15NITROGEN STUDY ON ABSORPTION,DISTRIBUTION AND UTILIZATION OF NITROGEN APPLIED IN EARLY SUMMER IN RED FUJI APPLE

Total nitrogen (N) concentration (N%), N derived from ¹⁵N-fertilizer (Ndff%), amount of ¹⁵N uptake (ANU) in main organs (leaves, shoots, roots, fruits), and N use efficiency (NUE) were measured to assess N absorption, distribution, and utilization of Red Fuji apple trees across two years using a ¹⁵N-enriched urea method. The N% in leaves and fruits decreased while those in shoots and roots increased in both years. The Ndff% and ANU in roots were highest at fruitlet stage than those in leaves, shoots and fruits at mature stages. This suggested that the absorbed ¹⁵N by roots was redistributed to new organs. The N% was lower while Ndff% and ANU were greater in 2008 than 2007. The most ¹⁵N absorbed was accumulated in the trunks, main and coarse roots and smaller in the fine roots and biennial branches. The NUE in 2007 and 2008 reached 9.9% and 12.2% respectively.