Chemical fertilizers have had a significant impact on food production in the recent past, and are today an indispensable part of modern agriculture. On the other hand, the oil crisis of the 1970s and the current Middle East problems are constant reminders of the vulnerability of our fossil fuel dependent agriculture. There are vast areas of the developing world where N fertilizers are neither available nor affordable and, in most of these countries, balance of payment problems have resulted in the removal of N fertilizer subsidies. The external costs of environmental degradation and human health far exceed economic concerns. Input efficiency of N fertilizer is one of the lowest and, in turn, contributes substantially to environmental pollution. Nitrate in ground and surface waters and the threat to the stability of the ozone layer from gaseous oxides of nitrogen are major health and environmental concerns. The removal of large quantities of crop produce from the land also depletes soil of its native N reserves. Another concern is the decline in crop yields under continuous use of N fertilizers. These economic, environmental and production considerations dictate that biological alternatives which can augment, and in some cases replace, N fertilizers must be exploited. Long-term sustainability of agricultural systems must rely on the use and effective management of internal resources. The process of biological nitrogen fixation offers and economically attractive and ecologically sound means of reducing external nitrogen input and improving the quality and quantity of internal resources. In this book, we outline sustainability issues that dictate an increased use of biological nitrogen fixation and the constraints on its optimal use in agriculture.

The 14th International Nitrogen Fixation Congress was held in Beijing, China from October 27th through November 1st, 2004. This volume constitutes the proceedings of the Congress and represents a compilation of the presentations by scientists from more than 30 countries around the World who came to Beijing to discuss the progress made since the last Congress and to exchange ideas and information. This year marked the 30th anniversary of the first Congress held in Pullman, Washington, USA, in 1974. Since then, this series of Congresses has met five times in North America (three in the United States and once each in Canada and Mexico), once in South America (Brazil), four times in Western Europe (once each in Spain, The Netherlands, Germany and France), once in Eastern Europe (Russia), and once in Australia; and now for the first time in Asia. China was a most appropriate choice because China is a big country with the largest population in the World, about 1. 3 billion people, which is about 22% of the World’s population. It is traditionally an agricultural country, even though China has only 7% of the available farming land. This situation explains why agriculture and its productivity are major issues for the Chinese people, its government and the scientists in the field.

Structural chemistry and biochemistry of nitrogenase; Signal perception, transduction and cell cycle genes in nodulation; Plant genes involved in nodulation; Bacterium - plant surface interaction; Molecular microbial ecology; Nitrogen fixation systems; Nitrogen fixation in sustainable agriculture; Carbon-nitrogen metabolism in symbiotic systems; Oxygen regulation in nitrogen fixation; Model plants for nitrogen fixation and legume genetics; Coevolution of symbiotic systems.

This book covers the most recent advances in all the topics with which researchers and professionals need to be familiar in order to obtain a better understanding of, and to better exploit, beneficial plant-microbe interactions. The use of microorganisms for agriculture and environmental applications is gaining importance worldwide to improve crop performance, but also for other environmental applications, such as bioremediation in chemically polluted soils. The search for an equilibrium between fundamental and applied aspects makes this book useful for professionals at various levels in the value chain of the “microbial biofertilizers”. Challenges of comercializing biofertilizers involve efficiency of the products and safety for human health and the environment, topics that have paid central attention in this book. Students, scientists and biofertilizers developers will find updated and comprehensive information about the different aspects to be considered to address a successful introduction of biofertilizers in sustainable agriculture and environmental actions.

Biological nitrogen fixation in tropical agrosystems: twenty years of biological nitrogen fixation research in Africa; Sustainable agriculture: definition and measurement; Biological nitrogen fixation systems in tropical ecosystems: an overview; A protocol for screening legumes as soil-improving crops; The sustenance of tropical agriculture with multipurpose azolla; Facteurs pedoclimatiques limitant la lixation biologique l'azole; Response of some tropical nitrogen-fixing woody legumes to drought and inoculation with mycorrhiza; Improvement to the Phaseolus/Rhizobium symbiosis, with particular reference to the Caribbean region; Effect of pest management systems on biological nitrogen fixation; Agronomic evaluation of a rock phosphate as a phosphorus source for Leucaena leucocephala grown on an utisol; Nodulation of soybean grown under field conditions and inoculated with Bradyrhizobium japonicum strains; Effect of fertilization and Rhizobium inoculation on the growth of Leucaena and Gliricidia on an alfisol in south-western Nigeria; Early growth and nodulation in Leucaena and Gliricidia and the effects or pruning on biomass productivity; Comparative stude on the growth and productivity of Sesbania and Leucaena in the Central Plateau region, Rwanda; Supernoculation and non-nodulation mutants of soybean; Genetically improved rhizobia and their use in agriculture; Sustainability of nitrogen-fixing cropping systems: Nodulation and nitrogen fixation and transfer in a cowpea/rice cropping system; The role of legumes in sustaiing soil productivity and controlling soil erosion; Fitting soil-improving legumes into inland valley rice-baes cropping systems in West Africa; Herbage yield and soil fertility restoration potential of some tropical forage legumes.

Sustainability has a major part to play in the global challenge of continued development of regions, countries, and continents all around the World and biological nitrogen fixation has a key role in this process. This volume begins with chapters specifically addressing crops of major global importance, such as soybeans, rice, and sugar cane. It continues with a second important focus, agroforestry, and describes the use and promise of both legume trees with their rhizobial symbionts and other nitrogen-fixing trees with their actinorhizal colonization. An over-arching theme of all chapters is the interaction of the plants and trees with microbes and this theme allows other aspects of soil microbiology, such as interactions with arbuscular mycorrhizal fungi and the impact of soil-stress factors on biological nitrogen fixation, to be addressed. Furthermore, a link to basic science occurs through the inclusion of chapters describing the biogeochemically important nitrogen cycle and its key relationships among nitrogen fixation, nitrification, and denitrification. The volume then provides an up-to-date view of the production of microbial inocula, especially those for legume crops.

Phylogenetic classification of nitrogen-fixing organisms. Physiology of nitrogen fixation in free-living heterotrophs. Nitrogen fixation by photosynthetic bacteria. Nitrogen fixation in cyanobacteria. Nitrogen fixation by methanogenic bacteria. Associative nitrogen-fixing bacteria. Actinorhizal symbioses. Ecology of bradyrhizobium and rhizobium. The rhizobium infection process. Physiology of nitrogen-fixing legume nodules: compartments, and functions. Hydrogen cycling in symbiotic bacteria. Evolution of nitrogen-fixing symbioses. The rhizobium symbiosis of the nonlegume parasponia. Genetic analysis of rhizobium nodulation. Nodulins in root nodule development. Plant genetics of symbiotic nitrogen fixation. Molecular genetics of bradyrhizobium symbioses. The enzymology of molybdenum-dependent nitrogen fixation. Alternative nitrogen fixation systems. Biochemical genetics of nitrogenase. Regulation of nitrogen fixation genes in free-living and symbiotic bacteria. Isolated iron-molybdenum cofactor of nitrogenase.