See the September 2015 USDA crop report.

Updated, 12:35 p.m., Aug. 12: USDA on Wednesday shocked the grain markets by raising its forecasts for the U.S. corn and soybean harvests and now estimates corn production at 13.686 billion bushels and soybeans at 3.92 billion.

Chicago corn futures crumbled after the report to initially trade about 28 cents per bushel lower, or 7%, in nearby months and soybeans about 60 cents lower, or 6%. Corn recovered some to trade about 18 cents lower within an hour of the report, while soybeans were down about 56 cents near midday.

USDA shocks market with huge corn and soybean crops

Analysts largely expected USDA to reduce the crop sizes on ideas abundant rain this spring and early summer had hurt the crops and prevented some acres from being planted.

"Many will argue with these numbers, and they don't match results from our surveys and weather models. But the yields USDA found aren't far from those suggested by our yield models based on the nationwide crop ratings," said Bryce Knorr, Farm Futures senior grain market analyst. "So the possibility that crops are this big can't be discounted."

Winter wheat futures were 15 to 16 cents lower, largely pulled down by corn and soybeans as USDA put winter wheat crop at 1.44 billion bushels versus the trade average of 1.45 billion. Spring wheat futures were 6 cents lower as USDA put that crop at 621 million bushels, versus the average trade forecast of 629 million.

USDA raised its average corn yield forecast to 168.8 bushels per acre, based on survey results, from its previous trend-based projection of 166.8 bushels. Harvested corn acreage was left at 81.1 million from its previous report, while soybeans were trimmed to 83.55 million from USDA's previous 84.45 million.

USDA's soybean yield increased 46.9 bushels from USDA's previous of 46, which offset the reduction in harvested acreage, to put production at 3.916 billion.

"The next question is acreage. USDA did cut its forecast of harvested acres some. This included a resurvey of growers in Arkansas, Missouri, Kansas and Texas. But this was only a sample," said Knorr. "The first report on government program certifications from the Farm Service Agency is due Monday, which could shed more light on acreage, especially totals farmers were prevented from planting."

 Ending stocks for the 2015 corn crop increased to 1.713 billion from July's estimate of 1.599 billion because of greater domestic use. Soybean ending stocks went to 470 million bushels from USDA previous 425 million, largely because of the higher expected production

."For now, today's reports put the $3.47 December futures low we've been talking about back in play. Added bearishness from China is another hurdle the market will have to overcome. USDA increased its forecast of Chinese imports, which looks suspicious given recent events, which could create even more headwinds," said Knorr.

Find full USDA August WASDE report info on the USDA website.