An active hydraulic down pressure system (100, 200, 300) is provided between implement rockshaft cylinders (112, 212, 312) and a load-sensed power source (130, 230, 330). However, to avoid a tractor starting difficulty, valve means are provided in a power beyond fluid line (144, 244, 344) to keep the fluid line (144, 244, 344) closed when starting the tractor. This valve means provides a hydraulic latching function that allows the load-sensed power source (130, 230, 330) to be activated and deactivated depending on the function of a selective control valve (132, 232, 332). The load-sensed power source (130, 230, 330) is activated when the rockshaft cylinder(s) (112, 212, 312) is fully extended and remains activated or latched when the selective control valve (132, 232, 332) is returned to neutral. The load-sensed power source (130, 230, 330) is deactivated or unlatched when the rockshaft cylinder (112, 212, 312) is retracted.
