---
title: "Soil Leaching Requirement Calculator: How Salinity Accumulates and What to Flush It Out"
canonical: "https://theyieldgrid.com/soil-leaching-requirement-calculator/"
model_id: "tyg-637"
model_version: "1.0.0"
last_reviewed: "2026-04-28T03:01:09"
reviewed_by: "Umer Hayiat"
---

# Soil Leaching Requirement Calculator: How Salinity Accumulates and What to Flush It Out

> Canonical calculator: [https://theyieldgrid.com/soil-leaching-requirement-calculator/](https://theyieldgrid.com/soil-leaching-requirement-calculator/)

## What this calculator does

Home - Free Gardening Calculators & Tools - Soil Leaching Requirement Calculator: How Salinity Accumulates and What to Flush It Out Every drop of irrigation water carries dissolved salts into the root zone. The water itself evaporates or gets absorbed by the plant, but the salt stays behind. Over successive watering cycles, this process concentrates salts to levels that flip osmotic pressure in reverse: instead of the plant drawing water in from the soil, the saltier soil begins pulling water molecules back out of the roots. A plant sitting in wet soil can die of osmotic dehydration. This is not a rare edge case. It is the default outcome for any irrigated system without a deliberate leaching strategy. Irrigation water quality, measured as electrical conductivity (ECiw in dS/m), determines how aggressively salt loads accumulate and how much extra water is required to flush them before crop damage occurs.

## Inputs

| Input | ID | Type | Unit | Range or choices | Required |
|---|---|---|---|---|---|
| Irrigation Water EC (EC iw ) | `soilsalin_eciw` | number | EC iw | 0 to 20 | No |
| Crop Salinity Limit (EC e ) | `soilsalin_ece` | number |  | 0 to 30 | No |
| Crop Water Requirement (per week) | `soilsalin_cwr` | number |  | 0 to 99999 | No |

## Outputs

| Output ID | Default state |
|---|---|
| `soilsalin_results` | ⚠ Crop Death Imminent — Your irrigation water EC ( dS/m) exceeds your crop’s salinity threshold ( dS/m). Osmotic pressure will reverse — the soil will pull water out of plant roots even in wet soil. Leaching math alone cannot save this crop. Leaching Fraction (LF) Leaching Required Ideal (0–10%) Moderate (10–25%) High (>25%) Total Water to Apply Leaching Volume Salt Removed per Cycle Water Efficiency Reference: Leaching Fraction for Common Water ECs at Your Crop Limit Water EC (dS/m) LF (%) Extr |
| `soilsalin_out_eciw_display` |  |
| `soilsalin_out_ece_display` |  |
| `soilsalin_normal_results` | Leaching Fraction (LF) Leaching Required Ideal (0–10%) Moderate (10–25%) High (>25%) Total Water to Apply Leaching Volume Salt Removed per Cycle Water Efficiency Reference: Leaching Fraction for Common Water ECs at Your Crop Limit Water EC (dS/m) LF (%) Extra Water per Unit Risk Level Tools That Help Manage Root-Zone Salinity |
| `soilsalin_out_primary` |  |
| `soilsalin_out_total` |  |
| `soilsalin_out_leach_vol` |  |
| `soilsalin_out_salt_removed` |  |
| `soilsalin_out_efficiency` |  |
| `soilsalin_warnings_box` |  |

