Ecological and agronomic effects of a microbiological biostimulant on growth, yield, and soil fertility in French bean (Phaseolus vulgaris L.)

Sustainable production of legumes in sub-Saharan Africa is increasingly threatened by soil degradation, nutrient depletion, and climate variability, underscoring the need for eco-friendly inputs that enhance productivity while supporting soil health. French bean (Phaseolus vulgaris L.), a short-cycle and high-value crop, is particularly sensitive to these constraints and thus provides an ideal model for evaluating bio-organic solutions. This study assessed the agronomic performance and ecological safety of Bonliga, a Georgian-developed microbiological biostimulant containing 10% organic matter, 1.2% nitrogen, 5% potassium, 5% calcium, and a microbial consortium including Bacillus spp., Azotobacter chroococcum, Cellulomonas uda, and Bacillus megaterium, all known for roles in nitrogen fixation, phosphorus solubilization, and soil organic matter decomposition. Multi-location field trials were conducted in four Kenyan agro-ecological zones (Kiambu, Kirinyaga, Machakos, Murang’a), where B Bonliga was applied at 2.0, 2.5, and 3.0 L ha⁻¹, alongside a commercial seaweed-based biostimulant and an untreated control. A randomized complete block design with three replications was used, and growth traits (plant height, leaf number, canopy spread), yield parameters (pod length, pod number, pod weight, and marketable yield), phytotoxicity, and soil fertility dynamics were evaluated. Results demonstrated that Bonliga significantly improved plant growth and pod yield across all sites, with the 2.5 L ha⁻¹ dose achieving the best balance between productivity and input efficiency. Pod yields were consistently higher than both the control and the reference product, while no phytotoxic effects were observed. Post-harvest soil analyses further revealed improvements in organic matter, total organic carbon, cation exchange capacity, and nutrient availability, indicating Bonliga’s dual role as a crop growth promoter and soil conditioner. These findings confirm Bonliga as a safe, sustainable, and climate-resilient bio-organic input with strong potential for integration into smallholder horticultural systems in sub-Saharan Africa.