[Effects of different nitrogen application rates on ¹⁵N-urea absorption, utilization, loss and fruit yield and...

Seven-year-old 'Yanfu3'/M₂₆/M. hupehensis Rehd. seedlings and ¹⁵N trace technique were used to explore the characteristics of ¹⁵N-urea absorption, utilization, loss and fruit yield and quality under different nitrogen application rates (N₁₀₀, N₂₀₀ and N₃₀₀). The main results were as follows: the plant growth, ¹⁵N absorption, utilization and loss differed significantly under different treatments. The plant leaf chlorophyll content (SPAD value), photosynthetic rate (P_n), total N content of leaves and the biomass, as well as the root-shoot ratio of N₂₀₀ treatment were obviously higher than the N₁₀₀ and N₃₀₀ treatments. Significant differences were observed in the ¹⁵N derived from fertilizer (Ndff value) of different organs under different nitrogen application rates. The Ndff of fruits (flowers), leaves, one-year-old branch, and perennial branches in each measurement period was N₁₀₀ >N₂₀₀＞N₃₀₀, while that of the roots at full-bloom and spring shoot growing slowly stage was N₁₀₀ >N₂₀₀＞N₃₀₀, and in a trend of N₂₀₀ >N₁₀₀＞N₃₀₀ at autumn shoot growing stage, fruit rapid-swel-ling stage and fruit maturity stage. At fruit maturity stage, plant ¹⁵N nitrogen utilization ratio of N₂₀₀ treatment was 23.6%, which was obviously higher than the N₁₀₀ (16.3%) and N₃₀₀ (14.4%) treatments, with the ¹⁵N loss rate of 56.4%, obviously lower than the N₁₀₀ (60.6%) and N₃₀₀ (66.1%) treatments. There were significant differences among the treatments in fruit mass, yield per plant, soluble solid, fruit firmness, soluble sugar, titratable acids and sugar-acid ratio of different nitrogen rates, and the N₂₀₀ treatment showed the best performance, followed by the N₃₀₀ treatment, and then the N₁₀₀ treatment.