School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemGenetic variation in Eucalyptus regnans F. Muell(University of Melbourne, 2010)Past climate changes and associated range contraction, expansion and introgression events are regarded as major forces shaping the evolution of the genus Eucalyptus. Previous investigations in south-eastern Australia have identified some putative refugia and recolonised areas for tall eucalypt forests during the last glacial cycle but the response of individual species are very little understood and in some regions, the evidence for migration or persistence is completely absent. Here I uncover the response of Eucalyptus regnans and two species (E. delegatensis and E. obliqua) which often occur with it and among all of which there is likely to be introgression. These results have important implications for understanding forest responses to climate change and for current gene pool management. Chloroplast variation in Eucalyptus regnans suggests that in spite of the narrow ecological tolerances of the species and the harsh environmental conditions of the Last Glacial Maximum (LGM), E. regnans was able to persist locally, in or near its current range, often in what would have been unfavourable conditions. Therefore, rather than the waves of recolonisation or long distance dispersal experienced by tree species in much of Europe or North America, E. regnans, with the exception of the Central Highlands region of Victoria in mainland Australia and the central region of Tasmania, does not appear to have migrated great distances. A comparative phylogeographic study of three south-east Australian Eucalyptus species (E. delegatensis, E. obliqua, and E. regnans) with different tolerances, in terms of cold, drought and soils revealed that, despite ecological differences, the three species have responded to past climatic changes in a similar way, by persisting in multiple refugia in similar locations. Inter-specific sharing of haplotypes was extensive, and fixation of shared, regional haplotypes, was more likely in areas postulated as treeless at the LGM. It seems likely that the process of recolonisation, in particular, results in loss of chloroplast diversity within species and interspecific haplotype sharing. A nuclear microsatellite study of range wide variation in E. regnans found a high level of diversity, and, in contrast to the findings from the study on chloroplast variation, a generally low level of geographic differentiation. The findings do not support the hypothesis of a high level of genetic differentiation in the species that was suggested by the chloroplast data and its disjunct distribution. No loss of nuclear diversity was found at locations fixed or nearly fixed for the hypothesised recolonising chloroplast haplotypes. I argue that a loss of diversity at recolonised locations has been offset by hybridisation with, and genetic displacement of a pre existing (species was already present at site), compatible species. Extensive pollen mediated gene flow both during and after recolonisation from E. regnans in refugia may have led to the displacement of a pre-existing species and the homogenisation of nuclear microsatellite allele frequencies but retained the pattern of chloroplast variation from the displaced species. This scenario would explain the maintenance of high nuclear and low chloroplast variation at recolonised locations and the low level of genetic differentiation between recolonised locations and adjacent refugia. These results suggest that E. regnans is a species with a strong phylogeographic structure but a low level of nuclear differentiation. Across the species range there is a complex mosaic of populations with different histories of colonisation, persistence and introgression. Phylogeographic patterns in this study indicate that the major biotic responses of tall eucalypt forest to climatic changes were persistence and resilience. The implications of these findings are discussed in the context of defining gene pool management strategies for E. regnans. They generally support the conservative management objectives of the current seed transfer guidelines for commercial forestry operations in both Victoria and Tasmania: seed should be sourced from the harvested coupe if possible or from nearby stands matched for environment. In the central highlands of Victoria and central Tasmania where there is low between stand differentiation longer distance transfers may be more acceptable provided the environment is matched. In other regions such as East Gippsland where long-term, in situ persistence has resulted in strong differentiation between stands, then transfer of seed over relatively small geographic distances will disrupt the established patterns of evolutionary lineages. Given the evidence of the importance of introgression in E. regnans and its relatives, the current policy of maintaining the pre-existing species mix on regeneration should also assist in preserving the collective adaptive potential of the species at a site.
