Agriculture Field-Scale Soil Moisture Sensing
Vision
Soil moisture sensing is an invaluable asset in modern farms, allowing farmers to predict crop yields and irrigate their fields in a timely manner. However, a serious gap exists in low-cost, low-energy sensing solutions that do not disrupt farmers’ daily routines, with modern sensor suites often requiring large batteries or grid connectivity to support active operation and long-range wireless mesh networks. LOAM aims to rectify this by introducing an easily deployable, battery-free sensing node that transmits data to mobile base stations transported by farmers as they traverse their daily routes, allowing data collection to coincide with rather than add on to their busy schedules.
Progress
Low-power, battery-free, passive operation
The LOAM node correlates soil moisture with the potential difference across a galvanic cell, measured using a high-impedance front-end to prevent sensor degradation. Active components like the onboard microcontroller are powered by a single supercapacitor charged by a small solar panel, with firmware reacting dynamically to weather conditions such that the sensor conserves power during dark periods and transmits data during clear sunny periods.
Data collection as a natural extension of farm duties
The mesh network created by a collection of LOAM nodes leverages the daily movements of farmers, with data transmitted opportunistically as farmers pass by in their vehicles. This minimizes communication overhead and subverts the need for permanent receiving infrastructure. Additionally, the solar panel and transmitting antenna are housed in an easily removable, height-adjustable PVC mast, enabling easy deployment.
Ongoing Research Questions
Further minimization of power consumption
Currently, a LOAM node determines whether to transmit by awaiting a remote acknowledgement from a passing base station. Additionally, the LoRaWAN standard imposes a 1-second delay for downlink transmission. This means a node spends the overwhelming majority of its duty cycle in an idle mode, which ultimately dominates its power consumption. Strategies to mitigate this are being explored in conjunction with efforts to improve charging efficiency by experimenting with the type and number of onboard storage capacitors.
Interaction with soil environment
The anode is naturally consumed in a galvanic cell, releasing some into the soil. This introduces the question of how the choice of anode material affects soil health over several seasons, with pH being a particularly important figure of merit. The change in pH additionally becomes a confounding variable in the sensor’s operation, and additional work will focus on characterizing its performance with respect to both pH and water content.
Data-informed path planning
Work on LOAM has thus far centered around the physical sensing hardware and the networking paradigm. Future work will be dedicated to transforming the LOAM ecosystem into a fully realized, convenient tool that uses maps and node positions to optimize vehicle path planning.
Publications
LOAM: Low-Cost Low-Power Off-Grid Farmer Activity-Based Soil Moisture Sensing Platform
Team
Collaborator
Adam Henkel
Ph.D and Postdoctoral
Jack Thoene
Undergraduate
Omar Kamil
Thekra Alkadee
Jack Whipple
Karam Al Bayaa
Nara Jung
VAK Embodied Systems Lab 