The most profitable seeding rate for any crop is a function of the size of its’ plants at maturity. Very large plants like corn need only about 30,000 plants per acre for maximum yield. Soybeans and wheat are much smaller and need about 150,000 and 1,250,000 plants per acre respectively for good yield. This function works for various sizes of soybean plants also. Recently conducted seeding rate studies indicate that when soybean plants are short at maturity (20 inches tall or less) a seeding rate of 225,000 to 250,000 plants per acre and a final population of about 210,000 plants per acre was the most profitable. When plants grew to a height of 30 inches the most profitable seeding rate was around 175,000 seeds per acre and a final population of about 160,000 plants per acre. For plants that got 40 inches tall the most profitable seeding rate was around 125,000 seeds per acre and a final population of about 110,000 plants per acre.
Producers can reduce their seed cost for the 2005 crop by reducing the seeding rate for tall varieties or for fields or soil types where plants get tall. The average cost of Glyphosate Tolerant varieties in 2005 is expected to be about $32.00 per 50-pound bag of seed. The following table indicates the cost of 125,000 seed per acre in 7.5- inch rows for different sizes of seed and varying seed cost.
For a seeding rate of 150,000 seeds/ac multiply table values by 1.2. For a seeding rate of 175,000 seeds/ac multiply table values by 1.4. For a seeding rate of 200,000 seeds/ac multiply table values by 1.6. For a seeding rate of 225,000 seeds/ac multiply table values by 1.8. For a seeding rate of 250,000 seeds/ac multiply table values by 2.0
The effect of seed size and seed price on the per acre soybean seed cost when planting (125,000 seeds per acre in 7.5” rows.
| Seed Cost ($/50 lbs) | |||||
| Seeds/pound | 26 | 28 | 30 | 32 | 34 |
| 2000 | 32.50 | 35.00 | 35.50 | 40.44 | 42.50 |
| 2200 | 29.55 | 31.82 | 34.10 | 36.37 | 38.64 |
| 2400 | 27.08 | 29.16 | 31.25 | 33.33 | 35.41 |
| 2600 | 25.00 | 26.92 | 28.85 | 30.77 | 32.69 |
| 2800 | 23.21 | 25.00 | 26.78 | 28.57 | 30.35 |
| 3000 | 21.70 | 23.37 | 25.04 | 26.71 | 28.37 |
Other facts to keep in mind are:
The most profitable seeding rate is 10-15 percent lower than the “highest yield” seeding rate. As the cost of seed increases the most profitable seeding rate decreases. As the value of grain increases the most profitable seeding rate also increases. A pound of seed cost six to seven times as much as a pound of grain, so each extra pound of seed planted must increase yield by six to seven pounds to pay for itself.