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Fertilization stability is an important index to evaluate the performance of variable rate fertilization system. In order to solve the problem that the precision of fertilization is reduced due to obvious fluctuation during fertilizer discharge with external trough wheel type fertilizer drainer. A piecewise PID control method using fertilizer flow rate as feedback value was proposed. And a high-precision fertilizer flow control system of fertilizer planter was designed. The system regarded the real-time fertilizer flow value collected by the fertilizer flow detection module as the feedback value of the fertilizer flow controller in the vehicle terminal. Controller calculated output based on target and real-time fertilizer flow, and sent to fertilizer motor through USB to CAN module. Accurate control of fertilizer flow rate was realized. Fertilizer application test stand was built. Mathematical model between fertilizer and accumulative value of capacitance was established and validated. The results showed that the maximum measurement error of sensor was 1.20% when using this model, which met the requirement of fertilizer flow detection. Indoor bench test on response of fertilizer flow rate change and fertilization accuracy was carried out. The results showed that the response time of the fertilizer flow control system was 1.42s, mean value was 0.98s, maximum overshoot value was 3.49%, mean value was 2.82%, maximum steady-state error was 0.89%, mean value was 0.64%, minimum fertilization accuracy was 97.83%, and mean value was 98.14%. Under different test conditions, the accuracy of fertilizer flow control and fertilization of fertilizer flow control system was better than that of constant speed system. Field tests showed that at vehicle speeds of 4km/h, 6km/h and 8km/h, the accuracy of fertilizer application rate of fertilizer flow control system was 97.84%, 97.78% and 97.82% respectively, and the average accuracy of fertilizer application rate was 97.81%, and the standard deviation was 0.28%, which met the requirements of fertilizer application accuracy of fertilizer system.