Microbial inoculation increases maize yield and root biomass across smallholder farming systems in Rwanda

Benjamin Bukombe , Anna Edlund, Peter G Saavedra, Josue William Mberwa, Jack A Gilbert, Francois X Naramabuye, Sylvere Sirikare, Paige M Hansen, Janet K Jansson, Thomas W. Crowther

Soil degradation, nutrient depletion, and increasing climate stress constrain food productivity across tropical smallholder farming systems. Microbial inoculants have emerged as a promising strategy to improve soil functions and crop yield, yet field-based data from African smallholder systems remain limited, particularly for multi-strain bacterial consortia. Using a multi-strain consortium in a Randomized Complete Block Design experiment, we quantified the effect that soil microbial inoculants have on maize yield and root biomass production across six farmer-managed field sites spanning four agroecological zones in Rwanda. Across all sites, we found that maize grain yield was significantly greater in SLP-treated plots than in untreated controls, and maize response magnitude varied among locations. The average grain yield uplift due to microbial inoculants varied between 59–68% compared to the untreated control fields. Root biomass followed a similar trend, with an increase of 62–74% in root biomass in the treated field compared to the untreated control fields. Altogether, these results suggest that soil microbial inoculants can improve crop yield and biomass productivity under heterogeneous smallholder field conditions and highlight the potential of microbiome-based interventions as complements to existing soil fertility management strategies in tropical African agricultural systems for food security and carbon sequestration.