Spraying system for agricultural machinery, comprising a spraying boom and a liquid circuit itself comprising: - a first main tank configured to contain a treatment liquid, - a first pumping assembly comprising a first pump comprising an inlet and an outlet, the first pump being designed to suck up liquid through said inlet and to discharge the sucked up liquid through said outlet, - at least one first suction line (15a-15c) connected, downstream, to the inlet of the first pump, the or one of the first suction lines (15a-15c), called first main tank suction line, connecting the first main tank to the inlet of the first pump, - at least one first discharge line (16a-16d) connected, upstream, to the outlet of the first pump, the or one at least of the first discharge lines (16a-16d), called spraying line, comprising spraying nozzles mounted on the spraying boom and designed to spray liquid onto plants to treat, - a second main tank configured to contain a treatment liquid, - a transfer line connecting the first main tank and the second main tank with one another and comprising a pumping mechanism designed to suck up treatment liquid coming from the second main tank and to discharge the sucked up treatment liquid to the first main tank, the transfer line further comprises a first valve installed downstream of the pumping mechanism and designed to: - in a first position, place in communication the pumping mechanism with the first main tank, so as to supply the first pump and the spraying line(s) with treatment liquid coming from the first and second main tanks (13, 17), via the first main tank, and the spraying system being characterized in that: - in a second position, the valve is adapted to place in communication the pumping mechanism with the inlet of the first pump, while bypassing the first main tank, so as to supply selectively the first pump and the line(s) for spraying treatment liquid coming from the first main tank or treatment liquid coming from the second main tank. - a first main tank configured to contain a treatment liquid, - a first pumping assembly comprising a first pump comprising an inlet and an outlet, the first pump being designed to suck up liquid through said inlet and to discharge the sucked up liquid through said outlet, - at least one first suction line (15a-15c) connected, downstream, to the inlet of the first pump, the or one of the first suction lines (15a-15c), called first main tank suction line, connecting the first main tank to the inlet of the first pump, - at least one first discharge line (16a-16d) connected, upstream, to the outlet of the first pump, the or one at least of the first discharge lines (16a-16d), called spraying line, comprising spraying nozzles mounted on the spraying boom and designed to spray liquid onto plants to treat, - a second main tank configured to contain a treatment liquid, - a transfer line connecting the first main tank and the second main tank with one another and comprising a pumping mechanism designed to suck up treatment liquid coming from the second main tank and to discharge the sucked up treatment liquid to the first main tank, - in a first position, place in communication the pumping mechanism with the first main tank, so as to supply the first pump and the spraying line(s) with treatment liquid coming from the first and second main tanks (13, 17), via the first main tank, and the spraying system being characterized in that: - in a second position, the valve is adapted to place in communication the pumping mechanism with the inlet of the first pump, while bypassing the first main tank, so as to supply selectively the first pump and the line(s) for spraying treatment liquid coming from the first main tank or treatment liquid coming from the second main tank.