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dc.contributor.authorRyan, Matthew
dc.date.accessioned2010-04-26T22:10:21Z
dc.date.available2010-04-26T22:10:21Z
dc.date.issued2002
dc.identifier.urihttps://hdl.handle.net/10182/1752
dc.description.abstractGreenhouse gas emissions are currently a major environmental concern that has led to the development of the 1998 Kyoto protocol agreement to the United Nations (UN) Framework Convention on Climate Change (FCCC), with the aim of reducing emissions of greenhouse trace gases worldwide. Unlike more industrialised nations where carbon dioxide (CO₂) is the main greenhouse gas emitted, in New Zealand nitrous oxide (N₂O) and methane (CH₄) are the main greenhouse gases emitted as a consequence of grazing ruminants in pastoral farming systems, e.g. dairy pastures. Of the total N₂O emitted annually, over 50% is directly from excretal (especially urinary) depositions to the soil by the grazing animal. The overall objectives of this work were to investigate methods of reducing N₂O emissions from urine patches in grazed dairy pasture soils, and compare artificial neural network (ANNs) modelling over traditional modelling techniques as a new modelling approach to simulating N₂O emissions from soil. Field and accompanying laboratory experiments were established using a Lismore stony silt loam soil from a dairy farm located at Winchmore in Mid-Canterbury, to determine the effect of a nitrification inhibitor dicyandiamide (DCD) and a Carbon Rich Organic Matter Amendment (CROMA) in the form of untreated sawdust on soil nitrogen (N) dynamics and N₂O emissions. The nitrification inhibitor, DCD, reduced N₂O emissions on average by 82% in the field experiment where the soil was treated with animal urine (1000 kg N ha⁻¹ ) and urea fertilizer (200 kg N ha⁻¹ ). This result was accompanied by the DCD having no adverse effect on soil microbial biomass activity, and a 23% increase in cumulative pasture DM yield. The CROMA treatment of the soil improved soil physical quality by reducing soil compaction and increasing the soil aeration status in the top 6 cm depth of soil, and thus reducing the soil's theoretical denitrification potential. However, the magnitude of these changes were not sufficient to have any significant effect on reducing N₂O emissions from the soil. The artificial neural network modelling approach developed in the study was extremely effective in simulating N₂O emissions from the soil as a function of the five input variables of daily precipitation, soil moisture content, soil temperature, soil NH₄⁺ content, and soil NO₃⁻ content. A linear regression of modelled versus observed data showed that the network simulation was able to account for 92% of the variation in the measured data (86% of the total N₂O emitted). This was a major advance on a simple mechanistic model tested from the literature, which could only account for 12% of the N₂O emitted. The findings from this work are of some significance, considering that the use of DCD in grazed pastures has the potential to dramatically cut back New Zealand's N₂O emissions, given the fact, that about 50% of New Zealand's greenhouse gas emissions of N₂O come from animal excreta returns. On top of this, the use of artificial neural networks as a modelling approach to soil N₂O emissions is a completely new development in this area. The results achieved using this new modelling methodology, clearly showed that there is now a viable tool available to accurately simulate highly variable and complex systems, that are commonly inherent in soil N₂O emissions and other natural processes.en
dc.language.isoenen
dc.publisherLincoln Universityen
dc.rights.urihttps://researcharchive.lincoln.ac.nz/page/rights
dc.subjectnitrous oxideen
dc.subjecturine patchesen
dc.subjectartificial neural networksen
dc.subjectmodellingen
dc.subjectsoilen
dc.subjectDCDen
dc.subjectureaen
dc.subjectemissionsen
dc.subjectnitrification inhibitoren
dc.subjectdairyen
dc.subjectcarbon rich organic material amendment (CROMA)en
dc.subjectdicyandiamideen
dc.subjectnitrogenen
dc.titleManipulating nitrogen dynamics in grazed dairy pasture soils to mitigate nitrous oxide emissionsen
dc.typeThesisen
thesis.degree.grantorLincoln Universityen
thesis.degree.levelDoctoralen
thesis.degree.nameDoctor of Philosophyen
dc.subject.marsdenFields of Research::300000 Agricultural, Veterinary and Environmental Sciences::300100 Soil and Water Sciences::300102 Soil biologyen
dc.subject.marsdenFields of Research::300000 Agricultural, Veterinary and Environmental Sciences::300100 Soil and Water Sciences::300103 Soil chemistryen
lu.thesis.supervisorDi, H. J.
lu.thesis.supervisorCameron, Keith
lu.contributor.unitDepartment of Soil and Physical Sciencesen
dc.rights.accessRightsDigital thesis can be viewed by current staff and students of Lincoln University only. If you are the author of this item, please contact us if you wish to discuss making the full text publicly available.en


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