Influence of Cover Crops and Winter Warming on Soil N₂O Content and Surface Fluxes During Freeze‐Thaw

Overwinter cover crops alter nitrogen dynamics and soil temperatures, potentially mitigating nitrous oxide (N 2 O) emissions during freeze‐thaw (FT). Meanwhile, increasing winter temperatures can remove the insulating snow layer intensifying FT cycles and N 2 O fluxes. Comparing the patterns of soil N 2 O content against surface fluxes under different management and environmental conditions can improve the understanding of what mechanisms enhance N 2 O fluxes at thaw. Soil profile (0–140 cm) N 2 O gas concentrations and fluxes were measured from December to April in large‐scale lysimeters with two dominant soils in Ontario, Canada (silt loam and loamy sand) over two years. The simultaneous heat and water model was used to simulate liquid water and ice content during freezing conditions, needed for total N 2 O content estimations (i.e., aqueous + gaseous). During year 1, the peak soil N 2 O content ranged from 23.6 to 79.0 mg N 2 O m −2 , and two significant emissions events occurred (9.6–41 g N 2 O‐N ha −1 d −1 ). In year 2, no significant N 2 O profile accumulation or emissions were observed due to warm winter conditions. Difference in soil physical conditions impacted the response of soil N 2 O content to cover crops, with N 2 O content decreasing by 42% in the loam soil and increasing 101% in sand. Intermittent heating caused colder soil conditions in year 1, increasing soil N 2 O content in loam soil while reducing it in sand. Despite changes in soil N 2 O content, the N 2 O surface flux was not impacted, indicating that alternative nitrogen loss pathways are likely responsible for reducing N 2 O content during FT events not surface fluxes.