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margin: 20px auto;
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border-radius: 8px;
background-color: #f9f9f9;
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.gypsum-calculator-container h2 {
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font-weight: bold;
cursor: pointer;
transition: background-color 0.3s;
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background-color: #45a049;
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#gypsumResult {
margin-top: 20px;
padding: 15px;
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border-radius: 4px;
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#gypsumResult h3 {
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.gypsum-article {
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.gypsum-article h3 {
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Correcting Sodic Soils with Gypsum
Applying gypsum (calcium sulfate dihydrate) is a crucial practice in agriculture for remediating sodic soils and improving overall soil structure. Sodic soils are characterized by a high concentration of sodium ions relative to calcium and magnesium on the soil's exchange complex. This imbalance causes clay particles to disperse, leading to poor water infiltration, surface crusting, and inhibited root growth.
Understanding the Inputs (ESP and CEC)
To accurately determine how much gypsum is needed, a soil test is essential. The calculator above relies on two critical metrics found in standard soil analyses:
- ESP (Exchangeable Sodium Percentage): This measures the percentage of the soil's cation exchange capacity occupied by sodium. An ESP above 6% to 15% (depending on soil texture) usually indicates a sodicity problem that requires treatment.
- CEC (Cation Exchange Capacity): Measured in milliequivalents per 100 grams (meq/100g), CEC represents the soil's total capacity to hold positively charged nutrients. Heavier clay soils typically have higher CEC values than sandy soils, meaning they require more gypsum to effect the same percentage change in ESP.
How the Calculation Works
Gypsum works by providing soluble calcium which displaces sodium from the soil particles. The displaced sodium then forms sodium sulfate, which must be leached below the root zone via irrigation or rainfall.
The calculation estimates the amount of calcium needed to replace the excess sodium to reach your desired ESP level, taking into account the soil's holding capacity (CEC) and the purity of the gypsum source you intend to use. This calculator assumes a standard incorporation depth of approximately 6 inches.
Disclaimer: This calculator provides an agronomic estimation. Always consult with a certified crop advisor or soil scientist for precise recommendations tailored to your specific field conditions and water quality.
function calculateGypsumNeeded() {
// Retrieve input values
var currentESPVal = parseFloat(document.getElementById("currentESP").value);
var desiredESPVal = parseFloat(document.getElementById("desiredESP").value);
var cecVal = parseFloat(document.getElementById("cecValue").value);
var areaAcresVal = parseFloat(document.getElementById("areaAcres").value);
var gypsumPurityVal = parseFloat(document.getElementById("gypsumPurity").value);
var resultDiv = document.getElementById("gypsumResult");
resultDiv.innerHTML = "";
// Validation
if (isNaN(currentESPVal) || isNaN(desiredESPVal) || isNaN(cecVal) || isNaN(areaAcresVal) || isNaN(gypsumPurityVal)) {
resultDiv.innerHTML = "Please fill in all fields with valid numerical values.";
return;
}
if (areaAcresVal <= 0 || gypsumPurityVal <= 0 || cecVal <= 0) {
resultDiv.innerHTML = "Area, CEC, and Purity must be greater than zero.";
return;
}
// Calculate the required reduction in ESP
var espDifference = currentESPVal – desiredESPVal;
if (espDifference <= 0) {
resultDiv.innerHTML = "
Your current ESP is already at or below your desired target level.";
return;
}
// CALCULATION LOGIC:
// A common agronomic rule of thumb for a 6-inch soil depth is that to lower the ESP by 1%
// in a soil with a CEC of 1 meq/100g requires roughly 20 lbs of pure gypsum per acre.
// The factor can range from 18-24, but 20 is a widely accepted average for estimation.
var pureGypsumLbsPerAcrePerCEC = 20;
// Total pure gypsum needed per acre (lbs) = ESP reduction * CEC * factor
var pureGypsumNeededLbsPerAcre = espDifference * cecVal * pureGypsumLbsPerAcrePerCEC;
// Adjust for purity of the commercial gypsum source
var purityDecimal = gypsumPurityVal / 100;
var commercialGypsumNeededLbsPerAcre = pureGypsumNeededLbsPerAcre / purityDecimal;
// Calculate total for the entire area
var totalLbsNeeded = commercialGypsumNeededLbsPerAcre * areaAcresVal;
var totalTonsNeeded = totalLbsNeeded / 2000;
// Format results for display
var resultHTML = "
";
resultHTML += "Total Required for " + areaAcresVal + " Acres: " + totalTonsNeeded.toLocaleString(undefined, {maximumFractionDigits: 2}) + " Tons (" + totalLbsNeeded.toLocaleString(undefined, {maximumFractionDigits: 0}) + " lbs)";
resultHTML += "Note: This assumes a standard 6-inch incorporation depth based on the provided CEC and ESP values.";
resultDiv.innerHTML = resultHTML;
}