School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemDecline of river red gum (Eucalyptus camaldulensis Dehnh.) on grazing lands in Western Victoria( 1988)River Red Gum (Eucalyptus camaldulensis Dehnh.) is a common and extensively distributed tree in western Victoria. Widely-spaced stands of this species are a prominent feature of pastoral landscapes in that area. Many of these remnant stands are in a state of decline, with individuals being lost through deliberate clearing, senescence or the effect of rural dieback disease syndromes. This thesis reports on a study of the decline of one stand of E.camaldulensis trees growing on part of a grazing property near Buangor, in west-central Victoria. The rate of tree loss from agricultural land in the Buangor district was assessed from aerial photographs taken in 1947 and 1980. The average compounding rate of tree loss over that period was 1.1% p.a.. Rates of tree loss were greater from the remnant box-stringybark stands (1.9% p.a.) occurring in the district than from remnant River Red Gum stands (0.8% p.a.). The size and crown condition of all trees in the stand under investigation were assessed. Dieback-affected trees had relatively small and open crowns, that often had many dead branchlets and branches. The crowns of dieback-affected trees were largely of secondary or epicormic origin. Tree height and stem girth were not affected by contemporary crown health. The age of one tree was estimated by radiocarbon dating to be 440. ± 110 y B.P.. Detailed investigations of trees classified as either "healthy", "average" or "unhealthy" were undertaken. The amount of organic matter in soil declined as the quality of tree cover changed from "healthy" to "unhealthy" tree to open pasture. This change was probably linked with reduced additions of organic material through litterfall as tree crown cover deteriorated. The possible consequences of reduced litterfall and declining soil organic matter levels were that; (i) it may have disrupted biogeochemical nutrient cycling; and (ii) it may have increased the susceptibility of trees to root damage and other problems associated with animal traffic. Measurements of soil strength and bulk density indicated that soil under open pasture had been compacted, presumably by animal traffic. Soil under trees was harder during winter than soil under open pasture and was therefore less susceptible to puddling. Soil under trees was not as strong as soil under open pasture during spring and hence provided more favourable conditions for root growth. Investigations into the mineral nutrition of study trees found that "unhealthy" trees did not appear able to mobilize some macronutrient elements (N,P, K, Mg) to the same extent as "healthy" trees. The apparent nutrient deficiency may have been due to disruptions to the biogeochemical nutrient cycle as dieback progressed. The nutrient deficiency may exacerbate this disruption, since it was associated and possibly linked with delayed new foliage production in "unhealthy" trees and reduced area growth in that foliage. Measurements of leaf water potential, diffusive conductance and transpiration showed that atmospheric, rather than soil water deficits had the greatest influence on water relations in the study trees. The measurements showed that "unhealthy" and "average" trees did not greatly restrict transpiration during periods of high evaporative demand. "Healthy" and "average" trees transpired more water and assimilated more carbon than did "unhealthy" trees. Differences in gas exchange were due only to large differences in leaf area. Soil under "healthy" and "average" trees remained drier than soil under "unhealthy" trees and open pasture throughout the study period. However, there was little difference in soil water depletion during the summer, even though the annual pasture had died off. Measurements provide evidence of deep infiltration of water beyond plant root zones, particularly under open pasture and "unhealthy" trees. The healthier trees appeared to have a beneficial impact on the local water balance. Continued rural dieback and/or tree loss is likely to exacerbate disruptions to the local water balance that commenced with clearing for agriculture.
