月例の第45回水田勉強会。前回に引き続き、水稲直播栽培の第2弾。

戦後直後、農村人口の減少と食料需要の急増に応えるべく始まった水稲直播栽培の研究。1970年代に田植え機が出現したことで、一気に下火となったものの、2000年代以降の大規模化で再び注目を集めるようになった。

代かき後に直播する湛水直播栽培と畑地状態で直播する乾田直播栽培に大別される。いずれの技術も苗作りに掛かる多大な労力を軽減することが最大の目的。一方で、そのトレードオフとして発生する出芽不良、苗立ち不良、雑草害を克服するために、各種要素技術を開発してきたというのが直播栽培研究の歴史。

苗立ちを確保後は通常の湛水栽培と同様に管理する。一方で、ここ数年で注目を集めてきたのが、苗立ち後も極力湛水しない節水型乾田直播栽培。湛水は簡便で強力な雑草管理技術だが、節水型では湛水の最大のメリットを享受できない。この問題を如何に克服するか。今後の技術開発に注目する必要がある。

犬飼様（中部電力）
「中部電力が取り組む節水型乾田直播栽培」
渡邊様（中日本農研）
「水稲直播栽培のこれまでと近年開発された新しい技術」

The 45th Monthly Rice Paddy Study Group Meeting.

Continuing from the previous session, this is the second installment on direct seeding cultivation of rice.

Research on direct seeding cultivation of rice began in the immediate postwar period to address the declining rural population and rapidly increasing food demand. The technology declined sharply in the 1970s with the emergence of rice transplanting machines, but has attracted renewed attention since the 2000s due to the expansion of large-scale farming operations.

Direct seeding cultivation is broadly categorized into flooded direct seeding, where seeds are sown after puddling, and dry direct seeding, where seeds are sown in upland field conditions. The primary objective of both technologies is to reduce the substantial labor required for seedling production. On the other hand, the history of direct seeding cultivation research has centered on developing various component technologies to overcome the trade-offs that arise from adopting direct seeding—namely, poor germination, poor seedling establishment, and weed damage.

After securing seedling establishment, management follows the same procedures as conventional flooded cultivation. Meanwhile, water-saving dry direct seeding cultivation, which minimizes flooding even after seedling establishment, has gained attention in recent years. While flooding is a simple and powerful weed management technique, water-saving systems cannot fully benefit from this major advantage of flooding. How to overcome this challenge requires close attention to future technology development.

Mr. Inukai (Chubu Electric Power Company)
“Water-saving dry direct seeding cultivation initiatives by Chubu Electric Power”

Dr. Watanabe (Central Region Agricultural Research Center, NARO)
“The history of direct seeding rice cultivation and recently developed new technologies”