Fertilizer producer Mosaic ( MOS) posted a tremendous jump in quarterly earnings and offered an upbeat forecast for the current calendar year, but its shares surrendered their early gains and turned lower.

For the second quarter ended Nov. 30, Mosaic earned $394 million, or 89 cents a share, up from last year's $65.9 million and 15 cents a share. Sales for the period surged 44% to $2.2 billion from $1.5 billion in the same period the prior year.

Analysts were looking for a profit of 73 cents and a top line of just under $2.2 billion.

Higher average prices for phosphate and potash were large factors in the improvement. Net sales in the phosphates segment were $1.2 billion for the second quarter, a 61% year-over-year increase, while potash sales rose 23% to $431.6 million.

"Our second-quarter results demonstrate that Mosaic is leveraging the robust agricultural economy and delivering record results," CEO Jim Prokopanko said in a statement. He added that his company is on track "to deliver strong results in fiscal 2008 and beyond."

Mosiac said industry fundamentals should remain robust this year. "Phosphate and potash prices increased to even higher record levels at the end of 2007 and this momentum is anticipated to continue into 2008," the company said in a press release. "Further increases in grain and oilseed prices during the last several weeks have bolstered farm economics worldwide and solidify strong nutrient demand prospects for 2008."

Third-quarter sales volumes for Mosaic's phosphates and offshore segments will probably be below the second quarter, but that's in line with expected seasonal patterns.

Phospates volume was 2.28 million tons for the just completed quarter, down 1% on the year.

For the fiscal year, volumes in the phosphates business should be 8.6 million to 9.1 million metric tons. Potash volume will probably total 8.5 million to 9 million metric tons. Both forecasts are unchanged from Mosaic's prior targets.

Mosaic's stock had been up 5% earlier, but lately it was down 5.6% at $83.43.