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

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

 or steel

Steel

Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

 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

Offset

The term offset may refer to:* Carbon offset, a financial instrument aimed at a reduction in greenhouse gas emissions* Offset agreement, trade practice in Aerospace and Defense Industry...

 so that they are not parallel

Parallel (geometry)

Parallelism is a term in geometry and in everyday life that refers to a property in Euclidean space of two or more lines or planes, or a combination of these. The assumed existence and properties of parallel lines are the basis of Euclid's parallel postulate. Two lines in a plane that do not...

 with the overall direction of the implement

Implement

Implement may refer to:* Implementation — the process for putting a design, plan or policy into effect.* A class of tools — such as farm implements or writing implements....

. 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.

History

In the olden days, disc harrows typically consisted of two sections and which were horse

Horse

The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...

-drawn and had no hydraulic functionality. These harrows were often adjustable so that the discs angle would not be offset so that they could be transported without ripping up the ground as much and so they did not pull as hard.

Today

Modern disc harrows are tractor

Tractor

A tractor is a vehicle specifically designed to deliver a high tractive effort at slow speeds, for the purposes of hauling a trailer or machinery used in agriculture or construction...

-driven and are raised hydraulically. Some large ones even have side sections which raise up vertically

Vertical direction

In astronomy, geography, geometry and related sciences and contexts, a direction passing by a given point is said to be vertical if it is locally aligned with the gradient of the gravity field, i.e., with the direction of the gravitational force at that point...

 to allow easier road transport or better storage configurations.

Uses

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 disc

An offset disc has two rows of discs that are in a line and angled to make a "V" instead of an "X". An offset disc harrow digs deeper in the soil and has larger, often serrated discs and is often referred to as a disc plow.