Response of soil N2 and N2O fluxes to denitrification control factors in two agricultural soils

Controlling soil N cycling to mitigate N-oxide emissions and optimize N use efficiency is an important aspect of agricultural soil management. Numerous denitrification models exist that can inform management decisions, but these are limited by the lack of soil N2 flux measurements to validate the model estimates. Measurements of soil denitrification - including both N₂O and N₂ fluxes - are challenging, however, due to methodological limitations for the measurement of N₂ and the spatial/temporal heterogeneity of denitrification in soils.

We used laboratory incubations of re-packed soil cores, combined with both soil flushing and stable isotope techniques, to measure denitrification in two agricultural soils, as part of the DFG-research unit “Denitrification in Agricultural Soils: Integrated Control and Modelling at Various Scales (DASIM)”. The laboratory incubations used an automated mesocosm system, with regular measurements of both N₂O and N₂, to assess the response of soil denitrification to a variety of control factors. Control factors simulated typical scenarios that might occur in the field, including different amounts/types of plant residue, and changes in moisture, temperature, NO₃^- and oxygen concentration. Both natural abundance and ¹⁵N labeling of the soil mineral N pool were used to assess denitrification pathways.

Here we contrast the results of the incubation data from a sandy Podzol and silt-loam Luvisol. These data will be used to calibrate newly developed DASIM models as well as denitrification sub-modules of existing biogeochemical models. They will also inform the next steps of this work, which will extend the laboratory incubation technique to measure denitrification in undisturbed field soils.