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ItemCommunity dynamics in natural resource governance : building adaptive management capacity towards ecological sustainability(University of Melbourne, 2010)The aim of the research was to analyze community dynamics and collective action for sustainable natural resource governance in decentralized Indonesia. The research was an ethno-methodology research in which in-depth interview and participant observation were used for data collection. Data analysis was carried out by examining the distribution of narratives provided by the respondents, and by carrying out a thematic analysis in which emerging themes were used to produce a complex and coherent narrative of the discourse found within the case study site. The research aims to explore the various practices of natural resource governance and the complex social relations which influence collective action for the sustainable governance of natural resources. Natural resource governance in modem Indonesia is marked by the tension between the centralized policy strategy of the Suharto period and the reactive strategy of Post-Suharto decentralization. To some extent, decentralization led to devolution of power and opportunities for local resource users to make consequential decisions over the natural resources upon which they depend. However, this approach rested upon the capacity of communities to reach a consensus untainted by local politics, commercial imperatives and traditional power stmctures. Moreover, decentralization had not given the majority access to strategic and structural decision making power. Empirical findings from Tongke Tongke�s mangroves in Sinjai, South Sulawesi, suggest that social institutions and local mles came into play and the people felt honored to protect the resource on behalf of the community. These social institutions took the form of neighborly ties, collective identity, reciprocity and social and ecological responsibilities. Access to Tongke Tongke�s mangroves was not free but governed by local and informal mles to maintain its benefits for the good of the community. The community, through the elders, was determining access and making decisions about management on behalf of them all. Community members acted in a way that benefited the overall good even when they were avowing individual rights. The thesis argued that individuals evolved behavior which was commensurate with their responsibilities, leading to innovative power stmctures which were more locally sensitive and environmentally appropriate. The case study in the village of Tongke Tongke within the Regency of Sinjai suggested a rebuttal of Hardin�s Tragedy of the Commons. In line with Ostrom�s theory, the commons is governed by local and often informal mles which induce behavior that are in line with a collaborative mentality to maintain its benefits for the good of the community. Nonetheless, as suggested by Bookchin and argued in the thesis, collective natural resource governance is also about individuals who resist and accept the shaping of civic collaboration and ecological sustainability. In addition, barriers and enablers for sustainable natural resource governance need to emerge from local contexts; they could not emerge as a consequence of top down devolution alone. Moreover, no preparation of local communities could be made to assume the unintentional consequences of complex power relations. In line with Etzioni�s theory, empirical findings suggest that real power relationships in real resource management contexts can undermine the possibility of democratic and equitable consensus making. The thesis argued that social reciprocity, identity validation and symbolic capital can motivate resource users to behave in line with a collaborative mentality for mangrove protection.
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ItemMaking sense of social research in forestry : an exploration of interactions in an interdisciplinary research process(University of Melbourne, 2010)Many social scientists believe their disciplines bring a critically important perspective to environmental problems (Ewert, Baker, & Bissix, 2004; Lockie, Higgins, & Lawrence, 2001; Reser & Bentrupperbaumer, 2001; Roughley & Salt, 2005). Problems involving natural resource management, particularly competing land uses, are often thought to inherently be social problems. Despite this, social researchers have faced challenges in contributing to solving these problems. A critical challenge is lack of understanding of social science by natural scientists, policymakers and non-academic research partners, such as industry. The complex nature of these problems requires coordination between these stakeholders. Gibbons et al. (1994) have described the trend towards collaborations which involve a broader range of academic and societal stakeholders as a new �mode� of knowledge production. Inroads have been made to understanding how knowledge production occurs in the new �mode�, especially in the area of study focused on interdisciplinary collaboration. Some of this work has specifically focused on collaboration across the �great divide� of natural-social sciences in natural resource management and environmental problem settings (e.g. L�l� & Norgaard, 2005), yet it is still unclear how social scientists can, and do, contribute alongside others. The aim of this study is to understand and conceptualise the processes in which social scientists and others engage to make social research usable. This study uses a narrative ethnographic approach (B. Tedlock, 1991), taking advantage of my position as a collaborator studying collaboration between social researchers and foresters in the Cooperative Research Centre Forestry (CRC) Communities Project based in Australia. Principal methods involved participant-observation over 21 months, detailed field note-taking, interviewing members of the Communities Project, and analysis by renarrating field experiences. Studies of natural-social scientific interdisciplinarity provided the expectation that there would likely be miscommunication, misunderstandings and missed opportunities. Instead, social researchers and industry partners managed to make connections. Social researchers were able to communicate the messages they saw as important (even when these had negative implications for industry partners) while industry partners increased their understanding of the methods, findings and implications of social research. I found that this was facilitated by two interactive processes. The first, I labeled �reframing�. This involved participants engaging in questioning and clarification as well as mutually learning each others� vocabularies and concepts. I labeled a second process �stretchy narratives�, referring to participants� stretching, or expansion of their original narrative to incorporate critical features of others� narratives. These interactive processes constituted integrative practice in this interdisciplinary collaboration, adding to previously abstract conceptualization of integration (e.g. Klein, 2001b; Newell, 2001). Working with industry partners, I redefined the nature of our differences, finding that they were focused on practical measures such as clear project explanations and valuable research outcomes. This, and the lack of obvious �disciplinary� struggle, suggests that in some �interdisciplinary� collaborations, particularly those with non-academic stakeholders, philosophical differences may be less relevant than social scientists have argued (e.g. Eigenbrode et al., 2007). Given the notion that disciplinarians have somewhat fixed epistemological positions, project partners� perspectives were more fluid than anticipated. My research suggests that those working in natural-social science collaborations in environment and natural resource management problem settings can make social research usable by adopting a gradual and incremental approach to educating and learning from others, engaging opportunistically in teaching moments.
