Electrical resistivity tomography as a non-destructive method for mapping root biomass in an orchard

Multi-electrode soil electrical resistivity () 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 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 values (up to 460 ohm m) were found close to tree trunks and variability in 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 was overshadowed by the presence of roots and therefore no significant multivariate relationship was found. A highly significant -RD gamma GLM model used to fit positively skewed data provides a useful framework for regression analysis when 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 needs to be taken into account in electrical surveys of soils.