Wetland rice field

Paddy fields are poorly drained fields in which agricultural work is difficult due to excessive humidity and water retention even during periods when irrigation is not performed, and which also make it impossible to grow second crops such as wheat. Wet paddy fields have a high groundwater level and never dry out all year round. The soil temperature is lower than in dry paddy fields in summer, and there is a lack of oxygen, so organic matter decomposes slowly and the humus content is high. Paddy rice is prone to root damage and the lower leaves die off rapidly. Yields are unstable due to lodging, disease, and delayed growth. To improve wet paddy fields, drainage through civil engineering work such as building culverts is necessary. In Japan, the conversion of wet paddy fields to dry paddy fields has been commercialized, and the number of wet paddy fields is on the decline, but on the other hand, the introduction of heavy machinery has formed a compacted layer under the cultivated soil, and this has led to an increase in wet paddy fields.

[Yuki Koyama]

"Wetland Farming" edited by Tadashi Kinoshita (1988, Iwasaki Bijutsusha)

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

水田の灌漑(かんがい)を行わない期間も過湿、滞水のために農作業が困難で、また麦などの裏作ができない排水不良田をいう。湿田は地下水位が高く一年中乾燥することがない。地温が夏は乾田より低く酸素不足の状態で、有機物の分解が遅く腐植含量が高い。水稲は根系障害をおこしやすく、下葉の枯れ上がりが激しい。倒伏や病害、生育遅延などで収量は不安定である。湿田の改良には暗渠(あんきょ)をつくるなど土木工事による排水が必要である。日本では湿田の乾田化が事業化され、湿田は減少傾向にあるが、一方において重量機械の導入により作土下の圧密層が形成され、これによる湿田が増加している。

［小山雄生］

『木下忠編『湿田農耕』（1988・岩崎美術社）』

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