Management of biological nitrogen fixation for the development of more productive and sustainable agricultural systems: extended versions of papers presented at the Symposium on Biological Nitrogen Fixation for Sustainable Agriculture at the 15th Congress of Soil Science, Acapulco, Mexico, 1994 - Ladha, J. K.; Peoples, M. B.; LADHA, J; PEOPLES, M (Developments in plant and soil sciences, 1995)