Bradyrhizobium inoculants impact on promiscuous nodulating soybeans cultivars in Ghana's farming systems

Abstract

Soybean is rarely inoculated with commercial Bradyrhizobium inoculants in Ghana's cropping systems. A 2-year field study was conducted at Council for Scientific and Industrial Research–Savanna Agricultural Research Institute's experimental field at Nyankpala, Ghana to assess how commercial inoculants affect growth, nodulation, nitrogen fixation, and grain yield of promiscuous nodulating soybean cultivars. The experiment was a split-plot design with the main plot factor as soybean [tropical Glycine max (L.) Merr. crosses (TGX) cultivars]; Jenguma (TGX1448-2E), Afayak (TGX1834-5E), and Songda (TGX 1445-3E). The subplot factor consisted of three commercial Bradyrhizobium japonicum inoculants, namely, Biofix (strain USDA 110), NoduMax (strain USDA 110), and Legumefix (strain 532c) plus uninoculated control. Shoot biomass and nodulation were assessed at vegetative (V8, 8-leaf stage), full bloom (R2), beginning to pod (R3), full pod (R4), and full seed (R6) stages, respectively, and N fixation and grain yield at maturity. Shoot dry matter increased with growth stage and peaked at the R6 stage with significant effect associated with Biofix and NoduMax. Nodulation on the upper root and the whole root also peaked at the R4 stage, with pronounced effects associated with Biofix and NoduMax. Enhanced grain yields of up to 30% were achieved with Biofix and NoduMax compared to the uninoculated control in both 2016 and 2017. Regarding the cultivars, shoot biomass increased with growth stage and peaked at R6 stage and Afayak yielded greater shoot biomass. On average (2 years), Afayak produced greater grain yields than Jenguma and Songda. In conclusion, Biofix and NoduMax were the most promising commercial inoculants for soybean production in Northern Ghana.