Modifying fertilizer rate and application method reduces environmental nitrogen losses and increases corn yield in Ontario.

Nitrogen (N) use in corn production is an important driver of nitrous oxide (NO) emissions and 4R (Right source, Right rate, Right time and Right place) fertilizer practices have been proposed to mitigate emissions. However, combined 4R practices have not been assessed for their potential to reduce NO emissions at the provincial-scale while also considering trade-offs with other N losses such as leaching or ammonia (NH) volatilization. The objectives of this study were to develop, validate, and apply a Denitrification-Decomposition model framework at 270 distinct soil-climate regions in Ontario to simulate corn yield and NO emissions across eleven fertilizer management scenarios during 1986-2015. The results show that broadcasting fertilizer at the surface without incorporation had the highest environmental N loss which was primarily caused by NH volatilization. When injected at planting or at sidedress, the NH loss was reduced considerably. However, because more N was left in the soil, injection and sidedressing induced more losses by nitrate leaching and NO emissions. Reduction of N rate as proposed by the DNDC model did not affect crop yield but decreased leaching and NO emissions. Addition of inhibitors promoted a further reduction in NO emission (11-16%) although lesser than the reduction in N rate. Overall, our results emphasize that N rate adjustment following improvements in placement, use of inhibitors, and application timings can mitigate NO emissions by 42-57% and result in 3-4% greater yields compared to baseline scenario in Ontario corn production.