Title	Controlled traffic farming - Road beds and root beds
Description	Advice Sheet - Southern Region - August 2000
GRDC Codes*	3.4 Soil and Water Management (DAW505)
Contact	Jeff Tullberg, Ph: (07) 5460 1354, j.tullberg@mailbox.uq.edu.au Don Yule, Ph: (07) 3362 9388, don.yule@dnr.qld.gov.au Paul Blackwell, Ph: (08) 9956 8537, pblackwell@agric.wa.gov.au Ben Jones, Ph: (03) 53 62 2111, ben.jones@nre.vic.gov.au

*Note - this report may contain independently supported projects which complement the work in this GRDC research program.

Are farmers in the southern region missing out on the benefits that can be gained by adopting controlled traffic farming systems?

In many Australian cropping districts, soil compaction by large machinery has been identified by researchers as a major problem.

Yield improvements of 15 percent have been recorded over a wide range of soil types by researchers and farmers. They suggest that it is time for more farmers to give CTF a go.

Other benefits from CTF are:

• Reduced costs - fuel, seed, fertiliser and sprays
• Lower tractor power requirements
• Improved timeliness of operations
• Greater accuracy of placing inputs
• Less operator fatigue
• Erosion and waterlogging control
• Improved efficiency and effectiveness of all operations

What is Controlled Traffic Farming?

CTF is a system where the wheel widths of heavy machinery are matched, allowing the tyres to run on the same permanent wheel tracks.

Raised bed farming systems are a form of CTF specifically used in cropping soils prone to water logging.

CTF is most suited to continuous cropping systems, which exclude livestock from the cropping area.

Researchers have found a key benefit of permanent wheel tracks is the elimination of soil compaction in the crop's root zone. Therefore, the paddock under CTF has two distinct areas - road beds and root beds. Road beds must be identified by not being cultivated or planted.

Compaction and Trafficking

Research by Don Yule, of Natural Resources Queensland and his colleagues found that the first pass of a tractor causes 85 percent of the soil damage recorded by multiple passes. Therefore, to minimise soil compaction and structural degradation in the root zone, a system must be developed that maintains all heavy traffic wheels to the same place.

Compaction in the root zone has been found to limit root growth as roots will only grow easily where the soil strength is less than 3 Mega Pascals. Compaction can also limit crop production by reducing rainfall infiltration and soil biological activity due to reducing the size and number of soil pores.

Growers can see these effects by pulling up plants and examining the soil and roots, and by looking for earthworms.

With traditional traffic systems, even in zero till systems, at least 50 percent of the surface will be run over by the tractor, implements and harvester wheels. Therefore, at least 50 percent of the root zone will be compacted. With CTF the area trafficked can be reduced to 16 percent and root zone compaction caused by trafficking reduced to zero.

To achieve this, tractors, sprayers and harvesters need to run on the same permanent tracks. Implement width should be equal or multiples of harvester width. Convenient widths are 2m or 3m wheel spacings and 6, 9 or 12m harvester width.

In practice it has been found, by Queensland research and extension teams, that most farmers adopting controlled traffic start by matching only the seeding and spray equipment. At harvest soil damage is small, providing conditions remain dry. Researchers indicate damage can be substantial when harvest conditions are wet.

Yield Benefits

Reduced infiltration of water is one consequence of soil compaction. This can prevent crops from maximising potential water use.

Work from Gatton, University of Queensland, found an average 30 percent improvement for rainfall infiltration under controlled traffic systems. This percentage was even larger where crop residues protected the soil surface.

Similar effects were seen in CTF trials on red brown earths in South Australia.

Improved infiltration results in more of the growing season rainfall being available for plant production. Following the rule of thumb that 50mm of available moisture equals 1 tonne of grain, then a 30 percent increase in infiltration offers significant opportunities for improved production.

Work in Western Australia in 1999 found wheat sown under CTF had a significant reduction in screenings. This may relate to improved infiltration and availability of soil moisture.

CTF leaves 16-18 percent of a paddock unsown and used for wheel tracks. This has resulted in the perception that paddocks under CTF will have a yield reduction of 16-18 percent.

This has not been found to be the case. Table 1 illustrates results from Western Australia for wheat yields under CTF and traditional traffic systems. Despite the fact that 16-18 percent of the CTF paddock was under wheel tracks, yield improvements of between 8 percent and 13 percent were recorded.

Table 1: Wheat yields in 1999 from controlled traffic and deep ripping trials in sands in WA (480mm in 1999). All treatments ripped in the same year were significantly different.

Treatment	Deep Ripped	Yield t/ha	percent increase over NT
CTF for 3 years	1997	2.77	13 percent
CTF for 1 year NT for 2 years	1997	2.61	-
NT for 3 years	1997	2.45
CTF for 1 year	1999	2.61	8 percent
NT for 1 year	1999	2.42

NT = normal traffic.

Seeding rates for CTF are the same as for normal traffic, but the seed which would normally be spread behind the tyre may be diverted to the adjacent rows.

Researchers point out that the soil volume, nutrients and moisture available to the plants is the same with CTF. It is only surface area which is affected by permanent tracks.

Other results from Western Australia also counteract the perception that CTF should result in a reduced yield per hectare. This work looked at the impact of late spray and fertilizer applications on crop performance. Where crops were driven over at anthesis, 100 percent yield loss was recorded.

Even with the widest spray booms and spreading width, 16-18 percent of the crop was trafficked.

Energy Benefits

Controlled traffic farming can reduce tractor power requirements by 50 percent. This result comes from work carried out on heavy clay soils at normal tillage moisture.

This saving is due to CTF reducing the energy required to improve traction and eliminating the need to till compacted soil.

In heavy clay soils the energy required to produce traction is 25 percent of the total tractor draft.

Where tines follow behind the tractor tyre the power requirement will increase. This increase will be the same as the percentage of the implement width that is trafficked. Observations suggest that tractors fitted with pneumatic tyres will rarely traffic less than 25 percent of the implement width.

Together these increase the power requirement by about 50 percent. With CTF this power becomes available for productive use allowing larger implements to be pulled or increased work rates. Alternatively, it allows smaller tractors to cover larger areas. Reduced power requirements also resulted in reduced fuel consumption.

Cost benefits

A major benefit introduced by CTF is improved accuracy of all operations. Queensland farmers operating between contour banks have reported time and material input reductions of more than 15 percent when they changed to downslope controlled traffic and row cropping, together with reduced driver fatigue.

Western Australian trials have reported a 3 percent reduction in seeding overlap and a 4 percent reduction in spray overlap when CTF is used. The addition of marker arms on seeding equipment, especially on equipment driven by novice drivers, was found to help reduce overlap significantly.

Where crops with wide row spacing are grown, eg beans and maize, the use of row spraying rather than blanket spraying has been shown to reduce herbicide use by as much as 66 percent.

In newly ripped sites in the Western Australian sands, spraying of herbicides was 10 percent faster with CTF due to reduced rolling resistance.

Other issues

Weed control in tyre tracks can be an issue and more work is being carried out on this in Western Australia.

Controlling woody weeds has been a problem in the northern districts as herbicide is less effective in the dusty tyre tracks or on the plants, which are stressed due to being squashed under the tyre. The use of two spray nozzles in the tramline and system layouts, which allow boom sprays to be driven down alternating tyre tracks, has been found to improve tramline weed control.

Don Yule from the Queensland Department of Natural Resources points out another important issue - precision. CTF helps farmers to be more precise with their operations, and they can do each operation in exact relation to a previous or future operation. The introduction of better guidance and automatic steering systems will enhance the benefits already being demonstrated by farmers adopting CTF.