Evaluation of optimized flux chamber design for measurement of ammonia emission after field application of slurry with full-scale farm machinery

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 emission measurement methods are needed. A new system of dynamic flux chambers (DFCs) with high-temporal-resolution online measurements was developed. The system was investigated in silico with computational fluid dynamics and tested using three respective field trials, with each trial assessing the variability in the measured emission after application with trailing hose at different scales: manual (handheld) application, a 3 m experimental slurry boom, and a 30 m farm-scale commercial slurry boom. For the experiments with machine application, parallel NH3 emission measurements were made using an inverse dispersion modeling method (backward Lagrangian stochastic, bLS, modeling). The lowest coefficient of variation among replicate DFC measurements was obtained with manual application (5 %), followed by the 3 m slurry boom (14 %), and lastly the 30 m slurry boom (20 %). Conditions in DFCs resulted in a consistently higher NH3 flux than that measured with the inverse dispersion technique, but both methods showed a similar emission reduction by injection compared with the trailing hose: 89 % by DFC and 97 % by bLS modeling. The new measurement system facilitates NH3 emission measurement with replication after both manual and farm-scale slurry application with relatively high precision.