The trial results challenged the thinking of many growers in the Mungindi region when it came to sustainable plant stand in wheat crops.
PHOTO: Arthur Mostead
When northern New South Wales agronomist Mick Brosnan started the wheat row spacing, plant density and planting date impact trial, he thought he had a reasonable idea of what the outcomes would be. The results proved him right, generally speaking, but there were still a few facts that surprised this experienced operator.
He now has “solid” trial data highlighting the value of May planting and setting a new minimum benchmark for growers when it comes to acceptable plant stand.
The three-year trial run on grower Andrew Earle’s property in Bullawarrie, Queensland, from 2012 to 2014, tested the yield outcomes from different wheat cultivars (Baxter, Suntop and EGA Gregory) planted at two different times (May and June) and at two different row spacings (25 and 50 centimetres).
Plant population per square metre was also set at five different densities (seven, 15, 30, 50 and 80).
An initiative of the Mungindi Cropping Group and funded by the GRDC, the trial had a strong region-specific focus, taking into consideration aspects such as the area’s average wheat yield of 1.6 to 1.7 tonnes per hectare on grey vertisols.
The most definitive data for the region’s growers to come from the trial was confirmation that May-sown wheat was more profitable than June-sown wheat, regardless of the cultivar or the row spacing.
Northern New South Wales agronomist Mick Brosnan.
PHOTO: B&W Rural
A more unexpected finding came in the plant density results: a population of seven plants/m2, although not ideal, still proved acceptable in terms of yield outcome.
“As an agronomist I was constantly being asked by growers the optimum row spacing and whether they should be moisture seeking, as well as at what plant density should they replant,” Mr Brosnan says.
“Many growers had gone up to 50cm row spacing, because 40cm wasn’t wide enough when we were moisture ‘delving’ at depths of up to 22cm.
“We were moisture seeking so deeply that we were pushing dirt into the next slot at anything closer than 50cm.
“However, we were still questioning whether we shouldn’t be going back to narrow spacing, particularly with late planting.”
New rule of thumb
Before the trial, when it came to planting density local growers and their resident agronomist had a colloquial rule of thumb: anything less than 20 plants/m2, consider replanting.
The GRDC-funded trial has altered this perspective.
“One of the most important things to come from the trial was the importance of timing: planting in May consistently produced a better yield result, regardless of variety or row spacing,” Mr Brosnan says.
Data shows the May wheat yielded 2.37t/ha on average over the trial duration, in comparison with June plantings, which averaged 1.31t/ha.
Yet when it came to row spacings there was no difference in yield, regardless of planting times.
The planting density component of the trial established a new minimum threshold in terms of acceptable plant stand.
“What we also found was the threshold for planting density was still acceptable, though not ideal at seven plants/m2,” Mr Brosnan says.
“At just seven plants/m2 wheat sown in May produced the equivalent yield of 80 plants/m2 sown in June.
“The lighter density stand doesn’t look good in the paddock, but it still performs reasonably yield-wise.”
Trial results from 2014, which are reflective of the three years, show the seven plants/m2 plot yielding 1.28t/ha, and with the region’s production costs at about 0.8t/ha, the lighter plant stand is still profitable.
“From a row-spacing perspective there was no difference in yield, but if you can stay on top of the weed pressure then 50cm works better when you are moisture seeking at the depth we need to for May plantings,” Mr Brosnan says.
“Date of planting is the critical message for growers and agronomists to come out of this trial.
“And retaining May-planted crop, even if the strike rate is patchy, as long as there are seven plants/m2.”
Mungindi Cropping Group project officer and agronomist Jo Weier, who collaborated on the trials, says the results have significant practical implications for growers, as they look to future planting-machinery purchases.
“Staying at 50cm instead of going to 25cm means there could be a significant cost saving for growers when it comes to the next planter purchase,” she says.
“Reduced machinery wear, decreased maintenance and operating costs and less downtime during seeding are also important considerations for growers as they opt to retain 50cm row spacing.
“This trial has given growers confidence to make critical decisions about on-farm practices and these decisions can make a significant difference to gross margins.
“As agronomists, this project offers us some solid trial data on wheat row spacing, planting time and plant density that relates very specifically to our region.”
Trial results in practice
What row spacing should I plant on?
With yield expectations up to 3.5 tonnes per hectare stick with 50 centimetres, provided you can control weeds.
Should I adjust my row spacing later?
Should I be moisture seeking early?
Absolutely. Planting earlier or on time results in better yields.
At what plant stand should I replant?
Even an uneven plant stand of seven plants per square metre was as good if not better than a late plant. So provided you can control weeds you would not replant under seven plants/m2.
What plant stand should I aim for?
Higher is generally always better. Aim for 80 if you have a good moisture profile, 50 otherwise.
Should I increase planting rate for late rain?
No. Aim for 80 if you have a good starting moisture profile, or 50 if you do not.
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