Combining low-N2 background and 15N soil gas flux - lessons from the field

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, due to the methodological limitations for the measurement of N₂ emissions, in particular high atmospheric N₂, only a very limited number of soil N2 flux datasets are available to validate model estimates of denitrification. As part of the DFG-research unit “Denitrification in Agricultural Soils: Integrated Control and Modelling at Various Scales (DASIM)”, we are building on existing methods to take in situ measurements of denitrification under a variety of field conditions, with an emphasis on the detection of non-peak events. Using static chambers, we establish a low-N₂ background through headspace and soil flushing, and then use stable isotope techniques (natural abundance and ¹⁵N labeling of the soil mineral N pool) to assess the response of soil denitrification to combinations of climate, soil and plant factors found in the field. Here we present results of N₂ and N₂O fluxes from the field, which highlight both the potential and the challenges of using this combined method.