Soybeans for January delivery fell 44.5 cents to settle at $14.5125 a bushel. That's a loss of 3 percent. Corn and wheat futures also fell, but not as much.
The declines came after the Agriculture Department predicted that soybean production would increase.
The USDA now expects national soybean production to hit 2.97 billion bushels, 4 percent higher than the October forecast. The crop yield is now expected to average 39.3 bushels an acre, up 1.5 bushels per acre.
Another reason for recent weakness in soybean prices has been slowing exports to China, said Sterling Smith, futures specialist at Citigroup in Chicago. "I think this correction will bring them back into the market a little bit," Smith said. Soybean prices traded as high as $17.38 a bushel in mid-September.
December wheat fell 16 cents to end at $8.865 a bushel and December corn fell 2.5 cents to $7.3875 a bushel.
In other commodities trading, energy prices were mostly higher, except for natural gas. Metals prices ended mixed.
December gold gained $4.90 to settle at $1,730.90 an ounce, December silver rose 35.90 cents to finish at $32.599 an ounce, December copper fell 2.4 cents to $3.4455 per pound and December palladium fell $3.30 to $611.05 an ounce.
January platinum ended up $16.90 at $1,559.40 an ounce.
In energy trading, benchmark crude rose 98 cents to finish at $86.07 a barrel. Heating oil rose 5.01 cents to finish at $3.055 a gallon, wholesale gasoline rose 9.19 cents to end at $2.6992 a gallon and natural gas slipped 10.5 cents to finish at $3.503 per 1,000 cubic feet.