Unlike iron, potassium is mobile in the plant, so symptoms first appear on older leaves. The most characteristic appearance is marginal scorching (marginal necrosis), which progresses inward.

Typical symptoms:
• Yellowing (chlorosis) on the edges of lower leaves.
• Marginal necrosis, a "burnt" appearance.
• Leaves curled downward or with dark spots.
• Weak stems and thin buds.
• Small, deformed, or poorly colored fruits.
• Decreased resistance to drought and disease.

Potassium deficiency develops progressively and directly affects crop yield and quality, even if the plant survives.

Developmental stages:
• Initial: marginal chlorosis on older leaves.
• Intermediate stage: necrosis on edges and tips, progressing inward.
• Advanced: Leaves with dry, brittle edges, premature drop.
• Final: Thin stems, sparse flowering, poorly developed fruit, and increased sensitivity to stress.