Consultant’s Corner: Wheels are moving on Controlled Traffic Farming – The research view
Date: 06 Jul 2015
Researchers who are reporting heightened grower interest in Controlled Traffic Farming (CTF) advise that the transition to CTF need not be costly or difficult.
The implementation of CTF systems can significantly improve grain yields on compacted soils, which have been calculated as costing agriculture in Western Australia alone at least $333 million annually.
Department of Agriculture and Food WA (DAFWA) economist James Hagan is involved with a Grains Research and Development Corporation (GRDC) funded project aimed at minimising the impact of soil compaction on crop yield.
Soil compaction is one of a range of soil constraints that cause significant production losses to growers each year.
To help meet this challenge in WA, the GRDC is investing with other research agencies in a $33 million, five-year Soil Constraints – West initiative to develop and deliver practical management solutions to issues including compaction.
Mr Hagan said renewed grower interest in CTF could be attributed to a number of factors.
“These include the need to improve access to stored subsoil moisture; growers wishing to minimise the need for costly ripping programs; and to protect investments made in amelioration techniques such as spading or mouldboard ploughing,” Mr Hagan said.
“While transitioning to CTF requires farm businesses to plan for the long term in choosing operating widths which will be suitable for a significant period of time, the benefits of adopting CTF certainly appear worth the effort.”
Increasing cost of compaction
Mr Hagan said that with the weight and size of farm machinery increasing, it was likely that the cost of compaction was also increasing.
“Not only are the impacts of compaction getting worse, it is becoming more expensive to fix,” he said.
“As compaction moves deeper through the subsoil to depths of 60cm and beyond, regular deep ripping programs, which may previously have been considered as an alternative to CTF, are no longer able to reach all the compacted layers.
“This is especially critical on deep sands where unrestricted root growth regularly needs to exceed 2m, as restricted root growth will limit plant available water and therefore yield potential.”
Mr Hagan said average rainfall had declined over the past 15 years in many WA cropping areas, which was likely to worsen the impact of compaction and other soil constraints on crop yields.
“This decline in annual rainfall has often been accompanied by dry spells within the growing season, with periods of four to eight weeks of minimal rainfall and higher temperatures,” he said.
“This period of minimal rainfall makes plant access to stored subsoil moisture a critical factor in the ability of crops to survive these periods of stress without incurring major yield penalties.
“The effect of this increasing reliance on access to stored moisture during the growing season means that addressing subsoil constraints such as compaction and acidity, which limit plant access to the soil profile, is going to be increasingly important in the future.”
Minimising the impact of soil compaction
Mr Hagan said numerous paddocks across the WA grainbelt had been measured for ‘moist penetration resistance’ in the past 15 years, providing a measure of the level of soil compaction.
“Data collected from these samples suggests that 80 per cent of sandplain paddocks had moist penetration resistance of 3MPa - which severely restricts root growth - at a depth of 30cm,” he said.
“More concerning is that 40 per cent of paddocks had resistance of greater than 3MPa at 50cm.
“In the most extreme examples of this compaction at depth, a carry grader used
for claying during a wet summer created a soil penetration resistance of greater than 3MPa to a depth of almost 70cm.
Mr Hagan said it was possible for uncontrolled farm machinery traffic to cover a significant portion of a paddock in a single year, and more than 90 per cent in two years.
“This is especially likely to happen if traffic directions change,” he said.
“A standard scenario with a 14m (45 foot header), 15m (50 foot seeding bar), a 36m (120 foot) boomspray and a chaser bin - not running on tramlines - can result in 46 per cent of a paddock carrying traffic in a season.”
Mr Hagan said the perfect scenario for minimising the impact of compaction was a fully matched CTF system, typically accomplished via a 1:3 ratio, where the header and seeder were one-third the width of the boomspray.
This system resulted in 10-12 per cent paddock wheel track coverage.
“But while a perfectly matching system is optimal for minimising the impact of compaction, there are often compromises that need to be made in order to work in with existing production systems,” Mr Hagan said.
“Considerations include straw, spreading widths for fertiliser and lime, time constraints for spraying and even basic factors such as the size of seeding and harvest programs.”
Mr Hagan said a current popular compromise, which accommodated the need of many growers for large seeding gear, was a 1:2:3 fit, with the harvester a third the size of boom spray and the seeding bar half the width of the boom spray.
“For example, a 12m (40foot), 18m (60foot), 36m (120foot) system on 3m centres, whilst not perfect, reduces the tracked percentage to approximately 18 per cent,” he said.
