Study on soil pH and nutrients in a roadside green belt in a central urban area of Lanzhou

To determine the pH and nutrient status in roadside greenbelt soil in a central urban area of Lanzhou, uncover the main limiting factors, and propose solutions, the soil around street trees, which was divided into 0 − 30 cm and 30 − 60 cm layers, were sampled. Depending on whether the soil was covered by vegetation, the samples were further divided into bare and vegetation-covered groups. The relationship between soil pH and soil nutrients was analyzed using the group regression method. The soil pH ranged from 7.91 to 9.39, with an average value of 8.49, and was generally high, with 33.42% and 0.47% of the soil being strongly and extremely alkaline, respectively. Soil organic matter content ranged from 5.30 to 47.80 g·kg⁻¹, with an average value of 18.29 g·kg⁻¹, and 37.64% and 21.77% of the soil were relatively and seriously deficient, respectively. Soil alkali-hydrolyzable nitrogen content ranged from 5.24 to 167.55 mg·kg⁻¹, with an average value of 48.54 mg·kg⁻¹, and 35.68% and 5.95% of the soil were relatively and seriously deficient, respectively. Soil available phosphorus content ranged from 4.68 to 184.46 mg·kg⁻¹, with an average value of 45.66 mg·kg⁻¹, and 19.58% and 1.67% of the soil were relatively and seriously deficient, respectively. Soil available potassium content ranged from 72.35 to 449.64 mg·kg⁻¹, with an average value of 177.60 mg·kg⁻¹, and was not deficient. Organic matter, available nitrogen, available phosphorus, and available potassium contents in the 0 − 30 cm layer of bare soil were significantly higher than those in the 30 − 60 cm soil layer. Additionally, available nitrogen and available potassium contents in the 0 − 30 cm soil layer covered by vegetation were significantly higher than those in the 30 − 60 cm soil layer. The results of correlation analysis showed that organic matter, alkali-hydrolyzable nitrogen, and available phosphorus contents were negatively correlated with soil pH, and that high pH was an important factor that limited the exertion of soil nutrients in the Lanzhou road greenbelt. Vegetation coverage significantly decreased soil pH and significantly increased the contents of organic matter, alkali-hydrolyzable nitrogen, and available phosphorus. Therefore, vegetation coverage on a bare surface can effectively improve the main problems that exist in roadside green belt soil.