Nutrient application systems are designed to apply a relatively uniform amount of a fertilizer to agricultural fields. However, considerable variation in soil texture and other characteristics often occurs within and across production fields, which could have a major impact on fertilizer management strategies. Therefore, uniform application of a fertilizer over the entire field can be both costly and environmentally unsound. Due to their rugged and fool-proof design, crankshaft type piston pumps are widely used in agriculture. The on-the-go outlet flow of these pumps can only be varied by changing the drive shaft speed for each pump stroke setting. But only a limited range of flow rates can be achieved by changing the drive shaft speed. There is a need for an electronic controller, which can adjust the pump stroke on-the-go, for real-time, variable-rate application of crop nutrients. The Clemson “Electro-me-chanical controller for adjusting pump stroke on-the-go” was designed to replace the current manual stroke adjustment system on positive displacement piston pumps. This affordable system can be retrofitted on most John Blue - piston pumps for real-time adjustment of the pump stroke and can be controlled using pre-described position sequences (map-based) or real-time sensor commands (such as optical, pressure, and flow sensors) combined with fertilizer calculation algorithms. In addition, it can adjust pump stroke manually, using an eclectic dial from the tractor’s cab.