From Wikipedia, the free encyclopedia
The plough (American spelling: plow) is a tool used in farming for initial cultivation of soil in preparation for sowing seed or planting. Ploughs are also used by industry underseas, for the laying of cables, as well as preparing the earth for side-scan sonar in a process used in oil exploration.
The plough can be regarded as a development of the pick, or of the spade. Ploughs were initially pulled by humans, later by oxen, and later still in some countries, by horses. In industrialized countries, the first mechanical means of pulling a plough used steam-power (ploughing engines or steam tractors), but these were gradually superseded by internal-combustion-powered tractors.
Ploughing has several beneficial effects. The major reason for ploughing is to turn over the upper layer of the soil. This may also incorporate the residue from the previous crop into the soil. Ploughing reduces the prevalence of weeds in the fields, and makes the soil more porous, easing later planting. Excessively deep ploughing or digging brings up subsoil and mixes subsoil with topsoil. This can damage the soil.
 History of the plough
When agriculture was first developed, simple hand held digging sticks or hoes would have been used in highly fertile areas, such as the banks of the Nile where the annual flood rejuvenates the soil, to create furrows wherein seeds could be sown. In order to regularly grow crops in less fertile areas, the soil must be turned to bring nutrients to the surface.
 Scratch plough
The domestication of oxen in Mesopotamia, perhaps as early as the 6th millennium BC, provided mankind with the pulling power necessary to develop the plough. The very earliest ploughs were simple scratch-ploughs and consisted of a frame holding a vertical wooden stick that was dragged through the topsoil. Because this form of plough leaves a strip of undisturbed earth, according to Lynn White, "cross-ploughing is necessary, with the result that, in regions where the scratch-plough is used, fields tend to be squarish in shape, roughly as wide as they are long." In the archeology of northern Europe, these squarish fields are referred to as "Celtic fields".
 Mouldboard plough
These were much later developed into mouldboard ploughs (American spelling: moldboard), which is a form of plough consisting of a plowshare (blade) and hitch attached to either a tractor or livestock. It turns the soil in one run across the field, depositing the weeds and undecomposed remains of the previous crop under the soil and raising the rain-percolated nutrients back to the surface. This plough also allowed for ploughing while the ground was wet. The water was drained due to channels formed under the overturned earth.
The French historian Marc Bloch, whose pioneering work contributed to our distinction between the scratch and mouldboard ploughs, emphasizes the difference between the two on the basis of having wheels. His research in medieval French agricultural history showed the existence of names for two different ploughs, "the araire was wheel-less and had to be dragged across the fields, while the charrue was mounted on wheels".
The mouldboard, carried below the frame, is tipped with a share (also called a ploughshare), an asymmetric arrow-shaped device designed to slice through the ground horizontally as it moves forward. It also has a coulter, a sharpened blade or disc, attached to the frame of the plough to cut down through the ground, ahead of the share, and also to cut deepset and tough roots. A runner extending from behind the share to the rear of the plough controls the direction of the plough, because it is held against the bottom land-side corner of the new furrow being formed. The holding force is the weight of the sod, as it is raised and rotated, on the curved surface of the moldboard. Because of this runner, the mouldboard plough is harder to turn around than the scratch plough, and its introduction brought about a change in the shape of fields -- from mostly square fields into longer rectangular "strips" (hence the introduction of the furlong).
It was originally designed for "sod busting": the reclaiming of raw land and creation of farmland. However, until the past two decades it was routinely used even on previously tilled land, in the Midwest of the United States and elsewhere. Awareness of the potential for soil damage has led to reduced use in favour of shallower ploughing and other less invasive tillage techniques.
Despite a number of innovations, the Romans never achieved the heavy wheeled mouldboard plough; Lynn White dates its first indisputable appearance after the Roman period to 643, in a northern Italian document. On the other hand, White describes the linguistic researches of B. Bratanič of the University of Zagreb, who showed that twenty-six technical terms connected with the heavy plough and its use "are to be found in all three of the great Slavic lingusistic groups, the eastern, western and southern", pointing to its adoption by these people before their division in the later sixth century, and indicating that the mouldboard plough was invented by 600 then introduced to Europe. Despite this, "Bratanič does not claim the invention of the heavy plough for the Slavs, but for 'some northern peasant culture' as yet unidentified." It appears to have been independently developed in Han Dynasty China, around 100 BC. Despite the date or place of its origins, White argues that adoption of the mouldboard plough, accompanied with adoption of the three-field system, occurred in the later eighth and early ninth centuries, and led to an improvement of the agricultural productivity per unit of land in northern Europe.
The Girard (or Gerard) plough was developed in the early 14th century in what is now Belgium by Girard de Liege. It was the first plough design to have an iron blade.
The first commercially successful iron plough was the Rotherham plough, developed by Joseph Foljambe in Rotherham, England, in 1730. It was durable and light, and was engineered after the mathematical principles of James Small, who designed a mouldboard that would cut, lift and turn over the strip of earth. (All the major components of the Rotherham plough had been well known in China for millennia, and diffusion of technology from China, probably by the Dutch, is highly likely).
