disc harrow

A disc harrow is a tillage implement pulled behind a tractor, consisting of multiple concave steel discs mounted on horizontal axles. As it moves through the field, the angled discs rotate and cut into the soil, breaking up clods, incorporating crop residue, and mixing the surface layers. The discs typically range from 16 to 24 inches in diameter, arranged in gangs that can number from 4 to 16 or more depending on the implement's width and the work required.

The discs are set at an angle, usually 15 to 20 degrees from vertical, which causes them to both cut downward and roll laterally as they spin. This combination of slicing and turning action makes the disc harrow effective for burying stubble and manure, leveling ridges left by plowing, and creating a more uniform seedbed than a tine harrow can achieve. The depth of operation is controlled by adjusting the angle of the gangs or by weight distribution across the frame.

Disc harrows come in two main configurations: tandem and offset. A tandem harrow has two sets of discs, one behind the other, both cutting in the same direction, useful for general-purpose secondary tillage. An offset harrow has the rear gangs angled to throw soil sideways, creating a ridge and filling in furrows more aggressively. Some models feature hydraulic adjustment of the gang angle from the tractor cab, allowing operators to fine-tune depth and soil flow without stopping.

The concave discs dull with use and stone strikes are common, requiring replacement after 40 to 80 hours of operation depending on soil type and stone content. Worn or cracked discs must be matched in sets to maintain even cutting. The bearings and seals that support each gang require regular inspection because moisture and soil penetration will cause corrosion and failure. Disc harrows are heavier than spike tooth harrows, demanding higher horsepower (typically 40 to 100 hp per implement width) and creating more compaction if used when soil is too wet.

The disc harrow sits between the moldboard plow and the final seedbed preparation equipment in the tillage sequence. Where plowing turns the soil inversion over, the disc harrow pulverizes and levels without creating a deep furrow. In reduced-tillage and no-till systems, disc harrows have become less common, though they remain standard on many conventional farms for incorporating residue after harvest and before the next crop.