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ItemA study of some aspects of adaptation and yield of Serradella (Ornithopus Spp.) in Victoria( 1989)Serradella (Ornithopus sp.) is potentially useful on deep acid sandy soils in the > 350mm average annual rainfall areas of southern Australia, where many other pasture legumes fail to persist. Subterranean clover (Trifolium sp.) is one of the most important annual pasture legumes usually sown on non-alkaline soils within this climatic region, but it often fails to establish and persist on deep acid sandy soils. In these situations serradella may be a more productive alternative and may become the dominant pasture legume. One of the main limitations to the widespread use of serradella has been the limited amount of genetic variation in Australia, with there being only very few naturalised and commercial strains. In its area of origin, serradella covers the full area of origin of subterranean clover in the Mediterranean region and extends farther into north-western Europe and onto acid sandy soils on which subterranean clover is absent. Yellow serradella (Ornithopus compressus) appears to have the greatest potential for commercial development in Australia, but only one relatively late flowering cultivar, derived from a chance introduction, was available. This was the cultivar Pitman which was suited to an average annual rainfall of 500mm and thus did not leave enough seed for survival of the species in the large areas of grazing land in drier (350-500mm average annual rainfall) areas. In the period from 1970-1980, mainly in an effort to extend the use of serradella to the drier areas, artificially induced mutants of the cultivar Pitman were produced and a wide range of serradella seed was collected from the Mediterranean region. This new variation available to Australian scientists and farmers has been, and is still being, assessed for characters considered to be important for the success of serradella as a pasture legume in Australia. In 1982 seed of 26 of the new accessions, the cultivar Pitman and the Pitman derived mutant, Uniserra, became available to the University of Melbourne for testing under Victorian conditions. These accessions were grown, in single rows and pots, in Gippsland and growth assessments and flowering times were recorded. There was considerable variation in growth response and flowering times and at the end of this trial six lines with good growth were chosen, so that the full range from early to late lines were represented. In the following season, also in Gippsland, the six chosen lines were each sown at five different dates, in single rows with two cultivars of subterranean clover. The flowering and growth responses were recorded allowing direct comparisons to be made. To clarify the comparative vernalization responses of serradella and subterranean clover, a range of accessions of serradella and two cultivars of subterranean clover were grown in the field and in pots in northern Victoria and southern N.S.W., in summer. A similar range of serradella and subterranean clover lines/cultivars was also subjected to artificial vernalization and the resultant flowering responses were recorded. Some of the new accessions flowered earlier than the cultivars Pitman and Uniserra, and the general flowering responses to climate appeared to be similar in both serradella and subterranean clover, with there being similar individual responses between early and late lines of both species. It has been widely reported that on deep acid sandy soils serradella has a more efficient root system, compared with other annual pasture legumes. The cultivar Pitman was grown alongside the subterranean clover cultivar Mt. Barker in an acid sandy loam, treated with varying lime application rates to achieve a range of pH levels (pH 4.3-6.3). The plants were grown in shallow (20cm deep) pots, deep (lm deep) pots and in the field. The application of lime had significant effects on root nodulation, root morphology and root growth of both species. The results generally support the findings of others that serradella's comparative advantage on deep acid sandy soils is due to a finely divided deep root system. A marked feature of serradella appears to be the extensive development of highly branched fine lateral root systems, which can also reach depths of lm.
