[Nitrogen application technology in dwarfed apple trees.]

15N trace technique was used to explore the characteristics of 15N-urea absorption, utilization, loss and fruit quality of eight-year-old 'Yanfu3'/M26/Malus hupehensis Rehd. seedlings. There were three different nitrogen fertilization treatments: one-time nitrogen application in spring (1), two times nitrogen application (2), the intensive technique of nitrogen application with several times application and reduction in amount (3). The results showed that leaf area, chlorophyll content (SPAD value), photosynthetic rate (Pn), total N content of leaves and the total biomass per plant (except fruit), as well as the root-shoot ratio of treatment 3 were obviously higher than those in the treatments of 1 and 2. Treatment 3 significantly increased the protective enzymes (SOD, POD and CAT) activities and decreased the malondialdehyde (MDA) content in leaves. Significant differences were found on the 15N derived from fertilizer (Ndff value) of different organs, with the fruit Ndff showing the highest, followed by the one-year-old branches, leaves and roots of the three treatments. The Ndff values of each organ were the highest in the treatment 3. At fruit maturity stage, total N content of plant in treatment 3 was 93.0 mg·kg-1, which was obviously higher than that in the treatments 1 (70.2 mg·kg-1) and 2 (81.9 mg·kg-1). 15N nitrogen utilization ratio of treatment 3 was 33.6%, which was obviously higher than that in the treatments 1 (20.4%) and 2 (26.0%). The 15N loss rate was 46.9% in treatment 3, being obviously lower than that in the treatments 1 (56.5%) and 2 (52.9%). There were significant differences of fruit mass, soluble solid, fruit firmness, soluble sugar content, titratable acids and sugar-acid ratio among different treatments, with the highest values in the treatment 3 and the lowest values in treatment 1.以8年生烟富3/M26/平邑甜茶为试材,采用15N同位素示踪技术,研究不同施氮方式(Ⅰ:春季1次性施氮,Ⅱ:分2次施氮,Ⅲ:集约技术施氮,即氮肥减量和分次施氮)对烟富3/M26/平邑甜茶15N-尿素吸收、利用、损失和果实品质的影响.结果表明: 处理Ⅲ植株叶片的叶面积、叶绿素含量(SPAD)、光合速率(Pn)、叶片全氮含量和生物量(果实除外)显著高于处理Ⅰ和处理Ⅱ,植株根冠比也显著增加.处理Ⅲ显著提高了叶片的保护酶活性(超氧化物歧化酶、过氧化物酶和过氧化氢酶),降低了叶片丙二醛(MDA)含量.3个处理各器官从肥料中吸收分配到的15N量对该器官全氮量的贡献率(Ndff)表现一致,果实的Ndff值最大,其次是一年生枝、叶片和根,且各器官的Ndff值均以处理Ⅲ最大.在果实成熟期,处理Ⅲ的单株总氮含量为93.0 mg·kg-1,显著高于处理Ⅰ(70.2 mg·kg-1)和处理Ⅱ(81.9 mg·kg-1);处理Ⅲ的15N肥料利用率为33.6%,显著高于处理Ⅰ(20.4%)和处理Ⅱ(26.0%);而 15N损失率为46.9%,显著低于处理Ⅰ(56.5%)和处理Ⅱ(52.9%).不同施氮方式下植株的平均单果质量、可溶性固形物、硬度、可溶性糖、可滴定酸、糖酸比均存在显著差异,且均以处理Ⅲ最高,其次是处理Ⅱ,处理Ⅰ最低.