Combining GPR and EMI for Root Phenotyping in Multiple Soils

The ability to phenotype roots in situ would provide information for carbon sequestration potential through increased root mass, possible water-seeking strategies by plants, and data generation for plant breeders. However, current phenotyping techniques are often labor intensive and destructive to the observed plant. One potential phenotyping technique that is both rapid and nondestructive is ground penetrating radar (GPR). This technology has been proposed due to its ability to detect fine-scale differences in dielectric permittivity, which is strongly influenced by soil moisture content. To detect small differences in soil moisture caused by root growth, we will need to remove the background soil signature from the GPR signal. The objective of this study is to test the feasibility of GPR data to be linked with soil moisture data as a means to detect and visualize a rooting system in different soil textural classes. This study focuses on three different field locations across Texas and one controlled experiment in PVC boxes to simulate ideal and in situ conditions. Two root types will be investigated: fibrous (grain sorghum and corn) and tap root (cowpea and cotton). Field data will be collected along multiple transects within each plot with a pulseEKKO GPR bi-static unit operating at a radio frequency of either 500 MHz or 1000MHz. To monitor soil moisture, an EM38-MK2 will be used, along with a ML3 ThetaProbe for surface soil moisture measurements and a neutron moisture meter for incremental depth moisture measurements. The controlled experiment will consist of 14 PVC boxes with half of the boxes filled with a local silt loam and the other seven with a sand mixture. The boxes will contain corn or cotton plants to represent both root types. Measurements for all experiments will be collected every two weeks throughout the growing season dry down, and unique post processing techniques will be explored to aide in root detection/visualization. GPR's ability to distinguish root types across different soils conditions will be assessed.