We reported the effects of transgenic glyphosate resistant soybean cultivars (GRC), glyphosateand weed management strategies (glyphosate + GRC vs. conventional herbicides + non-GRC)on biological nitrogen fixation (BNF), symbiotic efficiency (SyEf) and grain yield (SGY) in soybean. Six variables related to BNF were pooled and analyzed as SyEf. Data were obtained in field trials in six sites in Brazil and three growing seasons. Small effects of GRC and glyphosatewhere observed on SyEf in some sites. SyEf did not differ between the two weed managementstrategies. SGY was higher in the glyphosate + GRC management in three out of the six sites
