School of Agriculture, Food and Ecosystem Sciences - Theses

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    Epidemiology of mint rust and variation in the Pathogen, Puccinia menthae Pers
    Edwards, Jacqueline. (University of Melbourne, 1998)
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    Nitrogen dynamics after application of biosolids to a Pinus radiata plantation
    Robinson, Michael Barrett. (University of Melbourne, 1999)
    The application of biosolids (sewage sludge) to forests has the potential to increase plantation productivity. Environmental damage may result from pollution of nutrients, heavy metals or pathogens contained in biosolids, leaching of nitrogen (N) to groundwater is of particular concern. This thesis examines the rate of release of N from biosolids, its subsequent fate, and those factors controlling storage and loss of N. Integral to the release of N is the decomposition of biosolids, which is examined through the loss of mass, organic matter and carbon. The potential for increased productivity and environmental risk is assessed through comprehensive N budgeting in the ecosystem. The objectives were addressed through a series of field and laboratory experiments. To compare N dynamics, biosolids were obtained from three sewage treatment plants with contrasting processes (one aerobically- and two anaerobically-digested). The core work was carried out in a major field trial, where biosolids were applied to the forest floor of a 22 year-old Pinus radiata D. Don plantation. The experimental rate of application supplied between 965 and 1425 kg ha-1 of N. More than 85% of the NH4+-N applied in biosolids was volatilised in the first three weeks after application. Subsequent rates of volatilisation were small. The magnitude and temporal patterns were confirmed in a separate study. Volatilisation losses reported in the literature are generally much less, highlighting the variability of losses due to differing biosolids chemistry and environmental conditions at application. About 35% of the organic N was released from anaerobically-digested biosolids in the first year after application, and 54% from the aerobically-digested biosolids. These rates are considerably higher than those used in guidelines of the NSW Environment Protection Authority. There were no significant increases in total N in soil after application, but natural variability in soil precluded detection of increases of the order of 100 kg ha-1. Amounts of NH4+-N in soil increased immediately after application, the size and longevity of increases differing among biosolids. One year after application only very small amounts of inorganic N remained in soil. Throughout the trial, concentrations of NO3--N in soil solution at 60 cm in soil remained consistently below drinking water standards under the anaerobically-digested biosolids and consistently exceeded drinking water standards under the aerobically-digested biosolids. Loss of N in drainage below 60 cm depth in soil in the first year after application was about 20 kg ha-1 under anaerobically-digested biosolids and about 100 kg ha-1 under aerobically-digested biosolids. A controlled incubation study demonstrated that patterns of N mineralisation in the field could not be predicted from laboratory incubations. However relative rates of N mineralisation correlated with amounts of N leached in drainage. Application of biosolids significantly increased tree growth (20 - 34% in basal area) by the second growing season after application. Such a response is likely to be maintained for several years. Rates of volatilisation and mineralisation need to be considered when determining rates of application to ensure that the capacity of soil and plants to store N is not exceeded. Application of anaerobically-digested biosolids at 30 dt ha-1 can increase plantation productivity with minimal risk of groundwater contamination by N. Repeat applications at the same rate concomitant with plantation thinning operations should improve productivity and soil fertility with minimal risk of groundwater contamination.
