New disc machine designs offer greater capabilities than those designed two decades ago. They have wider frames, stronger construction, improved flotation and folding capabilities. Although it is important to understand prior to embarking on the use of a disc seeder, that they cannot be used in the same way as a tyne. The reason for this is that the way the implement operates in the soil is completely different. Attention needs to be given to the use of herbicides, soil strength, nutrition and, most importantly, residue handling.

Why discs?

Interest in discs is commonly due to their:

• Ability to minimise soil disturbance
• Generally precise seed placement
• Limited burial and stimulation of weed seeds
• Faster sowing speeds
• Reduced fuel usage due to lower draft
• Lower tractor horse power requirements
• Ability to retain stubble on top of the soil surface
• Handling of rocky paddocks 

Configurations

Disc openers are generally classified into four design categories:

• disc coulters
• double discs (including triple disc combinations), considered the most accurate for seed placement
• single discs (with vertical or ‘undercut’ variants)
• disc/tyne and disc/blade hybrids  

A disc coulter’s primary role is to provide furrow pre-loosening, residue cutting and fertiliser banding. Coulter blades can be flat or fluted with either a continuous or scalloped cutting edge.  

Double disc modules are considered the most accurate for seed placement of all disc configurations. In firm and compactable soil conditions, double disc designs are best operated behind leading coulters in ‘triple disc’ combinations.  

Single disc modules are characterised into two main categories:

• Single vertical disc with sweep angle - disc blade size ranges from 430mm (17 inch) to 660mm (26 inch) in diameter. The disc runs at a small sweep angle (typically 5 to 7 degrees) to the direction of travel.
• Single disc with tilt and sweep angles - this design combines an additional tilt angle to the vertical of up to 20 degrees with a similar sweep angle (between 3-7 degrees) to the horizontal. The tilt angle produces much greater penetration ability, but reduces the slicing component of residue cutting. 

Disc-tyne hybrids offer flexibility in seed/fertiliser banding without compromising seed placement quality, typically associated with deeper tillage depth. They can also be utilised for more effective moisture seeking at greater depth. Disc/blade hybrids have the ability to set seed and fertiliser depth independently, with separation occurring horizontally and/or vertically. 

Note: Care must be taken with discs to avoid smearing in wet clayey soils.