Aluminium Saturation & Acid-Soil Risk & Lime
Protects roots
Enter exchangeable aluminium and the base cations to get the effective CEC and aluminium saturationwith a root-toxicity risk band — so you know if your acid soil needs lime.
Check aluminium toxicity risk
Next: your soil is moderate for aluminium — 10–30% — sensitive crops may suffer; consider liming.
ECEC here is the effective CEC (Al + exchangeable bases) measured at field pH; Al toxicity stunts roots and locks up phosphorus, and liming to raise pH is the standard fix.
Aluminium saturation — key facts
- ECEC
- Al + Ca + Mg + K + Na
- Al saturation
- Al ÷ ECEC × 100
- Toxic above
- ≈ 30% for most crops
- Units
- cmol(+)/kg = meq/100 g
- The fix
- lime to raise pH
- Damage
- stunted, thickened root tips
- Tolerant crops
- cope with higher Al
- Privacy
- Runs in your browser; nothing uploaded
In acid soils, aluminium is the silent root killer
As soils acidify, aluminium comes off the clay and into solution where it becomes toxic to roots — stunting and thickening the root tips so the crop can no longer chase water and nutrients. The danger is not the raw amount of aluminium but how much of the soil's exchange it occupies, which is why aluminium saturation, the ratio of exchangeable Al to the effective CEC, is the number that matters.
This tool builds your ECEC from aluminium and the base cations, then reports the aluminium saturation percent and a risk band against the ~30% threshold where most crops suffer and lime is needed. Use it to read a soil test, decide whether to lime, and pick crops that match your soil. Pair it with the Lime Requirement, Buffer pH Lime and CEC & Base Saturation tools to size and plan the correction.
Spot toxic acidity
See Al saturation against the 30% threshold.
Decide on lime
Know when liming is actually warranted.
Read your soil test
Turn cation numbers into ECEC and risk.
Protect the roots
Stop hidden aluminium damage to yield.
Frequently Asked Questions
What is aluminium saturation?+
Aluminium saturation is the share of a soil's effective cation exchange capacity held by exchangeable aluminium, expressed as a percent. In acid soils aluminium comes off the clay and organic matter into solution where it is toxic to roots, so the higher the saturation the more the crop's roots are damaged and the more likely lime is needed.
How is aluminium saturation calculated?+
Effective CEC (ECEC) = exchangeable Al + the base cations Ca + Mg + K + Na, all in cmol(+)/kg (meq/100 g). Aluminium saturation = exchangeable Al ÷ ECEC × 100. For example 1.5 cmol Al against bases of 3.5 gives an ECEC of 5 and an Al saturation of 30% — the threshold where many crops start to suffer.
What is ECEC?+
ECEC, the effective cation exchange capacity, is the sum of the exchangeable cations a soil actually holds at its own pH — the base cations plus exchangeable aluminium and hydrogen. Unlike CEC measured at a fixed buffered pH, ECEC reflects the real conditions in an acid soil, which is why it is the right denominator for aluminium saturation.
What aluminium saturation is dangerous?+
As a rule of thumb, above about 30% aluminium saturation most crops suffer root damage and yield loss, and liming is warranted. Sensitive crops are hit below that, while aluminium-tolerant species such as some forages, tea or certain cereals cope with higher levels. Use the crop's own threshold where you know it.
How does aluminium harm plants?+
Toxic aluminium stunts and thickens root tips, so roots stop exploring the soil. That limits water and nutrient uptake — especially phosphorus and calcium — leaving plants drought-prone and stunted even when nutrients are present. The damage is at the root, so above-ground symptoms can look like a general nutrient deficiency.
How do I lower aluminium saturation?+
Lime is the main tool: raising soil pH precipitates aluminium out of the exchange and solution as harmless hydroxides, dropping its saturation. Adding calcium and organic matter also helps, and choosing aluminium-tolerant varieties buys time. Use a lime requirement or buffer-pH test to size the lime rate to your soil.
What units should I enter?+
Enter all cations in cmol(+)/kg, which is the same as milliequivalents per 100 g of soil (meq/100 g) — the standard reporting units on a soil test. Keep aluminium and the base cations in the same units so the saturation ratio is valid. If your report uses mg/kg, convert to cmol(+)/kg first.
Do I need to include sodium and hydrogen?+
Include the base cations your test reports — calcium, magnesium, potassium and sodium — in the ECEC. Some labs also report exchangeable hydrogen; where given it adds to the acidity but aluminium is usually the dominant toxic ion. This calculator builds ECEC from aluminium plus the four base cations, matching common soil-test outputs.
Are the figures precise?+
They are accurate for the values you enter, but the conclusion is only as good as the soil test. Aluminium varies across a field and changes with pH, so sample well, use the right crop threshold, and confirm a liming decision with a lime requirement or buffer-pH test rather than aluminium saturation alone.