A system for agricultural spraying including a solution reservoir and primary pump for delivering fluid to a plurality of laterally spaced nozzles interconnected by supply conduits. A chemical reservoir and chemical injection pump are interconnected to the output of the primary pump through a mixer. Controllers for the primary pump and chemical injection pump are coordinated to run the pumps a predetermined time to fill each of the supply conduits from the chemical injection pump and primary pump so as to automatically prime the injection system.