2D Geoelectrical Tomography for Detecting Root Biomass in Coffee Trees.

Roots play an important role in plants and are responsible for several functions, which include anchorage, nutrient and water absorption, exchange of growth substances with the shoots, source of organic materials, and others. Their study is laborious, time consuming and usually involves destructive sampling, which prevent future measurements at same location. Several methodologies are being tested and used to avoid destructive root sampling, such as ground-penetrating radar, x-ray imaging, isotopes, magnetic resonance, electrical and seismic methods. The use of electrical resistivity tomography is among these techniques and its use has been documented by several authors in trees, herbaceous plants, and orchards. The aim of this study is to use the 2D geoelectrical tomography for detecting root biomass in coffee trees. The research was conducted at Lavras, Minas Gerais-Brazil. Electrical resistivity measurements were performed in a soil transect under coffee plants. Pole-dipole configuration was used and measurements were taken 0.25 m apart by using an ABM AL 48-b resistivimeter (EEG Geofisica, Italy). The measured apparent-resistivity data sets were inverted by using the Res2DInv software. The 2D tomogram indicated variability in soil resistivity values ranging from 120 to 1400 Ω.m^-1. At the first 0.30 m soil layer these values were between 500-900 Ω.m^-1.Oriented by this soil depth, root samples were taken at 0.50 m intervals along the soil transect and at three different depths (0.10, 0.20, and 0.30 m) to compare soil resistivity with root dry mass per unit soil volume. Root mass density data, up to this depth, showed variability and significant relationship to the observed values of soil resistivity. These preliminarily results showed that the electrical resistivity tomography can contributes to root systems studies in coffee plants, however, considering the diversity of soils and conditions were plants are cultivated in Brazil, more experiments are necessary to confirm the found results.