Optimized biological nitrogen fixation (BNF) in pea (Pisum sativum L.) could increase crop productivity and reduce nitrogen (N) fertilizer use in western Canada. We tested the BNF capabilities and growth of three pea nodulation mutants [Frisson P64 Sym29, Frisson P88 Sym28, and Rondo-nod3 (fix )] compared with check cultivars [CDC Dakota, CDC Meadow, Frisson, Rondo, and non-fixing negative control Frisson P56 (nod–)] under field conditions in Saskatchewan, Canada, in three environments. CDC Meadow and CDC Dakota produced greater dry biomass and seed yield but less fixed N compared with the mutants. On average, Frisson P88 Sym29 fixed 19% and 31% more N per plot compared with CDC Dakota and CDC Meadow, respectively. Rondo-nod3 (fix ) fixed 12% and 23% more N per plot compared with CDC Dakota and CDC Meadow, respectively. All lines grown at Saskatoon in 2015 had longer time to flowering, greater biomass, and greater grain yield but less amounts of N fixation compared with these lines grown at Saskatoon in 2014 or Floral in 2015. Compared with the commercial checks, Frisson P88 Sym29 and Rondo-nod3 (fix ) had a high percent N derived from the atmosphere and good nodulation under relatively high soil available N content, while requiring at least one week shorter growing period to reach maturity, indicating that these mutants have potential as parents in breeding for improved BNF in pea.