Improving nitrogen use efficiency in crops is of great importance both in crop production and environmental protection. Genetically improving crop varieties has been considered as one of the most economical and effective ways to enhance nitrogen use efficiency (NUE) in crops. Many studies have reported the genotypic differences in NUE for biomass and grain production in rice. Yet, little information in the characteristics of yield components, biomass production and allocation, nitrogen uptake and allocation and structure of root system in rice varieties with higher NUE has been known. In this study, 88 and 122 conventional indica rice cultivars were solution-cultured in 2001 and 2002, respectively. Dry matter weight (including root system, culm and sheath, leaves, panicle), nitrogen content of different organs, yield and its components were measured. The tested rice cultivars were classified into 6 types (i.e. A, B, C, D, E, and F, A was the lowest, and F was the highest) based on their nitrogen use efficiency for grain output (NUEg) level by the MinSSw method, to study their differences of nitrogen accumulation and nitrogen translocation. Results were as follows: (1) Difference of NUEg of the cultivars used in this study was very large, the averages of NUEg for A, B, C, D, E, and F were 20.51, 31.04, 35.64, 39.46, 43.55, and 50.92 g Grain g-1 N in 2001, and 24.33, 31.61, 35.83, 39.06, 43.51, 50.00 g Grain g-1 Nin 2002, respectively; (2) In the cultivars with high NUEg level, the nitrogen ratio of culm, sheath and leaf to whole plant was lower, while that of panicle to whole plant was higher at heading stage and especially at maturing stage; (3) The amount and rate of nitrogen translocation in culm, sheath and leaf in cultivars with high NUEg level were higher during grain-filling stage; (4) Enhancing the amount and rate of nitrogen translocation in culm, sheath and leaf during the grain-filling stage could improve dry matter translocation and harvest index.
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