Long term impact of residue management on soil organic carbon stocks and nitrous oxide emissions from European croplands.

Application of crop residues to agricultural fields is a significant source of the greenhouse gas nitrous oxide (NO) and an essential factor affecting the soil organic carbon (SOC) balance. Here we present a biogeochemical modelling study assessing the impact of crop residue management on soil C stocks and NO fluxes for EU-27 using available information on soils, management and climate and by testing various scenarios of residue management. Three biogeochemical models, i.e. CERES-EGC, LandscapeDNDC and LandscapeDNDC-MeTrx, were used in an ensemble approach on a grid of 0.25° × 0.25° spatial resolution for calculating EU-27 wide inventories of changes in SOC stocks and NO emissions due to residue management for the years 2000-2100 using different climate change projections (RCP4.5 and RCP8.5). Our results show, that climate change poses a threat to cropping systems in Europe, resulting in potential yield declines, increased NO emissions and loss of SOC. This highlights the need for adapting crop management to mitigate climate change impacts, e.g. by improved residue management. For a scenario with 100% residues retention and reduced tillage we calculated that in average SOC stocks may increase over 50-100 years by 19-23% under RCP8.5 and RCP4.5. However, complete retention of crop residues also resulted in an increase of soil NO emissions by 17-30%, so that climate benefits due to increases in SOC stocks were eventually compensated by increased NO emissions. The long-term EF for residue N incorporation was 1.18% and, thus slightly higher as the 1% value used by IPCC. We conclude that residue management can be an important strategy for mitigating climate change impacts on SOC stocks, though it requires as well improvements in N management for NO mitigation.