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Effective irrigation control for precision agriculture requires timely and accurate supply of water to a farm field. An autonomous irrigation controller is useful in effectively managing soil water due to both proper decision of irrigation triggering and minimal loss of water. This study reports on the development of an irrigation controller for Korean greenhouse plants. The controller consists of an 8-bit microcontroller, a 12-bit analog-to-digital converter, SD memory card-based data storage, and a Zigbeemodule for wireless network. To easily input various configurations of IO channels and the conditions of irrigation decision based on soil and plant types, a GUI-based program was developed with Visual C++. Two algorithms for water control were developed to improve the efficiency of water use. One was to use irrigation and pause times in which the time for soils to be wet is considered for uniform coverage of water. The other was to determine the watering time based on a comparison in water potential between the measured and threshold values. The prototype irrigation controller system was tested in an experimental greenhouse to verify adequate operation of the system. The field results showed that two solenoid valves for different furrows were independently and timely activated when water potentials at a depth of 20 cm reached a target potential of -20 kPa, thereby resulting in an increase in water potential from -30 to -15 kPa. Further studies on the slow response of water potential to the wetting front under drip irrigation were needed to better control water use.