- U.S. grain futures plunged to multi-year lows on Friday, after the U.S. Department of Agriculture forecast higher-than-expected domestic supplies of wheat, corn and soybeans this year.

On the Chicago Mercantile Exchange, U.S. wheat for September delivery tumbled to a daily low of $5.2500 a bushel, before settling at a four-year low of $5.2600 by close of trade, down 4.1%, or 22.4 cents.

The September wheat contract plummeted 9.21%, or 53.4 cents, on the week.

Prices plunged on Friday after the U.S. Department of Agriculture raised its outlook for global inventories at the end of the 2014-15 season that started on June 1 to 189.54 million metric tons from the 188.61 million tons forecast last month.

Elsewhere on the Chicago Board of Trade, U.S. corn for September delivery slumped to a session low of $3.7560 a bushel, before settling at $3.7820, down 2.07%, or 8.0 cents.

On the week, the September corn contract plunged 7.62%, or 31.2 cents.

The USDA raised its estimate for U.S. corn inventories at the end of August to 1.246 billion bushels, up 8% from its forecast in June.

The agency also said that U.S. farmers will harvest 13.86 billion bushels of corn this year, down slightly from its previous forecast of 13.93 billion bushels.

Meanwhile, U.S. soybeans for August delivery fell to a session low of $11.5920 a bushel on Friday, before trimming losses to end the week at $11.9560, down 3%, or 37.0 cents.

On the week, the August soybean contract tumbled 8%, or $1.04.

The USDA raised its forecast for the U.S. soybean harvest by 4.5% to a record 3.8 billion bushels, above expectations for a 3.1% increase.

The agency also increased its forecast for soybean inventories by a larger-than-expected 12% to 140 million bushels.

In the week ahead, market players will focus on the release of key USDA data, including crop progress and weekly export sales figures.

Corn is the biggest U.S. crop, followed by soybeans, government figures show. Wheat was fourth, behind hay.

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