An automated system for controlling drought stress and irrigation in potted plants

Efficient, automated irrigation systems, which can irrigate the substrate of potted plants to a desired level and supply those plants with just the amount of water required for normal plant growth are currently not available. These systems, if developed, could reduce wastage of irrigation water due to excess application. This subsequently could reduce leaching and run-off, and aid growers to cope with increasing regulations of water-use by state governments in the US. Here we describe an irrigation controller that irrigates a substrate to a set-point (volumetric water content, θ) and maintains θ close to that set-point for several weeks. The controller uses calibrated, dielectric moisture sensors, interfaced with a datalogger and solenoid valves, to measure the θ of the substrate every 20 min. When the θ of the substrate drops below the set-point, the controller opens a solenoid valve, which results in irrigation. The θ of the substrate is maintained near a constant level as the datalogger is programmed to increase θ by only 2–3% during each irrigation. Using this controller with bedding plants, we were able to maintain four distinct levels of θ for a prolonged period (40 days), regardless of changes in plant size and environmental conditions. The daily average θ maintained was slightly higher (within 2–3% on any particular day) than the set-point. When the θ measured and maintained by the dielectric moisture sensors was tested using measurements with another probe placed in the same container, the θ measured by both probes was found to be similar, indicating that the controller can indeed maintain θ near the target level. This controller may also have applications in stress physiology, since it allows control over the rate at which drought stress is imposed on plants.