School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemEfficiency of nitrogen fertilization of dry-seeded rice in south-east Australia( 1986)The efficiency and fate of fertiliser nitrogen applied to combine-sown rice were investigated in field experiments in which fertiliser timing, water regime and soil type were varied. The information gained was used to predict strategies for optimising fertiliser efficiency using current techniques, and to predict and test improved fertilisation technologies. The stage of crop growth, water regime and soil properties all had large and interacting effects on agronomic efficiency. On an infertile alkaline grey clay soil, agronomic efficiency of urea applied at sowing was very low (8 kg kg-1) compared with later applications associated with continuous flooding (up to 56 kg kg-1). The low efficiency was due to nitrification and subsequent de-nitrification during the flushing period. Nitrogen-15 balance studies indicated that 80% of the urea nitrogen was lost from the soil-plant system. The rapid nitrification rate and high loss of nitrogen on the grey soil contrasted with the very low levels of nitrate and low losses of nitrogen (10-25%) from urea applied to rice growing on an infertile acidic red soil under alternating conditions of saturation and aeration (sprinkler-irrigation). Furthermore, on a fertile acidic red soil in the same region, other authors have measured large yield responses to nitrogen applied at sowing. These differences highlight the need to consider soil properties and water management when attempting to predict optimum fertilisation strategies. Yields of sprinkler-irrigated rice (managed to replace water lost by evaporation) were reduced by more than 50% compared with rice grown under continuous flood. However, this was not due to decreased plant uptake or increased loss of fertiliser nitrogen in the sprinkler-irrigated treatments. The low yields appeared to be associated with plant water stress, decreased nitrogen mineralization (by approximately half) and location of the fertiliser nitrogen near the soil surface where root activity was probably restricted due to inadequate moisture. On the grey soil, maximum agronomic efficiencies occurred with application shortly before permanent flood or at early panicle elongation. Efficiency was doubled when urea was applied before permanent flood compared with shortly after permanent flood. The greater efficiency appeared to be associated with the deeper transport of the applied nitrogen into the soil, and consequently lower losses by ammonia volatilisation and/or nitrification/de-nitrification. However, even with the most efficient fertilisation strategies, plant 15N recoveries were less than 40%, while losses exceeded 20%. When the 15N balance data were considered in conjunction with the agronomic data,. it appeared that it would be possible to further increase agronomic efficiency if plant recovery of applied nitrogen could be increased. In particular, minimisation of losses of nitrogen (via nitrification/de-nitrification) from fertiliser applied before permanent flood was a most attractive option. Potential methods identified for increasing agronomic efficiency by minimising losses of nitrogen applied before permanent flood were deep placement and the use of nitrification inhibitors and slow release nitrogen sources. Several experiments were conducted in an attempt to improve fertiliser efficiency by banding urea and modified urea sources 5-7 cm below the soil surface before permanent flood. Plant recovery of 15N was increased by up to 20% with banding compared with surface broadcasting. The best recoveries were from urea super-granules (USG). An experimental fertiliser rig and a commercial seeder fitted with a triple disc assembly were used to band the fertilisers in the main plots. There was no significant yield advantage with banded urea over broadcast urea applied before permanent flood. The fertiliser rig caused considerable plant damage. Using the triple disc applicator, it was possible to band fertiliser below the soil surface with minimal soil disturbance, and plant damage, but only under i ideal conditions of soil moisture. Furthermore, where the soil surface was dry and cracked, penetration with the triple discs was no greater than the depth of the cracks into which surface applied urea prills would be washed upon flooding. The yield test of USG was unsatisfactory because of the excessive plant damage with this method. With current technology, there appears to be little scope for improving the efficiency of urea applied before permanent flood by mechanical placement below the soil surface.
