Nitrogen fixation in breeding lines of Phaseolus vulgaris L.

Nitrogen fixation in nine common bean (Phaseolus vulgaris L.) lines was estimated using the 15N isotope dilution method at two locations in two seasons. In the first season at one location no N2 fixation was detected while in the second season up to 51 kg N ha?1 were estimated. There were significant differences between lines and correlations between trials were significant for the amounts of N2 fixed, but not for total shoot nitrogen. The plants that fixed the most nitrogen nodulated rapidly after germination. Differences in maximum nodule mass, but not specific nodule activity, were detected also.