Soil detachment by overland flow under different vegetation restoration models in the Loess Plateau of China

Abstract

Land use change has significant effects on soil properties and vegetation cover and thus probably affects soil detachment by overland flow. Few studies were conducted to evaluate the effect of restoration models on the soil detachment process in the Loess Plateau where a Grain for Green Project has been implemented in the past fourteen years. This study was performed to study the effects of vegetation restoration models on soil detachment by overland flow and soil resistance to rill erosion as reflected by rill erodibility and critical shear stress. The undisturbed soil samples were collected from five 37-year-restored lands of abandoned farmland, korshinsk peashrub land (Caragana korshinskill Kom.), black locust land (Robinia pseudoacacia Linn.), Chinese pine land (Pinus tabuliformis Carr.) and mixed forest land of amorpha and Chinese pine. The samples were subjected to flow scouring in a 4.0m long by 0.35m wide hydraulic flume under six different shear stresses ranging from 5.60 to 18.15Pa. The results showed that the measured soil detachment capacities were affected significantly by the restoration models. The mean detachment capacity of cultivated farmland was 23.2 to 55.3 times greater than those of the restored or converted lands. Abandoned farmland showed maximum soil detachment capacity and was 1.02 to 2.29 times greater than the other four restored lands. Soil detachment capacity of the restored lands was significantly influenced by shear stress, cohesion, bulk density, total porosity and root mass density. Detachment capacities were negatively related to cohesion (p<0.01) with linear function and root mass density (p<0.05) with exponential function, but positively to total porosity (p<0.01) with linear function. The rill erodibility would be negatively related to cohesion (p<0.01) with power function. Besides, the low rill erodibility in the restored lands always had a low soil detachment capacity, while the critical shear stress in the restored lands varied non-monotonically with detachment capacity. The mixed forest land of amorpha and Chinese pine was considered as the best restoration model for its important role in reducing soil detachment capacity.