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    Nitrogen dynamics after application of biosolids to a Pinus radiata plantation
    Robinson, Michael Barrett. (University of Melbourne, 1999)
    The application of biosolids (sewage sludge) to forests has the potential to increase plantation productivity. Environmental damage may result from pollution of nutrients, heavy metals or pathogens contained in biosolids, leaching of nitrogen (N) to groundwater is of particular concern. This thesis examines the rate of release of N from biosolids, its subsequent fate, and those factors controlling storage and loss of N. Integral to the release of N is the decomposition of biosolids, which is examined through the loss of mass, organic matter and carbon. The potential for increased productivity and environmental risk is assessed through comprehensive N budgeting in the ecosystem. The objectives were addressed through a series of field and laboratory experiments. To compare N dynamics, biosolids were obtained from three sewage treatment plants with contrasting processes (one aerobically- and two anaerobically-digested). The core work was carried out in a major field trial, where biosolids were applied to the forest floor of a 22 year-old Pinus radiata D. Don plantation. The experimental rate of application supplied between 965 and 1425 kg ha-1 of N. More than 85% of the NH4+-N applied in biosolids was volatilised in the first three weeks after application. Subsequent rates of volatilisation were small. The magnitude and temporal patterns were confirmed in a separate study. Volatilisation losses reported in the literature are generally much less, highlighting the variability of losses due to differing biosolids chemistry and environmental conditions at application. About 35% of the organic N was released from anaerobically-digested biosolids in the first year after application, and 54% from the aerobically-digested biosolids. These rates are considerably higher than those used in guidelines of the NSW Environment Protection Authority. There were no significant increases in total N in soil after application, but natural variability in soil precluded detection of increases of the order of 100 kg ha-1. Amounts of NH4+-N in soil increased immediately after application, the size and longevity of increases differing among biosolids. One year after application only very small amounts of inorganic N remained in soil. Throughout the trial, concentrations of NO3--N in soil solution at 60 cm in soil remained consistently below drinking water standards under the anaerobically-digested biosolids and consistently exceeded drinking water standards under the aerobically-digested biosolids. Loss of N in drainage below 60 cm depth in soil in the first year after application was about 20 kg ha-1 under anaerobically-digested biosolids and about 100 kg ha-1 under aerobically-digested biosolids. A controlled incubation study demonstrated that patterns of N mineralisation in the field could not be predicted from laboratory incubations. However relative rates of N mineralisation correlated with amounts of N leached in drainage. Application of biosolids significantly increased tree growth (20 - 34% in basal area) by the second growing season after application. Such a response is likely to be maintained for several years. Rates of volatilisation and mineralisation need to be considered when determining rates of application to ensure that the capacity of soil and plants to store N is not exceeded. Application of anaerobically-digested biosolids at 30 dt ha-1 can increase plantation productivity with minimal risk of groundwater contamination by N. Repeat applications at the same rate concomitant with plantation thinning operations should improve productivity and soil fertility with minimal risk of groundwater contamination.
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    Quantitative genetics of wood quality traits in Pinus radiata D. Don
    Nyakuengama, John Gwinyai. (University of Melbourne, 1997)
    In order to understand the variability of traits important in pulping and sawn timber (heartwood formation, moisture status, density and fibre cross-sectional dimensions, fibre coarseness and fibre specific surface), wood from 4 radiata pine (Pines radiata D. Don) plustrees, including parent 80055, and their progeny comprising of a small 4 x 4, 23 year-old, unthinned, diallel progeny test was studied. 80055 progeny is renowned for consuming low energy and producing bright newsprint during thermomechanical pulping. However, the newsprint is of low tear strength. No reciprocal or maternal effects were found in all the traits, probably because of the small number of reciprocal pairs in the diallel experiment. Otherwise, results imply that future wood quality experiments could be simplified by excluding reciprocal crosses. The study found that the o-anisidine and sodium nitrite method was useful to differentiate heartwood formation from sapwood in studies involving a large number of samples. A low narrow sense heritability (NSH) was found for heartwood and its formation was accompanied with a decrease in moisture content. This accounted for a strong inverse correlation found between heartwood formation and moisture content. 80055 progeny had the most heartwood and this explained why its corewood was the driest in the diallel experiment. Technologically, drier heartwood is undesirable in refining because its pulp fibres have a lower wettability, are more brittle and produce newsprint of inferior strength and lower brightness than wetter sapwood. Wood microstructure was studied using a recently commissioned Silviscan 1 system which incorporates an X-ray densitometer and video-microscope. Protocols were set up in this pioneer study for future CSIRO-Forestry and Forest Products progeny tests (and silvicultural studies). Area-weighted fibre size (ie., fibre perimeter, fibre radial and tangential diameters) and density had the highest NSH among traits but these had large standard errors due to a narrow genetic base. The NSH of fibre coarseness was intermediate while those of area-weighted fibre wall thickness and ring width were the lowest. Additive genetic variance was high in all arbitrary classes of fibre diameters, unlike in density and fibre coarseness where it was high in all but an intermediate class representing the transition zone between earlywood and latewood. 80055 progeny had the least dense wood and the highest fibre coarseness in the diallel experiment on account of possessing the largest amount of fibres with large diameters (tangential and radial) or earlywood (as defined as wood with a density less than 400 kg m-3). Technologically, this wood microstructure could translate to low strength in sawn timber. Density and fibre traits had different genetic structures, which accounted for difference in age-age correlations and selection efficiencies at a juvenile age in relation to those at a mature age in these traits. Results indicate that fibre coarseness increased with fibre size only, in 80055 progeny. Fibre coarseness increased directly with increases in fibre wall thickness only in progeny of other parents. Technologically, this implies that fibres of 80055 progeny have thinner fibre walls at a comparable fibre coarseness than non-80055 progeny. This finding could explain why make 80055 fibres make somewhat weak refiner pulp. NSH estimates of density and fibre traits calculated in whole-cores and individual growth rings from parent-offspring regressions were generally more conservative than those from sib analysis of the diallel progeny test but the magnitude of estimates was comparable. Despite large standard errors associated with NSH estimates which were caused by the narrow genetic base of the study material, estimates tended to differ between traits and with physiological and chronological age of parents and offspring. A holistic study based on principal component analysis concluded that fibre diameter and fibre coarseness, but not density, were directly related to tree height and diameter (growth traits). Heartwood formation was directly related to the growth traits, implying that selection of one trait would influence the other.
