The Effects of Sowing Depth of Cultivars with High Survival to Flooding for Rice Seedling Establishment of Wet Direct-Seeding.

Since 1990, cultivated rice areas have been declining in Korea. Moreover, wet direct-seeding areas have also been decreasing sharply because of poor seedling establishment, uneven growth of plant in low temperature and lodging in maturity stage.      This study is to investigate characters of germplasms and to identify them with tolerance to flooding during germination to enhance a stable seedling establishment in flooded paddy field. In experiment I, seven genotypes were tested for survival measurement. Dry seeds and pre-germinated seeds were sown on soil surface and in about 1cm and 2cm of soil depth, followed by flooding with about 10cm of tap water. In experiment II, four genotypes were used to study effects of sowing depth according to none-flooding and flooding on rice seedling establishment in wet direct-seeding. Dry seeds were sown on about 1cm, 3cm, 5cm, and 7cm of soil depth, followed by non-flooding and flooding with 5-7cm water. In experiment I, Plant survival was calculated based on the number of seedlings that emerged from floodwater. All trials were conducted using a randomized complete block design. Survival in pre-germinated treatment was higher than in dry-seeded treatments on soil surface and in about 1cm and 2cm of soil depth. The average survival of seven genotypes  pre-germinated were about 82.4% and 55.1% in about 1cm and 2cm of soil depth, respectively compared with dry-seeded genotypes(23.2%, 6.8%). Survival through dry seeding was highest on Khao Hlan On, 66.2%, 36% in both about 1cm and 2cm of soil depth, respectively. In effect on sowing depth of genotypes according to non-flooding, Khaiyan shown high survivals in about 5cm and 7cm of soil depth. Khao Hlan On and Kasalath followed by Khaiyan in about 3cm and 5cm of soil depth. On the other hand, there were different patterns according to genotypes in flooding. Khao Hlan On and Kasalath shown high survivals in about 1cm of soil depth. As soil depth advanced more, survival of genotypes was decreased sharply and four genotypes show hardly survivals in about 5cm and 7cm of soil depth.