NITROGEN RESPONSE OF RICE VARIETIES WITH REFERENCE TO NITROGEN ABSORPTION AT EARLY GROWTH STAGE

Nitrogen absorption at early growth stage (NAE), determined as the amount of N in the plant at 30 days after transplanting, was studied in relation to yield components and some N use efficiency parameters in 62 IR varieties and advanced lines of different growth durations (GD). Potential sink size was correlated with NAE in all GD groups in the dry season (DS) and wet season (WS). Sink degeneration was affected by NAE in medium-and long-duration groups. Sink size was correlated with NAE in the verieties with GD of 102-127 days in DS and 104- 122 in WS. Grain yield and NAE were correlated in varieties with GD of less than 116 and 122 days in DS and WS respectively. No significant relationship between ripening and NAE was noted. Sink degeneration and unripened grains disturbed the relationship between yield and NAE. Likewise, sink degeneration and unripened grains disturbed the sink size NAE and yield-NAE relationships in medium and long-duration groups. NAE was correlated with the contribution of N in the plant to sink and potential sink size in short and short to medium-duration varieties. Therefore, high NAE is an important characteristic of short-and short to medium-duration varieties. High basal N and narrow spacing increased NAE and the contribution of N in plant to yield determing factors in short duration varieties. Hence, low N absorption ability at early growth stage could be compensated by higher basal N and narrow spacing in short duration varieties. © 1990, CROP SCIENCE SOCIETY OF JAPAN. All rights reserved.