[Effects of different nitrogen application rates on N-urea absorption, utilization, loss and fruit yield and quality of dwarf apple].

Seven-year-old 'Yanfu3'/M/M. hupehensis Rehd. seedlings and N trace technique were used to explore the characteristics of N-urea absorption, utilization, loss and fruit yield and quality under different nitrogen application rates (N, N and N). The main results were as follows: the plant growth, N absorption, utilization and loss differed significantly under different treatments. The plant leaf chlorophyll content (SPAD value), photosynthetic rate (P), total N content of leaves and the biomass, as well as the root-shoot ratio of N treatment were obviously higher than the N and N treatments. Significant differences were observed in the N 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 N >N＞N, while that of the roots at full-bloom and spring shoot growing slowly stage was N >N＞N, and in a trend of N >N＞N at autumn shoot growing stage, fruit rapid-swel-ling stage and fruit maturity stage. At fruit maturity stage, plant N nitrogen utilization ratio of N treatment was 23.6%, which was obviously higher than the N (16.3%) and N (14.4%) treatments, with the N loss rate of 56.4%, obviously lower than the N (60.6%) and N (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 N treatment showed the best performance, followed by the N treatment, and then the N treatment.