Influence of pea cultivar and inoculation on the nitrogen budget of a pea-wheat rotation in northwestern Canada

Three field experiments were conducted in northwestern Alberta to assess the influence of pea (Pisum sativum L.) cultivars on the N economy and the performance of the sequent wheat (Triticum aestivum L.) crop. Three pea varieties and two levels of Rhizobium inoculant (none and 5 kg ha), in factorial combination, were tested at each site; overall, four pea cultivars were tested with barley (Hordeum vulgare L.) as the check. All plots were seeded to wheat in the second year. All but one experimental year had below-average growing season rainfall. Dinitrogen fixation decreased in the following order among pea cultivars: Grande > Carerra >= Eiffel >= Swing, the same order as net productivity: the correlation between fixed N and shoot dry matter at harvest was highly significant (R-2 = 0.982; P < 0.001). Only Grande pea resulted in balanced soil N (exported N = fixed N); the deficit in the N balance, in kg N ha(-1), was 7-38 for Carrera, 20-37 for Swing and 18-37 for Eiffel. However, even where the soil N balance was negative, wheat following pea mostly had higher seed protein content and yield than wheat following barley due to a high correlation between the yield of the sequent wheat and pea-fixed N. Rhizobium inoculation increased nodule formation and N-2 fixation in only one of the experiments; however, it did not affect the yield of the sequent wheat as compared with uninoculated soil. We conclude that selection of a high net productivity pea cultivar should typically result in greater N and yield benefits to the sequent cereal crop than a low net productivity cultivar.