on a long-term tillage experiment, in this proposal, we will take the fields with wheat-maize cropping system as our research cases. We will mainly monitor the accumulation and distribution of crop plant C and N in above- and belowground, the amount and quality of soil organic C and N and their distributions in soil aggregates and profiles, the activity and community structure of soil microbe and greenhouse gases emissions under field conditions. Our objectives are to understand the response of soil C-N relationships to soil tillage regimes and the consequent environmental effects. Simultaneously, field micro-experiments will be conducted using the methods of root-soil condition control, microbial community structure control and soil C and N transformation control in situ. We will focused on the situations of soil organic C and N forms, the isotopic natural abundances of 13C and 15N, the characteristics of soil microbiology, the decomposition of crop residues and the characteristics of soil respiration. The objectives of these micro-experiments are to learn the key processes and mechanisms underlying the impacts of tillage practices on soil C-N relationships. The above researches will provide great theoretical and technological references to the tillage system design for higher-yield of wheat-maize cropping system with great soil C sequestration and low greenhouse gases emissions in North China Plain.

土壤碳-氮关系动态不仅影响到农田系统生产力，而且与温室气体排放等环境问题相关。耕作对土壤碳氮状况影响显著，但至今关于土壤碳-氮关系对耕作措施响应的认识还非常不足。华北平原是我国粮食主产区，保护性耕作正在大面积示范推广。项目拟以该区小麦玉米两熟农田为对象，借助长期定位试验，重点监测不同耕作措施下，作物地上地下碳氮积累与分配、土壤有机碳氮数量与组分及其在团聚体和剖面中的分布、土壤微生物活性及群落结构、温室气体排放等特征，建立土壤碳-氮关系评价指标，明确耕作措施对土壤碳-氮关系的影响及其环境效应；采用根际环境、微生物群落结构和土壤碳氮转化过程等定向控制方法，进行田间微区试验，原位监测土壤有机碳氮形态及δ13C/δ15N自然丰度、微生物学特征、作物残茬分解、土壤呼吸特征等指标，阐明耕作措施对土壤碳氮关系的关键调控过程与机制，为华北平原小麦玉米持续增产和土壤固碳减排的耕作体系建立提供理论和技术支撑。

土壤碳-氮含量变化不仅影响到作物系统生产力，而且对农田温室气体排放等有显著的影响。本研究通过Meta分析和大田定位试验，研究保护性耕作对我国不同作物、不同区域作物产量的影响，分析不同耕作方式对小麦-玉米两熟区土壤理化性状、作物周年产量、氮肥利用效率及环境效应的影响，揭示保护性轮耕下，土壤碳氮含量的变化及其对农田温室气体排放的影响机制。结果表明：（1）秸秆还田下的少免耕对小麦和玉米的增产效应显著，而且保护性耕作的实施年份越长，增产效果越大；（2）深松耕作显著降低了0-25cm耕层的土壤紧实度以及稳定层和耕层的土壤容重；（3）深松耕作促进了0-20cm耕层的土壤有机质的矿化分解和土壤微生物氮的转化能力，提高了作物根系对土壤有效氮的吸收利用，深松+旋耕和深松+免耕处理的植株氮素积累量、氮素收获指数和氮肥偏生产力均高于旋耕和免耕处理；（4）深松+旋耕处理2个生长季小麦、玉米和周年产量均最高，免耕处理最低；深松+旋耕处理的小麦玉米周年平均产量为19643.9 kg ha-1，比深松、旋耕和免耕分别增加4.8，5.9和7.7%；（5）深松耕作导致小麦季农田N2O排放量较高，但是玉米季N2O排放量低于免耕处理，从周年的温室气体排放和全球增温潜势来看，耕作方式之间无显著差异。本研究可为华北平原小麦-玉米周年持续增产和土壤固碳减排的耕作体系建立提供理论和技术支撑。项目实施期间共发表（接受）学术论文4篇，其中SCI论文3篇、核心期刊1篇；参与编写专著1部；申报国家发明专利2项，获得实用新型专利和软件著作权各1项；培养博士和硕士研究生各1名，对照研究目标，全面完成各项任务。

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