Chicago soybean futures rose to a three-week high on Tuesday, underpinned by a U.S. report showing a slight deterioration in crop ratings, which could result in lower yields, before paring some gains.

Corn edged down after hitting a one-month high on expectations of lower U.S. output following wet growing conditions, while wheat fell following three sessions of gains - a rally seen as overdone as global supplies remain plentiful.

Chicago Board of Trade November soybeans advanced 0.2 percent to $8.85-3/4 a bushel by 1111 GMT, after hitting a session peak at $8.89-1/4 a bushel - its highest level since Aug. 25.

December corn fell 0.6 percent to $3.91 after rising to its highest since Aug. 11, at $3.95 a bushel.

The U.S. Department of Agriculture (USDA) rated 61 percent of the soybean crop good-to-excellent, down from 63 percent a week ago and 72 percent a year earlier.

The agency's weekly report, which was issued after the market closed on Monday, rated 68 percent of the corn crop good-to-excellent - unchanged.

There is additional support for soybeans stemming from concerns that the USDA might lower its estimates of soy harvested acreage next month.

The market is awaiting monthly acreage data due on Wednesday from the USDA's Farm Service Agency that might signal whether it will adjust official acreage estimates in its Oct. 9 supply/demand reports. Analysts said the USDA could reduce estimates for both corn and soybean output.

Wheat fell nearly 1 percent to $4.96-1/2 a bushel, after hitting $5.03-1/4 earlier in the session, its strongest level since Aug. 26.

"There is a feeling the rise (in wheat) may have been overdone. It was mainly supported by short covering, not fundamentals. The USDA raised its stock levels in wheat," a European trader said, stressing that the contract had fallen below the psychological level of $5 per bushel.