School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemThe occurrence of brittleheart in Eucalyptus regnans and its effect on various wood properties( 1990)This project is mainly concerned with a description of anatomical and ultrastructural characteristics of cell wall deformations in brittleheart of E. regnans, development of methodology for quantification of percentage of broken fibre pieces (PBFP) in E. regnans, and physical and anatomical properties of E. regnans in relation to the occurrence of brittleheart. Two 1939 regrowth E. regnans butt logs and one mature growth E. regnans butt log removed from a tree approximately 120 years old were used in the study. The anatomical and ultrastructural characteristics of cell wall deformations were examined with bright field, polarized light, and scanning electron microscopy. The microscopic compression lines were found to consist of slip planes, minute compression failures, corrugations, and buckles. The width of microscopic compression lines along the longitudinal fibre axis ranged from one single fold in the cell wall up to 7 times the average fibre width. The length of the microscopic compression lines ranged from ones which only crossed a few fibres to ones which crossed up to 200 fibres. The severity of microscopic compression lines appeared to be dependent on the type of cell wall deformations and degree of compaction in the deformed zone. In the methodology studies it was found that for a pulp sample prepared from a 2 mm by 2 mm by 15 mm wood chip approximately 400 cellular elements in 8 out of 16 areas on a slide needed to be counted in order to obtain PBFP with less than 10% error. For macerated thin sections, all the cellular elements on 2 slides each carrying about 600 fibres and fibre pieces needed to be counted. A highly significant correlation was found between the length of microscopic compression lines per unit area and the microscopically determined PBFP. A highly significant correlation was found between the theoretical PBFP and the microscopically determined PBFP. These findings confirm that maceration of wood containing cell wall deformations results in broken fibres and verifies the validity of the maceration technique for quantifying the amount of microscopic compression lines. PBFP was found to increase with macerating time. A maceration time around 10 hours appears sufficient to cause fibres having cell wall deformations to break but longer times cause fibres without cell wall deformations to also break due to overmaceration. A significant relationship was found between PBFP determined after 5 hours and after 10 hours of maceration at the same temperature. It was found that parameters extracted or derived from cell length distributions produced by the Kajaani FS-200 may be used to determine the amount of fibre fragments in pulp samples. These parameters were the high peak, the length weighted average, and the mass weighted average of the cell length distributions for pulps which had PBFP greater than 10. Based on the maceration technique, brittleheart was detected in both the mature and the 1939 regrowth logs. Brittleheart was more severe and occupied a larger area in the mature growth than in the regrowth wood. The PBFP was found to be mostly below 5 in the regrowth wood although relatively high PBFP values of 21 and 30 were observed. PBFP values as high as 85 was found in the mature growth wood. In general, PBFP was found to be higher nearer the pith, decreasing toward the bark, and dropping to zero before reaching the two-thirds theoretical point where the stress is assumed to be 0. A large circumferential variation in PBFP was observed in four adjacent growth rings of the mature log. A large variation in PBFP was also found within a volume of 1000 mm^3 for both the mature and the 1939 regrowth wood. The earlywood PBFP was found to be significantly higher than the latewood PBFP for the mature and regrowth logs. A total of 72 green and 132 12% MC Izod specimens were prepared from the two 1939 regrowth logs and tested for impact strength. The mean Izod value was found to be 9.9 ft.lb for the 132 12% MC Izod specimens and 9.2 ft.lb for the 72 green Izod specimens. For side-matched Izod specimens, the mean Izod value was found to be 9.2 ft.lb at green and 9.7 ft.lb at 12% MC and the mean for the 12% MC specimens did not reflect the expected increase in strength with moisture loss. Excessively low Izod values (eg. 1.8 ft.Ib) were found in the 12% MC Izod specimens located near the pith. For 76 12% MC Izod specimens, their PBFP, fibre length, and specific gravity were also measured. Significant relationships (p=0.01) were found between Izod values and specific gravity, PBFP, and fibre length for these 76 12% MC Izod specimens. Specific gravity and fibre length positively contribute to the impact strength whereas PBFP negatively affects the impact strength. Brash-break specimens showed a low mean Izod value, a low mean specific gravity, the presence of brittleheart, and a short mean fibre length.
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ItemEffect of GnRH and production levels on reproduction in dairy cattle( 1990)At 11-13 days after insemination, 1028 dairy cows on 19 farms were treated with an intramuscular injection of 10 ?g of the GnRH analogue Buserelin. Reproductive performance was compared to 1022 control cows receiving a placebo. Cows treated with the GnRH analogue had a reduced number of short interoestrus intervals compared to control cows but there were no significant differences in pregnancy rates to the insemination preceding or following treatment. Calving-to -conception intervals and percent pregnant by the end of mating were also unaffected. There were no differences between treatments in herds of high, average or low pregnancy rates, within different age groups or within different calving to first service intervals. The evidence here suggests that the use of 10 ?g of the GnRH analogue, Buserelin, 11-13 days post-insemination cannot be recommended as a method of improving reproductive performance in dairy herds.
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ItemQuality of goat milk produced in Victoria( 1990)Preparation of quality standards for the developing goat milk industry in Victoria required study of unknown current quality levels of chemical, physical and microbiological parameters. Milk delivered weekly or twice weekly to goat cheese manufacturers from 11 farms was sampled over 8 months. Samples were examined for composition, freezing point, extraneous matter, standard plate count, coliforms and inhibitory substances, using Australian Standards Methods. Mean values and (range) for fat, true protein, and lactose were 4.45 percent(2.96 to 5.88); 3.20 percent (2.70 to 4.61); and 4.60 percent' (3.92 to 5.17). Respectively average (range) total solids and ash content were 12.9 percent (11.9 to 15.8); and 1.02 percent (0.69 to 1.53). Freezing points (C) were lower than for cows' milk, viz: - 0.541C (-0.541 to -0.519 C ). Seventy percent of samples had low levels of extraneous matter. Standard Plate Count ranged from 500 cfu/ml to >106/m1 with only 26 percent of samples complying with the standard for cows' milk (5 x 104 cfu/ml). Seventy percent of samples contained coliforms >100 MPN/ml and 30% contained inhibitory substances at levels >0.002 microgram/mI. Setting microbiological standards is premature due to poor over-all quality and an advisory system coupled with quality monitoring is preferred. Standards for other parameters could be set.
