CHICAGO (Dow Jones)--Chicago Board of Trade corn futures ended lower Thursday as expectations of a large U.S. crop kept the market on the defensive.

September corn ended down 2 1/4 cents to $3.11 per bushel and December corn ended down 3 1/2 cents to $3.15 3/4.

The large crop was highlighted by Informa Economics' projection of a crop above 13 billion bushels, which helped December corn set a new summer low in morning trade.

"We took just a little bit of risk premium out of the market here," said Don Roose, president of U.S. Commodities in Des Moines.

Informa became the second private firm this week to project a crop above 13 billion bushels. The private analytical firm issued two projections, one for what it expects from the USDA along with its own expectations for the final crop.

Informa projected a final yield of 168 bushels per acre, which would shatter the previous record of 160.4 bushels per acre.

The numbers weren't a surprise to the trade, which was widely expecting a bearish estimate, but prices slipped anyway.

"It's not a secret that there's a huge crop out there, but when someone else says, 'Yeah, there's a big crop,' it's, like, OK, let's go down eight cents," said Thomas Grisafi, president and CEO of the Indiana Grain Company.

Prices rebounded as one midday weather model showed potential for frost across the Midwest two weeks from now.

T-storm Weather meteorologist Mike Tannura cautioned that following one run of the weather model "is a good way to make a bad forecast."

But a floor trader noted, "If I don't trade it I might be the loser."

Analysts say traders will be reluctant to push the market much lower Friday because of the three-day holiday weekend, and uncertainty about how weather forecasts could change during that time. The market will be closed Monday for Labor Day.

Analysts said that outside markets should have been a little supportive Thursday.

"A move like this we've had the last two days in the gold [market], if this was last year, corn would have put on 50 cents," Grisafi said.

Although the market rebounded after setting a new summer low of $3.11 1/2 in the December contract, the settlement was still the lowest close of the summer.

CBOT oats futures ended lower. September oats ended down 4 1/2 cents to $1.97 per bushel and December oats settled down 5 cents to $2.09.

Ethanol futures were mixed. September ethanol ended down $0.013 to $1.587 and November ethanol settled up $0.001 to $1.555.

-By Ian Berry, Dow Jones Newswires; 312-341-5778;