 Post-Industrial Revolution
Steel ploughs were developed during the Industrial Revolution and were lighter and more durable than ploughs made of iron or wood. The cast-steel plough was developed by U.S. blacksmith John Deere in the 1830s. By this time the hitch, to the draught animals, was adjustable so that the wheel at the front was held onto the ground. The first steel ploughs were walking ploughs, having two handles held by the ploughman to provide a degree of control over the depth and location of the furrow behind the draughting force. The ploughman often was also controlling the draught animal(s). Riding ploughs with wheels and a seat for the operator came later, and often had more than one share.
A single draught horse can normally pull a single-furrow plough in clean light soil, but in heavier soils two horses are needed, one walking on the land and one in the furrow. For ploughs with two or more furrows, one or more horses have to walk on the loose ploughed sod -- and that makes hard going for them, and treads the newly ploughed land down. It is usual to rest such horses every half hour for about ten minutes.
Amish farmers tend to use a team of about seven horses or mules when spring ploughing and as Amish farmers often help each other plough, teams are sometimes changed at noon. Using this method about 10 acres can be ploughed per day in light soils and about 2 acres in heavy soils.
In the Appalachian region, plows are still used on some rural farms. It is not uncommon to see very steep land, not tillable by mechanical means due to the threat of causing the vehicle to roll, being ploughed with one horse or mule and a "hillside plough". The hillside plow has the advantage of being easily and quickly switched from turning the soil to the left, to turning the soil to the right, and back and forth. When the farmer gets to the end of the row and the draught animal has completed the turn back to plough the next row, the plough is lifted just enough to clear the soil, a manual lever is depressed, and the plough blade itself can be swung back under the plough where it clicks into place into the opposite configuration. This saves the animal's strength by allowing the plough to always turn the soil downhill, which makes for easier pulling. The hillside plough is only good for use on steep hillsides with easily tillable soil, due to its light weight, which allows the farmer to do the lift and switch procedure at the end of each row.
 Steam ploughing
The advent of the mobile steam engine allowed steam power to be applied to ploughing from about 1850. In Europe, soil conditions were too soft to support the weight of the heavy traction engines. Instead, counterbalanced wheeled ploughs, known as "balance ploughs", were drawn by cables across the fields by pairs of ploughing engines.
In America the firm soil of the Plains allowed direct pulling with steam tractors, such as the big Case, Reeves or Sawyer Massey breaking engines. Gang plows of up to fourteen bottoms were used. Often these big ploughs were used in regiments of engines, so that in a single field there might be ten steam tractors each drawing a plough. In this way hundreds of acres could be turned over in a day. Only steam engines had the power to draw the big units. When gas engines appeared, they had neither the strength nor the ruggedness compared to the big steam tractors. Only by reducing the number of shares could the work be completed.
 Stump-jump ploughs
The Stump-jump plough is an Australian invention of the 1870s, designed to cope with the breaking up of new farming land, that contains many tree stumps and rocks that would be very expensive to remove from paddocks. The plough uses a moveable weight to hold the ploughshare in position. When a tree stump or other obstruction such as a rock is encountered, the ploughshare is thrown upwards, clear of the obstacle, to avoid breaking the plough'd harness or linkage; ploughing can be continued when the weight is returned to the earth after the obstacle is passed.
A simpler system, developed later, uses a concave disk (or a pair of them) set at a large angle to the direction of progress, that uses the concave shape to hold the disk into the soil -- unless something hard strikes the circumference of the disk, causing it to roll up and over the obstruction. As the arrangement is dragged forward, the sharp edge of the disk cuts the soil, and the concave surface of the rotating disk lifts and throws the soil to the side. It doesn't make as good a job as the mouldboard plough (but this is not considered a disadvantage, because it helps fight the wind erosion), but it does lift and break up the soil.
 Reversible plough
Traditional ploughs can only turn the soil over in one direction, as dictated by the shape of the mouldboard. The resulting method of traversing an entire field leads to the ridge and furrow effect seen in some ancient fields.
Modern ploughs are reversible, having 2 sets of mouldboards: while one is working the land, the other is carried upside-down in the air. During the cultivation process, hydraulics are used to turn over the whole plough at each end of the field so that the second set of moulboards can be used. The field can then be traversed in such a way as to keep the land level, avoiding ridges and furrows.
The modern reversible plough is mounted on a tractor via a three-point hitch. These commonly have sets of 2 up to 7 mouldboards, but semi-mounted ploughs, the lifting of which are supplemented by a wheel about half-way along its length, can have as many as 18. The hydraulic system of the tractor is used to lift and reverse the implement, as well as adjust furrow width and depth. The ploughman still has to set the draughting linkage from the tractor so that the plough is carried at the proper angle in the soil. This angle and depth can be controlled automatically by modern tractors. The goal for ploughing is to get the soil lose, enrich it with oxygen, get rid of unwanted plants and certain bacteria. The plants that get ploughed under decompose, and serve as compost.
