Optimized design of flux chambers for measurement of ammonia emission after field application of slurry with full-scale farm machinery

Abstract. Field applied liquid animal manure (slurry) is a significant source of ammonia (NH₃) emission, which is harmful to the environment and human health. To evaluate mitigation options, reliable measurements of effects are needed. A new system of dynamic flux chambers (DFC) with high time resolution online measurements was developed. The system was investigated in silico with computational fluid dynamics and tested in three field trials, each trial assessing the variability after application with trailing hose at different scales: manual (handheld), 3-m experimental slurry boom, and 30-m farm-scale commercial slurry boom. For the experiments with machine application, parallel NH₃ emission measurements were made using an inverse dispersion modelling method (backward Lagrangian stochastic modelling, bLS). The lowest coefficient of variation of replicate DFC measurements was obtained with manual application, followed by the 3-m slurry boom, and lastly the 30-m slurry boom. Conditions in DFCs resulted in a consistently higher NH₃ flux than what was measured with the inverse dispersion technique but both methods showed a similar emission reduction by injection compared to trailing hose: 89 % by DFC and 97 % by bLS. The new measurement system facilitates NH₃ emission measurement with replication after both manual and farm-scale slurry application with relatively high precision, with a coefficient of variation of 5 % among replicates with manual slurry application and 20 % for farm-scale slurry application.