Corn futures generated record trading as signs that U.S. farmers won’t harvest as large a crop as once expected fueled speculator buying.

A total of 556,034 corn futures contracts changed hands at the Chicago Board of Trade last Friday, exchange officials reported today. That was the corn market’s busiest day since the CBOT began trading the grain in 1877, topping the previous one-day record of 516,076 contracts on June 12, 2008.

Grain trading surged this summer after drought slashed Russia’s wheat crop and spotty harvest prospects in the United States pushed corn up 35 percent since the end of June to 15-month highs.

Many traders expect USDA will lower its estimate for this year’s corn harvest after excessive rains in some areas of the Midwest hampered crop development, said Jack Scoville, a vice president and analyst with Price Futures Group in Chicago.

“People are finally starting to realize that maybe the production isn’t there,” Scoville said today, referring to corn. “Some areas got too much rain, some areas got a combination of too much and then too little. For whatever reason, the yields don’t seem to be coming in so well.”

Based on early harvest results from Arkansas, Indiana, Ohio and southern Illinois, “yields have not been too impressive,” Scoville said.

USDA, in an Aug. 12 report, estimated the 2010 corn crop at 13.37 billion bushels, up 1.9 percent from the 2009 crop and an all-time high.

But the recent rise in corn futures suggests the market expects USDA to reduce its crop estimate to about 13.2 billion bushels, Scoville said.

A harvest at that size “is still a nice crop,” Scoville said. But “if we’re trading 13.2 (billion bushels), we’re not going down” in price.

USDA is scheduled to release its next Crop Production report on Sept. 10.

At today’s close, corn for December delivery was unchanged at $4.64 ½ a bushel, after reaching $4.69, the contract’s highest price since June 2009. December corn is up about $1.21 from a contract low of $3.4325 reached June 29.

The recent surge in grain futures trading has been primarily driven by speculators, Scoville said. An upswing in agricultural futures this year also reflects bull markets in cattle and hogs that have attracted hedge funds and other speculators.

Moreover, many investors have piled into crude oil and other commodities the past few years, seeking better returns as traditional investments such as stocks languished.

“With the Russian weather, people are looking to get involved in commodities,” Scoville said. “There’s still a lot of interest in owning commodities right now. People are starting to realize they better get something on the books” in commodities.

Corn futures trading this year through August averaged 249,146 contracts a day, up 23 percent from the same period in 2009. Wheat futures averaged 96,875 contracts a day, up 38 percent.

In addition to corn, futures contracts based on wheat, soybean meal, soybean oil and live cattle notched record trading days in 2010, according to Chicago-based CME Group, the exchange operator that bought the CBOT in 2007.

On Aug. 19, trading in CME’s live-cattle futures and options totaled an all-time high of 109,420 contracts, surpassing the previous record of 109,397 in June 2007.

At today’s close, October lean-hog futures fell 1.45 cents to 75.75 cents a pound, while October live-cattle fell 2.025 cents to 96.425 cents a pound. The CME hog contract is based on carcass values.