Effects of NO^-₃-N/NH⁺₄-N ratios on Chardonnay grape seedling growth and nitrogen nutrition

A sand culture experiment was conducted to determine the effect of different nitrogen supply forms on growth and nitrogen nutrition of Chardonnay grape seedling. Five NO-3-N/NH+4-N ratios were set up as 100/0, 70/30, 50/50, 30/70, and 0/100 with total nitrogen being equal amount. The results indicated that Chardonnay grape seedling fertilized with NO-3-N/NH+4-N ratios for 70/30 had the highest biomass and root nitrogen absorption (70.89%); While Chardonnay grape seedling had the lowest biomass when fertilized with ammonium as the sole nitrogen source. The Chardonnay grape seedling fertilized with NO-3-N/NH+4-N ratios for 100/0 had the highest amount of nitrogen concentration and total N in leaf, while Chardonnay grape seedling fertilized with NO-3-N/NH+4-N ratios for 0/100 had the lowest, which were 61.8% and 19.46% of fertilized with NO-3-N/NH+4-N ratios for 100/0, respectively. The concentration of NH+4-N in root significantly correlated to the nutrient solution (r=0.9805), and the concentration of NH+4-N in root increased significantly when the proportion of ammonium nitrogen was higher than 30%. Leaf nitrate reductase activity was the highest when fertilized with NO-3-N/NH+4-N ratios for 70/30. The leaf nitrate reductase activity was impaired significantly when the proportion of ammonium nitrogen was higher than 30%, but the root nitrate reductase activity was not influenced. The experiment proved that NO-3-N/NH+4-N ratios for 70/30 was appropriate for the Chardonnay grape seedling, and a lower proportion of the NO-3-N/NH+4-N ratios increased the concentration of NH+4 in Chardonnay grape seedling organs, consequently inhibited nitrogen absorption and the biomass accumulation.