Assessment of different inoculants of Bradyrhizobium japonicum on nodulation, potential N 2 fixation and yield performance of soybean ( Glycine max L.)

1 SUMMARY To identify the most efficient bradyrhizobium strain for promoting soybean performance, a study was conducted in a growth chamber to assess five different inoculants and N fertilization. Soybean ( Glycine max cv. Jutro) was subjected to inoculation with five bradyrhizobium strains viz DSM 1755, DSM 30131, DSM 1982, the multistrain DSM-MIX, a commercial peat inoculant, and to fertilization at 50 mg N kg -1 soil with Ca(N0 3)2, in a completely randomized design with four replicates. At 81 days after sowing, soybean was harvested and assessed for its yield, and N 2 fixation determined by N-difference method using wheat as reference crop. Dry matter, N and grain yield, nodulation and N 2 fixation in N-fertilized soybean were lowest compared to any bradyrhizobium inoculations although these latter differed. The commercial peat inoculant performed significantly better than N fertilization with 20% and 260% increase in the rate and amount of N 2 fixed respectively. Bradyrhizobium strains DSM 1755, DSM-MIX, and DSM 30131 are preferable to the commercial inoculant. Fertilization with 50 mg N kg -1 soil was deleterious to soybean, while combining 10 mg N kg -1 soil as N starter and bradyrhizobium strain inoculation significantly improved its yields, nodulation et N 2 fixation. This practice deserves recommendation for soybean growing.

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