Subnational nutrient budgets to monitor environmental risks in EU agriculture: calculating phosphorus budgets for 243 EU28 regions using public data

This paper presents a method to estimate soil surface phosphorus (P) budgets for 243 subnational regions in EU28. This is about the maximum spatial resolution that can be achieved mainly using international datasets that are regularly updated. Similar subnational budgets could be established for nitrogen (N) with some additions to this method. Increasing the spatial resolution from national to subnational is one way to address the well-known issue that national nutrient budgets sometimes mask considerable heterogeneity, i.e., regional surpluses and deficits that are not seen in national averages. Our results indeed show how a rich structure of different P budgets emerges when moving from national to subnational level. Another approach is to exclude the most extensively managed areas from the budgets, to better represent the surplus in intensive agriculture areas. Here, we show that both approaches are useful and sometimes important as they can affect P surplus estimates by about 10 kg P ha(- 1) y(- 1) or more. The choice of spatial resolution is a trade-off between accuracy and precision. National budgets are the most accurate thanks to good data coverage, but they sometimes fail to identify considerable P surpluses and deficits at subnational level. Increasing the precision (spatial resolution) gradually reveals this heterogeneity but comes at the cost of growing data gaps, which we discuss in detail. These subnational P surpluses represent a middle ground which may prove useful as one indicator among others to monitor the development of environmental risks and resource problems over time.