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Corn+Soybean Digest

How Low Can You Go?

At North Carolina State University, Jim Dunphy has been working for the last six years with county agents and producers, studying the effects of planting lower populations of determinate beans.

The result? On average, North Carolina producers have lowered populations by 10 lbs./acre without losing yield, resulting in an $8 million savings in seed.

“We started with southern determinates in 2002. In 2006 we took a survey of county agents who worked directly with producers,” says Dunphy. “We essentially asked, ‘How many pounds were your growers planting in 2002 and how many now?’ What the data revealed is that we can often lower populations without sacrificing yields.”

Dunphy reports that he has accumulated enough data to support his findings. However, he says some producers remain skeptical.

“It's important to remember that 50 years ago, the mindset focused on how many plants someone could get away with planting, primarily for weed control,” Dunphy says. “Today, we no longer have to rely on high populations to control weeds since we have products like Roundup.”

UNLIKE OTHER CROPS, Dunphy says that soybeans have similar yields over a wide range of populations. “That's the thing most of us have trouble accepting,” he says.

Dunphy says producers are planting three-quarters as many seeds per-acre as they planted 50 years ago, but that the old mindsets are hard to change. “We grew up wanting that thick stand, and when they first come up, the low populations coming up do look terrible.”

Just ask Earl York of Liberty, NC, who has been experimenting with his seed populations for five years. Having farmed for over 60 years, he worked closely with Dunphy when he modified his populations.

“We used to plant 90 lbs./acre in my daddy's time, and I followed his plan. Dunphy told me I was planting too thick. We cut back to 37 lbs. on a 50-acre field, but it was real sparse looking,” York says.

Like so many involved, York soon changed his mind. “When we harvested, we were amazed at the yield per acre for such a low population. I had to apologize to Dunphy,” he says with a chuckle.

York grows corn, wheat and soybeans and this year, like always, will plant 300 acres of beans. He has his own ideas as to the reasons that the lower populations work.

“We just have newer and better bean varieties than before. I've found that the thicker stands don't have pods at the bottom of the plant, just at the top. Fewer plants help that problem,” York says.

Dunphy has tested more than 40 varieties over the last six years and reports that there appears to be no significant difference among them. Eight populations have been tested in total. Although he's yet to publish his findings in any technical literature, the results have been distributed annually through county agents.

Dunphy also points out that producers often ask questions about lower populations and weed control. “Regardless of population, we've found we didn't change the rate of spray, so from a practical standpoint, we seldom have a change in weed-control costs,” he says.

What Dunphy stresses most is the difference between the technical and practical. “In practice, a producer has to decide what he can live with or what he'll lose sleep over.”

For York, he's settled on 50 lbs./acre after all his experimenting, and would tell skeptics one thing: “I'd say to try it because I think he'd be real pleased with the results.”

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