Identifying a suitable revegetation method for soil organic carbon, nitrogen, and phosphorus sequestration: A 16-year in situ experiment on abandoned farmland in a semiarid area of the Loess Plateau, China

Legume pasture species have been widely used to re-establish vegetation cover and control soil erosion in semiarid degraded ecosystems. Nevertheless, the long-term effects of revegetation on aboveground biomass (AB) and the soil properties under different topographies remain unclear. We conducted a 16-year in situ experiment to evaluate soil properties and biomass dynamics under fallow, sweet clover (Melilotus officinalis L.) and alfalfa (Medicago sativa L.), in northeast-facing, southeast-facing, and horizontal landscapes from 2003 to 2018. After 16 years of revegetation, soil organic carbon (SOC), soil total nitrogen (TN), soil total phosphorus (TP) concentrations were higher in alfalfa fields in the northeast- and southeast-facing landscapes and greater in sweet clover fields in the horizontal landscape alongside soil profiles. In the 0-20 cm, the SOC, TN, and TP concentrations in alfalfa fields increased at rates of 0.322, 0.034, and 0.010 g kg(-1) yr(-1) in the northeast-facing landscape and at rates of 0.189, 0.022, and 0.011 g kg(-1) yr(-1) in the southeast-facing landscape. The SOC, TN, and TP concentrations in sweet clover fields increased at rates of 0.129, 0.023, and 0.009 g kg(-1) yr(-1) in the horizontal. Alfalfa introduction is recommended for northeast-facing landscapes whereas alfalfa and fallow are recommended in southeast-facing landscapes, introduce sweet clover is recommended in a horizontal landscape to improve the soil nutrient concentrations at mid-long time. These results suggest that topography influences vegetation restoration by affecting plant growth and soil nutrient and should be considered during the revegetation process to ensure revegetation success and sustainable land use.