Controlling Site-Specific Irrigation

Site-specific irrigation systems, delivering precise quantities of water to targeted areas as needed, are critical for high value crops like vegetables, turf, and orchards. Most such systems depend on a central controller and a network of wires running to sensors and valves throughout the field. These systems are very susceptible to damage by lightning, and may require reprogramming when zones are added, removed, or altered in some way.

If autonomous controllers could be used, one in each zone, this would limit the damage done by lightning, and allow easy adjustment of zone counts and characteristics. However, the cost of the controller must be kept low (since there will be a number of them), power must be provided, and a way must be devised to sequence the irrigation of each zone without connecting wires.

Graduate student Fabio Miranda, working with professors Ron Yoder and John Wilkerson, developed a low-cost, solar-powered microcontroller to efficiently allocate limited water to each zone, based on the available water pressure, and a priority level assigned at the zone.

Four irrigation zones were installed, each containing three grass "plots." Each plot is instrumented with moisture and temperature sensors. When the sensors signal a need for irrigation, the controller opens a valve to release water from the common supply pipe, which lowers the pressure in the pipe. After a set amount of time, each controller checks the supply pressure and shuts itself off if the pressure is low. Low priority zones shut themselves off earlier, allowing higher priority zones to continue irrigating.

The researchers have found that the control system is successfully keeping soil moisture within the desired range, and the priority scheduling is working as planned. The zone controllers in this research setup cost about $200 each; the team is confident that costs would be significantly lower for a production system.

Joel Lown
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