Chicago Board of Trade (CBOT) grains futures closed mixed over the trade week which ended Sept. 22, as large export demand and uncertainty about the size of the U.S. crop continues to weigh on the grains market.

The most active corn contract for December delivery fell 1.25 cents weekly, or 0.35 percent, to 3.535 dollars per bushel. December wheat delivery rose 0.5 cent weekly, or 0.11 percent, to 4.495 dollars per bushel. November soybeans added 15.5 cents weekly, or 1.6 percent, to 9.8425 dollars per bushel.

CBOT corn ended slightly lower, as the market continues to flirt with major resistance at 3.55 dollars per bushel. A flood of combined yield data in the next few weeks will drive nearby direction. So far yield data has been variable, and a clear yield trend is lacking.

Analysts don't expect much of the corn market into mid-fall. South America continues to ship record amounts of corn abroad, and U.S. weekly export sales will be rather dull into early 2018.

It's far too early to be concerned, but a developing La Nina and delayed soybean seeding in Brazil, which in turn may delays corn planting, are being watched. The ethanol margins are strong so U.S. domestic use is record large.

Wheat futures rallied a little bit higher with premium added to spring wheat values ahead of the Final U.S. Small Grains Report next Friday. Fundamentally, it's common for U.S. and world wheat markets to bottom in late August or September, and with Russian fob offers rising rather quickly.

As to other major wheat exporters, Australia remains dry, Argentina has lost acreage, and a wetter pattern is needed in East Ukraine and South Russia for germination.

Soybeans traded back and forth through much of the week with export demand offering support on early week selling. There were export sales announcements of nearly 1.7 million tonnes of old crop soybeans for the week, while the weekly export sale report showed sales last week that were well above expectations and the largest since last October at 2.3 million tonnes.

Traders expect that by Sunday evening 11-14 percent of the U.S. soybean crop will have been harvested. The harvest in the Delta area will pass 50 percent.

November soybeans broke through several key layers of resistance in Friday's trading, leaving the next key technical level at a trend line near 10 dollars per bushel. However, trading looks to slow by the middle of next week as the market prepares for the uncertainty of the Quarterly Stocks report out next Friday.