02301naa a2200229 a 450000100080000000500110000800800410001910000160006024501540007626000090023052015950023965000100183465000220184465000120186665000290187865000290190765000230193665000140195970000170197370000180199077300630200815687492005-04-18       2003    bl uuuu     u00u1 u    #d1 aHUNGRIA, M.  aBenefits of inoculation of the common bean (Phaseolus vulgaris) crop with efficient and competitive Rhizobium tropici strains.h[electronic resource]  c2003  aCropping in low fertility soils, especially those poor in N, contributes greatly to the low common bean (Phaseolus vulgaris L.) yield, and therefore the benefits of biological nitrogen fixation must be intensively explored to increase yields at a low cost. Six field experiments were performed in oxisols of Paraná State, southern Brazil, with a high population of indigenous common bean rhizobia, estimated at a minimum of 10 e3 cells g e-1 soil. Despite the high population, inoculation allowed an increase in rhizobial population and in nodule occupancy, and further increases were obtained with reinoculation in the following seasons. Thus, considering the treatments inoculated with the most effective strains (H 12, H 20, PRF 81 and CIAT 899) nodule occupancy increased from an average of 28% in the first experiment to 56% after four inoculation procedures. The establishment of the selected strains increased  nodulation, N2 fixation rates (evaluated by total N and N-ureide) and on average for the six experiments the strains H 12 and H 20  showed increases of 437 and 465 kg ha -1, respectively , in relation to the indigenous rhizobial population. A synergistic effect between low levels of N fertilizer and inoculation with superior strains was also observed, resulting in yield increases in two other experiments. The soil rhizobial population decreased 1 year after the last cropping, but remained high in the plots that been inoculated. DGGE analysis of soil extracts showed that the massive inoculation apparently did not affect the composition of  the bacterial community.  aBeans  aNitrogen fixation  aFeijão  aFertilizante Nitrogenado  aFixação de Nitrogênio  aPhaseolus Vulgaris  aRhizobium1 aCAMPO, R. J.1 aMENDES, I. C.  tBiology and Fertility Soil, Berlingv. 39, p. 88-93, 2003.