One of the most important economic decisions corn producers make every year involves choosing the right seeding rate. The answer often varies from field to field, and among different hybrids. Seeding rate decisions not only affect upfront production costs but also the final yield, said Ignacio Ciampitti, assistant professor of agronomy at Kansas State University.
“Decisions on hybrid placement field-by-field and seeding rate go together,” said Paul Carter, senior agronomy sciences manager with DuPont Pioneer. “Corn hybrids stress tolerance has improved with time and matching improving hybrid genetics with appropriate seeding rates is key to capturing the full benefit of genetic gain.”
Selecting seeding rates is not a simple matter, however, and in some ways that decision is becoming even more complex. New variable-rate seeding technology allows for more precision in seeding rates within a single field by allowing producers to change seeding rates in a single field on the go, said Ciampitti, who is a crop production specialist with K-State Research and Extension.
While there is some value in conducting or reviewing corn population trials on your own fields or in your immediate area and state, results can vary from year to year. It can quickly become confusing to look at population study results without a way to put the information into an overall context, he said.
“When you start looking at population studies, it can be overwhelming. We wanted to see if we could find some general patterns that would help give producers some guidelines in selecting seeding rates,” Ciampitti said.
To accomplish this, a large-scale analysis of corn populations studies throughout North America from 2000-2014 was conducted in a collaborative effort between scientists at K-State and DuPont Pioneer, Ciampitti said. A meta-database of more than 100,000 corn population observations from studies by DuPont Pioneer in 22 U.S. states and 2 provinces in Canada was analyzed.
The plots at each location were uniformly fertilized according to recommendations, to remove that variable. The remaining factors included in the studies were plant population, hybrid relative maturity, latitude, and yield environment.
The scientists found the factor that correlated best between plant population and grain yields was the yield environment, Ciampitti said.
The results of all the studies were divided into four general yield environments: less than 100 bushels per acre (low); 100 to 150 bushels per acre (medium); 150 to 200 bushels per acre (high); and more than 200 bushels per acre (very high). Populations in the studies were 18,000, 26,000, 34,000, 42,000, and 50,000 plants per acre.
In a low yield environment, average yields were maximized at about 90 bushels per acre with a population of 25,000 plants per acre, then declined gradually in a more-or-less straight line as populations increased, Ciampitti said. This was true at all latitudes and across all hybrid maturities.
In a medium yield environment, average maximum yield near 140 bushels per acre was also achieved with a population of about 25,000 plants per acre. Yields did not decline dramatically with higher populations, but neither did they increase.
In a high yield environment, yields increased relatively sharply as populations increased from 18,000 to 30,000 plants per acre, then peaked at about 35,000 plants per acre at a maximum yield average near 180 bushels per acre. Beyond that population level, yields declined.
In very high yield environments, yield response to plant population were still increasing in a relatively straight line at populations above 35,000 per acre.
The conclusions from the meta-analysis study can apply to all regions and hybrid maturities, Ciampitti said.
“For example, let’s say you have a yield map of a given field showing a consistent yield pattern for several years. No matter where you are, if the yield in certain areas of the field averages about 125 bushels per acre, we would call that a low yield environment and yields would be optimized with a population of about 24,000 to 25,000 plants per acre,” Ciampitti said.
“If the remainder of the field averages 180 bushels per acre, populations should be about 35,000 plants per acre,” he added.
DuPont Pioneer has developed a planting rate estimator using these concepts to help growers work with its company representatives to refine these results for their specific hybrids and fields, including economic adjustments for grain and seed prices, Carter said. Hybrid agronomic characteristics, such as stalk and root strength, and harvest timing logistics can be used to fine tune seeding rate decisions.