Variability of nodulation and dinitrogen fixation capacity among soybean cultivars

In order to identify soybean cultivars with higher biological N-2 fixation capacities, North American and Brazilian soybean [Glycine max (L.) Merrill] cultivars, belonging to maturity groups VI-VIII, were evaluated for nodula tion parameters and N-2 fixation rates. The symbiotic performance of 152 cu ltivars was evaluated in pots containing 4 kg soil with an established popu lation of the three Bradyrhizobium elkanii strains [29w (SEMIA 5019):SEMIA 566:SEMIA 587, 22%:36%:34%] which are established in most Brazilian soils c ultivated with soybean. Differences were verified among cultivars, with som e accumulating up to twice as much nodule dry weight and N in tissues as ot hers. The variability among cultivars was also confirmed when six of them w ere used in a field experiment, resulting in differences in nodulation, yie ld and total N accumulated in grains. The analysis of nodule occupancy in 1 2 cultivars grown either under sterile conditions and receiving a double in oculum and N-free nutrient solution, or in pots containing soil with an est ablished population of bradyrhizobia, showed the preference of cultivars fo r specific strains.