Quantitative studies on root reinforcement resisting flow-induced erosion in the sandy loess region
LI Qiang, LIU Guobin, ZHANG Zheng, MA Chunyan, BAI Yun, ZHANG Chenchen
1. Yulin University, 719000, Yulin, Shaanxi, China; 2. Shaanxi Key Laboratory of Ecological Restoration in Shaanbei Mining Area, 719000, Yulin, Shaanxi, China; 3. State Key Laboratory of Soil Erosion and Dry-land Farming on the Loess Plateau, Institute of Soil and Water Conservation, Northwest A & F University, 712100, Yangling, Shaanxi, China
Abstract：[Background] In semi-arid areas, soil erosion is a serious threat to land productivity and sustainability for natural and human-managed ecosystems. Traditional vegetation techniques are recognized as effectively in reducing soil erosion, whereas the most evident vegetation source that protects soil against erosion is root wedging, which is an important mechanism where roots can bind soil together and tie weak surface soil layers into strong and stable subsurface layers. Plant roots significantly affect soil erosion process of overland flow by physical consolidation (root link and root-soil adhesive) and biological chemistry functions. The purpose of this study was to evaluate the relative contributions of root link, root-soil adhesive as well as root biological chemistry functions to soil reinforcement. Such study could provide the theoretical explanation for root reinforcement resisting erosion in the flow-induced erosion regions. [Methods] For this purpose, a simulated scouring experiment was conducted on a sandy soil with sand content 36.8%, silt content 51.2% and clay content 12.0%. Three treatments considered were:1) fallow (CK), 2) root-penetrated soil and 3) simulated-root-penetrated soil. Each treatment had four replicates. Rectangular, undisturbed soil samples (20 cm×10 cm×10 cm) were taken in the fallow and root pans and were conducted with a hydrological flume (2 m×0.10 m). The flume contained an opening at its lower base, equaling the size of metal sampling box, so that the soil surface of soil sample was at the same level of the flume surface. Space between the sample box and the flume edges was sealed with painter's mastic to prevent edge effects. The slope of the flume bottom could be varied and clear tap water flow was applied at 4.0 L/min rate discharge on a washing flume slope of 15° for 15 min. During the 15 minutes of each experiment, samples of runoff and detached soil were collected every 1 min in the first 3 min and 2 min in the following time using 10 L buckets for determining sedimentation. Therefore, this paper analyzed the relative role in creating the soil configuration of soil resistance to erosion quantitatively, using no root-penetrated soil, root-penetrated soil erosion simulation test. [Results] The results showed that the physical consolidation effect was the key role in soil erosion resistance, accounting for 70.9% in the total root effect. Compared with alfalfa density of 90 plants/m2, physical consolidation effect in the treatment of 360 plants/m2 increased by 6.8%. In addition, the root string function was the key manner in a proportion of 78.2% in the physical consolidation effect. Exponential function well expressed the relationship between root physical consolidation effect and root surface area density (P<0.01). [Conclusions] Physical consolidation effect is the key role in soil erosion resistance, and root surface area density can reflect the root soil consolidation effect.
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2017, Vol. 15 
