School of Agriculture, Food and Ecosystem Sciences - Theses

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Salinity control, water reform and structural adjustment : the Tragowel Plains Irrigation District

Barr, Neil F. (University of Melbourne, 1999)
Epidemiology of mint rust and variation in the Pathogen, Puccinia menthae Pers

Edwards, Jacqueline. (University of Melbourne, 1998)
Genetics of resistance to Heterodera avenae in Triticum tauschii and its transfer to bread wheat (Triticum aestivum)

Eastwood, Russell Francis. (University of Melbourne, 1995)
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.
Economic evaluation of feeding grain to dairy cows in Western Victoria

Kelly, Hugh D. (University of Melbourne, 1999)

This study is set in Western Victoria, where the dairy farming systems are characterized by springdominant pasture growth, low pasture growth in summer and moderate growth of pasture in autumn. This, coupled with either late winter calving or early autumn calving, creates pasture deficits, which occur in early and late lactation. The challenge for farmers in Western Victoria is to fill those feed gaps with supplements with the aim of maintaining or increasing profitability. Over a production year, feed supply is provided by a mix of fixed and variable inputs. Variable inputs such as working capital, fertilizers, seed, rainfall, irrigation, conserved fodders and concentrate feeds are added to the land, cows, labour and capital infrastructure. The worth of any one of these variable inputs is determined by the amount it contributes to the farm profitability during the production year. The aim of this study is to evaluate the economic effects of different grain feeding regimes on dairy farms in Western Victoria and determine whether net benefits could be gained from implementing a range of possible grain feeding regimes. Pasture based animal production systems are complicated because of the way the animals, water, pasture, fodder and concentrates interact during different stages of the production year. This means that both a short and medium term view has to be taken to make decisions about feed supply. There is also a need to evaluate the effect of unexpected changes to variable input supply and contingency measures that can be adopted to minimise negative impacts on the system. Further complications arise when trying to evaluate the changes to dairy farming systems because the production response function of each cow and the herd cannot be exactly known with great accuracy before the feed decisions are taken. As well, the law of diminishing marginal returns is at work all the time. The research undertaken in this project was based on a series of case studies of dairy farms in different areas throughout Western Victoria. These farms were selected to represent the different types of farming systems and areas within the region. The operation of the farms was studied at considerable depth to gain a thorough understanding of how each farming system operated. The operation of the farm was modeled using the dairy farm simulation program called UDDER, which can be used to simulate water-animal-pasture- fodder-concentrate interactions for different types of feeding strategies. Their effects on milk production over a year can be evaluated. A series of changes to the grain feeding regime were simulated on each farm to evaluate whether gains could be achieved from altering the timing and quantity of grain fed during the year. The technical information from the model UDDER was then analysed in an economic context using a partial budget model that was developed. This partial budget decision support tool helps farmers identify the essential feeding factors that affect the viability of a farming system and the relative merit of alternative grain feeding tactics and strategies. In this project it was identified that net gains could be made with strategic increases in grain feeding on the individual farming systems. Generally, if the grain fed to the dairy herd was increased during early and late lactation, extra gains were predicted to be achievable. However, substantial gains were also predicted if extra grain was fed to the herd during mid-lactation. When grain feeding levels were reduced, large losses were experienced. This indicates the reliance of the case study dairy herds on grain to produce milk if they are to maintain their current levels of profitability. This study shows that farmers may be able to earn larger profits with greater precision in quantity and timing of grain feeding. However, increases in some grain feeding will not always provide immediate extra gains. Like farm management in general, dairy feed management involves finding and mastering the key pieces of information and processing it in the whole farm context with both tactical and strategic perspectives in mind.
Economic evaluation of feeding grain to dairy cows in Western Victoria

Kelly, Hugh D. (University of Melbourne, 1999)

