In "Ruiju Sandai Kaku" (Assorted regulations from Three Reigns), two pieces of Daijokanpu (official documents issued by Daijokan, Grand Council of State) dated October 5, 723 and September 6, 839, respectively, ordering the promotion of buckwheat cultivation were included.
『類聚三代格』には養老7年8月28日（723年）と承和(日本)6年7月21日（839年）付けのソバ栽培の奨励を命じた2通の太政官符を掲載している。