Norway’s Yara International is in talks with Deerfield, Ill.-based CF Industries about a merger that would create a $20 billion-per-year plant nutrient powerhouse. Yara and CF, the largest nitrogen fertilizer makers in the world and North America, respectively, caution that the talks may not yield a transaction. Yara had operating income of $2.5 billion last year on sales of $14.4 billion. It established a toehold in North America in 2008 with its purchase of Saskferco from Mosaic and the government of Saskatchewan. Last year, it bought Bunge’s Brazilian fertilizer business, and it is planning an ammonia plant in Freeport, Texas, with BASF. CF had operating income of $2.4 billion last year on sales of $5.5 billion. In 2010, CF purchased the fertilizer maker Terra Industries, beating out a rival offer from Yara.