Nodulation and biological nitrogen fixation of 80 soybean cultivars in symbiosis with indigenous rhizobia

Eighty soybean cultivars were assessed for their potential for nodulation and nitrogen fixation with indigenous rhizobia in a Nigerian soil. Seventy-six days after planting (DAP) 87%, 3% and 10% of the soybean cultivars had from 0 to 30, 31 to 60 and over 61 nodules/plant, respectively. Only 8% had a nodule dry weight of 600 to 1100 mg/plant. At 84 DAP the proportion of nitrogen derived from the atmosphere (Ndfa) ranged from 0 to 65% 16% of the cultivars derived 51 to 65% of their N₂ from the atmosphere. The diversity of soybean germplasm and the variation in nodulation and N₂ fixation permitted the selection of the five best cultivars in terms of their compatibility with indigenous rhizobia, % Ndfa and the amount of N₂ which they fixed.