Competition between strains of Bradyrhizobium japonicum for nodulation of soybeans in Argentine arable soils

Naturalized bradyrhizobia in Argentinian soils originate from introduced inoculants with poor properties. Attempts to improve soybean production by new inoculants usually fail. We wanted to improve inoculation success by a careful selection of competitive inoculants. Initially a field with naturalized bradyrhizobia was used for soybean cultivation using seeds which were inoculated with several inoculant strains, added separately or in mixture in a replicated experiment. Strain E110 was the most competitive strain since it occupied most nodules and resulted in the highest dry matter production. In a second experiment, a soil free of bradyrhizobia was used where a bradyrhizobial strain was introduced to serve as a representative of the naturalized population, and E110 was used as an inoculant. We found that E110 increased plant growth, indicating a potential for use of this strain as an inoculant in soils with less efficient naturalized populations. (C) 1999 Elsevier Science B.V. All rights reserved.