Mosaic Co., the Plymouth-based producer of fertilizer components whose business in potash was hit hard by the collapse of a commodity cartel in Eastern Europe last year, on Tuesday signaled an end to the collapse in potash prices.

In announcing its fourth-quarter results, Mosaic said its average selling price for potash was 30 percent lower than a year ago but had leveled out, bringing back customers who were holding back on orders until they perceived they could get the lowest price.

““Customers believe a bottom in potash prices has been reached and are now exhibiting improved confidence in their buying decisions,” Mosaic CEO Jim Prokopanko said in a statement. “In 2014, we expect record global shipments and improving producer operating rates. Our long-term constructive outlook for potash has not changed.”

In an interview with the Star Tribune, Prokopanko said that a potash sales agreement last month between China and Canpotex — a group of producers that includes Mosaic — was a critical. “The rest of the world has grown (in potash sales) except China and India,” he said. Those countries are two of the world’s largest fertilizer markets.

The China deal was “a message to the world” that the potash market had bottomed out and is now recovering, Prokopanko said. Mosaic also recently instituted a price increase on potash.

The decline in potash, which accounts for about one-third of Mosaic’s revenue, was driven by the collapse last summer of a cartel of commodity producers in Russia and Belarus whose collaboration propped prices for potash and other goods in parts of Europe and Asia.

The fall in potash prices also helped spook the market for phosphate fertilizer, Mosaic’s other big product. But phosphate has been recovering, too, and even stronger so far than potash. Mosaic had record phosphate shipments during the fourth quarter, and phosphate prices are up about 40 percent since the beginning of the year.

Lower prices for both goods constrained Mosaic’s financial results in the second half of 2013. For the just-ended fourth quarter, Mosaic reported a net profit of $128.9 million, or 30 cents a share, down from $615.7 million, or $1.44 a share, a year ago. Adjusted for one-time charges and gains, Mosaic’s profit amounted to 36 cents a share, below the 44 cents a share investors and analysts were expecting according to a survey by Thomson Reuters.

Revenue was $2.18 billion, down 7.8 percent from a year ago but above analysts’ expectations of $1.89 billion.

Revenue from potash was down 10.2 percent while revenue from phosphates fell 6 percent. Mosaic said it shipped record volumes of both products in the quarter.

Mosaic also announced a plan to buy back $1 billion of its shares.

The positive news about a rebound in phosphate and potash markets helped push up Mosaic’s stock by about 3 percent. It was trading at $48.27, up $1.45, at midmorning.