Digging deep and controlling compaction

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Use of bigger and heavier cropping machinery across the Western Australian grainbelt is driving soil compaction deeper underground, prompting more research into management options.

As a general rule, a machine with a 10-tonne axle weight causes crop-constraining soil compaction to a depth of 30 centimetres.

However, most modern farm machinery is far heavier and can cause subsoil compaction at 40 to 60cm.

GRDC-funded research by the Department of Agriculture and Food, WA (DAFWA) is finding that deep ripping, or other soil-compaction amelioration tactics, combined with controlled-traffic farming (CTF) can help to overcome deep soil compaction and reduce the risks of re-compaction.

Portrait of Bindi Isbister

DAFWA researcher Bindi Isbister is part of a GRDC-funded project delving into the use of deep ripping and other soil-compaction-amelioration tactics with CTF to address deep subsoil compaction.

PHOTO: photo: DAFWA

DAFWA development and research officers Bindi Isbister and Dr Paul Blackwell outlined the success of such systems at the GRDC Grains Research Update in Perth and Regional Cropping Solutions Network Esperance soils forum earlier this year.

In 2015 trials, they found removing compaction in sandy textured soils by deep ripping to 55cm and topsoil slotting could boost wheat yields by 1 to 1.7 tonnes per hectare and provide a long-term return of $6 to $16 for every $1 invested.

This process used a ripper with a front row of tynes delving to 30cm ahead of a second set of in-line tynes (working to 60cm) with an inclusion plate attached.

The ripped slot is held open, while the topsoil – with or without ameliorants such as lime, gypsum, organic matter or clay – falls or is dragged into the ripped section by chains.

Portrait of Paul Blackwell

Dr Paul Blackwell looking at soil that has been deep ripped.

PHOTO: Peter Maloney 

Dr Blackwell says the profitability of the system is driven by providing plant roots with better access to vital deeper subsoil moisture and more effectively intercepting leaching nutrients to boost crop production.

“The combination of deeper ripping and topsoil slotting helped to reduce grain losses from the previous year’s dry and hot spring weather by providing some nutrients and water from the slot zone when the topsoil had dried out,” Dr Blackwell says.

“Deep tillage equipment can be modified to match CTF systems by removing some tynes or spades in line with the permanent wheel tracks and only cultivating to depth in between.”

Ms Isbister says the best way to decide on a CTF width is to map out the widths of existing machinery operations and tracks using graph paper or the ‘Wheeltrak’ calculator, developed by PrecisionAgriculture.com.au, DAFWA and other partners.

To optimise the effectiveness of deep ripping to 50 to 60cm and implementing CTF, DAFWA recommends:

  • identifying the soil type and location of the hard pan;
  • addressing any associated shallow subsoil constraints to a depth of 30cm (such as water repellence or soil acidity);
  • carefully analysing the best deep ripping and seeding system; and
  • implementing CTF in line with the farm machinery replacement schedule.

Ms Isbister says a compromised CTF system is becoming increasingly common in WA, with a match of 12.2-metre header, 36.6m sprayer and 18m seeder. Table 1 summarises, from grower experience, the benefits and pitfalls of using different operating widths in CTF systems

Dr Blackwell says implementing CTF is the best way to manage the very soft soil conditions after deep ripping, improve crop establishment, minimise re-compaction and erosion risks, and protect long-term investments into compaction amelioration methods.

“There are added advantages in achieving more reliable traction and flotation in wet conditions, reducing waterlogging, improving water use efficiency, using less fuel and potentially needing less fertiliser – all contributing to more profitable grain growing,” he says.

Table 1 Common compatability challenges to matching machinery for
controlled-traffic farming to various machinery operating widths.

Challenges to matching

 9.1 metres

 12.2 metres

13.7 metres 

15.2 metres 

 18.3 metres

 12.2 or 36.5 or 18 metres#

3 to 1 ratio

 Yes

Yes

Yes

Yes

Possible

No 3:1:2

Spreading lime evenly

Yes

Yes*

No*

No*

No*

Yes*

Applying liquid inputs

Yes

 Yes

Yes

Yes

Yes

Yes

Spreading straw evenly

 Yes

 Yes

 Yes, new headers

 No

No  Yes
Swathing  Yes  Can be problematic No No No Can be problematic
Chaser bin on wheeltracks  Yes  Yes No  No No Yes
 # Width of header:sprayer:seeder * Spreader curtain or extra spinners may be an option
Note: ‘Yes’ means compatible in a lot of experience

SOURCE: DAFWA

More information:

Dr Paul Blackwell,
08 9368 3333,
paul.blackwell@agric.wa.gov.au

GRDC Grains Research Updates 2016 papers

Controlled traffic farming fact sheet

DAFWA-Soils WA Facebook Group

NACC Controlled Traffic Farming Technical Manual

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GRDC Project Code DAW00243

Region West