Chicago Board of Trade corn futures closed firm on Thursday on tight stocks of corn and on spill-over buying from soaring soyabeans.
Positioning was noted ahead of the long holiday weekend.
CBOT futures markets will be closed on Good Friday, the annual Easter holiday.
Improved planting weather is seen for the US Midwest through next week and frosty temperatures early next week should cause no harm.
"This morning it looks drier in the Midwest late next week so there is a better planting outlook," said John Dee, meteorologist for Global Weather Monitoring.
Dee said temperatures would fall to freezing or a few degrees below in the northern Midwest early next week and warm up by the end of the week.
Position-squaring was noted ahead of the release on Tuesday of USDA's April supply/demand and crop production reports.
An average of analysts' estimates pegged the 2011/12 US corn ending stocks at 721 million bushels, which would be a fresh 16-year low.
Corn and soyabean prices may extend gains in the first half of this year on the back of tight supplies before easing the second half with new crops flowing into the market, a senior economist at the United Nations Food and Agricultural Organisation said.
USDA's weekly export sales report released on Thursday showed US export sales of corn last week at 1,122,700 tonnes, above estimates for 400,000 to 700,000 tonnes.
The July/December spread narrowed to $1.03 on Thursday from the $1.07-1/2 level at Wednesday's close which was the widest in 7 months.
The December corn/November soyabean ratio was 2.5.
Key support for the May contract at its 50-day moving average of $6.46-3/4 and resistance at the 200-day ma of $6.64.
The nine-day RSI was at 58.