Abstract
Nitrogen use efficiency (number of grains/amount of N in rice plant at heading) and grain weight affected protein content of milled rice. Topdressed N might contribute to protein content of milled rice through increasing photosynthetic rate and decreasing N use efficiency. To evaluate the effect of application rate of topdressed N at panicle formation stage on photosynthetic rate of leaf blade and root activity of rice plant, field experiments were conducted. The results obtained were as follows ; 1. When the application rate of topdressed N was increased, the number of grains per unit area, recovery rate of topdressed N by rice plant and protein content of milled rice increased. 2. There was a relationship between application rate of topdressed N and SPAD value, while photosynthetic rate of leaf blade during ripening stage of rice plant was not affected by application rate of topdressed N. 3. No relationship between amount of solution exudated from stem and application rate of topdressed N at the beginning of ripening stage of rice plant was observed. On the other hand, there was a negative relationship between them at the later stage of ripening. 4. When a larger amount of topdressed N was applied, light transmittance became worse.
