Farm nitrogen balances in six European agricultural landscapes; a method for farming system assessment, emission hotspot identification, and mitigation measure evaluation." Biogeosciences Discussions 9(7): 8859-8904.

Six agricultural landscapes in Poland (PL), the Netherlands (NL), France (FR), Italy (IT),Scotland (UK) and Denmark (DK) were studied, and a common method was developedfor undertaking farm inventories and the derivation of farm nitrogen (N) balances and5 N surplus from the in total 222 farms and 11 440 ha of farmland.In all landscapes, a large variation in the farm N surplus was found, and therebya large potential for reductions. The highest average N surpluses were found in themost livestock-intensive landscapes of IT, FR, and NL; on average 202±28, 179±63and 178±20 kgNha-1 yr-1, respectively. However, all landscapes showed hotspots,10 especially from livestock farms, including a special UK case with landless large-scalepoultry farming. So, whereas the average N surplus from the land-based UK farmsdominated by extensive sheep grazing was only 31±10 kgNha-1 yr-1, the landscapeaverage was similar to those of PL and DK (122±20 and 146±55 kgNha-1 yr-1, respectively)when landless poultry were included. However, the challenge remains how15 to account for indirect N surpluses and emissions from such farms with a large exportof manure out of the landscape.We conclude that farm N balances are a useful indicator for N losses and the potentialfor improving N management. Significant correlations to N surplus were found, bothwith ammonia air concentrations and nitrate levels in soils and groundwater, measured20 during the landscape data collection campaign from 2007-2009. This indicates thatfarm N surpluses may be used as an independent dataset for validation of measuredand modelled N emissions in agricultural landscapes. However, no significant correlationwas found to N measured in surface waters, probably because of the short timehorizon of the study.25 A case study of the development in N surplus from the landscape in DK from 1998-2008 showed a 22% reduction, related to statistically significant effects (p < 0.01) ofmeasures targeted at reducing N emissions from livestock farms. Based on the largedifferences between the average and the most modern and N-efficient farms, it wasconcluded that N-surplus reductions of 25-50% as compared to the present level wererealistic in all landscapes. The implemented N-surplus method was thus effective atcomparing and synthesizing results on farm N emissions and the potentials of mitigationoptions, and is recommended for use in combination with other methods for the5 assessment of landscape N emissions and farm N efficiency, including more detailedN sink and N source hotspot mapping, measurements and modelling.