---
title: "Base Saturation Calculator: The Ca:Mg Ratio Test That Exposes Concrete Soil Before You Fertilize"
canonical: "https://theyieldgrid.com/base-saturation-calculator/"
model_id: "tyg-661"
model_version: "1.0.0"
last_reviewed: "2026-08-25T01:18:06"
reviewed_by: "Umer Hayiat"
---

# Base Saturation Calculator: The Ca:Mg Ratio Test That Exposes Concrete Soil Before You Fertilize

> Canonical calculator: [https://theyieldgrid.com/base-saturation-calculator/](https://theyieldgrid.com/base-saturation-calculator/)

## What this calculator does

Home - Free Gardening Calculators & Tools - Base Saturation Calculator: The Ca:Mg Ratio Test That Exposes Concrete Soil Before You Fertilize A soil test that shows adequate calcium and magnesium numbers can still describe a field with the water infiltration of a parking lot. That is the core failure mode the Albrecht kinematics model was designed to catch. Raw elemental values do not tell you whether calcium and magnesium are in the right proportion to keep soil particles physically separated, and that ratio determines whether your soil breathes, drains, and allows root penetration at all.

## Inputs

| Input | ID | Type | Unit | Range or choices | Required |
|---|---|---|---|---|---|
| Cation Exchange Capacity (CEC) | `absbal_cec` | number |  | 0.1 to 100 | No |
| Current % Calcium (Ca) | `absbal_ca` | number |  | 0 to 100 | No |
| Current % Magnesium (Mg) | `absbal_mg` | number |  | 0 to 100 | No |
| Current % Potassium (K) | `absbal_k` | number |  | 0 to 100 | No |

## Outputs

| Output ID | Default state |
|---|---|
| `absbal_cec_err` |  |
| `absbal_ca_err` |  |
| `absbal_mg_err` |  |
| `absbal_k_err` |  |
| `absbal_results` | — Ca : Mg Ratio Ca:Mg Ratio — Soil Physical Condition 1:1 3:1 4:1–7:1 10:1 14:1+ Calcium (Ca) — 0% Target: 68–75% 100% Magnesium (Mg) — 0% Target: 10–15% 40% Potassium (K) — 0% Target: 3–5% 15% Warnings & Standards Calculated Amendment Recommendations Scenario Ca% Mg% K% Ca:Mg Soil Status Ideal (Albrecht) 68–75 10–15 3–5 ~5:1 Optimal High-Mg Concrete 60 22 4 ~2.7:1 Tight Soil Ca Deficiency 52 14 4 ~3.7:1 Low Ca K Lockout Risk 68 14 1.5 ~4.9:1 K Low Excess Ca / Sandy 82 8 3 ~10.3:1 Ca Excess Low |
| `absbal_out_primary` | — |