Growers using ‘compromised’ CTF systems are often planning to move to either one 24m (79 foot) wide seeder or two, 12m (40foot) seeders to replace their one 18m (60 foot) seeder, as part of their progression to a better matching system.
Calculating the cost of compaction
Mr Hagan said that while it was useful to know the approximate percentage of traffic driving over a paddock, it was more important to understand the yield penalty that this caused.
“Various WA trials suggest that yield penalties on deep sands can range from 20-47 per cent, while penalties on deep duplex soils average 22 per cent,” he said.
Mr Hagan said the best way to calculate yield benefits that could be achieved by moving to CTF was to compare the area currently trafficked with the area that would be trafficked under a CTF system.
“Yield benefits can be calculated by multiplying the difference in tracked area by the identified yield penalty for the relevant soil type,” he said.
Moving to CTF
Mr Hagan said moving to a CTF system required minimal effort if all gear was already at complementary widths and the only necessary changes were wheel spacing modifications.
“For others, it requires replacing machinery to create a system that works effectively,” he said.
“It is important in either scenario to forward plan carefully and consider long-term requirements.
“In the first, easy scenario, it is important to consider whether current operating widths are likely to fit in with your future plans.
“In the second more difficult scenario, it is important to recognise that while replacing all machinery to fit a system sounds expensive, it can be worked into your standard machinery replacement schedule.
“With purchases worked into a standard replacement program, the cost of moving to CTF can be minimised and some purchases may be brought forward once the farm business is close to reaching a full match.
“A proven method for creating a machinery investment plan is to note down current machinery, its age and when it is due to be replaced.
“This can help create a schedule for moving to CTF.
“In WA grower case studies conducted for a CTF technical manual, most businesses stated that their total cost of moving to a CTF system was less than $20,000 - largely attributed to the cost of moving wheel widths.”
Protect your investment in costly soil renovation
Mr Hagan said growing numbers of farms across WA were using mouldboard ploughs or rotary spaders to improve non-wetting soils, incorporate lime or bury resistant weeds, as well as remove compaction in the top 30cm of the soil.
“These treatments are producing some excellent yield responses in the same season, with some mouldboard treatments still delivering benefits seven years on if traffic has been controlled,” he said.
“A driving factor behind the adoption of these amelioration techniques has been the strong early returns that they can generate.
“However, a significant factor influencing the true value of costly subsoil amelioration strategies is the length of time for which the benefits persist.
“By protecting the benefits provided by costly subsoil amelioration, your return on this investment can be increased significantly.”
Soil compaction workshops, hosted by DAFWA and supported by the GRDC, were held in Geraldton and Bencubbin in WA in February, 2015, in order to provide information to growers interested in implementing CTF systems.
CTF information was also provided at a ‘Soils Masterclass’ workshop at Scaddan in March. This event was organised by the GRDC’s Esperance Regional Cropping Solutions Network (RCSN) in conjunction with the South East Premium Wheat Growers Association (SEPWA) and DAFWA.
DAFWA researcher Paul Blackwell, who was involved with the events, said he was encouraged to see a positive shift in grower attitudes towards CTF.
“There is a big change in grower awareness of CTF and their commitment to move towards implementing this system,” he said.
Dr Blackwell said that once a farm business had decided on a CTF schedule, everyone involved in the business needed to ‘own’ that plan, which could take years to implement.
“I suggest making that plan visible – such as pinning it to the fridge door – so that everyone sticks to it,” he said.
“This can help to discourage anyone from making ‘bargain’ purchases that don’t fit in with the schedule.
“CTF doesn’t have to cost the earth. Any business should be able to transition to this system fairly painlessly.”
Useful resources on CTF and compaction include:
- May 2015 DAFWA Northern AgMemo article Line up your machinery to reduce compaction by searching ‘AgMemo’ and ‘compaction’
- Controlled Traffic Farming Technical Manual, including grower case studies, available on the Northern Agricultural Catchments Council (NACC) website by searching ‘Controlled Traffic Farming’
- DAFWA Deep ripping for soil compaction article by searching ‘deep ripping’
- DAFWA Identifying soil compaction article by searching ‘compaction’
- GRDC Controlled Traffic Farming Fact Sheet
- Wheeltrack Calculator (to estimate your wheeling percentage)
James Hagan, DAFWA
08 9956 8520
Paul Blackwell, DAFWA
08 9956 8555
Natalie Lee, Senior Consultant, Cox Inall Communications
08 9864 2034, 0427 189 827
GRDC Project Code DAW00243