Strategic tillage puts the pressure back on weeds
GroundCover™ Issue: 123 | Author: Clarisa Collis
- Reduced weed pressure following strategic tillage has eliminated three fallow herbicide applications on the Jensen family’s Queensland property, decreasing spraying costs and herbicide-resistance risk
- Less in-crop weed competition as a result of tillage has allowed for reduced seeding rates, increasing yield potential and reducing seed costs
- Tillage has restored weed-infested farm area to cropping
For Central Queensland growers Darren and Tanya Jensen a strategic approach to cultivation has proven a profitable option for weed control on the family’s 1750-hectare Biloela property.
The Jensens have ploughed their cropping country for the past two years as part of a weed-management program primarily targeting feathertop Rhodes grass.
In 2015, they used two passes of a chisel plough to cultivate the soil across 1400ha; and in 2016, they again tilled this area using one pass of a disc chain.
Their decision to bring back tillage was influenced by the findings of GRDC-funded research from 2012 to 2014 on their farm.
The trials, led by Dr Yash Dang through the University of Queensland and the Queensland Department of Science, Information Technology and Innovation, demonstrated the potential for strategic tillage to lift both crop yields and gross margins, while maintaining soil health.
Of seven Queensland properties where trials looked at the effects of strategic tillage, the greatest reduction in weed pressure following cultivation was achieved on the Jensens’ farm.
Spurred by these results, the couple have overturned 15 years of no-till practices to test the whole-farm benefits of occasional tillage on their structured vertosol soils.
To date, tillage has increased the overall productivity and profitability of their summer and winter crops: sorghum, maize, chickpeas and wheat. These gains are thought to stem largely from the reduced in-crop weed competition for water and nutrients.
Highlighting the effectiveness of tillage as a weed-management tactic, researchers found a single cultivation halved the number of weeds in all the trial plots examined, including the Jensens’ 4ha trial.
However, Darren, who was the GRDC-supported 2015 Australian Grain Grower of the Year, says tillage has also provided other farm business gains.
Apart from helping to eliminate a mix of northern weeds (feathertop Rhodes grass, fleabane, sow thistle and African turnip) from their cropping program, cultivation has also enabled the Jensens to eliminate three fallow herbicide applications from their spraying regime.
Darren says the reduced spraying represents a herbicide cost-saving totalling about $84,000, based on the $20/ha price per spray for chemicals.
However, he estimates that using a ‘double knock’ approach to spraying would provide a $252,000 cost-saving based on the $60/ha price of each fallow spray using two different herbicides.
But as significant as this cost-saving is, Darren sees even greater benefit in being able to reduce their reliance on chemical weed control and mitigate herbicide-resistance risk.
He says less in-crop competition from weeds in the wake of cultivation has also allowed them to reduce their seeding rates.
For example, in the past two seasons, they have decreased their sorghum seeding density from 45,000 seeds/ha to 35,000 seeds/ha. Reducing the plant population for this mainstay summer crop has meant a $12/ha seed cost-saving.
In wheat, they have dropped their seeding density from one million seeds/ha to 800,000 seeds/ha, providing a $5/ha cost-saving for the winter crop.
More importantly, however, these lower seeding rates have helped to drought-proof their crops in dry seasonal conditions, Darren says.
This is because each crop plant can take up more moisture and nutrients from a larger soil area, making room for more robust plants and, ultimately, higher-yielding crops.
Before the Jensens implemented tillage, this extra ground would have been inundated with weeds, usurping moisture, nutrition and light from the crop at the expense of grains productivity and profitability.
“The effect of lower seeding rates on sorghum profitability can be huge,” Darren says. “In a very dry year it could rescue a crop from complete failure so it returns about $200/ha. Whereas in wetter seasons the yield gains tend to be smaller because there’s more moisture per plant to go around.”
Crop land rescued
Another benefit of strategic tillage on the Jensens’ property is that it has enabled them to reclaim about five per cent of their cropping country, which had become infested with feathertop Rhodes grass.
Restoring this 75ha area to summer and winter crops has further delivered a slight lift in the Jensens’ farm business gross margins.
Darren plans to alternate between using a chisel plough and a disc chain to plough the soil for weed control. His tillage strategy involves cultivating the soil to a depth of 10 centimetres using two passes of a chisel plough every second year, plus using one pass of a Brookfield disc to a soil depth of 5cm every other year.
“Using a Brookfield disc chain flicks established feathertop Rhodes grass out of the soil, and we then spray the tiny grass seedlings when they emerge on the next rain.
“Compared with a chisel plough, the disc chain only lightly tickles the soil, so it’s not damaging our soil structure. It also helps level the soil surface, and fills in ruts and wheel tracks across our paddocks.”
Darren says this approach is part of an initial, intensive push aimed at driving down the weed seedbank for feathertop Rhodes grass in the next few years.
Their strategy further draws on the research findings that demonstrated tillage had a “minimal impact” on a range of soil characteristics a year after cultivation, including bulk density, moisture, organic carbon and phosphorus to a soil depth of 10cm. The research also showed that the on-farm benefits of strategic tillage had completely subsided two years after cultivation, with no difference between no-till and tilled soils.
However, Darren says strategic tillage is an “opportunity operation” on the family’s property because its frequency mostly depends on seasonal conditions.
In the future, the Jensens aim to cultivate their paddocks in relatively dry conditions during February and March to avoid damaging the soil structure in wet conditions following rain. Although if they receive rain in these months, it provides their cue for seeding summer crops instead of strategic cultivation.
More information:Darren Jensen,
0429 054 511,
Dr Yash Dang, University of Queensland,
07 4529 1245,
GRDC Project Code ERM00003