Contrasting Rhizobium inoculation requirements of zero-tannin faba bean and narrow-leafed lupin in western Canada

Lopetinsky, K. J., Lupwayi, N. Z., Olson, M. A., Akter, Z. and Clayton, G. W. 2014. Contrasting Rhizobium inoculation requirements of zero-tannin faba bean and narrow-leafed lupin in western Canada. Can. J. Plant Sci. 94: 1117–1123. Zero-tannin faba bean (Vicia faba minor) and narrow-leafed lupin (Lupinus angustifolius L.) have shown potential as new pulse crops in Alberta cropping systems, but their inoculation requirements to maximize biological N2 fixation (BNF) are unknown. We conducted a 6 site-year study to compare the effects of several commercial rhizobial inoculant products (eight for faba bean and three for lupin) in different formulations (granular, peat and liquid) on nodulation, N accumulation, grain yield and grain protein of the two crops. The liquid and peat formulations were applied to the seed, while the granular inoculant was applied to the soil. Inoculation had no significant effects on nodulation, grain yield and seed weight of faba bean in all site-years. Un-inoculated and inoculated plants nodulated equally well, suggesting the presence of adequate populations of effective indigenous Rhizobium leguminosarum bv. viciae for nodulation of untreated plants. The indingenous rhizobia could have originated from previous field pea (Pisum sativum L.) crops or leguminous native plants/weeds. By contrast, narrow-leafed lupin responded to inoculation in all site-years, and poor nodulation of un-inoculated plants indicated inadequate populations of indigenous R. lupini for nodulation in the soils. The seed-applied peat inoculant Nitragin Lupin and the soil-applied granular inoculant Soil Implant Lupin were equally effective in increasing nodulation relative to the un-inoculated control in 3 of 5 site-years (nodulation was not assessed in 1 site-year). However, relative to the un-inoculated control, Nitragin Lupin increased grain yields in 4 of 6 site-years compared with 1 of 5 for Soil Implant Lupin (and 2 of 6 for seed-applied TagTeam Lupin). These results show that faba bean probably does not require inoculation in these soils, although periodic checking is required to ensure that its high BNF potential is always realized, but narrow-leafed lupin needs to be inoculated with suitable inoculant products to increase BNF.