Abstract: A tractor-mounted hitch is movable to control the working depth of an implement in response to control signals generated by a model reference adaptive control system. The control system senses draft force and rockshaft position and receives operator-controlled reference signals representative thereof. A model reference adaptive draft control signal is derived from a model error signal, an adaptive gain value and a compensated position feedback term. A position error control signal is also generated. One or the other of the control signals is used to control the implement, depending upon whether or not the implement is in the ground and depending upon the relationship of the control signals.