Diazotrophic bacteria convert atmospheric nitrogen to plant-useable form and this input of nitrogen through biological fixation is of great agronomic importance. The contributions presented in this volume relate to free-living nitrogen fixers and the diazotrophs associated with plants. Symbiotic association of Frankia with non-legumes and cyanobacterial associations are also discussed. Research topics covered in this volume include the biochemistry and genetics of diazotrophs, recent developments in improvement of plant-microbe interactions and their molecular basis, the use of molecular probes in taxonomy and ecology of diazotrophs and reports on field applications, agronomic importance and improvement in methodologies for assessing their contribution to plants. This book provides valuable information not only for researchers working in the field of biological nitrogen fixation but also for biochemistry, molecular biologists, microbiologists and agronomists.

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 subsistence agriculture of the pre-chemical era efficiently sustained the nitrogen status of soils by maintaining a balance between N loss and N gain from biological nitrogen fixation (BNF): the microbial conversion of atmospheric N to a form usable by plants. This was possible with less intensive cropping, adaptation of rational crop rotations and intercropping schemes, and the use of legumes as green manure. Modern agriculture concentrates on maximum output, however, overlooking input efficiency; It is not sustainable. Intensive monocropping, with no or inadequate crop rotations or green manuring, together with the excessive use of chemical N fertilizers, results in an imbalance between N gain and N loss. The losses are often larger than the gains, and soil N status declines. The challenge is to sustain soil N fertility in many different tropical and temperate farming systems operating at high productivity levels. This requires judicious integration of BNF components, maintaining a good balance between N losses and gains. In this book, papers on BNF in crop forage and tree legumes are augmented with discussions of integrated farming systems involving BNF, soil and N management, and recycling of legume residues. BNF by non-legumes are discussed, and attempts to transform cereals into nodulating plants are critically reviewed. Advances in the development of novel methodologies to understand symbiotic relations and to assess N2 fixation in the field are described, and means are presented to enhance BNF through plant and soil management or breeding and selection. Problems encountered in exploiting BNF under field conditions are examined, as are promising approaches to improving BNFexploitation.

Rice is the major staple food in Asia, and food security means rice security for most Asians. By the year 2025, we need to produce about 60% more rice than we do today to meet the growing demand. Efficient use of inputs is vital to safely produce the additional food from limited resources with minimal impact on the environment. This book reviews emerging knowledge-intensive technologies and decision aids for improved nutrient management in rice, technology adoption constraints at the farm level, and innovative approaches for field evaluation and promotion of new technologies to farmers. It is highly useful to rice scientists and development workers, students of agronomy, soil science, and plant nutrition, and crop consultants and extension workers in rice all over the world.

Diazotrophic bacteria convert atmospheric nitrogen to plant-useable form and this input of nitrogen through biological fixation is of great agronomic importance. The contributions presented in this volume relate to free-living nitrogen fixers and the diazotrophs associated with plants. Symbiotic association of Frankia with non-legumes and cyanobacterial associations are also discussed. Research topics covered in this volume include the biochemistry and genetics of diazotrophs, recent developments in improvement of plant-microbe interactions and their molecular basis, the use of molecular probes in taxonomy and ecology of diazotrophs and reports on field applications, agronomic importance and improvement in methodologies for assessing their contribution to plants. This book provides valuable information not only for researchers working in the field of biological nitrogen fixation but also for biochemistry, molecular biologists, microbiologists and agronomists.

The key to sustaining the soil resource base is to maintain, or enhance, soil quality. Soil quality cannot be seen or measured directly from the soil alone but is inferred from soil characteristics and soil behavior under defined conditions. In essence, the quality of soils is analogous to the health of humans, and just as there is no single characteristic that can be measured to quantify a person's health, there is no single measurement that can quantify soil quality. However, there are certain characteristics, particularly when considered together, that are good indicators. Soil quality, just as human health, can be maintained or enhanced by good management practices; and seriously degraded-sometimes irrevers ibly-with poor practices. Soil quality is also important because it has direct and indirect effects on air quality and water quality. While the enhancement of soil quality does not always assure parallel improvements in the quality of air and, particularly, water resources, this is often the case. However, soil deg radation is invariably accompanied by degraded qualities of both air and water resources. The consensus among many scientists is that the greatest challenge is not increasing production, but preventing serious deterioration of the soil and water resource base so that the production level can be sustained."

