School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemThe water and nitrogen dynamics of a lucerne-based farming system in the Victorian Wimmera( 1998)The water and nitrogen (N) dynamics of a lucerne-based farming system (grazed lucerne-annual medic-ryegrass pastures grown in rotation with crops) was compared to continuous cropping (cereal, pulse and oilseed crops) in the Victorian Wimmera. The growth dynamics and CO2-exchange behaviour of lucerne in the pasture phase was also investigated. Soil profiles under lucerne-based pastures remained consistently drier during the year as compared to annual cropping. The amount of plant-available soil water (0.0 to 2.0 m) after 3 to 4 years of pasture was on average 48 mm less than after annual crops (wheat, field pea), most of which (81%) was extracted at depth (1.0 to 2.0 m). In the field, crop yields (canola, wheat) after lucerne were not reduced because water use by these crops was predominantly in the top 1.0 m of the soil profile. A wheat simulation study predicted that a small median yield loss of 0.4 t ha-1 (15%) could be expected for the first wheat crop grown after lucerne, although this yield penalty varied from 0 to 0.87 t ha-1 depending upon seasonal rainfall. The risk of a large yield penalty (>0.8 t ha-1) was low (5 years in 100). From simulation studies, the time taken to fully recharge the soil profile after lucerne to levels equivalent to that under continuous cropping was estimated to occur within 4 to 5 years. The contributions of N2 fixation by the legumes (lucerne, annual medic, field pea) to the N economy of the farming systems in this study depended upon the amount of dry matter production. N2 fixation by field pea (121-175 kg N ha-1 yr-1) was greater than pasture legumes (40-95 kg N ha-1 yr-1), although a large amount of N was removed in grain at harvest (115-151 kg N ha-1 yr-1). N2 fixation by lucerne (19-90 kg N ha-1 yr-1) was consistently greater than annual medic (2-56 kg N ha-1 because the effects of seasonal rainfall patterns on dry matter production were more pronounced for annual medic. Winter-cleaning of ryegrass in the pasture before cropping resulted in both a high legume content (85%) and generally increased N2 fixation (up to 55 kg N ha-1 yr-1 ). Despite some benefits in N fertility, large responses to N fertiliser were still observed in crops following pastures; in grain yield (increases of 0.33-0.55 t ha-1 for canola, 1.0 t ha-1 for wheat), protein (0.7-2.3% for canola, 1.3% for wheat) and oil yield in canola (124-205 kg ha-1). The growth pattern of lucerne was similar to that of annual species (annual medic, ryegrass) contained in the pasture, with the majority (70%) of growth occurring between July and November. The small amount of lucerne growth from summer to early autumn (December to March) was due to the small supply of water (rainfall and stored in soil) during this period. A more detailed study of two lucerne pastures during summer revealed that the plant was under considerable water stress; leaf:stem ratios increased (from 0.9-1.6 to 2.6-3.2), leaf folding and paraheliotropic movement decreased the amount of leaf area exposed to incoming radiation in the middle of the day (by 14-29%), and it was estimated that the some 75-83% of assimilated carbon was partitioned below-ground to roots and crowns.
