Utilization of paddy nitrogen by different ages of rice seedlings

Changes in the dry matter of paddy, the dry weight of root and shoot of ric e (Oryza sativa L. cv. Hitomebore) seedlings (nursling, young, middle and m ature seedlings) and the utilization of paddy nitrogen by root and shoot we re investigated using N-15 labelled paddy. Effects of fertilizer nitrogen a nd paddy nitrogen on the growth of rice nursling seedlings were studied in comparison with those of young, middle and mature seedlings. Nursling seedl ings were raised with or without fertilizer and young, middle and mature se edlings were raised with fertilizer. Paddy dry weights of nursling seedling raised with or without fertilizer were about the same (44-46%). However, t he amount of paddy nitrogen remaining in nursling seedlings raised with fer tilizer was about 10% lower than that raised without fertilizer indicating the promotion of translocation of paddy nitrogen to root and shoot by the a pplication of fertilizer nitrogen. The translocation of paddy nitrogen to r ice root was completed before the nursling stage (2 leaves), whereas that t o rice shoot continued until the young seedling stage (3.2 leaves). Therefo re, the amount of paddy nitrogen remaining both in middle (4.5 leaves) and mature (5.5 leaves) seedlings was nearly the same and about 17-18%, nitroge n in paddy are considered to be an unavailable form to rice seedlings.