Effects of Vetiveria zizanioides hedgerow on the erosion of purple soil of slope land in the Three Gorges Reservoir Area of China

Purple soil erosion of slope land has posed a serious threat to the operation safety of the Three Gorges Project in recent years. Fortunately, the hedgerow has widely been one of the most important measures for soil and water conservation on slope land. Most studies have also demonstrated that the hedgerows can effectively reduce the runoff and sediment of the slope. However, the specific reduction was still lacking on the aboveground and underground part of hedgerows. Taking the purple soil of slope land in the Three Gorges Reservoir Area as the research object, this study aims to clarify the effects of Vetiveriazizanioides L. hedgerow on the erosion of purple soil. Simulated rainfall experiments were also conducted at 2 slope gradients (15o and 25o), 2 rainfall intensities (60 and 120 mm/h), and 3 slope conditions (CK-Control check, P-Hedgerow, and R-Only hedgerow roots). The specific characteristics were analyzed for the initial runoff time, runoff, and sediment with rainfall duration under different slope conditions. The results indicated that the average contribution rates were 48.28% and 51.72% of the aboveground and underground parts to the increase of initial runoff time, respectively. The runoff production showed a trend of first increasing and then fluctuating, finally stable under different rainfall intensity and slope conditions. In sediment yield, the erosion rate of slope always kept a fluctuating and stable trend under the condition of P slope, whereas, there was a slow increase at first and a rapid increase under the condition of CK and R slope. The runoff reduction efficiency of hedgerows ranged from 11.20% to 26.19%, while the sediment reduction efficiency of hedgerows ranged from 71.54% to 83.63%. The average benefits of sediment reduction, underground and aboveground parts were 75.59%, 29.45%, and 46.13%, respectively, which were 4.79, 4.60, and 4.92 times of the average. The average contribution rates were 62.25% and 37.75% for the aboveground and underground part of hedgerows to the runoff reduction, respectively, while the average contribution rates were 60.44% and 39.56% to the sediment reduction, respectively. Correspondingly, the hedgerows greatly contributed to delay the runoff generation, where the contribution rates were not significant for the aboveground and underground part of hedgerows to the initial time of runoff generation. Meanwhile, the hedgerows can be expected to effectively reduce the runoff rate and erosion rate, where the effect of the aboveground part was greater than that of the underground part. Consequently, there was a more obvious effect of hedgerows on sediment reduction. More importantly, the effect of the aboveground part on runoff and sediment reduction was greater than that of the underground part. Anyway, Vetiveriazizanioides L. hedgerow can widely be expected to prevent the erosion process of purple soil in slope land. The finding can also provide a scientific basis for the prevention and control of soil and water loss on purple soil slopes in the Three Gorges Reservoir Area.