it helps to fight wind erosion), but it does lift and break up the soil (see disc harrow). Modern ploughs Modern ploughs are usually multiply reversible, mounted on a tractor with a three-point linkage. These commonly have from two to as many as seven mould boardsand semi-mounted ploughs (whose lifting is assisted by a wheel about halfway along their length) can have as many as 18. The tractor's hydraulics are used to lift and reverse the implement and to adjust furrow width and depth. The plougher still has to set the draughting linkage from the tractor, so that the plough keeps the proper angle in the soil. This angle and depth can be controlled automatically by modern tractors. As a complement to the rear plough a two or three mould-board plough can be mounted on the front of the tractor if it is equipped with front three-point linkage. Specialist ploughs Chisel plough The chisel plough is a common tool for deep tillage (prepared land) with limited soil disruption. Its main function is to loosen and aerate the soils, while leaving crop residue on top. This plough can be used to reduce the effects of soil compaction and to help break up ploughpan and hardpan. Unlike many other ploughs, the chisel will not invert or turn the soil. This feature has made it a useful addition to no-till and low-till farming practices that attempt to maximise the erosion-preventing benefits of keeping organic matter and farming residues present on the soil surface throughout the year. Thus the chisel plough is considered by some to be more sustainable than other types of plough, such as the mould-board plough. Chisel ploughs are becoming more popular as a primary tillage tool in row-crop farming areas. Basically the chisel plough is a heavy-duty field cultivator intended to operate at depths from to as much as . However some models may run much deeper. Each individual plough or shank is typically set from to apart. Such a plough can meet significant soil drag: a tractor of sufficient power and traction is required. When ploughing with a chisel plough, per shank is required, depending on depth. Pull-type chisel ploughs are made in working widths from about up to . They are tractor-mounted, and working depth is hydraulically controlled. Those more than about wide may be equipped with folding wings to reduce transport width. Wider machines may have the