Agrium Inc. raised its takeover offer for rival fertilizer maker CF Industries Holdings Inc. to about $4.52 billion, four days after CF sweetened its own unsolicited bid for Terra Industries Inc.

"This is Agrium's best and final offer," the Calgary- based company said today in a statement. The bid values CF at $92.99 a share and marks the third time Agrium has raised the cash portion of its offer since its first proposal on Feb. 25. CF has rejected Agrium's previous offers.

Agrium's new offer focuses attention on a Nov. 20 vote by Terra shareholders on whether to elect an alternative slate of three directors backed by Deerfield, Illinois-based CF. Agrium extended the expiration date of the bid until midnight Nov. 18 in New York.

"If CF doesn't win at Terra's annual meeting, Agrium's potential for acquiring CF goes way up," Malcolm E. Polley, chief investment officer at Stewart Capital Advisors LLC in Indiana, Pennsylvania, said in an interview before Agrium's announcement. Polley manages about $1 billion, including CF and Terra shares and Agrium debt.

Terry Huch, a CF spokesman, didn't immediately respond to messages seeking comment.

CF fell $6.62, or 7.7 percent, to $79.77 at 8:13 a.m. in trading before the regular open of the New York Stock Exchange. The shares gained 76 percent this year before today.

Agrium Rises

Agrium climbed $1.57, or 3.3 percent, to $49.56 in early New York trading. Terra rose $2.06, or 5.8 percent, to $37.60.

Agrium has been at a disadvantage because earlier this year it missed an opportunity to nominate directors at CF's annual meeting, Polley said.

"Agrium just hasn't had the leverage to put the pressure on CF," Polley said.

CF has rebuffed Agrium's previous offers as too low.

CF boosted its takeover offer for Sioux City, Iowa-based Terra on Nov. 1 to $32 in cash and 0.1034 of a CF share for each share of Terra, valuing Terra at $4.07 billion at Nov. 3 closing prices.