## Formula and method

The Albrecht model focuses on the physical displacement of excess magnesium to prevent soil platelets from chemically sealing. Show the calculation steps Step 1: Validate inputs. The tool checks that CEC is between 0.1 and 100 meq/100g, that each percentage is between 0 and 100, and that Ca + Mg + K does not sum to more than 100. If any check fails, the calculation halts and the relevant field displays an inline error. Step 2: Compute Ca:Mg ratio. Ca:Mg Ratio = Ca% divided by Mg% If Mg% is zero, the ratio is treated as positive infinity and all ratio-dependent checks default to the excess-Ca branch. The ratio is displayed rounded to two decimal places. Step 3: Evaluate structural status. Two thresholds determine whether the tight-soil concrete warning fires: Mg% greater than 15% (Albrecht’s absolute Mg ceiling) Ca:Mg ratio less than 4:1 (the minimum structural ratio) Either condition alone is sufficient to trigger the warning. Both conditions firing together indicates a severe structural problem. Step 4: Calculate gypsum requirement. Ca deficit (lbs/acre) = (68 - Ca%) x CEC x 400 / 100 Gypsum tons/acre = Ca deficit / 380 The factor 400 is a field-weight conversion expressing meq/100g CEC to approximate pounds of cation per acre at a standard plow-layer depth. The factor 380 represents the pounds of elemental calcium delivered per ton of pelletized gypsum at approximately 19% Ca content. The division by 2000 to convert pounds to tons is incorporated into the 380 denominator by expressing it directly in lbs-per-ton terms. If Ca% is already at or above 68%, gypsum equals zero; the formula does not compute negative application rates. Step 5: Calculate K-Mag requirement. K deficit (lbs/acre) = (3 - K%) x CEC x 400 / 100 K-Mag tons/acre = K deficit / 440 The factor 440 represents the pounds of elemental potassium per ton of K-Mag (Sul-Po-Mag) at approximately 22% K content. If K% is at or above 3%, no K-Mag is recommended. Rounding: All output ratios display two decimal places. Amendment tonnage displays two decimal places. Bar chart widths are clamped to the visual range of the gauge and do not extrapolate beyond the display limits. Assumptions and Limits The Albrecht target ranges (Ca 68-75%, Mg 10-15%, K 3-5%) are guidelines calibrated primarily for temperate North American agricultural soils. Tropical soils, sodic soils, and highly weathered Ultisols may operate under different optimal profiles. The CEC conversion factor of 400 assumes a standard 6-inch plow layer at approximately 2 million pounds of soil per acre. Different tillage depths or soil bulk densities will produce proportionally different actual amendment requirements. The gypsum Ca content is assumed at 19% (380 lbs Ca per ton). Actual product purity varies; always verify the guaranteed analysis on the gypsum bag or delivery ticket. The K-Mag K content is assumed at 22% (440 lbs K per ton). Granular and powdered K-Mag products have similar analyses but different solubility curves; adjust application timing accordingly. The tool does not account for soil pH interactions. Calcium carbonate from liming can also raise Ca base saturation, but lime simultaneously raises pH and may exacerbate Mg release from clay minerals. For soils where pH adjustment is also needed, consult a soil pH lime calculator before deciding between gypsum and calcitic lime as the Ca source. Hydrogen, sodium, and aluminum cations can occupy substantial CEC capacity, particularly in acidic soils. The Ca + Mg + K sum reported by this tool may leave a large unaccounted fraction; that fraction does not mean the tool result is wrong, it means other cations are competing for exchange sites and should be addressed separately. Amendment response rate depends on rainfall, irrigation, and incorporation method. A deep-ripping pass after gypsum application accelerates Ca penetration into a physically sealed layer in ways that surface broadcasting alone cannot achieve.

## Verified worked examples

### Scenario 1: Classic High-Magnesium Concrete Soil

CEC: 18 meq/100g Calcium: 60% of CEC Magnesium: 22% of CEC Potassium: 4% of CEC Result: Ca:Mg ratio = 2.73:1. Tight-soil concrete warning activated. Estimated gypsum requirement = 1.52 tons per acre of pelletized gypsum (CaSO4). Both triggers fire here: Mg exceeds 15% and the Ca:Mg ratio falls well below the 4:1 floor. This is the profile that produces a field with acceptable N-P-K values and genuinely poor water infiltration. Gypsum supplies calcium without raising pH, which avoids further displacing magnesium from exchange sites.

### Scenario 2: K Lockout with Balanced Ca:Mg

CEC: 12 meq/100g Calcium: 68% of CEC Magnesium: 11% of CEC Potassium: 1.8% of CEC Result: Ca:Mg ratio = 6.18:1 (within safe range). K lockout warning activated. Estimated K-Mag requirement = 0.13 tons per acre. The Ca:Mg ratio is healthy, meaning soil structure is not the bottleneck. However, potassium at 1.8% of a 12 meq/100g CEC soil means exchange sites are not available for K uptake. Applying additional potassium fertilizer without correcting the base saturation percentage first would be largely ineffective.

