AN EXTRA 100mm of moisture for crops right as the plant begins to get into its growth cycle through spring. It sounds too good to be true, but this could be the benefit to Mallee growers from controlling summer weeds, according to Birchip Cropping Group research.
With some areas of the Mallee getting close to 250mm of summer rain already, and the prospect of more over January and February, BCG research agronomist Simon Craig said, working on BCG’s figures of being able to store 30 to 35 per cent of summer rain should weeds be controlled, that it would be possible for some growers to have 100mm of moisture in their subsoil profile by the end of summer.
Even more pleasingly for growers, Mr Craig said investigations had found that the moisture became available at a crucial stage of the season, as plants went into their reproductive phase during the spring.
“It’s coming into play at exactly the right time during the season, at flowering, right when growers need it.”
He said attitudes towards summer spraying were evolving throughout the Mallee.
What was formerly seen as an optional job and somewhat of a chore is now becoming one of the most crucial parts of the cropping program.
“In far north-western Victoria, over the past ten years or so, we are seeing summer rainfall become the most reliable rain for the year.
“We are consistently seeing falls of 100mm or more each year over the summer nearly every year now, while the growing season rainfall (GSR), traditionally regarded as the more reliable, is becoming more sporadic.
“With such a big chance of low rainfall totals during the growing season, farmers are looking to utilise that summer rain during the year.”
LaTrobe University research student Jackson Davis has been working with BCG to assess how farmers can more intelligently target their summer spraying programs.
In particular, Mr Davis, studying a double degree in ag science and international development, said he was investigating the differing amounts of moisture used by varying species of summer weeds.
“We are having a look at melons and heliotrope in particular.
“Having specific knowledge about different weeds means that in future, paddocks with particular weed burdens can be prioritised in the summer spray program.”
Speaking at BCG’s Hopetoun trial site, Mr Davis said it could be that some weeds, such as volunteer crops, used less moisture than some of the summer-specific species.
Neutron probes and soil tests will be used to measure the water use of summer weeds throughout the project while soil tests will also be used to monitor soil nutrient levels together with plant tissue tests.
Mr Craig said farmers needed to consider how they most economically controlled their weeds, whether through spraying, cultivation or running livestock.
At present, with glyphosate prices at record lows, he said many farmers preferred the chemical option, due to the thorough job it did.
He said there also needed to be considerations into weed burden and growth stage when assessing spraying programs.
“Farmers will need to consider how much weeds have grown when calculating rates, while in many areas, where there has been two lots of rain in many places, which may mean that repeat sprays are necessary.”
While acknowledging farmers could think of better things to do than sit on the boom spray just after the peak harvest period, Mr Craig said the results from ten years of trials were indisputable.
He said CSIRO modelling had shown that capturing and better use of summer rain is one of the best ways of improving crop yields and water-use efficiency in Victoria’s low rainfall zones.
BCG research has found that in certain years summer weed control can give a yield boost of up to 1.3t/ha, a huge increase in a region where 1.2t/ha is a money making crop.
This work came at Curyo, north of Birchip in 2008, where controlling summer weeds doubled wheat yields from 1.2 t/ha to 2.5 t/ha, after a heavy burst of summer rain.
“Despite high glyphosate prices there was still a 500pc return on investment in that year,” Mr Craig said.
However, he acknowledged that there would not be as spectacular results as this every year.
“Obviously, there is always more water available when you control weeds, but you have to weigh up the economies.”
He used the example of 2008-09, when only 90mm of rain fell at the Hopetoun site, with the biggest single fall 27mm.
Generally, researchers have found for summer rain to soak into the profile effectively, falls of over 25mm are needed.
Come planting in 2009, there was only 12mm stored, which did not translate into a significant increase in yield.
However, he said BCG’s studies had found this situation was the exception, rather than the rule.
BCG data shows that the percentage of years in which enough summer rain falls to bring up weeds but not be stored for subsequent crops varies from 29pc on a heavy clay at Charlton to 2pc on the sandy loams of the Mallee.
“Zero-tolerance of summer weeds pays off in the vast majority of years, particularly on lighter soil types with good fallow efficiencies,” he said.
“Given the large quantities of rain that much of the district has received this summer, growers should be confident that if paddocks are kept clean, water will be stored, vital for 2010 crops.”
He said farmers with cash flow difficulties needed to prioritise according to their best water storing paddocks, or high value paddocks, such as those coming out of fallow or a pulse.
Along with the benefits of stored moisture, Mr Craig said there was also an advantage for growers in terms of gaining access to mineralised nitrogen if moisture was stored.
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