USE OF COMPUTER-ASSISTED TOMOGRAPHY IN STUDYING WATER-MOVEMENT AROUND PLANT-ROOTS

Application of computer-assisted tomography to X- and y-ray attenuation measurements has provided an exciting new method for nondestructive imaging within a solid matrix, with considerable potential for studying soil behavior and soil/plant/water relations in space and time. However, the information provided is currently limited by the capabilities of the instrumentation available. Commercially available medical CT scanners have proved useful for visual studies of soil structure, the advancement and stability of wetting fronts, and the structural changes following wetting and drying. However, the usefulness of these systems and of single-source CAT scanning systems in studying soil systems is invariably restricted by their inability to distinguish between changes in water content and bulk density in swelling and shrinking soils and by the associated physical relocation of soil elements that can occur. Thus their quantitative applications have been limited to the measurement of water drawdowns in proximity to plant roots in nonswelling soils and statistical assessments of macroporosity distributions before and after complete wetting and drying cycles. Though fast in operation, the quantitative usefulness of X-ray scanners is limited by the polychromatic nature of the beam and the process known as “beam hardening.” Furthermore, the proprietary nature of these commercial systems usually makes software modification or extensions impossible. © 1993, Academic Press Inc.