|Ewing, Robert - IOWA STATE UNIVERSITY|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 18, 1997
Publication Date: N/A
Interpretive Summary: Length and perimeter are among the most basic and useful parameters used to describe the size of roots and are important measurements of root growth and function. Agricultural scientists and foresters are currently using desktop scanners and video cameras to collect images of plant roots for length measurements and need software for analyzing these images. Currently, available image analysis programs for measuring length and perimeter of digitized objects are expensive, require lots of computer memory and fast microprocessors, and are based on outdated methods for analyzing the images. This paper describes ROOTEDGE, a software program that requires minimal computer memory, uses a recently developed algorithm for determining length and perimeter, and performs some basic image processing operations. Additionally, a desktop scanner system and the methodology for acquiring images of roots is also described. ROOTEDGE and the image acquisition system were tested using corn root samples. The length measurements obtained using ROOTEDGE and the image acquisition system improved the speed and accuracy compared with the commonly used manual method. The scanner system settings, sample preparation, and image processing operations were shown to improve the quality of the digitized root images and the subsequent length measurements. This program will be made available to the scientific community free of charge and will improve the understanding of the root growth and function of important agricultural and forestry crops. The impact of this better understanding of crop roots will be improved irrigation efficiency, better fertilizer management, and economical control of root diseases and insect pests.
Technical Abstract: Root length and diameter measurements are necessary to determine the water and nutrient uptake potential of plants. One approach for measuring root length is to use desktop scanners to acquire digitized images of the roots and then to analyze the digitized root images to determine root length. The ROOTEDGE software was developed to analyze digitized images of roots using the recently developed edge chord algorithm, which is more accurate and precise than older algorithms. In addition to length, the program measures the area, width, and number of roots in images. ROOTEDGE also performs simple binary image processing operations to smooth object edges and to join fragments. The performance of ROOTEDGE and a scanner system for obtaining root images were tested using individual corn (Zea mays L.) root segments and corn root samples containing multiple root segments. Visual comparisons of digitized images to actual root segments showed that root segments with diameters less than 0.15 mm were not being completely digitized by the scanner system and were fragmented in the images. The most complete root images were produced using the highest available scanner resolution and the lowest threshold level for exposure. Using the ROOTEDGE binary image processing operation closing with a test coefficient of one also helped to join the fragmented roots segments in the image and improved the correlation of ROOTEDGE measurements to direct measurements. Ratios of ROOTEDGE length measurements to manual line-intersection length measurements ranged from 0.98 to 0.88 for four corn root samples of different sizes obtained from a field experiment. Much of the difference between the two measurements could be attributed to incomplete digitization of the roots and overlapping of roots in the image.