In this article, a variable rate liquid fertilizer applicator for deep-fertilization based on ZigBee technology was elaborated. A host computer with remote control software and a STM32F103RET6 microcontroller were combined to measure and control the liquid fertilizer output: monitoring the liquid fertilizer level and collection the liquid flow information by the flow meter, and an incremental PID control algorithm was used to dynamically adjust the converter frequency for reaching the set liquid fertilizer flow accurately. Through the field test, the influence of parameters, such as fertilization depth, frequency of inverter, pressure of fertilizer injection, and the valve opening for water return of liquid fertilizer pump, on precise flow control is analyzed, and the mathematical model is established by using experimental data. The results showed that, the applicator accuracy is able to reach 99.52% and the liquid fertilizer consumption in each fertilization process is within 0.2L.min-1, with the fertilizer application depth changing, the maximum flow output difference is within 0.2L.min-1and the inverter frequency difference is within 1Hz. When the valve opening for back water is 40%, the system works most stable and the flow output error is the smallest.
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