BEIJING - Chicago soybeans rose on Wednesday as traders adjusted positions ahead of the release of official U.S. data on global supply and demand on Friday, the first update in weeks, though the absence of large-scale purchases by China kept a lid on prices.

The most-active soybean contract on the Chicago Board of Trade (CBOT) gained 0.6% to $11.34 a bushel as of 0617 GMT.

China has begun modest purchases of U.S. farm products after the leaders of the two countries met last month, but traders are awaiting major soybean deals after the White House said Beijing had pledged to buy 12 million tons by year-end.

Chinese state trader COFCO's oilseed unit said on Monday it has signed agreements to buy over $10 billion worth of Brazilian soybeans, soybean oil, palm oil and other agricultural products. The statement did not mention any U.S. purchases.

At the same time China is grappling with a soybean supply glut and weak margins due to record imports in recent months, clouding prospects for large U.S. purchases.

"To see stronger support for US beans, we will need to see China book some business. But rallies will likely be capped with South American sales already made, and ample stocks still on offer," said Josh Lawrence, advisor at IKON Commodities in Sydney.

Corn added 0.12% to $4.32-1/2 a bushel as the market remained uncertain whether dryness and diseases during the growing period for the U.S. corn crop significantly affected yield and quality.

Wheat eased 0.09% to $5.51-1/4 a bushel.

"The euphoria on U.S. wheat purchases by China looks to have dimmed," said Lawrence.

Market participants are waiting for the U.S. Department of Agriculture to update its corn and soybean production and yield estimates in a monthly report on Friday.

A poll of analysts surveyed by Reuters projected that the USDA will lower its U.S. corn yield estimate to 184.0 bushels per acre (bpa) from 186.7 bpa in its previous September 12 forecast.

Analysts pegged the U.S. soybean yield at 53.1 bpa, below USDA's September 12 estimate of 53.5 bpa.