Soybeans edged higher before a meeting next week between negotiators from the United States and China as the countries seek to end their year-long trade war. Wheat prices were lower.
The most-active corn futures on the Chicago Board of Trade were down 0.35% at $4.25-3/4 a bushel at 1037 GMT.
The US Department of Agriculture reported export sales of old-crop US corn in the week to July 18 at 121,200 tonnes, down 59% from the prior four-week average.
"Weekly exports for corn as much on the old as on the new campaign have been disappointing, weighing on prices," analysts at Agritel said in a market note.
Dealers said the market remained anxious, however, about the impact of hot, dry weather across the United States, threatening production in several key growing regions.
"Warmer, drier conditions will not be what at least some of these crops need," said Tobin Gorey, director of agricultural strategy at Commonwealth Bank of Australia.
"The consequence is that the market is more likely to be cutting US corn production forecasts."
Very hot and dry weather could return to the US Midwest in the next two weeks, particularly in parts of producing states Illinois, Iowa and Indiana, Commodity Weather Group said.
The most-active soybean futures on the Chicago Board of Trade were up 0.2% at $9.01-3/4 a bushel.
Dealers said the market had derived support this week from hopes that there may be a thaw in trade relations between the United States and top soybean buyer China, with negotiators set to meet next week.
"Operators will remain cautious regarding the next meeting between China and the US awaited at the beginning of next week in Shanghai," Agritel said.
Wheat prices declined. The most-active CBOT contract fell 0.75% to $4.96 a bushel while December wheat on Paris-based Euronext lost 0.55% to 179.75 euros a tonne.
Dealers said the wheat harvest in western Europe had made rapid progress this week although rains were seen slowing it over the weekend.
FranceAgrimer said the French harvest was 63% complete, as of July 22, up from 33% a week earlier.
Prices remained underpinned, however, by a downgraded crop outlook in top exporter Russia.
SovEcon lowered its forecast for Russia's wheat exports in the new 2019/20 marketing season by 6.2 million tonnes to 31.4 million tonnes.