Smart inputs for stressed soils: assessment of biofertilizers, nanomaterials, biochar, and biostimulants for sustainable crop productivity in Sub-Saharan Africa

Sub-Saharan Africa (SSA) faces an existential food security crisis driven by severe soil degradation, chronic nutrient deficiency, escalating abiotic stresses, and a rapidly growing population projected to double by 2050. While mineral fertilizer application remains critically low, averaging 9–17 kg/ha compared with a global average exceeding 135 kg/ha, conventional intensification pathways are financially inaccessible to most smallholder farmers and environmentally unsustainable. This study synthesizes evidence from 317 peer-reviewed studies (published 2010–2025) to quantify the effects of bio-inputs, including biofertilizers, plant growth-promoting rhizobacteria (PGPR), arbuscular mycorrhizal fungi (AMF), biostimulants, and legume-based systems, and of advanced materials, including nanofertilizers (ZnO, SiO₂, Fe₂O₃ nanoparticles), biochar, and controlled-release formulations, on crop yield, nutrient use efficiency, and abiotic stress tolerance across SSA agroecological zones. Using a random-effects model and Hedges’ g as the standardized effect size, we observed a large positive standardized treatment effect (g = 0.91; 95% CI: 0.83–0.99; P < 0.001) indicating that bio-inputs and advanced materials consistently outperformed unamended controls across studies. With integrated systems combining bio-inputs and advanced materials yielding the largest effects (g = 1.47; 95% CI: 1.18–1.76). Nanofertilizers demonstrated the highest individual effect sizes under drought and salinity stress, while PGPR consortia showed the broadest applicability across diverse SSA agroecological zones. Subgroup analyses revealed that the effect size was significantly moderated by rainfall regime, soil type, crop species, and application method. These findings provide a robust evidence base for redesigning nutrient management strategies in SSA and offer actionable recommendations for policymakers, extension services, and the agricultural innovation ecosystem.