DAFWA looks at big picture

A Department of Agriculture and Food (DAFWA) potential wheat yield map paints a picture of extremes, with parts of WA tipped for bumper yields while others are not expected to break even.

Although potential wheat yields maps have previously been generated to inform government and for internal use, the department for the first time has released this map to growers.

DAFWA director of practice and systems innovation David Bowran said the map was intended to get growers thinking about some of the season's cropping opportunities and risks, particularly based upon the availability of stored water.

"We have been modelling wheat yields for some time now, but we've never put it together into a map that combines statistical seasonal forecasts ... and tries to incorporate the water that's in the ground left over and a reasonable emergence time," he said.

"It's just an aid for people to start to question, what am I doing, is this a realistic estimate and, if it's not, what should I be estimating?

"It allows people to think, if I've got that potential, how might I seek to capitalise on it? Or, if I've got a low yield potential this year, maybe I shouldn't spend a lot of money on fertiliser?"

The map models stored water estimates and rainfall to date and assumes the median statistical seasonal forecast for rain and timely emergence to generate potential wheat yields.

But Dr Bowran is quick to point out that the map is merely an estimate.

"It's only saying that ideally if everything was close to optimum that's probably the maximum sort of yield you can expect for the rain you would get," he said.

"We are going to look at trying to find ways to improve those outlooks in the next two months.

"We will probably do a monthly one and based on information coming back to us like when crops emerged and what other conditions are happening."

The map indicates that in a best-case scenario, Bruce Rock farmer Gary Buller can expect wheat yields of between 2-2.49 tonnes a hectare.

But Gary, who farms with his father Les and brother Tony, said it was far too early for the map to be of any use.

"We had two lots of 75mm in November to December and we've had 10mm to get us going and put the crop in," he said.

"We're less than a week off finishing (seeding) and there is no way we could have made decisions based on that map."

While Gary admitted he would look at potential yield maps for curiosity, he said he preferred to engage risk management strategies when and if conditions changed, rather than based on long-range forecasts.

"We use liquid cart behind the airseeders and we're putting about 20 litres out," he said.

"That's just for starters - if we get a heap more rain we'll go and spray more out. If it doesn't rain we'll leave it in the tank. We play the season from that front."

Gary believed it would take a substantial rain event to join the top layer of moisture to the valuable stored water below. He said the estimate of 2-2.49t/ha for wheat was too high.

"Where the home farm is just west of Bruce Rock we have a lot of heavy country and you need some pretty wet winters to generate those type of yields," he said.

"But then we've got a block towards Doodlakine and it's different country and you can get your two tonne each year."

The map shows a large tract of the Wheatbelt has the potential for good yields, with bumper yields predicted in the Great Southern due to the amount of stored water.

In other areas, the picture is less than desirable. Around Perenjori, potential wheat yields of less than 1t/ha are predicted.

"We know that some areas, based on the fact that they've got no stored moisture coming into winter … its chances of achieving average yields go down quite substantially," Dr Bowran said.

"It's dry out there at the moment. Indications are we probably aren't going to get an average winter, it may be more likely to be closer to decile three or four rather than a five or six."

The long-range outlook points to slightly better rainfall for the northern agricultural region after June, with largely normal rainfall forecast for the rest of the growing season.

However, the winter crop outlook acknowledges yields will likely be impacted by depleted nutrient levels due to last year's bumper crops.

The central agricultural region outlook is mixed, with good stored water in places, although eastern parts of the area are at risk of not achieving break-even yields.

For most of the Wheatbelt, the statistical seasonal forecast indicates median rainfall from May to October.

In the southern agricultural region, there are generally good levels of stored water, although achieving normal winter rainfall means there will be a greater risk of waterlogging events.