Addressing the challenge how agriculture can meet increasing demands for food, feed, fibre and fuel while simultaneously reducing its environmental impacts is crucial in the urgently needed sustainability transition. Nitrogen is at the core of this challenge.
Nitrogen use in agriculture causes many environmental problems, including eutrophication, acidification and climate change, but is also crucial for achieving high yields. The overall objective of this research is to analyse the impacts of nitrogen use in agriculture on greenhouse gas exchange, air quality and water quality, as well as the potential of different strategies to reduce these impacts at the European and the global scale.
The first aim of this PhD project is to improve our understanding of the degree to which anthropogenic disturbance of the N cycle affects terrestrial C storage. For this purpose we collected data from forest fertilization experiments worldwide, and performed a meta-analysis to gain insights into the magnitude of the response of the forest woody biomass C sink to N addition and factors influencing variation in this response. Meta-regression will be used in order to perform the first global spatially explicit assessment of C-N response ratios based on results from forest fertilization experiments. Results will show us how different factors interact to affect forest response to N addition.
The second aim is to assess pathways of agricultural intensification that allow us to remain within a “safe operating space” while also increasing land productivity both at European and global scale. For this purpose, we establish ‘critical limits’ of nitrogen losses that should not be exceeded in view of ecosystem and human health. We use the INTEGRATOR model to assess nitrogen losses, nitrogen use efficiencies and yields in Europe under three scenarios:
- Current yields and current nitrogen use efficiencies
- “Optimal yields” (defined as 80% of the physiological yield potential)
- Optimal yields and “required” nitrogen use efficiencies (defined as the nitrogen use efficiency that is required to obtain optimal yields while not exceeding critical environmental limits).
Results will give us an idea of the spatial variability in required (increases in) nitrogen use efficiencies. The potential to reach those increases will be discussed in the light of results achieved in experiments on sustainable fertilization techniques.
A similar assessment of current, critical and needed nitrogen inputs and nitrogen use efficiencies will be performed at the global scale, using the Integrated Assessment Model IMAGE. Earlier assessments of critical N limits at the global scale have focussed on one global “planetary boundary”, while results from our study will provide the first spatially explicit assessment of critical nitrogen losses. This is urgently needed as nitrogen inputs, losses and impacts are highly variable.