A plow assembly adapted for connection to a tractor and including a plurality of plow units commonly connected to a beam which is inclined relative to the direction of travel of the plow assembly. A ground engaging steering wheel supporting a rear end of the beam. A steering system is provided for holding the steering wheel generally parallel to rear wheels on the tractor and for turning the steering wheel through an angle and opposite to a steering angle of the tractor to bring the plow assembly behind the tractor during turns. The steering system includes a linkage mechanism for proportionately reducing the turning angle of the steering wheel relative to the steering angle of the tractor thereby allowing tractor turns to exceed 35.degree. to either side of the direction of travel of the plow assembly. The plow assembly further includes a mechanism for quickly and easily changing the spacing between adjacent plow units as the plow assembly is pulled through the field and with minimal operator involvement.