Nitrogen deficiency typically causes chlorosis starting with which leaves?

• A. Older leaves
• B. Newer leaves
• C. The topmost new growth
• D. All leaves equally

Answer: (A)

Nitrogen is mobile within the plant, meaning the plant can move available nitrogen from one part to another. When nitrogen is deficient, it is redistributed from older leaves to support new growth. The older leaves lose chlorophyll first and turn yellow, so chlorosis typically begins in the oldest leaves. If a nutrient were immobile (like iron), chlorosis would show up first in the newer, developing leaves because the plant can’t move that nutrient from young tissue. Because nitrogen deficiency follows this mobile-nutrient pattern, chlorosis starting in older leaves is the typical and most expected sign.