Agricultural soil fertilized with nitrogen is the main source of the greenhouse gas nitrous oxide (N2O). This gas is both produced and consumed by microorganisms in the soil. Bacteria capable of N2O reduction are essential for regulation of the N2O emissions from soils. It has been confirmed that if the soil microbial community has in increasing number of members that cannot consume N2O, the higher is the potential for emissions.
Based on previous research, we know that nitrogen fertilization seems to favor and disfavor certain microbial species. In theory, this will affect which N2O producers and consumers that are present, but the soil itself can also have a strong impact. To test this, 14 long-term field experiments across Sweden with fertilized and unfertilized field plots are compared. The analyses include measurements of which microorganisms are present, microbial activity and quantification of the number of organisms that produce or consume N2O. With this approach, we can see if N2O reduction is associated to specific community members, which are candidate indicators of N2O sinks.
In some of the field sites with contrasting cropping systems we also look at the fate of nitrate. We want to understand when nitrate is being transformed into nitrogen gas and lost, or when it is transformed to ammonium and kept in the soil. This affects soil fertility and emission of N2O.