School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemCycling of nitrogen in the biosphere and atmosphere( 2013)Selected publications are presented to illustrate Freney’s research on the development of new techniques for assessing the transfer of gaseous nitrogen from fertilizer and animal excreta to the atmosphere, determining the fate of fertilizer nitrogen in different agricultural systems in Australia, China, Indonesia, Malaysia, New Zealand, and the Philippines, establishing the factors controlling emission of gaseous nitrogen compounds from plants, soils and waters, and developing practices to improve efficiency of fertilizer nitrogen and reduce its deleterious effects on the environment
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ItemPhysiological basis of genotypic variation in plant response to elevated CO2( 2013)The CO2 concentration [CO2] in the atmosphere is increasing and is predicted to double by the end of the 21st century which is likely to have a profound effect on plant growth and yield, especially for C3 plants. Rising [CO2] has direct effect on photosynthesis (A), thus its potential stimulation drives the plant growth and development. However, these responses varied among species but, little is known about the underlying mechanism of genotypic variation in plant response to elevated [CO2]. In this study, wheat (Triticum aestivum L.) was used to test the hypotheses genotypic variation in response to elevated [CO2] exists within the wheat germplasm and if genotypic variability exists, whether it is related to leaf level A and related other traits. Based on above hypotheses, one experiment under glass house and two experiments under Australian Grains Free Air CO2 Enrichment (AGFACE) condition were conducted in the year 2010 and 2011. In experiment 1, seven wheat genotypes were grown at either ambient [CO2] (~384 µmol mol–1) or elevated [CO2] (700 µmol mol–1) in temperature controlled glass houses. Grain yield increased under elevated [CO2] by an average of 38% across all seven genotypes, and this was correlated with increases in both spike number (r = 0.868) and above ground biomass (AGB)(r = 0.942). Across all the genotypes, flag leaf A increased by an average of 57% at elevated [CO2]. The response of A to elevated [CO2] ranged from 31% (in H45) to 75% (in Silverstar). Only H45 showed A acclimation to elevated [CO2] which was characterised by lower leaf maximum RuBisCO carboxylation efficiency (Vc.max), maximum electron transport rate (Jmax) and leaf nitrogen (N) concentration. Leaf level traits responsible for plant growth, such as leaf mass per unit area (LMA), carbon (C), N concentration on dry mass basis (NFLAG LEAF), N content on an area basis (NLA) and the C:N increased at elevated [CO2]. LMA stimulation ranged from 0% to 85% and was clearly associated with increased NLA. Both of these traits were positively correlated with grain yield, suggesting that differences in LMA play an important role in determining the grain yield response to elevated [CO2]. Thus increased LMA can be used as new trait to select genotypes for a future [CO2]-rich atmosphere. In the second experiment, leaf blade elongation rate (LER) and leaf C and N dynamics in expanding leaf blade (ELB, sink) and A, C and N status in the last fully expanded leaf blade (LFELB, source) were determined using two wheat genotypes, Yitpi and H45. Plants were grown at either ambient [CO2] (~384 µmol mol–1) or elevated [CO2] (~550 µmol mol–1) within the AGFACE facility. Elevated [CO2] increased the leaf area and plant total above ground dry mass by 42% and 53% respectively for Yitpi compared to 2% and 13% for H45. Both genotypes showed increased LER at elevated [CO2] which was 36% for Yitpi compared to 5% for H45. In contrast, A increased by 99% for Yitpi at elevated [CO2] whereas H45 showed no change. For both genotypes, a strong correlation (r=0.807) was observed between LER of ELB and soluble carbohydrate concentration in LFELB over diurnal cycle. In ELB, the highest spatial N concentration was observed in the cell division zone, where N concentration was 67.3 and 60.6 mg g-1 for Yitpi compared to 51.1 and 39.2 mg g-1 for H45 at ambient and elevated [CO2] respectively. In contrast, C concentration in the cell division and cell expansion zone of the ELB increased only in Yitpi suggesting that C supply from the LFELB is genotypes dependent and well associated with LER, leaf area expansion and whole plant growth response to elevated [CO2]. In the third experiment, variation in A acclimation to elevated [CO2] at different leaf ontogeny was investigated. Seven wheat genotypes with contrasting growth and yield response to elevated [CO2], Janz, Yitpi, Silverstar, H45, Drysdale, Hartog, and Zebu were grown under rain fed