WeedSmart Big 6 focus tactic: Strategic tillage
Conservation farming systems offer multiple benefits for soil structural and biological health, crop production and weed management.
However, after decades of minimal or nil cultivation, growers and agronomists typically see soil constraints, such as acidity and compaction at depth and surface sealing or non-wetting, hampering crop growth and allowing weedy patches to establish.
WeedSmart’s agronomists in each cropping region have seen the benefits of infrequent aggressive cultivation implemented purposefully to renovate and refresh soils that have produced many profitable crops.
There are four main objectives for implementing strategic tillage operations for weed control within a conservation farming system:
Objective 1 – ameliorate soil constraints, improve crop competition and reduce crop variability.
Objective 2 – kill mature, resistant and hard-to-kill weeds.
Objective 3 – manage the seedbank, bury weed seed, stop seed set in small weedy patches.
Objective 4 – manage stubble for seeding, disease and insect disruption, reduce frost risk, pre-emergent herbicide efficacy.
Objective 5 – incorporate green manure crops.
Strategic tillage has a place in the WeedSmart Big 6 integrated weed management program when it is applied with specific objectives in mind and with awareness of the likely weed seedbank response.
Strategic tillage may take the form of full-depth cultivation (including inversion) and deep ripping, seedbed cultivation or patch management and chipping. Many different implements can be effective in different soils and situations. The key is to be clear about what you want to achieve.
Before using cultivation to manage weeds on the surface, consider the impact of soil disturbance on the weed seed bank. The seed of each plant species responds differently to burial and disturbance. Studies in weed ecology help to understand the potential risks and likely benefits of using this tactic to manage the weed seed bank. The potential benefit of cultivation is to control weeds that do not persist for long once the seed is buried, while crop competition may be a better tactic for weed seeds that do not remain viable for long on the soil surface. More…
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Sandy, non-wetting, acidic, compacted soils
in Western Australia and the Mallee regions of South Australia, Victoria and NSW
Peter Newman (WeedSmart western extension agronomist) says non-wetting sandy soils in the northern wheatbelt of Western Australia have responded well to the ‘lime, flip and rip’ soil amelioration program. This one-off, aggressive tillage operation aims to invert the non-wetting sand layer and surface-applied lime. In the process, weed seeds are buried, and nutrient mineralisation boosts crop performance. This tactic must only be applied when soil moisture is high in these non-wetting sands.
In 2024, a group of Planfarm and Farmanco consultants conducted a GRDC–DPIRD-funded study where 50 growers who had implemented the ‘lime, flip and rip’ tactic within the previous 10 years were interviewed, and their experiences and learnings were documented. More… Soil amelioration increases profit by $100/ha per year over 10 years
These growers also contributed their economic data for analysis, which revealed an average $100/ha/yr extra profit directly attributable to their soil amelioration program. More… How WA growers are practising soil amelioration
The benefits from improved water use efficiency and higher yields more than compensated for the cost of implementing the soil amelioration program. To maintain the benefit after implementing the initial ‘lime, flip and rip’, growers apply lime and deep rip every 4 to 5 years.
DPIRD research into the weed control aspect of deep strategic tillage indicates that soil amelioration programs often require additional weed control measures.
In summary, the weed response to strategic tillage is variable, and growers should not assume that tillage will eliminate an existing weed problem. In the first cropping season after soil amelioration, the timing of weed emergence is likely to be variable due to variable weed seed burial depth. This can result in some weeds evading pre-emergent herbicide control, so other in-crop and harvest weed seed control tactics should be planned. Avoid dry sowing the first crop after amelioration and take additional steps to establish a competitive crop in the first year. More… Strategic tillage in Australian conservation agricultural systems to address soil constraints
Sodic soil types in Western Australia benefit from gypsum applications mixed into the topsoil with multi-tool cultivators. Minimal weed seed burial occurs with these operations. The weed control benefits flow from stimulating weed germination, applying a pre-seeding double-knock to seedling weeds and from improved crop competition.
More Western Region resources:
How does renovating non-wetting sands help weed control
Mat Freeman, Walkaway, WA case study
Does soil pH affect weed management
Remove the fetters from crops and they’ll trample the weeds
Crop competition from the ground up
Heavy clay, alkaline soil
in Queensland and Northern NSW
Planting into high soil moisture underpins the farming systems in Queensland and northern NSW. Conserved soil moisture in minimum and zero-till systems has enabled the expansion of winter and summer cropping in the northern grains region.
