Editing Harrow (tool) (section)

==Types==
[[File:Yanju's tomb, ox and harrow driver.jpg|thumb|An ox-drawn harrow in a painting from Yanju's tomb, located in [[Jiuquan]], 5th century AD]]

In cooler climates, the most common types are the ''[[disc harrow]]'', the ''chain harrow'', the ''tine harrow'' or ''spike harrow'' and the ''[[Spring-tooth harrow|spring tine harrow]]''. Chain harrows are often used for lighter work, such as leveling the tilth or covering the 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 conditions before planting, remove small weeds in growing crops, and loosen the inter-row soils to allow water to soak into the [[subsoil]]. The fourth is a chain disk harrow.  Disks 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 {{Convert|1|in|cm|0}} deep.  A smooth seedbed is prepared for planting with one pass.
[[File:Man harrowing with tractor and disk harrow (1295027).jpg|thumb|left|180px|Harrowing with tractor and disk harrow in the 1940s)]]
Chain harrowing can be used on pasture land to spread dung and break up dead material (''thatch'') in the sward. Similarly, in sports-ground maintenance, light chain harrowing is often used to level off the ground after heavy use to remove and smooth out boot marks and indentations. Used on tilled land in combination with the other two types, chain harrowing rolls remaining larger soil clumps to the surface, where weather breaks them down and prevents interference with seed germination.

All four harrow types can be used in one pass to prepare soil for seeding.  Using any combination of two harrows for various [[Tillage|tilling]] processes is also common. Where harrowing provides a very fine tilth or the soil is very light so that it might easily be wind-blown, a [[Roller (agricultural tool)|roller]] is often added as the last of the set.

Harrows may be of several types and weights, depending on their purpose. They almost always consist of a rigid frame that holds discs, teeth, linked chains, or other means of moving soil—but tine and chain harrows are often only supported by a rigid towing bar at the front of the set.

In the southern hemisphere, so-called ''giant discs'' are a specialised kind of disc harrows that can stand in for a plough in rough country where a mouldboard plough cannot handle 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 cultivation is usually followed by broadcast fertilisation and seeding rather than drilled or row seeding.

A [[drag harrow|drag]] is a heavy harrow.
[[File:Erpice 1849.jpg|thumb|19th century spike harrows]]

===Power harrow===
A rotary power harrow, or simply a power harrow, has multiple sets of vertical tines. Each set of tines is rotated on a vertical axis and tills the soil horizontally. The result is that, unlike a [[cultivator|rotary tiller]], soil layers are not turned over or inverted, which is useful in preventing dormant weed seeds from being brought to the surface, and there is no horizontal slicing of the subsurface soil that can lead to hardpan formation.<ref>Jean-Martin Fortier. [http://store.farmstart.ca/blogs/farmerreviews/12354997-the-rotary-power-harrow-by-jean-martin-fortier "The rotary power harrow"] {{webarchive|url=https://web.archive.org/web/20150214064437/http://store.farmstart.ca/blogs/farmerreviews/12354997-the-rotary-power-harrow-by-jean-martin-fortier |date=2015-02-14 }}, FarmStart Tool Shed, February 18, 2014. Retrieved on 5 March 2015.</ref>