UPDATE 5-Potash sector rocked as Russia's Uralkali quits cartel
* Uralkali exits Belarus venture after "deadlock"
* Leaves Canpotex as world's top potash exporter
* Expects prices to fall to $300 a tonne from $400 a tonne
* Shares in North American potash firms sink
* Uralkali's shares plunge 19 pct
By Polina Devitt and Natalia Shurmina
MOSCOW, July 30 (Reuters) - Russia's Uralkali quit one of the world's two big potash cartels on Tuesday, heralding a price war for the key crop nutrient and pummelling the shares of companies that produce it.
The break-up of the Belarusian Potash Company (BPC), a joint venture with Belarussian partner Belaruskali, leaves North America's Canpotex as the dominant potash export venture.
It could lead to cancellations of projects by rivals as the industry weighs the effect of lower prices, but may bring better deals for farmers. Continued...