Symbiotic Nitrogen Fixation of Black and Navy Bean under Organic Production Systems

CORE IDEAS: Symbiotic nitrogen fixation of dry bean was evaluated under organic production systems. Lower performance in organic production systems resulted from inadequate levels of N fertility. Improving symbiotic nitrogen fixation of dry bean should contribute to improved performance in these systems. Greenhouse screening for biomass provided an indirect, cost effective method to select for improved symbiotic nitrogen fixation. Michigan is a leader in organic dry bean (Phaseolus vulgaris L.) production but previous research has shown that dry bean yields in Michigan were substantially lower under organic conditions compared to conventional production. Since pests are generally well controlled in both systems, fertility appears to be an issue where the two systems may differ. For organic dry bean production, fertility is managed through crop rotation, cover crops, and addition of composts and manures instead of the application of synthetically produced fertilizers. Symbiotic nitrogen fixation (SNF) may also be important for ensuring adequate dry bean yields when external N sources are limiting. Seventy‐nine black and navy bean elite breeding lines, including six commercial cultivars, and a non‐nodulating check were evaluated for yield, and SNF characteristics under organic field conditions in Frankenmuth, Caro, and Wisner, MI, in 2011 through 2013. These same genotypes were also assayed for SNF, nodulation characteristics, shoot and root growth in the greenhouse under N free conditions. Several traits measured in the greenhouse were significantly correlated to traits measured in the field. In particular, percent nitrogen derived from the atmosphere (%Ndfa) in the greenhouse was correlated with seed yield, N yield, and seed %Ndfa in the field in most site‐years. Measuring N in seed or plant tissue may not be necessary to estimate SNF characteristics when plants are grown under limited N fertility as the biomass difference from the greenhouse experiment was significantly correlated with seed yield and N yield grown under organic conditions in the field.