Effects of different nitrogen application amounts and seedling densities on nitrogen accumulation and transport in winter wheat at anthesis stage

To determine reasonable nitrogen (N) application amount and seedling density of wheat for improving N utilization efficiency and yield, N contents in organs in different parts of wheat plant were measured, and wheat response to N application (in terms of N accumulation and translocation) and planting density was studied. In the field experiment, ‘Zhoumai 22’ wheat cultivar was used in a split-plot design with N fertilization amount as the main plot and seedling density as the secondary plot. Nitrogen fertilization amounts during the whole growth period were 0 kghm^-2 (N₀), 120 kghm^-2 (N₁), 240 kghm^-2 (N₂) and 360 kghm^-2 (N₃), respectively, while seedling densities were 225×10⁴ seedlingshm^-2 (M₁), 375×10⁴ seedlingshm^-2 (M₂) and 525×10⁴ seedlingshm^-2 (M₃), respectively. The results showed that N application amounts, seedling densities and the interactions of the two factors had significant effects on N contents in organs in different positions of aboveground wheat at anthesis and maturity stages. N content and accumulation in the vegetative organs of wheat at maturity declined compared with those at anthesis. Total N accumulation in individual plant was changed within range of 7.2759.65 mgstem1 at anthesis and 8.4860.83 mgstem1 at maturity, and the maximum data was observed in N₃M₂ treatment, while the minimum level was observed in N₃M₂ treatment. N content and accumulation in vegetative organs of wheat apparently decreased with decreasing of spatial position at anthesis stage. Also N transport and contribution rate of vegetative parts to grain had the same spatial distribution trend. It suggested that flag-leaf and the first upper internode were higher while the fourth upper leaf and the fourth upper internode as well as the other bottom parts near the ground were apparently lower. N content, accumulation and transport capacity of vegetative organs increased with increasing N application rate. N transport rate in the organs of upper and middle spatial position exceeded 50%, and total N contribution rate of vegetative organs to grain exceeded 67%. Increased N fertilizer amount combined with suitable planting density improved the capacity of N accumulation and translocation in aboveground system. Among all the vegetative organs, the ones nearest the ground (such as the fourth upper leaf and internode) were more obviously affected by N application and seedling density while N content and accumulation in those parts were significantly higher under higher N application and medium-level density, narrowing the differences with upper parts of the plant. Also N transport of plant population (28.56549.49 kghm^-2) increased with increasing N application amount, especially for plant spike and internode. Grain yield, grain protein content and protein yield were significantly influenced by N application rate. While grain protein content and protein yield were significantly driven by applied N amount and N amount/seedling density interactions, protein yield was driven by seedling density. Considering N transport and grain yield, N application at 240 kghm^-2 and seedling density at 225 × 10⁴ planthm^-2 were suitable for ‘Zhoumai 22’ in wheat/corn double cropping in Huanghuai region.