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ItemPhysiological aspects of root growth of Eucalyptus pauciflora, subsp. pauciflora and Eucalyptus nitens( 1997)This thesis examined i) morphological and physiological effects of low soil temperatures on root growth of subalpine Eucalyptus pauciflora Sieber ex Sprengel subsp. pauciflora and montane Eucalyptus nitens (Deane & Maiden) Maiden, ii) determined the variability, and in particular the day/night variability, in root elongation, and iii) explored the physiological basis for such variability. A series of experiments were undertaken with seedlings of E. pauciflora and E. nitens grown at soil temperatures of 3, 7, and 13C, and where seedlings were transferred from one temperature to another. E. nitens grew faster than E. pauciflora at 7 and 13C, but E. pauciflora grew faster than E. nitens at 3C. E. pauciflora always produced greater total and white root length than E. nitens. E. nitens roots browned faster in response to lowering soil temperatures than E. pauciflora. The osmotic potential of the roots decreased with soil temperature, but more so in E. pauciflora than E. nitens. Proline was a prominent osmoregulant in roots of E. pauciflora and arginine in E. nitens roots. It is suggested that E. pauciflora is better adapted than E. nitens to root growth at low soil temperatures because it can keep roots white longer and can maintain lower root osmotic potentials. Root growth of E. pauciflora was examined for 31 months (December 1992 - June 1995) in a mature stand at an elevation of 1545 m on Mt Stirling, Victoria, Australia. Greater night than day root elongation was recorded from eight in situ rhizotrons during the summer and early autumn of 1993. Shoot growth was also monitored during part of this study (April 1994 - June 1995). It was found that root growth commenced in the spring at soil temperatures 5 1.5C, under 550 mm of snow, at least one month before the onset of shoot growth and continued at least two months longer that shoot growth during the autumn. A period of root dormancy for at least one month a year occurred in roots of E. pauciflora. The seasonal variability in root numbers of E. pauciflora appeared to be related mainly to soil temperature and to a lesser extent to soil water content. Moreover, there appeared to be some internal periodicity in root growth which was independent of the external environment on Mt Stirling. Greater night than day root elongation was recorded in seedlings of both eucalypts in a glasshouse. Root elongation rates were greatest in E. nitens, and root elongation of both eucalypt seedlings were greater than that of the mature E. pauciflora on Mt Stirling. The zones of day and night elongation were determined in root marking experiments. Histological studies of the zone of elongation showed that cell division occurred mainly during the day and cell elongation mainly at night. Night root elongation rates were increased by increasing day-time air temperatures, light-period, and light intensity; and by decreasing water stress during the night. The turgor pressure of the root tips was greater during the night than the day. It is suggested that the amount of root growth during the night is determined directly by turgor pressure during the night and indirectly by processes during the day (light duration and intensity, and temperature during the light period) which determine the extent of cell division during the day. A greater rate of cell division during the day will be translated into a greater rate of root elongation, especially in the night.
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ItemA marketing approach to recreation management in national parks( 1995)Recreation managers have always attempted to ensure that resources are used effectively in planning and delivering outdoor recreation opportunities. However the lack of a sound theoretical understanding of management's' role and function in the provision of these opportunities limits the ability of managers to meaningfully evaluate the effectiveness of their actions. Many authors believe that the challenge facing recreation research is the development of a model to provide this much needed theoretical base (Allen 1988, Watkins 1990). Using data derived from a visitor survey conducted at Wilsons Promontory National Park, this study examines the potential of defining and evaluating the role of outdoor recreation management from a market-oriented perspective. The concept of voluntary exchange underpins this perspective. Fundamentally, approaching recreation management from this perspective suggests that effectively providing opportunities for outdoor recreation is not necessarily contingent on fully understanding participants recreation experience outcomes. Rather, what is important, is understanding the nature of the exchange between management and participants and how well management performs in this exchange. The visitor survey principally contained two research instruments, importance-performance analysis (Martilla and James 1977), and recreation experience preference scales (Driver 1977, Driver 1983). This not only enabled the nature of the exchange between management and participants to be investigated, but also provided a means to compare a market oriented approach to outdoor recreation management with the more traditional approaches based on the recreation demand hierarchy. The results identified 13 general dimensions to the recreation opportunity provided at Wilsons Promontory National Park. Three visitor segments were identified in the Park visitor population. Analysis of the components of the recreation opportunity important in producing satisfaction for each of these segments suggests that the role of visitor management at the Park is to deliver recreation opportunities which primarily differentiate along a facility based comfort/asceticism continuum. The study also shows that visitor perceptions of management's performance in the voluntary exchange process can be used to help management ensure resources are used effectively in the delivery of recreation opportunities. The study concludes that a market-oriented approach to visitor management in national parks and outdoor recreation areas has considerable potential. However, further research is required to refine the methodology and techniques explored in this study.
