Regionalized nitrogen balances of Switzerland

For the agri-environmental monitoring of Switzerland, nitrogen balances on farm level for all Swiss farms were calculated and aggregated in order to obtain regionalized nitrogen balances. This monitoring attempts to incorporate as much existing data as possible to minimize multiple data collections from farmers. Data from the agricultural policy information system of Switzerland was used as basis for the calculation. This database contains information on livestock numbers, the crops grown, and the direct payments received for each farm. This information was supported with different data sources from federal offices, cantons, agricultural associations, and research institutions. Balances were calculated as a soil-surface balance according to the OECD method, which includes N input via organic and mineral fertilizers, biological N-fixation, atmospheric N-deposition, and seedlings as well as N outputs via plant yields.The regional balances showed a high variability, resulting in an average N surplus of around 105 kg N per hectare of utilized agricultural area in cantons with highly intensive livestock farming and around 16 kg N in cantons with more extensive farming practices, i.e. in mountain regions. On national scale, highest N input occurred via organic fertilizers, whereas mineral fertilizers and biological N-fixation account for around 15% of the total input each.Our approach of calculating N balances on farm level for the whole Swiss farming system has some limitations, which are mainly due to missing or incomplete data sources.  As an example, the use of mineral fertilizers had to be estimated by application data of a rather small sample of farms (~300 farms). Nevertheless, the obtained results show that this methodology is a promising tool to gain a regional overview of the environmental status of Swiss farms. Over the years, this approach will be refined and new data (e.g. additional administrative data, satellite data) can be incorporated in order to better estimate the N balances of Swiss farms.