Optimum seeding time and applicable region of rice [Oryza sativa] variety "Hiroshima 21" (brand name "Koimomiji") in Hiroshima prefecture [Japan] to direct sowing cultivation in submerged paddy field

3861 On direct sowing cultivation in submerged paddy field in Hiroshima prefectpre, it has been presented the guideline that the daily mean air temperature at seeding time should become 14 deg C and over. Therefore, this cultivation has been applicable only to the warm and low-altitude region of Hiroshima prefecture. Then, the aptitude for direct sowing cultivation in submerged paddy field of 'Koimomiji' suitable for the cool and high-altitude region developed by Hiroshima prefecture was examined. Conseqently, it was shown that if 'Koimomiji'was used, it is possible to spread direct sowing cultivation in submerged paddy field to the cool and high-altitude region of Hiroshima prefecture. l. In the case of direct sowing cultivation in submerged paddy field using drainage after seeding, when the mean air temperature during 15 days after seeding was over 1l deg C, the seedling establishment rate was 60% ond over. 2. When the seeding rate was 3 kg /10 a, the seedling establishment number came to 65 plants/m(2) and over on the condition that the seedling establishment rate was 60% and over. 3. When the seedling establishment number was in the range of 65 to 80 plants/m(2), no lodging occurred and the grain yield was about 600 kg/10 a as much as transplanting cultivation, and the inspection grade was the first. Therefore, 'Koimomiji' was admitted to have high aptitude for direct sowing cultivation in submerged paddy field. 4. The mean air temperature during 15 days after seeding becomes over 11 deg C when the daily mean air temperature at seeding time is over 10 deg C. 5. As the above result direct sowing cultivation in submerged paddy field is possible under the cool condition that the daily mean air temperature at seeding time is over 10 deg C. This temperature is lower than 14 deg C previously presented guideline. 6. Taking account of the condition of air temperature, it is possible to spread direct sowing cultivation in submerged paddy field using 'Koimomiji' to the area under 550 m altitude in Hiroshima prefecture. Then, we created the cultivation map which shows the possible region of direct sowing cultivation in submerged paddy field using 'Koimomiji' in Hiroshima prefecture.