Simulation and validation of greenhouse gas emissions and SOC stock changes in arable land using the ECOSSE model M.I. Khalil a, b, * , M. Richards c , B. Osborne a , M. Williams d , C. Müller a, e a School of Biology and Environmental Science, University College Dublin, Belfield, Dublin 4, Ireland b Climate Change Research Programme, Environmental Protection Agency, Johnstown Castle Estate, Wexford, Ireland c Institute of Biological and Environmental Sciences, School of Biological Sciences, University of Aberdeen, Scotland, United Kingdom d School of Botany, Trinity College Dublin, Dublin 2, Ireland e Department of Plant Ecology (IFZ), Justus Liebig University Giessen, Germany highlights  ECOSSE model simulated N 2 O fluxes from arable field well with EF (0.53  0.03%).  Predicted R H (3149 kg C ha 1 yr 1) was within the uncertainty ranges of croplands.  Simulated CH 4 showed a sink (26.61e31.37 g C ha 1 yr 1 ), decreased with N fertilizer.  Simulated SOC suggest a loss (516 kg C ha 1 yr 1 ) and within the uncertainty ranges.  The model is suitable for estimate the GHG balance but refinements are suggested. article info Article history: Received 4 April 2013 Received in revised form 1 September 2013 Accepted 19 September 2013 Keywords: Greenhouse gases Carbon balance Spring barley Tillage ECOSSE model abstract Model simulations of C and N dynamics, based on country-specific agricultural and environmental conditions, can provide information for compiling national greenhouse gas (GHG) inventories, as well as insights into potential mitigation options. A multi-pool dynamic model, ‘ECOSSE’ (v5 modified), was used to simulate coupled GHGs and soil organic carbon (SOC) stock changes. It was run for an equivalent time frame of 8 years with inputs from conventionally-tilled arable land cropped with spring barley receiving N fertilizer as calcium ammonium nitrate at 135e159 kg N ha 1 and crop residues (3 t ha 1 yr 1 ). The simulated daily N 2 O fluxes were consistent with the measured values, with R 2 of 0.33 (p < 0.05) and the total error and bias differences were within 95% confidence levels. The measured seasonal N 2 O losses were 0.39e0.60% of the N applied, with a modelled estimate of 0.23e0.41%. In contrast, the measured annual N 2 O loss (integrated) was 0.35% and the corresponding simulated value of 0.45% increased to 0.59% when the sum of the daily fluxes was taken into account. This indicates intermittent gas samplings may miss the peak fluxes. On an 8-year average the modelled N 2 O emission factor (EF) was 0.53  0.03%. The model successfully predicted the daily heterotrophic respiration (R H ), with an R 2 of 0.45 (p < 0.05) and the total error and bias differences were within the 95% confidence intervals. The simulated and measured total R H (3149 versus 3072 kg C ha 1 yr 1 ) was within the cropland average values previously reported. The total measured CH 4 fluxes indicated that the unfertilized treatments were a small source (2.29 g C ha 1 yr 1 ), whilst the fertilized treatments were a sink (þ3.64). In contrast, the simulated values suggested a sink (26.61e31.37 g C ha 1 yr 1 ), demonstrating fertilizer-induced decreases in CH 4 oxidation. On average, based on the simulated SOC content a loss of 516 kg C ha 1 yr 1 was indicated, which is within the uncertainty range for temperate regions. Results suggest that the model is suitable for estimating the GHG balance of arable fields. However, further refinements and analyses to fully determine and narrow down the uncertainty ranges for GHG estimates are required. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Agricultural activity is estimated to be responsible for w14% of anthropogenic greenhouse gas (GHG) emissions globally (IPCC, 2007) and for 10% of the European Union (EU). The two principle * Corresponding author. School of Biology and Environmental Science, University College Dublin, Belfield, Dublin 4, Ireland. E-mail addresses: khalil_ibrahim@yahoo.com, mi.khalil.dr@gmail.com (M.I. Khalil). Contents lists available at ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.atmosenv.2013.09.038 Atmospheric Environment 81 (2013) 616e624