Chicago Board of Trade (CBOT) corn futures slid one per cent while soybeans eased half a percent on Friday. as investors squared positions after fund buying earlier in the week boosted prices, leaving each commodity vulnerable to a downward correction.
Wheat inched up in late trading on late week buying tied to short-covering, but traders said there was a lack of bullish momentum in the wheat market.
For the week, soybeans and wheat rose one per cent and corn rose 1.3 per cent.
Soybeans tumbled as the prospect of a larger U.S. planted area this year pressured prices that had run up on concerns about port congestion in Brazil and the fund purchases.
U.S. corn and wheat prices also fell as the market focus increasingly turned to the prospect that larger crops this year could alleviate tight supplies.
"It's technically overbought and due for a correction. A lot of the buying has been from funds and that has been pretty much exhausted for now," said Shawn McCambridge, analyst for Jefferies Bache.
Soybeans surged to a one-week high on Thursday, corn rose to a six-week peak, and the wheat market earlier in the week rose to its highest level in nearly a month.
"In corn there also has been a pickup in cash movement this week," McCambridge said.
Farmers had been holding off selling their cash corn supplies as they waited for higher prices. When corn began nearing six-week highs, they began selling some of their corn stocks.
"Wheat is still looking at a potential rebound in world production and now we're looking at good precipitation in the Plains. Crop prospects look a lot better now than they did over the winter," McCambridge said.
Another winter storm over the weekend is expected to bring welcome snowfall and moisture to a large portion of the U.S. Plains hard red winter wheat region and to portions of the U.S. Midwest corn and soybean belt.
CBOT May soybeans were down 8-1/2 cents per bushel at $14.40-1/2, May corn was down 6-3/4 cents at $7.26-1/4 and wheat for May delivery was up one cent at $7.29-3/4 (all figures US$).
Traders said position-squaring also was noted ahead of the release next Thursday of the U.S. Department of Agriculture's (USDA) March planting intentions and quarterly stocks reports.
Widely-followed analytical firm Informa Economics on Friday forecast 2013 U.S. corn planted acreage at 97.753 million, the most in 77 years and soybean plantings at record 78.457 million, above the previous record 77.451 million four years ago.
Dealers said the market continued to be underpinned by concern about port congestion in Brazil, although the calling off of a national port strike set for next week may help to relieve some of the pressure.
"Shipping delays continue at Brazil ports and some cargoes have been cancelled, offering some support to the market," Jonathan Lane, trading manager for merchant Gleadell, said in a market note.
Analysts said soybeans and corn were under additional pressure because of expected big plantings numbers for each in USDA's report next Thursday.
Some analysts are expecting 2013 U.S. soybean acreage at a record high and corn acreage the largest in 77 years.
"In soybeans, we look for new-crop acreage of 78.8 million, up from this crop year's 77.2 (million) and USDA's initial projection of 77.5 million acres," Deutsche Bank said in a report Friday.
Dealers also noted China is selling between one million and 1.5 million tonnes of state soy reserves to some crushers, to ease tight supply after port congestion in Brazil interrupted shipments to the world's top soy importer.
South American soybean production concerns have also waned, analysts said.
Argentina's current soy crop is seen at 51.3 million tonnes, more than a million tonnes below the country's all-time record crop, but far higher than the drought-hit 2011-12 season, the agriculture ministry said Thursday.
-- Sam Nelson reports on the CBOT futures markets for Reuters from Chicago. Additional reporting for Reuters by Colin Packham in Sydney, Valerie Parent in Paris and Nigel Hunt in London.