North American potash inventories at the producer level, a main indicator of market sentiment, edged up in December to their highest level since March, according to the world's top producer of the crop nutrient.

Potash stockpiles rose 2.8 per cent to 3.145 million tonnes, according to data posted on PotashCorp's website.

Inventories at the producer level now stand 37 per cent above the previous five-year average.

Spot potash prices have eased to roughly US$460 per tonne.

Potash supplies have swollen as top global consumers China and India delayed signing new supply contracts with Canpotex, the offshore marketing company owned by PotashCorp, Agrium and Mosaic Co.

Canpotex announced a six-month contract with China on Dec. 31.

Potash exports by the North American producers bumped up sharply in December over the previous month to 586,000 tonnes, but were still 20 per cent below the pace set a year earlier.

Domestic sales, mainly to the United States, were flat from a year earlier at 467,000 tonnes.

Three mines operated by PotashCorp, the world's biggest producer by capacity, are currently shut down temporarily as the company whittles down supplies.

The vast majority of the potash produced in North America is mined in Saskatchewan, where PotashCorp has its headquarters. -- Reuters