### Scenario 3: Ideal Albrecht Balance (Verification Pass)

CEC: 22 meq/100g Calcium: 71% of CEC Magnesium: 13% of CEC Potassium: 4% of CEC Result: Ca:Mg ratio = 5.46:1. All three cations within Albrecht target ranges. No amendments flagged. This is the reference state the Albrecht model describes as structurally optimal. Soil particles should be pushed apart by calcium while magnesium provides adequate density without sealing. No gypsum or K-Mag is indicated at this profile.

## Assumptions

The Albrecht model focuses on the physical displacement of excess magnesium to prevent soil platelets from chemically sealing. Show the calculation steps Step 1: Validate inputs. The tool checks that CEC is between 0.1 and 100 meq/100g, that each percentage is between 0 and 100, and that Ca + Mg + K does not sum to more than 100. If any check fails, the calculation halts and the relevant field displays an inline error. Step 2: Compute Ca:Mg ratio. Ca:Mg Ratio = Ca% divided by Mg% If Mg% is zero, the ratio is treated as positive infinity and all ratio-dependent checks default to the excess-Ca branch. The ratio is displayed rounded to two decimal places. Step 3: Evaluate structural status. Two thresholds determine whether the tight-soil concrete warning fires: Mg% greater than 15% (Albrecht’s absolute Mg ceiling) Ca:Mg ratio less than 4:1 (the minimum structural ratio) Either condition alone is sufficient to trigger the warning. Both conditions firing together indicates a severe structural problem. Step 4: Calculate gypsum requirement. Ca deficit (lbs/acre) = (68 - Ca%) x CEC x 400 / 100 Gypsum tons/acre = Ca deficit / 380 The factor 400 is a field-weight conversion expressing meq/100g CEC to approximate pounds of cation per acre at a standard plow-layer depth. The factor 380 represents the pounds of elemental calcium delivered per ton of pelletized gypsum at approximately 19% Ca content. The division by 2000 to convert pounds to tons is incorporated into the 380 denominator by expressing it directly in lbs-per-ton terms. If Ca% is already at or above 68%, gypsum equals zero; the formula does not compute negative application rates. Step 5: Calculate K-Mag requirement. K deficit (lbs/acre) = (3 - K%) x CEC x 400 / 100 K-Mag tons/acre = K deficit / 440 The factor 440 represents the pounds of elemental potassium per ton of K-Mag (Sul-Po-Mag) at approximately 22% K content. If K% is at or above 3%, no K-Mag is recommended. Rounding: All output ratios display two decimal places. Amendment tonnage displays two decimal places. Bar chart widths are clamped to the visual range of the gauge and do not extrapolate beyond the display limits. Assumptions and Limits The Albrecht target ranges (Ca 68-75%, Mg 10-15%, K 3-5%) are guidelines calibrated primarily for temperate North American agricultural soils. Tropical soils, sodic soils, and highly weathered Ultisols may operate under different optimal profiles. The CEC conversion factor of 400 assumes a standard 6-inch plow layer at approximately 2 million pounds of soil per acre. Different tillage depths or soil bulk densities will produce proportionally different actual amendment requirements. The gypsum Ca content is assumed at 19% (380 lbs Ca per ton). Actual product purity varies; always verify the guaranteed analysis on the gypsum bag or delivery ticket. The K-Mag K content is assumed at 22% (440 lbs K per ton). Granular and powdered K-Mag products have similar analyses but different solubility curves; adjust application timing accordingly. The tool does not account for soil pH interactions. Calcium carbonate from liming can also raise Ca base saturation, but lime simultaneously raises pH and may exacerbate Mg release from clay minerals. For soils where pH adjustment is also needed, consult a soil pH lime calculator before deciding between gypsum and calcitic lime as the Ca source. Hydrogen, sodium, and aluminum cations can occupy substantial CEC capacity, particularly in acidic soils. The Ca + Mg + K sum reported by this tool may leave a large unaccounted fraction; that fraction does not mean the tool result is wrong, it means other cations are competing for exchange sites and should be addressed separately. Amendment response rate depends on rainfall, irrigation, and incorporation method. A deep-ripping pass after gypsum application accelerates Ca penetration into a physically sealed layer in ways that surface broadcasting alone cannot achieve. The Albrecht target ranges (Ca 68-75%, Mg 10-15%, K 3-5%) are guidelines calibrated primarily for temperate North American agricultural soils. Tropical soils, sodic soils, and highly weathered Ultisols may operate under different optimal profiles. The CEC conversion factor of 400 assumes a standard 6-inch plow layer at approximately 2 million pounds of soil per acre. Different tillage depths or soil bulk densities will produce proportionally different actual amendment requirements. The gypsum Ca content is assumed at 19% (380 lbs Ca per ton). Actual product purity varies; always verify the guaranteed analysis on the gypsum bag or delivery ticket. The K-Mag K content is assumed at 22% (440 lbs K per ton). Granular and powdered K-Mag products have similar analyses but different solubility curves; adjust application timing accordingly. The tool does not account for soil pH interactions. Calcium carbonate from liming can also raise Ca base