ABSTRACT
Biological nitrogen fixation is one of the most important processes for the maintenance of life on earth as it contributes about 70 per cent of all nitrogen required by natural and agricultural ecosystems (Burns and Hardy, 1975), and is environmentally friendly. Inoculation with NFLNB strains that are highly efficient and adapted to prevailing environmental conditions, to replace chemical N fertilizers, is currently practised in some countries for a small selection of legume crop species. In Brazil, inoculation with Bradyrhizobium strains completely replaces application of chemical fertilizers for soybean. In 2006, with a soybean yield of 57 million megagrams (Mg), about US$3.3 billion in fertilizer expenses were saved because of this biotechnology. Inoculant strains are sourced from a diversity of strains present in the soil. At the same time soil biodiversity may affect the nodulation behaviour positively or negatively, due to the complex and multiple interactions among soil organisms, and between soil organisms and plants. Thus, the knowledge of NFLNB diversity in the soil environment is the first step in the management and conservation of this valuable genetic resource.
