U.S. corn futures eased on Friday from an earlier five-week high while wheat declined for the first time in seven sessions on profit-taking before the weekend.
Soybean prices were narrowly mixed after falling in each of the previous three days, with old-crop months rising and new-crop contracts easing.
Trading volume was light and buyers were cautious ahead of the U.S. Agriculture Department's end-of-month reports on quarterly grain stocks and prospective plantings.
The market was "particularly looking at corn with some pretty high acreage numbers creeping out," said Brian Basting, commodity research analyst at Advance Trading.
"We have a long way to go to planting, but it's just enough to keep some buyers off balance," Basting said.
He said the Brazilian corn crop continues to have potential, with acreage up this year after last year's record crop.
Illinois-based Allendale Inc said Friday that U.S. farmers were preparing to sow 96.956 million acres of corn this spring, the second largest area since 1937 and slightly less than the 97.255 million acres planted last year.
Chicago Board of Trade May corn eased by 1/2 cent to $7.16 per bushel by 10:38 a.m. CDT (1538 GMT) after earlier touching a high of $7.18-3/4, the highest since Feb. 8. The contract was poised for a weekly gain of more than 1.5 percent.
CBOT May wheat fell 4-3/4 cents, or 0.7 percent, to $7.20 per bushel but remained on track for its largest weekly gain in eight weeks.
Wheat futures were lifted this week by robust export demand as well as strong demand from domestic livestock feeders struggling with high corn prices as U.S. supplies of the yellow grain were forecast to shrink to the lowest in 17 years by the end of the summer.
May soybeans rose 1-1/2 cents to $14.37 per bushel, but the contract was set to end the week down more than 2 percent in its steepest weekly break since early January.
New-crop November fell 4 cents to $12.55-3/4 a bushel, a considerable discount to nearby contracts due to expectations for more ample supplies.
Allendale Inc forecast U.S. soybean seedings this spring at 78.324 million acres, a record area and up 1.126 million from last year.
Gains in nearby soybeans were limited Brazil's record-large crop enters the market.
Premiums over Chicago futures prices paid for soybeans at Brazil's Paranagua port turned negative for the first time in the 2012/13 crop year on Thursday as the record harvest pressures prices and transportation delays crimp demand.
Brazilian soy was bid at 2 cents per bushel below prices on the CBOT at Paranagua, one of Brazil's two main grains ports along with Santos.
Brazilian dock workers postponed a 24-hour nationwide strike planned for March 19 to allow more time to negotiate with the government. The move eased concerns about worsening shipping delays as Brazil aims to export its record-large crop.