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

Owing to volatilization of ammonia, substantial amounts of inorganic n itrogen may be lost after surface application of animal slurry. The am monia volatilization rate is high within the first hour of application and declines rapidly thereafter. The change in loss rate during the f irst hours after application has been estimated by use of a new ammoni a gas analysing technique, differential optical absorption spectroscop y (DOAS), which has a short response time. The equipment is expensive and to reduce cost vertical fluxes may be calculated with single heigh t meteorological techniques. In this study, we compared vertical fluxe s achieved by the integrated horizontal flux (IHF) technique with meas urements by DOAS and two single height meteorological techniques for e stimating vertical ammonia fluxes. Losses of ammonia from a rectangula r experimental field (20 m times 140 m) to which pig slurry was applie d 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 t he TPS technique, which is simple in use, gave accurate loss estimates even when the parameters used for calculating losses were not correct ed 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 mi nutes after application of the slurry. During the two experimental per iods of 3 1/2 and 4 h about 50% of the ammonia applied in slurry volat ilized and half of this amount was lost within the first 1-1 1/2 h. Th e cumulative ammonia loss could be described with a Michaelis-Menten e quation.