Nitrogen deficiency is usually first noticed in the older leaves, which appear pale and weakened. Over time, the plant loses vigor, reduces its production, and becomes more susceptible to pests and diseases.

Typical symptoms:
• Yellow or pale green lower leaves (chlorosis).
• Thin stems and reduced growth.
• Small leaves and premature drop.
• Early and forced flowering.
• Poor fruit production or grains with low protein content.

Nitrogen deficiency progresses gradually, beginning with mild signs and reaching critical stages if not corrected promptly.

Developmental stages:
• Initial: Mature leaves are lighter than normal.
• Intermediate stage: Yellowing progresses from the lower leaves to the upper ones.
• Advanced: Stems and veins take on a reddish or purplish hue.
• Final: Generalized chlorosis, leaf necrosis, and premature wilting.
• Final consequence: sharp reduction in yield and even death of the plant.