Which nutrient deficiency is indicated by yellowing of the older leaves of a plant?

Yellowing of the older leaves of a plant is a classic symptom of nitrogen deficiency. Nitrogen is a vital nutrient for plant growth, as it plays a crucial role in chlorophyll production, which is essential for photosynthesis. Because nitrogen is mobile within the plant, when a deficiency occurs, the plant reallocates nitrogen from older leaves to support the growth of younger leaves, leading to a yellowing effect in the older foliage.

This symptom directly correlates with nitrogen's role in the overall development and health of a plant. Plants deficient in nitrogen are often stunted in growth and exhibit a general decline in vigor, which can further affect yield and biomass accumulation. Therefore, the yellowing of older leaves serves as a significant indicator of nitrogen deficiency, making it a fundamental concept in plant nutrition assessment.