Ammonia (NH3) volatilization from soil-applied manure not only causes environmental pollution but also reduces the fertilization value of the manure. Anaerobic digestion and solid/liquid separation alter the physical and chemical characteristics of slurry, which affect NH3 emissions after application. The present study measured potential laboratory NH3 losses from different manures, untreated pig slurry and the liquid fractions of each untreated and digested slurry, after their application to two different soil types. The experiment was carried out in dynamic chambers using a photoacoustic infrared gas analyser to determine the NH3 concentration in the air stream directly.
The estimated values of nitrogen (N) emitted for surface-applied, untreated pig slurry were 0·26±0·064 mg per mg of applied total ammoniacal nitrogen (TAN). For the liquid fractions of pig slurry and digested pig slurry, results were 0·13±0·064 and 0·16±0·064 mg/mg, respectively. Initial NH3–N emission rates from surface-applied, untreated pig slurry were higher than those measured for either liquid fraction; in the case of the untreated pig slurry, half was emitted in the first 4·9 h of measurement. Silty-loam soil showed a higher N emission than loam soil with surface-applied slurries. This result was probably due to the higher infiltration rate of loam soil, even offsetting the effect of its high soil pH. Immediate manure incorporation into the soil was shown to reduce NH3 emissions by 82%. Results demonstrated that a method combining dynamic chambers with a photoacoustic gas analyser was as reliable as the widely used acid traps method. Moreover, direct measurement with the gas analyser permits an increasing temporal resolution that gave a high-quality description of the NH3 emission dynamic.