CHICAGO, April 4 (Reuters) - Soybeans dropped on Thursday following lower-than-expected weekly export sales data from the U.S. Department of Agriculture (USDA), seasonally rising supplies from the South American harvest and falling soyoil prices.
Corn was flat as weekly export sales last week fell to the lowest in almost three months, but were still in line with trade estimates.
Wheat eased after Russian grain trader Aston denied that local authorities had halted some of its exports, lessening recent concerns about slowed shipments from the world's top wheat-supplying nation.
A weaker dollar, however underpinned the market.
Traders are monitoring weather in the U.S. Midwest ahead of corn planting that is due to ramp up over the coming weeks.
While rain and snow in the central corn belt are expected to boost soil moisture reserves, there are forecasts of higher temperatures later this month that could help field work.
Soybean futures neared Wednesday's one-month low as net U.S. export sales last week were short of market expectations at 194,220 metric tons, according to weekly USDA data released on Thursday.
Analysts said a daily USDA sales announcement of 152,404 tons in additional sales to Mexico offered little support as Brazilian shipments are accelerating and as season-to-date U.S. sales remain about 19% below last year.
CBOT May soybeans were down 7 cents at $11.75-1/4 a bushel at 12:29 p.m. CDT (1729 GMT), while May corn rose 1/2 cent to $4.57 a bushel.
CBOT May wheat dropped 1 cent to $5.55 a bushel.
In Russia, firmer prices, dry weather and reports of regulatory delays to export shipments have lent support to international wheat markets, but concerns about Russian supplies were tempered by signs that export flows remain large and Aston's denial. (Additional reporting by Gus Trompiz in Paris and Naveen Thukral in Singapore; Editing by Subhranshu Sahu, Sherry Jacob-Phillips and David Evans)