## Formula and method

LF = EC iw ÷ (5 × EC e − EC iw ) This gives the fraction of applied irrigation water that must pass beyond the root zone as drainage to prevent salt accumulation. Derived from the FAO-29 mass-balance method (Rhoades, 1974). EC iw = electrical conductivity of your irrigation water (dS/m) EC e = maximum soil EC your crop can tolerate (dS/m) A result of 0.10 = 10% of all water applied must drain past the roots The ratio between drainage flow and total applied water is set by irrigation EC and crop salt tolerance, independent of irrigation volume. Show the calculation steps Step 1: Compute Leaching Fraction The formula is derived from a steady-state mass balance of salt inputs and outputs in the root zone: LF = ECiw / (5 x ECe – ECiw) The denominator term (5 x ECe) reflects the relationship between average root-zone EC and the saturated paste extract (ECe): the root zone averages approximately 5 times higher in conductivity than the applied water EC at equilibrium under steady-state conditions. Subtracting ECiw accounts for the salt contributed by the water itself. Rounding rule: express LF as a percentage rounded to one decimal place for practical irrigation scheduling. Step 2: Compute Total Applied Water Total Water = Crop Water Requirement / (1 – LF) This formula inflates the crop requirement by the inverse of the non-leaching fraction. If LF = 0.20, then (1 – LF) = 0.80, meaning 80% of what you apply goes to the crop and 20% exits as drainage. Dividing the crop requirement by 0.80 gives the total that satisfies both needs in a single application. Units carry through unchanged: if the crop requirement is entered in gallons, the total water and leaching volume are returned in gallons. Step 3: Danger Condition Check IF ECiw >= ECe: Leaching fraction is undefined (negative or invalid) When the EC of the irrigation water already exceeds the soil EC threshold the crop can survive, no steady-state leaching scheme is mathematically valid. The formula produces a zero or negative denominator, and the physical meaning collapses: you cannot dilute a root zone below the salt concentration of the water you’re using to dilute it. Source water treatment is the only path forward in this condition. Assumptions and Limits The FAO-29 formula assumes steady-state conditions: salt inputs equal salt outputs over time. In practice, soil is rarely at true steady state, so the LF is a design target, not a precision measurement. Uniform irrigation application is assumed across the root zone. Channeling, preferential flow paths, or dry spots cause localized salt accumulation that the formula cannot predict. Adequate drainage capacity is required. If soil or container media cannot transmit the calculated leaching volume within the irrigation interval, salts will concentrate between events regardless of the formula result. Rainfall is not included. Subtract effective rainfall from your weekly crop water requirement before entering it into the calculator. ECe thresholds in this calculator are 50% yield-loss values from FAO and USDA salt-tolerance tables. For high-value or sensitive crops, use the 25% yield-loss ECe value, which is lower and will produce a higher (more conservative) leaching fraction. The formula does not account for precipitation of sparingly soluble salts such as calcium carbonate. In alkaline soils, calcite precipitation can reduce actual leaching efficiency below the calculated value. Soil layering (e.g., a clay lens below a sandy surface horizon) can trap drainage above the restrictive layer, locally spiking EC despite correct surface application.

## Verified worked examples

### Scenario 1: Strawberry in a Greenhouse with City Water

ECiw = 0.8 dS/m (filtered city supply) ECe = 1.5 dS/m (strawberry 50% yield-loss threshold) Crop Water Requirement = 2.00 inches per week LF = 0.8 / (5 x 1.5 – 0.8) = 0.8 / 6.7 = 0.119, or 11.9% Total Water = 2.00 / (1 – 0.119) = 2.00 / 0.881 = 2.27 inches per week Result: Apply 2.27 inches per week total; 0.27 inches (about 12% of the applied volume) exits as drainage carrying displaced salts. This is a manageable leaching overhead for drip systems. The key risk here is intermittent irrigation schedules that allow the soil surface to dry between events, which concentrates salts faster between flushes. Maintaining consistent moisture while still reaching the drainage target is the operational challenge.

### Scenario 2: Processing Tomato with Hard Well Water

ECiw = 2.0 dS/m (high-mineral well water) ECe = 4.0 dS/m (tomato 50% yield-loss threshold) Crop Water Requirement = 3.00 inches per week LF = 2.0 / (5 x 4.0 – 2.0) = 2.0 / 18.0 = 0.111, or 11.1% Total Water = 3.00 / (1 – 0.111) = 3.00 / 0.889 = 3.37 inches per week Result: Apply 3.37 inches per week; 0.37 inches exits as drainage. Although the ECiw is relatively high at 2.0 dS/m, tomato’s higher salt tolerance keeps the leaching fraction below 12%. This scenario illustrates why crop selection matters enormously in high-EC water regions: the same 2.0 dS/m water applied to strawberry would immediately exceed the crop’s ECe threshold and trigger the danger condition.

### Scenario 3: Bell Pepper with Moderately Hard Water (Elevated Risk)

ECiw = 1.2 dS/m (municipal blend with mineral content) ECe = 1.5 dS/m (pepper 50% yield-loss threshold) Crop Water Requirement = 1.50 inches per week LF = 1.2 / (5 x 1.5 – 1.2) = 1.2 / 6.3 = 0.190, or 19.0% Total Water = 1.50 / (1 – 0.190) = 1.50 / 0.810 = 1.85 inches per week Result: Apply 1.85 inches per week; 0.35 inches exits as drainage, representing 19% of total applied volume. At an ECiw of 1.2 dS/m against a crop threshold of 1.5 dS/m, the margin is thin. A single week where the drainage pathway becomes partially blocked could allow the root-zone EC to approach the danger zone. This scenario calls for weekly EC monitoring of both irrigation water and drainage runoff, and consideration of partial RO blending to reduce the water EC to below 0.8 dS/m.

