CBOT corn firms in light volume trading
* Concerns that high prices for US corn will weaken demand limited the gains.
* Corn volume was light with about 202,000 contracts changing hands, nearly 30 percent below the average of the last 30 days.
* Cargill has warned its North American customers to expect corn sweetener prices to rise by at least 30 percent in 2012.
* Argentina will authorize the export of an additional 7 million to 8 million tonnes of 2011/12 corn.
* Freezing temperatures hit some northern parts of the US Midwest on Wednesday morning but most of the corn crop was too mature to be hurt by the cold.
* DuPont's Pioneer unit to raise corn seed prices in mid-single digit range next year.
* Analysts expecting weekly export sales of corn in range from 400,000 to 700,000 tonnes. US Agriculture Department's report due on Thursday morning.
Copyright Reuters, 2011