SCREENING TECHNIQUES AND IMPROVED BIOLOGICAL NITROGEN-FIXATION IN COOL-SEASON FOOD LEGUMES

Dinitrogen fixation and legume productivity are greatly influenced thr ough the interactions of legume host, Rhizobium, and the above- and be low-ground environment. The benefits of improving legume N-2 fixation include reduced reliance on soil N, leading to more sustainable agricu ltural systems and reduced requirements for fertilizer N, enhanced res idual benefits to subsequent crops, and increased legume crop yields. Most of the gains in N-2 fixation to date have been derived from manag ement of legume cropping systems and through inoculation of legume see d with competitive and symbiotically effective rhizobia. Further gains are possible by developing plant cultivars with tolerance to soil abi otic factors, increased plant yield, and a broader and more effective matching of plant host and rhizobia. Techniques for screening material for superior N-2 fixation and examples of programs to increase fixed N, with attention to the major abiotic stresses, are discussed.