03173naa a2200157 a 450000100080000000500110000800800410001910000160006024500760007626000090015230000140016150000370017552026400021270000170285277301460286914659272005-11-21       2003    bl uuuu     u00u1 u    #d1 aHUNGRIA, M.  aMicrobial inoculants in agriculturebresearch and use in South America.  c2003  c1 CD-ROM.  aSeção: Microbiologia de Solos.  aThe use of microbial inoculants dates back to ancient times, with the practice of transferring soil from a field where legumes have been grown to new areas being planted to the same crop. An increased application followed after Hellriegel´s report on the N nutrition of leguminous plants in 1886, and with the first studies with Rhizobium. After over a century of rhizobial inoculation, great advances have been achieved in the research and use of rhizobia such that today it is possible to obtain inoculants with high rhizobial counts, free of contaminants, and with a longer shelf life. Alternative carriers and technologies of inoculation have also been identified. Used appropriately, inoculants can be important to agricultural sustainability, particularly in those countries where leguminous plants play a key role in the economy, as in South America. The best example is the soybean (Glycine max L. Merr.) cropping in Brazil, that has been very markedly affected by a research and extension effort focused on N2 fixation. Studies about the symbiosis with Bradyrhizobium japonicum and B. elkanii have traditionally been favored and there has been a consistent and marked effort to select the most efficient inoculant strains and agronomic technologies compatible with the inoculation. The result is that quantification experiments performed in Brazil have shown that the crop derives 69 to 94% of their N needs from symbiosis, with more than 50% of farmers practicing inoculation and reinoculation, resulting in the use of 14 million doses of inoculants in 2002/03. High rates of N2 fixation have also been reported for the soybean crop in Argentina, Paraguay, Bolivia and Uruguay. In contrast, in the USA, Canada and Australia the percentage of N derived from fixation is estimated in about 50% and only 15% of farmers inoculate soybean. For the common bean (Phaseolus vulgaris L.), an efficient strain of Rhizobium tropici has been recently identified and proven to consistently improve yield in Brazilian soils poor on N. However, further improvements in the strain selection for leguminous grain crops, pastures and trees, as well as in the inoculant production and quality control are needed, added to an improvement in the transference of technology to the farmers. There is also an increasing interest in the use of other microbial inoculants, as with Azospirillum and Herbaspirillum, plant-growth promoting bacteria as Pseudomonas and Bacillus, the use of Azolla-Anabaena in rice crops, among others. The studies with microbial inoculants may ensure high yields and profits, while land quality is maintained or improved.1 aCAMPO, R. J.  tIn: CONGRESSO BRASILEIRO DE MICROBIOLOGIA, 22., 2003, Florianópolis. [Resumos]. Florianópolis: Sociedade Brasileira de Microbiologia, 2003.