[Absorption and distribution of nitrogen from 15N labelled urea applied at core-hardening stage in winter jujube].

The study with pot experiment showed that at the rapid-swelling stage of winter jujube fruit, the percent of nitrogen derived from fertilizer (Ndff%) was the highest (10.64%) in fine roots, followed by new-growth nutritive organs. The absorbed urea-15N decreased in leaves and deciduous supers, and accumulated preferentially in root systems after harvest. The Ndff% in coarse roots was the highest (3.69%) before budding stage, while that in new-growth organs (new branches, deciduous supers, leaves and flowers) was the highest at full-blooming stage. The urea-15N applied at core-hardening stage mainly allocated in nutritive organs (leaves, deciduous supers, roots) in the first year, with the distribution rate 54.01% in root systems in winter, which was higher than that in branches (45.99%). The 15N stored in main branches changed drastically from post-harvest to budding stage. Main branches could be regarded as the 'target organs' of N storage, while coarse roots were the 'long-term sink' of N storage. The N reserve distributed preferentially in contiguity organs, and the distribution center changed with the growth and development of winter jujube in next spring.