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    Quantitative genetics of wood quality traits in Pinus radiata D. Don
    Nyakuengama, John Gwinyai. (University of Melbourne, 1997)
    In order to understand the variability of traits important in pulping and sawn timber (heartwood formation, moisture status, density and fibre cross-sectional dimensions, fibre coarseness and fibre specific surface), wood from 4 radiata pine (Pines radiata D. Don) plustrees, including parent 80055, and their progeny comprising of a small 4 x 4, 23 year-old, unthinned, diallel progeny test was studied. 80055 progeny is renowned for consuming low energy and producing bright newsprint during thermomechanical pulping. However, the newsprint is of low tear strength. No reciprocal or maternal effects were found in all the traits, probably because of the small number of reciprocal pairs in the diallel experiment. Otherwise, results imply that future wood quality experiments could be simplified by excluding reciprocal crosses. The study found that the o-anisidine and sodium nitrite method was useful to differentiate heartwood formation from sapwood in studies involving a large number of samples. A low narrow sense heritability (NSH) was found for heartwood and its formation was accompanied with a decrease in moisture content. This accounted for a strong inverse correlation found between heartwood formation and moisture content. 80055 progeny had the most heartwood and this explained why its corewood was the driest in the diallel experiment. Technologically, drier heartwood is undesirable in refining because its pulp fibres have a lower wettability, are more brittle and produce newsprint of inferior strength and lower brightness than wetter sapwood. Wood microstructure was studied using a recently commissioned Silviscan 1 system which incorporates an X-ray densitometer and video-microscope. Protocols were set up in this pioneer study for future CSIRO-Forestry and Forest Products progeny tests (and silvicultural studies). Area-weighted fibre size (ie., fibre perimeter, fibre radial and tangential diameters) and density had the highest NSH among traits but these had large standard errors due to a narrow genetic base. The NSH of fibre coarseness was intermediate while those of area-weighted fibre wall thickness and ring width were the lowest. Additive genetic variance was high in all arbitrary classes of fibre diameters, unlike in density and fibre coarseness where it was high in all but an intermediate class representing the transition zone between earlywood and latewood. 80055 progeny had the least dense wood and the highest fibre coarseness in the diallel experiment on account of possessing the largest amount of fibres with large diameters (tangential and radial) or earlywood (as defined as wood with a density less than 400 kg m-3). Technologically, this wood microstructure could translate to low strength in sawn timber. Density and fibre traits had different genetic structures, which accounted for difference in age-age correlations and selection efficiencies at a juvenile age in relation to those at a mature age in these traits. Results indicate that fibre coarseness increased with fibre size only, in 80055 progeny. Fibre coarseness increased directly with increases in fibre wall thickness only in progeny of other parents. Technologically, this implies that fibres of 80055 progeny have thinner fibre walls at a comparable fibre coarseness than non-80055 progeny. This finding could explain why make 80055 fibres make somewhat weak refiner pulp. NSH estimates of density and fibre traits calculated in whole-cores and individual growth rings from parent-offspring regressions were generally more conservative than those from sib analysis of the diallel progeny test but the magnitude of estimates was comparable. Despite large standard errors associated with NSH estimates which were caused by the narrow genetic base of the study material, estimates tended to differ between traits and with physiological and chronological age of parents and offspring. A holistic study based on principal component analysis concluded that fibre diameter and fibre coarseness, but not density, were directly related to tree height and diameter (growth traits). Heartwood formation was directly related to the growth traits, implying that selection of one trait would influence the other.
