Agriculture and Food Systems - Theses

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    Effects of organic applicants in a southern Victorian vineyard
    Lakey, Vincent G ( 2007)
    Mulch is a material applied to the surface of the soil to reduce weed growth and reduce soil moisture loss through evaporation from the soil surface. The use of organic mulches will alter the soil environment. This alteration may include reducing soil temperature fluctuations, increasing soil organic matter, increasing soil microflora populations modifying soil chemical properties and increasing soil moisture retention. An experiment was conducted to compare composted green waste mulch and barley straw mulch with herbicide as alternative means of maintaining the undervine strip in a cool climate vineyard. Plant and soil responses to the different undervine treatments were monitored. Grapevine budburst was retarded, however, by the fourth week of vine growth there were no observable differences in grapevine growth stage. Both mulches stimulated grapevine growth and increased yield, with the compost mulch increasing vegetative growth with respect to fruit yield. The fruit quality parameters juice pH and titratable acidity were not significantly altered by the different undervine treatments. In the second year of the experiment the juice soluble solids were lower on the straw mulched grapevines. The compost mulch increased soil pH and carbon levels. The straw mulch improved soil water retention and the mass of soil fungal hyphae. Both mulches increased soil cation exchange capacity. The straw mulch increased soil exchangeable Mg to a greater extent than was predicted from straw nutrient content. The significant variations seen in soil cation content under the mulch treatments were not observed in the tissue analysis. Mulch can be used in a cool climate vineyard to increased yield without deleterious side effects.
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    Investigation of boron toxicity in lentil
    Hobson, Kristy Bree ( 2007)
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    Identification of boron tolerance in Brassica rapa
    Kaur, Sukhjiwan ( 2006)
    There has been increasing interest in developing canola quality B. juncea for low rainfall areas across Australia over the past two decades. However, B. juncea genotypes are susceptible to high levels of boron in Western Victorian soils. An understanding of the genetics and the molecular basis of boron tolerance may enable fast and accurate tolerance selection and lead to improved boron tolerance. Being an allotetraploid species, B. juncea is difficult to understand at the genetic level because of chromosomal duplication and the potential presence of multiple copies of the loci of interest. Therefore, once the tolerance genes or chromosomal loci governing tolerance are identified in the diploid progenitor genomes, B. rapa and B. nigra, boron tolerant B. juncea lines may be resynthesized. Thus, as an initial step in this process, this thesis aimed to understand the physiological, genomic and molecular mechanisms involved in boron tolerance in B. rapa. Initially, B. rapa genotypes were screened for tolerance to boron toxicity using hydroponic and soil assays. On the basis of primary root length, severity of leaf toxicity symptoms, dry matter accumulation and shoot boron uptake, the B. rapa genotypes WWY Sarson and Local were identified as the most tolerant and the B. rapa genotypes Shillong and Kaga the most susceptible to toxic boron concentrations (1000 ?M B in hydroponic assay; 54 mg B kg-1 soil in soil assay). The main mechanism of tolerance to boron toxicity in B. rapa involved reduced net boron uptake by roots, with some boron accumulation in the tap roots and partial exclusion of boron from shoots. Furthermore, boron uptake was much lower in the WWY Sarson and Local genotypes than in the Shillong genotype, despite higher rates of transpiration. This implied that an active boron efflux mechanism may be operating in the tolerant genotypes. The inheritance pattern of tolerance to boron toxicity in B. rapa genotype, WWY Sarson best fitted a Mendelian model of two major dominant and epistatic genes. A B. rapa linkage map was constructed from an intraspecific F2 population (WWY Sarson X Shillong) with ISSR, RAPD, SRAP and SSR marker loci. The linkage map spanned a total length of 874.1 cM and contained 12 linkage groups. Chisquare analysis (P < 0.05) revealed 25 dominant markers that showed segregation distortion in the F2 progeny. QTL analysis using composite interval analysis identified three significant peaks on LG2 and LG8 that were associated with primary root length and which accounted for 17% of the trait variation. Differential transcript analysis of SRAP markers following exposure to a toxic boron concentration identified up-regulation of me4+em2570bp, me2+em2650bp, me2+em1 1600bp, me2+em1800bp and me4+em2500bp genes in Shillong and Kaga and down-regulation of me2+em2650bp, me2+em1 1600bp, me2+em1800bp and me1+em21200bp genes in WWY Sarson and Local. Of these, a UDP-glycosyltransferase gene (sharing 80% similarity to the Arabidopsis thaliana homolog) was highly transcribed only in the sensitive genotype, Shillong, and may be involved in excessive boron cross-linking to the glycosyl groups present in the cell walls and/or membranes eventually causing the observed reductions in shoot and root growth.
