U.S. soybean futures ended higher Thursday, settling at a new six-month high on increasing export demand and concerns over the size of the South American crop.

Soybeans for May delivery, the most actively traded month, ended up 11 3/4 cents, or 0.9%, at $13.38 1/2 a bushel at the Chicago Board of Trade. March soybean futures rose 11 cents, or 0.8%, to $13.32 1/2 cents a bushel, the highest settlement for the front-month contract since Sept. 20.

Soybean prices have rallied this year on expectations drought in Brazil and Argentina will reduce the size of the soy crops there, causing importers to turn to the U.S. for supplies. Analysts expect the U.S. Department of Agriculture to cut its forecasts for the South American crop in a supply-and-demand report due Friday. Cuts also are expected in end-of-season U.S. soybean inventories.

Thursday, Brazilian federal crop-forecasting agency Conab trimmed its outlook for Brazil's 2011-12 soybean crop, saying it now sees the crop at 68.75 million metric tons, down 0.7% from the previous forecast and 8.7% lower than in 2010-11, which was a record year.

Traders also are optimistic about export demand from China, the world's largest importer of soybeans. Thursday, China's Ministry of Commerce said the country's soybean imports in February likely will total 3.53 million metric tons, a 23% decline from January's imports, but a 52% increase compared with February 2011. Chinese economic indicators can be irregular early in the year due to the weeklong Chinese New Year holiday that usually falls in late January or early February.

Thursday, the USDA reported weekly net export sales of 1,646,000 metric tons of soybeans, including 1,015,200 for the current marketing year. That was higher than analysts' expectations for total sales of 600,000 to 900,000 metric tons.

Still, the recent rise in soybean prices led some traders to question whether factors such as the disappointing South American harvest already are priced into the market.

Corn futures ended mixed. CBOT May corn fell 3 1/4 cents, or 0.5%, to $6.35 1/2 a bushel, drawing pressure from traders reducing risk exposure ahead of the USDA report. March corn rose 1 1/4 cents, or 0.2%, to $6.45 a bushel, supported by tight cash markets as farmers wait for higher prices to sell their on-hand corn.

Wheat futures closed lower in the face of strong global supplies. CBOT May wheat fell 4 1/2 cents, or 0.7%, to $6.34 3/4 a bushel, while May futures at the Kansas City Board of Trade dropped 5 1/2 cents to $6.78 1/4. May wheat fell 5 1/4 cents to $8.03 1/2 at the MGEX in Minneapolis.

World wheat supplies already are ample and warm temperatures and wet weather are positive for the development of the U.S. winter-wheat crop.

"You've already got large supplies and you're going to add to it, the way things look," Tom Leffler, president of Leffler Commodities, said.

-By Owen Fletcher, Dow Jones Newswires; 312-750-4120; owen.fletcher@dowjones.com