US farmers may be treading on dangerous ground by setting course for their highest-ever cut in fertilizer applications, PotashCorp has warned.

The Canadian fertilizer giant said that the fall in US applications in the 2008-09 season may "significantly" exceed the current record cut of 15% in 1982-83.

However, farmers' crop ambitions had not dropped in tandem with nutrient use as they did 26 years ago, when plantings dropped by 40m acres.

"To put this reduction into context, it is now expected that US farmers will apply approximately the same amount of nutrients this fertilizer year as they did in 1983,"PotashCorp said.

"However, the current plantings include 37m more acres of corn and soybeans.

"This scenario is unprecedented in magnitude and unpredictable in consequences."

'Matter of science'

The group added that the drop in global nutrient use was unsustainable without threatening food supplies.

"Soil is the primary asset of every farm - and protecting soil fertility by replenishing nutrients is essential for sustainability and improved yields," PotashCorp said.

"To ignore proper fertilization - even for a season - creates the potential for significant food production shortages and higher crop prices.

"Crop nutrition is a matter of science, and with world population rising by more than 75m each year, logic dictates that more people will require increased food production."

PotashCorp made the comments as it announced a 52% fall in first quarter revenues and cut its full-year earnings forecast.