School of Agriculture, Food and Ecosystem Sciences - Theses
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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.