DRY sowing of wheat is on the increase in Australia’s south-eastern cropping belt says CSIRO’s James Hunt, with more farmers picking a sowing date and sticking to it.
Dr Hunt, who is a research scientist for CSIRO’s Sustainable Agriculture Flagship, said the summer weeds which had traditionally been used as sheep pick were now being “religiously” sprayed out as dry autumns and early winters became common.
He said research from the Grains Research and Development Corporation’s national water use efficiency project had shown that for every $1 spent on weed control, farmers got back $6 through extra yield achieved by conserving water and nitrogen.
However, it wasn’t just for the savings that farmers were spraying instead of grazing.
A trend of drier autumns was leading to more farmers adopting dry sowing and water conservation practices, which was seen at a workshop held by the Birchip Cropping Group in Birchip, Victoria, at which Dr Hunt presented recently.
“We asked what farmers would have done five years ago and about 50 per cent of people said they’d have sown about 30pc of their crop dry – when we asked what they’d do now, 80pc to 90pc said they would happily sow 90pc of their crop dry,” he said.
The Bureau of Meteorology (BOM) has predicted, and observed, drier autumns and winters.
Manager of climate monitoring at BOM’s National Climate Centre Karl Braganza, said contributing to the dry was an absence of “wet years” – seasons where there was either good falls of cool season rain; high rainfall in other seasons to compensate for a lack of cool season rain, or high rainfall throughout the whole year – altogether from 1995 to 2010.
He said the observed decline in autumn and winter rain had for some regions been faster than the BOM’s models had predicted, suggesting either its models had underestimated the rate of drying, or the climate had slipped into the drier trend at a faster rate than predicted.
Meanwhile, temperatures had uniformly been warming during these drier periods, which in higher rainfall areas would have a limited affect, but in drier regions could exacerbate the lack of moisture, he said.
Dr Braganza said the BOM had so far observed a 10pc to 20pc reduction in rain for the autumn/winter period in south-east Australia since the mid-1990s.
“When you get a 10pc to 20pc reduction in rainfall it’s amplified by a decline in soil moisture and streamflow because the vegetation is more thirsty. In a hydrological sense it’s the equivalent of a 60pc decline in run-off and available moisture in the environment,” he said.
The autumn/winter window which was becoming dryer also clashed with the sowing window for the majority of modern semi-dwarf variety wheats, Dr Hunt said.
“We’ve got to the point now where all our varieties have to be planted between April 25 and May 15 or they flower too early or too late” he said.
“But what we’re saying is maybe we need to look at some of the older, more flexible genotypes so that if you get a sowing break anytime from February to May you can go in and sow.”
This included using winter wheats (such as Wedgetail) or slow maturing spring wheat (such as Eaglehawk or Bolac) varieties to increase sowing flexibility.
Dr Hunt said research had shown these varieties, if sown in the right window, had the potential to out-yield the more commonly grown mid-fast maturing spring, or main season wheats (such as Lincoln, Gregory, Suntop etc).
He said a lot of farmers who had tried longer season wheats had failed to recognise their potential because they had sown them too late.
“However, we’ve shown that if you can plant at the right time they will out-yield main season varieties on average by 0.8 tonnes a hectare,” Dr Hunt said.
Some of the old tall wheat varieties the industry had left behind in the in the 1970s also had longer coleoptile length – as long as 15cm, which was another trait breeders were aiming to reintroduce to improve germination from depth when the season dictated farmers must chase moisture.
“So in lots of ways we need to go back to the future and use wheats that have a more flexible sowing date and have a longer coleoptile,” he said.
He said these adaptations, plus improved no-till sowing techniques and the availability of pre-emergent herbicides such as Sakura, have meant farmers were gradually adapting to a drier system where they didn’t have to wait for rain to sow and allowed farmers to take better advantage of smaller amounts of moisture.
“We have seen a lot more dry sowing in southern NSW this year, with only a handful of operators that hadn’t got their canola and wheat in by the time it rained,” Dr Hunt said.
