The effect of foliar feeding of potassium salts and urea in spinach on gas exchange, leaf yield and quality

Abstract

In a pot experiment conducted in a phytotron, the effectiveness of foliar feeding of different potassium salts, with and without the addition of 0.5% CO(NH₂)₂, in spinach (Spinacia oleracea L.) was investigated. Potassium was applied 3 times in the form of 1% solutions KCl, KNO₃, K₂SO₄ and C₆H₅K₃O₇•H₂O, compared to water as the control treatment. The obtained results show that foliar feeding of potassium salts in spinach is an efficient method of supplementing the level of K⁺ in plants during vegetation. Plants fed with KNO₃ had the highest content of potassium in leaves, and those fertilized with K₂SO₄, C₆H₅K₃O₇ × H₂O and KCl had an only slightly lower potassium content. The application of potassium salts resulted in more intensive gas exchange in leaves (stomatal conductance, photosynthesis, transpiration) and, as a consequence of that, increased leaf yield. Potassium nitrate and citrate influenced most effectively the abovementioned processes. The treatment of spinach with potassium salts resulted in an increased content of protein, chlorophyll, carotenoids, nitrates and iron as well as a decreased content of vitamin C and calcium in leaves.