Precision irrigation scheduling using ECH2O moisture sensors for lettuce cultivated in a soilless substrate culture

Abstract

Soilless culture has become an effective technique to avoid continuous cropping obstacles in protected horticulture. The reliable measurement of substrate moisture and a rational irrigation are difficult tasks because of the low water-holding capacity of the substrate. Our objectives were to study the irrigation scheduling based on the ECH2O moisture sensor(EC-5), using a matched model of wetting pattern and lettuce root zone in the substrate under drip irrigation. The EC-5 sensor was designed to connect to a controller, and a threshold value of 0.14 cm3/cm3 was set for irrigation scheduling. The controller turned on the irrigation system via communication with a solenoid valve on the irrigation line and with the EC-5 sensor in response to a threshold value and stopped when the overlap area of the wetting pattern and crop root zone was more than 90%. The EC-5 sensors were installed at a horizontal distance from each plant and depth of 3 and 4 cm, respectively, under the substrate surface to the check substrate moisture for lettuce cultivation, and at (3,15) cm or (6,15) cm to monitor leakage. These parameters were determined by simultaneously considering the distance from the plants, the depths of effective root water extraction, and the region of substrate wetted volume under drip irrigation. Leakage occurred during each irrigation process, but the leakage ratewas15.7% lower than that of conventional irrigation, as a result of irrigation scheduling in the presence of the EC-5 sensors.