Can application of enhanced efficiency fertilizers at planting reduce N losses from grain corn production in Ontario?

Nitrogen (N) is a key input for sustaining high crop yields, but fertilizer N uptake efficiency in crops is relatively low. Part of the applied N that is not taken up by crops is vulnerable to losses such as nitrate leaching and nitrous oxide emissions. The overall goal of this project is to determine how Right Time and Right Source practices for N fertilizer management affect N losses.

Nitrous oxide emissions were monitored continuously using micro meteorological towers, with 12 observations per day. Nitrate losses was assessed using soil solution samplers installed at a depth of 30 inches. Four plots, each ten acres in size, received four different N fertilizer treatments: two with urea applied pre-planting and two with urea-ammonium nitrate (UAN) applied as sidedress at the 6th leaf stage. At each timing, the fertilizer is applied with and without inhibitors of urease and nitrification.

Results from the 2015 growing season showed that large pulses of nitrous oxide emission occurred with the first rainfall events, following each of the applications. The plot with UAN applied at sidedress emitted about 5.5 lb/A of nitrous oxide-N from May through September, compared to about 3 lb/A for the other three treatments. The higher emission following sidedress was likely due to the considerably higher June-July rainfall and soil moisture than what is typical for Ontario corn. Within-plot yield variability was also higher than expected, partially due to the high rainfall and a tile drain issue that was corrected in the fall.

Owing to drier conditions in the 2016 growing season, nitrous oxide emissions were much smaller, and corn yields were higher and more uniform. Relative to urea applied pre-planting, both treatments involving inhibitors reduced nitrous oxide N emission by about 50% from 0.5 kg/ha. Corn grain yields averaged 12 t/ha and did not differ among N treatments. Nitrate-N leaching from November 2015 to July 2016 was reduced from around 12 kg/ha for the pre-plant timing to 9.5 kg/ha for UAN at sidedress and 8 kg/ha for UAN with inhibitors at sidedress.
This experiment has shown that combining source and timing components of 4R fertilizer management can improve sustainability, though their effectiveness varies with weather. These results come at an opportune time to inform concurrent development of a certification program for 4R Nutrient Stewardship, and initiatives to provide offsets to farmers for carbon trading in the province of Ontario.