Landform affects on profile distribution of soil properties in black locust (Robinia pseudoacacia) land in loessial gully region of the Chinese Loess Plateau and its implications for vegetation restoration

Black locust (Robinia pseudoacacia) has been widely planted in the Chinese Loess Plateau and other parts of the world for soil and water conservation as a greening important forest species. The response of soil properties to black locust varies with landforms. This study was conducted to understand the effects of landforms on profile distribution of soil properties in black locust land in the loessial gully region of the Loess Plateau. Soil samples were collected in sloping land and gully bottom where black locust has planted for 21 years. For the collected soils, physicochemical, nutritional and enzymatic properties were determined. The results showed that 21 years' growth of black locust increased organic matter and nitrogen stocks by 24.65 and 0.66 t hm(-2), but decreased soil P stocks by 2.41 t hm(-2) in 0-80 cm soil depth. Gully bottom soils were higher in organic matter, cation exchange capacity (CEC), total nitrogen and phosphorus, available potassium, alkaline phosphatase and invertase, while sloping land soils were higher in pH, nitrate, ammonium and Olsen P. Principle component analysis showed that the first principle component of soil properties can represent major variation of most properties and can reflect the effects of landform on distribution of soil properties in black locust land. These results indicate that the improvement of soil properties by black locust was more obvious in gully bottom than in sloping land and different management measures should be taken according to landforms, reflecting closed mutual interactions between soils and vegetation.