Even when conditions are dry and yields are low controlling in-crop grass weeds can make an $80/ha difference to the profitability of wheat crops in the Mallee.
BCG research conducted north of Birchip at Jil Jil last year found that yield, test weight, grain weight and screenings were significantly better where weeds were controlled. This finding was clear despite the crop only receiving 129mm of growing season rainfall and the weed density being reasonably low (42 plants/m2).
The research was undertaken as part of a GRDC initiative investigating the impact of an increasing reliance on agrochemicals, and a subsequent increase in herbicide resistant weed populations, in the Victorian Mallee.
As well as the influence of in-crop weeds on wheat crop performance, the trial also looked at the effect of sowing direction and crop row spacing to see if such practice changes might reduce the need for herbicides.
BCG researcher Kelly Angel said research carried out in other cropping regions suggested that narrow crop rows and sowing in an east-west direction improved weed suppression.
She said the aim of the experiment at Jil Jil in 2015 was to determine if these findings could be replicated in a Mallee environment and if there were any benefits from combining the two practices (adjusting row spacing and sowing direction).
While sowing direction was not found to have any influence on crop yield, possibly due to the seasonal conditions and the fact that much of the crop did not tiller posing any significant competition for light and nutrients, crop row spacing did impact crop performance.
“Crops sown on narrower row spacings (22.5cm or 30.5cm, as opposed to 38cm) produced more biomass and resulted in higher yields,” Ms Angel said.
“In a weed-free situation crops sown at the widest spacing (38cm) suffered a 0.13t/ha yield penalty.”
Ms Angel said this was because the more uniform pattern of crop present at narrower row spacings resulted in increased radiation inception, reducing evaporative losses and increasing dry matter production which leads to higher yields.
When weeds were present, the yield reduction was attributed to both a reduction in grain number (as a result of fewer heads produced) and lower grain weight.
“This illustrates well that competition for light and nutrient resources, particularly in a poor season, can have a dramatic effect on crop yields,” Ms Angel said.
A full report from this research will be published in the 2015 BCG Seasons Research Results compendium which will be released at the Trials Review Day at Birchip on February 19.
For details phone BCG on (03) 5492 2787.
