A basic parameter in precision agriculture is soil moisture, which controls the timing of irrigation, nutrient absorption, harvesting, and efficient management of water resources. Since the world is faced with a growing food demand coupled with an increasing freshwater scarcity, real-time, accurate and low-cost soil moisture monitoring has become a dire need of current agricultural systems. Traditional measurement methods such as gravimetric analysis, resistive sensors, capacitive probes, gypsum blocks, and Time-Domain Reflectometry (TDR) have their own inherent limitations namely, they are invasive, prone to calibration drift, sensitive to salinity of soil, and prohibitively costly to deploy at scale of application.

This work presents a comparative performance study of two antenna configurations for wireless soil moisture sensing based on Received Signal Strength Indicator (RSSI) measurements at 2.4 GHz using the ESP32 microcontroller platform. The two configurations investigated are: (i) ESP32 with built-in antenna, and (ii) ESP32 integrated with a custom-designed external modified microstrip patch antenna incorporating a vertical slot for enhanced directivity and bandwidth. Both configurations exploit the strong correlation between soil dielectric permittivity and Volumetric Water Content (VWC) — as moisture increases, the complex permittivity of the soil rises, causing progressive electromagnetic signal attenuation measurable as a decrease in RSSI. Experimental results confirm a monotonically decreasing RSSI trend across VWC levels of 10%–70%, with a total dynamic range of approximately 39 dBm observed in the built-in antenna configuration.

How it works!

The system uses ESP32-to-ESP32 wireless communication, where the transmitter (Tx) antenna with ESP32 sends a 2.4 GHz signal passes through a soil using patch antenna, and the receiver (Rx) antenna with ESP32 captures the signal after attenuation. The ESP32 in receiving mode measures the RSSI (Received Signal Strength Indicator) value, and based on calibrated RSSI thresholds, the system performs RSSI-based
leveling of soil moisture (dry, moderate, wet) and converts it into a moisture percentage.

What makes it different?

The compactness of prototype and communication between two ESP32 instead of WiFi based cloud system makes it more useful and practically implementable. Moreover, it provides on the spot analysis instead of time taking traditional methods.

Where it would be applied?

Since the manufacturing is easy and deployable, the product can be taken into the farming fields where real-time samples can be considered for measurements to get instant results.