School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemThe activity of glyphosate and other herbicides in soil( 1989)The effects of herbicides on a legume Rhizobium symbiosis were studied in laboratory experiments. Root applications of all herbicides examined reduced nodulation of legumes grown in aqueous nutrient media. The growth of Rhizobium trifolii TA1 was reduced by 2 - 20 mg ai 1-1 of diquat, 2 mg ai 1-1 of paraquat, 10 mg ai 14 of glyphosate and 2 mg ail-1 of chlorsulfuron. No other herbicide affected rhizobia growth when applied at 2 - 20 mg ai l-1 of nutrient medium. Inoculation with TA1 pre-treated with amitrole, atrazine or glyphosate decreased nodulation of sub-clover plants indicating that these herbicides may affect the nodulation potential of certain strains of Rhizobium. Residues of 2,4-D, amitrole, diquat, trifluralin and glyphosate persisted in a Walpeup sandy loam in sufficient concentration for four months after application to soil to affect growth and symbiotic activity of sub-clover. The behaviour of glyphosate in soil, under various conditions was studied in the laboratory. Adsorption of glyphosate as depicted by Freundlich K constant was greater in an acid soil than in three alkaline soils and values for this constant ranged from 8 - 67.8 at 23.5C and 4.3 - 57.8 at 10C. Rate of decomposition of 14C-glyphosate at 25C decreased slowly over the experimental period in all soils. Two compartments of adsorbed glyphosate in soil were identified as labile glyphosate and non-labile glyphosate and these reflected the strength of adsorption of the chemical. The amount of glyphosate in the labile firm for the soils ranged from 24 - 34.5% of the total and half-life ranged from 6 - 9 days. The amount of glyphosate in the non-labile form for soils ranged from 67 . 75% of the total and half-life ranged from 222 to 835 days. At 10C, the two compartments of glyphosate adsorption were identified for the Walpeup and Rutherglen soils but only one compartment could be identified in the Wimmera and Culgoa soils. Methodology was developed to permit extraction and analysis of glyphosate and AMPA in soil. Recovery of glyphosate from soils where time between fortification and extraction was only 30 sec. was 84.6 - 104%. However where extraction was delayed 13 hours, recoveries were 47.6 - 66.8%. The extractant (0.1 M triethylamine) was shown to be unable to desorb adsorbed glyphosate. Studies revealed that at 25C, the pool of extractable glyphosate was rapidly depleted by decomposition. At this temperature, the pool of extractable glyphosate was supplemented by slow desorption of non-labile glyphosate for each soil. At 10C, depletion of the pool of extractable glyphosate was considerably slower. For the Walpeup and Rutherglen soils, the rate of desorption of glyphosate from the non-labile pool was less than the rate of loss by decomposition of the herbicide. Rate of desorption of non-labile glyphosate in the Wimmera soil was shown to be the same as the rate of loss by decomposition of the herbicide. Loss of extractable glyphosate in the Culgoa soil occurred by decomposition and by slow adsorption of extractable herbicide from the labile to the non-labile form. The effects of residues of glyphosate in the field following an autumn and a summer application were investigated at selected field sites. Following the autumn application, phytotoxic activity of glyphosate was observed in sub-clover plants growing at the Walpeup and Culgoa sites but not at the Wimmera site. Growth and nodulation of plants sown up to 4 weeks after herbicide treatment were reduced at the Walpeup site. Only nodulation of plants sown up to 4 weeks after treatment was reduced at the Culgoa site. Results suggest that residues of glyphosate are only likely to significantly affect the growth of susceptible plants during winter on sandy soils. Following summer application of glyphosate, no phytotoxic activity of the herbicide was observed for sub-clover plants grown in the Walpeup sandy loam. Results suggest that in a hot summer, it is unlikely that residues of glyphosate in any soil would cause significant damage to plant growth.
