School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemSome effects of botanical composition of pasture on the liveweight and wool production of sheep( 1972)Until recently, the main evidence on which to base pasture mixture. recommendations in Victoria, has been district experience and the results from dry matter ( "mowing") experiments. The grazing experiments described in this thesis, were initiated by Messrs. R. Twentyman, R. Newman, R. Allen and K. Maher of the Department of Agriculture during the period, 1960-196. Their aim was to develop some objective appreciation of the relative value for animal production of some of the sown and unsown species in Western district pastures. In addition to pasture species evaluation, they sought information on the relationship between pasture growth and animal production. Such information is needed so that Agrostologists can better evaluate the many pasture management factors (such as fertilizers, seeding rates, seed. treatments, herbicides, insecticides and defoliation treatments) that affect pasture growth and for which advice is frequently sought.
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ItemThe effect of applied N and P under mowing and grazing on the yield and botanical and chemical composition of irrigated pasture and on the nutrient status of a red-brown earth at Kyabram( 1978)A split plot experiment was conducted over 4 years to study the effect of method of harvesting (grazing and mowing) and applied N and P (5 rates of nitrogen ranged from 0 to 112 kg N ha -1 cut-1 and 6 rates of superphosphate ranged from 0 to 188 kg P ha 1 year year-1) on the yield, botanical and chemical composition of irrigated phalaris (Phalaris tuberosa x Phalaris arundinacea)/white clover (Trifolium repens L. cv. Irrigation) pasture and nutrient status of a red-brown earth at Kyabram. A second experiment was conducted over 2 years to find out the effect of rates (0 to 112 kg N ha. 1) and frequency of N application (2, 4 or 8 times year ) o n dry matter production, botanical composition and crude protein content of paspalum (Paspalum dilatatum)/white clover pasture. Results: Mowed plots significantly out-yielded grazed plots in the first two years. However, grazed plots significantly out-yielded mowed plots in the following two years. Nitrogen application significantly (P <0.01) increased dry matter production of grass/clover mixtures. The size of response was governed by the growth rate of pasture species, clover percentage in the sward, climatic conditions and the status of other nutrients in the soil. Splitting N rates in smaller but more frequent applications had no effect on total herbage yield or seasonal distribution. Response to N (kg D.M. kg N-1 ) declined as N rates increased. Phosphorus application up to 94 kg P ha -1 year -1 significantly (P,(0.01) increased pasture production and relative response was greater in winter. Occasionally, the P and N requirements for maximum production were higher for grazing than for mowing. Both methods of defoliation and fertilizer applications affected pasture composition and IT, P and K content in the herbage. Nitrogen application decreased N in the herbage before increasing it and P application up to 141 kg P ha- 1 year -1 increased it. The return by the grazing animal increased total soil N by 106 kg ha 1 year 1 and soil P (Colwell) by 1:0 p.p.m. in four years compared with the start of the experiment. The relationship between plant P and soil P and P rates were significant (P < 0.01). The available soil P decreased with P withdrawal or the application of 23.5 kg P ha-1 year -1 under grazing and 47 kg P ha -1 year-1 under mowing. Phosphorus and nitrogen application significantly affected available soil P. 60-80% of the available P accuminulated in the 0-5 cm and the downward movement increased by increasing P rates. The continuous mowing and P application significantly reduced available soil K. Defoliation method affected C/t:N ratio. Phosphorus application increased soil N whereas N application decreased it. P application at the rate of 23.5 kg ha-1 year-1 increased total soil N by 0.068% which is equivalent to 952 kg N ha-1 in five years. It was estimated that 4 to 4.7 p.p.m of P was required to be removed or added to the soil to change the available soil P by 1 p.p.m. The application of 196 kg N ha-1 year -1 as NH4 NO3 did not change the soil pH and 784 kg N ha 1 year 1 reduced soil pH by an average of ').4 unit.
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ItemSelection of Rhizobium trifolii strains for inoculation of Persian clover (Trifolium resupinatum L.)( 1988)The studies reported in this thesis examined the Rhizobium trifolii (also reclassified Rhizobium leguminosarum biovar trifolii) strain requirements for inoculation of Persian clover (Trifolium resupinatum L.). The agronomic importance of T. resupinatum cv. Maral to agriculture in southern Australia had been recognised and new cultivars of T. resupinatum were being developed, but there had been no objective assessment of the inoculation requirements of this species. A diverse range of R. trifolii strains were examined for symbiotic competence (ability to nodulate) and effectiveness (nitrogen fixation) with T. resupinatum cv. Maral under bacteriologically controlled conditions ideal for plant growth. The results showed that strains varied in effectiveness from 18% to 145% compared to the standard commercial inoculant strain, TA1 (100). A strain selection programme was followed in which three selected strains (CC2483g, CC1317 and CC1305), all superior in effectiveness compared to TA1 (P<0.05) were assessed in glasshouse and field experiments in southwest Victoria. CC2483g was the best strain on T. resupinatum cv. Maral. This strain demonstrated good effectiveness, was highly competitive, persisted in the soil for 18 months under conditions of mild competition from naturalized strains and appeared particularly well adapted to sandy soils of low fertility. In contrast, TA1 was poorly effective, less competitive than other strains and the least persistent strain in the field. Strain differences in symbiotic effectiveness were demonstrated in the field where there was a low population (<5.0 x 102 R. trifolii per gram of soil) of naturalized R. trifolii. In soils with large populations (>1.0 x 104 R. trifolii per gram of soil), of naturalized R. trifolii , improvements in nitrogen fixation and herbage yield by inoculation with effective strains were dependant on the rate of inoculation and the relative symbiotic effectiveness of naturalized strains. T. resupinatum cv. Maral was capable of nodulation by a range of naturalized strains and it was concluded that commercial seed coat inoculation with highly effective strains and lime pelleting would, in general, not improve the nitrogen fixation of T. resupinatum cv. Maral in most areas of southwest Victoria. Host range experiments examined the effectiveness of the three selected strains compared to TA 1 and WU95 on important annual and perennial clovers and showed that CC2483g had a wider host.range that CC1317 and CC1305. The use of TA1 in the T. repens subgroup and WU95 in the T. subterraneum subgroup inoculants were verified in this study. Effectiveness tests with five lines of T. resupinatum var. majus and eight lines of T. resupinatum var. resupinatum suggested that T. resupinatum constituted a seperate symbiotic subgroup within the Trifolium species. The final step in the strain selection programme indicated that all selected strains satisfied the requirements for commercial inoculant production. It was concluded, that under the current policy of using single wide-spectrum strains for commercial inoculation, that a special single-strain inoculant should be produced for T. resupinatum containing CC2483g. Alternative inoculant recommendations to overcome the apparent deficiencies of both Australian commercial clover inoculants are discussed, of which the most practical solution could be mixed-strain culturing.
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