Implementing a cyber-physical system to monitor soil water status and environmental variables for irrigation scheduling

The most advanced research on irrigation at farm scale, following the paradigm “more crop per drop”, has beenaimed at the definition of strategies of precision irrigation, in order to optimize crop water productivity and to maximizethe economic benefits without affecting environmental quality.Water saving management strategies, such asregulated deficit irrigation (RDI), can be effectively applied if supported by the real time control of soil/plant waterstatus allowing the identification of appropriate irrigation scheduling parameters (irrigation timing and doses).This challenge can be achieved by integrating sensing technologies, internet of things and cloud computing supportedwith communication infrastructures. A cyber-physical system (CPS) is a measurement device controlledby computer-based applications and integrated with the Internet. Agricultural CPSs, based on the combination ofsensing technologies and agricultural facilities, allow disposing of robust systems to monitor in real time environmentalvariables useful for the decision making processes related to smart and eco-friendly water management.Objective of the paper is to present an example of CPS to monitor soil water contents and environmental forcingaimed at the precise irrigation scheduling of Mediterranean tree crops.The experimental station was installed at the end of June 2017 in a commercial citrus orchard located near thecity of Palermo, Italy (38 4’ 53.4" N, 13 25’ 8.2" E), in which a micro-sprinkler system with two 160 l/h microsprinklersper plant, typical of the area, is currently used for irrigation. Experimental layout was completed with theinstallation of a standard weather station (Spectrum Technologies, Inc) that sends ASCII messages at 9600 baudout a serial port every 30 minutes on average, and eight "drill & drop" sensors (Sentek, Stepney, Australia) usingthe MODBUS RTU protocol. All the sensors are interfaced with a communications board that can use the cellular3G data network to make an internet connection. This connection is used to become a client of a TCP/IP server,that decodes the packet transmission and saves the data into a MySQL database operated by AgriNET/Tuctronics.In this way it is possible to download, in real time the weather variables, as well as soil water content (SWC) andtemperature (T) in the root zone, at each 10 cm depth intervals. Based on the water availability, during the firstseason irrigation volumes were supplied every two weeks, as ordinarily practiced in the area.The big database of SWCs and Ts collected during the monitoring period allowed the identification of soil hydraulicparameters aimed at characterizing the soil-crop system and at defining the thresholds of SWCs for irrigationscheduling purposes.