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ItemPlacing the native pest in the postcolonial city : the relocation of Melbourne's flying foxes(University of Melbourne, 2010)As long as wildlife inhabits the urban environment, humans will experience interspecies conflicts. And as long as these conflicts occur, questions will be raised about who and what belongs in city places, and what it means to put native pests �in their place�. The ways we deal with animals judged to be �out of place� have effects: not only for the species and spaces involved, but also for our very ideas about these species and spaces, and for our ideas about the place of nature in our postcolonial urban lives. Human interventions with animals matter because they are not only reflective of the socio-spatial order, but productive of it. This thesis, grounded in cultural geography, investigates the way native animals figure in the socio-spatial orderings of the contemporary Australian city. It aims to make an original contribution to animal geography by paying sustained attention to the ways wild animals are placed discursively and practically by humans, and in turn, how those wild animals place themselves. I pursued this research by following the 2003 relocation of Melbourne�s colony of native greyheaded flying-foxes from the Royal Botanic Gardens (RBG) to Yarra Bend Park. I used this case of animal transgression and human intervention to make wider claims about the paradoxical place of the native pest in the postcolonial city. I took an in-depth and interpretive approach to the research, with the aim of providing qualitative, contextualised claims. My methods included: targeted interviews with key stakeholders; participant observation activities; field site visits; news media reviews; and content analysis of key documents and websites. The thesis structure follows the chronological journey of the relocation: from the flying-fox colony�s discursive rejection from the RBG via the Save Our Gardens Campaign; to the determination of the new roosting site by the Grey-headed Flying-fox Alternative Campsite Task Force; the embodied relocation of the flying- foxes across Melbourne; and, finally, the discursive and material work undertaken to accommodate the colony in Yarra Bend Park. The thesis concludes that, while the relocation has set a precedent for dealing with native pests, its supposed success sits in tension with the actual nature of the relocation. The relocation achievement was not as tidy, successful, nor as human as many post-relocation claims suggest. The relocation was constituted by a messy, hybrid process largely shaped by the bats, and resulted in hybrid and unstable outcomes.
