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agriculture Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people ...
, a harrow is a farm implement used for surface tillage. It is used after ploughing for breaking up and smoothing out the surface of the
soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former ...
. The purpose of harrowing is to break up clods and to provide a soil structure, called tilth, that is suitable for planting seeds. Coarser harrowing may also be used to remove weeds and to cover
seed A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiosper ...
after sowing. Harrows differ from
ploughs A plough or plow ( US; both ) is a farm tool for loosening or turning the soil before sowing seed or planting. Ploughs were traditionally drawn by oxen and horses, but in modern farms are drawn by tractors. A plough may have a wooden, iron or ...
, which cut the upper 12 to 25 centimetre (5 to 10 in) layer of soil, and leave furrows, parallel trenches. Harrows differ from cultivators in that they disturb the whole surface of the soil, while a cultivator instead disturbs only narrow tracks between the crop rows to kill weeds. There are four general types of harrows:
disc harrow A disc harrow is a harrow whose cutting edges are a row of concave metal discs, which may be scalloped or set at an oblique angle. It is an agricultural implement that is used to till the soil where crops are to be planted. It is also used to ...
s, tine harrows (including spring-tooth harrows, drag harrows, and spike harrows), chain harrows, 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 labour Manual labour (in Commonwealth English, manual labor in American English) or manual work is physical work done by humans, in contrast to labour by machines and working animals. It is most literally work done with the hands (the word ''manual ...
ers. In modern practice they are almost always
tractor A tractor is an engineering vehicle specifically designed to deliver a high tractive effort (or torque) at slow speeds, for the purposes of hauling a trailer or machinery such as that used in agriculture, mining or construction. Most commo ...
-mounted implements, either trailed after the tractor by a drawbar or mounted on the three-point hitch. A modern development of the traditional harrow is the rotary power harrow, often just called a power harrow.


Harrow action

In modern mechanized farming, generally a farmer will use two harrows, one after the other. The disk harrow is used first to slice up the large clods left by the mould-board plough, followed by the spring-tooth harrow. To save time and fuel they may be pulled by one tractor; the disk hitched to the tractor, and the spring-tooth hitched to, and directly behind, the disk. The result is a smooth field with powdery dirt at the surface.


Types

In cooler climates the most common types are the ''
disc harrow A disc harrow is a harrow whose cutting edges are a row of concave metal discs, which may be scalloped or set at an oblique angle. It is an agricultural implement that is used to till the soil where crops are to be planted. It is also used to ...
'', 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 deep. A smooth seedbed is prepared for planting with one pass. Chain harrowing can 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. 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. 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 Roller may refer to: Birds *Roller, a bird of the family Coraciidae * Roller (pigeon), a domesticated breed or variety of pigeon Devices * Roller (agricultural tool), a non-powered tool for flattening ground * Road roller, a vehicle for compa ...
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 sort of cultivation is usually followed by broadcast fertilisation and seeding, rather than drilled or row seeding. A drag is a heavy harrow.


Power harrow

A rotary power harrow, or simply 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
rotary tiller A cultivator is a piece of agricultural equipment used for secondary tillage. One sense of the name refers to frames with ''teeth'' (also called ''shanks'') that pierce the soil as they are dragged through it linearly. It also refers to ma ...
, 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.


Historical reference

In
Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
, harrows were used in antiquity and the
Middle Ages In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire ...
. The oldest known illustration of a harrow is in Scene 10 of the eleventh-century Bayeux Tapestry. An Arabic reference to harrows is to be found in Abu Bakr Ibn Wahshiyya's '' Nabatean Agriculture'' (Kitab al-Filaha al-Nabatiyya), of the 10th century, but claiming knowledge from Babylonian sources.


See also

*
List of agricultural machinery Agricultural equipment is any kind of machinery used on a farm to help with farming. The best-known example of this kind is the tractor. Tractor and power * Tractor / Two-wheel tractor *Tracked tractor / Caterpillar tractor Soil cultiv ...
* Roller (agricultural tool) * Harrower (surname)


References


External links

*
Harrows from the 11th-16th centuries"Little Harrows"
Song parody {{DEFAULTSORT:Harrow (Tool) Agricultural machinery Chinese inventions