[Effects of nitrogen application rate on the growth traits in seedlings of different quinoa cultivars]

Effects of five different nitrogen application rates (i.e., N₀, 0 g·kg^-1; N₁, 0.05 g·kg^-1; N₂, 0.1 g·kg^-1; N₃, 0.15 g·kg^-1; N₄, 0.2 g·kg^-1) on the growth of seedlings of eight different quinoa cultivars were investigated in a pot experiment. The results showed that: 1) Across different nitrogen application rates, cultivar GB22 and OY had the highest biomass, but cultivar B2 had the lowest value. The highest flower mass ratio, stem mass ratio, root mass ratio, and leaf mass ratio were found in cultivar B2, GB22, R1, and W23, respectively. 2) The rate of nitrogen application significantly affected seedling growth. Compared with the control (N₀), the maximum net photosynthetic rate and biomass accumulation were significantly higher in the lower nitrogen applications (i.e., N₁ and N₂ treatments), but were lower in the higher nitrogen applications (i.e., N₃ and N₄ treatments). The significant interactions between cultivar and nitrogen application rate on plant biomass indicated that different quinoa cultivars responded differently to nitrogen rate. The optimum nitrogen application rate (Nopt) required for cultivar R1, MY11, GB22 and OY was 0.05 g·kg^-1; while that of cultivar GB11, DB, and B2 was 0.1 g·kg^-1; but for cultivar W23, Nopt was less than 0.05 g·kg^-1. 3) The interactions between cultivar and nitrogen application rate significantly affected biomass allocation. Below the highest nitrogen rate used (i.e., less than 0.2 g·kg^-1), the flower and leaf biomass allocation increased with the increasing nitrogen rates. 4) Across different cultivars and nitrogen application rates, plant biomass was positively correlated to the maximum net photosynthetic rate, plant height, ground diameter, and specific leaf area, respectively. These results provided valuable information for the nutrition management of different quinoa cultivars.