School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemNo Preview AvailableControl of the black field cricket teleogryllus commodus (walker) (orthoptera: gryllidae) in Victoria(University of Melbourne, 1985)Techniques for improving control of the black field cricket Teleogryllus commodus were studied between 1981 and 1985 in series of laboratory and field trials in the western district of Victoria. In the laboratory, techniques were developed for assessing the palatability of substances to T. commodus. A number of plant extracts, especially water and acetone extracts from grasses, and other substances including sucrose and vegetable oils were shown to stimulate feeding in the cricket. Further laboratory trials showed that feeding stimulants could be used to encourage feeding on a commonly used substrate in cricket baits (wheat). Field trials to assess bait attractiveness revealed oats to be more attractive as a bait than wheat or barley. Efficacy trials conducted over consecutive years however, showed no differences in the level of control achieved with baits using wheat, oats or barley as the substrate. In addition, feeding stimulants added to the bait did not improve control, nor did the use of higher baiting rates. The level of control obtainable with the current recommended bait is between 80% and 95%.
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ItemLactation in mice as a model to study genetic improvement of dairy cattle in the tropics( 1989)In chapter one of this thesis aspects of reproduction and production, mainly milk production were reviewed. Components of reproductive efficiency such as the fertility components: age at calving, service periods, days open, calving interval and non return rate; were also investigated. The physiological relationship between those traits and milk production and persistency, in both temperate and tropical environments, was also considered, as well as longevity or stayability as other alternatives for evaluating reproduction. Attention was put on first and second lactation performance. With a view towards understanding physiological aspects of reproduction and production in dairy cows, the nature of lactation in mice was reviewed from the relatively few works that have been done. The papers reviewed included the role of pre-natal and post-natal maternal effects and the relationship between littersize and milk-yield. Daily yield and lactation from a number of studies were compared. Theories of genotype-environment interaction (GM) and adaptation, as well as their implications, were reviewed in the subsequent part of. chapter 1. Evidence of GEE in dairy cattle (Friesian, Holstein or Friesian-Holstein, crossbred with Friesian, and native) in both reproductive characters and milk production throughout the tropic regions were examined particularly closely. Mating systems and selection responses in genetic improvement programmes also were reviewed. Constraints and shortcomings for the achievement of genetic progress through natural mating, AI and progeny-testing in the tropics were examined in conjunction with attainment of high milk production in the temperate countries. The use of new technology (MOET) for manipulating reproductive efficiency was also introduced in the hope that it can be used to increase breeding efficiency in the tropics. The milk-yield and reproductive . characters, of two genotypes of mice (one genotype had been selected for high early reproductive and milking performance and the other was a random bred control) were measured in the normal and a hot environment to check if GEI were present. Both genotypes had been developed in the normal temperature. Evidence of interaction was found in the second parity and only in reproductive traits, e.g. fecundity, interval between mating and birth of second parity. These results are supported by many studies of GEI for both milk-yield and reproductive characters in dairy cattle in the tropics. Milk production does not show GEI, if the environment is defined merely as temperature. The previous selection of the improved genotype had resulted in positive correlated responses in: litter size and litter weight at birth in the first parity, production characters (growth characters and preweaning weight of the litters) in both parities, and on milk production but not on persistency. The selected line did maintain its superiority across environments. However females from the improved genotype performed worse in almost all characters in the hot environment compared to the normal environment. In an analogy with dairy cattle, the high production capacity of the selected line was not exhibited in the adverse environment. Problems of genetic improvement in the tropics were discussed. They included the use of appropriate selection criteria based on . more knowledge of both physiological and genetical relationships between milk-yield and other-characters, with the aim of increasing adaptability and productivity in the target environment. Other possibilities for genetic improvement of dairy cattle in the tropics and the use of synthetic breeds for overcoming the problems in the long term were also discussed.
