Mosaic Co.'s quarterly profit handily exceeded Wall Street estimates as the big fertilizer maker benefited from high prices for one of its key products and strong sales volume for another.

Plymouth-based Mosaic on Wednesday posted fiscal third-quarter net earnings of $542 million or $1.21 per share, more than double a year ago and ahead of the $1.07 per share expected by analysts.

Mosaic's sales of $2.2 billion topped last year's mark by 29 percent but were below analysts' forecasts of $2.34 billion.

The company's earnings were released after the market closed. In after-hours trading, Mosaic's stock was at $79.59, down 86 cents.

Operating earnings in Mosaic's phosphate fertilizer segment totaled $371.8 million, compared with $52.9 million in the same quarter last year. Mosaic primarily attributed the big jump to increased selling prices.

For the company's potash fertilizer business, operating earnings came in at $413.9 million, up from $326 million a year ago. Potash profits were pushed up by increased sales volumes and higher sales prices.

Fertilizer markets are getting a boost from record demand coupled with supply uncertainties, Mosaic said in a news release. "The company is running its plants at high rates to keep pace with demand, and potash inventories remain at historically low levels."

Mosaic is 64 percent-owned by Minnetonka-based Cargill, though the agribusiness giant is divesting its shares.