Soybean has the potential to bring significant benefits in diversified cropping systems, which could help restructuring soil fertility and allow smallholders to increase grain yield. Rhizobium inoculation improves the biological nitrogen fixation (BNF) in legume crops and assists resource-poor farmers to increase grain yield at lower financial costs. The efficacy of symbiotic bacteria on legumes can also be improved through supplementation of phosphorus fertilizer. In this work, a meta-analysis of 29 peer-reviewed studies was performed to understand the effects of various Rhizobium strains and phosphate fertilizer application on soybean nodules. Results showed that Rhizobium inoculation was highly effective in increasing the number of soybean nodules, nodule dry weight, and shoot dry weight. Application of phosphorus fertilizer increased the overall nodule number due to improved BNF processes by Rhizobia. The main effects of both Rhizobium inoculation and phosphate fertilizer resulted in moving grain yields to 1.67 t ha-1 and 1.95 t ha-1, respectively. Furthermore, the interaction of Rhizobium inoculants and phosphorus led to relatively higher grain yield (2.51 t ha-1). Therefore, African smallholders were advised to adopt Rhizobium inoculation in soybean fields concomitantly to phosphate fertilizer application, to improve soybean productivity at lower costs.

Keywords: Phosphorus application, nodule number, nodule dry weight, shoot dry weight, grain yield