Giant machinery soils farm productivity

BIGGER has always been deemed as better in broadacre agriculture.
Basically the reason is related to productivity.
That's why I describe WA's broadacre Wheatbelt as the land of the giants.
WA manufacturers have made the world's biggest self-propelled and trailed boomsprayers (Sonic Boomsprays), world's biggest chaser bin (Trufab) and the world's biggest seeding rig (Ausplow).
Other manufacturers have provided high horsepower 4WD tractors and class 10 combine harvesters and one manufacturer (Bourgault), equally big seeding rigs.
All good stuff.
But who has thought about what this giant machinery is doing to soil compaction?
Precision Agronomics Australia director Quenten Knight, Esperance, has, and for many years has carried a soil penetrometer with him on farm visits.
A penetrometer is a tool with which to test the compaction level and tilth of your soil.
Penetrometers measure the resistance of the soil in kilopascals (kPa) or in the old language, pounds per square inch (PSI), giving an indication of how compacted your soils are, as an indication of the soil quality.
The lower the kPa, the more oxygen is available for soil microbial life and also the more easily the roots of plants, nutrients and water can penetrate through the soil.
According to Quenten, a lot of WA's Wheatbelt suffers from compacted soils, particularly sandy soils, which provides a barrier to rooting depth.
The solution is deep tillage, which coincidently is enjoying somewhat of a renaissance, after an unexplained lull for two decades.

Deep tillage has been around since the early 1970s and is directly linked to higher crop yields.
So what's the problem?
"Deeper hardpans," Quenten said. "Deep tillage machines have been designed and built for working at depths between 25cm (10in) and 30cm (12in), which has been historically considered the depth at which you achieve crop yield responses to deep tillage.
"But heavier equipment traffic over paddocks means heavier axle loadings.
"As axle loadings increase, the depth of compaction increases and we're seeing hardpans forming down to 60cm (24in), so not even mouldboarding is getting rid of all the hardpans."
This story is being unwittingly exacerbated by clay spreading on sandy soils to remedy non-wetting soils.
"Firstly you have traffic from clay being spread, followed by smudging and then incorporating," Quenten said.
"The salient point is that 90 per cent of compaction occurs in the first pass and the soil can't repair itself.
"With deep tillage, roots have more accessibility to available subsoil moisture and in some cases, do it so well, plants can't hay off at the end of the season."
What Quenten suggests is that while deep tillage is the answer to fix historical compaction, you have to limit machinery traffic on the affected paddocks.
And the best way to do that is by tramlining, or controlled traffic (CT).
In ongoing trials with Department of Agriculture and Food (DAFWA) researchers David Hall and Jeremy Lemon, Quenten is assessing soil compaction and how it relates with deep tillage and CT.
In most sandy soils the plant available water is often limited to between 6 and 8mm per 100mm of soil.
Therefore, the control in figure 1, crop rooting depth ceases at 250mm and only 15 to 20mm of plant available water is accessible to the crop.
In spring-growing conditions, many crops are using between 2mm and 3mm a day, which only allows between five to 10 days without rain before crops start going into stress.
In contrast, the deep tillage trial saw crop rooting depth unrestricted to 70cm (28in).
With 70cm of soil available for crop root growth, the plant available water would be between 42 and 56mm, which allows for 14 to 28 days without rain before the crop moisture stress starts.
DAFWA started a deep tillage trial on Esperance farmer Ross Whittall's farm in 2006.
Ross has sown the paddocks every year since with one permanent tramline through the middle of the trial to prevent the reoccurrence of compaction.
In figure 2, the annual yield increases to deep tillage on this site vary from 50 per cent to more than 150pc.
In figure 3 the crop growth response in lupins is very obvious in the deep tilled plots compared to the control plots.
The results prompted Ross to deep till his entire farm with an Ausplow deep ripper working at 45cm (18in) on 60cm (24in) tine spacings.
A nine metre (30ft) CT system was implemented immediately after the deep till program to minimise any future compaction.
According to Quenten the combination of deep till and CT should be regarded as a system.
"It will accelerate a process towards better crop yields and has the potential for more cost effective input strategies."
The focus is on the system.
"The effects of deep tillage are short-lived with random traffic and the anecdotal belief it has a residual effect for several years is erroneous," Quenten said.
"If you have machinery going over deep-tilled paddocks at different widths, every pass you make will create 90pc compaction.
"In the CT trials on deep tilled plots, there was no resistance to penetrometer probes.
"But come off the plots and resistance returns at depths of about 20cm (8in)."
Generally once soil strength exceeds 2000kPa then roots will struggle to get down.
At 3000kPa you are considered to have a barrier (hardpan) to root growth.
"And at 4000kPa you have major problems," Quenten said.
p More information: Quenten Knight: 0427 720 004.


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