1. Research Faculty of Agriculture, Hokkaido University, Kita 9 Nishi 9, Kita-ku, Sapporo, Hokkaido 060-8589, Japan
2. Sansui Consultant, Yowa Building, 23 Nishi-Kazariya-chou, Shimogyo-Ku, Kyoto 600-8108, Japan
3. Hokkaido Kamikawa Subprefecture, Office of Northern Farmland, 3294-49 Higashiyama, Shibetsu, Hokkaido 095-0044, Japan