Precision farming in the northern grains region
Soil compaction and controlled traffic farming

Key points

• Soil compaction is the degradation of soil structure.
• Wet surface soil is at most risk, particularly clay soils.
• Compaction leads to rough seedbeds, poor crop establishment, slow root growth, reduced infiltration and reduced crop yields.
• Tracked tractors produce similar compaction to wheeled tractors but over a smaller area.
• Compaction is almost impossible to prevent - aim to avoid or control it.
• Repair compaction by planting "break crops" or by deep ripping (dry soil).
• Guidance systems can improve track layouts and provide steerage assistance.
• Controlled traffic can improve traction by reducing fuel usage, facilitating zero till systems, and separating traffic from cropping zones.

Soil compaction

What is soil compaction?

Soil compaction occurs when a pressure exerted by machinery tyres, tines or livestock compresses the soil increasing its density. Denser soil leads to reduced crop establishment, poor rainfall infiltration and lower crop yields, and can increase runoff and soil erosion. Estimates by McGarry et al. (1999) suggest that soil compaction in the Murray-Darling basin alone has caused $144 million of damage.

How does soil compaction occur?

Compaction occurs most often in moist or wet soil. In freshly cultivated soil, the first pass does the greatest damage usually in the top 20-30 cm of soil.

Representation of the type of forces acting on the soil as a tyre passes across a field. (Adapted from McGarry 2001).

In conventional tillage systems, most of the surface area of a paddock receives at least one wheel pass during a fallow (McGarry 2001), and even in zero tillage systems, the surface area is covered by wheel tracks from harvesters, sprayers and planting tines.

What does compaction look like?

On the soil surface, compaction is likely where there is "cloddiness" with soil resisting breakup by rain or tillage, deep ruts, ponding or pushed and deformed soil from tyres. In the soil profile, dense impenetrable layers are found, commonly with horizontal, plate-like structure (i.e. hard-pan).

Compaction is more likely in the subsoil. Dense subsoil can also have a "massive" (or featureless) appearance, a puggy feeling with peds breaking with force or tearing rather than along normal fracture lines.

Associated symptoms include poor establishment adjacent to the wheel tracks, water ponding in tracks and headlands, distorted crop root systems ("right angle" disease), crop lodging and "thirsty" crops due to shallow rooting. Crops with thick taproots (e.g. safflower, lupins, canola) have a better ability to penetrate these compacted layers than those with fibrous roots (wheat, barley).

What's the link between compaction and water content?

Soil water content at the time of traversing or cultivating a paddock is the greatest determinant of the severity of the soil compaction. Of less importance are factors such as tractor load, implement design, speed and tyre size, type and inflation. All soils can be compacted, but clay soils are most prone to compaction as they hold more water for a longer time than a sand/loam (McGarry 2001).

The pores in moist soil contain water. This water acts as a lubricant, so under a load, soil particles move more readily and pack tighter. Compaction commonly occurs away from the actual contact point of the implement or tyre with the soil. As the energy wave moves away from this contact point, soil particles are re-aligned and packed. Soils wetter than their "plastic limit" will smear and compact under tyres, implements and hooves. Clay soils are prone to compaction at depth as they are likely to be wetter than their "plastic limit" below the surface. To determine your soil's "plastic limit" use the method demonstrated in the Video 'Soil Physical Damage - Get Ahead of It!'.

Avoiding soil compaction by machinery

Regardless of how you manage your cultivation, some damage will occur. If high tyre pressures have to be used, use tall narrow tyres in preference to small wide tyres or duals. When trucks and field bins are used at harvest, confine travel to one area and do not drive all over the paddock.

The optimum soil conditions for crop production (soft, friable, permeable soil) are quite unsuitable for efficient traffic operation, and vice versa.

Track layers have the advantage of compacting considerably less area for the same amount of power. Dual and radial tyres do not reduce compaction when used at the same tyre pressures as single or conventional tyres. Wheel slip does not increase soil compaction unless it is greater than 15%. Compaction risk is greatest during wet harvests.

