A tractor comprises a tractor frame, driven ground engaging device, and an electronic tractor controller. A baler comprises a baler frame coupled or connected to the tractor frame, a crop receiving device, a baling chamber, a bale size sensor associated with the baling chamber, and an electronic baler controller. The baler controller is operable to submit a halt signal to the tractor controller when a bale size signal provided by the bale size sensor indicates that a bale has reached a size equal to or exceeding a first predetermined size. The tractor controller is operable to command the ground engaging means to automatically halt the tractor when receiving a halt signal from the baler controller. A steering controller is connected to a swath position sensor and operable to automatically steer the tractor along a swath based upon the signals of the crop swath sensor and of the bale shape sensor such that a uniform bale shape is obtained.