Abstract: A fluid delivery system (10) is provided for delivering at least one chemical (26) onto a field in a desired concentration. A carrier fluid (67) is provided for diluting the farm chemical (26). The mixture is pumped through a spray boom (18) onto the field by a main fluid pump (74). The chemical (26) is delivered to the inlet port (76) of the main fluid pump (74) by a chemical pump (54). The chemical pump (54) is operated by a variable speed stepping motor (56). The speed of the stepping motor (56) is controlled by a speed sensing wheel (88) to provide a uniform concentration of chemical on the field independent of vehicle speed. The motor speed is also controlled by a thumbwheel switch (116) to deliver a desired concentration on the field compensating for drive vehicle wheel slippage. The motor speed is also adjusted to calibrate the delivery concentration to the nozzle pattern through calibration switches.