Corn was down around 4 cents, soybeans off around 6 cents and wheat about 4 to 6 cents lower. Some downside corrective pressure is seen early Tuesday following recent gains.

The weekly USDA crop progress reports, out late Monday, also showed corn and soybean conditions a stable to a bit better than expected, which is getting a mildly bearish read. The US corn condition rating was 55 percent good to excellent, the same as last week. The soybean condition rating was at 54 percent good to excellent versus 55 percent GTE last week.

Geopolitical uncertainty in the marketplace this week, following the terrorist drone strikes against Saudi Arabia over the weekend, and the potential for retaliation from the Saudis and the US against Iran, are also keeping the grain market bulls at bay.

Weather in the US Corn Belt remains very warm. It appears the corn and soybean crops will escape a killing hard frost early this fall.

Traders will closely monitor the daily USDA reporting service for any new grain purchases coming from China. China has been buying US soybeans recently.