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Measuring agricultural greenhouse gas exchange over a conventionally managed highbush blueberry field Pow, Patrick Ka Chun


Agricultural fields are significant sources of carbon dioxide (CO₂), nitrous oxide (N₂O) and methane (CH₄), which has implications for future climate change. In Canada, studies incorporating all three greenhouse gases (GHGs) in agricultural settings are limited to Ontario, Quebec and the Prairies and generally involve short-duration static-chamber measurements. Results from these studies may not generalize well to British Columbia (BC) on the west coast, which has a milder climate and different cropping systems. This study quantified year-round (January 1, 2018 – December 31, 2018) CO₂, N₂O and CH₄ exchange over a conventionally managed highbush blueberry field on Westham Island in Delta, BC, Canada using the eddy-covariance (EC) method. Continuous measurements using EC allowed for quantification of diurnal courses of both CO₂ and N₂O exchange, whereas sporadic measurements may not accurately reproduce the complete diurnal cycle of GHG emissions. Sawdust mulching may have contributed to a reduction in evapotranspiration but has implications for increased CO₂ and N₂O emissions. Field management including fertilization and mowing was associated with substantial changes in GHG exchange, suggesting that management strategies can be targeted for potential GHG mitigation. The field was a net source of all measured GHGs and emitted 838 g CO₂e m-² year-¹, with CO₂ contributing the largest proportion (76%) followed by N₂O (20%) and CH4 (4%). The annual net ecosystem exchange (NEE) was 173 g C m-² year-¹ with the ratio of annual gross primary productivity (GPP) to ecosystem respiration (Re) being 0.88. After accounting for inputs and outputs of carbon (C), the field sequestered a net of 231 g C m-² year-¹. While soil temperature was found to be an important environmental factor controlling GHG emissions, soil moisture was also found to be an important factor, which has implications on future feedback cycles and climate change.

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