Rice terraces

A terraced rice field built on steep slopes such as mountainside. In mountainous areas, where even steep land has been cultivated, the rice fields are narrow strips with fairly high vertical walls built between the upper and lower rice fields, which are maintained with stones and other materials, giving them the appearance of shelves. Rice terraces are built along contour lines, so they are a type of terrace cultivation. They are also called Senmaida because of the many small rice terraces built on mountainsides. Cultivating rice terraces requires a lot of labor to transport agricultural tools, fertilizer, and materials, and it is difficult to mechanize the cultivation, so it must be done mainly by hand. Water can only be provided by irrigating each rice field with rainwater, or by small springs and reservoirs. In valley-shaped rice terraces in highland areas, snow melts slowly in the spring, so the water temperature does not rise, and frost falls early in the fall, so the high temperature period suitable for rice cultivation is short. Furthermore, rice terraces are made of volcanic ash soil with a lot of gravel, and many of the cultivated soil is shallow and leaks easily. Cold water irrigation is used here, so the fields are prone to cold damage when the extremely low temperatures hit in July and August during the height of summer. In years with little rainfall, they are also prone to drought damage. As such, rice terraces are economically disadvantaged because of the unstable growth and low productivity of the crops.

In Japan, terraced rice fields are particularly common in the Chubu region, at altitudes of 500 meters or more, and can also be found on the coasts of islands with little flat land. Rice terraces are not only found in Japan, but also in many parts of Southeast Asia, including the Philippines and Taiwan, and have developed on a large scale in the highlands of Yunnan Province in China.

[Hoshikawa Kiyochika]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

山腹などの急傾斜地につくられた棚状の田のこと。山間地で急峻(きゅうしゅん)な土地まで開田している場合には、田は幅の狭い帯状になり、その上・下段の田との間はかなり高い垂直の壁がつくられ、これらは石などで保守されていて、その形が棚のようにみえる。棚田は等高線に沿ってつくられるので、いわゆるテラス栽培の一種である。また、山腹などに小さい棚田がたくさんつくられている情景から千枚田ともよばれる。棚田の耕作には農具、肥料、資材の運搬に多くの労力を要し、機械化も困難でおもに手労働によらなければならない。用水も天水の田ごと灌漑(かんがい)や小規模の湧水(わきみず)や溜池(ためいけ)に頼るしかない。高冷地の渓谷型棚田では、春には雪融(ど)けが遅くて水温が上がらず、秋には早い時期に霜が降り稲作に適する高温期間が短い。また棚田は火山灰性の土で砂礫(されき)も多く、作土の浅い漏水田が多い。ここに冷水灌漑が行われているので、盛夏の7、8月に異常低温がくると冷害を受けやすい。雨量の少ない年には干魃(かんばつ)の被害も出やすい。このように棚田は生育が不安定で生産性が低く、経済上不利な条件にある。

　棚田は日本では中部地方の標高500メートル以上の高地にとくに多く、また平坦(へいたん)地の少ない島嶼(とうしょ)の海岸などにもみられる。棚田は日本のみならずフィリピン、台湾など東南アジアの各地にも多くみられ、中国の雲南省の高地にも大規模に発達している。

［星川清親］

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