Cornstalk mulching buffer strip is an effective soil and water conservation practice on slope. To enlarge our knowledge about the effects and hydrodynamic mechanism of cornstalk buffer strip reducing soil erosion on loessial hillslope, this paper studied the impact of different cornstalk buffer strip position (5 and 7 m of slope length) on slope erosion process and its hydrodynamic characteristics under the typical high intensity erosive rainfall (100 mm/h) and the slope gradient that most rills happened (20o). Successive rainfall simulation experiments were carried out at rainfall simulation laboratory of the State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Yangling, from April to September in 2014. A slope adjustable pan (10 m long, 3 m wide, and 0.5 m deep) and a down sprinkler rainfall simulator system were included in the experiments. Loesial soil collected from 0 to 20 cm in the Ap horizon of a well-drained site in Ansai, Shaanxi Province, was packed according to natural soil structure on the Loess Plateau. Cornstalks collected in Yangling after harvest were settled on the different hillslope position based on rill developmental stage. 3 treatments including 1 control treatment and 2 mulching treatments were designed, and 3 successive 30-min rains were conducted in each treatment. The 1st rain was used to form rills on the hillslope with no buffer strip; cornstalk buffer strip was settled on the 5 m of slope length in both mulching treatments during the 2nd rain; while it was settled on the 5 and 7 m of slope length in mulching treatment I and II, respectively. Runoff and sediment samples were collected during successive rainfalls and rill morphology was measured after each rain. Rill flow hydraulic characters such as Reynold number, Froude number, Darcy-weisbach resistance coefficient, shear stress, unit power and unit energy of cross section were also calculated based on the measurement of runoff velocity and depth during the rains. The results showed that compared with the control, cornstalk buffer strip reduced total sediment yield and rill erosion amount by 27.2%-54.8% and 40.8%-59.2% respectively, and the contribution of rill erosion to total sediment yield was also reduced. In the aspect of rill morphology, cornstalk buffer strip reduced rill total surface area and rill average depth by 23.0%-32.0% and 6.7%-10.5%, respectively. At the late development stage of rills, buffer strip on the 7 m of slope length resulted in more sediment reduction and better rill morphology control effects. Studies on the individual rill showed that rill width appeared in a similar distribution every 1.2 m along slope length, which was shown after buffer strip was laid on the slope. Moreover, buffer strip also reduced the rill depth by accelerating the deposition process of sediment from upslope and protected the hillslope surface and rills below the buffer strip. Hydrodynamic analysis results showed that rill flow state extended from turbulence supercritical flow to laminar subcritical flow as a result of buffer strip. Compared with the rill flow above the cornstalk buffer, rill flow velocity was significantly decreased by 19.6%-21.9%, Reynold number and Froude number was decreased by 29.6%-37.9% and 8.3%-18.5% respectively, while Darcy-weisbach resistance coefficient was increased by 22.4%-43.3%. After rill flow going through the cornstalk buffer strip, shear stress, unit power and unit energy of cross section was reduced by 13.6%-21.5%, 20.0-21.0% and 9.5%-21.0% respectively, and the reduction of flow energy finally reduced the total sediment yield on hillslope. It can be drawn that cornstalk buffer strip can be settled on the hillslope surface every 5-7 m to decrease the runoff erosivity and finally decrease the rill erosion amount and total sediment yield, which can provide the valuble information for the settlement of soil conservation measures in similar terrain conditions.%玉米秸秆覆盖缓冲带是一项有效的坡面水土保持措施，为探究其减少细沟侵蚀的效果及水动力学机理，在室内人工模拟连续降雨条件下，选取黄土高原高强度侵蚀性降雨标准和细沟发育活跃的典型坡度，根据细沟发育的不同阶段，研究了不同布设部位（坡面中部5 m和坡面下部7 m）的秸秆覆盖缓冲带对细沟侵蚀及其水动力学特征的影响。结果表明：与裸露处理相比，玉米秸秆覆盖缓冲带可以减少坡面侵蚀量27.2%～54.8%，减少细沟侵蚀量40.8%～59.2%，减小细沟侵蚀量对坡面总侵蚀量的贡献率。对于细沟形态，缓冲带可减少细沟割裂度23.0%～32.0%，减少细沟平均深度6.7%～10.5%。比较2种布设部位，在坡面细沟发育后期，坡面下部7 m处布设的秸秆缓冲带可以取得更好地减少侵蚀和约束细沟形态变化的效果。对于单条细沟，裸露坡面上的细沟宽度沿坡长方向呈现约1.2 m长的周期性变化规律，而秸秆缓冲带改变了细沟宽度沿坡长方向的周期性变化趋势，此外还通过拦截淤积上方来沙减小了布设位置细沟侵蚀深度，通过拦截径流保护下方有限长度内的细沟。分析其水动力学原因可知，玉米秸秆覆盖缓冲带可使细沟水流向缓层流流态方向延伸，与缓冲带上方相比，秸秆缓冲带下方的细沟水流流速显著减小19.6%～21.9%，雷诺数和佛汝德数分别减少了29.6%～37.9%和8.3%～18.5%，而通过秸秆缓冲带后，细沟水流Darcy-weisbach阻力系数增加了22.4%～43.3%，水流剪切力、单位水流功率和断面单位能量分别减小13.6%～21.5%、20.0～21.0%和9.5%～21.0%，径流能量和侵蚀能力的降低最终导致了坡面总侵蚀量的减小。因此，在坡面上每隔5～7 m布设缓冲带可以有效的削弱坡面径流侵蚀能力，减少坡面细沟侵蚀量和总侵蚀量。该研究结果可为类似地形条件下的坡面水土保持措施合理配置提供理论基础。
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