Non-Invasive Phenotyping of Sugar Beet and Maize Roots Using Field-Scale Spectral Electrical Impedance Tomography.

Root systems are essential for plant water and nutrient uptake, but are difficult to characterize in-situ due to their inaccessibility. Spectral electrical impedance tomography (sEIT) is a non-invasive geoelectrical method that has shown potential to quantify root traits at the laboratory scale. However, field applications remain scarce due to technical limitations and challenges in separating soil and root polarization signatures. This study explores the use of sEIT for in-situ phenotyping of sugar beet and maize root systems. We conducted multi-frequency sEIT measurements at varying crop growth stages to derive the subsurface complex resistivity distribution. Spectral analysis revealed high-frequency polarization peaks for both species. Additionally, sugar beets exhibited an additional low-frequency peak late-season, which we attribute to the development of large storage parenchyma. For sugar beet, the high root-to-soil volume fraction allowed a direct correlation of electrical parameters to root biomass density. For maize, the superimposed soil polarization necessitated an alternative approach: We introduce an electrical root index ( $\mathrm{ERI}$ ) as a spectral dispersion measure indicative of root presence and show its correlation to root biomass density. Our findings demonstrate that sEIT is sensitive to macro- and microscopic root traits under field conditions, holding great potential for non-invasive phenotyping of plant roots.