秸秆覆盖对红壤坡耕地壤中流的影响及侵蚀响应

Sloping farmland is one of the most important sources of soil erosion in the red soil region of southern China. Long-term tillage of sloping farmland leads to a loose and high permeability tillage layer but tight and poor permeability plow layer. The loose-tight soil structure promotes the generation of subsurface flow in the tillage layer. Straw mulch plays a great role in altering the hydrological processes and erosion processes for the infiltration and surface roughness increasing. In this study, the long-term tilled sloping farmland under straw mulch is employed as the object to analyze the impacts of different mulch rates, slope degrees, rainfall intensities and soil bulk densities on the infiltration, runoff generation and sediment production by the field investigation, runoff plots monitoring and rainfall simulation tests. The impacts of straw mulch and soil structure on the rainfall-runoff features and subsurface flow generation will be clarified. Based on the analysis of eroded sediment particle size distribution and erosion dynamics, the response of soil erosion to the interactive of surface and subsurface flow runoff will be revealed. This research is important to understand the slope erosion mechanism and erosion control in the red soil region of southern China.

坡耕地是南方红壤区土壤侵蚀的重要策源地。坡耕地长期耕作导致耕作层疏松且渗透性强，犁底层紧实而透水性差，形成典型“上松-下紧”二元土壤结构，促进耕作层壤中流发育。秸秆覆盖调节入渗增加地表粗糙度，影响坡耕地近地表水文过程和侵蚀过程。本项目拟以秸秆覆盖的坡耕地为研究对象，通过野外调查、径流小区观测和室内外模拟降雨试验，研究秸秆覆盖量、坡度、雨强、容重等因子对坡耕地降雨入渗、产流、产沙等过程的影响。明确秸秆覆盖和土壤剖面结构对坡耕地降雨-径流输出特征的影响，阐明秸秆覆盖对坡耕地壤中流发育的影响机制，结合侵蚀泥沙粒径分选和侵蚀动力学特征分析，揭示秸秆覆盖影响下侵蚀对地表径流和壤中流交互作用的响应。该研究对进一步认识坡面侵蚀机制及其防治有重要理论和应用价值。

坡耕地是南方红壤区土壤侵蚀的重要策源地。秸秆覆盖调节入渗增加地表粗糙度，影响坡耕地近地表水文过程和侵蚀过程。本项目以秸秆覆盖的坡耕地为研究对象，通过野外调查、径流小区观测和室内外模拟降雨试验，研究秸秆覆盖密度、还田形式等因子对坡耕地降雨入渗、产流、产沙等过程的影响，阐明了秸秆覆盖坡面壤中流形成机制，结合侵蚀泥沙粒径分选和侵蚀动力学特征分析，揭示坡耕地侵蚀产沙对壤中流与地表径流交互作用的响应机制。研究结果发现：（1）不同秸秆覆盖措施均能有效减少地表产流产沙，增加壤中流发育。与裸地对照相比较，免耕覆盖、覆盖+熵沟和秸秆覆盖减少地表径流72.48-80.46%，减少泥沙98.59-99.29%，壤中流增加76.92-153.85%。聚类发现观测期间降雨雨型以前期型为主，占比为50%。在裸露对照和常规耕作条件下不同降雨雨型的产流产沙差异显著，以前期型最高。当地表进行秸秆覆盖后，降雨雨型对产流产沙的影响显著降低。（2）秸秆覆盖显著影响降雨分配规律，有效促进耕层壤中流发育。地表裸露底层渗漏量大于壤中流输出量，地表秸秆覆盖后壤中流输出量大于底层渗漏量。秸秆覆盖后，壤中流初始产流时间缩短，产流历时延长，径流系数显著增加，主要表现在耕层。降雨结束后，壤中流和底层渗漏的消退过程可用指数函数进行预测（R2=0.81~0.99）。（3）随者秸秆覆盖密度和平均入渗速率增加，壤中流初始产流时间减小，径流系数、平均流量、峰值流量增加。壤中流特征指标与覆盖度（密度）的关系可用指数函数、线性函数表达，决定系数为0.41~0.97，与平均入渗速率的关系可用幂函数、对数函数、指数函数、二次函数表达，决定系数为0.50~0.97。（4）壤中流的存在显著增加了红壤坡面产流产沙，产沙显著大于产流，径流量增大6.72-50.08%，侵蚀量增大54.44-393.32%；侵蚀泥沙颗粒组成上，黏粒和粉粒含量分别减少2.86-48.37%和5.18-35.59%，砂粒含量增加11.09-84.56%；平均流速增大23.43-60.01%，径流深6.25-24.69%，雷诺数12.38-158.39%，弗汝德数增大9.09-19.05%，阻力系数减小6.40-18.33%；径流剪切力和水流功率分别增大36.16-53.13%和75.00-138.46%。该研究对进一步认识坡面侵蚀机制及防治有重要意义。