A GRDC investment is starting to shed light on the optimum time of sowing for winter wheat varieties in the low to medium-rainfall zones of Victoria and South Australia.
Leading the investment are La Trobe University’s Dr James Hunt and South Australian Research and Development Institute research scientist Dr Kenton Porker, who agree growers looking to plant such varieties should do so in April – whether that be early, mid-month or late – to maximise yields.
“March is too hot and dry for winter wheats in the low and medium-rainfall zones and in most situations May is too late, because the winter types flower too late, resulting in a yield penalty,” Dr Hunt says.
Now heading into its third season of trials in 2019, the research has found the yield of winter types sown any time in April to be equivalent to spring variety Scepter (PBR) sown in early May, which is being used as the benchmark in the trials.
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Dr Hunt says the main advantage of winter wheats to farming systems is when spring varieties cannot be sown in the optimum window between 25 April and 10 May.
“The other clear advantage of winter wheats is for those with a mixed farm, and their use for both grazing and grain,” he says.
“Trials as part of this investment have shown grazing or defoliation has either no effect, or a small negative effect, on grain yield, which is cultivar dependent.”
Trials as part of this investment have shown grazing or defoliation has either no effect, or a small negative effect, on grain yield, which is cultivar dependent.
Because of the stability of flowering times of winter wheat, different cultivars are required to match different environments. This is unlike spring wheats, where the flowering date can be adjusted with sowing date.
In low-rainfall environments with yields below three tonnes per hectare – where flowering windows tend to be earlier – faster-developing winter wheats are required. In this instance, Longsword (PBR) has been a standout, achieving yields closest to that of Scepter (PBR).
In medium-rainfall environments with yield potential of three to five tonnes per hectare, Illabo (PBR) and DS Bennett have performed well. Both are later-flowering than Longsword (PBR), Dr Porker says.
“Illabo (PBR) is a mid-winter cultivar that is faster-developing than DS Bennett, but the latter still seems to yield well even though it is flowering a bit later," he says.
Dr Porker says in yield environments above 5t/ha, DS Bennett was again dominant. He says it seems to have a fit over a wide range of medium-rainfall environments.
Dry conditions in 2017, and even drier conditions in 2018, at many of the trial sites meant the researchers could study the amount of rainfall needed for winter wheats to successfully establish and survive.
Based on results from these two seasons, they concluded that if sowing in the non-recommended time before the start of April, clay soils will need at least 25 millimetres of rainfall and sandy soils will need at least 10mm of rainfall.
“These amounts will keep the crop alive until June,” Dr Porker says.
“When I say alive, the crop will be extremely stressed but will be surviving beneath the soil surface.
“But more (rain) isn’t always better. At one site we got negative responses to irrigation when sowing on 15 March. Plants would grow too much and start using soil moisture too early in the season, and there is little relationship between vegetative growth and grain yield.”
In regard to nitrogen management and sowing density, Dr Porker says reducing plant populations of winter wheats to about 50 plants per square metre from 150 plants per square metre resulted in a 0.1-0.2t/ha increase in yield, but this came at the expense of reduced weed competition.
“Therefore, growers sowing into a clean paddock might be able to afford to drop their sowing rate,” he says. “Deferring nitrogen to stem elongation rather than up-front at sowing also gave a slight yield increase of 0.1 to 0.2t/ha.”
Other organisations working on the project include Hart Field Site Group, Moodie Agronomy, Birchip Cropping Group, Agriculture Victoria, Foundation for Arable Research Australia, Mallee Sustainable Farming and Riverine Plains.
More information: Dr James Hunt, 03 9032 7425, email@example.com