Chicago Board of Trade (CBOT) grains futures have seen a week full of fluctuations, with a overall downturn prevailing.

During the trading week which ended Aug. 18, the most active corn contract for December delivery fell 9 cents, or 2.40 percent, to 3.6575 dollars per bushel. A bearish report of U.S. Department of Agriculture was believed to be the main factor for the fall.

Apart from the USDA report on Monday mentioning better corn crop conditions, the favorable weather in leading agricultural State of Iowa added more pressure on corn futures.

Addition pressure came from South American corn exports, which were ramping up.

The good news for corn was that the ethanol market remained strong in the U.S. Ethanol plants, using corn as raw material, responded to the recent boost in production margins, producing nearly record-high ethanol in recent weeks.

December wheat delivery this week suffered a three-straight-day sharp decrease, but managed to recover some losses in the end.

Ample world supplies and fund selling contributed to the downturn. Traders were talking about record-high combined Ukraine/Russian production, though logistic issues might prevent Russia from exporting more than 29-31 million metric tons of wheat. That's roughly the volume of last year.

Price is another factor. Gulf wheat of the U.S. is the world's cheapest supply, on a FOB basis. A weak U.S. dollar will help American farmers export more.

November soybeans went down 7.25 cents this week, or 0.77 percent, to 9.3775 dollars per bushel.

Brazil's soybean exports are almost on track to meet USDA's record projection, which is expected to rise 21 percent. Export commitments are now lagging only a bit below the pace.

China's crushing margins are reportedly up sharply this week thanks to lower soybean futures and a stronger Yuan. The "spot" crush margin jumped 114 Yuan and is now is profitable for the first time since late February.

China remains the world's largest soybean importer. CBOT soybean prices were lifted, though moderately, for three consecutive sessions this week, obviously boosted by the news that a group of Chinese importers signed letters of intent to buy 3.8 million metric tons of U.S. soybeans in Omaha, Nebraska. However, soybean futures failed to post gains on a weekly basis.

Now all the eyes are on next week, when agricultural scouts plan to spread through the U.S. Midwest and hit more than 2,000 corn and bean fields in a bid to determine yield and production. A clearer picture will emerge when traders get the results of the crop tour.