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ItemConflicting agendas : illicit drugs, development and security in the Wa special region of Myanmar(University of Melbourne, 2010)This thesis examines the reasons behind the persistent conflict and underachievement in global efforts to control illicit drug production in the South and argues for a new approach. This underachievement is explored through a detailed case study of a remote illicit drug producing area in Myanmar, the Wa Special Region (WSR), and through a comparative examination of the illicit drug problem in Afghanistan. Using extensive field interviews, results from existing quantitative studies and drawing on literature that examines the relationship between security and development, a comprehensive picture is painted that describes the perspectives, motivations and actions of both Northern and Southern actors over time with respect to three key inter-related themes: drug control, security and development. The conceptual framework that is used for the thesis uses security and development research and illicit drug studies to map and analyse conflict in actor policy around these three themes. The thesis makes a number of findings and recommendations. Firstly, new information on an under-researched region, its people and leaders is presented. The WSR is a poorly understood region that has been dependent on illicit opium cultivation and trade for over a hundred years and a more detailed understanding of its history, security concerns and recent actions may assist in future policy development towards the region. Secondly, the thesis argues that, at a relatively localized level, each drug growing region is context specific and the details of local economies and political complexes at this level are often not well understood. This lack of understanding can contribute to project failure or irrelevance of drug control efforts. More consistent progress on the illicit drug control issue requires that the complexity of individual production areas needs to be analysed, particularly local governance structures, the underlying economy and perceptions and actions of local leaders. The thesis also shows that drug control is characterised by conflicting perspectives and actions by local and external actors. Policies are often based on self-interest and may be single-minded in that they ignore the interdependency of drug control, security and development. A general inattention to gathering evidence through research and analysis of the underlying social, economic, political and cultural factors, compounds this conflict and actors are informed by a partial assessment of the drug control problem. Limited interaction between different actors leads to lack of coordination, coherence and opportunities for consensus-building on drug control action and policy, which may adversely impact local populations or the level of drug production. In some cases, local actors may be criminalised by external ones foreclosing opportunities for continuing cooperation and progress. This thesis argues that local actors and governance structures are paramount and must be considered in areas where illicit drug production is to be addressed. Local leaders must be respected and local achievement should be recognised and reinforced. Further, that the security concerns of all actors including local leaders need to be considered and compared as a starting point in any drug reduction programme. The thesis recommends that drug control should be underpinned by evidence-based complexity analysis of drug producing regions that incorporates both local and external actors and be overseen by a single UN body to build consensus. Finally, there must be a concomitant willingness on the part of powerful international actors to share intelligence and to pursue a more cooperative approach to drug control and less unilateralism.
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ItemQuantification and mitigation of gaseous nitrogen emissions from pasture and cropping systems(University of Melbourne, 2010)Due to the application of nitrogen (N) fertilizers and animal excreta agricultural soils emit large quantities of ammonia (NH3), nitrous oxide (N2O) and nitric oxide (NO) to the atmosphere. As well as negative environmental effects, such as contribution to acid precipitation and enhancement of the greenhouse effect, the processes that produce these gases are the main cause of the low efficiency of N fertilizers. A series of field studies were carried out in Australia and China to quantify emissions of NH3, N2O and NO to investigate how farming practices impact on the soil N dynamics responsible for their loss and to recommend strategies to reduce them. A micrometeorological method using a backward Lagrangian stochastic model (bLs) was used to determine NH3 volatilization resulting from grazing a pasture by a herd of dairy cows and from subsequent urea application. Emissions were 4.9 and 1.9 g N cow"1 d"1 in summer and autumn, respectively, with the larger losses in summer due to higher temperatures and evaporation rates. Loss of fertilizer N in summer was 1.2% of applied- N when irrigation followed fertilizer application immediately and 5.3% in autumn when irrigation took place 3 days after application. Measurements of N2O emissions were made with 100 static chambers from an approximately 1 ha area in the same pasture a few days after the sequence of grazing, fertilizer application and irrigation. The key soil physical and chemical properties from under each chamber were analyzed. The N2O emissions were extremely variable, ranging from 45-765 (average 165) ng N m"2 s"1 in the summer and 20-953 (average 138) ng N m"2 s"1 in autumn. Emissions showed spatial dependence up to 73 and 51 m in autumn and summer, respectively, and were significantly correlated with soil nitrate (r2 = 0.79) and ammonium (r2 = 0.41) through the effects of animal traffic in the field, indicating both