Effect of nitrification inhibitors on N-fixing bacteriaRhizobium leguminosarum andAzotobacter chroococcum

The nitrification inhibitor dicyandiamide [DCD] did not inhibit growth and respiration of N-fixing bacteria (Rhizobium leguminosarum andAzotobacter chroococcum) in cell suspensions with concentrations of 400 ppm DCD. Growth ofRhizobium leguminosarum was inhibited by 17% with 100 ppm nitrapyrin (N-Serve), but respiration was not affected. Growth ofAzotobacter chroococcum was inhibited by 10 ppm (10%) and 100 ppm nitrapyrin (50%); in the latter case, respiration was also impaired (36%). Thiourea only caused a minor growth inhibition ofAzotobacter chroococcum with 100 ppm (8%) and had no effect onRhizobium leguminosarum.