Can Enhanced Efficiency N Fertilizers Mitigate N2O Emissions without Compromising Crop Yield?
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Optimizing N fertilizer management is imperative to minimize nitrous oxide (N2O) emissions from croplands and to lower the environmental footprint of canola. This field study evaluated the effects of enhanced efficiency N fertilizers (EENF; fertilizers containing urease inhibitors and/or nitrification inhibitors) when applied in the fall vs. in the spring at the soil-test recommended rate vs. a reduced rate (70% of soil-test rate) on agronomic and environmental performances and compared to the conventional practice in dryland canola (Brassica napus L.) over 2 years in Saskatoon. Also, a soil incubation study investigated the N2O reduction potentials from urea-treated soils with and without Nitrapyrin (nitrification inhibitor) throughout a freeze-thaw event. Results from the field study showed the marginal differences in yield, seed N, and crop nitrogen use efficiency (NUE) between conventional urea and EENFs. Under the prolonged drought in 2021, crop NUE was improved with N application in the fall or at a reduced rate although crop yield remained low across N treatments. The modification of N source, rate, and timing did not influence N2O emissions, indeed, N2O emissions was primarily controlled by soil moisture conditions. Dry conditions during the growing season in 2020 and 2021 contributed to low emissions. The different soil moisture conditions and thaw intensity during the spring thaw periods affected N2O production where the fall N application produced higher cumulative emissions during the spring thaw and annually compared to the spring N application in Year 1, but the opposite results were observed in Year 2. Yield-scaled N2O emissions were exceedingly high across N treatments. In 2020 and 2021, the provincial average yield did not provide positive economic returns on EENF investments. Results from the incubation study demonstrated that soil moisture, temperature, and N levels had a greater impact on regulating N2O production than Nitrapyrin. Fertilized soils regardless of N formulations produced higher N2O than non-fertilized soils. High soil moisture and temperature conditions favoured denitrification and magnified the intensity of emissions. Based on these results, yield gains and N2O mitigation may not always be achieved by applying EENFs to soils in dry years.
DegreeMaster of Science (M.Sc.)
CommitteeFarrell, Rich; Skolrud, Tristan; Tar'an, Bunyamin
Enhanced efficiency N fertilizer
Nitrous oxide emissions