Development and performance evaluation of a control system for variable rate granular fertilizer application

•Variable rate application (VRA) of agricultural inputs is essential for optimum crop yield.•This study was conducted to develop a control system for VRA of granular fertilizers.•The manual fertilizer rate adjustment system of a seed drill was modified to an automatic control system.•The overall error of the developed VRA system was ±2.6%. A study was conducted to develop a control system for variable rate application (VRA) of granular fertilizers and evaluate its performance. By the use of a microprocessor, a pneumatic cylinder and a rotary shaft encoder, the manual mechanical fertilizer rate adjustment system of a seed drill (SOLA TRISEM 294/R ESP, Model: 37193 TIPO250) was modified and transformed to a real-time automatic control system. Laboratory based tests were conducted to evaluate the developed system performance in automatically applying the predetermined desired application rates at different ground speeds, which were within the range of 3–12 km h−1. Linear regression and ANOVA tests were among the measures used to assess the accuracy of the developed system. Results of this study revealed that the developed system enabled an efficient automatic setting of the desired fertilizer application rate. The investigated operating speeds showed no significant effects on the performance of the system (P > F = 0.7968). In addition, the system exhibited an overall application rate error (difference between desired and actual application rate) of ±2.6%. The response time of the developed system was found to range between 6 and 11 ms for a change of one kilogram in the application rate.