Impact of compost amendments and Morus alba L. on soil restoration, microbial communities, and crop yield in rare-earth tailings

Rare-earth mines worldwide urgently need sustainable, low-cost methods to restore soil quality and productivity. The application of remediation plants, such as Morus alba , combined with organic fertilisers (vermicompost), is promising for enhancing soil quality around rare-earth tailings and improving crop yields; however, the effects of phytoremediation combined with organic fertiliser are not fully understood. We conducted a 4-year study to assess the impact of four fertilisation regimes combined with M. alba on soil properties, enzyme activities, microbial diversity, and crop yield in rare-earth tailings. Organic amendments markedly improved soil quality. The treatment combining vermicompost and biogas slurry increased soil pH from 4.37 in the chemical fertiliser control to 6.67, soil organic matter from 4.87 to 30.58 g·kg −1 , and available phosphorus from 8.31 to 264.52 mg·kg −1 , while significantly enhancing soil enzyme activity. In soil bacterial communities, relative abundances of environmentally adapted taxa (e.g., Acidobacteria and Verrucomicrobia) increased, accompanied by a tendency toward greater stochastic assembly. The combination of earthworm casts and biogas slurry increased crop yield from 6.72 t·ha −1 in the control to 42.18 t·ha −1 in 2023. Functional prediction suggested enhanced microbial potential for carbon and nitrogen cycling. Random forest and structural equation modelling revealed that the dominant driver of crop yield shifted from available nitrogen in the early stage to organic matter in the later stage. Collectively, these results suggest that organic fertilisation combined with phytoremediation is a viable strategy for mine tailings, supporting global efforts toward sustainable ecological restoration and improved soil health.