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ItemStudies of barley yellow dwarf virus infection in ryegrass (Lolium spp.)( 1989)Measurements were made of the effect of barley yellow dwarf virus (BYDV) infection on the early growth of four commercial cultivars of ryegrass (Lolium spp.) under two different temperatures (24C and 16C). At 24C, BYDV infection was associated with reduced root dry weight (30-40%) in all cultivars; the effect of infection on shoot dry weight and leaf area was variable. At 16C, the effect of BYDV infection was variable, being associated with increases in both leaf area and root and shoot dry weight in one cultivar (Grasslands Arild) and decreases in another (Victorian). In two other cultivars, both leaf area and root and shoot dry weight were not significantly affected (p > 0.05) by infection with BYDV. There was no evidence of visible symptoms associated with BYDV infection. At 240C, reductions in root dry weight associated with BYDV infection were not reflected in reductions in the relative growth rates of the roots. Up to at least 28 days after inoculation (46-50 days after germination) reductions in root dry weight were associated with both aphid-feeding damage and virus infection. Experiments with the cultivar Victorian showed that shoot dry weight was not significantly affected (p > 0.05) by feeding with either viruliferous (BYDV) or non-viruliferous aphids (Rhopalosiphum padi L.). At 16C, changes in root and shoot dry weight were associated with changes in the respective relative growth rates. Both visual scoring and changes in plant dry weight were found to be unreliable criteria for assessing disease severity. Two assay systems, an enzyme-linked immunosorbent assay (ELISA) and a nucleic acid, or complementary DNA (cDNA) probe, were developed for the detection of BYDV in ryegrass. The conditions for detecting BYDV with the ELISA (the "double sandwich" variant) were optimized. Exposure of the virus to extracts of ryegrass leaf tissue for 30 min or more resulted in reductions in absorbance, with the amount of the reduction dependent on the antigen (virus) incubation temperature. The optimization of conditions for the immunoglobulin (IgG) used for coating microtitre plates (coat IgG), the IgG - alkaline phosphatase conjugate (conjugate IgG) and the antigen (virus), in conjunction with the use of polyethylene glycol - 6 000 in the preparation of the conjugate buffer, gave a rapid and reliable ELISA procedure for the consistent detection of BYDV at levels of 2 ng/ml. Both ELISA and cDNA probe techniques were used to study the incidence of BYDV isolates in perennial ryegrass at three sites (Balmoral, Mininera and Hamilton) in south-western Victoria. BYDV was detected in perennial ryegrass cultivars from the three sites, with different levels of incidence of BYDV isolates between cultivars. While the PAV-related isolate was prevalent at the three sites, the incidence of the MAV- and RPVrelated isolates varied with the site and the cultivar. One difficulty with the ELISA was that absorbance values did not fall in to distinct infected and uninfected groups within the cultivars, and at Mininera, the incidence of BYDV varied significantly between the various positive - negative ELISA thresholds that were used. At Balmoral, the incidence of BYDV determined with each threshold was compared with that determined by cDNA probing using a Spearman correlation test. A threshold of double the mean negative (uninfected ryegrass) control showed the highest correlation with the cDNA probe for a number of replicate plots at the site. The incidence of the PAV-related isolate was compared for the two cultivars Ellett and Victorian, and significant (p < 0.01) reductions in its incidence in cv. Ellett compared with cv. Victorian at the three sites, suggested that cv. Ellett is resistant to the PAVrelated isolate of BYDV. The comparative resistance of cv. Ellett to at least this isolate of BYDV indicated the feasibility of breeding and selecting for resistance to other isolates of BYDV in perennial ryegrass. In attempts to quantify resistance in perennial ryegrass, the ELISA was further developed to allow measurement of BYDV titre in ryegrass shoot tissue. In twenty selections of cv. Victorian, the performance, as measured by changes in both root and shoot dry weights, of individual selections to infection with BYDV, did not significantly (p < 0.05) correlate with virus titre measurements. Experiments with twenty selections of cv. Ellett indicated that its resistance to BYDV that was e' ident at the three field sites was not associated with resistance to aphid (Rhopalosiphum path) feeding, and consequently, transmission of the virus. Attempts to inoculate cv. Ellett with either the PAV- or RPVrelated isolates were of limited success, and it was speculated that its resistance to the virus may be due to reductions in the level of virus replication.
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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.