Two decades of micrometeorological measurements show dynamic drivers of springtime N2O emissions

Nitrous oxide (N₂O) is a potent greenhouse gas with a global warming potential 265 times that of carbon dioxide and the ability to destroy stratospheric ozone. Agricultural soils contribute over two-thirds of anthropogenic N₂O emissions. Field observations in temperate climates have commonly shown N₂O emission peaks occurring in the spring during a period of snow melt and soil thaw. This freeze-thaw period typically accounts for approximately 35% of annual N₂O emissions, however, current understanding of its drivers is based off of relatively short observation periods. The analysis of such data over decadal time spans is therefore needed to improve our understanding of key drivers. Here, we report on 21 years (2002-2022) of micrometeorological N₂O flux data from a field site in Ottawa, Ontario. Correlation analyses were conducted between the N₂O flux during the spring thaw period and variables that are commonly considered drivers. Little to no correlation was seen from linear or multilinear regressions across a range of meteorological, management, and soil variables. The non-linear response of non-growing season cumulative N₂O emissions to cumulative freezing degree-days was consistent with previous studies (Wagner-Riddle et al., 2017). However, in isolating freezing degree-days we may be neglecting other possible controls. These results show that the relationship of N₂O flux with environmental variables may be related to complex, potentially non-linear, interactions between agricultural practices, weather, soil quality, and other variables. We will further examine the data using other multivariate statistical methods to further investigate potential drivers of these non-growing season emissions with a focus on those emissions occurring specifically during the spring thaw. As these relationships are used in nitrification/denitrification models, improved understanding is still needed to accurately simulate these processes, which is imperative to improving nitrogen budgets and ultimately achieving climate goals.