An active hydraulic down pressure system for an agricultural implement having down pressure cylinder structure and operable in an automatically controlled down pressure mode, the system adapted to be coupled to a source of hydraulic fluid under pressure through a multi-position selective control valve connected between the source and the down pressure system, the selective control valve having a neutral, a raise, a lower and a float position, the system also including: a cylinder structure, an adjustable pressure valve, having an input and an output, connected between the selective control valve and the cylinder structure for maintaining down pressure of the cylinder structure at a preselected level, and a fluid line connected to the fluid output on the source and to the input of the adjustable pressure valve, the fluid line providing a source of hydraulic fluid under pressure to the adjustable pressure valve independently of hydraulic fluid under pressure from the selective control valve so that the selective control valve is operable in the neutral position and the float position while the implement is operating in the automatically controlled down pressure mode, a load-sense line extending from the output of the adjustable pressure valve to the source of hydraulic fluid under pressure, and a valve in the fluid line for opening and closing the fluid line to fluid flow, the valve operable to close the fluid line until the cylinder structure is extended and the valve operable to open the fluid line when the cylinder structure is extended and to maintain the valve in the open position when the selective control valve is returned to the neutral position whereby the system is operated in the automatically controlled down pressure mode with the selective control valve in the neutral position, characterized in that the system further comprises: a first pressure sensor positioned between the selective control valve and the adjustable pressure valve to detect fluid pressure and operably connected to the valve to close the valve when the fluid pressure reaches a predetermined level. a cylinder structure, an adjustable pressure valve, having an input and an output, connected between the selective control valve and the cylinder structure for maintaining down pressure of the cylinder structure at a preselected level, and a fluid line connected to the fluid output on the source and to the input of the adjustable pressure valve, the fluid line providing a source of hydraulic fluid under pressure to the adjustable pressure valve independently of hydraulic fluid under pressure from the selective control valve so that the selective control valve is operable in the neutral position and the float position while the implement is operating in the automatically controlled down pressure mode, a load-sense line extending from the output of the adjustable pressure valve to the source of hydraulic fluid under pressure, and a valve in the fluid line for opening and closing the fluid line to fluid flow, the valve operable to close the fluid line until the cylinder structure is extended and the valve operable to open the fluid line when the cylinder structure is extended and to maintain the valve in the open position when the selective control valve is returned to the neutral position whereby the system is operated in the automatically controlled down pressure mode with the selective control valve in the neutral position, characterized in that the system further comprises: a first pressure sensor positioned between the selective control valve and the adjustable pressure valve to detect fluid pressure and operably connected to the valve to close the valve when the fluid pressure reaches a predetermined level.