Non-invasive monitoring of hydraulic processes in the rhizosphere using shortwave infrared imaging

Existing methods for non-destructive, ex-situ investigation of the rhizosphere include X-Ray Computed Tomography. However, this method is time-consuming, requires specialist skills to operate, and, most of all, it is impractical for multiple replications. This paper evaluates a Short Wavelength Infrared (SWIR) method for imaging the hydraulic processes within the rhizosphere and presents a preliminary investigation of accuracy, spatial resolution, and data quality. The calibration relating pixel intensity to volumetric water content was developed by imaging mini-rhizotrons with size 170 x 80 x 10 mm and a viewing window, which were filled with sand at different water contents. The SWIR imaging could capture volumetric water content with good accuracy. The camera allowed for sub-millimetre resolution that enabled capturing water content variations very close to the root surface. When imaging mini-rhizotron during flooding, the camera could capture the progressive saturation of the narrow hydrophobicity zone surrounding the roots.