Measuring ammonia fluxes after slurry spreading under actual field conditions

A large fraction of atmospheric ammonia is emitted during the application of slurry to fields. Two micrometeorological methods were used to obtain a consistent estimate of emissions under actual field conditions. The mass balance method (MBM) was used to quantify the very large emissions that occur during slurry spreading and for the first few hours. Wind speed was measured at 5 heights, and ammonia was sampled at these heights by trapping it in dilute sulphuric acid. A two-height aerodynamic gradient method (2AGM) was used for later automated hourly monitoring of the long-term flux over a large surface (over a hectare). The ammonia concentration gradient was measured continuously with a chemiluminescence analyser. The hourly estimates of ammonia fluxes were similar to the data from a labelled nitrogen recovery method ((NRM)-N-15). The MBM gave reliable flux estimates using only two measurement heights. Thus, ammonia fluxes could be determined directly in real time using the chemiluminescence analyser, and two air temperature measurements by two anemometers, beginning from the first minutes after the start of slurry spreading, and continuing until several weeks later. (C) 1998 Elsevier Science Ltd. All rights reserved.