FRANKFURT, Germany » The U.S. seedmaker Monsanto agreed to a $57 billion buyout offer from Germany’s Bayer in a deal that would create a global agricultural and chemical giant.

The deal comes with record harvest driving crop prices to painfully low levels for farmers.

It was the third time in four months that Bayer returned with a richer offer to sell the acquisition to Monsanto, and hopefully, its shareholders.

Including debt, the deal is valued at $66 billion. If approved, Monsanto will continue to be based in St. Louis.

Bayer said today that it would pay Monsanto shareholders $128 per share — in cash. That represents a 44 percent premium over Monsanto’s closing price on May 9, the day before a proposed deal was announced.

The deal must still get the nod from both Monsanto shareholders and regulators, who in the U.S. have recently rejected a pair of megadeals in the health sector.

Signaling its confidence that it would be able to push the deal through, Bayer as part of negotiations told Monsanto that it would pay a $2 billion break-up fee if it falls apart.

Bayer said the transaction brings together two different but complementary companies. Bayer makes a wide range of crop protection chemicals that kill weeds, bugs and fungus, while Monsanto is known for its seeds business and the weedkiller Glyphosate.

Bayer, based in Leverkusen, said the companies’ combined agriculture business would keep its seeds business and North American business headquarters in St. Louis, where Monsanto is currently based.

Bayer initially offered $122 per share, then $125 per share, before the companies agreed to a final per-sale sale price of $128.

Monsanto Chairman and CEO Hugh Grant said the deal “represented the most compelling value for our shareholders, with the most certainty through the all-cash consideration.”

Bayer said it would raise the cash to pay for Monsanto by issuing debt and $19 billion in equity, including a mandatory convertible bond and a rights issue.

Bayer shares rose 3 percent to 96.11 euros. Shares of Monsanto, which are up 8 percent this year, rose 77 cents, less than 1 percent in early trading.