Improved N application methods and N sources for corn in Southwestern Ontario

Corn producers often apply nitrogen (N) fertilizer by either streaming urea-ammonium nitrate (UAN) or broadcasting urea onto the soil. Producers are considering adding inhibitors to reduce losses of applied N. Compared to other N sources, urea and UAN fertilizers have higher risks of ammonia loss. As with other N sources, denitrification and nitrous oxide (N₂O) losses can also be substantial. The objectives of this project are to measure the impact of these N sources, and their timing and placement, on corn yield, ammonia loss, and nitrous oxide emissions.

Phase 1 of this study compared N fertilizer treatments applied at sidedress in 2013 and 2014. The inhibitors and the band-injection treatments had large beneficial effects on reducing losses. Compared to broadcast urea, on average over the two years, injection of UAN with urease and nitrification inhibitors increased yields by 19% to 174 bu/A, while reducing loss of ammonia-N by 98% to less than 1 lb/A, and reducing N₂O-N emission during the growing season by 30% to 1.5 lb/A.

Phase 2 of this study expanded the treatments to include the timing of N fertilizer application, during the period of 2015 to 2017. Averaged over the three years, injecting UAN at sidedress, in comparison to broadcast urea at planting, increased yield by 17% to 198 bu/A, reduced N₂O-N emissions during the growing season by 36% to 1.2 lb/A, and reduced ammonia-N emissions by 80% to 4 lb/A. Additionally, the combined urease and nitrification inhibitors increased yields by 4%, reduced ammonia emissions by 49%, and reduced nitrous oxide emissions by 8%.

Crop N uptake data remain to be analyzed. The results from this project demonstrate that implementing the 4Rs (right source, rate, time, and place) for N management can dramatically improve sustainability of corn production in terms of productivity, profitability and environmental impact.