Paul McIntosh (WeedSmart northern extension agronomist) says that growers are reluctant to cultivate and compromise the moisture levels in the soil. However, there is a place for one-off cultivation, and the soil repairs quickly. More… Is one-time tillage a weed control option in a no-till farming system
Nutrient stratification strands immobile nutrients, such as phosphorus (P) and potassium (K), in the dry topsoil, where crop roots cannot access them. Crops have responded to deep banding P and K, with more competitive crops competing more strongly against weeds. More… Deep-banding P and K
One-off cultivation can redistribute nutrients, reduce disease inoculum, bury weed seeds and improve seed-to-soil contact for improved crop germination. Cultivation is often tied to wheel-track renovation, erosion restoration, and addressing surface sealing in some soils.
Implements such as Kelly chains can be used to good effect on fleabane and feathertop Rhodes grass when used as a double-knock partner with herbicide. These implements can also assist with stubble management, but frequent use can have a detrimental impact on the surface soil structure. More… Lance Wise, Bowenville, Qld case study
Patch management for weed control can also be done using a small set of offset discs and pins on a GPS map to destroy large plants and bury the seed in the surrounding soil.
A targeted tillage implement to detect and chip out weeds without causing full disturbance of the soil surface is under development. More… Targetted tillage machines
More Northern Region resources
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Medium clay, acidic soils
in Central and Southern NSW, and Victoria
No-till farming improves soil structure, timeliness of machinery operations (including spraying), and water-use efficiency. However, it also results in nutrient stratification, and aluminium toxicity at depth in acidic soils. More… Soil acidity: its stratification and amelioration with lime
Greg Condon (WeedSmart southern extension agronomist, NSW and Vic) says aluminium toxicity reduces barley and pulse production, with a knock-on detrimental effect on canola that otherwise benefits from fixed nitrogen from a well-nodulated pulse crop, such as faba bean or vetch. Once gaps open up in a crop, weeds can thrive.
To get lime to the required depth requires cultivation to a depth of 200 to 250 mm. The benefits of raising the subsoil pH include increased crop growth, fewer gaps for weeds to exploit, increased nodulation and N-fixation in legumes, larger crop root systems and less rhizoctonia. All these benefits combine to increase the crop’s ability to produce higher yields and to outcompete weeds.
Late in a summer fallow, survivor weeds are very hard to control. Destroying established, mature plants, such as windmill grass, with cultivation can reset the seedbank, and when small, actively growing seedlings emerge, they are easier to kill with pre-seeding herbicide sprays. This ‘cultivation plus herbicide’ double-knock is a very effective strategy against herbicide-resistant and hard-to-kill weeds, such as annual ryegrass, windmill grass and fleabane.
Attempts to incorporate lime with offset discs or scarifiers have been largely unsuccessful. Modern ‘one-pass’ cultivators provide more aggressive mixing of the lime into the soil profile.
Greg says that a one-pass cultivation to incorporate lime is generally only required once every 10 years, and that the benefits of no-till farming quickly return. Targeting paddocks with hard-to-kill weeds present is a two-fold weed control strategy.
When testing soil pH, collect samples at 5 cm intervals to get a full picture of where the acidity layer is within the soil profile.
Any cultivation represents an erosion risk. Growers generally minimise the risk by cultivating a small area, say 10–15 per cent, of their cropping program at any one time. Committing to a long-term soil amelioration program can be daunting, but the crop response is immediate, and experience suggests that the investment more than pays for itself.
If the cultivation is done just prior to seeding, some soils may require a consolidation pass with a roller or prickle chain to allow a modern no-till planter to operate effectively. Cultivation can result in the planting furrow collapsing, bringing pre-emergent herbicides into contact with the emerging crop.
Additionally, some weeds, such as wild oats, respond to disturbance and growers need to be ready to treat potentially large germinations following the first rain.
More Southern Region resources
Using fodder crops to manage resistant weeds
Strip-grazing cattle to manage weeds
Is one-time tillage a weed control option in a no-till farming system
Variable soil constraints
in South Australia
Growers in South Australia face similar soil constraints to those in NSW, Victoria and Western Australia, including acidity, sodicity, compaction and non-wetting properties.
Chris Davey (WeedSmart southern extension agronomist, SA) says soil amelioration and improved management of constrained soils can lead to healthier crops that compete strongly against weeds and generate more profit for growers.
Legume and barley crops do not tolerate acidic conditions. In contrast, annual ryegrass can better tolerate low pH conditions and will proliferate in areas of poor crop growth. Ameliorating soil pH using variable rate or broadacre applications of lime improves overall crop performance and suppresses annual ryegrass.
Delving, spading and deep ripping are used to incorporate lime and address soil physical constraints. Breaking up compacted and reconsolidated layers expands the crop root zone and access to soil moisture and nutrients. Redistribution of clay improves water infiltration and the soil’s water-holding capacity.
Implements such as the Reefinator have a place in some paddocks to break up limestone sheet rock, allowing crops to establish and grow in deeper soil.
More Southern Region resources
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