Factors affecting nitric oxide and nitrous oxide emissions from ...

Nitric oxide is very reactive and is converted to nitrogen dioxide (NO2) by reactions with O3,
oxygen and other oxidising radicals (Crutzen, 1979).
Because NOx gases have relatively short life times and undergo complex nonlinear
chemistry, with opposing indirect effects occurring as ozone enhancement and CH4 reduction,
the calculations of a Global Warming Potential (GWP) for NOx emissions are highly
uncertain (Forster et al., 2007). The non-linear chemistry means that the net radiative forcing
of NOx emissions depends significantly on where the emission occurs and on the relative
daily and seasonal intensities of the emissions (Forster et al., 2007). Thus there is currently no
global mean GWP for NOx.
In the troposphere increased concentrations of NOx have been shown to enhance the
production of O3 in the troposphere (Stohl, 1996). Thus soil emissions of NO may have a
significant role/impact at the local level while at the regional or global level the role of NO
compared to that of industrial combustion processes is described by Davidson and Kingerlee
(1997) as being uncertain.
Thus recent attention has intensified and focused on these gases because of the role(s) they
play as either a greenhouse gas, as ozone regulators or as a result of the implications for
redeposition of NOx.
There is a general dearth of information and a lack of understanding regarding the
magnitude, processes and factors responsible for NOx emissions arising from ruminant urine
patches under grazed pasture conditions. Thus this research project was performed to improve
the fundamental understanding of the processes and soil factors that affect NOx emissions.
The main objectives were:
To measure NOx emissions in-situ in the field on a seasonal basis.
To examine the effects of urine-N rate and the fundamental soil variables (temperature,
moisture, and pH) on the associated NOx emissions.
To relate the NOx emissions observed to the N2O flux profiles.
This thesis is constructed of the current introduction, a literature review (chapter 2) of relevant
information, a general materials and methods chapter (3) that presents materials and methods
common to all studies, a series of chapters (4, 5, and 6) that describe three laboratory
experiments and then two chapters (7 and 8) that report on two seasonal, in-situ field
experiments, followed by a chapter (9) presenting the general conclusions.
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