Acid soil: seedlings stall, root tips go brown
pH is a measurement, not a disease. On grain land, consider lime only when pH is below about 5.5.
- When seedlings stall, wash the roots first.
- Brown, bald tips look like aluminium toxicity.
- Rusty water is extra evidence, not required.
- Test pH at zero to twenty centimetres.
- On grain land, consider lime only below about five point five.
- Farm lime is often fifty to one hundred fifty kilograms per mu, about seven hundred fifty to two thousand two hundred fifty kilograms per hectare, split in two.
- Sandy soils take the low end.
- Not the same day as urea. No builder's lime.
- Do not push tea to neutral. Tea stays around four point five to six.
- Do not pour urea on bald roots.
What you see in the field
A stall means new leaves come slowly, the heart leaf will not open, and few new roots show when you crouch. Do not judge from yellow leaves alone. Pull one plant from the worst ridge, carry the root ball to the ditch, and rinse gently so you do not rub off the tips. White growing points mean the root can still take water. Brown, bald tips with few laterals look like aluminium injury. Rusty irrigation water is extra evidence, not required. Lay that plant next to a green neighbour. Grain land and tea are not the same rule: on grain land, consider lime only below about 5.5; tea stays around 4.5 to 6.0 and must not be pushed to neutral.
Tap to enlarge. The caption says what to photograph. Missing field photos are marked as to-be-added.
Why it looks like this
When the plough layer is too acid, aluminium leaves the mineral and injures the growing tip. Once the tip is bald, water and nutrients cannot enter, so the top looks like a shortage of nitrogen or phosphorus. More urea will not grow a canopy. Years of ammonium nitrogen as the only nitrogen source, and rain leaching calcium and magnesium, push pH down. Southern red-yellow soils start acid; physiological acid fertilisers make them more so. Tea tolerates acid. Grain land is not better the more acid it gets.
A sketch. Do not fertilise from the picture alone.Easy to mix up
Looks like “Nitrogen yellowing”
Nitrogen yellows the lower old leaves while new leaves stay green, and washed roots are often still white. Acid injury hits the tip first and the whole plant stalls, so more nitrogen will not make a canopy.
Looks like “Cold stall”
Cold recovers in a few warm days. Acid stall does not grow new white roots after the warm-up. Still stalled a week later: take pH paper to the field before you add urea.
Do this / don’t do that
- 1Pull one plant from the worst ridge and rinse the roots at the ditch. Read the tips before you add fertiliser, because a bald tip cannot take a feed and urea will only burn what is left.
- 2Test 0–20 cm pH. On grain land, consider lime only below about 5.5. Agricultural lime is commonly 50–150 kg/mu (about 750–2250 kg/ha), split in two; sandy soils take the low end. Not the same day as urea. No builder’s lime.
- 3Do not push a tea garden to neutral. Tea stays around 4.5–6.0. Wait for new white roots, then a thin feed. Retest pH next season and stop once you are in range.
Don’t do this first
- Do not push tea to neutral as if it were grain land. Tea stays around 4.5–6.0.
- Do not pour urea on bald roots. The feed cannot enter and will burn what is left.
- Do not copy another field’s lime rate. Test this plough layer first.
Rate range
| Crop × texture | Texture | Rate | Note |
|---|---|---|---|
| Grain (rice, maize, peanut) | Sandy | Agricultural lime about 50 kg/mu (about 750 kg/ha), split in two | Amend only if pH < 5.5; not the same day as urea |
| Grain | Clay | Agricultural lime up to about 150 kg/mu (about 2250 kg/ha), split in two | Retest next season; stop once the target is reached |
| Tea | Any | Do not push tea to neutral | Tea window is about pH 4.5–6.0 |
| Protected vegetables | Any | Use the low end of the grain range | Test first. No builder’s lime. |
These are ranges. Confirm with your local extension station and the product label.
| Cell | Low | Mid | High |
|---|---|---|---|
| pH | < about 5.5, tips brown easily | 6.0–7.5 grain and vegetables are comfortable | > 8 iron often locks |
| Exchangeable Al | Little injury | Becoming active | Root tips brown and bald |
| Organic matter | Thin buffer, aluminium worse | Can complex some aluminium | Liming is steadier |
One number example
The same grain field at pH 5.2 can discuss agricultural lime: sandy soil at about 50 kg/mu (about 750 kg/ha), split in two; clay can see the 150 kg/mu (about 2250 kg/ha) end of the range, still split. A tea garden at the same 5.2 often still sits in the 4.5–6.0 window. Do not copy the grain recipe onto tea. Not the same day as urea. No builder’s lime.
Mix several points from the plough layer. A neighbour ridge is a useful pair. Retest pH the season after you amend.
Lesson video
2026-03-12 · Li Zeyu · For learning. Serious damage: local agronomist or a soil test.
Sources：Rates are customary grain-land ranges; confirm with a local station and the label. Tea pH targets differ from grain.
For learning only. Fertiliser and pesticide decisions need a local agronomist and a soil test.
Not sure? Photograph the field to identify the problem