Soil quality evaluation of different soil reconstruction models in spoil dumps of the southeastern Tibet railway

We arranged soil reconstruction models with different materials and covering soil thicknesses in the spoil dumps at the entrance of the Sejila Mountain Tunnel, and selected the local dominant herb Festuca arundinacea for planting experiments to reveal the effects of different soil reconstruction modes on soil properties and plant growth. This study aims to find a soil reconstruction mode that is suitable for the ecological restoration needs of the Southeastern Tibet Railway spoil dumps. The ecological restoration effect of the spoil dumps under different soil reconstruction modes was analyzed by studying the biological properties of F. arundinacea and the physical and chemical properties of the reconstructed soil. The results showed that different reconstruction materials had significant effects on the soil physicochemical properties and growth of F. arundinacea (P < 0.05), and the thickness of the covering soil was positively correlated with the biomass of F. arundinacea. The addition of 30% biocompost matrix resulted in the bulk density of the rhizosphere soil to be 21.4% lower than that of the original topsoil, the total nitrogen was 113% higher, the total phosphorus was 90% higher, the organic matter was approximately 3.5 times higher, and the plant height and aboveground biomass of F. arundinacea were significantly increased (P < 0.05). The addition of 30% waste rock to the soil increased the carbon and phosphorus content; however, it did not significantly promote the growth of F. arundinacea (P > 0.05). The research shows that both waste rock and biocompost can be used as topsoil substitute materials, and the increase in the covering soil thickness is beneficial to the growth of plants. The model with the best reconstruction effect is biocompost + topsoil 60 cm. This study provides a scientific basis for land reclamation and vegetation restoration of the southeastern Tibetan Railway spoil dumps.