Chicago wheat was on track for its biggest weekly fall in nearly six months on Friday after a forecast of a bumper harvest in the top U.S. wheat growing state.
Corn was poised to shed 4 percent over the week, while soybeans were set to fall for the first time in four weeks after traders cashed in on a recent rally linked to investment fund flows and adverse South American weather.
Wheat crop prospects in Kansas are well above average as rains last month should more than offset the impact of an earlier drought, scouts on an annual tour said on Thursday.
"The U.S. hard red winter wheat market was headed for indigestion at harvest anyway," said Tobin Gorey, director of agricultural strategy at Commonwealth Bank of Australia, commenting on a market that already has a sizeable surplus which he said would be even bigger if the forecasts prove to be correct.
Adding to the bearish picture, the USDA on Thursday said that weekly old-crop export sales of wheat totalled just 178,900 tonnes, down from 351,800 tonnes a week ago. New-crop wheat export sales of 140,000 tonnes fell below market forecasts.
The Chicago Board of Trade most-active wheat contract is down more than 5 percent, which would mark the biggest weekly loss since late November.
Prices were little changed on Friday as grain markets steadied after this week's losses, helped by a weaker dollar.
Investors were awaiting Canadian stocks data at 1230 GMT, and also looking ahead to Tuesday's monthly world report from the U.S. Department of Agriculture (USDA) that will feature its first supply and demand forecasts for 2016/17.
By 1052 GMT, the most active CBOT wheat contract was up a quarter of a cent at $4.63-1/2 a bushel. Corn was one cent higher at $3.74-3/4 and soybeans up three quarters of a cent at $10.13.
Both corn and soy fell on Thursday after a run-up in prices in the past month when the risk of drought damage to Brazil's corn crop and rain losses to the Argentine soybean harvest encouraged funds to cover short positions.
Traders were also monitoring news from China which has estimated its corn planting area will fall by more than a million hectares this year, the first drop in 13 years, as Beijing embarks on major agricultural reforms.
A sell-off in Chinese commodity markets, notably in steel, spread to soy products, with Dalian soybeans down 3 percent.