Abstract: In this study, the planted Robinia pseudoacacia forest with different site conditions in the Loess Plateau of China was selected as the research object, and the soil properties at different sites were analyzed so as to provide the advices for soil and water conservation in the loess hilly-gully region and improve the ecological environment and the rational use of resources. The results showed that the soil moisture content, pH value and enzyme activity under the 24 a R.pseudoacacia forest were higher than those under the 14 a R.pseudoacacia forest, and the contents of soil organic matter, total nitrogen and available nutrient under the 14 a R.pseudoacacia forest were higher than those under the 24 a R.pseudoacacia forest. The contents of soil moisture, organic matter and total nitrogen as well as the enzyme activity under the R.pseudoacacia forest on shady slope were higher than those on sunny slope, but the contents of soil available nutrients under the R.pseudoacacia forest on sunny slope were higher than those on shady slope. With the increase of soil depth, the contents of soil moisture, total nitrogen and available nutrients as well as the enzyme activity under the R.pseudoacacia forest were decreased, but the soil pH value was increased. The integrated soil quality index was in an order of 24 a R.pseudoacacia forest on shady slope>24 a R.pseudoacacia forest on sunny slope>14 a R.pseudoacacia forest on sunny slope>14 a R.pseudoacacia forest on shady slope. Therefore, the older the stand age was, the better the soil quality would be. It is more advantageous for regenerating the ecology to choose a better site conditions of soil ecological environment.

Key words: community of Robinia pseudoacacia, soil quality assessment, soil moisture content, soil nutrient, loess hilly-gully region, north Shaanxi Province