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Nutrients fighting each other: phosphorus vs zinc, potassium vs magnesium

More of one bag can starve another.

Nutrient shortageFertiliser burn
Speed
  1. One column on the sheet is off the chart; the crop shows the missing one.
  2. High P, little zinc.
  3. High K, little magnesium.
  4. A straight shortage is low on the matching cell; antagonism is not low — sometimes very high.
  5. Spray injury has a clock; antagonism is a long fertiliser habit.
  6. Add zinc when phosphorus is high: Foliar: labelled lower rate. Cut phosphorus at the same time
  7. Name what you see before you feed.
  8. If leaves, roots and the surface disagree, stop.

What you see in the field

One column on the sheet is off the chart; the crop shows the missing one. High P, little zinc. High K, little magnesium.First the leaf position: new or old, even yellow or between the veins. If that does not match, do not fertilise yet. Pull one plant and read whether the roots are white, brown or foul.

A sketch. Do not fertilise from the picture alone.

Tap to enlarge. The caption says what to photograph. Missing field photos are marked as to-be-added.

Why it looks like this

The field looks like this because the root cannot take water or nutrients the usual way. Fix the soil condition first — drainage, salt, acidity, compaction or a salt of fertiliser — then a thin feed. Rates live in the range on this page; confirm with a local station and the label.

Easy to mix up

  • Looks like “A nutrient shortage alone”

    A straight shortage is low on the matching cell; antagonism is not low — sometimes very high.

  • Looks like “Spray injury”

    Spray injury has a clock; antagonism is a long fertiliser habit.

Do this / don’t do that

  1. 1One column on the sheet is off the chart; the crop shows the missing one. High P, little zinc. High K, little magnesium.
  2. 2Stop pouring the high one. Foliar-rescue the locked one if the crop is in season. Next year, a balanced plan from the whole sheet.
  3. 3Don’t add the missing one while still pouring whatever is already extreme. Use the range on this page only as a range. Confirm with a local station and the product label.

Don’t do this first

  • Don’t add the missing one while still pouring whatever is already extreme.

Rate range

Add zinc when phosphorus is high

Foliar: labelled lower rate

Cut phosphorus at the same time.

Add magnesium when potassium is high

Foliar or soil: follow a soil test

Stop the heavy potassium first.

These are ranges. Confirm with your local extension station and the product label.

pH / organic matter / salt

Read these three first

Then nitrogen, phosphorus, potassium and the micronutrients.

A field check

Which leaves, the roots, the soil surface

Compare a healthy neighbour plant.

When you see One column on the sheet is off the chart; the crop shows the missing one. High P, test. Mix several spots of the tilled layer; skip the edge and the manure heap.

Lesson video

2026-05-27 · Li Zeyu · For learning. Serious damage: local agronomist or a soil test.

For learning only. Fertiliser and pesticide decisions need a local agronomist and a soil test.

Not sure? Photograph the field to identify the problem