Flatbed scanning is one of the most common and useful methods for measuring root traits like length and diameter. Use of graphical scanners with transparency units (or top lights) allows acquiring images of root silhouettes that are easily analyzed using RhizoVision Explorer. This page highlights recommendations for reproducible and accurate scanning of washed roots. The Epson Expression 12000XL has twice the scan area of the Epson Perfection v850, but costs four times more. Still, both are great investments for accurate and reproducible root measurements.
The protocols are deposited on Zenodo. Please follow the link to Zenodo for citation information. Direct downloads of PDF by clicking on image. Plans for root scanning trays are available here.