Continuous measurements of atmospheric ammonia (NH<sub>3</sub>) exchange were conducted for a period of 19 months (May 1998-November 1999) over intensively managed grassland (cut twice for silage and grazed) in southern Scotland using the aerodynamic gradient method. The mean NH<sub>3 </sub>concentration and flux for the whole measurement period were 1.52 μg m<sup>-3</sup> and 13.9 ng m<sup>-2</sup> s<sup>-1</sup>, respectively. Enhanced emissions of NH<sub>3</sub> were observed following three separate grass cutting events (June 1998, August 1998 and June 1999) with peak emissions of 380, 200 and 539 ng m<sup>-2</sup> s<sup>-1</sup>, respectively. The magnitude of these emissions was up to an order of magnitude greater than the emissions observed from the grassland prior to cutting. Enhanced NH<sub>3</sub> emissions from cut grassland have been observed, but not quantified prior to this study. The NH<sub>3</sub> exchange was bi-directional with large diurnal and seasonal variation, which was strongly linked to grassland management in addition to meteorological conditions. The grassland varied from being a net sink for NH<sub>3</sub> during winter months (-6.0 g NH<sub>3</sub>-N ha<sup>-1</sup> d<sup>-1</sup>) and prior to cutting of the grass (-4.9 g NH<sub>3</sub>-N ha<sup>-1</sup> d<sup>-1</sup>) to being a net source after the grass was cut (29.3 g NH<sub>3</sub>-N ha<sup>-1</sup> d<sup>-1</sup>) and after nitrogen fertilisation (153.6 g NH<sub>3</sub>-N ha<sup>-1</sup> d<sup>-1</sup>). Net emission was also observed during grazing periods (33.0 g NH<sub>3</sub>-N ha<sup>-1</sup> d<sup>-1</sup>). The pattern of Nh<sub>3</sub> exchange was similar for 1998 and 1999. The net annual budget of NH<sub>3</sub> exchange for the grassland for May 1998-April 1999 was emission of NH<sub>3</sub> of 1.9 kg N ha<sup>-1</sup> yr<sup>1</sup>, equating to 1.6% of the fertiliser N applied. The gross emission flux for the year was 4.2 kg N ha<sup>-1</sup> yr<sup>-1</sup>. Scaling up these gross emissions across the whole of the UK improved grassland (60,500 km<sup>2</sup>) would lead to 25 kt NH<sub>3</sub>-N, equivalent to 9.5% of the UK total emissions. These results indicate that the gross emission from all processes in fertilised grassland, including emissions from fertilisation, grazing and from cutting, make a significant contribution to the NH<sub>3</sub> emission budget of the UK.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:657757 |
| Date | January 2004 |
| Creators | Milford, Celia |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/28627 |
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