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Title: Dynamics of atmospheric ammonia exchange with intensively-managed grassland
Author: Milford, Celia
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2004
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Continuous measurements of atmospheric ammonia (NH3) 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 NH3 concentration and flux for the whole measurement period were 1.52 μg m-3 and 13.9 ng m-2 s-1, respectively. Enhanced emissions of NH3 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-2 s-1, 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 NH3 emissions from cut grassland have been observed, but not quantified prior to this study. The NH3 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 NH3 during winter months (-6.0 g NH3-N ha-1 d-1) and prior to cutting of the grass (-4.9 g NH3-N ha-1 d-1) to being a net source after the grass was cut (29.3 g NH3-N ha-1 d-1) and after nitrogen fertilisation (153.6 g NH3-N ha-1 d-1). Net emission was also observed during grazing periods (33.0 g NH3-N ha-1 d-1). The pattern of Nh3 exchange was similar for 1998 and 1999. The net annual budget of NH3 exchange for the grassland for May 1998-April 1999 was emission of NH3 of 1.9 kg N ha-1 yr1, equating to 1.6% of the fertiliser N applied. The gross emission flux for the year was 4.2 kg N ha-1 yr-1. Scaling up these gross emissions across the whole of the UK improved grassland (60,500 km2) would lead to 25 kt NH3-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 NH3 emission budget of the UK.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available