Science Fair Project Encyclopedia
The plough (American spelling: plow) is a tool used in farming for turning the earth in which one is to plant new seeds. The plough is a development of the pick, and was initially pulled by oxen or humans, and later horses. Modern ploughs are, in industrialized countries, powered by tractors.
Ploughing has several beneficial effects. The major reason for ploughing is to incorporate the residue from the previous crop into the soil. Ploughing also reduces the prevalence of weeds in the fields, and makes the soil more porous, easing later planting.
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 rejuvinates the soil, to create furrows in which seeds could be sown. In order to regularly grow crops in less fertile areas the soil must be turned to bring saturated nutrients to the surface. The domestication of oxen in Mesopotamia some time around 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. These were much later developed into mouldboard ploughs (American spelling: moldboard) which turned 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 ploughing while the ground was wet. The water was drained due to channels formed under the overturned earth.
The mouldboard, carried below the frame, is tipped with a share, 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, to also 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".
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. (It should be noted that all the major components of the Rotherham plough had been well known in China for millenia, and diffusion of technology from China, probably by the Dutch, is highly likely).
Steel ploughs were developed during the Industrial Revolution and were lighter and more durable than ploughs made of iron or wood. The cast-steel plow 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 animals 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. It is usual to rest such animals every half hour for about ten minutes.
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 harness or linkage of the whole plough; ploughing can be continued when the weight is returned to the earth after the obstacle is passed. Developed later, a simpler system 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.
Modern ploughs are mounted on tractors. They can have as many as six mouldboards. They are quite short and the hydraulic system of the tractor is used to lift and carry the unit. The ploughman still has to set the draughting linkage from the tractor so that the plough is carried at the right angle in the soil to maintain its depth.
- 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.
On a vehicle such as a tram, a plough is also the name commonly given to the pair of shoes, one pick-up and one return, both attatched to a busbar, which draw power from a pair of live rails underneath the road.
- Aratrum (Ancient Greek plough)
- Ploughman's lunch
- Ridge and furrow
- Operation Plowshare
- Plowshares Movement
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