Calculate Seeding Rate Based on Thousand Kernel Weight

Seeding Rate Calculator (TKW Method)

function calculateSeedingRate() { var targetPop = parseFloat(document.getElementById('targetPop').value); var tkw = parseFloat(document.getElementById('tkw').value); var germination = parseFloat(document.getElementById('germination').value); var survival = parseFloat(document.getElementById('survival').value); var fieldSize = parseFloat(document.getElementById('fieldSize').value); if (isNaN(targetPop) || isNaN(tkw) || isNaN(germination) || isNaN(survival)) { alert("Please fill in all required fields with valid numbers."); return; } if (germination <= 0 || survival <= 0) { alert("Germination and Survival rates must be greater than zero."); return; } // Formula: Seeding Rate (kg/ha) = (Target Plants/m2 x TKW) / (Germination % x Survival %) // This is derived from: (Plants/ha * TKW / 1000) / (Germ% * Surv%) var seedingRateKgHa = (targetPop * tkw) / (germination * survival / 100); var totalRequired = seedingRateKgHa * (fieldSize || 0); document.getElementById('ratePerHa').innerText = seedingRateKgHa.toFixed(2); document.getElementById('totalSeed').innerText = totalRequired.toFixed(2); document.getElementById('results').style.display = 'block'; }

How to Calculate Seeding Rate Using TKW

Calculating the seeding rate based on Thousand Kernel Weight (TKW) is the most accurate way to ensure you achieve your target plant population. Unlike measuring by volume (bushels) or a fixed weight, the TKW method accounts for the physical size and weight of the specific seed lot you are planting, which can vary significantly due to variety, moisture levels, and growing conditions of the parent crop.

The Seeding Rate Formula

Seeding Rate (kg/ha) = (Target Plants/m² × TKW) ÷ Emergence Rate

Where Emergence Rate is the Germination % multiplied by the Expected Survival %.

Key Variables Explained

• Target Plant Population: The number of established plants you want per square meter. For example, wheat usually targets 250-350 plants/m².
• Thousand Kernel Weight (TKW): The weight in grams of 1,000 individual seeds. Small seeds (low TKW) require fewer kilograms per hectare than large seeds (high TKW) to reach the same population.
• Germination Rate: Found on the seed tag; represents the percentage of seeds capable of sprouting under ideal conditions.
• Expected Survival Rate: An estimate of how many germinated seeds will actually survive to become plants. This accounts for seedling blight, deep seeding, insects, or frost.

Practical Example

Imagine you are planting spring wheat with the following specs:

• Target Population: 300 plants/m²
• TKW: 42 grams
• Germination: 95%
• Expected Survival: 90% (Expected Emergence = 0.95 * 0.90 = 0.855 or 85.5%)

Calculation: (300 × 42) ÷ 85.5 = 147.37 kg/ha.

Using this precise method prevents under-seeding (which leads to weed competition and lower yields) and over-seeding (which wastes money and increases the risk of lodging or disease).