Abstract: 【Objective】 The objective of the experiments is to investigate the differences in nitrogen uptake and utilization and analyze the ways to improve nitrogen uptake and utilization of the conventional rice varieties with different growth duration (GD). 【Method】 A total of 88 and 122 conventional indica rice varieties were used in 2001 and 2002 and 94 conventional japonica rice varieties were used in 2008 and 2009 in solution culture experiments. The GD, dry matter weight of each plant organ (including root), nitrogen content and grain yield and yield components were measured. Based on GD (from sowing to heading stage) by the MinSSw (dynamic clustering method-minimum sum of squares within groups) method, these rice varieties were clustered into 6 types in the alignment from low to high (A, B, C, D, E and F) for determining the differences in nitrogen uptake and utilization and analyzing their causes. 【Result】The rice varieties with longer GD had larger amount of nitrogen absorption (ANU) (indica rice varieties) or comparatively larger ANU (japonica rice varieties) at heading stage and maturing stage, however it is not predominant of ANU at grain filling stage. The rice varieties with longer GD showed a lower nitrogen concentration (NC) (japonica rice varieties) or no difference in the NC among varieties (indica rice varieties), also had less panicle numbers per unit area (indica rice varieties) or less difference in the panicle numbers among varieties (japonica rice varieties). However they had longer growing days, higher dry matter weight, higher ANU per single panicle, stronger nitrogen uptake intensity per single panicle (indica rice varieties) or comparatively higher nitrogen uptake intensity per panicle (japonica rice varieties). The dry matter weight, the ANU per single panicle, nitrogen uptake intensity per single panicle had more impact on the amount of nitrogen uptake than nitrogen concentration, panicle numbers per unit area, growing days in both indica and japonica rice varieties. The rice varieties with longer GD had low nitrogen use efficiency for grain yield (NUEg) (indica rice varieties) or over medium NUEg (japonica rice varieties) and comparatively higher nitrogen use efficiency for dry weight (japonica rice varieties). And the rice varieties with longer GD showed a higher nitrogen distribution percentage in leaf and stem and sheath at heading and maturity stages, and lower or comparatively lower nitrogen ratio in panicle (japonica rice varities at ripening stage). 【Conclusion】 The rice varieties with longer GD had stronger nitrogen uptake ability (indica rice varieties) or comparatively stronger nitrogen uptake ability (japonica rice varieties) at heading and maturing stages, and had lower NUEg (indica rice varieties) or over medium NUEg (japonica rice varieties). Although, the rice varieties with longer GD had low nitrogen concentration or panicle number, they had longer growing days, larger dry matter weight, higher and comparatively higher amount of nitrogen uptake per single panicle and nitrogen uptake intensity per single panicle. Improvement of dry matter weight, nitrogen uptake ability per single panicle and nitrogen uptake intensity per single panicle were helpful to improve the amount of nitrogen uptake. The promotion of nitrogen translocation from vegetative organs to panicle, and the decrease of the nitrogen percentage remained in sheath and stem and leaves were both beneficial to improving nitrogen use efficiency in rice varieties (indica rice varieties or japonica rice varieties) with longer GD. For japonica rice varieties, the low nitrogen concentration of rice plant at maturity was also one of the important factors on improving nitrogen use efficiency.

Key words: indica rice, japonica rice, growth duration, nitrogen uptake, nitrogen utilization