A working vehicle such as an agricultural tractor may be used as a source of tractive power and/or power take-off (PTO) power, depending upon the application.  In the case of a tractor configured as a front end loader, a bucket or other attachment is used to push or lift various objects.  Ballast at the rear of the tractor is recommended for more stable and productive use of the front end loader. 
One type of ballast is in the form of wheel weights which are attached to the rear wheels, typically radially within the wheel rim.  Another type of ballast is fluid, such as calcium chloride or other suitable fluid, which is injected into the inner tubes within the rear tires.  A further type of ballast is a ballast assembly which is carried by a pair of lower lift arms on a 3 point hitch assembly at the rear of the tractor.  Examples of such ballast assemblies are disclosed in U.S. Pat.  No.  6,533,319 (Denby et al.)  and U.S. Pat.  No.  4,664,404 (Schultz), which are each assigned to the assignee of the present invention and incorporated herein by reference. 
Although advantageous for counter-balancing a load on a front end loader of a tractor, a ballast assembly as described above which is carried by the lower lift arms of a 3 point hitch assembly may interfere with use of the drawbar and/or PTO shaft at the rear of the tractor. 
What is needed in the art is a ballast which effectively counter-balances a load on a front end loader of a tractor, while at the same time not interfering with use of the drawbar and/or PTO shaft at the rear of the tractor.