Method: A standardised laboratory method for measuring ammonia volatilisation in pig slurry using a dynamic flux multi-chamber system

Ammonia (NH3) emissions generated by animal manure represent a challenge for the current livestock system, especially in the context of pig production. Standardised methods for measuring NH3 concentration in pig slurry are needed to assess whether specific management strategies (e.g. low-protein diets and feed additives) can reduce NH3 emissions. Therefore, the aim of this study was to provide a standardised procedure and test the repeatability in measuring NH3 concentration in pig slurry using a laboratory-controlled method based on a dynamic flux multi-chamber system. Five slurry mixes of 348 g each were prepared using spot faeces and urine samples from a single pig. Every mix was composed of 87 g of faeces, 87 g of urine, and 174 g of distilled water. For each mix three replicates of 100 g were realized, for a total of 15 slurry replicates of five slurry mixes. The 15 slurry replicates were contained in jars, placed in a water bath (21°C), and injected with an even flow of synthetic air (approx. 0.3 L/min). The replicates were connected to a cavity ring-down spectrometer, which, combined with a multichannel sampler, measured the NH3 concentration of the outgoing air flow from the slurry replicates for 168.75 consecutive hours. Each slurry replicate was measured cyclically for 15 min, with a 10-min interval between two slurry replicates over 168.75 h of measurements. The values recorded during the final 60 s of each 15-min period were interpolated on an hourly basis, obtaining one NH3 concentration value per hour. To test the repeatability of the method, coefficients of variation (CV) of area under the curve for NH3 concentration (AUC NH3, ppm × h), NH3 concentration peak value (PV NH3, ppm) and time to reach the peak (TTP, h) were calculated within pairs of replicates from the same mix and within pairs of mixes. For the slurry mixes, all the CVs calculated showed a variation lower than 10%. Among the replicates, only the CV related to the TTP registered a value higher than 10% for four pairs of replicates out of 15. These findings suggest that the proposed dynamic flux multi-chamber system provides a standardised and repeatable approach for measuring NH3 concentration in pig slurry under controlled laboratory conditions.