Abstract: To evaluate soil quality status of forest, grassland, and cropland in the southern and northern Tibetan Plateau, and to clarify the key influencing factors of productivity levels under three land use types, we measured the basic physical and chemical properties of 101 soil samples collected in the northern and southern Qinghai-Tibet Plateau. Principal component analysis (PCA) was used to select three indicators as the minimum data set (MDS) to comprehensively evaluate soil quality of the southern and northern Qinghai-Tibet Plateau. The result showed that soil physical and chemical properties of the three land use types were significantly different in the north and south. The contents of soil organic matter (SOM), total nitrogen (TN), available phosphorus (AP) and available potassium (AK) in the north were higher than those in the south, while the contents of SOM and TN of forest were signi-ficantly higher than those of cropland and grassland in both the north and south. Soil ammonium (NH₄⁺-N) content showed a pattern of cropland > forest > grassland, with significant difference in the south. Soil nitrate (NO₃^--N) content in the north and south was the highest in the forest. Soil bulk density (BD) and electrical conductivity (EC) of cropland were significantly higher than those of grassland and forest, and that of cropland and grassland in the northern part was higher than that of southern part. Soil pH of grassland in the south was significantly higher than that of forest and cropland, and that of forest was the highest in northern part. The selected indicators for eva-luating soil quality in the north were SOM, AP, and pH, and soil quality index of forest, grassland, and cropland was 0.56, 0.53 and 0.47. The selected indicators were SOM, total phosphorus (TP), and NH₄⁺-N in the south, and soil quality index of grassland, forest and cropland was 0.52, 0.51 and 0.48, respectively. There was a significant correlation between soil quality index obtained by the total data set and the minimum data set, and the regression coefficient was 0.69. Soil quality in the north and south of the Qinghai-Tibet Plateau were grade Ⅲ, and soil organic matter was the main indicator limiting soil quality in this area. Our results provide a scientific basis for eva-luating soil quality and ecological restoration in the Qinghai-Tibet Plateau.

Key words: Qinghai Tibet Plateau, soil quality, minimum data set, land use pattern