Sensor-based irrigation management of soilless basil using a new smart irrigation system: Effects of set-point on plant physiological responses and crop performance

Dielectric moisture sensors are particularly suitable for irrigation management in greenhouse soilless production. Identifying the practical effects of substrate water content set-points on crop performance is crucial for successful sensor-based irrigation. We designed and constructed a prototype cloud-connected system for wireless, sensor-based irrigation management, and tested it on basil, grown in a perlite-coco (1:1 v:v) soilless substrate under greenhouse conditions. Dielectric moisture/salinity sensors (GS3, Decagon Devices, Pullman - WA, USA) were used. The study, with two subsequent experiments, assessed i) the effects of a progressive decline in substrate water availability, corresponding to moisture levels from water holding capacity to ≈0.10 m3 m−3, on the gas exchange parameters and leaf water status of basil plants; ii) the short-term recovery response of plants when re-watered after substrate water content has decreased to different levels; iii) the effects of different irrigation set-points (0.40, 0.30 and 0.20 m3 m−3) and leaching rates (≈8% or ≈18%) on the basil crop performance over a complete growing cycle. No physiological stress responses were observed on basil plants when moisture level was higher than approximately 0.20 m3 m−3, while plants showed drought symptoms at approximately 0.17 m3 m−3, corresponding to a substrate matric potential and hydraulic conductivity of −300 hPa and 0.0005 cm day−1, respectively. Photosynthesis and leaf water potential recovered to values similar to non- stress conditions following a short drought (with moisture level as low as ≈0.10 m3 m−3). Basil growth was similar when plants were grown with irrigation set-points of 0.40, 0.30 or 0.20 m3 m−3 for the complete growing cycle. Fresh weight tended to increase when a higher leaching rate was used, probably because leaching lowered substrate EC. Water use efficiency (basil fresh weight/unit water used) was similar at different irrigation set-points and leaching rates. Our results indicate that the use of a wireless sensor network for real-time sensing of substrate water status, combined with precise information on the effects of water availability levels on plants, is an effective tool for precision irrigation management of greenhouse soilless basil.