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ItemEconomic incentives for private softwood plantations in Victoria( 1987)More than 90 per cent of the privately-owned softwood plantations in Victoria are owned by a small number of companies involved in the further processing of softwood timber. This study examines the economic factors influencing the establishment of softwood plantations by other private landholders (i.e. those that do not own softwood processing facilities) and evaluates the economic incentives currently offered to encourage these landholders to establish their own plantations. A number of economic factors contribute to the current low level of planting by private landholders that are not directly involved in the further processing of softwood. These include the structure of the market for softwood in Victoria, the price private growers can expect to receive for their wood, and the long term nature of the investment. The current taxation arrangements for private forestry offer a number of incentives for the establishment of softwood plantations. However they also contain a number of anomalies and disincentives to private forest investment. Various proposals to reform the income tax legislation have been put forward by private grower organizations and by the Commonwealth Government and this study critically evaluates these proposals. The Farm Forestry Agreement Scheme is an incentive scheme that has been offered by the Victorian Government since 1967 to encourage the establishment of private plantations. It offers low-interest loans with repayments deferred for the first 12 years. After more than 15 years operation the total plantings under the Scheme are approximately 8,300 hectares or less than four per cent of the total Victorian softwood resource. Inflation has seriously eroded the incentive value of the Scheme and it is also a very costly and cumbersome scheme to administer. Many Agreement holders are experiencing difficulties in selling wood from their plantations to meet loan repayments and interest in the Scheme has steadily declined in recent years. A number of softwood processing companies operating in Victoria also offer assistance schemes to encourage private landholders to establish their own plantations. The schemes offered by Softwood Holdings Ltd. and APM Forests Ltd. provide private growers with an assured outlet for their timber and have assisted a number of private growers in marketing wood from their plantations. In addition Australian Newsprint Mills Ltd. have recently introduced a scheme known as the Joint Venture Agreement Scheme which offers assistance in the establishment, management and marketing of wood from plantations established jointly by the company and private landholders. The formation of co-operatives of private forest growers offers a number of potential benefits to the owners of private plantations. Of these increased bargaining strength in the marketing of wood and a mechanism for better communication between private growers and softwood processing companies appear to be the most important. The existing incentives and assistance schemes offered by the Government have not been particularly successful in encouraging the establishment of softwood plantations by private landholders. New economic incentives are therefore required if these landholders are to supply an increased proportion of Victoria's future softwood requirements.
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ItemA study on damping-off in a regeneration mixed eucalypt forest( 1986)Although damping-off is known to cause considerable loss before and after emergence of seedlings in forest nurseries, little is known of its role in seedling mortality after direct seeding in artificial regeneration of mixed eucalypt forests. Findings reported in this thesis are the result of a survey for the presence of damping-off fungi in soils and dying seedlings, and tests of their pathogenicity to a range of eucalypts found in the Wombat State Forest of Victoria. This study was carried out in conjunction with a research programme established by the Victorian Department of Conservation, Forests and Lands to determine which factors govern the successful establishment of E. obliqua and E. radiata in three seed-bed types under five levels of overwood. Propagule counts for Pythiaceous fungi in burnt and unburnt soils from field experiment, plots prior to sowing indicated that the inoculum level was low and differed with levels of overwood retained following site preparation in summer (Chapter 2). Baiting the soils with E. sieberi cotyledons, apples or directly sowing E. sieberi seed in samples of the field soil showed that both burnt and unburnt soils were variably infested with Pythium spp., Fusarium spp., and Cylindrocarpon destructans. A small portion of the seed to be sawn in the field plots without any fungicidal pre-treatment was found to harbour a range of fungi, sane of which had the potential to inhibit germination of the eucalypts sown on the plots (Chapter 3). The fungi having this ability were however not isolated from damped off seedlings in the experimental plots. Field studies showed that the proportion of germinated seedlings killed as a result of damping-off was lower than that attributable to frost heave, droughting following freezing and insect damage (Chapter 4). Damping-off was found to be widespread over the entire study site and the rate of damping-off to differ with seed-bed type. Overwood density did not affect the disease level. Although Pythium spp. were responsible for most deaths, Cylindrocarpon destructans and Fusarium spp. also caused some mortality. Pathogenicity tests (Chapter 5) confirmed that the fungi associated with seedling mortality in the field can cause significant pre- and post-emergence damping-off in a range of eucalypts found at the study site. The fungi differed in their pathogenicity to the eucalypts and sane induced feeder root necrosis after the two leaf stage of seedling development. No differences in susceptibility to post-emergence damping-off were found between the tree species sown on the plots and others of economic importance in the forest. The overall findings and their implications for direct sowing as a management option in future field regenerations are discussed in Chapter 6.
