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. |
Horse-drawn plough.
A pair of metal wheels from a plough on a farm near Dordrecht, Eastern Cape. |
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Chisel plough
The chisel plough is a common tool to get deep tillage with limited soil disruption. The main function of this plough is to loosen and aerate the soils while leaving crop residue at the top of the soil. This plough can be used to reduce the effects of compaction and to help break up plowpan and hardpan. Unlike many other ploughs 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 plough is considered by some to be more sustainable than other types of plough, such as the Mouldboard Plough.
The chisel plough 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 ploughs, 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 plough with a chisel plough it is important to bear in mind that 10 to 15 horsepower (7 to 11 kW) per shank will be required.
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