Electric Tomography Maps Root Systems Without Excavation

By Hugo Francisco de SouzaReviewed by Lauren HardakerJul 17 2025

In a recent study published in Plant, Cell & Environment, researchers demonstrate the utility of spectral electrical impedance tomography (sEIT), a cutting-edge geophysical imaging technique previously rarely applied outside controlled environments, in non-invasively visualizing root growth in crops at the field scale.

Image credit: Burdejnij/Shutterstock.com

The study analysed a spectrum of underground electrical signals (23 frequencies; 0.1 Hz–1 kHz) and accurately measured critical root traits, including biomass and storage cell size, offering a powerful tool for future agricultural phenotyping.

However, the authors caution that sEIT’s field-scale applications require careful experimental design, especially to address environmental variability, technical noise, and potential measurement artifacts.

Background

Root systems represent plants' hidden nutrient acquirers, and while they may be out of sight, they should never be out of mind. Roots form complex networks below the soil surface, vital for water and micronutrient uptake, and can significantly determine plant (and crop) success, especially under today’s drought-prone climatic regime.

Unfortunately, observing root systems and measuring their traits noninvasively has long been challenging. Most current methods (digging, trenching, coring) are destructive and often cause more harm than the benefits their measurements may provide. These methods are also extremely labor-intensive and provide snapshot data, sometimes requiring repetition even over the same crop season.

Recent research aims to leverage real-time non-invasive technologies for root system monitoring and assessment to address traditional measurement deficits. Innovations such as X-rays, computed tomography (CT) scans, and magnetic resonance imaging (MRI) are now extensively used in controlled laboratory environments. Still, their deployment in open fields and real-world agricultural applications remains elusive.

About The Study

The present study addresses this challenge by demonstrating the application of sEIT in accessing plant root systems directly in soil, at multiple time points over an entire growing season. sEIT is a non-invasive geophysical imaging technique that maps electrical conductivity distributions, particularly those of subsurface spaces of interest. While often used in geophysics research, its field deployment for agricultural root phenotyping has been limited.

The study used the technique to monitor the root systems of maize (Zea mays, variety “Sweet Nugget”) and sugar beet (Beta vulgaris, variety “BTS 440”) in farms in Meckenheim, Germany. These crops were chosen for their contrasting root types: sugar beet with thick taproots and maize with finer, fibrous roots. All farms under study were surveyed three times (July 6^th, August 10^th, September 13^th, 2021) using a sEIT setup comprising 40 stainless steel electrodes (length = 17 cm, diameter = 1 cm) spaced 25 cm apart (total profile length = 9.75 m).

Accounting for the normal depth of maize and sugar beet root systems, the sEIT electrodes were drilled ~15 cm into farmland soil. Monitoring involved injecting low-voltage alternating currents and recording the resulting voltage shifts across a broad, logarithmically evenly spaced (n = 23) frequency spectrum (0.1 Hz to 1 kHz; EIT40 impedance tomograph protocol).

Complex resistivity inversion algorithms converted the resultant electrical recordings into 2D maps of underground root structures. Debye decomposition, a method for analyzing complex electrical conductivity data by interpreting the data as a distribution of relaxation times, was used to model soil and root system polarization signatures by converting data into total chargeability (a measure of polarization strength) and mean relaxation time (linked to physical root cell dimensions) metrics.

Researchers further developed a novel electrical root index (ERI) that quantifies root-specific electrical signatures by comparing high- and low-frequency responses while accounting for soil moisture and temperature variations. This index aims to isolate the root signal from the often-dominant background polarization of the soil, particularly for fine root systems like maize. Finally, the study ground-truth validated sEIT and model results via “shovelomics”, the age-old measurement technique of excavating and washing roots.

The authors note that shovelomics can introduce measurement uncertainty, particularly for fine root systems, and suggest that future validation might benefit from more precise techniques like minirhizotrons or root coring.

Study Findings

Study findings revealed the sEIT system to be effective, especially concerning sugar beet measurements. Electrical chargeability results were observed to closely track root biomass across the growing season (Pearson correlation coefficient = 0.67, p = 0.005).

Furthermore, data highlighted a low-frequency polarization peak shifting from 17 milliseconds to 80 milliseconds in relaxation time from July to September, indicating the growth of large parenchyma storage cells as sugar beet matured, thereby providing additional insights into internal cell structures. Estimated cell diameters based on these signals ranged from 11 to 25 µm, aligning well with literature-based biological expectations, though direct validation was not performed.

In contrast, maize roots were fine and extensively overlapping, confounding direct measurements. The study’s novel ERI metric solved this issue, as demonstrated by the metric significantly correlating with root biomass density (Pearson r = 0.74, p = 0.027). This suggests that ERI-augmented sEIT can detect even minute changes in fine root growth when standard resistivity measures fail.

The researchers acknowledge that ERI is site-specific and may be affected by soil moisture, salinity, and temperature factors. They emphasize the need for baseline measurements or calibration to ensure comparability across conditions.

Conclusions

The present study demonstrates the significant benefits of leveraging sEIT and similar lab-standardized technologies in open- and real-world applications by using the technology to non-invasively assess root biomass, architecture, and even cell dimensions. It highlights the feasibility of field-scale imaging up to 1 kHz frequencies, made possible by recent advances in instrumentation, data correction techniques, and inversion modelling.

Notably, the system demonstrated consistent performance under varied field conditions, rounding off its holistic advantages over traditional root system monitoring approaches.

However, the authors reiterate that the technique requires carefully designed measurement schemes, and its accuracy may vary depending on crop type, root architecture, and environmental factors such as moisture and temperature. Future improvements in validation methods, environmental correction protocols, and large-scale repeatability will be essential for broader adoption.

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