School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemEffects of urea and superphosphate fertilizers and soil moisture and temperature on forest soil respiration in a radiata pine plantation( 1987)The effect of urea and superphosphate fertilizers and the influence of temperature and soil moisture on forest soil respiration were investigated over a 9- month period. The investigation was conducted in an 18- year-old Pinus radiata D.Don. plantation in southeastern Australia. The fertilizers were applied to the forest floor at two rates (200 and 400 kg N ha-1, and 100 and 200 kg P ha-1) in a 3 x 3 factorial design. Soil respiration was measured as CO2 evolution using a soda lime absorption technique. Measurements were conducted at 14-day intervals from the 18th November, 1985 to the 6th August, 1986. The influence of temperature and soil moisture on soil respiration was more marked than fertilizer application, rates being highest when soil moisture was non-limiting. When soil moisture was under 12.5% (oven-dry weight basis), CO2 evolution was strongly moisture-dependent and 31% to 90% of the variability in CO2 evolution was explained by soil moisture. At soil moisture levels above 12.5%, soil maximum temperature was the best predictor of soil respiration, showing a significant positive correlation. This correlation explained 35% to 88% of the variation in CO2 evolution. The influence of moisture and temperature could be accurately predicted by a model which incorporated a moisture dependent Q10. The same model and model parameters successfully estimated soil respiration in the majority of fertilizer treatments. The addition of superphosphate fertilizer resulted in a significant stimulation of respiration rates, while the effect of urea addition was less marked. In treatments which received urea alone, CO2 evolution was depressed, although not significantly. However, in the presence of superphosphate, urea addition increased CO2 evolution with rates being highest in treatments which received the highest urea application rate. This result was attributed to an increased availability of phosphorus since microbial and faunal activity in this ecosystem appeared to be limited by P availability. An attempt was made to estimate the contribution of the forest floor, roots and soil to total forest soil respiration. Measurements were taken on two sampling occasions. On the first occasion, the forest floor plus mineral soil and roots contributed 85.0% and 15% to total soil respiration, respectively. On the second contribution was 68.7% and 31.3% respectively. In the field experiment, inorganic nitrogen concentrations in the soil and forest floor were measured on 60, 90, 240, 270 and 300 days after fertilization. Ammonium-N was the dominant N form. Inorganic-N concentrations were consistently highest in the treatments which received urea alone. Nitrate concentrations were highest in the treatments which received the highest urea application rate. A 30-day incubation experiment was conducted in the laboratory using the forest floor and soil collected from the experimental site one year after fertilization. Initial water-soluble phosphate (W-S P) concentrations were considerably higher in superphosphate treatments in the forest floor, while no appreciable concentrations were detected in any of the soil samples or in the forest floor of the control and treatments which received urea alone. During incubation, W-S P concentrations increased in all treatments with the highest rates being found in the treatments which had received phosphorus. Nitrate production and net N mineralization rates were highest in treatments which received urea alone, both in the soil and the forest floor samples. Superphosphate addition increased net N mineralization in soil samples. However, it only increased net N mineralization in the forest floor in the presence of added N. Urea elevated pH while superphosphate depressed it. No clear influence of pH changes on CO2 evolution were evident.
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ItemRoot and top growth of the wheat plant as affected by water supply( 1987)Two experiments were conducted to study the growth, particularly the root growth, of wheat in relation to moisture supply. One was conducted in an igloo house at the Mt Derrimut Field Station of the School of Agriculture and Forestry, University of Melbourne and the other in a glass house on the main campus. The plants were grown in a mixture of soil, sand and ligna peat contained in plastic bags to give columns about 0.8 m deep. In the first experiment the effects on both above-ground and below-ground growth of withholding water at different stages of growth and for different times were studied on three cultivars of wheat. In the second experiment effects of supplying different amounts of water were studied. Plants were harvested periodically for measurement of dry weights of the various plant parts, measurement of leaf area and root length and counts of tillers, heads, grains and roots. The soil columns were dismantled 20 cm at a time to enable the distribution of roots in the profile to be observed. Withholding water at any stage of growth and for any period reduced the above-ground dry matter at maturity; the longer the period of non-watering the greater the reduction. Reduction in above-ground dry matter resulted from reductions in number of tillers, leaf area and grain yield. Tillering was most affected by non-watering during early and mid-season growth, and yield by non-watering after anthesis, especially when it occurred during the first two weeks after anthesis. Non-watering after anthesis reduced yield mainly by reducing grain size (1000 grain weight). The quantity of recoverable roots, measured either by weight or by length, reached a maximum about the time of anthesis and then declined as roots died and were lost during harvest. The quantity of roots formed was reduced when non-watering was imposed during early or mid-growth. The distribution of roots in the profile was also affected by the watering treatments. Withholding water during early and mid-growth resulted in a greater proportion being located in the deeper soil zones. However, with the soil initially below field capacity, withholding water from sowing onwards resulted in shallow rooting presumably because an absolute lack of water limited the plants' ability to produce deep roots. Watering the soil to field capacity every three days in Experiment 2 resulted in less above-ground dry matter than watering to field capacity once a week. It resulted also in a greater proportion of the roots being in the upper part of the profile suggesting that root penetration of the lower part was inhibited by poor aeration as a consequence of overwatering. Watering to field capacity once a week resulted in less above-ground dry matter than giving half the amount of water needed to restore the whole soil column to field capacity. Moreover, the proportion of roots in the bottom zone of the rofile was less under the former treatment than under the latter suggesting that watering to field capacity once a week was causing some restriction of root growth in the bottom zone, presumably through poor aeration. These two facts taken together suggest that in this experiment watering to field capacity once a week even amounted to over-watering.
