A hybrid may have a fixed-ear type, a flex-ear type or something in between.
- A fixed-ear hybrid makes the same size ear, regardless of plant population.
- A flex-ear hybrid makes either longer or girthier ears when interplant competition is decreased by reducing population.
Fixed-ear Northern hybrid
When planted at their optimal plant populations on highly productive fields, fixed-ear hybrids, with their tolerance to high plant population, tend to be the highest yielding. Northern and Eastern genetic types, found in most fixed-ear hybrids, have unusually strong silking characteristics and exceptional uniformity of ear size at high plant densities.
Strong silking genetics are expressed by a hybrid that prioritizes the movement of water directly to the silks at the time of pollination. Silks are more than 90 percent water. Fast silking hybrids ensure pollination and ear set, thereby driving yield. During years with favorable emergence and growing conditions, fixed-ear hybrids planted at high plant populations are often the test plot winners.
Flex-ear Southern hybrid
A flex-ear hybrid has a competitive advantage when plant populations are reduced by stress-related conditions such as planting in cool, wet soils; emerging in no-till systems; and using lower populations as a drought-control mechanism.
The Southern Genetic Family has the greatest ability to flex its ear size at low populations, making ears that expand in length as the population is reduced. Western and High Yield genetic types stretch in diameter by increasing kernel rows as a result of decreased populations. Alternatively, the strength of Eastern and Northern types is making consistent ear size at high populations, but they have little ability to increase ear size at low populations.
Therefore, Northern and Eastern types require higher populations to produce high yield. Conversely, Southern, Western and High Yield Genetic Family hybrids make relatively higher yield at lower populations by flexing ear size. The Tropical Genetic Family tends to have poor tolerance to high plant populations and therefore responds better to planting densities in the medium-to-low range.
The stresses of cooler soil temperatures and greater soil surface residues at emergence in no-till causes a loss in plant stands. Southern, Western and High Yield flex-ear hybrids react to lower populations by forming longer or girthier ears, thereby retaining their yield potential. Fixed-ear hybrids in no-till quickly lose their yield potential if plant population is reduced. Therefore, to minimize risk in no-till systems, use flex-ear hybrids or use fixed-ear hybrids with only the highest seedling vigor scores.
- Southern: Longest ear of all genetic families. Ear size is determined by the amount of available nitrogen. Adaptable to lighter soil types by decreasing plant population.
- Eastern: Fixed-ear type where yield is driven by increasing the plant population. Best on heavier soil types that have the water-holding capacity to support high plant densities. Fertility programs need to be increased as plant population is increased.
- Western: Girthy ear type that flexes in diameter, developing on a small plant that flowers early. Requires medium plant populations to drive plant height and works well with the Roundup Ready® system to control late-emerging weeds.
- Northern: Fixed-ear type that requires higher plant population.
- High Yield: Large ear type that flexes in diameter with decreasing plant population.
- High Yield/Late Health: Loses girthiness compared to a straight High Yield Genetic Family type. Plant health, emergence and test weight are improved.
- High Yield/Early Health: Loses girthiness compared to a straight High Yield Genetic Family type. Plant health, emergence and test weight are improved.
- Early Health: Fixed-ear type that requires high plant populations to drive yield. Flowers early with good emergence, test weight and plant health.