EVALUATION OF METEOROLOGICAL TECHNIQUES FOR MEASUREMENTS OF AMMONIA LOSS FROM PIG SLURRY

Owing to volatilization of ammonia, substantial amounts of inorganic nitrogen may be lost after surface application of animal slurry. The ammonia volatilization rate is high within the first hour of application and declines rapidly thereafter. The change in loss rate during the first hours after application has been estimated by use of a new ammonia gas analysing technique, differential optical absorption spectroscopy (DOAS), which has a short response time. The equipment is expensive and to reduce cost vertical fluxes may be calculated with single height meteorological techniques. In this study, we compared vertical fluxes achieved by the integrated horizontal flux (IHF) technique with measurements by DOAS and two single height meteorological techniques for estimating vertical ammonia fluxes. Losses of ammonia from a rectangular experimental field (20 m times 140 m) to which pig slurry was applied were estimated by the theoretical profile shape (TPS) technique and the Phillips theoretical solution of the diffusion profile shape (PTPS). Results agreed with estimates based on the IHF technique using acid traps and wind speed measurements at five heights. It is shown that the TPS technique, which is simple in use, gave accurate loss estimates even when the parameters used for calculating losses were not corrected for change in fetch length, until length increased by more than 30%. Losses of 0.24 kg NH3-N min-1 ha-1 were measured within the first minutes after application of the slurry. During the two experimental periods of 3 1/2 and 4 h about 50% of the ammonia applied in slurry volatilized and half of this amount was lost within the first 1-1 1/2 h. The cumulative ammonia loss could be described with a Michaelis-Menten equation.