Effect of the herbicide glyphosate on nitrification, denitrification, and acetylene reduction in soil

Abstract

The effect of glyphosate on N2 fixation, denitrification, and nitrification in an agricultural soil was investigated. Effects of the pure herbicide and commercial formulation, Roundup+ (Monsanto Company), were compared in soil under aerobic and anaerobic conditions. Anaerobic C2H2 reduction was inhibited by high herbicide levels. Denitrification in non-amended soil was either unaffected (N2O reduction) or stimulated (NOinf3sup−reduction); in glucose-amended soil, N2O reduction was inhibited and NO3-reduction unaffected by both glyphosate and Roundup. Roundup caused greater stimulation of N2O reduction than pure glyphosate; no other significant formulation effects were observed. Nitrification was inhibited by the two formulations. Ammonium oxidation were both influenced. Pure glyphosate was more inhibitory than Roundup. No toxicity to any of these activities should be seen at recommended field application rates of the herbicide.