Next week's influential US plantings report may have a joker in the pack – a larger-than-expected overall crop acreage, Rabobank analyst Luke Chandler has warned.

While investors may be right in expecting the report to show that US farmers have sown less wheat and corn than previously thought - and more soybeans - the recovery in crop markets may have prompted farmers to have second thoughts of leaving large acreages unproductive.

Prices of soybeans and wheat rose by up to 31%, with corn adding 19%, since the last official US planting estimates in March, which forecast farmers sowing 7.8m acres fewer than last year.

A fall in plantings of major crops – comprising as barley, corn, cotton, oats, sorghum, soybeans and wheat - at this level would be the biggest in 19 years.

"However, such a sharp rally in prices will logically have encouraged US farmers to bring a percentage of these unallocated acres into the 2009-10 production mix," Mr Chandler said.

"Some historical evidence supports this development, with US farmers planting more than they had indicated in March in seven out of the past 10 years."

Delay factor

Analysts are currently expecting Tuesday's plantings report to show a drop of a little over 1m acres, to 84.0m acres, in US Department of Agriculture estimates of US corn plantings, with wheat sowings pegged nearly 400,000 acres lower at 58.2m acres.

Soybean plantings are expected to come in at a record 78.1m acres, 2.1m acres higher than the USDA's previous forecast, a poll for Reuters, the news agency, showed.

Informa economics last week pegged plantings at 78.9m acres, with corn sowings put at 83.1m acres.

Besides the soybeans' soaring price, spurred by the prospect of the lowest US stocks since 1977, farmers have been encouraged to sow beans by weather-induced delays which meant some potential corn plantings would have missed the optimum window.