Leveraging biological nitrogen fixation and soybean yield by planting duration under varying onset of rainy seasons in Uganda
Rainfall distribution and onset of rainy seasons, both of which are key determinants of the decision to plant most annual crops in sub-Saharan Africa (SSA), are increasingly difficult to predict due to climate change. Consequently, planting schedules affect both crops and vital natural systems such as biological nitrogen fixation in legumes. The objective of this study was to establish the optimum planting duration for soybean (Glycine max L.), from the onset of the rainy season, in the context of nodulation and grain yield, and diversity of rhizobia in rhizosphere soil and nodules. A field experiment was set up with treatments, Bradyrhizobia inoculated and non- inoculated soybean variety Maksoy3N planted at four dates; 0, 10, 20 and 30 days from the onset of rain season. Diversity of rhizobia in the rhizosphere soil and nodules were fingerprinted using Single Strand Conformation Polymorphism (SSCP) method. Inoculation significantly (P<0.05) increased the number but not effectiveness of nodules and grain yield; which was attributed to presence of native strains in the soil. Planting after 10 days following the onset of a rainy season significantly (P<0.05) reduced grain yields and total yield loss was realised when seasonal cumulative rainfall was about 500 mm. Planting after 20 days from onset of rainy season significantly (P< 0.05) reduced the total number of nodules. A total of 8 and 12 clusters of bacteria from the soil and nodules at 5% dissimilarity, respectively, were recorded. The Bradyrhizobia species consisted of B. japonicum, B. japonicum (USDA 6), B. elkanii, B. liaoningense, B. canariense, and B. yuanmingense.
Key words: Climate change, inoculation, nodulation, rhizobia