The effect of foliar nutrition of spinach (Spinacia oleracea L.) with magnesium salts and urea on gas exchange, leaf yield and quality

In a pot experiment conducted in a phytotron, the effectiveness of foliar nutrition of spinach (Spinacia oleracea L.) with different magnesium salts with and without the addition of 0.5% CO(NH₂)₂ was studied. Magnesium was applied 3 times in the form of solutions of MgSO₄ x 7H₂O, Mg(NO₃)₂ x 6H₂O, MgCl₂ x 6H₂O, C₄H₆O₄Mg x 4H₂O, compared to water as the control treatment. The obtained results showed that foliar feeding of spinach with inorganic magnesium salts was an efficient method for supplementing the Mg level in plants during the growing period. But the application of a metalo-organic complex in the form of magnesium acetate (C₄H₆O₄Mg x 4H₂O) at a concentration of 1.7%, in spite of a similar effect on leaf Mg content, induced phytotoxic symptoms in the form of chlorotic and necrotic spots on the leaves. The application of the solutions of inorganic magnesium salts had a significant effect, resulting in more intensive leaf gas exchange (stomatal conductance, transpiration and photosynthesis) and an increase in leaf yield. Magnesium sulphate affected the abovementioned processes in the most effective way, while magnesium acetate had a negative impact. Foliar feeding of spinach with the magnesium salts resulted in an increased leaf content of protein, chlorophyll, carotenoids, nitrates and proline, but a decrease in vitamin C content. The addition of urea to the applied magnesium salt solutions increased the plant gas exchange rates and the leaf content of protein, chlorophyll, carotenoids, nitrates and proline, but it decreased the content of vitamin C, potassium and magnesium.