El Niño hammers wheat crop

Modelling by the Queensland Alliance for Agriculture and Food Innovation (QAAFI) suggests that from mid-NSW south, a dry spring has stripped tens of millions of dollars from the wheat crop’s potential.

That was compounded by the heat wave that rolled across south-eastern Australia at the beginning of October - an event not captured in the modelling.

The heat spell was particularly damaging for Victoria’s Mallee and Wimmera regions, Hannah Janson of Australian Crop Forecasters (ACF) said, because those crops were already struggling on insufficient soil moisture.

The yield potential of the Mallee-Wimmera alone dropped by about 14 per cent in the week of the heatwave, ACF calculated. Elsewhere, the yield reduction was more in the order of five per cent.

Overall, ACF thinks the week of heat may have cost the nation’s wheat crop 1.6 million tonnes of yield, or about $500 million, on top of the effects of a dry spring.

ACF’s latest harvest estimate puts the Australian crop at 24.3Mt, better than the 23.6Mt crop of 2014, but with considerable uncertainties around how the remainder of the crop will finish, and what headers will report when they start stripping.

ACF also reduced estimated Australian canola and barley production by three and four per cent respectively, month on month.

QAAFI scientist Graeme Hammer said although the loss of yield potential is disheartening, it could have been much worse. One of the top four El Niño events on record had the potential to wreak much greater drought havoc on winter crops, but fortunately, El Niño’s drying trend was countered up until September by moisture streaming off a warm Indian Ocean.

The Indian Ocean has now cooled substantially off Australia, meaning that it will reinforce the drying effects of El Niño until the Asian monsoon starts streaming moisture across the continent again - hopefully in the next month or two.

Professor Hammer said although the 2015 winter crop season and its warm, dry spring are within the bounds of natural climate variability, climate trends are moving the envelope of that variability in a direction that promises to make such seasons more common.

Lack of moisture is not the only threat inherent in this pattern.

“With the heat effect pushing the crop earlier, you have to be careful not to run yourself into a frost,” Prof. Hammer said.

“You get a hot season, your crops flower earlier, and you increase your frost risk.”

The extra carbon dioxide (CO2) in the atmosphere that is shifting climatic patterns carries some benefits to croppers. Heightened levels of CO2 change many plants’ response to water stress, and in the case of wheat it will lead to greater water efficiency, at least in the northern wheat zones that QAAFI has studied.

The kicker: by mid-century, Prof. Hammer said, the climate change effects of heat and altered rainfall patterns are likely to have a greater negative effect on wheat’s water efficiency than the positive effects of CO2 fertilisation.

That may not be the case with sorghum, though, which has such a strong response to CO2 fertilisation that it could outweigh adverse effects from rainfall and heat.

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