Ecological studies of root-nodule bacteria introduced into field environments. II. Initial competition between seed inocula in the nodulation of Trifolium subterraneum L. seedlings

The ability of three strains of Rhizobium trifolii used in legume inoculants to form nodules on inoculated Trifolium subterraneum L. was examined in field experiments on a soil containing a large natural population of clover rhizobia. The identity of cultures isolated from nodules on young seedlings was established by a gel immune diffusion technique. When a mixture of broth and peat inocula was applied to seed, a large proportion of nodules was attributable to peat-borne rhizobia. In competition with the natural population in the production of nodules on the roots of the host legume, strain WA67 = TA1 > UNZ29. In competition with each other as well as with the naturally occurring rhizobia, WA67 > TAI > UNZ29. The significance of the findings in relation to the persistence in soil of Rhizobium strains applied as inoculant to clover seed is discussed.