A mixture of flooding and a summer heatwave have deprived the US corn harvest of setting a fresh yield record, officials have said, making a deeper-than-expected cut to their forecast.

The US Department of Agriculture slashed by 2.5 bushels per acre, to 162.5 bushels per acre, its estimate for America's corn yield this year.

The reduction, which was bigger than the 2.1-bushels-per-acre cut that analysts had expected, and took the yield estimate below last year's 164.7-bushels-per-acre figure.

The USDA attributed the reduction to a decline in the condition of the crop "throughout much of the central and western Corn Belt… mainly due to above normal temperatures and less than ideal soil conditions".

"Forecasted yields decreased from last month throughout much of the Corn Belt, Tennessee Valley, and Delta."

In Iowa, America's biggest producing state, "excessive rainfall early in [August] left many low-lying fields completely saturated, stunting growth and yellowing portions of the crop".

'Bullish' data

With US farmers sowing more corn this year, the downgrade was not quite big enough to strip the crop too of its claim for the production record, although, at 13.16bn bushels, its estimated lead over last year's high was cut to a slim 50m bushels.

"Demand is strong, which is helping create a bullish situation for corn," said John Anderson, economist at the American Farm Bureau Federation.

Indeed, the crop's stocks-to-use ratio - a key measure of market tightness, which in turn has a big impact on prices - was to fall to 8% on the latest estimates, the lowest since 1995.

"This puts us in a very tight supply situation," Mr Anderson said.

'Slow start'

Prices gained further support from a cut by the USDA to its forecast for global stocks too, by 3.6m tonnes to 135.6m tonnes, reflecting also weaker hopes for Europe's corn harvest.

"Spring weather was cooler than average, causing a slow start for corn and other grains," the USDA said.

"As a result, a portion of the corn originally intended for grain production will instead likely be cut for silage or for raw material for biogas fermenters."

US Commodities said: "With world carryout also shrinking… the corn numbers can be viewed as bullish."

Chicago corn for December delivery closed 1.6% higher at $4.78 ¼ a bushel, with the September lot adding 1.7% to a 23-month high of $4.64 a bushel.