A spraying system for an agricultural machine, comprises a spray ramp , a control unit and a liquid circuit itself comprising: - a pump comprising an inlet and an outlet , the pump being designed to suck a liquid through the inlet and to discharge the sucked liquid through the outlet , - discharge paths (14a-14g) each connected, upstream, to the outlet of the pump through a discharge valve (18a-18g) designed to open and close said discharge path (14a-14g), at least one of the discharge paths (14a-14g), called a main discharge path, comprising spray nozzles mounted to the spray ramp and designed to spray liquid onto plants of a field to be treated, the other discharge path(s) (14b-14g), called secondary discharge path(s), being devoid of spray nozzles mounted to the spray ramp , - a regulation valve , the regulation valve being connected, upstream, to the outlet of the pump and, downstream, to the inlet of the pump , the regulation valve being further designed to selectively regulate, as a function of said open discharge path(s) (14a-14g), a liquid flow rate in the open discharge path(s) (14a-14g) to a predetermined regulation flow rate, or a liquid pressure in the open discharge path(s) (14a-14g) to a first predetermined regulating pressure, the spraying system being characterised in that the control unit is designed to command the regulation valve to flow-regulate the open discharge path(s) (14a-14g), when at least one of the open discharge path(s) (14a-14g) is predetermined as being to be flow-regulated, and to pressure-regulate the open discharge path(s) (14a-14g) when none of the open discharge path(s) (14a-14g) is predetermined as being to be flow-regulated. - a pump comprising an inlet and an outlet , the pump being designed to suck a liquid through the inlet and to discharge the sucked liquid through the outlet , - discharge paths (14a-14g) each connected, upstream, to the outlet of the pump through a discharge valve (18a-18g) designed to open and close said discharge path (14a-14g), at least one of the discharge paths (14a-14g), called a main discharge path, comprising spray nozzles mounted to the spray ramp and designed to spray liquid onto plants of a field to be treated, the other discharge path(s) (14b-14g), called secondary discharge path(s), being devoid of spray nozzles mounted to the spray ramp , - a regulation valve , the regulation valve being connected, upstream, to the outlet of the pump and, downstream, to the inlet of the pump , the regulation valve being further designed to selectively regulate, as a function of said open discharge path(s) (14a-14g), a liquid flow rate in the open discharge path(s) (14a-14g) to a predetermined regulation flow rate, or a liquid pressure in the open discharge path(s) (14a-14g) to a first predetermined regulating pressure, the spraying system being characterised in that the control unit is designed to command the regulation valve to flow-regulate the open discharge path(s) (14a-14g), when at least one of the open discharge path(s) (14a-14g) is predetermined as being to be flow-regulated, and to pressure-regulate the open discharge path(s) (14a-14g) when none of the open discharge path(s) (14a-14g) is predetermined as being to be flow-regulated. <EOS>