Aluminium injury: brown, bald root tips
On grain land, consider lime only below about 5.5. Do not push urea onto bald tips.
- Phosphorus shortage is dark green with purple; roots are not always brown and bare. Aluminium toxicity starts at the root tip.
- Root burn lines the fertiliser furrow and you can see grains; aluminium toxicity is the whole acid layer.
- Don’t pour urea on bald roots; don’t treat it as hunger without a test.
- Agricultural lime: Follow a soil test. Commonly tens to about a hundred kg per mu. The aim is to drop aluminium, not to go alkali
- Name what you see before you feed.
- If leaves, roots and the surface disagree, stop.
- When soil is acid enough, aluminium comes off the clay and bites tips.
- A bitten root cannot eat fertiliser.
What you see in the field
Washed tips are brown and bald, with few laterals. More nitrogen will not make a canopy. Pull one stalled plant, rinse, and look for remaining white points. A starved root is still there, only thin; aluminium has destroyed the tip. Aluminium dissolves once pH is low. Lay a brown-bald root next to a still-white neighbour. Let a new tip grow before a thin feed.
Tap to enlarge. The caption says what to photograph. Missing field photos are marked as to-be-added.
Why it looks like this
In strongly acid soil, aluminium injures the meristem of the tip. Once the mouth is gone, later fertiliser cannot enter. The fix is to lift plough-layer pH past the injury threshold — on grain land, consider lime only below about 5.5 — not more nitrogen. Thin organic matter buffers poorly. Tea tolerates acid; do not use the grain target on tea.
A sketch. Do not fertilise from the picture alone.Easy to mix up
Looks like “Starved thin roots”
A starved root is still there and can still extend, only thin. Aluminium has destroyed the tip — brown, bald, few laterals. Washing shows it.
Looks like “Fertiliser-black roots”
Fertiliser burn follows a dressing, in a row, with granules in the furrow. Aluminium stall is often a whole patch that matches low pH.
Do this / don’t do that
- 1Pull one plant and wash the roots. Brown, bald tips with few white points: then aluminium injury is on the table. Still-white roots: do not lime from this page.
- 2Test 0–20 cm pH. On grain land, consider lime only below about 5.5. Agricultural lime split in two, sandy soils at the low end, not the same day as urea.
- 3Wait for new white roots, then a thin feed. Do not push tea to neutral. Retest next season.
Don’t do this first
- Do not pour urea on bald tips. The feed cannot enter and will burn what is left.
- Do not push tea to neutral as if it were grain land. Tea stays around 4.5–6.0.
- Do not spread agricultural lime before you have a plough-layer pH on this field.
Rate range
Agricultural lime
Follow a soil test. Commonly tens to about a hundred kg per mu
The aim is to drop aluminium, not to go alkali.
Organic manure
Rotted, follow local advice
Tie up aluminium, grow new roots.
This is a diagnosis guide. Rates live in Agricultural lime: how much, and when
These are ranges. Confirm with your local extension station and the product label.
One number example
Grain-land tips brown and bald, pH 5.2: agricultural lime in the usual range, sandy soil at the low end, split, not the same day as urea. Wait for new white roots, then a thin feed. Tea with the same bald tips may still want to stay acid — do not push it to neutral.
When you see Root tips look scalded, test. Walk an S and mix — one hole is not the field.
Lesson video
2026-04-02 · 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