Measurement methods for ammonia emissions after field application of slurry

Agricultural sources of atmospheric ammonia after slurry application vary over space and time, which makes it difficult to accurately quantify emissions. Different methods for concentration and emission estimation have been used by different institutions for many years, and these differences may contribute to variability in measurements. There is an need for commonly acceptable and reliable measurement methods.

Ammonia emission measurements show a strong connection to the group that conducted them, suggesting effects of local soil properties, application techniques, or measurement method biases. The aim of this work was to clarify one source of these institutional effects related to applied measurement methods. Emission measurements with several common measurement methods were compared by three different research institutions simultaneously in the same field plots. This approach eliminates any variation from soil properties and application technique, making it possible to obtain new insight into the effect of measurement technique on model ammonia flux estimates.

Two joint experiments were conducted at Research Center Foulum, Aarhus University (AU), Denmark, and one at Wageningen University and Research (WUR), the Netherlands. The four measurement methods included in the first experiment in Denmark were the backwards Lagrangian model (bLS) with online concentration measurement and wind tunnel measurements conducted by a AU group, while a group from Thünen Institute for Climate-Smart Agriculture conducted measurements with the Dräger Tube Method (DTM) and ALPHA passive diffusion samplers combined with bLS. The second experiment in the Netherlands included the integrated horizontal flux (IHF) method conducted by a WUR group using impingers as ammonia traps, while AU conducted bLS and wind tunnel measurements again. Furthermore, emission from both experiments were also estimated with the ALFAM2 model (v2.10, https://github.com/sashahafner/ALFAM2) based on the specific slurry and climatic parameters after slurry application.

The difference in season and application method between the two experiments caused large differences in emissions as expected. The low time resolution measurements methods (DTM, ALPHA samplers with bLS, and IHF) tended to have lower emissions compared to the online and high time resolution methods (bLS and WT). More comparative measurements are needed to allow for more complete assessment of different methods.