Understanding and Managing Nitrous Oxide Emissions from Agricultural Soils: Knowledge Gained through Year-Round Micrometeorological Measurements

Nitrous oxide (N₂O), a trace gas that contributes to the enhanced greenhouse effect and stratospheric ozone destruction, is the focus of climate change mitigation efforts in crop production due to its importance for the global agricultural greenhouse gas budget. 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. inorganic nitrogen addition) and weather (e.g. severity of winter freezing) are external factors driving this interaction, ultimately determining the magnitude of N₂O production and large temporal variability in emission. Micrometeorological techniques do not interfere with source conditions and hence, can be used quasi-continuously (at hourly to half-hourly intervals) to capture the temporal dynamics of N₂O fluxes. We have deployed a multi-plot flux gradient (FG-M) method over the last two decades that has the advantage of providing side-by-side comparisons of total N₂O emissions from contrasting agricultural management under similar climatic and soil conditions using field-scale plots with one gas analyzer. Evaluation of the FG-M technique against the standard eddy covariance technique showed promising results. Here, we present an overview of our approach and results from long-term experiments which revealed freeze-thaw induced N₂O emissions as a significant underestimated global source. Agricultural practices identified for mitigation of N₂O emissions using the FG-M method will be discussed.