Grass hedge effects on controlling soil loss from concentrated flow: A case study in the red soil region of China

Abstract

Grass hedges are widely applied on sloping croplands as a low-cost measure to reduce soil and nutrition loss. Therefore, it is important to understand the role of hedgerows in runoff and sediment processes. In this study, 36 field runoff simulation experiments were conducted in the red soil region of China to determine flow hydraulics and soil loss processes under 12 different hedgerow conditions. Specifically, two types of hedgerow widths (two-row and three-row) were planted for each of three species of vegetation (Bahia grass (Paspalum notatum), Vetiver (Vetiveria nigritana) and Daylily (Hemerocallis fulva)), and these plots were tested both before and after the removal of the grass stems. Grass stems played an important role in decreasing the flow velocity and filtering sediment. For the three selected vegetation types, the final flow velocities (V3) were ranked in the following order: Bahia grass (0.12m/s)<Vetiver (0.17m/s)<Daylily (0.19m/s). There was no significant difference between the three grass species in trapping sediment under the condition of this study. A comparison between the two different hedgerow widths revealed that the three-row hedges were more effective (decrease ratio >30%) than the two-row hedges (decrease ratio <20%) in reducing the flow velocity ahead of the grass barriers (V2). Nevertheless, soil losses from the grass hedges were mainly related to the final flow velocity (Pearson’s R=0.66, N=36) rather than the V2. The final flow velocity and the total soil loss rate did not decrease remarkably when using the three-row hedges. These results could be used to provide sound field recommendations for designing and managing hedges in the red soil region of China.