Cerrado a region of high agricultural potential that requires nitrogen; Potential for nitrogen fixation in tropical legumes and grasses; Free-living bacteria; Nitrogen fixation by soil algae of temperate and tropical soils; Contribution of the legume-Rhizobium symbiosis to the ecosystem and food production; Plant influence in symbiotic nitrogen fixation; Plant photosynthesis; Interactions of plant photosynthesis with dinitrogen fixation and nitrate assimilation; Some aspects of the Alnus-type root nodule symbiosis; Legumes and acid soils; Micronutrient requirements of legume-Rhizobium symbiosis in the tropics; Ecology of legume-Rhizobium symbiosis; Nitrogenase systems; Relationship between hydrogen metabolism and nitrogen fixation in legumes; Ammonia assimilation in N2-Fixing systems; Genetics and regulation of nitrogen fixation; Leghaemoglobin, oxygen supply and nitrogen fixation: studies with soybean nodules; Nitrogen fixation by Rhizobium spp. in laboratory culture media; Limiting factors in grass nitrogen fixation; Physiology and biochemistry of Spirillum lipoferum; Taxonomy of the root-associated nitrogen fixing bacterium Spirillum lipoferum; Abstracts of original papers; Abstracts of posters.

The 15th Latin American Symposium ''laS held in Brasilia (FD) on J1UY 18-22, 1977, on a topic of great interest for agriculture, especially in the tropics. Many new developments have taken place in the field of research in N2 fixation during the last few years. They "Tere made possible by the improved methods of measuring of nitrogenase activity, progress in genetic engineering fields and the increased interest in taking advantage of natural sources for biological nitrogen fixation. The approach used in this Symposium together with the one held four months earlier in Brookhaven on ;'Genetic Engineering for Nitrogen Fixation" gives an interesting picture of the present status of nitrogen fixation from two diverse approaches. This is my 20th year visiting Latin i'-J11.erica. I am most impressed with the tremendous development which has taken place during these years in Latin American science. I want to congrat ulate our Brazilian colleagues for arranging this excellent and timely symposium and its excellent organization. These symposia are a cooperative effort between our Latin colleagues and scientists allover the world. They are made possible by excellent local support and support by a number of international agencies and several groups in the United States. Earlier symposia in this series are listed on pp. viii-x. Alexander Hollaender vii viii PREFACE I. International Symposium on Tissue Transplantation--Santiago, Vifia del Mar, and Valparaiso, Chile. Published in 1962 by the University of Chile Press, Santiago; edited by A. P. Cristoffanini and Gustavo Hoecker; 269 pp.

Keynote addresses. Plant factors affecting N2 fixation. Technology for inoculant production. Environmental factors affecting symbiotic n2 fixation. Inoculation trials. N2 fixation in grain legumes. N2 fixation in pasture legume. N2 fixation in trees. Associative n2 fixation. The azolla/ananaena association. Critique of methodologies. The nitrogen relationships of maize/bean associations. Assessing the nitrogen contribuktion of cowpea (Vigna unguiculata) in monoculture and intercroped. Nitrogen fixation by groundnut (Arachis hypogeae) in intercropped and rotational systems. Effect of cowpeas in cereal rotations in conditions in Upper volta. Residual effects of pigeopea (Cajanus cajan). Atechology assessment of biological nitrogen fixation. Economic analysis of biological nitrogen fixation. Research and development for biological nitrogen fixation in India. The brazilian program in biological nitrogen fixation. Internationally sponsored development of biological nitrogen fixation technology. Research on biological nitrogen fixation in the international agricultural research centers.