Corn slid, having touched a one-week high earlier in the session, while wheat tracked lower.
Chicago Board of Trade January soybeans rose 0.62 percent to $15.05-1/4 a bushel by 0350 GMT, having hit a session high of $15.08 a bushel, the loftiest since Nov. 8.
Soybeans rose 1.32 percent in the previous session, after data from the National Oilseed Processors Association showed US soybean processors crushed 157.308 million bushels in November, the largest for the month since November 2009, and the biggest overall since January 2010.
Export demand for soybeans has also been strong, especially from top global soy buyer China, which has forced domestic processors to bid up for soybean supplies.
"There is continued talk of further Chinese soybean imports, which was further supported by data published last week," said Lynette Tan, an investment analyst at Phillip Futures in Singapore, referring to data that showed China's manufacturing sector expanded in December at its fastest in more than a year.
Soybean prices were also underpinned by forecasts for low US stockpiles and worries about South American supplies.
The US soybeans stockpile is expected to shrink to a nine-year low by the end of the marketing season that runs from Oct. 1 to Sept. 30, the US Agriculture Department said.
Traders are now eyeing output from key producer Argentina, which suffered heavy rainfall from August through October, slowing 2012/13 soy and corn plantings and delaying the South American country's wheat harvest as well.
Argentina's soybean harvest has been pegged at 53 million tonnes by the Rosario grains exchange.
South American weather woes are also keeping a floor under wheat and corn prices, analysts said.
March corn fell 0.38 percent to $7.28 a bushel, coming off a one-week high of $7.34-3/4 hit earlier in the session. Corn firmed 1.46 percent on Friday.
March wheat fell 0.37 percent to $8.11 a bushel, giving back some gains from the previous session, when it rose 0.68 percent.
The Rosario grains exchange forecast Argentina's 2012/13 corn production at 24 million tonnes, and cut its estimate for wheat output to 9.5 million tonnes from a previous 10.1 million, factoring in damage done by waterlogged fields in the Pampas grains belt.
Center>Copyright Reuters, 2012