CF Industries and OCI have canceled their $8 billion fertilizer merger in light of Treasury Department rules meant to discourage tax inversions, acquisitions in which U.S. companies lower their tax bills by domiciling overseas. CF is U.S.-based; OCI is Dutch. The combined company would have been the world’s largest publicly traded nitrogen fertilizer maker. The Treasury rules, announced in April, “materially reduced the structural synergies of the combination,” the companies say. CF will pay OCI a $150 million termination fee. The huge planned merger between Pfizer and Allergan was similarly scuttled by the new tax rules.