Evaluating the nitrous oxide mitigation potential of enhanced efficiency nitrogen fertilizer products in a Saskatchewan irrigated cereal production system
Ogilvie, C. A. 2022. University of Saskatchewan
Abstract
Nitrogen fertilizers added to agricultural field crops are a significant source of nitrous oxide
(N2O) emissions from Canadian soils. Irrigated cropping systems are of particular concern due to
intensive management and higher fertilizer rates corresponding to higher yield potential, which
result in higher N2O emissions. Fall fertilizer applications are also at risk of greater N2O-N loss
due to the length of time between application and crop uptake in the subsequent growing season.
Enhanced efficiency nitrogen fertilizers (EENFs) can be used to mitigate environmental losses that
contribute to greenhouse gas (GHG) emissions by slowing the release rate of N. Nitrous oxide
emissions experience spatial and temporal variability and are highly dependent on management
practice, thus, it is important to evaluate mitigation techniques across different geographies and
cropping systems.
Over the course of two growing seasons and the subsequent spring thaw periods, fall and spring
applications of conventional fertilizers (CF) and EENFs were evaluated in spring wheat under
irrigation in south-central Saskatchewan. Nutrient supply rate of nitrate (NO3-) and ammonium
(NH4 ) were measured using PRS® probes and N2O emissions were collected from non-steady state vented chambers that were placed both on and off the fertilizer bands. Treatments included
an unfertilized check, two conventional N sources (urea and anhydrous ammonia), a polymer-
coated urea (ESN), two nitrification inhibitors (eNtrench, N-Serve), a dual%u2212action urease inhibitor
(Limus), and a dual (nitrification urease) inhibitor (SuperU).
In this study, the supply rate of NO3- and NH4 from EENFs was consistent with the mode of action
of the product. Polymer-coated urea and products containing a urease inhibitor (UI) reduced the
supply rate of NH4 compared to CFs and products containing a nitrification inhibitor (NI) reduced
the supply rate of NO3-. Interestingly, increased supply rates of bioavailable N were observed in
all treatments over the winter when the soil was frozen. Unsurprisingly, the greatest N2O emissions
fluxes corresponded with the spring melt periods and the period shortly following spring
fertilization. Up to 75% of the annual, cumulative N2O flux occurred during the spring thaw.
Enhanced efficiency nitrogen fertilizer N2O emission reductions were inconsistent when applied
in the fall, whereas, spring applications of EENFs were much more consistent at reducing N2O
emissions. Fall-applied SuperU (U/NI) and eNtrench (NI) reduced N2O emissions compared to untreated urea but only in the second field season. Spring-applied SuperU (U/NI), eNtrench (NI)
and Limus (DAUI) consistently and significantly reduced N2O emissions across both field seasons
(78-99%). The PCU (ESN) and AA-based NI (N-Serve) successfully reduced N2O emissions (43%
and 68%, respectively) in the second field season only. Although environmental benefits are clear,
specifically from using EENFs in a spring application of N, an agronomic benefit of increased
yield was not observed in any of the N source treatments or application timings.
