Studies on the flooding irrigation of rice. : (II) The effects of continuous submergence on the growth and tillering of rice plants.

[摘要] In the preceding paper the author reported preliminarily on the effect of continuous submergence upon the growth and structure of rice plants. In the present studies, he intends further to ascertain the influence of continuous submergence on the growth of rice with special reference to its tillering. The plan and the methods of investigation are, therefore similar to those of the previous year. The variety used is Norin-ichigo, an early lowland rice. The submerged plot: The water level of 8 cm high is kept continuously since 2 weeks after seeding till harvest. The no-submerged plot: Soil is always moist enough with no submergence. The tendencies being recognized through the results of both studies are summarized as follows. (1) In Kanto District, the temperature of May (when the rice is seeded) is rather low, hence the submergence of water raises the temperature of earth and water surrounding rice plants, especially at night, because of its high specific heat, and promotes the growth of rice and advances the date of heading several days. But later in June, the temperature rises fairly high, and the submergence is not so effective as in May, but becomes rather infavourable for growth of rice chiefly due to want of aeration. Therefore, the plants seeded and submerged later in June are reduced in growth and the date of heading is not promoted. (2) In the submerged plot, the number of tillers is increased in May seeded Plants and decreased in June seeded ones, and the lowest tillering locus on the main stem is always moved upwards by submergence. (3) The culm and panicle length seems to become less variable by submergence, but the grains per plant or per head may diminish in number, the reason of which is to be studied later. (4) The form of tillering curve in rice may be analogous with that of the autocatalytic one, and each tillering curve of the first, second and third (and rarely forth) orders is its formative stuff.

[学科分类] 农业科学（综合）