Soy was on track to post its biggest weekly gain on a percentage basis in over 2-1/2 years.
While US farmers have made rapid progress in harvesting this year's crop, they have refused to sell into what they consider a down market. The lack of fresh available supply has bolstered prices.
CBOT December corn for delivery in the winter of 2012 rose 5 cents per bushel to nearly $6 after widely followed research and analytical firm Informa Economics trimmed its forecast for next year's US corn plantings to 93.1 million acres from its previous 94.3 million.
Wheat and corn turned lower in thin dealings. Prices rose in early trading on perceived progress in the euro zone debt crisis and upbeat corporate earnings.
"Another day of gains in markets like metals, equities and crude oil and the weak dollar I think lifted everything. There wasn't much change in fundamentals but there were good export sales of corn," said Shawn McCambridge, analyst for Jefferies Bache.
At 11:02 a.m. CDT (1602 GMT), CBOT December delivery wheat was down 1 cent at $6.17, December corn was down 3-1/4 at $6.35 and November soybeans were up 4 at $12.61.
Traders said a US government report on Friday showing good weekly export sales of grains and soy helped keep a firm foundation under each market.
"The weaker dollar earlier helped lift prices, but the dollar has clawed back a fair amount and that's making traders a little bit nervous. After the export sales, there are not a lot of drivers," said Sterling Smith, analyst with Country Hedging.
"The weather is mediocre. Harvest is a little hampered in the east and there are some concerns about some freezing temperatures in Ohio and that may be working to give the market a little lift," Smith said.
US farmers are harvesting corn and soybean crops with only brief slowdowns in harvest late this week and early next week tied to light rainfall.
"A few instances of rain, nothing real important and no major delays," said Andy Karst, meteorologist for World Weather Inc.
Cash grain merchants in the Midwest confirmed that farmers were busy harvesting crops and were not selling.
"Even though it's the middle of harvest its been quiet," an Iowa dealer said.
Wheat, corn and soybeans have rebounded from their recent lows set in late September, yet each market is sharply below 2011 highs.
Copyright Reuters, 2011