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Symbol: K. A soft alkali metal, atomic number 19, atomic weight 39.09, required as a macronutrient by plants. It is the most abundant cation in plant tissues and is believed to have a role in chlorophyll and protein synthesis and in carbon dioxide fixation. Potassium deficiency is most likely to occur in siliceous and peaty soils, symptoms being poor root growth and a characteristic red or purple coloration of the foliage. Growing points are especially affected and flower and fruit formation is poor. The potassium content of compound fertilizers is called potash and is usually measured as the proportion of potassium oxide, K2O, present.
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