Potash Corp. of Saskatchewan Inc. fell the most in more than two months after Canada blocked BHP Billiton Ltd.’s $40 billion hostile bid for the world’s largest fertilizer producer.

Potash Corp. dropped $5.21, or 3.6 percent, to $140.29 at 10:13 a.m. in New York Stock Exchange composite trading. The shares earlier tumbled 3.8 percent to $139.91, the biggest intraday decline since Aug. 11. The Saskatoon, Saskatchewan- based company gained 34 percent this year through yesterday.

“The stock is trading on its fundamentals” rather than speculation that BHP will increase its offer, Louis Meyer, a New York-based special-situations analyst at Oscar Gruss & Son Inc., said today in a telephone interview.

Canada yesterday denied approval of BHP’s $130-a-share offer for Potash Corp., saying the transaction wouldn’t provide a “net benefit” to the country. BHP has 30 days to appeal, at which point the government will make a final decision, according to a statement read by Industry Minister Tony Clement.

Clement declined to give additional reasons for the ruling.