The Yeomans Plow was specially developed by P.A. Yeomans for the Keyline system. Originally modelled off the Texan-built Graham Hoeme Chisel Plow, the Yeomans Plow evolved the design to suit the more extreme conditions usually found in Australia.
Its shanks can deeply penetrate the subsoil without turning it, leaving the vital soil structures undisturbed and allowing water, nutrients and oxygen to permeate much deeper. This increases the water holding capacity of the land and improves the fertility of the soil.
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Allan Yeomans (son of P.A. Yeomans) talks about the invention of the Keyline plow
Yeomans also developed machinery along with Keyline. In 1952 a Graeme Hoeme Chisel plow was imported into Australia (from the United States) by a family friend of the Yeomans. The design was promising and the implement was trialled effectively in the early years to restore eroded valleys. In June of the same year, Yeomans and his son Allan travelled to the United States and met with Bill Graeme of the Graeme Hoeme Chisel Plow Co. and negotiated a deal to make the plow in Australia under their patent. The patent was found to be unenforceable in Australia and the design was copied. Yeomans himself modified and strengthened the design until it could be used in any farm landscape.
Yeomans sold his plow business in 1964 and both he and son Allan, as a design engineer, were required to remain out of the agricultural machinery business for a minimum of 5 years.
Their designs for a “sub soiler chisel plow”, a deep working, low disturbance chisel plow with the strength of earth moving rippers were put on hold. After the 5 year period expired, the idea re-emerged as the “Bunyip Slipper Imp” with “Shakaerator” which won the Prince Philip award for Australian design in 1974.
The new plow had a strong and rigid frame, with tynes or shanks made from cast tool steel. The design allowed deep cultivation, lifting and loosening the earth and allowing it to resettle with no mixing between soil profiles and minimal root disturbance.
The new plow prototypes were developed in Allan Yeomans independent engineering business and after the death of P.A Yeomans in 1984, Allan Yeomans' company took over the complete manufacture of the plow.
Improvements have continued and 6 new patents have been issued.
While the basic principles of keyline have remained the same, the designs of the cultivating equipment and the techniques for soil building have changed. These new developments have meant that the soil building processes of keyline are no longer restricted by the use of chisel plows and the techniques have been streamlined. The new equipment also improved the ability of soils to absorb higher quantities of run off which have to be considered in the design of new farm layouts. For instance, greater emphasis is now placed on the placement and capacity of the first dam, which now tends to be of greater capacity than previously required. Fewer and larger farm dams now prove to be more economically viable. Ken Yeomans has also developed computer simulation design techniques to assist in farm layout and design.
The 1971 book The City Forest also illustrated how the system could be more broadly applied, including to the urban environment.
The almost universal adoption of chisel ploughs has been one of the most beneficial and noticeable changes in Australian agriculture this last century.