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ItemEffects of urea and superphosphate fertilizers and soil moisture and temperature on forest soil respiration in a radiata pine plantation( 1987)The effect of urea and superphosphate fertilizers and the influence of temperature and soil moisture on forest soil respiration were investigated over a 9- month period. The investigation was conducted in an 18- year-old Pinus radiata D.Don. plantation in southeastern Australia. The fertilizers were applied to the forest floor at two rates (200 and 400 kg N ha-1, and 100 and 200 kg P ha-1) in a 3 x 3 factorial design. Soil respiration was measured as CO2 evolution using a soda lime absorption technique. Measurements were conducted at 14-day intervals from the 18th November, 1985 to the 6th August, 1986. The influence of temperature and soil moisture on soil respiration was more marked than fertilizer application, rates being highest when soil moisture was non-limiting. When soil moisture was under 12.5% (oven-dry weight basis), CO2 evolution was strongly moisture-dependent and 31% to 90% of the variability in CO2 evolution was explained by soil moisture. At soil moisture levels above 12.5%, soil maximum temperature was the best predictor of soil respiration, showing a significant positive correlation. This correlation explained 35% to 88% of the variation in CO2 evolution. The influence of moisture and temperature could be accurately predicted by a model which incorporated a moisture dependent Q10. The same model and model parameters successfully estimated soil respiration in the majority of fertilizer treatments. The addition of superphosphate fertilizer resulted in a significant stimulation of respiration rates, while the effect of urea addition was less marked. In treatments which received urea alone, CO2 evolution was depressed, although not significantly. However, in the presence of superphosphate, urea addition increased CO2 evolution with rates being highest in treatments which received the highest urea application rate. This result was attributed to an increased availability of phosphorus since microbial and faunal activity in this ecosystem appeared to be limited by P availability. An attempt was made to estimate the contribution of the forest floor, roots and soil to total forest soil respiration. Measurements were taken on two sampling occasions. On the first occasion, the forest floor plus mineral soil and roots contributed 85.0% and 15% to total soil respiration, respectively. On the second contribution was 68.7% and 31.3% respectively. In the field experiment, inorganic nitrogen concentrations in the soil and forest floor were measured on 60, 90, 240, 270 and 300 days after fertilization. Ammonium-N was the dominant N form. Inorganic-N concentrations were consistently highest in the treatments which received urea alone. Nitrate concentrations were highest in the treatments which received the highest urea application rate. A 30-day incubation experiment was conducted in the laboratory using the forest floor and soil collected from the experimental site one year after fertilization. Initial water-soluble phosphate (W-S P) concentrations were considerably higher in superphosphate treatments in the forest floor, while no appreciable concentrations were detected in any of the soil samples or in the forest floor of the control and treatments which received urea alone. During incubation, W-S P concentrations increased in all treatments with the highest rates being found in the treatments which had received phosphorus. Nitrate production and net N mineralization rates were highest in treatments which received urea alone, both in the soil and the forest floor samples. Superphosphate addition increased net N mineralization in soil samples. However, it only increased net N mineralization in the forest floor in the presence of added N. Urea elevated pH while superphosphate depressed it. No clear influence of pH changes on CO2 evolution were evident.
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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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ItemStepwise adoption of a complex agricultural technology( 1989)Previous studies of technology transfer have frequently treated the process as being controlled by the providers of the technology, with minimal involvement of the potential users. However, technology transfer is likely to be more effective and beneficial when based on a model with gives more thought to the needs and demands of the potential adopter. Complex technologies have been regarded previously as monolithic: adopted as a whole, but more slowly than simpler technologies. A complex technology is redefined as one which can be broken up into separate technological components, each of which may be adopted separately. It is proposed that adoption of a complex technology, as defined, occurs in a stepwise manner. Components are adopted in some order, which reflects the adopter's perception of their value to his operation. Not all components are taken up by all adopters. The theory was tested using, as a case study, the Tatura Permanent Beds system, a complex technology for irrigation cropping, in Northern Victoria and Southern New South Hales. The first three years of use of the technology by the 43 identifiable adopters was examined. It was found that adoption of the components of Tatura Permanent Beds occurred in a stepwise manner, but more components were adopted in the first year of use than in later years. It was also found that different farmers adopted different numbers of components, and adopted them . in different orders. Attempts were made to discover demographic, attitudinal and cognitive reasons for these differences. Possible refinements of the theory are suggested, and implications for extension discussed.
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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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