CHICAGO (Dow Jones)--U.S. soybean futures dropped for the fifth straight day Friday, extending a slide that began when federal forecasters unexpectedly raised harvest and inventory outlooks.

Soybeans for November delivery, the most actively traded contract, fell 3 1/4 cents, or 0.2%, to a one-month low of $13.55 1/2 a bushel on the Chicago Board of Trade. The losses left the contract down 5% for the week and 7.5% from a three-year high reached in late August.

Prices continued to weaken after the U.S. Department of Agriculture, in a monthly report issued Monday, surprised traders by raising its output and supply forecasts. The increases sparked a sharp sell-off because money managers, in weeks before the report, started building up long positions, or bets that prices would rise.

"The market was bloated to the long side, and it's rebalancing right now," said Don Roose, president of U.S. Commodities, a commodities brokerage in Iowa.

Wheat and corn futures also fell hard this week.

Corn for December delivery on Friday slid 9 cents, or 1.3%, to $6.92 a bushel. It settled down 6% for the week and 11% from a contract high reached in late August. Soft red winter wheat for December delivery on Friday lost 7 3/4 cents, or 1.1%, to $6.88 1/4 a bushel.

Traders next week will look to see whether the break in prices has attracted buyers to the market. It seems prices are "in the zone for the end user where it works" to step up purchases, Roose said.

Other markets

Soy products were mixed, despite continued weakness in soybeans. December soymeal stumbled 0.3% to $353.10 per short ton, while December soyoil edged up 0.5% to 56.85 cents a pound. November rice slipped 0.2% to $17.89 per hundredweight, and December ethanol lost 1% to $2.566 per gallon. December oats rose 0.4% to $3.45 1/2 a bushel.

At the Kansas City Board of Trade, hard red winter wheat for December delivery sank 1.4% to $7.84 a bushel as forecasts called for beneficial rains in dry, wheat-growing areas of the U.S. Plains. Hard red spring wheat for December delivery dropped 1.7% to $8.56 1/4 a bushel at MGEX in Minneapolis.