School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemA systems analysis approach to drought reserves in the Hamilton region( 1971)Following a discussion of drought strategies available to the grazier, one particular strategy, the holding of drought fodder reserves, is examined in detail. The study estimates the least-cost fodder reserves for a range of stocking rate-pasture production regimes in the Hamilton region. The amount of hay feeding required on any stocking-pasture regime is determined from a simulation model of the grazing complex. In this model, three levels of pasture production are stocked at rates ranging from one to ten wethers per acre. The pasture production assumed ranges from "excellent" (i.e. equivalent to the Hamilton Research Station pastures which produce about 10,000 lb. dry matter per annum) to "poor" (35% less). The climatic inputs into the grazing model are the date of Autumn break, for which a formula is derived, and the June to October rainfall. The pasture sub-model is specified and used to derive the pasture which is "grown" in the grazing model. The sheep aspects of the model are reviewed in detail to derive the relationships which are used in the next set of four sub-models in which animal intake is simulated and liveweight changes determined. This set of four sub-models provides for the four situations of animal intake which may be met. These are: The intake of green pasture alone (i.e. all pasture grown after the Autumn Break); the intake of hay alone; the intake of hay and green pasture together; the intake of hay and dry pasture (pasture remaining when the Autumn Break occurs and dry pasture alone which are handled in the same sub-model) The grazing model was validated for the years 1965-67 using data from the Pastoral Research Station, Hamilton, and showed good agreement for all three years simulated, one of which featured a severe drought. Drought feeding requirements (hay) are determined for each of the years 1879 to 1967 and for the ten stocking rate-pasture production regimes, using specific hay feeding rules. These rules, which aim at sheep survival, do not attempt to specify optimum feeding rates per sheep, and any change in them could significantly alter the drought requirements for any of the regimes studied. Furthermore, the estimates are Lased on the assumption that all sheep are fed through the drought. A pre-drought strategy which permitted the sale of certain classes of sheep at some stage during drought would entail lower feed requirements and might have a lower expected cost, especially at high acquisition costs for feed and low replacement costs for sheep. An inventory analysis is then undertaken, based on a 12 month planning period, which utilises the hay feeding probabilities generated in the grazing model, and provides estimates of the least-cost hay reserve. In contrast to previous studies, the price of hay is related to drought length in calculating the penalty cost of inadequate reserves. The effects of varying several parameters of the inventory model are then examined. The parameters varied are hay costs ($4, $10 and $16 per ton), interest rates (7%, 20% and 50%), and salvage values, and these vary in association with the parameters varied in the grazing model (stocking rate, pasture production and the area closed for hay). At the intermediate values for pasture production and hay cost and a 7 per cent per annum interest rate, the minimum-cost reserve rises sharply, from 2 bales per acre at 2 wethers per acre, to 4.5 bales per acre at 3 wethers per acre, 8 bales per acre at 4 wethers per acre, and 15 bales per acre at 5 wethers per acre. The minimum-cost reserve was found to be relatively insensitive to changes in acquisition costs, except at low stocking rates, where a change in reserve of one or two half-bales per sheep was common as acquisition cost varied over the three levels. The effect of interest rates was also examined for the average pasture regime. On the lowest level of hay acquisition cost, ($4 per ton) increasing the rate of interest from 7 to 50 per cent caused reductions of only one half-bale per sheep. However, at high acqusition cost ($16 per ton) raising the interest rate to 20 per cent resulted in a considerable reduction in the minimum-cost reserve, especially on the lower stocking rates, and raising the interest rate to 50 per cent made holding fodder reserves uneconomic for any stocking rate. One measure of the risk in holding various levels of fodder reserve is the standard deviation of the total expected cost. As expected, it was found that this declines as the reserve is expanded to the maximum ever required. However, only a small reduction in standard deviation results from expanding the reserve beyond the minimum-cost level. Finally, estimates were made of the income-maximising stocking rate for each level of pasture production and hay cost, with the wool price at 30, 40 and 50 cents per lb.. At the intermediate values for pasture production (8,000 lb. D.M.) and hay cost ($10 per ton), and with wool at 30 cents per lb. net, the income-maximising stocking rate was 3 wethers per acre. Each increase of 10 cents per lb. in the wool price was generally associated with an increase of one or two wethers per acre in the income-maximising stocking rate. An increase of 2,000 lb. D.M. (from "average" to "excellent") in average annual pasture production was generally associated with an increase of one wether per acre in the income-maximising stocking rate. A reduction of 1,500 lb. from "average" to "poor" pasture. production reduced the income-maximising stocking rate by about one wether per acre. Increasing the hay cost from $4 to $10 per ton reduced the profit-maximising stocking rate by one wether per acre for all combinations of pasture production and wool price examined. However, a further increase in acquisition cost from $10 to $16 per ton only caused a further reduction in the income-maximising stocking rate at the poor level of pasture production: with average pasture production there was little change and with excellent production there was no change in the income-maximising stocking rate.
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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.