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Challenges

The challenges can be divided into three principal areas:

1. Designing the machinery system around existing mechanisation
2. Introducing and maintaining the soil-based wheelways, particularly in areas of high rainfall
3. If mouldboard ploughing is the principal annual cultivation, the challenge is in making the switch to a non-inversion or zero tillage system.

Designing the Machinery System

This is largely a case by case assessment and design. There are however some guiding principles which will form the basis of an initial feasibility study. In general, the wheel track gauge selected will be based on the machine with the widest non-adjustable track gauge. Within a cereals rotation, this is generally the combine harvester. The width of the cutting table may also form the basis of the module width of implements, because the aim will be to match all the working widths of the equipment. However, it is possible to have a module width less than the width of the cutting table, for example a 9 m cutting table could operate with an 8 m base module of cultivators and drill for example. This is not ideal and in the long term the machinery replacement plan would aim to match or have everything on a multiple of the base module width, as shown in the figure below.

Assuming that use on the public highway is needed, the next decision relates to the maximum overall acceptable width of the main tractor or tractors to be used within the system. It is very unlikely, based on currently available combine harvesters, that an overall width for the tractors of less than 3 m will be possible. Feedback from a number of farmers in the UK suggests that the maximum width acceptable is likely to be around 3.2 m (in terms of regular road use and access), and this relates to a track gauge of around 2.7 m. As the overall vehicle width is greater than 3m, most countries in Europe will require that farmers comply with certain additional regulations and restrictions on road use. In the UK, it means applying annually to the local police force for a special dispensation. This gives reasonable freedom, but each force will impose slightly different constraints depending upon local conditions and the routes that you wish to travel.

Even at an overall width of 3.2 m, it is likely that the inside edge of the tractor tyre will be outside the inner extremity of the harvester’s tyres (see figure above). This might be acceptable in the short term, but plans should be made to improve the situation. One option that can be considered is to fit tracks to the harvester. In general, this reduces the vehicle’s overall width and also the track gauge, because the tracks can be accommodated beneath the drum and concave. Alternatively, once the wheelways have become firmly established, one can assess the feasibility of using narrower tyres on the harvester.

Introducing and maintaining the soil-based wheelways

A great deal of practical experience has been gained in Australia on permanent wheelways, but in their climate the soil conditions are predominantly dry, but with periods when it can get very wet. In other parts of the world, and especially in temperate regions, soil conditions may be predominantly wet, but with periods when they are very dry. We therefore have fundamentally different starting conditions depending upon local climate. There are however a number of things to remember:

1. The Australian experience suggests that the wheelways should be planned to run up and down the principal slope. This is against conventional thinking, but there are good reasons why this works in most cases.
2. Try to make your first pass in reasonably dry conditions, and preferably not on soil that has just been deep loosened or ploughed.
3. Unlike annual temporary tramlines, permanent wheelways provide the opportunity for maintenance and repair, and this will be needed, especially in the first year of operation.
4. If the wheelways get very wet, they will carry far less load and will easily become rutted. A reasonable degree of drainage must therefore be provided, especially in low lying areas, and this implies that deep rutting should be avoided.

It will be inevitable that the wheelways will become rutted after the first few passes – after all, we are trying to compact the soil to provide a firm base. It is therefore necessary to plan in a "sweep" procedure – a surface operation that will draw soil across the wheelways from as great a width as possible (a reciprocating or rotary harrow, used very shallow can be an ideal tool for this). The next pass will then compact this soil onto the top of the already firm wheelway. Be particularly aware though that if you bring fine soil into a depressed wheelway and it rains heavily before this new soil is compacted, a horrible slurry can result! Once the wheelways have been built up to just below the surrounding surface, they should remain reasonably dry. If there are low areas where they don't, some physical inter-connection between the wheelway and the surrounding bed may have to be established – a few channels may be dug, or a specific tool may be designed for the job (see "Machine modifications and customised equipment").

Once the wheelways have become established, and providing they are not abused, relatively little maintenance may be needed. An Australian farmer designed the tool shown below as a means of annual low input maintenance.

Rolling wheelway maintenance tool. This works along the side of the wheelways and levels any ridge that might build (Photo: Courtesy Jamie Grant, Kielli, Jimbour, QLD)

If the field has an artificial drainage system and associated mole channels, it will be a good idea to draw a mole channel down the centre of each pair of wheelways and a further channel immediately outside each wheel track (see below).

Suggested location of mole channels in relation to wheelways, which should be on a downhill slope.

If very wet conditions are encountered and it is vital to carry out an operation, the tyre inflation pressures should be lowered to the minimum recommended for the load being carried. Providing road use is not extensive and speeds can be kept to around 10 km/h, somewhat lower pressures can be used, but consult with the tyre manufacturer. Other measures include minimising the load being carried, and perhaps putting larger tyres on a non-driven front axle (see below).

Illustration of the potential for reducing the ground pressure of tyres on a non-driven front axle. The existing stub axles have been replaced to allow the larger diameter rear tyres to be fitted on the front axle. (Photo Silsoe Research Institute)

Finally, most CTF farmers in Australia have found that it is possible to reverse the tread of traction tyres (see below). This is possible because of the lower draught operations and is preferred because the tyres do less damage to the wheelways when fitted in this way, they give a smoother ride and wear less.

Australian farmers have found that lower draught and shallower working allow them to fit their tyres in reverse. This improves wheelway maintenance, reduces tyre wear and provides a smoother ride. (Photo: Courtesy Jamie Grant, Kielli, Jimbour, QLD)

Making the transition from ploughing to non-inversion or zero tillage

Crucial to the success and sustainability of CTF is its ability to deal with residues, diseases and weeds when ploughing is absent. To a large extent crop residues are only a problem if they are unevenly spread and/or if the following implements are unable to deal with them. They are rarely a crop problem other than their interaction with some diseases. The challenge must therefore be addressed initially by ensuring that whatever residues are left on the field are spread evenly, and if possible reduced to short lengths (less than 100 mm). This helps to ensure that they pass easily between the soil engaging parts of cultivation implements, which should themselves have as much clearance as possible between adjacent elements. An alternative is to use an implement which is less sensitive to residues, such as rolling cultivators, discs or widely staggered tines.

Remember though that the soil condition you are dealing with now is far more friable and less aggressive but more closely spaced elements may be needed. The ideal could be something like a spiked rotor that is braked slightly to give slip between the soil and spikes, but which allows surface residues to clear as it rotates. For sowing cereals, a similar principle might be adopted or even the same cultivator used with seed being delivered in front of the rotor. Again, remember that if things have been done correctly, a friable and moist tilth should be available, giving this semi-broadcasting method a high chance of success. In many instances a single sowing pass may be all that is needed.