Effects of different nitrogen application rates on 15N-urea absorption, utilization, loss and fruit yield and quality of dwarf apple

Abstract

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 (Pn), 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.