Example inputs and outputs
| Scenario | Current pH | Target pH | Area | Depth | Texture | Amendment | Estimated material |
|---|---|---|---|---|---|---|---|
| Vegetable bed adjustment | 5.5 | 6.5 | 20 m² | 15 cm | Loam | Calcitic lime | ≈ 122 kg |
| Blueberry area acidification | 6.8 | 5.2 | 30 m² | 15 cm | Sandy | Elemental sulfur | ≈ 17 kg |
| Ornamental bed fine-tuning | 6.2 | 6.8 | 10 m² | 10 cm | Clay | Dolomitic lime | ≈ 33 kg |
Examples are illustrative; your soil test may differ.
Formula used
Step 1: Soil mass
Soil mass (kg) = Area (m²) × Depth (m) × Bulk density (kg/m³)
Step 2: CaCO3-equivalent requirement
CaCO3 eq. (kg) = Soil mass (kg) × |ΔpH| × Buffer coefficient × Application factor
Step 3: Convert to selected amendment
- Raise pH: Material (kg) = CaCO3 eq. ÷ (CCE%/100) ÷ Reactivity
- Lower pH: Elemental sulfur eq. (kg) ≈ CaCO3 eq. × 0.32 ÷ Oxidation efficiency
- Lower pH (salts): Material (kg) = Sulfur eq. × Relative factor
How to use this calculator
- Enter your current pH from a recent soil test.
- Set a target pH suitable for your plants.
- Add area and mixing depth you plan to amend.
- Select texture, then adjust OM and CEC if known.
- Choose an amendment that matches your pH direction.
- Click Calculate, review the rate, and download reports.
Apply in smaller doses when possible, mix well, water in, and re-test after a few weeks.
Soil pH buffering explained
Soil pH is not changed by acidity alone; it is resisted by buffering from clays, organic matter, and exchange sites. Two soils can show the same pH but require very different amendment masses to move one full pH unit. This calculator estimates that resistance by combining texture, organic matter percentage, and cation exchange capacity (CEC) into a practical buffer coefficient. Most vegetables prefer pH 6.2–6.8, blueberries 4.5–5.5, and lawns often perform best near 6.5 in many temperate garden soils.
Interpreting buffer coefficient inputs
Texture sets the baseline: sandy soils often respond faster, while clay and organic-rich soils respond slower. Organic matter and CEC add resistance because more exchange sites must be neutralized. Typical garden CEC values range from about 3–10 cmol(+)/kg for sands, 10–20 for loams, and 20–40 for clays. Higher CEC usually means more material per square meter.
Material selection and quality factors
To raise pH, liming materials are compared using calcium carbonate equivalent (CCE) and reactivity. A CCE of 90% means 1 kg behaves like 0.90 kg of pure CaCO3. Reactivity reflects particle size and how quickly the material dissolves; 0.80–0.95 is common. To lower pH, elemental sulfur is most concentrated, while sulfate salts need several times more mass for a similar shift.
Application rates and timing
The report provides total kilograms plus normalized rates (kg/m², per 10 m², and per 100 ft²) so you can scale from beds to lawns. Large adjustments are safer when split into two or three applications, mixed into the top 10–20 cm. Moisture and warmth speed reactions; sulfur oxidation is slower in cool seasons, so plan changes months ahead.
Recordkeeping and retesting targets
Saving CSV or PDF outputs helps track amendments by date, area, and depth. Re-test soil after the material has had time to react—often 6–12 weeks for lime in warm conditions and longer for sulfur. Small corrective applications are more predictable than one large dose. For sensitive crops, verify targets with local recommendations and adjust gradually.
FAQs
What does the buffer coefficient represent?
It estimates how strongly your soil resists pH change, based on texture, organic matter, and CEC. A higher coefficient means more amendment is needed per pH unit and per kilogram of soil.
Should I always use the default bulk density?
Defaults are reasonable for planning, but a measured bulk density improves accuracy, especially in raised beds, compacted lawns, or very organic soils. Enter your value if you have one.
Why does the calculator show CaCO3 equivalent?
CaCO3 equivalent is a common reference that normalizes liming power. The tool converts that requirement into your chosen material using neutralizing value and reactivity, so you can compare products consistently.
Can I lower pH with sulfur quickly?
Sulfur works through microbial oxidation, so it is slower in cool or dry conditions. Split applications, keep soil moist, and allow several weeks to months before retesting, especially for larger shifts.
Is wood ash a good alternative to lime?
Wood ash can raise pH, but its neutralizing value varies and it adds soluble salts. Use modest rates, avoid repeated heavy applications, and monitor pH and potassium levels to prevent imbalance.
How often should I retest after amending?
Retest after the material has reacted: commonly 6–12 weeks for lime in warm seasons and longer for sulfur. For large changes, test between split applications to avoid overshooting the target.