Seedling Establishment of Rice Sown on Soil Surface in Flooded Paddy Field. I. Varietal difference in seedling establishment.

Field experiments were carried out to clarify the differences and key factors in the rate of seedling establishment among rice varieties sown on the soil surface in flooded paddy fields. The percentage of seedling establishment in flooded paddy fields with average temperatures of 17.9 and 22.7°C using 7 varieties of rice (4 Japanese, 1 Portuguese, 1 Chinese and 1 Hungarian) varied from 18 to 94% with a significant varietal difference. The main causes for lower seedling establishment rate existed in floating and seedling mortality in the younger stage. These two causes were independent of each other, and their relative importance differed among varieties. The percentage of floating seedling in cv. Arroz da Terra was relatively low compared with other varieties. No clear correlations were found between the percentage of floating seedling and the plant length, the seminal root length or the apparent weight of seedling underwater. It was presumed that the varietal difference in the percentage of floating seedling might be caused by differences in the rooting abilities into the soil up to the 2nd leaf stage.