Pasture growth predictions - south west September 2021

Pasture growth predictions for this spring are modelled and produced by Brendan Cullen, Senior Researcher grazing systems at Melbourne University, using soil moisture probe information at the specified sites. This is part of an Enhanced Producer Demonstration Site (funded by Agriculture Victoria and Meat and Livestock Australia) at sites with soil moisture probes.  These are in central Victoria (Baynton) and in south west Victoria (Harrow; Coojar and Dartmoor).  Pasture cuts to validate the data are being collected where possible.

MLA Producer Demonstration logo

To access all soil moisture probe real time data (and other pasture sites) go to: https://extensionaus.com.au/soilmoisturemonitoring/category/resources/meatwool/

Pasture growth predictions – 1 September 2021

Brendan Cullen, University of Melbourne, 30 August 2021

Pasture growth rate predictions are from 1 September – 31 December 2021.

Initial soil water content was obtained from the Agriculture Victoria soil moisture probe network in late August 2021.  The soil was saturated at each site in late August (same as last year).

Pasture growth rates are predicted using the SGS pasture model as weekly growth rates from September to the end of December.  Predictions are done two ways:

  • Using soil water content only.
  • Using soil water content plus seasonal forecast.  Bureau of Meteorology spring seasonal forecast show 65 % chance of above medium rainfall at Harrow, Coojar and Dartmoor as per Figure 1.
Bureau of Meteorology Spring (September-November) 2021 rainfall outlook for western Victoria.
Figure 1. Bureau of Meteorology Spring (September-November) 2021 rainfall outlook for western Victoria. (Source: Australian Bureau of Meteorology http://www.bom.gov.au/climate/outlooks/#/rainfall/median/seasonal/0, accessed 26 August 2021).

Harrow

In general, the prediction is very similar to last year.  Prediction based on soil water only is very similar to the long term median, with just a slightly higher prediction in early- mid November (Figure 2).  With the projection for a higher chance of above median spring rainfall, the growing season is predicted to extend for 2 weeks (Figure 3).

Harrow site pasture growth prediction from September 1 2021 based on soil water content only at Harrow
Figure 2. Pasture growth prediction from 1 September 2021 based on soil water content only at Harrow.
Pasture growth prediction from 1 September 2021 based on soil water content and seasonal forecast for 75% chance of above median spring rainfall at Harrow
Figure 3. Pasture growth prediction from 1 September 2021 based on soil water content and seasonal forecast for 75% chance of above median spring rainfall at Harrow

Coojar

Coojar was not modelled in 2020 but has a similar pasture growth pattern to Harrow, with just a slightly longer spring growing season.  Prediction based on soil water only, is very similar to the long-term median, with just a slightly higher prediction in early- mid November (Figure 4).  With the projection for a higher chance of above median spring rainfall, the growing season is predicted to extend for 3-4 weeks (Figure 5).

Pasture growth prediction from 1 September 2021 based on soil water content only at Coojar.
Figure 4. Pasture growth prediction from 1 September 2021 based on soil water content only at Coojar.
Pasture growth prediction from 1 September 2021 based on soil water content and seasonal forecast for 75% chance of above median spring rainfall at Coojar.
Figure 5. Pasture growth prediction from 1 September 2021 based on soil water content and seasonal forecast for 75% chance of above median spring rainfall at Coojar.

Dartmoor

The long-term pasture growth rate (kg DM/ha/day) and variability is shown in Figure 6. 

Prediction based on soil water only is very similar to the long term median (Figure 7).  With the projection for a higher chance of above median spring rainfall, the growth rate is predicted to be 5-10 kg DM/ha/day higher for 3-4 weeks in the period mid-November to mid-December (Figure 8).

Long term pasture growth rate variability at Dartmoor based on SGS pasture model simulation from 1990-2020 (phalaris-lucerne pasture)
Figure 6. Long term pasture growth rate variability at Dartmoor based on SGS pasture model simulation from 1990-2020 (phalaris-lucerne pasture)
Pasture growth prediction from 1 September 2021 based on soil water content only at Dartmoor.
Figure 7. Pasture growth prediction from 1 September 2021 based on soil water content only at Dartmoor.
Pasture growth prediction from 1 September 2021 based on soil water content and seasonal forecast for 75% chance of above median spring rainfall at Dartmoor
Figure 8. Pasture growth prediction from 1 September 2021 based on soil water content and seasonal forecast for 65% chance of above median spring rainfall at Dartmoor

To access all soil moisture probe real time data (and other pasture sites) go to: https://extensionaus.com.au/soilmoisturemonitoring/category/resources/meatwool/