Effects of Bradyrhizobium Japonicum on Nitrogen Concentration in Soybean Leaves and Seeds Cultivated on Acidic Soils

The legume-rhizobium symbiosis plays an important role in Nitrogen (N) uptake by plants, more particularly in the humid tropical region where soils are deeply weathered and have poor electrochemical properties. However, the influence of Bradyrhizobium on N allocation in soybean organs is not clearly understood. Here, we assessed the effect of Bradyrhizobium japonicum on the N concentration of soybean leaves and seeds cultivated on acidic soils. We conducted two experiments using a randomized full device with three replicates in two sites (i.e., Kasapa and Kanyameshi). The main plots included three strains of Bradyrhizobium and the uninoculated control while the subplots included soybean variety. We found that different strains of Bradyrhizobium did not induce significant effects on total N concentration in soybean leaves and seeds in the Kasapa site. In contrast, Bradyrhizobium strains affected significantly N concentration in soybean leaves in the Kanyameshi site. We demonstrated that soil N concentration, which varies between investigated sites, positively influences yield and nodulation. We conclude that the efficiency of the soybean-Bradyrhizobium symbiosis and its influence on the allocation of N through soybean organs strongly depend on the chemical characteristics of soil and particularly on the initial N concentrations in soils.