condition at either ambient [CO2] (~384 µmol mol–1) or elevated [CO2] (~550 µmol mol–1) in the AGFACE facility. Leaf gas exchange measurements were conducted at two stages of flag leaf blade development: pre and post-anthesis. Immediately after the gas exchange measurements, flag leaf blade was sampled for biochemical analysis. Vc.max was calculated from gas exchange data to estimate the A acclimation to elevated [CO2]. Genetic variation in A acclimation to elevated [CO2] was observed. H45 showed strong acclimation to elevated [CO2] where Silverstar showed no acclimation. A acclimation to elevated [CO2] was observed only at post-anthesis, which was characterized by both reductions of Vc.max and Jmax. In both stages of the flag leaf, soluble protein concentration was significantly decreased at elevated [CO2]. Nevertheless, association of A acclimation and soluble protein concentration was not significant. In particular, Silverstar showed a large reduction in soluble protein concentration at elevated [CO2] at post-anthesis, but still showed no significant A acclimation (no reduction in Vc.max) to elevated [CO2]. The reductions in total soluble protein content at elevated [CO2] were not similar either between growth stages or genotypes. These findings suggest that A acclimation to elevated [CO2] varied between wheat genotypes but it is not fully associated with changes in soluble protein concentration. In summary, elevated [CO2] stimulated A, growth and grain yield and found large genetic variability of CO2 response. Variation in growth and yield response to elevated [CO2] was closely associated with leaf level traits such as LMA, leaf N and A capacity suggesting that plasticity of leaf level A related traits play a key role in response to elevated [CO2]. Particularly, genotypes showed higher A response to elevated [CO2], also showed increase LER which later translate to biomass and greater grain yield under elevated [CO2].
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ItemThe effectiveness of nitrogen fertiliser use for wheat production with an emphasis on elevated carbon dioxide environments( 2013)Variability in crop responses to nitrogen (N) is influenced by many factors that are subject to complex interactions. A meta-analytic approach was used to study variability in crop responses to N fertiliser application using a large dataset of Australian annual N fertiliser trials. This analysis provided baseline information about existing performance and management of N fertilisers for crop production. However under predicted changes in atmospheric CO2 concentration, new challenges exist for N management and there is limited information on this. A series of controlled environment and field experiments were established to examine the effects of N fertiliser strategies (inhibitors, foliar applications) on N availability, crop N status, grain protein, and soil nitrous oxide emissions under ambient and elevated CO2 (e[CO2]) conditions to better understand the challenge of effective N use under future climates. The findings from the meta-analysis revealed that the effectiveness of N use will be more predictive when making N management decisions for moderate yielding environments but require caution when applied in low and high yielding environments; splitting high N application rates by considering the timing of N application can significantly alter the response, especially for N uptake; urease inhibitor (at a higher concentration of inhibitor) and nitrification inhibitor can enhance the yield and grain N uptake of basic N products; nitrification inhibitors will enhance N uptake in high yielding areas under particular soil texture conditions; and in coarse texture soils, high rates of N application will produce lower relative responses when rainfall is high compared to when seasonal rainfall is lower. The findings from the studies conducted under e[CO2] conditions suggest that at maturity the use of nitrification inhibitor might play a role to compensate the slow mobilisation of N towards grain. Foliar N application might not be a viable strategy to be used to influence grain N characteristics under e[CO2]. Nitrous oxide emissions may increase in legume based cropping systems but the interaction with [CO2] was not significant. The meta-analysis can be used as a guideline for N management. However, this analysis was limited to agronomic responses and further studies while considering economic factors are needed for more informed N management decisions. Under future climate of e[CO2], it is debatable whether better synchronisation of N supply with crop demand can compensate for a decrease in tissue N concentration, or whether a physiological constraint exists that needs to be overcome through further research.
