Effect of Nitrogen form and pH of Nutrient Solution on the Uptake of Fe, Zn, Cu and Mn by Spinach Plant in Hydroponic Culture

To study the effect of nitrogen form and pH of nutrient solution on the uptake and concentration of Fe, Zn, Cu and Mn in roots and shoots of spinach plant, a factorial experiment was conducted with two factors including nutrient solution pH in three levels (4.5, 6.5 and 8.0) and nitrate to ammonium ratio of nutrient solution in five levels (100:0, 75:25, 50:50, 25:75 and 0:100). The experiment was carried out in a completely randomized design with four replications in perlite culture and greenhouse conditions. The results showed that the effect of nutrient solution pH on the root concentration of Fe and Cu, shoot concentration of Fe, Cu and Mn, uptake of Fe, Cu, and Mn was significant, but the effect on the root and shoot concentration of Zn and Zn uptake was not. By increasing the nutrient solution pH from 4.5 to 8.0, uptake of Fe, Cu and Mn, as well as in shoot concentration of Fe, Cu and Mn were significantly diminished, but root concentration of Fe and Cu was significantly increased. While Zn uptake, root concentration of Zn and Mn, and shoot concentrations of Zn did not change significantly. The effect of nitrate to ammonium ratio of nutrient solution on the root and shoot concentration of Fe, Mn and Zn, shoot concentrations of Cu, as well as the uptake of Fe, Mn, Zn, and Cu by plant was significant. By increasing the ammonium concentration of nutrient solution, the root and shoot concentration of Fe, Mn, Zn, and Cu, as well as their uptake (by spinach plant) were significantly increased, but by further increasing the ammonium concentration, their uptake, the root concentration of Mn and Cu, and the shoot concentration of Fe and Mn further decreased. Also, the effect of nitrate to ammonium ratio of nutrient solution on the root and shoot concentration of Fe, Mn, Zn, and Cu, along with their uptake by the plant was dependent on the nutrient solution pH and vice versa. In general, the maximum amount of Fe and Zn uptake by spinach plant was in nitrate to ammonium ratio of 75:25 and pH of 6.5, but a maximum level of Mn and Cu uptake was observed in nitrate to ammonium ratio of 75:25 and pH of 4.5. The plant accumulated Mn and Zn in its shoots but Cu and Fe in its roots.