横垄垮塌诱发浅沟形成机制与侵蚀过程响应

Contouring failure could induce the ephemeral formation, which is the main cause to increase soil erosion dramatically on slopeland with contour ridge tillage adopted. The influence of contouring failure on runoff routing and erosion dynamics makes the soil erosion process different from that on traditional slopeland. Therefore, the objective of this project is to understand the mechanism of ephemeral formation based on the influence of contouring failure on runoff routing and erosion dynamics, and to reveal the response of soil erosion process to contouring failure and ephemeral formation. Taking the slopeland in brown soil in Yimeng mountain area as research object, this project would take field observations in plots, contour-ridge slopeland and traditional slopeland with the aid of the three dimensional scanning and GIS. The ephemeral formation and development mechanism could be revealed with the effect of rainfall and microtopography factors (e.g., ridge height, row grade) on contouring failure process analyzed, and the response of runoff routing and erosion dynamics to contouring failure process studied. Through describing the soil loss caused by contouring failure and ephemeral formation and quantifying the soil erosion in furrows increased by ephemeral formation, the influence of contouring failure and ephemeral formation on slope erosion and soil loss process could be interpreted. The findings of this project would improve our understanding of the mechanism for contour ridge influence on soil erosion process, and would be of great importance to assess and apply the contour ridge tillage for soil erosion control.

横垄垮塌诱发浅沟形成是横坡垄作坡面土壤流失剧增的主要原因。横垄垮塌对坡面汇水与侵蚀动力的作用，使横坡垄作坡面的侵蚀过程有别于传统坡面。因此，本项目研究目标是：在明确坡面汇水与侵蚀动力对横垄垮塌过程响应基础上，揭示横坡垄作坡面浅沟形成机制，并阐明横垄垮塌与浅沟形成对土壤侵蚀过程的影响机理。项目拟以沂蒙山区的棕壤区坡面为研究对象，通过对垄作小区、横坡垄作与自然坡面进行野外观测，结合3D扫描与GIS技术，分析垄向坡度、垄高等微地貌与降雨因子对横垄垮塌过程的影响，明确横垄垮塌过程中坡面汇水与侵蚀动力的动态变化特征，揭示横坡垄作坡面浅沟的发生与发展机制；定量刻画横垄垮塌与浅沟形成过程中引起的土壤侵蚀，分析垄沟内土壤侵蚀对浅沟形成过程的响应，探明横垄垮塌与浅沟形成对坡面侵蚀与土壤流失过程的影响。研究结果将有助于深入理解横坡垄作对坡面侵蚀过程的作用机制，并为横坡垄作措施的水保效益评价及合理利用提供依据。

横垄垮塌对坡面汇水与侵蚀动力的作用，使横坡垄作坡面的侵蚀过程有别于传统平作坡面。本项目基于次降雨事件对垄作小区、横垄坡面与自然（平作）坡面进行野外观测，结合室内人工模拟降雨实验与冲刷实验，利用3D扫描与GIS技术，在明确土壤抗蚀性基础上，定量分析了垄作微地貌因子对横垄垮塌过程的影响。基于坡面汇水与浅沟形态分析，阐明了浅沟形成机制，揭示了横垄垮塌与浅沟形成对土壤侵蚀过程的影响。主要结论如下：（1）明确了棕壤分离能力与土壤抗蚀性及影响因素：棕壤的分离能力与可蚀性随着土壤含水量的增大呈下降的趋势，临界剪切力呈先增大后降低趋势；坡度对土壤分离能力的影响最大，贡献率为29.64%，其次是含水量和流量，贡献率分别为22.29%和19.72%；含水量变化可解释土壤临界剪切力与土壤可蚀性变化的76%与99%。（2）阐明了横垄垮塌侵蚀过程及其影响因素：渗流过程曲线多呈“S”型长趋势，起对垄面沉积量有显著影响；垄沟坡度及其与垄长的交互作用对未垮塌横垄垄高降低影响显著，垄长影响不显著；相对于平作，垄作可改变含沙量时间序列趋势，随着垄沟坡度增大，土壤流失量呈现增大后减小的趋势，在垄沟坡度为18°时，达到最大值。（3）解析了横垄垮塌汇水产流与浅沟发育响应过程：垄作坡面由于垄台垮塌导致垄沟蓄积的雨水下泻，并与下方积水汇集，导致径流量迅速上升，汇水下泻后径流量回落；次降雨单位长度剪切力越大，坡中坡下沟宽越小，坡上垄顶处沟深越大而坡中垄顶处沟深越浅；垄沟坡度主要控制沟深，垄沟坡度越大，垄顶处沟深、坡上与坡中垄沟处沟深越浅，沟宽越小。（4）揭示了侵蚀过程对横垄垮塌与浅沟形成的响应机制：横垄棕壤在饱和状态下，土壤抗蚀性差，极易被漫流冲刷引起横垄垮塌，导致细沟迅速发育至浅沟；在此过程中，前期以横垄垮塌自身侵蚀为主，侵蚀贡献为29.98-42.58%；后期以侵蚀沟下切伴随沟壁扩张为主。在本实验强降雨（100 mm/h左右）条件下，垄沟坡度较小时，被冲毁横垄长度较大，对农作物生长破坏越严重。