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High Yield Team: Start with variety selection

"Variety selection is the most important factor in soybean production," says Palle Pedersen.

Palle Pedersen had a specific marching order when he became an Iowa State University Extension soybean agronomist in 2003. "We're missing 20 bushels an acre off our soybean yields in Iowa," he was told. "Find it."

On the surface, this seems simple. After all, today's varieties pack up to a 100-bushel-an-acre yield potential.

Plus, U.S. soybean yields have held up pretty well over the years. "There was a perception after 2003 that yields were flat due to drought, soybean aphids, and things like the continuing spread of soybean cyst nematode (SCN) and sudden death syndrome," says John Soper, head of soybean breeding at Pioneer Hi-Bred International.

Yet, U.S. Department of Agriculture data compiled by Pioneer shows otherwise. Since 1976, soybean yields have steadily increased an average of .5 bushels an acre. On a percentage basis, that’s comparable to the 1.6-bushel-an- acre annual corn yield increase made during that same time, says Soper.

So why have soybean yields got a bum rap in recent years? Part of it has to do with its comparison to corn yields and modern corn production.

"In Iowa, we have a 32,000-an-acre plant population, spray, and harvest," says Pedersen, who also is a High Yield Team expert panelist. "There is no in-season management. It's all in the seeds."

Compare that to soybeans, where many in-season maladies strike. For example, soybean aphids can attack plants during the heart of the growing season. Meanwhile, U.S. farmers are wrestling with the potential havoc of Asian rust, which devastates plants during critical flowering and pod-filling stages.

"The matrix is more complex with soybeans," Pedersen adds. "You might have 10 fields and have to select six different varieties to deal with all the variables. Soybeans are also more sensitive than corn to the environment during seed fill."

You can't eliminate all the alligators snapping at soybeans these days. Yet, you can manage many of the pests that chip away at yield potential.

"It's not about increasing yield, it's about maintaining yield," says Pedersen. "Look at it as a house. The foundation has to be solid."

How to deal with SCN

Part of building a solid foundation is properly matching soybean variety and field. In many Corn Belt areas, this means planting SCN-resistant varieties on fields infested with SCN.

"Soybean cyst nematode really costs us," says Pedersen. It infests more than 75% of Iowa soybean fields and can clip yields by more than 50%.

Yet, Pedersen says seed company personnel inform him that less than 40% of soybean seed sold in Iowa is SCN-resistant. It is estimated SCN cost Iowa farmers 50 million bushels in losses in 2004, says Pedersen. He expects 2005 losses to be greater when tallied up. In a dry year like 2005, SCN yield loss will likely be greater because less soil moisture exists for damaged soybean roots to access.

The good news is there are numerous high-yielding SCN-resistant varieties on the market. Unlike transgenic traits, SCN-resistant varieties also have no technology fees.

Pedersen adds farmers may be reluctant to plant SCN-resistant varieties, since yield drag existed in the early 1990s when these varieties became available. That's changed.

"Since there isn't any yield difference between the best SCN-resistant varieties and the best SCN-susceptible varieties, we recommend farmers start planting them at low SCN populations," says Pedersen.

Though soybean yields decreased during a droughty 1988 and 2003, U.S. soybean yields have steadily increased an average annual .5 bushels an acre over 30 years. Excellent 2004 and 2005 yields more than average out poor years.

Darle Elkin, a Webster City, Iowa, farmer, considers SCN when he picks soybean varieties. "You can have an 80-bushel variety in one field, and it will do 20 in another field if the moisture isn't there and there is high pH and soybean cyst nematode," he says.

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