School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemRoot and top growth of the wheat plant as affected by water supply( 1987)Two experiments were conducted to study the growth, particularly the root growth, of wheat in relation to moisture supply. One was conducted in an igloo house at the Mt Derrimut Field Station of the School of Agriculture and Forestry, University of Melbourne and the other in a glass house on the main campus. The plants were grown in a mixture of soil, sand and ligna peat contained in plastic bags to give columns about 0.8 m deep. In the first experiment the effects on both above-ground and below-ground growth of withholding water at different stages of growth and for different times were studied on three cultivars of wheat. In the second experiment effects of supplying different amounts of water were studied. Plants were harvested periodically for measurement of dry weights of the various plant parts, measurement of leaf area and root length and counts of tillers, heads, grains and roots. The soil columns were dismantled 20 cm at a time to enable the distribution of roots in the profile to be observed. Withholding water at any stage of growth and for any period reduced the above-ground dry matter at maturity; the longer the period of non-watering the greater the reduction. Reduction in above-ground dry matter resulted from reductions in number of tillers, leaf area and grain yield. Tillering was most affected by non-watering during early and mid-season growth, and yield by non-watering after anthesis, especially when it occurred during the first two weeks after anthesis. Non-watering after anthesis reduced yield mainly by reducing grain size (1000 grain weight). The quantity of recoverable roots, measured either by weight or by length, reached a maximum about the time of anthesis and then declined as roots died and were lost during harvest. The quantity of roots formed was reduced when non-watering was imposed during early or mid-growth. The distribution of roots in the profile was also affected by the watering treatments. Withholding water during early and mid-growth resulted in a greater proportion being located in the deeper soil zones. However, with the soil initially below field capacity, withholding water from sowing onwards resulted in shallow rooting presumably because an absolute lack of water limited the plants' ability to produce deep roots. Watering the soil to field capacity every three days in Experiment 2 resulted in less above-ground dry matter than watering to field capacity once a week. It resulted also in a greater proportion of the roots being in the upper part of the profile suggesting that root penetration of the lower part was inhibited by poor aeration as a consequence of overwatering. Watering to field capacity once a week resulted in less above-ground dry matter than giving half the amount of water needed to restore the whole soil column to field capacity. Moreover, the proportion of roots in the bottom zone of the rofile was less under the former treatment than under the latter suggesting that watering to field capacity once a week was causing some restriction of root growth in the bottom zone, presumably through poor aeration. These two facts taken together suggest that in this experiment watering to field capacity once a week even amounted to over-watering.
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ItemEvaluation of the concepts and methods of response farming using crop growth simulation models( 1989)This thesis considers aspects of the application of the CERES-Maize simulation model of the growth and yield of the maize crop to the analysis of "response farming" in the semi-arid region of East Kenya. Response farming comprises a set of management tactics by which sowing density and nitrogen application can be targeted to the yield potential of the season based upon the timing and nature of the opening rains. Sowing density and nitrogen application are set by the timing of the opening rains and then further adjustments are made four to five weeks after sowing. The in-season adjustments involve additional nitrogen fertilizer in seasons that promise high yield potential and crop thinning when yield promises to be low. These combinations have the purpose of maximizing yield in seasons of high potential and minimizing fertilizer and seed input in seasons in which the rainfall is too low for it to have any advantage. The scheme is possible, it is proposed, because the timing and nature of the opening rains are closely correlated with total seasonal rainfall and hence yield potential. The thesis discusses the potential that simulation models hold in the analysis of alternative cropping strategies (Chapter 2). It presents a validation study of the model with experimental data collected in the region (Chapter 3) and discusses the relationships between maize agronomy in the region and the components of response farming (Chapter 4). The tuned model is shown to provide a good explanation of the response of the common cultivar of maize to a range of combinations of water and nitrogen supply and a reasonable capacity to describe the response of the crop to thinning (Chapter 5). The model is then used (Chapter 6) to compare response farming with conventional practices at various levels of inputs. It shows that the common practice of the region by which-crops are sown at low density without fertilizer has the least risk of failure but low expected yields. Fertilizer is required to increase yields, but its use incurs a greater chance of crop failure. Compared to alternative strategies using fixed or variable sowing dates at comparable levels of crop density and nitrogen fertilizer, it is shown that response farming does provide higher mean yield with less chance of failure. It is proposed that continuing experimentation with the current and improved versions of the model have an important role to play in the identification of better management strategies for East Kenyan farmers.
