Well, it finally happened. After well over a year of rumor and innuendo, BHP Billiton (NYSE: BHP) has made a move on fertilizer king PotashCorp (NYSE: POT). The Australian mining giant's offer: $130 per share -- all to be paid in cash.

We've witnessed BHP's hunger for potash grow over the past several years. In 2008, the company bought out its partner in the massive Jansen project, which may be the world's biggest potash mine when it comes online. BHP also snapped up junior explorer Athabasca Potash earlier this year, expanding its foothold in the mineral-rich Canadian province of Saskatchewan. All of that proved a prelude to today's takeover attempt, at a purchase price approaching ExxonMobil's (NYSE: XOM) valuation of XTO Energy.

PotashCorp's board of directors is having none of it. Not only did these folks disclose their rejection of the proposal with the usual language about substantial undervaluation and opportunism on the part of the acquirer (shades of CF Industries' (NYSE: CF) three-way tussle with Terra Industries and Agrium (NYSE: AGU) there), but PotashCorp took the extra step of putting a poison pill in place. Oh, sorry -- I mean a "shareholder rights plan."

PotashCorp shareholders are not crazy to bid up the shares above the level offered by BHP. As we saw with the long, drawn-out Terra takeover, these bouts can go many rounds. BHP must be prepared to pay well over $130 per share. The company could theoretically build another PotashCorp organically, but it would take decades. A takeover would give the megaminer an instant commanding position in the industry -- estimated at about 30% by one analyst quoted in The Wall Street Journal today.

One thing I do object to is the pop in shares of a company like Intrepid Potash (NYSE: IPI). Just because PotashCorp is in play doesn't mean every company that produces the fertilizer suddenly has a target on its back. While Intrepid Potash is nowhere near as egregiously overpriced as at the time of its IPO, I still don't think it deserves the bump today, so I've rated it to underperform the market over the near term in Motley Fool CAPS. Let your fellow Fools know which fertilizer company you favor in CAPS or in the comments section below.

Fool contributor Toby Shute doesn't have a position in any company mentioned. Check out his CAPS profile or follow his articles using Twitteror RSS. The Fool owns shares of ExxonMobil. The Motley Fool has a disclosure policy.