U.S. grain and soybean futures ended mixed Tuesday, with the three major crop futures failing to sustain initial advances.

Grain and soy prices found stability after stumbling Monday, but lacked enough fresh fundamental news to overshadow seasonal pressure, as traders brace for the influx new supplies from the fall harvest.

Corn futures led the slide in the grain complex at Chicago Board of Trade, as sluggish demand and seasonal harvest selling overcame support from reports that China was poised to import more U.S. corn.

Corn prices climbed in the face of negative economic news Monday, fueled by talk of China buying U.S. corn. But the unconfirmed reports failed to buoy prices Tuesday.

"The pricing of the China business would have been accomplished Monday, and once the pricing is done, it's done," says John Kleist, senior analyst with ebottrading.com.

"That's why the corn market failed to sustain the early session gains," Kleist added.

Corn and other agricultural commodities received support from outside financial markets, which were a negative factor Monday. Equities climbed on possible progress on Greece's debt crisis and potential stimulus efforts by the U.S. Federal Reserve, easing worries about the economy for the moment.

It will be tough to mount any sustained rallies until the harvest progresses further, Kleist said. "It's not a surprise for the U.S. to drum up business after the recent break in prices, and crop scares have been factored in prices already."

Traders are also cautious of a tenuous global economy, fearful of slumping demand.

U.S. wheat faces stiff export competition from countries in the Black Sea region like Russia, and soybeans are competing with Brazil, where China is sourcing supplies longer than expected.

Traders were encouraged that recent price declines brought China back to the market to buy some cargoes of U.S. soybeans.

CBOT November soybeans ended up 2 cents to $13.38 a bushel. CBOT December corn ended down 2 cents at $6.90 1/4 per bushel, 13 cents off the intraday high.

December CBOT wheat ended up 1 3/4 cents at $6.74 3/4 per bushel, while KCBT December wheat closed down 3 cents at $7.65.

Other Markets

CBOT December soymeal end up 0.5% at $350.30 per short ton, and December soyoil dropped 0.4% to 55.63 cents per pound. CBOT November rice closed down 19 1/2 cents at $17.19 1/2 per hundredweight.

Ethanol for December delivery climbed 0.4% to $2.560 per gallon. Oats for December delivery ended up 1% at $3.49 per bushel.