Measuring Fluxes of Nitrous Oxide (N2O) From an Intensively Farmed Wasted Peatland Field in the UK Using the Eddy Covariance Method.

While the number of studies quantifying emissions of the greenhouse gases (GHGs) carbon dioxide (CO2) and methane (CH4) from peatland farming has increased in recent years, high uncertainty regarding the magnitude and drivers of emissions of the powerful GHG nitrous oxide (N2O) from farmed peatland soils remains. This study used eddy covariance to measure fluxes of N2O over a 3-year period from a commercial farm in the East Anglian Fens, in a rotationally cropped field with a 56 cm surface layer of peaty soil. Over the 41-month measurement period, the average (±95% CI) monthly field-scale emission was 0.50 ± 0.17 kg N2O-N ha-1, which equates to approximately 6.0 ± 2.0 kg N2O-N ha-1 year-1. Emissions of N2O at the field site were controlled by thresholds in both soil temperature (low fluxes below ~12°C) and volumetric water content (low fluxes below ~65%). Where these thresholds were simultaneously exceeded at any depth within the top metre of the soil profile, N2O emissions increased by an order of magnitude. Higher water level management in the summer months resulted in a significant increase in annual N2O emissions, estimated to be up to 10 kg N2O-N ha-1 year-1 higher than in years when the water table was lower. Elevated emissions of N2O were largely controlled by environmental conditions (i.e., moisture and temperature). These conditions were in turn influenced by crop management, with higher emissions occurring when the field was cultivated for potatoes (compared to wheat and beans) which we attribute to a combination of higher water level management, overhead irrigation, relatively low crop nitrogen demand and solar heating of the exposed soil surface.