saturation, but lime simultaneously raises pH and may exacerbate Mg release from clay minerals. For soils where pH adjustment is also needed, consult a soil pH lime calculator before deciding between gypsum and calcitic lime as the Ca source. Hydrogen, sodium, and aluminum cations can occupy substantial CEC capacity, particularly in acidic soils. The Ca + Mg + K sum reported by this tool may leave a large unaccounted fraction; that fraction does not mean the tool result is wrong, it means other cations are competing for exchange sites and should be addressed separately. Amendment response rate depends on rainfall, irrigation, and incorporation method. A deep-ripping pass after gypsum application accelerates Ca penetration into a physically sealed layer in ways that surface broadcasting alone cannot achieve. The Albrecht base saturation model treats soil fertility as a physical and chemical system, not merely a nutrient inventory. The most important distinction it draws is between a soil that has enough calcium and one that has calcium in the right ratio to magnesium to remain structurally open. These two conditions are not the same, and many soil programs that focus only on elemental sufficiency miss the structural failure entirely. Critical Warnings The Ca:Mg ratio below 4:1 is a structural emergency, not a mild deficiency. Magnesium ions draw aluminosilicate clay platelets together through electrostatic attraction, and when Mg occupies too large a fraction of CEC, those platelets physically pack against each other. The result is reduced macro-porosity, poor water infiltration, and roots that cannot penetrate the sealed zone regardless of how nutritionally complete the soil analysis appears. Potassium below 3% of CEC is a lockout event, not a deficiency level to manage slowly. Below this threshold, the root-zone concentration gradient required for K uptake through cation exchange cannot be maintained. Applying more potassium fertilizer to a soil in K lockout adds to the total K pool but does not correct the exchange-site deficit that prevents uptake. Excess magnesium above 15% persists for multiple growing seasons after amendment. Gypsum displaces Mg from exchange sites slowly through leaching. A single gypsum application that is correct in tonnage may still require two to three seasons to fully express in the Ca:Mg ratio depending on rainfall and soil depth. Testing annually after application is essential. For sites where soil sulfur accumulation is a concern, cross-referencing with a fertilizer salt index calculation helps confirm that repeated gypsum applications are not introducing secondary salinity stress. A Ca% within the 68-75% target range does not confirm the Ca:Mg ratio is safe. Ca at 70% and Mg at 20% produces a 3.5:1 ratio, which falls below the tight-soil threshold despite Ca being within range. Always evaluate both the individual percentages and the ratio output before concluding the profile is balanced. Minimum Standards Ca:Mg ratio must be at or above 4:1 for soil to maintain open physical structure. The Albrecht ideal is approximately 5:1. Mg% must remain below 15% to prevent structural sealing regardless of the absolute Ca level. K% must be at or above 3% for potassium exchange uptake to function. This is a hard floor, not a guideline range. CEC should be measured at consistent pH (typically buffered at pH 7) to allow comparison across test dates. Labs using different pH buffers may report CEC values that are not directly comparable year over year. Competitor Trap: Most online base saturation calculators check whether each cation falls within a target percentage range and report a pass or fail for each individually. They do not compute the Ca:Mg ratio as a separate diagnostic. This matters because a soil can pass all three individual percentage checks simultaneously and still carry a 3.8:1 Ca:Mg ratio, which is below the structural threshold. A farmer using a pass/fail checklist tool would see three green lights on the report while their field is actively sealing. The ratio test is not a refinement of the percentage test; it is a different test that catches failures the percentage check cannot detect. Ca:Mg ratio must be at or above 4:1 for soil to maintain open physical structure. The Albrecht ideal is approximately 5:1. Mg% must remain below 15% to prevent structural sealing regardless of the absolute Ca level. K% must be at or above 3% for potassium exchange uptake to function. This is a hard floor, not a guideline range. CEC should be measured at consistent pH (typically buffered at pH 7) to allow comparison across test dates. Labs using different pH buffers may report CEC values that are not directly comparable year over year. Competitor Trap: Most online base saturation calculators check whether each cation falls within a target percentage range and report a pass or fail for each individually. They do not compute the Ca:Mg ratio as a separate diagnostic. This matters because a soil can pass all three individual percentage checks simultaneously and still carry a 3.8:1 Ca:Mg ratio, which is below the structural threshold. A farmer using a pass/fail checklist tool would see three green lights on the report while their field is actively sealing. The ratio test is not a refinement of the percentage test; it is a different test that catches failures the percentage check cannot detect.

