Browsing by Autor "Keith G. Pembleton"

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Climate change effects on pasture-based dairy systems in south-eastern Australia
(CSIRO Publishing, 2020) Keith G. Pembleton; Brendan Cullen; RP Rawnsley; Thiagarajah Ramilan
Increases in temperature, along with possible decreases in rainfall, will influence the production of forage on Australian dairy farms. A biophysical simulation study was undertaken to compare the performance of perennial pastures and annual forage cropping systems under a historical scenario and two possible future climate scenarios for three key dairy locations of south-eastern Australia. Pastures and forage-cropping systems were simulated with the biophysical models DairyMod and APSIM, respectively, for a location with a heavy reliance on irrigation (Dookie, Victoria), a location with a partial reliance on irrigation (Elliott, Tasmania), and a dryland location (Terang, Victoria). The historical climate scenario (baseline scenario) had no augmentation to climate data and an atmospheric CO2 concentration of 380 ppm, whereas the two future climate scenarios had either a 1°C increase in temperatures (with an atmospheric CO2 concentration of 435 ppm) and a concurrent 10% decrease in rainfall, or a 2°C increase in temperatures (with an atmospheric CO2 concentration of 535 ppm) and a concurrent 20% decrease in rainfall. At Dookie, mean annual dry matter yields of the forage-cropping options and the pasture systems increased under both future climate scenarios but more irrigation was required. At Terang, the yield of forage-cropping systems increased whereas the yield of the pasture systems decreased under the future climate scenarios. At Elliott, yields of irrigated pastures and cropping systems increased but there was minimal or a negative impact on yields of dryland pastures and cropping systems under the future climate scenarios. At all three locations, forage production increased in the colder months of the year with a decrease in production during the warmer months. This study indicates that double-cropping and irrigated-pasture systems at all three locations appear resilient to projected changes in climate; however, for irrigated systems this assumes a reliable supply of irrigation water. The systems implications of how a shift in the seasonality of forage supply within these options impacts on the farm system as a whole warrants further investigation.
Quantifying the interactions between defoliation interval, defoliation intensity and nitrogen fertiliser application on the nutritive value of rainfed and irrigated perennial ryegrass
(CSIRO Publishing, 2017) Keith G. Pembleton; RP Rawnsley; LR Turner; Ross Corkrey; D. J. Donaghy
A key goal of temperate pasture management is to optimise nutritive value and production. The influence of individual components such as irrigation, nitrogen (N) fertiliser, and grazing interval and intensity has been well researched, yet conjecture remains regarding practices that optimise pasture nutritive value, largely because interactions between inputs and grazing management have not been quantified. A 2-year, split-split-plot experiment was undertaken to investigate these interactions in a perennial ryegrass (Lolium perenne L.) dominant pasture at Elliott, Tasmania. Irrigation treatments (rainfed or irrigated) were main plots and defoliation intervals (leaf regrowth stage: 1-, 2- or 3-leaf) were subplots. Defoliation intensity (defoliation height: 30, 55 or 80 mm) and N fertiliser (0, 1.5 or 3.0 kg N/ha.day) were crossed within sub-subplots. Herbage samples were collected from each plot four times during the experiment and analysed for concentrations (% dry matter, DM) of neutral detergent fibre (NDF), acid detergent fibre (ADF) and crude protein (CP). Metabolisable energy (ME) concentration (MJ/kg DM) was estimated from these values. ME concentration decreased as defoliation height and interval increased for all time points except during winter. Crude protein concentration increased with increasing N fertiliser applications in the plots defoliated at the 1-leaf stage, but only as N applications increased from 1.5 to 3.0 kg N/ha.day for the plots defoliated at the 2- and 3-leaf stages. As N application rates increased from 0 to 1.5 kg N/ha.day, plots defoliated at the 3-leaf stage had greater increases in NDF concentration than plots defoliated at the 1-leaf stage, except during spring. As defoliation height and interval increased, ADF concentration increased in both spring and summer. Although defoliating at frequent intervals (1-leaf stage) and lower heights (30 mm) produced pasture of marginally higher nutritional value, these benefits are mitigated by the previously established, negative consequences of lower pasture yield and poor pasture persistence. Consequently, grazing management that maximises pasture productivity and persistence (i.e. defoliation between the 2- and 3-leaf regrowth stages to a height of 55 mm) should be applied to perennial ryegrass pastures irrespective of input management.