Soil quality evaluation of the alluvial fan in the Lhasa River Basin, Qinghai-Tibet Plateau

Determining the soil quality of alluvial fans and its influencing factors is essential for understanding, utilizing, and protecting alluvial fans. In this study, a soil quality index (SQI) was constructed, and the soil of river terrace farmland was used as a control to evaluate the soil quality of alluvial fans in the Lhasa River Basin of the Qinghai-Tibet Plateau. Meanwhile, the influencing factors of soil quality of the alluvial fan were studied using correlation analysis. The results demonstrated that: 1) There is no significant difference in physicochemical indicators between the soil of the alluvial fan and river terrace farmland, namely the total nitrogen, total phosphorus, total potassium, available nitrogen, available phosphorus, available potassium, soil organic matter, pH, electrical conductivity, and soil erodibility; however, the coefficient of variation of each physicochemical indicator of the alluvial fan is greater than that of river terrace farmland. 2) The mean SQI value of alluvial fans and river terrace farmlands are 0.37 and 0.38, respectively. There is no significant difference between the values, demonstrating that the soil quality of alluvial fans is not lower than that of river terrace farmland. 3) The soil quality of alluvial fans has a highly significant positive correlation with vegetation coverage, land use, annual precipitation, altitude, and geomorphic divisions; a significant positive correlation with geomorphic location; and a highly significant negative correlation with annual temperature. Therefore, from the perspective of soil quality, the alluvial fan in the Lhasa River Basin can be used as a reserve arable land resource.