黄淮轮作农田土壤氧化亚氮排放机理及其反硝化贡献研究

Nitrous oxide (N2O) is one of the major greenhouse gases. On a molar basis, N2O is about 250 times more effective as an absorber of infrared radiation than CO2 on a 100 year time frame. Field soils play an active role in N2O dynamics. N2O is produced in soils during microbial nitrification, denitrification and chemo-denitrification. The unreasonable irrigation and fertilization in recent years, especially flooding irrigation and nitrogen over-application in field, caused N2O emission increasingly sharpened, and also water and nitrogen use efficiency decreased. It will greatly threaten farmland eco-environmental quality. It is generally assumed that N2O produced in farmland occurs usually mainly from soil microbial nitrification in rice and wheat rotation system in Huang-Huai Plain of China (HHPC). However, considerable N2O produced from microbial denitrification is usually ignored after irrigation or rainfall on dry farmland in practical agricultural situation. In this study we will analyze nitrogen-15 changes of N2O-N, ammonium nitrogen and nitrate nitrogen in soil to clarify mechanism and denitrification contribution on N2O emission during water event treatments using nitrogen-15 isotope tracer technique through indoor simulation tests. In addition, further studies will be certified on effects of water and nitrogen application on N2O emission at intensive farmland region in HHPC through series of field experiments. Through above series of studies, there will reach expected effects of objectively evaluating N2O emission characteristics and improving N2O theories produced in soils, and also will help to provide theories basis for strategy of energy-saving and emission-reduction based on optimizing water and nitrogen management at representative regions in wheat and corn rotation system of HHPC.

农田土壤是氧化亚氮（N2O）重要的排放源。近年来的不合理灌溉、施肥尤其农田大水漫灌、高氮施用更加剧了N2O的排放，直接导致水肥利用率降低，极大地威胁着农田生态环境质量。通常认为，小麦/玉米轮作体系农田N2O排放主要来自土壤的硝化作用，但在实际生产中灌溉、降雨引起的土壤反硝化产生N2O的贡献未引起足够重视，更鲜有结合农田实际供水、供氮状况开展N2O减排机理的研究。本研究通过室内培养实验采用15N同位素示踪技术对土壤N2O、土壤硝态氮、铵态氮等观测项目的15N丰度变化及N2O排放规律的深入研究，揭示黄淮典型农田土壤N2O排放特征及其产生机理；通过田间试验进一步验证解析当前研究区域农田水、氮供应状况对土壤反硝化产生N2O的贡献。预期结果将对科学评价当前黄淮典型农田土壤N2O排放特征，完善补充土壤N2O排放理论,优化区域农田水氮管理以及制定N2O减排措施提供理论依据。

农田土壤是氧化亚氮（N2O）重要的排放源。近年来的不合理灌溉、施肥尤其农田大水漫灌、高氮施用更加剧了N2O的排放，直接导致水肥利用率降低，极大地威胁着农田生态环境质量。通常认为，小麦/玉米轮作体系农田N2O排放主要来自土壤的硝化作用，但在实际生产中灌溉、降雨引起的土壤反硝化产生N2O的贡献未引起足够重视，更鲜有结合农田实际供水、供氮状况开展N2O减排机理的研究。通过开展本项目研究，取得以下研究结果：（1）采用15N同位素示踪技术通过模拟干湿交替过程土壤N2O产生排放机制研究表明，加水后第3d出现N2O排放峰，各处理N2O排放峰消退后，再提高或降低水分含量均未能促进N2O排放，甚至个别处理还出现N2O的吸收现象；相关分析表明，土壤N2O排放通量与土壤水分、铵态氮含量呈极显著正相关关系；干旱条件下N2O排放量较少，而高水分含量均有利于肥料和土壤产生N2O排放。（2）通过模拟田间栽培管理措施（土壤、氮肥、秸秆还田）与农田土壤N2O排放关系研究表明，农田N2O排放与不同秸秆源还田（小麦、玉米）、不同土壤类型（砂姜黑土、潮土）关系密切；土壤N2O排放可能与16S rRNA基因无明显关系，而与nosZ 和 nirS 基因关系密切。（3）通过大田栽培管理措施对N2O排放贡献研究表明，施肥、灌水明显提高N2O排放通量，等量水分供应下施肥量越高N2O排放量越高，尤其在下雨或浇水后N2O排放通量明显提高，等量施氮相同灌水量下，开沟追氮处理明显较撒施追氮处理N2O累计排放量低。（4）通过不同类型土壤N2O排放特征试验研究表明，施肥播种后土壤 N2O排放峰值迅速出现，3d后各土壤N2O排放均迅速下降，在4种农田土壤（砂姜黑土、褐土、潮土和砂壤土）中，褐土N2O平均总累积排放最少，与其他3种土壤差异达显著水平，而砂姜黑土N2O累积排放最多，且与褐土、潮土间差异显著。综上所述，上述研究结果对科学评价当前黄淮典型农田土壤N2O排放特征，完善补充土壤N2O排放理论,优化区域农田水氮管理以及制定N2O减排措施提供理论依据。