Take home messages

• Many soils are prone to compaction even with current no-till farming systems.
  
  
• An effective no-till sowing system is one that can handle the stubble residue and soil tilth conditions in any given year.
  
  
• 10 to 15% improvements in cereal crop yields have been measured in Australia as a result of reduced soil compaction. Sandy soils are some of the worst for compaction due to low clay content.
  
  
• Significant operational efficiency benefits exist with controlled traffic systems compared with our conventional minimum and no-tillage systems.
  
  
• New technology with respect to guidance equipment and a considerable reduction in the cost of such technology increases the economic viability of introducing controlled traffic systems.
  
  
• Many farmers in Australia require only a few modifications to farm equipment to implement controlled traffic systems.

Benefits of a controlled traffic farming system

Many farmers are now practicing no till systems and it is important that traffic management is considered to avoid the need for future deep ripping to ameliorate compaction effects. However even under conventional tillage systems controlled traffic can still offer some significant advantages.

There are many benefits of controlled traffic described by Rainbow and Long (2001) and these include

• Reduced costs. Considerable savings occur with fuel seed chemical and fertiliser. Reduced overlapping can reduce fertiliser seed and spray applications by 4%. Up to 10 % input cost savings have been reported (Blackwell et al. 2004) Where wide row spacing crops are sown (beans and summer crops) inter-row spraying can reduce chemical applications by 66%.
  
  
• Reduced draft requirements. Smaller tractors are being used as less power is required to pull the same machine at sowing. In heavy clays power requirements can be reduced by as much as 50% with normal seeding moisture (Tullberg 2001). This results in significant reductions in fuel use. It is feasible on a 250 hp tractor to have a reduction in power requirement of up to 50 hp in controlled traffic compared to a conventional system.
  
  
• More timely operations. Herbicide and fertiliser applications can occur at more appropriate times due to increased trafficability in wet conditions. Crucial operations such as fungicide application to coincide with rainfall events can take place sooner reducing disease levels. Post seeding fertiliser applications can occur during wet periods increasing the efficiency of these applications.
  
  
• Improved spray window and night spraying accuracy. With defined permanent wheel tracks or global positioning guidance systems this increases the accuracy of night spraying operations giving a wider window of opportunity for spraying operations to take place if poor weather conditions occur regularly.
  
  
• Reduced fertiliser and herbicide application costs. Applications can be made with farmer equipment rather than relying on contract operators. Better weed and disease control is likely with higher water rates being used with ground application units. Less over and under-dosing results in less crop damage and fewer weed escapes.
  
  
• Better placement of seed and fertiliser. Plant emergence is more even and uniform and combined with more accurate fertiliser placement results in increased plant nutrition and better plant growth.
  
  
• More accurate sowing systems allow for more accurate herbicide and fertiliser placement. Between row weed control is already practiced in wide row spacing crops. A combination of between row shrouded spray units with highly accurate +/- 2 cm autosteer tractors and guidance equipment allows the use of non - selective herbicides for weed control in winter crops. This will delay the development of herbicide resistance to selective herbicides. Inter-row or side dressings of fertiliser are also possible to increase fertiliser use efficiency.
  
  
• Opportunity for inter-row sowing. With highly accurate +/- 2 cm autosteer tractors it is possible to sow between the previous year's crop row increasing stubble residue handling with less management required at harvest. Research results in Australia have demonstrated a 6% increase in barley crop grain yield due to less soil borne root disease inoculum in the crop row (McCallum 2005).
  
  
• Improved soil drainage with raised beds. In the 500 mm + annual rainfall farming regions where land is relatively flat causing poor surface drainage raised beds offer some significant advantages. The system is a form of controlled traffic which also improves water drainage.

Machine track width

• Matching agricultural machine track width is the issue that creates the greatest degree of difficulty for farmers. It is unlikely that any farmer will sell an entire farm plant in one step to enable the transition towards matching of tractor wheels. The ideal is to align all tractor implement and harvester wheels on wheel tracks on the same track width. For most farmers in Australia the options are generally 2 m track widths (distance between the centre line of each wheel) which generally require the least amount of modification and adjustment to tractors' air-seeder carts and spraying equipment.
  
  
• To align harvester wheel tracks with other equipment it is necessary to spread tractor and other equipment axle lengths out to 3 m centres (Figure 12). This is relatively easy on many tractors with adjustable track width stub axles and many front wheel assist tractors can have axle spacers inserted to increase the front axle spacings. Some farmers have inserted cotton reel inserts in the front axle to widen out spacings on early model front wheel assist tractors however this does cause premature bearing failure in the hub assemblies.

