The effect of soil water content and crop canopy on passive UHF-RFID wireless links

The maximum wireless reading distance between and RFID tag and a reader depends on soil moisture and crop type. • Wet soil limits read range of battery-free RFID tags. • A few cm of space between tag and soil increases read range by 1 m or more. • Soil can be a more significant range limiter than scattering from crops for battery-free RFID tags. • RFID can enable above-canopy reading of battery free sensors which are in the soil. High spatial density agricultural sensors that monitor soil fertility and moisture levels are quickly developing and could revolutionize precision agriculture once they are integrated with wireless communication systems. Passive Ultra High Frequency Radio Frequency Identification (UHF-RFID) is a wireless communication protocol for battery-free sensor nodes which could enable continuous soil monitoring. Soil texture, soil water content, and crop canopy impact the vertical read range between a passive RFID tag near the soil and a reader raised above the crop. Here, we evaluated these impacts and found that increases in soil water content decreased read range by 30–40 cm compared to dry soil. Adding 3.4 cm of distance between the wet soil and the tag increased the read range by 1–1.4 m. Crop canopy did not have a significant impact on read range once the soil water content had been accounted for.