Which symptom indicates nitrogen deficiency in plants?

• A. Yellowing older leaves
• B. Purplish or dark green leaves
• C. Leaf margins scorched/browned
• D. Brown spots on leaves

Answer: (A)

Nitrogen is a mobile nutrient in plants, so when nitrogen is limited the plant moves what it has to the new growth and withdraws it from older leaves first. That loss of nitrogen in older leaves causes chlorophyll to break down, making those leaves turn pale yellow while newer leaves stay greener for longer. This older-leaves yellowing pattern is a clear sign that the plant is short on nitrogen, since nitrogen is essential for chlorophyll production and overall growth.

Other symptoms don’t fit nitrogen deficiency: purplish or very dark green leaves often point to phosphorus issues; leaf margins that look scorched or browned suggest potassium deficiency or stress; brown spots can indicate disease or other nutrient problems.