Abstract
In order to make clear varietal difference of the amount of reserved carbohydrate at heading stage, total carbohydrate and total nitrogen contents of the same varieties used for the experiment of planting density in the second paper in this series were analyzed. Also relationships between the total carbohydrate content and plant height, culm length and ear number at heading stage were studied. The results obtained are summarized as follows : 1. Total carbohydrate content at heading stage differed with rice varieties. Varieties with shorter culm and less ears showed higher content of total carbohydrate (Table 1, Table 2). 2. Varieties with a higher plant height at vegetative stage and shorter culm length at heading stage, that is, the ratio of plant height to culm length is greater, had higher reserved carbohydrate until heading stage. This is caused by a difference between higher dry matter productivity and lower carbohydrate consumption during the period until heading stage (Fig. 1). 3. Recently improved high-yielding varieties, such as Nishihomare, Shinrei and Milyang 23 showed a greater ratio of plant height to culm length than that of old varieties. Therefore, it is considered that the ratio of plant height to culm length is one of the indices for improving a high-yielding variety (Fig. 1). 4. There was negative correlation between total carbohydrate content and total nitrogen content at heading stage. The improved high-yielding varieties showed higher contents of total carbohydrate and total nitrogen than that of low-yielding ones (Fig. 3).
