Enter Water and Site Details
Example Data Table
| Case | ECw | Na | Ca | Mg | Cl | HCO3 | LF | Crop | Expected Rating |
|---|---|---|---|---|---|---|---|---|---|
| A | 0.5 | 2 | 2 | 1 | 2 | 1 | 0.15 | Moderate | Low–Moderate |
| B | 2.2 | 6 | 2 | 1 | 6 | 2 | 0.15 | Moderate | Moderate–High |
| C | 5.5 | 12 | 2 | 1 | 12 | 4 | 0.10 | Sensitive | High–Very High |
Formula Used
- SAR (Sodium Adsorption Ratio): SAR = Na / √((Ca + Mg) / 2) (ions in meq/L).
- RSC (Residual Sodium Carbonate): RSC = (HCO₃ + CO₃) − (Ca + Mg) (meq/L).
- Estimated root-zone salinity: ECe ≈ 5 × ECw / LF, where LF is leaching fraction (0.05–0.30 used here).
- TDS estimate (when missing): TDS ≈ ECw × 640 (or ×700 for saltier mixes).
How to Use This Calculator
- Measure irrigation water ECw with a meter or lab report.
- If available, enter ions in meq/L (Na, Ca, Mg, Cl, HCO₃).
- Select irrigation method and drainage quality to reflect your setup.
- Set a leaching fraction (e.g., 0.10–0.20) based on how you water.
- Choose crop tolerance group, then press Calculate Risk.
- Use recommendations to adjust leaching, mulching, blending, or amendments.
- Export results using the CSV or PDF buttons after calculating.
Water EC and Salt Load
Electrical conductivity (ECw, dS/m) is the fastest indicator of total dissolved salts. In many garden supplies, ECw < 0.7 is usually low risk, 0.7–3.0 often needs leaching and drainage, 3.0–7.0 requires salt-tolerant choices, and > 7.0 is strongly restrictive. When a lab reports only TDS, a practical conversion is TDS ≈ ECw × 640–700 mg/L, which this calculator can estimate.
Sodium Hazard and Soil Structure
Sodium can disperse soil particles and reduce infiltration. The calculator uses SAR = Na / √((Ca + Mg) / 2) (meq/L). As a guide, SAR < 3 is low, 3–9 is moderate, 9–18 is high, and > 18 is very high. High SAR is most damaging in fine soils and raised beds that receive frequent shallow watering.
Carbonates and Calcium Balance
Residual Sodium Carbonate (RSC) flags waters that can precipitate calcium and magnify sodicity. RSC = (HCO3 + CO3) − (Ca + Mg) in meq/L. Values < 1.25 are commonly treated as safer, 1.25–2.5 are marginal, and > 2.5 can be unsuitable without amendments. Gypsum adds calcium without changing salinity much and can stabilize structure.
Leaching Fraction and Root-Zone Salinity
Salts accumulate when evaporation exceeds deep percolation. A practical planning metric is leaching fraction (LF), often 0.10–0.20 for garden beds with good drainage. The calculator estimates root-zone salinity with ECe ≈ 5 × ECw / LF (LF constrained to 0.05–0.30). If estimated ECe exceeds your crop group limit (about 2, 4, 6, or 8 dS/m), increase leaching or choose more tolerant plants.
Example Data and Management Targets
Use this compact example set to compare outcomes and validate inputs:
| Parameter | Example | Unit |
|---|---|---|
| ECw | 2.2 | dS/m |
| Na / Ca / Mg | 6 / 2 / 1 | meq/L |
| Cl / HCO3 | 6 / 2 | meq/L |
| LF | 0.15 | fraction |
| Expected | Moderate–High risk | — |
Practical targets that reduce salinity stress include mulching to cut evaporation, watering deeply to move salts down, and flushing containers periodically. If overhead sprinklers are used, keep chloride and sodium low to reduce leaf burn, and irrigate early so foliage dries quickly.
FAQs
1) What units should I use for sodium, calcium, and magnesium?
Use meq/L from a lab report. If you only have mg/L, convert first, or ask your lab for meq/L to avoid mistakes in SAR and RSC.
2) Can I rely on EC alone for salinity risk?
EC is a strong starting point, but sodium hazard (SAR), carbonate hazard (RSC), and chloride toxicity can change how the same EC behaves in your soil and plants.
3) What leaching fraction should home gardens aim for?
Many beds perform well around 0.10–0.20 with good drainage. Containers may need periodic heavier flushes because salts concentrate faster in limited soil volume.
4) Why can high SAR reduce infiltration even when EC is moderate?
Excess sodium disperses clay and organic colloids, sealing pores. In fine soils, this can slow water entry and trap salts near roots, increasing stress.
5) When is gypsum helpful?
Gypsum can help when SAR is high or RSC is marginal to high, because calcium supports soil aggregation. It will not remove salts; it improves structure and leaching effectiveness.
6) How do I confirm the calculator’s prediction in the field?
Measure soil EC during the season, especially in the top 5–10 cm. White crusts, poor infiltration, and leaf tip burn are practical warning signs that match rising salinity.
7) Does rainfall change salinity risk?
Yes. Rain can leach salts below the root zone, lowering risk. In covered gardens or dry climates, you must recreate that leaching with deeper irrigations and drainage.