Science From The Field

New Standards for Corn Hybrid

Analysis of Pioneer corn plant population studies indicates populations needed to optimize yields has increased steadily, Image by Pioneer

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Setting the seeding rate on a corn planter is a simple task, but there's plenty of science involved in knowing just where to set it. Thanks to a new scientific analysis of nearly 30 years of Pioneer's corn plant population studies, there's now more proof than ever behind that science.

"We have collaborated with Kansas State University to dive into the long-term planting rate data that we have collected," says Mark Jeschke, Pioneer Agronomy Manager. "The effort has resulted in a confirmation of trends in seeding rates plus a better understanding of corn's response to plant population and how it has changed with today's modern hybrids."

Pioneer worked with Kansas State University's crop production specialist Ignacio Ciampitti to analyze the results of nearly 200,000 yield and plant population data points gathered from 23 states and three provinces between 1987 and 2016. "Our objective was to examine how the agronomic optimum plant density had changed over that period and also to determine the contribution that changes in plant density were having on final yields," says Ciampitti.


The analysis revealed that the plant population needed to optimize yields from an agronomic standpoint has increased steadily--growing at an average rate of 235 plants per acre per year. In the period from 1987 to 1991, the optimum plant density was 30,500 per acre, while from 2012 to 2016, the maximum yield was obtained with a population of 37,900 plants per acre.

The average yield over all locations at the agronomic optimum plant density also increased steadily--from 135 bushels per acre in 1987 to 188 bushels per acre in 2015. "There was an average annual yield increase of 2.23 bushels per acre at the agronomic optimum plant density," explains Ciampitti.

Jeschke says that in addition to increasing yields over the years, the range of agronomic optimal plant density where the best yields occurred has widened, as shown in the chart. In the period 1987 to 1991, the plant density where top yields occurred was in a narrow range around 30,000 plants per acre. In contrast, the range where top yields occurred in the 2012 to 2016 period was much wider from 35,000 to over 40,000 plants/acre.

"This means that modern hybrids offer growers more flexibility to have at or near an optimum population when seasonal conditions vary--modern hybrids are less susceptible to stress from high population in dry years. Old hybrids did not have this stability," says Jeschke.


Another intriguing aspect of the analysis was that yield increases at the agronomic optimum plant density weren't only due to the greater number of plants. "The rate of gain in yield outpaced the rate of change in plant density. Plant density contributed from 9% to 18% of the yield gain during the last 30 years, and this gain has more recently also been accompanied by a significant change in other yield components," says Ciampitti.

He explains that corn yield is a function of four components:

- the number of plants per acre (plant density)

- the number of ears per plant

- the number of grains kernels per ear

- weight per kernels

Typically, as the plant density increases, the contribution of the three other yield components declines when the plant is under stress. However, this data indicates there may be a new relationship between the various yield components.

"There is evidence from this and other recent studies that we are seeing yield per plant increasing even as plant density increases," says Jeschke.

Ciampitti theorizes that some factors for this new relationship may include that modern corn hybrids have shown improved nitrogen use efficiency. He notes

that other researchers have also recently reported an increase in leaf chlorophyll in new versus old hybrids.

"More research is needed to understand the changes related to the components of yield to quantify potential sources for future yield improvement," he adds.

"This research allows us to provide information to growers on how to manage the hybrids we sell," says Jeschke. "That's even more important now as they carefully manage inputs using variable-rate seeding prescriptions."Trends In Corn Production

- Optimum agronomic plant density from 1987--1991 was 30,500 plants per acre.

- Optimum agronomic plant density from 2012--2016 was 37,900 plants per acre.

- Average annual yield increase at the agronomic optimum plant density from 1987 to 2015 was 2.23 bushels per acre.

- Plant density contributed from 9% to 18% of the yield gain during the last 30 years.


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