Restoring damaged soils

Cultivation will be effective only in soil that is dry below the tillage depth. Cultivate only the damaged areas of the paddock, leaving permanent wheel tracks uncultivated

Deep ripping is rarely necessary as soils, especially clays, are seldom dry enough to achieve a positive effect. If considering ripping check the soil water content in the ripping zone. If wetter than the "plastic limit" do not rip. Do not attempt to rip-up deep-compacted subsoils in one operation. Use repeated shallow workings and allow the weather to break down the exposed clods and produce a seed bed. Consider "break crops" rather than ripping - crop roots create soil pores and promote the formation of cracks in cracking soils.

A robust planter is needed for successful crop establishment in compacted soil. Adequate weight and heavy construction are needed to ensure consistent penetration of soil openers to the desired planting depth.

Field studies have shown that most damage occurs in the top 30 cm of soil. This compaction remains unless repaired. This can be achieved through deep cultivation of dry soil, or the growing of "break crops" to dry and crack clay soils.

Controlled traffic farming system

What is controlled traffic?

 

Controlled Traffic Farming (CTF) is about separating traffic zones from cropping zones. This means that the same wheel tracks are used for every tillage, planting, spray and harvest operation (shown above). In practice, this usually means all tractor and harvester wheels are aligned on the same tracks - although significant advantages are still available simply by using the same wheel track for each tractor and spraying operation. CTF impinges on many facets of a cropping system including weed management, water management, crop production, crop nutrition, disease management, and farm machinery. Currently, it is estimated that 250 000 hectares are currently under a CTF system in the northern cereal region.

Why control traffic?

Controlled traffic improves traction and field efficiencies, avoids damage to soil structure through continual compaction and re-loosening and facilitates zero till management. The normal situation under conventional tillage is shown in Table 1.

Table 1. Power used in conventional tillage.

Power usage	% of total power available
Tractor power used in soil compaction	20 - 30
Implement power used to break up soil compaction	15 - 25
Wheel tracks as proportion of working width	15 - 20
Total tractor power absorbed in its own wheel tracks	50 - 75

A 50% reduction in fuel use can be expected from using untilled permanent wheel tracks even when cultivating. The crop loss from unplanted wheel tracks is an issue with narrow spaced rows. However, crop roots explore under the tracks and crop yields are greater from the non-trafficked areas.

Figure 1 depicts the wheel track (footprint) coverage of a grower who moves from conventional tillage to the zero-till system, and then to controlled traffic. This comparison is based on a 3 m track system. The harvester, boom spray, and cultivator/tractor are multiples of this 3 m (in this case 9 m). It is possible to use larger equipment in this set-up (e.g. a 15 m boom spray).

Figure 1. A comparison of wheel tracks

Most farmers without controlled traffic have poorly matched machinery widths which contributes to about 80% wheel track coverage. Moving to no-till reduces coverage to 46% while controlled traffic can reduce this even further to less than 15% (Powell and Chapman 1998; Walsh 1998).

What are the benefits of controlled traffic?

Through the use of controlled traffic, tractive and field efficiencies are improved, damage to soil structure through continual compaction and re-loosening is avoided, and zero till management is facilitated. A reduction in fuel use of up to 40% may be expected on some soil types from using permanent wheel-tracks even when cultivating, due to reduced draft and improved tractive efficiency.

Research results indicate that CTF, in association with zero tillage, significantly improves water infiltration into the soil, and thereby increasing the amount of moisture available for crop growth. The crop loss from unplanted wheel tracks may be an issue with narrow spaced rows, but crop roots explore under the tracks and crops yield better from within the non-compacted areas. This effect, along with the greater moisture storage, generally leads to a potential increase in yield over the whole paddock.

Other potential benefits include:

• reduced operating costs by lowering fuel usage, less time/labour, saving on seed, sprays and fertiliser, and improving efficiency (10-25% savings can be expected immediately)
• control of soil erosion and increased moisture retention, provided properly designed layouts are used
• increased productivity
• improved farming practices and opportunities due to easier management
• enables maximum gain to be derived from zero-till farming
• side-dress fertilising if required
• inter-row cultivation and planting
• furrow planting which increases planting opportunities, trafficability, and timeliness
• improved integration and management of precision farming tools and systems.

Guidance systems and controlled traffic

What are guidance systems?

The commercial release of guidance systems in the last 5 years has provided enormous potential for growers wishing to initiate controlled traffic farming. Guidance systems are made up of several interlinked components:

• a global positioning system (GPS) to locate the exact position of the vehicle,
• a steerage assist tool which might be a cab-mounted light-bar or an on-board display screen, and
• a steerage assembly housed near the drive-shaft that adjusts the direction of movement (only in automated systems).

