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It is the foundation of precision agriculture to collect comprehensive information on water, soil, plants, and the environment in the field. A wireless sensor network (WSN) is a new platform for real-time information access, and soil electrical conductivity (EC) is one of the most important indicators of soil variability because it is an integration of the physico-chemical properties of soil. Therefore, a WSN for monitoring soil EC is developed. The WSN is equipped with soil EC sensor nodes and a coordinator based on ZigBee. The sensor nodes adopt a four-electrode method and consist of two units: a probe unit, and a processing and communication unit. The probe unit injects a constant electrical current into the soil and detects the voltage drop between two output electrodes. Data are then transmitted to the ZigBee coordinator. The coordinator consists of a keyboard module, an LCD display module, and an RS232 transceiver. The RS232 transceiver connects the personal computer and the coordinator. Finally, soil EC is calculated using the voltage drop received from the sensors. Performance tests are implemented to check the correlation between the measured voltage and soil EC, and that between soil EC and ammonia nitrogen content. Results showed that the soil EC WSN provided highly accurate performance in both experiments, indicating that the developed platform is effective and reliable.