Expectations that the US will cut its estimate of corn acreages by 500,000 acres have fuelled a 5% rebound in corn prices from a 2009 low.
The US Department of Agriculture said it was to collect "updated information" on American corn plantings for an updated crop production report to be released on August 12.
With existing plantings estimates based on data collected in early June, before rain delayed sowings, many investors believe the USDA announcement will herald a reduction in its corn acreage figure.
"People are saying that there will be a 500,000-acre cut in the next report," Brett Cooper, a trader at MF Global Australia, told Agrimoney.com.
"That is what's moving the market."
Vic Lespinasse, analyst at GrainAnalyst.com, said the trim could be even more severe, with some talk of a 1m-acre cut although "history suggests" a reduction of no more than 900,000 acres.
"If one excludes the flood year of 1993 and the severe drought year of 1988, 900,000 acres is the largest acreage change the USDA has made from their end June acreage report to their August crop production report," he said.
The August 12 report "will almost certainly show lower corn acreage, by how much being the only question".
Chicago corn for September stood 17.75 cents higher at $3.25 ¾ a bushel in late trading in Chicago. New crop contracts showed comparable gains.
Corn on Wednesday closed at its lowest since December, and down 30% since the beginning of June.
At the yield of 153.4 bushels per acre that the USDA is expecting, a reduction of 500,000 acres - equivalent to plantings in one of the smaller US corn states such as Maryland or South Carolina - would equate to a reduction of about 77m bushels in output.
However, Mr Cooper said he was "surprised" that corn, which closed on Wednesday at its lowest for seven months, had bounced so far, given that recent US weather had prompted talk of better yields.
"There is talk of yields of 160 [bushels per acre] plus," he said, adding that traders may come to view the current bounce as a selling opportunity.
By Mike Verdin