Although dry bean (Phaseolus vulgaris L.) is a legume capable of fixing nitrogen, fertilizer N is usually recommended for its production in Canada because it is believed to be an inefficient N fixer. Using genotypes with high N use efficiency (NUE) would reduce the amount of applied N, which usually has deleterious environmental effects. We evaluated 22 bean genotypes for N uptake efficiency (NUpE) in a greenhouse trial and 16 genotypes for N use efficiency (NUE) and its components: NUpE and N utilization efficiency (NUtE) in two seasons (2012 and 2013) of a field trial at 30 kg N ha −1 (30N) and 100 kg N ha −1 (100N) soil levels. Root biomass and surface area were highly correlated with NUpE in the greenhouse, where NUpE at 100N was 48% lower than that at 30N. In the field trial, grain yield was highly correlated with NUpE and NUtE at both 30N and 100N. The NUpE at 100N was 65% lower than that at 30N, and NUE at 100N was 68% lower than that at 30N. The low NUE at 100N in the field trial was mainly due to the difference in NUpE. This study also identified nine genotypes, including five germplasm lines (PI 136692, GH-196, UNS-117, UI-239, and LEF2RB) and four cultivars (Othello, Viva, AC Redbond, and Island), that were both N-efficient (at 30N) and N-responsive (to 100N).

Dry bean (Phaseolus vulgaris L.) is usually considered to be poor at biological nitrogen fixation (BNF), but large variations in this trait have been observed among bean genotypes. We evaluated 16 bean genotypes for N2 fixation ability in four N treatments: (i) uninoculated in low-N soil (30 kg N ha−1), (ii) inoculated with commercial Rhizobium leguminosarum bv. phaseoli inoculant Nitrastik-D® in low-N soil, (iii) inoculated with commercial R. leguminosarum bv. phaseoli inoculant Nodulator® in low-N soil, and (iv) uninoculated in high-N soil (100 kg N ha−1). There were differences between genotypes in all the plant parameters that were measured, but only nodulation was affected by N treatment. The 100 kg N ha−1 treatment suppressed nodulation. Seven genotypes nodulated well with either inoculant, two genotypes nodulated better with Nitrastik-D than with Nodulator, three nodulated better with Nodulator than with Nitrastik-D, and four nodulated poorly with either inoculant. Cultivars AC Redbond, Island, and Resolute, all currently commercially grown, did not fix much N2 at flowering (4–8 kg N ha−1) or maturity (19–34 kg N ha−1). By contrast, germplasm lines PI 136692 (red bean), GH-196 (pinto bean), and LEF2RB (carioca bean) had high BNF capability at flowering (10–11 kg N ha−1) and especially at maturity (60–72 kg N ha−1), in addition to high seed yield (2778–2897 kg ha−1), indicating their superior ability to support both of these economically important traits throughout plant growth. These three genotypes would be valuable to breeders for the genetic improvement of BNF in dry bean cultivars.

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