A field trial to test the efficiency of previously selected strains of alfafa rhizobia was conducted at the Centro de Nutrição Animal de Nova Odessa. Four strains which had been tested previously in the greenhouse using the Leonard jar technique were employed in the study. The field trial was conducted under mulch and no mulch treatment. The mulch treatment was used to immobilize nitrate nitrogen which is inhibitory to nodulation at high levels. Inoculation was by conventional peat methods of application and toy pelleting with inoculum and lime. Natural nodulation for this specialized legume was found to be practically nil. In this acid soil, normal inoculation method were not sufficient in supplying nodules to the plants, with resulting nitrogen fixation. Nodulation under pelleting was good to excellent and gave evidence of nitrogen fixation under both, mulch and no mulch treatment, with differences in yield being greater between the check and inoculation plus pelleting treatment where mulch has been used.