Fig. 1 Profiles of specific nodule activity for crown nodules of the soybean cultivars Alpha, Chippewa, Hardin, and Hodgson 78 from 10 to 66 d after emergence following inoculation with Bradyrhizobium japonicum strain UMR161. Nodule activity is measured as acetylene reduction to ethylene. Each point is the mean of three replicates, with vertical bars representing ± standard error