Abstract: An appaatus is provided for automatically longitudinally shifting a horizontal transverse tool bar and the tillage unit or units supported therefrom relative to the lift hitch of a tractor from which the tool bar is supported responsive to crop row sensing structure sensing misalignment of the tillage unit relative to an associated crop row whereby to reestablish proper alignment of the tillage unit relative to the crop row and the crop row position sensing structure is adjustable for crop row width, elevation of the sensing structure relative to the tillage unit and also in a manner to adapt the crop sensing unit for sensing the stems or stalks of a row crop or opposite sides of an earth ridge in which a row crop is growing or is to be planted.