Hans Henrik Pedersen is completing a PhD at Aarhus University in Denmark. He was a key speaker at LandWISE 2013: “New Ideas”. Hans told delegates about his work investigating a wide-span tractor as an option for cropping farmers.

Vegetable farmers, who adopt CTF, face serious challenges at harvest because very few harvesters are designed to match CTF systems. The soil structure is severely damaged when heavy harvest machines run over the well structured growing beds. A few farmers have modified harvesters, but to our knowledge only one CTF vegetable farmer has succeeded in matching harvest machines for all his crops.

As CTF farmers are still a minority the limited demand means that machinery manufacturers do not yet perceive a need. Also 3 m track width, as used by most CTF vegetable farmers, is a challenge as mass produced harvest machines need to meet road regulations in different countries.

In a Danish project partly funded by the Danish Business Innovation Fund a 9.6 m prototype wide span tractor has been developed. It will be tested by a commercial farmer (Jens Kjeldahl, Samsø) who will grow onions on 9.6 m wide beds spanned by the tractor. ASA-Lift A/S has designed and built the wide span tractor. Besides cultivation, drilling and plant care operations, the tractor will be used as a bunker harvester for onions and possibly for other crops. At harvest, the machine will unload at the field edges, thereby avoiding tractors and trailers in the field.

 First presentation of the ASA-Lift WS-9600 tractor, summer 2012. Photo: Brdr. Kjeldahl

A wide span tractor solves two main challenges facing the traditional tractor:

• Restrictions in width (e.g. due to road regulations) are solved by changing the direction of travel between field work and road transport. The machine is wide in the field and long when transported on roads but only 2.55 m wide.
• Weight of the tractor can be reduced as implements can be mounted within the span of the tractor. The forces from the implements are transferred directly to the tractor as opposed to traditional mounting systems, where the tractor needs weight to pull the implement. Also, in conventional implement designs, a strong, heavy and often complex structure is needed to transfer the forces through the tractor hitch, as well as to fold the implement for transport.

Earlier work on wide span tractor designs e.g. as described by Chamen et al. (1994), unfortunately did not lead to commercial production.

A key point in design of any technology is to ensure that the development process is targeted to the priorities of potential customers. As part of my PhD. Studies I have performed a Quality Function Deployment (QFD) to derive user-requirements and design parameters.

Twenty eight farmers and farm managers in Europe and Australia have been interviewed about their priorities for the design of a new growing concept based on wide span machines. The majority of those interviewed were CTF farmers. The farmers were asked to score 28 specific requirements on a scale from 0 to 4.

The 10 requirements with the highest priority were: (average scores are given in parentheses)

• Automatic accurate steering of the carrier (3.9)
• Reducing soil compaction (3.8)
• Durability of the machine (3.4)
• Overview of the entire machine from the operator’s seat (3.4)
• Total costs per hour (3.3)
• Clear view and manoeuvrability to avoid damage (3.3)
• Semi-automatic control for increased productivity and ease of operation for the driver (3.3)
• Comfort of the driver (3.3)
• Automatic accurate steering of mounted implements (3.3)
• Capability to carry heavy loads in the field (3.2)

A next step involved technical experts suggesting technical solutions (Design Parameters) to accommodate the priorities set by the farmers. The results of this QFD analysis can be used by any manufacturer who wishes to develop wide span machines.

Tractors as we know them today were very successful in replacing horses. Since they were introduced in the 1920s, rubber tyres and four-wheel drive have been established, along with other features, but basically the design has not changed. However, the power output has increased more than 10 fold and the weight of tractors has increased by a similar factor. The load of agricultural machines is challenging the productivity of soils. We believe it is time for a change to the traditional tractor and that the wide span alternative can be designed to suit the needs of modern agriculture while significantly improving production efficiency.

Reference:  Chamen, W. C. T., Dowler, D., Leede, P. R., and Longstaff, D. J. (1994). Design, Operation and Performance of a Gantry System: Experience in Arable Cropping. Journal of Agricultural Engineering Research 59, 45-60.

Look also at the CTF-Europe website for more from Hans Pedersen, Tim Chamen and colleagues