Response of soil detachment capacity to plant root and soil properties in typical grasslands on the Loess Plateau

Abstract

It is likely that grassland has a significant effect on the process of soil detachment by overland flow. This study tests how soil detachment capacity responds to variation in plant root and soil properties between ten typical grasslands found on the Loess Plateau. 300 soil samples were collected from five grasslands with tap root system and five grasslands with fibrous root systems representing the typical community compositions of different succession stages, then subjected to flow scouring in a hydraulic flume under six shear stresses (ranged from 4.98 to 16.37 Pa). The results showed that the mean soil detachment capacity of each grassland fell between 0.030 kg m−2 s−1 (Poa sphondylodes Trin.) and 3.297 kg m−2 s−1 (Astragalus melilotoides Pall.). The mean soil detachment capacity across all grasslands with tap root systems was 14.7 times greater than that of grasslands with fibrous root systems, indicating that fibrous root systems are significantly more effective at reducing soil erosion. Soil detachment capacity was effectively simulated by power functions of flow velocity, shear stress, or stream power (with mean R2 values ranging from 0.87 to 0.90) and less effectively simulated by a power function of unit stream power (mean R2 = 0.74). Soil detachment capacity decreased exponentially with soil bulk density, aggregate, and cohesion (with R2 values ranging from 0.87 to 0.99) as well as with root mass density (R2 = 0.31, n = 150 for tap root systems and R2 = 0.17, n = 150 for fibrous root systems). Soil detachment was significantly worse in grasslands with tap root systems where the root mass density was less than 4 kg m−3. A model was developed to estimate soil detachment capacity based on hydraulic parameters, plant root, and soil properties on the Loess Plateau, and its performance was satisfactory (R2 = 0.86; NSE = 0.73). Root mass density, soil aggregate, and soil cohesion were indicated as the primary features of grasslands which influencing the process of soil detachment.