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    Sexual dimorphism of the somatotropic axis in growing lambs
    Gatford, Kathryn Leanne (University of Melbourne, 1995)
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    Soil water and nitrogen dynamics of dryland wheat in the Victorian Wimmera and Mallee
    O'Leary, G. J. (Garry John), 1953- (University of Melbourne, 1994)
    In semi-arid environments where water supply is the major factor limiting grain yield, the agronomic option of fallowing provides a way to increase water and nitrogen (N) supply. A study was carried out for four years at two sites in semiarid, north-west Victoria, Australia to examine the effect of fallow management on water and N supply at sowing and their subsequent effect on growth and yield of wheat. The fallow treatments comprised the four combinations of stubble management (retention - SR, removal - NS) and tillage (frequent - CT, none - NT) in year-long fallows of a fallow-wheat rotation (i.e. SRNT, SRCT, NSNT and NSCT), together with a tilled summer fallow prior to alternating pea and wheat crops (PeCT). The two sites, which have different rainfall, represent the major soil types of the region; a chromic vertisol at Dooen and a calcic xerosol at Walpeup. At Dooen, grain yield provided a diverse response to fallow method that generally reflected biomass response and water use. NSCT increased yield every year over PeCT by an average of 0.9 t ha-1 (range 0.5 to 1.3 t ha-1). Stubble retention (SRNT and SRCT) further increased yield above the non-stubble fallows (NSNT and NSCT) in three of the four years, averaging an additional 0.56 t ha-1 (range; 0.24 to 1.04 t ha-1). At Walpeup, NSCT increased yield above PeCT in two years, by 0.7 t ha-1 from 2.6 to 3.2 t ha-1 in 1990 and by 0.6 t ha-1 from 1.7 to 2.3 t ha-1 in 1991. Stubble retention increased yield by 0.45 t ha-1 in only one year, 1988, and that was without tillage (SRNT). Zero tillage did not have any independent overall effect on yield. Crops responded differently to the distinct soil conditions at each site. At Dooen, NSCT increased soil water storage at sowing by an average of 76 mm (range 24-122 mm) above PeCT. Stubble retention added a further 52 mm (range 36-65 mm). Zero tillage was slightly beneficial, and was enhanced by the presence of stubble. Similarly, at Walpeup, NSCT provided an average of 37 mm (range 23-56 mm) more water at sowing than PeCT. SRNT increased water storage by 27 mm in only one year. Fallow and its surface treatments provided large differences in soil mineral nitrogen (SMN) accumulation, but levels were generally sufficiently high (66-222 kg N ha-1) to not greatly affect yield. At Dooen, NSCT accumulated 46 kg N ha-1 more SMN than PeCT, whereas at Walpeup PeCT increased SMN in two years by an average of 46 kg N ha-1 above NSCT. At Dooen stubble retention depressed SMN by an average of 26 kg N ha-1 in two years and in one, increased it by 20 kg N ha-1. Stubble retention had little effect on SMN at Walpeup. A simulation model was developed to apply the responses of the field experiment to a wider range of weather conditions. It includes soil carbon (C) and N and crop N submodels. The model showed a pattern consistent with observed response. Validation showed that soil water was simulated more accurately than SMN (R2=0.95 cf. R2=0.61), and there was no significant bias in any fallow treatment. Crop biomass followed the general pattern of observations throughout the season well (R2 =0.77). Grain yield was simulated with less accuracy than biomass (R2 =0.42) and was shown to be largely due to poor simulation of grain number (R2 =0.07) because accuracy of yield prediction was markedly increased (R2 =0.59) when predictions were made on observed grain numbers. Grain [N] was simulated with fair accuracy (R2 =0.29), pointing to the need for improvements not only in the simulation of grain size (R2=0.61), but also in the partitioning of N to grain. Overall, the performance of the model is comparable to the CERFS-Wheat-N model even though it is less complex. Analyses with the model over long-term weather conditions supported the field observations of the advantage of stubble retention in predicting a median increase in yield of 0.8 and 0.6 t ha-1 at Dooen and Walpeup, respectively. However, at Walpeup, field observations indicate that other factors may limit this advantage. Zero tillage had a small advantage in the presence of stubble (0.2 t ha-1) with no consistent advantage without stubble at Dooen nor under any system at Walpeup. The model displays a general level of behaviour known to occur in the field and provides a useful tool, not previously available, to examine water and N interactions in conservation tillage systems in north-west Victoria. The model should have relevance in other semi-arid environments where wheat is grown.
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    Sexual dimorphism of the somatotropic axis in growing lambs
    Gatford, Kathryn Leanne (University of Melbourne, 1995)