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(NH<sub>2</sub>)<sub>2</sub>, in spinach (<i>Spinacia oleracea</i> L.) was investigated. Potassium was applied 3 times in the form of 1% solutions KCl, KNO<sub>3</sub>, K<sub>2</sub>SO<sub>4</sub> and C<sub>6</sub>H<sub>5</sub>K<sub>3</sub>O<sub>7</sub>&#8226;H<sub>2</sub>O, 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<sup>+</sup> in plants during vegetation. Plants fed with KNO<sub>3</sub> had the highest content of potassium in leaves, and those fertilized with K<sub>2</sub>SO<sub>4</sub>, C<sub>6</sub>H<sub>5</sub>K<sub>3</sub>O<sub>7</sub> × H<sub>2</sub>O 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.
Highlights
The yielding of spinach (Spinacia oleracea L.) depends primarily on water and nutrient availability in soil (Orłowski and Kołota, 1999)
The results presented in Tab. 1 and 2 show that foliar feeding of all the applied potassium salts had a significantly beneficial effect on the stomatal conductance of spinach leaves and, what follows, their transpiration and photosynthesis
The data presented in Tab. 4 show that leaves treated with potassium nitrate contained the largest amount of potassium (5.51%), there was a smaller amount in those fed with potassium citrate and potassium sulphate, and the least amount in those treated with potassium chloride (5,24%)
Summary
The yielding of spinach (Spinacia oleracea L.) depends primarily on water and nutrient availability in soil (Orłowski and Kołota , 1999). Potassium is the main ion of osmotic solution in plants (Mengel and Arneke , 1982). Its accumulation in cells leads to osmotic water uptake and generates cell turgor necessary for growth (Mengel and Arneke , 1982; DeLaGuardia and Benlloch , 1980) and pore opening (Fisher and Hsiao , 1968). The only way to quickly supplement any potassium deficiencies during cultivation is to apply foliar feeding of this element. Data available in foreign literature show that potassium, as the monovalent cation with a relatively small diameter, passes through the leaf epidermis (Mengel , 2002). When applying different foliar fertilisers in spinach cultivation, A l a n and Padem (1994) found its highest content in leaves already after 24-48 hours after application
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