The crop appears on course for a record yield of 8.40 tonnes per hectare, equivalent to 133.8 bushels per acre, the US Department of Agriculture said, in comments explaining its decision on Wednesday to lift its estimate for Argentine corn production this year by 22%.

A yield at that level would represent a 40% improvement on last year, when farms were struck by drought, and beat the current record of 8.04 tonnes per hectare set in 2006-07.

'Patchy process' 

However, much late-planted corn will require "ideal conditions" to complete its maturation process, the USDA said. Already delayed development meant many crops would be fit only for forage use.

And limited drying facilities could also pose "a problem" if cool and wet conditions delay the dry-down of the crop in the field.

"Output will depend on harvest weather," the department said.

The chill weather was already posing problems for crops in Buenos Aires province, where 10% of the crop in some fields was suffering poor pollination rates.

Three in a row

The USDA also highlighted that an upgrade of 2.0m tonnes to its estimate for South Africa's harvest had followed a farm tour last month, which noted crops in the core eastern production region on course for yields to match last year's record.

The crop's condition reflected plentiful rains, during a summer where the onset of the El Nino weather pattern had been expected to bring drought.

"This is the third excellent crop season in a row, which is rare for South Africa where seasonal rainfall is highly variable," the department said.