A tractor has a control system configured for disengaging the clutch a first time, selecting a first transmission ratio of the change speed gearbox, engaging the clutch a first time to drive the PTO shaft determining the speed of the PTO shaft, disengaging the clutch a second time when the PTO shaft attains a predetermined first speed, selecting a second transmission ratio of the change speed gearbox and engaging the clutch a second time to drive the PTO shaft up to a desired second speed.
