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G. Landcare - Limiting Land Degradation

Determining rangeland response to drought and sheep grazing in the northern Mitchell grasslands

Phelps, D.G. Mr; Ph: (07) 4658 4400; Fax: (07) 4658 4433; phelpsd@dpi.qld.gov.au

Research organisation: Queensland Department of Primary Industries, Sheep and Wool Institute, PO Box 519, Longreach Qld 4730

Sponsors: AWRAPO: Australian Wool Research and Promotion Organisation

Objectives:

1. To determine the processes involved in the degradation and recovery of Mitchell grassland;

2. To quantify the role of climatic variability and stocking rates within this process;

3. To assist in developing guidelines for sustainable management practices within a variable climate.

Methodology: Climatic information collected at Toorak will be interpreted through the Australian Rainman computer package and GRASP pasture growth model. This will allow pasture performance and animal productivity to be related to climatic variability. Paddocks will be grazed with Merino wethers at six utilisation levels: 0, 10, 20, 30, 50 and 80 per cent, set in May of each year. Liveweight, greasy fleece weight, clean fleece weight, yield, fibre diameter, tensile strength and staple length will be recorded. Pasture yield, dry weight composition and frequency will be determined in May and November of each year. Permanent quadrants in the 10, 30, 50 and 80 per cent treatments will be read annually to provide basal diameter, basal area, tussock survival and recruitment information. Germinable seed banks will be collected annually. Pasture recovery rates will be explored in the 80% paddock and enclosures will be erected in the 30 and 80 per cent paddocks to determine primary pasture production. Economic parameters from animal measurements and current market values will be combined with pasture and/or soil parameters to provide a measure of the long-term economic effects of grazing within a variable climate, and provide a definition of optimal grazing strategies.

Progress:

As a result of this research it is now possible to:

  • recommend to graziers that they stock northern Mitchell grass pastures at a rate to achieve 30% use of end of summer standing dry matter in the medium (10 to 20 years) term;
  • suggest that Mitchell grass pastures should be grazed no lower than 10 cm height;
  • gauge the financial and resource impact of longer term grazing pressure in the northern Mitchell grasslands;
  • predict annual wool production and sheep liveweight gains from seasonal rainfall in the northen region;
  • predict pasture growth from rainfall for Mitchell grass pastures grazed moderately and heavily in the medium term.

This means that graziers will be able to:

  • maximise long term profitability whilst maintaining the condition of their pastures;
  • make more informed strategic stocking rate decisions over 10 to 20 years;
  • budget their pasture resource through tactical grazing strategies

Practical tools developed in conjunction with this work include:

  • the "Managing Mitchell Grass - a graziers guide" booklet distributed free to 3200 graziers with Mitchell grass pastures in Queensland and available for purchase to other interested parties;
  • a series of new DPINotes detailing the impact of grazing Mitchell grass pastures, available to graziers over the counter at DPI Client Service Centres, for purchase on CD-Rom, or through the DPI world wide web site (http://www.dpi.qld.gov.au/);
  • photo-standards widely used in conjunction with property planning and pasture monitoring to enable objective assessment of pasture yield;
  • the GrazeOn Mitchell grass pasture budgeting software.

Scientific tools developed in conjunction with this work include:

  • greater accuracy in the ability to model Mitchell grass growth using the dynamic GRASP forage production model;
  • the ability to predict the impact of overgrazing on the pasture resource using the dynamic GRASP pasture production model;
  • modelling software to enable wool production and gross margins to be predicted on a regional basis from rainfall and market information when used in conjunction with the dynamic GRASP forage production model;

It is still not possible to:

  • predict the impact of grazing accurately beyond 10 to 20 years;
  • predict the impact of grazing on a known age group of Mitchell grass plants;
  • predict the impact of grazing on pasture composition within a variable climate;
  • predict the impact of grazing strategy on pasture recovery from drought;
  • predict the impact of grazing in some geographic areas within the Mitchell grasslands.

This is because:

  • it is not possible in short term trials to clearly separate the effects of climate and grazing on pasture dynamics in highly variable semi arid and sub-tropical native pasture systems;
  • the Toorak research work was not designed to test grazing strategies or to compare different geographic areas.

Period: starting date 1994-07; completion date 1997-06

Status: AWRAPO component finished, current work continuing through internal funding

Keywords: agronomy; land degradation; Merino; Mitchell grass; rangelands; modelling

Publications:

Beale, I.F., Cobon, D.H. and Milson, J.A. (1990). Effects of grazing utilisation of mitchell grass rangeland in northwest Queensland. Proceedings of Native pasture workshop, Dubbo. Oct 1990.

Beale, I.F, Phelps, D.G., Cobon, D.H. and Connolly, P. (1991). Effects of grazing utilization of mitchell grass rangeland in northwest Queensland. Final report to WRDC, Sept. 1991.

McArthur, S.R., Chamberlain, H.J. and Phelps, D.G. (1995). State and Transition models for rangelands. 12. A general state and transition model for the mitchell grass, bluegrass-browntop and Queensland bluegrass pasture zones of northern Australia. Tropical Grasslands 28, 274-278.

Novelly, P.E. and O'Rourke, P.K. (1988). Analysis of plant and animal relationships in grazing trials. Proceedings of the 5th Biennial Conference of the Australian Rangelands Society, Longreach, June 1988.

Orr, D.M. (1986). Factors affecting the vegetation dynamics of Astrebla grasslands. Ph.D. Thesis, University of Queensland.

Orr, D.M. (1988). Interaction of rainfall and grazing on the demography of Astrebla spp. in north western Queensland. Proceedings of the 3rd International Rangelands Congress, New Delhi, India, November 1988.

Orr, D.M. (1992). Astrebla grassalnds - a resilient ecosystem. Proceedings of the 7th Biennial Conference of the Australian Rangeland Society, Cobar. October 1992.

Orr, D.M. and Phelps, D.G. (1994). Basal area changes in Astrebla grassland - in harmony with trends in rainfall and grazing. Proceedings of the 8th Biennial Conference of the Australian Rangelands Society, Katherine, June 1994.

Orr, D.M. and Phelps, D.G. (1995). Rainfall and grazing influence cohort development in Astrebla grasslands. Proceedings of the Vth International Rangeland Congress, pp. 418-419.

Phelps, D.G. (1997). Mitchell Grass (Astrebla spp.). Australia's own grass. DPI Note SW97012002.

Phelps, D.G. (1997). Wool Production from Mitchell Grass: the role of long-term grazing pressure. DPI Note SW97013003.

Phelps, D.G. and Bates, K.N. (1994). Estimating pasture yield in mitchell grasslands using photostandards. Proceedings of the 8th Biennial Conference of the Australian Rangelands Society, Katherine, June 1994.

Phelps, D.G. and Milson, J.A. (1997). Identifying Mitchell Grasses. DPI Note SW97011004.

Phelps, D.G. and Orr, D.M. (1998). Determining rangeland response to drought and grazing in the Northern Mitchell Grasslands. (DAQ120). Final funding milestone report prepared for the International Wool Secretariat.

Phelps, D.G., Orr, D.M., Newman, P.A. and Bird, A.R. (1994). Grazing northern mitchell grasslands to foster sustainable wool production. (DAQ31). Final report to AWRAPO.

Roberts, G.M.O'B. (1989). The implications of the additional wool measurements of staple length, staple strength and position of break for wool growers in north-west Queensland. M. Agric. Thesis, University of New South Wales

 

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