Objective In order to achieve accurate application of micro flow liquid fertilizer near rice root, an electromechanical flow regulating valve was designed and integrated with the developed pneumatic ejector fertilizer applicator to construct a variable application regulation system of liquid fertilizer.

Method The theoretical model of system mass flow rate was calibrated through experiments, and the transfer function model of control system was established. The structure, rules and initial parameters of the PID controller based on fuzzy reasoning (fuzzy PID control) were designed. The regulatory response capabilities of PID control and fuzzy PID control were compared through simulation experiment.

Result The simulation experimental results showed that the overshoot, adjustment time, and steady-state error of step signal response for fuzzy PID control were 0.12%, 2.51 s, and 0.007 respectively, which were lower than 42.9%, 4.44 s, and 0.010 of PID control, and suggested fuzzy PID control had better dynamic adjustment and stability. Under interference of pulse signal with amplitude of 0.5 and duration of 0.1 s, the adjustment time of fuzzy PID control was 0.61 s, which was less than 1.67 s of PID control, and had stronger anti-interference ability. The performance test showed that under ten-target mass flow rate condition, the absolute error of mass flow rate of fuzzy PID control was lower than that of PID control, with a control accuracy of 93.93% to 96.88%, which was higher than 90.00% to 95.21% accuracy of PID control. When the fertilizer amount changed, the average overshoot was 12.2%, and rise time, adjustment time and peak time of fuzzy PID control were 1.5, 10.7 and 1.7 s respectively, which were lower than 17.4%, 2.1 s, 13.3 s and 2.3 s of PID control.

Conclusion The variable rate application and regulation system for liquid fertilizer in rice based on fuzzy PID control has higher quality flow rate control accuracy and tracking performance, laying a foundation for the development of variable rate fertilizer equipment for liquid fertilizer in rice field.