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

Naturalized bradyrhizobia in Argentinian soils originate from introduced in oculants with poor properties. Attempts to improve soybean production by ne w inoculants usually fail. We wanted to improve inoculation success by a ca reful selection of competitive inoculants. Initially a field with naturaliz ed bradyrhizobia was used for soybean cultivation using seeds which were in oculated 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 brad yrhizobial strain was introduced to serve as a representative of the natura lized population, and E110 was used as an inoculant. We found that E110 inc reased plant growth, indicating a potential for use of this strain as an in oculant in soils with less efficient naturalized populations. (C) 1999 Else vier Science B.V. All rights reserved.