FUTURE BENEFITS FROM BIOLOGICAL NITROGEN-FIXATION - AN ECOLOGICAL APPROACH TO AGRICULTURE

Strategies for the enhancement and exploitation of biological nitrogen fixation are assessed with attention to the likely timescales for rea lization of benefits in agriculture, Benefits arising from breeding of legumes for N-2-fixation and rhizobial strain selection have less pot ential to increase inputs of fixed N than alleviation of environmental stresses or changes in farming systems to include more legumes. Genet ic engineering may result in substantial enhancement of N-2-fixation, particularly if the ability to fix N-2 is transferred to other crops b ut these are long-term goals. Immediate dramatic enhancements in input s from N-2-fixation are possible simply by implementation of existing technical knowledge. Apart from the unfortunate political and economic barriers to the use of agricultural inputs, better communication betw een researchers and farmers is required to ensure proper focus of rese arch and development of appropriate technologies. Legumes must be cons idered within the context of the farming systems within which they are grown and not in isolation. Proper integration of legumes requires a good understanding of the role of the legume within the system and a b etter understanding of the relative contributions of N sources and of the fates of fixed N.