CBOT settled down 6-3/4 cents at $9.75-3/4 a bushel, dropping below its 200-day moving average near $9.77.
CBOT January soymeal ended down $3 at $324.70 per short ton while January soyoil ended down 0.01 cent at 33.45 cents per pound.
Forecasts called for much-needed rain this weekend in main crop areas of Argentina, the world's top exporter of soymeal.
Brazilian government food supply agency Conab forecast the country's 2017/18 soybean crop at 109.2 million tonnes, topping its month-ago range of estimates for 106.4 million to 108.6 million tonnes.
Abiove, a Brazilian oilseed processors association, raised its Brazilian soy crop estimate to 109.5 million tonnes, from 108.8 million previously.
The US Department of Agriculture in a monthly supply/demand report raised its forecast of US 2017/18 soybean ending stocks to 445 million bushels, from 425 million last month.
Market had little reaction to USDA confirmation that private exporters sold 168,300 tonnes of US soybeans to unknown destinations for 2017/18 delivery.
Through its daily reporting system, the USDA also changed the destination of 492,000 tonnes of US soybeans sold for 2017/18 delivery to China, from unknown destinations.