Adaptability of Early–Winter Direct–Sowing Cultivation of Paddy Rice using Different Seed Coating Types at 11 Locations in Japan

To clarify the adaptability of cultivation of paddy rice by direct sowing in early winter, we compared the seedling establishment at 11 locations in Japan in two seasons (2018/19 and 2019/20) using different coating types and sowing dates. Although winter–sown seeds (October, November, January) had poorer seedling establishment than spring-sown seed (April), seed coating decreased the gap between winter-sowing and spring-sowing. Seedling establishment was not affected by the sowing date between October and November in Aomori, Iwate, Akita, Yamagata (2 locations) and Fukushima prefectures over the two seasons. On the other hand, in Niigata prefecture, the seedling establishment was poorer in October than in November due to untimely germination after sowing, and in Mie, Hiroshima and Fukuoka prefectures, it was better in January than in November. In contrast, in Hokkaido, seedling establishment was better when sown in October than in November. The ratio of seedling establishment per unit seed survival rate was 55% (2018/19) and 69% (2019/20) for seeds sown in spring. The seedling establishment in 2019/20 was higher than in 2018/19 at many locations. The maximum seedling establishment at 11 locations ranged from 39% to 86%, which satisfied the target seedling establishment of 35%. These results showed that seed coating is effective over a wide area for improving seedling establishment of seeds direct sown in early winter.