Effects of nitrogen application rate and a nitrification inhibitor dicyandiamide on ammonia oxidizers and N2O emissions in a grazed pasture soil

► Ammonia oxidizing bacteria (AOB) amoA gene copy numbers were greater than those of ammonia oxidizing archaea (AOA). ► The AOB amoA gene copy numbers increased with increasing nitrogen application rates. ► DCD significantly reduced the AOB amoA gene copy numbers especially in the high nitrogen application rates. ► DCD had the most significant effect in reducing N2O emissions in the highest nitrogen application rate. ► The N2O flux and NO3−-N concentrations were significantly correlated to the growth of AOB, rather than AOA.