Agricultural nutrient budgets in Europe: data, methods, and indicators

Doctoral thesis, 2020

Agricultural production systems feed humanity but also cause a range of adverse environmental effects, including climate change, loss of biodiversity, and pollution of air and water. A main cause of these effects is the emissions of nitrogen (N) and phosphorus (P) that occur as a side effect of nutrient cycling in agriculture. One of the things that is needed to mitigate N and P pollution is a quantitative understanding of N and P flows in agricultural systems. A common tool for this is the nutrient budget. A nutrient budget quantifies inputs and outputs of nutrients in a system and can be used to understand how the system functions as well as to calculate quantitative environmental indicators for farms, regions, or products.

This thesis aims to explore and expand the limits of how agricultural N and P budgets can be used to support environmental research and decision-making, focusing on European agriculture. To this end, the thesis looks into two broad research questions: (1) What are the limits to the accuracy and level of detail that can be attained in N and P budgets of European agricultural systems? (2) How are present and proposed uses of agricultural N and P budgets and derived indicators limited by (a) the inherent property that agricultural nutrient budgets do not account for environmental impacts, and (b) by uncertainties and lack of data in the estimation of nutrient budgets?

This thesis builds on five appended research papers that explore various aspects of data sources, uncertainties, and possible uses of N and P budgets in Europe. International and national data sources are scrutinized and used to estimate N and P budgets. Novel ways to combine existing data sources are explored. The use of nutrient budgets with various system boundaries, with different degrees of spatial resolution, and in different time periods is discussed, emphasizing that the best approach is not only a question of data supply but also of intended audience and purpose.