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.

New frontiers of science offer exciting opportunities to stretch rice research horizons. Recent advances in understanding symbiotic Rhizobium-legume interactions at the molecular level, the discovery of endophytic interactions of nitrogen-fixing organisms with non-legumes and the ability to introduce new genes into rice through transformation have created an excellent opportunity to investigate the possibilities for incorporating N2 fixation capability in rice. During a think-tank workshop organized by IRRI in 1992, the participants reaffirmed that such opportunities do exist for cereals and recommended that rice be used as a model system. Subsequently, IRRI developed a New Frontier Project to coordinate the worldwide collaborative efforts among research centers committed to reducing dependency of rice on mineral N resources. An international Rice Biological Nitrogen Fixation (BNF) working group was established to review, share research results/materials, and to catalyze research. This volume contains the deliberations made at the second working group meeting, held 13-15 October, 1996 at the National Institute of Biotechnology and Genetic Engineering (NIBGE) in Faisalabad, Pakistan. The papers presented in the meeting deal with the recent findings on different approaches related to the establishment of endophytic association, development of N2-fixing nodules similar to legumes and transfer of nif genes to rice.

The Future Rice Strategy for India presents forward-looking insights toward achieving sustainable development of the rice sector, ensuring future food and nutritional security. As a staple food for many in India, including the economically disadvantaged, there are many concerns that affect the development of rice sector. Facing issues from environmental demands to economic stagnation, access to food, food inflation, and the Food Security Act (demand - supply - distribution of rice) achieving sustainability in production and exports is an important and urgent challenge. Using case studies to illustrate existing and potential issues, challenges and solutions, The Future Rice Strategy for India presents key strategic options while considering the implicit consequences. In addition, the findings enrich the strategy and policy formulation considerations for the role of rice in the country. This multidisciplinary approach features the expertise of rice scientists covering different aspects of rice sector; from breeding to consumer preferences and markets and trade.

The Future Rice Strategy for India presents forward-looking insights toward achieving sustainable development of the rice sector, ensuring future food and nutritional security. As a staple food for many in India, including the economically disadvantaged, there are many concerns that affect the development of rice sector. Facing issues from environmental demands to economic stagnation, access to food, food inflation, and the Food Security Act (demand - supply - distribution of rice) achieving sustainability in production and exports is an important and urgent challenge. Using case studies to illustrate existing and potential issues, challenges and solutions, The Future Rice Strategy for India presents key strategic options while considering the implicit consequences. In addition, the findings enrich the strategy and policy formulation considerations for the role of rice in the country. This multidisciplinary approach features the expertise of rice scientists covering different aspects of rice sector; from breeding to consumer preferences and markets and trade.

New frontiers of science offer exciting opportunities to stretch rice research horizons. Recent advances in understanding symbiotic Rhizobium-legume interactions at the molecular level, the discovery of endophytic interactions of nitrogen-fixing organisms with non-legumes and the ability to introduce new genes into rice through transformation have created an excellent opportunity to investigate the possibilities for incorporating N2 fixation capability in rice. During a think-tank workshop organized by IRRI in 1992, the participants reaffirmed that such opportunities do exist for cereals and recommended that rice be used as a model system. Subsequently, IRRI developed a New Frontier Project to coordinate the worldwide collaborative efforts among research centers committed to reducing dependency of rice on mineral N resources. An international Rice Biological Nitrogen Fixation (BNF) working group was established to review, share research results/materials, and to catalyze research. This volume contains the deliberations made at the second working group meeting, held 13-15 October, 1996 at the National Institute of Biotechnology and Genetic Engineering (NIBGE) in Faisalabad, Pakistan. The papers presented in the meeting deal with the recent findings on different approaches related to the establishment of endophytic association, development of N2-fixing nodules similar to legumes and transfer of nif genes to rice.