The Canpotex marketing agency for three of the largest potash producers in Canada has agreed to sell one million tonnes of the crop nutrient in the first half of 2013 to a major Chinese customer.

Canpotex says the price will be $70 US per tonne lower than in the contract established in March 2012.

A Canpotex spokesman says the company doesn't disclose its contract pricing.

The agreement is with a subsidiary of Sinofert, China's largest integrated agriculture company and a long-time partner of Canpotex.

Canpotex is jointly owned by Potash Corporation of Saskatchewan, Agrium and Mosaic Corp., a U.S. company with major potash operations in Saskatchewan.

Potash is a major raw material for fertilisers that are used to stimulate plant growth, especially food crops.

Canada has one of the world's largest supplies of potash and exports much of it to other countries including the United States, China, and India.