等高犁耕朝向对紫色土坡面土壤再分布的影响

选择一块坡长15 m、坡度14.16%的坡地，采用磁性示踪法分析等高向下犁耕（向下坡方向翻垈）和等高向上犁耕（向上坡方向翻垈）的土壤再分布特征，利用模拟耕作（15次）检验两种等高犁耕的长期作用下对土壤剖面和微地貌演化的影响。结果表明:等高向下犁耕导致土壤发生向下坡移动，土壤位移量为15.62～28.70 kg/m，坡度对其影响不显著（p=0.93）；等高向上犁耕导致土壤同时发生向下坡和向上坡移动，土壤净位移量为-10.91～8.23 kg/m，坡度对其有显著影响（p < 0.001），土壤净位移方向随着坡度的增大由向上坡转为向下坡，本研究条件下临界坡度为14%；等高向下犁耕15次后坡顶侵蚀深度是原土层深度的132%，耕作后土层深度与耕作深度相当，表明等高向下犁耕加速土壤侵蚀和促进母岩成土的双重作用共同维持着坡顶土层深度的稳定；等高向上犁耕15次后坡顶土层深度增加了12.7%，表明等高向上犁耕具有保护坡顶土层深度的作用。等高向上犁耕是一种防治类似紫色土的薄层土壤耕作侵蚀和土壤退化的有效措施。

Effect of Contour Plowing Orientation on Soil Redistribution on Hillslope in Purple Soil

A hillslope with a length of 15 m and a slope gradient of 14.16% was selected as the experimental site in the hilly areas of the Sichuan Basin, China. The magnetic tracer method was used to determine the rates and patterns of soil redistribution for downward contour plowing (i.e., downslope turning the soil) and upward contour plowing (i.e., upslope turning the soil), respectively. Consecutive tillage by ox-drawn ploughing was performed 15 times for downward contour plowing and upward contour plowing, respectively, to simulate the impact of long-term tillage on soil profile transformation and microtopography evolution at different slope positions. The results showed that downward contour plowing caused only downslope soil translocation. Soil translocation rates ranged from 15.62 to 28.70 kg/m and no significant correlation was found between soil translocation rates and slope gradient for downward contour plowing (p=0.93). For upward contour plowing, the soil extended to both sides of plough blade, i.e. the soil moved both upslope and downslope simultaneously. Net downslope translocation rates ranged from -10.91 to 8.23 kg/m. Soil translocation rates were significantly correlated with slope gradients for upward contour plowing (p < 0.001), and net displacement direction turned from uphill to downhill when slope gradient increased to 14% under this study condition. The eroded depth of soil profile at the summit position after 15 times downward contour plowing was 132% more than its original depth of pre-tillage soil profile, and the depth of post-tillage soil profile was equal to tillage depth, indicating that the downward contour plowing plays a dual roles: enhancing soil erosion and accelerating pedogenic processes when the depth of soil profile was less than tillage depth. For upward contour plowing, the depth of post-tillage soil profile at the summit position increased by 12.7%, indicating that it plays an important role in protecting soil profile. Upward contour plowing could be an effective protective measure in reducing tillage erosion and preventing soil from degradation on the sloping land in such as purple soil with thin soil over bedrock.