Exploring nitrogen indicators of farm performance among farm types across several European case studies

Nitrogen (N) indicators are key for characterizing farm performance, because of the role of N in food production and environmental sustainability. A systematic monitoring of N balance at the farm level could contribute to understanding differences in N management and impacts among farms and among regions. The objective of this study was to increase the understanding of differences in N indicators at the farm level across Europe, and to derive possible target values. Farm-level data were collected through surveys of 1240 farms from Atlantic, Continental and Mediterranean Europe, that were diverse rather tahn country representative. The data were analysed according to a common procedure, using three related indicators: N use efficiency (NUE, farm-gate ratio of N outputs to N inputs), N surplus and N output in agricultural products. Specific target values were derived for farm type (arable, dairy, pig and mixed farms) based on the statistical analysis of the data set. The effect of not accounting for N losses involved in the production of purchased feed and the end use of exported manure (externalisation) on the animal farm indicators was evaluated by recalculating inputs with adjusting factors. The results show a wide variation in NUE and N surplus, mainly related to differences in farming systems and management. Arable farms presented lower mean N input and surplus than livestock farms, and therefore had the highest median NUE. The modest targets (i.e. median of data) for arable farms were NUE 61% and N surplus 68 kg N ha−1, for dairy farms NUE 30% and N surplus 155 kg N ha−1, and for pig farms NUE 40% and N surplus 135 kg N ha−1. Externalisation had a large effect on animal farm indicators. After adjusting for externalisation, the modest target NUE for dairy farms was 19% and for pig farms 23%. Farms outside their agro-environmental optimum could approach their specific targets by increasing or reducing N inputs (intensification or extensification) or adopting additional strategies (sustainable intensification). In conclusion, N indicators were useful to compare farm performance among different farming systems and to define a characteristic operating space for a farm population, but caution should be taken when comparing livestock farms before externalisation adjustment, and consideration should be given to changes in soil N stocks. Farm system-specific targets for N indicators and linkages with the Common Agricultural Policy may create the necessary incentives to optimise NUE and reduce N losses to air and water