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ItemBiometric studies of some eucalypt plantations in South China( 1987)Biometrical studies Of introduced tree species in the Dongmen area are presented in two parts. In the first part, a number of tree volume functions were fitted to data for E. exserta. A simple weighted regression model was found to be most appropriate. This model proved to be better than that recommended by local mensurationists in Guangxi. In the second part, fertilizer trials are reported for eighteen seed strains under five fertilizer regimes. These strains were finally clustered into four groups in terms of performance. All strains of E. camaldulensis proved most successful for all levels of fertilizer used. Further analysis showed that E. camaldulensis responded best with highest levels of nitrogen, phosphorus and potassium plus trace elements used, and that the addition of trace elements did not significantly improve response.
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ItemPasture utilization for wool growth of weaner sheep in south western Victoria( 1988)Two series of experiments are described in this thesis. The first set of experiments report on the use of young, oesophageally fistulated sheep to collect herbage samples in grazing experiments. Secondly, the biological responses of Merino and Comeback weaner sheep to changes in pasture type and season of birth are described. The experiments were conducted at the Pastoral Research Institute, Hamilton, Victoria during 1982-86, where the author is employed as a Science Officer by the Victorian Department of Agriculture and Rural Affairs. Chapters 4 and 5 report the effects of several variables on the chemical composition of oesophageal fistula samples and have been submitted for publication (see below). Mr. P.C. Flinn and Professor A.R. Egan have been included as co-authors of Chapter 4 due to their contribution to chemical analysis of samples, and to planning of the experiment respectively. Mr. P.C. Flinn and Mr. J.F. Heard have been included as co-authors due to their assistance during the experiment described in Chapter 5. Differences between the growth, composition and nutritive value of lucerne/subterranean clover and perennial ryegrass/subterranean clover pastures are reported in Chapter 6. (More detailed data on the growth and composition of the pastures is available on request to the author). The effects of these pastures on the productivity of autumn and spring born, Merino and Comeback weaner sheep are presented in Chapters 7 and 8. It. is intended to submit these three chapters for publication. Mr. R.L. Thompson and Dr. J.M. Obst will be. included as co-authors when the results reported in Chapter 7 are published. The experiments reported in this thesis make up part of a larger project (Sheep Production Systems) for which Mr. Thompson and Dr. Obst are responsible. However I accept full responsibility for the collection of all data, analysis of results and preparation of the manuscripts. In addition, I was responsible for the design of experiments reported in Chapters 4, 5, 6 and 8. Details of publications are as follows:- Chapter 4 : Saul, G.R., Flinn, P.C. and Egan, A.R. (1988). The effect of fasting, breed and sample size on the chemical composition of pasture samples from fistulated weaned lambs (submitted to Australian Journal of Experimental Agriculture). Chapter 5 : Saul, G.R., Flinn, P.C. and Heard, J.F. (1986). The nutritive value of roughages before and after mastication by oesophageally fistulated sheep. Proceedings Australian Society of Animal Production 16, 351-54.
