MINCA "MItigation of Nitrogen pollution at CAtchment scale"

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The intensification of agriculture, and in particular the use of fertilizers, is the key to securing food supplies for a growing world population. The nitrogen contained in the fertilizer is not only absorbed into the plant biomass and finally harvested, but is also released into the environment as reactive nitrogen (Nr) via various gaseous and hydrological pathways. This leads to serious environmental problems such as eutrophication, greenhouse gas emissions or groundwater pollution.We assume that science-based nitrogen mitigation strategies make it possible to reduce N2O and NH3 emissions and reduce NO3 inputs into waters while maintaining yields. The aim of the MINCA project is therefore to establish a coupled, process-based hydro-biogeochemical model as an instrument for identifying field management strategies that make it possible to reduce the Nr-surplus and thus reduce N pollution in agriculturally dominated landscapes.We are particularly interested in the Nr conversion mechanisms at the interfaces of fields, groundwater, riverbanks and streams. In order to overcome the current limitations of understanding the temporal and spatial hydro-biogeochemical fluxes in Nr-transformation on the landscape scale, we will combine innovative field experiments with a process-based modelling approach. However, the representation of the N cycle in hydro-biogeochemical models is complex and the validation of the underlying processes is data-intensive. The measurements are therefore carried out on four different agricultural, one grassland and one forest area. MINCA consists of four closely linked work packages (WP). WP1 describes the ongoing measurement of water and nitrogen flows in the Vollnkirchener Bach study area. The already relatively extensive continuous measurements, e.g. N2O emissions, soil moisture, runoff and water quality, will be extended by further measurements such as NO3 leaching and concentrations, seasonal development of the leaf area index, yields, biomass and their C and N content. In addition, 15N2O and 15NO3 isotopomers will be measured in field campaigns. Multi-criteria measurements for model experiments in WP1 and model-based upscaling methods within WP2 will allow parameter reduction, uncertainty analysis and process plausibility testing in WP3. This will enable to identify when and where N pollution occurs in the landscape.This in-depth knowledge will form the basis for the development of science-based mitigation scenarios in WP4. The coupled model is executed in a real-time data assimilation mode in order to achieve the target values set by the German Federal Ministry of Food and Agriculture. Tailor-made in-situ experiments on N2O emissions and NO3 leaching will demonstrate the effectiveness of the mitigation potential.