This study aimed to evaluate the correlations between different agronomic parameters and their contribution to soybean performance under Bradyrhizobium japonicum influence. The experiment was carried out at Kanyameshi (Kipushi), following a Split Plot design, with three strains of Bradyrhizobium japonicum (GraphExTM, Bradyrhizobium sp and Sojapak ® 50) and four soybean varieties (TGX 1740-7F: V1, PAN 1867: V2, TGX 1880-3E: V3 and LUKANGA: V4). The strongest correlations were obtained between fresh biomass and plant height, the number of stems and collar diameter, fresh biomass and collar diameter, number of stems and plant height, number of roots and number of stems, fresh biomass and number of roots, number of pods and number of leaves. The collar diameter is the most positively correlated parameter with both growth and soybean yield parameters. While lifting rate, collar diameter, plant height, number of stems, number of leaves, fresh biomass, number of nodules and number of pods are the most linked to soybean grain yield. A significant negative correlation was observed between number of leaves and the weight of 100g. Fresh biomass was found to be more predictable, whereas number of leaves is the growth parameter that contributes most to soybean fresh biomass. Based on their decreasing contribution to fresh biomass, the various parameters can be classified as follows: Number of leaves>number of root>plant height> collar diameter. Among examined agronomic parameters, only four contribute directly to the soybean yield, namely number of leaves, number of pods, fresh biomass and collar diameter. By applying Bradyrhizobium japonicum to the four soybean varieties, the correlations between observed parameters were enhanced. This study is a major contribution in the conduct of soybean cultivation as it identified the parameters on which the farmer should focus to maximize soybean grain yield.

This study was conducted on acidic soils in two different agroecological zones in order to evaluate the influence of Bradyrhizobium japonicum on soil chemical properties in the Upper-Katanga (DR Congo). A split plot design with three replicates was installed in two sites. The main plots included three strains of Bradyrhizobium japonicum plus the untreated control and four soybean varieties in subplots. Seed inoculation was performed in the shade and sown on the same day. The results showed that Bradyrhizobium strains did not influence soil pH, Nitrogen, C: N ratio and organic matter neither at flowering nor at harvest. However, total and available phosphorus (P) were influenced by the different treatments at harvest in Kanyameshi site. The strain S1 induced the highest average of total and available P whereas, the strain S2 had the lowest value of total P, and S3 induced the lowest content in available P. By comparing the timing of soil sampling at flowering and harvesting, the Student test revealed significant differences in pH, total nitrogen, C: N ratio, organic matter and available P indicating that soil chemical properties was improved at harvest and are only partially influenced by applied Bradyrhizobium strains.