Effect of nitrogen-use efficiency on the grain number at heading and weight of milled rice [Oryza sativa] on the protein content of milled rice

It is a well known fact that the protein content of milled rice affects its eating quality. Field experiments were conducted from 1990 to 1996 to evaluate the relationship between protein content of milled rice, number of grain per amount of nitrogen (N) in plant at heading (NG/N) , amount of N in grain, amount of N in milled rice and weight of a milled rice. To clarify the effect of N cultural practices on N-use efficiency for the total number of grains produced per amount of N in a plant at heading (NUE for G/N) , a field experiment was carried out. Furthermore, the effects of translocation of top-dressed N applied at different dates and the amount of total available carbohydrate (TAC) in the plant at heading on the protein content in milled rice was evaluated. The results oftained were follows. 1There was negative correlation between NG/N and amount of N in plant at heading while the amount of N in grain and NG/N were positively correlated regardless of cultivars. The relationship between the amount of N in grain and protein content of milled rice was indicated in a linear equation. These results suggested that the protein content of milled rice is affected by NG/N. 2 Cultivar Haenuki had lower NG/N but had higher amount of N in grain than cv. Sasanishiki when they observed the same amount of N at heading. More than 80% of cv. Haenuki samples had 60 to 70 grains per panicles, while cv. Sasanishiki had 55 to 80 grains per panicle. This indicates that varietal differences in NG/N and number of grain per panicle affect difference in the protein content of milled rice between varieties.3 A negative correlation existed between protein content of milled rice and grain weight when the amount of N in rice plant at heading was less than 13.0g m-1. Increased of grain weight resulted to a decrease in protein content of milled rice if the amount of N in milled rice was same. Furthermore, same trend was obtained if N use efficiency on grain number was same.4 No significant differences were obtained in the number of differentiated grains among the application times of top-dressed N and shading treatments. However, the number of degenerated grains was affected by both top-dressed N timing and shading. A delay in the applications date of top-dressed N and increase of shading percentage resulted in an increase in the