Effects of Nitrogen Form and pH of Nutrient Solution on the Uptake and Concentrations of Potassium, Calcium, Magnesium and Sodium in Root and Shoot of Spinach Plant

In hydroponic cultures, the effects of nitrogen form and pH of nutrient solution on the chemical composition of plants are important. In order to study their effects on the uptake and concentrations of K, Ca, Mg and Na in root and shoot of spinach plant, a factorial experiment was conducted with two factors including nutrient solution pH at three levels (4.5, 6.5 and 8) and nitrate to ammonium ratio in nutrient solution at 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 under greenhouse conditions. Three seedlings of spinach plant (Spinacia oleracea L. Sirius cultivar) were cultivated per pot and with 15 different nutrient solutions were nourished. The concentrations of nitrogen and other nutrients in all nutrient solutions were identical. The plants were harvested after seven weeks and spinach root and shoot concentrations of K, Ca, Mg and Na were measured by wet digestion method. Results showed that the effects of nutrient solution pH on the root and shoot concentrations of K, root concentration of Ca, Ca uptake, shoot concentration of Mg were significant, but on the root and shoot concentrations of Na, Na uptake, root concentration of Mg, and Mg uptake were not. By increasing the nutrient solution pH from 4.5 to 8, K and Ca uptake by plant, and root concentration of K significantly decreased, while shoot concentrations of K and Mg, and root concentration of Ca significantly increased. The main effect of nitrate to ammonium ratio in nutrient solution, and the interactive effects of pH and the ratio of nitrate to ammonium on the root and shoot concentrations of K, Ca, Mg and Na, and their uptake by plant beca,e significant. In general, by decreasing the nitrate to ammonium ratio in nutrient solution, the root and shoot concentrations of K, Ca, Mg and Na, and their uptake by spinach plant became significantly decreased. Also, the effect of nitrate to ammonium ratio of nutrient solution on the root and shoot concentrations of K, Ca, Mg and Na, and their uptake by spinach plant was dependent on the nutrient solution pH and vice versa. The average shoot concentrations of K, Ca, Mg and Na were higher than those in root. There were significant correlations between the shoot and root concentrations of these elements, and also between the elements concentrations in the shoot and their uptake by spinach plant.