DELVING up subsoil to mix with topsoil is a soil improvement technique with a long history and many recent developments in Western Australia, South Australia and Victoria.
One of the earliest records of a slanted tyne to deliberately lift subsoil to mix it with topsoil was published in 1969 about work done by Smith and Ede to lift subsoil (often clay) to mix with surface peat in the English Fens, old marshland converted to agriculture by drainage.
The same principles were investigated for water repellent sand over dispersive clay by Agriculture WA in the 1990s.
Subsequent technical investigations of the idea in South Australia were also found successful and the method became commercialised by Australian machinery companies by about the end of the decade.
In southern Australia the main initial reason delving was introduced was for the mixing of subsoil clay with non-wetting topsoil when the clay was accessible from the surface, initially from depths of about 300-500 millimetres.
Deeper clay required carting from a suitably close pit.
In more recent times the purpose has extended to many other soil types to lift subsoils with high nutrient value and/or alkalinity into topsoils of poor nutrition or/and acidity to reduce costs of applied fertiliser and limes, especially on yellow sands.
General delver designs have involved a broad tyne set at about a 45 degree slope with a wide cutting point to penetrate and displace the clay and a wide face for the clay to slide up to reach the surface and sometimes to also slide off the edge to mix with the soil in the profile.
These delvers have usually been units dedicated to only delving, or deep ripping units which can have delvers fitted on the tynes as an alternative operation.
Nufab Industries, Geraldton, with the help of collaborative growers and researchers, has developed a new trailed machine which can deep rip and delve at the same time - the Hydramax Deep Ripper with the option of delving tynes (HDR-D).
Shallower leading ripper tynes weaken the profile to make delving from greater depth easier and breaking out the compaction between the delvers.
Rear adjustable depth delving tynes lift subsoil towards the surface.
Then a following pressurised crumble roller breaks up the clods of subsoil and does some mixing with the topsoil.
This design introduces more efficiency of field operations into soil management by incorporating three operations into one pass, when the field conditions are suitable for the available draft.
Nufab has tried different shaped flat broad tynes and found that the best result was from what it is using.
A curved tyne face design was not experimented with due to fabrication costs and problems.
The plastic-coated tyne faces reduce adhesion between the tyne face and the moist clay and sliding friction, allowing clay subsoil to slide more easily up the tyne face rather than build-up, this helps with flow of other subsoils than clay and reduces draft.
The green plastic, delving slide wear plate is inexpensive and from field work to date expected to last about 200ha.
Draft is also an especially important consideration in the design.
Additional draft from the attached tractor is needed for the delving tynes to dig deeper and to lift more subsoil.
Compromises between draft and lift are inevitable, according to the capacity of the tractor and the soil types and soil moisture status at the time of delving - optimum time is often in the summer after enough rain or fallow to moisten the clay layers and with a dry surface topsoil.
Shallow leading tynes reduce draft and enable delving in conditions that would otherwise be considered too difficult to pull them through.
This improves the efficiency of the delving ripper by allowing penetration to desired depth in more conditions, especially in paddocks with variable soil types.
Leading tynes working between the delving tynes can also improve the general breakout and decompaction of the operation.
The most effective delving point angle used by most designs does not shatter well between the delvers when on one metre spacing.
These designs require spacing too close together to get good breakout between delvers.
Thus the reason for a shallow leading tyne working ahead of the delvers to improve soil breakout in the new Nufab delving and ripping unit.
Nufabs Hydramax Deep Ripper with the option of delving tynes (HDR-D) is thinking outside the box and, as far as they are aware, an industry first.
Hydramax was the first hydraulic tyne ripper with shallow leading tynes designed for WA conditions, because it is able to rip well beneath hard pans at 450-550mm.
Nufab offers this new model ripper and delver that can rip to 700-800mm and delve to 600mm.
Delving can raise material from 450-600mm depending on the angle of the slide.
Delving slide angle can be altered depending on soil variables/ conditions - from initial notes.
Most clay delving activity requires a second pass of a mixing device, such as a spader or offset discs, to provide enough breakup of the delved clay and mixing into the topsoil.
Other subsoils are generally more friable when delved and a rear mounted mixing roller is enough for sufficient incorporation in one pass.
The new Nufab ripper/delver is the first WA built deep ripper to offer an adjustable hydraulic downward pressure crumble roller, which does the crushing and mixing of the clay delved to the surface.
However the surface finish is firm rather than loose, to help minimise erosion and water repellence issues.
A more level surface can also reduce complications in the subsequent seeding operation.
Nufab is confident that this versatile new design will be a useful step forward in the profitable management of WA soils in a changing climate and economy.
Fine tuning still ongoing as always looking at improving performance no different to any other product.
Nufab always value customer feedback.
Like deep ripping, delving is expected to have trade-offs on depth, how much subsoil is lifted and seed bed finish.
The effectiveness of the operation is very dependent on soil moisture content and timing of the ripping and delving.
