Abstract: Soil improvement in the open-pit mine dumps of grasslands plays an important role in the restoration of degraded grasslands. To explore the role of soil improvement in vegetation restoration, we examined the effects of two soil amendment pathways, humic acid (30 t·hm^-2) and vermicompost (30 t·hm^-2) addition, on soil and vegetation in the open-pit mine dumps of a grassland in eastern Inner Mongolia. The results showed that single applications of humic acid and vermicompost could significantly promote plant growth. The combined application of the two showed a significant interactive effect, with a 3.67-fold increase in biomass compared with the control. Humic acid effectively reduced soil pH (by 1.08) and increased soil organic carbon content (by 8.5 times), while vermicompost significantly increased the content of total phosphorus (by 77%), alkaline nitrogen (by 1.5 times), available phosphorus (by 2.4 times), and available potassium (by 50%) in the soil. The dominant bacterial phyla were Actinobacteria and Proteobacteria, while the dominant fungal phyla were Ascomycota and Basidiomycota in open-pit mine dump soil. Soil amendments significantly increased the bacterial Shannon index and enhanced ecosystem stability. Plant biomass was significantly positively correlated with soil nitrogen content. This study proposes a synergistic improvement technology of humic acid and vermicompost, which synchronously regulates soil physicochemical properties and microbial community structure, providing an efficient solution for ecological restoration in grassland mining areas, and having promotional value for the restoration of similar fragile ecosystems.

Key words: humic acid, vermicompost, eastern Inner Mongolia grassland, ecological restoration of mining area, synergistic improvement