耕作对红壤坡耕地活性氮侵蚀和渗漏损失过程的影响

Erosion and leakage are not only the major pathways for reactive nitrogen loss from sloping farmland, but also the important causes for eutrophication and groundwater pollution. Tillage has a significant effect on soil erosion and water infiltration, which thus affect reactive nitrogen loss by erosion and leaching in sloping farmland. Nevertheless, it still a scientific question worthy of research to uncover the effects and mechanisms of tillage on reactive nitrogen erosion and leakage loss from sloping farmland. This study will focus on typical sloping farmland in red soil and adopt typical tillage. Continuous in-situ monitoring under natural rainfall, rainfall simulation test and 15N stable isotope tracer will be conducted, so as to investigate the processes of reactive nitrogen losses by erosion, leaching and gaseous emission from the sloping farmland. The characteristics of reactive nitrogen loss by erosion and leaching with different treatments were analyzed, and the contribution rates of erosion and leakage to the total reactive nitrogen loss were quantified. In addition, by applying the comparative study and multivariate statistical methods, the effects of tillage on the erosion and leakage loss of reactive nitrogen were elucidated, and the mechanism was revealed. This research results will help to deepen the understanding of the law on reactive nitrogen loss in sloping farmland, providing a reference for applying scientific and reasonable soil and water conservation and nutrient management measures as well as raising the effective utilization rate of nitrogen fertilizer in red soil farmland.

侵蚀和渗漏被认为是坡耕地活性氮损失的主要途径，也是导致河湖富营养化及地下水污染的重要原因。耕作对坡耕地土壤侵蚀和水分入渗影响显著，进而影响活性氮的损失过程。当前对坡耕地活性氮损失过程，尤其是耕作对活性氮侵蚀和渗漏损失的影响与机理尚不完全清楚。本研究以典型红壤坡耕地为研究对象，通过设置代表性耕作方式处理，开展自然降雨下的连续定位监测、模拟降雨试验和稳定同位素15N示踪，同步观测红壤坡耕地活性氮侵蚀流失、渗漏淋失和气态排放的损失过程，重点分析不同坡度条件下耕作对活性氮侵蚀流失和渗漏淋失的影响，量化侵蚀和渗漏对活性氮损失的贡献，阐明耕作对活性氮侵蚀和渗漏损失过程的作用机理。研究结果有助于深化对坡耕地活性氮损失规律的认识，为红壤丘陵区采取科学合理的水土保持与养分管理措施，提高农田氮素有效利用率提供参考。

侵蚀和渗漏被认为是坡耕地活性氮损失的主要途径，也是导致河湖富营养化及地下水污染的重要原因。耕作对坡耕地土壤侵蚀和水分入渗影响显著，进而影响活性氮的损失过程。当前对坡耕地活性氮损失过程，尤其是耕作对活性氮侵蚀和渗漏损失的影响与机理尚不完全清楚。本项目以典型红壤花生旱作坡耕地为研究对象，设置常规翻耕、轻简化免耕和条带间作3种代表性耕作方式，开展自然降雨下的连续定位监测，同步观测活性氮侵蚀流失和渗漏淋失等损失过程，重点分析了活性氮侵蚀流失和渗漏淋失过程及赋存特征，量化了活性氮侵蚀流失和渗漏淋失通量及贡献；结合稳定同位素15N示踪等室内外降雨试验，探究了耕作、坡度、生育期、施肥水平对侵蚀和渗漏运移氮素的作用机理。结果表明：（1）3种典型耕作方式下红壤旱坡花生地活性氮径流损失的热点时段是结荚期，其在整个花生季的占比为59.56%～62.63%；活性氮径流损失的关键途经是深层渗漏，其在径流总损失的占比为91.53%～96.50%；地表径流、壤中流和深层渗漏对活性氮径流损失的贡献分别为0.94%～7.14%、1.26%～2.56%和91.53%～96.37%。（2）与常规翻耕相比，轻简化免耕显著增加了地表径流硝态氮和氨氮流失量，而条带间作显著降低了地表径流硝态氮流失量，但对其他径流组分活性氮流失量的影响不显著。在常规翻耕的15N稳定同位素示踪试验中，随侵蚀泥沙、渗漏水和地表径流输出的15N分别为65.44%、24.77%和9.79%。（3）耕作方式、坡度条件、施肥水平和作物生育期对坡面产流产沙、水分渗漏及氮素损失过程均有影响，故宜在合理坡度范围内开发利用红壤坡耕地资源，90 kg/hm2氮肥施用量为花生地的合理施氮量，并采取水土保持措施（如条带间作）以阻控侵蚀和渗漏活性氮损失，尤其是结荚期活性氮随深层渗漏的损失。研究结果有助于深化对坡耕地活性氮损失规律的认识，为红壤丘陵区采取科学合理的水土保持与养分管理措施，提高农田氮素有效利用率提供参考。

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