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ItemBiometric studies of some eucalypt plantations in South China( 1987)Biometrical studies Of introduced tree species in the Dongmen area are presented in two parts. In the first part, a number of tree volume functions were fitted to data for E. exserta. A simple weighted regression model was found to be most appropriate. This model proved to be better than that recommended by local mensurationists in Guangxi. In the second part, fertilizer trials are reported for eighteen seed strains under five fertilizer regimes. These strains were finally clustered into four groups in terms of performance. All strains of E. camaldulensis proved most successful for all levels of fertilizer used. Further analysis showed that E. camaldulensis responded best with highest levels of nitrogen, phosphorus and potassium plus trace elements used, and that the addition of trace elements did not significantly improve response.
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ItemThe degradation of chloroplast galactolipids during leaf senescence in wheat (Triticum aestivum L.)( 1987)Acyl hydrolase activities were investigated in the primary leaves of wheat (Triticum aestivum L., cv. Egret). Preparations from both mature leaves and leaves induced to senesce in darkness were tested for their ability to hydrolyse the endogenous acyl lipids in wheat leaf thylakoid membranes. The liberation of fatty acids was measured using a sensitive high performance liquid chromatagraphic technique. A lipolytic activity was found to be associated with the thylakoid membranes in mature, non-senescent wheat leaves, which partially hydrolysed the major class of lipid in the thyiakoids, monogalactosyl diacylglycerol (MGDG), producing a lysolipid and free linolenic acid (LIA). The enzyme became active when isolated chloroplasts were incubated at pH 6.0-6.2. Up to half the MGDG present in the membranes may be degraded by this enzyme within one minute from the start of the assay. However, the activity was rapidly terminated under the conditions of the assay. The 'galactolipase' was inhibited by phenylmercuric acetate and p-chloromercuti-benzoic acid, and was inactivated by preincubation temperatures greater than 35C, mild detergents and sonication. Calmodulin antagonists were inhibitory to 'galactolipase', but modulation of the enzyme activity by calcium could not be demonstrated. Effects of galactolipid hydrolysis by the endogenous 'galactolipase' on the physiology and ultrastructure of thylakoid membranes were examined. Incubation of chloroplasts at pH 6.0 rapidly inhibited electron transport activity particularly through photosystem II, and caused uncoupling of ATP synthesis. However,'these effects were attributable to the accummulation of free fatty acids in the membranes, and in the presence of bovine serum albumin (BSA), which sequesters fatty acids from the membranes, no inhibition was observed. Ultrastructural studies revealed preferential degeneration of stromal lamellae and extensive swelling of granal stacks following gaIactolipid hydrolysis, resulting in thylakoid structures similar in appearance to those reported in senescing leaves. This effect was only partly prevented by BSA. In contrast, exogenous LIA caused unsticking of the membranes, but had no effect in the presence of BSA. 'Galactolipase' was able to activate a thylakoid associated, LNA-dependent oxidative chlorophyll-bleaching activity (CHLOX) which has been proposed as a likely mechanism for chlorophyll catabolism in viva. LIA released by galactolipase was four times as effective as exogenous LIA in activating CHLOX. Galactolipase activity in chloroplast preparations declined with leaf age after maturity, reaching a negligible level when only half the MGDG in the tissue was lost. Galactolipase activity was also found to be present in a non-yellowing mutant of Festuca pratensis , whose ability to degrade thylakoid acyl lipids during leaf senescence is impaired. Therefore, no direct evidence was obtained linking the thylakoid-associated galactolipase activity with gaIactoIipid degradation during leaf senescence. However, an alternative role for the enzyme in lipid turnover in non-senescent tissue was discounted, as no turnover of galactolipids could be detected in wheat primary leaves. It is thought likely that the enzyme participates in thylakoid degradation during senescence, but an understanding of its mode of activation in vivo may be required to verify this role.
