Field measurements of soil denitrification using 15N gas flux

Accurate models of soil N cycling are an important tool for optimizing N use efficiency within agricultural systems and predicting N emissions to the environment. However, within such models, denitrification remains a challenge to describe and predict. One issue in achieving accurate denitrification estimates is the limited number of soil N₂ flux datasets that can be used to validate model estimates. Measurements of soil denitrification, which include both N₂O and N₂ fluxes, are challenging, however, due to methodological limitations for the measurement of N₂ and the heterogeneity of denitrification in soils.

As part of the DFG-research unit “Denitrification in Agricultural Soils: Integrated Control and Modelling at Various Scales (DASIM)”, we are building on previous data collected from laboratory incubations to take in situ field measurements. We use soil flushing and stable isotope techniques, combined with real-time monitoring of soil conditions, to assess the response of soil denitrification to a variety of control factors. These include: soil texture, previous crop, irrigation, and fertilizer application, in addition to the ambient changes in field conditions over one growing season of winter wheat. Both natural abundance and ¹⁵N labeling of the soil mineral N pool will be used to assess denitrification pathways.

Here we introduce the experimental field setup, summarize key elements of method testing and present early results of N₂ and N₂O. Once complete, this data set will provide valuable insight into the temporal and spatial heterogeneity of denitrification in agricultural soils. Data will be used to calibrate newly developed DASIM models as well as denitrification sub-modules of existing biogeochemical models.