Background Mine waste and soil-like materials lack nutrients such as nitrogen and phosphorus, while Medicago sativa as a leguminous plant, has strong nitrogen-fixing characteristics, and its root tumors can fix more nitrogen and carbon. Its rhizomes, leaf residues, and root secretions are released into the soil with many organic substances, and they can be used as green fertilizers for flip pressure and decomposition, and have a good fertilization effect and improve soil microbial properties, thereby improving soil quality.

Methods To master its restoration efficiency and timeliness, M. sativa sites with different plantation ages, respectively, for 2 years, 4 years, 6 years and 10 years in Ordos Wujiata dump were selected as the research objects (respectively expressed as for M2, M4, M6, and M10). Replacing time with space was used to study the changing characteristics of soil seed bank during alfalfa restoration.

Results There were 8 species plants in the soil seed bank during the recovery of M. sativa, which were mainly leguminous and annual plants, belonging to 8 genera and 4 families of Gramineae, Compositae, Chenopodiaceae and Leguminosae. The index of species diversity, richness and evenness in the soil seed bank were the best in the M4 stage. The density of soil seed bank changed at 459.68-3 900.72 seeds/m², which was significantly higher in M4 stage than in M10 stage. The similarity coefficient of soil seed bank between different planting years of M. sativa was between 0.44-0.80. Under the M. sativa restoration mode of dumping site, there was a certain scale of soil seed bank, which provided seed source for vegetation restoration. However, the species was relatively poor, thus it increased the community diversity and stability by artificially introducing the dominant seeds of regional stable ecosystem. With the increase of the recovery period, the ecological characteristics of the soil seed bank were reduced. It is possible to consider introducing artificially dominant seeds of regionally stable ecosystems to increase the diversity and stability of the community. Renewal, transformation, and utilization may also be considered to ensure the efficiency and sustainability of the restoration of ecological systems at the dump.

Conclusions Under the condition of no intensive operation and management in the study area, combined with field observation and investigation, the community restoration and soil improvement benefits are better when the planting of M. sativa is restored at 4 years, its community restoration and soil improvement benefits are both good, and it can be considered for reclamation and utilization, or it can be renewed or artificially introduced in time before it declines, which is conducive to ensuring the ecological restoration benefits of the mining area and land reclamation.