This study is set in Western Victoria, where the dairy farming systems are characterized by springdominant pasture growth, low pasture growth in summer and moderate growth of pasture in autumn. This, coupled with either late winter calving or early autumn calving, creates pasture deficits, which occur in early and late lactation. The challenge for farmers in Western Victoria is to fill those feed gaps with supplements with the aim of maintaining or increasing profitability. Over a production year, feed supply is provided by a mix of fixed and variable inputs. Variable inputs such as working capital, fertilizers, seed, rainfall, irrigation, conserved fodders and concentrate feeds are added to the land, cows, labour and capital infrastructure. The worth of any one of these variable inputs is determined by the amount it contributes to the farm profitability during the production year. The aim of this study is to evaluate the economic effects of different grain feeding regimes on dairy farms in Western Victoria and determine whether net benefits could be gained from implementing a range of possible grain feeding regimes. Pasture based animal production systems are complicated because of the way the animals, water, pasture, fodder and concentrates interact during different stages of the production year. This means that both a short and medium term view has to be taken to make decisions about feed supply. There is also a need to evaluate the effect of unexpected changes to variable input supply and contingency measures that can be adopted to minimise negative impacts on the system. Further complications arise when trying to evaluate the changes to dairy farming systems because the production response function of each cow and the herd cannot be exactly known with great accuracy before the feed decisions are taken. As well, the law of diminishing marginal returns is at work all the time. The research undertaken in this project was based on a series of case studies of dairy farms in different areas throughout Western Victoria. These farms were selected to represent the different types of farming systems and areas within the region. The operation of the farms was studied at considerable depth to gain a thorough understanding of how each farming system operated. The operation of the farm was modeled using the dairy farm simulation program called UDDER, which can be used to simulate water-animal-pasture- fodder-concentrate interactions for different types of feeding strategies. Their effects on milk production over a year can be evaluated. A series of changes to the grain feeding regime were simulated on each farm to evaluate whether gains could be achieved from altering the timing and quantity of grain fed during the year. The technical information from the model UDDER was then analysed in an economic context using a partial budget model that was developed. This partial budget decision support tool helps farmers identify the essential feeding factors that affect the viability of a farming system and the relative merit of alternative grain feeding tactics and strategies. In this project it was identified that net gains could be made with strategic increases in grain feeding on the individual farming systems. Generally, if the grain fed to the dairy herd was increased during early and late lactation, extra gains were predicted to be achievable. However, substantial gains were also predicted if extra grain was fed to the herd during mid-lactation. When grain feeding levels were reduced, large losses were experienced. This indicates the reliance of the case study dairy herds on grain to produce milk if they are to maintain their current levels of profitability. This study shows that farmers may be able to earn larger profits with greater precision in quantity and timing of grain feeding. However, increases in some grain feeding will not always provide immediate extra gains. Like farm management in general, dairy feed management involves finding and mastering the key pieces of information and processing it in the whole farm context with both tactical and strategic perspectives in mind.
Fallow-crop water balance and recharge relationships in the Victorian Mallee

O'Connell, M. G. (Mark Glenn) (University of Melbourne, 1998)