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ItemFactors affecting microwave modified wood permeability and strength( 2013)Microwave treatment can be used to increase wood permeability, speeding subsequent drying or impregnation processes with potential savings in time, energy and cost. However microwave treatment can reduce the strength of the treated timber. Treatment pressure can be used to alter the boiling point of water, which could have a significant effect on the resultant strength and permeability. Three methodologies were used to investigate the relationship between microwave treatment conditions, in particular pneumatic pressure, and the resultant strength and permeability of the timber. A device was designed and constructed with the aim of enabling the simultaneous measurement of the permeability of small cylindrical samples during microwave treatment. Testing of the individual components proved successful, however moisture vapour generated during microwave heating of the timber samples presented problems during combined testing. Permeability measurements were performed separately in the second and third methodologies and utilised larger samples. Controlled temperature and controlled power density treatments were trialled with the controlled power density treatment providing more consistent results. Bending testing and an impregnation cycle were found to be the most reliable methods of assessing strength and permeability respectively. High power microwave treatment increased the permeability and reduced the strength of the treated timber. Treating the samples under elevated pressure, followed by an immediate pressure delta minimised this strength loss. A ranking system was proposed to assess the combined strength and permeability resulting from treatment. Using this ranking system, an optimum balance between high permeability and maximum strength was obtained using a high power, Elevated Pressure Microwave treatment followed by an Immediate Pressure Delta (EPMIPD). This treatment performed better than atmospheric pressure microwave treatments conducted as part of this research.
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ItemWheat grain quality dynamics under elevated atmospheric CO2 concentration in Mediterranean climate conditions( 2013)Since 1959, carbon dioxide concentration [CO2] in the atmosphere increased from 315 µmol mol-1 to approximately 389 µmol mol-1 by 2009 in a rate of 1.5 µmol mol-1 per year. Within the next 50 years, atmospheric [CO2] will likely to rise to 550 µmol mol-1. Carbon dioxide is a greenhouse gas and a major factor that contributes to global warming. In parallel, global temperature is predicted to increase by an average of 1.5-4.5 ºC with more frequent occurrences of extreme climatic events such as heat waves and/or drought by the mid of this century. There is a limited understanding on the impact of elevated atmospheric [CO2] (e[CO2]) on wheat grain quality in semi-arid and Mediterranean cropping systems. The research reported in this thesis investigated the effects of e[CO2] on wheat grain physical, chemical, flour rheological properties under two main climate conditions: semi-arid and Mediterranean which represent the water-limited “mega-environment 4”, larger wheat grown area in the world as defined for wheat (Braun et al., 1996). The experiments were carried out using state art technology of free- air CO2 enrichment (FACE) facilities located in Walpeup and Horsham, Victoria, Australia. (See thesis for full abstract)
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ItemA study of salinity tolerance in field pea( 2013)Preliminary research was aimed at identification of parental germplasm that could be used for improvement of tolerance to toxic effects of sodium chloride (NaCl) in field pea. An initial screening experiment of 780 globally-distributed Pisum L. accessions identified significant variation in response to applied NaCl, based on plant symptoms. Lines with relatively higher tolerance as compared to commercial varieties grown in Australia were most frequently identified within landraces originating from the central, eastern and southern provinces of China. The most tolerant identified accession was an unadapted landrace ‘ATC1836’ originating from Greece. Variation for salinity tolerance was validated using a sub-set of 70 accession lines. Salinity-induced toxicity symptoms were closely associated with reductions of plant growth rate, height, shoot and root dry matter and with increased concentration of Na+ at the plant growing tip. The level of salinity tolerance based on these factors varied substantially and provides an important basis for genetic improvement of field pea for Australia. Seven field pea genotypes that vary significantly for salinity tolerance showed a range of symptom development and growth responses over time under increasing levels of NaCl salinity applied using watering treatments. The genotypic responses were closely associated with Na+ accumulation in leaflet tissue on the lower plant and a parallel reduction in K+ concentration. Increasing salinity caused strong but variable inhibition of root and shoot dry matter accumulation and final grain yield for all genotypes. The genotype ATC1836 showed the highest relative tolerance based on measured parameters, but