Controlled traffic tramline layout

• Length of run - It is not uncommon for tramline runs in Australia to be up to 3 to 4 km long. The longer the tramline run the greater is the efficiency of the system as turns on the corners are kept to a minimum.
  
  
• Access roads - These are important in very wet conditions on clay soils and are best placed at the end of the longest tramline runs. This allows easy truck access for re-filling of crop inputs while minimising truck access onto the field itself. Loaded trucks due to their high axle weights and small tyres with high pressures create significant compaction effects in the field.
  
  
• Orientation - Generally most farmers lay out the tramline direction which allows the longest tramline run. This is based on a series of factors to minimise interference from existing fence lines creeks and trees. A little hint when setting up tramlines across a farm is to align tramlines with each other each side of a fence line. This allows for tramlines to pass through and seeding efficiency increases if the fence line is removed in the future.

Agronomic Issues

• Need for deep ripping - Using the simple rod and palm penetrometer method described in section 4 the potential need for additional deep ripping can be assessed. It is important to understand that deep ripping without controlled traffic can lead to additional problems with deep soil compaction with short term benefits to crop production. Deep ripping in Australia in the absence of controlled traffic may only last for 1-2 seasons. Deep ripping should be carried out when soil is below the 'plastic limit' of water holding capacity which is a soil engineering measurement that describes the point which soil passes from the soil to a plastic state or is the lowest water content at which the soil can be rolled into threads of 3 mm in diameter without the threads breaking into pieces.
  
  
• Permanent tramline wheel tracks versus sown or fuzzy tramlines - There are several options of controlled traffic tramline systems that have been used in Australia. The simplest and most popular has been permanent wheel tracks as these can be constructed and defined with simple end-marker arms at planting with the sowing rows in the wheel tracks removed. This is usually only 1 sowing row per wheel track. This has had some problems with weed competition in the wheel track particularly an Australian grass weed called annual ryegrass or Lolium rigidum. For this reason many farmers are now going to a system called fuzzy tramlines where crop seed is scattered or sown at very shallow depth in the wheel tracks but without fertiliser to save cost but compete with weeds. This has been preferred to the option of sowing tramlines as trafficability benefits in wet conditions are lost when this is done.
  
  
• Controlling weeds in permanent tramlines. - Some farmers have used shallow cultivation in the wheel tracks to control weeds however the timing of this is very critical to get effective control and its practice has not been all that successful particularly as it reduces trafficability benefits in wet soil conditions and can contribute to wind and water soil erosion in the wheel track. Some farmers have dumped the chaff from the harvester into the wheel track to create a mulching effect to control weed growth. This is referred to as furry tramlines.
  
  
• CT farming on sloped soils - Controlled traffic has been successfully implemented on fields with significant slopes. The benefits of controlled traffic on slopes are even greater as water infiltration and hence run-off and erosion are reduced particularly when implemented in conjunction with no-till and stubble residue retention. Many farmers have found sowing straight up and down the slopes preferable to sowing across the slope as it is more difficult to hold a straight track position particularly with a trailing air-seed and fertiliser delivery cart. Contour banks that mitigate water erosion can be engineered if there is sufficient topsoil so the planter can seed straight over the top as the planter seeds up and down the slope.

Machinery Modification issues

• Implement and tramline swath width - Seeding equipment is ideally matched up to the same maximum width as the harvester front to minimise soil compaction at harvest. Spray booms have to be in multiples of either 2 or 3 times the seeder width (Figure 13). Spray boom widths 3 times the seeder width are preferable as it makes overlap management of the first and last run easier to manage. Many now have for example 12m seeding equipment with 24 metre or 36 metre boom sprays which can spray along every second or third sowing run.
  
  Figure 13. Spray boom tramline options to begin spraying tramlines for 2x and 3 x seeder width.
  
  
  
  
• Harvesting and chaser bins - Harvesters with 11 metre pick-up fronts are commonly offset and cause difficulties for matching up and back operations. Harvester pick-up fronts that are centred and have a belt or draper delivery system are now available in Australia with widths of up to 14 metres. Grain tank discharge auger extensions sometimes must be extended to allow for the wider pick-up fronts. Also if chaser bins are to be kept to the same wheel tracks an offset loading chute to the chaser bin tank is required to move product to the centre of the grain bin.