School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemAn analysis of the problems of estimating the thyroid hormone level in the blood of domestic animals, and the effects of varying that level on the marketable products of such animals( 1957)In the field of animal husbandry it is becoming increasingly apparent that maximum efficiency of production cannot be attained without careful attention to the health of the animal, and to the balance between the animal and both the internal and external environments. For example, if artificial methods are used to increase production of milk without at the same time increasing, the feed intake the result is generally a decline in the health of the cow which may eventually lead to serious illness. Much recent research in this field has been concerned with the function and activities of specific organs rather than with the body as a whole, showing; that the factors involved in production are much more numerous and varied than was originally thought. Examples of this type of research are the intensive investigations at present being conducted into rumen activity and microflora, wool fibre growth, mammary gland function, reproductive activity and the role of various endocrine glands in production. Of the endocrine glands, apart from those directly concerned in reproduction, the one most studied has been the thyroid which has been shown to play an important part in practically all spheres of animal production so far investigated. It was the aim of this experiment to establish a method for determining thyroid activity which would then allow us to investigate the relationship between this activity and various body processes in the normal animal. In the normally functioning animal the thyroid serves chiefly as a homeostatic mechanism maintaining the body functions at a steady level of activity and, to a certain extent, controlling the response of the body to changes in the external environment. Its effects are more apparent when the thyroid activity is altered in any of the many ways to be considered later. The lowering of the thyroid hormone output produces an animal with typical symptoms - low Basal Metabolic Rate, low body temperature, low reproductive capacity, decreased growth and development in young animals, increased fat deposition, sluggishness, drying and thickening of the skin and falling hair. On the other hand the hyperthyroid animal shows an. increased Basal Metabolic Rate, high body temperature, leanness, restlessness and, in some cases, protruding eyes. These facts have recently been put to practical agricultural use. Raising the thyroid output leads to a significant increase in growth rate, milk yield and egg production. Lowering; the level has proved a successful method of fattening pigs and fowls for meat production. These aspects are dealt with in the review of literature.
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ItemA study of wheat crop physiology in relation to time of sowing, rate of sowing and fertilizer application( 1963)A crop physiological study upon yield in wheat was undertaken at Wagga, located in the wheat belt of southern New South Wales, in 1961 and 1962. The effects of time of sowing, rate of sowing and fertilizer application were investigated. The variety, Heron, was used throughout. Comprehensive measurements during the growth cycle of the crops were made upon total dry weight and its components, photosynthetic area, evapotranspiration, soil moisture stress and plant moisture stress (using the leaf relative turgidity technique). Time of sowing had little effect on the soil moisture available to the crop at flowering. However post flowering climatic conditions were hotter and drier for the later sown crops, and consequently plant moisture stress occurred sooner after flowering. Yields fell in both years with later sowings,at an average rate of 2 bushels/acre for each week' s delay in sowing. Increased fertilizer application and increased rate of sowing increased the vegetative growth, and the potential yield at flowering, but this was associated with small reductions in the soil moisture at flowering and an earlier onset of plant moisture stress. The increased vegetative growth usually resulted in increased grain yields, but under drier conditions grain yields were reduced. Nitrogenous fertilizer appeared to have additional effects on the crop which may under some conditions be detrimental to grain yield. Certain interrelationships within the soil/crop system were evident from these trials. Evapotranspiration increased as photosynthetic area index increased when soil moisture was adequate. Leaf relative turgidity at sunrise was closely related to soil moisture stress. Grain yield variation was highly correlated with variation in photosynthetic area duration after flowering. Photosynthetic area duration was related to photosynthetic area index at flowering and to the level of plant moisture stress after flowering, which governed the rate of senescence of this photosynthetic tissue. These results and the value of this type of crop physiological study of yield in wheat are discussed. The application of some aspects of the results to wheat agronomy and breeding is apparent.
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ItemExperiments in animal husbandry( 1961)
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ItemTree growth modelling of Eucalyptus delegatensis (R. T. Bak.) and other eucalyptus species utilising early-aged stand measurements( 1999)Growth modelling methods for Eucalyptus species that can make use of minimal measurement information are scarce but necessary for those involved in small-scale forestry to make informed decisions about investment and management options. A computer program, FARMTREE, is available for evaluating the costs and benefits of trees on farms, however its growth modelling functions could be improved. This thesis achieves this for Eucalyptus delegatensis (R. T. Bak.) and provides a series of stand basal area, survival, diameter distribution and individual tree diameter increment models that could be incorporated into a FARMTREE-like program. While not a major farm forestry species, the models have been related to other Eucalyptus species and when more later-age data become available, the methods used here could be fully applied to more suitable species. A systematic series of growth predictions were made, with estimates from the earlier processes being used in the next. Initially, the Gompertz function was selected as the best of five non-linear equations and used to model stand basal area based on two, early-age measurements, while keeping the asymptotic parameter constant. Survival was modelled using a modified logistic function with basal area and age as the predictor variables. The results from the above procedures were then used to model diameter distributions using a percentile-based parameter recovery procedure. The predicted distributions were assessed by comparing them to the actual cumulative density functions. Comparing the predicted estimates of basal area, mortality and diameter distributions to those produced by FARMTREE showed that the new estimates were better, both for the stands for which the models were developed, and for an independent data set. Individual tree diameter increment models based on distance-independent competition indices were also studied. Overall, the predictions for two-year diameter increment were not as good as for the previously studied areas of growth. This was especially noticeable when observing the results for the verification data set. These poorer results for diameter increment may be because of the less flexible methods used or perhaps partially due to the accumulation of previous prediction errors. The research approaches and functions used are easy to apply, efficient, accurate and require minimal actual growth measurement information. They could be applied to other species in greater detail when more information becomes available and could be incorporated into FARMTREE or a similar package for use by owners and managers of small farm forests with the expectation of providing improved growth predictions.