Background: The Victorian Mallee has a semi-arid climate and cereal production is the major agricultural landuse. Alkaline calcareous soils dominate the region. Cropping in the Mallee is subject to variation in growing season rainfall. Long (winter) fallows are a robust and common practice prior to wheat. Fallows may be viewed as a drought prevention strategy in the rainfed Mallee. Water conserved by fallows supplements growing-season rainfall and thereby reduces annual yield variability. The risk is wind erosion and deep drainage beyond the rootzone of crops. Deep drainage represents incomplete utilisation of water for crop production and contributes to dryland salinity when it enters saline groundwater (potential groundwater recharge) (Chapter 1). This thesis presents work conducted in the field by experimentation and by simulation modelling. A field study at Walpeup (35� 07' S., 141� 58' E.) was conducted over 5 years (1993-1997) to investigate substituting mustard (Brassica juncea) for 18-month long-fallows. Two crop sequences (fallow-wheat-pea [FWP] v. mustard-wheat-pea [MWP]) were examined. The field experiments were designed to appraise FWP v. MWP sequences by investigating soil-water balance, productivity, potential recharge to groundwater and episodic drainage (Chapters 2 & 3). Determination of crop interception and utilisation of photosynthetically active radiation (PAR) were investigated in the field (Chapter 4). Simulation modelling was used to identify cropping practices conducive to longterm productivity and minimal drainage in the region. The O'Leary-Connor model (O'Leary and Connor 1996a,b) was appraised against observed measures (1993- 1998) of growth and yield of wheat, and rootzone soil-water balance under wheat and fallow (Chapter 5: Experiment I). Effects of crop rotation, stubble and tillage management on deep drainage of light (sandy loam) and heavy (clay) textured soils were then investigated by running the O'Leary-Connor model using 58 y of historical climatic data (Chapter 5: Experiment II). Field experimentation: The field experiment demonstrated effects of substituting mustard for fallowing. Aspects of water balance, growth and yield of FWP and MWP sequences were investigated in Chapter 2. Water limited crop production in each growing-season throughout the study. Rootzone soil-water conservation from fallowing in sequence FWP increased wheat growth, yield and water use under severe drought. By contrast, the data reveal that pea water relations and productivity was not influenced by crop sequence. Mustard growth was variable with low yields. Deep drainage was investigated (1993-1998) under FWP and MWP sequences by measuring changes in subsoil-water and by drainage lysimetry (Chapter 3). The former showed greater drainage of FWP (12 mm/y) compared to MWP (5 mm/y). Two major drainage events were confined to a specific phase of the FWP sequence (5.0 mm & 4.3 mm), illustrating the difficulty of reconciling drainage estimates by alternative approaches in a semi-arid environment over a relatively short period 5 y). Radiation interception by wheat, pea and mustard was investigated in Chapter 4. The fraction of intercepted PAR (f), canopy extinction coefficient and radiation-use efficiency were determined for each crop. Aridity resulted in incomplete canopy cover. Fallowing increased f of wheat under favourable (1996) and drought (1994) growing seasons. Estimates of extinction coefficient for wheat, pea and mustard were 0.82, 0.76 and 0.68, respectively. Estimated pre-anthesis radiation-use efficiency for wheat, pea and mustard were 1.75, 1.47 and 1.85 (g aboveground biomass/MJ intercepted PAR), respectively. Simulation modelling: The O'Leary-Connor model provided a good representation of wheat growth, and rootzone soil water (Chapter' 5: Experiment I), justifying use of the unadjusted model, as a tool for examination of water balance under agronomic scenarios in this study (Chapter 5: Experiment II). The investigation suggested greater soil-water conservation under fallowing compared to continuous cropping. Simulated grain yield responded to trends in soil water in accordance with water limitations imposed by the rainfed environment. Simulated drainage was episodic. Soil hydraulic properties and agronomic management influenced total drainage. Least drainage occurred on the heavy textured clay, reflecting soil-water holding capacity and water use associated with crop production. No direct relationships between drainage and rainfall were evident. Continuously cropped (WW) sequences drained less than fallow-wheat (FW). Fallow management influenced water storage and drainage. Stubble-retained zerotilled fallows conserved more soil water and subsequently had greatest drainage. Conventional tillage and stubble burning decreased drainage, but increased runoff and soil surface evaporation. On the lighter soil type, WW and FW drained ~6 % of years without stubble retention, but 10-70 % of years when stubble was retained, with a increase in drainage from 0.5 mm/y to 10-20 mm/y, respectively. By contrast, the heavier clay failed to drain without stubble, and drained in the range, 5-24 % of years when stubble was retained (range, 2-17 mm/y). Overall, fallowing reduced yield failure, but, in conjunction with stubble retention, increased episodic and total drainage on both soil types under the climatic conditions experienced in the Mallee. Conclusion: Outcomes of both field and simulation studies confirms that fallowing increases drainage (potential groundwater recharge). Although, non-fallow annual cropping sequences failed to provide a dry soil profile at sowing for prevention of drainage, especially in wet years. Strategies that use agronomic perennials to dewater subsoils prior to sowing require further investigation.
Fallow-crop water balance and recharge relationships in the Victorian Mallee

O'Connell, M. G. (Mark Glenn) (University of Melbourne, 1998)

