Rising fertilizer and seed costs will deter farmers from fulfilling the jump that officials have forecast for US spring crop sowings this year, with soybean acres set to drop, broker Allendale said.

The Illinois-based broker, following a survey of growers, estimated US corn plantings at 91.3m acres this year, 700,000 acres fewer than the US Department of Agriculture has forecast.

Soybean seedings will come in at 77.2m acres - 800,000 acres down on the USDA's initial estimate and 200,000 acres less than last year's total, depressed by relatively low profitability compared with corn.

Corn's returns were seen $188 an acre higher than soybeans' this year.

Overall, farmers will plant some 1m acres less to major crops than the USDA has forecast, Allendale said, estimating that some of the disappointment in corn and soybean numbers would be offset by a bigger-than-expected rebound in wheat plantings.

Soaring costs

Growers' reluctance to plant corn and soybeans fence-to-fence, which some analysts believe is necessary to ensure any replenishment of thin stocks, reflects the raised prices of sowing crops, which on Allendale estimates were $685 an acre for corn and $505 an acre for soybeans.

"Sure, it pays to plant corn when prices are at current levels. But from the producer's mentality, they are used to spending $400 an acre.

"They are resistant to taking on so much debt this early in the season."

Raised fertilizer and seed costs were particularly worrisome to farmers, Mr Nelson said.

Data earlier this week from PotashCorp, the world's biggest fertilizer group, showed potash prices up by some 14% over the past year, with ammonia prices up by roughly 50%, and phosphate values near-doubled.

Sell the rumour, buy the fact?

Allendale's report comes in the run up to a March 31 report at which the USDA will unveil more detailed sowings estimates, in a report viewed as one of the key events of the farm commodities year.

Indeed, the prospect of a jump in sowings, particularly for corn, has been attributed as a major reason for a weakening in crop prices over the last month.

"The market could be setting itself up for a sell-the-rumour, buy-the-fact mentality for the upcoming March 31 report," Jon Michalscheck at Benson Quinn Commodities said.

Purdue University has estimated the variable costs of sowing corn – including factors such as fertilizer, seed, pesticides and fuel - at about $400 per hectare on average land, roughly twice that for soybeans, with the bill for wheat planting at $181 per acre.

These figures are 10-20% higher than a year ago.