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 October 2021

Brendan Cullen, University of Melbourne, 4 October 2021

Pasture growth rate predictions from 8 November – 31 December 2021 were modelled at three sites in south west Victoria,  Pigeon Ponds, Coojar and Dartmoor.

Initial soil water content was obtained from the Ag Vic soil moisture probe network in late September 2021.  The soil water content was drier in the top 40 cm compared to early October when the profile was full.  On 8 November 2021, soil water content was approximately 30% at Pigeon Ponds, 70% at Dartmoor and 65% at Coojar.

Pasture growth rates are predicted using the SGS pasture model as weekly growth rates from October 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 Pigeon Ponds, 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).

Graphs with the predictions done both ways are included below for each site, with graph on “How did we go?” to show the measured growth rates against the predictions – where available.

Pigeon Ponds

Prediction based on Soil water only the pasture growth rate prediction is similar to the long term (Figure 2).  With the projection for higher chance of above median spring rainfall, November growth rates are predicted to be higher that the long term average, and the growing season is predicted to extend for 1 week longer than the long term median (Figure 3).  Pasture growing is predicted to finish by end of November in all scenarios.

Figure 2. Pasture growth prediction from 8 November 2021 based on soil water content only at Pigeon Ponds.
Figure 2. Pasture growth prediction from 8 November 2021 based on soil water content only at Pigeon Ponds.
Figure 3. Pasture growth prediction from 8 November 2021 based on soil water content and seasonal forecast for 65% chance of above median spring rainfall at Pigeon Ponds.
Figure 3. Pasture growth prediction from 8 November 2021 based on soil water content and seasonal forecast for 65% chance of above median spring rainfall at Pigeon Ponds.

how did we go?

Figure 4 shows the predicted growth rates with the ‘actual’ or measured growth rate for October as the blue dot.  It indicates that growth rates at this site were close to, but slightly above, the predicted median and the long term median for the month. 

Figure 4. Pasture growth predictions at Pigeon Ponds site, with the measured pasture growth for October.
Figure 4. Pasture growth predictions at Pigeon Ponds site, with the measured pasture growth for October.

Coojar

Prediction based on Soil water only is similar to long term, but with slightly higher pasture growth rates predicted in mid-late November (Figure 5).  With the projection for higher chance of above median spring rainfall, the growing season is predicted to extend for 1 week (Figure 6).

Figure 5. Pasture growth prediction from 8 November 2021 based on soil water content only at Coojar.
Figure 5. Pasture growth prediction from 8 November 2021 based on soil water content only at Coojar.
Figure 6. Pasture growth prediction from 8 November 2021 based on soil water content and seasonal forecast for 65% chance of above median spring rainfall at Coojar.
Figure 6. Pasture growth prediction from 8 November 2021 based on soil water content and seasonal forecast for 65% chance of above median spring rainfall at Coojar.

Dartmoor

Prediction based on Soil water only is very similar to long term (Figure 7).  With the projection for higher chance of above median spring rainfall, the growth rate is predicted to be 0-10 kg DM/ha.day higher in the period mid-November to end-of-December (Figure 8).

Figure 7. Pasture growth prediction from 8 November 2021 based on soil water content only at Dartmoor.
Figure 7. Pasture growth prediction from 8 November 2021 based on soil water content only at Dartmoor.
Figure 8. Pasture growth prediction from 8 November 2021 based on soil water content and seasonal forecast for 65% chance of above median spring rainfall at Dartmoor.
Figure 8. Pasture growth prediction from 8 November 2021 based on soil water content and seasonal forecast for 65% chance of above median spring rainfall at Dartmoor.

How did we go?

Whilst measured October growth rates were not available at this time, Figure 9 shows the measured growth rates for August and September at the Dartmoor site with the predictions from last month. This indicates the September growth rates was close to but slightly higher than the predicted growth rates for the month, and August was well above, possibly reflecting the productive species in the pasture. 

Figure 9. Pasture growth predictions from September, with the measured growth rates for September and August.
Figure 9. Pasture growth predictions from September, with the measured growth rates for September and August.

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