Precipitation reduction overrides edaphic controls on nitrous oxide emissions along a soil carbon, texture and pH gradient in a cereal field

Abstract. Nitrous oxide (N₂O) is a potent soil-borne greenhouse gas (GHG) which increases in the atmosphere due to the widespread use of synthetic nitrogen (N) fertilisers. Soil N₂O emissions are intrinsically controlled by soil moisture and edaphic properties such as soil organic carbon (SOC) content, texture and pH. With a future climate projected to increase frequency and severity of droughts in northern Europe, understanding how these factors interact to affect N₂O emissions is critical for predicting climate feedbacks. In this study, we investigated N₂O emissions along a hillslope gradient in an agricultural field in southeast Norway, characterised by increasing SOC and clay content and decreasing pH from top to bottom. Eight rainout shelters were installed along the hillslope, nominally reducing precipitation by 49 %. N₂O emissions were measured weekly using static chambers over two years during the snow-free period. In the first year, N₂O emission measurements started two months after fertilisation and covered a four-month period, which included episodes of heavy rainfall; during this time, we found no effect of precipitation reduction or edaphic factors on emission rates. In the second year, reduced precipitation significantly decreased N₂O emissions (~25 %). Under ambient precipitation, cumulative N₂O emissions were positively correlated with SOC content and showed weak negative and positive trends with soil pH and clay content, respectively. No significant correlations were found in plots with reduced precipitation. Altogether, our findings illustrate that soil physicochemical controls on N₂O emissions depend on the interaction between soil properties and climate. This has consequences for parameterising process-based N₂O models driven by soil properties and weather and calls for more in-depth studies on interdependencies of edaphic and climatic drivers of N₂O emissions.