EFFECTIVENESS OF BRADYRHIZOBIUM SP INOCULANTS ON DIFFERENT SUBSTRATES

The aim of this work was to establish the ideal conditions for surviva l and effectiveness of Bradyrhizobium sp on alternative substrates wit h varying matric potentials. Diatomite, dried sugarcane vinasse, vermi culite and urban compost were used as substrates and compared to peat. Strain UMKL-58 of Bradyrhizobium sp, selected in a previous work, was used as inoculant. Substrates were equilibrated at water matric poten tials (Psi m) of -0,33, -1,0 acid -3,0 bar and incubated for 240 days. Strain survival was evaluated by the plate dilution technique on days 0, 12, 30, 60, 90, 120, 150, 180 and 240 after substrate inoculation and also by plant infection using the legume cunha (Clitoria ternatea L.). Biological nitrogen fixation as a function of the substrate was a lso studied. The results demonstrate that Bradyrhizobium sp survived b etter in diatomite with a Psi m of -3,0 bar. although at the other wat er potentials its behaviour was similar to that observed in peat. For all the substrates, low water content (low matric potentials) reduced survival rates and also affected the quality of the inoculum, decreasi ng the effectiveness of the strain.