In the research project Mapfield, which is led by The Geological Survey of Denmark and Greenland (GEUS), researchers have developed a concept for field-scale mapping to support targeted regulation and management of nitrogen in agriculture. The aim is in part to help ensure an economic and environmentally sustainable development of the Danish agricultural production, and in part to ensure that Denmark is able to meet the demands of EU’s environmental directives. The project is supported by the Innovation Fund Denmark and builds on the former rOPEN project, which was also supported by the Innovation Fund Denmark.
The concept is based on the collection of large amounts of data to more precisely calculate the transport and turnover of nitrogen in the subsurface. For that reason, it also depends on monitoring data from e.g. stream stations. Based on that, the researchers can produce maps of the nitrogen retention of the subsurface at field level. The new concept is developed to contribute with important knowledge to a targeted regulation and management of nitrogen at field level, so that actions and mitigation measures can be adapted to the nitrogen turnover under each field.
“This new concept gives a very precise overview of the amount of nitrogen that flows from each field through the subsurface and into the surface water system. If it is implemented, it can contribute with opportunities for more targeted regulation and management of nitrogen on agricultural fields,” says Birgitte Hansen, Senior Researcher in Department for Groundwater and Quaternary Geological Mapping and project manager for Mapfield.
Flexible and cost-efficient
The new concept for the production of nitrogen retention maps at field level consists of five steps and is adapted for ID15 catchment areas (approx. 1500 hectares). It is flexible in the sense that catchment areas can be prioritised in different ways, e.g. depending on specific demands regarding reduction of nitrogen or uncertainties in the existing knowledge foundation. The concept makes it possible to only complete step 1 or step 2 in a catchment area if for example it turns out not to be cost-efficient to continue. In other catchment areas, it might be necessary to complete all five steps.
Preliminary estimations show that the concept is quite cost-efficient, despite the collection of large amounts of data, and will become less costly if the concept is moved from research level to large-scale production.
Groundwater protection
The concept includes a detailed groundwater model in 3D, which can estimate the transport and turnover of nitrogen in the entire hydrological cycle. According to Birgitte Hansen, the groundwater model can also be used to produce detailed assessments of the nitrate vulnerability of aquifers.
“We can use this very detailed knowledge to point out nitrate-vulnerable groundwater abstraction areas and create action plans for the protection of our groundwater resources on a very detailed basis. The possibility of using the concept for groundwater protection has not been completed but can be added to the presented concept,” says Birgitte Hansen.