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ItemEffects of post-anthesis drought on wheat( 1985)The experiments presented in this thesis investigate, firstly, the effects of drought on the cellular processes occuring in the wheat grain and, secondly, some of the possible causes of the reduction in grain growth. The main conclusions are: 1. Drought occurring during the early period of grain growth leads to a reduction in number and size of endosperm cells and a reduction in the number of starch granules initiated per cell. The reductions in numbers of endosperm cells and starch granules are greater in grains of top spikelets (distal grains) than in basal grains of middle spikelets (basal grains). 2. Final grain weight is closely correlated with the number of endosperm cells in basal grains of the variety Warigal. However, in basal grains of Condor, a variety more drought-sensitive than Warigal, grain weight is more reduced than cell number. This is also the case in distal grains of both varieties. The greater reduction in final grain weight relative to cell number is at least partly due to to a reduction in number of small starch granules per cell. 3. Although the supply of sucrose to the endosperm cells is reduced under drought, this is unlikely to cause the reductions in numbers of cells and starch granules per cell. Rather, it is concluded that the reduction in sucrose supply to the endosperm observed under drought is a response to, and not a cause of, the reduction in numbers of endosperm cells and starch granules per cell. This conclusion is based on two results: (i) despite a constant level of sucrose per cell, the number of small starch granules per cell is reduced under drought, and (ii) a reduction in photosynthesis of ca. 40% is accompanied by a reduction in grain growth and an accumulation of stem reserves in droughted plants of Warigal. Stem reserves would not be expected to accumulate to the extent occurring in control if assimilates were in short supply for grain growth. 4. Among the photosynthetic organs supplying assimilates to the grains, the glumes show the greatest drought-tolerance. Glumes have a better osmotic adjustment and a greater integrity of the cell membranes under drought than leaves. These two characters are probably at least partly due to anatomical characteristics of the glumes, in particular, small cell size and thick cell walls. 5. Carbon and nitrogen budgets of droughted plants indicate that the roots and the stem play an important role in the transfer of assimilates to the grains. Larger osmotic adjustment of the roots and greater accumulation of stem reserves are two aspects of the better drought-tolerance of Warigal relative to Condor. 6. The loss of turgor and the accumulation of abscisic acid in the grains are the most likely causes of the reduction in numbers of endosperm cells and starch granules. Distal grains lose turgor more rapidly and accumulate more ABA per endosperm cell than basal grains. The implications of these results for drought tolerance of wheat are discussed.
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ItemA study of the growth of subterranean clover (Trifolium subterraneum) in acid soil from Strathfieldsaye in East Gippsland( 1984)Legume-based pastures are widely used in the farming and pastoral regions of Australia. In southern Australia, subterranean clover has been the cornerstone of pasture improvement and increased crop and animal productivity since the 1930's and 1940's (Donald 1970). It has been estimated that as much as 80% of the present area of sown pasture in southern Australia may have been sown with subterranean clover (Donald 1970). The importance of subterranean clover is due to its ability to utilize atmospheric nitrogen and ultimately to improve soil fertility. Additionally, however, it provides high quality stock feed, is tolerant of grazing and possesses traits such as the ability to bury its seeds and also seed coat impermeability (hardseededness) which enable the plant to reappear reliably in pastures every year (Morley 1961). It is widely believed that the productivity of subterranean cloverbased pastures may have declined over the years since they were first established (Flemons and Siman 1970; Williams and David 1976; Osborne et al. 1978; Cregan et al. 1979; Williams 1980; Reeves 1981; Gillespie 1983; Evans and Hochman 1984). The cause of this 'decline' has been variously attributed to increased cropping, incidence of diseases and pests, poor grazing management (e.g. Cregan 1981; Gillespie 1983), but also has been associated with decreasing pH of soil under the pastures (e.g. Cook 1939; Donald and Williams 1954; Russell 1960; Watson 1969; Barrow 1969; Flemons and Siman 1970; Kohn et al. 1977; Williams 1980; Bromfield et al. 1983a). This thesis is concerned with a study of the growth of subterranean clover in acid soil from 'Strathfieldsaye' at Stratford, in the East Gippsland region of Victoria. The soil was taken from beneath a legume based pasture in which subterranean clover represented only a small proportion of the plants in the pasture. This situation was regarded as undesirable. The study was initiated because it was considered possible that the very low pH of the soil may have contributed to the low occurrence of subterranean clover in the pasture.
