Fears of a potash price war triggered by a Russian company has sparked upheaval in the market for the key industrial fertiliser component and wiped 40 percent off the share price of German fertiliser maker K+S. K+S, which has annual sales of 4.0 billion euros ($5.3 billion), last week saw more than 15 billion euros shaved off its market value after Russia\'s biggest potash maker Uralkali abandoned a cartel-like system and said prices could possibly fall by 25 percent. Uralkali said it was willing to accept lower prices and that it expected the price of potash could fall to $300 (225 euros) per tonne by the end of the year from $400 in July. This sparked what analysts described as a \"Black Tuesday\" on the potash market and sent K+S stock spiralling. The plunge in K+S shares continued this week as ratings agency S&P put the company\'s debt rating on watch. On Tuesday, its shares closed down 8.1 percent to 15.92 euros, now having lost nearly 40 percent of their value since the Uralkali announcement. That left K+S the smallest company by capitalisation on the DAX, threatening its place on the index of 30 blue-chip stocks. S&P said that Uralkali, one of the lowest cost producers in the industry, was \"well positioned to withstand lower prices.\" In contrast, \"K+S will be in a more difficult position, given its much higher production costs,\" added the ratings agency. DZ Bank analyst Heinz Mueller said that the price of potash \"is the most important parameter for K+S\". When the price drops below $300 per tonne, K+S \"won\'t recover its costs\" and a capital injection will be necessary, said analyst Marc Gabriel at Bankhaus Lampe. Uralkali chief executive Vladislav Baumgertner has speculated the price war could push some rivals out of business. \"Consolidation will be a logical step in conditions where the price falls to a level of marginal producers,\" he told the Russian daily Vedomosti in an interview. K+S, based in the central German city of Kassel, tried Tuesday to reassure investors, pointing to the fact that it is also the world\'s top salt maker, and has a reliable revenue stream from the sale of road salt to melt snow. \"In contrast to our competitors, who are focused exclusively on potash, we have a robust second pillar to our operations with our global salt business, which follows different market conditions,\" chief executive Norbert Steiner said in a statement. Along with a wider product range, \"that makes us more robust in the event that competition intensifies,\" Steiner said. However, the company, which employs 14,000 people, acknowledged that salt sales would not prevent an erosion in profits, and said it was no longer standing by its previous guidance of a slight increase in operating earnings this year. Analysts are also worried because K+S has hefty investments, and is in the process of building a new three-billion-euro potash plant in Canada that is due to come on line in 2016.