Effect of Rhizobium Inoculants and Reproductive Growth Stages on Shoot Biomass and Yield of Soybean (Glycine max (L.) Merril)

The experiment was conducted during the 2012 farming season in the agricultural experimental field of the University for Development Studies, Nyankpala in the Northern Region of Ghana. The objective of the study was to determine the influence of Rhizobium inoculants and growth stages on shoot dry matter and grain yield of soybean. Two levels of inoculation regimes (inoculation (+In) and uninoculation (-In)) were combined with four sampling developmental stages (vegetative stage, flowering stage, pod stage and physiological maturity stage). The experimental design was a 2 x 4 factorial laid out in a Randomized Complete Block Design with eight treatments at four replications. Plants inoculated with Rhizobium and harvested at flowering stage recorded significantly higher fresh and dry shoot matter of 74.2 g and 23.57 g per plant, respectively as compared to plants that were not inoculated and harvested at the physiological maturity stage. The latter recorded the lowest fresh and dry shoot weights of 45.2 g and 15.5 g per plant, respectively. Rhizobium inoculation significantly increased grain yield (1262 kg/ha) compared to the yield obtained in the uninoculated treatments (1044 kg/ha). Grain yield positively correlated with plant height, plant stand, canopy spread, number and weight of nodules, number and weight of pods. From the results, it is recommended that soybean seeds should be inoculated with Rhizobium before planting in order to obtain higher grain yields. It is also recommended that for higher nodule numbers, which can be a good indication of higher N2 fixation if the nodules are effective, and higher shoot biomass which is required for effective green manuring, soybean should be harvested at full pod stage.