Plow - Plow (English spelling)

In the UK, it is also spelled plough. Like the Japanese plough, it is a primary tillage tool that turns over and breaks up the soil, but compared to the Japanese plough, it has better turning performance, is better at turning over and burying grass and organic matter, tills deeply and widely, and has a fast working speed, making it highly efficient. The soil clods are coarse, which has a drying effect, the tillage pan is flat and stable, and it is easy to operate, making it suitable for leveling fields and plowing pastures. However, its structure is somewhat complex, large, and heavy, and secondary tillage (soil crushing) must be done separately afterwards compared to rotary tillers, and in paddy fields it creates more resistance than a plough, making it unsuitable for ridge plowing. However, since around 1980, it has become possible to attach a soil crusher to the rear and perform the work in one process.

Plows have been used in agriculture since around 3500 BC in ancient Mesopotamia and Egypt, using curved, L-shaped pieces of wood pulled by humans or livestock. At that time, the ploughs did not turn over, but were used to crush, dig and stir the soil, but they were later passed on to Rome, and then to the Netherlands, where the prototype of today's curved, soil-removing board ploughs was created. This was brought to America around 1620, where it was gradually improved. At that time, only the plowhead and plow knife were made of iron, but around 1930 they became all cast iron. Plows were imported to Japan from America in 1870 (Meiji 3) to Hokkaido for use with animal power, and a lightweight, small paddy field plough was manufactured in 1881. Plows for use with tractors were not made until the Showa era began.

There are many types of plows, depending on the shape of the plow body, purpose, traction method, gravel (ridges made by the plow) turning direction, material, number of connections, etc., but the most typical is the mouldboard plow. This is further divided into three types: re-cultivation plows (with a cylindrical mouldboard curved surface, suitable for already cultivated land or sandy land, intended for crushing and mixing the soil), new reclamation plows (twisting type, suitable for heavy clayey soil, grassland, and uncultivated land, has low crushing power and turns completely), and dual-purpose plows, which are intermediate between the two. To ensure the plowing effect, ploughs are equipped with coulters, jointers (also called front plows, used for two-stage plowing), auxiliary blades, and straightedge wheels, as well as obstacle avoidance safety devices.

To increase efficiency, high-speed plows operated at speeds of 8 to 12 kilometers per hour, subsoil plows that till the subsoil and topsoil separately, subsoiler plows that till only the subsoil, disc plows that tilt a rotating spherical plate to perform drag tilling, reciprocating plows that can be rotated to either the left or right, and plastic plate plows that can prevent soil adhesion on volcanic ash or clay soils are also commonly used. Recently, attention has been paid to vibration tillage aimed at reducing resistance, installation on the front and rear of tractors, and combinations to improve efficiency and prevent compaction.

[Masaki Matsuo]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

イギリスではploughとも綴(つづ)る。和犂(わすき)とともに土を反転破砕する一次耕うん用農機具であるが、和犂に比べて反転性能がよく、草や有機物の反転埋没に優れ、深く幅広く耕うんし作業速度も速いので能率が高い。土塊が粗いので乾土効果があり、耕盤は平坦(へいたん)で安定がよく、操作が容易であるため、畑地の平起しや牧草地耕起に適している。しかし構造がやや複雑で大型で重く、ロータリー耕に比べ二次耕うん（砕土）をあとから別に行う必要があり、また水田では犂より抵抗が大きく、うね立て耕には適さない。ただし1980年ごろより砕土機類を後ろに備え一工程で行うこともできるようになった。

　プラウは、古代メソポタミアやエジプトにおいて紀元前3500年ごろから、くの字型の曲木(まげき)を人か家畜に引かせて農耕に用いていた。当時のものは反転せず、破砕、掘り起し、攪土(かくど)型であったが、以後ローマに渡り、さらにオランダで現在の曲面状の撥土(はつど)板プラウの原型がつくられた。これが1620年ごろアメリカに渡り、しだいに改良された。そのころのプラウは、犂先(すきさき)と犂刀(りとう)のみが鉄であったが、1930年ごろ全鋳鉄製となった。わが国へは1870年（明治3）アメリカから北海道に畜力用として輸入され、1881年に軽量小型の水田プラウが製作された。トラクター用は昭和に入ってからつくられた。

　プラウは犂体(りたい)形状、用途、牽引(けんいん)法、れき（プラウでつくられるうね）の反転方向、材質、連結数などにより多くの種類があるが、もっとも代表的なものは撥土板（モールドボード、ボットム）プラウである。これはさらに再墾プラウ（撥土板曲面が円筒型で既耕地や砂質地向きで砕土混耕が目的）、新墾プラウ（捻転(ねんてん)型で重粘地、草生地、未耕地向きで、破砕力が弱く完全反転する）、およびこれらの中間型である兼用プラウの3形態に分けられる。プラウ耕の作用を確実にするためコールター（犂刀）、ジョインター（前犂(ぜんり)ともいい二段耕に用いる）、補助羽根、定規車などを備えたり、障害物回避安全装置をつけたりする。

　能率増進のため毎時8～12キロメートルの速度で用いる高速度プラウ、心土と作土を別々に耕す心土プラウ、心土のみを耕すサブソイラ、自転する球面皿板を傾けて牽引耕うんするディスクプラウ（円板プラウ）、左右どちらにも反転できる互用プラウ、火山灰や粘土地で土壌付着を防止できる樹脂板プラウなどもよく用いられる。最近は抵抗減をねらった振動耕うんやトラクター前後装着、能率向上と踏圧防止のための複合化などが注目されている。

［松尾昌樹］

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