nitrification and denitrification contributed to N2O emissions. Ammonia loss from fertilizer application to winter cereals in western Victoria was measured following application of urea, ammonium sulfate and urea-ammonium nitrate. Ammonia loss varied with location and fertilizer type and ranged from 1.3 to 23% of N applied. The variation with location seemed to be due to a combination of factors including soil texture, soil moisture when fertilizer was applied and rainfall (how soon and how much) after fertilizer application. Addition of a urease inhibitor [N-(n-butyl) thiophosphorictriamide] to a urea treatment reduced losses by more than 80%. Emissions of NOx and NH3 from a maize crop fertilized by deep-placed urea in northern China were 1.2% and 6.5% of the applied N, respectively. The loss of NOx was far greater than that reported by others, possibly because the measurements were made continuously in this study rather than as spot measurements with static chambers. Soil analyses to depth indicate that little nitrate was leached down the profile and a study using soil cores and acetylene inhibition to measure denitrifying activity suggested that the rate of denitrification was very slow in this soil. The results suggest that in this soil with a slow denitrification rate and little leaching, deep placement of the urea to limit NH3 volatilization is an effective method for decreasing N loss to the atmosphere and increasing fertilizer use efficiency. The soil N dynamics of an irrigated maize system in which stubble retention and stubble burned treatments were superimposed over treatments of varying N fertilizer rate were studied at a site near Whitton, NSW. Field measurements using 15N-labelled urea recovery from microplots with and without the nitrification inhibitor ammonium thiosulfate (ATS), showed significantly more fertilizer N was recovered in the grain from a stubble incorporated treatment than a stubble burned treatment (P < 0.05), and more fertilizer N remained in the soil in the stubble burned treatment. This indicated lower denitrification losses of fertilizer N applied to the stubble burned system. The high N recovery in grain in the stubble incorporated treatment was thought to be due to improved soil structure in the heavy texture soil. Inclusion of 5% ATS in the fertilizer formulation did not appear to have an impact on N recovery of fertilizer N. Nitrous oxide emission was strongly dependent upon fertilizer rate and there was no statistically significant effect of stubble management on N20 emission rate found using static chambers. The effects of soil fertility on emission of NO and N20 from mixed pasture converted to high clover pasture, and subsequently to a cereal crop were studied for 21 months. More NO and N20 was emitted from the high fertility than from the low fertility paddocks likely due to restriction of legume growth by phosphorus deficiency. This effect was amplified by increased N cycling due to higher stocking densities on the high fertility pasture and stubble-grazed wheat treatments. Overall, changing the land use from a mixed clover grass pasture to a wheat crop resulted in increased emissions of NO and N2O (2.03 kg as NO and 2.09 kg as N2O). Most of the N2O was emitted when the water filled pore space (WFPS) was high and most of the NO was emitted when the WFPS was low suggesting that the N2O was formed during denitrification and the NO was formed by nitrification.
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ItemEnvironmental factors influencing inflorescence differentation and development, and bunch architecture, of Vitis vinifera L.cvs. Chardonnay, Shiraz and Sauvignon Blanc(University of Melbourne, 2010)Annual yield fluctuations create problems for harvest intake scheduling, fruit ripening and matching supply to demand which results in significant cost to the industry. An understanding of the early development of yield components and the influence of environmental conditions on them is a necessary step toward better yield estimates and ultimately. the future manipulation and stabilisation of yield. The purpose of this research was to bridge the gap between observation-based science and quantitative science in the field of grapevine reproductive biology and to identify critical windows in the development of the grapevine. The factors affecting the timing of initiation and the extent of differentiation of inflorescence primordia (IP) in latent buds of Vitis vinifera L. cvs Shiraz, Chardonnay and Sauvignon Blanc, representing varied environmental zones in Australia and New Zealand were investigated using, interalia, Scanning Electron Microscopy (SEM). Subsequent morphometric analyses were carried out and novel insights into fundamental reproductive development were elucidated. Vineyards located in warmer sites promoted earlier initiation and differentiation of IP and development was more advanced at each phenological stage. Moreover, larger IP were observed where initiation and differentiation had occurred earlier in the season and where the apex diameter range was larger. The process of differentiation may be earlier and more dynamic than previously thought at warmer sites with anlagen visible in Chardonnay by October, primary branch differentiation by anthesis, secondary branch differentiation by veraison and tertiary branch formation occurring on the lower third of basal IP of Shiraz and Chardonnay by dormancy in some instances. Evidence of the timing and extent of differentiation of reproductive structures within latent compound buds has not been previously documented in Sauvignon Blanc and is minimal for Chardonnay and Shiraz. The timing of initiation and extent of primordial branching attained by dormancy may have an important role in determining yield components. Strong correlations were found between IP width and IP length (approximately 80%, P<0.001) for all cultivars at all phenological stages which provide insight into