| However, the decreasing trend did not stop even in the Heisei period (1989 -), and during the decade starting in 1998 the production amount fell to 20,000 tons, which was one quarter of the amount produced in the decade starting in 1965. |
しかし、平成に入っても減少傾向が止まらず、平成10年代では昭和40年代の1/4である2万tにまで落ち込んでいる。 |