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ItemInterregional trade in sawntimber in Australia( 1989)The purpose of this study has been to develop a modelling framework which incorporates the essential features of the sawntimber market in Australia and which is capable of being used to study both the interregional trade patterns within Australia and the impacts of various changes on the sector. This firstly involved the determination of demand and supply relationships for the market and secondly the development of a spatial equilibrium model of trade. The basic structure of sawntimber market was studied with the use of two different approaches. The first was an ad hoc, statistical model of the sawntimber market in Australia. The statistical model provided new results for price elasticity of sawntimber demand in Australia. Elasticity of demand for sawntimber was found to be -0.783, an improvement on previous studies which found no relationship between sawntimber demand and the price of sawntimber. It also provided new information on the structure of the sawntimber market in Australia and the substitution between imported and domestic supplies. In particular, the results showed that domestic and imported sawntimber do not compete on the basis of price in the Australian Market. The second approach was through a theoretical model of the production structure of the sawmilling industry using the translog cost function. The estimation of the cost function served two purposes, the first to provide a measure of the slope of the supply curve for the trade model, and the second to provide information about the production structure of the industry. Although .data problems ultimately prevented the use of the translog cost function in the spatial equilibrium model, it did provide new information on input substitution, technological change and scale economies in the sawmilling sector. In particular, the results found that most inputs are substitutes, there are diseconomies of scale, and that technological change has been capital and energy using, and labour saving. The second component of the study was the development of a spatial equilibrium model of the sawntimber sector. This was done with a non-linear programming framework and based on demand and supply elasticities provided by the statistical model. The result was a model which could be used to study the impacts of demand and supply changes. The model was used to study the impact of the forecast increase in log availability by the year 2000. An important result from the use of this model was to demonstrate that an 11.5 percent price decrease could cause the domestic market to absorb 60 percent of the sawntimber which the increased log availability could allow. To summarise, the research encompassed in this thesis has provided new information on the economic structure and performance of the sawntimber sector in Australia. It has also provided a basis for new research and applications of the results. In this study the results were applied to a spatial equilibrium trade model of the sector in Australia. This in turn has provided a new basis for policy analysis in forest industry, in particular issues involving trade and demand or supply shocks.
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ItemSelection of Rhizobium trifolii strains for inoculation of Persian clover (Trifolium resupinatum L.)( 1988)The studies reported in this thesis examined the Rhizobium trifolii (also reclassified Rhizobium leguminosarum biovar trifolii) strain requirements for inoculation of Persian clover (Trifolium resupinatum L.). The agronomic importance of T. resupinatum cv. Maral to agriculture in southern Australia had been recognised and new cultivars of T. resupinatum were being developed, but there had been no objective assessment of the inoculation requirements of this species. A diverse range of R. trifolii strains were examined for symbiotic competence (ability to nodulate) and effectiveness (nitrogen fixation) with T. resupinatum cv. Maral under bacteriologically controlled conditions ideal for plant growth. The results showed that strains varied in effectiveness from 18% to 145% compared to the standard commercial inoculant strain, TA1 (100). A strain selection programme was followed in which three selected strains (CC2483g, CC1317 and CC1305), all superior in effectiveness compared to TA1 (P<0.05) were assessed in glasshouse and field experiments in southwest Victoria. CC2483g was the best strain on T. resupinatum cv. Maral. This strain demonstrated good effectiveness, was highly competitive, persisted in the soil for 18 months under conditions of mild competition from naturalized strains and appeared particularly well adapted to sandy soils of low fertility. In contrast, TA1 was poorly effective, less competitive than other strains and the least persistent strain in the field. Strain differences in symbiotic effectiveness were demonstrated in the field where there was a low population (<5.0 x 102 R. trifolii per gram of soil) of naturalized R. trifolii. In soils with large populations (>1.0 x 104 R. trifolii per gram of soil), of naturalized R. trifolii , improvements in nitrogen fixation and herbage yield by inoculation with effective strains were dependant on the rate of inoculation and the relative symbiotic effectiveness of naturalized strains. T. resupinatum cv. Maral was capable of nodulation by a range of naturalized strains and it was concluded that commercial seed coat inoculation with highly effective strains and lime pelleting would, in general, not improve the nitrogen fixation of T. resupinatum cv. Maral in most areas of southwest Victoria. Host range experiments examined the effectiveness of the three selected strains compared to TA 1 and WU95 on important annual and perennial clovers and showed that CC2483g had a wider host.range that CC1317 and CC1305. The use of TA1 in the T. repens subgroup and WU95 in the T. subterraneum subgroup inoculants were verified in this study. Effectiveness tests with five lines of T. resupinatum var. majus and eight lines of T. resupinatum var. resupinatum suggested that T. resupinatum constituted a seperate symbiotic subgroup within the Trifolium species. The final step in the strain selection programme indicated that all selected strains satisfied the requirements for commercial inoculant production. It was concluded, that under the current policy of using single wide-spectrum strains for commercial inoculation, that a special single-strain inoculant should be produced for T. resupinatum containing CC2483g. Alternative inoculant recommendations to overcome the apparent deficiencies of both Australian commercial clover inoculants are discussed, of which the most practical solution could be mixed-strain culturing.
