Cobalt application markedly increased the growth of and nitrogen concentrations in tops of Lupinus angustifolius irrespective of inoculation with an effective strain of Rhizobium. Cobalt-deficient plants produced a greater weight of lateral nodules and total nodule weight than cobalt-adequate plants. Cobalt-sufficient plants produced more crown nodule weight than cobalt-deficient plants.
Cobalt concentrations were higher in roots and nodules than in tops irrespective of cobalt application. In plant tops cobalt concentrations in young leaves were considerably lower than those in old leaves at both cobalt levels. Cobalt concentrations and contents increased in old leaves throughout the experiment.
Under cobalt deficiency cobalt appeared to be preferentially distributed to nodules. Six weeks after sowing cobalt contents of nodules of cobalt-deficient plants were similar to those in whole tops. By contrast at this time cobalt contents of nodules of cobalt-adequate plants were only approximately one-third those of whole tops.