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High Yield Team: Give soybeans a head start

A 2004 Iowa State University study in southern Iowa found yield potential began declining as early as May 1. No-till was particularly prone to yield declines, as yields declined by .3 bushels a day from May 1 through May 15.

Bring your thermos brimming with hot coffee. Don your long johns. And grab a stocking cap. It's a small price to pay for the yield gains made by early soybean planting in the Corn Belt.

How early is early?

"Most Iowa recommendations have been to plant around May 15-20, when the soil temperature is 55 degrees F. or higher," says Palle Pedersen, Iowa State University (ISU) Extension soybean agronomist.

"We're finding it is more important to focus on the calendar and seedbed condition than soil temperatures. If seedbed conditions are good, we recommend planting on April 25 in the bottom two thirds of Iowa and May 1 in northern Iowa."

Similar recommendations apply elsewhere. "We would have little reservation about early soybean planting once we're past April 20, as long as the soil is in good shape," says Emerson Nafziger, University of Illinois Extension agronomist.

The head start that soybeans gain from early planting favor early canopy formation and sometimes early flowering. Soybeans are inefficient converters of sunlight. Having a full canopy during flowering and seed fill helps plants make the most out of the sunlight they do harvest. This spurs photosynthesis, which ultimately boosts yields.

Late frosts are always a drawback to early planting. Yet, 18 ISU tests conducted from 2003 to 2005 across three Iowa locations showed early planting boosted yields 83% of the time.

"There's a significant chance of getting a yield increase by planting early," says Pedersen

Seed treated with fungicide can pay dividends in areas with consistently wet soils filled with soil pathogens.

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