How Effective is Reduced Tillage–Cover Crop Management in Reducing N₂O Fluxes from Arable Crop Soils?

Field management is expected to influence nitrous oxide (N₂O) production from arable cropping systems through effects on soil physics and biology. Measurements of N₂O flux were carried out on a weekly basis from April 2008 to August 2009 for a spring sown barley crop at Oak Park Research Centre, Carlow, Ireland. The soil was a free draining sandy loam typical of the majority of cereal growing land in Ireland. The aims of this study were to investigate the suitability of combining reduced tillage and a mustard cover crop (RT–CC) to mitigate nitrous oxide emissions from arable soils and to validate the DeNitrification–DeComposition (DNDC) model version (v. 9.2) for estimating N₂O emissions. In addition, the model was used to simulate N₂O emissions for two sets of future climate scenarios (period 2021–2060). Field results showed that although the daily emissions were significantly higher for RT–CC on two occasions (p < 0.05), no significant effect (p > 0.05) on the cumulative N₂O flux, compared with the CT treatment, was found. DNDC was validated using N₂O data collected from this study in combination with previously collected data and shown to be suitable for estimating N₂O emissions (r ² = 0.70), water-filled pore space (WFPS) (r ² = 0.58) and soil temperature (r ² = 0.87) from this field. The relative deviations of the simulated to the measured N₂O values with the 140 kg N ha⁻¹ fertiliser application rate were −36 % for RT–CC and −19 % for CT. Root mean square error values were 0.014 and 0.007 kg N₂O–N ha⁻¹ day⁻¹, respectively, indicating a reasonable fit. Future cumulative N₂O fluxes and total denitrification were predicted to increase under the RT–CC management for all future climate projections, whilst predictions were inconsistent under the CT. Our study suggests that the use of RT–CC as an alternative farm management system for spring barley, if the sole objective is to reduce N₂O emissions, may not be successful.