## Limitations and safety

The Albrecht target ranges (Ca 68-75%, Mg 10-15%, K 3-5%) are guidelines calibrated primarily for temperate North American agricultural soils. Tropical soils, sodic soils, and highly weathered Ultisols may operate under different optimal profiles. The CEC conversion factor of 400 assumes a standard 6-inch plow layer at approximately 2 million pounds of soil per acre. Different tillage depths or soil bulk densities will produce proportionally different actual amendment requirements. The gypsum Ca content is assumed at 19% (380 lbs Ca per ton). Actual product purity varies; always verify the guaranteed analysis on the gypsum bag or delivery ticket. The K-Mag K content is assumed at 22% (440 lbs K per ton). Granular and powdered K-Mag products have similar analyses but different solubility curves; adjust application timing accordingly. The tool does not account for soil pH interactions. Calcium carbonate from liming can also raise Ca base saturation, but lime simultaneously raises pH and may exacerbate Mg release from clay minerals. For soils where pH adjustment is also needed, consult a soil pH lime calculator before deciding between gypsum and calcitic lime as the Ca source. Hydrogen, sodium, and aluminum cations can occupy substantial CEC capacity, particularly in acidic soils. The Ca + Mg + K sum reported by this tool may leave a large unaccounted fraction; that fraction does not mean the tool result is wrong, it means other cations are competing for exchange sites and should be addressed separately. Amendment response rate depends on rainfall, irrigation, and incorporation method. A deep-ripping pass after gypsum application accelerates Ca penetration into a physically sealed layer in ways that surface broadcasting alone cannot achieve. The Albrecht base saturation model treats soil fertility as a physical and chemical system, not merely a nutrient inventory. The most important distinction it draws is between a soil that has enough calcium and one that has calcium in the right ratio to magnesium to remain structurally open. These two conditions are not the same, and many soil programs that focus only on elemental sufficiency miss the structural failure entirely. Critical Warnings The Ca:Mg ratio below 4:1 is a structural emergency, not a mild deficiency. Magnesium ions draw aluminosilicate clay platelets together through electrostatic attraction, and when Mg occupies too large a fraction of CEC, those platelets physically pack against each other. The result is reduced macro-porosity, poor water infiltration, and roots that cannot penetrate the sealed zone regardless of how nutritionally complete the soil analysis appears. Potassium below 3% of CEC is a lockout event, not a deficiency level to manage slowly. Below this threshold, the root-zone concentration gradient required for K uptake through cation exchange cannot be maintained. Applying more potassium fertilizer to a soil in K lockout adds to the total K pool but does not correct the exchange-site deficit that prevents uptake. Excess magnesium above 15% persists for multiple growing seasons after amendment. Gypsum displaces Mg from exchange sites slowly through