Effects of multiple times of topdressing nitrogen application under equal level on utilization and distribution characteristics of 15 N and 13 C in winter jujube

We explored the effects of multiple times of topdressing nitrogen application under equal level on the characteristics of absorption, utilization, accumulation, and distribution of N and C in four-year-old potted winter jujube during fruit developmental periods using the stable isotope tra-cer technology. The results showed that with the increases of nitrogen application times, the N derived from fertilizer (Ndff) in each organ significantly increased at the fruit maturity. The distribution rates of N in reproductive organ (fruit) and vegetative organs (leaf, deciduous spur, new branch, and fine root) were highest under four-time application, and lowest under one-time application. The opposite pattern was observed in storage organs (trunk, perennial branch, and coarse root). The N utilization rate under four-time application was 27.4% and 15.5% higher than one-time and two-time application, respectively. The more times N being applied, the more total N content and N absorption amount of plant. Soil N abundanc