Delaying application and injecting nitrogen fertilizer with urease and nitrification inhibitors decreased nitrous...

Early season nitrous oxide (N₂O) emissions following nitrogen fertilizer application can be significant if spring rains lead to anaerobic conditions before the crop is established and able to utilize the applied N. However, delaying fertilizer application by 4-5 weeks after planting usually results in warmer temperatures which promote ammonia (NH₃) volatilization losses. This 3-year study on a clay loam soil compared NH₃ losses, N₂O emissions, and corn (Zea mays L.) grain yields for pre-plant urea ammonium nitrate (UAN) injection versus side-dress UAN injection using no inhibitors, a urease inhibitor, or a urease and nitrification inhibitor. Side-dress N-application resulted in 13% greater corn grain yields compared to pre-plant N application when averaged over the inhibitor treatments. Pre-plant UAN with a urease inhibitor had 59% greater N₂O emissions (2.15 kg N ha^-1) than pre-plant injected UAN with a urease and nitrification inhibitor (1.35 kg N ha^-1); pre-plant UAN injection with no inhibitors produced intermediate N₂O losses (1.89 kg N ha^-1). Delaying UAN application to side-dress in 2015, the year with above-normal spring precipitation, decreased N₂O emissions (1.24 kg N ha^-1) by 52% compared to pre-plant UAN (2.56 kg N ha^-1); however, side-dress application had minimal impact on N₂O in the subsequent 2 years which had drier spring conditions. The dual urease and nitrification inhibitor treatment reduced yield-scaled N₂O emissions by 37% compared to urease only when averaged over the timing treatments. Side-dress N application reduced yield-scaled N₂O emissions by 28% compared to pre-plant application when averaged over the inhibitor treatments. Urease plus nitrification inhibitors combined with side-dress UAN application increased corn yields and decreased N₂O losses, whereas urease inhibitors alone increased N₂O emissions.