Comprehensive evaluation of soil quality of different land use types on the northeastern margin of the Qinghai-Tibet Plateau, China

Abstract

Soil quality evaluation is an important prerequisite for the rational soil resource utilization. We collected soil samples from forest (n=9), grassland (n=18) and cropland (n=38) in Tianzhu County, Gansu Province, which is located on the northeastern edge of the Qinghai-Tibet Plateau. Soil quality was evaluated based on thirteen soil physical and chemical indicators, including soil bulk density, field capacity, and organic matter. A minimum data set (MDS) was constructed using principal component analysis and correlation analysis to establish a soil qua-lity evaluation index (SQI) system, which was used in the soil quality evaluation for the three land-use types. The results showed that total porosity, capillary porosity, field capacity, capillary water capacity, saturated water content, organic matter, total nitrogen and available potassium content were significantly higher in forest than those in grassland and cropland. The SQI system of forest was based on field capacity, organic matter, total nitrogen, available nitrogen, and available potassium, and the SQI ranged between 0.329 to 0.678, with a mean value of 0.481. Grassland SQI system was based on field capacity and available nitrogen, with the SQI ranging between 0.302 to 0.703 and a mean value of 0.469. Cropland SQI system was based on capillary water capacity, non-capillary porosity, available nitrogen, available phosphorus, and available potassium, and the SQI ranged from 0.337 to 0.616 with a mean value of 0.462. The most important barriers to soil quality improvement in forest, grassland, and cropland were available potassium, field capacity, and capillary water capacity, respectively. The MDS-based SQI enabled an accurate evaluation of soil quality across different land-use types in the study area, which was best in forest followed by grassland and cropland. The evaluation results would provide important reference for sustainable soil management in the local area.