In agriculture, a harrow (often called a set of harrows in a plurale tantum sense) is an implement for breaking up and smoothing out the surface of the soil. In this way it is distinct in its effect from the plough, which is used for deeper tillage. Harrowing is often carried out on fields to follow the rough finish left by ploughing operations. The purpose of this harrowing is generally to break up clods (lumps of soil) and to provide a finer finish, a good tilth or soil structure that is suitable for seedbed use. Such coarser harrowing may also be used to remove weeds and to cover seed after sowing. Harrows differ from cultivators in that they disturb the whole surface of the soil, such as to prepare a seedbed, instead of disturbing only narrow trails that skirt crop rows (to kill weeds).

There are four general types of harrows: disc harrow, tine harrow, chain harrow and chain disk harrows. Harrows were originally drawn by draft animals, such as horses, mules, or oxen, or in some times and places by manual labourers. In modern practice they are almost always tractor-mounted implements, either trailed after the tractor via a drawbar or mounted on the three-point hitch.

Types

In cooler climates the most common types are the disc harrow, the chain harrow, the tine harrow or spike harrow and the spring tine harrow. Chain harrows are often used for lighter work such as levelling the tilth or covering seed, while disc harrows are typically used for heavy work, such as following ploughing to break up the sod. In addition, there are various types of power harrow, in which the cultivators are power-driven from the tractor rather than depending on its forward motion.

Tine harrows are used to refine seed-bed condition before planting, to remove small weeds in growing crops and to loosen the inter-row soils to allow for water to soak into the subsoil. The fourth is a chain disk harrow. Disk attached to chains are pulled at an angle over the ground. These harrows move rapidly across the surface. The chain and disk rotate to stay clean while breaking up the top surface to about 1 inch (3 cm) deep. A smooth seedbed is prepared for planting with one pass.

Chain harrowing may be used on pasture land to spread out dung, and to break up dead material (thatch) in the sward, and similarly in sports-ground maintenance a light chain harrowing is often used to level off the ground after heavy use, to remove and smooth out boot marks and indentations. When used on tilled land in combination with the other two types, chain harrowing rolls the remaining larger clumps of soil to the surface where the weather will break them down and prevent interference with seed germination.

All four harrow types can be used in one pass to prepare the soil for seeding. It is also common to use any combination of two harrows for a variety of tilling processes. Where harrowing provides a very fine tilth, or the soil is very light so that it might easily be wind-blown, a roller is often added as the last of the set.

Harrows may be of several types and weights, depending on the intended purpose. They almost always consist of a rigid frame to which are attached discs, teeth, linked chains or other means of cultivation, but tine and chain harrows are often only supported by a rigid towing-bar at the front of the set.

In the southern hemisphere the so-called giant discs are a specialised kind of disc harrows that can stand in for a plough in very rough country where a mouldboard plough will not handle the tree-stumps and rocks, and a disc-plough is too slow (because of its limited number of discs). Giant scalloped-edged discs operate in a set, or frame, that is often weighted with concrete or steel blocks to improve penetration of the cutting edges. This sort of cultivation is normally immediately followed by broadcast fertilisation and seeding, rather than drilled or row seeding.

Disc harrow

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 pickup the soil they cut.

History

In the olden days, 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 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-driven and are raised hydraulically. Some large ones even have side sections which raise up vertically to allow easier road transport or better storage configurations.

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.

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.

Drag harrow

A drag is a heavy harrow. A drag harrow, a type of spring-tooth harrow, is a largely outdated type of soil cultivation implement that is used to smooth the ground as well as loosen it after it has been plowed and packed. It uses many flexible iron teeth usually arranged into three rows. It has no hydraulic functionality and has to be raised/adjusted with one or multiple manual levers. It is a largely outdated piece of farm equipment, having been replaced by more modern disc harrows and deeper, stiff-toothed rippers.

Uses

A drag harrow is used to loosen and even out soil after it has been plowed and packed. It pulls up large rocks which may then be picked up manually and put in the tractor’s stone box to remove from the field. The drag harrow also kills some weeds that may be present, but it is not very efficient in doing so due to its highly flexible teeth, hence it is not one of its primary functions.

In modern times

The drag harrow is not often used in modern farming as other harrows have proven to be more suitable, such as the disc harrow. Another reason they are not often used is because they cannot be controlled hydraulically, meaning that the operator is required to dismount from the tractor to adjust it or unclog it. However it is used as a drag behind several other implements such as a rod weeder. Due to their low cost and simplicity, drag harrows are still used widely by small farmers.

Drag harrows can be a name used for several different types of equipment. A spike tooth harrow or flex harrow is often called a drag harrow and is in use extensively throughout the US for seedbed preparation and for grooming grassland pastures. See also:

• Spike harrow
• Spring-tooth harrow

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