Sensor-based technology for the rational management of fertigation in tomato soilless cultivation

In Mediterranean areas open (free drain) system, with high leaching rate and consequent environmental discharges, represents the most widespread method in soilless cultivation, due to the use of brackish water for irrigation purposes. These bring into question greenhouse environmental sustainability, especially when they are associated to empirical methods for fertigation management such as timer. Conversely, in case of adoption of closed cycle in these areas, periodic replacements of the recirculating nutrient solution are need, due to Na accumulation in nutrient solution (NS). In this study an innovative precision automatic irrigation system based on real time measurements of substrate volumetric water content (VWC) and electrical conductivity (EC) performed by a wireless sensor network (GS3, Decagon Devices, Pullman-WA, USA), in tomato open-cycle soilless cultivation (sOC), was evaluated. Results were compared with those obtained in semi-closed cycle (CC) and empirically timer-based open free drain soilless cultivation (OC), in terms of water use efficiency and effects on crop yield and quality. The experiment, carried out at the Experimental Farm "La Noria" (ISPA-CNR) in Mola di Bari, provided the use of moderately saline water (EC=3,7 dS/m). Compared to the control (OC), sOC and CC treatments reduced plants growth and crops yield (?30%, on average). However, these decreases were compensated by a better fruits quality (6,8 °Brix in OC vs. 7,8 °Brix in CC and sOC, on average), thanks to controlled salinity stress conditions involved by the automatic irrigation system (5 dS/m as EC set-point for substrate leaching and NS replacement in sOC and CC, respectively). sOC treatment, has also allowed to increase water use efficiency (68%) compared to the other two systems.