Biofertilizers for Sustainable Production of Grass Crops in Sub-Saharan Africa: Mechanisms, Agronomic Responses, Constraints, and Pathways to Adoption

Abstract

Sub-Saharan African grass-crop production is constrained by declining soil fertility, variable nutrient availability, drought and heat stress, high input costs, and limited access to mineral fertilisers. This review evaluates the mechanisms, agronomic responses, constraints, and adoption pathways of biofertilisers in major grass crops across sub-Saharan Africa. Evidence published mainly between 2020 and 2026 was synthesised for arbuscular mycorrhizal fungi, plant growth-promoting rhizobacteria, nitrogen-fixing and phosphate-solubilising microorganisms, cyanobacteria, and microbial consortia. Across the reviewed evidence, maize had the strongest and most consistent response base, including reported improvements in yield, nutrient acquisition, root development, and stress resilience, whereas evidence for sorghum, pearl millet, rice, wheat, and forage grasses remained comparatively fragmented. Biofertiliser performance was strongly context-dependent and varied with soil properties, crop genotype, native microbial communities, inoculant quality, fertiliser regime, water availability, and season. The evidence therefore supports the use of microbial inoculants as targeted components of integrated soil fertility management rather than as universal substitutes for mineral fertilisers. Major constraints to wider adoption include inconsistent field efficacy, inadequate quality control, limited shelf life, restricted local production, and insufficient economic evidence. Future work should emphasise locally adapted strains, multi-location and multi-season field testing, co-inoculation strategies, nutrient-use efficiency, long-term soil-health effects, and economic performance under realistic farming conditions.