壤中流和地表径流耦合下红壤坡耕地氮素迁移机制

Soil interflow and surface runoff which are important ways and carriers for slope-land nutrient transfer and loss under rainfall erosion，not only result in decline in land productivity , but also lead to water eutrophication. Interflow on red-soil slope farmland has developed and taken up a considerable share in the total runoff under the influence of climate, soil structure characteristics, tillage and so on. The interflow exerts significant impacts on both soil water erosion and soil nutrient loss. In this study, the field site was located at Jiangxi Eco-science Park of Soil and Water Conservation, China. Taking typical red soil slope farmland as the research object, field runoff plots experiments will be performed to investigate the natural rainfall-seepage-runoff yielding process and interflow forming mechanism of different slopes and tillage measures with large-sized drainage lysimeter. Through monitoring the N concentrations and its yields in surface runoff and sediment, as well as interflow of different soil layers, the transfer characteristics and influence mechanism of nitrogen, will be studied. Besides, the contributions of interflow in N loss in red soil and the differences with those of surface runoff will be explored by combining with 15N isotope tracer techniques. The coupling relationship among runoff, sediment and nitrogen nutrient loss also will be researched to construct a quantitative model of surface runoff - interflow - N transfer loss on red soil slope. Research results will help to further the study on the mechanism of surface runoff and interflow influencing the N transfer, and provide a scientific basis for soil and water conservation construction and agricultural non-point source pollution control.

壤中流和地表径流是降雨侵蚀条件下坡地土壤养分迁移损失的重要途径与载体，不仅造成土地生产力下降，还易引起水体富营养化。受气候条件、土壤结构特性和人为耕作等影响，红壤坡耕地壤中流发育且占有相当份额。壤中流对地表径流侵蚀和土壤养分迁移与流失都有重要影响。本研究以典型红壤坡耕地为对象，利用国家级水土保持生态科技园内野外大型土壤水分渗漏试验系统，探讨不同坡度和耕作措施下降雨-入渗-产流过程与壤中流形成机制；通过测定地表径流泥沙和不同土壤层次壤中流中氮素含量与通量，研究地表径流泥沙和壤中流氮素迁移输出特征及其影响机制；结合15N同位素示踪技术，揭示壤中流在红壤氮素损失中的贡献及其与地表径流的区别；研究土壤各层径流、泥沙、养分耦合关系，构建红壤坡面地表径流-壤中流-氮素迁移输出机理量化模型。研究结果将有助于深化壤中流和地表径流对红壤坡耕地氮素迁移规律的理解，为水土保持生态建设和农业面源污染防治提供基础。

壤中流和地表径流是降雨侵蚀条件下坡地土壤养分迁移损失的重要途径与载体。本项目以典型红壤坡地为研究对象，利用Lysimeter试验装置、试验土槽和人工模拟降雨系统，采用自然降雨条件下的长期定位观测、人工模拟降雨试验、15N稳定同位素示踪与模型模拟相结合的方法，研究了坡面降雨-入渗-产流特征、壤中流和地表径流（泥沙）氮素输出特征及其影响机制，构建了壤中流和地表径流氮素输出机理模型。结果表明：（1）红壤供水能力弱，有效水含量少，仅为8.2%～11.0%；土壤水吸力呈现明显的时空差异：各月之间，7月份土壤水吸力最高、12月最低，不同水保措施间，裸露对照最高、枯落物敷盖最低，不同土层深度间，底层最高、中层最低。（2）壤中流是红壤坡面径流的主要组分，也是红壤坡地氮素流失的主要途径：百喜草覆盖、枯落物敷盖和裸露对照3种处理下壤中流量占总径流量的63.3%~97.7%，3种处理下经壤中流流失的氮占径流总流失量的85.0%～99.5%，削减壤中流（尤其是105 cm壤中流）的氮素流失是减少红壤坡面氮素径流流失的关键所在。（3）红壤坡地经地表径流输出的氮素中，颗粒态和溶解态均是重要形态，百喜草覆盖、枯落物敷盖和裸露对照3种处理下颗粒态氮占地表径流输出总氮的35.1%~64.4%；而经壤中流输出的氮素则均以溶解态（尤其是以硝态氮为主的无机氮）为主，占比高达54.8%~86.9%。（4）红壤坡地随壤中流和地表径流泥沙流失的氮素总量随雨强的增加而增加，随坡度的增加先减少后增加，花生播种期高于花生收获期。（5）红壤坡地随地表径流流失的氮素主要源于当季施入的肥料氮，而随壤中流和侵蚀泥沙流失的氮素则主要源于土壤中的存量氮，随地表径流（含泥沙）、壤中流流失的肥料氮分别占总施氮量的11.6%和6.6%。（6）建立了具有一定物理意义的坡面径流—泥沙—壤中流过程机理模型，并通过耦合经验模型较好地（R2>0.63）模拟了壤中流和地表径流耦合下的总氮输出过程。研究成果初步揭示了壤中流和地表径流耦合影响下土壤氮素迁移机制，为防治红壤坡地水土流失与面源污染、发展坡地生态农业提供了理论依据。