Evaluation of soil quality along two revegetation chronosequences on the Loess Hilly Region of China

Highlights: • SQI was developed from physicochemical and biological properties. • Key indicators are microbial biomass carbon, silt, clay, total phosphorus and pH. • SQI values for Robinia pseudoacacia L. markedly increased with restoration age. • SQI values for abandoned land reached a steady-state after 27 years of restoration. • SQI values were higher in Robinia pseudoacacia L. than abandoned land. Vegetation restoration has been widely implemented to control soil degradation, reduce soil erosion, and improve soil quality. It is vital to understand the mechanisms affecting soil quality in soil restoration processes and to determine an appropriate recover pattern for soil restoration. Thus, a soil quality index was developed using integrated approach to assess soil quality after vegetation restoration in this study. Soil samples were collected from two restoration pathways (afforestation by Robinia pseudoacacia L. and natural recovery of abandoned farmland) with ages sequence of 0, 17,27 and 42 years old at two soil depths (0–10 and 10–20 cm) to measure soil physicochemical and biological properties on the Loess Hilly Region of China, China. The results showed that soil quality index (SQI) was developed based on microbial biomass carbon (MBC), fine particles (FP), and total phosphorus (TP). The MBC, which had the fastest increase rate than TP and FP, had the highest contribution to the final SQI and these contributions increased with recovery age. The MBC values were higher in Robinia pseudoacacia L. than in abandoned land sites at all recovery ages with greater increases along with restoration age. The SQI values significantly increased with increasing restoration age up to 27 years (P < 0.05). After 27 years, SQI values for the AL sites remained stable, while SQI values for RP sites continually improved with increasing restoration age. In addition, SQI values were higher for RP sites than for AL sites for all restoration ages.