Denitrification, the anaerobic microbial conversion of nitrate and nitrite to the gases nitric oxide, nitrous oxide, and dinitrogen, is important to soil fertility, water quality, greenhouse gas emissions. The process is notoriously difficult to quantify and therefore difficult to manage. The "Managing Denitrification" community of the Environmental Quality Section of the ASA is a great example of how scientists can come together, grapple with uncertainty, and produce useful conclusions.
Here, I highlight recent work including: 1) New measurements of dinitrogen and nitrous oxide flux. 2) Analysis of differential controls of these fluxes. 3) The occurrence of "hotspots" and "hot moments" of denitrification in soil profiles. 4) The emergence of nitrogen oligotrophication as a controller of denitrification at larger scales.
New measurements show that dinitrogen fluxes are much larger than nitrous oxide fluxes and are controlled by different factors. These measurements also show the importance of hotspots of activity associated with confining layers at depth (up to 50 cm) in the soil profile, and hot moments of activity associated with drying and rewetting events. At broader spatial and temporal scales, declines in nitrogen deposition, lengthening of the growing season, increases in atmospheric carbon dioxide levels, and other changes are reducing nitrogen availability in the environment. While this oligotrophication has led to reductions in nitrous oxide flux and denitrification potential in forest ecosystems, its importance in agronomic systems has yet to be analyzed.
Continued work on denitrification will likely lead to further increases in our ability to model and manage nitrogen pollution problems at field, landscape and regional scales. Still we must always recognize that the world is changing in complex and surprising ways. A community of researchers will be needed to address the challenges of denitrification and its importance to nitrogen dynamics in a changing world.