A new Danish concept for hectare-scale groundwater N-retention mapping – Presentation, implementation, and validation of the concept

This abstract consists of a presentation of a new Danish concept for hectare-scale groundwater N-retention mapping called N-MAP. It encompasses how the concept could be implemented on a national scale by using a decision support prioritization tool which can assist in selecting, which catchments and areas are most suitable for implementing the NMAP concept. N-retention maps from the Danish Agricultural Monitoring Areas (the LOOP areas) used for validation of the concept, will be presented.

Targeted N-regulation is an important cost-efficient measure in the Danish governmental agreement of a green transition of Danish agriculture from October 2021 where targeted Nregulation is aimed to reduce the annual load to coastal areas by up to 6,500 ton N out of a total N reduction demand of 13,100 ton N.

The idea of targeted N-regulation is to adjust the local N-regulation of a field to the natural denitrification potential of the subsurface, which depends on the water pathways and the N-reduction rates and capacities of the subsurface media below the field (Hansen et al., 2021). The N-MAP concept and technologies have been developed through the Innovation Fund Denmark projects rOPEN and MapField (http://mapfield.dk/) to support targeted N-regulation at field level. It is based on the collection, interpretation, and modelling of large amounts of geophysical, geological, hydrological and geochemical data to calculate the transport and turnover of water and N in the subsurface (Kim et al., 2021; Madsen et al., 2021; Sandersen et al., 2021). In the concept, hectare-scale groundwater N-retention maps are produced with a horizontal scale down to 25 m × 25 m, and a vertical subsurface mapping depth of down to 100 m.

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