寒地水稲の湛水土中直播栽培における収量および食味関連形質の特性  [in Japanese] Grain Yield and Palatability of Rice Direct-seeded under Submerged Soil Condition in Hokkaido, in Northern Japan  [in Japanese]

北海道での洪水土中直播栽培(以下,直播と記す)の生産性と食味特性を明らかにするため,中央北部,中央南部および南部で,1997〜2002,2004〜2006年に,直播の精玄米収量,収量構成要素および食味関連形質を,同一窒素施肥量の移植と比較した.中央部で早生品種(3品種)の直播と早生,中生(3品種)の移植を,南部で中生の直播と中生,晩生(1品種)の移植を行った.直播の出穂期は,同一品種やそれより出穂が1ランク遅い品種の移植に比べ,各8.1〜10.7日,4.0〜7.9日遅く,そのため出穂後35日間の日平均積算気温が低かった.収量構成要素では,直播は移植に比べ,m^2当たり穂数が多く一穂籾数は少なく,m^2当たり稔実籾数に一定の傾向はなく,精玄米収量との関係で登熟性を表す稔実籾収量粒数比[(精玄米収量/千粒重)/m^2当たり稔実籾数]が低かった.また,収穫指数も低かった.そのため,直播の精玄米収量は,熟期のより遅い品種での移植対比で76.9〜99.7%,平均86.9%と低く,収量性の向上には粒の肥大を促進し登熟度を高めるなど登熟期の生育を改善する必要があった.食味関連形質では,直播は移植に比べ出穂期が遅く出穂後35日間の日平均積算気温が低いため,アミロース含有率がやや高く糊化最高粘度がやや低かった.蛋白質含有率は,同一品種では直播が移植よりやや低いが,直播の熟期が早い場合には両栽培法間に差がなかった.農水栽培の直播は主に移植より熟期が早い品種で行われるため,アミロース含有率が高く糊化最高粘度が低くなる点で良食味生産に不利であった.

Grain Yield (GY), its components and palatability of rice direct-seeded under a submerged soil condition (direct-seeded rice, DSR) were compared with those of transplanted rice (TR) applying a similar amount of nitrogen fertilizer during 1997-2002 and 2004-2006 in Hokkaido. In central Hokkaido, three early maturity varieties (early MVs) were cultivated as DSR, and the early and three medium MVs as TR. In southern Hokkaido, the medium MVs were cultivated as DSR, and the medium and a late MV as TR. The heading date of DSR was 8.1-10.7, and 4.0-7.9 days later than that of TR with the same and one-rank later MV, respectively. The ratio of kernel number of GY to total ripened glumes and harvest index were lower in DSR than in TR. Thus, GY in DSR was only 76.9-99.7%, 86.9% on the average, of that in TR with a later MV, and promotion of growth after heading is needed for improving GY of DSR. In DSR amylose content was higher and the max value of gelatinization property was lower due to the lower temperature during ripening. The protein content in DSR was lower than that of TR in the same MV, but similar to that in TR with a later MV. Farmers cultivate earlier MV by direct seeding and DSR is disadvantageous for producing palatable rice.