What Do Leaf Colours Mean? Identifying Plant Nutrient Deficiencies

Yellow leaves do not always mean nitrogen deficiency. Waterlogging, drought, root disease, insects, unsuitable pH, salt injury, and several nutrient disorders can produce similar symptoms. Leaf colour is therefore a diagnostic clue, not a final diagnosis.

Are old or young leaves affected first?

This is a useful starting question. Deficiencies of some mobile nutrients tend to appear first on older leaves, while problems involving less-mobile nutrients may appear first in new growth.

• General yellowing: When it begins on older leaves, nitrogen deficiency is one possibility among several.
• Yellowing between green veins: Depending on leaf age, magnesium, iron, or another issue may be involved.
• Scorched leaf margins: Possible causes include potassium deficiency, salinity, drought, or chemical injury.
• Distorted new leaves: Check calcium or boron supply, insects, roots, and possible herbicide injury.

A five-step field check

1. Study the pattern across the field, not just one plant.
2. Inspect roots, soil moisture, drainage, and compaction.
3. Check both sides of leaves for insects and disease signs.
4. Review recent fertilizer, irrigation, and spray records.
5. Confirm the suspicion with soil or plant-tissue testing where appropriate.

Why not apply micronutrients immediately?

Excess micronutrients can become toxic and may interfere with the uptake of other nutrients. A pH problem can make an element unavailable even when it is present in the soil, so simply adding more may not correct the underlying issue.

Takeaway: Read the plant, roots, soil, field pattern, and management history together before choosing a corrective product.