Novel aspects of nitrogen fixation

Only a fraction of the total agricultural need for nitrogen comes from natural or synthetic fertilizers. The remainder is satisfied largely through the biological fixation of atmospheric nitrogen. Whilst this is most efficiently effected by the Rhizobium-legume root nodule, free-living bacteria and blue-green algae are known to be capable of fixing appreciable amounts. Recently, attention has been focused on bacteria closely associated with roots of certain tropical grasses.