Abstract
In a Western Nigerian soil low in available N, soybean nodulation by indigenous rhizobia was much better on the Indonesian cultivar Orba than on the American-bred cultivars TGm 80 (Bossier) and TGm 294-4. The American cultivars responded to 12 inoculation treatments with significant improvements in nodulation, shoot growth, N content and seed yield. The responses of the Indonesian cultivar varied with the rhizobial strain; some strains significantly improved nodulation, acetylene reduction activity and/or shoot growth, but only one increased seed yield. After a two-year fallow, uninoculated soybeans were replanted in the same plots. Serological typing of the nodules of TGm 80 and TGm 294-4 revealed a high frequency of occupancy by inoculant rhizobia demonstrating their survival in the soil without the host legume. However, nodulation was reduced after the fallow and seed yields of TGm 80 and TGm 294-4 were not consistently higher in previously inoculated plots, indicating a need to inoculate American soybeans at yearly intervals.
