Method: a standardised in vitro method for measuring ammonia concentration in pig slurry using a dynamic flux chamber system

Ammonia (NH3) emissions generated by animal manure represent a challenging topic 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, 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 an in vitro method based on a dynamic flux chamber system. Five slurry mixes of 348 g each were prepared starting from spot faeces and urine samples of a single pig. Every mix was composed of 87 g of faeces, 87 g of urine and 174 g of water. For each mix three replicates of 100 g were realized, obtaining 15 slurry replicates coming from five slurry mixes. The 15 slurry replicates were contained in jars and placed in a water bath (21oC) and an even flow of synthetic air (approx. 0.3 L/min) was injected through them. At the same time, the replicates were connected to a cavity ring-down spectrometer (CRDS, model G2103, Picarro Inc., Santa Clara, CA, USA) which, combined with a multichannel sampler (model A0311-s1, Picarro Inc., Santa Clara, CA, USA), was able to measure for 168.75 consecutive hours the NH3 concentration of the outgoing air flow from the slurry replicates. Each slurry replicate was measured cyclically for 15 min, with a 10 min-interval between two slurry replicates over the 168 h of measurements. The values recorded during the final 60 seconds of each 15-minute period were interpolated on hourly basis, obtaining one NH3 concentration value per hour. To test the repeatability of the method, coefficients of variation of area under the curve for NH3 concentration (AUC NH3, ppm x hour), NH3 concentration peak value (PV NH3, ppm) and time to reach the peak (TTP, hours) 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%. For the slurry replicates only the CV related to the TTP registered a value higher than 10% for four pairs of replicates out of 15. In conclusion, the dynamic flux chamber system proposed in the present paper provides a standardised and repeatable approach for measuring in vitro NH3 concentration in pig slurry.