How Effective is Reduced Tillage-Cover Crop Management in Reducing N_2O Fluxes from Arable Crop Soils?

摘要

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 DeNitrifi-cation-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 (γ~2=0.70), water-filled pore space (WFPS) (γ~2=0.58) and soil temperature (γ~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-N ha~(-1) day~(-1), respectively, indicating a reasonable fit. Future cumulative N_2O fluxes and total denitrifi-cation 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.