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    Grazing ecology and high producing dairy cows
    Stockdale, C. R (1948-) ( 2005)
    This body of work (82 papers in scientific journals and 2 books) encompasses two broad areas of work. They are 1) growth, nutritive value and management of pastures grazed by dairy cows (40 publications), and 2) supplements for grazing dairy cows, with a particular focus on responses associated with supplement use and digestion in the rumen (44 publications). These two areas of research are inextricably linked and, taken together, have been termed `Grazing Ecology'. Of the 84 publications included, the candidate was the senior or sole author of 67% of them. The chronological development of the work reported includes research on stocking rates reported in the early 1980's through to the development of Diet Check, a decision support tool incorporating much of the information generated during the previous two decades, in the early 2000's. The publications cover aspects of grazing management to optimise growth, persistence and nutritive value of irrigated annual and perennial pastures for dairy cows. Most of this research has incorporated some aspect of stocking rate, whether it be stocking rate per se in long term experiments or frequency and/or intensity of defoliation in shorter term experiments. The aim was to establish optimum grazing strategies that best effected the compromise of maximum intake of pasture of high nutritive value while satisfying the requirements for maintenance of pasture growth and persistence of a balance of desirable pasture species. The research allowed the definition of the intake and nutritive characteristics of pasture grazed by lactating dairy cows under a range of management conditions. At the same time, strategies to effectively feed supplements were investigated. When more than one feed is offered to dairy cows, associative effects play an important role in the eventual responses achieved. Balance of nutrients, particularly in the rumen, and substitution of supplement for pasture in the diet of grazing dairy cows, were the main aspects of the associative effect between feeds considered in the research reported here. Substitution can have a huge effect on the responses obtained from supplements, and the type of supplement, by influencing the balance of nutrients ingested into the rumen, affects the composition of the milk produced. Finally, some attempt has been made to draw much of the information on pasture management and supplementation of grazing dairy cows together for use by dairy farmers and their advisers, and to define gaps in knowledge. This has been done by reviewing the scientific literature, and by the use of modelling to provide simple tools for tactical decision making. Although the research was undertaken in northern Victoria, many of the results apply equally in other areas of the world where pasture constitutes a major proportion of the diet of dairy cows. Victoria currently produces more than 60% of Australia's milk, with northern Victoria producing more than 40% of that. The development of dairying in Victoria mirrors much of the progress of the research reported in this collection of scientific publications. Before 1982, dairy farming was almost totally based on grazed pastures and the use of pasture supplements (hay and silage). A severe drought occurred in 1982, which prompted a serious consideration of the use of supplements for lactating cows grazing pasture. Today, dairy systems in Victoria vary to a huge extent, with the energy provided by pasture ranging from 0 to 100%. Over this period, average milk production has increased, from about 3000L/cow per lactation to more than 5000L/cow. With a fine line separating profit and loss in dairy businesses that basically depend on the price received for manufactured products on overseas markets, both grazed pasture and supplements need to be used optimally. The challenge has been to provide information and tools to allow dairy farmers to achieve this objective. I believe that my research, particularly in relation to pasture intake, substitution and associative effects, has been instrumental in allowing pasture-based dairy farmers to continue to remain viable in Australia, and that many of the principles developed apply wherever pasture constitutes a significant proportion of a cow's diet.
