Near-record soybean and corn plantings in 2010 will support a jump of roughly one-quarter in US fertilizer applications, PotashCorp has said, warning of "agronomic consequences" if farmers skimp for another year.

The Canadian potash giant forecast that corn plantings would increase for a second successive year in 2010, although soybean sowings would fall back near to 2008 acreages.

While declining to detail the reasoning behind its forecasts, PotashCorp said they reflected "projected growth" in demand for the crops, and said that, even at $3.50 a bushel, farmers' margins from growing corn would be twice the average from 2000-05.

The group added that, with America's corn and soybean production "fed on potash", fertilizer demand would, in 2009-10, rebound sharply near to 2007-08 levels from the "unprecedented decline" last year.

Farmers cut back on applications of all the major nutrients - nitrogen, phosphate and potash – amid a decline in crop prices and a squeeze on credit.

Yield-loss threat

Growers could not continue "indefinitely" curbing fertilizer use "without agronomic consequences", PotashCorp added.

"Every time fertilizer is under-applied or skipped, soil nutrient levels are reduced and the odds of losing significant yields increase," the company said in a quarterly market report.

"The long-term need for sustainable crop production makes it essential that nutrients are replenished."

The group estimated that the level of potash removed from the soil, in the form of harvested crop, averaged more than 9m short tons a year from 2006-08, more than twice the level applied through fertilizer during the period.

The comments came shortly before Noerbert Steiner, the chief executive of German potash group K+S, said in an interview with Reuters that he was "seeing prices bottoming out at the moment".