Abstract
The effects of nitrogen content and the rate of nitrogen uptake on kernel quality of rice were examined in relation to nitrogen application and transplanting time. We clarified the amount of nitrogen application and transplanting time optimal for the soil with differences in soil fertility. On condition that the number of kernel per area was optimum, milky white, white-based and white-back kernels tended to decrease with increasing nitrogen content, and increasing rate of nitrogen uptake at panicle formation stage and full heading time. The rate of soil nitrogen absorption by rice plant, and nitrogen content of rice became high at the panicle formation stage and full heading time when transplanting time was delayed. In the field with a high soil fertility, the rate of nitrogen uptake during the panicle formation stage and full heading time, so that inspection grade was improved by the late transplanting and decreased amount of basal application. In the field with moderate soil fertility, inspection grade and yield were improved by topdressing with controlled release fertilizer at the panicle formation stage and keeping nitrogen content high at the panicle formation stage. The technique that maintains high nitrogen content and high nitrogen uptake rate during the maximum tiller number stage and panicle formation stage may be important for improving inspection grade and protein content of rice grains.