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    Spring water use in raised bed cropping
    Clark, Gary John ( 2004)
    Cultivation of heavy clay soils with the application of gypsum is often used to improve root exploration of the soil profile and hence more efficient use of the soil resource to enable higher grain yields of cereal crops. Soils in south-western Victoria are derived from tertiary basalts with high clay content and often dispersive subsoil. Cereal crops grown on these soils are prone to waterlogging. Waterlogging has been overcome with the use of raised beds. The hypothesis was that the heavy subsoil restricted rooting depth and hence efficient water extraction from the soil profile, particularly in the grain filling period during spring. Deep cultivation of the soil was proposed to overcome subsoil limitations. This study has compared the use of deep ripping, with and without the use of gypsum, to the use of direct drill techniques. Soil water use and plant root density have been compared for the different cultivation treatments. Soil water use indicated that the use of direct drill, compared with deep ripping, was favoured during years with dry autumn or delayed autumn breaks. Surface soil water was conserved in the direct drill treatments. The use of deep ripping, with and without the use of gypsum did not significantly increase the rooting density to a greater depth than direct drill. Furthermore the deeper roots failed to access soil water to improve grain yield compared with direct drill treatments. An increase in grain yield, with the use of deep ripping, was recorded in a year of above average rainfall in the growing season. The addition of gypsum, when deep ripping, provided no additional benefit to grain yield in the above average rainfall year.
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    The economic evaluation of forage research results
    Gaffy, Joseph ( 2004)
    Three economic analyses were conducted on the results of dairy forage production experiments undertaken in Victoria. The first analysis investigated the level of pasture production increases that would have to be achieved to warrant the investment in different soil modification options. This analysis took pasture production data and using a computer program "UDDER" (Larcombe 1990) generated farm data which was then applied to development budgets. The increase in pasture growth rate required was such that it is unlikely that investment in the soil modification systems tested here will produce a satisfactory return on investment. The second analysis investigated the use of different pasture species combinations on a dairy farm in northern Victoria. A linear programming model was developed that balanced the energy requirements of the milking herd with the energy supplied from pasture and supplements. The results showed that the most profitable mix of pasture depended on the energy supply profile of the pasture and the requirements of the herd. The proportion of autumn and spring calving cows in the herd in part determined the most profitable pasture mix. The effect of grazing management on profit was the subject of the third study. A farm model was constructed that balanced the energy, protein and neutral detergent fibre requirements of the milking herd with that supplied by pasture and supplements and optimised operating profit. The results of a grazing trial conducted in south-west Victoria were entered into the model and the operating profits for each treatment compared. The results suggested that while Operating profit was related to total pasture consumption, the timing of the pasture consumption impacted on operating profit. The results also suggested that grazing frequency may have affected operating profit more than grazing intensity.
