Pea green manure management affects organic winter wheat yield and quality in semiarid Montana

Miller, P. R., Lighthiser, E. J., Jones, C. A., Holmes, J. A., Rick, T. L. and Wraith, J. M. 2011. Pea green manure management affects organic winter wheat yield and quality in semiarid Montana. Can. J. Plant Sci. 91: 497-508. Organic farmers in semiarid Montana desire green manures that supply sufficient soil nitrate-N (NO3-N) to subsequent crops with minimal soil water depletion. Spring and winter pea (Pisum sativum L.) green manures were compared at the bloom and pod stages for soil NO3-N contribution and water use, and subsequent winter wheat (Triticum aestivum L.) grain yield and quality in a long-term organic farm in northern Montana. Winter wheat was managed with three additional variables (cultivar, row spacing, and seeding rate). Winter pea had 15-33 kg ha-1 greater shoot N content (at pod stage only), contributed 14-20 kg ha-1 greater soil NO3-N, used 26-31 mm less soil water, and increased winter wheat grain yield by 13-39% and protein by 1.5 percentage units (2007 only), compared with spring pea. Pea green manure type was of primary importance, pea manure termination timing and wheat cultivar generally were of secondary importance, and row spacing and seeding rate were relatively unimportant to wheat yield and quality. Although wheat yield and quality were superior following winter pea green manure in this study, grain protein concentrations were inadequate to meet organic milling industry standards following both green manure types. This suggests that a long-term organic farmer in semiarid northern Montana may not solely rely upon annual legume green manures to sufficiently condition soil NO3-N for milling wheat production.