Issue 28
April 2000

Calculating how much seed to plant

Seeding rate is often treated as a constant within each crop, i.e. seed barley at 80 lbs/acre, and wheat at 90 lbs/acre. The downfall of this approach is, it does not take into account percent germination, seedling survival, and kernel weight of different cultivars.

These factors can easily be included in calculations to determine an exact seeding rate for a specific crop.  The variables that must be known are seeds per pound, percent germination, and estimated seedling mortality.  The following formulas can be used to calculate seeding rates of any crop for a specified plant density per square foot (example 1) or million plants per acre (example 2).

1. Determining seeding rate based on desired plants per square foot

[(plants/ft²) ¸ (seeds/pound) ¸ 43,560)] ¸ germination X (1 + mortality) = seeding rate in lbs/acre

Example:
Desired rate 30 plants/square foot
Seeds per pound 14,300
Germination .96
Seedling mortality .10
[(30)¸ (14,300) ¸ 43,560)] ¸ .96 X (1 + .10) = 105 lbs/acre

2. Determining seeding rate based on desired plants per acre

(plants/acre ¸ seeds/lb) ¸ germination X (1 + mortality) = seeding rate in lbs/acre

Example:
Desired rate 1.25 million plants/acre
Seeds per pound 14,300
Germination .96
Seedling mortality .10

(1,250,000 ¸ 14,300) ¸ 96 X (1+ 0.10) = 100 lbs/acre