PORTABLE RHIZOTRON AND COLOR SCANNER SYSTEM FOR MONITORING ROOT DEVELOPMENT

Rhizotrons allow the examination of spatial and temporal in situ root development. Permanent rhizotron installations provide 2-D images of w hole root profiles, but their immobility limits the number of soil-pla nt systems that can be studied. Our objectives were to develop a porta ble rhizotron and color scanning system for studying the development o f whole root systems. Potato root development was monitored in an irri gated experiment at Othello, WA. Covered, rectangular hollow boxes wit h a transparent glass face were installed perpendicular to planted pot ato rows, and a seed piece was planted in the soil adjacent to the gla ss. Rooting in the hill furrow topography was measured at 2 to 4 week intervals. Images of roots growing along the glass face are captured w ith five scans with a portable, color scanner and a portable computer. Image thresholding discriminated roots from soil using primary color values, color intensity differences, color proportions, or overall int ensity. Seasonal patterns of computed root lengths by image analysis w ere comparable to manual tracing. Primary roots extended to 15 cm from the seed piece prior to shoot emergence, 21 days after planting. Late ral roots began to develop shortly thereafter. Potato roots extended t o depths of 60 cm by 4 to 6 weeks after planting, and maximum root den sity in the hill and furrow was observed by tuber initiation to early tuber bulking. Temporal and spatial trends were similar to previous re sults using destructive sampling. The method has promise for studying the root growth and development of field-grown plants.