![]() The productivity of a two-bottom lister is 1.4–1.7 hectares per hr. The distance between the axes of adjacent ridges is 135–140 cm. The ridges thus formed are 20 cm high and up to 90 cm wide. In the second pass, a second, newly formed half-ridge is added to one half-ridge. A single pass of the body of the plow bottom forms one ridge and two half-ridges the graders level the surface of the ridges, and the small harrows loosen the soil. Four fertilizer distributors and four injection knives are mounted on the cultivator to introduce inorganic fertilizers. The working parts of listers made in the USSR are two plow bottoms with graders and three small harrows. It operates in a unit with a vegetable planter and fertilizer distributor. It is used to cultivate vegetables on soils with high groundwater levels. The plow often symbolizes agriculture, as in the great seals of New Jersey, Pennsylvania, Tennessee, and other states. Among the various types of plows in use today are the reversible two-way plow for contour plowing listers and middlebusters, which prepare shallow beds the disk plow, whose revolving concave disks are useful in working hard or dry soil the rotary plow, with an assembly of knives on the shaft that mix the surface growth with the soil and the chisel plow, with points mounted on long shanks to loosen hard, dry soils and shatter subsurface hardpan. With more powerful tractors, larger plows have come into use. Tractors now supply this power in most developed parts of the world. In 19th-century America horses largely replaced oxen for drawing plows. Standardized by 1870, the modern moldboard plow has been improved by various attachments, e.g., the colter, a sharp blade or disk that cuts the ground in advance of the share. They included streamlined moldboards, replaceable shares, and steel plows with self-scouring moldboards. Important improvements in design and materials were made in the early part of the 19th cent. saw the introduction into England of the moldboard, a curved board that turns over the slice of earth cut by the share. The plow evolved gradually until c.1600, when British landlords attempted greater improvements. Such implements were capable of breaking but not of inverting the soil. The early plow consisted simply of a wooden wedge, tipped with iron and fastened to a single handle, and a beam, which was pulled by men or oxen. The plow is depicted on Egyptian monuments, mentioned in the Old Testament, and described by Hesiod and Vergil. Its beginnings in the Bronze Age were associated with the domestication of draft animals and the increasing demand for food resulting from the rise of cities. The plow is generally considered the most important tillage tool. ![]() Plow or plough, agricultural implement used to cut furrows in and turn up the soil, preparing it for planting.
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