Improved Understanding of Nitrous Oxide Emissions from Seasonally Frozen Cropland for Mitigation of Agricultural Greenhouse Gas Emissions

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Agricultural soils are significant emitters of the greenhouse gases nitrous oxide (N2O) and carbon dioxide (CO2) and these emissions are related to nitrogen and carbon inputs of cropping systems. The long-term objectives of my program are to validate and modify models predicting net GHG fluxes from agro-ecosystems and to identify soil and crop management practices for sustainable agro-ecosystems. In cold regions more than half of annual N2O emissions for agricultural soils can occur outside the growing season due to soil freeze-thaw (FT) events. Seasonally frozen land coincides with large areas of intensive cropping, but research into FT-induced N2O emissions has been limited. This is because N2O emissions are highly variable in time and space and present a challenge for typical measurement methods, particularly in cold regions. My research group is one of few in the world using micrometeorological techniques addressing this challenge. At our long-term study site, we have observed that differences in management are often most prevalent during the non-growing season, but we have not identified the underlying causes leading to large FT N2O emissions in a range of conditions. If these differences are understood, then practices for reduced N2O emissions at thaw could be designed.The objectives of this proposal are: 1) to quantify the magnitude and temporal dynamics of CO2 and N2O fluxes from agro-ecosystems under soil and crop management that result in contrasting FT conditions; 2) to evaluate the effect of winter warming on non-growing season N2O fluxes on two soil types; 3) to investigate the differences in FT-induced N2O between perennial and annual crops; 4) to compare the underlying factors for enhanced N2O emissions in FT and dry-wet cycles in a range of soil types; and 5) to improve the prediction of FT-induced N2O fluxes in process-based and empirical models. I propose a combination of approaches: 1) micrometeorological experiments in an agricultural area of importance for Canada, that has not been studied before using year-round micromet methods; 2) new high-precision weighing soil lysimeters with winter warming; 3) laboratory experiments using soil columns subjected to FT and dry-wet cycles to control drivers affecting emissions. Tunable diode laser trace gas and Fourier Transform Infra-red analyses will be coupled with micromet or automatic chambers to measure gas fluxes at high temporal resolution. Carbon and nitrogen substrates released by FT events and enhanced microbial processes will be characterized through sophisticated techniques (e.g. NMR, molecular microbial analysis). Process-based models will be improved in collaboration with government scientists. Six graduate and 10 undergraduate students will be trained in this stimulating environment. Findings will have a significant impact on Canada's ability to predict agricultural GHG emissions.