An improved belt tensioning system for an agricultural round baler that temporarily bypasses a bale density, belt tension increasing system while the baler tailgate is moved out of a closed position thereby allowing the tailgate to be opened without encountering resistance form the belts and the belt tensioning system. Bypass operation is coordinated with the tailgate position so that the bypass is not activated when such activation would frustrate operation of the belt tensioning system. In balers equipped with a belt tensioning pre-tensioning system, the bypass operation is further coordinated with the pre-tensioning system to maintain proper pre-tension function.