Using the Rhizometer and Root Analyzing Software to Measure Root Growth of Seedlings

The use of digital imaging and computer software programs to analyze plant root growth has increased in recent years due to advances in quality and resolution of digital imaging, as well as advancing technology creating objective software to allow for greater measurement capabilities. The rhizometer was developed at North Carolina State University to observe plant root growth and measure the effect of root growth on substrate physical properties over time. The clear cylinder design of the rhizometer allows for visible observations of the rhizosphere so that root data collection, such as root count, root length, and root hairs can be quantified without disturbance. The objective of this study was to measure several root system parameters with plants grown in the rhizometer using image software. Three substrates were compared in this study; peat amended with 20% (v/v) of either perlite (PL), pine-wood-chips (PWC) or shredded-pine-wood (SW). Both PWC and SW were produced by hammermilling freshly chipped or shredded loblolly pine trees (Pinus taeda) through a 6.35 mm screen. Twenty rhizometers were filled with each individual substrate and four species of seeds were planted directly into the rhizometers; bean (Phaseolus vugaris ‘Gold Rush’), corn (Zea mays ‘Jubilee’), tomato (Solanum lycopersicum L. ‘Better Boy’), and marigolds (Tagetes erecta ‘Inca Orange’) resulting in 60 rhizometers used. Three root measurements were taken once root tips were visible along the rhizometer cylinder; number of root tips (RT), number of roots with visible root hairs (RH), and cumulative root length (RL). Root length was measured by tracing the roots on a transparency sheet, taking a digital photograph, and using RootReader 2D software to select the traced roots and calculate total root length of the picture. Number of root tips, RH and RL measurements had linear responses over time for all four species.  At 12 days after emergence (DE), corn had the largest total RL in the SW substrate, and tomato had a higher total RL in PWC substrate at 12 DE. The higher total RL observed with these two species with SW and PWC substrates at 12 DE could be attributed to the physical properties of the substrates, such as increased air space. However, as the roots of these plants grew into the substrates and likely altered the substrates’ physical properties over time, there were no observable differences in RT, RH, or RL among the substrates for each species at measurement dates after 12 DE.