Reports of very large soybean yields from the US Midwest harvest also weighed on prices.
Soymeal and soyoil futures closed lower.
Chicago Board of Trade November soybeans fell 6 cents, or 0.6 percent, to settle at $9.75-1/2 a bushel after earlier hitting a four-week high. Selling accelerated as the contract fell below its 200-day moving average.
The US dollar rose to its highest point in seven months against a basket of currencies after the European Central Bank President left the door open to more monetary stimulus at its policy meeting.
The 19-market Thomson Reuters Core Commodity CRB Index dropped about 0.9 percent.
Early-session gains were fueled by stronger-than-anticipated soybean export demand.
The US Department of Agriculture reported export sales of US soybeans in the latest week at just over 2 million tonnes, well above a range of trade expectations for 1.0 million to 1.3 million tonnes.
The USDA also confirmed private sales of 192,000 tonnes of US soybeans to unknown destinations for 2016-17 delivery.