Which system suits my purpose?

A number of guidance systems are available at various prices depending on the extent of steerage assistance required (Table 2).

Visual guidance systems offer steerage-assist options where accuracy is not essential. However, most of these systems provide accuracy to less than 1 metre. Automated systems are applicable to applications, such as row cropping, where accuracy would need to be less than 10 cm. Automated systems have the added benefits of less driver fatigue and improved confidence of night operations over the visual systems.

Table 2. Overview of types of guidance systems available (Source: Conservation Farmers Inc./Kondinin 2000).

Level	Cost	Examples
Visual	$12,000-35,000	Beeline Navigator Visual  OnTrak Pro/Lite, AgLeader PF3000  Parallel Tracking FarmLap Visual (Precision Farming Australia)   FarmTrax/Saturn Parallel Swathing Options Satloc Lite
Automated	$25,000-90,000	Beeline Navigator  RowGuide AutoFarm  FarmLap (Precision Farming Australia) AutoPilot

The accuracy of these systems is related to the type of GPS used. High-accuracy GPS units, known as real-time kinematic (RTK) receivers, have superior hardware which enables positions to be reported to within 5 cm. A local base station may also be necessary. Differential GPS units provide accuracy to within 1 m using correction signals received from either coastal beacons or satellites.

Commonly asked questions

Does CTF imply zero tillage?

CTF makes it much easier to move to zero-till, but it is also of benefit to farmers employing tillage based farming practices. CTF provides benefits in terms of reduced input costs, reduced energy and capital costs and increased precision of operations, independent of whether farming practices are based on tillage or no-till. Elimination of the need for spray markers, ability to spray at night and avoidance of wheel-track depressions at planting have been noted as major benefits by zero-till farmers. Many farmers who considered zero-till too difficult in random traffic farming are now moving back to zero-till under controlled traffic.

Will I need to purchase new machinery?

Most farmers currently employing CTF have not purchased new machinery. In many cases, they have been able to obtain the benefits of CTF using existing machinery. The addition of marker arms and the removal of planter/cultivator tines from behind the tractor tyres, and where appropriate the removal of the outside dual tyres from the tractor has been all that was necessary to test the system.

The harvester probably causes the worst compaction, and is the most difficult to match wheel-tracks. What is the best approach?

There are now tractors available for which the manufacturer will provide warranty for use on 3 metre wheel track. As the range of such tractors expands, this will become a realistic option allowing the tractor to be matched to the harvester.

In the interim, there are two approaches to handle the harvester width. The easiest is to forget about it. This enables the farmer to pick up many of the benefits of CTF and still use his existing harvester or harvest contractor. The other approach is to match the width of the harvester to the planter or cultivator, or even half this width. This provides a major advantage, even if the harvester does not run on the main permanent wheel tracks. The harvester tracks are in a fixed relationship to the main wheel tracks so that crop rows may be organised to avoid them, or the appropriate planting tines may be set up to account for deep wheel ruts. Narrow tyres fitted to the header may reduce stubble trampling and help isolate compaction.

How does CTF work with contour banks or strip cropping?

Very well! Many down slope layouts involving work-over contour banks have been set up in South and Central Queensland, and South Burnett areas. In large storms, the wheel-tracks, the planter furrows and the crop rows tend to maintain the flow spread over the paddock until it is safely disposed into the contour bank or waterway. The tendency for concentration of flow and rilling inherent in contour layouts is reduced. Similarly, on steeper slopes in the South Burnett, furrowed layouts angled to the prevailing land slope have been developed to limit furrow slope but eliminate the inherent inefficiencies of contour farming. Research is currently underway throughout central and southern Queensland to examine erosion issues related to layout.

CTF is ideally suited to flood plain areas, where strip cropping is normally employed. In this situation, CTF layouts have been placed at the same orientation as the strip crops to provide maximum protection. By facilitating the use of zero tillage and maximisation of stubble cover, CTF provides additional protection against flood flows.

Is there any proof of the claimed yield benefits?

The best available information is from Gatton College where 10 years of replicated trials have produced an overall average yield improvement of 14%. Much of this benefit may have come from the significantly improved water infiltration and storage in the Controlled Traffic treatments. (On average an additional 100 mm per year is stored approximately.) There are many farmers reporting yield improvements, but these are difficult to compare as most farmers have elected to convert their whole farm to CTF.

