Characteristics of Nitrogen Distribution and Translocation in Conventional Indica Rice Varieties with Different Nitrogen Use Efficiency for Grain Output

To investigate the characteristics of nitrogen distribution and translocation in conventional indica rice (Oryza sativa L.) varieties with high nitrogen use efficiency for grain output (NUEg), a total of 88 and 122 conventional indica rice varieties were solution-cultured in 2001 and 2002, respectively. These varieties were classified into 6 types on the basis of NUEg. Dry matter weight and nitrogen content of roots, culm and sheath, leaf, and panicle were measured at heading and maturity stages, and the grain yield and the grain number per panicle, filled grain percentage, and one thousand-grain weight of each variety were tested after harvest. The NUEg of the tested varieties varied from 20.51 to 50.92 g g−1 in 2001 and from 24.33 to 50.00 g g−1 in 2002, respectively. For varieties with high NUEg, the nitrogen content percentages in culm and sheath and leaf were lower than varieties with low NUEg at heading and maturity stages. On the contrary, nitrogen content percentage in panicle was larger in high-NUEg varieties, especially at maturity stage. The amount and rate of nitrogen translocation in culm and sheath and leaf in the varieties with high NUEg were high during grain-filling period. Thus, enhancement of the amount and rate of nitrogen translocation in culm, sheath, and leaf during grain filling could improve dry matter translocation and harvest index in rice.