was comparatively slow growing. Three genotypes (03H090P-04HO2002, 03H556P-04HO2012, 99-410-2-14-2) with moderate tolerance obtained substantially more dry matter under the highest salinity treatment of (18 dsm-1) compared to the commercial variety ‘Kaspa’. The genotype OZP0812 was also able to maintain relatively higher growth rate at the lower salinity treatment level of 6 dsm-1. The high salinity tolerance of the landrace genotype ATC1836 that is evident at early growth stages was also apparent in this study at later ontogeny, on the basis of lower biomass reduction, reduced symptom development and delayed rate of Na+ accumulation in plant tissue. In this study, sodium accumulated more rapidly and to a higher degree, and symptoms developed faster on lower growth nodes when compared to the growing tip. Plant biomass and main plant height showed lower correlation with Na+ concentration in plant tissue than plant chlorosis. The taller genotype OZP0812 produced more biomass under conditions of increasing salinity than the dwarf genotypes Kaspa and OZP0809 and the landrace genotype ATC1836. Applied salinity exerted deleterious and varying effects on seed yield components such as reduced seed and pod set and seed size. The genotype OZP0812 maintained both higher seed yield and larger seed size compared to the salinity tolerant landrace genotype ATC1836, despite accumulation of more Na+ in plant tissue. Increased salinity resulted in earlier flowering and increased Na+ concentration in seed tissue. Segregation ratios for salinity tolerance were analysed in 3 field pea populations derived from crosses between the sensitive genotype Kaspa and the tolerant genotypes ATC1836, Parafield and Yarrum, revealing probable multigenic control. A comparatively higher proportion of tolerant progeny was observed in the ATC1836 x Kaspa population. However, a high degree of trangressive segregation for enhanced salinity tolerance was apparent in progeny from crosses of either Parafield or Yarrum with Kaspa, suggesting that parental combining abilities should also be assessed for improvement of salinity tolerance. Positive broad sense heritabilities for measures of symptom response to salinity, and repeatability of results between experiments and generations implied high potential for genetic gain from use of pot-based screening methods. Differences in assessment of salinity symptom response based on a numerical scale as compared to percentage plant necrosis were not significant. Variation for salinity tolerance within recombinant inbred lines (RILs) progeny derived from the Kaspa x Parafield cross was documented on the basis of rate of symptom development and a salinity tolerance index. A frequency analysis showed that the proportion of field pea germplasm with higher salinity tolerance in advanced yield testing nurseries in Australia had increased in the period 2005-2011. However, a multivariate canonical analysis based on 14 yield nurseries in 2011 indicated that the degree of salinity tolerance in advanced germplasm currently provides significantly less yield benefit than degree of boron toxicity tolerance, indicating a need for further pre-breeding efforts. Boron tolerant accessions as a group were higher yielding at 7 sites during 2011. All of these sites were in regions with highly alkaline sub-soils, and six sites had comparatively lower growing season rainfall. The high rainfall exception (Kingsford, South Australia) was affected by powdery mildew, for which resistance is positively linked with high boron tolerance. Genotypes with dual sensitivity to both boron and salinity mostly performed better at sites with higher rainfall in the growing season. For sites at which salinity tolerance was more important, the only sensitive genotypes that performed well were all early flowering (i.e. PBA Twilight). One boron sensitive genotype (119) showed specific adaptation across sites at which boron tolerance was important, and is hence suitable as a key parent for improving general adaptation of crop. Linkage maps based on molecular genetic marker polymorphism were constructed for RIL populations of Kaspa x Parafield and Kaspa x Yarrum populations. RIL progeny and parents from these populations were screened at the seedling growth stage for growth symptom responses to salinity stress imposed by adding NaCl in the watering solution at a concentration of 18 dsm-1. Phenotypic variation for salinity induced symptoms was normally distributed and increased with severity over time. A salinity index was developed to quantify variation for salinity tolerance and was used in concert with statistical correlation analysis to identify quantitative trait loci (QTLs) and flanking single nucleotide polymorphism (SNP) markers that could be useful for implementation of marker assisted selection (MAS) strategies. This thesis has identified valuable variation in salinity tolerance in Pisum for field pea breeding programs. A knowledge of critical growth responses at the seedling and reproductive growth stages for salinity tolerance now provides a guide to screening of populations for useful genetic variation or marker-tagged QTLs. Preliminary investigation has identified QTLs for seedling tolerance to salinity stress for implementation of MAS for the purposes of parent building and routine screening.
