AcCLIMATise - A DAFWA project December 2007
The Season Finishes
While most of the Southern Agricultural Region received reasonable September falls, our trial sites had a particularly dry September and October.
- Neutral El Nino conditions and a strengthening sea surface temperature gradient in the Indian Ocean at the beginning of the season saw cumulative rainfall tracking at about decile 7-9. Subsequent monthly totals fell to below average.
- Late October rain assisted some wheat crops, but barley, canola and pea crops were already mature.
- Of the Esperance AcCLIMATise sites, Neridup, Salmon Gums and Hopetoun had cumulative growing season rainfall on decile 3 while Mt Madden ended below decile 1 and Cascade on 5 (that is, about average).
- November and December had good harvest weather.
Further discussion on conditions up to the end of September is available on The DAFWA October Seasonal Update, on line at www.agric.wa.gov.au/climate.
Nitrogen Management
As would be expected, the poor spring rainfall had the largest influence on crop yields. While nitrogen fertiliser rates were applied at all sites, crop yields did not respond to extra N as each site had enough organic and starter fertiliser nitrogen for optimum yield with the exception of Cascade.
Nitrogen trials were carried out at Salmon Gums, Cascade, Mt Madden and Neridup, and results are still to be completely analysed.
Seasonal Outlook for summer 2007-08
Conditions in the Pacific indicate a La Niña event of moderate strength has developed. DAFWA analogue years currently suggest that this event should persist well into 2008.
- Since June, cooler than normal sea surface temperatures northwest of Australia reduced the inflow of moisture and cloud bands from the northwest. This pattern has broken and we now have warmer than normal sea surface temperatures around most of the northern coast of Australia.
- This is being accompanied with below normal pressure across the continent. Consistent with this trend towards improved rainfall prospects, heavy rain was experienced across large parts of eastern Australia in early November.
These same trends have improved the chance of an active cyclone season in the coming months.
These conditions need to persist if the wheat belt is to return to normal winter rainfall. Using previous analogue years with these conditions, the current outlook is for average season rainfall for Western Australia, and average to above average for the east Australian wheat belt.
The experimental outlook map (above, left) produced by DAFWA based on analogue years (1948, 1949, 1965, 1962 and 1996) with similar conditions suggests for the WA grain belt an average to below average rainfall through to January while seasonal outlooks from other agencies including the National Climate Centre (top, right) give a slightly above average rainfall prognosis.
For more discussion on these predictions go to
www.bom.gov.au and follow the
Water and Land prompts.
Further details on these outlooks are also given in the DAFWA October
Growing Season Outlook available on line at
www.agric.wa.gov.au/climate. Updated on 16 November.
Predicted against Average Yields
The AcCLIMATise project has been using models to follow the season as a possible tool for growers to use in managing climatic risk. Yield forecasting can be a valuable indicator of optimum nitrogen fertiliser rates.
A wide range of nitrogen application rates was applied by growers at each site, but actual and potential yields proved to be similar:
| |
Cascade |
Salmon Gums |
Neridup |
Mt Madden |
Hopetoun Emu H |
Hopetoun Emu M |
Hopetoun Emu L |
| Total fertiliser N (kg/ha) |
72 |
26 |
47 |
12 |
81 |
81 |
81 |
| PYCAL estimate (t/ha) |
2.8 |
2.3 |
3.6 |
1.7 |
3.7 |
3.7 |
3.7 |
| Actual paddock yield (t/ha) |
2.7 |
2.4 |
2.9 |
1.3 |
3.2 |
2.1 |
2.4 |
Comparing forecast yield from Yield Prophet for each site against what was actually harvested gave mixed results as the following charts indicate:
Yield Prophet tended to overestimate the yield at Salmon Gums and under estimate at Neridup, while at Cascade was about right.
Note the large jumps in yield forecast at Cascade and Neridup (centre and right):
- Why? Modelled yields reflect a low N status of the crops so the model responded strongly to N fertiliser.
Growers surveyed at the end of the season indicated that the most valuable time for them to get a good yield estimate was at pre-sowing and 6 weeks after sowing (mid-May and early July), but it was not till mid-September that forecast yields started to come close to actual.
Further details for each site are in the attached individual reports.
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