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ItemSclerotinia minor in sunflowers : onset of disease and bioprotection with gliocladium virens( 1994)Sclerotinia stem rot (Sclerotinia minor) is a serious constraint to sunflower production in south-eastern Australia, where the lack of cultivars with adequate levels of resistance and the costs of chemical control make biocontrol an attractive option. Onset of disease in the field occurs at bud development. Field trials with the highly susceptible inbred line, PacF2582, confirmed the absence of disease during vegetative growth. A study of root development found a marked proliferation of lateral roots at GS 3.1-3.3 (early to mid-bud) in field-grown sunflowers and slightly earlier in glasshouse plants. Glasshouse studies demonstrated the susceptibility of vegetative stage plants to infection of lateral roots by one or 2 pre-germinated sclerotia. Onset of disease in soil inoculated to a high density with sclerotia was also delayed, generally until GS 1.5 (8 leaf), suggesting that occasional contact between roots and sclerotia is not sufficient for disease initiation. A model system was developed to examine the effects of surface microflora and exogenous nutrient on sclerotial germination. Field sclerotia, incubated on water agar disks, required surface sterilisation to relieve fungistatic dormancy. Root sap and exudates from sunflower lines stimulated germination of partially surface sterilised field sclerotia, as did root sap from non-host species. Germination rates were significantly higher with root nutrient from plants during vegetative growth than from plants at mid-bud stage. Exposure to root sap for more than 3 days was required for stimulation of germination in vitro. The germination response of soilconditioned culture sclerotia to nutrients was less consistent than that of field sclerotia. The results indicate that root nutrients have potential to stimulate germination during vegetative growth, but onset of disease awaits root proliferation at bud development. It was proposed that a threshold of root activity prolongs the exposure of sclerotia to root exudates, while overlapping rhizospheres may provide a critical concentration of nutrient for germination and mycelial development. An isolate of Gliocladium virens from disease-affected soil proved highly antagonistic to S. minor in culture. Seed treatment with G. virens suppressed disease induced by inoculation of lateral roots in pasteurised potting medium and in field soil. Significant disease control was also obtained by sowing seed into a plug of G. virens growing on V8-vermiculite or by pre-germination of seed with a culture of G. virens. Bioprotection by seed treatment with G. virens was evaluated at two field sites, and was effective in field microplots where disease incidence was less than 50%. Since G. virens, applied on seed, did not affect root growth and did not grow into the lateral root zone, it was concluded that seed treatment with G. virens creates a "cordon sanitaire" around the upper tap root, sufficient for bioprotection of inoculated plants in pots and field microplots. If seed priming techniques can be adapted to allow germination of G. virens on seed before sowing, it may be possible to enhance the cordon sanitaire and delay onset of disease in the field to obtain commercial yields.
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ItemDevelopment of a technique to overcome the problems associated with high dieldrin concentration in soil( 1995)Degradation of dieldrin in soils was studied in laboratory experiments. Application of powdered zinc in dilute acetic acid, nickel chloride in sodium borohydride and potassium tertiary butoxide in dimethyl sulphoxide to pots containing solonized brown soil, podzol, red brown earth, grey clay, alluvial and krasnozem soils had little effect on the rate of degradation. Application of potassium tertiary butoxide in dimethyl sulphoxide solution to soil samples containing dieldrin achieved a rapid decrease in pesticide concentration in some cases. However, the undesirable effects of these chemicals on soil fauna and flora and on soil physical properties indicate that their use in the field could not be recommended. Adsorption of dieldrin (as illustrated by the Freundlich constant) was greater in red brown earth and grey clay soils than in the solonized brown soil. The rate of dieldrin desorption from these soils was found to be in the order solonized brown soil > red brown earth > grey clay. Dieldrin uptake by plants was determined, with carrots being found to absorb the greatest quantities of dieldrin. All plant species took up considerably more dieldrin when grown on sand than on clay. Lupin translocated very little dieldrin to the plant tops. The amounts of insecticide translocated to the plant tops were not proportional to the amounts of insecticide present in soil. Brown coal was found to be a very good dieldrin adsorbent. Addition of brown coal in the proportion 4:1 soil:brown coal reduced the uptake of dieldrin by carrots from contaminated soil to acceptable levels. Both mice and sheep did not show any obvious symptoms of ill-health after being fed diets containing 10 ?g g-1 dieldrin plus 10% brown coal for 16 weeks. Animals fed diets containing 10% brown coal and 10 ?g g-1 dieldrin had lower concentrations of the insecticide in the internal organs. The concentration of dieldrin in the kidney fat of sheep fed this diet was above the maximum limit suggested to apply to animals raised for human consumption.
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