School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemNutritional physiology of eucalyptus grandis and pinus radiata irrigated with municipal effluent( 1998)The aim of this study is to compare the processes of accumulation and use of N, P, K, Mg and Ca between two and four years of age in plantations of Eucalyptus grandis and Pinus radiata irrigated at several rates with municipal effluent, and with bore water. A series of five harvests over two years was used to estimate above-ground biomass and nutrient content. Growth rate was greater in E. grandis than in P. radiata. Total biomass at 34 months ranged from 34 to 45 t ha-1 in E. grandis and from 21 to 26 t ha-1 in P. radiata, with a trend towards higher rates of growth with increased irrigation rate. Foliage mass and leaf area index (LM) were initially greater in E. grandis than P. radiata. However, the rate of increment in foliage mass and LAI in E. grandis decreased after canopy closure (at about 20 months). At 34 months foliage mass averaged 5.9 t ha-1 in E. grandis and 7.4 t ha-1 in P. radiata. Nutrient accumulation was primarily a function of growth rate, in particular the rate of canopy development. Rate of nutrient accumulation in E. grandis was greatest prior to canopy closure, decreasing thereafter, and in P. radiata it was greatest in the last year. As a result, mean annual increment of nutrient accumulation was maximum in E. grandis at 28 months, and in P. radiata at the end of the study. Implications for management of effluent-irrigated plantations are discussed. The mass of each nutrient accumulated varied greatly and decreased in the order Ca
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ItemAgroforestry strategies for catchments in the humid tropics( 1995)Catchments in the humid tropics play an important role in the ecosystems and the economies of countries they are in. They are slowly deteriorating because of inappropriate land-use systems being practised by people in them. Agroforestry is seen as a potential land-use system which could help rehabilitate degraded catchments and prevent others from deteriorating. However, selection of appropriate agroforestry strategies to be used for a particular catchment is a problem. The aim of this study was to develop a method that would be able to determine the best combination of agroforestry strategies for a catchment in the humid tropics, that is the one that would yield the maximum net social benefit subject to the constraints of maintaining agricultural yield and net income, keeping erosion within acceptable limits, enhancing soil nutrition, and providing a source of firewood for the catchment users. To achieve this aim, Mt. Masaraga catchment in the Philippines was selected as a case study from which some implications could be drawn that would relate to other similar catchments. Potential agroforestry strategies were presented to the upland farmers in the catchment for acceptability. The selected agroforestry strategies were then evaluated for their capability to prevent soil erosion, to supply firewood, and to provide organic fertiliser for three slope classes. A fuel study was also conducted to determine the fuel consumption of the catchment users. Financial and economic analyses of each selected agroforestry strategy for the three slope classes were then conducted. Linear programming models for the catchment were constructed using average value of the rainfall erosivity index value for the computation of soil erosion. A chance-constrained model which takes into account the probability of rainfall erosivity index value exceeding the average was also constructed. Four agroforestry strategies were found to be acceptable to the upland farmers: contour hedgerow; hedgerow with contour canal; live fences; and combination of contour hedgerow and hedgerow with contour canal. Two models were formulated, a model which assumed that the whole catchment would be converted to agroforestry immediately, and one that incorporated the time of adoption of the agroforestry technologies as a further constraint. It was established that in the Mt. Masaraga catchment, it would be profitable to farmers to adopt agroforestry strategies, but the benefit to society was far greater than to the farmers. The cumulative NPV of the incremental net benefits for the optimum combination of agroforestry strategies for the Mt. Masaraga was P72.4 million greater than if the catchment remained under conventional farming. The chance-constrained model indicated that savings would be even higher if the rainfall erosivity index value in individual years exceeded the average rainfall erosivity index value used in the deterministic model. It was established that the land with steepest slopes should be converted to agroforestry first, because of its ability to reduce the high level of erosion expected on these slopes with conventional farming. More rapid adoption of the strategies resulted in greater savings, indicating that it would be worth spending money on education programs to speed up the rate of adoption. Although these results were specific to the Mt. Masaraga catchment, there is nothing to prevent construction of similar models for similar catchments in the humid tropics, and similar results could be expected.
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ItemAn analysis of radiata pine-pasture agroforestry systems( 1993)Agroforestry, the integration of forestry and agricultural production, requires an understanding of the interactions between trees, agriculture and the environment. This thesis presents an analysis of the effects of a variety of Radiata Pine-pasture agroforestry treatments on soil water, tree growth and form and pasture production together with a series of economic analyses using the FARMTREE model to simulate the various agroforestry regimes established at Carngham in western Victoria. The Carngham study site consists of a replicated randomized block design of five Radiata Pinepasture treatments. The treatments were: open pasture (no trees), 100 trees/ha (8 m x 12 m), 277 trees/ha-wide-spaced (4 m x 9 m), 277 trees/ha-5 row (5 rows, 4 x 3 m, with 10 row gap) and 1650 trees/ha (no pasture). Results, 11 years after tree establishment, show that soil water content under the various treatments has a cyclical pattern of recharge and discharge with an annual amplitude of approximately 100 mm. Within the 100 trees/ha and 277 trees/ha-5 row and 277 trees/ha-wide-spaced treatments, the soil water content was generally significantly less than under open pasture in the upper 170 cm of the upper profile. Within the 1650 trees/ha treatment, the trees utilize water to a depth of at least 270 cm. Tree form was influenced by tree density. Tree diameter decreased but height increased with tree density with the trees of largest volume produced in the 277 trees/ha-wide-spaced treatment. Variable-lift pruning was routinely applied on an annual basis from tree age 6 years, to minimize the internal knotty-core and to maximise the volume of knot-free timber produced. Pruning was virtually completed (to 6 m) after five or six annual treatments, and significant relationships between DOS (diameter over stubs) and various tree parameters were identified as predictors for determining the volume of the knotty-core. Agricultural production was assessed as net pasture production using rising-plate methodology during the major growth seasons. Trees in single rows, as in the 100 trees/ha and 277 trees/ha-wide-spaced treatments, had only a limited effect on net pasture production compared to the zone within 4.5 m from the trees in the 277 trees/ha-5 row treatment where pasture production was significantly less than in open pasture, or in the zone from 4.5 to 18 m from the tree line where there was a possible shelter benefit. Although pasture production was similar between treatments, animal production decreased with increasing tree density. Economic analyses using the FARMTREE model and progressive data from the Carngham trial showed that simulations of the agroforestry regimes at Carngham were more profitable than grazing alone using real discount rates up to 7%. The 277 trees/ha-wide-spaced regime returned the greatest net present values over the range of discount rates used. The optimum rotation length, assuming a 5% real discount rate, was 26 years. Based on the 277 trees/ha-5 row treatment, shelter benefits for agricultural production could be obtained with a distance between belts of 150 to 200 m and by leaving at least 10% of the trees unpruned. The Carngham trial represents one case study of Radiata Pine-pasture agroforestry for south west Victoria. On this basis, the data presented provides information on patterns and trends likely to be encountered in applying agroforestry to other locations in Victoria. The adoption of agroforestry requires ongoing research trials and demonstrations and the Carngham trial has been well planned and maintained and should be seen as a valuable asset for the advancement of agroforestry in Victoria.