What is a common symptom of a nitrogen deficiency in plants?

A common symptom of nitrogen deficiency in plants is the yellowing of older leaves. Nitrogen is a vital nutrient that plays a crucial role in plant growth, particularly in the formation of chlorophyll, which is necessary for photosynthesis. When plants lack nitrogen, they cannot produce enough chlorophyll, leading to a yellowing, or chlorosis, primarily in the older leaves since nitrogen is mobile within the plant and is reallocated to newer growth. This deficiency affects the plant's ability to synthesize food effectively, resulting in overall growth issues and reduced vigor.

While other symptoms such as stunted growth and changes in stem texture can occur due to various deficiencies or stresses, the specific yellowing of older leaves is most characteristically associated with nitrogen deficiency, making it the most recognizable and significant symptom in diagnosing this particular nutrient imbalance.