A supplemental down force system is shown for a ground working implement (10) having a frame (12) and a plurality of ground engaging row units (30A, B, C, D, E, F) movably mounted to the frame (12) for up and down movement relative to the frame (12). The down force system includes at least one actuator (100) between the frame (12) and each row unit (30A, B, C, D, E, F) to apply an up or down force to each row unit (30A, B, C, D, E, F). The actuators (100) are assigned to one group of at least two groups of actuators (100). A control system (98) controls the down force applied by each group of actuators (100) separately so that each group of actuators (100) is given the amount of supplemental down force that group of row units (30A, B, C, D, E, F) needs. In a closed loop feedback system, at least one row unit (30A, B, C, D, E, F) in each group of row units (30A, B, C, D, E, F) is equipped with a load sensor (108) so that feed back of the soil reaction force on the row unit (30A, B, C, D, E, F) is supplied to the control system (98).
