Effects of Different Highway Slope Disturbance on Soil Bulk Density, pH, and Soil Nutrients

Soil is inevitably affected by highway construction, resulting in a large volume of bare soil exposed to degradation. As an increasingly important and demanding area, identifying and assessing soil quality and stability on highway slopes are important for ecological management. In this study, principal component analysis, clustering analysis, and integrated matter-element model were used to evaluate the effects of highway slopes (embankment slopes [ES] and cutting slopes [CS]) on soil nutrients in the Qinghai-Tibet Plateau using grassland soil (GS) and natural slopes (NS) as controls. Our results show that, compared to NS, soil pH was significantly higher under GS, while ES and CS had no significant effect. Compared with NS, soil total nitrogen (TN) results for ES and CS recorded declines of 26.58% and 40.77%, respectively; TN increased by 263.04% in GS. Compared with NS, soil total phosphorus results declined by 25.44%, 34.37%, and 11.45% in GS, ES, and CS, respectively. Our results suggest that bare soil on highway slopes can be prone to degradation over time, and they have a negative effect on the accumulation of nitrogen and phosphorus in the soil nutrient status of slopes in the Qinghai-Tibet Plateau. Findings from this study will increase current understanding of soil nutrient responses to slope disturbance for high-cold highway slopes.