Reclamation of coalmine spoils with topsoil, grass, and legume: a case study from India

Accretion of carbon (C) and nitrogen (N) content in reclaimed mine soil is a major objective to restore mine soil fertility. The present study investigated the impact of grass and legume seeding in fertility enhancement, nutrient accumulation, and accretion of C and N pool during the early stages of reclamation. Four land covers were studied—unreclaimed mine spoil dump, topsoil dump, and 2-year-old coal mine spoil dumps revegetated with legume (Stylosanthes hamata) and grass (Cenchrus ciliaris). Results showed that above- and below-ground biomass of legumes as well as biomass C and N contents were significantly higher than grass. Reclaimed mine soils under legumes cover had greater soil organic matter (SOM) (42%), soil organic carbon (SOC) (66%), available N (79%), and total N (62%) than the applied topsoil. The rates of SOC (1.57 Mg SOC ha⁻¹ year⁻¹) and total N (0.47 Mg N ha⁻¹ year⁻¹) accumulation were higher under legume than the grass. Soil CO₂ flux was in the order of legume (2.34 ± 0.27 µmol CO₂ m⁻² s⁻¹) > grass (2.17 ± 0.19 µmol CO₂ m⁻² s⁻¹) > topsoil (1.23 ± 0.19 µmol CO₂ m⁻² s⁻¹). Total cost of reclamation was US$ 6761 ha⁻¹, out of which 59% was contributed by technical reclamation and 41% by biological reclamation which includes aftercare and maintenance for 2 years. Legumes showed advantages over the grass species to restore mine soil fertility. Therefore, this study recommends the application of legumes as an initial colonizer to reclaim coal mine spoils.