In this paper, a flexible graphene oxide-based antenna sensor is designed on the biodegradable substrate. It resonates at a frequency of 3.92 GHz. The flexible sensor is used in assessing water content in sandy loam subsoil near the Arabian Sea from the Western Ghats in India. The volumetric water content (VWC) of dry soil varies between approximately 0.06 VWC m 3 m −3 to 0.7 VWC m 3 m −3 . The antenna sensor exhibits a linearity of 92.02% and a sensitivity of 402.6 MHz/ VWC(m 3 m −3 ). The limit of detection (LOD) and limit of quantification (LOQ) of the antenna sensor are 0.75 VWC and 2.5 VWC m 3 m −3 . The sensor is beneficial for examining soil water to enhance crop productivity for precision agriculture.