CEC & Base Saturation & Read Your Soil's Balance
Balances calcium
Enter Ca, Mg, K, Na and exchangeable acidity to get your cation exchange capacity, base saturation percent, each cation's share, the Ca:Mg and Mg:K ratios and a fertility band.
Exchangeable cations
Next: if base saturation is low or the soil is acid, lime to raise Ca and pH; if Mg is low relative to K, use dolomitic lime or Mg fertiliser.
Ideal ratios per Albrecht/standard soil-test interpretation; confirm with a lab report and local advice.
CEC & base saturation — key facts
- CEC
- Ca+Mg+K+Na+acidity, cmol(+)/kg
- Base saturation
- bases ÷ CEC × 100
- Ideal Ca / Mg / K
- ≈ 65–75 / 10–15 / 2–5%
- CEC bands
- <8 low · 15–25 good · >25 high
- cmol = meq
- cmol(+)/kg = meq/100 g
- ppm → cmol
- Ca/200.4 Mg/121.5 K/391 Na/230
- Low base sat.
- acid soil → lime
- Privacy
- Runs in your browser; nothing uploaded
Turn a soil test into a picture of nutrient balance
A soil test lists exchangeable calcium, magnesium, potassium and sodium, but the numbers only come alive once you see how they share the soil's exchange sites. Cation exchange capacity is the size of that reserve, base saturation is how much of it holds nutrients rather than acidity, and the ratios between cations show whether one is crowding out another. Together they explain why two fields with similar nutrient totals can behave very differently.
This tool computes CEC, base saturation percent, each cation's share of CEC, the Ca:Mg and Mg:K ratios and a fertility band from values in cmol(+)/kg or ppm. Use it to spot a calcium-poor acid soil that needs lime, a magnesium shortfall hidden by high potassium, or a sandy low-CEC soil that needs little-and-often feeding. Pair it with the Lime Requirement, Fertilizer (NPK) and Soil Texture tools for a full fertility plan.
Size the reserve
CEC shows how much your soil can hold and buffer.
Spot acidity
Low base saturation flags a lime requirement.
Check the ratios
Ca:Mg and Mg:K reveal hidden imbalances.
ppm or cmol
Enter lab results in either unit and convert.
Frequently Asked Questions
What is cation exchange capacity (CEC)?+
CEC is the soil's capacity to hold positively charged nutrients (cations) on clay and organic matter and release them to plants. It's the sum of the exchangeable cations — calcium, magnesium, potassium and sodium — plus the exchangeable acidity (hydrogen and aluminium), expressed in cmol(+)/kg, which is the same as the older meq/100 g. A higher CEC means a bigger nutrient and water buffer.
How is base saturation calculated?+
Base saturation % = (sum of the basic cations Ca + Mg + K + Na) ÷ CEC × 100. The 'bases' are the four base cations; the rest of the CEC is taken up by exchangeable acidity. A soil at 80% base saturation has four-fifths of its exchange sites holding bases and one-fifth holding acidity, so it's near-neutral and well supplied with Ca, Mg and K.
What is each cation's percent of CEC?+
Dividing each cation by the total CEC and multiplying by 100 shows how the exchange sites are shared out. A commonly cited balanced range is roughly Ca 65–75%, Mg 10–15% and K 2–5% of CEC, with the rest as Na and acidity. The tool shows every cation's share so you can see at a glance which nutrient is over- or under-represented.
Why do Ca:Mg and Mg:K ratios matter?+
Cations compete for uptake, so their balance can matter as much as their amounts. The Ca:Mg ratio (often targeted around 4:1 to 8:1) affects soil structure and magnesium availability, while a sufficient Mg:K ratio guards against potassium suppressing magnesium uptake. The tool reports both so you can spot an imbalance even when individual levels look adequate.
How do I convert ppm to cmol(+)/kg?+
Divide the ppm by the cation's equivalent weight: Ca ÷ 200.4, Mg ÷ 121.5, K ÷ 391 and Na ÷ 230. So 1600 ppm Ca ≈ 1600 ÷ 200.4 ≈ 8.0 cmol(+)/kg. The tool handles the conversion so you can enter lab results in ppm and still get CEC, base saturation and the cation percentages in consistent units.
What do the CEC bands mean?+
CEC reflects soil texture and organic matter. Roughly, below 8 cmol(+)/kg is low (sandy soils that hold little and leach easily), 8–15 is moderate, 15–25 is good, and above 25 is high (heavy clays and organic soils with a large nutrient reserve). Low-CEC soils benefit from smaller, more frequent inputs; high-CEC soils buffer change and respond more slowly.
What does low base saturation tell me?+
Low base saturation means much of the CEC is held by exchangeable acidity rather than bases, which usually goes with a low, acidic pH and a shortage of calcium and magnesium. The fix is liming, which replaces hydrogen and aluminium on the exchange sites with calcium (and magnesium if dolomitic lime is used), raising both pH and base saturation. See the Lime Requirement tool to size the application.
What is the fertility band output?+
The tool combines CEC and base saturation into a simple band — for example a high-CEC soil with healthy base saturation reads as a strong, well-buffered fertility status, while a low-CEC, low-saturation soil flags as a weak, leaching-prone, acidic one needing lime and careful nutrient management. It's a quick summary on top of the detailed numbers.
Is the soil nutrient balance the whole story?+
No — base cation saturation is one lens. Crop response also depends on pH, organic matter, phosphorus and micronutrients, soil structure and biology, and there's healthy debate about how tightly the 'ideal ratios' should be chased versus simply correcting deficiencies. Use this tool to read your test and flag imbalances, alongside, not instead of, agronomic judgement.
Where do I get the numbers to enter?+
From a standard soil test report. Labs report exchangeable Ca, Mg, K and Na (in ppm or cmol(+)/kg) and usually an exchangeable acidity or estimate it from pH. Enter those values and the tool computes CEC, base saturation, each cation's percent, the Ca:Mg and Mg:K ratios and the fertility band, turning a dense report into a clear picture.