Using Ground Penetrating Radar to Detect Fine Roots of Agricultural Crops in the Field.

Breeding new crop varieties with vigorous root systems adapted to target environments is a key approach to meet increasing global food demands, but a major challenge is the limited ability to phenotype roots. Ground penetrating radar (GPR) is a recent, non-invasive and time/labor-saving technology with potential for root phenotyping. However, its usefulness has so far been limited to detection of large and coarse roots (>2 mm diameter). In the current study, we investigated the possibility of using an improved GPR technology to detect crop fine roots (<0.5 mm diameter) in the field. This study was conducted in four locations in Texas with different soil types. The study included several winter wheat and sugarcane varieties grown in commercial-scale fields with soil types ranging from clay, silty clay loam to sandy clay loam. In total, 152 plots were scanned with GPR (1600 MHz antenna). Soil cores (5 cm dimeter and 15 cm depth) were collected immediately after scanning to determine root parameters including root diameter and root biomass. Four pixel indicies with or without a threshold range representing GPR signal were used to assess their relationship with root parameters. There were significant relations between GPR indicies and root parameters depending on soil conditions. Winter wheat roots were more easily detected in wet soil conditions. GPR-estimated root traits had lower variation than those from the core-based measurement. Average pixel intensity without a pixel intensity threshold may be better to reflect root information than other pixel indicies with a pixel intensity threshold. This investigation demonstrated the potential of GPR technology to quantify fine roots and reveal difference in root traits among crop species and varieties in the field. Further investigations are ongoing to calibrate the technology and define optimal soil conditions to obtain accurate and reproducible measurements.