Are there benefits in moving to a rubber- tracked tractor?

Rubber tracked tractors can provide benefits in CTF systems, which can offset their higher purchase cost, when compared to wheel tractors. The smaller Caterpillar Challenger models are available on 3 metre track width to match many grain harvesters. Tracked vehicles can also produce narrower tracked zones for equivalent power, reducing the percentage of the paddock lost to wheel-tracks. Tracked vehicles are designed to provide high linkage lift capacity for wide mounted and semi-mounted implements.

How can I develop the confidence to change over to CTF on my farm?

The best start is to see CTF as a farming system, not just a farming practice. The whole system has been embraced by groups of farmers in central Queensland, the Darling Downs, the South Burnett and in northern New South Wales. Many farm visits and field days are occurring, arranged by agencies and farmer groups. It is important to get involved in field days and farm visits to see the system in action and talk to the farmers using it.

How do I get started?

It is recommended that you start with a layout plan. Your local NR&M soil conservationist should be able to help with this. Marking the layout on the ground is usually done with marker arms after pegging out the key line chosen on the layout map. Alternatively contractors are now available to layout very accurately using the Global Positioning System (GPS) for less than $5 per ha.

Controlled traffic is worth investigating.

Further information

• ACIAR (Australian Centre for International Agricultural Research) report into CTF in China and Australia. (http://www.aciar.gov.au/web.nsf/doc/JFRN-5J472T/$file/IAS10.PDF)
• Bray SG, McGarry D, Littleboy M (1997) Soil Physical Damage - Get Ahead of It! QDNR Video. DNR-D 149/2. Brisbane, Australia.
• Conservation Farmers Inc. (2000) The Farmers' Guidance and Precision Farming Expo, Roma Qld. (CFI/Kondinin/Grainco/QDPI). 45p.
• An overview of precision farming management available through The Farmshed Online http://www.thefarmshed.com.au/features/precision/content.jhtml .
• GRDC Research Update on CTF (http://www.grdc.com.au/growers/as/traffic_farming.htm)
• Kondinin Group (July 2000) Controlled traffic farming report.
• McGarry D, Sharp G, Bray, SG (1999) The Current Status of Soil Degradation in Queensland Cropping Soils. DNRQ990092. (www.nrm.qld.gov.au)
• McGarry D (2001) NRM facts: Soil compaction in cropping soils. QNRM01181. (www.nrm.qld.gov.au)
• On-line module on CTF (http://www.bettersoils.com.au/module6/6_4.htm)
• Powell G, Chapman W (1998) Controlled traffic, Croplink, DPI, Dalby
• Walsh P (1998) Controlled traffic: reduce overlap to save on crop inputs. Farming Ahead 83: 50-51, Kondinin Group
• Wylie P (2001) Assessment of the potential benefits of precision agriculture in Australia. (GRDC, Kingston.)

See also the other notes in the Precision Farming in the Northern Grains Region series.

• What is "precision farming"?
• Application of GPS in farming systems.
• Using variable rate technology (VRT) in cropping land.
• Identifying subsoil constraints.

Further information can also be obtained through consultants dealing in field layouts, CTF systems, and contour siting. Examples in southern Queensland include:

• Wayne Chapman, Waysim Consulting, ph. (07) 4627-3434 email: waysim@bigpond.com
• Tim Neale, Spot-on Ag, ph. (07) 4662-3913 email: spotonag@bigpond.com
• Don Yule, Yule Consulting, ph. (07) 3870-0454 email: yules@bigpond.com
• Stewart Cannon, ph. (07) 4637 0228 email: ruralpropertydesign@bigpond.com

CTF is being embraced by dryland growers throughout Australia. Check out some of these perspectives at Grains Research & Development Corporation Grower Updates on CTF (e.g. http://www.grdc.com.au/growers/res_upd/south/02.htm)

Key contacts

The DPI&F Business Information Centre (phone 13 25 23) provides generalist information and specialist referral services for the cost of a local call from anywhere in Queensland. The Business Information Centre is open Monday to Friday 8 a.m. to 6 p.m. (excluding public holidays).

Last updated May 2004
FS0405