Soybean yield response to Bradyrhizobium inoculation on southeastern coastal plain soils

Abstract Biological nitrogen fixation (BNF) in soybean [ Glycine max (L.) Merr.] is an important process to supply nitrogen (N) for the crop. However, the N fixation capacity of soybean varies widely among soils and climatic conditions. The N fixation potential is purportedly minimum in soils that do not have any prior history of soybean cultivation, and the application of inoculum is reported as necessary to facilitate this process. Rhizobium inocula can be applied at planting to promote BNF; however, their efficacy remains highly variable. A field experiment was conducted at irrigated and dryland sites in 2017 and 2018, where soybean was not cultivated in the preceding 10+ years. Bradyrhizobium inoculum was applied in liquid, dry, and a combination of liquid and dry formulations. The results showed that inoculum addition, in any formulation or combination, did not significantly increase soybean yield compared with the untreated control at any site. This study showed that inoculum application did not consistently increase yield in fields without soybean in the previous crop rotation for years. Future research is needed to identify soils, varieties, management practices, and environmental conditions for soybean inoculation which can increase yield and net farm profits.