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ItemAgroforestry : a study of agroforestry extension and a model of light interception in agroforestrry( 1986)This thesis examines two important aspects of agroforestry in Australia: agroforestry as an agricultural innovation and light interception by the tree crop. (1) Agroforestry as an innovation The ideas and opinions of farmers and professionals involved in agroforestry in Australia were studied by mail-return questionnaires. Questionnaires were sent to all farmers and professionals known to be actively involved in agroforestry. - The study is not a statistical survey of a population. The potential of agroforestry as an agricultural innovation is discussed with reference to the response to the survey and the literature. The need for a universally accepted classification of agroforestry practices is demonstrated and a system suitable for agroforestry in Australia and New Zealand developed. The classification is an adaption of agroforestry classifications developed for use in less industrially developed countries. The adopters of agroforestry involved in the study are shown to be more educated, of-higher social status, and more innovative than farmers in general. Most show opinion leader status within their local community and have a positive attitude towards agroforestry, as do the professionals involved in the research and extension of agroforestry. It is argued that agroforestry adoption is following the general trend of innovation adoption and can be expected to be adopted at an increasing rate in the near future. Factors that may limit the extent or rate of adoption are identified and a strategy developed to ensure good two-way communication between researchers and potential adopters so as to encourage successful adoption of agroforestry by interested farmers. (2) Light interception Light is shown to be a major limiting factor affecting agricultural production in agroforestry. Light interception by the tree crop reduces light availability at ground level and therefore growth of agricultural crops. Past models of light interception by discontinuous tree canopies are reviewed and a new computer based model developed. The model, TREE-SHADE, allows estimates to be made of the light interception by a stand of widely spaced trees at any time on any date. Input variables include the nature of the site, the mean size and shape of the tree crop, the spatial arrangement of the trees and the times and dates of interest. The model is tested against field results collected in a seven year old agroforest of Pinus radiata near Canberra. The model was shown to slightly underestimate solar radiation availability at ground level beneath the trees. The difference was partly explained by variability in spacing and was not considered significant enough to detract from the value of the model.
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ItemStudies on the rehabilitation of manganese tailings at Groote Eylandt, Northern Territory( 1986)The thesis briefly-describes the location where the work was conducted ie Groote Eylandt, Northern Territory, its climate, biophysical environment, mining operation, ore beneficiation process, tailings dams and rehabilitation research programmes. A review of tailings disposal methods used throughout the world, including land and marine based systems, alternative uses, and reprocessing are discussed. The potential for air and water pollution from tailings, including the local examples of Captains Flat and Rum Jungle are described. Examples of the various means of surface stabilization ie vegetative, physical, and chemical and a brief outline of tailings stabilization work conducted at most major metalliferous mining and ore processing operations in Australia is given. An overview of the major aspects of soil manganese chemistry is presented in Chapter 2. Subjects discussed include manganese mineralogy, heating, storage and drying effects, the influence of lime, organic matter, and compaction and the interactions between manganese and other ions, in particular Calcium, Iron, Phosphorus, Aluminium and Cobalt. The research work was conducted in the period 1987-83 and had the primary objective of "finding a long term, self sustaining vegetative cover to stabilize tailings and prevent them from becoming sources of air and water pollution, while enhancing the aesthetics of the area". Detailed chemical and physical characterization of tailings from a 2 hectare study area was conducted. The study area was located within a major group of earthen walled tailings dams, some of which were being actively used for tailings disposal. The analyses found that the black coloured tailings were variable in physical properties with textures ranging from sands to clays, with corresponding variations in bulk density and water holding capacity. No extreme pH, soluble salt, or exchangeable aluminium levels were recorded, although total nitrogen and available phosphorus levels were found to be low. A series of sequential extractions were used to determine water soluble, exchangeable, easily reducible and dithionite soluble manganese fractions. The results obtained indicated that the exchangeable, easily reducible and total manganese levels would be above the critical levels for plant growth to occur. Characterization of the temperature regime on the tailings dams during starrier was undertaken using mercury in glass thermometers over the summer months. Comparisons obtained between the tailings study area, undisturbed open forest and a backfilled area rehabilitated with pasture, indicated that the tailings were not hotter