The Danish Commission on Nature and Agriculture recommends a paradigm shift in the national regulation from the current general and uniform regulation, to a spatially differentiated regulation taking advantage of the spatial variation in natural nitrate reduction. New regulation principles are presently developed based on national screening of nitrate reduction at a scale of 15 km2. However, denitrification varies spatially even at small scale due to heterogeneity in the hydrogeological and geochemical conditions. Assessments of the spatial variation in denitrification are hampered by critical knowledge gaps specifically related to the importance of drainage systems and seasonal variations in water table fluctuations and redox dynamics in the upper soil profile.

Three intensively drained agricultural field sites characterized by highly variable water table fluctuations were selected for a more detailed investigation on the influence of nitrate reduction on nitrogen (N) drainage losses. The fields were equipped with drainage stations to continuously monitor drainage discharge and drainage N losses. The fields were further equipped with piezometers and redox probes at variable depth to monitor water table fluctuations and redox dynamics, as well as nitrogen transformation as a function of depth. Results from three years of measurement were used to compare model predictions of N losses with actual measured losses, and to evaluate the influence of nitrate reduction on resulting drainage N losses.