Mastering Seeding Rates with TKW and Germination Data
Calculating the precise seeding rate is one of the most critical steps in modern agronomy. Moving away from the "bushels per acre" rule of thumb towards a calculation based on Thousand Kernel Weight (TKW) and specific Germination Rates ensures that you achieve your target plant population. This approach accounts for seed size variability and expected seedling mortality, maximizing yield potential while optimizing seed costs.
Why TKW Matters More Than Bushel Weight
Seed size varies significantly between varieties and even between years for the same variety. A "heavy" seed lot with a high TKW (e.g., 45g) contains fewer seeds per pound than a smaller seed lot (e.g., 30g). If you plant both at the same weight per acre (e.g., 120 lbs/ac), the heavy lot will result in a much thinner plant stand, potentially reducing yield. By calculating based on TKW, you ensure the correct number of seeds are placed in the ground.
The Seeding Rate Formula
This calculator uses the industry-standard formula to determine the pounds of seed required per acre:
Target Plant Density: The number of plants you want to survive per square foot. For wheat, this is typically 30-35 plants/ft².
TKW (Thousand Kernel Weight): The weight of 1,000 seeds in grams. This is the density factor.
Germination Rate: The percentage of seeds capable of sprouting, usually found on your certified seed tag.
Emergence/Survival Rate: The percentage of germinated seeds that actually establish as plants. This accounts for environmental factors like soil temperature, depth, moisture, and pests.
How to Determine TKW
If your seed analysis tag does not list the TKW, you can calculate it easily:
Count out 1,000 seeds accurately.
Weigh them in grams.
The resulting weight is your TKW.
Example Calculation
Let's say you are planting Hard Red Spring Wheat:
Target: 32 plants/ft²
TKW: 36 grams
Germination: 98% (0.98)
Emergence: 90% (0.90) due to good soil conditions.