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ItemStructural variations in the ovine genome: their detection and association with phenotypic traits( 2013)Growth and meat yield traits are important to the New Zealand sheep industry. Genomic selection (GS) of these traits uses information from high density ovine SNPs to produce estimated breeding values (EBVs). The aim of GS is to account for loci directly influencing the trait (quantitative trait loci, QTL). This relies on the assumption that high density SNPs tag QTL effects via linkage disequilibrium (LD), however, it is unlikely that all QTL are adequately tagged by high density SNPs. Copy number variants (CNVs) are a type of genetic variant that may not be well tagged by SNPs and have been shown to be involved in phenotypic variation. To date, there has been little published work on CNVs in the sheep genome. While there is a well known example of a CNV affecting coat colour (agouti) in sheep, little is known of how CNVs affect phenotypic variation of production traits. The studies in this thesis employed multiple methods to identify CNVs in the sheep genome. Animals (including trios) were assayed on a Roche NimbleGen 2.1M CGH array. CNV calls from trios were used along with known false-positive calls to build a logistic regression to predict the probability calls from the 2.1M CGH array were correct. 3,488 autosomal CNVRs were identified. On a large scale, CNVRs were hard to accurately detect without using a combination of approaches. CNVRs were verified against CNVRs detected with the Roche NimbleGen 385K CGH array, Illumina OvineSNP50 BeadChip and Illumina HiSeq 2000 sequence data. Results of this work contribute a comprehensive resource of CNV regions to the literature on sheep CNVs. Given the importance of growth and meat yield traits in the New Zealand sheep industry, and the possibly unaccounted effects of CNVs on these traits, an association analysis was carried out with these traits and loci that potentially represent CNVs. Firstly, it was determined that EBVs produced by Sheep Improvement Limited (SIL) were appropriate to use as the dependent variable in the association analysis. Loci that potentially represent CNVs were SNPs from the Illumina OvineSNP50 BeadChip that were previously discarded from GS and genome wide association studies (GWAS) because they could not be genotyped. Reasons why these SNPs can’t be genotyped include the presence of the SNP in a CNV. Raw data from these SNPs were tested to determine if they were associated with the growth and meat yield traits. Seventeen associations, involving nine SNPs, were detected and validated in independent datasets. Two SNPs were in CNVRs detected using the CNV detection methods described above - one involved the agouti CNV. Raw data from this SNP was associated with ultrasonic eye muscle depth. Associations remained significant after fitting genotypes of flanking SNPs (from surrounding ~1Mb of sequence) used in GS and GWAS, suggesting that the effect of these associations are not accounted for in GS or GWAS. Including information from these SNPs in GS could improve the reliability of EBVs, contributing to genetic improvement of growth and meat yield traits in the New Zealand sheep industry.
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ItemThe role of the antioxidants ascorbate and glutathione, in the plant-pathogen interaction between Phytophthora cinnamomi Rands and susceptible and resistant Eucalyptus species( 2013)This study investigates the role that the low molecular weight antioxidants, ascorbate and glutathione, play in the plant-pathogen interaction between Eucalyptus spp. and Phytophthora cinnamomi - Rands. The study has shown that plant responses (i.e. antioxidant concentration changes, rates of photosynthesis, stomatal conductance, quantum efficiency of photo-system II and carbohydrate levels) to P. cinnamomi root infection in roots and leaves differ significantly between susceptible and resistant Eucalyptus species. Antioxidant concentration decreases and an increased sensitivity to leaf photoinhibition were associated with infection in susceptible E. sieberi. In contrast, early antioxidant increases were associated with resistant E. sideroxylon.
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ItemPasture investment decisions: returns, risk and time( 2013)Making risky investment decisions well is an important part of farm business management. Risky investment decisions are those for which the rate of return on capital is not known when the decision to invest is made. To be complete, analysis of such decisions must include consideration of expected returns, risk and the dynamic element of time. This thesis contains such an analysis, in relation to decisions to invest in pasture improvement on farms in south west Victoria, Australia. The return and risk of these investments were estimated using stochastic simulation of a whole farm economic model. The real options approach was used to value the risk associated with these investments. This analysis revealed that pasture investments generate risk-adjusted returns which compare favourably to those generated by other readily-available investments, such as bank deposits or shares. The estimates of return and risk are static – they do not change over time. As such, this analysis generates no insight into the dynamic aspect of decisions to invest in pasture improvement, and cannot explain some elements of observed pasture investment decisions. To remedy this deficiency, the dynamic aspect was investigated by representing the ability of investors to reduce uncertainty over time in a Bayesian learning model. Learning alters the perceived distribution of values that can be taken by a variable of interest over time. As this occurs, the decision to invest in pasture improvement may also be revised. Performing this analysis revealed that a learning model is a suitable tool for representing the dynamic aspect of decisions to invest in pasture improvement, even when the data required to calibrate the model are relatively scarce. Furthermore, insights were obtained into the quantity and quality of data obtained at different stages throughout the learning process. These estimates indicate that, in this case, more information is obtained from a one-year on-farm trial than is obtained from three years of collecting information from off-farm sources. This study shows how a comprehensive analysis of risky farm investments can be performed, and hence represents a contribution to the discipline of farm management economics. Furthermore, information about the return, risk and dynamic aspects of decisions to invest in pasture improvement can help various groups and organisations make better decisions. In particular, the implications of this study are considered for farmers and their advisors, rural merchandise sellers, research and development organisations and policy-makers.
