Fortu, S. T.; Tening, A. S.; Ndzeshala, S. T.; Ngosong, C.

Poor soil fertility constraint for common bean (Phaseolus vulgaris L.) production is often resolved using chemical fertilizers, but microbial inoculant can be used as sustainable option. Microbial inoculant formulation was tested on common bean in a randomized complete block design field experiment with eight treatments and four replicates. Treatments include untreated control, chemical NPK (nitrogen, phosphorus and potassium), poultry manure (PM), Microbes, NPK+PM, NPK+Microbes, PM+Microbes, and NPK+PM+Microbes. Microbes had higher fertilizer replacement value relative to poultry manure (41.6%) and chemical NPK (26.7%), while poultry manure had 64.3% higher fertilizer replacement value relative to NPK. Bean yield was significantly (P<0.001) higher in NPK+PM+Microbes (3.46 tons ha-1) and microbial inoculant (1.71 tons ha-1) than untreated control (1.42 tons ha-1). Higher 1000-grain weight (P<0.05) occurred in NPK+PM+Microbes (494 g) and microbes (457 g) than NPK (448 g), PM (436 g) and untreated control (421 g). Effective root nodules correlated positively (P<0.05) with bean yield (r = 0.77) and 1000-grain weight (r= 0.9). Application of NPK+PM+Microbes had higher (9) number of nodules and effectiveness than untreated control (2-3). Treatments increased soil pH significantly (P<0.05) in NPK+PM+Microbes and Microbes+PM (6.5) than untreated control (5.5) and NPK (5.0). Soil nitrogen and available phosphorus increased significantly (P<0.05) in NPK+PM+Microbes than untreated control, while higher potassium occurred in NPK than untreated control. These findings highlight the potential to explore the ability of bio-inoculant to boost root nodulation, enhance soil macro-nutrients and modulate soil pH buffer in bean production systems.