<資料・研究ノート>与那国島の水田立地と稲作技術 : 東南アジア島嶼部稲作との関連において

Abstract

Yonaguni Island, located at the southwestern end of the Ryukyu Islands, has a humid sub-tropical climate. Information on traditional rice culture on the island prior to the introduction of the socalled Horai rice, the new high-yielding varieties bred in Taiwan in the 1930s, was collected by interviewing old farmers, and the characteristics of rice culture were compared with those in the Southeast Asian archipelago. Wet-rice fields on Yonaguni Island were classified into three groups according to their water and soil conditions : rain-fed (tinchida), inundated (minta), and muddy or swampy (kada). The technical components characterizing the rice culture of the island varied widely with the locational conditions. For land preparation, for example, the dominant method in each group was as follows : tilling and levelling by hand only in kada; tilling by wooden hoe and by cattle-trampling, and levelling by harrow in minta; and tilling by plough, preventing seepage by cattle-trampling, and levelling by harrow in tinchida. The traditional cropping season of wet rice prior to the adoption of Horai rice, with which double cropping of rice was established, differed from that of the mainland of Japan. Wet rice was generally transplanted in January and February with two-month-old seedlings and harvested in June and July. This cropping season was favoured by the rainfall during the northeastmonsoon season, commencing in October, and could avoid danger of typhoons between July and September. A similar cropping season can be found in Taiwan and the east coast of the Philippines as well as throughout the Ryukyu Islands. The local varieties replaced by the Horai rice had the following morphological characters : long culm, long panicle, low tillering-capacity, long awn, black or brown husk, large grains, etc. These characters are considered to resemble those of local varieties grown in the Southeast Asian archipelago, which belong to the so-called bulu or javanica type. Traditional rice culture on Yonaguni Island thus appears to have been characterized by components common to rice cultures of the Southeast Asian archipelago, and is consequently thought to have had a close genealogical relation with this region, as indicated by the practice of cattle-trampling and the similarity of rice varieties and cropping season.