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ItemEffects of mulching logging residue on soil water relations, soil temperature and early growth of Pinus radiata on sandy soils in south-west Victoria( 1990)The timber industry in Australia is becoming increasingly dependent on plantations of exotic softwoods, with Pinus radiata D. Don (Monterey pine) the most important species planted in Victoria and South Australia. In general, these plantations have been highly productive in the first rotation. However, in the second rotation there is evidence of a decline in productivity on relatively infertile sandy soils, particularly where the litter and logging residue remaining after clearfelling is burnt. Research has indicated that this decline can be arrested by careful control of cultural inputs, such as chemical weed control, fertiliser and planting of legumes, or by mulching the litter and logging residue. This thesis reports on a study that examined the interacting effects of mulch, weed control and fertiliser on soil and plant water relations, weed biomass, soil temperature, root development, tree growth, and biomass and nutrient accumulation during the first five years following re-establishment of a P. radiata plantation. Mulch, weed control and fertiliser were applied (present, absent) in a 2 x 2 x 2 split-plot factorial design, resulting in eight treatment combinations. Mulch was applied prior to planting; weed control prior to planting and at regular intervals thereafter to age two years; fertiliser at 1.5, 10 and 14 months after planting, a total of 58.1 kg ha-1 of nitrogen and 19.1 kg ha-1 of phosphorus (as part of a complete mineral mix, including zinc). During the first two years after planting, soil and plant moisture levels, soil temperature and tree growth were monitored at four-weekly intervals, and weed biomass three-monthly. Annual growth was also monitored to age five years. Root development, tree biomass and nutrient accumulation were examined in detail at age two years. In the absence of mulch and weed control, soil moisture was significantly reduced during the first two summers after planting due to evapotranspiration losses, with a consequent reduction in tree growth. Both mulch alone and weed control alone were similarly effective in conserving soil moisture in the surface 10 cm of soil, through a reduction in evaporation and transpiration losses respectively. There was evidence that transpiration losses from weeds in mulch had a greater impact than evaporation losses from bare soils at depths from 10 to 40 cm. Maximum soil moisture levels during the summer months occurred where the mulch and weed control treatments were applied together. Mulch reduced weed biomass on average by half for the first two years after planting compared to that on bare soils with no weed control, though weed biomass by mid- to late- summer was similar for both treatments. Weeds which establish in the mulch treatment benefit from improved soil moisture availability as do the P. radiata trees. Mulch significantly reduced soil temperatures compared to those under bare soils during the spring and summer months, particularly in the surface 10 cm of soil. This is likely to have led to less favourable conditions for root growth and mineralisation of soil nitrogen under mulch during spring, when soil moisture availability is not limited by any of the treatments. During summer however, conditions were more favourable under mulch due to higher soil moisture availability. Where mulch and weed control were both applied, root length at age two years was almost twice compared to that for weed control alone. This difference occurred in the surface 10 cm of soil, and is attributed to the combined effect of higher soil moisture availability and stable temperatures within the optimum range for root growth under mulch during the summer months. Roots were also found in the mulch, which indicates that P. radiata roots can either extract nutrients, water or both from the mulch itself. All growth parameters show that in the absence of fertiliser, the responses to mulch alone and weed control alone were similar up to age five years, and that growth was significantly increased when both treatments were applied. These responses were however confounded, as severe zinc deficiency was induced on the weed control alone treatment. In the presence of fertiliser, the responses to mulch alone, weed control alone and both treatments combined were similar by age four years. The largest response to fertiliser was for the weed control alone treatment, probably due to the correction of zinc deficiency. A fertiliser response was initially found where both the mulch and weed control treatments were applied, but by age four years this response was no longer detectable. Growth at age five years was a maximum on, and not significantly different between, the mulch and weed control, mulch and fertiliser, weed control and fertiliser, and mulch, weed control and fertiliser treatment combinations. The nitrogen concentration in needles less than one year-old was at or below the critical level of 14 g kg-1 for all treatment combinations at age two years, except for the weed control alone treatment which was affected by severe zinc deficiency. Despite this, foliage on the treatments associated with good growth did not show obvious nitrogen deficiency symptoms. It is likely that there was net immobilisation of nitrogen under the mulch treatment during the first two years, but subsequent to this it is considered that the mulch would have been a source of nitrogen to the P. radiata trees. Foliar concentrations of both phosphorus and potassium were adequate for all treatment combinations. Foliar concentrations of zinc were at or below the critical level of 10-11 mg kg-1 for those treatments showing maximum growth, which indicates that demands were just being met. They were well below the critical level for the weed control alone treatment. There is clear evidence that the mulched litter and logging residue is a source of zinc to the replanted P. radiata. Relationships between concentration of nutrients in biomass components and tree diameter were generally weak and not significant, and thus nutrient accumulation closely mirrored the pattern of biomass production. The results show that mulching of the litter and logging residue in situ has the beneficial effects of conserving soil moisture, which in combination with more favourable soil temperature conditions during summer, resulted in satisfactory early growth. The results also indicate that mulch is a source of nutrients to the re-established crop. Although care must be taken in extrapolating these results, forest managers should consider mulching as an alternative site preparation technique to burning, particularly on infertile sandy soils.