Oct 10 (Reuters) - The world's biggest fertilizer producer, Potash Corp of Saskatchewan Inc , estimated quarterly profit would be below analysts' expectations as its customers delayed purchases due to near-term market uncertainty.

The U.S.-listed shares of Potash Corp were trading down 3 percent in extended trading after closing at $31.74 on the New York Stock Exchange.

Potash Corp now expects third-quarter earnings of 41 cents per share, below its earlier forecast of 45 cents to 60 cents per share.

Analysts on average expected earnings of 47 cents per share, according to Thomson Reuters I/B/E/S.

"The change primarily reflects lower than forecasted potash sales volumes late in the quarter," the company said.

Potash prices have slipped since mid-summer when Russian producer Uralkali OAO quit its export partnership with Belarus and said it would seek to maximize sales volumes.

In September, Agrium Inc also warned of lower potash volumes in the current quarter.

Rival Mosaic Co on Monday lowered its outlook for 2013 global potash shipments, citing weaker demand in India and a delay in settling a second-half contract between its export agency Canpotex Ltd and China's Sinofert Holdings Ltd.