Abstract: A positioner for automatically positioning a farm implement, such as a sugar beet harvester, in line with rows of crops such as sugar beets and for automatically maintaining the height of the implement relative to the ground surface. The positioner includes a harness pivotal about an upright axis, and a pair of crop and ground level sensing shoes mounted to the harness pivotally to permit the trailing ends of the shoes to swing vertically and horizontally. Hydraulic controls respond to swinging of the shoes vertically (as when the height of the implement varies) and horizontally (as when the implement strays toward one side or the other of a crop row) and return the implement to its correct vertical and side-to-side alignment with the crop row.