U.S. corn futures retreated on Friday in a profit-taking setback following strong gains a day earlier and on a slightly wetter forecast that could support the Midwest crop's strong yield potential. Soybeans also eased after a four-day rally, though declines were limited by strong export demand, highlighted by government confirmation of another large sale to top importer China.

Forecasts for a greater chance of rainfall by late next week in the central and northern U.S. Midwest would benefit the kernel-filling corn crop and pod-setting soybean crop.

"A mostly dry pattern is expected through the middle of next week in the Midwest, but shower potential has improved in varying degrees," said Joel Widenor, meteorologist at Commodity Weather Group.

The best chance for rains would be in North Dakota, Minnesota, northeastern Iowa and the Great Lakes, he said.

"This could lower the driest parts of the Midwest from more than a third currently to 25 percent or less by the end of next week."

Some skepticism about a U.S. Department of Agriculture report on Thursday that showed fewer-than-expected corn and soy acres were planted this spring due to wet weather also pressured prices on Friday. The data, which will be updated monthly, may be less reliable than in previous years due to late spring planting and lagging crop development.

"The trade has a little more understanding today about the USDA data. People realize that the USDA numbers are very preliminary, whereas August is normally a solid month," said Rich Nelson, chief strategist at Allendale Inc.

Chicago Board of Trade December corn settled down 8-3/4 cents, or 1.9 percent, at $4.63-1/2 per bushel, after peaking at a two-week high of $4.75-3/4. Yet the contract ended the week up 2.3 percent, its first gain in five weeks.

November soybeans fell 6-1/4 cents to close at $12.59-1/4 a bushel, after hitting a three-week high of $12.72 earlier in the session. For the week, the contract rose 77 cents, or 6.5 percent, the second-biggest advance in its history.

Wheat futures retreated with sinking corn and on pressure from advancing wheat harvests across the Northern Hemisphere.

CBOT September wheat settled down 6-1/2 cents, or 1 percent, at $6.31 a bushel. The spot-month contract posted a second straight weekly decline as it hovered near a 14-month low of $6.23 posted earlier this week.