Abstract: In this paper,soil pH value,the organic matter,total nitrogen,and available nitrogen (fifteen indexes) were chosen as evaluation indexes in principal component analysis in order to provide data supports for sustainable forest management of the continuous planting of Chinese fir in Guangxi,and offer the references to the soil fertility quality assessment of forest ecosystems of other regions.Soil fertility quality between the first and second generations of the young Chinese fir plantations were further assessed with principal component analysis and clustering analysis methods.The results were showed as following:macronutrient contents and secondary element contents were the pivotal factors for the soil fertility quality in the study area with comprehensive scores from -1.253 to 1.536.Among three Chinese fir producing areas,negative values occupied most.Soil fertility status of continuous planting of the young Chinese fir plantations could be divided into eight ranks by clustering analysis,that each root soil was divided into a separate rank,in which soil fertility was higher.Soil in the region of Guangxi(except for the root soil) and 20～40cm soil could be classified into a category,in which soil fertility was lowest.Other soils could be classified into a category,consequently plenty of organic and compound fertilizer are uesd for the fields of low soil fertility.The Soil fertility quality of the second generation of the young Chinese fir plantations was slightly higher the first one,it may be a temporary effect because of the forest management measures,for example,burning and cutting ways.Therefore,the forest managenments to fertilize the soil was proposed for prevention of land capability degradation.

Key words: soil fertility quality assessment, continuous planting of Chinese fir, Guangxi Zhuang Autonomous Region, principal component analysis, clustering analysis