| Abstract | As agricultural production becomes more intensive, the capacity of soils to replace the nitrogen, which is removed during harvest, becomes limiting. For this reason, further increases in yield must be accompanied by the addition of nitrogen in a form suitable for use by crop plants. In recent years, an increasing reliance on nitrogen fertilizers has gone hand in hand with improvements in yield, and on a global basis we can antipate a continuing need to supplement soil nitrogen supplies (Hardy 1976).
Biological fixation of nitrogen by microorganisms provides an alternative approach to nitrogen incorporation into established crops of known nutritional value. Because fixation in legume-Rhizobium symbioses is capable of providing the total nitrogen requirements for growth, it is tempting to think that the energy and economic costs associated with fertilizer use can be eliminated in legumes, and perhaps even in other crops. Thus there is now considerable research effort directed to the study of symbiotic fixation in legumes, and an increasing interest in the biological energy requirements of nitrogen metabolism. |
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