Electrical resistivity tomography as a non-destructive method for mapping root biomass in an orchard
2011
Rossi, R. | Amato, M. | Bitella, G. | Bochicchio, R. | Ferreira Gomes, J.J. | Lovelli, S. | Martorella, E. | Favale, P.
Multi-electrode soil electrical resistivity (ρ) tomography was used for the non-invasive study of tree roots in situ and their spatial distribution in an agricultural soil. The quantitative relations of ρ and root biometry and the contribution of different root size classes were investigated with two- and three-dimensional 48-electrode tomograms in an orchard in southern Italy on a Typic haploxeralf fine, mixed termic soil. Root biomass density (RD) and root length density (RLD) were measured destructively on coarse (>2 mm diameter) and fine roots, and soil paste electrical conductivity, water content, stone content, texture, organic matter and pH were measured on soil samples taken up to 0.48-m deep. Areas of large ρ values (up to 460 ohm m) were found close to tree trunks and variability in ρ was related to RD (0-0.137 Mg m⁻³) only; the resistive response was from coarse roots. The effect of other soil variables on ρ was overshadowed by the presence of roots and therefore no significant multivariate relationship was found. A highly significant ρ-RD gamma GLM model used to fit positively skewed data provides a useful framework for regression analysis when ρ is dominated by roots. Soil electrical resistivity is promising as a proxy for RD in orchards, but not for RLD, and the effect of tree roots on ρ needs to be taken into account in electrical surveys of soils.
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