Raw data and R scripts

Ammonia (NH3) pollution generated by animal manure represents a focal topic for the current livestock system, especially in the context of pig production. Standardized methods for measuring NH3 concentration in animal slurry are needed to assess whether the different strategies applied at animal level (i.e. low-protein diets, additives) can reduce NH3 pollution. Therefore, the aim of this study was to provide a standardized procedure and test the repeatability in measuring NH3 concentration in pig slurry samples using an in vitro method based on a dynamic chamber system. Five slurry mixes of 348 g each were prepared starting from feces and urine samples of a single pig. Every mix was composed of 87 g of feces, 87 g of urine and 174 g of water. For each mix three replicates of 100 g were realized, obtaining fifteen slurry replicates coming from five different mixes. Then, the fifteen replicates were transferred in jars and placed in a water bath (21oC) and a constant flow of synthetic air (2.8 L/min) was injected through them. At the same time, the samples 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 seven days the NH3 concentration (ppb) of the outgoing air flow from the slurry samples. Every sample was measured cyclically for 15 min, with a 10 min-interval between two different samples over the 168 h of measurements. For statistical analysis (R, v. 4.4.1), only the NH3 concentration of the last minute out of the fifteen was considered, and data were interpolated on hourly basis, obtaining one NH3 concentration value per hour. To test the repeatability of the method, coefficients of variation (CVs) of area under the curve for NH3 concentration (AUC NH33, ppb x hour), NH3 concentration peak value (PV NH3, ppb) and time to reach the peak (TTP, hours) were calculated between pairs of replicates of the same mix and between pairs of mixes. For the mixes all the CVs calculated showed a variation lower than 10%. For the replicates only the CV related to the TTP registered a value higher than 10% for four pairs of replicates. In conclusion, the dynamic chamber system proposed in this paper represents a time-saving method with a good repeatability for measuring in vitro NH3 concentration in pig slurry samples.