Effect of Nitrogen Form and pH of Nutrient Solution on the Shoot Concentration of Phosphorus, Nitrate, and Nitrogen of Spinach in Hydroponic Culture

In order to study the effect of nitrogen form and pH of nutrient solution on the shoot concentration of P, nitrate, organic N + inorganic ammonium, and total N of spinach, a factorial experiment was conducted with two factors including pH of nutrient solution 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). This factorial experiment was carried out in a completely randomized design with four replications. Three seedlings of spinach plant (Spinacia oleracea L. Sirius cultivar) were cultivated per pot and were nourished with 15 different nutrient solutions. The results showed that while the effect of nutrient solution pH on the shoot concentration of P, nitrate, and organic N + inorganic ammonium was significant, it was not significant on the shoot concentration of total N. By increasing the nutrient solution pH from 4.5 to 8.0, the shoot concentration of P and nitrate was significantly decreased, but the shoot concentration of organic N + inorganic ammonium, and total N did not change significantly. The main effect of nitrate to ammonium ratio of nutrient solution on the shoot concentration of P, nitrate, organic N + inorganic ammonium, and total N of spinach plant was significant. By increasing the ammonium concentration of nutrient solution, the shoot concentration of nitrate was significantly decreased, while the shoot concentration of P, organic N + inorganic ammonium, and total N of spinach plant was significantly increased. The effect of N form of nutrient solution on the shoot concentration and content of P, nitrate, and total N of spinach plant was dependent on the nutrient solution pH and vice versa. The greatest P concentration in spinach shoots was obtained in nitrate to ammonium ratio of 0:100 and pH of 8.0. The greatest spinach shoots nitrate concentration was found in nitrate to ammonium ratio of 100:0 and pH of 8.0, while the greatest concentrations of organic N + inorganic ammonium and total N in spinach were observed in nitrate to ammonium ratio of 25:75 and pH of 6.5.