Challenges in Disentangling the Links Between Weather and Management Effects on Nitrous Oxide Emissions in Cold Climates

English Abstract:

The complex interplay of microbiological processes and soil conditions regulates N₂O dynamics in the soil profile, and when N₂O is released from the soil surface. Management practices (e.g. manure or inorganic nitrogen addition) and weather (e.g. severity of winter freezing or spring rainfall events) are external factors driving this interaction, ultimately determining the magnitude of N₂O production and temporal variability in emission. Determining the optimal agricultural practices for emission reduction is challenging as year-round measurements of N₂O flux in side-by-side management systems over multiple years are needed. We have conducted several studies deploying a multi-plot micrometeorological technique to measure surface N₂O fluxes at a long-term Ontario site established in 2000 with the objective of improving our understanding of how management affects N₂O emissions. We have observed significant seasonal variation with on average 70% of emissions occurring from January to June in this northern mid-latitude site. Management practices applied in the fall (e.g. manure application) are affected by winter conditions and can result in large N₂O winter or spring thaw emission events. In contrast, application of nitrogen in the spring can induce large and sustained N₂O fluxes if followed by timely rainfall. Over a three-year study comparing fall vs. spring manure application effects on corn we found no difference (year 1), larger N₂O emissions for spring (year 2), and larger emissions for fall-applied manure (year 3). These results illustrate the difficulty in making recommendations to producers based on short-term studies (<5 yr) and without clearly identifying the role of management and weather. We will discuss the role of process-based models in considering average and extreme climatic conditions to interpret research results and make recommendations on N₂O mitigation practices.