A Hall Effect-Based Sap Flow Measurement System for Optimized Irrigation*

Water scarcity poses a growing challenge worldwide, with inefficient agricultural irrigation being a major contributor to freshwater loss. In California, irrigation accounts for 80% of total water usage, and 84% of that is not absorbed by plants.

This project presents a novel solution to improve irrigation efficiency using real-time sap flow data—an indicator of plant water status—obtained with a Hall effect sensor.

We developed a new sap flow measurement method based on the Hall effect, detecting voltage induced by charge carriers in sap under a magnetic field. Unlike conventional heat dissipation-based methods, our technique is non-invasive and applicable to crops with thin stems (<10 cm)

The sensor was constructed using a custom 3D-printed mount, neodymium magnets, and Arduino pumps, and integrated into an automated drip irrigation system. The method was validated on tomatoes in both controlled environments and local farms, demonstrating high accuracy (R² = 0.97). In a 60-day trial, the system achieved an 18% reduction in water use compared to standard irrigation methods, with no reduction in crop yield.

By applying fundamental electromagnetic principles to sap-flow monitoring, this work demonstrates how low-cost, scalable sensing technologies can improve irrigation strategies and support climate-resilient agriculture.