免耕秸秆覆盖对东北黑土区土壤氮素转化更新和去向的影响

No-tillage plays an important role in protecting food safety, increasing soil carbon storage, improving the quality of cultivated land, and promoting the sustainable development of agriculture. The black soil region in Northeast China is an important commodity grain base of China. Natural and artificial factors lead to serious soil degradation, and decline of nitrogen utilization rate. To accelerate the research and application of nitrogen-based nutrient management of conservation tillage is the inevitable choice to promote sustainable development of agriculture in this region. Study on the transformation, update and regulation of soil nitrogen is the key to solve above-mentioned problem in no-tillage farmland. Based on a 9-year no-tillage farmland with corn stover mulch as the research object, we will investigate: 1) utilization rate of fertilizer nitrogen to crop, 2) transformation characteristics of fertilizer nitrogen in soil different form nitrogen pool, 3) loss potential of fertilizer nitrogen via different pathways, 4) mechanism and main microbiological route of soil N2O emission using in-situ micro-plot and incubation experiments combined with the 15N and 18O stable isotope tracer technique. According to the isotope mass balance principle, we will evaluate the effects of no-tillage with corn stover mulch on the transformation, update and fate of soil nitrogen. The result from this project will provide important scientific basis for efficiently using nitrogen in no-till farmland, decreasing nitrogen loss, improving and promoting no-tillage fertilization technique system in black soil region of Northeast China.

免耕在保障粮食安全生产，增加土壤碳储量，提高耕地质量，促进农业可持续发展中具有重要意义。东北黑土区是我国重要的商品粮基地，自然和人为因素导致土壤退化严重，氮肥利用率下降，加快推进该区域保护性耕作氮素养分管理技术研发和推广是促进农业可持续发展的必然选择。开展免耕农田土壤氮素转化、更新及调控研究是解决这一问题的关键。鉴于此，本项目以连续9年免耕秸秆覆盖农田为研究对象，通过田间原位微区试验、实验室培养试验与15N-18O同位素示踪技术相结合的方法，系统研究：1) 作物对肥料氮的利用率；2) 肥料氮在土壤不同形态氮库中的转化特征；3) 肥料氮通过不同途径发生损失的潜能；4) N2O排放机理及主要微生物途径，从而根据同位素质量平衡原理，揭示免耕秸秆覆盖对东北黑土区土壤氮素转化更新和去向的影响。本研究可为进一步调控免耕农田氮素的高效利用，减少氮素损失，完善和推广东北黑土区免耕施肥技术体系提供科学依据。

免耕在保障粮食安全生产，增加土壤碳储量，提高耕地质量，促进农业可持续发展中具有重要意义。自然和人为因素已导致东北黑土退化严重，氮肥利用率下降，加快推进该区域保护性耕作氮素养分管理技术研发和推广是促进农业可持续发展的必然选择。为此，本项目以连续9年免耕秸秆覆盖农田为研究对象，通过田间原位和室内培养的同位素示踪试验，首先准确量化了作物对肥料氮的利用效率；其次根据同位素质量平衡原理，准确量化了肥料氮在土壤中的转化特征，明确了肥料氮通过不同途径发生损失的潜能；最后揭示了土壤N2O的排放机理和主要途径。主要研究结果如下：(1) 三个生长季肥料氮累积的利用效率变化在53%-59%之间；与RT处理相比，免耕秸秆覆盖措施提高了肥料氮的当季利用效率，提高比例达8%，同时也显著增加了三个生长季玉米的平均产量，增加比例达12%以上。(2)玉米苗期肥料氮主要向矿质氮和固定态铵库转化，抽雄期向矿质氮和有机氮库转化，成熟期主要是向有机氮库转化；与RT处理相比，免耕秸秆覆盖措施显著降低了玉米苗期肥料氮向矿质氮库的转化，增加了肥料氮向固定态铵和有机氮库的转化，提高了土壤对肥料氮的截获。(3) 肥料氮通过氨挥发和硝化反硝化途径发生的当季和下一季的气态损失比例平均为16%和5%，三个生长季肥料氮的淋溶损失比例达5%左右，免耕秸秆覆盖措施降低了肥料氮的气态和淋溶损失风险。(4) 室内培养实验结果表明，与RT处理相比，免耕秸秆覆盖措施增加了硝化-反硝化过程中N2O总的排放通量；土壤N2O的排放主要来自于硝化作用过程的贡献，其占整个硝化-反硝化作用过程的90%以上。与土壤N2总的排放通量相比，土壤N2O总的排放通量显著降低，土壤N2O总的排放通量占N2O和N2二者之和的比值不到10%，说明长期常规垄作和免耕秸秆覆盖条件下硝化-反硝化过程的气态氮素损失主要是以N2的形式释放到大气中。

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