Change of soil physical properties under long-term natural vegetation restoration in the Loess Plateau of China

A 150-year chronological study of semi-arid abandoned farmland in the central Loess Plateau of China indicated that soil physical properties were closely related to the date of being abandoned and the vegetation recovery stages. Bulk density of the surface layer (0–20 cm) significantly reduced with time while soil porosity, water-holding capacity, aggregate stability, and saturated hydraulic conductivity significantly increased. In the early period of abandonment, up to 14 years, these changes were relatively fast due to a significant increase of soil organic matter content. However, amelioration of soil physical properties of subsurface layers (20–40 cm) was relatively slow. Decline of soil bulk density of surface layers could be used as an indicator of soil structure amelioration since it was related to most other properties. Changes of soil textural properties and specific surface area were not significant, which suggested that these properties were mainly inherited from parent materials and difficult to change. Emergence of dominant woody plants during the natural vegetation recovery process could be a useful and reliable indicator of obvious improvement in soil physical properties.