- One-way disc ploughs are a low-cost alternative to mouldboard ploughs for soil amelioration
- As one-way disc ploughs have more components, they require more time to optimise but may be used on a greater range of soil types than mouldboard ploughs
One-way disc ploughs offer a lower-cost alternative to mouldboard ploughs to ameliorate constrained soils, with added scope to work across a wider range of soil types.
From 1900 to the 1970s, disc ploughs were favoured over mouldboard ploughs by Australian grain growers due to their lower draught requirements, faster mode of operation and ability to break up heavy soils.
During this period, one-way disc ploughs were used to tip soil on its side as a primary tillage operation.
However, these ploughs can be modified to work deeper than traditionally intended to more effectively invert the soil.
Additionally, the unpowered, rolling action of the disc of one-way ploughs makes them better able to ride over rocky ridges and cemented gravels than a mouldboard plough, enabling them to work in a wider range of soil types.
Australian growers have been innovative in modifying one-way ploughs for greater and deeper soil inversion. This typically involves removal of every second disc and fitment of larger-diameter discs, allowing deeper working and more space for soil to turn over.
Often known as 'Plozza ploughs' after the Western Australian growers Ben and Sean Plozza, who first developed the concept, the discs are usually more concave (have a greater 'dish depth') with greater curvature, assisting the soil to roll beyond 90 degrees and end up inverted.
The plough's capacity to work deep is improved by increased break-out pressure on the jump arms and increasing the ballast (weight) on the plough if required.
Insights into the operation of one-way disc ploughs to optimise their set-up have been assessed through the use of discrete element method (DEM) simulations, carried out by researchers at the Agricultural Machinery Research and Design Centre at the University of South Australia.
As the disc is a passive tool, with its rotation driven by the force of the soil on the disc, it requires more complex simulation to accurately model its operation and the resulting impact on soil movement.
Disc size and curvature simulations
DEM simulation results have shown that increasing the disc diameter increases the topsoil burial if the disc has a curvature depth that is approximately one-sixth of the disc diameter.
Figure 1(a) shows that increasing the disc diameter without changing the curvature does not improve the topsoil burial. However, Figure 1(b) shows that increasing the curvature depth of a 1130-millimetre diameter disc increases the topsoil burial.
Increasing the approach angle for disc ploughs (angle of the disc face relative to the direction of travel) can increase topsoil burial.
Working speed and depth
As depth of work is increased for a one-way disc plough, the rotational speed of the discs reduces for a fixed forward speed.
DEM simulation results showed that increasing the operation depth reduced the amount of topsoil buried into deeper layers.
Increasing forward speed improved topsoil burial up to a specific tillage depth (about 200mm). At lower speeds, the percentage of topsoil buried into deeper layers increased at 300 and 350mm operation depths, while it decreased at 200 and 250mm operation depths.
Field tests and DEM simulated results using a deep-working modified one-way plough also showed similar trends.
It was found that, at slower speeds, more distinct and vertical burial profiles were obtained (see Figure 2a and 2b).
The complexity and number of variables involved in disc ploughs greatly affect their operation and quality of work.
Simulation results with modified working angles of the one-way plough discs showed that reducing the tilt angle (angle of the effective disc face, edge to edge, relative to the soil surface) from 20 degrees to 0 degrees (disc face vertical) and increasing the approach angle (angle of the effective disc face relative to the direction of travel) from 15 degrees to 45 degrees could increase topsoil burial (see Figures 3 and 4).
The complexity and number of variables involved in disc ploughs greatly affected their operation and quality of work, based on the initial analyses with DEM.
Further investigation is needed around adjusting the disc plough components and potentially improving and optimising their use, whether that be for better inversion or greater soil mixing.
GRDC Research Code DAW00244