Soil Quality Assessment under Different Land Use Types in Typical Oasis of the Upper Reaches of the Tarim River
塔里木河上游典型绿洲不同土地利用方式下土壤质量评价

Soil quality assessment under different land use types is important for ecologically sustainable development. In 2008, soil samples from 0-20 cm layers for different land use types, i. e., 8-year cotton field, 30-year cotton field, plantation forest, natural forest, grassland, abandoned land, and saline-alkali land, across the Aler reclamation area of the upper reaches of the Tarim River were collected. By analyzing seven soil physical and chemical properties, including soil water content, bulk density, pH, organic matter, total N, available P, available K, and five soil enzymatic activities, including catalase, polyphenol oxidase, urease, invertase, and alkaline phosphatase, this study made an attempt to evaluate soil quality under different land use types. Soil quality assessment values (SQAV) were calculated using principal component analysis (PCA). Soil quality grades were classified by clustering diagram. The sustainable yield indexes (SYI) were calculated to verify the evaluation results. Results show that there were differences in the physical, chemical, and enzymatic properties under different land use types. Land use had a great influence on various soil properties. The influence of varying land use types in descending order is natural forest>plantation forest>8-year cotton field>30-year cotton field>abandoned land>grassland> saline-alkali land. The higher nutrients and enzymatic activities were observed in forest land whereas the lower ones were observed in saline-alkali land. Soil quality of cotton field was worse than that of forest land. Different land use intensity and cropping patterns would have a significant impact on soil quality of cotton field. Extensive cultivation for more than 10 years may have caused the decline of soil quality to varying degrees under unreasonable tillage practices. The soil quality assessment values decreased from -0.003 for 8-year cotton field to -0.406 for 30-year cotton field. The assessment values for abandoned land and grassland were close to those of 30-year cotton field. Spatial differences in soil quality assessment under different land use types reflected influences of human activities. Therefore, management practices need to take into account increasing soil quality, such as returning cultivated land to forests, building natural reserve in arid land areas, strengthening forest construction, and improvement in salinized soil. This study could be beneficial in an enhanced understanding of complexity of the interactions between human and land systems.