Design of a passive irrigation controller for efficient water use in low-income countries

Efficient irrigation water usage is vital for low-income countries to keep up with projected population and income growth. Current weather- and soil-moisture-based smart irrigation controllers are not easily transferable to the economic and technological context of low-income countries and small remote farms. This paper presents the design of a passive automated irrigation controller that uses standard PVC fittings locally available to our community partner in Nicaragua. The actuation of the valve in the controller is driven by the soil water tension (SWT) from unsaturated soil. The key components of the controller are a ceramic tip connected to a tube of water, a rubber membrane, and a piston that acts like a stopper for the irrigation. The piston length is designed with an initial deflection in the membrane, causing it to push back against the inlet to shut off irrigation. A model of the system composed of the Green-Ampt equation for soil-water dynamics, empirical data for the relationship between soil moisture and controller pressure, and finite element model of the membrane is used to design a controller. The initial system consists of a 2″ diameter rubber membrane and a 1″ diameter piston. The initial deflection is 1.6cm to create enough force to stop the irrigation until the SWT reaches −35kPa. The controller costs approximately $CDN130 with PVC parts purchased in Canada with retail prices. The cost is expected to drop when discounts from retail prices are actualized. The design has the potential to greatly reduce water usage in drip irrigation systems.