CF Industries has rejected a third bid from Agrium, its Canadian rival, as too low, saying it would better serve its shareholders by remaining independent.

The US fertilizer group said that Agrium latest offer, valuing CF at more than $4bn, "continues to substantially undervalue the company".

The $5.00 a share Agrium added to its bid was only $0.58 above the increase in CF's cash position in the first three months of the year, the statement said.

And although Agrium's latest offer was nearly 23% higher than its original bid, lodged in February, that was less than the average rise for shares in fertilizer groups since then.

CF said stock in its peer group had, on average, rebounded 37%.

'Superior value'

Stephen Wilson, the CF chief executive, said: "Agrium has not significantly changed the terms of its offer since it was first made and the board believes that the offer continues to substantially undervalue CF Industries."

CF's own growth plans, which include its own attempt at a takeover, of US rival Terra Industries, "will deliver superior value to stockholders", Mr Wilson added.

The statement was made after the close of New York markets on Friday, when CF shares closed up $2.07 at $79.75, nearly 10% shy of the value implied by Agrium's bid.

Agrium shares ended $1.26 higher at $48.18.