Soil anti-scouribility and its related physical properties on abandoned land in the Hilly Loess Plateau

Abstract: The abandoned land plays an important role in degraded ecosystem restoration. Large areas of abandoned land and the relatively little disturbance by human activity made it the optimal mode in the process of the project to "convert the farmland into forestland." Our objective was to determine the impact of abandoned land and their different stages on soil anti-scouribility (AS) and related soil physical properties. In this paper, five natural lands with various abandoned stages (0-43 a) were selected to study the soil AS by using a spatio-temporal substitution method in the Hilly Loess Plateau. Rectangular, undisturbed soil samples (length=20 cm, width=10 cm, and height=10 cm) were taken in the field and were conducted with a hydrological flume (length=2 m, width=0.10 m). The flume contained an opening at its lower base, equaling the size of a metal sampling box, so that the soil surface of the sample was at the same level of the flume surface. The space between the sample box and the flume edges was sealed with a painter's mastic to prevent edge effects. The slope of the flume bottom could be varied and clear tap water flow was applied at an adjusted rate of 4.03 L/min discharge on a washing flume slope of 15° for 15 minutes. During the 15 minutes of each experiment, samples of runoff and detached soil was collected every one minute in the first three minutes and two minutes in the following time using 10 L buckets for determination of sediment concentration. Before being tested, the aboveground biomass was cut level with the soil surface. In this way, only the effects of roots were accounted for. The physical properties mainly included soil bulk density (g/cm3), soil water-stable aggregate content (%), soil shear strength (cohesion C and angle of internal friction φ), and soil disintegration rate (cm3/min). Root biomass was determined by the harvest method and dried in the oven. The results indicated that as the years of the abandoned land increased, compared with control (stageⅠ), soil bulk density in the surface layer (0-15 cm) and middle layer (>15-30 cm) were significantly reduced, while little change occurred in the lower soil layer (>30-50 cm). The soil water-stable aggregate content and shear strength, including C and φ were also significantly increased in the three studied soil layers. Soil disintegration rate was reduced in all soil layers, especially for the middle and lower soil layers, about 4.2 and 1.8 times the rate of those in the surface soil layer. Soil AS in the surface layer increased rapidly before stage Ⅲ, and kept stable in the following abandoned stages, while the soil AS in the middle and lower soil layers increased steadily, in approximately 76.9% and 30.7% increments as compared with those of the control. Linear regression equations between the soil AS and the soil physical properties studied in the present paper were well fitted in the three soil layers and the soil water-stable aggregate content and dry root biomass were the determining factors in the reinforcement of soil AS in the abandoned land of the Hilly Loess Plateau.