Tracing N2O from dairy processing sludge amended soil with visualizing microscale heterogeneity of NH3 and pH (Short Communication)

Nitrous oxide (N₂O) emissions from organic waste and animal slurry contribute to climate change and endanger our ecosystems. For the development of efficient mitigation technologies, in-depth knowledge of emission processes is needed. This can be obtained by non-destructive, temporal measurements of in-situ soil profiles and the transformation of ammonium (NH₄⁺) during events of emissions. Planar optode imaging is a non-destructive measuring method that can be used to visualize spatiotemporal changes of ammonia (NH₃) and pH in soil systems. In this study, soil amended with dairy processing sludge (DPS) was incubated in static chambers for 23 days, and GHG emissions, NH₃ concentrations and pH in the soil were measured simultaneously over time. The aim was to investigate the potential of applying different planar optodes to provide information that gives insight into processes of N₂O emissions. The DPS was applied to the soil as a surface layer (SL), with untreated soil as a control (CK). We were able to measure N₂O emissions while monitoring spatiotemporal changes of soil pH and NH₃ concentrations. The visualized microscale heterogeneity of the soil contributed to a better understanding of N₂O emission processes. While technical challenges (e.g., humidity sensitivity of the NH₃ optode and airtightness of the chambers) still need to be overcome, the method is a promising non-destructive method to study soil processes after application of different types of soil amendments.