Abstract: The zone tillage coulters on a drilling or planting implement are maintained at an essentially constant running depth by control apparatus that includes a programmed microprocessor-based controller and a hydraulic operating system that receives commands from the controller based upon inputs received from various sensors. One such sensor comprises a ground wheel which rides along the ground and swings up or down as changes in the terrain are encountered, such motions thus imparting voltage inputs to the controller which compares such inputs with previously selected data inputted by the operator. If the comparison results in a sufficiently large difference between the operator-selected data and the actual data coming from the sensor, the controller will cause a tongue cylinder to be actuated in the appropriate direction to buckle the tongue about a horizontal axis and thus either raise or lower the tongue and coulter gangs fastened thereto.