Bridgestone Americas Tire Operations LLC plans a $56.6 million upgrade to its Des Moines agricultural tire plant. The Polk County Board of Supervisors on Tuesday approved a $50,000 zero-interest loan and a $50,000 grant for the project. It is expected to create 72 new jobs at the plant, which is located north of Des Moines. The project includes $53 million in new manufacturing equipment to be installed and $3.6 million in remodeling to accommodate the upgraded equipment. The manufacturer is also on the Iowa Department of Economic Development Board’s agenda tomorrow to request state incentives. Bridgestone’s agricultural tire operations are based at the Polk County plant.