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The effect of inoculation of crested wheatgrass (Agropyron cristatum L.), perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) with the soil diazotroph Bacillus polymyxa was studied. Plant growth responses to inoculation varied from slightly negative (perennial ryegrass) to highly positive (white clover and crested wheatgrass) when root, shoot and plant dry weights were measured. Root-to-shoot ratios were also increased in the latter two species. Seedling emergence in crested wheatgrass was shown to be enhanced by inoculation with the bacterium. Possible mechanisms of the growth response include suppression of pathogenic organisms in the rhizosphere by the inoculant strain, root-associated nitrogen fixation, solubilization of phosphorus compounds or the bacterial production of plant growth-promoting substances. Use of sterilized soil in experiments and a lack of antibiotic production …