Abstract: Soil quality is one of the most important environmental factors in sustaining the earth biosphere and developing sustainable agricultural product. Zhifanggou catchment of Ansai county of Shaanxi province was selected as the study area. Field investigations had been carried out and 8 sample plots with different vegetation types and ages were chosen. The effects of vegetation types on soil properties were analyzed through measuring soil particle size distributions, soil water stable aggregates, soil organic matter, total nitrogen, alkali-hydrolyzable nitrogen, ammonium nitrogen, nitrate nitrogen, available phosphorus, soil enzyme activities (invertase, alkaline phosphatase, and urease catalase), microbial biomass (carbon, nitrogen and phosphorus). The effects of vegetation types on soil quality were studied by calculating soil quality index (SQI) using factor analysis and membership function. Results indicate that SQI were 0.09-0.73, SQI in the crop land was the lowest, which was 0.09;SQI in the Robinia pseudoacacia forestland with 31-years age was the highest, which was 0.73. Under the same vegetation type, SQI increased with an increase of restoration year. Meanwhile, under the same restoration year, SQI in the Robinia pseudoacacia forestland was greater than that in the Pinus tabulaeformis forestland. These results showed that vegetation restoration and abandoned land can improve soil quality and extensive agricultural farming can decrease soil quality.

Key words: vegetation type, soil quality, factor analysis, membership function, loess hilly-gully regions