Fertiliser prices: Rich in potassium POTASH has rarely seen such excitement. Even among fertilisers, it struggles for top billing. The global markets for phosphates and nitrogen outrank potassium, of which potash is the most common form. But this week's announcement that Uralkali, a Russian giant producing around a fifth of world supplies, was quitting a price cartel with a big Belarusian producer thrust the commodity into the public eye. Some likened the move to Saudi Arabia leaving OPEC. Potash producers are generally quiet but profitable. A $40 billion bid for Canada's PotashCorp by BHP Billiton in 2010 was the last time the stuff hit the headlines. BHP liked the look of a bulk commodity that was easy to transport and promised steady growth as the world added ever more mouths to feed. The deal fell through but BHP, Vale and other miners still plan big potash projects. They have been encouraged by margins of up to 75%. Production is concentrated in a few mines in a handful of countries. This helped producers get together to control output and keep prices high. Two marketing groups, BPC, which included Uralkali and a big Belarusian miner, and Canpotex, which sets export quotas for North America's three large producers, controlled over two-thirds of global supply. Uralkali's sudden decision to leave BPC, boost output and sell its potash on the spot market, rather than at prices pegged to annual negotiations with China, sent its shares plunging. But Uralkali has the world's lowest production costs at around $60 a tonne; its mines are in the middle of nowhere, meaning there are few barriers to expanding output. So it has the most to gain among big producers by boosting output. Higher-cost producers in Europe and Canada face tumbling profits to match diving share prices. Prices for potash could fall from $400 a tonne to $300 by the end of the year. Uralkali's move will cost the industry in the medium term, but prices will not collapse. Plans for pricey new mines are sure to be delayed or abandoned, constraining supply. Farmers, on the other hand, should benefit if prices are at last determined by the market.