New N2O emission factors for crop residues and fertiliser inputs to agricultural soils in Germany

Direct agricultural N2O emissions in Germany have so far been estimated using the default Tier 1 emission factor of 1% (0.3–3%) in accordance with the IPCC’s default methodology. Since direct N2O emissions is a “key category” in the German National Greenhouse Gas Inventory, the IPCC recommends the use of country-specific emission factors or models. With the aim of deriving country-specific and stratified N2O emission factors, a metaanalysis was conducted using data collected from 71 individual studies comprising 676 separate emission measurements taken at 43 locations across Germany. A Bayesian generalised linear mixed-effects modelling approach was used to model N2O fluxes and derive emission factors. In contrast to what is suggested by the 2019 Refinement to the 2006 IPCC Guidelines, the model results did not support a distinction being made between emission factors for synthetic and organic fertilisers. Instead, a model based on four environmental zones roughly representing the north-west, north-east, south-east and south-west parts of the country was developed. It was used to derive district-wise emission factors for direct N2O emissions and revealed that northern districts had relatively lower emission factors than southern districts. The district-wise emission factors ranged from 0.38% to 0.92%. The national implied emission factor for direct N2O emissions from managed agricultural soils was 0.62% (0.43–0.85%). Accordingly, the estimate of German national GHG emissions from agriculture in 2015 is 8.59% (calculated with global warming potentials from IPCC’s fifth assessment report) lower than the estimate reported in the 2021 inventory submission to UNFCCC.