U.S. soy futures fell almost 3 percent on Monday, the biggest one-day decline in four months as the dollar gained on worries about the euro zone debt crisis and as more-than-expected rainfall nursed South America's crop back to health. 
Corn also fell, dropping for the first time in seven trading sessions, posting its biggest one-day drop in over a week. 
Wheat eased for the second session in a row on the firm dollar and spillover selling from tumbling soy but found underpinning from concerns about potential winterkill in the
Black Sea region because of bitter cold temperatures. 
CBOT March soybeans were down 33-3/4 cents at $11.85-1/4 per bushel, March corn was down 10 at $6.31-3/4 and March wheat was down 2-1/2 at $6.44-3/4. 
Traders and analysts said there was a one-two punch for grains and soybeans on Monday with the firm dollar and falling equities lending pressure while soy came under more weight from
a shift to much better crop prospects in Argentina and Brazil, two global soy producing giants. 
"The weather has improved in South America, much better crop prospects there and prices are under pressure from the uncertainty in Europe," said Mark Schultz, analyst for Northstar
Commodity Investment's Co. 
The dollar rose nearly a half percentage point and the Dow stock index eased on Monday as concerns grew about the state of Europe's finances while Greece and Germany sparred over budget measures for Athens.