Mosaic Co., the fertilizer giant whose business was upended this summer by melodrama among Eastern European competitors, reported a 70 percent decline in third-quarter profit and said it expects to be under pricing pressure into next year.

The Plymouth-based company said Tuesday that it earned $124 million, or 29 cents per share, in the three months ended Sept. 30, down from $417 million, or 98 cents per share, a year earlier. Excluding one-time charges and benefits, Mosaic earned 51 cents per share, below analysts' estimates of 55 cents.

Revenue was $1.91 billion, down 28 percent from $2.65 billion a year ago. Analysts expected revenue of about $1.97 billion, according to Thomson Reuters.

"The current situation is primarily driven by good old supply and demand," Mosaic CEO Jim Prokopanko told analysts in a conference call. "Supply is increasing and shipments are temporarily soft."

Mosaic's stock closed Tuesday at $46.05, down 68 cents or 1.5 percent. The company's shares are down nearly 19 percent for the year as investors absorb a blow to its pricing dynamic.

Mosaic, the world's largest maker of phosphate fertilizer and leading U.S. producer of potash, forecast lower prices for both of its key products in the fourth quarter compared with the just-ended period.

Mosaic in September lowered its third-quarter production and profitability outlook, citing the impact on fertilizer markets of the July collapse of a Russian potash marketing cartel.

The world's leading potash producer, Russia's OAO Uralkali, backed out of a marketing agreement with its Belarusian partner, Belaruskali. That led buyers to delay making purchase agreements.

Staff writer Mike Hughlett contributed to this report.