Role of arbuscular mycorrhizal fungi and Pongamia pinnata for revegetation of tropical open-pit coal mining soils

Open-pit coal mining activities may cause forest and environmental degradation. Thus, forests need to be reclaimed and revegetated after coal mining. This study aimed to determine the combined effects of arbuscular mycorrhizal fungi (AMF) inoculation on the revegetation of postcoal-mining lands with Pongamia pinnata. This completely randomized study was conducted for 6 months in a greenhouse. The first factor consisted of four different levels based on soil medium type: forest soil, mined-out soil, overburdened soil, and landfill soil. The second factor consisted of three levels based on three different dosages of AMF: control, 2 g of AMF, and 4 g of AMF. Open-pit coal mining activities in East Kalimantan caused serious land degradation in tropical ecosystem. Revegetation with P. pinnata accelerated land reclamation by passing the land preparation stage and decreased the costs of land preparation. Forest soil was the optimal medium for the growth of P. pinnata seedlings. However, when the seedlings were planted in degraded soil of mining, their average height, diameter, and total biomass decreased drastically. The inoculation of 2 g AMF colonized the root and therefore improved growth of seedling. This result may reduce cost of chemical fertilizer. AMF inoculation improved Fe absorption by 11.7% that was higher than that under control, whereas 90.4% of the assimilated Fe was retained in plant roots. Revegetation by exotic fast-growing pioneer legume species of P. pinnata and application of AMF drastically improved some chemical soil properties that suitable for rehabilitation program in tropical post-mining areas.