Exemplary embodiments are directed to a herbicide resistant N2-fixing microorganism and to a method for enhancing N2 fixation by the herbicide resistant rhizobia in symbiosis with herbicide resistant or tolerant leguminous plants treated with herbicide. At least one preferred embodiment comprises mutant rhizobia strains selected based on tolerance of the broad spectrum glyphosate weed control agent, originally Roundup®. Preferred embodiments can be expected to outcompete both indigenous soil rhizobia and/or commercial rhizobia that are not resistant to the herbicide.