Campbell Scientific Bert Tanner Student Presentation Award

Tin Satriawan, University of British Columbia
Interannual Variability of Carbon Dioxide and Methane Fluxes in a Temperate Bog over a 6-Year Period

Peatland ecosystems are important carbon dioxide (CO2) sinks and methane (CH4) sources. However, changes in climatic conditions and functional responses can shift these ecosystems towards being CO2 sources and weaker or stronger CH4 sources. In peatlands undergoing rewetting, these responses are often more unpredictable. Here, we evaluated the impact of climate variability and functional change on the interannual variability of carbon (C) fluxes at Burns Bog, a rewetted bog in Canada, based on five years of continuous eddy-covariance measurements. We found that on a five-year average, CH4 emissions (13.7 g CH4-C m-2 year-1) completely offset the CO2 sink (-12.3 g CO2-C m-2 year-1) on a carbon equivalent basis, resulting in the site losing an average of 1.4 g C m-2 year-1. This finding indicates that excluding the CH4 flux from the net C budget results in a significant overestimation of the net C uptake at this peatland site. During the year with a dry and warm summer, the bog had the greatest annual CO2 loss, thus highlighting the importance of temperature and water control in the bog. Aside from climatic drivers, a declining trend in annual GPP along with decreasing light use efficiency over the years suggested that there may have been a shift in the composition of the vegetation community from vascular plants to moss-dominated vegetation in the ecosystem. Regardless of the GHG metrics (i.e., global warming potential and sustained global warming potential of 20- and 100-year timeframes) used in calculating the annual CO2-eq GHG budget, the bog consistently contributed to climate warming (i.e., positive radiative forcing) during each year of the study period.

Kayla Wicks, University of Guelph
Controls of Differing Non-Growing Season Cover Crops On Winter Soil Temperatures

One of the largest known anthropogenic sources of nitrous oxide (N2O) are cropland soils, and over half of these emissions are associated with soil freeze-thaw cycling (FTC) throughout the winter season (November-April). The magnitude of N2O fluxes directly correspond with the number of frozen soil days (TNDF) and frequency of FTC. Therefore, the goal of our study is to assess soil temperature temporal variability under a variety of common cover crop alternatives and understand how effectively soil FTC are represented by the Simulated Heat and Water Model (SHAW). Temperature i-buttons were inserted in the topsoil of eight cover crop alternatives at 25 locations across the experimental area in Elora, Ontario. Comparisons were drawn for FTC and TNFD among cover types, highlighting that the number of FTC and TNFD were significantly reduced under vegetative covers, specifically for oat, 3 mix and heavy residue treatments. In our modelling study, FTC and TNFD were significantly overestimated for both vegetative and heavy residue treatments, while FTC were slightly underestimated for bare soil dominant covers using the SHAW model. In summation, both winter cover crops and residues influence soil temperature by reducing the frequency and extent of soil freezing. Therefore, choosing a vegetative winter cover crop could reduce the magnitude of associated N2O fluxes in agricultural topsoil by insulating the soil below. However, much of these processes are inadequately represented by the SHAW model.

CSAFM-SCMAF Student Presentation Award

Nicole Menheere, University of Guelph
Mitigating nitrous oxide emissions from corn using nitrification and urease inhibitors following cover crop adoption

Increased N2O emissions have a higher chance of occurring when cover crops are terminated just before fertilizer application to corn. Nitrification and urease inhibitors (NUIs) have been shown to reduce N2O emissions, but their use after cover cropping has not been well studied with year-round studies. The micrometeorological technique used in this study is ideal to capture high temporal variability caused by the episodic nature of N2O emissions. The objective of this study was to evaluate the potential of the nitrification inhibitor (Pronitridine) and the urease inhibitor (N-butyl thiophosphoric triamide) to reduce N2O emissions in corn following cover crop use, in a humid temperate climate in Ontario, Canada. The flux-gradient method was deployed in four 4-ha fields using a tunable diode laser trace gas analyzer. Two 4-ha fields have been managed with a conventional rotation (soybean-soybean-corn) and two 4-ha fields were managed with a diverse rotation (soybean-winter wheat-corn with cover crops) since 2018. Nitrogen starter fertilizer (4.78 kg N/ha) was applied to corn at planting, followed by urea-ammonium-nitrate (UAN) (162 kg N/ha) injected 10 cm below the soil surface at the sixth leaf stage (June 17, 2021). One conventional and one of the diverse rotation fields received NUIs mixed into UAN at the time of fertilization. N2O fluxes were measured from September 1, 2020, to April 30, 2022, with supporting data including soil ammonium and nitrate concentrations, corn yield, and nitrogen uptake. N2O flux measurements indicated the use of NUIs reduced annual cumulative N2O emissions by 7.4% and 20.6% in the conventional and diverse rotations, respectively. NUIs were effective in reducing the N2O emissions associated with fertilizer application in both the conventional and diversely managed fields. These initial results show the potential of NUIs to reduce N2O emissions associated with cover crop use, but more studies are necessary.