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ItemThe effect of growing location and time of sowing on the production of premium quality oilseeds in south-eastern Australia( 1998)New Brassica oilseeds with modified fatty acid profiles tailored to specific end-uses are being developed in southern Australia. However, the fatty acid composition of Brassicas are known to vary markedly with environmental conditions during growth. A series of experiments were conducted to establish the most appropriate regions and sowing times within south-eastern Australia for the production of high oleic acid canola (HOAC), low linolenic acid canola (LLAC) and high erucic acid rapeseed (HEAR). Controlled experiments were conducted to evaluate the, effects of water deficit and temperature stress on fatty acid composition of conventional canola, HOAC, LLAC and HEAR. Ten years of data from the advanced canola trials of Agriculture Victoria were analysed, and a three-year trial was undertaken to identify the south-eastern Australian locations which produced specialty cultivars with the highest oil and seed protein content, lowest glucosinolate concentration, and premium oil quality (i.e. most appropriate fatty acid composition). Two glasshouse trials were performed to determine the separate effects of severe water deficit and three days of high (32C) and very high temperatures (37C) at 10, 20 and 30 days after flowering (DAF) on the oil composition of a HEAR cultivar and HOAC cultivar. In contrast to earlier work on the effects of sustained high postflowering temperatures, three hot days had no effect on oil composition or yield of the two cultivars, except that 37/25C (day/night) from 30-33 DAF reduced erucic acid content of HEAR from 52% to 44%. Severe drought reduced the quality and yields of both cultivars. Erucic acid content of the HEAR cultivar decreased by up to 10% and the oleic acid content decreased by up to 4% with post-flowering drought. Within each year, most variation in the quality components of the three year field trial was due to site. Oil ,content and seed yield were highest, and seed protein content and glucosinolate concentration were lowest, in the cooler and wetter sites and years. Generally, warmer post-flowering conditions enhanced oleic acid content at the expense of linoleic and linolenic acids in the canola quality cultivars, although all regressions between quality and weather variables were fairly weak. In 1995, for. every 5C increase in the average temperature between flowering and maturity, oil content decreased and seed protein content increased by an average 4%, glucosinolate concentration increased by 4.0 ?mol/g, and the linoleic and linolenic acid content each decreased by 1-2% in the different canola quality types. Each 100 mm increase in rainfall between flowering and maturity increased yields by 0.4 t/ha and oil content by 1.6%, and reduced seed protein content by 0.5% and glucosinolate concentration by 1.1 ?mol/g, on average. Oil content was strongly negatively correlated with seed protein content (r=-0.75 for conventional canola). Upon removing the effects of year and cultivar from the ten year dataset, the mean oleic acid content, of conventional canota was very stable across regions, but varied more between years. Canola grown in - central Victoria and the Wimmera produced consistently high levels (>60%) of oleic acid. Canola consistently achieved a low linolenic acid content in central Victoria (<10.8%), and a moderate to low: linolenic acid content in the Wimmera. The Mallee produced canola with highly variable levels of oleic acid and linolenic acid, despite warm post-flowering temperatures which are known to increase oleic acid content. In the three year trial, time of sowing did not have a consistent effect. on the fatty acid composition of canola, probably due to the interactions between temperature and rainfall. These results identified central Victoria and the Wimmera as the most appropriate locations for the production of HOAC and LLAC cultivars. One year of data indicated that Wagga Wagga is capable of producing canola with extremely high oleic acid and low linolenic acid levels. The results of the three year trial identified lower south-eastern South Australia and the Victorian Wimmera as regions most conducive to the production of HEAR with consistently high levels of erucic acid. The erucic acid content of HEAR was often reduced by late sowing. However, this trend was not always observed, and possible reasons for deviations from trends have been discussed. One year of data demonstrated high levels of erucic acid in HEAR produced in the southern part of central Victoria. As the time of sowing did not have a consistent effect on the erucic acid content of HEAR, or the oleic and linolenic acid content of HOAC and LLAC, it was recommended that growers sow at the same time as recommended for conventional canola, to maximise yield and oil content.
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ItemEffects of irrigation on the roots of pastures( 1969)An experiment was conducted in order to investigate the effects of wetting the soil to a range of depths, on the root growth and top growth of some pasture species. The experiment was done within a glasshouse, using a sandy loam soil; the pasture species studied were white clover, ryegrass and subterranean clover. Gypsum block readings, and visual assessment of the moisture status of the soil (as seen through the transparent walls of the containers) were used to decide when to apply water. The soil was maintained within the wetter 2/3 of the available moisture range, so that the effects of drying cycles were avoided. For each species the depth of wetting had a marked effect on the depth of roots; in all treatments, the roots completely occupied the depth of wetted soil. With the deeper wetting treatments both of the perennial species showed a marked increase in the weight of tops, but the annual subterranean clover showed no significant differences. On the other hand, the effect of deeper wettings on the weight of roots was significantly greater for white clover; it was not significantly different for ryegrass; but it was significantly less for subterranean clover.