## Assumptions

Uses the FAO steady-state leaching fraction formula (Rhoades, 1974). Assumes uniform irrigation application and adequate drainage. Does not account for rainfall contribution to leaching — subtract rainfall before entering crop water requirement. Assumes the crop grows in a single soil layer with uniform salinity. Layered soils or hardpan may require field measurement. Soil texture affects drainage speed: sandy soils drain faster, clay soils need lower application rates over more time. EC e thresholds are 50% yield-loss values. For premium crops, target 25% yield-loss threshold (lower EC e value). Does not account for precipitation of sparingly soluble salts (e.g., calcium carbonate). Actual salt behavior may vary. The ratio between drainage flow and total applied water is set by irrigation EC and crop salt tolerance, independent of irrigation volume. Show the calculation steps Step 1: Compute Leaching Fraction The formula is derived from a steady-state mass balance of salt inputs and outputs in the root zone: LF = ECiw / (5 x ECe – ECiw) The denominator term (5 x ECe) reflects the relationship between average root-zone EC and the saturated paste extract (ECe): the root zone averages approximately 5 times higher in conductivity than the applied water EC at equilibrium under steady-state conditions. Subtracting ECiw accounts for the salt contributed by the water itself. Rounding rule: express LF as a percentage rounded to one decimal place for practical irrigation scheduling. Step 2: Compute Total Applied Water Total Water = Crop Water Requirement / (1 – LF) This formula inflates the crop requirement by the inverse of the non-leaching fraction. If LF = 0.20, then (1 – LF) = 0.80, meaning 80% of what you apply goes to the crop and 20% exits as drainage. Dividing the crop requirement by 0.80 gives the total that satisfies both needs in a single application. Units carry through unchanged: if the crop requirement is entered in gallons, the total water and leaching volume are returned in gallons. Step 3: Danger Condition Check IF ECiw >= ECe: Leaching fraction is undefined (negative or invalid) When the EC of the irrigation water already exceeds the soil EC threshold the crop can survive, no steady-state leaching scheme is mathematically valid. The formula produces a zero or negative denominator, and the physical meaning collapses: you cannot dilute a root zone below the salt concentration of the water you’re using to dilute it. Source water treatment is the only path forward in this condition. Assumptions and Limits The FAO-29 formula assumes steady-state conditions: salt inputs equal salt outputs over time. In practice, soil is rarely at true steady state, so the LF is a design target, not a precision measurement. Uniform irrigation application is assumed across the root zone. Channeling, preferential flow paths, or dry spots cause localized salt accumulation that the formula cannot predict. Adequate drainage capacity is required. If soil or container media cannot transmit the calculated leaching volume within the irrigation interval, salts will concentrate between events regardless of the formula result. Rainfall is not included. Subtract effective rainfall from your weekly crop water requirement before entering it into the calculator. ECe thresholds in this calculator are 50% yield-loss values from FAO and USDA salt-tolerance tables. For high-value or sensitive crops, use the 25% yield-loss ECe value, which is lower and will produce a higher (more conservative) leaching fraction. The formula does not account for precipitation of sparingly soluble salts such as calcium carbonate. In alkaline soils, calcite precipitation can reduce actual leaching efficiency below the calculated value. Soil layering (e.g., a clay lens below a sandy surface horizon) can trap drainage above the restrictive layer, locally spiking EC despite correct surface application. The FAO-29 formula assumes steady-state conditions: salt inputs equal salt outputs over time. In practice, soil is rarely at true steady state, so the LF is a design target, not a precision measurement. Uniform irrigation application is assumed across the root zone. Channeling, preferential flow paths, or dry spots cause localized salt accumulation that the formula cannot predict. Adequate drainage capacity is required. If soil or container media cannot transmit the calculated leaching volume within the irrigation interval, salts will concentrate between events regardless of the formula result. Rainfall is not included. Subtract effective rainfall from your weekly crop water requirement before entering it into the calculator. ECe thresholds in this calculator are 50% yield-loss values from FAO and USDA salt-tolerance tables. For high-value or sensitive crops, use the 25% yield-loss ECe value, which is lower and will produce a higher (more conservative) leaching fraction. The formula does not account for precipitation of sparingly soluble salts such as calcium carbonate. In alkaline soils, calcite