By Alistair MacDonald in Toronto and Eyk Henning in Frankfurt 

An attempt by Canada's Potash Corp. to buy rival miner K+S AG and create a dominant potash player in the Americas faces likely pushback from the German company and regulatory hurdles.

A tie-up between two of the world's largest potash miners would create a company capable of controlling up to 30% of the global market just two years after the collapse of a global cartel system that had helped regulate prices of this key agricultural commodity sent potash prices sharply lower.

But some analysts say a deal could be nixed by German federal regulators, who stopped a similar takeover attempt in 1997.

Many analysts saw Potash Corp.'s approach as being driven by a desire to re-establish greater control over a market once dominated by two large trading groups.

Potash Corp. is "trying to re-establish its influence through controlling more tons in the hope of trying to raise prices around the world," said Joel Jackson, an analyst at BMO Capital Markets.

A combination would control 52% of the North American potash market and 42% of European supply by 2017, according to data from Scotiabank.

"There is a recognition that the industry is at an inflection point where there is a lot of supply coming," he said.

As new mines come into production during the next five years, supply is expected to surge. Unless demand, especially in China and India, increases as sharply as was expected when companies invested in expansion, prices could suffer further.

K+S, Germany's largest miner, said on Thursday that Potash Corp. informally approached its board, a move the Saskatoon-based company confirmed later. Potash Corp. offered just over EUR40 ($44.80) a share in cash, according to a person familiar with the matter.

That person said the German company is likely to reject what would be the largest mining deal since 2012 because it undervalues the dominant position the two could achieve in North America, where Potash has major mines and K+S is developing a mine that could produce some 2.9 million metric tons of potash a year by 2023.

People close to K+S said a combination with Potash Corp. could yield $370 million in annual synergies by shifting production from K+S's costlier German mines to Potash's underused Canadian sites, and by increasing the pricing power of the combined company on the global market.

The people close to K+S said synergies would add around EUR18 to K+S shares, which were trading at EUR27 before the news of a potential transaction broke Thursday, meaning K+S is looking for at least EUR45 a share.

People close to both companies are privately playing down the possibility that antitrust concerns could derail a deal.

But Many analysts say the combined market share in North America and in other markets including Germany mean that German regulators would likely reject the combination. The German Cartel Office rejected a 1997 attempt by Potash Corp. to take over K+S, after the company had been spun off by BASF SE.

Such a combination would have taken away a potential source of competition to K+S's dominant position in Germany, the Cartel Office said in a report at the time.

"At the same time, the global oligopoly would have tightened further and K+S would have been incorporated into [Potash Corp.'s] pricing policy for the world market," the report said.

The Canadian offer for K+S comes as the potash market remains in flux following the July 2013 collapse of an informal cartel system that had helped shape the global price of this $22 billion market. The end of that system sent the price of potash about 25% lower and led potash miners' profits to decline sharply.

The miners, including Potash Corp., that formed the two trading groups often described as cartels say they didn't act to set prices and weren't cartels. They said the groups just marketed, sold and transported the potash.

Analysts suggested Friday that Potash Corp. could seek to close down K+S's North American production, taking supply out of the market and boosting the price of the fertilizer, which strengthens plants and makes them more resistant to disease.

"If Potash Corp is successful in closing some supply...then all potash-levered equities should rejoice," Scotiabank said in a note.

If Potash Corp. doesn't shut the mine, then it would at least have more control over the supply and reap the benefits of its sale by controlling a mine that is set to open in its home base of Saskatchewan.

Analysts also said that Potash Corp could look to close down some of K+S's high-cost German mines. K&S is considered to have among the highest costs among the major producers, and had a cash cost of around $230 for every metric ton of potash it produced in 2013, according to Scotiabank. Potash Corp. is expected to mine every metric ton at $95 this year.

Mine closures, though, will likely stoke political opposition in Germany.

Volker Bouffier, premier of Hesse, the region where K+S is based, said on Friday that "jobs musn't be at risk," adding he offered K+S's chief executive support in protecting jobs.

Outside of oil, potash is among the most politically charged of commodities, given that some governments see it as a strategic asset. In 2012, Potash Corp.'s attempt to buy Israeli Chemicals Ltd. was thwarted by the Israeli government. Two years earlier, the Canadian government stopped BHP Billiton from buying Potash Corp itself.

Potash Corp. is expected to mine around 9.2 million metric tons of potash this year, according to Scotiabank, with K+S producing around 3.2 million metric tons. A merger would give the combined company almost 27% of global potash capacity by 2017, when both companies are set to complete new mines. Adding K+S to the production from the Canpotex trading group that includes Potash Corp. and two other miners would give the combined entity almost 44% of the world's potash capacity by 2017.

Analysts believe that Potash Corp. would also try to spin off the salt business of K+S should it succeed in a deal.

Ulrike Dauer in Frankfurt contributed to this article.

Write to Alistair MacDonald at alistair.macdonald@wsj.com and Eyk Henning at eyk.henning@wsj.com

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