抄録
In ripening period, rate of photosynthesis per unit leaf area, respiratory activity, leaf area, dry-matter-production, grain yield and yield components of six rice varieties grown under different nitrogen levels were determined in reference to adaptability for heavy manuring. Results obtained are as follows: (1) Under high nitrogen level, the rate of photosynthesis was greater in varieties more suitable for heavy manuring than in less suitable ones. On the other hand, the rate of increase in respiration and leaf area were greater in less ones. (2) When solar radiation was scarce promotion of dry-matter-increase during ripening period by increasing supply of nitrogen was higher in suitable varieties. (3) Further, as the more general characters of rice varieties : When solar radiation was not scarce, varietal difference in dry-matter-increase and panicle weight were governed mainly by photosynthetic activity. (4) It was seen through all the varieties tested that the percentage of ripened grains was determined chiefiy by the ratio of photosynthetic rate on unit leaf area to the product of leaf area and the number of total spikelets both on unit field area.
