The biomass attributed to fine and small roots contained within soils is challenging to quantify in situ. We examined the effect of fine roots on the bulk dielectric properties of soil to explore the potential for assessing volumetric root content using ground-penetrating radar (GPR). We found a positive relationship between fine root content and bulk dielectric permittivity in relatively dry sand. We fit the data with a mixing model that accounted for the mineral, air, and root components of the sample. Our results indicate that changes in volumetric root content can be detected by GPR under such simple, controlled conditions; however, the presence of pore water, along with its spatial variability and the inherent structural heterogeneity of soils, will probably render detection of fine root biomass from a GPR measurement very challenging in the field.

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