<p>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 <strong>diagnostic clue</strong>, not a final diagnosis.</p>
<h2>Are old or young leaves affected first?</h2>
<p>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.</p>
<ul>
<li><strong>General yellowing:</strong> When it begins on older leaves, nitrogen deficiency is one possibility among several.</li>
<li><strong>Yellowing between green veins:</strong> Depending on leaf age, magnesium, iron, or another issue may be involved.</li>
<li><strong>Scorched leaf margins:</strong> Possible causes include potassium deficiency, salinity, drought, or chemical injury.</li>
<li><strong>Distorted new leaves:</strong> Check calcium or boron supply, insects, roots, and possible herbicide injury.</li>
</ul>
<h2>A five-step field check</h2>
<ol>
<li>Study the pattern across the field, not just one plant.</li>
<li>Inspect roots, soil moisture, drainage, and compaction.</li>
<li>Check both sides of leaves for insects and disease signs.</li>
<li>Review recent fertilizer, irrigation, and spray records.</li>
<li>Confirm the suspicion with soil or plant-tissue testing where appropriate.</li>
</ol>
<h2>Why not apply micronutrients immediately?</h2>
<p>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.</p>
<p><strong>Takeaway:</strong> Read the plant, roots, soil, field pattern, and management history together before choosing a corrective product.</p>