Chicago corn slid more than 1 percent on Tuesday to give up some of the previous session's gains, with a U.S. report indicating a better-than-expected condition for this year's crop.
Soybeans slid for a second session under pressure from an improved U.S. crop rating, while wheat fell for a fourth session amid plentiful world supplies.
The U.S. Department of Agriculture (USDA) in its weekly crop progress report rated 75 percent of the U.S. corn crop in good-to-excellent condition, unchanged from the previous week and better than last year's 73 percent. Analysts had expected a slight decline.
The good-to-excellent rating for the U.S. soybean crop was at 74 percent, up from 72 percent a week ago and 67 percent last year, the USDA said after the market closed on Monday.
"U.S. crop conditions still look strong, but the market continues to worry about dryness in July," said Tobin Gorey, director of agricultural strategy at Commonwealth Bank of Australia. "Forecasters say the U.S. upper Midwest will at least see widespread rain this week. Precipitation in the lower Midwest won't be as substantial though and more will be needed soon to support crop development."
Chicago Board of Trade most-active corn contract fell 1.3 percent to $4.24-1/2 a bushel by 1022 GMT, and soybeans lost 0.8 percent to $11.60-1/2 a bushel.
Wheat gave up 0.9 percent to $4.86-3/4 a bushel.
Corn rallied on Monday on worry over hot, dry weather hurting yields, especially in the Mississippi Delta, where corn is starting to pollinate, a key phase for determining yield.
Strong soybean demand is keeping a floor under prices. U.S. soybean processors likely boosted crush levels to a record high for the month of May due to stepped-up demand for soymeal because of problems with the South American crop, analysts said.
Some analysts expect the USDA to raise its U.S. soybean plantings estimate and lower its corn area forecast in a hotly anticipated June 30 acreage report.
Private analytics firm Informa Economics raised its estimate of U.S. 2016 soybean planted area to 83.8 million acres, up from its May forecast of 83.0 million and higher than the USDA's March figure of 82.2 million.
Informa cut its estimate of U.S. corn plantings to 92.6 million acres, down from 93.4 million previously and below the USDA's forecast of 93.6 million. Indonesia's wheat imports could climb 35 percent to a record 10 million tonnes in 2016 to replace corn for use as animal feed amid limited domestic supply, an industry group said on Tuesday.
Indonesia imports wheat from Australia, the United States and Canada, it said.