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ItemPhytocaps as biotic systems to mitigate landfill methane emissions( 2013)Landfill gas is a significant source of anthropogenic methane emissions and accounts for more than half of greenhouse gas emissions from waste sectors. While harvesting landfill gas for energy is the best mitigation option, methane oxidation by landfill cover soils is considered an important secondary measure to reduce landfill methane emissions. In recent years, regulatory control has evolved to allow consideration of alternative options for final covers. An evapotranspiration cover, also commonly known as phytocap in Australia, is one of the alternative cover options that has been widely considered and investigated. A phytocap presents a soil-plant alternative to the traditional barrier cap approach. It relies on the capacity of a porous layer of soil to store water, and the combination of evaporation and transpiration of vegetation to control the percolation of water into a landfill. When planted with native vegetation, it also improves the ecology and sustainability of a closed landfill. While the hydrological performance of phytocap has been investigated by a number of studies resulting in positive outcomes, its ability to serve also as a “biocover” for effective methane oxidation to mitigate emissions has received little attention. The main aim of this thesis was to assess phytocap performance in terms of enhancing methane oxidation activity in the cover soil and mitigating methane emissions. The research methodology included a full-scale field comparison between phytocaps and conventional compacted clay covers in terms of methane oxidation and emissions. A supplementary glasshouse experiment with both blank and planted soil columns was also conducted to investigate vegetation-methane interactions, and to identify plant influenced soil properties that would affect methane oxidation and emissions. This research forms a part of the 5-year Australian Alternative Cover Assessment Project (A-ACAP), co-funded by the Australian Research Council and Waste Management Association of Australia. In the full-scale field comparison, trial sites located at five landfills under a broad range of Australian climatic conditions have been monitored. The 5 A-ACAP trial sites with side-by-side phytocap and conventional cover test pads were built directly on top of active landfills with an aim to study their hydrological performance as well as methane mitigation efficiency. This thesis related to the methane mitigation component focused on the trial site located in Melbourne where more frequent monitoring campaigns have been conducted. The results of the field trial indicated that phytocaps could mitigate methane emissions more effectively compared to conventional covers. Emission rates detected from the Melbourne phytocap averaged at 1.45 gCH4/m2/day (out of the 17% measurements that resulted in significant positive fluxes), compared to the conventional cover which averaged at 5.57 gCH4/m2/day (out of the 65% measurements that resulted in significant positive fluxes). This positive finding is supported by the gas concentration profile data obtained from both types of covers. The field trial also concluded that the effectiveness of methane oxidation in phytocaps can be significantly enhanced with methane emission reduced to a negligible level when used in combination with gas extraction systems. In contrast, only a marginal gas extraction influence was observed on conventional covers. In addition to the overall reduction in emissions, phytocaps can also significantly reduce the amount of hot spots in surface emissions. For the glasshouse experiment, at both high and low gas influx rates, the planted soil columns showed high oxidation fractions (mostly higher than 0.5), which are comparable to the performance of some biocovers reported in the literature. Rather unexpectedly, the blank soil columns exhibited an even higher average CH4 oxidation fraction (average 0.89 under 36.5-73 gCH4/m2/day load) compared to the planted soil columns (average 0.67 under 36.5-73 gCH4/m2/day load). This finding appeared to be contradictory to the positive methane oxidation enhancement effects of vegetation in soil covers commonly reported in previous studies. With a closer examination, it was observed that the plant roots brought in a significant increase in soil gas diffusivity of the planted columns, which significantly shortened the methane retention time in the soil and subsequently reduced the methane oxidation capacity of the planted columns. The high oxidation fraction of the blank columns was attributed to the organic rich soil. Combining the research of this thesis with the findings of a concurrent A-ACAP hydrological study, it can be concluded that phytocaps provide an economical and sustainable option for new and old landfills to minimise water percolation and to mitigate methane emissions. As a result of achieving the objective of minimising percolation, the soil moisture profile of a phytocap may not be at its optimum for methane oxidation during certain periods of the year. Maintaining a balance between minimising water infiltration and promoting methane oxidation has to be addressed in a phytocap design in order to achieve optimum performance in both functionalities.