Adequate nitrogen fertilization is needed to obtain maximum crop yields. Without sufficient nitrogen available to the plant, other inputs are wasted. There are great differences between developed and develop ing areas of the world with regard to nitrogen-fertilizer production and application, resulting in serious food deficits in some of the most needy areas. Although nitrogen fertilizer is an inexpensive input in comparison to the resulting yield increases, chemical fertilizers must be purchased and do represent a direct cash outlay, sometimes the only cash require ment for the peasant farmer, often an insurmountable obstacle in subsistence farming situations. If present economic trends continue, poor farmers may find it increasingly more difficult to pay for nitrogen fertilizers. Biological nitrogen fixation offers the most promising alternative or supplement to chemical nitrogen fertilizers. Furthermore, nitrogen fixation does not present any hazard to the environment which may be the case with excessive application of chemical nitrogen fertilizers. It is there fore of utmost importance to promote the use of nitrogen fixing crops, especially grain legumes which are also an important source of dietary protein. Although legumes only account for some 9% of the combined world dry matter yield of cereals and legumes, they con stitute as much as 24% of the total protein yield of these crops because of the high protein content in legumes.

Incorporating contributions from microbiologists, molecular biologists, plant breeders and soil scientists this volume reports the results and recommendations of an FAO/IAEA meeting of twelve experts on biological nitrogen fixation. This volume will be invaluable to scientists working on nitrogen fixation, soil microbiology, agronomy and crop production as well as farm advisers and extension specialists.
Maximising the Use of Biological Nitrogen Fixation in Agriculture is unique in that it:

-reviews the latest thinking on various aspects of biological nitrogen fixation technology and applications;
-reviews the possibilities in enhancing nitrogen fixation in various cropping systems;
-shows ways how biological nitrogen fixation can be used to enhance crop production;
-considers the applicability of these technologies to small farmers in developing countries.

Grain legume crops, e.g. common bean (Phaseolus vulgaris L.), and soyabeans (Glycine max L.) are amongst the main sources of protein in Africa, Asia and Latin America. Their high protein content derive from their ability, in symbiosis with Rhizobium bacteria, to fix atmospheric nitrogen. Incorporating contributions from molecular biologists, microbiologists, plant breeders and soil scientists, this volume reports the results of an FAO/IAEA Co-ordinated Research Programme (1992-1996), whose main objective was to develop molecular biological methods to study rhizobial ecology. Use of better tracking methods will help enhance biological nitrogen fixation and thus grain legume yields, while reducing their reliance on soil- and/or fertilizer-nitrogen. This volume will be invaluable to scientists working on biological nitrogen fixation, soil microbial ecology and legume production.