For most Iowa farmers, the biggest pre-plant decisions have already been made, and their current focus is on fine-tuning management plans to ensure their corn hybrids will yield as well as possible in 2018. One of those fine-tuning variables is plant population.

Advancements in genetic technology now allow farmers to plant at higher populations, but it wasn’t always like that. Historically, populations had to be kept low to minimize ears being aborted. The ability of hybrids to support higher seeding rates is considered one of the key components that drove annual yield increases in recent decades, according to Iowa State University Extension and Outreach.

Given today’s hybrids, there are even more opportunities to increase yields by pushing seeding rates.

seed rates

After all, logic would have it that the more seed planted per acre, the more harvestable ears available which, consequently, means better yields.

But higher seeding rates do not always mean higher yield. At a certain point, yields will plateau as plants have to compete more for light, water and nutrients. The highest-yielding seeding rate may not actually provide the best return on investment at the end of the day.

“There is no one-size-fits-all optimum plant population, so farmers have to consider a range of elements,” said Rich Lee, a Golden Harvest agronomist based in Iowa. “One of the most important of those is the hybrid’s ear type, which directly influences number of kernels per ear. Ear types can be a component of hybrid responses to plant populations, so plan accordingly.”

The three basic ear types are:

• Flex ears, which can adjust in different ways to their environment, either through lengthening of the ear or increasing kernel depth. As population goes up with flex ear hybrids, the ears will become shorter or kernel depth is reduced. Typically, flex ear hybrids will produce or maintain better yields at lower seeding rates, since they have the most ability to compensate for not having neighboring plants.

• Semi-flex ears, which adjust less in length and girth, giving them the ability to better handle higher seeding rates while also tending to still do fairly well at lower seeding rates.

• Determinant ears, the size of which tends to stay the same regardless of seeding rate. Hybrids with this ear type are less likely to abort ears at excessively high seeding rates. However, determinant ear types are not able to maintain yields as well as other ear types where seeding rates may be lower or stand loss may occur.  

“Given all these differences, you can see how a hybrid that produces a full flex ear requires a different planting strategy than a hybrid with a determinant ear,” Lee said. “Before starting the season, review and adjust plant populations as needed. It’s a great way to maximize yield potential from the get-go.”

Regardless of ear type, it is difficult to fine-tune hybrid seeding rate recommendations without testing them across many yield environments at different seeding rates.  

“Golden Harvest has annually tested every new hybrid for seeding rate response since 1992, providing one of the largest data sets in the industry to understand what the most profitable seeding rate will be for every productivity zone of your farm,” said Bruce Battles, Golden Harvest head of agronomy. “We have found that the highest-yielding seeding rate often does not provide the best return on investment.”

Farmers should be careful not to focus only on the highest-yielding seeding rates, ignoring important hybrid agronomics such as root and stalk strength. If plant populations end up too dense, they can develop smaller root systems and weaker stalks, resulting in poor standability at harvest.

Understanding each hybrid’s yield response to population by yield environment and its agronomic characteristics can allow farmers to best match seeding rates with their different hybrids, taking advantage of increased yield potential.

“We encourage farmers to talk to their local seed dealers to determine ideal seeding rates for each of their hybrids,” Lee said. “Tapping into the knowledge of a local expert like a Golden Harvest Seed Advisor will help to start the season on the best foot possible.”

Article courtesy of Syngenta.