Calculation of atmospheric nitrogen emissions from manure in Norwegian agriculture

Manure management in Norway is a source of emissions to air of ammonia (NH3), nitrous oxide (N2O), nitric oxide (NO) and nitrogen (in the form of N2). The dominating pollutant emitted from manure management is NH3, with cattle being by far the most important source in Norway, followed by pigs and then sheep. Emissions of NH3 from manure depend on several factors, e.g. type of animal, nitrogen content in fodder, manure management system, climate, time of spreading of manure and cultivation practices. These parameters need to be taken into consideration when building a model to
calculate emissions of ammonia and other nitrogen species.

The Norwegian model for calculating the agricultural nitrogen emissions to atmosphere is used for reporting for the Norwegian emission inventory. The model closely follows the stepwise approach proposed in the EMEP/EEA 2019 guidebook, with all the 15 steps proposed in the former being followed in the Norwegian model. Although based on this tier 2 technology-specific approach, the updated Norwegian model includes certain aspects which are more in line with the EMEP/EEA tier 3 approach. The effect of abatement measures and improved manure management and manure use practices are described in the revised model. The main manure management and use phases considered in the model are (i) animal housing, (ii) manure storage, (iii) manure spreading on agricultural land, and (iv) deposition as a result of animal grazing, plus (v) use of manure for biogas production. The latter was introduced in the model during 2020 revision and includes nitrogen emissions from pre-storage of manure before anaerobic digestion, separation of digestate into solid and liquid fractions and storage of digestate. In line with the EMEP/EEA guidebook, the emissions from spreading to land of digestate produced from manure are reported together with the emissions from spreading of untreated manure.

In line with EMEP/EEA 2019 guidebook and IPCC 2006 guidelines, the Norwegian model calculates direct emissions of N2O, NO and N2 in order to more accurately estimate the TAN available at each stage of manure management, in addition to calculating emissions of NH3. The model integrates the mineralisation of N and the immobilisation of TAN during storage of manure, and also estimates indirect emissions of N2O from leaching/run-off during storage, application to land and grazing and through volatilisation of N from manure management, application to land and deposition during grazing. In 2020 revision, the emission factors for NH3 and NOX have been updated in accordance to the EMEP/EEA 2019 guidebook.