Collecting the carbon data needed for Climate-Smart agriculture in Saskatchewan
Term: 4 years, ending June 2025
Status: Complete
Researcher(s): Kate Congreves, Daphnee Ferland, Rich Farrell, Maryse Bourgault & Warren Helgason, University of Saskatchewan, Claudia Wagner-Riddle, University of Guelph
SaskCanola Investment: $111,011
Total Project Cost: $409,817
Funding Partners: ADF, Sask Wheat, SaskOats
Objectives
Provide direct, year-round field-scale measurements of greenhouse gas emissions from a representative cropping system in Saskatchewan.
Test the hypothesis that Saskatchewan cropping systems are a net carbon sink by determining net ecosystem exchange and carbon footprint of the cropping system.
Provide field-scale assessments that encompass 4R+ practices aimed at minimizing carbon footprints.
Project Description
Arable croplands are a significant source of nitrous oxide (N2O) emissions, largely due to nitrogen (N) fertilizer applications to support crop production. However, there is limited research measuring N2O dynamics from canola-wheat rotations in the semi-arid Prairies, an important agricultural region of Canada. Here, we present micrometeorological N2O fluxes measured using the flux gradient technique from Jan 2021 to Apr 2025 in Saskatchewan to evaluate the impact of N fertilizer management on year-round N2O emissions from a canola-wheat rotation. A combination of two 4R N management practices (a reduced N rate and an enhanced efficiency N fertilizer source) was compared to conventional fertilizer management practices for the region (urea-N fertilizer for regional yield targets). Two periods at high risk for N2O flux events were identified i) after N fertilizer application and ii) during spring thaw; but the magnitude of emissions varied over the multi-year period. The crop growing season (GS) contributed, on average, half of the annual emissions, presenting an opportunity to reduce N2O emissions via improved N fertilizer management. Indeed, in our study, the improved 4R N management treatment reduced N2O emissions by 57% over the entire study period, without impacting yields.
The reduction of GS N2O was due to smaller mean daily fluxes during periods with high water-filled pore space (WFPS, > 50%). In other words, by reducing the magnitude of fluxes during wet periods after fertilization, the 4R N management strategy translated into lower total N2O emissions. But what about the non-growing season? Importantly, the non-growing season (NGS, overwinter and spring thaw periods) represented an equally important source of N2O—the other half of average annual N2O emissions. Fall soil nitrate levels were a strong explanatory variable of NGS emissions, but the magnitude of NGS N2O emissions depended on the thawing conditions (lower fluxes during drier thaws, higher fluxes during wetter thaws). Putting it altogether, better N management reduced cumulative N2O emissions in the canola-wheat rotation, in part due to lowering N2O fluxes during wet periods of the GS, but also due to reducing fluxes during the NGS by lowering residual soil nitrate levels.
The next question that our research addressed was if the cropping system represented a net source or sink of carbon (C)? Throughout the study period described above, CO2 fluxes were also measured using the flux-gradient micrometeorological technique, enabling the calculation of net ecosystem exchange (NEE), net ecosystem carbon balance (NECB), and greenhouse gas budget (GHGB). Total GHG emissions (CO2 and N2O in CO2-equivalents) tended to be lower from the improved N management vs conventional N fertilizer treatment. As for whether the system was a C source or sink: 2021 was exceptionally dry such that the canola crop did not produce net CO2 uptake and represented a C source. Wheat in 2022 and canola in 2023 both favoured net CO2 uptake during the GS, but the balance tipped the system to a net C loss once the grain/oilseed (and the C in it) was removed at harvest. In the final year (2024), wheat production acted as an overall C sink, sequestering 0.19 kg C m-2 yr-1. For the complete rotation over the 4-year period, the system was C neutral on average.
When all is said and done, the improved N management reduced N2O emissions, and for the 4-year period the cropping system was C neutral on average. Flipping the system to a net C sink might involve management that supports vigorous crop growth in-season and favours including wheat in the rotation. Our measurements provide some of the first year-round direct measurements of GHGs in a canola-wheat rotation for Saskatchewan and are a valuable starting place to build from and develop further strategies for reducing emissions and supporting crop production on the Prairies.
Grower Benefits
The measurements from this project are among the first to provide direct, year-round, field-scale GHG data—specifically N2O and CO2 fluxes—for a canola-wheat rotation in Saskatchewan.
On average, half the annual N2O emissions were attributed to the growing season (GS), other half attributed to non-growing season (NGS).
4R N management reduced cumulative N2O emissions by 57% without impacting yields, compared to conventional practice.
N2O reductions due to lowering mean daily fluxes during GS wet periods after fertilization, and also due to reducing NGS emissions by lowering fall soil nitrate levels.
The cropping system remained a net C source for three years, but conditions tipped the system to a net C sink in the fourth year. Averaged over the 4-yr period, cropping system was net C neutral.