The fundamental concept of developing a controlled-traffic farming (CTF) system is to match the operation width and wheel track width of all cropping machinery.

About 20 years ago, the early adopters used nine-metre - or 30-foot - systems.

Today, 12m is the most common - although the combined pressures of increasing crop areas, limited access to labour and a shrinking optimal seeding window mean that growers making the move to CTF are reluctant to sacrifice their wide seeding machinery.

For this reason, systems in multiples of 13.5m, 15m or 18m - which match wide seeders - are becoming more prevalent.

Choosing a ratio

The ideal machinery-matching ratio for CTF is 1:3 - such as a 12.2m seeder and header, and a 36.6m sprayer (see Figure 1, top).

Figure 1: The 1:3 machinery-matching ratio (top) includes a 12.2m header (light green), 12.2m seeder (brown) and 36.6m sprayer (dark green). The 1:1.5:3 ratio (bottom) includes a 12.2m header, 18m seeder, and 36.6m sprayer with the seeder overlapped by 9m on the left edge (red circle). Each square represents 3m, direction of travel (AB-line) is up/down. Source: DPIRD

However, 1:3 is a challenging ratio to match with seeders that are more than 15.24m (50ft).

Although there are header fronts and sprayers to match wide seeders at a 1:3 ratio, they are often not very practical to manoeuvre around the paddock - and it is difficult to evenly spread lime or straw at that width.

It is possible to set up a compromised CTF system that uses a matching ratio of 1:1.5:3 - effectively a 12.2m header, 18m seeder and 36.6m sprayer. This system requires some overlap on the edge of the paddock by either the seeder or the sprayer - and the header to line-up the seeding and spraying wheel tracks (see Figure 1, bottom).

While some systems will work more easily than others, it is important to consider all of the components of the farming system when selecting the best ratio for your system. - DPIRD development officer Bindi Isbister

In the 1:1.5:3 ratio system, the header lines up on the main wheel tracks every fourth run. This system is the preferred option for many growers and can achieve 18 per cent wheel track coverage of a paddock.

This is not the nine to 12 per cent target of a 1:3 ratio, but it is better than an unmatched system that can traffic about 40 per cent of the paddock - and often more if duals are used.

While there is no set rule for selecting the optimum ratios, experience has shown that some widths work more easily than others once all components of the farming system are considered (see Table 1).

The key steps to develop a CTF plan

1. Decide on imperial or metric. Working in one or the other helps keep it simple, as 40ft is not 12m - it is 12.1m. However, some growers do choose to run seeders and sprayers in metric and the header in imperial, enabling a small overlap of the cutter bar so that no crop is missed.
2. Choose a machinery matching width. Ideally, use the header width as a base, as this is the hardest machine to modify (both operating width and wheel track spacing). The wheel base for the header is often set to carry the full load weight.
3. Choose a wheel track width. Most equipment will fit around 3m - but this may need to be 3.2m or 3.4m. Often the header is the widest wheel axle and footprint, therefore aim to have most machinery wheel tracks within that range. Off-the-shelf modification kits are available for many tractors. If you modify equipment, check the warranty.
4. Develop an implementation plan. For some this will be easy and may involve dropping a tyne, adding a few nozzles or modifying axles to a common width - such as 3.0m. For others it will be more challenging. It is recommended to develop a CTF machinery investment plan and align it with the farm machinery replacement schedule. There are many examples of successful CTF farmers who have taken up to eight years to fully match machinery wheel spacing.

It is important to consider all of the components of the farming system when selecting the best ratio for your system.
Photo: Bindi Isbister

More information: Bindi Isbister, 0436 682 497, bindi.isbister@dpird.wa.gov.au