Soil Moisture Estimation based on the RSSI of RFID Modules

Nowadays the RFID technology and Internet of Things are becoming empowering and enabling tools in various fields, including smart and precision agriculture. The aim of this research is to propose an innovative system for the detection of soil moisture based on the use of standard UHF RFID tags and on the measurement of the received signal strength detected by a reader that can be hosted on board drones or farm vehicles. The reader detects the RSSI received from tags placed below the ground level and according to the measured value is able to discriminate if the ground is dry or wet. Microwave propagation is, in fact, strongly influenced by the presence of water in the soil and by exploiting the instantaneous and average RSSI values it is possible to discriminate the conditions of dry and wet soil and, thus, optimize irrigation in a wide area. The results obtained by using a first prototype show that the approach is suitable for any type of soil: sandy, clayey or loamy; further studies must be conducted in order to identify different levels of soil moisture and to determine the moisture levels at different depths.