Nitrous oxide (N2O) is a potent greenhouse gas (GHG) which is released naturally into the atmosphere as a
by-product of the microbial processes of nitrification and denitrification. Agricultural activities are believed to
account for up to 80% of anthropogenic N2O emissions at a global scale; however, these estimates are prone to
large uncertainties due to the large temporal and spatial variability associated with flux measurements. This
thesis contains five studies which aimed to improve the ability to measure and predict N2O emissions from
agricultural activities.
A closed loop dynamic chamber was developed using a quantum cascade laser (QCL). This method
provided high precision chamber measurements of N2O flux from soils with a detection limit below
4 μg N2O-N m-2 h-1. Using the dynamic chamber method allowed for a detailed investigation of uncertainties in
individual measurements including contributions from regression fitting, temperature and pressure. The lack of
negative fluxes measured that were outwith the detection limits of the methodology (0.3% of all measurements)
highlighted that the uptake of N2O reported in some previous literature is likely to have been the result of
detection limits of measurement methods applied.
Spatial variability of N2O flux was investigated at the plot, field and farm scale. Fluxes were measured
from a grassland field plot before and after a tillage event. These measurements highlighted the large spatially
variability present in N2O fluxes from agricultural soils. Fluxes varied by up to three orders of magnitude over
distances less than 5 metres after the tillage event. A field scale experiment carried out on grazed grassland
investigated relationships between soil properties and N2O flux. This study found that N2O emissions correlated
strongly with available nitrogen content in the soil and that animal waste was likely responsible for the spatial
variability of N2O flux observed at the field scale. A farm scale inventory of N2O emissions was carried out
investigating several large point sources of N2O and emissions from the wider field coverage. The inventory
estimates that nitrogen fertiliser application is the single largest N2O source from the livestock farm accounting
for 49% of annual emissions