Population Potential

Shoot For Optimum Corn Ear Numbers Per Acre to Increase Yields

Nearly 30% of the U.S. corn grown in 2013 was planted at a rate ranging between 33,000 and 36,000 seeds per acre. (Progressive Farmer photo by Dave Tonge)

When Todd Christians started farming in 1987 near Kanawha, Iowa, the target population for corn was 25,000 to 26,000 plants per acre -- a far cry from the 35,000 to 36,000 plants per acre common in his area today. Even so, Christians hasn't stopped pushing the envelope in his 30-inch rows, and he expects those numbers will increase in the future.

"I've planted up to 44,000 seeds on some of my acres," said Christians, who manages his corn acres with the help of SciMax Solutions, the precision ag program offered through MaxYield Cooperative. "I've also planted 25,000 plants per acre in lower-producing parts of the same field. Using zones is a high-management system, and I've seen a consistent 3- to 5-bushel-per-acre yield increase each of the past three years."

Christians continues to test higher plant populations on his best acres. In areas where soils have corn suitability ratings between 65 and the low 80s (based on a total possible score of 100), average yields range between 180 and 200 bushels per acre in high-management zones. In medium- to low-management zones, yields range between 165 and 175 bushels per acre.

THE SURVEY SAYS

More growers nationwide are testing what's possible with higher plant populations. About 30% of the corn acres in North America is currently planted with between 30,000 and 33,000 seeds per acre. The fastest-growing category is a planting rate that ranges between 33,000 and 36,000 seeds per acre, according to DuPont Pioneer's latest survey of growers regarding the seeding rates currently used on their farms.

This latter category has increased from less than 12% of corn acres in 2007 to nearly 30% of corn acres in 2013. The 36,000-plus category is also gaining acres at a rate of about 1 percentage point per year.

"Optimizing the number of corn ears per acre is a key to producing the higher yields that will be needed to feed a growing global population," said Scott Nelson, a Pioneer agronomy research manager.

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To see what's possible, Pioneer has conducted plant population research at more than 700 locations throughout the U.S. and Canada in the last 12 years. Data were divided into four-year groupings to evaluate if progress was made in increasing hybrid tolerance to high plant-density stress. Specifically, yield data of the five highest-yielding hybrids from each of three different periods (2001 to 2004, 2005 to 2008 and 2009 to 2012) were averaged within each grouping.

For the top five yielding hybrids per time period, the plant population that maximized yield increased from 36,000 plants per acre in the two earliest groups to 40,000 plants per acre in the most current hybrid group (2009 to 2012). This is due to improved genetics, including the hybrids' ability to handle stress at higher plant populations. In addition, yield increased by 10.7 bushels per acre in the most current group compared to those in the previous four-year period.

Peter Bixel, SciMax Solutions team leader, is a proponent of using variable-rate plant populations to maximize yield potential on every acre. "On 30-inch rows, we've worked with populations of 30,000 up to 38,000 plants per acre on better soil," said Bixel, who has helped SciMax clients implement management zones for nearly six years. "There's no reason to plant 36,000 seeds in poorer areas or only 32,000 seeds in better areas."

EVALUATE CONDITIONS

Some growers may be wondering if they took full advantage of this year's high-yielding conditions, but increasing plant populations would not necessarily have made for bigger yields in 2014, explains University of Illinois crop scientist Emerson Nafziger.

"Did we all miss the boat by planting 'only' 35,000 or so seeds per acre this year? Fortunately, we have data to answer this question," Nafziger said.

Since 2011, Nafziger has conducted trials at a dozen sites around Illinois in which six to eight hybrids are seeded at a range of plant populations, including rates of 34,000 and 42,000. At yield levels less than 150 bushels per acre, 42,000 plants yielded 9 bushels more than 34,000 plants. At yields above 250 bushels per acre, 42,000 plants yielded a half-bushel less than 34,000 plants.

"This reinforces that low-yielding conditions tend to make yield less consistent," Nafziger said.

He adds that the data don't support the idea that a corn crop planted at populations in the mid-30,000 range is incapable of taking full advantage of high-yielding conditions. The data also confirm that risks of having populations too high increase when conditions for maximum yields fail to materialize.

"Because we don't know what conditions will be at the beginning of the season, it makes no sense to push populations above 40,000 in hopes that we'll get the weather to make this pay off," Nafziger said. He notes that it takes nearly 1 bushel of yield to pay for 1,000 more seeds. "In fact, the response of yield to population tends to be fairly flat over the range of the lower to upper 30,000s, regardless of yield level or conditions," he adds.

Beyond plant populations, some growers and companies are looking at narrower rows in an effort to maximize yield potential. Starting in 2012, Iowa-based Stine Seed planted 2,300 acres of corn and 100 acres of soybeans in equidistant narrow rows at populations as high as 51,000 plants per acre. Even with the 2012 drought conditions, yield results were impressive.

"In areas with the best growing conditions, our corn yields consistently topped 300 bushels per acre," said Myron Stine, vice president of sales and marketing for Stine Seed. "Those results reaffirmed our belief that proper hybrid selection, allowing for more efficient utilization of space and higher plant populations, will shape the future for higher corn yields."

In 2013, Stine planted 100% of its 15,000 corn and soybean acres at the Stine Farm, near Adel, Iowa, in 12-inch rows, using machinery customized for the effort. In 2014, Stine used a new narrow-row, twin-row planting configuration. This system could best be described as 20-inch twins with 12 inches of main-row spacing, then 8 inches separating each pair of twin rows. "This configuration allows us to make even more efficient use of each acre planted, where 60-foot planter bars hold 72 rows in the space where we formerly had 60," Stine said. "That figures to an average row spacing of just 10 inches."

Ultra-narrow-row spacing opens the door to new possibilities with high-population hybrids, Stine adds. He notes that Stine's seeding populations have ranged from 45,000 to 75,000 plants per acre in the company's trials.

"You can't take hybrids developed and tested under 30-inch rows, plant them in narrow rows at a high population and expect them to perform," Stine said. He describes the company's high-population hybrids as "shorter, with more upright leaves that stand much better and offer more efficient water usage."

Christians realizes hybrids are constantly changing, and he regularly evaluates new genetics and plant populations that can help take his corn yields to the next level. He realizes the process will require experimentation and a willingness to take some production risks. "I like the challenge," he said. "We're pushing things as far as we can."

(BAS)

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