precipitation can reduce actual leaching efficiency below the calculated value. Soil layering (e.g., a clay lens below a sandy surface horizon) can trap drainage above the restrictive layer, locally spiking EC despite correct surface application. Critical Warnings Osmotic Salt Lockout in wet soil: Plants visually wilting while the substrate is thoroughly moist is a diagnostic symptom of osmotic lockout, not drought. Salt-saturated media creates a solute concentration gradient that forces water molecules out of root cells. Increasing irrigation frequency in this situation accelerates root damage. The correct response is a corrective flush with low-EC water, followed by a recalculated leaching schedule. Blocked drainage invalidates the formula entirely: A leaching fraction calculation is only valid if the drainage pathway is open. Compressed or compacted growing media, waterlogged container bases, or clogged drain holes mean the “leaching” water simply accumulates below the root zone rather than carrying salts out. Before implementing any leaching schedule, verify that drainage flow is unobstructed. The fertilizer salt index calculator can help identify whether fertilizer-contributed salts are compounding water-EC-driven accumulation in your system. No leaching formula is valid when ECiw exceeds ECe: This is mathematically and physically absolute, not a conservative precaution. Continuing to irrigate with ECiw greater than or equal to ECe without source water treatment guarantees progressive root-zone salt enrichment regardless of drainage volume. High sodium content requires separate analysis: Electrical conductivity measures total ion concentration, not sodium specifically. A water source with moderate overall EC but high sodium may cause structural damage to clay soils that reduces drainage capacity over time, undermining the leaching fraction assumptions. The sodium adsorption ratio (SAR) calculator addresses this dimension and should be run alongside ECiw evaluation for well water or recycled irrigation sources. Minimum Standards Leaching fractions above 25% indicate a water quality problem that leaching alone addresses inefficiently. At this level, water treatment such as partial reverse osmosis blending is typically more cost-effective than accepting the ongoing water and nutrient waste. Drainage runoff EC should be monitored periodically. A runoff EC that is 2 to 3 times your applied water EC confirms active salt displacement. Runoff EC below 1.5 times applied water EC suggests insufficient leaching is occurring despite the application volume. The cation exchange capacity of your growing medium affects how quickly salts accumulate and how effectively leaching flushes them. Low-CEC media (sand, perlite, rockwool) respond faster to leaching schedules than high-CEC organic soils. The CEC soil calculator provides context for interpreting how your medium type interacts with your calculated leaching fraction. Competitor Trap: Most salt management guides tell growers to “add 10 to 20% extra water as a leaching fraction.” This generic range ignores the critical interaction between actual water EC and crop-specific salt tolerance. A 10% leaching fraction applied with 2.0 dS/m water to a strawberry crop (ECe = 1.5 dS/m) is useless: the water itself exceeds the crop’s threshold. Conversely, a 20% leaching fraction with 0.3 dS/m rainwater collected in a cistern is wasteful overkill. The formula-derived result from your actual inputs is not interchangeable with a blanket percentage recommendation. Leaching fractions above 25% indicate a water quality problem that leaching alone addresses inefficiently. At this level, water treatment such as partial reverse osmosis blending is typically more cost-effective than accepting the ongoing water and nutrient waste. Drainage runoff EC should be monitored periodically. A runoff EC that is 2 to 3 times your applied water EC confirms active salt displacement. Runoff EC below 1.5 times applied water EC suggests insufficient leaching is occurring despite the application volume. The cation exchange capacity of your growing medium affects how quickly salts accumulate and how effectively leaching flushes them. Low-CEC media (sand, perlite, rockwool) respond faster to leaching schedules than high-CEC organic soils. The CEC soil calculator provides context for interpreting how your medium type interacts with your calculated leaching fraction. Competitor Trap: Most salt management guides tell growers to “add 10 to 20% extra water as a leaching fraction.” This generic range ignores the critical interaction between actual water EC and crop-specific salt tolerance. A 10% leaching fraction applied with 2.0 dS/m water to a strawberry crop (ECe = 1.5 dS/m) is useless: the water itself exceeds the crop’s threshold. Conversely, a 20% leaching fraction with 0.3 dS/m rainwater collected in a cistern is wasteful overkill. The formula-derived result from your actual inputs is not interchangeable with a blanket percentage recommendation.

