| dc.description.abstract | The economic and environmental costs of the heavy use of chemical N fertilizers in agriculture are a
global concern. Sustainability considerations mandate that alternatives to N fertilizers must be urgently
sought. Biological nitrogen fixation (BNF), a microbiological process which converts atmospheric
nitrogen into a plant-usable form, offers this alternative. Nitrogen-fixing systems offer an economically
attractive and ecologically sound means of reducing external inputs and improving internal resources.
Symbiotic systems such as that of legumes and Rhizobium can be a major source of N in most cropping
systems and that of Azolla and Anabaena can be of particular value to flooded rice crop. Nitrogen
fixation by associative and free-living microorganisms can also be important. However, scientific and
socio-cultural constraints limit the utilization of BNF systems in agriculture. While several environmental factors that affect BNF have been studied, uncertainties still remain on how organisms respond to a
given situation. In the case of legumes, ecological models that predict the likelihood and the magnitude
of response to rhizobia! inoculation are now becoming available. Molecular biology has made it possible
to introduce choice attributes into nitrogen-fixing organisms but limited knowledge on how they interact
with the environment makes it difficult to tailor organisms to order. The difficulty in detecting
introduced organisms in the field is still a major obstacle to assessing the success or failure of
inoculation. Production-level problems and socio-cultural factors also limit the integration of BNF
systems into actual farming situations. Maximum benefit can be realized only through analysis and
resolution of major constraints to BNF performance in the field and adoption and use of the technology
by farmers. | en_US |
