Abstract: A supplemental downforce system is shown for a ground working implement having a frame and a plurality of ground engaging row units movably mounted to the frame for up and down movement relative to the frame. The downforce system includes at least one actuator between the frame and each row unit to apply an up or down force to each row unit. The actuators are assigned to one group of at least two groups of actuators. A control system controls the down force applied by each group of actuators separately so that each group of actuators is given the amount of supplemental down force that group of row units needs. In a closed loop feedback system, at least one row unit in each group of row units is equipped with a load sensor so that feed back of the soil reaction force on the row unit is supplied to the control system.