Corn Seeding Rates – Adjusting for Germination Values

Ensuring adequate plant stands to enable optimum yields is key in corn cropping systems, and it begins with optimizing seeding rates. Plant stands to optimize yield depending on hybrid and location can range from 24,000-34,000 per acre. Lower-yielding fields likely optimize yield with final stands ranging from 24-26,000 plants/acre, but a value of over 34,000 plants/acre may be needed in high-yielding environments. In most environments, based on OSU research, a plant population of 31-32,000 plants/acre at the end of the season should optimize yield in most environments.

 Adjusting seeding rates to ensure the final stands are achieved can be done by using the seed tag information related to germination. By law, results of the standard warm germination test need to be printed on these labels. This value is a measure of seed lot germination under optimal conditions and is often below 100% indicating that every seed in the bag is not expected to germinate, a common germination rate for corn is 95% (Figure 1).

With the addition of Refuge in a Bag (RIB) of seed, each hybrid contained in the bag will have had a separate germination test conducted on it, with each lot reporting its own germination test values (Figure 2). In the example seed tags, there are two germination totals shown, one for the main hybrid, and a second for the refuge component. Figure 2A has a split of 89% for one hybrid and 10% refuge, whereas Figure 2B shows 95% for one hybrid and 5% for the refuge component.

Figure 2. Blended corn hybrid product where germination percentages are identical for both seed sources in the bag, 95% (A). Blended hybrid product with differing hybrid germination values, 92% and 95% (B).

To calculate your planting or seeding rate, consider the following equation:

Planting Rate=Desired Population per AcreGermination Rate (%)

As is shown in the case of Figure 1 as well as both hybrids in Figure 2A, germination percentages are all 95% for each seed lot in these products. In this case, the target plant stand population should be divided by the germination percentage to increase the seeding rate accordingly. Assuming that a target stand of 32,000 plants/acre was desired, 32,000 / 0.95 = 33,684 seeds/acre should be planted. A table showing various germination percentages and target plant stands has been developed to aid in this process (Table 1).

Table 1. Calculated seeding rates needed to achieve target final stands based on germination percentages reported on seed tags.

In the event you are planting refuge in a bag seed that has two differing germination percentages (Figure 2B), you should consider calculating a composite “product” germination value. You can do this by multiplying each component’s germination percentage value by its percentage total of the bag as a decimal and adding the values together. Using our example tag from Figure 2B:

(92% * 0.95) + (95% * 0.05) = 87.4% + 4.75% = 92.15% product germination total (use this value).

In addition to germination totals, further adjustments due to expected losses from biotic or abiotic factors (e.g., cold soils, wet soils, insects, diseases, crusting, compaction) may need to be considered and factored in your seeding rate estimates to ensure that an adequate number of seeds is being planted as a function of seed tag germination rates and expected seed/plant survival conditions.

Some recommendations to consider include, planting into good conditions (45-50% plant available water content) with adequate soil temperatures (above 50ºF) and avoiding planting ahead of a strong weather front likely to cause large temperature decreases or bring with it cold precipitation are ways to help minimize seed/plant losses. Utilizing practices that minimize surface crusting can also help improve emergence and ensure that a uniform stand is established. In conventional systems, the use of seed treatments for insect/disease management is a recommended practice as well. More can be considered when it comes to establishing an adequate crop stand, such as selecting hybrids best suited to specific growing environments.