Plow

Plow, agricultural implement used to break and turn over soil. An important agricultural tool, the plow has been used since prehistoric times. The first plows were probably forked tree boughs; the end of one of the branches was used to dig into the soil, and the other branch (or branches) was used as a handle. The implement could be pushed, or pulled by ropes attached to a person or animal. Such simple plows are still used in light soil in some parts of the developing world. The Romans of antiquity used a light scratch plow with an iron share (also called a blade) drawn by oxen. The heavy wheeled plow was developed in the Middle Ages (from about the 5th to the 15th centuries ad) to turn over the heavier soil of northwest Europe. It had a sharp point of iron or steel to cut under the soil; this sharp vertical cutter (also called a colter) was located directly in front of the share, making a preliminary cut that the share deepened and widened. It also had a moldboard behind the share to heave up the cut sod, and a tongue in front of the plow that could be attached to a team of from two to eight oxen.

The plow changed little until the 1830s, when the heavy prairie soils of the North American Midwest brought about the invention of the steel plowshare by the American blacksmith John Deere. The two-wheeled sulky plow, which had a seat for the rider, appeared during the American Civil War (1861-1865). In the 1890s, steam-powered tractors were successfully used on a few large farms, and after 1900 cheaper gasoline-powered tractors began to replace horses as plow traction. Tractors were not widely adopted, however, until the introduction of the small all-purpose tractor in 1924 and the development of low-pressure rubber tires in 1932.

Modern tractor-drawn plows may have as many as five sets of plowshares and moldboards, which can be raised and lowered hydraulically. Disk plows, for use in tough soils, are equipped with several concave disks. Rotary plows, also known as rototillers, have cutters mounted on a rotating horizontal shaft. Deep plowing is done by subsoilers, with long steel-pointed shanks that can penetrate the soil up to about 1 m (about 3 ft), or by chisel plows, with several shanks carrying double-ended shovels, capable of plowing about 50 cm (about 20 in) deep.