The proposed device is based on monitoring the electrochemical impedance between the electrodes in the plant stem and the soil. The device will build on previous work on developing inexpensive impedance readers capable of wireless communication (cost ~ $100) and miniature electrodes costing less than $1. This approach offers several advantages, including non-invasiveness, low cost, and continuous monitoring, making it an ideal tool for soybean research. In the proposed work, we will develop a proof-of-concept for our approach by building a root monitoring device and using it to monitor the root system of several soybean varieties.

Our objectives are to:
1. Utilize the impedance reader and electrodes to build a device capable of monitoring impedance changes between a single stem electrode and 25 different electrodes distributed in a grid in a rhizotron.
2. Utilize the device to monitor the root growth in several soybean varieties grown in rhizotrons and validate the root distribution measurements through comparison with root measurements at different time intervals.
3. Investigate the influence of thermal stress on root growth and development in soybean varieties.

The successful completion of the research will provide an opportunity to rapidly develop low-cost sensors for monitoring root growth. The research will also provide insights into the relationship between impedance parameters and root morphology and the impact of stress factors on root growth. We aim to complete the following milestones to demonstrate the efficacy of the proposed instrument in monitoring root growth:

Year 1 Milestone: We have already developed an instrumented rhizotron and computer models capable of creating spatial and temporal (4DMap) of the plant root. We will validate the instrument with the measurement of soybean plants of a single variety.
Year 2 Milestone: 4DMaps of the root development in soybean varieties with different root architectures.

Updated September 4, 2025:
We have built four instrumented rhizotrons and the software for converting the measured potentials to a current source distribution corresponding to the root map. The initial measurements conducted on the plant seedlings indicated that the current sources are focused on the transition between the hypocotyl and root transition region due to the highest root density being in the region for seedlings. We are working on techniques to improve the root imaging so that thinner roots further away from the plant stem may be visualized.
We have conducted experiments in both rhizotron filled with soil as well as surface based calcined clay to investigate the efficacy of the phenotyping in different soil environments.
Dr Danny Singh has helped identify five soybean varieties that will be planted in both soil and calcined clay based rhizotron for root phenotyping. In addition, we will apply our techniques to saplings that have grown for few weeks in the rhizotron rather than planted seedlings to visualize a more developed root structure.

Developing root growth monitoring instruments will significantly affect soybean farmers and the industry. Researchers will be able to identify soybean varieties with greater resistance to biotic stresses, leading to increased crop protection and higher yields. Additionally, the instruments will aid in identifying varieties that can maintain high yields under future climate scenarios characterized by higher temperatures and carbon dioxide content. The ability to select varieties with optimized root architecture will benefit farmers and the soybean industry and contribute to global food security.