Effects of bedrock erosion by tillage on architectures and hydraulic properties of soil and near-surface bedrock

摘要

Tillage erosion provides an opportunity for the occurrence of bedrock erosion in hilly croplands with shallow soil layer, influencing the hillslope architecture to some extent. In this study, tillage simulation, hydraulic tests and dye-staining tracing were performed to identify the variation in architectures and relevant hydraulic properties of the soil and near-surface bedrock caused by tillage-induced bedrock erosion. Results show that tillage-induced bedrock erosion played an important role in shaping the rock fragment architecture. Under the condition of no-soil cover, the coarse rock fragment content increased from 29.8% to 38.2% when tillage depth increased from 2 to 6 cm. The field-saturated hydraulic conductivity (K_(fs)) ranged from 18.63 to 23.78 m d~(-1) by the Guelph method and 24.26 to 98.46 m d~(-1) by the single ring (SR) method, but effects of tillage depth on K_(fs) did not show a clear pattern. Under the condition of overlying soil layer, the contents of medium, coarse and total rock fragments in soil increased significantly with tillage depth (P < 0.05). Correspondingly, the K_(fs) for the soil increased significantly with tillage depth (P < 0.05), implying that the higher content of rock fragments due to the greater tillage depth created the more water flow channels. With respect to the near-surface bedrock, the results of dye-staining tracing show that bedrock fragmentation by tillage tended to promote the development of fracture-preferential flow. The infiltration data derived from the SR method show that the K_(fs) increased by 33.3% to 50.0% after bedrock fragmentation by tillage compared with that for the control treatment, corresponding to the results of dye-staining tracing. These results suggest that tillage-induced bedrock erosion exerts positive effects on infiltration in the soil and near-surface bedrock by increasing preferential channels.