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A disc harrow is a farm implement that is used to cultivate the soil where crops are to be planted. It is also used to chop up unwanted weeds or crop remainders. It consists of many iron or steel discs which have slight concavity and are arranged into two or four sections. When viewed from above, the four sections would appear to form an "X" which has been flattened to be wider than it is tall. The discs are also offset so that they are not parallel with the overall direction of the implement. This is so they slice the ground they cut over a little bit to optimize the result. The concavity of the discs as well as their being offset causes them to loosen and pick up the soil they cut.
Before the invention of the modern tractor, disc harrows typically consisted of two sections and which were horse-drawn and had no hydraulic functionality. These harrows were often adjustable so that the discs could be changed from their offset position. Straightening the discs allowed for transport without ripping up the ground; also they were not as difficult to pull.
Disc harrows are primarily used to chop up soil that has been recently plowed to eliminate clumps and loosen the soil if it has been packed. They are also used to chop up old crops, such as cornstalks, to make the land easier to plow and to eliminate clogging in the plowing process.
Offset Harrow disc
The disc is a secondary implement primarily used to break down soil clods into smaller units. By so doing it allows easier penetration of water into the soil, increases soil aeration and enhances the activity of soil biota.