CF Industries Holdings rejected rival fertilizer producer Agrium Inc.’s increased $4.52 billion takeover offer, saying it “substantially” undervalues the company.

Agrium’s offer “is not in the best interests of CF Industries and its stockholders,” Deerfield, Illinois-based CF said today in a statement.

Agrium, based in Calgary, boosted the cash portion of its bid for CF to $45 a share from $40 yesterday. CF shareholders also would receive one of Agrium’s U.S. shares, valuing CF at about $92.99, based on the shares’ closing prices the day before the offer was made.

“Agrium’s latest revised offer is very far from compelling,” CF Chief Executive Officer Stephen Wilson said in the statement.

At stake is whether CF or Agrium will become the world’s second-largest publicly traded maker of nitrogen fertilizer, which farmers use to increase crop yields. Agrium, also the largest retailer to U.S. farmers, announced its takeover plans for CF in February. CF, which also produces phosphates, has been trying to buy Terra Industries Inc. since January.

Agrium said today in an e-mailed statement its offer for CF is “far superior to any alternative articulated by CF, and we continue to be disappointed by their lack of engagement.”

CF increased its hostile bid for Sioux City, Iowa-based Terra on Nov. 1 to about $4.02 billion, based on CF’s closing share price yesterday. Terra rejected that offer on Nov. 4.

CF Industries declined 85 cents, or 1.1 percent, to $79.05 at 4:15 p.m. in New York Stock Exchange composite trading. The shares have gained 61 percent this year.

Agrium increased 67 cents, or 1.3 percent, to C$53.94 on the Toronto Stock Exchange. Terra rose 10 cents to $36.10 in New York.