GM soybean nodulation and yield in response to glyphosate applications and co-inoculation

Abstract

Glyphosate is the main herbicide applied post-emergence to GM soybean. Previous research showed that glyphosate can affect the number and mass of nodules that affect yield. However, with the use of techniques to increase nodulation, the effect of glyphosate on the yield of GM soy may be lessened. The objective was to evaluate GM soybean nodulation and yield as a function of glyphosate applications and co-inoculation. Four experiments were carried out in one area with a history of co-inoculation. The treatments of glyphosate included: weed burned-down 10 days prior to sowing plus one post-emergence application, weed burned-down 10 days prior to sowing plus two post-emergence applications, one post-emergence application, two post-emergence applications and weed control carried out mechanically with a hoe. The treatments of inoculation involved three types: co-inoculation, inoculation and no inoculation. Glyphosate applications reduced nodulation in only one of the four experiments. Co-inoculation increased nodule number and dry weight by 105 and 168%, respectively, in one experiment of the 2018/19 crop year compared to no inoculation. In this study, glyphosate applications altered nodulation but did not influence grain yield.