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ItemThe effects of plant spacing on the shape, size, uniformity and yield of onions( 1986)The effects of plant spacing on size, shape, uniformity and yield of onion bulbs; including ware (35-85mm) and pickling (25-45mm) grades; were studied at the Vegetable Research Station during 1980-82. The study first examined the effect of plant density at a constant rectangularity of 1:1. Seed was hand-sown at 178, 400, 625, 816, 1111 and 1600 plants m-2 (cv. White Spanish) in 1980 and 51, 69, 83, 100, 178 and 400 plants m-2 (cv. Pukekohe Longkeeper) in 1981. Total, ware and pickling bulb yields followed parabolic relationships with plant density and were highest at 420, 148 and 666 plants m-2 respectively. Increases in plant density reduced plant size, mean bulb weight, plant fresh and dry weights, number of leaves, cumulative leaf length, time to maturity and the proportion of round bulbs, but did not affect the soluble solids content, bulb ratio or percentage dry matter per plant. Density had no effect on bulb uniformity but could be used to determine the distribution of size grades within the crop. The second part of the study examined the effect of plant arrangement at a constant density. Seed (cv. White Spanish) was hand-sown at densities of 178, 400, 625 and 816 plants m-2 and rectangularities of 1:1, 2:1, 1:2, 4:1, 1:4 and 16:1. Plant arrangement had no significant effect on total bulb yield, mean bulb size or bulb uniformity but altered bulb shape. Yield and number of round bulbs decreased as rectangularity increased. However, the response of onion bulbs to plant arrangement decreased as plant density increased. The final part of the study examined the effect of plant arrangement in a direct-drilled crop. Seed (cv. Pukekohe Longkeeper) was sown with a Stanhay (precision) seed drill at .a constant density and at rectangularities from 1.25:1 to 20:1 in 1981 and 1.08:1 to 14:1 in 1982. The response of onion bulbs to plant arrangement was more. dramatic for direct-drilled crops than hand-sown crops. Total and round bulb yields decreased as rectangularity increased. The practical implications of these results are discussed.
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ItemEffects of soil and water management on the productivity of irrigated pastures in the Goulburn Valley( 1986)The water status and productivity of perennial pastures were monitored during irrigation cycles. Measurements of leaf water potential reflected the water status of the pastures and when this deteriorated with the developing shortage of water after irrigation, various responses of the pastures were recorded. These included the rate of leaf elongation, canopy conductance, and the rates of net photosynthesis and evapotranspiration. The Parameters of gas-exchange were Measured using open-system, field chambers. The studies were designed to characterise and Compare the responses of these Pastures as water deficit developed, and to quantify their,effects on productivity. Experimental plots included swards of white clover (Trifolium repens), perennial ryegrass (Lolium perenne) and paspalum (Paspalum dilatatum) both as monocultures and as mixtures of the three species. These swards were growing on two soil profiles, both of which were Lemnos loam. The first profile was in its normal state and had been under pasture for fifteen years. The second had been structurally and chemically modified in 1979 to minimise the limitations to plant growth. It had been re--sown to pastures in 1980. The productivity of monocultures and mixed swards of each species on each profile was investigated as water shortage developed. In all species the responses to water shortage were the same, involving a reduction in the rate of development of leaf area,, followed by a reduction in photosynthesis per unit leaf area as the lack of water became more severe. The sensitivity of each species was distinct, with white clover being the most sensitive, ryegrass intermediate and paspalum the least. On modified soil, all species were less affected than on the normal profile but the order of sensitivity was the same. Overall, these experiments showed that after a typical irrigation cycle, which is about 8 days, water shortage reduces the productivity of white clover by 50%, ryegrass by 20% and paspalum by 5-10%. These limitations to productivity were overcome to some extent by modifying the profile, so that after an equivalent period the productivity of white clover was only reduced by about 208 and paspalum was not affected at all. The ability of paspalum to maintain high levels of productivity during an irrigation cycle had the effect of promoting this species in a mixed sward, its dominance becoming greater as the shortage of water became more severe. In order to achieve balanced pastures of maximum productivity, farmers in the Goulburn Valley need to reduce the limits to growth imposed by the physical and hydraulic characteristics of the soils. This may be achieved by irrigating more frequently or by undertaking some form of profile modification.