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    Peach tree water use
    Goodwin, Ian (1961-) ( 2004)
    Peach tree water use (TWU) was measured and simulated in order to improve both current understanding of water use and to devise a practical irrigation scheduling method for orchards in northern Victoria. TWU was appraised in terms of a basal crop coefficient (Kcb) and reference crop evapotranspiration (ETo). Weighting of ETo by measures of vegetative ground cover and solar radiation interception were explored as techniques to account for changes in TWU associated with tree size, row orientation and tree training method. Sap flow (SF), using the compensation heat pulse technique, was evaluated as a method to measure TWU. Field experiments explored the variation in sap velocity (SV) in the trunk of peach trees and the accuracy of the technique to measure TWU. Sap velocity varied radially across the sapwood so a sap velocity profile was used to calculate sap flow (SF) from measurements made at specific depths in the sapwood. Analysis of the variation in SF around the circumference of a tree revealed the need for at least four sensors installed at different positions in the trunk. Calibration using the cut-tree method established the relationship: TWU = 1.44 (� 0.04) SF. A short-term experiment was conducted to determine effects of reducing tree size on TWU. Tree size was progressively reduced by de-branching an individual isolated tree over a 15-day period. Measures of TWU by sap flow were compared with estimates derived from ETo, and either canopy cover (CC; estimated from the horizontal extent of the canopy) or the area of shade cast by the tree on the soil surface (ASH). ASH was estimated prior to each de-branching event using a combination of photographs of the tree taken from the direction of the sun together with measures of fractional radiation interception in the area of shade cast by the tree. TWU and ETo averaged 42.1 litre/d and 4.7 mm/d, respectively, in the 6-day period prior to de-branching. CC and effective canopy cover (ECC; estimated as ASH measured at solar noon) were 7.8 and 5.8 m2 respectively, in that period. Five de-branching events reduced TWU, CC and ECC by > 95 %. To account for the daytime variation in ASH, effective area of shade (EAS) was calculated from estimates of ASH at solar noon and 3 h each side of solar noon. Kcb, the basal crop coefficient defined by Allen et al. (1998), was related to EAS by Kcb = 1.12 EAS. The effects of row orientation on TWU were investigated by a combination of field and modelling studies on isolated trees and hypothetical hedgerow orchards. TWU was measured by sap flow in six isolated field-grown trees pruned in a hedge shape and orientated north-south (NS) and east-west (EW). TWU was simulated by weighting ETo by the area of shade cast by the tree on the horizontal soil surface (ASH). The model effectively weighted ETo (`Big Leaf') by the fraction of direct beam radiation intercepted by tree foliage in orchards. ASH was estimated using a radiation interception model. Maximum rates of TWU in NS trees were attained in the morning when ETo was approximately half its maximum, and these rates were maintained for much of the day, whereas TWU for EW trees increased linearly with increase in ETo. Leaf area density (p) was estimated as 1 m2/m3 by comparison of observed and simulated TWU and was subsequently used in simulation of ASH in hedgerow orchards. The maximum rate of simulated TWU (TWU') occurred approximately 3 h each side of solar noon in a NS orientated hedgerow but declined in the middle of the day. Shaded leaf transpiration was suggested as a possible contributor to TWU that was not considered in the radiation interception model. The study demonstrated that EAS-weighted ET0 provided a reliable estimate of daily TWU irrespective of row orientation, leaf area density and hedgerow width. TWU and ASH were compared in Tatura trellis (TT) and central leader (CL) orchards. Field observations indicated that TWU in TT orchards attained a maximum near solar noon (matching ET0) whereas in CL it reached a maximum in the morning then remained constant during the middle of the day. Measured ASH revealed a substantial depression at solar noon in CL compared with TT. ECC was 2.3 and 1.7 m2 in the TT and CL trees, respectively. By comparison, EAS was 14 and 30 % greater than ECC for TT and CL trees. These differences between ECC and EAS were even greater in simulated hedgerows taller than used in the field experiment, leading to considerable variation in the relationship between simulated ECC-weighted ETo and TWU. On the other hand, the relationship established between simulated EAS-weighted ET0 and TWU for hypothetical TT trees (TWU = 1.17 EAS ETo) was the same as that established for isolated trees. The results of this thesis suggest that TWU of well-watered trees is slightly above the unit rate of water use described by ET0 (Allen et al. 1998) over the area of shade cast by the tree on the soil surface. Assuming negligible understorey water use, irrigation amount can be simply estimated from 1.12 EAS ETo where EAS accounts for daytime changes in ASH associated tree size, row orientation, training system, and leaf area density. Given this, irrigation requirement can be calculated from ETo and routine measures of orchard EAS. This is a simpler procedure than current FAO recommendations based on ET0 that require a look-up table of Kcb values for different growing periods and further adjustments for vegetation cover. In contrast, the EAS-weighted ETo proposed here provides an objective estimate of TWU for which EAS can be readily established by routine measurements of the fraction of shade in an orchard by irrigation consultants, extension officers, or growers.
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