The demand for an accurate model of the denitrification process in the drainage zone

Denitrification is an important process in the soil that leads to the degradation of nitrate into nitrous oxide or dinitrogen. It prevents the leaching of nitrate from the soil into groundwater. For this reason, denitrification is implemented in many models. However, most of the models only consider the root zone in their calculations. Denitrification below the root zone (deep vadose zone or drainage zone) is overlooked. The current state of research is that most of the denitrification takes place in the root zone. The lack of organic carbon and oxic conditions probably prevent denitrification in the drainage zone, with the exception of microsites with high organic carbon content. Nevertheless, due to the potentially large thickness of the drainage zone and the associated long travel time of the nitrate, some nitrate could be degraded on its way to the groundwater.

To date, there is no model that can accurately predict denitrification in the drainage zone. Most models completely ignore the fact that nitrate could be degraded in this zone. The few models that do consider denitrification in the drainage zone rely on knowledge from the topsoil. Due to the differences between the root zone and the underlying drainage zone, this approach may be overestimate denitrification rates in the drainage zone. Therefore, there is a need for a model that simulates denitrification in the drainage zone. In the DeniDrain project, we will adapt existing models to the conditions in the drainage zone using actual denitrification rates from soils across Germany.