Management Affects Soybean Nodulation.

Symbiotic dinitrogen fixation may contribute 40 – 70% of the nitrogen required by soybean [Glycine max (L.) Merr.] during the growing season, therefore, sustaining nitrogen input is critical for profitable grain yield and sustaining long-term soil productivity. We evaluated management practices used in conventional soybean production for impacts on the dinitrogen-fixing symbiosis. Studies conducted in the field, greenhouse, and growth chamber with transgenic glyphosate-resistant and non-transgenic soybean, with and without herbicide treatment, were conducted in which rhizosphere microbial communities and root nodulation were monitored. Nodulation was consistently lower on glyphosate-resistant soybean with or without glyphosate compared with non-transgenic soybean cultivars. Molecular analysis of rhizosphere soils revealed that all cultivars and herbicide treatments harbored the microsymbiont, Bradyrhizobium japonicum, based on reference to known gene markers in PCR-denaturing gradient gel electrophoresis assays. Therefore, although management components did not affect the rhizosphere community, other factors appear to interfere with rhizobial infection of the root and/or nodule initiation and development.