leaching. A single gypsum application that is correct in tonnage may still require two to three seasons to fully express in the Ca:Mg ratio depending on rainfall and soil depth. Testing annually after application is essential. For sites where soil sulfur accumulation is a concern, cross-referencing with a fertilizer salt index calculation helps confirm that repeated gypsum applications are not introducing secondary salinity stress. A Ca% within the 68-75% target range does not confirm the Ca:Mg ratio is safe. Ca at 70% and Mg at 20% produces a 3.5:1 ratio, which falls below the tight-soil threshold despite Ca being within range. Always evaluate both the individual percentages and the ratio output before concluding the profile is balanced. Minimum Standards Ca:Mg ratio must be at or above 4:1 for soil to maintain open physical structure. The Albrecht ideal is approximately 5:1. Mg% must remain below 15% to prevent structural sealing regardless of the absolute Ca level. K% must be at or above 3% for potassium exchange uptake to function. This is a hard floor, not a guideline range. CEC should be measured at consistent pH (typically buffered at pH 7) to allow comparison across test dates. Labs using different pH buffers may report CEC values that are not directly comparable year over year. Competitor Trap: Most online base saturation calculators check whether each cation falls within a target percentage range and report a pass or fail for each individually. They do not compute the Ca:Mg ratio as a separate diagnostic. This matters because a soil can pass all three individual percentage checks simultaneously and still carry a 3.8:1 Ca:Mg ratio, which is below the structural threshold. A farmer using a pass/fail checklist tool would see three green lights on the report while their field is actively sealing. The ratio test is not a refinement of the percentage test; it is a different test that catches failures the percentage check cannot detect.

## Related calculators

- [Calculators & Tools](https://theyieldgrid.com/category/garden-calculators/)
- [soil texture analysis](https://theyieldgrid.com/soil-texture-calculator/)
- [CEC soil calculator](https://theyieldgrid.com/cec-soil-calculator/)
- [fertilizer salt index calculation](https://theyieldgrid.com/fertilizer-salt-index-calculator/)
- [agricultural lime calculator](https://theyieldgrid.com/agricultural-lime-calculator/)
- [soil pH sulfur calculator](https://theyieldgrid.com/soil-ph-sulfur-calculator/)
- [NPK calculator](https://theyieldgrid.com/npk-calculator/)
- [nitrogen rate calculator](https://theyieldgrid.com/nitrogen-calculator/)
- [soil pH lime calculator](https://theyieldgrid.com/soil-ph-lime-calculator/)
- [Prev Previous](https://theyieldgrid.com/soil-infiltration-rate-calculator/)
- [Next Next](https://theyieldgrid.com/well-pressure-tank-calculator/)

## Provenance

- Model ID: `tyg-661`
- Model version: `1.0.0`
- Reviewed by: Umer Hayiat
- Page modified: 2026-08-25T01:18:06
- Runtime SHA-256: `9a8059bc0c2b250472c5c95e584e6819582ac6c1178b3b91febf3b1da6080b98`

This Markdown document is a machine-readable mirror. The canonical interactive calculator is the HTML page linked above.