Effect of combination of vetiver grass cultivation and fertilization on soil restoration in spoil ground along expressways

Soil degradation of the spoil ground generated during the construction of expressways is a serious concern, which affects the surrounding ecological environment. In this study, the combination of vetiver grass cultivation and fertilization was used to repair the soil in spoil ground. Therefore, 12 treatments were set up to evaluate the effects of ecological restoration, including no fertilization (CK), nitrogen fertilizer only (N1:150 kg/ha, N2:300 kg/ha, and N3:450 kg/ha), phosphorus fertilizer only (P1:350 kg/ha and P2:700 kg/ha), and a chemical fertilizer combination (NP: N1P1, N2P1, N3P1, N1P2, N2P2, N3P2). Compared with the CK, the fertilization treatments significantly increased the contents of soil ammonia nitrogen, soil total nitrogen, soil total phosphorus, and soil available phosphorus in rhizosphere soil increased by 6.91–48.49%, 1.36–153.81%, 63.40–333.44%, and 3.22–138.12%, respectively; the activity of β-xylosidase and N-acetyl-glucosaminidase increased significantly by 41.25–119.84% and 13.54–128.45%, respectively; and the Chao1 and observed species microbial diversity indices increased by 19.98–55.62% and 16.49–53.29%, respectively. In addition, NP treatment had a higher path coefficient for plant traits [NP (0.897) > P (0.767) > N (0.373)] and enzyme activities [NP (0.807) > N (0.703) > P (− 0.993)]. Furthermore, N2P2 had the highest comprehensive score (34), indicating that N2P2 could be used as an effective fertilizer combination. These results indicate that combined fertilization treatment (NP) improved the path coefficient of soil physicochemical properties to plant traits and soil enzyme activities, and thus better restored the habitats of spoil ground.