 Chisel plough
The chisel plow is a common tool to get deep tillage with limited soil disruption. The main function of this plow is to loosen and aerate the soils while leaving crop residue at the top of the soil. This plow can be used to reduce the effects of compaction and to help break up plowpan and hardpan. Unlike many other plows the chisel will not invert or turn the soil. This characteristic has made it a useful addition to no-till and limited-tillage farming practices which attempt to maximize the erosion prevention benefits of keeping organic matter and farming residues present on the soil surface through the year. Because of these attributes, the use of a chisel plow is considered by some to be more sustainable than other types of plow, such as the moldboard plow.
The chisel plow is typically set to run up to a depth of eight to twelve inches (200 to 300 mm). However some models may run much deeper. Each of the individual plows, or shanks, are typically set from nine inches to twelve inches apart. Such a plow can encounter significant soil drag, consequently a tractor of sufficient power and good traction is required. When planning to plow with a chisel plow it is important to bear in mind that 10 to 15 horsepower (7 to 11 kW) per shank will be required.
 Use of the mouldboard plough
In modern use, the mouldboard plough was used for three reasons:-
- Foremost was the control of weeds. In this function, mouldboard ploughing is very successful, a farmer can control weed growth with far fewer herbicides by using this technique than is otherwise possible with any other method, aside from hand weeding, which is labor-intensive and not practical for large operations.
- To break up the soil for planting.
- To warm the soil for planting.
Only the first reason for mouldboard ploughing really paid off. Most plants require little soil agitation to germinate, so breaking up soil is unnecessary beyond what a planting implement accomplishes on its own. Soil warming is also unnecessary beyond two or three inches below the surface, therefore bringing black fresh soil which heats more quickly and more deeply after the final frost of the year in unneeded.
 Problems with mouldboard ploughing
Mouldboard ploughing has become increasingly recognized as a highly destructive farming practice with the possibility of rapidly depleting soil resources. In the short term, however, it can be successful, hence the reason it was practised for such a long time. A field that is mouldboarded once will generally have an extraordinary one time yield as the larvae of pests and seed from weeds are buried too deeply to survive. After the first harvest, however, continued mouldboarding will diminish yields greatly.
The diminishing returns of mouldboard ploughing can be attributed to a number of side effects of the practice:-
- Foremost is the formation of hardpan, or the calcification of the sub layer of soil. In some areas, hardpan could once be found so thick it could not be broken up with a pickaxe. The only effective means of removing hardpan is using a "ripper", or chisel plow, which is pulled through the hardpan by an extremely powerful and costly tractor. Obviously, this layer eventually becomes impenetrable to the roots of plants and restricts growth and yields. This layer also becomes impenetrable to water, leading to flooding and the drowning of crops.
- Mouldboard ploughing rapidly depletes the organic matter content of soil and promotes erosion; these two problems go hand in hand. As soil is brought to the surface, the root structure of the previous harvest is broken up, and the natural adhesion of soil particles is also lost; though loose soil appears good for plant germination (and it is), this loose soil without cohesion is highly susceptible to erosion, multiplying the rate of erosion by several factors compared to a non-mouldboarded plot. This increased rate of erosion will not only outpace the rate of soil genesis but also the replacement rate for organics in the soil, thus depleting the soil more rapidly than normal.
- Mouldboard ploughing leads to increased soil compaction and loss of pore space within the soil. Soil is a bit like a bucket full of balls filled with sand. Each ball represents a cohesive particle of soil, and when stacked the balls leave a great deal of air space, required for healthy root growth and proper drainage. Mouldboarding so disturbs the soil that it breaks these balls and releases their contents. When this happens, the much smaller particles that are within the larger particles are released and pore space diminishes, leading to hard compacted soil that floods easily and restricts root growth.
 Soil erosion
One negative effect of plowing is to dramatically increase the rate of soil erosion, both by wind and water, where soil is moved elsewhere on land or deposited in bodies of water, such as the oceans. Plowing is thought to be a contributing factor to the Dust Bowl in the US in the 1930s. Alternatives to plowing, such as the no till method, have the potential to limit damage while still allowing farming.
 Plough parts
- Share (also called a plowshare or ploughshare)
- Knife or coulter
On modern ploughs and some older ploughs, the mouldboard is separate from the share and runner, allowing these parts to be replaced without replacing the mouldboard. Abrasion eventually destroys all parts of a plough that contact the soil.
 See also
- Ard (plough) (Prehistoric plough)
- Aratrum (Ancient Greek plough)
- Sokha (Old Russian scratch-plough)
- Ridge and furrow
- Railroad plough
- Foot plough
- Museum of Scottish Country Life
- ^ Lynn White, Jr., Medieval Technology and Social Change (Oxford: University Press, 1962), p. 42. However, White notes later in the same book "that there is no absolute correlation between field-shape and plough-form", citing several examples (p. 46).
- ^ Following White (Medieval Technology, p. 41), who nonetheless acknowledges the work of August Meitzen.
- ^ Marc Bloch, French Rural History, translated by Janet Sondheimer (Berkeley: University Press, 1966), p.50
- ^ White, Medieval Technology, p. 50
- ^ White, Medieval Technology, pp. 49f
- ^ White, Medieval Technology, pp. 69-78