[Effects of multiple times of topdressing nitrogen application under equal level on utilization and distribution characteristics of N and 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 abundance and total N content continued to drop under one-time application and increased at the beginning and then declined with the time under two-time application. The relatively stable soil N abundance and total N content appeared in four-time application, which was significantly higher than those in the other treatments in later treatment stages. The chlorophyll content, leaf nitrogen content and photosynthetic rate displayed an order of four-time application > two-time application > one-time application during fruit white-mature period to fruit harvest period. The accumulation and distribution of C varied across different treatments. Increasing nitrogen application times would promote more C being transported to fruit and storage organs but decrease that in annual vegetative organs. Our findings indicated that four-time nitrogen application could enhance and optimize the accumulation and distribution of photosynthetic products by ensuring steady and adequate supply of nitrogen and improving the absorption and utilization of nitrogen during fruit development period, which facilitates the growth, yield and quality of winter jujube.