[Effects of different integration of water and fertilizer modes on the absorption and utilization of nitrogen fertilizer and fruit yield and quality of apple trees].

We examined nitrogen use efficiency of N-urea of 15-year-old 'Gala' apple trees by broadcast fertilization (T), nitrogen fertilization with drip irrigation (T) and nitrogen fertilization with subsurface irrigation (T), to further improve the water and fertilizer integration technology for apple orchard and to improve nitrogen utilization efficiency. The results showed that leaf area, chlorophyll, and leaf nitrogen content of leaves were significantly higher in T treatment than those in T and T treatments. Soil mineral nitrogen content (20-40 cm) in each period followed the order of T>T>T, while that in 0-20 cm followed an order of T>T>T. The Ndff value at organ level (the contribution rate of the N amount absorbed by various organs of the tree to the total nitrogen content of the organ) was the highest in T treatment in each period, followed by T and T treatments. The utilization rate of N in the fruit ripening period followed an order of T>T>T. The N utilization rate of T reached 24.2%, being 1.19 and 1.65 times of T and T, respectively. The N distribution rate in the fruits during the fruit maturity stage was the highest in T treatment, while that in the storage organs was the highest in T treatment and that in the reproduction organs was the highest in T treatment. The single fruit weight, yield, soluble solids, hardness, soluble sugar and sugar-acid ratio were the highest in T treatment, followed by T and T treatments. In summary, nitrogen application by percolation irrigation (subsurface application) significantly promoted leaf growth and nitrogen utilization of apple tree, and improved fruit yield and quality.