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ItemThe influence of nutritional factors in the development of postweaning diarrhoea in early weaned pigs( 1984)1. The study concerned the significance of change of diet and feeding method on the clinical, pathological and growth responses of 3- to 4-week-old pigs when subjected either to challenge with an enterotoxigenic serotype of Escherichia coli or exposed to 'natural' infection with E.coli. It involved experiments with both hysterotomy-derived specific pathogen-free (SPF) piglets and conventionally reared animals. The dietary treatments involved comparisons between (i) wet versus dry feeding and (ii) skim milk versus soyabean (SB) meal as the major dietary protein source. 2. Under closely controlled SPF conditions, thirty-five 28-day-old piglets were used in five experiments. In the first four experiments, two groups were changed from a liquid cow's milk diet to a milk-based diet (termed the 'basal' diet), given either in wet or dry form. Within each group, half of the animals were orally challenged with enterotoxigenic E.coli (ETEC) bearing the K88 antigen and the remainder, serving as controls, were challenged with a non-pathogenic K12 E.coli strain. ETEC-infected piglets fed the dry, basal diet developed severe diarrhoea, depression and dehydration and at necropsy exhibited severe lesions in the small intestine associated with extensive bacterial adherence and marked reduction in intestinal lactase activity. Infected piglets fed the basal diet as a gruel had only mild diarrhoea, accompanied by limited bacterial adherence and minor mucosal and physiological changes. Control piglets, fed either dry or wet, remained clinically healthy and the morphology of the intestinal mucosa was normal. In the fifth experiment, two groups were changed from the liquid cow's milk diet to either a dry-fed basal diet or a dry-fed SB-based diet; each group consisted of both infected and control animals. Control piglets on both diets remained clinically normal with only minor mucosal changes; but the intestinal lactase activity of those fed the SB diet was depressed. Infected piglets fed the SB diet developed mild diarrhoea, depression and dehydration. Infected piglets fed the basal diet had no diarrhoea but were depressed. Bacterial colonization, mucosal and physiological changes were relatively more severe in the SB-fed animals than in those fed the basal diet. 3. Under conventional conditions, a total 0f one hundred and seventy-six piglets, from the Mt Derrimut herd, were used in three experiments. In each of these experiments, pigs were allocated among four dietary treatments: dry, basal; wet, basal; dry, SB; and wet, SB. In Expt 1, a total of twenty-four pigs were orally inoculated with K88 ETEC following their transfer at weaning to non-specialized pen accommodation (at the Attwood Institute for Veterinary Research). In Expts 2 and 3, (conducted at the Mt Derrimut Pig Centre), ninety-six and fifty-six pigs respectively were moved at weaning into specialized weaner accommodation that was routinely used for early weaning on a batch basis. No inoculations with ETEC were performed in these two experiments. In Expt 1, all pigs remained clinically normal except for one pig fed the SB diet dry. Post-mortem studies conducted on four selected pigs from each treatment group revealed very limited colonization by ETEC but without marked changes in gut morphology (although K88 ETEC were present in faecal materials). In Expts 2 and 3, natural infection with ETEC and manifestation of PWD (postweaning diarrhoea) occurred. As compared with the SB diet, the basal diet particularly when fed wet, resulted in a less severe diarrhoea. Morphological and physiological changes in the small intestine were less pronounced and bacterial adherence was less extensive. Whether the SB diet was fed wet or dry made little difference in these respects. In the first 14 days post-weaning pigs fed the basal diet, especially when this was fed wet, made faster and more efficient weight gains than those given the SB diet. The degree of infection was more widespread and severe in Expt 3 than in Expt 2. In Expt 3, the superiority of the milk-based diet compared to the SB diet was relatively greater during the first 14 days post-weaning. 4. The results indicated that both the type of diet and the form in which the diet was fed, significantly influenced the extent of colonization of the gut by ETEC, the severity of PWD and growth performance. The effects of feeding method were more apparent in the SPF piglets than in the conventional piglets. This was attributed to the greater influence of uncontrolled variables in the latter situation. 5. The greater variability of performance under the conventional rearing conditions and the marked difference in response to ETEC in Expt 1 compared with that in Expts 2 and 3 suggest that in addition to the dietary factors examined, other factors, such as the immune status of the animal, the level of 'background' pathogenic challenge and the physical environment were implicated in the pathogenesis of PWD.
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ItemGrain lupin cultivation in Victoria : some agronomic aspects( 1981)The results of five field experiments and one laboratory experiment, have been included in the chapters of this thesis. They describe the adaptation of lupins to the environment of North-East Victoria in terms of seed germination, establishment, growth and grain yield. Chapters 2, 3 and 4 have been submitted as scientific papers and published (or are to be published) in the Australian Journal of Experimental Agriculture and Animal Husbandry. I was actively involved in field work at the Rutherglen Research Institute and at the regional sites during these investigations. Mr. T. G. Reeves was my supervisor during the time when the experiments reported in Chapters 2 and 3 were being conducted. I carried out the field work and analysed and reported the data under the supervision of Mr. Reeves. We shared senior authorship of the two scientific papers resulting from this work. For the experiment reported in Chapter 4, Dr. C. M. Piggin assisted me with experimental design and facilities, however, I conducted measurements and analyses and solely prepared these for publication. I was responsible for the lupin research and development programme at Rutherglen Research Institute from 1976 to 1981.