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弥生時代の米収量を推定する
ー赤米の栽培実験から


        菊地有希子     1,2
        1早稲田大学シルクロード調査

          研究所
        2株式会社パレオ・ラボ
現状と問題点
• 奈良・平安時代の文献史料に書かれた米収量
  – 唯一の確かな手がかり
  弥生時代だからと、さらに低く見積もる
    → 低い収量推定値:64 kg/10a以下
• 弥生時代後期の水田跡で検出されている稲株痕
  – 高密度:1㎡あたり121株(坪あたり412株)
 株密度に対する否定的見解が多いが、誰も
  実際に試したことがない
稲株痕の発掘事例
・百間川原尾島遺跡 (岡山県)
・弥生時代後期 : 0-250 AD
・田植えの痕跡と考えられている(列状)

                  7cm
株密度の問題
・百間川原尾島遺跡
 1m2あたり121株
  (株間8cm)
・現代の水田
 1m2あたり18株
  (株間25cm)
・否定的見解
・密過ぎて育たない説
・育ったとしても、計算上、
 高収量になり、弥生時代
 としては非現実的説
方法
• 栽培実験
   2種類の赤米を異なる植え方(散播・田植
   え)および密度で栽培し、収量を調べる

• 復元水田(実験田)
   無農薬
   無施肥(堆肥も無し)
a   b
実験に使用する赤米
• 豆酘 ーa
 ・長崎県対馬豆酘産
 ・籾殻が黒褐色
• 北上   ーb
・東北地方の農家から
・籾殻が黄褐色

注:両者とも実験での便宜上の名称
なぜ赤米なのか?
• 赤米は、現存する米の中最も昔の米に近い種類
   の1つだから
• 赤米は、昔の米が持っていたと推測される特徴
   の多くを色濃く残している
 草丈が高い(倒れやすい)、収量が低い、芒が長い、etc.
•古代米が赤米だったかどうかは,分析技術が確
  立していないため、現状では不明


             ?
             =
栽培方法
・散播
・田植え 1m2あたり18株
 (坪あたり60株)
                      散播
・田植え 1m2あたり30株
 (坪あたり100株)
・田植え 1m2あたり121株
 (坪あたり400株)

                  田植え直後 (2009年6月)
周辺地形 埼玉県入間市宮寺




                ☆
周辺環境と実験田の位置
  実験田




• 狭山丘陵の谷水田
• 東:雑木林
  西:茶畑
             西久保湿地
1区画=3坪
実験区画


      散播 →
1m2あたり121株→
1m2あたり30株→

1m2あたり18株→
収量計算の方法
• 収量構成4要素を調査
   1単位面積あたりの穂数
   2平均1穂籾数
   3登熟歩合
   4玄米1,000粒重
・1 & 2 : 各区画において平均的な20株を調査
・3 & 4 : 各区画において平均的な10株を調査


• 単位面積あたりの玄米収量
             = 収量構成4要素の積
kg/10a
         実験結果
 350
                豆酘 散播

300
                豆酘
                1㎡あたり18株
250             豆酘
                1㎡あたり30株
200             豆酘
                1㎡あたり121株
150             北上 散播

                北上
100             1㎡あたり18株
                北上
 50             1㎡あたり30株
                北上
  0             1㎡あたり121株
奈良・平安時代の米収量
        水田の等級                玄米重量 (㎏
                                 /10a)

        上       田              106.635

        中       田               85.333

        下       田               64.031

         下々田                    32.016
沢田吾一1972による試算,寺沢薫・寺沢知子1981の度量換算表より、10aあたり玄米重量
に換算
弥生時代の米収量を推定する
 350

 300
         実験の結果   従来の推定値
 250

 200

 150

 100

  50

   0
kg/10a
結論
• 密植(1m2あたり121株)は、弥生時代後期におい
  て、単位面積あたりの収量を上げる方法の一つ
  だった可能性がある
   – 肯定的に捉えられる

• 弥生時代の米収量は、従来の推定値(32-64
  kg/10a)よりも高かった可能性がある
       1m2あたり18株 : 102-113 kg/10a
       1m2 あたり121株:144-212 kg/10a
   などの実験結果が今後、手がかりとなる
ご清聴ありがとうございました

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弥生時代の米収量を推定するー赤米の栽培実験から