than the other sites studied. Although the results indicated that no adverse microclimate exists in the tailings in terms of temperature regime, measurements with thermocouple needles at all three sites to confirm this finding would be useful. Because some local plants were growing on the dams, a series of agronomic trials were initiated using nine tropical pasture grasses and five tropical legumes, without the addition of any soils. Vigorous growth of the grasses occurred and despite many different treatment combinations, no successful growth of legumes occurred. The main fertilizer response from the grasses was dependent upon phosphorus with the addition of nitrogen, and various trace elements in the absence of phosphorus not resulting in any significant growth. Analysis of the results led to the conclusion that the key factor in determining the growth of the grasses in the tailings was the level of water soluble manganese. Following the success of the agronomic trials, work was then directed towards utilizing local plant species in the tailings rehabilitation work. Botanical surveys identified G1 plant species comprising 19 families growing on the dams. These were found to be nearly twice the number of plants identified by Langkamp, Ashton and Balling (1981) as growing on a manganese ore outcrop on Groote Eylandt. Comparisons between the tailings and ore outcrop, suggest that physical impedence to plant establishment and growth on the ore outcrop, rather than the manganese levels is the reason for the many differences between the two plant communities. The use of seed traps and a surface roughness and phosphorus trial, showed that a large number of grass seeds were being blown across the dams. It was shown that if a rough surface was provided, together with a phosphate fertilizer, colonization of abandoned dams would occur at a much faster rate than currently occurs. To complete the study programme, a large trial using the seed of 26 local trees and shrubs and four provenences of Eucalyptus cemadulensis was conducted. Treatments applied to the seeds included combinations of phosphorus, mulch and Rhodes grass. The trial determined that there are some local species which do not grow and survive in the tailings, yet many other common local species had impressive germination, survival and growth rates. The application of surface mulch resulted in higher germination percentages and the application of the cover crop appeared to be beneficial to the young seedlings. Overall, the regeneration trial established that the tailings dams can be rehabilitated by similar methods to the forest regeneration programme for mined out and backfilled quarry areas and that the broad objective of the research programme was achieved.
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ItemFlystrike in sheep : producers' knowledge, opinions, and management methods( 1986)Blowfly strike was recorded as a serious problem of Australian sheep during the first decade this century, and has remained a problem ever since. The cost of control was estimated at $44 million in 1975-76, and rising each year (Brideoake 1979). Much of the present knowledge of blowfly biology and strike aetiology was gained in the 1920's and '30's, and by the end of the 1940's simple, cheap and effective procedures were recommended which reduced flystrike by about 90 per cent. In the early 1970's, flystrike still caused major problems. The pest species had not changed, and the original recommendations had not been universally adopted (Graham 1979). This two stage survey assessed awareness of flystrike management among sheep producers, identified some commonly used communication channels for strike control information, and identified and assessed the importance of some socio-psychological and communication factors inhibiting access to or use of strike control information. Communication strategies were suggested for overcoming ineffective use of strike control information. Producers had poor knowledge of theoretical aspects of strike aetiology and the blowfly life cycle, but were well aware of readily observable aspects. Thirty percent of producers used three-joint tails, and the remainder used sub-optimal lengths. The advantages of using three-joint tails were not obvious to producers using other tail lengths, or manifested in practice. There was no association between three-joint tails and expressions of easier or more flexible management, or indications that flystrike was less important in management decisions. Low awareness, and poor capitalisation of the established advantages of three-joint tails probably are barriers which impede extension efforts. Evidence suggested that managers of flocks smaller than 1500 (more than 60 per cent of Australian enterprises) did not aim to maximise net flock revenue. This would be an important and profound barrier to current. extension practice. Mulesing was much more common among larger flocks, and was paradoxically used as an adjunct of other preventative management. Consequently, the majority of Australian flocks were relatively unprepared for strike control, and mulesed flocks were disproportionately well prepared. Producers' assessment of information and its sources varied according to the type of information sought. Popular sources for tail length, mulesing and jetting equipment information included the Department of Agriculture. There is an opportunity for state extension services to work together with other identified sources to stimulate the process of information transfer, and to improve producers' understanding of the practical advantages of strike management recommendations.