Disc Harrow

A disc harrow is defined by its rotating disc gangs, which cut and stir soil rather than fully inverting it. This gives a shallower, more residue-retentive form of tillage compared with a moldboard plough, useful for breaking clods, levelling the surface, and managing crop residue.

1. Concave discs, set at an angle to the direction of travel, are pulled through the soil
2. Each disc cuts and lifts a thin layer of soil, partially turning it and slicing residue
3. Opposing gangs of discs mix soil and residue and level the surface
4. Working depth and disc angle can be adjusted to change the intensity of soil disturbance

Disc harrowing is commonly used after primary tillage to break down clods and create a finer, more uniform seedbed ahead of planting, and it is also used on standing stubble or crop residue to size and partially incorporate it before or between crops.

Because it disturbs the soil less than full inversion tillage, disc harrowing can be one component of a reduced-tillage approach, though the level of soil disturbance still depends on depth, disc type, and number of passes.

Tandem disc harrow

Front and rear gangs angled in opposite directions for balanced, even tillage

Offset disc harrow

Gangs offset to one side, suited to working under tree canopies or near obstacles

Vertical-tillage disc

Uses near-vertical, wavy-edged discs to size residue with minimal soil inversion

Disc angle, weight, and working depth affect how aggressively the implement mixes soil and residue, and repeated shallow discing over time can create a compacted layer (a tillage pan) at a consistent working depth in some soils.