Abstract
The effects of deep irrigation and reduced amounts of basal nitrogen dressing on the emergence of upper nodal tillers (UNTs) were examined in a deep-flood irrigation plot and a control plot using the extremely early rice cultivar ”Kirara 397”. In both plots different amounts of nitrogen was applied as basal dressing (BD) and top-dressing at 36 days before heading (TD). However, top-dressing at the panicle formation stage (TDP) was 3 gm-2 in all plots. Three fertilization management regimes were designed: 2 gm-2 BD, 0 gm-2 TD and 3 gm-2 TDP (2･0･3 plot), 2 gm-2 BD, 2 gm-2 TD and 3 gm-2 TDP (2･2･3 plot), and 4 gm-2 BD, 0 gm-2 TD and 3 gm-2 TDP (4･0･3 plot). UNTs emerged the heading time in all experimental plots. The number of UNTs was greater in deep-flood irrigation plots than in control plots, and the number of UNTs was greatest in the 2･0･3 plot. The number of primary tillers (including main culms) showed a significant negative correlation with the number of UNTs. In the 2･2･3 plot, the UNT production was suppressed because of the increased emergence of tillers of secondary and higher orders. Thus excessive suppression of normal tillering resulted in increased UNT emergence. It was suggested that nitrogen top-dressing just before the young panicle formation stage can suppress the emergence of UNTs even if the normal tillering is suppressed.
