Biological N2-Fixation, Nodulation and N Accumulation in Pulse Crops on the Canadian Prairie.

Pulses play a significant role in nitrogen cycling because they fix atmospheric N₂ through biological nitrogen fixation (BNF). BNF efficiency is reported to vary among pulse species, cultivars, and environments, but information relevant to the Canadian prairie is scarce. We conducted a 3-year field study and quantified the ability of BNF and related traits, and determined the effect of BNF on crop yield in chickpea (Cicer arietinum L.), dry bean (Phaseolus vulgaris L.), faba bean (Vicia faba L.), dry pea (Pisum sativum L.), and lentil (Lens culinaris Medik.). BNF varied with the growing season, being greater in the wetter 2010 than in the drier 2009. In 2010, faba bean and chickpea fixed as much as 106 kg N ha^-1, followed by lentil and pea with 87 and 69 kg N ha^-1 respectively, and dry bean, the poorest N fixer, with 12 kg N ha^-1. Across years, pea had the most stable BNF ability and seed yield. There are large differences in BNF and yield among cultivars within a species and the magnitude of the difference varied with years. All pulses except dry bean had a higher number of nodules at early flowering in 2010 with faba bean having the highest nodule number, followed by pea and chickpea. At late flowering, chickpea had the highest number of nodules in 2008 (36.7 plant^-1). Nodule weight of chickpea, field pea and lentil was higher at late than early flowering in both years. Both seed and straw N accumulation varied with years and were highest in 2010. Large genetic variability in BNF, N accumulation and yield suggest the possibility that pulse cultivars with a higher N₂-fixing ability and seed yield can be developed through selection of the N₂-fixing traits.