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 rice (Oryza sativa L. cv. Hitomebore) seedlings (nursling, young, middle and mature seedlings) and the utilization of paddy nitrogen by root and shoot were investigated using ¹⁵N labelled paddy. Effects of fertilizer nitrogen and paddy nitrogen on the growth of rice nursling seedlings were studied in comparison with those of young, middle and mature seedlings. Nursling seedlings were raised with or without fertilizer and young, middle and mature seedlings were raised with fertilizer. Paddy dry weights of nursling seedling raised with or without fertilizer were about the same (44-46%). However, the amount of paddy nitrogen remaining in nursling seedlings raised with fertilizer was about 10% lower than that raised without fertilizer indicating the promotion of translocation of paddy nitrogen to root and shoot by the application of fertilizer nitrogen. The translocation of paddy nitrogen to rice root was completed before the nursling stage (2 leaves), whereas that to rice shoot continued until the young seedling stage (3.2 leaves). Therefore, 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% nitrogen in paddy are considered to be an unavailable form to rice seedlings.