Bacterial inoculants and Lablab purpureus for mine soil fertility in Sub-Saharan Africa: a systematic review

Mining in Sub-Saharan Africa (SSA) has generated extensive degraded soils characterized by heavy metal contamination, nutrient depletion, and loss of biological activity. Conventional remediation methods are often costly and unsustainable. This systematic review evaluates the synergistic potential of combining bacterial inoculants with the legume Lablab purpureus (hyacinth bean) as a low-cost, ecological strategy for rehabilitating mine soils and enhancing fertility. Following the PRISMA framework, we synthesized evidence from studies across SSA, focusing on mechanisms such as microbial nutrient cycling, nitrogen fixation, and phytostabilization. The analysis reveals that plant-growth-promoting rhizobacteria (e.g., Bacillus, Pseudomonas, Rhizobium) significantly enhance L. purpureus performance by improving nutrient solubilization, mitigating metal toxicity, and increasing biomass production. Field studies demonstrate that this synergy can elevate soil organic matter by 20-50% and reduce bioavailable heavy metals by 30-40% within several growing seasons. However, effectiveness is constrained by environmental variability, microbial survival challenges, and socio-economic barriers. The review identifies key opportunities for scaling up, including omics-assisted microbial selection, long-term monitoring frameworks, and integration with circular economy models. We conclude that tailored bacterial-Lablab partnerships offer a promising pathway for sustainable mine soil rehabilitation in SSA, but widespread adoption requires supportive policies, community engagement, and context-specific adaptations. This work provides a consolidated evidence base to guide researchers, practitioners, and policymakers in advancing ecological restoration and soil fertility enhancement in post-mining landscapes.