MEASURING AMMONIA FLUXES AFTER SLURRY SPREADING UNDER ACTUAL FIELD CONDITIONS

A large fraction of atmospheric ammonia is emitted during the applicat ion of slurry to fields. Two micrometeorological methods were used to obtain a consistent estimate of emissions under actual field condition s. The mass balance method (MBM) was used to quantify the very large e missions that occur during slurry spreading and for the first few hour s. Wind speed was measured at 5 heights, and ammonia was sampled at th ese heights by trapping it in dilute sulphuric acid. A two-height aero dynamic gradient method (2AGM) was used for later automated hourly mon itoring of the long-term flux over a large surface (over a hectare). T he ammonia concentration gradient was measured continuously with a che miluminescence analyser. The hourly estimates of ammonia fluxes were s imilar to the data from a labelled nitrogen recovery method ((NRM)-N-1 5). The MBM gave reliable flux estimates using only two measurement he ights. Thus, ammonia fluxes could be determined directly in real time using the chemiluminescence analyser, and two air temperature measurem ents by two anemometers, beginning from the first minutes after the st art of slurry spreading, and continuing until several weeks later. (C) 1998 Elsevier Science Ltd. All rights reserved.