How effective is reduced tillage-cover crop management in reducing N ₂O fluxes from arable crop soils?

Field management is expected to influence nitrous oxide (N ₂O) production from arable cropping systems through effects on soil physics and biology. Measurements of N ₂O 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 N ₂O emissions. In addition, the model was used to simulate N ₂O 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 N ₂O flux, compared with the CT treatment, was found. DNDC was validated using N ₂O data collected from this study in combination with previously collected data and shown to be suitable for estimating N ₂O 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 N ₂O 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 N ₂O-Nha-1 day-1, respectively, indicating a reasonable fit. Future cumulative N ₂O 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 N ₂O emissions, may not be successful.