Erratum to “Construction of Minirhizotron Facilities for Investigating Root Zone Processes” and “Parameterization of Root Water Uptake Models Considering Dynamic Root Distributions and Water Uptake Compensation”

Root counts and root lengths determined in minirhizotron images need to be normalized by the image area. To do so in our publications (Cai et al., 2016, 2018), in which we used a minirhizotron camera (Barth Technology Corporation), we used the values of 13.5 mm (width) and 18 mm (length) suggested by Bartz (Cahill et al., 2010; Trager and Wilson, 2017). However, these values are applicable when rhizotubes of the same inner and outer diameters as the ones that are sold by Bartz are used. Because we used rhizotubes with slightly different diameters, we should have recalibrated the image size. Calibration showed that the actual image size in our setup was 16.5 mm (width) by 23.5 mm (length). For the calibration, a piece of paper with grid lines (5 by 5 mm) was wrapped on a rhizotube which was the same tube that is used in our rhizotron facilities. A picture was taken from the inside of the rhizotube using the camera. The actual captured size of the picture was subsequently obtained by measuring the grids in millimeters. The pixels per millimeter (PPMM) value was determined as