Plants feed themselves by drawing nutritional elements from the soil. Of those elements, six are considered "macronutrients" because plants need them in very large quantity. Potassium is one of these.
Potassium is the most important nutrient plants need for healthy growth. They absorb potassium in even larger amounts than they do other macronutrients. Unlike other nutrients, potassium does not wind up in a plant's chemical structure. Instead, plants require it for ongoing processes important for their growth and health.
Potassium helps to activate more than 60 enzymes needed for healthy plant growth, while at the same time optimizing the plant's pH for enzyme reactions. Another process potassium regulates is the opening and closing of the stomates, those pores through which plants exchange oxygen, carbon dioxide and water vapor with the atmosphere. Potassium also plays a complex role in photosynthesis, the process by which plants synthesize energy from sunlight, carbon dioxide and water. Further, a sufficient supply of potassium helps increase root growth, crop quality and reduce vulnerability to crop diseases.
Deficiency symptoms: in many plants, the first signs include discoloration along the outer edge of the leaves. In some plants such as corn and soybeans this manifests as a consistent firing or scorching. In others, such as alfalfa, it may be a series of small white or yellowish dots. Leaves that curl, crinkle or turn leathery at the edges may also indicate potassium deficiency. Stunted growth, smaller leaves and thinner stems may also point to a lack of potassium in the soil.