Crop farming · Seeding
Seeding rate by TKW.
Turn a target plant stand, thousand kernel weight, germination and seedling mortality into pounds per acre and kg per hectare of seed.
Inputs
Your seeding rate
Enter the values.
How to calculate a seeding rate from TKW
Seeding rate in pounds per acre is the target plants per square foot times the thousand kernel weight in grams, divided by expected seedling survival times 10. Survival is germination multiplied by one minus seedling mortality. Manitoba Agriculture publishes this formula for spring cereals, and Saskatchewan Pulse Growers publishes the metric version: kg/ha = plants per m² × TKW ÷ survival percent, then multiply kg/ha by 0.89 for lb/ac.
Worked example. The Manitoba example: 28 plants per sq ft, TKW 39 g, germination 99 percent, mortality 15 percent. Survival = 0.99 × 0.85 = 0.8415. Seeding rate = 28 × 39 ÷ (0.8415 × 10) = 129.8, or about 130 lb/ac. For 160 acres that is 20,763 lb of seed. The same inputs in metric: 28 plants/ft² is 301.4 plants/m², and 301.4 × 39 ÷ 84.15 = 139.7 kg/ha.
Why two pounds-per-acre figures. The ÷ 10 in the published formula is a shortcut. Converting grams to pounds and square feet to acres exactly divides by about 10.41 (453.6 g per lb ÷ 43.56 for thousands of sq ft per acre), so the exact answer is about 4 percent lower: 124.6 lb/ac in this example, which matches the 139.7 kg/ha figure. The tool shows both. Seed drills are calibrated in practice, so neither replaces a field check of your seeding rate.
Choosing mortality. Alberta Agriculture gives 5 to 20 percent seedling mortality for cereals and a common cereal survival of 80 to 90 percent. Saskatchewan Pulse Growers puts pulse survival at 5 to 15 percent below germination in good conditions. Canola loses far more seedlings, so use your own emergence counts.
Frequently asked questions
How do I find thousand kernel weight?
Count out 1,000 seeds and weigh them in grams. Seed lots vary a lot in size, so use the weight of the lot you are seeding, not a book value. A seed analysis certificate usually lists it.
Which formula does this use?
The published Manitoba Agriculture formula for spring cereals: target plants per sq ft x TKW divided by (survival x 10), where survival = germination x (1 - seedling mortality). The metric result uses the Saskatchewan Pulse Growers equation.
Why is the kg/ha result not just the lb/ac result converted?
The published pounds-per-acre formula divides by 10 as a shortcut. Exact unit conversion divides by about 10.41, so lb/ac from the shortcut is about 4 percent higher than kg/ha converted at 0.892. The tool shows the exact lb/ac too.
What seedling mortality should I enter?
Alberta Agriculture gives 5 to 20 percent for cereals. Raise it for cold or dry seedbeds, heavy residue, deep seeding or seed-placed fertilizer, and lower it for good conditions. Your own plant counts from past years are the best guide.
Sources
Checked
- Manitoba Agriculture: Seeding Rates for Spring Cereals
- Saskatchewan Pulse Growers: Calculating Seeding Rates
- Alberta Agriculture: Using 1,000 Kernel Weight for Calculating Seeding Rates and Harvest Losses
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Not professional advice
Seeding rates depend on the crop, variety, soil and local recommendations. Use this as arithmetic and check the rate against your agronomist, seed supplier and provincial or state guidance.