Field management activities have significant impacts on greenhouse gas (GHG) emissions from cropland soils. In this study, the effectiveness of combining reduced tillage with a mustard cover crop (RT-CC) to mitigate present and future GHG emissions from a fertilized spring barley field in the southeast of Ireland was assessed. The field site which had a free-draining sandy loam soil with low soil moisture holding capacity, had been managed for three years prior to measurements under two different tillage systems; conventional (CT) and RT-CC. Field measurements of soil CO2, N2O and CH4 emissions, crop biomass, water filled pore space (WFPS), soil temperature and soil nitrate were made to capture both steady state conditions as well as the management events. Field data were used to validate the DNDC (DeNitrification-DeComposition) model and future GHG emissions under two sets of climate projections were predicted. Although fertilizer use was the same for both treatments the RT-CC treatment had significantly (p < 0.05) higher N2O emissions for both present and future climate. However, the inclusion of a cover crop with the RT treatment increased predicted soil organic carbon (SOC), which more than compensated for the higher N2O flux resulting in a lower total GHG balance (TGGB) compared with the CT treatment. Results show that the effectiveness of RT-CC in mitigating GHG emissions will depend crucially on the magnitude of compensatory increases in carbon dioxide uptake by the cover crop that will contribute to a reduction in the total GHG balance. (C) 2014 Elsevier B.V. All rights reserved.