Key points

• The fuel and power savings from controlling traffic depend on soil type and the farming system.
• Savings in fuel use and power requirements of about 15 per cent or more have been observed by no-till croppers in the southern low-rainfall zone.

Saving fuel and power are some of the key benefits of controlled-traffic farming (CTF) systems, but there are many factors that can affect these savings.

In the early days of CTF, during the mid-1980s, there was a big focus on fuel savings and reported machinery power reductions of up to 50 per cent.

These results applied at a time when stubble-mulch tillage was a common practice on the black, self-mulching soils in Queensland.

But the potential power savings depend very much on the soil type and farming system.

The heavy black clay soils of Queensland and northern New South Wales are more 'plastic' than many soils of southern or Western Australia. In other words, they usually deform more under load, and absorb more energy from a tyre rolling over them or a tyne pushing through them.

Machinery power requirements are reduced by CTF in two ways:

• firstly, by reducing the motion resistance (or rolling resistance) of vehicles travelling over permanently compacted wheel tracks; and
• secondly, by reducing the tillage draught required to pull implements, such as seeders, through the soil.

Motion resistance

Reducing motion resistance generally has the biggest impact on direct energy requirements when controlling traffic in no-till systems. This is because less deformation (soil movement) occurs under tyres or tracks on the stronger soil of permanent traffic lanes, reducing the force required for motion.

A GRDC investment led by the Australian Controlled Traffic Farming Association (ACTFA) - in partnership with Agriculture Victoria, the South Australian Research and Development Institute (SARDI) and local farmer groups - looked at the impact of compaction at four sites in the low-rainfall zone (LRZ) of Victoria and South Australia.

Motion resistance, evaluated as part of a postgraduate study by the University of Southern Queensland, was highly variable. But controlling traffic produced a mean reduction of about two per cent of equipment weight.

This may not seem much, but for a 15-tonne sprayer travelling at 20 kilometres per hour - or a 25t header travelling at 12km/h - this represents a 25 to 50 per cent reduction in motion resistance.

This would save approximately 20 kilowatts (or 27 horsepower) of engine power and seven litres of fuel per hour.

Although wheel slip plays a small part in wasted tractor power, slip losses are also reduced when working on the firmer soil of permanent traffic lanes.

Growers in the southern low-rainfall zone estimate controlled-traffic savings of around 15 per cent in fuel use and power requirements. - Australian Controlled Traffic Farming Association's Jeff Tullberg

Draught resistance

Tillage operations are rare in most Australian grain-production areas, so any draught energy saving from CTF mainly applies to the seeder.

Draught measurements in the study demonstrated that about 25 per cent less draught was required to pull a tyne seeder through the soil in the untrafficked crop zone.

Those CTF growers who choose to sow the wheel tracks to prevent erosion and improve weed management will need 20 to 25 per cent extra power, but this only applies to the tynes working in the wheel track.

Given that permanent lanes are only 10 to 15 per cent of the seeder width, the overall draught power reduction will be only two to four per cent.

This will often be smaller than the motion resistance effect, which is reduced for the tractor and air-cart on traffic lanes, but sometimes increased for press wheels and depth wheels on the soft soil in the crop zone.

Soil condition varies widely with moisture content and type, so generalisations can be dangerous. But the results of this study match local grower observations.

Growers estimate that the combined impact of reductions in motion resistance, slip and draught led to a 15 per cent reduction in fuel use and power requirements, with some reports as high as 30 per cent.

These savings can enable growers to shift to tractors and machines with lower power, which are cheaper to buy and run.

More information: Jeff Tullberg, 0417 134 372, jtullb@bigpond.net.au