Abstract: The tractor has a main frame, supported by a pair of steering/driving wheels, to which is fitted the engine and transmission. A pair of booms are pivotally mounted on the frame (or on a sub-frame pivotally connected to the frame) and are provided with castor wheels. The track between the castor wheels is selectively adjustable by hydraulic rams connected to the booms and the frame (or sub-frame). Agricultural implements may be connected to the frame, to the booms inside the wheelbase of the tractor or to a draw-bar interconnecting the booms.