On Germination and Subsequent Early Growth of Seedling in Direct Seeding Culture of Paddy Rice on Upland Field

[摘要] In direct seeding culture of paddy rice on upland field condition, germinating processes as influenced by the seeding depth, hardness of covering soil and hardness of bed soil layer were examined morphologically. Under all conditions, the rate of germination were more than about 95 %, but the rate of emergence of seedling at 30 days after seeding decreased with the increase of seeding depth. In case of 5 and 7 cm depth of seeding, the number of perished seedlings under ground were increased remarkably. Plant height of deep seeded plots were more than those of shallow seeded plots. Dry weight of seedlings of deep seeded plots exceeded those of the shallow ones under soft soil conditions, but the relation was reversed under hard soil cover conditions. Age of seedlings decreased with the increase of seeding depth. The first tiller was shooted out from the third node of main stem in 1-5 cm plots, while in the case of 7 cm plots it came out from the fourth node. In this experiment it was observed that the length of mesocotyl increased with the depth, reaching its maximum at 5 cm depth but decreased again at deeper seeding. The process of elongation of the underground internodes in 5 and 7 cm plots are illustrated in Fig. 2. In the perished seedlings the internode elongation did not occur at all, and root formation in the nodes were also lacked. Coleoptile also elongated in proportion to the seeding depth as shown in Fig. 3. The first foliage leaf became the longest one in 3 cm plots, but in 5 and 7 cm plots their length were shorter than their coleoptile. The second leaf, therefore, appeared above the ground after penetrated through the cover soil layer in these cases. While, those of the perished seedlings were unrolled, twisted, and could not appear above the ground. The elongation of the internodes and coleoptile, the ability of rooting and the power of the foliage leaves to penetrate through the soil layer were considered to be the determining factors for the emergence of good and healthy seedling in direct seeding culture of rice on upland field where the deep seeding is necessary. And that, these factors showed remarkable variation in the same condition examined and also in the same variety. Therefore, it is suggested that the attention should be paid to these factors in the breeding of varieties suitable for the direct seeding culture on upland field.

[学科分类] 农业科学（综合）