Long-term research has brought into focus the impacts of controlled-traffic farming (CTF) in low-rainfall cropping areas, dominated by sandy soils across Victoria, South Australia and New South Wales.

The GRDC-invested study, managed by the Australian Controlled-Traffic Farming Association (ACTFA), aims to inform farm business decisions on transitioning to CTF in low-rainfall zones (LRZ).

In these zones, most growers are currently reluctant to restrict heavy farm machinery operations to permanent wheel tracks.

Leading the research, South Australian Research and Development Institute (SARDI) farming systems leader Dr Nigel Wilhelm says just four per cent of LRZ growers had implemented CTF when the six-year study commenced in 2014.

This compares with a relatively high adoption rate in parts of the medium and high-rainfall zones, where 25 to 30 per cent of growers have implemented CTF, Dr Wilhelm says.

"Grower uncertainty about the benefits of CTF in terms of crop performance in low-rainfall environments has traditionally posed a barrier to adoption," he says.

Providing new incentive to make the switch to permanent wheel tracks is the study finding that CTF could lift the overall, long-term grain yield of LRZ farming systems by up to five per cent.

"Growers who move to CTF could see a three to five per cent increase in long-term grain yields over their whole farming system," Dr Wilhelm says.

However, the research also showed CTF benefits depended on the intensity of farm machinery traffic.

It found low-intensity uncontrolled traffic, using one machinery pass is unlikely to cause yield penalties, in both wet and dry conditions across the LRZ.

Whereas intermediate and high-intensity uncontrolled traffic, using multiple machinery passes resulted in significant yield losses on sandy soils, as well as some heavier soils.

For example, six machinery passes on heavy soil types in western New South Wales reduced crop yields by up to 50 per cent (or one tonne per hectare).

And where researchers simulated high-intensity uncontrolled traffic on deep sands at Loxton, SA, yield penalties ranged from 240 to 380 kilograms/ha in wheat, and 212kg/ha in field peas.

Growers who move to CTF could see a three to five per cent increase in long-term grain yields over their whole farming system - SARDI farming systems leader Dr Nigel Wilhelm

Improved machinery efficiency was another benefit of CTF in the LRZ measured as part of the collaborative study in partnership with ACTFA, SARDI, Agriculture Victoria and the Society of Precision Agriculture Australia.

Dr Wilhelm says confining machinery use to permanent wheel tracks delivered a 15 to 20 per cent cost saving on fuel in low-rainfall farm businesses. This compares with a 30 to 50 per cent fuel cost saving under CTF systems in the high-rainfall zone.

But he adds that increased risk of wind erosion where permanent wheel tracks are established on fragile sandy soils may require careful management.

These findings were drawn from four long-term trials, representing a range of soil types and agro-ecological cropping zones at: Minnipa and Loxton, SA; Swan Hill, Victoria; and Lake Cargelligo, NSW.

Now adding to this mix of research sites, however, is a fifth trial site exploring the relationship between deep-ripping and CTF practices at Kooloonong in north-west Victoria.

The trial, deep-ripped to a depth of 40 centimetres on orange deep sand, aims to determine how CTF principles might extend the beneficial effects of soil amelioration and protect the soft, friable soil from heavy machinery post-ripping.

Also contributing to this study are five farming systems groups: Eyre Peninsula Agricultural Research Foundation, Upper North Farming Systems, Mallee Sustainable Farming, Birchip Cropping Group and Central West Farming Systems.

GRDC Project Code: ACT00004

More information: Dr Nigel Wilhelm, 0407 185 501, nigel.wilhelm@sa.gov.au; Chris Bluett, 03 5341 2103, chris.bluett@hrzconsulting.com