patterns of development that occur some 12-15 months prior to budburst. In climates where initiation was delayed, primordial differentiation was similarly delayed. The SEM examination of latent buds of Shiraz and Sauvignon Blanc for the stage of differentiation of their IP, revealed crystal idioblasts containing raphide bundles of calcium oxalate inside exposed primordial bract tissue. These phytolithic crystals are produced by many plant taxa and have a characteristic morphology which gives them taxonomic significance. Morphometric analysis determined raphides to be on average 35.92 � 2.47 ?m in length and no more than 1 ?m wide. Raphide length was determined by the length of the crystal idioblast housing the bundles. A higher proportion of raphide bundles were observed at apical node positions of both Shiraz and Sauvignon Blanc. The physiologic role of these structures was not determined but it is speculated that they may have a role in nutrient sequestration and regulation. The response of yield components and inflorescence morphology to incremental temperature increases at budburst and to differing vine vigour, were investigated in an integrated series of experiments in the field and in controlled environments on Chardonnay and Shiraz. These experiments revealed contrasting fruiting behaviour of these cultivars in response to environmental stresses imposed by different temperatures and or growth conditions (vigour). Shiraz exhibited opportunistic fruiting behaviour in response to increased root volume with increased internode diameter, increased bud size and increased bud fertility resulting. Chardonnay, on the other hand was more conservative showing an increase in bud fertility with minimal shoot and bud response to increasing vine vigour. The studies presented in this thesis provide valuable new insights into the fundamental developmental stages of important cultivars in response to environmental variables and the influence of these on yield components. Linking observational research and molecular biology may provide further insight into the mechanisms that drive the kinds of differences in development, morphology and yield components that were explored in this thesis. To face the challenge of global climate change, a fundamental understanding of what is likely, in terms of phenology and inflorescence morphology, is required to move toward the formulation of management strategies to maintain desirable production levels and wine quality. Of immediate importance are the grapevine morphological and physiological responses to extreme heat events such as those experienced in Australia over the 2008-2009 and 2009-2010 growing seasons, and expected to be more frequent in future hotter climates.
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ItemAssessing site quality of South Australian radiata pine plantations using airborne LiDAR data( 2011)Site quality information underpins many aspects of radiata pine plantation management in South Australia. Site quality assessment is essentially a problem of assessing the spatial variation of standing volume in unthinned stands at reference age nine or ten. Data collected during three experimental trials and two operational surveys were used to research a new site quality assessment system relying on airborne LiDAR data. A two-stage method was adopted characterised by the calibration of predictive models relating forest and LiDAR variables, and the subsequent application of these models to predict the forest variable across an area of interest. The four parts of the study examined the properties and behaviour of LiDAR prediction models, the sampling design and timing of field data collection, the spatial resolution of model application and the special case of partially thinned plantations. Single-variable, linear models, fitted to high altitude/low density LiDAR data captured across 20 sites scattered over an area of 10,000 km2 , had RMSE of 10-11% and 3-4% for stand volume and predominant height respectively. Evidence of site effects in the models was inconclusive. Models fitted to four LiDAR and field datasets acquired in 2002, 2006, 2007 and 2009 had consistent structure but model parameters were sensitive to the differences in operational LiDAR campaign parameters, indicating that prediction models should be re-calibrated each survey. Fifty field plots were found to be adequate to fit a regionally applicable volume prediction model. Sample selection methods only influenced model precision when sample sizes were small (less than twenty plots). The correlation between forest and LiDAR variables remained strong when field and LiDAR data were collected several years apart, but model parameter values changed rapidly as a result of tree growth. A time lag between LiDAR and field data collection can be tolerated but field measurements, once commenced, should be concentrated in time. The LiDAR predictor variable for volume was found to be insensitive to changes in the reference plot area indicating that volume prediction models may be applied in partitions (spatial units) with areas different than those of the calibration field plots. Comparison of alternative configurations of size, shape and arrangement of partitions, coupled with one of four spatial interpolation techniques, demonstrated significant differences in precision of predicted volume surfaces, with key factors being the dimensions of the interpolation neighbourhood and LiDAR data density. Several configurations closely approximated or, in the case of low density data, exceeded the precision of the prediction models. A method for assessment of partially thinned plantations appeared effective but requires further validation. The results of this study will be used to guide the second operational LiDAR-based site quality survey in South Australia, scheduled for early 2012.
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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.