In-situ cassava root size measurement using ground penetrating radar (GPR)

Ground penetrating radar (GPR) has been used increasingly to measure the growth of coarse roots (>2 mm diameter) of woody trees and other large plants. We used high-frequency GPR (1000 MHz) to measure the growth of the storage roots of two cassava cultivars in Flanagan/Drummer soils periodically over the course of three months during the 2017 field season. Growth conditions included plots with elevated concentrations of carbon dioxide ([CO2] = 600 ppm, test) and ambient carbon dioxide levels ([CO2] = 400 ppm, control). We had 168 plants of each cultivar, which were divided into 8 subplots (12 m²) containing 21 plants per subplot. Four of these subplots were treatment plots (elevated [CO2]) and four were control (ambient [CO2]). We used a consistent GPR measurement grid for data collection at every cassava plot throughout the growing season to ensure we were measuring at the same location with each GPR pass. After the baseline measurement, 1-4 plants were excavated each month of the season to ground-truth the GPR data. The GPR data were processed using EkkoProject 5 and visualized in 3-dimensions using Voxler, which allowed for volumetric modeling. The locations of the roots were interpreted and annotated at each time interval. We show qualitatively that the increase in biomass created by cassava plants in an elevated-CO2 environment can be captured non-destructively using GPR.