Permanent tramlines in a controlled-traffic farming (CTF) system offer a range of benefits including less soil compaction across the whole paddock, fuel savings, higher yields and better in-crop access, including getting back on to paddocks sooner during wet periods. But tramlines are effectively roads and, just like roads, need maintenance.

Over time, tramlines can compact to more than 20 centimetres deeper than the rest of the paddock. Tramlines become rutted, and ridges form where tyres push soil to the sides of the tramline. A hump can form between tramlines regularly used for spraying, particularly after mechanical soil amelioration and where wheel track width and size are not closely matched.

All can lead to trafficability problems, in turn causing uneven and suboptimal seeding depth, crop emergence and applications of inputs, more wear and tear on machinery and an uncomfortable ride for operators.

Deep, compacted tramlines increase the risk of water erosion if water concentrates in the lines and picks up speed . Wind erosion of tramlines can also be a problem in some areas.

Renovation options

Renovating tramlines re-forms them so they are as flat and even with the rest of the paddock as possible, and provide a firm surface to drive on. An unexpected renovation benefit one grower found was less food and refuge for mice in a CTF system that used chaff decks.

Various companies are developing track renovators. The ideal machine depends on soil type and the condition the tracks are in. On heavier soil types, the soil squelches out either side of the wheels, forming walls or soil piles at the sides of the wheel tracks. Sandier soils tend to compact without forming walls, and therefore need renovators that can pull soil in from a wider span. Heavier soils can cope with a machine that brings the sidewalls back into the tracks.

Growers have restored tramlines using renovators with discs that loosen the sides of the tracks and bring that soil in to the centre. A crumble roller or tyres are then used to level the surface. Spring tyne harrows can be attached at the back to help level heavier soils.

Depending on how much the renovator discs cut up the tramline, additional levelling and rolling might be necessary to firm the surface. If the renovation has left a mound on the track, rolling before the next operation is ideal and prevents machinery slipping off the line of the tracks. If the surface is flat, the next pass of machinery will firm the tracks.

Other types of renovators have blades or a lateral auger flight that bring soil from either side of the wheel track back on to the track, then packs this soil down with compression wheels or a roller. This system will not cut up the track; however, some machines also have following disc coulters that then work the soil and break up clods, followed by a cage roller to flatten the track.

Where a mound of soil has formed between the wheel tracks, some growers use a small disc machine (about four metres wide) to level the tramline zone (the wheel tracks and hump in the middle).

Rocks can be a problem for all machines. Smaller rocks can get pulled into the tramlines; bigger rocks run the risk of hooking and breaking discs. Renovators with individually mounted discs tend to cope better as they will ride over the rocks.

Some growers get decent renovation results when ripping at an angle to the main traffic direction. For this method to work, operators need to rip in the right conditions (not too dry to avoid bringing up big clods) and tow a heavy roller behind the ripper to smooth the surface.

When working

Setting machines up correctly and testing them is critical to avoid problems like hollows on either side of the wheel track or mounds of soil on the track, which can lead to machinery falling off the tracks. Each renovator will have specific adjustments and some growers find they need to make modifications for machines to suit their conditions.

For example, roller height setting is important for renovators with discs. If the machine is not bringing in enough soil, the roller needs to be lifted so the discs can go deeper; if it is bringing it too much the roller needs to be lowered.

Optimal working speed depends on the equipment. Many renovators can operate at 10 to 15 kilometres per hour, but experience suggests operators should start working very slowly, at about two to 4km/hr, then gradually increase the speed, checking the job as they go to determine the best speed. Generally, the worse condition the track is in, the slower the operator needs to go.

Rut location and depth will vary, so operators need to check the machine is working over the ruts.

Renovation can get tricky where tracks vary in depth as renovators are typically three-point linkage machines, so they follow the tractor up and down.

Avoiding traffic in very wet conditions and rotating wheel tracks for spraying so the same tracks are not used every time can reduce tramline rutting.

Renovators using a roller for depth control are often set to manage the most-damaged, deeper track sections. But in areas of the paddock that are undamaged, the linkage is manually controlled and lifted to avoid cutting up shallow sections. A trailed renovator could be better-suited to highly variable tracks.

Some growers farming over contours put a hydraulic top link in to adjust the machine pitch as they go.

Renovators tend to work better with a crumbling soil that has a little soil moisture and stubble. Mixing stubble and soil creates a ‘thatched track’, which helps the soil compact and set.

Anecdotally, some growers have had success pulling renovators using a tractor with a wheel centre that is smaller than the tramlines they are renovating. For example, if the tracks are 3m, using a tractor on 2m wheel centres gives the tractor a smoother track to run on, making it easier on the tractor pulling the renovator and easier for the renovator to do the job.

Prevention

Minimising the extent of tramline damage in the first instance makes renovation easier when it is required. To start, consider wind direction and potential wind erosion when establishing tramlines. Tracks aligned with strong winds are more prone to wind erosion. But beware that aligning tramlines to minimise potential wind erosion on the paddock could result in headland tramlines being highly vulnerable to erosion.

Surface water management requires careful consideration. Tramlines oriented up and down the slope have a lower risk of rill formation, but during heavy rainfall, lines that are too deep, on a greater slope, that are too long or have excess water flow in from elsewhere can act as a channel that concentrates water flow and causes massive erosion problems.

Tramlines across the slope are more likely to lead to rill and gully erosion, and machinery is prone to creeping down the hill, making it harder to stay on the lines. High-accuracy steering guidance systems are usually necessary. However, in dry periods, working across the slope can beneficially trap water in furrows.

Careful consideration to surface water control and farm layout planning should be done before setting tramline orientation.

Avoiding traffic in very wet conditions and rotating wheel tracks for spraying so the same tracks are not used every time can reduce tramline rutting.

Tyre selection and pressure is another important factor. The optimal tyre pressure changes depending on working speed, travel speed, on versus off-road and changing load weights. Over-inflated tyres cause more soil compaction (more pressure on a smaller area), create excessive wheel slip, reduced working efficiency, and make it more uncomfortable for drivers. Under-inflation usually reduces tyre life, although increased flexion (IF) and very-high-flexion (VF) tyres offer increased wall flexibility and lower operating inflation pressures.

Fine-tuning tyre pressure can mean earlier paddock access during wet periods with lower risk of damaging the tracks. Generally, optimal tyre inflation pressure means reduced soil compaction, improved crop recovery after wheel traffic, reduced ruts and therefore less tramline maintenance and less wind and water erosion.

Manually changing tyre pressure is usually too time-consuming, as the optimal pressure changes with axle load, as a tank empties and soil conditions. However, central tyre inflation systems are now available that can change the tyre pressure with a push of a button from the cab or even automatically in some machines.

It is better to renovate before tracks become severely degraded. A bumpy ride is one clue tracks need attention.

Acknowlegements

Bindi Isbister (DPIRD), Ben White (BM White)

References and further reading

Hollaway K, 2020. ‘Renovating to prevent tramline erosion is now a key priority for CTF grower.’ GroundCover Controlled Traffic Farming Supplement March-April 2020. GroundCover - Renovating to prevent tramline erosion is now a key priority for CTF grower.

Isbister B, 2020. ‘Wheel-track renovation critical to controlled traffic success.’ GroundCover Controlled Traffic Farming Supplement March-April 2020.

GRDC publication - Controlled Traffic Farming: Case studies of growers in Western Australia.