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ItemHigh Ph (dark-cutting) meat in beef carcasses( 1987)The research work in this thesis was undertaken between 1983 and 1986 whilst employed as a research officer (1983 -1984) and as a meat marketing officer by the Department of Agriculture and Rural Affairs (DARA), Victoria. The development of techniques and experimental work formed a part of my training as a research officer at the Animal Research Institute, Werribee. At this time I was professionally supervised by Dr T G Truscott and Mr G A Eldridge. The statistical analyses were conducted under the supervision of Dr T G Truscott and Mr P Franz (DARA Biometrician). The occurrence of dark-cutting high pH beefmeat is recognised as a problem by the meat industry world-wide. In Australia, early pioneering work on the problem suggested the importance of the animal's stress response to marketing procedures in determining the occurrence of dark-cutting beef. More recently, the majority of Australian research investigating the problem has been conducted in Queensland where the climate and marketing conditions for cattle are often quite different to that experienced in south-eastern Australia. During 1980 - 1983 the Victorian meat industry reported several outbreaks of dark-cutting beefmeat at certain times of the year. Supermarket buyers of beef carcasses were found to discriminate against this "dark" beef. It became obvious that research work was required to establish the seasonal incidence of dark-cutting beefmeat under Victorian conditions and to investigate the contributing factors. It was on this basis that I was employed as a trainee with the Victorian Department of Agriculture and Rural Affairs. The material presented in chapters 2, 3 and 4 is largely reproduced or adapted from published reports or papers (see Bibliography) of Halpin and Warner (1985); Warner, Eldridge, Barnett, Halpin and Cahill (1986); Warner, Eldridge, Truscott and Cahill (1986) and Warner (1985). Chapters 5 and 6 present new material. I was responsible for the preparation and writing of these papers and Chapters. I initiated and organised the survey, experiment and technique developments described in Chapters, 3, 4 and 6 and was responsible for the organisation of post-slaughter meat quality measurements described in Chapter 5.
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ItemEconomic incentives for private softwood plantations in Victoria( 1987)More than 90 per cent of the privately-owned softwood plantations in Victoria are owned by a small number of companies involved in the further processing of softwood timber. This study examines the economic factors influencing the establishment of softwood plantations by other private landholders (i.e. those that do not own softwood processing facilities) and evaluates the economic incentives currently offered to encourage these landholders to establish their own plantations. A number of economic factors contribute to the current low level of planting by private landholders that are not directly involved in the further processing of softwood. These include the structure of the market for softwood in Victoria, the price private growers can expect to receive for their wood, and the long term nature of the investment. The current taxation arrangements for private forestry offer a number of incentives for the establishment of softwood plantations. However they also contain a number of anomalies and disincentives to private forest investment. Various proposals to reform the income tax legislation have been put forward by private grower organizations and by the Commonwealth Government and this study critically evaluates these proposals. The Farm Forestry Agreement Scheme is an incentive scheme that has been offered by the Victorian Government since 1967 to encourage the establishment of private plantations. It offers low-interest loans with repayments deferred for the first 12 years. After more than 15 years operation the total plantings under the Scheme are approximately 8,300 hectares or less than four per cent of the total Victorian softwood resource. Inflation has seriously eroded the incentive value of the Scheme and it is also a very costly and cumbersome scheme to administer. Many Agreement holders are experiencing difficulties in selling wood from their plantations to meet loan repayments and interest in the Scheme has steadily declined in recent years. A number of softwood processing companies operating in Victoria also offer assistance schemes to encourage private landholders to establish their own plantations. The schemes offered by Softwood Holdings Ltd. and APM Forests Ltd. provide private growers with an assured outlet for their timber and have assisted a number of private growers in marketing wood from their plantations. In addition Australian Newsprint Mills Ltd. have recently introduced a scheme known as the Joint Venture Agreement Scheme which offers assistance in the establishment, management and marketing of wood from plantations established jointly by the company and private landholders. The formation of co-operatives of private forest growers offers a number of potential benefits to the owners of private plantations. Of these increased bargaining strength in the marketing of wood and a mechanism for better communication between private growers and softwood processing companies appear to be the most important. The existing incentives and assistance schemes offered by the Government have not been particularly successful in encouraging the establishment of softwood plantations by private landholders. New economic incentives are therefore required if these landholders are to supply an increased proportion of Victoria's future softwood requirements.