Estimation of N2O emission factors for soils depending on environmental conditions and crop management

Nitrous oxide (N2O) contributes 8% to anthropogenic global warming, of which about one third are direct emissions of agricultural soils. These N2O emissions are often estimated using the default IPCC 2006 emission factor of 1% of the amount of N applied for mineral fertilizer, manure and crop residues. However, a large variation in emission factors exists due to differences in environment (e.g. weather and soil conditions), crops (grassland, arable land, crop residues) and management (e.g. type of manure and fertilizer, application rates, time of application). We developed a simple approach to determine N2O emission factors that depend on environmental, crop and management factors. The main factors controlling N2O emission are nitrate content, oxygen content, available C content, temperature and pH. The starting point of the method was a two-year monitoring study of Velthof et al. (1996), who found an emission factor of exactly 1% for grassland on a sandy soil fertilized with calcium ammonium nitrate. The conditions of this experiment were set as the reference from which the effects of other environmental conditions and management on the N2O emission factor were estimated. Based on literature and expert knowledge we determined for 19 sources of N input, three soil types, two land use types, three precipitation classes, two pH classes and three temperature classes the effect on the default emission factor. The calculated N2O emission factors ranged from 0 to 10%. The approach was applied to a European scale, using the INTEGRATOR model. The results were also produced with the standard IPCC approach and the empirical approach by Stehfest and Bouwman (2006). Differences in the overall results at EU27 scale and at regional scale are discussed. The emission factors derived from this inference scheme can improve predictions of N2O emissions with integrated large-scale model