雑草からみた縄文時代晩期から弥生時代移行期におけるイネと雑穀の栽培形態

縄文時代晩期から弥生時代移行期におけるイネと雑穀（アワ・キビ）の栽培形態を，随伴する雑草の種類組成から検討した。最古の水田は，中国の長江中・下流域で，約6400年前頃から見つかっているが，湖南省城頭山遺跡では，この時期に既に黄河流域で発展した雑穀のアワ栽培も取り入れており，小規模な水田や氾濫原湿地を利用した稲作と微高地上での雑穀の畑作が営まれていた。この稲作と雑穀作のセットは，韓半島を経由して日本に到達したが，その年代にはまだ議論があり，プラント・オパール分析の証拠を重視した縄文時代の中期～後期頃とする意見と，信頼できる圧痕や種子の証拠を重視して縄文時代晩期終末（弥生時代早期）の突帯文土器期以降とする意見がある。縄文時代晩期終末（弥生時代早期）には，九州を中心に初期水田が見つかっているが，最近，京都大学構内の北白川追分町遺跡で，湿地を利用した初期稲作の様子が復元されている。この湿地では，明確な畦畔区画や水利施設は認められていないが，イネとアワが見つかっており，イネは湿地で，アワは微高地上で栽培されていたと考えられる。この湿地を構成する雑草や野草，木本植物の種類組成を，九州の初期水田遺構である佐賀県菜畑遺跡と比較した結果，典型的な水田雑草であるコナギやオモダカ科が見られず，山野草が多いという特徴が抽出できた。この結果から，初期の稲作は，湿地林を切り開いて明るく開けた環境を供出し，明確な区画を作らなくても自然地形を利用して営まれていた可能性を示した。

This paper examined the initial form of rice and millet cultivation during the Jomon-Yayoi transition era from the archaeobotanical weed assemblages. The earliest paddy field was found from the middle and lower Yangzte region in China around 6400 cal BP. Archaeobotanical finds from Chengtoushan show the millet cultivation from northern China was already spread to the Yangtze region in this stage. Rice was probably cultivated on the small initial paddy field as well as on the wetland of flood plain around the site. Millet was probably cultivated on the dry farmland at the upland terrace area in the site. The set of rice and millet cultivation was spread to Japan via southern Korea however the timing of arrival is still under debate. Those who think that the timing was Middle to Late Jomon from the evidence of phytolith records and on the flip side, those who think the timing was after Final Jomon or Initial Yayoi (Tottaimon pottery stage) from the reliable impressions and macro-remains evidences. Although the earliest paddy field in Japan was found from Kyusyu during the Final Jomon or Initial Yayoi era, newly discovered Kitashirakawa-Oiwakecho site in Kyoto shows one of the initial form of wetland rice cultivation. Rice and millet were found from the wetland site without clear evidence of paddy ridges and water facilities for irrigation. The evidences suggest that rice was probably cultivated on the wetland and the millet was cultivated on the dry upland around the site. The composition of archaeobotanical weed and other wild plants from the site was compared with the early paddy field at Nabatake site in Kyushu. The main characteristics of the Kitashirakawa-Oiwakecho wetland site are that there were no typical paddy field weeds such as Monochoria and Alismataceae and there were still a lot of forest herbs compared with the Nabatake paddy field. This results suggest that the initial stage of rice cultivation was practiced by the clearing of swamp forest and making open wetland using natural micro-topography without making clear paddy ridges.

source:https://www.rekihaku.ac.jp/outline/publication/ronbun/ronbun8/index.html#no187