INTERVIEW-Iowa State climate expert sees lower corn yields 2013

CHICAGO, Dec 5 (Reuters) - A top Iowa State University agricultural scientist predicted on Wednesday that the United States would see below-trend yields for a fourth straight year in 2013 and spotlighted long-term climate risks for farmers in the years ahead.

"It's looking likely that we will have a fourth year of below-trend U.S. corn yields. But not as bad as in 2012, but still below trend," Elwynn Taylor, Iowa State University climatologist, told Reuters Ag Forum, an on-line chatroom.

Taylor is using a corn trend yield of 160 bushels an acre, based on the U.S. Agriculture Department's past 30 years of crop data. He sees the 2013 U.S. corn yield at 147 bpa, compared with the USDA's drought-hit estimate of 122.3 for 2012.

"Our short-term trend is decreasing, and I do not see a change in the trend within the next five years," said Taylor, adding that the effects of this year's historic "drought will probably ease, but not be erased."

U.S. farmers recently saw six straight years, 2004-2009, of increasing corn yields. But volatile weather patterns from floods to droughts have hurt crop production, including this year's drought that cut yields and affected two-thirds of the U.S. land mass.

The drought, the worst in 50 years, continues to stress winter-seeded crops such as hard red winter wheat and causing nightmares for grain shippers on Midwest rivers as low water slows barges moving grain to Gulf export terminals. The U.S. remains the largest single exporter of corn, soybeans and wheat.

Key will be moisture, a wild card, as well as trends such as El Nino and La Nina - weather anomalies that occur irregularly with changes in sea-surface temperatures in the South Pacific and that in turn affect weather patterns around the world.

"At present the trend is toward a La Nina pattern, but neutral, trending toward La Nina," Taylor said. "On average during a La Nina year, there is a 70 percent chance of below-trend yield for the Corn Belt. For 2013, the chances are somewhat higher because of the existing subsoil dryness."

Subsoil moisture in big crop states such as Iowa and Nebraska is already rated more than 90 percent short to very short, according th e US DA's latest crop condition reports.

Iowa soil moisture map: link.reuters.com/dab54t

Taylor does not expect subsoil moisture to be fully recharged by the 2013 spring planting in Minnesota, Iowa, the Dakotas and Illinois, but he said Indiana and Ohio should be in better shape. The western Corn Belt is suffering from below-normal rains, but last summer's root development also further depleted soil moisture, he said.

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