Background: The Victorian Mallee has a semi-arid climate and cereal production is the major agricultural landuse. Alkaline calcareous soils dominate the region. Cropping in the Mallee is subject to variation in growing season rainfall. Long (winter) fallows are a robust and common practice prior to wheat. Fallows may be viewed as a drought prevention strategy in the rainfed Mallee. Water conserved by fallows supplements growing-season rainfall and thereby reduces annual yield variability. The risk is wind erosion and deep drainage beyond the rootzone of crops. Deep drainage represents incomplete utilisation of water for crop production and contributes to dryland salinity when it enters saline groundwater (potential groundwater recharge) (Chapter 1). This thesis presents work conducted in the field by experimentation and by simulation modelling. A field study at Walpeup (35� 07' S., 141� 58' E.) was conducted over 5 years (1993-1997) to investigate substituting mustard (Brassica juncea) for 18-month long-fallows. Two crop sequences (fallow-wheat-pea [FWP] v. mustard-wheat-pea [MWP]) were examined. The field experiments were designed to appraise FWP v. MWP sequences by investigating soil-water balance, productivity, potential recharge to groundwater and episodic drainage (Chapters 2 & 3). Determination of crop interception and utilisation of photosynthetically active radiation (PAR) were investigated in the field (Chapter 4). Simulation modelling was used to identify cropping practices conducive to longterm productivity and minimal drainage in the region. The O'Leary-Connor model (O'Leary and Connor 1996a,b) was appraised against observed measures (1993- 1998) of growth and yield of wheat, and rootzone soil-water balance under wheat and fallow (Chapter 5: Experiment I). Effects of crop rotation, stubble and tillage management on deep drainage of light (sandy loam) and heavy (clay) textured soils were then investigated by running the O'Leary-Connor model using 58 y of historical climatic data (Chapter 5: Experiment II). Field experimentation: The field experiment demonstrated effects of substituting mustard for fallowing. Aspects of water balance, growth and yield of FWP and MWP sequences were investigated in Chapter 2. Water limited crop production in each growing-season throughout the study. Rootzone soil-water conservation from fallowing in sequence FWP increased wheat growth, yield and water use under severe drought. By contrast, the data reveal that pea water relations and productivity was not influenced by crop sequence. Mustard growth was variable with low yields. Deep drainage was investigated (1993-1998) under FWP and MWP sequences by measuring changes in subsoil-water and by drainage lysimetry (Chapter 3). The former showed greater drainage of FWP (12 mm/y) compared to MWP (5 mm/y). Two major drainage events were confined to a specific phase of the FWP sequence (5.0 mm & 4.3 mm), illustrating the difficulty of reconciling drainage estimates by alternative approaches in a semi-arid environment over a relatively short period 5 y). Radiation interception by wheat, pea and mustard was investigated in Chapter 4. The fraction of intercepted PAR (f), canopy extinction coefficient and radiation-use efficiency were determined for each crop. Aridity resulted in incomplete canopy cover. Fallowing increased f of wheat under favourable (1996) and drought (1994) growing seasons. Estimates of extinction coefficient for wheat, pea and mustard were 0.82, 0.76 and 0.68, respectively. Estimated pre-anthesis radiation-use efficiency for wheat, pea and mustard were 1.75, 1.47 and 1.85 (g aboveground biomass/MJ intercepted PAR), respectively. Simulation modelling: The O'Leary-Connor model provided a good representation of wheat growth, and rootzone soil water (Chapter' 5: Experiment I), justifying use of the unadjusted model, as a tool for examination of water balance under agronomic scenarios in this study (Chapter 5: Experiment II). The investigation suggested greater soil-water conservation under fallowing compared to continuous cropping. Simulated grain yield responded to trends in soil water in accordance with water limitations imposed by the rainfed environment. Simulated drainage was episodic. Soil hydraulic properties and agronomic management influenced total drainage. Least drainage occurred on the heavy textured clay, reflecting soil-water holding capacity and water use associated with crop production. No direct relationships between drainage and rainfall were evident. Continuously cropped (WW) sequences drained less than fallow-wheat (FW). Fallow management influenced water storage and drainage. Stubble-retained zerotilled fallows conserved more soil water and subsequently had greatest drainage. Conventional tillage and stubble burning decreased drainage, but increased runoff and soil surface evaporation. On the lighter soil type, WW and FW drained ~6 % of years without stubble retention, but 10-70 % of years when stubble was retained, with a increase in drainage from 0.5 mm/y to 10-20 mm/y, respectively. By contrast, the heavier clay failed to drain without stubble, and drained in the range, 5-24 % of years when stubble was retained (range, 2-17 mm/y). Overall, fallowing reduced yield failure, but, in conjunction with stubble retention, increased episodic and total drainage on both soil types under the climatic conditions experienced in the Mallee. Conclusion: Outcomes of both field and simulation studies confirms that fallowing increases drainage (potential groundwater recharge). Although, non-fallow annual cropping sequences failed to provide a dry soil profile at sowing for prevention of drainage, especially in wet years. Strategies that use agronomic perennials to dewater subsoils prior to sowing require further investigation.
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.
Sexual dimorphism of the somatotropic axis in growing lambs

Gatford, Kathryn Leanne (University of Melbourne, 1995)

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