Recent Ohio State University evaluations indicate that final stands of 32,000 plants/A or higher may be required to optimize grain yield of some corn hybrids. If the recommended plant population for a corn hybrid is 32,000 plants/acre based on various factors including site yield and potential hybrid characteristics, what should the seeding rate be? Remember a recommended plant population refers to final plant stand or the number of plants/A at harvest not seeding rate.

The number of plants/acre at harvest is always less than the number of seeds planted (unless you have a lot of volunteer corn!) Planting date, tillage practices, pest problems, chemical injury, planter performance, and seed quality can affect final corn populations obtained in the field. To compensate for these losses, a corn grower needs to plant more seed than the desired population at harvest.

To determine an appropriate seeding rate, use the following formula: Seeding rate = Plant population per acre at harvest/(Seed germination x Expected survival).

Seed germination is the percent germination shown on the seed tag. Most seed corn has a germination rate of 95 percent or higher. Expected survival is the percentage of plants that you expect to survive to become harvestable plants in the fall. Keep in mind that survival rates for corn may be in the range of 85 percent to 95 percent but can vary considerably depending on planting conditions and other environmental factors. When early planting is likely to create stressful conditions for corn during emergence (e.g. no-till in early to mid April), consider seeding rates at least 10-percent higher than the desired harvest population.

EXAMPLE: A grower wants to achieve a final stand of 32,000 plants/acre. The seed tag indicates a germination rate of 95 percent and the grower expects that 95 percent of the germinable seed will survive until harvest. Based on the formula above, divide the desired plant population at harvest, 32,000 plants/acre, by 0.95 x 0.95 (0.90) to obtain a seeding rate of 35,555 seeds/A. (Note that % germination and % survival are converted to decimal form for use in the formula.) Since actual germination rates are often nearly 100%, with a seed germination of 98%, the seeding rate would be slightly less, i.e. 32,000 plants/acre divided by 0.98 x 0.95 (0.93) = 34, 409 seeds/A.

SOURCE: Ohio State.