## Limitations and safety

Uses the FAO steady-state leaching fraction formula (Rhoades, 1974). Assumes uniform irrigation application and adequate drainage. Does not account for rainfall contribution to leaching — subtract rainfall before entering crop water requirement. Assumes the crop grows in a single soil layer with uniform salinity. Layered soils or hardpan may require field measurement. Soil texture affects drainage speed: sandy soils drain faster, clay soils need lower application rates over more time. EC e thresholds are 50% yield-loss values. For premium crops, target 25% yield-loss threshold (lower EC e value). Does not account for precipitation of sparingly soluble salts (e.g., calcium carbonate). Actual salt behavior may vary. The FAO-29 formula assumes steady-state conditions: salt inputs equal salt outputs over time. In practice, soil is rarely at true steady state, so the LF is a design target, not a precision measurement. Uniform irrigation application is assumed across the root zone. Channeling, preferential flow paths, or dry spots cause localized salt accumulation that the formula cannot predict. Adequate drainage capacity is required. If soil or container media cannot transmit the calculated leaching volume within the irrigation interval, salts will concentrate between events regardless of the formula result. Rainfall is not included. Subtract effective rainfall from your weekly crop water requirement before entering it into the calculator. ECe thresholds in this calculator are 50% yield-loss values from FAO and USDA salt-tolerance tables. For high-value or sensitive crops, use the 25% yield-loss ECe value, which is lower and will produce a higher (more conservative) leaching fraction. The formula does not account for precipitation of sparingly soluble salts such as calcium carbonate. In alkaline soils, calcite precipitation can reduce actual leaching efficiency below the calculated value. Soil layering (e.g., a clay lens below a sandy surface horizon) can trap drainage above the restrictive layer, locally spiking EC despite correct surface application. Critical Warnings Osmotic Salt Lockout in wet soil: Plants visually wilting while the substrate is thoroughly moist is a diagnostic symptom of osmotic lockout, not drought. Salt-saturated media creates a solute concentration gradient that forces water molecules out of root cells. Increasing irrigation frequency in this situation accelerates root damage. The correct response is a corrective flush with low-EC water, followed by a recalculated leaching schedule. Blocked drainage invalidates the formula entirely: A leaching fraction calculation is only valid if the drainage pathway is open. Compressed or compacted growing media, waterlogged container bases, or clogged drain holes mean the “leaching” water simply accumulates below the root zone rather than carrying salts out. Before implementing any leaching schedule, verify that drainage flow is unobstructed. The fertilizer salt index calculator can help identify whether fertilizer-contributed salts are compounding water-EC-driven accumulation in your system. No leaching formula is valid when ECiw exceeds ECe: This is mathematically and physically absolute, not a conservative precaution. Continuing to irrigate with ECiw greater than or equal to ECe without source water treatment guarantees progressive root-zone salt enrichment regardless of drainage volume. High sodium content requires separate analysis: Electrical conductivity measures total ion concentration, not sodium specifically. A water source with moderate overall EC but high sodium may cause structural damage to clay soils that reduces drainage capacity over time, undermining the leaching fraction assumptions. The sodium adsorption ratio (SAR) calculator addresses this dimension and should be run alongside ECiw evaluation for well water or recycled irrigation sources. Minimum Standards Leaching fractions above 25% indicate a water quality problem that leaching alone addresses inefficiently. At this level, water treatment such as partial reverse osmosis blending is typically more cost-effective than accepting the ongoing water and nutrient waste. Drainage runoff EC should be monitored periodically. A runoff EC that is 2 to 3 times your applied water EC confirms active salt displacement. Runoff EC below 1.5 times applied water EC suggests insufficient leaching is occurring despite the application volume. The cation exchange capacity of your growing medium affects how quickly salts accumulate and how effectively leaching flushes them. Low-CEC media (sand, perlite, rockwool) respond faster to leaching schedules than high-CEC organic soils. The CEC soil calculator provides context for interpreting how your medium type interacts with your calculated leaching fraction. Competitor Trap: Most salt management guides tell growers to “add 10 to 20% extra water as a leaching fraction.” This generic range ignores the critical interaction between actual water EC and crop-specific salt tolerance. A 10% leaching fraction applied with 2.0 dS/m water to a strawberry crop (ECe = 1.5 dS/m) is useless: the water itself exceeds the crop’s threshold. Conversely, a 20% leaching fraction with 0.3 dS/m rainwater collected in a cistern is wasteful overkill. The formula-derived result from your actual inputs is not interchangeable with a blanket percentage recommendation.

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## Provenance

- Model ID: `tyg-637`
- Model version: `1.0.0`
- Reviewed by: Umer Hayiat
- Page modified: 2026-04-28T03:01:09
- Runtime SHA-256: `eb0e84542defa1f7433244d358bcfd0cc38eaed0a5cedf1744329699f672b7eb`

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