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 developed for undertaking farm inventories and the derivation of farm nitrogen (N) balances and 5 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 thereby a large potential for reductions. The highest average N surpluses were found in the most livestock-intensive landscapes of IT, FR, and NL; on average 202±28, 179±63 and 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-scale poultry farming. So, whereas the average N surplus from the land-based UK farms dominated by extensive sheep grazing was only 31±10 kgNha-1 yr-1, the landscape average 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 how 15 to account for indirect N surpluses and emissions from such farms with a large export of manure out of the landscape. We conclude that farm N balances are a useful indicator for N losses and the potential for improving N management. Significant correlations to N surplus were found, both with ammonia air concentrations and nitrate levels in soils and groundwater, measured 20 during the landscape data collection campaign from 2007-2009. This indicates that farm N surpluses may be used as an independent dataset for validation of measured and modelled N emissions in agricultural landscapes. However, no significant correlation was found to N measured in surface waters, probably because of the short time horizon 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) of measures targeted at reducing N emissions from livestock farms. Based on the large differences between the average and the most modern and N-efficient farms, it was concluded that N-surplus reductions of 25-50% as compared to the present level were realistic in all landscapes. The implemented N-surplus method was thus effective at comparing and synthesizing results on farm N emissions and the potentials of mitigation options, and is recommended for use in combination with other methods for the 5 assessment of landscape N emissions and farm N efficiency, including more detailed N sink and N source hotspot mapping, measurements and modelling.