School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemDevelopment of a technique to overcome the problems associated with high dieldrin concentration in soil( 1995)Degradation of dieldrin in soils was studied in laboratory experiments. Application of powdered zinc in dilute acetic acid, nickel chloride in sodium borohydride and potassium tertiary butoxide in dimethyl sulphoxide to pots containing solonized brown soil, podzol, red brown earth, grey clay, alluvial and krasnozem soils had little effect on the rate of degradation. Application of potassium tertiary butoxide in dimethyl sulphoxide solution to soil samples containing dieldrin achieved a rapid decrease in pesticide concentration in some cases. However, the undesirable effects of these chemicals on soil fauna and flora and on soil physical properties indicate that their use in the field could not be recommended. Adsorption of dieldrin (as illustrated by the Freundlich constant) was greater in red brown earth and grey clay soils than in the solonized brown soil. The rate of dieldrin desorption from these soils was found to be in the order solonized brown soil > red brown earth > grey clay. Dieldrin uptake by plants was determined, with carrots being found to absorb the greatest quantities of dieldrin. All plant species took up considerably more dieldrin when grown on sand than on clay. Lupin translocated very little dieldrin to the plant tops. The amounts of insecticide translocated to the plant tops were not proportional to the amounts of insecticide present in soil. Brown coal was found to be a very good dieldrin adsorbent. Addition of brown coal in the proportion 4:1 soil:brown coal reduced the uptake of dieldrin by carrots from contaminated soil to acceptable levels. Both mice and sheep did not show any obvious symptoms of ill-health after being fed diets containing 10 ?g g-1 dieldrin plus 10% brown coal for 16 weeks. Animals fed diets containing 10% brown coal and 10 ?g g-1 dieldrin had lower concentrations of the insecticide in the internal organs. The concentration of dieldrin in the kidney fat of sheep fed this diet was above the maximum limit suggested to apply to animals raised for human consumption.
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ItemVariation of some vessel characteristics of plantation Eucalyptus regnans F. Muell( 1993)Some vessel characteristics of six 15-year old plantation grown Eucalyptus regnans F. v. Muell. trees from a progeny trial in Narbethong, Victoria were studied. The within and between tree variation of vessel frequency and percent tyloses with distance from the pith, between six heights and between the six trees was examined. Vessels and vessels containing tyloses present on the cross-sectional surface of 7 mm by 7 mm wood blocks taken from pith to bark were counted using a stereo zoom microscope. Analysis of variance was used to examine the variation of vessel frequency and percent tyloses with: distance from the pith; between the north and south axes; between the base, breast height, 20%, 40%, 60% and 80% of total tree heights; and between the six trees. Data in graphical form coupled with microscopic observations were used to examine the within and between growth ring variation. The overall mean vessel frequency for the six 15-year old trees was 7.885 vessels/mm2. Variation of mean vessel frequency with distance from the pith, between heights and between trees was statistically significant. However, after area weighting the vessel frequency values, there was not a significant difference between trees. Mean vessel frequency generally increased with height, with means of 7.100 vessels/mm2 at the base and 10.722 vessels/mm2 at the 80% height, and decreased from the pith to the bark. The variation between axes and with all interactions between the main factors were not significant. Vessel frequency was observed to vary within and between growth rings. Vessel frequency was lowest in the region at the latewood to earlywood boundary and highest in the central portion of the growth ring. Vessels containing tyloses were found at all six heights of all six trees and the mean percent tyloses for the six trees ranged between about 7 to 18%. The variation of mean percent tyloses with distance from the pith, between heights, between trees and the interaction between height and tree was statistically significant. The percent tyloses was lower in the region near the pith and in the sapwood region near the bark and highest in the central region between the pith and the bark. The percent tyloses varied between about 10 and 40% in a cyclic or wave-type manner over distances of about 10 to 15 mm from pith to bark but did not appear to be related to vessel frequency. The mean percent tyloses showed a general decrease with height, with the base height having a mean of 20.387% and the 80% height a mean of 6.448%. The largest tree mean was 17.568% and the lowest was 7.219%. The relative magnitude of the mean percent tyloses at each height and the ranking between heights varied between trees. For all six trees the frequency of vessels was greater toward the top of the trees but fewer vessels contained tyloses at these upper heights. It may be that timber removed from the upper portions of the stem might be more permeable to liquids such as in the preservation and pulping processes and may release moisture upon drying more easily.